Belt Conveyor K. Pathak The belt conveyor is an endless belt moving over two end pulleys at fixed positions and used for transporting material horizontally or at an incline up or down. The main components of a belt conveyor are: 1. Th The belt that that form formss the the movi moving ng and and supp suppor orti ting ng surf surface ace on whic which h the the convey conveyed ed material material rides. rides. t is the tractive tractive element. element. The belt belt should should be selected considering the material to be transported. !. The idlers" which form the supports for the carrying and return stands of the belt. #. The pulleys that support and move the belt and controls its tension. $. The drive that imparts power to one or more pulleys to move the belt and its loads. %. The structure that supports and maintains the alignments of the idlers and pulleys and support the driving machinery. machinery. &ther components include: 1. Loading chute or feeder chute that organises organises the flow of material material and directs it on the belt conveyor. !. Take-up-device whic which h is used used to main mainta tain in the the prop proper er tens tensio ion n of the the belt belt for for effective power transmission. #. Belt cleaner that that keeps the belt free from materials sticking to the belt. $. Tramp removal device " which is optionally used in case the conveyed material bears the chance of having tramp iron mixed with it and subse'uent subse'uent handling of the material" demands its removal. %. Continuous weighing device for constantly measuring the load being carried by the conveyor belt. (. Discharge chutes to guide the discharged pro)ectile to subse'uent conveyor or other receiving point. *. Surge hopper hopper and feeder " which is essential for supplying material to the conveyor at uniform rate when the supply of material is intermittent. +. Tripper Tripper arrangement to discharge material at different point or to other device.
Application ,onveyor belts are widely used in mineral industry. -nderground mine transport" opencast mine transport and processing plants deploy conveyor belts of different kinds to adopt the specific )ob re'uirements. The main advantages of conveyor belt system are: 1. wide widerr range range of mate materi rial al can can be hand handle led d whic which h paus pausee prob proble lems ms in othe otherr transportation means. /elt conveyor can be used for abrasive" wet" dry" sticky or
1
dirty material. The lump size of the transported material is limited by the width of the belt. /elts up to !%00 mm wide are used in mining industry. !. igher capacity can be handled than any other form of conveyor at a considerably considerably lower cost per tonne kilometre. ,onveyor belts with capacity of 11000t2h and even higher can be deployed to match with higher capacity mining machinery. #. 3onger distances can be covered more economically than any other other transportation system. single belt conveyor or a series of belt conveyors can do this. /elt conveyors can be adopted for cross4country laying. $. /y the use of many forms of ancillary e'uipment such as mobile trippers or spreaders bulk material can be distributed and deposited whenever re'uired. %. 5any other functions can be performed with the basic conveying like weighing" sorting" picking" sampling" blending" spraying" cooling" drying etc. (. 6tru 6truct ctur ural ally ly it is one one of the the ligh lighte test st form formss of conv convey eyin ing g mach machin ine. e. t is comparatively cheaper and supporting structures can be used for many otherwise impossible structures such as crossing rivers" streets and valleys. *. The The belt belt conv convey eyor or can can be adop adopte ted d for for speci special al purp purpos oses es 7fire 7fire resist resistan ant" t" wear wear resistant" corrosion resistant" high angle negotiation etc.8 and can be integrated with other e'uipment. +. t can be horizontal" incline incline or decline or combination combination of all. 9. 5inimum labour is re'uired for the operation and maintenance of belt conveyor system. 10. n undergroun underground d mine mine transport" transport" belt conveyor conveyor can be used in thin seams as it it eliminates the rock works that might otherwise be re'uired to gain haulage height. 5oreover" 5oreover" belt conveyor conveyor can provide provide continuous continuous haulage haulage service service from pit bottom bottom to the surface.
The limitations of conveyor belt are: 1. The loading loading and transfer transfer points points need to be properly properly designed. designed. !. umbers umbers of protective protective devices devices have to be incorporated incorporated to save the belt from getting getting damaged by operational problems. #. The belt needs needs higher initial initial tension 7$04!00 7$04!00; ; of useful pull8. pull8. $. The The use use of belt is restr restric icted ted by the the lump lump size. size. f the the maxi maximu mum m diag diagon onal al of a irregular lump is X is X then then the belt width 7/8 is approximately given by: B ≥ Xa + !00
where" /: /elt width" mm <: 3ongest diagonal of irregular lump" mm a: =actor to account for grading. a is taken as !.% for graded material and # for un4graded material. owever" for particular material these values must be properly estimated. %. ,onveying ,onveying of sticky sticky material is associated with problems problems of cleaning cleaning and discharge discharge causing poor productivity.
!
(. igher elongation of the belt 7$; elongation may take place at the working load8. 6ome of the applications of belt conveyors are shown in =igures below:
3evel or inclined ,onveyor receiving material at tail end and discharging at head end.
3evel ,onveyor receiving material at any point through travelling opper and discharging at head end.
3evel and inclined ,onveyor receiving material at and near tail end" having vertical curve to incline" and discharging at head end.
#
3evel and inclined ,onveyor with chute. 5aterial received from bins too close to elevated head end to permit use of vertical curve.
nclined and level ,onveyor receiving material at tail end and discharging from level section through a movable Tripper.
3evel ,onveyor on raised structure with double4wing Tripper forming storage piles on both sides of ,onveyor.
$
nclined ,onveyor receiving material at tail end and discharging at several points through a series of fixed Trippers.
3evel ,onveyor with 6tacker or /oom ,onveyor mounted on revolving turntable so as to discharge to both sides of ,onveyor.
INFORMATION REQUIRED TO DESIGN A BELT CONVEYOR 1. 3ength of conveyor from centre to centre of end pulleys. !. nclination4level or inclined. >ither degree of inclination" or distance to be lifted or lowered. #. verage capacity per hour. $. 5aximum capacity per hour. %. 5aterial to be conveyed" and weight per cubic foot. (. verage size of material. *. 6ize of largest pieces and percentage in feed. +. 7a ) ature of material 4dry or wet 7moisture content8. 7b8 brasive or corrosive? 9. ow material is to be fed to the belt and particulars of feed point or points. 10. ow material is to be discharged from the belt i.e. overhead pulley or by trippers" and particulars of discharge points. 11. @eneral indication of supporting structure.
%
1!. Power available for driving. f by .,. electric motor" state voltage" phase and fre'uency. f A.,. motor state voltage. tems 1 and ! determine the suitability of belt conveyors" since inclination is a limiting factor. tems 14* determine the speed and width of the conveyor belt" the power needed for the drive" the type of drive" the number of belt plies" size of pulleys" shafts and spacing of idlers. tems +410 determine the 'uality and thickness of the rubber cover on the belt.
Suitability o a B!lt Con"!yo# Table shows the maximum safe inclination for troughed belt conveyors handling various bulk materials and for convenience" chart shows the rise in feet corresponding to the horizontal distances at various angles of inclination. 5aterial
ngle
Bise in 5aterial m per 100 m
ngle
Bise in m per 100 m
,ement43oose
!!C
$0.$
,oal4/it 6lack
!#C
$!.$
,lay4=ine Ary
!#C
$!.$
,oal4nthracite
1(C
!+.(
,lay4Det
1+C
#!.%
,oke oven run
1+C
#!.%
,oal45ine Bun
1(C
!+.(
,oke46ized
1(C
!+.(
,oal46ized
1(C
!+.(
,oke4/reeze
1+C
#!.%
,oncrete4Det
1%C
!(.+
&re46ized
1+C
#!.%
>arth43oose
!0C
#(.$
Packages4Paper Drap.
1(C
!+.(
@lass4/atch
!1C
#+.$
Bock4=ine ,rushed
!!C
$0.$
@rain
1(C
!+.(
Bock45ixed
1+C
#!.%
@ravel4/ank Bun
1+C
#!.%
Bock46ized
1+C
#!.%
@ravel46creened
1%C
!(.+
6alt
@ypsum4Powdered !#C
$!.$
6and4Ary
1%C
!(.+
lime4Powdered.
!#C
$!.$
6and4Aamp
!0C
#(.$
limestone
1+C
#!.%
6and4Tempered =oundry
!$C
$$.%
&re4=ine
!0C
#(.$
6ulphur4 Powdered
!#C $!.$
(
!0C
#(.$
&re4,rushed
1+C
#!.%
Dood4,hips
!r %0.94 @
6hould the horizontal distance be more than sufficient for the re'uired rise" it may be more economical to run the first section of the conveyor horizontally" and incline it upwards at the discharge end" rather than use a smaller angle of inclination for the entire length. n such a case" the transition from the horizontal to the inclined sections must be made by a vertical curve" to ensure that the belt does not lift off the idlers.
B!lt Con"!yo# Typ!$ This type of conveyors is installed for the life of Permanent: the mine. They are used in main line" slope" long overland installation" preparation plants and stockpiles. Portable: These are characterised by relative ease of assembling and disassembling to facilitate advances and recovery in development and retreat operations in underground mining. Portable conveyors mounted on crawler or wheels are also used in mechanised 'uarries and surface mines. Shiftable: -sed in continuous surface mining this type of conveyor is mounted on skid or supporting structures aligned together and the whole can be shifted transversely to follow the advancing working face. High Angle Conveyor: These are special type of conveyor belt arrangement used for negotiating steeper angle of inclination. 6uch belts can work in slope up to *04+0 0. 6andwich belt conveyor is a type of such belt conveyor. Cable Belt Conveyor: Dhere the belt is carried on moving wire ropes and the tractive force is applied through the rope to the belt is known as cable belt conveyor. 3,& 7in collaboration with =rance8 is using such system for long distance conveying of bauxite in their mines in &rissa.
D!$c#iption o Co%pon!nt$ Belt The belt consists of a carcass covered from all sides with a filler material like PE, and neoprene as shown in =igure 1.
*
Top ,over 7,arrying 6ide8
>nd ,over
>nd ,over
,arcass /ottom ,over 7:on4,arrying 6ide8
=igure 1 ,onstruction of conveyor belt. Essential Properties
The belt works as a tractive element as well as load4carrying element. t may be used for different kind of material transportation at a higher speed 7 (4+ m2s8. =or this purpose the belt need to have the following essential properties: 1. !. #. $. %. (. *. +. 9.
=lexibility Transverse rigidity 3ow mass per unit length igh strength 6implicity and inexpensive 3onger life 6hould not stretch under normal working stresses "i.e." low relative elongation. Dear resistant =ire resistant
Becommended maximum belt speeds are given as shown in Table 1
6peed 7m2sec8
6peed 7fpm8
Didth 7mm8
Didth 7inches8
$00
$%*.!
1+
(00
(09.(491$.$
!$4#(
+00
10((.+41%!$
$!4(0
%.0+
1000
1+!+.+4!$1#
*!49%
1.**+
#%0
$%*.!
1+
!.%$
%00
(09.(491$.$
!$4#(
#.0$+
(00
over 91$.$
over #(
,oal" damp clay" soft ore" !.0#! fine crushed stone" &ver #.0$+ burden and earth $.0($
eavy" hard" sharp edged ore. ,oarse crushed stone
The carcass can absorb the longitudinal tensile stresses and make the belt rigid transversely. =iller protects carcass against moisture" mechanical damage" abrasion and combine the carcass into an integral body forming top cover and bottom cover. The filler can be synthetic rubber or polymer like PE, with ade'uate additives for
+
getting particular expected characteristics. The carcass can be a fabric type with plies of fabric or steel chord type. fabric ply has a longitudinal thread called warp and a transverse thread called weft. The fabric plies are made of capron" nylon or lavsan etc. The longitudinal member of the carcass transfers the tension. /oth the warp and weft carry the load via the cover. The cover while protecting the carcass from external damage bear the impact and abrasion at the feeding points and wear at the cleaning points. =igure ! shows the cross section of the types of conveyor belt.
T o p , o ve r
/ ot to m , ov e r
Bubber nterply
Figure 2 ,ross section of a multi ply conveyor belt.
The belt ends are )oined together by mechanical means or by vulcanising. The belt needs to be protected from damage of its sides that may occur due to sway of the belt. n case of belt carrying wet sticky material fixtures for cleaning the belt should be properly selected. 5aterials coming on to the return side of the belt needs to be arrested from coming under the end pulley by ade'uate scrapers. s shown in the =igure $ belt cleaners are used to clean the return side of the conveyor belt. These cleaning belt can be of E shape as well.
Figure 3 /elt scrapers
s shown in the =igure #7a8" the pow bladeFs !0C leading edge GspiralsG debris off the return4side belt surface. There are specially designed belt cleaners for the tail pulley" they are engineered to clean the inside of the belt so rocks" lumps and other debris never get the chance to damage the pulley" belt" splices or lagging. ormally plows are easy to install on virtually any conveyor structure" and come with universal mounting brackets. Though there are suppliers of such scrapers" these can be fabricated at the mineHs workshop. The diagonal deflector plow 7=igure #a8 is installed on a $%C angle across the belt to discharge debris to one side of the belt. n such cleaners the blade is installed in a fixed position" eliminating bouncing problems associated with some floating style plows.
9
Twin4bladed plow 7 =igure #b8 is designed to clean belt in both directions of travel. This cleaner discharges material to either side of the belt. t is installed securely to conveyor structure and can work on conveyors with severe belt vibration. CONVEYOR BELT FASTENERS
&ne of the important components that re'uire attention in maintaining services of belt conveyor is the conveyor belt fasteners. 6election of fasteners should consider re'uired performance" expected life and ease of installation and maintenance so that higher availability of the belt conveyor is ensured. There are different types of fasteners. 5echanical fasteners are commonly used in underground coal mining. The re'uired rating of the mechanincal fasteners is calculated based on the re'uired belt tension and it may be upto !(# k2m of belt width. &ne such fastener is =lexcoI 6BJ 6calloped >dgeJ BB+ belt fastener" designed for use on mainline and panel belts with mechanical fastener ratings up to 1"%00 PD 7!(#k2m8. The +4rivet pattern" along with the scalloped edge design" ensures 'uality performance in high4tension applications.
Figure $ 5echanical /elt )oint
=asteners are available with self4setting rivets which allow to install 'uickly from the topside of the belt. 5ost important in belt fastening is to take care that the plates must be accurately positioned to get perfect edges and stress distribution should be uniform along the )oints. >ffectiveness of maintenance will be enhanced by provision of ade'uate and improved tools for carrying out the )ob. 5anagement should encourage innovation of workers for making work tools or improvement of work environment and safety.
Idlers n a conveyor belt installation different types of idlers or roller supports are used. The idlers are re'uired for proper support and protection of the belt and proper support of the load being conveyed.dlers are designed with different diameters and are provided with antifriction bearings and seals" and are mounted on shafts. =rictional resistance of idlers influences the belt tension and conse'uently the power re'uirement.
10
dlers are mounted on a support frame" which can be shiftable or permanent. The carrying side of the belt is supported on the carrier rollers sets. set of three rollers are arranged to form a trough for the troughed belt conveyor. The return side of the belt is supported on straight return idlers. The spacing of the idlers is determined based on the belt sag between the idlers. The sag depends on the belt tension" belt width" belt properties and the pay4load per meter of the belt. The idlers are specified by its length and diameter. These parameters are selected based on the re'uired belt speed for the particular width of the belt.
Figure 5 Aifferent types of roller supports
11
Figure 6 6elf aligning idler
dlers are classified as shown in Table ! Table ! dler ,lassification. ,lassification
Aiameter 7inches8
/elt Didth 7nch8
Aescription
/$
$
1+ $+
3ight duty
/%
%
1+ $+
3ight Auty
,$
$
1+ (0
5edium Auty
,%
%
1+ (0
5edium Auty
,(
(
!$ (0
5edium Auty
A%
%
!$ *!
5edium Auty
A(
(
!$ *!
5edium Auty
>(
(
#( 9(
eavy Auty
1!
>*
*
#( 9(
eavy Auty
,losely spaced impact idlers with rubber cushions are used the support the belt at the loading point" below the skirt board. =igure *. A6,1.B@> 1&&A
TBPP>B
6KBT /&.BA >:A P-33>L
6,B.P>B
>:A P-33>L
5P.,T A3>B6 />:A P-33>L 6:-/ P-33>L
,.BBL:@ A3>B6
B>T-B: A3>B6
/>3T ,3>.:>B
@B.ETL T.K>4-P
Figure 7 ,omponents of belt conveyor
6elf aligning idler set is used infront of the loading point. This set of idlers can rotate on a horizontal plan depending on the belt sway and restores true running of the belt. /elt training idlers should be spaced 100 to 1%0 feet apart and at least one such idlers should be used on conveyors less th'an 100 feet long. 6uch idlers are not used in the areas of belt transition. =ixed guide rolls placed perpendicular to the edge of the conveyor belt are not generally recommended as they cause edge wear and reduce belt life. &ffcentre running of the belt occurs when the belt loading is not proper. @arland type idlers assist true running of the belt under difficult loading conditions. n this type of idlers the idlers are connected to form a string. The connections are through universal type coupling that allows each idlers to rotate about its own axis independently. @arland idlers are available as two roll" three roll or five roll units. ormally two4roll units are used as return idlers and three4rolls or five4rolls units are used in carrying idlers. /elt weight" material weight" idler load rating" belt sag" idler life" belt rating" belt tension and radius in vertical curves determine the spacing of idlers. 6ome suggested normal spacing are shown in Table #. Table 3 dler spacing
/elt Didth 7inches8
Troughed dler 6pacing
Beturn dler
Deigh of 5aterial andled 7lbs2cu ft8 #0
%0
*%
100
1#
1%0
!00
1+
%.%
%.0
%.0
%.0
$.%
$.%
10.0
!$
%.0
$.%
$.%
$.0
$.0
$.0
10.0
#0
%.0
$.%
$.%
$.0
$.0
$.0
10.0
#(
%.0
$.%
$.0
$.0
#.%
#.%
10.0
$!
$.%
$.%
$.0
#.%
#.0
#.0
10.0
$+
$.%
$.0
$.0
#.%
#.0
#.0
10.0
%$
$.%
$.0
#.%
#.%
#.0
#.0
10.0
(0
$.0
$.0
#.%
#.0
#.0
#.0
10.0
*!
$.0
#.%
#.%
#.0
!.%
!.%
+.0
+$
#.%
#.%
#.0
!.%
!.%
!.0
+.0
9(
#.%
#.%
#.0
!.%
!.0
!.0
+.0
Pulley conveyor belt system uses different types of pulleys like end pulley" snub pulley" bend pulley etc. as shown in the =igure #. The end pulleys are used for driving and sometimes for making tensioning arrangements. 6nub pulleys increase the angle of wrap thereby increasing the effective tension in the belt. The pulley diameter depends on the belt width and belt speed. Pulleys are used for providing the drive to the belt as well as for maintaining the proper tension to the belt. 5inimum transition distance as shown in Table $ should be followed while placing idlers in front of pulleys.
Table Becommended minimum transition distance Troughing angle
!00
#%0
! "ate# Ten$ion
Fabri% Belt
Fabri% Belt
&for half trough #e'th()
&for full trough #e'th(
Steel Cor# Belt
Steel Cor# Belt
&for half trough #e'th()
&for ful trough #e'th(
M90
0.9b
!.0b
(0 90
0.+b
1.(b
1.(b
#.!b
N(0
0.(b
1.!b
1.ob
!.+
M90
1.(b
#.!b
#.$b
(.+b
(0 90
1.#b
!.$b
!.(b
%.!b
1$
$%0
N(0
1.0b
1.+b
1.+b
#.(b
M90
!.0b
$.0b
$.0b
+.0b
(0 90
1.(b
#.!b
#.!b
(.$b
N(0
1.#b
!.$b
!.#b
$.$b
6nub pulleys may be fitted in as shown in the following figures:
3oose 6nub
Tight 6nub Figure *
The angle of wrap is increased by using tandem drive as shown in =igure below:
Figure + Tandem drive
Drive /elt drive is provided normally at the discharge ends" however" it may be provided through the head end or through intermediate pulley by coupling the pulley shaft to the reducing gearHs output shaft. The coupling is selected based on the load characteristics and applications. =lexible coupling or fluid couplings are often used. Earious drive arrangements are shown in the =igures below:
Take-up The purposes of take4up are: 1. To allow for stretch and shrinkage of the belt. !. To ensure that the minimum tension in the belt is sufficient to prevent undue sag between idlers.
1%
#. To ensure that the tension in the belt in the rear of the drive pulley is sufficient to permit such pulley to transmit the load. There are different types of take4up systems as shown in the =igures below:
Figure ,- 6crew take4up
1(
1*
Figure ,, @ravity Take up
Conveyor Support The support of conveyor is normally a structural frame. Aepending on the situation the structure can be mounted on floor or on skid. The main )ob of the support is to let the belt run without getting skewed. Aepending on situations the support can be made moving type. n such cases idler a wheel mounted or crawler mounted platform keeps the necessary provision to support the idlers on which the conveyor runs.
BELT CONVEYOR MAINTENANCE /elt conveyor system can serve economically provided it is maintained well. 5aintenance of this system involves number of routine works. nspection of the various components and initiating timely repair or servicing of these components in case any default is noticed is of premier importance. To maintain a belt conveyor system following items must be carefully looked into:
Belt cleaners, /elt cleaners are re'uired for both the carrying side and the non carrying side of the belt. 5aterial falling on the non4carrying side of the belt needs to be arrested before it get traped in the tail pulley to cause damage to the lagging and sway of the belt. The carrying side needs cleaning when carried material is sticky in nature. To deflect the material coming on the non4carrying side deflector belt plows are used. 6uch plows can be selected from number of available sources or can be locally made considering that the rubber used in it should be softer than the surface of the belt conveyor. t must be easy to install and maintain.
Belt trainers /elt trainer is a device that helps true running of belt conveyor. t prevents off4center loading and belt mistracking. The belt trainers are also called self aligning idlers designed with a pivot and tilt action. They can immediately centre and control the misalignment problems of a running belt.
1+
Skirt clamps, Skirt clamps are used for eliminatin loadin point spillae at t!e con"e#or loadin and transfer points$ T!e skirt ru%%er used for t!is s!ould %e selected considerin its !ardness &it! respect to t!e top co"er of t!e %elt$ As it &ill %e re'uirin ad(ustments after &ear so t!e fi)in arranement s!ould %e simple* easil# accessi%le and less time consumin$
Pulley lagging Pulle# lains are necessar# for %etter traction and to eliminate %elt slippae$
CONVEYOR BELT MAINTENANCE TOOLS To sa"e time and mone#* and to simplif# routine %elt maintenance procedures* proper ser"ice and maintenance tools s!ould %e procured$ Some e)amples are+
,-LT.PLE R.VET /R.V.N0 TOOLS
This tool is used for mechanical belt fastening. 7 =lexco produces 56BT A 56BT+ 8.This easy4to4use" portable tool makes multiple rivet driving simple and fast. 6ome tools have drive rods that can drive five rivets simultaneously. BELT C-TTER
/elt cutters are designed to enhance operator safety. 6ome belt cutters are chain4 driven" double4edged safety blade and are shielded from operator contact. 6uch blade can be driven from either end of the cutter and cuts in both directions.
B!lt &#ot!ction Cont#ol$ There are number of devices provided for protecting conveyor belt system. These are: 1. /elt alignement control: /elt should be aligned with the drive pulleys and the carrying and return idlers. /elt alignment sensors are typically positioned along the edges of the conveyor fabric. They are usually at the discharge and at the loading zones" however can be distributed over the length of the conveyor. 6witches consists of "oller S.it%he$/ 0imit S.it%he$/ Pro1imity S.it%he$/ Photoele%tri% S.it%he$/ et%) Dhen the edge of the belt trips the alignement switch for a timed period" the conveyor is halted. n steel cord belts edge tracking is done by using alignment sensors. This helps to get signature of tension distribution within the carcass which in turn does the condition monitoring. !. /elt &verload: The electric drive motor has overload protection. The motor overload can be a simple bi4metallic or melting eutectic alloy or a complex computer based motor4thermal model. 6ometimes belt weigh scales are also used for overload protection. #. /elt 6lip: /elt slip is the loss in traction of the drive pulley7s8 to the belt cover. /elt slip can destroy a belt or drive pulley. /elt slip protection provides a belt drive speed sensor that compares the present belt speed with the belt intended speed. =or constant speed belts belt slip monitoring is done by a slip switch with a setpoint that trips the conveyor drive when the belt speed is below +0; of full speed. The belt slip switch is bypassed during starting and stopping.
19
=or variable speed conveyor belt slip monitoring consists of a speed sensor that measures the belt speed and compares with the speed reference sent to the drive system. Dhen the belt speed is below +0; of the intended speed the conveyor drive is tripped. method to ad)ust and test belt slip is normally provided in the belt control system. $. Take4up &vertravel : &vertravel limit switches can be placed at the far extremes of the counterweight or take up device travel. n a gravity counterweight take4up" the top overtravel switch trip may suggest a )ammed conveyor belt condition. bottom overtravel switch may indicate belt stretch" or a broken belt fabric flight. >xcessive take4up motion during starting and stopping indicate that the type of drive control is either inade'uate or that is not working properly. %. Transfer ,hute Plug: f the conveyor transfers material through a transfer chute" the transfer chute plug monitors blocked flow as blocked flow may damage the conveyor belt. -nder blocked condition the transfer chute plug switch trips the conveyor drive. (. /in 3evel ,ontrol: f the conveyor belt is used to fill bins or stock piles over dumping may damage the belt. /in level sensors protect the belt from probable beltdamage. 6imple hanging tilt switch or analogue devices like ultrasonic" radar or laser devices may be used. *. Pull4chord 6top 6witches: These are emergency switches that can be actuated by pulling a chord provided along the belt conveyor. +. Bip Aetectors: Bip detectors provide belt protection in case of a rip or tear of the belt. 6imple rip detector is spill switch located below the conveyor near the loading point. There are complex rip switches available" which re'uire periodic maintenance. 9. =ire Aetection: Thermal trip switches are provided with smoke sensors" ,& sensors or fibre optic temperature sensors. 10. Aust 6prays: Dater or chemical based dust suppressing system can eliminate or reduce dust problems in certain special conveyor belt installations
B!lt Cont#ol$ The belt control involves the following: 6top2start: t single or multiple stations. 6tart warning: udible or visual signal for pre4start warning nterlock: The se'uence control between the master and slave conveyors. Telemetry: Aistribution of belt control and information over significant distance. 3ockout: Physical lockout of the all motive power sources.
Regulatory Provisions =or use of belt conveyors in special applications like under ground coal mining state imposed regulations must be followed. A@56 circulars and ,5B should be considered during installation" running and maintenance of belt conveyor in underground coal mines.
!0
B!lt Con"!yo# T#oubl! S'ootin( 7The number refers to the list below the table.8 Com'laint
Cau$e
Com'laint
Cau$e
n or#er of 'robable o%%urren%e$
/elt runs pulley
off at
tail
n or#er of 'robable o%%urren%e$
* 1% 1$ 1* !1
>xcessive wear" including rips" gouges" ruptures" and tears
1!" !%" 1*" !1" +" %
>ntire belt runs off at all points of the line
!(" 1*" 1%" !1" $" 1(
>xcessive wear
cover
!1" 1$" %" 19" !0" !!
&ne belt section runs off at all points of the line
!" 11" 1
>xcessive edge broken edges
wear"
!(" $" 1*" +" 1" !1
/elt runs off at head pulley
1%" !!" !1" 1(
/elt slip
19" *" !1" 1$" !!
,overs become checked or +" 1+ brittle
/elt slip on starting
19" *" !!" 10
3ongitudinal grooving cracking of top cover
>xcessive belt stretch
1#" 10" !1" (" 9
3ongitudinal grooving or 1$" !1" !! cracking of bottom cover
/elt breaks at or behind fastenersO fasteners tear loose
!" !#" 1#" !!" !0" 10
=abric decay" carcass cracks" ruptures" soft spots in belt7gouges8
1!" !0" %" 10" +" !$
Eulcanised separation
1#" !#" 10" !0" !" 9
Ply separation
1#" !#" 11" +" #
splice
bottom
/elt hardens or crack
+" !#" !!" 1+
or 1$" !1" !!
1. /elt bowed: void telescoping belt rolls or storing them in damp locations. !. /elt improperly spliced or wrong fasteners: -se correct fasteners. Betighten after running for a short while. f temporarily spliced remove belt splice and make new splice. 6et up regular inspetion schedule. #. /elt speed too fast: Beduce belt speed $. /elt strained on one side: llow time for new belt to break inQ. f belt does not break in properly or is not new" remove strained section and splice in a new piece. %. /reaker strip missing or inade'uate: Dhen service is lost" install proper breaker strip 7 /reakers are woven fabric of nylon R2or polyster placed above the carcass to dissipate impact energy and to prevent belt puncture8 (. ,ounterweight too heavy: Becalculate weight re'uired and ad)ust counterweight accordingly. Beduce take4up tension to point of slip then lighten slightly.
!1
*. ,ounterweight too light: Becalculate and ad)ust or screw take4up accordingly. +. Aamage by abrasive" acid" chemicals" heat etc: -se belt designed for specific purpose. Bepair cuts. -se enclosure where needed. 9. Aifferential speed on dual pulleys: 5ake necessary ad)ustments 10. Arive underbelted: Becalculate maximum belt tensions and select correcxt belt. Aetermine if extension is feasible or another belt to be installed. ,heck the carcass is rigid enough for load" replace if service is lost. 11. >dge worn or broken: Bepair edge. f the edge is out of s'uare or badly damage replace the worn portion of the belt. 1!. >xcessive impact of material on belt or fasteners: -se correctly designed chutes and baffles. 5ake vulcanised splices. nstal impact idlers. Dhere possible load fines first. Dhere material is trapped under skirts " ad)ust skirtboards to minimum clearance or install cushioning idlers to hold belt against skirts. 1#. >xcessive tension: Becalculate and ad)ust tension. -se vulcanised splice within recommended limits. 1$. =rozen dlers: =ree idlers. 3ubricate. mprove maintenance. AonHt over lubricate. 1%. dlers or pulleys out of s'uare with centre line of the conveyor: Bealign. nstall limit switches for greater safety. 1(. dlers improperly placed: Belocate idlers or insert insert additional idlers spaced to support belts. 1*. mproper loading" spillage: =eed should be in direction of belt travel and at belt speed" centred on the belt. ,ontrol flow with feeders" chutes and skirtboard. 1+. mproper storage or handling: Befer to the manufacturerHs instructions for storage and handling. 19. nsufficient traction between belt and pulley: ncrease wrap angle with snub pulley. 3ag drive pulley. n wet condition use grooved lagging. nstall correct cleaning devices for safety. !0. 5aterial between belt and pulley: -se skirtboard properly. Bemove accumulation. 5aintain properly. !1. 5aterial build4up: Bemove accumulation. nstall cleaning devices" scrapers and inverted E decking. mprove housekeeping. !!. Pulley lagging worn: Beplace worn pulley lagging. -se grooved lagging for wet conditions. Tighten loose and protruding bolts. !#. Pulleys too small: -se large diameter pulleys. !$. Badius of convex vertical curve too small: ncrease radius by vertical realignment of idlers to reduce excessive edge tension. !%. Belative loading velocity too high or too low: d)ust chute or correct belt velocities. -se impact idlers. !(. 6ide loading: 3oad in the direction of belt run and at the centre of the belt.
!!
!*. 6kirts improperly Placed: -se ad)ustable skirtboards and check that it does not rub the belt.
A#%ou#!) Fac! Con"!y!#$ o# Un)!#(#oun) Coal T#an$po#tation -nderground coal conveyers widely employed in collieries relate to the group of conveyers with low flights" but differ substantially from the conveyers used in other industries. They perform many various operations in collieries and accordingly have a large number of design versions.
Figure ,2 rmoured face conveyor
n underground coal conveyer has one 7two or three8 hauling chain with low flights attached to it. The chain along the bottom of an open trough draws the flights. The chain bends around terminal 7drive and take4up8 sprockets at the ends of the conveyer and is moved by a drive. The conveyer is mounted directly on the ground of a mine drift. &ne of the principal re'uirements to underground coal con veyers is that their height" and especially that of the carrying run" must be as low as possible in order to minimize the loading height.
Aepending on the scheme of arrangement of the tractive element 7of the carrying and return run8" it is distinguished between vertically closed conveyers 7 a to d in the above figure8 , horizontally closed 7e8 , and those with a combined path. n the last type" the terminal sprockets are arranged at an angle of $% 0 to the horizontal. The flights are attached to the chain at an angle of $% 0 and are oriented in the horizontal plane in the carrying run and in the vertical plane" in the return run. Eertically closed conveyers are made 7with one" two or three parallel hauling chains 7a , b, and c respectively8. three4chain conveyer may have a greater length and higher reliability" since breakage of. a chain does not disturb the stability of flights and the operating capability of the conveyer. Their application is however limited by
!#
their higher cost and large mass. n single4chain conveyers" the flights may have symmetrical 7the chain at the centre of flight8 or unsymmetrical and rigidly fixed or hinged attachment to the hauling chain. The path of a vertically closed conveyer for coal transportation in curved drifts may be either straight 7horizontal" inclined or horizontal4inclined8 or bending in the horizontal plane 7spatial8. The tra%tive element is in the form of one" two or three detachable chains of elevated strength with the pitch +0 mm or round4link chains with the chain pitch of %0 or ($ mm and rod links. of a diametet of 1$ or 1+ mm. The chains are made of steel of specified grade and heat4treated.
The flight$ are made of steel and have a height roughly e'ual to the height of chain. The pitch of flights is $+0"($0 or 10!$ mm" and the linear mass of a chain with flights is 104 1+ kg2m on the average. The trough is stamped from steel sheets 7steel grades #% or #0f8 in sections of a length of !4!.% mO the working portion 7bottom8 is hardened. The #rive is electrical" pneumatic or electro4hydraulic in an explosion4safe embodiment. Arives with one or two motors at the front end and one motor at the rear end of a conveyer have found wide application. The transmission mechanism is of the reducer typeO the electric motor is connected with the reducer gear through a hydraulic coupling.
To'i%$ for #i$%u$$ion in the %la$$room
1. 6teep ngle conveying and their applicability in underground use. !. /elt tension and power calculation #. ,onveyor accessories $. Practical problems and innovative solutions %. nformation 6ystem for /ulk 6olid andling
!$
Con"!yo# Calculation nitial Aata: 1. ,haracteristic of material like lumpiness" density" moistue content" angle of repose" particle flowability" abrasiveness" particle strength" slumping 7losing of mobility on long storage" e.g. lime" cement etc.8" stickyness etc. !. The average and maximum load carrying capacity #. Aiagram of the designed conveyor with its principal dimensions $. Aata on the exceptional working conditions %. rrangements of the operation of the conveyors.
etermining Belt 4i#th
The belt width depends on maximum rated capacity and lump size. The cross sectional profile of the bulk material on the conveyor belt is determined by the profile of the load carried on the belt. &n straight roller this area is : A
1 =
bh
! h A
=
0. %b tan φ
=
0 .!%b
!
tan φ
where" b: width of the base of material on the belt h:height of material on the belt φ: ngle of repose : area of cross section of the material &n an inclined conveyor this area will be reduced depending on the angle of inclination of the belt" mobility or particles and angle of repose. =or a belt running over the troughed idler the cross sectional area of the material is the sum of the trapezium and the circular sector as shown in =igure:
!%
The area is given as: Ab =
l 1 + l ! π r
A s =
!
m sin β
!α
#(0
− r
!
sin !α !
where" the symbols are as illustrated in the figure. Total area is the sum of b and s.
,apacity of ,onveyor in te2hr Q
#(00. A.v . ρ
78
=
f belt width is / and area of cross section of material is " it is often taken that: A
B =
!
7/8
10
Thus from e'uation 78 and 7/8 the belt width can be calculated.
To test the calculated belt width for suitability with lump size the following relation is used: B
>
Xa +
!00
where
!(
S!.% for ungraded material aS maximum linear size of the represntative lump / is selected from the available width as: $00" %00"(%0" +00" 1000"1!%0" 1$00" 1(00" !000" !%00" #000 mm.
dler 6pacing The spacing of idlers depends on belt width and bulk density of material. This is calculated from : !
S W =
+T
where" : sag" in feet 6: 6pacing in feet T: Tension in pound D: Deight of the loaded belt in lb2ft.
dler spacing in the mid portion of the conveyor in meter for different material is given in the following table. /elt Didth
Aensity t2m#
Aensity t2m#
Aensity t2m#
Aensity t2m#
Aensity t2m#
mm
N0.+
0.+141.(
1.(14!
!.14 !.%
M!.%
$00
1.%
1.$
1.$
1.#
1.!
%00
1.%
1.$
1.$
1.#
1.!
(%0
1.$
1.#
1.#
1.!
1.!
+00
1.$
1.#
1.#
1.!
1.1
1000
1.#
1.!
1.!
1.1
1.1
1!00
1.#
1.!
1.!
1.1
1.1
1$00
1.#
1.!
1.!
1.1
1.1
1(00
1.#
1.!
1.!
1.1
1.1
!000
1.#
1.!
1.1
1.1
1.0
The return idlers are spaced at ! to !.% times the spacing of carryng idler sub)ect to the condition that it is not more than #.% m.
!*
