Tillage Machinery―Passive, Active and Combination 9819963303, 9789819963300

Table of contents :
Preface
Acknowledgements
Contents
About the Authors
1 Tillage
1.1 Introduction
1.2 Objectives of Tillage
1.3 Types of Tillage
1.4 Tillage Mechanics
1.5 Tillage Tool Design Factors
1.6 Classification of Tillage Implements
1.7 Patterns of Tillage Operation
References
2 Moldboard Plow
2.1 Introduction
2.2 Components of a Moldboard Plow
2.2.1 Share
2.2.2 Moldboard
2.2.3 Landside
2.2.4 Frog
2.2.5 Attachments to Moldboard Plow
2.3 Representation of Forces Acting upon a Plow Bottom
2.4 Resistance Developed During Plowing
2.5 Geometry of Share of Moldboard Plow
2.6 Furrow Inversion
2.7 Effect of Forward Speed on Longitudinal, Lateral, and Vertical Soil Reactions
2.8 Effect of Depth and Width of Cut on Draft/Specific Draft
2.9 Effect of Plow Bottom Shape and Design on Draft
2.10 Effect of Attachments and Rear Furrow Wheel on Draft
References
3 Disk Implements
3.1 Introduction
3.2 Forces Acting on the Disk
3.3 Disk Plow
3.3.1 Types of Disk Plow
3.3.2 Soil Reactions on Plow Disks
3.3.3 Horizontal Hitching of Pull-Type Disk Plows
3.4 Disk Harrows
3.4.1 Types of Disk Harrow
3.4.2 Soil Reactions on Disk Harrow Blades
3.4.3 Forces Acting upon a Disk Harrow
3.4.4 Couple Acting on Disk Harrow Gangs
3.4.5 Disk Harrow with Hinged Pull Members but Without Gage Wheels or Runners
3.5 Design of Disk Implements
3.5.1 Width of Disk Implements
3.5.2 Diameter of Disk
3.5.3 Thickness of Disk
3.5.4 Spacing between Disks
3.5.5 Number of Disks per Gang
3.5.6 Design of Shaft
3.5.7 Design of Frame
References
4 Cultivator
4.1 Introduction
4.2 Cultivator Teeth (Working Elements)
4.3 Working Zone of the Cultivator's Tooth
4.4 Shanks of Rigid Teeth
References
5 Rotary Tillage Implements
5.1 Introduction
5.2 Rotavator
5.2.1 Construction and Different Components of a Rotavator
5.2.2 Kinematics of Blade-Soil Interaction
5.2.3 Angles Associated with Cutting Trajectory
5.2.4 Forces Acting on the Furrow Slice and Specific Work
5.2.5 Design of a Rotavator
5.3 Powered Disk Harrow
5.3.1 Disk Diameter
5.3.2 Disk Blade
5.3.3 Disk Spacing
5.3.4 Cutting Width of Single Acting Disk Harrow
5.3.5 Calculation of Total Power Required
5.3.6 Gang Shaft Design
References
6 Combination Tillage Implements
6.1 Introduction
6.2 Classification of Combination Tillage Implements
6.3 General Approach for Prediction of the Power Requirement of Combination Tillage Implements
6.3.1 Passive-Passive Combination Tillage Implements
6.3.2 Active–Passive Combination Tillage Implements
6.4 Performance Evaluation of Combination Tillage Implements
6.4.1 Cone Index
6.4.2 Mean Weight Diameter (MWD)
6.4.3 Width of Cut
6.4.4 Actual Field Capacity (AFC) and Field Efficiency (FE)
6.4.5 Volume of Soil Handled Per Unit Time
6.4.6 Soil Inversion
6.4.7 Fuel Energy Input to the Tractor
6.4.8 Overall Performance
6.5 Design of Combined Offset Disk Harrow
6.5.1 Disk Diameter
6.5.2 Disk Blade Material
6.5.3 Disk Spacing
6.5.4 Cutting Width of Single Acting Disk Harrow
6.5.5 Prediction of Soil Disturbance Area for Calculation of Specific Draft
6.5.6 Specific Draft Estimation Model for Powered Disk Harrow
6.5.7 Estimation of Draft Requirement of Powered and Unpowered Disk Gangs
6.5.8 Estimation of Equivalent PTO Power of the Tractor
6.5.9 Gang Shaft Design
References
7 Measurement of Parameters for Performance Evaluation of Tillage Implements
7.1 Introduction
7.2 Testing of Tillage Implements
7.2.1 Testing of Plow
7.2.2 Testing of Disk Harrow
7.2.3 Testing of Rotary Tiller
7.3 Instrumentation for Measuring Tillage Performance Parameters
7.3.1 Draft Measurement
7.3.2 Torque Measurement
7.3.3 Wheel Slip Measurement
7.3.4 Measurement of Fuel Consumption
References

Citation preview

Hifjur Raheman Pranay Sarkar

Tillage Machinery— Passive, Active and Combination

Tillage Machinery—Passive, Active and Combination

Hifjur Raheman · Pranay Sarkar

Tillage Machinery—Passive, Active and Combination

Hifjur Raheman Department of Agricultural and Food Engineering Indian Institute of Technology Kharagpur Kharagpur, West Bengal, India

Pranay Sarkar Department of Agricultural and Food Engineering Indian Institute of Technology Kharagpur Kharagpur, West Bengal, India

ISBN 978-981-99-6330-0 ISBN 978-981-99-6331-7 (eBook) https://doi.org/10.1007/978-981-99-6331-7 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable.

Dedicated to our parents

Preface

Tillage is an important farming operation which requires maximum energy input and is accomplished by using different tillage implements. Hence, a suitable design of these implements will reduce power requirements and improve efficiency in carrying out tillage operations. The design of tillage implements is very challenging as these implements have to tackle different soil conditions. Information on the behavior of tillage implements to different soil and operating conditions as well as design procedures available for different machine elements are very much required. While offering the course on Farm Machinery Design and Testing at the Indian Institute of Technology Kharagpur, Prof. Raheman collected adequate literature on the design aspects and tried to apply these to successfully design and develop a few tillage implements with the help of his research team. This inspired him and gave him the confidence to write a book on Tillage Machinery. In this textbook, attempts have been made to present the tillage implements from an engineering viewpoint with functional analysis, principles of operation, design of different components, and testing of tillage machinery for performance evaluation in a simplified and unified way. This book has been designed as a textbook for the graduate course in farm machinery that might be required for all professional agricultural/mechanical engineering students. Intense care has been taken to explain the subject with neat diagrams and details of design for easy understanding. The design procedures and numerical examples related to design have been included to reinforce the theoretical concept. This textbook contains 7 chapters. Following the introduction on tillage, i.e., objectives of tillage, tillage methods, classification of tillage, and tool design factors in Chaps. 1–4 describe in detail the passive tillage implements. Chapter 2 presents the details of the moldboard plow, its components, and their design along with draft requirements and estimation. Chapter 3 describes the details about the disktype tillage implements, i.e., disk plow and harrow, force representation in disks, and design of disk harrows. Chapter 4 describes the most commonly used tillage

vii

viii

Preface

implement, i.e., the cultivator, design of its components, and its power requirement. Chapter 5 presents the working principle and design of active tillage implements such as rotavator and powered disk harrow, and their power requirements. Chapter 6 elaborates on the design principles and power requirement of combination tillage implements for better utilization of tractor power; both passive-passive and passiveactive as well as active-passive tillage implements developed by Prof. Raheman’s research team at IIT Kharagpur are discussed in detail along with their performances. Chapter 7 describes the instrumentation needed and the procedure to be followed to measure different parameters required for the performance evaluation of different tillage implements. We hope this book will be a valuable reference to be used by students, faculty members of Agricultural Engineering in the specialization of Farm Machinery, and practicing engineers engaged in the design of farm machinery. The design procedure discussed here with suitable examples will make them understand easily and help them to develop efficient tillage machinery in future. Kharagpur, India

Hifjur Raheman Pranay Sarkar

Acknowledgements

All praises to Almighty, who has given me wisdom, strength, and patience and made me capable of writing a book which covers in detail the design of different tillage implements. I am indebted to my teachers late Prof. C. P. Gupta and Prof. V. K. Jindal of Asian Institute of Technology, Bangkok, Thailand, for introducing me to the field of Farm Machinery and Power. I am grateful to Prof. S. K. Upadhyaya, Biological and Agricultural Engineering Department, University of California, Davis, USA, for his encouragement and constant support. A special mention to my colleagues Prof. E. V. Thomas, Prof. P. S. Chattopadhyay, and Prof. N. Mohapatra for their encouragement in writing this book. I want to acknowledge with gratitude the blessings of my parents, and the love and support of my elder brothers and sisters. Mere words can’t express my gratitude to my loving wife, Shagufta, and sons Mehfooz and Faiz, whose patience, generous support, and constant encouragement made me complete my dream of writing a textbook. I also appreciate the encouragement of my daughter-in-law, Naaz. I strongly acknowledge the sincere efforts made by my research team members Dr. Rohit K. Sahu, Dr. Showkat Rasool, Dr. Ajay K. Roul, and Dr. Ganesh Upadhyaya for developing efficient tillage implements under my guidance which are included in this book and for their suggestions in preparing this book. A big thanks to my Ph.D. students, Anshu, Rajesh, Manish, Anup, Lokesh, Swagatika, Vinay and Sunny who have directly or indirectly helped me in preparing this book. I wish to place in the record the support of publishers like Elsevier and Springer Nature for permitting me to use the copyright of materials without which this book would not have been possible. I am incredibly grateful to Ms. Priya Vyas and Mr. Suresh Dharmalingam for all their assistance and technical support.

ix

x

Acknowledgements

Despite sincere efforts made to keep this book error-free, still there may be some mistakes. For that, I sincerely apologize and invite readers of this book to offer constructive criticism and suggestions for further improvement in the subsequent editions. Hifjur Raheman

Contents

1 Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Objectives of Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Types of Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Tillage Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Tillage Tool Design Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Classification of Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Patterns of Tillage Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 2 4 6 7 8 9

2 Moldboard Plow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Components of a Moldboard Plow . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Share . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Moldboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Landside . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Frog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.5 Attachments to Moldboard Plow . . . . . . . . . . . . . . . . . . . . . . 2.3 Representation of Forces Acting upon a Plow Bottom . . . . . . . . . . . 2.4 Resistance Developed During Plowing . . . . . . . . . . . . . . . . . . . . . . . 2.5 Geometry of Share of Moldboard Plow . . . . . . . . . . . . . . . . . . . . . . . 2.6 Furrow Inversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Effect of Forward Speed on Longitudinal, Lateral, and Vertical Soil Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Effect of Depth and Width of Cut on Draft/Specific Draft . . . . . . . 2.9 Effect of Plow Bottom Shape and Design on Draft . . . . . . . . . . . . . 2.10 Effect of Attachments and Rear Furrow Wheel on Draft . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 13 14 14 15 17 17 18 19 21 24 27 28 30 31 31 43

xi

xii

Contents

3 Disk Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Forces Acting on the Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Disk Plow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Types of Disk Plow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Soil Reactions on Plow Disks . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Horizontal Hitching of Pull-Type Disk Plows . . . . . . . . . . . 3.4 Disk Harrows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Types of Disk Harrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Soil Reactions on Disk Harrow Blades . . . . . . . . . . . . . . . . . 3.4.3 Forces Acting upon a Disk Harrow . . . . . . . . . . . . . . . . . . . . 3.4.4 Couple Acting on Disk Harrow Gangs . . . . . . . . . . . . . . . . . 3.4.5 Disk Harrow with Hinged Pull Members but Without Gage Wheels or Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Design of Disk Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Width of Disk Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Diameter of Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.3 Thickness of Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Spacing between Disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.5 Number of Disks per Gang . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.6 Design of Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.7 Design of Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

45 45 45 46 46 48 50 51 51 52 53 55

4 Cultivator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Cultivator Teeth (Working Elements) . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Working Zone of the Cultivator’s Tooth . . . . . . . . . . . . . . . . . . . . . . . 4.4 Shanks of Rigid Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

77 77 77 80 84 93

5 Rotary Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Rotavator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Construction and Different Components of a Rotavator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Kinematics of Blade-Soil Interaction . . . . . . . . . . . . . . . . . . . 5.2.3 Angles Associated with Cutting Trajectory . . . . . . . . . . . . . 5.2.4 Forces Acting on the Furrow Slice and Specific Work . . . . 5.2.5 Design of a Rotavator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Powered Disk Harrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Disk Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Disk Blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

95 95 96

56 57 57 58 59 59 61 62 65 76

96 99 101 104 109 112 113 114

Contents

5.3.3 5.3.4 5.3.5 5.3.6 References

xiii

Disk Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting Width of Single Acting Disk Harrow . . . . . . . . . . . . Calculation of Total Power Required . . . . . . . . . . . . . . . . . . . Gang Shaft Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....................................................

114 114 115 116 128

6 Combination Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Classification of Combination Tillage Implements . . . . . . . . . . . . . . 6.3 General Approach for Prediction of the Power Requirement of Combination Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Passive-Passive Combination Tillage Implements . . . . . . . . 6.3.2 Active–Passive Combination Tillage Implements . . . . . . . . 6.4 Performance Evaluation of Combination Tillage Implements . . . . 6.4.1 Cone Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Mean Weight Diameter (MWD) . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Width of Cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.4 Actual Field Capacity (AFC) and Field Efficiency (FE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.5 Volume of Soil Handled Per Unit Time . . . . . . . . . . . . . . . . . 6.4.6 Soil Inversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.7 Fuel Energy Input to the Tractor . . . . . . . . . . . . . . . . . . . . . . 6.4.8 Overall Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Design of Combined Offset Disk Harrow . . . . . . . . . . . . . . . . . . . . . 6.5.1 Disk Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.2 Disk Blade Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.3 Disk Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.4 Cutting Width of Single Acting Disk Harrow . . . . . . . . . . . . 6.5.5 Prediction of Soil Disturbance Area for Calculation of Specific Draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.6 Specific Draft Estimation Model for Powered Disk Harrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.7 Estimation of Draft Requirement of Powered and Unpowered Disk Gangs . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.8 Estimation of Equivalent PTO Power of the Tractor . . . . . . 6.5.9 Gang Shaft Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

129 129 130

7 Measurement of Parameters for Performance Evaluation of Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Testing of Tillage Implements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Testing of Plow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Testing of Disk Harrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Testing of Rotary Tiller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

132 132 134 137 137 137 138 138 138 139 139 139 147 147 147 147 148 148 148 150 151 152 157 159 159 159 159 164 165

xiv

Contents

7.3

Instrumentation for Measuring Tillage Performance Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Draft Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Torque Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Wheel Slip Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 Measurement of Fuel Consumption . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

168 168 174 176 178 182

About the Authors

Prof. Hifjur Raheman is working at present as Professor in the Department of Agricultural and Food Engineering, Indian Institute of Technology Kharagpur, India. He obtained his B. Tech. from Odisha University of Agriculture and Technology, Odisha, M. Tech. with specialization in Farm Machinery and Power from Indian Institute of Technology Kharagpur, and Doctor of Engineering in Agricultural Machinery and Management from Asian Institute of Technology, Bangkok. He has so far guided 16 Ph.D. students in the area of Farm Machinery and Power and is the Fellow of prestigious professional bodies such as the National Academy of Agricultural Sciences (NAAS), India, the Institution of Engineers (India), and the Indian Society of Agricultural Engineering. He has published 105 papers in peer-reviewed journals. He is at present the Associate Editor for the Journal of Institution of Engineers Series A. He is a well-known expert in his field and has been honored with several awards. Pranay Sarkar is currently working as Research Scholar under the supervision of Prof. H. Raheman in the Department of Agricultural and Food Engineering, Indian Institute of Technology Kharagpur, India. He obtained his B. Tech. (Agricultural Engineering) from Bidhan Chandra Krishi Viswavidyalaya, West Bengal, and M. Tech. (Farm Machinery and Power) from the Indian Institute of Technology Kharagpur. His research areas are application of robotics arm in agriculture, vegetable harvesting machinery, and electric-powered agricultural machines.

xv

Chapter 1

Tillage

Abstract The most important objective of tillage has been to create soil conditions that meet the requirements of the crop. In this chapter, various types of tillage, like primary tillage, secondary tillage, minimum tillage, and mulch tillage are discussed along with tillage implements used in each of these categories of tillage. Classification of tillage based on the power source used to operate the tillage implements as well as to its soil working parts is also discussed. The basic concept of soil failure due to tillage implement has been included in this chapter with tool design factors. In the end, different tillage patterns followed in carrying out tillage operations in the field are described. Keywords Minimum tillage · Mulch tillage · Draft · Passive tillage implement · Active tillage implement · Tillage pattern

1.1 Introduction Tillage is the process of mechanically modifying soil to create an environment conducive to grow crops (Lamandé et al., 2005). To allow the roots of the crops to penetrate and disseminate throughout the soil easily, the compact surface of the ground is opened and loosened to a specific depth during soil tillage. The physical state of the soil, which is largely reliant on its water, air, biological, and thermal regimes, is altered by soil tillage. It is a useful tool for controlling weeds, pests, and diseases as well as for enhancing soil fertility and producing the ideal environment for plant growth and development (Upadhyay & Kishor, 2019). Compared to all other crop raising practices, it is the most difficult and time consuming practice.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_1

1

2

1 Tillage

1.2 Objectives of Tillage 1. Tillage loosens up compacted soil layers, which improves soil permeability and aids in root penetration to the required depth (Cai et al., 2014). 2. Tillage enhances soil-seed contact to allow water to reach seed and seedling roots. For fast and uniform germination, water must be able to travel freely between the soil particles (Blunk et al., 2021). 3. Tilling the soil at the right moment destroys weeds and unwanted crop plants. 4. Tilling the soil when the soil moisture is at its ideal, better soil structure can be achieved (Hadas & Wolf, 1983; Dexter & Rechard, 2009). 5. Tillage across the slope of the field will generate furrow dikes, which will slow down the velocity of runoff water and hence will prevent soil erosion on sloppy terrain. Contour tillage and strategic placement of trash can both help to decrease soil erosion (Jia et al., 2020). 6. Tillage decreases volatilization losses of fertilizers or any other agro-chemicals applied for the control of weeds, insects, and pests, and it also aids in the incorporation of weeds, crop residues, green manures, and other organic manures (Alleto et al. 2010).

1.3 Types of Tillage Types of tillage systems are represented by a schematic diagram in Fig. 1.1. There are two types of tillage systems in general: conventional and conservation. In contrast to the conventional tillage system, which inverts the soil, the conservational tillage system retains the crop residue from the previous year’s standing crops. In addition, the traditional or conventional tillage system includes primary, secondary, and special-purpose tillage. Depending on the use, special-purpose tillage is further divided into different types (Khan, 2019). Primary tillage: Primary tillage is the initial major soil tilling operation that is usually carried out to reduce soil strength, cover plant residues, and rearrange soil aggregates. The operations performed to open up any cultivable land to prepare a seedbed for growing plants are known as primary tillage. Moldboard plow, disk plow, subsoiler, chisel plow, and other similar implements are used in primary tillage. Different primary tillage implements may have varying effects on soil loosening and may change the macrostructure of soil, particularly its porosity, over time throughout the tillage zone (Bengough et al., 2011). These potential variations may also affect the hydraulic characteristics of the soil, particularly infiltration (Allmaras et al., 1977). Long-term use of such conventional tillage practices creates various soil quality problems, damages soil structure, and erodes the soil (Wang et al., 2019). Tillage erosion refers to net soil losses and accumulations in the landscape due to the uneven

1.3 Types of Tillage

3

Fig. 1.1 Different types of tillage

distribution of the amount of soil moved during plowing. The design of tillage implement, the depth and speed of operation, tractor-implement compatibility, and tillage operator skill all affect how much soil is moved during tillage (Lobb, 2008). Secondary tillage: Secondary tillage operations are carried out after primary tillage to prepare a seedbed (Aldaoseri and Muhsin, 2022). Secondary tillage reduces clod size, pulverizes soil, destroys grasses and weeds, and mixes crop residues with topsoil in the field. In addition to eliminating weeds, secondary tillage equipment operation creates an acceptable level of soil granule cohesiveness to maintain a balance between the amount of water and air for the seed that will be planted in the soil (Al-Sharif and Ghoneim, 1984). Generally, different types of harrows and cultivators are used as secondary tillage implements. Several studies have shown that lower bulk density and higher porosity of soil are achieved by the secondary tillage implements than a primary tillage implement (Abrougui et al., 2014; Mushin, 2017). Special-purpose tillage: Special-purpose tillage is performed for specific purposes to prepare the soil for the upcoming main-season crop. The time of special-purpose tillage could be in the off-season, before or after harvest, during summer, winter, or fallow. Some important special-purpose tillages are discussed below: • Subsoiling: Hardpan beneath the topsoil is broken up via subsoiling (Raper, 2005). To reduce the compaction of the earth, a special tool, like a chisel, is used. Once in every four to five years, subsoiling is advised. But when heavy machinery is used in farming, subsoiling is recommended after every three years. Subsoiling aids in providing an extra soil layer for crop development, allows excess water to percolate, reduces runoff and erosion, and makes it easier for roots to penetrate the soil below the water table and draw moisture from there (Busscher et al., 2002; Rathinavel, 2020). • Leveling: The soil surface is leveled, and smaller clods are broken using tools like rollers and planks. By leveling the soil surface, an uniform crop height is achieved

4

1 Tillage

because the smooth soil surface distributes moisture to the seeds uniformly (Jat et al., 2009). • Contour tillage: Contour tillage is the tillage technique used on the slopy field to reduce the rate of erosion. Increased surface roughness parallel to the slope is achieved through contour cultivation to prevent runoff. The velocity of any running water is decreased by the increased surface roughness, allowing more time for infiltration and thus lowers the erosion rates (Stevens et al., 2009). Mulch tillage: In mulch tillage, crop residues are spread and left over the soil surface or mixed with the top few centimeters of the soil (Becher, 2005; Pabin et al., 2003). Thus, runoff is reduced, and water can be conserved. It also minimizes wind and water erosion by reducing the splash effect of raindrops (Sumner & Stewart, 1992; Giller et al., 2011). Mulch tillage helps to increase nitrogen uptake efficiency, high nutrient supply, and crop yield (Głab & Kulig, 2008). A lot of crop residues on the surface or nearby safeguard the soil, but they complicate planting (as planting is to be done by penetrating the mulch). Minimum tillage: The least amount of soil disturbance is involved in a minimum tillage operation. It also involves less soil surface-breaking and involves planting crops into the vegetative cover of the soil during the dry season. The basic principle of minimum tillage limits the soil disturbance to a specific region, resulting in a minimal amount of soil turnover. Minimum tillage enhances soil structure, promotes plant growth and development, and lowers fuel cost (Grabowski et al., 2016; Rusu et al., 2009). The zero-till seed drill is a minimum tillage implement, in which a soil opening device like a chisel, sweep, or tine is attached just ahead of the planter. With this type of seed drill, seeds can be planted directly into the field just after the harvest of the previous crop with the minimum disturbance of the soil. Thus, the cost of fuel, tractor operation, water, fertilizer, and herbicides can be saved easily, and timely sowing can be achieved.

1.4 Tillage Mechanics Before entering into tillage mechanics, it is essential to know the definitions of a few terminologies associated with tillage and the fundamentals of tillage mechanics. Force is an action that changes or attempts to change the body’s condition of rest or motion. Pull on an implement is the total force exerted upon the implement by a power unit. With tillage implements, pull acts at some angle above the horizontal, and it may or may not be in a vertical plane parallel to the line of motion. Draft and side draft are the horizontal components of pull, parallel and perpendicular to the direction of motion, respectively. The specific draft is the draft per unit area of the tilled cross-section, usually expressed as N/cm2 or kgf/cm2 . Most tillage tools have a draft that increases as forward speed increases, primarily due

1.4 Tillage Mechanics

5

to the greater acceleration force brought on by increased frictional resistance and increased kinetic energy imparted to the soil (Eq. 1.1). Ds = D0 + K S 2

(1.1)

DS = draft at speed S, D0 = static component of the draft, independent of speed, K = a constant whose value is related to the implement type and soil condition. Power is the rate of doing work and drawbar power in relation to a pull-type or a mounted implement is the power required to pull or move the implement at a uniform speed. The reactions of soil to forces applied by the tillage tools are affected by the resistance of the soil to compression, resistance to shear, adhesion, and frictional resistance. These are dynamic properties associated to soil movement. There are two types of soils: plastic and non-plastic. Within a certain range of moisture content, plastic soils can be molded, and they will keep their formed shape after drying. Sands or other soils containing less than 15 to 20% clay are generally considered to be nonplastic. If a plastic soil is saturated with water and then allowed to dry, it goes through four stages: sticky, plastic, friable (crumbly), and hard (cemented)—in that order. Tillage tools consist of devices for applying pressure to the soil often by means of inclined planes or wedges. As tool advances, compressive stress is imposed on the soil in the tool’s path. In friable soil, it results in a shearing action. The shearing of soil is considerably different than the shearing of most solids, in that the reaction may extend for a considerable distance on either of the shear plane because of internal friction and the cohesive action of moisture films. Cohesion and internal friction are sometimes referred to as the real physical properties of the soil. In reality, they are the only parameters of shear as indicated in Eq. 1.2. Due to internal friction and the cohesion of moisture layers, the reaction may extend significantly on either side of the shear plane (Kepner et al., 1978). τ = C + σ tanϕ

(1.2)

τ = shearing stress at soil failure, C = cohesion (a force that binds two identical particles together), σ = stress normal to the plane of shear failure. By measuring the shear stress (τ) for various values of normal stress (σ), C and ϕ values can be calculated. (Fig. 1.2, based on experiments conducted at the traction laboratory, IIT Kharagpur, India). Generally, the values for C and ϕ are zero for sand and clay, respectively. Shear strength has an important influence on the draft of tillage tool. Compression-related soil failure is typically accompanied by a volume drop. Failure by compression and failure by shear are not separate occurrences but rather result from a combined action. Every tillage process involves soil sliding across a tool surface. That friction is essential for the draft requirement. This phenomenon differs from the internal friction as expressed in Eq. 1.2. So, in the tillage tool, the friction is usually soil-on-steel in the tangential direction of the tillage tool surface. There is also adhesive force due to

6

1 Tillage

Fig. 1.2 Typical failure envelope of sand

moisture content which varies depending on the amount of moisture present in the soil. This creates a perpendicular force on the surface of the tillage tool and results in an apparent coefficient of friction, i.e., the combination of forces in both tangential and perpendicular directions. Abrasiveness is a dynamic property of soils. When a large amount of soil passes over the surface of the tillage tool, abrasive wear may take place, which can change the shape and size of the tillage tool, making it ineffective. The strength of the soil and the efficiency of the implement in using energy determine how much energy is needed to achieve a given degree of pulverization. The type of soil and its physical state have an impact on soil strength. More energy is needed to break up clay soils than sandy or loamy soils. The physical state of the soil is influenced by the climate, farming techniques, cultural customs, and other elements. For a particular soil condition, the parameters which may affect draft and energy utilization efficiency include travel speed, tool shape, tool arrangement, depth of cut, and width of cut.

1.5 Tillage Tool Design Factors Tool shape, arrangement, and movement of tillage tools and soil condition control the overall soil manipulation. The shape can be classified as macroshape, edgeshape, and microshape (Gill & Vandan Berg, 1967). The term macroshape defines the shape of the gross surface, and edge shape refers to the peripheral and cross-sectional shapes of the boundaries of the soil working surfaces. Notched and smooth disk blades have different edge shapes but the macroshapes are the same. Microshape refers to surface roughness. The shape of the edge of the tool has an effect on the draft and components of soil forces. Compared to disk blades sharpened from the convex side, the disks sharpened from concave disk blades penetrate more quickly. The roughness of the surface influences friction force and other aspects of soil movement, such as scouring.

1.6 Classification of Tillage Implements

7

Manner of the tool means arrangement, orientation, its path, and speed along the path. Speed is a relatively easy factor to change when power is adequate. Although speed primarily influences draft, it also has an impact on soil breakage and movement.

1.6 Classification of Tillage Implements Tillage implements may be classified as passive tillage implements, active tillage implements and combination tillage implements and they are discussed below: Passive tillage implements: In this group, the implements are pulled by the tractor. However, the tractor does not provide any power to the soil-working components. Moldboard plows, disk plows, and cultivators are a few examples of passive tillage implements. Active tillage implements: In this group, the implements are pulled by the tractor, and the soil-working components get power from the tractor (mainly from tractor PTO). Generally, these types of implements provide more degree of pulverization. Rotavators and powered disk harrows are common examples of active tillage implements. Combination tillage implements: When two or more tillage operations are carried out in the same soil simultaneously by combining two or more groups of tillage implements, that is called a combination tillage operation and the group of tillage implements is called combination tillage implement. By combining two or more tillage operations, time, fuel requirement, and compaction of soil can be reduced (Sahu, 2005; Sarkar et al., 2021). Cultivator-Disk harrow (passive-passive) and Rotacultivator in which cultivator tines (passive unit) are attached in front of a rotavator (active unit) are a few examples of combination tillage implements. In passive implements, tillage energy utilization efficiency is low due to poor power transmission at the soil tire interface and, rolling resistance and improper matching of tractor and implements. On the other hand, active tillage implements generally till with greater pulverization consuming more power per unit width. Active tillage implements produce a negative draft (forward thrust) when the working elements are rotated in the direction along the direction of travel of the tractor. This may require further energy inputs to control tractor steering. In combination tillage implements, the negative draft developed by the active implement reduces the draft requirement of the tillage implement. Another way of classifying tillage implements is according to the sources of power used for their operations and are as follows: (i) Hand-operated tools. (ii) Animal-drawn implements. (iii) Tractor or power tiller-drawn implements.

8

1 Tillage

Hand tools are operated by the muscle power to impart its pulling, pushing, or swinging motions. Because of the limited power availability, only tools are used for small-scale jobs and smaller holdings. When implements of smaller size are pulled by the animals, they are called animaldrawn implements. Usually, animal-drawn implements are of two types walking type and riding type. There is no provision for an operator to sit in a walking-type implement. This means that the operator must walk behind the implement to control it. In contrast, riding type implements feature seating arrangements for the operator. The frame carrying the seat is supported on wheels. Hence, the operation of these implements is much more balanced as compared to the walking type. Tractor or power tiller-operated implements are operated at higher speeds and the size of implements are bigger than the animal-drawn implements, hence covering more width and are operated at higher depth. These implements can be classified as trailed, semi-mounted type, and mounted type. A trailed implement is one that has a pin joint connecting it to the tractor drawbar. The main body of the implement is supported on the grounds. Such an implement is easily attached or detached from the power source. An implement that is firmly attached to the tractor or power tiller is referred to as a semi-mounted type. Attachment and detachment take more time but control is much easier. A mounted implement is one that is attached as an integral part of the power source, most often a tractor. It is attached to the three-point linkage of the tractor and is lifted or lowered by the tractor hydraulics. Since the tractor steers it directly, it needs the least amount of space to turn. These implements can be mounted either at the front or rear of the tractor with a suitable hitching arrangement.

1.7 Patterns of Tillage Operation Tillage operations can be initiated in the field in two ways. (i) Starting at the center In the center of the field, a small area is marked, and it is plowed first. After that, plowing of the entire plot is completed by working around this little area (Fig. 1.3). This approach is not very cost-effective. (ii) Starting at the outer end The tractor begins plowing at one end of the field, goes along the entire perimeter, and then gradually progresses from the edges to the center of the field (Fig. 1.4). This technique avoids rear furrows. Typically, this approach is used for conventional plowing.

References

9

Fig. 1.3 Round and round plowing (starting at the center)

Fig. 1.4 Round and round plowing (starting at the outer end)

References Abrougui, K., Boukhalfa, H. H., Elaoud, A., Louvet, J. N., Destain, M. F., & Chehaibi, S. (2014). Effects of three tillage systems on physical properties of a sandy loam soil. International Journal of Current Engineering and Technology, 4(6), 3555–3561. Aldaoseri, M. J., & Muhsin, S. J. (2022). The influence of some secondary tillage implement and mixing organic residues on some physical properties of soil at the beginning and end of the Oat (Triticum aestivum L.) growing season. IOP Conferences Series: Earth and Environmental Science, 1060, 012139. Al-Sharif, S., Ghoneim, A. Y. A. (1984).Tillage and plows (1st ed.). The General Establishment for Publishing and Distributing and Advertising (pp. 277). Tripoli, Libya. Alletto, L., Coquet, Y., Benoit, P., Heddadj, D., & Barriuso, E. (2010). Tillage management effects on pesticide fate in soils. A Review. Agronomy for Sustainable Development, 30, 367–400. Allmaras, R. R., Rickman, R. W., Ekm, L. G., & Kimball, B. A. (1977). Chiseling influences on soil hydraulic properties. Soil Science Society of America Journal, 41, 796–803.

10

1 Tillage

Bengough, A. G., McKenzie, B. M., Hallett, P. D., & Valentine, T. A. (2011). Root elongation, water stress, and mechanical impedance: A review of limiting stresses and beneficial root tip traits. Journal of Experimental Botany, 62(1), 59–68. Becher, H. H. (2005). Impact of the long-term straw supply on loess-derived soil structure. International Agrophysics, 19, 199–202. Blunk, S., Bussell, J., Sparkes, D., Sturrock, C., de Heer, M. I., Mooney, S. J., & Sturrock, C. J. (2021). The effects of tillage on seed-soil contact and seedling establishment. Soil and Tillage Research, 206, 104757. Cai, H., Ma, W., Zhang, X., Ping, J., Yan, X., Liu, J., Yuan, J., Wang, L., & Ren, J. (2014). Effect of subsoil tillage depth on nutrient accumulation, root distribution, and grain yield in spring maize. The Crop Journal, 2, 297–307. Dexter, A. R., & Richard, G. (2009). Tillage of soils in relation to their bi-modal pore size distributions. Soil and Tillage Research, 103(1), 113–118. Gill, W. R., Vanden Berg, G. E. (1967). Soil dynamics in tillage and traction. USDA Agriculture Handbook No. 316. Giller, K. E., Corbeels, M., Nyamangara, J., Triomphe, B., Affholder, F., Scopel, E., & Tittonell, P. A. (2011). A research agenda to explore the role of conservation agriculture in African smallholder farming systems. Field Crops Research, 124, 468–472. Głab, T., & Kulig, B. (2008). Effect of mulch and tillage system on soil porosity under wheat (Triticum aestivum). Soil and Tillage Research, 99, 169–178. Grabowski, P. P., Kerr, J., Haggblade, S., & Kabwe, S. (2016). Determinants of adoption and disadoption of minimum tillage by cotton farmers in eastern Zambia. Agriculture, Ecosystems and Environment, 231, 54–67. Hadas, A., & Wolf, D. (1983). Energy efficiency in tilling dry clod-forming soils. Soil and Tillage Research, 3, 47–59. Jat, M. L., Gathala, M. K., Ladha, J. K., Saharawat, Y. S., Jat, A. S., Kumar, V., Sharma, S. K., Kumar, V., & Gupta, R. (2009). Evaluation of precision land leveling and double zerotill systems in the rice–wheat rotation: Water use, productivity, profitability and soil physical properties. Soil and Tillage Research, 105, 112–121. Jia, L., Zhao, W., Zhai, R., An, Y., & Pereira, P. (2020). Quantifying the effects of contour tillage in controlling water erosion in China: A meta-analysis. CATENA, 195, 104829. Kepner, R. A., Bainer, R., & Barger, E. L. (1978). Principles of farm machinery (3rd ed.). USA: The AVI Publishing Company, Inc. Khan, A. (2019). Tillage and crop production. In Agronomic crops. Volume 1: Production Technologies. Springer. Lamandé, M., Munkholm, L. J., & Børresen, T. (2005). Soil tillage. Reference Module in Earth Systems and Environmental Sciences. Lobb, D. A. (2008). Soil movement by tillage and other agricultural activities. Encyclopedia of Ecology (pp. 3295–3303). Academic Press. Muhsin, S. J. (2017). Performance study of moldboard plow with two types of disk harrows and their effect on some soil properties under different operating conditions. Basrah Journal of Agricultural Sciences, 30(2), 1–15. Pabin, J., Lipiec, J., Włodek, S., & Biskupski, A. (2003). Effect of different tillage systems and straw management on some physical properties of soil and on the yield of winter rye in monoculture. International Agrophysics, 17, 175–181. Raper, R. L. (2005). Effect of annual, biennial, and triennial in-row subsoiling on soil compaction and cotton yield in southeastern U.S. silt loam soils. Applied Engineering in Agriculture, 21(3), 337−343. Rathinavel, S. (2020). Effects of subsoiler on farm Fields-A review. International Journal of Current Microbiology and Applied Sciences, 9(10), 554–556. Rusu, T., Gus, P., Bogdan, I., Moraru, P. I., Pop, A. I., Clapa, D., Marin, D. I., Oroian, I., & Pop, L. I. (2009). Implications of minimum tillage systems on sustainability of agricultural production and soil conservation. Journal of Food, Agriculture and Environment, 7(2), 335–338. Sahu, R. K. (2005). Development and performance evaluation of combination tillage implements for 2WD tractors. Unpublished Ph. D. thesis. Indian Institute of Technology Kharagpur, Kharagpur, India.

References

11

Sarkar, P., Upadhyay, G., & Raheman, H. (2021). Active-passive and passive-passive configurations of combined tillage implements for improved tillage and tractive performance: A review. Spanish Journal of Agricultural Research, 19(4), e02R01. Stevens, C. J., Quinton, J. N., Bailey, A. P., Deasy, C., Silgram, M., & Jackson, D. R. (2009). The effects of minimal tillage, contour cultivation and in-field vegetative barriers on soil erosion and phosphorus loss. Soil & Tillage Research, 106, 145–151. Sumner, M. E., & Stewart, B. A. (1992). Soil Crusting—Chemical and physical processes. In Advances in soil science. Boca Raton: CRC Press, Lewis Publication. Upadhyay, B., & Kishor, K. (2019). Soil tillage. In Current research in soil science. New Delhi: AkiNik Publications. Wang, S., Guo, L., Zhou, P., Wang, X., Shen, Y., Han, H., Ning, T., & Han, K. (2019). Effect of subsoiling depth on soil physical properties and summer maize (Zea mays L.) yield. Plant, Soil and Environment, 65(3), 131–137.

Chapter 2

Moldboard Plow

2.1 Introduction A moldboard plow is a primary tillage implement used for the mechanical manipulation of soil. The main function of a moldboard plow is to cut, lift, turn, and pulverize the soil. Its main components are moldboard, share, land side, frog, and shank, and it is sometimes provided with plow accessories such as a colter and jointer. The variation in the design of components of moldboard plow is to accommodate varying soil and working conditions and for use with different power sources. Moldboard plows are basically of two types, animal-drawn and tractor-drawn. Tractor-drawn moldboard plow may be one-way (Fig. 2.1a) or two-way (reversible) type (Fig. 2.1b). Moldboard plows are typically made to turn the furrow slices solely to the right. The two-way plows, on the other hand, feature two sets of bottoms in the opposite direction that can be employed selectively. This allows all of the furrows to be directed toward the same sides of the field, which are used by the right-handed bottom for one direction of travel and the left-handed bottom for the return journey. To switch from one set to the other, the two sets of moldboard plow bottoms are attached on a single frame that is rotatable about a longitudinal axis. Most of the time, rotation of two-way plow is achieved with a hydraulic cylinder attached to the plow that is powered by the tractor’s PTO (Power take-off). Back and dead furrows are eliminated with a two-way plow. As a result, the field will be virtually levelled, allowing for effective watering and drainage. Two-way plows are also helpful for terraced fields, contour plowing, and small uneven fields. During tillage operation the one-way plow must be operated beginning with back furrows (two furrow slices thrown back-to-back) and ending with dead furrows (two open furrows together). The top and side views of a moldboard plow are shown in Fig. 2.2.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_2

13

14

2 Moldboard Plow

Fig. 2.1 Tractor-drawn moldboard plow a one-way, b reversible

(a) Tractor-drawn 2 bottom one-way

moldboard plow

(b) Tractor-drawn two-way (reversible) moldboard plow

2.2 Components of a Moldboard Plow 2.2.1 Share It is the main bottom end of the plow. It cuts the underside of the furrow and slices it away from the land. Share is bolted to the front of the frog. The main parts of the share are the share point, wing, and gunnel. • Share point—It is the front end of the cutting edge that penetrates into the soil. It takes the greatest load hence it is provided with a gunnel from below which constitutes a material reserve in case of removing and resharpening when it becomes dull. • Wing of share—It represents the outside of the share’s cutting edge. It provides plow bottom support.

2.2 Components of a Moldboard Plow

15

Fig. 2.2 Top and side views of a moldboard plow

• Gunnel—It is the share’s vertical face, which moves along the wall of the furrow. It supports the plow bottom against the furrow wall and absorbs the side thrust of the soil. Different types of shares There are different types of shares used in moldboard plow and they are summarized in Table 2.1. The shares are constructed from solid steel (C-1095), soft-centered steel, or chilled cast iron. Along with other minor elements, solid steel includes 0.90 to 1.05% carbon and 0.50 to 0.80% manganese. Soft-centered steel is used where the soil doesn’t stick. Solid steel is used where the soil is not abrasive and can withstand shocks. Cast iron is used when the soil is sandy or stony.

2.2.2 Moldboard It is the curved part that lifts, turns, and breaks the furrow slices. It receives the furrow slice from the share. To accommodate various soil conditions and crop requirements, moldboard has been developed in a variety of designs. Some mostly used moldboards are of the following types:

16

2 Moldboard Plow

Table 2.1 Different types of shares Types

Materials

Remarks

1. Slip High carbon steel, share soft-centered steel, cast iron

Slip share is the common type of share on animal-drawn plows and tractor-drawn plows. When worn out, a complete share is replaced

2. Slip Cast iron nose share

The share point of such a share has a replaceable unit. Only the nose is replaced before the full share needs replacement

3. Shin High carbon steel share

Similar to slip share but with an extension that fits at the side of the moldboard instead. It decreases moldboard’s cutting edge’s wear over time

4. Bar High carbon steel Share

It has an extension on its gunnel side that serves as the plow bottom’s landside

5. Bar High carbon steel point share

In addition to the main share, a long steel bar is used. It is pushed forward as the point wears out. Replacement of complete share is avoided

• General purpose—This type of moldboard has a moderate curve. The surface slope is gradual. It thoroughly crushes the soil when turning the furrow slice. It features a moldboard that is fairly long and has a face that is slightly convex (Fig. 2.3a). • Stubble type—In stubble soils, this moldboard is employed because it is short, wide, and has an abrupt curvature that lifts, breaks, and turns the furrow slice (Fig. 2.3b). Any old ground that needs to be well-pulverized can be plowed with it. • Sod or breaker type—It is used in grassy land where it is desired to turn the furrow slice completely so that the grass may not continue to grow. For complete inversion of soil, this type of moldboard is used (Fig. 2.3c). • Slat type—It is a moldboard whose surface is made of slats instead of a continuous sheet so that there are gaps between the slats. This type of moldboard is used in sticky soil, where it is difficult to get moldboard to scour (Fig. 2.3d). • High-speed type—High-speed bottoms are used with tractor-drawn plows for general farm use.

2.2 Components of a Moldboard Plow

17

Fig. 2.3 Different types of moldboards. a general purpose, b stubble type, c sod or breaker type, d slat type, e high-speed type

Moldboard is made up of 3-ply steel, the outer layer being high carbon steel (C1095) and the center layer being low carbon steel (C-1010, 0.08–0.13% carbon). The center layer is soft and tough, providing shock resistance.

2.2.3 Landside A component, which slides against the furrow wall and transmits lateral thrust of the plow bottom to the furrow wall. It also helps in stabilizing the plow while it is in operation. The rear bottom end of the landside is known as the heel, which rubs against the furrow sole.

2.2.4 Frog A triangular piece of metal to which other components of the plow bottom are attached. It is made of mild steel and it is sturdy. Usually, it doesn’t get damaged in case of an accident. If by chance it is damaged, it has to be replaced with a new one as its shape is very odd.

18

2 Moldboard Plow

Fig. 2.4 Different types of colters

2.2.5 Attachments to Moldboard Plow 2.2.5.1

Colter

Rolling colters are employed to help in cutting the furrow slice and to cut through the trash that might otherwise collect on the shin or beam and cause clogging. Colters mainly are of four types (Fig. 2.4)—plain colters (used in sod or relatively clean fields), notched colters (in heavy trash), ripple-edge colters (grassy land), and concave or disk colters (grassy land).

2.2.5.2

Jointer

A stationary jointer is a miniature plow bottom (Fig. 2.5) that is usually used in conjunction with a rolling colter and cuts a narrow, shallow furrow ahead of the shin. Its function is to move the trash and roots from this strip toward the main furrow.

Fig. 2.5 A moldboard plow fitted with jointer and colter

2.3 Representation of Forces Acting upon a Plow Bottom

19

Plow adjustments (Horizontal suction and vertical suction) For proper penetration and efficient operation, the moldboard plow needs 0.3–0.5 cm clearance, where the share joins the landside (Fig. 2.2). This is known as the vertical suction of the plow. Similarly, there should be a side clearance of about 0.5 cm (the point of the share bent away from where the landside is connected to the gunnel, Fig. 2.2). This is also known as horizontal suction. Plow size: The size of the moldboard plow is expressed by the width of the furrow that is designed to be cut. It can be measured by measuring the perpendicular distance from the share to the line joining point of share and heel of landside.

2.3 Representation of Forces Acting upon a Plow Bottom Forces acting upon the tillage tool help to determine total power requirements, proper hitching or application of the pulling force, and design for adequate strength and rigidity. Tillage implements moving at a constant velocity are subjected to three main forces or force systems, which must be in equilibrium. These are as follows: 1. Gravity force acting upon the implement. 2. Soil forces acting upon the implement. 3. The forces acting between the implement and the prime mover. The implement weight decides the working depth in the case of disk implements. In the case of moldboard plow, the vertical suction maintains operational depth. The useful soil reaction acting upon a moldboard plow bottom results from cutting, lifting, and inverting the furrow slices. Parasitic forces are those that act upon the side and bottom of the landside (including friction), as well as the rolling resistance of support wheels. In the following discussion, the useful resultant force R and its longitudinal, lateral, and vertical components are denoted as L, Ss , and Vv , respectively (Figs. 2.6 and 2.7). The term Qh indicates the resultant of all parasitic forces, where P, Pv , Ph , and Px include the effect of both useful and parasitic forces and the force of gravity on the implement. Here, the moldboard plow cuts a rectangular soil block and the pulling force is P. The angles of pull with horizontal and vertical planes are θ and Φ, respectively. Fig. 2.6 Soil reaction forces acting on the moldboard

20

2 Moldboard Plow

Fig. 2.7 Pull, draft, side draft, and lift forces acting on a moldboard plow

Fig. 2.8 Typical location of Rh and its relation to the land side force and the pull. a Straight pull, b angled pull, c long landside

Hence, the draft (horizontal component of pull in the direction of motion), L = PcosθcosΦ. The side draft (horizontal component of pull in a direction perpendicular to the direction of motion), S s = P cosθsinΦ. The vertical component of pull, Vv = PsinθcosΦ. When both parasitic and useful forces are considered, the horizontal component of useful soil reaction force consists of two components L and S s (Fig. 2.8). / Rh =

L 2 + Ss 2

(2.1)

Qh the horizontal component of parasitic force comprised two forces—thrust (T ) from the side wall, which is equal to the value of side draft (S s ) but in the opposite

2.4 Resistance Developed During Plowing

21

direction and friction force which acts tangentially along the landside and opposite to the direction of travel. This friction force is equal to the product of thrust value with coefficient of soil metal friction. / Q h = T 2 + (μT )2 (2.2) So, considering useful and parasitic forces, the magnitude of the draft along the line of pull / Px =

Rh 2 + Q h 2

(2.3)

But for angled pull, the draft will be Px = Ph cosθ

(2.4)

where, / Ph =

Rh 2 + Q h 2

(2.5)

Point H, the intersection of Rh and Qh is called the horizontal location of the center of resistance of the plow bottom. Referring to Fig. 2.8a, when the horizontal pulling force is in the direction of travel, a parasitic side force is automatically introduced on the landside to counteract side force (S). Qh is the resultant of this side force S and the accompanying frictional force on the landside. A pull angled to the left (Fig. 2.8b) increases the landside force and it will increase Px . Increasing the landside length (Fig. 2.8c) moves Qh to the rear, thus relocating the horizontal center of resistance farther back. H is closer to the landside because the line of Rh does not change.

2.4 Resistance Developed During Plowing Resistances developed in the tillage process are divided into useful and harmful resistance. The resistance overcome by working tools during the deformation and disintegration of tilled soil is useful resistance. They are not constant but depend on the physical properties of the soil (composition, hardness, moisture, weed content, and others), operating width and depth, form and state of working tool surfaces, the material from which tools are made and the plow working speed. Unit draft (Du ) is defined as draft required by the plow (Px ) per unit of the crosssection of the furrow. Du =

Px ab

(2.6)

22

2 Moldboard Plow

Table 2.2 Values of unit draft

Type of soil

Unit draft (Du ), kg/dcm2

Light soil

20–30

Medium soil

30–50

Heavy soil

50–70

Very heavy soil

>70

(Source Bernacki et al., 1972)

where a and b are the plowing depth and operating width of the plow, respectively. The typical values for Du experienced during field operation are given in Table 2.2. Assuming a rectangular furrow section, the cross-sectional area of the furrow is a × b. The tractive effort of the plow is determined using the Goryachkin (1968) formula: P = P1 + P2 + P3

(2.7)

The term P1 in this expression represents the constant resistance to plow motion in the furrow. P1 = f G

(2.8)

where f is the coefficient of resistance to plow motion in the furrow. For stubble, f = 0.3–0.5 and for clover f = 1; G is the plow weight. The second term of Eq. 2.7 P2 represents that part of the resistance caused by soil slice deformation. It is proportional to the slice cross-sectional area. P2 = Du ab

(2.9)

The third term of Eq. 2.7 P3 shows the fraction of resistance developed during transmission of kinetic energy to the soil mass when slices are thrown aside. If a × b is the dimensions of the slice and V is the plow forward velocity, then the volume of soil handled by the moldboard plow per unit time is given by Vs = abV

(2.10)

Thus, the mass of soil passing the moldboard per second is m = ρabV

(2.11)

where ρ is soil density, ρ=

γ g

(2.12)

2.4 Resistance Developed During Plowing

23

(Here, γ is the specific weight of the soil, and g is the acceleration due to gravity). m=

abV γ g

(2.13)

If the plow moves with a velocity V, soil particles are thrown aside with a different velocity V 1 V1 = ε´ V

(2.14)

The resistance expressed by the third term of Eq. 2.7 is given by P3 = mV1   γ ab´ε V 2 P3 = g

(2.15)

Considering that ε´ ( γg ) = ε, we get P3 = εabV2

(2.16)

where ε is a constant depending on the form of working surface of the moldboard and soil properties: ε = 150–200 kgf.s2 /m4 . Substituting the values obtained for P1 , P2 , and P3 in Eq. 2.7, the final expression of the Goryachkin formula for the tractive effort: P = fG + Du ab + εabV2

(2.17)

Tractive effort acts on the plow, which has a constant weight, and the soil, which is continuously placed on the moldboard in definite proportions. In this case, the tractive effort can be given by variation of momentum, that is P=

md V V dm d(mV ) = + dt dt dt

(2.18)

Here, first term mddtV determines the tractive effort lost in transmitting a certain acceleration to the plow. The second term Vdtdm represents the tractive effort loss upon providing a constant velocity to a certain quantity of soil with variable mass placed ). on moldboard per unit time ( dm dt On the basis of the above, we have γ dm = m = abV ( ) dt g V

γ dm = ( )abV 2 dt g

(2.19) (2.20)

24

2 Moldboard Plow

Hence, P=

γ md V + ( )abV 2 dt g

(2.21)

Comparing two Eqs. 2.17 and 2.21, the term mddtV corresponds to the first two terms of the Goryachkin rational formula ( f G + Du ab); which do not depend on plow speed. So, the second term ( γg )abV 2 equals εabv 2 .

2.5 Geometry of Share of Moldboard Plow The share forms a spatial wedge with three basic angles (Fig. 2.9): load angle (α), cutting angle (γ) and setting angle (θ0 ). OB OC OD = sinθ0 OB = sinθ0 OD OB = OD = tanγ sinθ0

tanα = OC tanα tanγ tanα

(2.22)

Load angle (α) and cutting angle (γ) are reciprocally proportional and exert an influence on the quality of the furrow slice crushing and the value of soil resistance. When the share arrangement is steeper, then it results in better soil crushing but increases the soil resistance. For light and medium firm soils, plowing is performed Fig. 2.9 Share as spatial wedge

2.5 Geometry of Share of Moldboard Plow

25

Fig. 2.10 Forces acting on share (neglecting friction)

by bottom with shares having larger cutting angles because these soils are easy to crush. On the other hand, heavy soils are hard to crush, hence for plowing these soils, shares with smaller cutting angles are taken in order to meet the low resistance. Setting angle, within limits of values used, does not have any effect on crushing and on total cutting resistance. When cutting by share is perpendicular to the share edge, the soil resistance is proportional to edge length and unit draft (when frictional force is neglected as shown in Fig. 2.10). Soil resistance force (K), acting on plow share, K = PL × L L

(2.23)

where PL = force per unit length of share, L L = length of share, b = width of cut, V = forward speed of plow, and vS = slip speed of share K S = K sinθ0 = PL L L sinθ0

(2.24)

Ks is the horizontal component of K. But from Fig. 2.10, sinθ0 =

b LL

By putting the value of sin θ0 , in Eq. 2.24 K S = PL b

(2.25)

But when the friction force is considered (Fig. 2.11) cosϕ =

K K'

(2.26)

26

2 Moldboard Plow

Fig. 2.11 Forces acting on share (including friction)

ϕ is the friction angle. K' =

K PL L L PL b = = cosϕ cosϕ cosϕsinθo

(2.27)

From Fig. 2.11, sin(ϕ + θ0 ) =

K S' K'

K S' = K ' sin(ϕ + θ0 ) K S' =

PL b (sinθ0 cosϕ + cosθ0 sinϕ) cosϕsinθ0

(2.28) (2.29) (2.30)

K S' = PL b(1 + tanϕcotθ0 )

(2.31)

K S' = PL b(1 + μcotθ0 )

(2.32)

where μ is the coefficient of share friction on soil = tanϕ. When θ0 increases PL increases, but cotθ0 decreases. So, within the limit of 30 to 50° for θ0 , the effect of θ0 on the total cutting resistance value is insignificant.

2.6 Furrow Inversion

27

2.6 Furrow Inversion The manner in which furrow slices are inverted depends on the form of moldboard, lateral dimension of the furrow slice, and plowing speed. As the furrow slices get deformed during operation of moldboard plow, it is somewhat difficult to define in theory the real process of inversion. It is assumed approximately that • Furrow slice does not change its cross-section in the process of inversion. • Plow speed is very low. • Moldboard shape is disregarded. The furrow slice ABCD (Fig. 2.12) is first turned around at the point D to a vertical position DA1 B1 C1 and afterward it is turned around at point C 1 and then laid on the previously tilled slice at an angle θ. sinθ =

C 2 D2 a = C1 C2 b

(2.33)

where a and b are the tillage depth and furrow width, respectively. From the above equation (Eq. 2.33), it can be seen that the greater the tillage depth or smaller the furrow slice width, the greater the angle θ, i.e., the steeper the furrow slices arranged. The outer furrow slice profile L S is as given below L s = E A2 + A2 B2 = E B2 cosθ + a = b(cosθ + sinθ ) The expression (cos θ + sin θ) attains its maximum when θ = 45° . Since, sin45◦ = cos45◦ = √12 . Then, √ (L s )max = b 2 For angle θ = 45° , the relation

b a

amounts to

Fig. 2.12 The course of theoretical inversion of the furrow slice by the moldboard bottom

(2.34)

28

2 Moldboard Plow

√ 1 b = = 2 ◦ a sin45 or, b = 1.41 a where b = width of cut per bottom, m.

2.7 Effect of Forward Speed on Longitudinal, Lateral, and Vertical Soil Reactions The effect of speed upon L, Ss , and Vv forces acting on a 36 cm general-purpose plow bottom tested in a soil bin at the National Tillage Machinery Laboratory is shown in Fig. 2.13. From this figure, it can be seen that all three of the soil-force components increase with speed in both fine sandy loam and sandy soil. A moldboard plow bottom has a downward acting vertical component of useful soil force (suction). The magnitude of Vv is influenced by soil type, soil condition, depth of cut, share edge shape, and sharpness. Hence, its magnitude varies widely in relation to L. From the results of soil bin test of 36 cm general-purpose moldboard plow as shown in Fig. 2.13, Vv /L ratio varied from 0.5 to 0.6 for sand and from 0.35 to 0.45 for fine sandy loam soil. McKibben and Reed (1952) experimented the variation of draft with speed and plotted the percentage increase in draft as a function of speed taking the draft at 4.83 km/h. The data for draft ranged from a speed of 1.6 to 13 km/h. The draft data for moldboard plows is represented by the following equation (Eq. 2.35) Dv = 0.83 + 0.0073V 2 Dr

(2.35)

where Dr = draft at reference speed, 4.83 km/h, and D v = the draft at speed V (Unit of Dv and Dr are same). V is the speed in km/h. The draft per meter width of cut of a tillage implement can be predicted from Eq. 2.36 given by ASAE (American Society of Agricultural Engineers), (ASAE, 2000).    D f i = Fi A + B(V ) + C V 2 Td

(2.36)

where Dfi = draft required per meter width of cut (N), F = dimensionless soil texture adjustment parameter; i = 1 for fine, 2 for medium and 3 for coarse soil; A, B, and C = machine specific parameters, V = speed of plowing operation (km/h), T d = depth of plowing (cm).

2.7 Effect of Forward Speed on Longitudinal, Lateral, and Vertical Soil …

29

Fig. 2.13 Effect of speed upon L, Ss , and Vv forces acting on a 36 cm general-purpose plow bottom tested in a soil bin with and without landsides (Source Kepner et al., 1978)

The machine specific parameters, A is the function of soil strength and B and C are the functions of soil bulk density. For computation of draft, values of F i , A, B, and C can be taken from ASAE Standard 2000 (given in Table 2.3). Table 2.3 Coefficients for predicting draft requirement (ASAE, 2000) Implements

SI unit Machine parameters

Soil parameters

A

B

C

F1

F2

F3

Moldboard plow

652

0

5.1

1.0

0.70

0.45

40

Offset disk harrow

254

13.2

0

1

0.88

0.78

30

Tandem disk harrow

216

11.2

0

1.0

0.88

0.78

30

32

1.9

0

1.0

0.85

0.65

25

Field cultivator

Variation range (±%)

30

2 Moldboard Plow

Table 2.4 Coefficients for predicting draft requirement of tillage implements (Roul & Raheman, 2017)

Tillage implements

Coefficients A

Moldboard plow

0.42

Cultivator Offset disk harrow

B

C

0.00

16.40

0.04

5.50

0.40

0.32

37.96

0.00

However, this draft prediction model does not take soil strength value (cone index) into consideration. Also, the range of variation in predicting draft values is very high (±40%). Hence, an attempt has been made at IIT Kharagpur, India to develop a similar equation (Eq. 2.37) for predicting the draft of tillage implements in sandy clay loam soil (Roul & Raheman, 2017). Implement width, soil cone index, depth, and speed of operation were taken as the input parameters in this equation. D f = {A × C I + B × V + C × V 2 } × W × Td

(2.37)

where Df = draft of the implement (N), A, B and C = machine specific parameters, A = f (soil strength) B or C = f (speed of operation); CI = cone index of soil (kPa), V = speed of operation (km/h), W = machine width (m) or number of furrow opener or tools and T d = tillage depth (cm). The values of A, B, and C for moldboard plow, cultivator, and offset disk harrow are given in Table 2.4. In sandy clay loam soil with varying soil strengths, this equation could precisely predict the draft requirements for moldboard plows, cultivators, and offset disk harrows with an absolute variation of 11.6, 5.5 and 10.5%, respectively.

2.8 Effect of Depth and Width of Cut on Draft/Specific Draft Previous studies show that the specific draft of a plow often decreases as the depth of operation increases until it reaches an ideal depth/width ratio, after which it tends to increase as the depth is increased further. Because the total force for cutting the lower portion of the furrow slice should be independent of depth, there has been an initial decrease in the specific draft. But beyond the optimum depth, clogging of the thick furrow slice on the moldboard probably increase the specific draft. The minimum specific draft for plow bottoms was observed to be at a depth of 13 to 18 cm. In sandy soil, varying the width of cut with 30 and 41 cm plow bottom (landside removed) has little effect on the specific draft for the bottom alone. But, landside friction, draft due to colter and rolling resistance of the plow wheels would change very little and hence would increase the specific draft as the width of cut is reduced.

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

31

2.9 Effect of Plow Bottom Shape and Design on Draft The shape of the moldboard plow has a definite influence on draft, although the relative effects are influenced by soil types and conditions, speed and perhaps other factors. In general, shapes that give the best trash coverage or the greatest degree of pulverization tend to have the highest drafts, although the reverse is not necessarily true. Share edge shape can significantly affect draft. Worn shares may have substantially greater draft than new shares. Share wear occurs rapidly in many types of soil particularly when moisture content is low. Draft increases by 15% or more only after a few hours of field operation (Gill and Vanden Berg, 1967). Changes in design or materials to reduce soil metal friction offer considerable potential for reducing draft. According to Wismer et al. (1968), friction on moldboard plow surfaces may account for up to 30% of the overall draft. Covering a plow bottom with Teflon reduced the draft by 23% in a soil where steel would not scour and by 12% in a soil where both scour.

2.10 Effect of Attachments and Rear Furrow Wheel on Draft According to findings from a number of sources, the draft of a rolling colter may be between 10 and 17% of the total draft for the plow-colter combination. The draft was decreased by 5 to 7% by absorbing the majority of the side thrust on the rear furrow wheel rather than entirely on the landside. There was a reduction of draft from 30 to 40% in sand and about 20% in fine sandy loam soil, when the landside was removed and all the side force was absorbed by the test car.

Design procedure of moldboard plow

Share The design parameters of share are load angle (α), cutting angle (γ), setting angle (θ0 ) and its length, width, and thickness. Figures 2.14 and 2.15 show slip and slip nose share respectively. Appropriate dimensions of share according to the tillage depth are given in Table 2.5. Moldboard Steps for designing moldboard are as follows:

32

2 Moldboard Plow

Fig. 2.14 Slip share

Fig. 2.15 Slip nose share

Table 2.5 Appropriate dimensions (mm) of share according to the tillage depth Dimensions

Maximum depth of tillage, mm 150

200

250

300

350

450

L1 , mm

400

450

500

550

500–700

500–700

S1 , mm

115

125

135

150

150

160

S2 , mm

100

105

115

125

125

130

(Source Bernacki et al., 1972)

• Selection of type and kind of moldboard. • Decision on tillage depth (a) (normally maximum permissible is taken) from Table 2.5. • Calculation of furrow slice width (b) from the assumed ratio (b/a) using the reference values from Table 2.6. • Selection of α, θ0 , and γ values from Table 2.7. Table 2.6 Ratio of b/a for different types of tillage S. no

Type of tillage

Tillage depth (a), mm

Width of furrow slice (b), mm

b/a

1

Very deep

350–1000

400–700

0.7–1.1

2

Deep

250–350

300–400

1.1–1.5

3

Medium

180–240

250–350

1.3–1.8

4

Skimming

50–120

240

2.0–5.0

(Source Bernacki et al., 1972)

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

33

Table 2.7 Values of different angles commonly used in different moldboard plows Types of moldboard

Angles, degrees θ0

α

γ

Helical, semihelical, and cylindrical for lea tillage and rapid tillage

30–35 12–15 20–25

Semihelical and Cylindroidal moldboard

35–45 14–18 22–28

Cylindroidal and cylindrical moldboard plow for animal-drawn plows 40–50 15–20 20–30 (Source Bernacki et al., 1972)

• Drawing the frontal plan as in Fig. 2.16. Frontal plan is the characteristic feature of design, irrespective of the method used. Frontal plan starts with establishing the line of the share blade corresponding to the width B of the share which amounts to B = b + Δb

(2.38)

where b is structural width of furrow slice (furrow width, mm), Δb is the change in the structural width of furrow slice taken from Table 2.8. • The height of the breast edge of moldboard (h) depends on the width of the furrow slice and also on tillage depth (a) and on the forward velocity.

h = b + Δh1 + Δh2

Fig. 2.16 Drawing the frontal plan of a moldboard (Bernacki et al., 1972)

(2.39)

34

2 Moldboard Plow

Table. 2.8. Values of Δb, Δh1 , Δh2 , Δh3 , ΔS 1 , and ΔS 2 for different plows Values of Δb for different plows Standard plow

(+20) to (+40) mm

Lea plow

(−20) to (−40) mm

Values of Δh1 for different soils Medium firm and firm soil

(0) to (−20) mm

Light sandy soil

(0) to (+20) mm

For grasslands

(−0.1b) to (−0.2b)

Values of Δh2 (0) If velocity of operation v < 7 kmh−1

For grassland

(+5) to (+10) mm per 1 km/h, above v > 7 kmh−1 Values of Δh3 For general plows

(0) to (−30) mm

Helical and semihelical moldboard

Slightly less than the general plow

Values of ΔS1 and ΔS2 ΔS 1

(+5) to (+10) mm

ΔS 2

20 mm

(Source Bernacki et al., 1972)

where h is height of the breast edge of the moldboard (mm), Δh1 , Δh2 , and Δh3 are breast height factors taken from Table 2.8. The entire height of the moldboard is given by H=

√ a 2 + b2 + Δh 3 + Δh 2

(2.40)

where H is entire height of the moldboard, mm In order to determine the lower edge of the moldboard, the line of profile of an inverted furrow slice is plotted on the front plane. For this purpose, a line is plotted at an angle θ at a distance (tillage depth, a) from the furrow wall. The value of angle θ is calculated using Eq. 2.41 given below sinθ =

a b

(2.41)

• The breast edge of the moldboard falls from the perpendicular by ΔS1 = 5 to 10 mm. • The lower edge of moldboard can be determined by a line passing over the same point as the profile line of the furrow slice at an angle θ1 given by sinθ1 = where Δa = 2.5 mm

a + Δa b

(2.42)

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

35

Fig. 2.17 Design of a cylindrical moldboard (Bernacki et al., 1972)

Cylindrical moldboard plow is designed using the following steps: • After plotting the frontal profile of moldboard, the plotting of the horizontal plan is started on the lower left quarter of the drawing paper (Fig. 2.17). • The length of the share blade is determined after plotting the assumed angle θ0 . • Assume value of angle γ from Table 2.7. • The curve of moldboard interception is to be determined. • The slope L’ can be calculated from the accepted ratio L1 /H L1 L' = sinθ0 H H

(2.43)

L ' = L 1 sinθ0

(2.44)

From the point F, the line FE is drawn at an angle 90° + Δγ up to the section GF (Fig. 2.18). The angle Δγ should be 0 to 5°. The greater is this angle, the more concave the moldboard will be. The line B’E and FE are tangential to the directrix. The directrix is always assumed to be a parabola, but a section B’E over the length s = 40 to 60 mm is left as a straight line. The remaning part of the section B’E is divided into 10 parts and the points of division are numbered successively (Fig. 2.18). The section FE is also divided into ten parts and points of division are numbered according to the sequence as shown in Fig. 2.18. Points with same numbers are joined with straight lines to obtain a series of tangents to the parabola. But before drawing

36

2 Moldboard Plow

Fig. 2.18 Plotting of parabola by the tangential methods (Bernacki et al., 1972)

the parabola, it is necessary to make sure that the height and slope of the moldboard and the angles of the share as assumed are correct so that the length of the directrix should not be less than the section BC in Fig. 2.17. The directrix can be considered as an arc of the circle with radius R. R ≥ π 2

b  − γ cosθ0

(2.45)

After having checked the assumptions and plotted the directrix, lines of intersection are drawn by vertical planes at equal intervals. The above lines correspond with contour lines in the revolved section. The points of intersection of contour lines with the directrix in a revolved section is subsequently numbered and transferred onto the plan of the directrix BC in the horizontal plan. Then drawing through points 1’, 2’, 3’ etc., lines parallel to the share blade, contour lines in the horizontal plan are obtained (Fig. 2.17). After this outline of the share is to be drawn. For this the directrix in the revolved section B’F is measured. The width of the share B’M’ = S1 from the share point and B’K’ = S2 from the end of the share (Fig. 2.15 and Table 2.5). Points M’ and K’ are referred to the horizontal plan. The rear edge of the share most frequently makes a right angle with its blade. After drawing the the outline of share in the horizontal plan, the outline of share is drawn in the frontal plan by means of transferring the points K and M. Thus the outline of the entire moldboard with share is drawn in frontal plan and then in the same plan contour lines 1, 2, 3 etc., are drawn. Points of

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

37

intersection of contour lines with the outline of the moldboard are transferred onto contours in the horizontal plan and the outline of the moldboard is plotted in this plan ensuring that angle α is equal to that calculated using Eq. 2.22. To obtain a full profilogram with all cross-sections in the remaining planes, cross-section lines I. II. III etc., are drawn in horizontal plan (Fig. 2.17). Intersections of these lines with contour lines are transferred onto corresponding contours in the vertical plan. Thus a series of parabolas is obtained on this plan by connecting successive points of the cross section. These parabolas should be parallel to each other. Then lines of cross section a, b, c etc., are drawn on the horizontal plan and points of intersection are transferred onto contour lines in frontal plan and curves of cross sections are plotted. Frog The frog of the moldboard plow bottom may form a single complete element or may consist of two parts. The holder is a dihedral element. One wall, adequately bent, fastens the share and the moldboard; another wall called lateral has a flat surface. Landside It is a long flat metal piece bolted to the side of the frog. It helps to absorb side force caused when furrow slice is turned. The length of the landside (L1) is calculated by using the following equation: L1 =

  bcosϕ 1 2 sinθ0 cos(ϕ + θ0 )

(2.46)

Pressure acting on landside is given by p=

ρs d 2

(2.47)

where p = landside pressure on furrow wall (g/cm2 ), d = pressing depth of landside end into soil (cm), ρs = soil density (g/cm3 , 1 to 2.5 depending upon soil type and state). The soil reaction component (R) is calculated by R = nle p

(2.48)

d sinΔ

(2.49)

le =

where n = number of plow bottom, l e = length of landside pressed in to soil, Δ = angle between longitudinal plane of the landside and furrow wall (º). Landside width can be calculated using the following equation, w=

2RsinΔ ρs d 2

(2.50)

38

2 Moldboard Plow

Numerical problems

1. A 3-bottom trailed type moldboard plow experiences a draft 150 kg, while operating at a depth of 15 cm in sandy clay loam soil and at a forward speed of 3 km/ h. Calculate unit draft, if the bottom size is 40 cm and the cross-section of the furrow is rectangular. Total width, w = 3 × 40 = 120 cm h = 15 cm Draft = 150 kg. Area of cross-section of a rectangular-shaped furrow, A = w × h = 120 × 15 = 1800 cm2 Unit draft =

150 Draft = = 0.083 kg/cm2 A 1800

Hence, unit draft is 0.083 kg/cm2 . 2. Using ASAE equation, find out the increase in the draft of a 3 × 40 cm moldboard plow operating at a depth of 15 cm in sandy clay loam soil, when operating speed is increased from 3 to 4 km/h The ASAE equation is as follows: D f i = Fi [A + B × V + C × V 2 ]Td where Dfi draft required per meter width of cut, N; F = dimensionless soil texture adjustment parameter; i = 1 for fine, 2 for medium and 3 for coarse soil; A, B, and C = machine specific parameters; V = speed of plowing operation, km/h; T d = depth of plowing, cm. Hence, total draft requirement = Dfi × W d . For moldboard plow, A = 652, B = 0, C = 5.1. For sandy loam soil F 2 = 0.7. Cutting width, W d = 3 × 40 = 120 = 1.2 m From the above equation for draft estimation,    Total draft at 3 km/h = 0.7 × 652 + 0(3) + 5.1 32 × 15 × 1.2 = 8793.54 N = 896.38 kg    Total draft at 3 km/h = 0.7 × 652 + 0(4) + 5.1 42 × 15 × 1.2 = 9243.36 N = 942.24 kg So, the increase in draft will be = (942.23–896.38) kg = 45.86 kg.

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

39

3. The line of pull on an implement is 15° above the horizontal and is in a vertical plane which is at an angle of 10° with the direction of travel. Calculate draft and side draft for a pull of 500 kg. Also calculate drawbar horsepower required to pull the implement at a forward speed of 3 km/h. P = 500, θ = 15◦ and Φ = 10◦ Draft, L = PcosθcosΦ = (500 × cos15◦ × cos10◦ ) = 475.63 kg Sidedraft, S = PcosθsinΦ = (500 × cos15◦ × sin10◦ ) = 83.87 kg Drawbar horse power = Draft × Velocity = 5.28 Drawbar horse power = 475.63×3×1000 75×3600 Hence, the drawbar power required to pull the implement at a forward speed of 3 km/h is 5.28 hp. 4. A two bottom 30 cm moldboard plow was operated at a forward speed of 3 km/h in a rectangular plot of length 40 m and width 25 m. During operation, the overlap observed between adjacent passes was of 4 cm. The turning loss was found to be 5 seconds per turn. The time lost in adjustment and repair was 50 min/ha. Calculate the field efficiency. W = 2 × 30 = 60 cm A = 40 × 25 = 1000 m2 V = 3 km/h = 50 m/min Overlap = 4 cm Effective width = (60 4) cm = 56 cm. 10000 0.60 × 3000 = 5.56 h.

Theoretical time taken (without overlap) to cover one hectare land = Actual time taken to cover one hectare land = Number of turns to plow the field = Number of turns =

10000 0.56×3000

Width of the land −1 Width of the plow

25 − 1 = 43.64 ≈ 44 0.56

Turning losses per hectare =

5 × 44 × 10000 = 0.611 h 40 × 25 × 3600

Time lost in adjustment and repair per ha = Field efficiency =

= 5.95 h

50 = 0.833 h 60

Actual field capacity × 100 Theoretical field capacity

40

2 Moldboard Plow

10000/(5.95 + 0.611 + 0.833) × 100 10000/5.56 = 75.196%

Field efficiency =

The field efficiency is 75.2%. 5. A right-handed moldboard plow-bottom experiences a draft of 1.96 kN when it operates without side draft. The thrust on the land side is 590 N and coefficient of soil metal friction is 0.35. What will be the change in draft if the plow is pulled at an angle 10° towards the left side of the plow. The useful soil reaction forces are unchanged. In the following figure H is the center of resistance, Rh is the soil resistance force. Pull Px is making an angle θ with soil resistance force.

The resultant parasitic force, √ Q√ T 2 + (μT )2 h = 2 Q h = 590 + (0.35 × 590)2 Q h = 625.1 N Pull, Px = 1960 N / Rh = Px2 − Q 2h √ Rh = 19602 − 625.12 Rh = 1857.65 N So, the angle between line of pull and soil resistance is

2.10 Effect of Attachments and Rear Furrow Wheel on Draft

41

  θ = sin−1 625.1 1960 θ = 18.6◦ Now, when the line of pull makes 10° with the direction of travel, applying Lami’s theorem in the triangle ABH, Rh Ph = sin90 ◦ sin{90◦ −(10◦ +θ )} Ph 1857.65 = ◦ ◦ ◦ sin{90 −(10 +18.6 )} sin90◦

Ph = 2115.82 N

So, the draft for angled pull, Px = Ph cos10° = 2083.68 N Change in draft = 2083.68 − 1960 = 123.68 N. Hence, the change in draft when the plow is pulled at an angle of 10° is 123.68 N. 6. In a tractor, the following drawbar powers are obtained at different forward speeds. Sl. no

Gear position

Speed (km/h)

Drawbar power (kW)

1

1st

1.5

3.5

2

2nd

2.1

4.8

In the market two-bottom moldboard plows are available in sizes of 2 × 30 cm, 2 × 35 cm, and 2 × 40 cm. Find out the suitable size of plow for utilizing maximum tractor drawbar power when the maximum operating depth is 15 cm. Assume a power reserve of 20% and unit draft of soil as 0.6 kg/cm2 . Unit draft, Du = 0.6 kg/cm2 , Td = 15 cm Keeping 20% power reserve, drawbar power available at different gears, 1st gear, P1 = (3.5 × 0.8) = 2.8 kW 2nd gear, P2 = (4.8 × 0.8) = 3.84 kW Draft of moldboard plow = unit draft × cross-sectional area Drawbar power = draft × forward velocity Plough size (cm)

Cross sectional area (cm2 )

Draft (N)

Power required (kW) 1st gear

2nd gear

2 × 30

60 × 15 = 900

0.6 × 900 × 9.81 = 5297.4

2.207

3.09

2 × 35

70 × 15 = 1050

0.6 × 1050 × 9.81 = 6180.3

2.575

3.60

2 × 40

80 × 15 = 1200

0.6 × 1200 × 9.81 = 7063.2

2.943

4.12

42

2 Moldboard Plow

From the above table, it can be concluded that 2 × 40 cm moldboard plow is not suitable as its drawbar power requirement is more than the drawbar power available. For utilizing maximum drawbar power, 2 × 35 cm moldboard plow is to be used in 1st and 2nd gears. 7. A 4 × 30 cm trailed type right hand moldboard plow is operated at a depth of 15 cm and at a forward speed of 3.0 km/h using a tractor which is fitted with 6.0–16 and 13.6–28.0 size tire, respectively in front and rear axles. Assuming a clearance of 5 cm between the furrow wall and inner surface of wheel, calculate the horizontal distance of centre of resistance of the moldboard plow from the centre of the rightside rear wheel of the tractor. Number of plow bottom, n = 4. Depth of cut, a = 15 cm Forward speed = 3 km/h = 0.833 m/s Width of each plow, w = 30 cm. Center of resistance of each bottom lies at 3/4th of the width of cut measured from the share wing or 1/4th of width of cut measured from land side.

Let the distance of center of resistance of the implement from the existing furrow wall is x’. The distance of center of resistance for first, 2nd, 3rd, and 4th plow bottom from the furrow wall is 3w/4, 7w/4, 11w/4, and 15w/4, respectively. Hence, taking moment about the furrow wall.

References

43

7w 11w 15w 3w +R +R +R 4 4 4 4 x ' = 0.675 m

4R x ' = R

Width of wheel = 13.6 × 2.54/100 = 0.3454 m. Distance of center of resistance of the implement from the centre of the right side rear wheel = (0.675 + 0.05 + width of wheel/2) = (0.675 + 0.05 + 0.3454/2) = 0.898 m.

References ASAE Standards. (2000). Agricultural Machinery Management Data. St. Joseph, MI USA: ASAE. D497.4. Bernacki, H., Haman, J., & Kanafojski, C. Z. (1972). Agricultural machines, theory and construction (Vol. 1). Gill, W. R., & Vanden Berg, G. E. (1967). Soil dynamics in tillage and traction. USDA Agriculture Handbook No. 316, 171–181, 221–238, 246–248, 316–318. Goryachkin, V. P. (1968). Collected works, (Vol 2, 3rd ed.). Moscow: Kolos Publishing House. Kepner, R. A., Bainer, R., & Barger, E. L. (1978). Principle of farm machinery (3rd ed.). USA: The AVI Publishing Company, Inc. McKibben, E. G., & Reed, I. F. (1952). The influence of speed on the performance characteristics of the implements. Paper presented at SAE National tractor meeting. Roul, A. K., & Raheman, H. (2017). Draft prediction of commonly used tillage implements for sandy clay loam soil in India. Journal of Agricultural Engineering, 54(4), 1–15. Wismer, R. D., Wegscheid, E. L., Luth, H. J., & Romig, B. E. (1968). Energy application in tillage and earthmoving. SAE Transactions, 77, 2486–2494.

Chapter 3

Disk Implements

3.1 Introduction Disk plows (Fig. 3.1), one of the important primary tillage implements, are used for weed control and mixing stubbles with the soil. Disk harrows (Fig. 3.2) are used for seedbed preparation. Blades of disk plows and disk harrows are concave and represent the sections of hollow spheres. A concave-type disk blade lifts the soil, pulverizes, inverts it partially, and moves it to one side. Disk plows move all the soil towards one side, whereas disk harrows have opposing gangs that move the soil in opposite directions. Multiple-disk implements leave a scalloped furrow-bottom profile. Disk tools may roll over the roots of the crops and chop through crop residues, and they can be used in non-scouring soils by utilizing scrapers. They don’t cover all trash completely.

3.2 Forces Acting on the Disk As illustrated in Fig. 3.3, there are several ways to depict the combined effect of all soil forces operating on a disk blade due to cutting, pulverizing, elevating, and inverting the furrow slice, as well as any parasitic forces. Two nonintersecting forces, one of which is a thrust force T parallel to the disk axis and the other which is a radial force U, are used to describe the resulting effect. When estimating the load on the bearings that support the disk, this method is especially helpful. Due to the soil acting against the lower part of the disk face, the thrust force is always much below the disk centerline. To generate the torque required to overcome bearing friction and cause the disk to rotate, the radial force which includes the vertical support force on the disk blade must pass just slightly below the disk centerline. The resultant effect can also be expressed by the method, which is based on the longitudinal (L), lateral (Ss ), and vertical components (Vv ) and the resultants of these

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_3

45

46

3 Disk Implements

Fig. 3.1 Disk plow

Fig. 3.2 Disk harrow

forces (Fig. 3.3b). When analyzing how soil forces affect equipment as a whole unit, this sort of force representation is more helpful than the other one. In Fig. 3.3b, the draft (L) and side draft (Ss ) are combined into the horizontal resultant Rh so that the entire effect is represented by the two nonintersecting forces, Vv and Rh . Due to the fact that these two forces do not intersect, they introduce a couple (Vv × a) that causes the implement to be rotated about the axis of forward motion (the distance ‘a’ is identified in Fig. 3.3b). For a right-hand disk plow, as seen from the rear, this couple is always in the clockwise direction.

3.3 Disk Plow 3.3.1 Types of Disk Plow Disk plows are classified as standard disk plows and vertical disk plows and they are discussed below.

3.3 Disk Plow

47

Fig. 3.3 Forces acting on a disk blade

3.3.1.1

Standard Disk Plow

A standard disk plow has a frame supported by wheels and a number of individually placed inclined disk blades (3 to 6 disks). Moldboard plows perform poorly in a variety of situations, including hard, dry soils, sticky soils where a moldboard plow won’t scour, and in peatlands. But these situations are best suited for disk plow use. The angle between the disk face and the direction of travel is known as the disk angle and it ranges from 42 to 45º (Fig. 3.4). The disks are tilted rearward at an angle with respect to the vertical, known as the tilt angle, and it has a value between 15 and 25º (Fig. 3.4). Any disk implement must be driven into the soil by its own weight in hard, dry soils rather than relying on suction like a moldboard plow. As a result, large frames and wheels are used to construct disk plows. In the moldboard plow, side forces are absorbed mainly by the landside, whereas the disk plow depends upon its furrow wheel. Because of the large off-center thrust forces encountered, the disks are supported through tapered roller bearings.

3.3.1.2

Vertical Disk Plow

The vertical disk plow is also known as a one-way disk, disk tiller, harrow plow, and wheatland plow. The disks are evenly spaced along a common axle connected

48

3 Disk Implements

Fig. 3.4 Disk angle and tilt angle

to one another using spacer spools. It is similar to a typical disk plow but revolves as a single unit. This tool is employed for stubble mixing and shallow plowing of the soil. The disks of a vertical disk plow have smaller diameters (between 51 and 61 cm) than a standard disk plow. They are usually separated by 20 to 25 cm along the gang bolt. The distance between disks and the angle between the gang axis and the direction of travel determines the width of the cut. Generally, the disk angle is kept as 40 to 45° in most field operations. Widths of cut obtainable with various sizes of vertical disk plow range from 2 to 6 m. Some of the larger sizes have several gangs of disks in line, joined by flexible couplings. Since vertical disk plows are primarily for relatively shallow plowing, they are built much lighter than standard disk plows (usually 45 to 90 kg per disk).

3.3.2 Soil Reactions on Plow Disks The influence of different variables on soil reactions is discussed below: The effect of speed has been reported for a disk angle of 45°, a tilt angle of 18 to 20°, at a depth of 15 cm, and widths of cut of 18 and 23 cm (Gordon, 1941). When the speed of operation for this plow was increased from 4.8 to 9.6 km/h, the draft (L) increased by 40% and 90% in clay loam soil and fine sandy loam soil, respectively.

3.3 Disk Plow

49

Fig. 3.5 Effect of disk angle and tilt angle on horizontal (L), vertical (Vv ), and side force (Ss ) acting on the disk (Gordon, 1941), a at 0° tilt angle, b at 15° tilt angle, c at 45° disk angle

The side force (Ss ) also increased with speed because the soil was thrown farther to the side. The vertical upward force (Vv ) decreased as the speed increased. Tilted blade penetrates more by increasing the speed but vertical blades just do the opposite, they give reduced penetration at higher speed. The effect of disk angle, and tilt angle on horizontal, vertical, and side forces acting on the disk in two different soils (Gordon, 1941) is shown in Fig. 3.5. From this figure, it can be seen that at lower values of disk angle, the draft tends to increase because of the greater contact area between the furrow wall and the convex side of the disk. Due to this greater contact area, there is a reduction in measured side force at smaller angles. The increased draft at higher values of disk angle is due to a greater throw of soil. The optimum disk angle for the minimum draft is around 45°. By increasing the disk angle, vertical force (Vv ) decreases considerably, which results in an increase in penetration. When the tilt angle is increased between 15 and 25°, the observed side force drops while the draft and vertical upward force increase. So, with lesser tilt angles, penetration is better. An increase in the disk concavity (i.e., the smaller radius of curvature) increases the vertical upward force, especially in heavier soils, and tends to increase the draft. Considering both draft and penetration, larger disks are better when they are operated vertically but smaller disks are better with tilt angle around 20°.

50

3 Disk Implements

Penetration of a standard disk plow is also improved by decreasing the tilt angle. Better inversion of the furrow slice will be achieved when using a larger tilt angle if penetration is not a challenge. A large tilt angle is best for sticky soils. From Fig. 3.5, it is clear that soil type in addition to disk and tilt angles has a pronounced effect on soil reactions.

3.3.3 Horizontal Hitching of Pull-Type Disk Plows The horizontal forces acting on a pull-type disk plow are shown in Fig. 3.6. Because all side thrust must be transmitted through the wheels and the pull member (DF) on a disk plow being a free link in terms of horizontal forces, the horizontal force relations for a disk plow are considerably different from those for a moldboard plow. The position of the hitch points D and F determine the horizontal line of pull for a disk plow, but the horizontal line of pull for a moldboard plow must pass through the tractor’s hitch point and the center of resistance mainly defined by the plow and soil conditions. The intersection of Ph (component of pull in horizontal plane) and Rh (resultant of longitudinal and side forces) then determines the location of the horizontal center of resistance H and the resulting side force Qh . The line of Qh must pass in the middle of the front and rear furrow wheels to allow the side force to be distributed equally between them. The pull-type disk plows may approximate this condition by adjusting the hitch so that the line of pull passes through a point that is slightly to the left of the average position of all disk centers (as a result, H is placed where it is needed). H and Qh will be shifted towards the rear of the plow if hitch point D on the plow frame is moved to the left, and the rear furrow wheel will carry a greater amount of the side thrust. When D is shifted to the right (or F is moved to the left), the front wheel experiences more side thrust.

Fig. 3.6 Horizontal forces acting on pull-type disk plow with front and rear furrow wheels

3.4 Disk Harrows

51

3.4 Disk Harrows 3.4.1 Types of Disk Harrow There are three types of disk harrows available which are shown in Fig. 3.7. A single acting disk harrow throws soil outward from the center of the tilled strip using two opposing gangs of disk blades. This type is seldom used except when ridges or raised beds are to be split out. A tandem or double acting disk harrow has two additional gangs that throw the soil back towards the center as a second operation, thus tilling the soil twice and leaving the field more nearly level, but with unfilled furrows along both sides of each pass. An offset disk harrow has one right-hand gang (a gang that moves the soil to the right) and one left-hand gang, operating in tandem. This type is suited for operation in orchards. Traditionally, tandem disk harrows are built lighter than offset disk harrows and are used extensively for secondary tillage operations. The main use of offset disk harrows has been for primary tillage. The typical size and mass of disk harrows are listed in Table 3.1. Small, lightduty disk harrows are usually tractor mounted. Most of the pull-type tandem disk harrows are provided with wheels in between the front and rear gangs for leveling and depth control, to raise the implement for turning, and for transport. The wider units have hinged outer sections that provide flexibility during operation in uneven fields and are folded upward hydraulically to reduce the width for transport. When a disk harrow has wheels, the hitch between the frame and the tractor drawbar must be rigid or semi-rigid in the vertical direction to provide uniform depth control for front and rear gangs. The pull member is usually hinged to the frame and has an adjustable control arm. Bearings on disk harrow gangs are subjected to both radial and thrust loads and operate in dirt conditions. Most of the disk harrow gangs have sealed ball bearings. Tapered roller bearings are usually used for wheels. The maximum operating depth for a disk harrow is usually one-fourth of the disk diameter. The larger sizes and wider spacings are preferable for cutting up heavy cover crops and for other primary tillage, and they permit greater operating depths than do smaller blades. Small-diameter disks penetrate more readily than large disks because they require less vertical force to hold them to a given depth. Reducing the

Fig. 3.7 Types of disk harrow

52

3 Disk Implements

Table 3.1 Typical sizes and masses of disk harrows Type

Disk diameter (cm)

Disk spacing (cm)

Available widths (m)

Mass per unit of width (kg/m)

Tandem, Mounted 41,46,51,56

18–23

1.5–4.0

150–270

Tandem, wheel type Light-duty

46,51,56

18–24

2.4–6.4

270–370

Medium-duty

46,51,56

19–24

3.4–9.5

370–480

Heavy-duty

56,61,66

23–28

3.4–13.7

480–700

Offset, pull-type with wheels

56,61,66,71

23–28

2.1–7.3

400–750

No wheels

61,66,71

23–28

2.7–9.1

390–650

concavity and sharpening disks from the concave side rather than the convex side also improve penetration. Some disk harrows are equipped with cut-out or notched blades, Notched blades penetrate a little better than plain blades because of the reduced peripheral contact area. They cut heavy trash more readily because they tend to pull it under instead of pushing it ahead. They are also more expensive and wear more rapidly.

3.4.2 Soil Reactions on Disk Harrow Blades The variation of the draft (L), side force (Ss ), and vertical force (Vv ) of a single disk in sandy soil at 8.4% moisture content, when operated at 4 km/h with zero tilt angle at different disk angles, is shown in Fig. 3.8 (McCrerry, 1959). From this figure, it can be seen that with an increase in disk angle up to 25°, all the forces (L, Vv , and Ss ) are decreased that is because the contact area between the convex (back) side and furrow wall is decreased. The total vertical force for a pull-type disk harrow without wheels is approximately equal to the gravitational force on the implement and any added mass. If a disk harrow has wheels (or is tractor mounted), the mass of the implement merely establishes the maximum V for the condition when the wheels or tractors are carrying no vertical load from the implement. The ratios of L/Vv and Ss /Vv for 46 and 56 cm size disks for previously untilled soil are summarized in Table 3.2. These ratios are somewhat different for the rear gangs of tandem or offset disk harrows because they operate in disturbed soil.

3.4 Disk Harrows

53

Fig. 3.8 Effect of disk angle on draft, vertical upward force, and side force (McCrerry, 1959)

Table 3.2 Ratios of L/Vv and Ss /Vv are given for 46 and 56 cm diameter disks Disk angle, degrees

46 cm disk

56 cm disk

L/Vv

Ss /Vv

L/Vv

Ss /Vv

15

0.5–0.75

0.6–0.9

0.7–0.85

0.15–0.8

19

0.7–1.0

1.0–1.3

0.95–1.1

0.4–1.1

23

0.9–1.2

1.25–1.55

1.3–1.5

1.2–1.4

3.4.3 Forces Acting upon a Disk Harrow The combined soil reactions for a group or a gang of disks can be considered as acting upon a single disk blade in the average position of all blades (i.e., at the center of the gang). A disk harrow is subjected to the following forces: (a) the resultant soil reaction on each gang, (b) gravity force acting upon the implement and any additional mass, (c) any supporting soil forces provided by wheels or as a result of being mounted on a tractor, and (d) the pull of the power source. To maintain uniform motion, these four forces must be in equilibrium. The side components of all soil reactions must add up to zero in order for there to be no side draft.

54

3 Disk Implements

Fig. 3.9 Representation of horizontal forces for a pull-type, right-hand offset disk harrow without wheels

The horizontal forces acting upon an offset disk harrow without wheels are shown in Fig. 3.9. The intersection of Rhf and Rhr in this diagram shows where the horizontal center of resistance H is located (resultant of L and Ss components of soil reaction is Rhf and Rhr for front gang and rear gang, respectively). For the condition of no side draft, the hitch linkage of the disk harrow must be adjusted so that the hitch point F0 , is directly in front of H. The operating conditions of the harrow vary if the hitch linkage is altered to move the implement from the no-side-draft position either to the right or to the left. The force equilibrium is temporarily disturbed, if the hitch point is changed from F0 to F2 , and the side component of the new pull, acting at point H, causes the implement to rotate counterclockwise about F2 . This rotation moves on until the disk angles of the two gangs have been adjusted (the front increasing and the rear decreasing since the total included angle remains constant) for the difference of lateral force components (Sf and Sr ) to equal the side draft Py . During this readjustment, the magnitudes of Lf and Lr as well as the location of H also shift and less volume of soil is moved by the rear gang. In contrast, the rear gang is primarily working in the extreme right-offset position. The rear gang operates at greater angles and moves more soil than the front gang even when there is no side draft because it is in softer soil. Due to the fact that both front gangs of a tandem disk harrow are operating on the same type of soil (untilled), their side components are equal and in opposition to one another, and both rear gangs are working on tilled soil, it has symmetrical force relations about the

3.4 Disk Harrows

55

implement centerline. Thus, H for the 2 front gangs and H for the 2 rear gangs are both on the centerline and the implement operates with no side draft and no offset. The amount of offset is calculated by taking the moments about the hitch point, assuming that Rhf and Rhr pass through the centers of the gangs eL f + eL r + bS f − (b + d)Sr = 0

(3.1)

  b Sr − S f + d Sr e= L f + Lr

(3.2)

d Sr L f + Lr

(3.3)

Now,

e = btanα +

where e = amount of offset from the hitch point to the center of cut, α = horizontal angle between the line of pull and direction of forward motion, d = longitudinal distance between the centers of two gangs, b = longitudinal distance from the center of the front gang to the hitch point, In case of no side draft, S f = S r = S s and α = 0, then the offset with no side draft is given by eo =

d Ss L f +L r

(3.4)

The lateral and longitudinal soil reactions and the distance between gangs determine how much offset is possible without a side draft.

3.4.4 Couple Acting on Disk Harrow Gangs Disk harrows often penetrate the soil more deeply on their concave ends than their convex ends. Due to the fact that the perpendicular soil force component (T) acted below the axle, while the balancing force T’ acted at axle height (through the bearings) as shown in Fig. 3.10, a couple of (T × f) is formed. In case of uniform penetration, the vertical soil reaction force (V) will act roughly at the center of the gang. The resultant downward force W’ (force of gravity on the gang and any additional mass, minus any vertical component of pull) must act at a distance ‘h’ from the center of the gang (towards convex end) in order to achieve uniform penetration with a single gang. W 'h = T f where W’ = resultant downward force and Tf = couple

(3.5)

56

3 Disk Implements

Fig. 3.10 Couples acting on the gang of disk harrow

With tandem and single acting disk harrows, uniform penetration can be attained by having the couples of the laterally opposed gangs counterbalance one another through the frame. Because the opposing couples create torsion in the frame between the gang in an offset disk harrow, the design problem is more difficult. It is important to have adequate torsional stiffness and to make the right adjustments for lateral leveling of one gang in relation to the other. Another complicating factor in an offset disk harrow is that a couple of the front gang in an offset disk harrow is usually larger than that of the rear gang because the rear gang is operating in looser soil. The larger front couple results in a tendency for the right side of the entire harrow to run deeper than the rest of the harrow (considering a right-hand offset disk harrow). Sometimes transport wheels are used for depth control, and these wheels minimize the problem of uneven penetration).

3.4.5 Disk Harrow with Hinged Pull Members but Without Gage Wheels or Runners Vertical force relations for an offset or tandem disk harrow without wheels are shown in Fig. 3.11. The disk blades are the only points of contact with the soil. The point at which W and the line of pull (Pv ) intersect is designated as point G. As a result of depth variations caused by the soil forces, Rvf and Rvr naturally adjust themselves such that their final Rv passes through point G and in equilibrium with W and Pv . When the hitch of the implement frame is raised, G is raised and Rv is brought closer to the front gang, increasing Rvf and lowering Rvr . As a result, the depth of penetration of front gang would increase while the depth of penetration of rear gang would decrease. In Fig. 3.11, Rvf is shown as greater than Rvr because the front gang is operating in firm soil and the rear gang is in loosened soil.

3.5 Design of Disk Implements

57

Fig. 3.11 Vertical forces acting on pull-type offset or tandem disk harrow without wheels

3.5 Design of Disk Implements 3.5.1 Width of Disk Implements Pdb = ηt × Pa

(3.6)

where ηt = Tractive efficiency, Pdb = Drawbar Power, (kW), Pa = Axle power (kW), generally taken as 95% of PTO power (ASAE standards, 2000). L=

Pdb × 3600 V

(3.7)

where L = draft available for harrowing (N), V= speed of operation (km/h). Now, the draft required per meter width of the harrow is calculated by using the equation given below:    D f i = Fi A + B(V ) + C V 2 Td

(3.8)

where Dfi = draft required per meter width of harrow, N F = dimensionless soil texture adjustment parameter i = 1 for fine, 2 for medium, and 3 for coarse A, B, and C = machine-specific parameters V = speed of operation, km/h = depth of operation, cm. Td For values of F i , A, B, and C, refer to Agricultural Machinery Management Data published by ASAE Standards 2000. The width of the disk harrow is given by

58

3 Disk Implements

W =

L Dfi

(3.9)

where W = width of cut, m. If the width of the machine is too high, then there will be a buckling effect and it will also create problems during transportation as well as during turning.

3.5.2 Diameter of Disk The diameter of the disk is given by the following formula (Bernacki et al.,1972): D=k

a cosβ

(3.10)

where D = disk diameter, cm; a = maximum depth of harrowing (cm) (generally 15 cm), β = tilt angle (it is zero for disk harrow and 15° to 25° for disk plow), k = dimensionless coefficient (value ranges from 2.5 to 3 for deep tillage plows, 3 to 4 for medium tillage plows, 3 to 6 for tillage harrows, and 5 to 6 for skimming harrows). From the geometry of the disk in Fig. 3.12, the diameter of the disk at depth ‘a’ (Da ) can be calculated: 

Fig. 3.12 Disk diameter

Da 2

2

 2  D 2 D −a = − 2 2 √ Da = 2 a(D − a) 

(3.11)

3.5 Design of Disk Implements

59

3.5.3 Thickness of Disk Disks of harrow are made from carbon steel sheets. The thickness of the disk depends on the diameter of the disk and it is given by t = (0.008D + 1)

(3.12)

where t = thickness of the disk, mm; D = Diameter of the disk, cm. The disk is hardened only over a width not exceeding 4 cm up to a hardness of 300 HB .

3.5.4 Spacing between Disks The spacing between the disks should be such that they do not get clogged with soil. Too much spacing between disks will result in untilled soil, hence there should be adequate spacing between the disks of the harrow. It depends on the height of ridges, formed on the bottom of the furrow. From Fig. 3.13, DC sinθ 0 = Scosθ 0 Fig. 3.13 Spacing of disk harrow

(3.13)

60

3 Disk Implements

√ DC = 2 (c(D − c))

(3.14)

√ S = 2 (c(D − c))tanθ 0

(3.15)

where S = spacing between disk (cm), θ0 = setting angle (15° − 35° for disk harrows and 40° to 50° for plows), c = height of the ridge, cm (c ≤ 0.3a for disk plows, c ≤ 0.5a for skimming harrows, and c ≤ a for tiller harrows). The spacing of inclined disks of the plow is determined by using spacing S and transposition e. The geometry of the disk plow is shown in Fig. 3.14. It is clear that BC = F D − E F

(3.16)

BC = Dc sinθ0

(3.17)

F D = F Gcosθ0 = Scosθ0

(3.18)

E F = C Fsinθ0 = esinθ0

(3.19)

Also,

Fig. 3.14 Spacing of disk plow

3.5 Design of Disk Implements

61

Dc sinθ0 = Scosθ 0 − esinθ 0

(3.20)

Dc = Scotθ0 − e

(3.21)

Also, / Dc = 2

c c (D − ) cosβ cosβ

(3.22)

where β is the tilt angle. Then,

/

  c c D− + e tanθ0 S= 2 cosβ cosβ

(3.23)

The value of the transposition of disks ‘e’ should be such that S > 2a.

3.5.5 Number of Disks per Gang The cutting width of the disk harrow should cover the wheel track of the tractor. According to IS: 6635- 1972, cutting width can be calculated as follows: for single acting disk harrow, W = (0.95 × N × S + 0.3 × D)/100

(3.24)

for double acting disk harrow, W = (0.95 × N × S + 1.2 × D)/100

(3.25)

W = (0.95 × N × S + 0.6 × D)/100

(3.26)

for offset disk harrow,

where W = cutting width, (m), N = total number of disks spacing, S = spacing between disks (cm), D = diameter of disk blades (cm). According to ASAE standards S290.2 (2004), cutting width can be calculated as follows: For single acting disk harrow, W =

{0.95 × (N 1 − 2) × S + 0.3 × D} 100

(3.27)

62

3 Disk Implements

For double acting disk harrow, W =

{0.95 × (N 1 − 2) × S + 1.2 × D} 100

(3.28)

{0.95 × (N 1 − 1) × S + 0.6 × D} 100

(3.29)

For offset disk harrow W =

where W = cutting width (m), D = diameter of disk blades (cm), N1 = number of disk blades, S = Spacing between disks (cm). The above formulas are based on 18° gang angle and 10 cm cutting depth and can be used to determine the cutting width of disk harrows with gang angles from 14 to 22° with minimal error. The number of disks (N1) per gang for offset disk harrow can be calculated by using either IS or ASAE equations given above.

3.5.6 Design of Shaft The length of the shaft is given by Ls = N 1 × S

(3.30)

L s is the length of the shaft in cm. For the fitting purpose, consider some extra length. The width of cut for different disk harrows is computed using either Eq. 3.24 to Eq. 3.26 or Eq. 3.27 to Eq. 3.29 depending on the type of harrow. Assuming cross-sectional area of soil disturbed as rectangular. The cross-sectional area (A) of tilled soil is given by A = W ×a

(3.31)

Draft required (Df ) per gang is equal to the product of the cross-sectional area of tilled soil and unit draft (DU ) and it is given by D f = A × DU

(3.32)

The ratio of the draft to vertical force is given by Df L = = RF Vv Vv

(3.33)

3.5 Design of Disk Implements

63

Fig. 3.15 Vertical forces acting on the shaft of a disk harrow with six disks in each gang

The value of RF can be taken from Table 3.2 depending upon the diameter of the disk and disk angle. Then, the total vertical force acting on the gang is given by Vv =

Df RF

(3.34)

Vertical force acting on each disk, V1 = Vv /N 1

(3.35)

In a single acting disk harrow, the weight of the disk gang assembly, W g is equal to half the weight of one disk harrow, W t and it is given by Wg =

Wt 2

(3.36)

Vertical forces acting on the shaft of a disk harrow with six disks in each gang are shown in Fig. 3.15. Reactions at both bearings (RA and RB ) can be given by RA = RB =

Wg − 6V1 2

(3.37)

Bending moment (MS ) due to vertical forces M S = R A × 3S + V1 × 2.5S + V1 × 1.5S + V1 × 0.5S − 4.5V1 S + 3R A S −

Wg × 1.5S 2

Wg × 1.5S 2

(3.38) (3.39)

64

3 Disk Implements

Horizontal soil reaction force acting on each disk tends to produce a torsional moment (TS ) which is equal to TS = (horizontal soil reaction force acting parallel to the face of the disk (3.40) ×moment arm × number of disks) Assuming that the horizontal soil reaction force parallel to the face of the disk is acting at a height of 1/3rd of the depth of operation, then TS = (D i /cosα) × (r −

a ) × N1 3

(3.41)

As Di × N1 = Df = total draft force for the gang of disks TS = (D f /cosα) × (r −

a ) 3

where Di = draft of each disk, r = radius of disk, α = gang angle, and a = depth of operation. Equivalent moment (MeS ) acting on gang shaft is given by (Khurmi and Gupta, 2005; Norton, 2012) / MeS =

(K M × M S )2 + (K T × TS )2

(3.42)

K M and K T are combined shock and fatigue factors for bending and torsion, respectively. Assuming the gang shaft to be a solid square, the following equation can be used to calculate its side b: τmax × Q = MeS

(3.43)

3.5 Design of Disk Implements

65

Fig. 3.16 Forces acting on the frame of one gang of a disk harrow with 6 disks

τmax ×

b3 = MeS 4.8

(3.44)

where τmax = allowable shear stress (kg/cm2 ), b = length of sides of the gang shaft b3 = 0.208 b3 . (cm), Q = Section modulus of gang = 4.8

3.5.7 Design of Frame The frame is subjected to bending moment as well as torsional moment due to horizontal and vertical soil reaction forces and its own weight (Fig. 3.16). Maximum bending moment due to vertical forces M F = 3R A S −

Wg × 1.5S 2

(3.45)

Horizontal forces tend to produce twisting effect on frame and moment (TF ) due to these forces is given by:   a TF = (D f /cosα) × D − + clearance 3

(3.46)

Equivalent moment acting on the frame is given by (Khurmi and Gupta, 2005; Norton, 2012): MeF =

/ (K M × M F )2 + (K T × TF )2

Stress developed on frame section; τ is given by

(3.47)

66

3 Disk Implements

Fig. 3.17 Square cross-section of frame

τ=

MeF Zm

(3.48)

where Z m is the section modulus for the frame. Considering the hollow square cross-section for the frame (Fig. 3.17) Section modulus for frame, Z m is given by (Norton, 2012) Z m = 2t(b − t)2

(3.49)

Assuming the value of the width of the toolbar cross-section and its thickness, the stress developed on the frame can be computed. If this stress is less than the permissible stress value of the frame material, then the design dimensions of the frame are acceptable.

Design problem

1. Design a single acting disk harrow for a 45 hp two-wheel drive tractor weighing 2200 kg and assuming rolling resistance of the tractor as 8% of its total weight. Assuming the weight of the harrow as 400 kg. Total weight of tractor and implement = 2600 kg. The rolling resistance (RR) of the tractor is 8% of its weight. R R = (2600 × 0.08)kg = 208 kg

3.5 Design of Disk Implements

67

If the forward velocity of operation is 4 km/h, the power required for propelling is PP =

208 × 4 × 75

5 18

= 3.08 hp

Assuming a transmission efficiency of 82% from engine to axle and tractive efficiency of 60%, drawbar power available from the tractor = (45 × 0.82 × 0.6) = 22.14 hp Drawbar power available for carrying out tillage = 22.14 − 3.08 hp = 19.06 hp Taking 20% power reserve, drawbar power available for carrying out tillage = (19.06 × 0.8) = 15.248 ≈15.25 hp So, the draft available is Dav =

15.25 × 746 = 10.24 k N 5 4 × 18 × 1000

Let the number of disks in a gang = 6 and the depth of operation (a) as 10 cm a So, the disk diameter will be, D = k cosβ Here, β = 0. So, D = k × a For harrow, the value of k = 3 to 6 Let k = 5 D = 5 × 10 = 50 cm So, the disk of diameter 51 cm available in the market will be taken Now spacing between two disks √ S = 2 a(D − a)tanθ0 θ0 is the setting angle is equal to the gang angle and can be taken as 20° √ S = 2 10(51 − 10)tan20◦ S = 14.74 cm According to the ASAE equation for single acting disk harrow, the cutting width of the single gang,

W =

W = 0.95(N −2)S+0.3D 100 [0.95×(6−2)×14.74+0.3×51] = 100

0.713 m

Length of the shaft, Ls = (14.74 × 6) = 88.44 cm Taking unit draft as 0.25 kg/cm2 and the cross-sectional area of soil disturbed as rectangular, the total draft acting on one gang = (0.25 × 9.81 × 71.31 × 10) = 1748.88 N

68

3 Disk Implements

For two gangs, the total draft = 1748.88 × 2 = 3497.76 N = 3.498 kN. This is much less than the draft available, Dav . Hence, the tractor can easily pull the implement. D Let us take, VLv = Vvf = 1.1 (Table 3.2), V v is the total vertical force. Vv =

Df 1748.88 = = 1589.89 N 1.1 1.1

The vertical force acting on a single disk, V 1 = V v /6 = 264.98 ≈ 265 N Weight of the implement: Single acting disk harrow: 150 to 270 kg/m of cutting width Weight of the implement, W g = (270 × 0.7131) = 192.54 kg = 1888.92 N Here, W > V v . This condition is necessary for penetration of disks into the soil. Design of shaft: Length of shaft = N1 × Spacing between two adjacent disks = 6 × 0.1474 = 0.884 m W g is uniformly distributed along the shaft RA = RB =

Wg − Vv 1888.92 − 1589.89 = = 149.515 N 2 2

The positive sign indicates that the direction of R1 and R2 are acting upward (Fig. 3.18). The shaft is subjected to bending due to vertical forces and is subjected to torsion due to draft) Wg × 1.5 × S 2   M S = (149.515 × 3 × 0.1474) + (265 × 4.5 × 0.1474) − 1888.92 × 1.5 × 0.1474 2 MS = 33.07 Nm    a Di × r− × N1 Torsional moment, TS = cosα 3 Bending moment, M S = R A × 3S + V1 × 4.5S −

Di = draft on each disk. r = radius of the disk, n = number of disks and α = gang angle Total draft = Di × N1 = 1748.88 N T or sional moment, TS = (

1748.88 )× cos20◦



0.51 0.1 − 2 3

 = 412.55 N m

3.5 Design of Disk Implements

69

Fig. 3.18 Forces acting on the gang shaft

Equivalent moment √ 2 2 MeS √ = (K M × M S ) + (K T × TS ) = (1.5 × 33.07)2 + (1.5 × 412.55)2 = 620.81 Nm Taking the shaft as a solid square section with side b and assuming KM and KT as 1.5 Section modulus, Z = 0.208b3 τmax × 0.208b3 = MeS b3 =

620.81 τmax × 0.208

The gang axle is made of mild steel. The maximum allowable stress of mild steel is 150 MPa and taking the factor of safety as 3, allowable design stress is taken as 50 MPa. b = 0.039 m ≈ 4 cm

70

3 Disk Implements

Fig. 3.19 Forces and moments acting on the frame

Design of frame: Frame (Fig. 3.19) encounters: • Bending due to vertical forces on the frame (RA and W g ) • Torque due to draft: It will try to twist the frame

W

M F = R A × 3S − 2g × 1.5S × 1.5 × 0.1474 M F = 149.515 × 3 × 0.1474 − 1888.92 2 M F = −142.704 Nm Torsional Moment, TM = Horizontal soil reaction parallel to the face the disc × Ma



Depth (a) + clearance Ma = moment ar m = Diameter o f disc, D − 3   10 + 10 = 57.67 cm = 51 − 3 Df ) × Ma TM = ( cosα TM = (1748.88/ cos 20◦ ) × 0.5767 = 1073.31 N m MeF =

√ √

(K M M F )2 + (K S × TM )2

= {(1.5 × −142.704)2 + (1.5 × 1073.31)2 } = 1624.13 Nm Taking the shaft as a hollow square section of thickness t = 5 mm



3.5 Design of Disk Implements

71

Allowable strees =

MeF section modulus

Section modulus, Z = 2t(as − t)2 , where t = thickness of the frame material and “as ” is the side of the frame cross-section. The frame is made of mild steel. The maximum allowable stress of mild steel is 150 MPa and taking the factor of safety as 3, allowable design stress is taken as 50 MPa. 1614.064 2 × 0.005 × (as − 0.005)2 as = 0.0619 m = 6.19 cm

50 × 106 =

Numerical problems

1. A single bottom disk plow with a diameter of the disk as 76 cm is operated at a disk angle (α) of 50°, tilt angle of 25°, and depth of 12 cm. Determine the width of cut of the disk plow.

Depth of cut, d = 12 cm

y=

√

x = cosd25◦ = 13.24 cm / 2Rx − x 2 = (2 × 76 × 13.24) − (13.24)2 = 28.82 cm 2

72

3 Disk Implements

actual width of cut = 2y sin α, where α = disk angle = (2 × 28.82 × sin 50◦ ) = 44.154 cm Hence, the width of the cut of the disk plow is 44.154 cm So,

2. A right-hand offset disk harrow is in operation with front and rear gang angles of 15° and 21°, respectively. The centers of the two gangs are located 2.5 m and 4.25 m behind a transverse line passing through the tractor drawbar’s hitch point. The horizontal soil force components are L f = 3 kN, L r = 3.5 kN and S f = 2.75 kN, S r = 4 kN. Calculate the amount of offset of the center of the cut with respect to the hitch point and horizontal component of the pull.

b = 2.5 m d = (4.5 − 2.5) = 1.75 m So, offset   b Sr − S f + d Sr e= L f + Lr 2.5 × (4 − 2.75) + 1.75 × 4 = 1.558 m e= 3 + 3.5 Px = L f + L r = (3 + 3.5) = 6.5 kN Py = Sr − S f = (4 − 2.75) = 1.25 kN

3.5 Design of Disk Implements

Ph =

73

/

Px2 + Py2 = 6.62 kN

3. A tractor-operated single acting trailing type disk harrow has 8 disks on each gang. The gang angle of both gangs is maintained at 35°. The horizontal component of the resultant horizontal soil reaction forces (longitudinal and side forces) on each disk is 600 N and it makes an angle of 30° with a gang axis. If the speed of operation is 6 km/h, what will be the required drawbar power in kW to operate the harrow? From Figure, α = 90° − 65° = 25° And resultant of horizontal soil reaction forces in right gang center = FR = (8 × 600) = 4800 N = FL So, Draft P = FR cosα + FL cosα = 8700.55 N Drawbar pull = Draft × velocity = 8700.55 × 6 ×

5 18

= 14500.9 W = 14.5 kW

4. A tandem type disk harrow has 11 disks of diameter 50 cm in each gang. Each gang axle is supported on two tapered roller bearings. While working at a gang angle of 20°, the resultant effect of soil reactions is to produce a radial force of 60 kg at an angle of 45° and an axial thrust of 100 kg acting at a distance of 20 cm below the center of each disk. The total weight of the rotating assembly per gang is 300 kg and the coefficient of rolling resistance is 0.45. Assuming that the radial force passes through the center of the disk, calculate:

74

3 Disk Implements

(i) Radial load on each bearing (ii) Total thrust load on each bearing (iii) Total power required to pull the harrow at a speed of 4.5 km/h

(a) Total radial force on two bearing = radial thrust of each disk × number of disks in each gang Rf = 60 × 11 = 660 kg Rf will be acting along the center of the central disk, i.e., the 6th disk from either end and it will be inclined at an angle of 45° The weight of the gang, Wg = 300 kg, is acting vertically downwards which also acts radially. So, the resultant radial load on two bearing R=

√

6602 + 3002 + (2 × 660 × 300 × cos45◦ ) = 897.56 kg

Radial load on each bearing = 897.56/2 = 448.78 kg (b) The resultant axial thrust load on each gang will be the sum of the axial thrust on each disk. Total thrust load = (11 × 100) = 1100 kg

3.5 Design of Disk Implements

75

(c) Total draft is the sum of horizontal components of the forces acting on each gang. The horizontal component of axial thrusts will cancel each other as it is a tandem type. Horizontal component of radial thrust on each gang = (660 cos 45° cos 20°) = 438.5 kg Rolling resistance for each gang = coefficient of rolling resistance × weight = (0.45 × 300) = 135 kg Draft on each gang = (438.5 + 135) = 573.5 kg Total draft for 4 gangs = (573.5 × 4) = 2294 kg =  22.50 kN  5 So, Power requirement = draft × forward speed = 22.5 × 4.5 × 18 = 28.125 kW. The total power required to pull the harrow is 28.125 kW. 5. Each gang of a right-hand offset disk harrow without wheels has seven 61 cm blades spaced 24 cm apart. The total mass is 1400 kg. During operation, the vertical force experienced at the front and rear gang is 6.7 and 4.3 kN with a disk angle of 16° and 22°, respectively. If the total longitudinal to vertical force and lateral to vertical force ratio are 0.9 and 0.7 for the front gang, respectively, as compared to 1.2 and 1.1 for the rear gang, calculate the total draft, side draft, and draft per unit mass of the offset disk harrow.

Θf = 16°

Θr = 22°

76

3 Disk Implements

For the front gang, Disk angle (θf ) = 16˚ Vertical force = 6.7 kN. Total longitudinal force/ vertical force = 0.9 Longitudinal force (Lf ) = 6.03 kN Total lateral force/ vertical force = 0.7 Lateral force (Sf ) = 4.69 kN For the rear gang, Disk angle (θr ) = 22˚ vertical force = 4.3 kN. Total longitudinal force/ vertical force = 1.2 Longitudinal force (Lr ) = 5.16 kN Total lateral force/ vertical force = 1.1 Lateral force (Sr ) = 4.73 kN Total longitudinal force = Total Draft = (Lf + Lr ) = 11.19 kN Side draft (S) = (Sr − Sf ) = 0.04 kN − Draft per unit mass of the offset disk harrow = (11.19×1000)/(1400×9.81) = 0.815

References ASAE Standards S497.4. (2000). Agricultural machinery management data. ASAE Standards S290.3. (2004). Determining cutting width and designated mass of disk harrows. Bernacki, H., Haman, J., & Kanafojski, C. Z. (1972). Agricultural machines, theory and construction (Vol. 1). Gordon, E. D. (1941). Physical reactions of soil on plow disks. Agricultural Engineering, 22, 205–208. Kepner, R. A., Bainer, R., & Barger, E. L. (1978). Principle of farm machinery, 3rd ed. USA: The AVI Publishing Company, Inc. McCrerry, W. F. (1959). Effect of design factors of disks on soil reactions. ASAE paper 59–622. Norton, R. L. (2012). Machine Design an integrated approach (pp. 182–192). Pearson Education, Inc.

Chapter 4

Cultivator

4.1 Introduction A cultivator is a secondary tillage implement used for pulverizing and partly crushing the tilled soil beds. It can be used for scarifying stubble before sowing crops, for destroying turf on the land to facilitate the sinking of the plow during tillage, for mixing fertilizers with soil, and for other works connected with the preparation of soil for sowing (Kepner et al., 1978). Generally, cultivators are mounted types. But there are some semi-mounted types cultivators available with transport wheels. Mounted cultivators are lighter than semimounted ones. Cultivators coupled with tractors, equipped with hydraulic lifts with automatic draft control, have no wheels and can still be lighter. The main parts of a cultivator are the frame, three-point linkage, and cultivator’s teeth (Fig. 4.1). • Frame—The frame of a cultivator consists of horizontal bars on which teeth are attached. Tractor-drawn cultivators are provided with frames made up of mild steel flat, channel, or I-section. • Three-point hitch—Three-point hitch is attached to the frame of the cultivator for attaching it to the tractor. • Cultivator teeth/tines—Tines are the portion of cultivators that are fastened to the cultivator frame. It consists of two parts. The upper part, which is attached to the frame, is called the shank, and soil-working tools are attached to these shanks at their bottoms. Cultivators are provided with tines made up of carbon steel of grade C55 Mn75.

4.2 Cultivator Teeth (Working Elements) The working element of the cultivator is a shovel, sweep, or knife (Fig. 4.2). The latter is often called scarifiers. The cultivator teeth may be flexible, semi-rigid, or rigid. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_4

77

78

4 Cultivator

Fig. 4.1 Tractor drawn mounted cultivator

Fig. 4.2 Types of working element of a cultivator

Flexible tooth: Spring teeth are fastened to the frame of the cultivator using yokes (Fig. 4.3) and are strengthened by another spring. When operating teeth bend backward, the shape of the spring camber and its dimensions should be selected in such a manner that the deflection “f” of the tooth be proportional to the component K x of soil resistance (Fig. 4.4). K x = C f (kg)

Fig. 4.3 Cultivator spring teeth: a “S”-shape; b circular

(4.1)

4.2 Cultivator Teeth (Working Elements)

79

Fig. 4.4 Spring tooth deflection

The constant of the spring should amount to C ≤ 6 kg/cm. The spring of the tooth is calculated for double average resistance Kx . Maximum tooth deflection should not exceed 10 cm, and the load angle (α) of the shovel (or sweep) should not exceed 30°. The load angle (α) of the shovel, without the spring deflection, should be contained within limits of 15–20°. Spring teeth cannot be applied under each soil condition. As a result of high deflection, the teeth can pull wet soil out onto the surface, and thus facilitate harmful drying up of soil. Clods pulled upward onto the surface quickly dry up and become hardened. A drawback of spring teeth is their lack of securing uniform working depth and their difficult penetration into the soil; their advantage, on other hand is their capacity to pull out rootstocks of couch grass onto the surface without ripping them. Semi-rigid tooth: It consists of two parts—a lower rigid and upper spring part fastened by a yoke to the frame (Figs. 4.5 and 4.6). Semi-rigid teeth are provided at their ends with sweeps, which penetrate more easily into the soil than shovels. The constant of the spring of the semi-rigid tooth is higher and amounts to C ≤ 15 kg/ cm. The spring of the tooth is also calculated for twice the average resistance Kx . Fig. 4.5 Semi-rigid tine

80

4 Cultivator

Fig. 4.6 Semi-rigid cultivator teeth: a with single plain spring; b with additional helical spring; 1-plain spring, 2-shank, 3-sweep, 4-helical spring

Fig. 4.7 Rigid teeth of a cultivator: a with a vertical shank; b with a chisel

Rigid tooth: The rigid tooth of a cultivator (Fig. 4.7) consists of a shank and a working element, either a sweep or a shovel. The shank can be rigidly connected to the frame by using screws or joints.

4.3 Working Zone of the Cultivator’s Tooth The working zone of the cultivator’s tooth is shown in Fig. 4.8. The cultivator’s tooth acts sidewise and forward on the soil. The width of zones “t s ”, acting on both sides of the tooth, can be calculated by using the following equation ts = atanϕ Transversal spacing (t 0 ) of cultivator’s teeth should amount to

(4.2)

4.3 Working Zone of the Cultivator’s Tooth

81

Fig. 4.8 Operating zones of cultivator’s teeth

t0 = 2amax + B0 + Δt

(4.3)

where Bo = width of the shovel or sweep, ϕ = angle of internal soil friction, amax = maximum working depth, Δt = spacing between maximum working zones of two adjacent teeth of a cultivator = 2–5 cm for shovels and 0–5 cm for sweeps. The mean value of the angle of internal friction of soil is assumed, ϕ = 45°. The zone of forward action of the cultivator amounts to t s = a tanϕ. Assuming ϕ = 45°, the spacing L of the rows of teeth should amount to L ≥ amax + l

(4.4)

where l is the distance of the blade point from the tooth shank (Fig. 4.8). Sweeps are spaced in the cultivator most frequently in two rows, while shovel teeth are spaced most frequently in three rows so that their tracks overlap on a width C = 2–3 cm. Sweeps of the second row are wider than that of the first row. The working width of the cultivator with sweeps amounts to Bk = B0 n − C(n − 1)

(4.5)

where n = number of sweeps, B0 = width of sweep, and C = overlap. Load angle α of a shovel is contained within limits of 20°–45°. Narrow shovels with load angles greater than 30° are used with rigid teeth called chisels. The apex angle of the points of the shovels (2θ) amounts to 70°–90° (Fig. 4.9). The width of the shovel ranges from 45 to 100 mm; their thickness is 7–10 mm. Shovels are made of the same carbon steel as plowshares or disks. The blade of the shovel is hardened on a width of about 40 mm up to the hardness of 500 HB . The hardness of the remaining part of the shovel should be below 300 HB . Soil resistance acting on the shovel is directed downward and makes 10°–25° angle with horizontal. It can be assumed that the average soil resistance is applied to the shovel at a height of h = 0.2a measured from the point of the blade. The horizontal component of the soil resistance, acting on the rigid tooth with a shovel and sweep, increases with the increase in depth (Fig. 4.10a and b).

82

4 Cultivator

Fig. 4.9 Apex angle of sweep and shovel-type working elements

Fig. 4.10 Variations of soil resistance and specific soil resistance with working depth: (a) Variation of soil resistance, Kx for a cultivator tine with a shovel; (b) Variation of Ps - specific resistance, (kg/ cm of working width) for a cultivator tine with sweep. (source Bernacki et al., 1972)

Sweeps form a kind of two interconnected shares (Fig. 4.11); the relation between angles of sweep is the same as in plow shares tanγ =

tanα tanθ0

where α = load angle, θ 0 = setting angle, and γ = cutting angle.

(4.6)

4.3 Working Zone of the Cultivator’s Tooth

83

Fig. 4.11 Distribution of cutting forces of weed roots by the sweep blade: a—sweep sharpened from above; b—sweep sharpened from below

Sweeps are used to pulverize the soil and remove weeds by cutting their roots. Therefore, easy undercutting of weeds by the sweep blades should be considered while choosing the apex angle 2θ0 . From Fig. 4.11, pressure Q on weeds or roots, as the sweep is moving, indicates the direction of motion. The distribution of this pressure is a tangential force S and a normal force N. The normal force causes friction between the root and the blade. This friction force can be expressed as T = Ntanϕ (ϕ is the angle of friction between weeds and cutting edge). When the tangential force exceeds the friction force, the root is cut. From Fig. 4.11, N tan ϕ < Q cos θ0 N = Q sin θ0 tan ϕ < cot θ0 = tan(90 − θ0 ) ϕ < (90 − θ0 )

(4.7)

And then the angle of the setting of the blade amounts to θ0 ≤ (90 − ϕ) Crushed roots and stalks of weed have friction angles that are lesser than 45◦ . Assuming that ϕ = 45°, we obtain 2θ0 ≤ 90◦

(4.8)

84

4 Cultivator

The apex angle of the sweep can vary in practice between 60° and 90°, but is often 70°. The load angle of the sweep is between 12° and 20°. Smaller angles are taken for sweeps of spring teeth, while larger angles are taken when rigid teeth are used. The cutting angle (γ) should be in the range of 18°–30°. The angle of the sharpness (i) should be within a limit of 12°–15° to keep the blade more durable. Sharpening of sweeps or shovels of a cultivator can vary but sharpening from above is considered as being the best, because, in this case, the angle of relief (ε) is equal to the cutting angle, and the blade does not blunt quickly, but this type of blade involves a reduction in its cutting capacity of roots. There are two types of sweeps: straight and with a nose. Sweeps with a nose are more difficult to make. Sweeps are pressed from a steel sheet with a carbon content of about 0.70%. The thickness (δ) of the steel sheet depends on the working width Bo of the sweep. Bo < 200 mm, δ = 3–4 mm, Bo = 200–300 mm, δ = 5 mm, Bo = 300 mm, δ = 6 mm. The blade of the sweep is hardened on a width of 25–40 mm up to the hardness of about 500 HB . The remaining part of the sweep hardness should not exceed 350 HB .

4.4 Shanks of Rigid Teeth The shape of the shank (Fig. 4.12) is determined by the slope l and by the radius of curvature R which is dependent on the load angle (α) of a shovel or a sweep R=

h 0 − l1 sinα cosα

(4.9)

where l 1 is the length of the breast of the sweep. The slope of the shank is most frequently adopted in the range from 200 to 250 mm, and the radius of curvature R ≤ 120 mm. The height H of the shank depends on the manner of its fastening to the frame. Minimum clearance H1 between the land surface and lower edge of the frame should amount to greater than 200 mm. H1 equal to about 300 mm is most commonly used in practice H = amax + H1 + ΔH

(4.10)

where ΔH is the length of the upper part of the shank serving for shank fastening. The shank of the tooth is exposed first of all to bending as consequence of soil resistance. For calculation purposes, the soil resistance K obl is assumed to be horizontal and acts in the axis of symmetry of shovel or sweep. This calculated resistance

4.4 Shanks of Rigid Teeth

85

Fig. 4.12 Shank of cultivator with a sweep

K obl of the soil is assumed to be 3–5 times higher than the average resistance K x , similarly as adopted for the calculation of tightening springs. The average resistance of one tooth can be calculated by the following formula Kx = a

Bk pk n

(4.11)

where a = working depth, Bk = cultivator working width, n = number of teeth of cultivator, and pk = specific resistance of soil cutting using sweep. The specific resistances of soil pk when operating at a depth of 15 cm are given in Table 4.1. The shank of the cultivator is subjected to bending or bending and torsion both depending on the type of working element attached to it. For a shank fitted with either a full sweep or shovel-type working element, it is only subjected to bending. Table 4.1 The specific resistance of soil

Type of soil

Specific soil resistance (kN/m2 )

Light soil

12

Medium soil

15

Heavy soil

20

Very heavy soil

25

(Source Data book for agricultural machinery design, CIAE Bhopal)

86

4 Cultivator

Referring to Fig. 4.12, stress causing the shank to bend amounts to σ =

6K obl (H1 + a) Mb = z bh 2

(4.12)

where M b = bending moment, z = section modulus, h = width of the shank, b = thickness of the shank and σ = allowable stress.

If the shank is fitted with a half sweep, it is subjected to both bending and torsion due to soil resistance. Equivalent twisting moment, √ Te = B M 2 + T M 2 Bending moment, BM = K obl (H1 + a) and Torsional moment, TM = K obl × (cutting width of half sweep/2), with an assumption that the horizontal component of resultant soil reaction is acting at the center of the width of half sweep. Maximum torsional stress is calculated according to the following formula Te = τ= Q

√

B M2 + T M2 Q

(4.13)

But when the cultivator is operated in field condition, it encounters the fluctuation of load. Hence, combined shock and fatigue factors must be considered for bending and torsional moments (Eq. 4.14) √ (K b × B M)2 + (K t × T M)2 Te = τ= Q Q

(4.14)

where b = thickness of shank, h = width of shank, and Q = section modulus (for a rectangular cross-section of the shank with thickness b and width h, Q = h2 b2 / (3 h + 1.8b)). Assuming h:b as 3:1, Q = 9 b4 /10.8 b = 0.833b3 . K b and K t are the combined shock and fatigue factors for bending and torsion, respectively and their values can be taken as 1.5 or 2.

4.4 Shanks of Rigid Teeth

87

Shanks are manufactured with carbon steel with a carbon content of 0.45–0.65%.

Design problem Design 1: Design a tractor-drawn 9-tine cultivator for a 45 hp two wheel drive tractor. Assume, Weight of the tractor = 2000 kg and weight of the cultivator = 250 kg. Total weight of tractor and cultivator = 2250 kg. Rolling resistance = 4% of total weight = 90 kg. Assume, forward velocity of travel = 4 km/h = 1.11 m/s. = 1.31 hp. Power required for propelling = 90×9.81×1.11 746 Engine power = 45 hp. Assuming transmission efficiency as 82% and tractive efficiency as 60%, drawbar power = (45×0.82×0.6) = 22.14 hp. Taking 20% power reserve, power available for tilling = {(22.14 × 0.80) − 1.31} = 16.40 hp. Let the width of the shovel = B0 = 6 cm. Working depth, a = 10 cm and Δt = 2 cm. Spacing of the tines = t0 = (B0 + 2a + Δt) = {6 + (2 × 10) + 2} = 28 cm.

Spacing between front and back tines = L = {(a × tan45°) + l} = 10 + 30 = 40 cm. (taking l, i.e., the distance of the blade point from the tooth shank = 30 cm). Width of the cultivator = (9 × 28) = 252 cm = 2.52 m.

88

4 Cultivator

Let the design of the cultivator is for hard soil in which specific soil resistance is 25 kN/m2 . Taking the soil resistance 3–5 times higher than the actual average soil resistance and assuming a rectangular cross-section of the soil disturbed area made by the cultivator tines, draft acting on the shovel Kobl = KH = (25 × 0.06 × 0.10 × 3) = 450 N   KV = KH × tan(90 − α) = 450 × cot25◦ = 965.028 N α = load angle, max 25◦ .

Design of Shank Design of Shank for Shovel and Full Sweep Type Blade The dimension of the shank is shown in Fig. 4.12 and the height of the shank is calculated from Eq. 4.10. H = amax + H1 + ΔH amax = 100 mm, H1 = 250 mm and ΔH = 50 mm So, the height of the shank, H = 400 mm Since, shovel is symmetrical about the vertical axis, the bending moment acting on the shank due to horizontal component of soil reaction force, Mb = KH (H1 + a) = 157.5 Nm σ =

Mb Z

where Mb = bending moment acting on the shank, z = section modulus = I/y, σ = design stress Design stress for mild steel =

Maximum allowable stress Factor of safety

The maximum allowable stress of steel is 150 MPa and taking the factor of safety 3, the design stress is 50 MPa.

4.4 Shanks of Rigid Teeth

89

Section modulus of a rectangular section is z = h = width, b = thickness. Assuming, h/b = 3

bh 2 6

Z = 1.5b3 157.5 50 × 106 = 1.5×b 3 b = 0.0128 m b = 0.0128 m = 1.3 cm and h = 3.9 cm Design of Shank for Half Sweep Type Blade A half sweep is not symmetrical about the vertical axis. So, both bending moment and torsional moment will act on the shank due to soil resistance force. The width of the half sweep is “w” and the moment arm for the torsional moment is w/2. Assuming w = 10 cm and cross-section of the furrow as rectangular.

Torsional moment (TM) = Design draft on half sweep × w/2 = {(25 × 0.10 × 0.10 × 3) × 0.1/2} = 37.5 Nm Bending moment (BM) = Kobl × (H1 + a) = {(25 × 0.10 × 0.10 × 3) × (0.25 + 0.1)} = 262.5 Nm Assuming h:b = 3:1 and K b and K t as 1.5 each √ (K b × B M)2 + (K t × T M)2 Te = Maximum torsional stress, τ = Q Q √ 2 (1.5 × 262.5) + (1.5 × 37.5)2 50 × 106 = 0.833 b3 √ 158203.125 50 × 106 = = 397.748/0.833b3 0.833b3 b = 0.0212 m = 2.12 cm Hence, h = 2.12 × 3 = 6.36 cm

90

4 Cultivator

Design of Frame: (A) Bending moment The frame fitted with more number of tines will be designed and same dimension will be followed for the other frame. A cultivator with nine shanks is shown in the following figure. The design will be made for the frame fitted with five tines. There will be bending moment due to both vertical soil reaction and weight of the cultivator (W1 ) itself. The horizontal component of soil reaction will cause a torsional moment to act on the frame.

Considering reaction R1 and R2 acting at the same distance t0 /4 from the end of the frame on either side. 5K + W 1×5

(5×965.028)+ (250×9.81×5)

9 R1 = R2 = V 2 9 = = 3093.82 N 2  t0 B MV = R1 × 4t0 + 4 − (K V × 4t0 ) − (K V × 2t0 ) − 2to + t40 W1 /2 = 3093.82 × 4.25 × t0 − 965.028 × 6 × t0 −2.25 × t0 × 250 × 9.81 × 5/(9 × 2)

For to as 28 cm, BM V = 3681.646 − 1621.247 − 429.188 = 1631.211 Nm Torsional moment, T M = K H (H 1 + a). Here a = 10 cm and assuming H1 = 25 cm, T M = (450 × 0.35 × 5) = 787.5 Nm Now equivalent twisting moment,

4.4 Shanks of Rigid Teeth

91

√ Meq = (K b × B Mv)2 + (K t × T M)2 = 2717.03 Nm M = 2717.03/0.231 h3 τ = Qeq = 2717.03 Q Assuming a hollow square section for the frame, section modulus Q = 2t(h−t)2 , where t = thickness and h = size of each side. Considering t/h as 1/6, Q = 0.231 h3 h3 =

2717.03/0.231 τ

The maximum allowable stress of steel is 150 MPa and taking the factor of safety 3, the design stress is 50 MPa. h = 0.0617 m = 6.17 cm

Numerical problems

1. The total distance between the left-most tine and the right-most tine of a 9-tine cultivator is 160 cm. If the cultivator is operated at 3 km/h with a field efficiency of 78%, calculate the actual field capacity. Total width = 1.6 m + 1.6/8 = 1.8 m. Operating speed = 3 kmph. 

ha Theoretical field capacity h

 =

V ×W 10

where V = operating speed, kmph W = width of the implement, m

Theoretical field capacity =

3 × 1.8 = 0.54 ha/h 10

Actual field capacity = Theoretical field capacity × Field Efficiency Actual field capacity = 0.54 × 0.78 = 0.421 ha/h

92

4 Cultivator

2. The average draft of a 9×30 cm cultivator in sandy loam soil when operated at a depth of 10 cm and forward speed of 4 km/h is 1.5 kN. If the tractive efficiency is 55%, calculate the power required at the axle of the tractor. Draft = 1.5 kN. Drawbar power = Draft × Forward velocity = (1.5 × 4 × 5/18) = 1.667 kW. Tractive efficiency = Axle power =

Drawbar power Axle power

1.667 = 3.031 kW 0.55

3. Find the volume of soil handled per unit time when a tractor drawn 11×30 cm shovel-type cultivator is operated in sandy loam soil at a depth of 10 cm and at a forward speed of 4 km/h. Width of cut = (11 × 30) = 330 cm = 3.3 m. Depth = 10 cm. Forward speed = 4 km/h = 4 × 10/36 m/s = 1.11 m/s. Assuming a rectangular furrow section, the volume of soil handled per unit time = (width of cut × depth × forward speed) = 3.3 × 0.1 × 1.11 = 0.3663 m3 /s. 4. If the unit draft of a tractor drawn 9×25 cm shovel-type cultivator when operated in sandy loam soil at a depth of 10 cm is 25 kN/m2 , find the total draft requirement of the cultivator. The total weight of tractor and cultivator is 2500 kg. Assuming rolling resistance of tractor and cultivator as 10% of its total weight, find out the total power requirement to carry out tillage, when the cultivator is to be operated at 4 km/h. Assuming a rectangular cross-section of the furrow, the draft experienced by a single tine = (25 × 0.25 × 0.1) = 0.625 kN. The total draft experienced by the cultivator = Total number of tines × draft experienced by a single tine = (9 × 0.625) = 5.625 kN. Power required to pull the cultivator = total draft × forward speed = (0.625 × 9 ×4 × 10/36) = 6.25 kW. Power required to overcome rolling resistance = 10% of the total weight × forward speed = (0.1 ×2500 × 9.81 × 4 × 10/36) = 2725 W = 2.725 kW. Total power requirement for operating the cultivator at a forward speed of 4 km/ h = Power required to pull the cultivator + power required to overcome rolling resistance. Hence, total power required = 6.25 +2.727 = 8.975 kW.

References

93

References Bernacki, H., Haman, J., & Kanafojski, C. (1972). Agricultural machines, theory and construction (Vol. 1). Data book for Agricultural Machinery Design. Central Institute of Agricultural Engineering, Bhopal. Kepner, R. A., Bainer, R., & Barger, E. L. (1978). Principle of farm machinery (3rd ed.). The AVI Publishing Company, Inc.

Chapter 5

Rotary Tillage Implements

5.1 Introduction Rotary tillage is carried out by implements where the working elements are powered, unlike the moldboard plow, disk plow, and cultivator (examples—rotavator and powered disk harrow). These implements are also called active tillage implements. The most commonly used rotary tillage implements are tractor-drawn rotavators and power tiller-drawn rota-tillers. The total power requirement of these implements includes power requirements for cutting the soil slices, throwing the soil slices, and power requirements for propelling. The power requirement for propelling is reduced due to the negative draft generated by the interaction of working elements with soil when the working elements rotate in the same direction as the direction of travel of the tractor or power tiller. A rotavator is a tractor-drawn implement (Fig. 5.1) that is mainly used for seedbed preparation within one or two passes and is suitable for removing and mixing residual crops such as maize, wheat, paddy, sugarcane, etc. As a result, it enhances soil health and reduces the amount of fuel, money, time, and energy needed to prepare the field. The working elements of the rotavator are powered by the tractor PTO. The power train for rotating the rotavator using a tractor is shown in Fig. 5.2. Rotary tillers attached to the power tiller are very commonly used in preparing dryland for sowing seeds and the rice field for carrying out puddling operations. Rotary tillage operation provides a high degree of pulverization and has higher power requirements as compared to passive tillage implements. Generally, it consists of the following: • • • • • • •

Universal shaft (driver) Gearbox (bevel pinion) Speed reduction unit Main shaft Cutting blade (J, L or C type) Shield Depth adjusting skids.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_5

95

96

5 Rotary Tillage Implements

Fig. 5.1 Rotavator

Fig. 5.2 Power flow in tractor-drawn rotavator

5.2 Rotavator 5.2.1 Construction and Different Components of a Rotavator Blades: The rotavator blades are made of high-carbon steel or chilled cast iron. Generally, three different types of blades are attached. The L-shaped blade is for wetland and trashy conditions but doesn’t pulverize well. A C-type blade is for dry land and a J-shaped blade is for grassy land (Fig. 5.3). Besides this, a straight type of blade is also used on mulches and is designed mainly for secondary tillage and to conserve moisture of the soil. The blade geometry of the “L” shaped blade is shown in Fig. 5.4. The soil slice produced by the interaction of the rotavator blade and soil is shown in Fig. 5.5. Main shaft: The shaft is made up of carbon steel and it comprises of number of disks. Blades are attached to the periphery of these disks.

5.2 Rotavator

97

Fig. 5.3 Different types of blades

Fig. 5.4 Blade geometry of L-shaped blade: C—chord of the blade, L—vertical section height (stem or leg), S—horizontal section height (span), bt —thickness of the blade, R—radius of the rotor

Primary speed reduction unit: The main function of this unit is to transmit the tractor power to the second speed reduction unit and to reduce standard PTO rpm (540 and 1000 rpm). In general, bevel gears are used in the primary speed reduction unit. These are made from high-strength carbon steel. Secondary speed reduction unit: This unit is also known as the side drive, and it transmits the tractor PTO power to the rotor shaft through a bevel gear to reduce the

98

5 Rotary Tillage Implements

Fig. 5.5 The soil tool interaction for a down-cutting rotavator fitted with an L-shaped blade (Ltr — length of the cut, w—width of cut, d—depth of tillage, l—tilling pitch). Face ABEF—Previously cut surface by the span of the preceding blade, Face ABCA—Soil surface is being cut by the vertical part of the blade, Face ACDF—Soil surface cut by the horizontal part of the blade, Face FEDF—Soil surface sheared from the uncut soil body

speed to approximately 210 rpm. It consists of a chain and sprocket assembly. Some rotavators may instead have three spur gear assemblies for transmitting the power. Trailing board/skid: This unit helps in leveling the ground during the operation of the implement and it also provides an additional safety feature. This unit is made of a mild steel plate. Generally, the speed of the PTO shaft is 540 rpm but the desired degree of pulverization can be obtained when the speed of the rotavator is only 210 ± 10 rpm. It can be achieved by using a suitable gearbox. Blades can rotate in both clockwise, i.e., concurrent revolution mode (when the rotor rotates in the same direction as forward travel), and counterclockwise, i.e., reversed revolution mode (when the rotor rotates in the opposite direction to forward travel). In the case of concurrent revolution mode, a negative draft is generated which pushes the rotavator in the forward direction, thus reducing the power required to propel the rotavator as compared to reversed revolution mode. The shape of the soil slice depends on the direction of rotation of the rotary cultivator and the peripheral to forward speed ratio (u/V) of the rotavator as shown in Fig. 5.6.

5.2 Rotavator

99

Fig. 5.6 Dependency of the shape of soil slice on the direction of travel and u/V ratio of the rotavator

5.2.2 Kinematics of Blade-Soil Interaction 5.2.2.1

Cutting Trajectory

The path traced by the rigid blade is a cycloid (Fig. 5.7) and its equation can be given as X = V t + Rcos(ωt)

(5.1)

Y = Rsin(ωt)

(5.2)

V = forward velocity of the rotavator and α = ωt, the angle of rotation of the blade during the time t measured from the x-axis, ω = angular speed of the blade. In case of concurrent revolution for the horizontal axis of rotation, blades first come in contact with soil at an angle of 20° and remain in contact with it up to 100°; for reversed revolution, the range of contact is from 260° to 340°. Thus, in both cases, blades remain in contact with soil for around 80°. For the cutting elements with a vertical axis of rotation, the cutting operation of soil slices begins at angle α0 amounting to −100°, and the process comes to an end when the value of α0 is about +100° or lower if the working width is equal to or smaller than the rotor diameter. Due to the high peak torques generated after each cut, it is crucial to stagger the blades with equal angular gaps between them so that two blades don’t strike the soil

100

5 Rotary Tillage Implements

Fig. 5.7 Path traced by the blade and shape of soil slices, a—working depth; b—working width; l—length of soil slices; V—travel speed (a) For rotary cultivator with rigid teeth and horizontal axis of rotation (b) For rotary cultivator with rigid teeth and the vertical axis of rotation (c) For rotary cultivator with spring tines and horizontal axis of rotation

5.2 Rotavator

101

at the same time. The staggered pattern should be approximately symmetrical about the longitudinal centreline.

5.2.2.2

Tilling Pitch

The length of soil slice cut by the blade is called tilling pitch and is the function of both the forward speed of the rotavator, the peripheral speed of the rotor and number of blades working in the same orientation. It can be expressed as l=

60 × V n×z

(5.3)

where V = forward speed of the rotavator (m/s), n = rotor RPM, and z = number of blades on a disk in the same orientation or number of blades on a disk which follows the same path (usually it varies from 2 to 3). l=

2×π × R×V u×z

R = rotor radius (m), u = peripheral speed of rotor (m/s) =

(5.4) 2π Rn . 60

Hence, tilling pitch (l) is inversely proportional to ( Vu ). If this fraction increases, the number of strikes of the blade to the soil increases thus tilling pitch reduces, and soil pulverization increases, which is the main purpose of rotary tillage. To achieve this, the forward speed of the rotavator is reduced. The same is the situation in the case of reversed revolution.

5.2.3 Angles Associated with Cutting Trajectory Different angles associated with the cutting trajectory are shown in Fig. 5.8 and are described below: Cutting angle (γ): It is the angle between the plane of the blade and the tangent drawn to the cutting trajectory. The minimum cutting angle is 15°. Setting angle (γo ): It is the angle contained between the plane of the blade and the tangent drawn to the rotary circumference. Upper-end clearance angle (δ): Angle between the back surface of the sharpened edge and tangent to the rotary circumference. Effective clearance angle (δ/): Angle between the back surface of the sharpened edge and tangent to the cutting trajectory. It is always greater than zero to reduce the cutting resistance and thus prevents the back face of the blade from compressing the uncut soil. From the wear and tear point of view, it is usually taken as 5°.

102

5 Rotary Tillage Implements

Fig. 5.8 Angles and speed of blade with the axis of rotation perpendicular to the direction of travel

Path intersection angle (Δδ): It is the angle between the tangent to the rotary circumference and the tangent to the cutting trajectory. Relationship among different angles γ =β +δ

(5.5)

where β is the angle of knife sharpening. From the durability point of view, βminimum = 10°. Thus, γmin = 15◦ γ0 = γmin + Δδ max From Fig. 5.8 tanΔδ =

V cosα u − V sinα

(5.6) (5.7)

The magnitude of Δδ depends upon the value of the ratio of the peripheral speed of the rotor to forward speed (u/V), the angle of rotation (α), and the direction of rotation (Fig. 5.9).

5.2 Rotavator

103

Fig. 5.9 Variation of the path intersection angle, Δδ with the angle of rotation, α for various u/V ratios (Source: Bernacki et al., 1972)

For the same (u/V) ratio, Δδ in concurrent revolution will be more than that of the reverse. When the (u/V) ratio increases, then Δδ in both concurrent and reverse revolution will reduce (Fig. 5.9). αP is the angle at which the blade of the rotary cultivator touches the land surface. Cutting speed (us ): It is the resultant of the peripheral speed of the rotary cultivator (u) and the forward speed of the rotary cultivator (V) and can be written as u − V sinα cosΔδ (u) − sinα or, u s = V cosΔδ us =

or, u s =

v[

(u)

V

− sinα] cosΔδ

V

(5.8)

us will be more in case of reversed revolution as compared to concurrent because the sinα is negative in case of reversed rotation. When the ratio (u/V) reduces then cutting speed (us ) reduces in both concurrent and reverse revolutions (Fig. 5.10).

104

5 Rotary Tillage Implements

Fig. 5.10 Variation of the cutting speed us with the angle of rotation of blade, α for various u/V ratios (Source: Bernacki et al., 1972)

For u/V greater than 5, cos Δδ = 1. In that case, Eq. 5.8 reduces to us = V

(u V

− sinα

)

For lower ( Vu ) ratio, the path intersection angle (Δδ) increases, and because of that, there is a fluctuation in the cutting angle which results in a fluctuation of cutting resistance. Thus, to reduce the fluctuation of the cutting angle, Δδ should be minimum and to achieve that, the ratio ( Vu ) should be greater than 5.

5.2.4 Forces Acting on the Furrow Slice and Specific Work 5.2.4.1

Soil Resistance Force (K)

Resistance force offered by the soil during cutting (Fig. 5.11) is acting on the knife and can be calculated as: K =

M R'

(5.9)

5.2 Rotavator

105

Fig. 5.11 Representation of soil resistance forces acting on the blade

where M = Moment at that point, R/ = arm of the force = R cos (ψ – Δδ), R = blade radius and, ψ = angle between force K and tangent to the cutting trajectory varying between 10 and 15°. The value of K obtained from the above equation is not constant; rather, it is variable and all the angles, ψ, Δδ, and α are also variable. Thus, this value of K cannot be used for design purposes. For design purposes, it is assumed that instead of cutting resistance K, peripheral force (Ko ) acting on the blade is to be taken which has a constant value.

5.2.4.2

Peripheral Force (Ko )

Peripheral force is acting on the constant arm R, i.e., rotor radius, and can be calculated as: Ko =

M R

(5.10)

It increases with the increase in forward speed (V) and has two components, one is static force (K s ) and the other one is dynamic force (K d ). The static component is related to the force needed to rotate the blades to overcome the frictional forces without engagement with soil. Part of the dynamic force is engaged in the process of cutting off soil slices and the other part in throwing the slices.

106

5 Rotary Tillage Implements

Ko = Ks + Kd

5.2.4.3

(5.11)

Specific Work (A)

Work done by a rotavator during one revolution of working sets or for a unit volume of soil handled in one revolution is called specific work. A=

2×π×M z × l × a × bm

(5.12)

where A = work done by a rotavator in one revolution, z = number of blades working in one plane, M = moment acting on the shaft, l = tilling pitch, a = depth of operation, and bm = width of rotavator. For concurrent revolution, A=

M2π − AX zlabm

(5.13)

where Ax is due to the negative draft developed because of the rotation of the blade = Draft/(a×bm ). In the case of concurrent revolution, it can be neglected and can be written as A=

2×π×M z × l × a × bm

(5.14)

But for a reversed revolution, it cannot be neglected and has to be added. Thus, for a reversed revolution A=

M×2×π + AX z × l × a × bm

(5.15)

From the expression of peripheral force (K o ), i.e., Eq. 5.10 and tilling pitch (l), i.e., Eq. 5.4, respectively, K o can be expressed as ( Ko = A

) V abm u

(5.16)

This specific work (A) has also two components. One is the static work done by the rotavator (Ao ) when the soil slices are being cut off, and the other one is the dynamic work done by the rotavator (AB ). A = Ao + A B

(5.17)

The value of Ao depends on the soil-specific resistance, Ao = Co ko kg/cm2 .

5.2 Rotavator

107

Table 5.1 Values of k0 in different soil

Type of soil

Value of ko (kg/cm2 )

Light soil

0.2–0.3

Medium soil

0.3–0.5

Heavy soil

0.5–0.7

(Source: Bernacki et al., 1972)

Where Co = coefficient, for a rotary tiller with ‘L’ type blade and operating at 10– 15 cm depth, its value lies between 2.5 and 3.5 (Bernacki et al., 1972), ko = Specific draft, its value depends on the type of soils (Table 5.1). Dynamic specific work (AB ) depends on the peripheral speed of the blade or the forward speed of the rotavator. If the length of the soil slices cut is constant, then it can be expressed as. A B = αv V 2 or αu u 2 kg/m2

(5.18)

where αv and αu are coefficients and both are related as αv = αu (u/V)2 . Values of Co and αu are given in Table 5.2. From the expression of peripheral force Ko (

and

) V abm K s = Ao u ( ) V abm Kd = AB u

(5.19) (5.20)

Part of the dynamic force is engaged in the process of cutting of soil slices and the other part is used in throwing the soil slices. Energy required to throw the soil slices is expressed as Table 5.2 Values of Co and αu Type of implement

Type of knife

Working depth(cm)

Length of soil slices(cm)

Soil

Co

αu (kg s2 / m4 )

Rotary Cultivator

L-knife

10–15

6–15

Tilled

2.5–3.5

400–500

„

3.5–6

6–12

Meadow

5–10

400–500

„

6–12

6–12

Meadow

3–5

400–600

Bent

5–15

6–15

Tilled and meadow

1.5–3

300–400

Hoe

12–20

15–30

Tilled

1–2

400–500

Civello plow Bent

20–35

3–12

Tilled

1.2–3.5

200–300

Rotary hoe

(Source: Bernacki et al., 1972)

108

5 Rotary Tillage Implements

( E=

mc2 2

) (5.21)

where m = mass of soil slices and c = average speed at which the soil slices are thrown and is proportional to the peripheral speed of the rotor blade (c = m×u and m = 0.4–0.7) Considering the losses of energy due to soil friction and ventilation resistance to be expressed by a coefficient, η whose value is 0.5, the energy necessary for throwing the soil slices back amounts to E=

m(εu)2 . 2η

Dividing energy with the volume of soil slices, the specific work in throwing the soil slices can be obtained as: A B' =

5.2.4.4

m(∈u)2 2abm lη

(5.22)

Arrangement of Working Elements

The arrangement of working elements on the disk or rotor should adhere to the following guidelines to achieve the least amount of fluctuations in the peripheral force: (i) For each working element to penetrate the soil individually in the same time interval, the angle between them should be uniform. (ii) To avoid clogging with soil, which creates additional resistance, the distance between adjacent blades should be as wide as possible. To maintain the uniformity of cut, blades are provided at equal angular intervals and that can be given as θ=

360◦ i × zt

(5.23)

where θ = angle at which blades are provided, i = number of sets of the blade, and zt = number of blades on each set. This condition is true only when one blade from the set touches the soil at one time. But maximum, 1/4th of the total number of blades remain in contact with the soil at any point of time.

5.2 Rotavator

109

5.2.5 Design of a Rotavator 5.2.5.1

Design of Shaft of a Rotavator

The shaft of the rotavator is subjected to both torsion and bending. The bending moment is due to both the vertical soil reaction and the weight of the rotavator itself. The horizontal component of the soil reaction will create a torsional moment in the shaft. If the blade strikes soil at an angle “α” from the horizontal plane (Fig. 5.11), vertical soil reaction force will be Ky = K cos (α + ψ − Δδ) = RM‘ cos(α+ψ −Δδ) and horizontal soil reaction force will be KX = K sin (α + ψ − Δδ) = RM‘ sin(α +ψ −Δδ). where R’ = Rcos (ψ − Δδ). For concurrent revolution, the blade touches the soil at 20° and remains in touch with soil up to 100° (discussed in Sect. 5.2.2). So, the horizontal component will be maximum at an angle of 90° (KX = K sin 90° = K) and the vertical component will be maximum for the angle of 20° (Ky = K cos 20°). Maximum allowable stress (τs ) on the shaft is given as (Norton, 2012) τs =

Me y J

(5.24)

where M e = Equivalent moment acting on the shaft / (K m × Mb )2 + (K t × Mt )2

(5.25)

Mb = Bending moment (given below in sub section calculation of bending moment) Mt = Torsional moment = KXmax × R × number of blades in contact with soil at a time Km and Kt are the combined shock and fatigue factor for bending and torsion, respectively. J = Polar moment of inertia of the shaft 4 For solid circular shaft, J = π32d (1−t ) For hollow shaft, J = π do 32 where d = diameter of solid shaft do = outer diameter of hallow shaft tr = ratio of inner diameter to outer diameter, tr = di /do di = inner diameter of hollow shaft y = distance from the neutral axis where stress is maximum for solid shaft, y = d2 for hollow shaft, y = d20 Maximum allowable stress (τs ) can be taken as 1000 kg/cm2 depending on the material selected. Transmission efficiency and power reserve were taken into account while calculating the available PTO power. 4

4

110

5 Rotary Tillage Implements

P = B H P × ηt × ηr

(5.26)

where P = power available at PTO, BHP = brake horsepower, ηt = transmission efficiency of tractor gearbox, ηr = coefficient of power reserve, which also includes power required for propelling the tractor with implement. The torque available at PTO,T =

P×60 2π n P T O

where nPTO = Tractor PTO rpm = 540. The torque available at rotavator shaft, T1 = T × G.R 1 × G.R 2 × (1 − losses in transmission)

(5.27)

where G. R1 = gear reduction in gear box; G. R2 = gear reduction in side gear assembly. The diameter of the rotavator shaft can be determined by considering maximum shear stress in the shaft and using maximum normal stress theory (Norton, 2012) π × τmax × d 3 = 16

] [/ 2 2 (K m × M) + (K t × T1 )

(5.28)

where τmax = maximum allowable shear stress, N/mm2 , d = diameter of shaft, mm, M = maximum bending moment, N-mm; T 1 = maximum torsional moment, N-mm, K m = combined shock and fatigue factor for bending; K t = combined shock and fatigue factor for torsion. Higher of the two dimensions obtained for the shaft (based on Eqs. 5.24 and 5.28) is to be selected. Calculation of Bending Moment The middle of the rotavator is considered as the reference plane. The reaction force (R1 ) acts at the end of the shaft at a distance of 1/4th of the gap between two adjacent drums on which blades are mounted (Fig. 5.12). Reaction forces R1 and R2 at the support (i.e., at the two ends),

Fig. 5.12 Forces acting on a rotavator with 48 blades

5.2 Rotavator

111

R1 = R2 ={Total weight of the rotavator, W‘ − vertical forces acting at the blades ( ) Ky in contact with soil, i.e., 1/4th of the total number of blades}/2 { ‘ ( )} = W − Ky × n/4 /2

(5.29)

where n = total number of blades in the rotavator. Assuming that out of the n/4 number of blades, two blades each of the central drum and the drums adjacent to the central drum and one blade from the rest of the drums are acting with soil at a time. Bending moment is maximum at the center of the shaft Mb = (R1 × 4.25Wd ) + K S × cos 20◦ × (4Wd + 3Wd + 2Wd + 2Wd ))−(W‘ /2) × bm /4

(5.30)

where W d = spacing between two adjacent drums, bm = total width of the rotavator, Ks cos 20° = vertical soil reaction acting in each blade in contact with soil = (total peripheral force, Kpt /number of blades in contact with soil)cos 20°, and W ’ = weight of the rotavator.

5.2.5.2

Design of “L” Type Blade

Blades are subjected to both bending moment and torsion. Force acting on the blade and its direction are shown in Fig. 5.13. Total peak peripheral force acting on the rotavator K pt = f K o

(5.31)

where f is the factor of safety = 1.5–2 (1.5 for stone less soil and 2 for stony soil). Peak force acting on each of the blade Fe =

K pt Total peak peripheral force = number of blades striking at a time n1

n1 = number of blades striking at a time =

Total number of blades 4

Bending moment, Mb = Fe S1 where S1 = R – r – space to fix the blade to the drum (5–7 cm). R = rotor radius and r = radius of rotor shaft Torsional moment, Mt = Fe S Equivalent moment on the blade (Khurmi & Gupta, 2005),

112

5 Rotary Tillage Implements

Fig. 5.13 Force acting on the blade and its direction

/ Me =

(K m × Mb )2 + (K t × Mt )2

Maximum allowable stress, τ S =

Me Q

(5.32)

where Q = Polar section modulus of the blade, be = thickness of the blade and he = width of the blade Q=

be 2 h e 2 1.8be + 3h e

(5.33)

he /be ratio for all cases can be taken as 6–10.

5.3 Powered Disk Harrow In powered disk harrow, disks get powered from the tractor PTO and rotate usually in the direction of travel, i.e., in the concurrent mode (Fig. 5.14). Although pulverizing ability of the powered disk harrow is good but it requires higher total power for its operation as compared to unpowered disk harrow. Highly stubble condition of the field after paddy harvesting forces the farmers to burn the leftover crop residues before using the rotavator to prepare a seedbed. This leads to environmental pollution. To overcome this problem, a powered disk harrow can be used as it can cut the paddy

5.3 Powered Disk Harrow

113

Fig. 5.14 Powered disk harrow (single acting disk harrow) developed at Agricultural and Food Engineering Department, IIT Kharagpur

stalks. Also, it has got positive cutting and throwing action, better crop residue incorporation, soil pulverization with the reduced draft requirement in a lesser number of passes, and improved efficiency with less tractor slippage (Hann and Giessibl, 1998). These advantages of powered disk harrows over unpowered ones may balance the overall increase in power needed to operate. Generally, a powered disk harrow comprises the following components: • • • • • • •

Disks Gang shaft Leveler Gearbox Universal shaft Side gear assembly Power transmitting shaft The design of a powered disk harrow includes the following.

5.3.1 Disk Diameter As the required load for penetration of disks into the soil increases sharply with increase in diameter, disk diameter should be selected minimum. For harrows, disk diameter (D) is related to the tilling depth (a) by the following Eq. (5.34) as proposed by Bernacki et al. (1972). D=K

a cosβ

(5.34)

where K is a dimensionless coefficient and its value ranges from 3 to 5, a = depth of operation, β = tilt angle = 0° for disk harrow.

114

5 Rotary Tillage Implements

5.3.2 Disk Blade The material for disk blades should be chosen depending on their minimal rate of wear. For disk blades constructed of SAE 1080 steel (carbon steel C75), the lowest wear rate can be achieved when the hardness is in the range of 44–48 (Rockwell C Scale) (Bernacki et al., 1972). Cross-rolled steel disks outperform disks constructed of straight-rolled steel. The concavity of disk plays an important role in penetration and draft requirements. Penetration is inversely proportional to the concavity, whereas the draft is directly proportional to the concavity. Disks sharpened from outside give better results.

5.3.3 Disk Spacing On the shaft, the disks should be positioned so as to both prevent clogging and generate a desirable furrow profile. Too much spacing between disks will result in untilled soil. It also depends on the height of ridges formed. As proposed by Bernacki et al. (1972), disk spacing (tt ) can be determined as ] [ √ S = tt = 2 c(D − c) tanα

(5.35)

where c = ridge height ≤ depth of operation, a; α = gang angle = 15° to 25° (for disk harrows).

5.3.4 Cutting Width of Single Acting Disk Harrow The cutting width of powered disk harrow should be wide enough to cover the tractor wheel track. According to BIS standard (IS:6635 1972), cutting width (W) can be calculated as. W = (0.95 × N × tt + 0.3 × D)/100

(5.36)

where W = cutting width (m), N = total number of disks spacings, tt = spacing between disks (cm), and D = diameter of disk blades (cm). According to ASAE (S290.2), the cutting width can be calculated as W = (0.95 × (N 1 − 2) × tt + 0.3 × D)/100

(5.37)

where W = cutting width (m), N1 = total number of disk blades, tt = spacing between disks (cm), and D = diameter of disk blades (cm).

5.3 Powered Disk Harrow

115

5.3.5 Calculation of Total Power Required The total power required will be the sum of the drawbar power required for pulling the powered disk harrow and the PTO power required for rotating the disks. The total drawbar power required will be the sum of the power required for pulling the disk harrow and for moving the tractor. It should be less than the available drawbar power of the tractor and it can be calculated by using Eq. 5.38. For drawbar power calculation, Total drawbar power = (Unit draft × cutting width × depth of operation + rolling resistance of tractor) × forward speed (5.38) Cutting width can be computed using the Eq. 5.36 or Eq. 5.37. Assuming a rectangular cross-section for the area tilled and knowing the unit draft in different soils, the draft force required will be equal to the product of the unit draft, cutting width, and depth of operation. The value of the unit draft varies from 15 to 20 kN/m2 . The rolling resistance of the tractor depends on the total weight of the tractor and implement and soil condition. For hard soil, it is 4% of the total weight of tractor and implement and it can increase up to 8% in loose soil. Total horizontal soil reaction force acting parallel to the face of the disk, Dx . DH = cosα Assuming that the horizontal soil reaction force parallel to the face of the disk is acting at a height equal to one third of the depth of operation from the bottom of the disturbed soil surface, the torque or moment acting on the gang shaft due to soil reaction force is ( a) (5.39) Mgs = D H × r − 3 where r = radius of the disk and a = depth of operation. Power required at the gang shafts Pgs = 2π n g Mgs /60

(5.40)

where ng = rpm of the gang shaft. In a single acting disk harrow, there are two gang shafts, hence, power required at PTO will be PPTO =

2 × Pgs Losses from PTO to gang shaft

(5.41)

Engine BHP required (for operating the powered discs) = PPTO Drawbar power + ηtep ηtractive × ηaxle to PTO × ηtep

(5.42)

116

5 Rotary Tillage Implements

where ηtep = transmission efficiency from the engine to PTO, ηtractive = tractive efficiency and ηaxle to PTO = transmission efficiency from axle to PTO. The required engine BHP should be less than the available engine BHP.

5.3.6 Gang Shaft Design The gang shaft is a solid shaft of square cross-section and is subjected to both bending and torsional moments. The bending moment is due to the vertical soil reaction and the weight of the implement. The torsional moment is the maximum of the input torque due to power transmission and torque due to the soil reaction force. The available PTO power can be calculated taking transmission efficiency and power reserve into consideration, which includes power required for propelling the tractor with implement P = B H P × ηtg × ηr

(5.43)

where P = power available at PTO, BHP = Brake horsepower ηtg = transmission efficiency of tractor gearbox, ηr = coefficient of power reserve, which includes power required for propelling the tractor with implement. The torque available at PTO, T = 2πP×60 n PT O where nPTO = tractor PTO rpm = 540. The torque available at each gang shaft, T1 =

T × G.R 1 × G.R 2 × (1 − losses in transmission) 2

(5.44)

where G. R1 = gear reduction in 1st gear box of the disk harrow, G. R2 = gear reduction in side gear assembly of the disk harrow Length of shaft is given by Ls = N 1 × S

(5.45)

L is the length of the shaft in cm. For the fitting purpose, some extra length should be considered. W = (0.95 × N × S + 0.3 × D)/100 for single acting disk harrow. Assuming the cross-sectional area of tilled soil as rectangular, the cross-sectional area (A) of tilled soil is given by A = W ×a

(5.46)

Draft required (Df ) per gang is equal to the product of the cross-sectional area of tilled soil and unit draft (DU ) and it is given by

5.3 Powered Disk Harrow

117

Fig. 5.15 Vertical forces acting on the shaft of a disk harrow with six disks in each gang

D f = A × DU

(5.47)

The ratio of the draft to vertical force is given by D f /Vv = R F

(5.48)

The value of RF can be taken from Table 3.2 depending upon the diameter of the disk and disk angle. Then, vertical force is given by Vv =

Df RF

(5.49)

In a single acting disk harrow with twelve disks (Fig. 5.15), the weight of the disk gang assembly, W g is equal to half the weight of the disk harrow, W t and it is given by

Wg =

Wt 2

(5.50)

Reactions at both bearings (RA and RB ) can be given by. RA = RB =

Wg − 6V1 2

(5.51)

Maximum bending moment (Mb ) due to vertical forces: Mb = V1 × 2.5S + V1 × 1.5S + V1 × 0.5S + R A × 3S − Mb = 4.5V1 S + 3R A S −

Wg × 1.5S 2

Wg × 1.5S 2

(5.52)

118

5 Rotary Tillage Implements

The size of the gang shaft can be determined by considering the maximum shear stress in the shaft and using the maximum normal stress theory (Norton, 2012). Maximum allowable stress,τ S =

Te Q

(5.53) ]

[/ Equivalent moment, Te =

(K m × Mb ) + (K t × T1 ) 2

2

Considering the gang shaft to be a square cross-section of sides equal to as, Q= as3 × τmax = 4.8

as 3 4.8

(5.54)

] [/ (K m × Mb )2 + (K t × T1 )2

(5.55)

where τ(max) = maximum allowable stress (N/mm2 ), as = size of square shaft (mm), Mb = maximum bending moment (N-mm), T1 = maximum torsional moment (Nmm), Km = combined shock and fatigue factor for bending, and Kt = combined shock and fatigue factor for torsion. Size of the gang shaft, as = [

√ (K m × Mb )2 + (K t × T1 )2 τmax 4.8

1/3

]

(5.56)

Design problem

1. Design a Rotavator (Concurrent Revolution Mode) for a 45 hp Tractor Step 1: Calculation of Peripheral Force Assumptions: Transmission efficiency from engine to PTO is 87% (normally 87– 90%). Losses in gear box as well as in chain and sprocket as 10% and keeping 10% of power as reserve including power required to propel the tractor and the implement, total loss and reserve account to 20%. Power available at PTO of the tractor (P) = 45 × 0.87 × 0.8 = 31.32 hp = 23.36 kW. Assuming rotor diameter d = 50 cm, u/V = 5 and forward velocity of tractor V = 4 km/h = 1.11 m/s. The tip peripheral velocity of the rotor, u = 5.55 m/s

5.3 Powered Disk Harrow

119

u=

2π Rn 60

Speed of rotor n = ngs = 211.99 ~ 215 rpm. Power = Peripheral force × Peripheral velocity Peripheral force = P/u = (31.32 × 746) /5.55 = 4209.85 N = 429.13 kg Step 2: Calculation of Number of Blades and Width of Rotavator Static specific work, Ao = Co ko A0 = C 0 k0 Taking C o = 2.5 and k o = 0.3 kg/cm2 for medium soil. Thus, Ao = 7500 kg/m2 Dynamic specific work, AB = αu u2 Taking αu = 300 kg-s2 /m4 AB = 300 x (5.55)2 = 9240.75 kg/m2 Total specific work A = (Ao + AB ) = (7500 + 9240.75) = 16,740.75 kg/m2 4×1000×60 Tilling pitch l = nVgs×60 = 3600×215×3 = 0.1033 = 10.33 ×Z e where Ze = number of blades of a disk on the same plane. Let Ze = 3. Tilling pitch, l = 10.33 cm Specific work done(A) =

2π × Peripheral force × rotor radius 2π M = Volume of soil handled abl(i Z )

where a = working depth (m), b = blade width (assuming 10.5 cm), i = number of disks on shaft, l = tiling pitch and Z = number of blades on a disk = 2Ze . Assuming the depth of operation as 10 cm, hence 16740.75 =

2π × 429.13 × 0.25 0.1 × 0.105 × 0.1033 × (i Z )

iZ = 37.12 ≈ 36 ◦ Hence, angular interval θ = 360 iz θ=

360◦ = 10◦ 36

So, the total number of blades will be 36 and it can be arranged in 7 disks (3 blades on each extreme two disks and 6 blades on each intermediate 5 disks). There is a gap of 1 cm between the tip of the blades of two adjacent disks. So, total length of the shaft will be. bm = (10.5 + 10.5) × 5 + (10.5 × 2) + 6 + 22= 154 cm = 1.54 m. Step 3: Design of Shaft of a Rotor The available PTO power was calculated taking transmission efficiency and power PT O T = 23.36 kW. reserve into consideration P = 2π n60

120

5 Rotary Tillage Implements

Fig. 5.16 Vertical soil reaction forces acting on the blades of a rotavator

The torque available at PTO T =

P×1000×60 2π n P T O

= 413.095 Nm.

where nPTO = Tractor PTO rpm = 540. The torque available at the rotavator shaft Tt = T × Gear reduction × transmission efficiency Tt = 413.095 × (540/215) × 0.9 = 933.786 Nm. Arrangements of blades and vertical soil reaction forces acting on the blades of the rotavator are shown in Fig. 5.16. Number of blades touching the soil surface at any instant of time = 36/4 = 9. Forces acting on each blade Ks = Peak peripheral force/9 = 429.13/9 = 47.68 kg. Assuming the weight of the rotavator to be 450 kg. The vertical component of soil reaction acting at each blade, Ky = Ks cos (α + ψ − Δδ) = Ks cos α. For concurrent mode of rotation, Ky is maximum at α = 20 ◦ . R1 = R2 =

W ‘ − (9 × K s cos 20◦ ) (W‘ − Total soil resistance force acting upward) = 2 2

R1 = R2 =

450 − 429.13cos 20◦ = 23.375 kg 2

Assuming that out of the 9 blades, two blades in each extreme drum and one blade in the rest of the drums are in contact with soil at a time. Bending moment will be Mb = (R1 × 3.25Wd ) + K S × cos 20◦ × (3Wd × 2 + 2Wd × 1 + Wd × 1)) −(W‘ /2) × bm /4

5.3 Powered Disk Harrow

121

Mb = (R1 × 3.25Wd ) + K S × cos 20◦ × (3Wd × 2 + 2Wd × 1 + Wd × 1)) −(W‘ /2) × bm /4 bm = Width of the rotavator = 1.54 m Wd = Spacing between two adjacent disks = (10.5+10.5+1) cm = 22 cm Bending moment, Mb = 16.713 kgm = 184.41 Nm [√ + 88.71 − 86.625 = 18.798 ] 2 2 Equivalent moment, M = (K m × Mb ) + (K t × Tt ) Taking K m and K m as 1.5 / M = (1.5 × 184.41)2 + (1.5 × 933.17)2 = 1473 Nm Maximum allowable stress, τs = MJ y Assuming that the rotor shaft is a solid circular shaft 4 y = d2 and J = π32d where d = diameter of the rotor shaft. Considering a factor of safety as 2, the allowable stress is 500 kg/cm2 = 49050 kN/m2 49050000 =

1426.825 × π × d4 32

d 2

Diameter of rotor shaft d = 0.0529 m = 5.29 cm. Step 4: Design of Blade Blade width = 10.5 cm Width of one disk = 2 × blade width = 21 cm Taking, factor of safety = 1.5 Total peak force acting on each blade Fe =

Total peak peripheral force number of blades strikes at a time Fe =

429.13 36 4

= 47.68 kg

122

5 Rotary Tillage Implements

S1 = (R–r–spacing to fix the blade) Rotor radius R = 25 cm Rotor shaft radius r = 5.29/2 = 2.645 2.65 cm Spacing is assumed as 6 cm S1 = 25 – 2.65 − 6 = 16.35 cm. R/ = arm of the force = R cos (ψ – Δδ), Soil resistance force or peak peripheral force Fe =

M M = R‘ R cos(ψ − Δδ)

The value of ψ should be between 10–15° and Δδ value should be 15° to minimize the fluctuation in cutting speed. Considering these factors, Fe will be equal to M/R. Bending moment, Mb = Fe × S1 = (47.68 × 16.35) kg-cm = 779.568 kg-cm. Torsional moment, Mt = Fe S and S = Blade width/2 = 10.5/2 = 5.25 cm Mt = 47.68 × 5.25 = 250.32 kg-cm √ (K m × Mb )2 + (K t ×M t )2 = √ Equivalent moment on the blade, M = 2 2 (1.5 × 786.72) + (1.5 × 250.32) = 1228.157 kg-cm. Maximum allowable stress, τ S = M Q be = thickness of the blade. he = length of the blade Q=

be 2 h e 2 1.8be + 3h e

τs is taken as 500 kg/cm2 assuming a factor of safety as 3. Assuming he/be = 6/1

5.3 Powered Disk Harrow

123

Fig. 5.17 Free-body diagrams of gang axle with different soil reaction forces, applied torque, and moment arms (RA and RB are the reactions at bearing supports) a) Vertical forces and applied torque b) Horizontal force

500 =

1228.157 1.818be 3

be = 1.105 1.11 cm, Hence, he = 6.66 cm. 2. Design of the gang shaft of a single acting powered disk harrow (with 6 disks in each gang) suitable for a 45 hp tractor Based on the availability, the size of the disk is chosen as 56 cm in diameter with a concavity of 6 cm. The free body diagram of the disks mounted to a shaft is shown in Fig. 5.17. The depth of operation “a” is assumed to be 12 cm. Draft on each gang Dg = (specific draft × depth × width). According to ASAE, Eq. 5.37, the cutting width will be W = (0.95 × (N − 2) × tt + 0.3 × D)/100 where W = width of disk, m; D = Diameter of disk blades, cm; N = Number of disk blades; tt = Spacing between disks, cm. [ √ ] tt = 2 c(D − c) tanα where c = ridge height ≤ depth of operation, a; α = gang angle = 15° to 25° (for disk harrows) Taking α = gang angle = 20° for disk harrow and c = 10 cm. t t = 15.61≈ 16 cm, the cutting width of each gang, W = 0.776 m. Assuming unit draft as 0.204 kgf/cm2 ≈ 20 kN/m2

124

5 Rotary Tillage Implements

The total draft acting on the gang, Dg = (Unit draft × cutting width × depth) = 20 × 0.776 × 0.12 = 1.86 kN. Total horizontal soil reaction force acting parallel to the face of the disks. DH =

Dg 1.86 Dx × N 1 = = = 1.979 ≈ 1.98 kN cosα cosα cos 20◦

Torsional moment acting on the gang due to the horizontal soil reaction force Mt = Horizontal soil reaction force × ( radius of disk − depth/3) ) ( depth Mt = D H × radius of disc − 3 Mt = 1.98 × 1000 × (0.28 − 0.12/3) = 475.2 Nm Power available at PTO of the tractor P = B H P × ηtg × ηr where BHP = Brake horsepower, ηtg = transmission efficiency of tractor gearbox, ηr = coefficient of power reserve. This includes the power required for propelling the tractor with the implement) P = (45 × 0.87 × 0.8) = 31.32 hp = 23.36 kW where nPTO = Tractor PTO rpm = 540. The torque available at PTO. T = 2πP×60 = 23.36×1000×60 = 413.095 Nm. n PT O 2π ×540 The torque available at single gang shaft T1 =

T × G.R 1 × G.R 2 × (transmission efficiency) 2

where G. R1 = gear reduction in 1st gear box of the disk harrow G. R2 = gear reduction in side gear assembly of the disk harrow where G.R1 = gear reduction in central gear box (2:1). G.R2 = gear reduction in side gear assembly (4:3). Transmission efficiency = (1 − losses in gear box) × (1 − losses in side gear assembly). = 0.95 × 0.95. Considering spur gear efficiency as 95% from one spur gear to another. T1 =

(413.095 × 2 × 1.33 × 0.95 × 0.95) = 495.848 Nm 2

5.3 Powered Disk Harrow

125

Since, the torque available from the PTO is higher than the torque required to rotate the disks, hence, the proposed harrow can be easily operated by the tractor. For designing the gang shaft, the torque available from the PTO (T1 ) to rotate the gang shaft is considered unlike the torque acting on the gang shaft because of soil reaction in the case of a conventional single acting disk harrow. Hence, the maximum design torque is 495.848 Nm. Calculation for bending moment Ratio of horizontal (DX ) to vertical soil reaction force (Vv ) on the disks for 46 cm blade and 56 cm blade at different gang angles are given in the Table 5.3 (Kepner et al. 1978). Using Table 5.3, and knowing the draft, vertical force can be calculated. Corresponding to a gang angle of 20°, the Dx /Vv can be taken as 1.1. Hence, total vertical force on each gang = draft force/1.1 = 1.86/1.1 = 1.69 kN. Vertical force acting at each disk = 1.69/6 = 0.282 kN. Assuming the weight of the disk harrow (W) = 400 kg = 3924 N. The weight of each disk gang W1 = W/2 = 1962 N = 1.962 kN. By simple force analysis, RA and RB are found to be. RA = RB = (1.962 − 1.69)/2 kN = 0.136 kN. Calculation of bending moment: Maximum bending moment Mb = R A × 2.75tt + Vv × (2.5tt + 1.5tt + 0.5tt ) − Mb = 0.136 × 2.75 × 0.16 + 0.282 × 4.5 × 0.16 −

W × 1.5tt 4

3924 × 1.5 × 0.16 = 0.02744 k N m = 27.44 N m 4000

Mb = 27.44 Nm The size of the gang shaft can be determined by considering the maximum shear stress in the shaft using the maximum shear stress theory (Khurmi & Gupta, 2005). Maximum allowable ] [√stress. τ S = TQt and Tt = (K m × Mb )2 + (K t × T1 )2 Considering the gang shaft to be a square cross-section of sides equal to as Table 5.3 L/Vv = Dx /Vv ratios at different gang angles for different sizes of disks Disk angle, °

Disk diameters, cm 46

56

Dx /Vv

Dx /Vv

15

0.5–0.75

0.7–0.85

19

0.7–1.0

0.95–1.1

23

0.9–1.2

1.3–1.5

Note Dx = draft on a single disk

126

5 Rotary Tillage Implements

Q= as3 × τmax = 4.8

as 3 4.8

] [/ (K m × Mb )2 + (K t × T1 )2

where τmax = maximum bending stress (N/mm2 ), as = size of square shaft (mm), Mb = maximum bending moment (N-mm), T1 = maximum torsional moment (N-mm), Km = combined shock and fatigue factor for bending, Kt = combined shock and fatigue factor for torsion. √ 1/3 (K m ×Mb )2 +(K t ×T1 )2 Size of the gang shaft, as = [ ] τmax 4.8 Using the previous equation and assuming Km = 1.5, Kt = 1.5 and τ(max) = maximum shear stress for C-45 steel = 450 N/mm2 Size of the gang shaft (as ) = 19.954 ≈ 20 mm. As the gang shafts are available in square cross-sections, so gang shaft having a 20 × 20 mm cross-section has to be selected.

Numerical problems

1. A tractor-drawn rotavator when operated at 210 rpm in concurrent revolution mode at a depth of 120 mm and forward speed of 3.6 km/h experienced a mean torque of 440 N-m at the rotor shaft. The radius of the working set is 300 mm and the number of blades that would cut identical paths is 3. The working width of the cultivator is 1.8 m. Calculate the tilling pitch and specific work done in one complete revolution. The formula for calculating the tilling pitch is l = n60×V r otor ×z where V = forward velocity of the tractor nrotor = RPM of rotor shaft Z = number of blades working on the same plane of a disk. l=

60 × 3.6 × 1000 3600 m = 0.0952m = 9.52 cm 210 × 3

Speci f ic wor k done per one complete r evolution = =

2π M distur bed soil volume

2π × 440 (0.0952 × 3) × 1.8 × 0.12

= 44814.71 = 44.81 kJ/m3 2. A tractor-drawn rotary cultivator is operated in concurrent revolution mode at a depth of 130 mm and forward speed of 3.6 km/h. The radius of the working set is 280 mm and the number of blades that would cut identical paths is 3. The

5.3 Powered Disk Harrow

127

working width of the rotavator is 1.8 m. The rotavator is to be powered from the tractor PTO running at 540 rpm through a suitable gear box. What should the gear ratio be for getting a tilling pitch of 74.1 mm? Let rotor shaft speed = nrotor rpm Tilling pitch, l = n60×V r otor ×z 0.0741 =

60 × 3.6 × N ×3

1000 3600

n r otor = 269.91 ≈270 rpm So, gear ratio, G = 540 =2 270 3. A tractor-drawn rotavator in reverse revolution mode is tested at a PTO speed of 540 rpm and at a depth of 150 mm with a gear reduction of 2:1. The radius of the working set is 300 mm. The number of blades that would cut identical paths is 3. What would be the forward speed of the tractor with respect to ground to keep the u/V ratio as 5? = 270 rpm Rotor shaft rpm = 540 2 r otor Peripheral speed of the blade = 2π Rn = 60 5=

2π ×0.3×270 60

= 8.48 m/s

8.48 V

V = 1.696 m/s = 6.11 km/h So, the forward speed of the tractor should be 6.16 km/h. 4. The total number of blades each of width 10.5 cm fitted to a tractor-drawn rotavator is 36 and are arranged in 7 disks (3 blades on each extreme two disks and 6 blades on each intermediate 5 disks) with a gap of 1 cm between the blades of two adjacent disks. When this rotavator is operated at an rpm of 200, depth of 10 cm, and forward speed of 3 km/h, the drawbar power required to propel the tractor with rotavator is found to be 2.3 kW. The specific work done by the rotavator is 17000 kg-m/m3 . Assuming tractive efficiency, transmission efficiency between tractor axle to PTO, and tractor PTO to engine as 62%, 95%, and 87%, respectively, decide the size of the tractor engine with a power reserve of 20%. Cutting width bm = (10.5+10.5) ×5 + (10.5×2) + 6 = 132 cm = 1.32 m Total specific work A = 17000 kg-m/m3 Tilling pitch l = nrVotor×60 = 0.0833 = 8.33 cm. ×Z e where Ze = number of blades of a disk on the same plane. Let Ze = 3 Tilling pitch l = 8.33 cm Specific work done(A) =

2π M Volume of soil handled

128

5 Rotary Tillage Implements

where a = working depth, b = cutting width, i = number of disks on shaft l = tiling pitch and Z = number of blades on a disk = 2Ze 2π M = (A × a × bm × l × i) 2π M = (17, 000 × 0.1 × 1.32 × 3 × 0.0833) = 560.776 kg-m = 5501.21 Nm. r otor PTO power requirement for cutting furrow slice = 2π M×n 60 5501.21×200 = = 18337.375W = 18.34 kW 60 power for propelling Engine power required = ( PηPTO + Drawbar ))/0.8 ηtractive ×ηaxle to PTO ×ηtep tep where, ηtep = transmission efficiency between the engine and PTO = 0.87. ηtractive = tractive efficiency = 0.62. ηaxle to PTO = transmission efficiency between the tractor axle and PTO = 0.95 2.3 Engine power r equir ed = ( 18.34 + 0.62×0.95×0.87 )/0.8 0.87 = 31.96 ≈ 32 kW The engine power required will be 32 kW.

References ASAE Standards. (2004). Determining cutting width and designated mass of disk harrows. ASAE., S290, 2. Benercki, H., Haman, J., Kanafojski, C. (1972). Agricultural machines, Theory and Construction (Vol. 1). Hann, M. J., & Giessibl, J. (1998). Force measurements on driven disks. Journal of Agricultural Engineering Research, 69, 149–157. IS: 6635. (1972). Specification for tractor operated disk harrows. Kepner, R.A., Bainer, R., & Barger, E.L. (1978). Principle of farm machinery (3rd edn.). The AVI Publishing Company, Inc. USA. Khurmi, R.S., & Gupta, J.K. (2005). Chain Drives, A textbook of machine design (pp. 759–775). Eurasia. Norton, R.L. (2012). Machine Design an integrated approach (pp. 182–192). Pearson Education, Inc.

Chapter 6

Combination Tillage Implements

6.1 Introduction To cope with the constantly growing demand for food with the increasing population, mechanization of agriculture is very much necessary. It requires appropriate machinery with a reduction in drudgery for ensuring timely field operations and increasing productivity utilizing different power sources. In traditional tillage practices, conventional tillage implements are used with any range of tractors. This causes improper matching of tractor and implement combinations resulting in underloading of the tractor engine, leading to poor overall power utilization efficiency. These practices cause more soil compaction due to a greater number of passes of heavy machinery required for seedbed preparation leading to compaction of subsoil layers, resulting in a reduction in crop yield. Further, the higher time requirement in conventional tillage practices limits the field capacity and increases the labor cost for short working periods. Increasing the speed of operation or reducing the number of passes by increasing the width of the implement can solve this problem. But in India, these are not the possible solutions as a majority of Indian farmers have land holding less than 2 ha (Sarkar et al., 2021). Hence, the better solution is to combine two or more field operations with the use of combination tillage implements so that the number of passes is reduced. The combination tillage implements, i.e., combining two or more tillage implements to be operated simultaneously to carry out tillage helps to reduce time, labor, and fuel requirements for seedbed preparation. The drawbar power required to pull the passive implements is developed by the tractor engine and is transmitted through the tire-soil interface. The poor power transmission efficiency at the tire-soil interface reduces the overall tillage energy utilization efficiency. Also, tractors having heavy weight cause soil compaction, and more power may be required to overcome the rolling resistance of the tires on this compacted soil. Active tillage implement requires considerable power per unit width as it tills a greater volume of soil. Also, these implements produce a negative draft (forward thrust) that may create problems in controlling tractor steering and may be

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_6

129

130

6 Combination Tillage Implements

harmful to the three-point hitch and tractor drive train. A way to overcome the abovementioned problems is to combine passive and passive tillage implements or passive with active tillage implements so that the total power available from the tractor is better utilized with less number of passes required to prepare the field. Moreover, when active implements are combined with passive implements, the forward thrust by active implements contributes toward the reduction in draft requirements of the passive elements.

6.2 Classification of Combination Tillage Implements Combination tillage implements can be classified as (i) Passive-passive combination tillage implements and (ii) Active–passive or passive-active combination tillage implements. For passive-passive tillage implements, tractor power utilization is improved by combining two or more passive tillage implements. There must be proper matching between the power available from the tractor and the power required to pull the implement. For active–passive or passive-active tillage implements, the total draft requirement for operating these implements is reduced because of the development of a negative draft force. Hence, a smaller power source can prepare the seedbed with a lesser number of passes using these combination tillage implements. The possible benefits of an active–passive combination tillage implement are. • Power transmission through a mechanical power train gives more efficiency than through the tire-soil interface. The overall average power transmission efficiency for PTO-powered active tillage elements is 82% as compared to 49% for drawbarpowered passive tillage implements. • The negative draft produced by the active elements can be utilized to meet the draft requirements of the passive implements partially or fully. • Field productivity is improved with a reduced draft of tillage implements and less wheel slip. • Reduced draft of tillage implements will allow the use of lighter tractors to carry out tillage operations with reduced soil compaction. • Due to the reduced draft of combination tillage implements, these can be operated in more difficult traction conditions. A few combination tillage implements developed at Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, India are shown in Figs. 6.1 and 6.2 (Sahu, 2005; Upadhyaya, 2020; Upadhyay and Raheman 2020; Behera et al., 2021).

6.2 Classification of Combination Tillage Implements

(a) Moldboard plow-Disk harrow

131

(b) Cultivator-Disk Harrow

Fig. 6.1 Passive-passive tractor-drawn combination tillage implements Fig. 6.2 Passive-active and active–passive tractor-drawn combination tillage implements

(a) Passive-active combination tillage implement

(b) Active-passive combination tillage implement

132

6 Combination Tillage Implements

6.3 General Approach for Prediction of the Power Requirement of Combination Tillage Implements 6.3.1 Passive-Passive Combination Tillage Implements The schematic views of combination and individual tillage implements with passive elements operating in undisturbed soil conditions are shown in Figs. 6.3 and 6.4, respectively. The specific draft (draft per unit cross-sectional area of soil disturbed) of the combination tillage implement “Ac ” consists of the specific draft of both passive sets used. Therefore, from Fig. 6.3 Ac = Afc + Arc

(6.1)

where Afc = specific draft of the front passive set of the combination tillage implement and Arc = specific draft of the rear passive set of the combination tillage implement.

Fig. 6.3 Tillage implements operating in combination

Fig. 6.4 Tillage implements operating individually in undisturbed soil conditions

6.3 General Approach for Prediction of the Power Requirement …

133

The specific draft of the combination tillage implements can also be expressed as (Fig. 6.4): Ac = Afi + λ Ari

(6.2)

where Afi = specific draft of the front passive set when operating individually (Afi = Afc , because in both cases the front set will be operating in the same soil condition) Ari = specific draft of the rear passive set when operating individually λ = fraction of the draft of the rear passive set operating as an individual implement and is named as draft utilization ratio for the rear passive set. For various passive-passive combination tillage implements, the maximum value of λ can be taken as 1 and is dependent on the type of soil, width, and type of rear passive implement, bulk density and cone index of soil, speed, and depth of operation (Bernacki et al., 1972). Total specific draft for combination tillage implements can be expressed as: Ac = Afc + Arc = Afi + λ Ari

(6.3)

Comparing Eqs. 6.1 and 6.2, the draft utilization ratio for the rear passive set could be expressed as λ=

Ar c Dr c Dri =( )/( ) Ari ar c ari

(6.4)

Assuming Drc = Dc – Dfc , Dfc = Dfi , and arc = ari , Eq. 6.4 can be written as  λ=

Dc − Dfi Dri

 (6.5)

where Drc = draft of the rear passive set of the combination tillage implement Dri = draft of the rear passive set operating individually. Dc = draft of the combination tillage implement. Dfc = draft of the front passive set operating in the combination tillage implement. Dfi = draft of the front passive set operating individually. ari = cross-sectional area of furrow made by the rear passive set operating individually. arc = cross-sectional area of furrow made by the rear passive set of the combination tillage implement. On rearranging Eq. 6.5, the draft of the passive-passive combination tillage implement can be expressed as Dc = Dfi + λ Dri

(6.6)

134

6 Combination Tillage Implements

Based on the above equation, the draft of the combination tillage implement in any soil and operating conditions can be obtained by knowing the draft of the front and rear passive sets as individual implements in the same soil and operating conditions and the draft utilization ratio (λ). The draft requirements of the front and rear passive sets of combination tillage implement can be predicted using the ASAE draft equation (ASAE Standards, 2000). Therefore, only λ needs to be modeled by the various factors affecting it for predicting the draft requirement of the combination tillage implement. For any passive-passive combination tillage implement, λ is a function of depth of operation, the forward speed at which the implement is operated width of cut, bulk density, and cone index of soil. The power requirement for operating the passive-passive combination tillage implement can be computed by multiplying the draft by the actual forward speed.

6.3.2 Active–Passive Combination Tillage Implements A schematic view of passive-active combination tillage implements with passive elements operating in undisturbed soil conditions is shown in Fig. 6.5. The specific work, i.e., the work done by the combination tillage implements during one revolution of the active set is the sum of specific work done by the passive set and of the active set, which can be expressed as. AC = λ P A P + λ A A A

(6.7)

AC = specific work of combination tillage implement, AP = specific work of passive set operating as an individual implement, AA = specific work of active set operating as an individual implement, λA and λ P = draft utilization ratio for active and passive tillage implements, respectively, i.e., the fraction of specific draft of

Fig. 6.5 Schematic diagram of passive-active combination tillage implement

6.3 General Approach for Prediction of the Power Requirement …

135

active and passive tillage implements, respectively, when operated as an individual implement. These fractions are always less than unity. Ac can also be written as a summation of specific work of combination tillage implement resulting from pulling resistance, (AR ), and specific work of combination tillage implement resulting from torque (AT ). AC = AR + AT

(6.8)

Comparing Eqs. 6.7 and 6.8, the following equations can be obtained: λP .AP = AR

(6.9)

λA .AA = AT

(6.10)

Draft of the passive-active combination tillage implement, DC , amounts to. DC = DP + DX

(6.11)

where DP = draft of passive implement in passive-active combination tillage implement and DX = horizontal component of peripheral force acting at the tip of the soil working element. In a combination tillage implement, implements are to be selected so that the total power requirement to pull the implement should be lesser than the available drawbar power from the tractor. An active tillage implement in concurrent mode is to be used in combination tillage implement to reduce the draft of passive tillage implements because of the development of a negative draft. Specific work of individual implements used in combination tillage is calculated according to the formulae given below: AP =

DP aP bP

(6.12)

AR =

DC aC bC

(6.13)

AA =

2π T A a A b Alg

(6.14)

AT =

2π TC aC bC l g

(6.15)

2π V ω

(6.16)

lg =

136

6 Combination Tillage Implements

where suffices P, A, and C indicate passive, active, and combination tillage implement, respectively, a = depth of operation, b = width of implement, D = draft of the implement, T = torque acting on the implement, lg = the travel length covered by the combination tillage implement in one full revolution of the shaft of the active set, V = forward velocity of the combination tillage implement, and ω = angular speed of the active set. From Eqs. 6.9, 6.12, and 6.13, the following relationship can be obtained: AR λP = = AP



      DP DC aP bP DC / = aC bc aP bP aC bc DP

(6.17)

From Eqs. 6.10, 6.14, and 6.15, the following relationship can be obtained: λA =

AT = AA



      TA TC αAbA TC / = aC bC l g α A b Alg aC bC TA

(6.18)

Considering the width of operation of individual implement to be same as the combination tillage implement, i.e., bC = bP = bA , and depth of operation of passive tillage implement to be same as depth of operation of combination tillage implement, i.e., aP = aC , Eqs. 6.17 and 6.18 can be written as  λP =  λA =

TC TA

DC DP 

 (6.19) aA aC

 (6.20)

Total power requirement for operating an active–passive combination tillage implement, PC , is the sum of power (drawbar) required to pull the combination tillage implement (PP ) and power required to rotate the active tillage implement (PA ): PC = PP + PA

(6.21)

PC = AC (aC bC V )

(6.22)

Substituting for AR from Eq. 6.13 and AT from Eq. 6.15, Eq. 6.22 becomes. PC = (A R + A T )(aC bC V ) = (DC /aC bC )aC bC V + (2π TC /aC bC l g )aC bC V

(6.23)

substituting for lg from Eqs. 6.16 and 6.23 becomes PC = (DC V ) + (TC ω)

(6.24)

6.4 Performance Evaluation of Combination Tillage Implements

137

where Dc = draft of combination tillage implement, ω = angular speed of the rotavator shaft, and TC = torque acting on the active tillage implement.

6.4 Performance Evaluation of Combination Tillage Implements The tillage performance of the tractor-implement combination is evaluated by taking into consideration the cone index (CI) of the soil before and after the operation of the implement, width of cut, field capacity, volume of soil handled, mean weight diameter of the soil aggregates, and fuel energy input to the tractor. Instead of measuring CI before and after the operation of the implement, the mean weight diameter of soil aggregates can be measured to represent soil pulverization. The parameters used for evaluating the performance of combination tillage implements are described below.

6.4.1 Cone Index Cone Index is defined as the force required to penetrate a cone-shaped probe (base area 3.22 cm2 ) into the soil up to the desired depth (ASAE S313.3). Reduction in CI values taken in the field before and after the operation of the tillage implement shows the amount of pulverization. It is computed by using the following equation (Eq. 6.25): \ ΔC I C I b Cone index be f or e tillage operation, C Ib − Cone index a f ter tillage operation, C Ia = Cone index be f or e tillage operation, C Ib

(6.25)

6.4.2 Mean Weight Diameter (MWD) Sieve analysis is carried out to find the MWD of the clods which represents soil pulverization. Sieve sizes 60, 40, 26, 17, 11.2, 8, 5.6, 4, 2.8, and 2 mm are used for the test. MWD is calculated using Eq. 6.26 given below n i=1 Wi Mi MWD =  n i=1 Wi

(6.26)

138

6 Combination Tillage Implements

where MWD = mean weight diameter of soil aggregates (mm), Wi = weight of soil sample retained over ith sieve (g), and Mi = class of mean size for ith sieve (mm). MWD of soil aggregates are to be taken before and after tillage operation, and the difference will indicate the degree of soil pulverization.

6.4.3 Width of Cut The width of cut of the combination tillage implement is measured by taking the width of the furrow with a measuring tape at an interval of about 3 m along the length of the furrow. The average of a number of readings is taken to determine the width of cut of the implement.

6.4.4 Actual Field Capacity (AFC) and Field Efficiency (FE) Actual field capacity (AFC) is the total time required to carry out tillage operation including the time lost during the field operation for turning, idle travel, etc., and it is computed by using Eq. 6.27:  \  Total area covered, ha AFC ha h = Time taken, h

(6.27)

Theoretical field capacity (TFC) is the product of the working width of the machine and the forward speed of the tractor. The field efficiency is computed by using Eq. 6.28 as given below Field efficiency, FE(%) =

Actual field capacity × 100 Theoretical field capacity

(6.28)

6.4.5 Volume of Soil Handled Per Unit Time The volume of soil handled per unit time (Vs ) is expressed using Eq. 6.29 as given below Vs = AFC × a/100

(6.29)

where Vs = volume of soil handle (m3 /h), AFC = actual field capacity (ha/h), and a = depth of operation (cm).

6.4 Performance Evaluation of Combination Tillage Implements

139

6.4.6 Soil Inversion Soil inversion is quantitatively expressed as the ratio of the mass of weeds or stubbles of the previous crop removed or buried under the soil surface after tillage operation to that present before tillage operation. A light frame of size 1 × 1 m is to be thrown randomly in the field, and wherever it falls, the weeds and stubbles present in that 1 m2 area are collected before tillage operation and their mass is to be measured. Similarly, after the operation again the ring is to be thrown randomly and wherever it falls, the mass of weeds and stubbles which are not uprooted is to be measured. The difference between these two masses of weeds and stubbles indicates the amount of weeds incorporated in the tilled soil, i.e., it indicates the amount of soil inversion. The soil inversion can be computed by using Eq. 6.30. This procedure has to be taken several times at different locations in the field, and then the average of these readings can be taken to represent soil inversion percentage: Si (%) =

W b − Wa × 100 Wb

(6.30)

where Si = soil inversion (%), Wb = mass of weeds and stubbles present before tillage operation (g), and Wa = mass of weeds and stubbles not uprooted after tillage operation (g).

6.4.7 Fuel Energy Input to the Tractor The fuel energy input to carry out a tillage operation is computed using Eq. 6.31: Fe = FC × CV

(6.31)

where Fe = Fuel energy input (MJ/h), FC = Fuel consumption (l/h), and CV = Calorific value of diesel (MJ/l). Fuel consumption can be measured by using auxiliary tank or fuel flow meter as described in Sect. 7.3.4.

6.4.8 Overall Performance Considering the above-mentioned performance parameters, the overall performance of a combination tillage implement is measured using a parameter known as the tillage performance index (TPI).

140

6 Combination Tillage Implements

6.4.8.1

For Passive-Passive Implement

The tillage performance index for passive-passive tillage implement, TPIpp , is directly proportional to Vs and Si and inversely proportional to MWD and Fe . Mathematically, it can be expressed as given in Eq. 6.33): TPIPP ∝

Vs × Si MWD × Fe

TPIPP = K

(6.32)

Vs × Si MWD × Fe

(6.33)

where K is the proportionality constant. The value of K is taken as 1 when the performance of different tillage implements is compared under the same soil condition. Moldboard Plow-Disk Gang and Cultivator-Disk Harrow Performances of combination tillage implements, i.e., moldboard plow and disk gang (MBP-DG) and cultivator-disk harrow (C-DH) as well as individual implements, i.e., moldboard plow, offset disk harrow and cultivator, when operated with a 31 kW PTO power two-wheel drive tractor in sandy clay loam soil at a moisture content of 10 ± 1% (d.b.) are summarized in Table 6.1. From this Table, it can be seen that the lesser MWD of soil aggregates are obtained with combination tillage implements as compared to individual tillage implements due to proper shattering of the soil mass by the rear passive set in addition to the cutting made by the front passive set during tillage operation. The overall performance, TPIpp , of tillage implements tested are found to be in the range of 4.31–14.15 (Table 6.1). The combination tillage implement C-DH showed Table 6.1 Tillage performance of different tillage implements Tillage implement

Mean weight diameter (MWD), mm

Soil inversion (Si ), %

Volume of soil handled per unit time (Vs ), m3 /h

Actual field capacity (AFC), ha/h

Field efficiency (FE), %

Fuel Energy used (Fe ),a MJ/h

TPIpp

Moldboard plow

59.1

91.2

316.1

0.16

78.3

113.15

4.31

Cultivator

24.1

42.4

828.5

0.87

76.3

127.75

11.41

Offset disk harrow

19.1

60.7

575.0

0.63

79.5

135.05

13.53

MBP-DG

25.9

85.4

360.8

0.20

82.1

131.40

9.05

C-DH

20.3

52.5

858.5

0.84

75.8

156.95

14.15

a Caloric

value of diesel is equal to 36.5 MJ/l (Source Sahu, 2005)

6.4 Performance Evaluation of Combination Tillage Implements

141

the highest TPIpp (14.15), whereas the lowest TPIpp (4.31) is found for the moldboard plow. The TPIpp of combination tillage implements MBP-DG and C-DH are found to be higher than the individual tillage implements moldboard plow and cultivator, respectively due to better pulverization and more volume of soil handled by the combination tillage implements as compared to individual tillage implements. The field efficiency of different tillage implements is found to vary from 75.8 to 82.1%. MBP-DG and C-DH have the highest and lowest field efficiency, respectively because of more turning time loss with C-DH as compared to other tillage implements.

6.4.8.2

For Passive-Active and Active–Passive Implement

The overall performance of a passive-active or an active–passive tillage implement is expressed in terms of tillage performance index, TPI  ap , which is considered to \ ΔC I be directly proportional to the reduction in cone index C Ib , volume of soil handled per unit time (Vs ), and soil inversion and inversely proportional to fuel energy (Fe ). It can be expressed by using Eq. 6.34 as given below \ Vs × ΔC I C Ib × Si TPIap ∝ Fe \ K × Vs × ΔC I C Ib × Si TPIap = Fe

(6.34)

(6.35)

where K is proportionality constant, and its value can be taken as 1 when the comparison of different tillage implements is done under the same soil condition. Rota-Cultivator Performances of a rota-cultivator (passive-active combination tillage implement) and combined offset disk harrow (CODH) (active–passive combination tillage implement) are evaluated when operated with a 31 kW PTO power two-wheel drive tractor in sandy clay loam soil at a moisture content of 9.5 ± 1% (d.b.) and are compared with individual tillage implements such as rotavator and offset disk harrow (ODH), respectively by operating in the same soil conditions. The tillage performance parameters of these implements along with TPI (computed using Eq. 6.35) are summarized in Tables 6.2 and 6.3. For both the depths of operation, the TPI of the rota-cultivator increased, when forward velocity increased up to 3.77 km/h. However, it decreased with a further increase in forward velocity beyond 4 km/h. This indicates that the performance of the rota-cultivator is at its maximum at a particular forward speed. As the peripheral speed of the rota-cultivator is kept constant, hence, the maximum TPIap is dependent on the peripheral to forward speed ratio. Beyond this ratio, there is no significant improvement in the volume of soil handled or in soil inversion as compared to fuel consumption.

8

8

12

12

12

L2

L3

L1

L2

L3

4.34

6.48

8.71

3.76

5.26

7.97

8

8

12

12

12

L2

L3

L1

L2

L3

4.02

5.40

8.37

4.15

5.35

8.45

4.12

3.04

2.23

4.41

3.38

2.28

4.68

3.42

2.50

5.00

3.77

2.64

0.425

0.293

0.199

0.576

0.395

0.245

0.597

0.401

0.275

0.622

0.438

199.65

166.80

159.79

164.57

133.23

107.68

230.68

181.77

161.48

187.25

156.51

114.61

Fuel Energy Used, Fe , MJ/h

509.54

352.17

239.11

460.80

316.24

196.36

477.60

320.80

220.00

497.60

350.40

238.40

Volume of soil handled, Vs , m3 /h

0.30

0.43

0.54

0.36

0.40

0.49

0.43

0.62

0.69

0.47

0.56

0.53

0.42

0.50

0.55

0.45

0.49

0.53

0.49

0.54

0.57

0.48

0.53

0.57

32.16

45.39

44.44

46.52

0.488

47.36

43.62

59.09

53.58

59.95

66.44

62.84

Reduction Soil TPIap inversion, % in CI, decimal

(AFC = Actual field capacity; Vs = volume of soil handled per unit time; Fe = fuel energy input calculated on the basis of calorific value of diesel equal to 36.5 MJ/l)

8

L1

Rotavator (working width 1.55 m)

8

L1

0.298

Actual Actual Field Capacity, forward AFC, ha/h speed, Vactual, kmph

Rota-cultivator (working width 1.55 m)

Gear Depth of Peripheral to operation, forward speed ratio, cm u/V

Table 6.2 Tillage performance of rota-cultivator and rotavator at different operating conditions

142 6 Combination Tillage Implements

6.4 Performance Evaluation of Combination Tillage Implements

143

Table 6.3 Overall tillage performance of CODH and free rolling ODH when working at an average operating depth of 12 cm Implement

Forward speed(V), km/h

NFGA , rpm (u/v ratio)

Volume of soil handled (Vs ), m3 /h

Fuel Energy (Fe ), MJ/h

(CIbefore –CItilled )/ CIbefore decimal

Soil inversion (Si ), %

TPIap

3.46

150 (4.59)

491.1

216.08

0.67

59.0

89.84

133 (4.06)

470.2

192.72

0.66

56.0

90.18

95 (2.91)

466.5

204.40

0.60

53.0

72.58

Free rolling ODH

3.46

–

404.7

132.13

0.36

28.0

30.87

CODH

4.55

150 (3.49)

602.1

232.51

0.63

56.0

91.36

133 (3.09)

598.2

211.70

0.62

53.0

92.85

95 (2.21)

574.4

223.75

0.54

49.0

67.93

Free rolling ODH

4.55

–

496.3

175.57

0.40

39.0

44.10

CODH

6.82

150 (2.33)

795.2

272.66

0.53

51.0

78.83

133 (2.06)

785.9

251.85

0.52

49.0

79.51

95 (1.48)

762.7

276.31

0.48

48.0

63.60

–

659.4

213.53

0.44

44.0

59.79

Free rolling ODH

6.82

(NFGA = rpm of the front gang axle; Vs = volume of soil handled per unit time; Fe = fuel energy input to the tractor = fuel consumption (l/ h) × calorific value of diesel (MJ/l); Fe is calculated on the basis of calorific value of diesel equal to 36.5 MJ/l)

In Table 6.2, it can also be seen that the TPIap of the rota-cultivator is higher compared to the TPI of the rotavator in all operating conditions due to more pulverization of soil by rota-cultivator than operating rotavator alone in the same field and operating conditions. Though the operation of a rota-cultivator requires higher fuel energy than a rotavator, it also produces better pulverization. The conditions of the field surface before and after operation with a rotavator and rota-cultivator are shown in Figs. 6.6, 6.7, and 6.8, respectively.

144 Fig. 6.6 Typical field surface before tilling with rotavator and rota-cultivator

Fig. 6.7 Typical field surface after operation with rotavator

Fig. 6.8 Typical field surface after operation with rota-cultivator

6 Combination Tillage Implements

6.4 Performance Evaluation of Combination Tillage Implements

145

Combined Offset Disk Harrow (CODH) Performance of active–passive combination tillage implement, CODH (combined offset disk harrow with front gang active and rear gang passive), is evaluated with a 31 kW PTO power two-wheel drive tractor in sandy clay loam soil at a moisture content of 9.5 ± 1% (d.b.) and is compared with the free rolling offset disk harrow (ODH), when these two implements are operated in the same soil condition. The tillage performance parameters of these implements along with TPI are summarized in Table 6.3. The TPIap of CODH is found to be higher than the ODH at forward speeds of 3.46, 4.55 and 6.82 km/h. This could be due to the greater volume of soil handled, higher reduction in CI values, i.e., better pulverization and higher soil inversion with a comparatively lesser increase in fuel energy requirement at these operating conditions with CODH compared to the free rolling ODH. It can also be seen in Table 6.3 that TPI of free rolling ODH improved with an increase in forward speed due to more Vs , higher reduction in CI values, better pulverization, and higher soil inversion. The best performance of CODH in terms of TPIap is obtained at a front gang axle speed (NFGA ) of 133 rpm and forward speed of 4.55 km/h corresponding to the u/v ratio of 3.09. No significant improvement in tillage quality parameters with a significant increase in Fe could be the reason behind the reduction in the performance of CODH obtained at NFGA of 150 rpm as compared to 133 rpm. This indicates the existence of an optimum combination of forward speed and NFGA (i.e., u/V ratio) with the active rotation of disks considering both qualitative (soil tilth and soil inversion) and quantitative (volume of soil handled and energy consumption) tillage performance parameters. The field condition before tillage operation is shown in Fig. 6.9. The field conditions obtained after the first and second passes of tillage operation with CODH and free rolling ODH are shown in Figs. 6.10a, b and 6.11a, b, respectively. As shown in the above figures, the CODH tilled the soil surface more evenly and properly incorporated the crop residues with soil properly. After the second pass with CODH, the soil surface is found to be smooth and contains small clods. In the case Fig. 6.9 Typical field surface before tilling with combined offset disk harrow and offset disk harrow

146

6 Combination Tillage Implements

(a) with free rolling ODH

(b) with CODH

Fig. 6.10 Typical field surface after the first pass of tilling

(a) with free rolling ODH

(b) with CODH

Fig. 6.11 Typical field surface after the second pass of tilling

of ODH, the uneven tilled surface is left with bigger size clods and non-incorporated crop residues. A seedbed for immediate sowing can be prepared by two passes of CODH whereas a higher number of passes are required to achieve the same quality of soil tilth by using free rolling ODH. Thus, the use of combination tillage implements reduces time, cost of cultivation, and compaction of soil as it requires a lesser number of passes of a tractor with individual tillage implement for seedbed preparation.

6.5 Design of Combined Offset Disk Harrow

147

6.5 Design of Combined Offset Disk Harrow The design of a combined offset disk harrow is similar to the design of single acting powered disk harrow. Hence, the procedure given for designing single acting powered disk harrow in Sect. 3.5 in Chap. 3 is to be followed for the design of CODH.

6.5.1 Disk Diameter For harrows, disk diameter (D) is related to the tilling depth (a) by the following equation as proposed by Bernacki et al. (1972): D=K

a cosβ

(6.36)

where K is a dimensionless coefficient and its value ranges from 3 to 5; β = tilt angle = 0° for disk harrow.

6.5.2 Disk Blade Material The material for disk blades should be chosen depending on their minimal rate of wear. For disk blades constructed of SAE 1080 steel (carbon steel C75), the lowest wear rate can be achieved when the hardness is in the range of 44–48 (Rockwell C Scale) (Kepner et al., 1978). Cross-rolled steel disks outperform disks constructed of straight-rolled steel.

6.5.3 Disk Spacing Disks should be spaced on a shaft so that it prevents clogging and also produces a good furrow profile. Too much spacing between disks will result in untilled soil. It also depends on the height of the ridges formed. As proposed by Bernacki et al. (1972), disk spacing (S) can be determined as  √

S = 2 c(D − c) tanα where c = ridge height = a/2; α = gang angle = 15˚–25˚ (for disk harrows).

(6.37)

148

6 Combination Tillage Implements

6.5.4 Cutting Width of Single Acting Disk Harrow The width of cut by the powered disk harrow should not be less than the wheel track of the tractor. According to (IS: 6635-1972), cutting width can be calculated as W = (0.95 × N × S + 0.6 × D)/100

(6.38)

where W = cutting width (m), N = total number of disk spacings, S = spacing between disks (cm), and D = diameter of disk blades (cm). According to ASAE Standard 2004 (S290.2), cutting width can be calculated as W = (0.95 × (N 1 − 2) × S + 0.6 × D)/100

(6.39)

where W = cutting width (m), N1 = total number of disk blades, S = spacing between disks (cm), and D = diameter of disk blades (cm).

6.5.5 Prediction of Soil Disturbance Area for Calculation of Specific Draft The area of soil disturbance (Asd ) for a disk is significantly affected by the geometry of disks, disk angle and depth of operation, and consequently the specific draft (Spoor & Godwin, 1978; Watts & Dexter, 1994; O’Dogherty et al., 1996). Disk harrows produce scalloped furrow profiles during operation. Some cross-sectional profiles of scalloped furrows obtained by different sizes of offset disk harrow (i.e., 3 × 3 and 4 × 4) with each disk having diameter 51 cm and concavity 6 cm working at different operating conditions are shown in Fig. 6.12 (Upadhyay, 2020). Soil disturbance areas are predicted precisely by projecting the different engineering drawings of 3 × 3 ODH made in Solidworks 2015 (Dassault Systèmes, Velizy-Villacoublay, France) on a vertical plane normal to the direction of operation up to the desired working depth instead of tediously measuring the excavated area after each pass (Upadhyay, 2020). The predicted values of Asd for different operating depths and gang angle “α” are given in Table 6.4.

6.5.6 Specific Draft Estimation Model for Powered Disk Harrow The developed model for estimating the specific draft of a powered disk harrow (PDH) is given in Eq. 6.40:

6.5 Design of Combined Offset Disk Harrow

149

Fig. 6.12 Some cross-sectional profiles of scalloped furrows generated by different sizes of ODH during tillage when working at different operating conditions

Table 6.4 Asd working at different operating conditions (Source Upadhyay, 2020) Area of soil disturbance (Asd ) × 10–4 m2 Operating depth, mm

Gang angle of the front active set (α), degrees 25

30

35

40

100

608.75

629.65

632.45

645.25

120

723.18

747.05

780.81

798.47

140

840.50

867.65

931.78

954.47

Values are for spherical disks with diameter 51 cm and concavity 6 cm

SDCODH = C0 + C1 × α + C2 × α 2 + C3 × CIb + C4 × Td + C5 × e(− V ) (6.40) u

where SDCODH is the specific draft requirement of CODH, kN/m2 ; α is the gang angle of front set, degrees; CI is the cone index of the soil before tillage, MPa; Td is the operating depth, mm; u/V is the speed ratio; u is the peripheral speed of the powered disk, m/s; V is the forward speed, m/s; Ci = regression coefficients whose values are given in Table 6.5 with standard error where i = 0, 1, 2, 3, 4, 5.

150

6 Combination Tillage Implements

Table 6.5 Regression coefficient estimates and their standard error for the specific draft and specific torque models of CODH

Regression coefficients

SDCODH model (Eq. 6.40) (R2 = 0.93; RMSE = 1.43) Estimate

Standard error

C0

35.665

2.912

C1

−2.355

0.180

C2

0.046

0.003

C3

11.763

0.282

C4

−0.044

0.004

C5

82.876

2.285

(Source Upadhyay, 2020)

6.5.7 Estimation of Draft Requirement of Powered and Unpowered Disk Gangs The draft of the powered disk gang (DA ) is equal to the product of specific draft (Eq. 6.40) and soil disturbance area (as given in Table 6.4). The area in which soil is disturbed by the disk harrow can be taken from Table 6.4. Draft of each disk of the powered disk gang (Dxf ) = (DX )/total number of disks in the powered disk gang

(6.41)

Draft force for the unpowered gang can be estimated from the ASAE draft equation (Eq. 6.42) given below   D f i = Fi A + B(V ) + C V 2 Td

(6.42)

where Dfi = draft required per meter width of cut, N F = dimensionless soil texture adjustment parameter i = 1 for fine, 2 for medium, and 3 for coarse A, B, and C = machine-specific parameters V = speed of harrowing operation, km/h T d = depth of harrowing, cm Agricultural Machinery Management Data (ASAE Standards, 2000) are to be referred for values of Fi, A, B, and C. For an offset disk harrow operating in soil already disturbed, the values of A, B, and C can be taken as 254, 13.2, and 0, respectively. F values for i = 1, 2, and 3 are 1.0, 0.88, and 0.78, respectively. Knowing the width of cut either from Eq. 6.38 or Eq. 6.39, the draft of rear disk gang (DP ) in case of combined offset disk harrow can be obtained by multiplying draft per unit width obtained using Eq. 6.42 with width of cut.

6.5 Design of Combined Offset Disk Harrow

151

Draft of each disk on the rear gang (Dxr ) = (DP )/total number of disks on the rear gang

(6.43) Hence, the total draft obtained for the combined disk harrow, Dc = the draft for the front powered disk gang (D X ) + draft of the rear disk gang (D P ) (6.44)

6.5.8 Estimation of Equivalent PTO Power of the Tractor A passive tillage implement utilizes the tractor’s drawbar power to perform tillage, whereas an active–passive combination tillage implement uses both tractor’s PTO and drawbar power. Hence, the total power required for carrying out tillage with combination tillage implement can be expressed either in terms of drawbar power or PTO power. Knowing the transmission efficiency, the drawbar power can be converted to PTO power and vice versa. The total power requirement is expressed as equivalent PTO power (Pe ) in kW, i.e., the summation of drawbar power required for pulling the implement converted to PTO power, drawbar power required for moving the tractor converted to PTO power, and PTO power for rotating the disks and can be given as Eq. 6.45: Dc × Va Rolling resistance of tracter × Va + 3.6 × ηPTO to DB 3.6 × ηPTO to DB 2 × π × (N)FGA × TFGA + 60 × ηtrans

Pe =

(6.45)

where Dc is the total draft in kN = DA + Dp ; Va is the actual forward speed in km/h; TFGA is the torque available at the front gang axle in kN-m; NFGA is the rpm of front gang axle; ηPTO to DB is the transmission efficiency from PTO to drawbar; ηtrans is the transmission efficiency from PTO to the front gang axle = 0.98 × 0.98 considering two-stage reduction. According to ASAE standards D 497.5 (ASAE, 2000), transmission efficiency from PTO to drawbar (ηPTO to DB ) for two wheel drive tractors is considered as 0.55 for soft (500 ± 50 kPa), 0.67 for tilled (800 ± 50 kPa), and 0.72 for firm (1100 ± 50 kPa) soil conditions for calculating estimated Pe of the tractor. The rolling resistance of the tractor depends on the total weight of the tractor with implement and soil condition. For hard soil, it is 4% of the total weight of tractor with implement and it can increase up to 8% in loose soil.

152

6 Combination Tillage Implements

6.5.9 Gang Shaft Design For combined offset disk harrow, the front gang is powered by taking power from the PTO and the rear gang is unpowered or passive. Both the gang shafts are solid shafts of square cross-section and are subjected to both bending and torsional moments. The bending moment is due to the vertical soil reaction and the weight of the implement. The torsional moment is the maximum of the input torque due to power transmission and torque or moment due to the soil reaction force acting on the front gang. Since the front gang is only powered, hence, the design calculations are to be made for the front gang shaft, and whatever dimensions are decided for the front gang, the same dimensions are to be taken for the rear gang. The available PTO power (P) in kW can be calculated by taking transmission efficiency and power reserve into consideration: P = B H P × ηtg × ηr × 0.746

(6.46)

where BHP = Brake horsepower (hp), ηtg = transmission efficiency of tractor gearbox (0.87–0.9), and ηr = coefficient of power reserve. From Eq. 6.45, the PTO power equivalent to the total drawbar power (Pe1 ) required in kW is Pe1 =

Dc × Va Rolling resistance of tractor × Va + 3.6 × ηPTO to DB 3.6 × ηPTO to DB

(6.47)

PTO power available for rotating the front gang of disks:

Pe2 =

Pe2 = P − Pe1

(6.48)

2 × π × NFGA × TFGA 60 × ηtrans

(6.49)

TFGA =

Pe2 × 60 × ηtrans 2π NFGA

(6.50)

where NFGA is the speed of rotation of the front gang shaft, rpm, and TFGA is the maximum torque available on the front gang shaft, kNm. Length of shaft, L = N1 × S where N1 = number of disks and S = spacing between two adjacent disks The spacing between two adjacent disks can be computed using Eq. 6.37. Width of cut can be computed using either Eq. 6.38 or Eq. 6.39.

(6.51)

6.5 Design of Combined Offset Disk Harrow

153

Draft of the front power gang (DA ) can be obtained by multiplying the specific draft (using Eq. 6.46) with soil disturbed area from Table 6.4 depending on the depth of operation and gang angle (α) of the front gang. The ratio of the draft to vertical force is given by D X /V v = R F

(6.52)

where V v is the total vertical force acting on the disk gang. The value of RF can be taken from Table 3.2 depending upon the diameter of the disk and disk angle. Then, the vertical force acting at each disk is given by Eq. 6.53: V1 =

1 DX × RF N1

(6.53)

In an offset disk harrow, the weight of each disk gang assembly, W g , is equal to half the weight of the total offset disk harrow, W t , and it is given by Wg =

Wt 2

(6.54)

Usually, the total weight of the disk harrow varies from 390 to 650 kg per m width (Table 3.1, Chap. 3). Assuming the number of disks to be 4 each in the front and rear gangs (Fig. 6.13), then reactions at both bearings (RA and RB ) can be given by

RA = RB =

Wg − 4V1 2

(6.55)

Maximum bending moment (MbS ) due to vertical forces: MbS = V1 × 0.5S + V1 × 1.5S + R A × 2S − (W g /2) × S MbS = 2V1 S + 2R A S − (W g /2) × S

Fig. 6.13 Vertical forces acting on the shaft of a disk harrow with four disks in each gang

(6.56)

154

6 Combination Tillage Implements

The size of the gang shaft can be determined by considering the maximum shear stress in the shaft and using the maximum shear stress theory (Norton, 2012). Maximum allowable stress,τ S =

Te Q

(6.57) 

/ Equivalent moment, Te =

(K m Mbs ) + (K t TF G A ) 2

2

(6.58)

Considering the gang shaft to be of square cross-section of sides equal to as, Q= as3 × τs(max) = 4.8

as 3 4.8

(6.59)

 / (K m Mbs )2 + (K t TF G A )2

(6.60)

where τs(max) = maximum allowable shear stress, N/mm2 , as = size of square shaft, mm, MbS = maximum bending moment, N-mm; TFGA = maximum torsional moment, N-mm, Km = combined shock and fatigue factor for bending, and Kt = combined shock and fatigue factor for torsion. √ Size of the gang shaft, as = [

(K m Mbs )2 + (K t TF G A )2 τs(max) 4.8



1/3

]

(6.61)

Numerical problems

1. The draft of a passive-passive combination tillage implement comprising moldboard plow in the front gang and disk harrow in the rear gang when operated at a forward speed of 3.5 km/h and depth 15 cm in sandy clay loam soil is 4 kN. For the same operating condition, the draft of the moldboard plow when operated alone is 3.3 kN and the draft utilization ratio is 0.6. Compute the power requirement of the disk harrow without moldboard plow for the same operating condition. Draft of combination tillage implement, DC = D F + λD R DF = Draft of tillage implement in the front gang. DR = Draft of tillage implement in the rear gang. λ= draft utilization ratio = 0.6 4 = 3.3 + 0.6 × D R

6.5 Design of Combined Offset Disk Harrow

155

D R = 1.167k N The power requirement of the disk harrow when operating alone will be P = (1.167 × 3.5 × 1000/3600) = 1.135kW 2. For a tractor operated rota-cultivator (passive-active combination tillage implement) of working width 1.55 m when operated in sandy clay loam soil with an average cone index of 450 kPa, depth 10 cm and forward speed 2.7 km/h, the fuel consumption was found to be 3 l/h with a field efficiency of 76%. The soil inversion was observed to be 67%. The heating value of diesel is 36.5 MJ/l. Find out the volume of soil handled. In the same soil condition, when a tractor drawn rotavator of same working width was operated at a depth of 10 cm, the fuel consumption was found to be 2.5 l/h with a field efficiency of 79%. The soil inversion was observed to be 47%. The average cone index of soil measured after the tillage operations was measured to be 250 and 310 kPa for the rota-cultivator and rotavator, respectively. Find out the difference in the tillage performance index between the two tillage implements. The theoretical field capacity of the rota cultivator, TFC = Working width × forward velocity. Actual field capacity of rota cultivator, AFC = TFC × field efficiency. TFC = (1.55 × 2.7 × 10/36) = 1.163 m2 /s AFC = (1.163 × 0.76) = 0.884 m2 /s The actual volume of soil handled by the rota-cultivator will be = AFC × depth of operation = (0.884 × 0.1) = 0.0884 m3 /s = 318.24 m3 /h: \ K × Vs × ΔC I C Ib × CRBE TPIap = Fe Here, K is the proportionality constant. As both the implements were operated in the same soil condition, hence, K is taken as 1. Actual field capacity of rotavator = (1.163 × 0.79) = 0.919 m2 /s. The actual volume of soil handled by the rotavator will be = AFC × depth of operation = (0.919 × 0.1) = 0.0919 m3 /s = 330.84 m3 /h: ΔC I /C Ib f or r ota−culti vator = ΔC I /C Ib f or r otavator = TPI for rota-cultivator =

318.24×0.444×67 3×36.5

450 − 250 = 0.444 450

450 − 310 = 0.311 450

= 86.46

156

6 Combination Tillage Implements

TPI for rotavator = 330.84×0.311×47 = 53.0 2.5×36.5 The difference in TPI between rota-cultivator and rotavator = (86.46 − 53.0) = 33.46. Hence, the rota-cultivator performed better than the rotavator. 3. A combined offset disk harrow with 4 disks of diameter 51 cm in each gang with a disk-to-disk spacing of 26 cm is operated by a two-wheel drive tractor (with a bhp of 45 hp) in sandy clay loam soil at an average moisture content of 9.5% (d.b.). The actual forward speed and average operating depth are 3 km/ h and 12 cm, respectively. The front gang of the offset disk harrow has a gang angle 25° and is powered by the tractor PTO and is rotated at 200 rpm. The draft required to pull the implement is measured to be 1.6 kN. The rolling resistance of the tractor with offset disk harrow is 0.65 kN. The horizontal soil reaction force acting on each disk parallel to its face is 350 N and it is acting at a height 1/3 rd of the depth of operation from the bottom of the soil surface disturbed. Find out the maximum torque available on the front gang and the total power utilized for operating the combined offset disk harrow. Assume transmission efficiency from engine to tractor PTO as 87%, from PTO to drawbar as 86%, from PTO to gang shaft as 0.95%, and a power reserve of 20%. The available PTO power can be calculated by taking transmission efficiency and power reserve into consideration using Eq. 6.46: P = B H P × ηtg × ηr × 0.746 where P = power available at PTO; BHP = brake horsepower = 45 hp; ηtg = transmission efficiency of tractor gearbox = 0.87; ηr = coefficient of power reserve = 1- 0.2 = 0.8: P = 45 × 0.87 × 0.8 × 0.746 = 23.36 kW From Eq. 6.47, the PTO power equivalent to total drawbar power (Pe1 ) is. Pe1 =

Dc × Va Rolling resistance of tractor × Va + 3.6 × ηPTO to DB 3.6 × ηPTO to DB

Draft of combined offset disk harrow Dc = 1.6 kN and Va = 3 km/h = 0.833 m/ s. Rolling resistance of the tractor is 0.5 kN: Pe1 =

0.65 × 3 1.6 × 3 + = 2.18 kW 3.6 × 0.86 3.6 × 0.86

PTO power available for rotating the front gang of disks, Pe2 = P – Pe1 : Pe2 = 23.36 − 2.18 = 21.18 kW

References

Using Eq. 6.49, Pe2 =

157 2×π×N F G A ×TF G A 60×ηtrans

where NFGA is the speed of rotation of the front gang shaft, rpm, and TFGA is the maximum torque available at the front gang shaft, kNm: ×0.95×60 TF G A = Pe22π = 21.18×1000×0.95×60 = 960.71 Nm. NFG A 2π ×200 Torque acting due to soil reaction, Ta = 4 × 350 × (51/2 − 12/3)/100 = 301 Nm. The maximum torque available on the front gang is 960.71 Nm. Power required to rotate the front gang = 2 × π × 200 × 301/(60 × 1000) = 6.30 kW. Hence, the total power utilized = Pe1 + 6.30 = 2.18 + 6.30 = 8.48 kW.

References ASAE Standards. (2000). Agricultural Machinery Management Data. St. Joseph, MI, USA: ASAE. D497.4. ASAE Standards. (2001). Soil Cone Penetrometer. St. Joseph, Michigan, USA, ASAE S313.3. ASAE Standards. (2004). Determining cutting width and designated mass of disk harrows. St. Joseph, MI, USA: ASAE. S290.2. Behera, A., Raheman, H., & Thomas, E. V. (2021). A comparative study on tillage performance of rota-cultivator (a passive–active combination tillage implement) with rotavator (an active tillage implement). Soil and Tillage Research, 207, 104861. Bernacki, H., Haman, J., Kanafojski, C. (1972). Agricultural machines, Theory and Construction (Vol. 1). Kepner, R. A., Bainer, R., & Barger, E. L. (1978). Principle of farm machinery (3rd ed.). USA: The 640 AVI Publishing Company, Inc. Norton, R. (2012). Machine Design. An integrated approach (3rd ed.). Pearson/Prentice Hall, New Jersey. ISBN 0-13-14190-8 O’Dogherty, M. J. (1996). The design of octagonal ring dynamometer. Journal of Agricultural Engineering Research, 63, 9–18. Sahu, R.K. (2005). Development and performance evaluation of combination tillage implements for 2wd tractors. Unpublished Ph. D. thesis. Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, India. Sarkar, P., Upadhyay, G., & Raheman, H. (2021). Active-passive and passive-passive configurations of combined tillage implements for improved tillage and tractive performance: A review. Spanish Journal of Agricultural Research, 19 (4), e02R01. Spoor, G., & Godwin, R. J. (1978). An experimental investigation into the loosening of soil by rigid tines. Journal of Agricultural Engineering Research, 23(3), 243–257. Upadhyay, G. (2020). Development and performance evaluation of a front active rear passive set combined offset disk harrow. Unpublished Ph.D. Thesis, Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, India. Upadhyay, G., & Raheman, H. (2020). Effect of velocity ratio on performance characteristics of an active-passive combination tillage implement. Biosystems Engineering, 191, 1–12. Watts, C. W., & Dexter, A. R. (1994). Traffic and seasonal influences on the energy required for cultivation and on the subsequent tilth. Soil and Tillage Research, 31, 303–322.

Chapter 7

Measurement of Parameters for Performance Evaluation of Tillage Implements

7.1 Introduction To determine appropriateness and evaluate performance of agricultural machinery under various agroclimatic conditions, they are tested primarily with the following goals in mind: • To help in selecting the type of machine best suited for a specific field condition. • To serve the farmers and other potential buyers to get the comparative performance of available machinery in the market. • To set guidelines for engineers, extension workers, and researchers/designers working on agricultural machinery.

7.2 Testing of Tillage Implements 7.2.1 Testing of Plow According to Regional Network for Agricultural Machinery (RNAM) test code, the testing of any tillage implements should be carried out at selected fields of area not less than 0.2 ha. According to Bureau of Indian Standards (BIS), the minimum size of the plot for an animal-drawn plow should be 0.25 ha and for a tractor-drawn plow, it should be 1 ha. The layout should ideally be a rectangle with the sides that are in the ratio 2:1. Under various soil conditions, at least three sets of field experiments should be conducted and at least five soil samples should be taken for testing about 3 m inside the boundary under each set of conditions. Soil type, moisture content, weed growth, crop residue, and traveling speed affect the performance of the plow considerably. Therefore, these conditions of the test have to be clearly mentioned.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 H. Raheman and P. Sarkar, Tillage Machinery—Passive, Active and Combination, https://doi.org/10.1007/978-981-99-6331-7_7

159

160

7 Measurement of Parameters for Performance Evaluation of Tillage …

Table 7.1 Format for reporting summary of field performance test of a plow

S. No

Parameters

1

Type of soil

2

Soil bulk density (g/cc)

3

Average soil moisture (%)

4

Engine speed (rpm)

Range

–No load –On load 5

Average speed of operation (kmph)

6

Average depth of cut (cm)

7

Average working width (cm)

8

Area covered (ha/h)

9

Time required to cover one hectare (h)

10

Field efficiency (%)

11

Soil inversion (%)

12

Soil pulverization (cm)

13

Fuel consumption (l/h)

14

Fuel consumption (l/ha)

15

Average implement draft (kgf)

16

Power requirement (kW)

Field conditions: (a) plot size, (b) soil type, (c) last crop grown, (d) date of harvesting of last crop, (e) date and details of previous tillage treatments undertaken, (f) topography, (g) moisture content of soil, and (h) Bulk density. The items to be measured in laboratory testing of a plow are: (a) Specifications, (b) hardness of soil engaging components, (c) wear analysis, and (d) chemical analysis. The items to be measured in field testing of a plow are: (a) Width of plowing, (b) depth of plowing, (c) actual travel speed, (d) actual operating hours, (e) time spent for turning at headland, (f) time spent for adjusting the implement, (g) time spent for troubles and others (non-productive time), (h) fuel consumption, (i) degree of inversion, (j) degree of pulverization, (k) entangling of weed and crop residue to the implement, (l) adhesion of soil to implement, (m) evenness of furrow sole, (n) percentage of wheel slip, and (o) draft. The format for reporting the summary of the field performance test of a plow is as given in Table 7.1. Power Requirement A dynamometer can be used to measure the draft of a trailed tractor-drawn plow. First, a space of 30 m should be laid off in the middle of a long row, and marking has to be provided at each end. As the plow operates in that space, dynamometer readings are to be recorded at about 4–5 min intervals. These readings are to be averaged to get

7.2 Testing of Tillage Implements

161

Fig. 7.1 Measurement of draft of a tractor drawn moldboard plow

an average draft for a 30 m run. The time to cover this distance should be recorded to get the average speed of the implement. For mounted-type tractor-drawn tillage implements, a dummy tractor is used. A dynamometer (hydraulic-type or direct reading spring) is attached in front of the dummy tractor. Another tractor is used to pull the dummy tractor and the plow attached to it (Fig. 7.1) in such a way that the line of pull is horizontal, i.e., parallel to the ground. Then, the plow is to be detached and the draft required to pull only the dummy tractor is to be measured. The draft of the plow is obtained by deducting the draft of the dummy tractor from the draft of the plow and dummy tractor in combination. The power (drawbar power) required can be calculated from the following formula (Eq. 7.1): Drawbar Power, kW = Draft, kN × Speed, m/s

(7.1)

Field Efficiency Effective field capacity: The plow should be operated for at least 4 hours continuously in the field, and the area covered during that period is measured in hectares. Effective field capacity is expressed in ha/h. Theoretical field capacity: Theoretical field capacity is determined by the following formula (Eq. 7.2) based on the width of the implement and speed of operation: Theoretical field capacity,

Width, m × Speed, km/h ha = h 10

(7.2)

Field efficiency: The ratio of effective field capacity to the theoretical field capacity expressed in percentage is known as the field efficiency. It represents time lost in the field while turning and making adjustments to the implement, and failure in

162

7 Measurement of Parameters for Performance Evaluation of Tillage …

utilising the entire working width of the implement. The following formula (Eq. 7.3) is used to calculate the field efficiency: Field efficiency =

Effective field capacity × 100 Theoretical field capacity

(7.3)

Wheel Slip Slip of a two wheel drive tractor is calculated from the difference of rotational speed of the front and rear wheels of a two-wheel drive tractor. The actual and theoretical speeds of the tractor can be obtained from the front wheel and rear wheel speed of revolutions (rpm), respectively. Slip of a two wheel drive tractor can be expressed as given below (Eq. 7.4) ) ( Va × 100 Sl = 1 − Vt

(7.4)

where S l = wheel slip (%), V a = actual speed (m/s), and V t = theoretical speed (m/ s). Soil Inversion Soil inversion is measured by using a square ring (30 × 30 cm). The ring is thrown in the field randomly before starting the test (Fig. 7.2) and wherever it falls in the field, the weight of weeds and stubbles included within this ring is measured by manually uprooting them and then taking the weight. At least five observations at different places (selected randomly) in the test plot must be taken before plowing. This process is repeated after plowing. Soil inversion is calculated by using the following formula (Eq. 7.5): Soil inversion(%) =

100 × (Mass of weeds and stubbles before test − Mass of weeds and stubbles after test) Mass of weeds and stubbles before test

(7.5)

Soil Pulverization According to BIS standard, soil pulverization is measured by using a penetrometer. A random place is selected in the plowed field and the penetrometer is held vertically at that place. A hammer is dropped onto it from the height of one meter two times with no time gap between two consecutive droppings of the hammer. The depth to which the penetrometer penetrates is recorded after every two drops. Soil pulverization can also be evaluated by measuring mean soil clod diameter using a set of sieves (RNAM test code). Sieves of appropriate mesh shall be selected according to the type of implement and soil. Each sampling area from which soil is collected will be either 15 × 15 cm, 50 × 50 cm, or 100 × 100 cm depending on the degree of pulverization. The larger the clod size, the bigger the ring area recommended. The soil sample collected has to pass through a set of sieves. It is

7.2 Testing of Tillage Implements

163

Fig. 7.2 Selection of plot for soil sample

necessary to weigh the soil that has been retained on the sieve with the largest aperture, passed through each subsequent sieve while being retained on the next one, and then passed through the sieve with the smallest aperture. An example for computing mean soil clod diameter using Eq. 7.6 is given below in Table 7.2. MMD =

1 ( A × RD1 + B × RD2 + C × RD3 + D × RD4 + E × RD5 + NF) W (7.6)

where MMD = mean soil clod diameter (mm), RD1 to RD5 = representative diameter of soil clods retained on the sieves (mm); A to F = weight of soil retained in respective sieves (kg), W = A + B + C + D + E + F (kg), and N = mean of measured diameter of soil clods retained on the largest aperture sieve (mm). Some researchers express the soil pulverization using cone index of the soil before and after the operation of tillage implements. Performance Index The performance index of a moldboard plow can be calculated by using the following formula (Eq. 7.7) as given by BIS: PI =

d× A×I ×P Du

(7.7)

164

7 Measurement of Parameters for Performance Evaluation of Tillage …

Table 7.2 Mean soil clod diameter measurement Size of aperture, mm Diameter of soil passed Representative diameter Weight of soil, kg the left sieve and retained of soil in the left on the next small aperture column (RD), mm sieve, mm 10

N

F

where PI = performance index, d = depth (cm), A = effective field capacity (hectare/day), I = soil inversion (%), P = pulverization in terms of penetrometer reading (cm), and Du = draft (kgf/cm2 ).

7.2.2 Testing of Disk Harrow Five fields that have previously been plowed should be used for testing the disk harrow. For mounted or trailed type harrows, the area must be at least 0.2 ha, and for other types of harrows, it must be at least 0.1 ha. Test conditions can be defined in the same way as mentioned for plow testing. The items to be measured in the laboratory tests are: (a) Specifications, (b) hardness of soil engaging parts, (c) wear analysis, and (d) chemical analysis. The items to be measured and observed in the field test are: (a) Width of harrowing, (b) actual traveling speed, (c) number of passes, (d) actual operating hours, (e) time spent for adjusting of implement, (f) time spent for trouble and others, (g) fuel consumption, (h) degree of pulverization of top soil, (i) degree of mixing vegetative matter with the top soil, (j) evenness of harrowed surface, (k) percentage of wheel slip, and (l) draft. Short-Run test: For short-run tests, at least three series of field testing should be conducted on various types of soil. The tests should be carried out as closely as possible in a field with the ideal soil moisture level for tillage operations. Depending on the special feature of the harrow, tests may also be performed in relatively dry and wet soil conditions. The parameters to be measured in a short-run test are (a) width and depth of cut, (b) soil pulverization, (c) power requirement, (d) field efficiency, (e) ease of operation and adjustment, and (f) soundness of construction. Long-run test: For long-run tests, a minimum of 50 hours should be spent operating the harrow, excluding the time used for short-run tests. Ideally, it should be run for

7.2 Testing of Tillage Implements

165

200 hours. It is important to document the significant breakdowns, newly created defects, and repairs undertaken during this time. Width and Depth of Cut When using a tractor-drawn harrow, the harrow should be set up with the minimal operational gang angle recommended by the manufacturer, at the lowest position of three-point hitch, and without any additional mass. It is recommended to operate for two or three row lengths in the field. To determine the width and depth of the cut, measurements should be taken at a maximum of 10 different locations and averaged. Soil Pulverization The mean mass diameter (MMD) of the soil aggregate is used to measure soil pulverization. The method of determining MMD is as follows: (a) After the tillage operation, soil samples need to be taken from a 150 × 150 mm area and the working depth of harrow. (b) The weight of the collected sample is to be taken accurately and then the sample is to be passed through a set of sieves with aperture sizes 11.2, 8, 5.6, 4.0 2.8, and 2 mm. (c) The percentage mass of soil shifted through each sieve and that shifted and retained on the 11.2 mm sieve are to be calculated (Fig. 7.3). The amount of soil passed through and retained on the 11.2 mm sieve should be taken as cent percent. (d) A curve with sieve sizes on the X-axis and the percentage of the mass of the soil sample shifted through each sieve on the Y-axis is to be plotted (Fig. 7.4). (e) Using a planimeter, the area of the shaded region of the curve can be found. (f) By multiplying the area of the shaded region in the graph by the mass mean diameter that corresponds to one unit area in the graph, the mean mass diameter is determined. Power Requirement Power requirement can be measured by the same procedure as discussed in Sect. 7.2.1. Field Efficiency Field efficiency can be calculated by the same procedure as discussed in Sect. 7.2.1.

7.2.3 Testing of Rotary Tiller Soil of moderate hardness can be prepared more rapidly with rotary tillers than by alternative means. In double- or multiple-cropping systems when there is little time available for field preparation, these implements can be quite helpful. The good pulverizing functions of a rotary tiller and the surface produced are most suitable for carrying out sowing in dryland.

166

7 Measurement of Parameters for Performance Evaluation of Tillage …

Fig. 7.3 Soil retained on the sieve

Fig. 7.4 Soil pulverization curve

Testing of rotary tillers should be carried out at five selected fields. The minimum size of the plot for a rotary tiller mounted or trailed by a tractor should not be less than 0.2 ha and for others, it should be 0.1 ha. The layout should ideally be a rectangle with sides that are in the ratio 2:1. Test conditions can be defined in the same way as given for plow testing. In laboratory tests, the following things must be measured: (a) Specifications (chassis, side support, shield, trailing board, rotor shaft, rotor blade, skid, adjusting rack, three-point hitch, mast, gearbox of primary and secondary reduction, and overall dimension), and (b) chemical composition of blade and hardness of blade at edge and shank position.

7.2 Testing of Tillage Implements

167

Table 7.3 Format for reporting summary of field performance test of a rotavator S. No

Parameters

1

Tractor used

2

Type of soil

3

Gear used

4

Average soil moisture (%)/ Average depth of standing water (cm)

5

Soil bulk density (g/cc)

6

Field efficiency (%)

7

Puddling index (%)

8

Average speed of operation (kmph)

9

Average depth of cut (cm)/depth of puddle (cm)

10

Average working width (cm)

11

Area covered (ha/h)

12

Time required to cover one hectare (h)

13

Fuel consumption (l/h)

14

Fuel consumption (l/ha)

Dryland operation

Wetland operation (puddling)

The items to be measured and observed in field testing are: (a) Width of tilling, (b) depth of tilling, (c) actual travel speed, (d) actual operation hours, (e) time spent for turning at the headland, (f) time spent for adjustment of the machine, (g) time spent for trouble and others, (h) fuel consumption, (i) degree of burying weed and crop residue in the soil, (j) pulverization of soil, (k) entanglement of weed and crop residue to the machine, (l) adhesion of soil to the machine, (m) evenness of tilled sole, (n) percentage of wheel slip, and (o) power consumption. The format for reporting summary of the field performance test is listed in Table 7.3. Working Width and Depth Effective working width will be the total working width divided by the number of runs. For measuring working depth, the width scale has to be on the surface of untilled land and the tip of the depth scale on the tilled sole, and the reading of the depth scale at baseline is to be taken as working depth. Degree of Burying Weed and Crop Residue in the Soil This can be measured following the same method as used for soil inversion and expressed with a ratio of the weight of buried weeds and crop residues to the weight of these before operation.

168

7 Measurement of Parameters for Performance Evaluation of Tillage …

Wear of Blades The wear of blades due to working in both wetland and dryland tillage operations is to be measured based on the mass of the blade. The weight of individual blades is to be taken before and after tillage operation of 25–26 and 16–18 hours for dryland and wetland, respectively. And then, the average of the total number of blades will be computed to find the wear of the blade. The other parameters can be measured following the procedure discussed in Sect. 7.2.1.

7.3 Instrumentation for Measuring Tillage Performance Parameters The main objective of instrumentation in tillage operations is to improve accuracy in measuring the performance parameters such as draft, torque, wheel slip, and fuel consumption. There may be some display or warning system which alerts the operator when the above parameters go beyond their safe limits. The instrumentation required for measuring tillage performance parameters is discussed under the following subheadings.

7.3.1 Draft Measurement 7.3.1.1

Draft Measurement of Trailed Type Implements

Trailed implements are pull-type implements, and drafts of these implements are measured by a drawbar dynamometer (Chen et al., 2007; Godwin, 1975; Kirisci et al., 1993; Zoerb et al., 1983). Drawbar pins: The usual procedure to measure the draft is to insert the drawbar pin in the implement hitch point. A pin transducer has an outer ring and an inner ring. The outer ring protects the inner ring which represents sensing elements with strain gauges. During drawbar operation, the outer ring halves are compressed against the inner ring by the implement and tractor hitch. Thus, compressive and tensile stresses are developed on the outer surface of the inner ring in the plane parallel and perpendicular to the direction of the load, respectively. Only free linkage systems are compatible with this instrument (Kirisci et al., 1993; Reece, 1961; Zoerb et al., 1983). Ring transducer: Due to friction in bushes, drawbar pins cause substantial errors in measuring drafts (Wilkinson, 1971). Extended ring transducers are the alternatives in the dynamometer system. It can be divided into three categories: plain extended ring (Hoag & Yoerger, 1975), extended octagonal ring (O’Dogherty, 1975), and double extended octagonal ring type (Godwin et al., 1993; Leonard, 1980; Tessier et al.,

7.3 Instrumentation for Measuring Tillage Performance Parameters

Plain extended ring and extended octagonal ring (Chen et al., 2007)

169

Double extended octagonal ring (developed at IIT Kharagpur)

Fig. 7.5 Instruments for draft measurement of trailed-type implements

1992). The horizontal force, vertical force, and pitch moment can all be measured by using these ring transducers. Extended octagonal ring transducers (EORs) are easy to fabricate than the circular outer face because of flat outside surfaces (Fig. 7.5). Ring transducers have a machined block made of steel or aluminum. There are some specific positions on the ring transducer called nodes where strain from the other force component has no contribution. In order to measure the horizontal and vertical force components as well as the resulting moment, strain gauges are positioned at these strain nodes (Godwin, 1975). The diametrical forces and tangential forces are zero at angles of 39.5° and 90°, respectively on the surface of the ring transducer (O’Dogherty, 1996).

7.3.1.2

Draft Measurement of Mounted Type Implements

The draft of a mounted-type implement can be measured by strain gauges mounted on the lower links (Khan et al., 2006) and by a three-point hitch dynamometer (Al-Janobi and Al-Suhaibani, 1998; Gupta et al., 2019). In the first type, strain gauges are directly mounted on the lower links. This is a simple and effective system for draft measurement with less error. However, this method can only be used to measure the draft of small to medium-sized equipment. Additionally, the abrupt application of stresses could harm the strain gauges on the links (Khan et al., 2006; Kirisci et al., 1993). The draft of the tillage implement is measured using a system which comprises an instrumented three-point linkage of the tractor, as shown in Fig. 7.6a. It consists of strain gauges configured as a Wheatstone bridge circuit to measure draft in the field (Sahu, 2005; Roul, 2014). In order to measure the tensile and bending forces, electrical strain gauges must be installed on the lower links. For measuring the compressive force acting on the top link during tillage, a proving ring made of mild steel must be installed on the top link. The angles of the lower links in the horizontal

170

7 Measurement of Parameters for Performance Evaluation of Tillage …

Fig. 7.6 Instrumented three-point linkage of the tractor to measure draft of tillage implements (Source Sahu, 2005)

1 - Top link and 2 - lower links (a) Strain gauges fixed on three links

1 - Lower link vertical angle, 2 - Lower link horizontal angle, 3 Top link vertical angle (b) Potentiometer fixed to measure angles of links

and vertical planes and the top link in the vertical plane are to be measured using three rotary potentiometers (Fig. 7.6b). Measurement of Tensile Force in the Lower Links Eight strain gauges are required to be mounted in the lower links to measure the tensile force. In this arrangement, four active gauges are required to be mounted directly on the theoretical neutral axis of lower links, and four dummy gauges are required to be mounted on a separate mild steel block. Figure 7.7a depicts the arrangement of strain gauges on the lower links. It is important to place gauges R1, R2, R3, and R4 so that they are only sensitive to tensile force and insensitive to bending force. Similar to this, gauges R1 and R3 must be placed opposite to R2 and R4 to compensate for lateral forces in the lower links. Gauges R1’, R2’, R3’, and R4’ must be installed on a separate mild steel block for temperature compensation. A Wheatstone bridge circuit, as shown in Fig. 7.7b, is to be designed with these strain gauges to measure the tensile force.

7.3 Instrumentation for Measuring Tillage Performance Parameters

171

Fig. 7.7 Configurations of strain gauges and circuit diagrams for measuring forces on the lower link

Measurement of Bending Force in the Lower Links For measuring the bending forces acting in lower links, eight active strain gauges (S1, S2, S3, S4, S1’, S2’, S3’, and S4’) are mounted directly on the top and bottom surfaces of the links (Fig. 7.7a). The output of the Wheatstone bridge circuit is not impacted by a tensile force since all eight gauges are stretched to the same extent when subjected to a tensile force. Because of this, all active gauges are solely responsive to bending force. Tensile stress is induced in gauges S1, S1’, S2, and S2’, and compressive stress is induced in gauges S3, S3’, S4, and S4’ because of bending force. A Wheatstone bridge circuit, as shown in Fig. 7.7b, is to be designed with these strain gauges to measure the bending force. Measurement Force Acting on the Top Link To measure the force on the top link, a proving ring is to be used in place of the turnbuckle of the top link. The proving ring can be made from a mild steel ring by considering the design procedure of Godwin et al. (1993) and O’Dogherty (1996). Four electrical strain gauges are to be fixed on the the proving ring at 90° to the

172

7 Measurement of Parameters for Performance Evaluation of Tillage …

direction of applied force and connected to the Wheatstone bridge configuration to measure the compressive force. The compression in the top link induces tensile stress in gauges fixed on the outersides of the ring and compressive stress in the gauges fixed on the inner sides of the ring. Bending force on the top link has no effect on the bridge as it causes similar strain in outer gauges and equal and opposite strain in inner gauges. Angle Measurement of Top and Lower Links A rotary potentiometer (10k ohm) is to be mounted on the fabricated frame attached to the tractor above PTO for measuring the vertical angle made by the top link. In addition, two additional 10 k ohms rotary potentiometers are utilized to measure the lower link’s vertical and horizontal angles. In order to gauge the horizontal angle made by the lower link, one of these rotary potentiometers must be fixed to the fabricated frames attached to the tractor on one side of the PTO, and the other one must be fixed to the rocker arm of the tractor’s hydraulic system. With the activation of the three-point linkage, the potentiometers’ knobs should rotate freely. These rotary potentiometers must be calibrated with the use of a digital protractor. The draft of the implement can be calculated using the following expression (Eq. 7.8) in accordance with vector geometry if the amount of the forces acting on the bottom and top links as well as the angles created by these links in the horizontal and vertical planes are known: D f i = T f cosθ cos∅ + B f cosθ sin∅ − C f cosγ

(7.8)

where Dfi is the draft force, T f is the tensile force in the lower link; Bf is the bending force in the lower link, C f is the compressive force in the top link, θ is the angle of the lower link in the horizontal plane, φ is the angle of the lower link in the vertical plane, and γ is the angle of top link in the vertical plane. The second type of draft measurement is the use of a three-point hitch dynamometer, either chassis type or linkage type. The chassis-type dynamometer (Fig. 7.8) has a specially constructed frame and transducers that are mounted on it. This frame is inserted between the tractor and the implement. The chassis is made with an adjustable telescopic shaft to accommodate various implements of different dimensions. The force-sensing elements are three load cells. Usually, the load cells in a three-point hitch dynamometer are arranged in such a way that when top link load cell experiences compressive forces then the lower links are subjected to tensile forces, and vice versa (Alimardani et al., 2008; Aljalil et al., 2001; Askari et al., 2011; Tewari et al., 2012). The draft (Dfi ) of the implement can be obtained from the algebraic sum of horizontal forces acting in the upper link and lower links as given in Eq. 7.9: D f i = FtlR + FtlL − FcT

(7.9)

7.3 Instrumentation for Measuring Tillage Performance Parameters

173

Fig. 7.8 Three-point hitch dynamometer (Kumar et al., 2016)

where F tlR = tensile force at the right lower link, F tlL = tensile force at the left lower link, and F cT = compressive force at the top link. In the chassis-type dynamometer, the position of the implement relative to the tractor is changed which limits the movement of the implement and also increases the chance of damaging the load cells due to sudden application of forces. To solve this problem, Upadhyay and Raheman (2020) developed a special type of draft sensing unit. The sensing units are to be attached one each to the three-point linkage of the tractor in such a way that it allows only the resultant horizontal forces to act on the load cell mounted between the two curved plates, as shown in Fig. 7.9. Each sensing unit has two detachable mild steel frames attached to two curved plates. The load cell is to be mounted in such a way that the force experienced by the threepoint linkage will be transferred laterally to the load cell by means of the curved plates. This arrangement reduces the magnitude of the imposed force and vibration to the load cell and thereby increases the life of the load cell and accuracy while measuring the draft. As the load cell is mounted laterally between the curved plates perpendicular to the direction of travel, the nature of force acting on the load cell will change accordingly (Fig. 7.9a). When the linkage is under tension, the two curve plates get compressed and compressive force is imposed (Fig. 7.9a). Similarly, for the linkage under compression, two curve plates get extended and the load cell is subjected to a tensile force (Fig. 7.9a). The isometric view of one sensing unit is shown in Fig. 7.9b. As the upper link of the three-point hitch remains in compression and both of the lower links are in tension during the tillage operation, the draft is calculated by adding the force on both the lower links and subtracting the force on the top link (Eq. 7.10): D f i = FR + FL − FT

(7.10)

174

7 Measurement of Parameters for Performance Evaluation of Tillage …

Fig. 7.9 Developed draft sensing unit (Upadhyay & Raheman, 2020)

where Dfi is the draft force, kN; F R , F L , and F T are the measured forces in kN in the right, left, and top link sensing units, respectively.

7.3.2 Torque Measurement Different torque sensors used by the researchers in measuring PTO torque requirements for operating active tillage implements in the field are contact type and non-contact type. Slip-ring torque sensor: Slip-ring torque transducers are contact-type transducers. The measurement of torque of active tillage implements by a slip-ring strain gauge

7.3 Instrumentation for Measuring Tillage Performance Parameters

175

torque meter was first experimented by Ghosh (1967). In a slip-ring-type sensor, strain gauges are bonded on a suitably designed shaft. The shaft twists when a torsional moment is applied to it, which results in shear stresses. These are measured by bonding the strain gauges at 45° to the horizontal axis. Typically, a Wheatstone bridge is constructed using four strain gauges, with temperature correction components built into the bridge circuitry. A linearly proportionate electric output is produced when the bridge is subjected to an excitation voltage and torque is induced in the shaft. By mounting strain gauges on the circular shaft adjacent to the universal joint connected to the PTO, torque can be measured (Hoki et al., 1988). An in-line measurement system was created by Brassert and Dahlstrand (1996) for use with an absorption dynamometer. A sensor on the adjacent static frame detected the twisting motion of the rotating PTO shaft. The PTO shaft of the machinery was modified by Kheiralla et al. (2004) to include a built-in slip-ring torque sensor. This shaft can only fit to one size of PTO shaft since it is secured to an universal joint with a female coupling, which cannot be changed without altering the universal joint and coupling. Upadhyay and Raheman (2018, 2020) used a HBM torque transducer (1000 N-m capacity) to measure the torque of a combined offset disk harrow in a test rig and field (Fig. 7.10). The torque transducer and telescopic shaft were connected by a bellow coupling to safeguard the measuring unit and maintain an in-line connection. Additionally, a pillow block bearing was installed to support the spinning shaft between the coupler and telescopic shaft. A Datum Universal Interface (DUI) with an integrated display for torque, speed, and power was attached to the output of torque transducer. Non contacting/Wireless PTO torque sensor: In contact-type PTO torque sensors, there is a risk of damaging the associated electronic items due to the cables connected to PTO torque transducers. Use of this contact-type torque sensor requires a data acquisition system for acquiring torque data and modifications in the driveline of the PTO shaft for mounting the transducer, and it affects the alignment of the Cardan

1. Torque transducer; 2. Bellow coupling; 3. Pillow block bearing; Fig. 7.10 Torque transducer attached to the tractor PTO

176

7 Measurement of Parameters for Performance Evaluation of Tillage …

shaft. A wireless PTO torque sensor can eliminate all these problems and measure the torque at a lesser cost (Hensh et al., 2021). It comprises a receiver with a decoder and a transmitter with an encoder. With the aid of a specific steel strip and fiber-reinforced tape, the encoder and transmitter units are mounted on the revolving shaft. There is an antenna with a transmitter that transmits the signal to the receiver in terms of frequency. The transmission part is powered by a battery. The receiving component consists of a receiver with a decoder and a cabled receiving antenna. The receiver contains an LED bar indication that displays the signal’s actual strength and whether auto-zero calibration is achieved or not.

7.3.3 Wheel Slip Measurement The difference in the rotational speed (rpm) in the front and rear wheels of a two wheel drive (2WD) tractor is used to calculate wheel slip. The actual speed and theoretical speed are obtained from the front and rear wheels, respectively by knowing the rolling radius of these wheels (Pranav et al., 2010, 2012). A Hall effect sensor is used to count the wheel rpm (Kumar et., 2017; Gupta et al., 2019). The front and rear wheels of the tractor are equipped with metallic disks that have tiny circular magnets around their periphery (Fig. 7.11). In order to detect changes in the magnetic field and count the rotations of the wheel per minute, the Hall effect sensors are fitted nearer to the magnets. When the sensor comes closer to a magnet, a voltage signal pulse is produced, and the total number of pulses produced during one revolution is equal to the number of magnets positioned on the metallic disk. The more the number of magnets, the higher is the accuracy. A microcontroller is used to record the signal pulses that the sensor senses, and an integrated development environment (IDE) algorithm calculates the actual and theoretical speeds of a tractor by providing rolling radius of front and rear wheels as input data. An inductive proximity sensor is also used to measure the angular speed of the front and rear wheels of the tractor. An inductive proximity sensor is a non-contacttype sensor that detects the presence of any metallic object when the object interrupts the electromagnetic field around the sensor’s surface. Each pass of a metallic object results in an electric pulse. The number of such pulses per unit of time is counted to calculate the angular speed of the front wheel and rear wheel axle (Nataraj et al., 2021). To measure the angular velocity of the front and rear wheels, a circular ring with 8 spikes is to be attached to one of the front rims as well as both the rear wheel rims. Proximity sensors are to be mounted on a rigid frame at the tractor chassis as shown in Fig. 7.12. For every 8 pulses generated, the number of wheel revolutions is to be taken as 1. The speed of the wheel is computed using Eq. 7.12. 2π R N 60

(7.11)

1 × 60 corresponding time for every 8 pulses (second)

(7.12)

V = N=

7.3 Instrumentation for Measuring Tillage Performance Parameters

177

Fig. 7.11 Wheel slip measurement with Hall effect sensor (Kumar et al., 2016)

Fig. 7.12 Wheel slip measurement with inductive proximity sensor (Nataraj et al., 2019)

where N = wheel revolution per minute, R = rolling radius (m), and V = peripheral speed of wheel (m/s). In a two-wheel drive tractor, as the front wheels are towed wheels and rear wheels are powered wheels, the speed of the front wheel is taken as the actual speed of the tractor, and the speed of the rear wheel is taken as the theoretical speed of the tractor. Hence, the slip is calculated by using the following equation (Eq. 7.13): (

Actual speed Wheel slip(%) = 1 − Theoretical Speed

) × 100

(7.13)

178

7 Measurement of Parameters for Performance Evaluation of Tillage …

Fig. 7.13 Schematic view of the fuel consumption measuring system

7.3.4 Measurement of Fuel Consumption A fuel measurement system consisting of a capillary tube, auxiliary fuel tank, measuring scale, valve, and pipelines can be used to measure what quantity of fuel the tractor consumes during tillage operations. The block diagram representing the fuel measuring system is shown in Fig. 7.13. A two-way valve is to be used to control the flow of fuel from the auxiliary tank to the fuel pump. A measuring scale has to be fixed close to the capillary tube of the auxiliary fuel tank for measurement of fuel consumption. During calibration, the tank is to be kept horizontal to the ground by keeping the tractor on a level surface. For a known volume of diesel fuel added to the auxiliary tank, the corresponding rise of the fuel level in the capillary tube is to be noted from the scale, placed closer to it. A similar procedure has to be repeated for several known volumes of fuel, and the calibration curve has to be obtained. As discussed above, the fuel measuring system attached to the tractor during field tests is shown in Fig. 7.14. Fuel flow meters (FFM) fitted on the fuel supply line and return line of the instrumented tractor is also used to measure the fuel consumption (FC) of the tractor, as shown in Fig. 7.15. The outputs from both FFMs are recorded and shown using a Contoil DFM-BC display board. A 12 V DC battery is required to power the display board. The Contoil DFM-BC display meter subtracts the supply line FFM readings from the return line FFM readings to measure the total amount of fuel used during the operation. Additionally, a stopwatch is used to record the duration of the operation. By dividing the entire amount of fuel used during operation with the duration of operation, fuel consumption is computed. The schematic view of the fuel consumption measuring system is shown in Fig. 7.16.

7.3 Instrumentation for Measuring Tillage Performance Parameters

179

Fig. 7.14 Fuel consumption measurement setup attached to the tractor

Fig. 7.15 Fuel consumption measurement system 1. Supply line of FFM, 2. Return line of FFM, 3. Display board, 4. Three-way gate valve, and 5. Auxiliary fuel tank

180

7 Measurement of Parameters for Performance Evaluation of Tillage …

Fig. 7.16 Schematic view of the fuel consumption measuring system using fuel flow meter

Numerical problems

1. A field was tilled by using a tractor-drawn moldboard plow followed by a disk harrow. Soil samples were collected from areas of 50 × 50 cm in the field selected randomly and were sieve analyzed using a set of sieves. The amount of soil retained in each sieve is given in the following table. Find out the mean soil clod diameter of the tilled soil in the field. Size of aperture (mm)

Diameter of soil passed the left sieve and retained on the next small aperture sieve (mm)

Representative diameter of Weight soil in the left column (mm) of soil (g)

60

>60

65

1050

40

40–60

50

350

26

26–40

33

1000

11.2

11.2–26

18.6

1250

5.6

5.6–11.2

8.4

800

2.8

2.8–5.6

4.7

Pan