Belt Conveyors in Modern Mine Mechanization

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BELT CONVEYORS

IN MODERN MINE MECHANIZATION

LIBRARY COLORADO SCHOOL OF GOLDEN,COLORADO

by II* John Bernstein

ProQuest N um ber: 10781414

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A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Hines in partial fulfillment of the requirements for the degree of Master of Mining Engineering '

r_ .l

t-' Signed:

Golden, Colorado Date: °'Vv^

A 4~

1950

Approved:

» breaking and transporting ore*

By being separated^ into

their simplest elements# these operations can be critically examined and appraised*

There are as many variations and

combinations in the breaking and transporting methods as there are variations in orebodies, but employment of the appropriate means will result in the most economical method* The term stoping

(from Middle English step* meaning ex­

traction of ore by steps) is unsatisfactory because it

coiobines the operation of breaking and transporting — though the line of demarcation is not always sharp#

al­

For

example* material is made to run directly into raises or slides v;hen broken by picking or blasting#

Breaking and

transporting# nevertheless, are distinct functions, and It is desirable that they be recognised as such#

The three

fundamental methods of brooking ore /Op*

or other materials

p. 33___________________________________

are (a) by drilling and blasting* (b) by mechanical or manual excavation* and (c) by caving#

The transportation

of ore from the stope face to the surface may be regarded as one function requiring two or more stages*

The stream­

lined methods of tomorrow* under ordinary conditions* will convey ore (a) by gravitational or mechanical conveyance from the stope face to the mining or stope conveyors* (b) , by mining or stope conveyors to the truck conveyor (main haulage conveyor)* and (c) by truck conveyor to the surface# The timeliness of the preceding paragraphs is emphasized most sharply and vividly* in the problems that have arisen in Great Britain in the mining of depleted iron ores*

The

mining Industry in America can well bear in mind the lessons brought out by the following discourse* which is an omen for our future operations# Dr# Dm D* Howat*

of the Koy&l Technical College*

/Howat* D# D*» Britain*s Iron Mines and Problems: Engineer*log and Mining Journal, p» 7k. May 19k9.____________ , . Glasgow, Scotland* speaks as follows on the decreased iron ore production in Great Britain: Most Important of the metalliferous ore resources of Britain are the Jurassic iron ores* The iron^bearing measures of the Jhrassic system extend from the vicinity of the HIver Tees southwest to the Bristol Channel* The Ironstone Is generally phos­ phoric and of low iron content* rarely ex­ ceeding 3O to 33$* With almost half of the

10 burden composed of a 20$ Iron*-or©f blasts furnace practice at Frodingham is claimed to be the leanest ore-smelting practice in the world* The Jurassic deposits* which were known In prehistoric times, became import­ ant as large-scale sources of Iron about the middle of the 19th century* In the early stages of their development* th© Cleveland field was a determining factor in establishing the extensive iron in­ dustry of the northeast of England* Later, the work Involved in building railways led to rediscovery of many of the deposits of the Midlands* As the overburden in the east Midlands was comparatively light In places, open-cut mining was introduced* Methods of hand mining, originally employed, permitted the deposits to be worked selec­ tively, only weathered ore high enough in grade being extracted* During the past US to SO years, mechanized open-cut methods have been d eveloped* A striking example of the possibilities of those now In use Is the stripping of 80 ft of overburden to mine 8 ft of ore* In the Cleveland field where all the ore is mined by underground methods^ a Steady decline in output has been noted from 1913 to the present*

Howat attributes this

decline to the following elements: The lack of adequate mechanisation for mining and transporting the ores In the ■ ■ !*|**I*|*W W W ****W *^*— 1 *»

I**|»»*I«II*> |K M I—

iw ^h *

*1 ***— |W — **Wn**M* I«|lli*

—I|»ln *■ijjw Tn I w i J

m l i* i W n n *n— ■*ni|# - Sliding t ail

end on

side

channel

framing

Figure

26* - Mine

belt

conveyor

with

a boom

discharge

conveyor

Figure

27• - Boom

discharge

conveyor

Figure 28* - A roller

switch

Figure

33 . - A pneumatic-tire

impact

idler

unit.

Figure

3^

- Spacing

of inpact

idler

at loading

station

GRAVITY TY PE S

R ex V e r t i c a l A ls o f u r n

F ig u r e 35#

-

G r a v :5_ t

r a v i l y Take-Up equipped w i t h roller-bearingjpillow blocks. with babbitted angle p illo w blocks. S j

-y

and h o r i z o n t a l ty p e t a k e - u p .

Figure

- A type of stacker

conveyor

ELEMENTS IN CQMVETOH BELTING-

As most mine...'haulage problems involve the handling of large tonnages of ores at lowest cost, and as the average conveyor belt represents nearly I4.0 of the total conveyor line cost, some pertinent factors should be kept in mind regarding the nature of the conveyor belt and associated operating elements* The mining operator should have predetermined (in view of the large capital costs the conveyor belt entails) the tonnage he expects, not merely per shift but maximum tons per hour; for short periods of a few minutes; not only the first year, but for several years#

These must be estimated

to realize the actual dollars and cents value of the conveyor belting involved* The mine belt comes in direct contact with the ore conveyed, and is the only part of the conveyor actually to handle the ore*

As the belt is subject to damage, wear, and

replacement, the mine operator should have a working lmow< ledge of tho belt and its limitations*

Olarity and uadep-

standing of basic belt problems, *and terminology used, make for a more efficient use of the conveyor machine* Mine conveyor belts handle all types of ores, from the very abrasive to the sticky, and most ores occur under vary-

ing physical conditions#

Where belt conveyor unit3 are to

b© utilized, the mine operator should be aware of th© factors that will make his conveyor more efficient and economical to operate*

Among these factors are type of belting used, hors©

power requirements, belt tensions, speeds, and capacities# Duck and Cord Belting The carcass or body of the belt consists of plies of cotton-duck or cord to provide either the necessary thickness to withstand th© impact and punching effect of the ore jf-

handled, or the necessary strength to pull the load*

The

duck or cord does all the work In pulling and supporting the ore load, supplying all th© structural strength required* /Hudson, Wilbur G>, Conveyors and Related Equipment, 2d ed*, p» 232, New York, John Wiley & Sons* 1949* The rubber provides no structural strength, only protection ft

against corrosion, blows, and abrasive wear*

Though it Is

necessary for a mine belt to have proper strength and body, mine operators should be chary of mine belts which seem to _/ exhibit excessive transverse stiffness as this condition /Jeffrey Belt Conveyors, Catalog 7^5# P* 34* Ohio, Jeffrey — 'Kanufaoturinp' Company. 19k7. may prevent proper troughing and straight travelling over the troughlng idlers under varying ore-loading conditions* A ply or layer In the carfcass consists of cotton-duck, a closely woven fabric, or may consist of cord construction in which there are no cross or transverse threads, only spaced thread’ s*

The spaced threads of th© cord belt would

88 seem to give better or© conveying service, as each cord is surrounded and imbedded in a thick cushion of rubber* advantages claimed Tor this construction

The

are easier

/Hudson* Vim G*, Conveyors and Related Equipment, 2d ed*, p* 188, Hew York^ John Wiley and Sons, 19h9» troughing, a lower percentage of creep or elastic stretch because of the parallel cords, greater percentage of rubber, end permissible Increase in the number of plies without troughing resistance*

In any mine conveyor belt the type

and number of plies necessary

must be of sufficient body

/staacke* * V/*, and Traveler., E* R*, Engineering Rubber Conveyor Etelting, p* 53, B* P* Goodrich Company, 19^1-7♦ to withstand the Impact at the loading point, and be suffi­ cient to withstand the maximum belt operating tension*

Th©

plies must provide proper support of the or© load between idlers, and maintain proper troughablllty when the belt Is lightly loaded or empty* Eviction is the term given to th© rubber compound that is smeared between each ply of cord or duels#

It bonds to- *

gether the layers of material, insulating against abrading friction In and between the layers while providing the necessary resilience and resistance to deformation as the belt passes around the pulleys#

The selection of friction

quality Is determined by frequency and severity of flexing* Th© flexing life of a conveyor bolt Is the length of time a belt will continue In operation without failure from the

89 flexing of the belt over the conveyor pulley.

It might be

here stated that the fundamental flex-life 'formula govern­ ing belt conveyor structure was first read by Goodyear Hubber and Tire Company before the American Society Testing Materials in 1929# The formula w as-as-follows: F L s IC x D ^«3g x b___________ P 6.27 x t )-}-«12 x 3 0,5 D K L P S T

• » • m * •

Pulley Diameter Constant of BeltConstruction Belt Length Carcass thickness of Belt Speed Tension per Inch of belt width * Pfr»e# P« 82# Wisconsin# Chain Belt

11

____

size# abrasiveness# type of loading# Impact frequency end speed of the belt conveyor*

A mining belt conveyor of 100-

foot centers# for exfB3^>l©# will be subject to ten times as many ore impacts as one of 1000-foot centers* . For extremely arduous loading service where large lumpy ore pieces are hauled# and tears in the rubber cover result# a breaker strip is built into the belt between the carcass and top . i cover# serving to Increase the adhesion of the cover to the }

carcass*

#

When mine bolts handle ore# Staacke and ^raxler state /staacke, c* v/.# and Sraxler# B* R*# Engineering Rubber Conveyor Belting# P* 6l* B* P» Goodrich Company* 1914.7•

t X*

For any given set of loading conditions there is a minimum requirement for cover gauges which should be used regardless of belt length* YJhere loading causes material to be fed be belt at an angle crosswise to belt travel# or where there is appreciable vertical drop# the rubber cover sizes should be increased* Qlie greatest belt economy will result to the mint ©per* ator when hla loading operations are so geared as to permit eventual failure of carcass and cover at approx^nafely *the same time* Some idea of top cover gauges may be obtained from the

following table

s

Vop. cit.Y p» 60~ TABLE B Top loading Conditions Covey and G-aug© Service (Inohep) 1/%"

Average Severe

5/16"

Severe

Very Sever©

3/3"

Type, or Material Abrasive materials such as Anthracite coal* coke and sinter* Book* stone, or coal up to 10" size* Heavy abrasive materials such as ores or iron# copper * zinc* and lead* foundry refuse* limestone* and slag* Heavy sharp abrasive materials such as trap rook* quartz* glass cullet, and iron pyrites and exceptionally large lumps of any material*

Figure 37 emphasizes the principal points outlined in th© preceding paragraphs on due1^,and cord belting. Leading rubber belting companies of America have made rapid strides in improving upon the conventional rubber fabric belts; IT* S* Rubber Company has perfected a new belt* th© strength of which permits its application to conveyor installations having longer centers* end higher lifts and carrying greater loads than can be handled by present rubber fabric belts*

This new belt embodies a duck in which two *

textiles are combined — IJstex for strength* Nylon for flexi­ bility.

The IJstex treatment is a special patented U* S.

Rubber development which increases the tensile strength of

the cotton fibres themselves when twisted into yarn*

Be­

cause nylon is supple and flexible* the addition of nylon brings unusual troughabllity to the belt*

This gives in­

creased loading capacity and more efficient operation* The first conveyor system on the Mesabi Range using this new type belting was the Hawkins open-pit mine of the Cleveland Cliffs Iron Company at Nashwauk* Minnesota* lift is 225 ft*

The

Trucks deliver the ore to a screening

plant in the pit* dumping into a drive-over pocket*

From

thief, two flights of 30-in* belt* with a transfer station between* deliver the ore to a railroad-loading bln on the surface# wide*

The belts used in this installation are 30 in*

Operating at 55>0 feet per minute* they haul 700 long

tons per hour on an incline of 15 degrees 9 minutes*

Th©

belt has handled over 2 million tons of ore* and belt stretch has been under 1 per cent*

Figures 38 and 39 show

details of Hawkins belt conveyor installation* Steel Wire Cable Belting For high lift systems where extremely heavy ore loading and conveying conditions exist* steel wire cable, conveyor 1

belts are being used*

Steel cable belts have one ply of

high tensile* finely stranded flexible steel aircraft cable in place of multiple cord layers*

These steel cables (brass

plated and rubber coated) placed in parallel* side by side on the neutral plane of the belt* permit far greater ten­ sion stresses than i^ovild be available in reinforced duck and cord belting*

The multi-strand airplane-type steel

co

Q>

o o ro

>

~o T3 CD

o

0

IT) ro

z

o

ro m




O >-

o o

0

LU

> Z

o

a

_*_T

JC

O

O

r o

UJ

CL


(regenerated)* In some declining mine conveyors* the weight of ore on th© belt becomes a negative quantity*

In this case* the loaded

belt will drive the mine conveyor* which must be provided with braking means* 2|*. Horsepowerto operate pulleys and belt accessories* 5*

Horsepowerto compensate for power lost from motor

drive to conveyor head shaft* The sum of the above factors gives the total horsepower required to run the mine belt conveyor* a motor of

As a consequence*

of greateror equal horsepower should be used* Motors

high starting torque ore useful for operations where mine

conveyors are started under load* A general picture of the power allotment in a belt conveyor system can be obtained from Table C *

TABLE C« Distribution of power in a belt conveyor system. _/ivlercier, S. M. f Belt Conveyors: Engineering Mining Journal* vol. li?l# 1*. p.*. 79# 1950. Slop©

Level 0

Angle Material Lift Power Use

+10#

+20*,?

+3o>;...

6°

11.3°

16.7°

67#

80#

86#

Percent of total power used

Machinery Friction

13# . 100#

Total Power

20#

100'?

12$

8#

11 CO

6o#

Material Friction

.6#.

loo;.?

.

100#

Conveyor Belt Tensions Beferring to Figure IjJL a clearer understanding of the basic tension f actors inherent in mine conveyor transporta­ tion can be obtained* Maximum Tension

Slack Side Initial Tension f*igure ifl# - Basic belt tensions The drive pulley must apply tension to do th© work in moving the loaded ore belt over the idlers.

This tension

is known as effective horsepower pull or tfeffective tension.n

101

To transmit thi3 tension or power from the drive pulley to the mine belt, a certain amount of initial belt tension or frictional grip must be maintained#

The initial tension is

pr actic ally the same on both sides of the drive pulley when the conveyor is idle#

Then the mine conveyor is in

*

operation, a difference in belt tension exists on the tv*o sides of the drive pulley*

On th© carrying run there is th©

ntight sideu or maximum tension, which includes the initial and effective tension#

On the return m m side there is only

the initial or slack side tension* Effective Tension: This tension is the difference be­ tween total tension and initial tension, and is th© horse­ power pull which does the work in moving the belt#

It may

be determined by the following formula: Horsepower Pull) m Tens ion in lbs *)

Slack side tens1ons sary to drive the belt#

Total horsepower to operate conveyor x 33,000 Speed in fpm of conveyor belt This Is the Initial tension neces­ It Is somewhat greater than the

minimum tension required for the pulley to grip th© belt#

It

Is to maintain slack side tension that takeups are employed to tense the belt sufficiently#

In some mine installations,

where inclined conveyors with high lifts are used, the pull of the return run belt produces a greater slack side or Initial tension than the minimum required for tractive pur­ poses (traction)#

It would b© a waste of capital investment

to install pressure pulley or tandem pulley drives where such

W M

a tension condition exists*

From an operating point or

view* th© initial tension required varies with angle of wrap between drive pulley and belt* and use of pulley lagging* The general formula in use for slack side tension calculation is2 Initial or slack, side tension « HP pull X Drive factor (lb) (lb) Belt ©lop© conveyor tension! "/here.mine conveyor© operate on an incline* the empty belt weight on the inclined runs causes tension at the slope top*

To determine this

tension* the following formula may be used: Belt slope tension » Vertical lift In ft x belt weight in lb per ft Tight side tension:

The maximum tension or tight side

tension is found at the driving pulley on the carrying run side*

Maximum belt tension may not always occur at the

head or drive pulley* but may be found at seme intermediate point*

Mine conveyor belts of varying contours

combining

/Jeffrey Belt Conveyors* Catalog 795* P* ^5* Ohio* Jeffrey Manufacturing Company, 19kl* declines and inclines need to be analysed In detail with proper combinations of partial loadings to determine the point of maximum tension*

w

Mine Belt Speeda

Full ore lead L Partial ore load

Cross sectional loading When mine belt conveyors are placed in operation* the speed oT the belt should be so chosen as to enable the mine belt to operate under full cross-section ore load* See Figure 1^2*

This means that a mine belt conveyor should

carry its Pull crosa-section ore load regardless of oon«> veyor speed* to more fully realize the mine run life of the belt measured in ore tonnages handled.

Hill ore loads mean

deeper piles/ less ore in contact with the belt* and more efficient distribution of ore over more of the belt*

A light

ore load concentrates itself directly in the middle of the mine belt and wears the belt more quickly! consequently the belt must ,be replaced. From an operating standpoint* it is generally consider** ©d that the most efficient mine belt conveyor operation will result by using the narrowest belt at- the highest speed at which good loading is obtained.

Heavy ores and abrasive

materials are conveyed by belts In widths ranging from 12 to^ 60 in*, and speeds ranging from 300 to 600 feet per minute

♦

A/staack# C, W** and Traxler, £« R* * Engineering Rubber » , .. Conveyor Belting p. 13*. B, P. Goodrich Company, 19lj-7« . Wet ores are conveyed at a minimum speed of $00 feet per

minute*

If ore lump size indicates the use of a wider

mine belt than required for the ore tonnage handled* the belt speed should be reduced so that the mj.ne belt can carry the proper pay load - a full cross-sectional ore load* At above normal belt speeds* it has been found that the belt Rapacity is not directly proportional to the higher speeds as the ore load on th© mine belt la relatively unstable* and a full cross-sectional ore load is not carried* Good loading conditions are important factors in govern­ ing the mine belt speed*

Staaok and Traxler

state:

Pi» S>M»* p« U The type of ohut© or mechanical feeder will often determine th© speed at which belt may operate satisfactorily* Xf the carrying Idler spacing is graduated and the belt ten­ sion Is maintained correctly so that the load travels smoothly* higher speeds are often possible* If it Is necessary to load onto a belt where belt Is at a slope angle of 10 or more then slower belt speed may have to be used to get full capacity loading* When declining conveyors are considered* th© amount of slope at loading point is usually the determining factor as far as maximum belt speeds are concerned* *In the basic analysis* mine belt speed will be deter­ mined* to a very large extent* by the loading facilities available* Mine Belt Capaofti©g« The carrying oopacity

of a troughed mine belt depends

/HetzeX* F* V** and Albright* H* K** Belt Conveyors and Belt Elevators* 3d ©d** p* 5.92# New York* John Wiley & Sons* 19t|JU ______

10$

on how the ore can be piled ^and efficiently carried on the conveyor belt*

The size and shape of the ore load cross-

section depends on the manner in which it piles on the belt, and the spillage margins which must be maintained at the belt edges*

The above factors should not be glossed

over lightly, if the mine operator wishes to utilise his mine belt to the fullest possible extent, and that means carrying peak loads (maximum ore tonnages) during the periods of mine belt operation*

Primarily, the maximum capacity of

a mine conveyor belt will depend largely on the manner in which the mine belt is loaded*

lining belt conveyors are

handling capacities per minute varying from 2 tons on the 12-in* belts, at 300 ft per minute of X50—lb~per~cubio~ft material, to I30 tons per minute on the 60—in* belt at 600 ft per minute of 150~lb~per—cubic-ft material*

Xt will

be noted that the above-mentioned capacities are given In the quantity of tons per minute rather than tons per hour* Mine belt capacity in underground ore conveying is often rated In tons per minute because of intermittent feeding conditions, because of lack of suitable loading devices (or conditions which restrict the use thereof) and because the mine belt may receive ore from a unit such as an ore crusher,

Z j

whose output rate for a period of minutes may

greatly exceed its average hourly rate* Maximum capacities practical for general use have been

predicated upon, the use of the Goodyear formula*"^which

/Handbook of Belting, ij-th ed*, p* 87, Ohio, Goodyear Tire & Rubber Company, Inc*, lylUu___________________ _ states: T = (W + 180) W2SM 12,000,000 wherein M » S * T * \7 m

Vfeight of material in lb per cu foot Speed of belt in feet per minute Peak capacity in tons (of 2000 lb) per hour Belt width in inches

Mine operators will find (having determined the mine belt capacity) that they can increase their belt capacity as much as 25

cent if they are willing to spend time, money,

and effort in constructing their mine conveyor unit accord­ ing to the follov/ing approach, plainly outlined by Staaek and Traxler~^: /staack, 0# Y/*,. and Traxler, E* H., Engineering Rubber Conveyor Belting, p» 18, B« F* Goodrich Company, 19^1?« 1, Perfect chute design and skirting at loading point# 2# Get load onto belt from a wider feeder apron or belt, travelling at a slower speed* 3* Vary the idler spacing from head *to tall pulleys to give Liniform support to belting and load with regard to tension in the belt* If.* At the loading point, have load shaped to conform to belt and travelling at the same speed and in the same direc­ tion as the belt* 5* Belting under loading point must be horizontal or nearly so* 6* The conveyor must be in perfect alighment, with load centered on belt and belting centered on idlers*

*

10? The above approach Would not appear to be warranted In a condition where a slueher travelling either up or down a stop© discharges ore onto a belt conveyor situated in a development or conveyor drift - simply because there is intermittent ore reading, irregular loading facilities* and periods when the" belt is not in operation# However* if the brealring operation and load feed opera­ tion can be coordinated so as to insure a steady flov/ of ore onto the belt* th© above approach would seem Justified*

1*0m

CENTER —

FIXED LENGTH MINE CONVENORS

In 1argo-tonnage operations mine management may be faced v/ith the ore conveying problem* wherein they must decide upon the installation of either long center — • fixed length mine conveyors (a single-belt flight opera-* tion) or a series of belt conveyors (multlple-belt flights)• Considering that Initial capital costs may range from |>it.OO*OQO to §1 million* the economic aspects of one long~centered belt versus a series of shorter belts should ' be given careful consideration#

True* th© first estimated

capital cost of a series of belt flights may be less than that of a single-flight belt —

but factors of ore degrada­

tion* belt wear* and replacement may tend to shift the final decision to th© sIngle-flight bolt* In hauling large tonnages of ore* mine management must bear in mind that the cost per ton of or© handled will depend on the physical properties of the ore, how often th© mine belt Is damaged* the center—to—center length of th© mine belt* th© design of the conveyor system* and the suitability of mine belt chosen for the particular ore haulage problem*

Conditions permitting* there is much in favor of long centered—3Ingle flight operation*

Where a mine belt is to

*

i

haul or© over a horizontal distance* it is possible to operate such a belt rive miles or more from tall to head pulley ~

ten fiiles long including the return belt run.

Based on th© use of steel cable belting* a single night belt o,f 5800-ft centers can convey 1000 tons of ore up a slop© (1700 ft vertical lift)* from the bottom of a mine pit or shaft*

The advantages of long centers in terms of life

expectancy is in th© belt time cycle*

There is a gain %o

be made in reduced cyclic passes of the belt tinder th© load** * ing point* v^here major abrasion occurs* As an example* a section of a mine conveyor belt with * mile ©enters travelling 200 ft per minute would pass the loading point only once ©very 4 hours and

2ij-

minutes*Under

such conditions, millions of tons of ores would cause* on the belt cover* little or no wear resulting from th© load** ing operation* In comparison to multiple belt flights* single-belt flights

can operate with a minimum number

ups* motor drives* and supervisory personnel*

of

controls*take-

Th© savings

accrued might well pay the *cost of th© mine belt in largetonnage operations* In the conveying of ores* coals* and specification aggregate where breaking up of material must be avoided* transfers from on© belt to another tend to reduce ore and material size by attrition action as th© material flows

110 through transfer chutes*

The use of single-flight conveyor

tends to overcome the attrition action by the absence of transfer chutes or the minimizing of th© same*

Heretofore*

where dimensions of the transfer chute limited lump size to about one-third of the belt width* the elimination of the transfer chut© in single belt flight operation permits carry-* ing ore lumps of a size up to two-thirds of the belt width or twice normal lump size*

Using multiple-belt flights over

long distances* materials such as clays and iron ores gum up — 'stick to the belt cover* making transfers a difficult pro­ blem*

The efficient us© of single-belt flight operation

would alleviate this problem* Single Belt Flight Speed On slope or Inclined belts of conventional cotton de­ sign* it is necessary to operate at speeds faster than dictated by the hourly tonnage In order that th© unit load be reduced*

In these oases th© unit load (pounds of or©

per foot of belt length) must be reduced to keep the belt tensions within the capacity of th© cotton load-carriers* In single—belt flight operation* using steel wire, cable belting* th© slowest speed commensurate with hourly tonnage * can be selected*

At slow speeds* capacity cross-sectional

loading is attained* allowing wear of th© cover to b© dis­ tributed across th© full belt length* At slow speeds, with maximum belt loading* idler units (shells and bearings) last longer* A 7-in* idler at $00 ft * per minut© makes over 39 million revolutions per operating

Ill year*

At 2j?0-ft pea? minute belt speed* the same Idler in

the Identical operating year would make approximately 19 million revolutions

a reduction of over 5>0^*

less replacement cost and longer Idler unit life.

This moans At slow

speeds* the belt has a long time operating cycle; Tor in i

alngle-belii flight* each belt point passes under the load station fewer times than in multiple flights* Single Belt Flight Horsepower WPom the standpoint of initial capital costs* mine management should consider the factor of horsepower as re** quired for the conveyor unit*

Field tests

bn long center

/Staaek* C* V7** and Trsocler* B . R** Engineering Rubber ,Conveyor Belting* p* Ilf., B* F* G-oodrieh Company* 19U-7* single flight operations have shoxm that the horsepower re** quired to move belt empty and to move the load horizontally* is considerably less than would be calculated by a formula using actual length*

Goodyear*s engineering

on the use

/Handbook of Belting* Ipbh ed** p* 91# Goodyear Tire & _____ Rubber Company* Inc* » 19kh* of long center conveyors has brought out the following: The use of long center conveyors has brought out the fact that the usual formulas for finding the amount of power gives values mxoh too High for those longer units* This is another instance of a formula being de­ veloped to fit the small units originally in use and giving erroneous values when applied to long center conveyors* There are some power absorbing factors which are independ­ ent of the length* and which are therefore not increased when the length is increased*

112

The hprsepov/er required is Independent of conveyor length; it (power absorbing factor) is related to the tonnage carried by the conveyor, and is represented by power re­ quired for the terminals of the conveyor#

As on example

a 2000—ft horizontal mine conveyor uses less than twice the horsepower necessary for a 1000-ft-center conveyor.

Thus,

in mine conveying layouts, where ore must be transported long distances,

there Is a distinct power advantage to be

gained by using long centered mine conveyors where possible. Therefore* the installation of a single-belt flight operation (in opposition to mnltiple-bolt flights) would effect considerable capital cost savings in that less elec­ trical equipment* In the form of motor drives, reducers, and interlocking devices, would be required# Transfer Stations Where single-belt flight systems can be efficiently operated, th© need of transfer stations is greatly lessened, and In some cases completely eliminated# transfer points* savings

By eliminating

have been estimated to rang©

/staack, e* W*, and Traxler, E# R#, Engineering Rubber Conveyor Belting# p* llu B# F# Goodrich Company, 19^7* from 55,000 to #15,000 per transfer year* By evaluating the weaknesses of transfer points in multiple belt flights, (and their absence in single belt flights) the above savings can be more clearly shown# (a) In multiple bolt operation, transfer points are

113 th© place where most of th© accidental belt damage occurs* Clogging of loading devices and chutes can cause a great amount of lost time and shut-down of operations. Single­ belt flights minimize lost-time delays and makes for more continuous operating cycles# (b) Multiple-belt flights require greater supervisory personnel at the transfer stations* necessitating higher labor cost.

A three-flight operation may require three men

for supervision of the conveying run, while a single flight may require but one man for the whole belt run. (c) In imiltiple-belt flights* there will be greater abrasive action by ore impact on the belt at the transfer points. Greater belt life and minimum belt replacement can be expected in single-flight operation* wherein transfers are kept to a minimum. (d) A greater number of power Installations are re­ quired In multiple flights than In single-flight operation. In the multiple operation each belt conveyor will require at least a motor drive and interlocking device*

Savings

inherent in single-flight operation* when considering power equipment* are most apparent. V/hen the above factors are taken into consideration by mine operators* it is clear that the use of single-belt flight conveyors can account for considerable savings over on operating year.

It should not be forgotten that longer

center mine conveyors will require a heavier conveyor belt than would be required in multIple-belt flights.

The

Hi).

cost of the heavier belt may b© so great as to make mean­ ingless the positive value of savings apparent in single­ night operation* Physical conditions permitting* long center conveyors should find their greatest application in handling ores in main haulage tunnels* along inclines leading to mine sur­ face* and open pit installations*

Ore tonnages should be

plotted well in advance of proposed long center conveyor installations* to determine whether the large capital costs involved are warranted* A Portfolioyof Long Center Installations Hi© following photographs illustrate clearly the advan­ tages to be derived by using long center conveyors where tonnages and physical conditions (terrain features) permit their use*

Where mine operations allow th© use of long

center conveyors* mine management can be certain to obtain low cost-per-ton figures as increased ore tonnages are conveyed* Figures i|3 and

In 194$ there was constructed a

12-mile overland conveyor system to deliver sand and gravel aggregates from Bedding* California, to th© Shasta dem site* There were twenty-six 36-in* conveyor belt units (6-ply belts) operating at 550 ft per minute delivering a top load of 1100 tens per hour* 3500 ft*

Conveyor centers ranged from OOO to

Bach conveyor was driven by a 200-hp motor* except

for th© last conveyor unit, which v/as driven by a 75-hp motor,

115

as the belt unit was on a downgrade and th© load drove th© motor as a generator#

Over 13 million tons of aggregate were

handled to be utilized in making over 6 million yd of con-, crete*

After th© conveying Job was completed* about 80 per

cent of the conveyor unit was sold in sections and is being used in various mine and quarry projects# Figures \\$ and IpSi At San Jose* California* the Per-* manente Cement Corporation utilized a longer center installa­ tion to deliver aggregates to their cement plant; and also utilized a similar installation as part of their materialshandling program within the plant Itself* Figure Iff: The Bull Shoals Bam project on the v/hlt© River near Flippin* Arkansas* is aided by a

conveyor

system* composed of 21 belt flights of 30-in* belt which delivers 650 tons of crushed rock per hour*

Over 1$. million

tons of aggregates needed to build the dam will have been moved by December 1950*

The conveyor belt travels over

9000 steel troughing idlers* returning empty over $600 steel rolls*

Th© belt flights are driven by 100-hp electric

motors and moved at a speed of $2$ ft per minute*

The con­

veyor system varies in height above th© ground from k to 20 ft*, A 20*000—ton surge pile handles the aggregates at the feed end of th© first conveyor flight*

About 3 1/2 miles

of th© conveyor systom runs over fairly level country; the latter half runs through hilly* wooded areas*

Maximum rise

for any one of th© conveyor units is lll\. ft* and maximum drop is lfl\. ft*

,

Figure l\Bi

At the Grand Coulee Dam in Washington* it

was found necessary to haul aggregates from the preparation Plant

across the Columbia River.

A straight line belt con-

veyor* composed of belt flights 1000 ft in length* was in­ stalled*

The conveyor system transported 1000 tons an hour*

and by the aid of a low-cost suspension bridge {3£00—ft span) crossed the Columbia River* Figure l\$t

This particular photograph Shows part of a

3-mile—long conveyor system which was used to haul earth from a pit to the dam sit© for building an earthen dam* y

As is shown* terrain features do not affect the efficient operation of long center conveyer installations*

Figure

lj.6. - Permanent©

Cement

conveyor

unit

following

terrain

of land#

Vi-'.:v» .

-'VA'* *

117

. /

STEEL BELT CONVEYORS

/

Steel belt conveyors have been used In Europe since the early 1920*3; 500*000 to 800*000 horsepower has been utilized by steel belts in European operations*

Within the past three

years stainless steel belt conveyors have been tested and evaluated in this country to determine operating efficiency in mineral conveying systems^ Recent successful tests

have been conducted above

/Stainless Conveyor Belt is successful in first mine test: Iron Aj*e» vol» l61u p* Il8 » August 191*9*______ _____ ground at the Johnstown Coal & Coke Company* Crichton #1|. mine in Nicholas County* West Virginia*

A stainless steel belt

was used with conventional rubber-belt equipment and run for several h o w s with maximum load of 100 pounds per running foot*

Regular operating conditions are carried under a load

of 1|.0 pounds per running foot*

The tests showed the stain­

less steel belt to be lighter* cheaper* and better able to stand up under coal mine conditions than rubber belts now in use* SteeJL belts* however* cannot be expected to function efficiently on steep slopes* and there appears a definite limitation to the width of stainless steel sheet that can be continuously rolled*

The most efficient arrangement in a

,

118

mine would involve the wise use of rubber and steel conveyor belts# At present prices* It should be realized that high priced rubber belt conveyor units* as compared to other transporta­ tion units* find restricted application in many mines*

A com­

bination of rubber belts and stainless steel belts in mineral haulage might bring about a more feasible “capital cost" as­ pect* which would be conducive to the further use of conveyor Systems in mineral handling programs# At the present time stainless steel belt units would appear to find their greatest application in open pit surface operations* over horizontal distances, and in underground mining operations, where the belt can be permanently placed In main haulage drifts and tunnels# Sandvlk Stainless Steel Belt Conveyor One of the outstanding steel belt conveyors Is the Sandvlk belt conveyor used, in Europe for over thirty years* and more recently finding use in the United States In various materials handling programs* In connection with mineral conveying programs* the Sandvlk belt conveyor can convey the following materials: TABLE D Materials conveyed Chalk Clay* dry Coal* coke Coal* bituminous* crushed Coal* bituminous* screenings Gravel* coarse or fine

Max* Incline in degrees

34 - 15 15 13 10

* 18 14-15

119 10

Iron ore* crushed Iron ore, concentrate Iron ore, moist concentrate Limestone Pyrite, concentrate Quartz, crushed Rock, crushed Rock salt, ground Sand Sandstone

18 23 ll|. - 15 21 - 22 11

The Sandvlk stainless steel belt applicable to mineral, haulage problems Is a cold rolled, tempered steel band with-* out hinges or Joints* to

The length of belt rolled is from $Q0

ftp its width ranges from 20 to 32 in*, and its thicks

ness varies from 0*03 to 0,06 in*

The tensile strength of

the belt Is approximately 170,000 pounds per square inch. The modulus of elasticity is 26,35^,000 pounds per square inch and the hardness Is about Rockwell 1|2C*

One of the engineer-*

Ing advancements which has taken place In the last few years Is the ability to pre-trough the steel belt by producing a permanent trough at the time of rolling at the Sandvlk mill in Sweden*

This troughing effect allows the steel belt to

carry cross-sectional ore load equal to that previously carried by rubber belts .only*

The troughing Is produced.*in

the same way as the troughing evident in today* s steel measur­ ing tapes*

Self troughing belts may be obtained by using

thin steel belts 20 to 32 in* wide where the weight of both the ore load and belt deflect the carrying belt.

In this way,

characteristics of the troughed belt are obtained, but should only be used for non-abrasive ores because of thickness limita­ tions*

The carrying side of the steel belt Is supported by

120

rollers spaced from 2 to 6 ft apart, the distance depending upon the weight of

the ore load on the belt.

Rollers set

from 5 to 15 ft apart carry the return run of the steel belt. Carrying, Capacity Speed: The carrying capacity of the steel belt conveyor depends on how freely the ore material flows and how the ore piles on the belt.

The capacity of the

conveyor decreases when moving, the reduction in capacity depending upon the* properties of the material (minerals and rock) and upon the working conditions of the conveyor. Table E gives a list of the load capacities# in cubic feet per foot, that a steel belt conveyor is capable of transport­ ing.

When the belt is in motion a reduction in rated capaci­

ties will range within the limits of 20 to 30 per cent. / Sandvlk Steel Belt Conveyors, Sandvik Steel Inc., Conveyor Dept.. New York. 19ll9» TABLE E

3/ Carrying cap., ft ft Hominal width of belt, in. 12 li f . 16 18 20 • a l|.

28 32

Pre-troughed belts O . l l j .0 O .X 8 3 O .2 3 6 0 .3 0 2 O .3 7 6 0 .5 5 8 0 .8 0 7 1 .1 3 0

Self-troughing belts mm mm mm

0 .3 0 2 0 .1 )5 2 0 .6 4 5 0 .9 1 2

The ore material is fed through an opening in the bottom of a hopper onto the steel belt; as with rubber belt system,

J ■

121

caution must be exercised when handling lumpy ore loads great care must be taken to prevent direct ore impact upon the steel belt*

Idler sets spaced closely together at the

load station will aid in solving the Impact problem* The speed in feet per minute for a steel belt conveyor should be equal to, or a little less than, the distance in feet between the head and tail pulleys*

A speed of 3&0 fpm is

considered the limiting speed, but in some cases 480.fpm is allowed* Sandvlk stainless steel belts are heat resistant, and their smooth dense surface make thorough cleaning possible* Being thin and lightweight, they will utilize less power for driving than is required by conventional rubber belt units* As steel belts do not stretch from wear in service, no takeup is necessary, other than some means to allow for expansion and contraction due to temperature changes*

This Is a substan­

tial saving to be kept in mind when considering capital cost expenditure in an initial mine conveyor installation* of the most important points to be kept In mind when

One consider*

ing steel belt conveyors Is the fact that steel belts are very rigid transvers ally; as a result nearly the whole belt width can be utilized for ore conveying*

Because of this stiffness

of the edges, the Idlers can be spaced quite far apart

• this

results in fewer Idlers being used and a subsequent lower cost outlay*

122

Steel Belt Conveyor Pictorial Section Figure j?0 ; This photograph gives a general view of a steel* belt conveyor and .its different parts* Figure

Sketches A to H and 1 to 6 represent various

designs with reference to the principal layout*

These

sketches show only the general outline of the conveyors* and * only certain elements are indicated* In reality, the conveyors must be furnished with the additional accessories shown in Figure 50,

A conveyor installation is always influenced by

the locality and must in each case be fitted individually* Figure 52: A photograph showing idler details of a steel belt conveyor*

Carrying idlers are set 2 to 6 ft apart, and

return idlers are set 5 to 15 ft apart* Figure 53^ Idler set for a troughed Sandvlk Belt*

Each

idler is by means of its shaft suspended on a pivotable frame so as to adapt itself to the transversal curvature of the troughed belt*

Figure

53*

- Idler

set for

a troughed

Sandvlk

belt

CASE STUDIES OF MINING BELT COHVEYOHS

Each and every mining belt conveyor installation is a separate entity within itself#

Each conveyor installation

has its ovm solution and requirements*

The need, design,

and application for a conveyor system differ from mine to mine, locality to locality —

from orebody to orebody*

Each and every ore conveying problem has two planning cycles which must be developed to insure the proper, efficient use of an ore conveyor installation: the most efficient, prac­ tical method available to solve the ore haulage problem, and the kind of conveyor equipment to aid the solution to the individual problem* On the basis of field examination, discussion with supervisory personnel, and degree of availability of costs and operating data, two case studies are presented: (l) The D* 0* Clark Coal Mine, Superior, Wyoming; (2) The Climax Molybdenum Mine, Climax, Colorado. The D* 0* Clark Coal Mine* Superior, Wyoming The D* 0# Clark Coal Mine at Superior, Wyoming, is one of a series of mines owned and operated by the Union Pacific Coal Company.

This mine is representative of the company-

owned coal mines in the Hock Springs district of ’ Wyoming*

The coal mined Is of a sub-bituminous quality*

It is over-

lain by shale, sandstone and shaly sandstone, with layers of varying depth gradations# The coal mined has oome from * four seams which lay at a pitch of ‘If. degrees* This pitch Is constant for some miles around, even into the Rock Springs area, which is twenty miles distant*

The thickness of the

seams mined varies from 5 to 32 ft, and until very recently the thickest seam has had the greatest pitch#

All seams

outcrop so that the cover starts -approximately at zero, and varies to about 250 ft*

The top is considered good until a

point called water level is reached, after which the top needs more attention* Part of this is caused by Increased A cover# The room and pillar system — driving entries to an established boundary and working oh the retreat —

has proved

the best mining method for the Union Pacific coal, properties* Problem: In 1937# mine management embarked upon a mechanization program to increase the output of mechanically loaded coal#

Because of the length and position of the coal

seams at the D* 0* Clark Mine, the management, when deciding upon the type of main haulageway, had the two following choices: (1) driving a flat rock tunnel to intersect all four pitching seams or (2) constructing and using an Inclined belt conveyance system# Solutions If a flat, straight-line haulage tunnel had been driven to intersect all four pitching seams, an enormous amount of capital would have been required*

The cost factors

*

involved showed the inclined belt conveyor system to be the

125 more advantageous of the two methods considered*

The belt

conveyance unit entailed lower capital costs for initial installation and could be readily adapted to the coal seams* In the final analysis* the building of a rock haulage tunnel would have been prohibitive* Equipmenti This particular belt conveyance system* in­ stalled in 1938 and in continuous operation from then on* can be classified as a main haulage conveyor of the multiple v

belt flight design*

The first belt flight at the bottom

most loading point in the mine workings is 716 ft long; the second section Is 73&

long; the third belt section is

531 it long; and the last belt flight coming out at the portal and discharging the coal into the shaker conveyor on the tipple is 521 ft long*

Each belt flight has a drive section

at the top with the motor directly coupled to the drive pulley* The conveyor belt which Is 250l|. ft long (overall length 2600 ft) is rated at J00 tons per hour haulage from pit to

tipple.

In a double shift (l6 working hours)* the belt has

a maximum carrying capacity of 10*000 tons of coal delivered to the tipple*

The greatest tonnage so far obtained since

inception of the system has been 6600 tons per 16 hours work­ ing time*

The rubber belt is 1^.8 in* wide, and belt speed is

350 ft per minute*

The original belt provided in the installa­

tion is still being used* This particular conveyor system has three transfer sta­ tions and two dump stations*

The transfer stations are so

126 called simply because the coal is transferred from one belt flight to another, while the dump station is so named be­ cause coal from the level overlying the belt conveyor system is ^dumped through a loading hopper at this particular points Thus in reality, the dumping station is both a transfer and a dump point, receiving coal as It does from an overhead level and from the belt flight behind it*

All underground

coal haulage to the belt system is based on the use of pit car transportation along a 60-pound rail system. The .entire belt conveyor system is inclined 10 degrees 18 minutes 2 seconds from the horizontal, and the highest elevation from the gallery floor is approximately 8 ft* Idler units are spaced on 3-ft centers, with a self-aligning idler jilaced between every l£ idlers#

The conveyor rolls

(which make up the idler units) are 18 in# long and 6 in# in diameter, the legs of the conveyor system are made of steel plate and rest on a continuous concrete sill.

The carrying

belt width which actually conveys the coal measures 32 In* In the continuous operation of the belt conveyor system no particular problems In Its operation have been noticed* Oc­ casionally a solitary frog or track switch has got mixed up with the coal^ but an electric eye mechanism

has been devised

to signal the presence of large iron objects, and give warning to the conveyor maintenance man for their removal before they enter the shaker conveyor at the tipple*

Upon the electric

eye signal, the conveyor section In question is automatically stopped and the impediment removed from the belt*

127

The belt conveyor system as outlined In the preceding paragraphs Is an Integral part of the mechanized program the Union Pacific Coal Company started in the D* 0. Clark mine at Superior*

The original investment has been repaid three

times over, and if a similar ore body Were to be developed* a similar belt system would be placed Into operation* Summation* This particular case has demonstrated quit© clearly that a belt conveyor system can be satisfactorily adapted to an or© body*

The belt system is flexible in operas

tlon, Insures continuous loading at all times, and requires negligible maintenance outside of greasing and cleanup on the belt*

128

Climax Molybdenum Mine# Lake County* Climax, Colorado The or© area

of the Climax Mine lies around a dome

/Peele. R.. Mine Engineers Handbook, Section 10. vol. 1# PP« 3p 7~3o 8» Hew York, John Wiley and Sons, I9h8« ,____ of silicified and sparsely mineralized granite; the molyb­ denite occurs in disseminated form, also in veinlets along fracture planes in altered schist and granite.

Block cav­

ing is the main mining method used, and established slush­ ing systems scrape the ore into hoppers, discharging directly into Granby cars in haulage drifts* to the surface.

The cars then proceed

Because the haulage system present was not

capable of sustained production, a proposal was made to trans­ port ore (at minus 12 in*) from the 300 level by means of a ij-238«*ft single-flight belt conveyor system to the surface; the discharge would take place at the crusher plant. The Climax case represents a negative problem in thJe application of an underground belt conveyor system.

The

proposed underground conveyor system was deferred in favor of a haulage tunnel to the surface, then serviced by a surface conveyor belt system to the mill bins*

Because of uncertain

ground conditions, the underground belt conveyor system was not projected into reality* Basically, the case resolved itself into a considera­ tion of positive versus negative factors of the underground belt system*

The first 2$0Q ft of the belt conveyor was in­

clined from 10 degrees to l/ij. degree through rather firm ground, bedrock consisting of granite, schist, grading into

129

sandstone shale and quartz porphyry*

The remaining 1700 ft

of conveyor system was inclined at 16 degrees through till grouikl which consists of boulder, gravel, sand, and clay — * loose end unstable*

If anything went wrong with the till

ground, the conveyor system would be rendered inoperative* The calculated overall savings of 3^ per ton ore haulfed was determined not to be large enough to warrant the use of a belt system, against the possible troublesome conditions of till ground#

From the standpoint of capital expenditures,

the driving of a haulage tunnel where all factors were known was considered less risky than erecting a belt conveyor in questionable ground#

* Problem: The estimated tonnage for the 300 level is ap­

proximately 8? million tons, and the daily production amounts to 15,000 tons of ore in a 3-shift operation*

What would he

the best method of transporting 15,000 tons of ore per day (crushed or uncrushed) from the 300 level of this mine? Solution: The following four solutions were proposed as methods to solve the transport problems* Plan 1* Haulage out an adit to the Arkansas Valley where the ore will be crushed to minus 9 in*, conveyed first to a 2000-ton bin in the

Arkansas Valley, then to a !j.000-ton

storage bin located within the present haulage loop, and finally to the standard cone crushers in present crushing plant* Plan 2* Ore will be crushed to minus 9 in* in an tinderground primary crusher, discharged into a 2000-ton bin below

the crusher, then be conveyed to a l}.000-ton storage bln on surface located within the present haulage loop, and finally to the standard cone crushers in the present crushing plant* Plan 3* Haulage from marshalling yards on the 300 level through an adit up a 2 1/2-percent grade 11,000 ft to a primary crushing plant located on the surface# Ore will be crushed to minus 9 in*, and delivered by belt conveyor to a i|000-ton storage bin on the surface located within the present haulage loop, and finally to, the standard cone crushers in the crushing plant* Plan l^* Haulage from marshalling yards on the 300 level through an adit up a 2 l/2-percent, 11,000-ft grade to the present crushing plant# Table F on page 131# and Table G on page 132 are In­ cluded in this case to show the relative Importance of financial data as an aid in solving the basic ore haulage problem*

13*

Financial analysis: The following estimates of cost of capital expenditures drawn up in support of the plans are direct costs only and do not include supervision, overhead, engineering, *contingencies* TABLE F

Plan

~i— fi. i

0•j

r '~r ■ .it" r

Estimated Capital Coat Expenditures 1 2 3 Arkansas Underground 2-J^ haul*Valley crushing age to crushing and conadditional and con- v eying primary veving crusher —r -- - -j r . . ttiti

r

r*

—

—

—

'

-- —

—

— -—

..... ■

300

level, 552,311). haulage, drift ing, tracks,etO*

637,305

1,135,101

Surface, plant , 1,991,925 yard, crusher, bins, conveyor

3k9,3k0

9l)-6,029

Surface haul­ age, trestle, snowshed

83,1).88

Underground plant crusher, bln, conveyor

- -

Adit haUlage

-

-

--

age to present crushing plant _____ 1,135,101

333,1)^2

213,558

921,282

921,282

1,865,375

- -

21)5,700

Rolling stock, 25 ton loco­ motives Tower control, signal tele­ phone

k.

2g% haul-

_ -

2, 627,737

--

2 ,8 5 2 ,3 2 0

21)5,700

76,500

3 , 6 5 8 , o il ) .

76,500

2 ,5 9 2 ,ll) i

%

132 The following analysis of operating costs and capital expenditures is based on 3 0 0 days per operating year and is a further factor in determining the most practical solution* TABLE Q Analysis of Operating Coats and Capital Expenditures Plan 1 ' 2 3 4 Arkansas Underground 2-g^ haul- 2g$& haulValley crushing age* to age to crushing and convey- additional present and con- ing primary crushing veylng crusher plant 2 J4-.2

23.1

15 1*5

.

13.63

13.1}-

31^83

37.83

38.5

Direct hdlg* , cents/ton

21*9

19.1^

Total clash­ ing and conveylng, cents/ton

13* 85

Total cost, cents/ton

37*75

Total capital expenditure Cost on cap­ ital expendi­ ture, cents/ton Total cost, cents/ton

2*627,727 3.1

40. 83

2 ,8 3 2 ,3 2 0

3.3£

3 8 .2 0

3,658,031).

2,592,11)1

4.3

3.0

1}2.15

1)1.5

133 Application or Plan Zx Loaded trains from the loading drifts will be hauled into the crusher plant where the ore will be dumped directly into a bowl of a 60-in* double dis­ charge gyratory crusher on the 300 level.

The ore will be

crushed to a minus 9 In*, and fall vertically below the crusher into a 2000-ton surge bin*

This bin is designed to

take crusher product for a two-hour period should the conveyor to the surface be shut down* tion during the shutdown*

This will protect the mine opera­

Ore will be drawn from the bottom

of this bin by two 5 ft x 10-ft pan feeders which discharge onto a f$4— 1n* picking belt from which waste wood and tramp iron will be removed*

This

n* belt will discharge upon

\

a vibrating grizzly or other feeding device from which the ore will be loaded on a ij-8-in* single-flight conveyor (no transfer points) and be carried to the surface*

Pneumatic

impact idlers are to be used for belt protection at the load­ ing points*

A welghtometer v/ill be installed near the tail

of the l4-8-in* belt* The ore from the lj,8-in. conveyor will discharge into a 60-ft-diameter cylindrical concrete bln about I4.5 ft deep of I4.OOO tons available capacity*

The top of the bin, at a

little above ground surface, will be covered by a conical steel roof having an opening through which the ore from the conveyor will fall without further distribution*

The carry­

ing capacity of the conveyor would produce the required 15#000 tons in two shifts running time, but storage is not sufficient for capacity production in two shifts*

134

Equipment for Plan 2: The belt system contemplated was a single-flight slope conveyor; the maximum size of ore material to be conveyed determined largely the width of the !j.8-in* belt# A steel cable belt having a tensile strength of l£00 lb# per inch of width was selected for the installation#

Use of this

belt would permit a single head-pulley type of drive#

Other

types of belting were examined but they did not seem to have the necessary tensile strength found in the steel cable belts, which have been in operation about five years on the iron range of the Mesabi District* The single-flight slope conveyor system was based upon the following design data: Horizontal length Vertical lift Belt speed Maximum capacity Maximum Incline ,Weight ore loose Weight ore in place Size largest lump Proportion fines Expected duty Operating temperature

I(.238 ft 3VO ft 4.OO fpm 1250 tons per h o w 16° 15« 37" 100 lb per cu ft l6£ lb per cu ft 10 x 16 x 2l|. in# 15 to 5>0 percent 80.million tons 48° P.

To keep the conveyor below the 300 level out of the ore body and below any 300 level workings, a slope of plus 11 degrees was adapted for the lower 85>0 ft; then a slope of .plus l/ij. degree was extended until it intersected a l6-degree slope from the top of the if.000-ton bin on the sur­ face#

A drift from the 300 level v/ill connect to the conveyor

gallery near the southwest corner of the ore body and a 36-in#-gauge track is to be run the full length of the con-

135

veyor gallery for handling supplies*

The conveyor gallery

will be lighted by lights spaced every 25 ft*

These lights

are to be energized from the trolley wire serving the track in the gallery*

Control buttons for starting and stopping

the conveyor will be spaced every 200 ft the full length of the gallery* upward*

Ventilating air movement In the gallery will be

Hoists will be Installed at the top of the steep

sections for handling cars to the tail of the conveyor or to the surface* Drive machinery: The drive machinery for the belt will be located at ground level In the housing near the head end of the conveyor*

The necessary horsepower to drive the

ijfWin* belt will be provided by three Identical 250-hp units placed one on each end of the primary drive pulley shaft and one only on the secondary drive pulley shaft*

The drive Is

of the tandem pulley design with the head pulley snubbed about 2i|X> degrees*

See Figure

for details*

Carrying run

Return run

Figure

• Proposed drive for Climax belt

Management Vs Analysis of Plan 2* In the capital cost for this plan, the greatest uncer­ tainty lies in the cost for underground excavation and con­ crete*

The degree of ground control exercised for efficient

belt conveyor Installation may greatly enlarge the original capital expenditure cost*

Experience with long-length high-

lift conveyors using steel cable belts appears to be satis­ factory as indicated by the extension of their use on the Iron Range in Minnesota*

Steel belts generally exceed their

expected-life duty* Basically, the advantages inherent in this plan are as follows: (a) ore haulage by belt conveyors has a good reputa­ tion for safety; (b) this plan will be less affected by weather conditions; (c) no heating will be required In the conveyor gallery* Some of the disadvantages may be listed as follows; (a) the plan will result in higher pay for operators and a shorter working shift; (b) supervision will be more difficult than would surface supervision; (c) difficulty will be experi­ enced In transporting heavy crusher parts and supplies through the mine openings; (d) removal of waste wood and tramp Iron will be more costly than for surface operation; (e) salvage value of the equipment will be greatly decreased by Its position underground* Final Summation of Case Plan 2: This plan concerned Itself mainly with under-

ground crushing and conveying*

Capital expenditure for this

plan is §22l4*593 greater than for Plan 1*

There is a greater

chance for error and possible difficulties of installation in this plan than in Plan 1*

The operating cost is 2*9

cents per ton less than Plan 1*

The operating, plus capital

expenditure is 2*6f> cents per ton less than Plan 1*

On

15*000 tons a day, this would be #397, or about §11*9,000 annually* Plan 1*

This plan concerned itself mainly with a surface

conveyor system*

The capital expenditure for this plan is

§22J4.*593 lass than Plan 2, and these estimated costs are more accurate than those of Plan 2*

Operation costs are 2*9 cents

per ton greater* Y/ith the uncertainty and lack of flexibility in Plan 2, it appears advisable to accept the increased operating cost of Plan 1*

CONCLUSIONS

At the present time there are few underground metal mines which make use of mining belt conveyors, wholly or in part, for underground ore transportation*

As far as

conveyor belt usage Is applied to metal mining, the application of its use is so new that no definite con­ clusions for Its evaluation can be determined#

It is

known that belt conveyor transportation can be efficiently and economically applied where proper conditions exist — conditions that depend upon the character and formation of the orebody, and the mining methods used#

When develop­

ment, in the form of insuring dally ore production quotas Is undertaken, and reserve tonnstges are calculated —

when

Underground mining operations are fully coordinated (from the drilling operation to the haulage operation) —

only

then will it be worthwhile to calculate the economies re­ sulting from the use of raining belt conveyors# The mining method swiftly fades into the realm of obscurity when the ore Is blasted from a working face, or caved in stopes#

This moment of instantaneous release

into a free state brings into immediate focus the ore conveyance problem#

Np to the preseiit time the metal min-

139 lng industry has attempted to solve the ore transportation problem by the use of hoisting methods, motor-hauiage methods, and a combination hoisting-motor-haulage approach* Today1s economic conditions in the metal mining industry demand a new approach to ore handling and recovery under­ ground*

Applying conveyorized transportation methods to

yQQovery and handling of mass mineral tonnages is a logical approach to today1s and tomorrow's mineral problems* The recovery of mineral from heretofore unprofitable ore bodies can add immeasurably to the total extraction of ores in the fast diminishing domestic supplies by the application of an improved mineral handling program* Conservatism and prejudice against new mining innova­ tions in metal mining must give way to logic, experiment, planning, and adaptability of new mechanical machines, one of which is the mining belt conveyor*

LIBRARY Co l o r a d o s c h o o l o f

mines

BOLDEN# COLORADO

li*0

BIBLIOGRAPHY

Ball Beamings for Conveyor Systems: New Departure Division, General Motors Corp., Bristol, Conn*, 19q-9* Barber-Green© Min© Conveyors: Book no* 66, Aurora, Illinois, 19^7* Belt Conveyors: Catalog no* 785# I1 **® Jeffrey Mfg. Co*, Columbus, Ohio, 19^7• Belt Slope Guts Colliery Costs: Coal Age, pp* 78-82, May 19JJ-9* Bigelow, R* S*, Progress in' Mechanical Loading: Can* Min* and Met, Dull*, vol* 2l\.$ pp* 822-835* July 1931* Brinton, C* P*, Conveyor System at Barnesboro Minos: Min* Cong* Jour*, vol# 21, pp* 27-29# April 193?* Bull Shoals Dam Conveyors: Pit and Quarry, pp* 90-93# 102, September 19^9* Cannon, J. M*, Simpson Creek Collieries' Company: Min. Cong.

Jour*,, vol# 27, pp. 36-39# August 191*1# Claghorn* C# R** Conveyor Mining: Min. Cong. Jour., vol. 21, p. 4S* July 193?. Cooley, L. M*, Hilltop stripping in Boutt County: Mines sine* vol* 38* no# 8, pr>. 13-15# and 1|2, Axigust Cutler, C* R*, Mechanization and Labor In the Mineral Industries: Mines Magazine, vol. 30, no. 3, pp. 116-118, March 191*0#

Gardner, E* D#, Metal Mining Haulage: Mining and Metallurgy, vol* 186, no. 3, p. 6l, March 19lj.9* Given, I# A#, Mechanical Loading of Coal Under ground, p. 397# New York, McGraw-Hill Book Company, Inc#, 191*3•

ilia

Haworth* R# G*# Kriell# R* R*# Edmunds# J*# Belt Conveyors Tor Gathering Haulage; I;!In* Cong# Jour*# val* 33# pp# 26-29 and Ip.# October 19£f-7* Hayashl#. M*# Construction of Belt Conveyor System and Coal Tipple in Boutt County; Mines Magazine# vol* lj-0# ho* 1# January 1950# Betzel# F* V## Albright# R* K*# Belt Conveyors and Belt Elevators# 3d ed## p* i|39# Bow York# John Wiley and Sons# 1914Holt, G-* J#, Open Pit Mining on the Iron Ranges~19l|9 * Mining Engineering# vol# 187# no# 1# January 195°* Bowat# Dr# D* D*# Britain's Iron Mines and. Problems: Engin­ eering and Mining Jour*# vol# 15°# PP* 7^-77# May 1914*9* Hudson# W# G## Conveyors end Belated Equipment# 2nd ed*# / p* I4.08# Hew York# John \7Iley cc Sons# 19149* j Jackson# C* F*# Gardner# F# D## Top Slicing; IT* S* R*r* Mines# Miners * Circular $2, pp# 22-23# X9li-5* Lambly# Chas# A* R*# A Hew Incline In the Met aline District; Mining Transactions# vol# 10k# pp* lj.29-ii-32# December 19!{9* Long#. A# E*# Conveyor Mining: Min* Cong# Jour*# vol# 35# pp* 56-58# December 19q9# liarshall# I# M## Mechanization In Canadian Gold Mines: Canadian Mining Journal# vol* 7°# no* 7# PP* 62-65# July 1914-9# McGuire# T* W* Conveyor Mining in Multiple Shifts; Min* & Cong# Jour*# vol* 27# pp* 22-23# July 19ip-* Meador# H* V/## Reversing Conveyor Belts; Min* Cong* Jour*# Vol* 26# no* 3# pp# 1^9-51# March 195°* Mechanisation; Min. Cong* Jour*# vol* 23# P* 29# July 1937* Mercier# 3* M*.4Belt Conveyors: Engineering and Mining Jour## vol* 151# no# 1# pp* 70-Sl# January 195°* Mollard# E# S## Reese, H#.E*# South Agnew Stripping Scheme XJnique In Mesabl Practices Engr* and Min* Jour*# vol* I48# no* 8# pp* 71-7!]., August 191x8* Hielson# A* # Planning and Mechanizations Mine and Quarry Engr*# vol* 9# no* 9# pp* 211-212# and 2II4,* September ^*^4^

Peele# R** Mining Engineers Handbook# Secitlon 10# vol* 1# pp# 4 1 7 ^ 2 1 # Hew York# John Wiley and Sons# I9 I48 * Philips# Wi E*j Belt Conveyors in Metal Llinlng: Min* Cong* Join?*# vol* 28# pp# 2 4 -2 6 # June 19^*2# Piokel* L# W* # Jenne# C* A*# Salient Features ofthe Cherry Hill Mine in Western Kentucky: Min* Cong# Jour# # vol# 27 pp# 15-17# June 1 9 4 I* Rausch# R* W*# Continuous Ore Transports ■Mining and Metal­ lurgy# vol# 184* nd* 12# pp* 590-595# December 194?* Rex Conveyors: Catalog no*

445#

Chain Belt Company*

Milwaukee# Wisconsin# 1945* Roberts# W* F*# Controlling Belt Conveyors: Coal Age# vol# 55# no# 2# pp* 97-101* February 1950# Robinson# c** Latest Developments in Belt Haulage, American Mining Congress# Ohio# May 1949* Robinson* C## Underground Belt Transportation; Mining and Metallurgy# vol# 1 7 8 , no* 11* pp# 535-538# November

194^*' Sandvik Steel Belt Conveyors# Sand vile steel Inc*# Conveyor Dept*# New York* 1949* Sawitske# B« A#* Modern Trends of Mineral Handling; Hines Magazine# vol# 3 C# no* 1# pp* 485-489# September 194 O# Smith# M* A*# Tomorrov/1s Mining Methods: Engr* and Min* Jour* * vol* II4.0 # pp* 33-37# March 194c* South Agnew Stripping Practice: Mining World# vol* 12# no# 3# PP* 36-39# 6l* March 1950* Staacke# C* W** Traxler# E* R»# Engineering Rubber Conveyor Belting# B* F* Goodrich Company# 1947* Stainless Belt Conveyor: Iron Age# vol* 164# p* 118* August 1949* Standards for Mining Belt Conveyors# Pub# no# 49-142# pp# 2—18# New York* National Electrical Manufacturers Association* February 1949# Stephens—Adamson Belt Conveyors* Catalog no* 146* S* A# Mfg# Co## Aurora# Illinois*'1946* Strong Fight Looms on Controversial Belt Conveyor System from Erie to Ohio: Iron Age* vol* 164# PP* 136-137# March I7 * 1949*

Thompson# C* W. # Transportation Problem Solved at New 171 erton Mine: Min. Cong* Jour** vol* 35# PP# 29-33# November 1949# 7/orId* s Longest Belt Conveyor Will Reduce Transportation Costs In the American Rhur: Engr. and Min. Jour.# vol. 150# no. 3# p. 94# March 1949. Young# L. E.* Mechanization for greater productivity and lower costal Min. Cong. Jour.» vol. 34# PP* 16-21* January 1948. Zem, B. N#* Power Transmissions Coal Miners1 Handbook# 12th ed*# pp* 392 and 483# Hew York and London* McGraw-Hill Book Company# Inc.# 1928*

LIB RA RY fcOLORADO SCHOOL OF MINES GOLDEN, COLORADO