Care of Belting

7/30/2019 Care of Belting

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DUNLOP BELTING PRODUCTS

SECTION 1

Care of Belting

Ozone and Ultra Violet Light

Heat

Oil and Solvents

Abuse

Handling of Conveyor Belt Rolls

Rubber compounds are subject to attack by ozone (0 ), ultraviolet light, heat, oils and solvents. The conveyor belting is

continually subjected to varying degrees of human abuse. What

are the effects of these on the life of the rubber conveyor belts?

The presence of ozone is predominant in the atmosphere where

electrical storms occur. South Africa ranks high in the world for

this climatic condition. A high concentration of ozone together

with ultra violet light causes oxidisation of the rubber.

Degradation of the rubber compound from oxidisation manifests

itself as surface cracking or perishing as it is commonly termed.

Such attack is most severe when the rubber is static and under

stress. Thus the rubber covers of a rolled up conveyor belt instorage can degrade. Also a belt left static on the structure for

long periods would suffer from rubber degradation. In order to

minimise the problem Dunlop Belting Products incorporate anti-

oxidants and anti-ozonants into the rubber compound which act

as a barricade against attack. The user can also assist by storing

the belting in a position well sheltered from direct sunlight and

sources of ozone such as operating electric motors and arc

welding equipment.

Rubber compounds are degraded by heat. Some polymers

withstand the effects of heat better than others but all are

degraded. Additives can be added to the cover rubber ofconveyor belts to enable them to perform under conditions of

prolonged high temperature. These are termed 'heat resistant'

conveyor belts. Conveyor belting should not be stored in a hot

environment as it will seriously effect the life expectancy. Ideal

storage temperature for conveyor belting is between 10C and

25C.

As is the case for heat resistant belting, specially formulated oil

resistant compounds are available. These oil resisting

compounds are based on synthetic polymers. Standard Grade N

and M rubber covers (which have a very high Natural rubber

content) are readily attacked by oils causing swelling and

reduction of physical properties.

One of the most common enemies of the conveyor belt is abuse

of one kind or another. Abuse arises either through ignorance or

the desire for ever increasing achievement. The consequences

of abuse are vast. Between 80% and 90% of all belts are

replaced due to physical damage before they have worn out.

The correct way to lift rolls of belting is with a bar passed through

the centre core, then depending on the width and weight, the roll

may be lifted by a fork lift truck or crane. If chains or slings are

used on the bar at each side of the roll, a spreader bar should be

used to prevent damage to the edges of the belt. If a spreader bar

is not available use off-cuts of belting between the sling and the

belt edge to help prevent damage.

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Correct Storage Procedures

Section 3

Conveyor Belt TrainingThe important factor for continuous central belt training isstable alignment of the conveyor

Alignment

The belt should be stored upright in its original packaging. Ifstorage is likely to be for a long period it is preferable that the rollbe suspended on a bar passed through the centre. Thisfacilitates regular turning of the roll to relieve pressure

concentration points. The belt roll should be rotated through 45every 3 to 4 months. Always store belting out of direct sunlight.Never store belting in the vicinity of operating electric motors.Always keep belting clear of arc welding or other sources of highvoltage. Ideal storage temperature is between 10 and 25C.Store belting on firm ground away from any possibility of oilcontamination. A waxy film appearing on the surface of theconveyor belting is normal, It should not be removed as thisprovides protection against ozone.

1. The conveyor structure must be true.2. All pulleys and idlers must be centred on the centre

line

3. Pulleys must be perpendicular to the centre line.4. Idler bases must be perpendicular to the centre line.5. All idler bases or brackets must be horizontal.6. Gravity take-ups and trippers must move centrally on

the centre line and the moving pulleys must remainparallel to the other pulleys on the system.

7. All idler rolls and non-driven pulleys must rotatefreely.

8. There must be no build up of material on idler rolls orpulleys.

9. The belt joins must all be true.10. The belt must not be so stiff as to prevent troughing

when empty.11. The load must be placed centrally on the belt. If the

basic alignment factors are thoroughly checkedthere should be no difficulty training the belt.

Section 2

Protection of Conveyor Belting

The conveyor structure should be assembled so that the beltruns true on both the carry and return strands. The loading of thematerial onto the belt should not affect the true running.Clearances between the belt and structure should be sufficientto prevent fouling at all points. International standards forstraight running of belting allow a movement of 5% of the beltwidth or 75mm whichever is the smaller, a larger clearance isrequired in the conveyor structure. Conveyor structure shouldhave sufficient clearance to accommodate belt movement.Movement of the structure will require that regular inspectionand adjustment is carried out to ensure that the belt always runstrue and free. Long conveyors with high installed power areprone to extensive damage when foreign objects becomejammed between belt and structure. Many belts have beenripped from end to end in such circumstances. Long conveyors

should therefore be provided maximum protection.

Means of protection can take the form of:1. Overhead magnets to remove foreign magnetic material.2. Magnetised head pulley for removal of small magnetic

objects.3. Regular checks for loose liner plates.4. During inspections checks must also be made for

jammed, seized and missing idler rolls.5. Belt run out limit switches should be installed at loading

and discharge points.6. Blocked chute detection must be installed and checked

regularly for correct operation.7. Scrapers or other types of belt cleaning devices should be

installed and correctly maintained to limit material carryback.

8. Vee ploughs installed on return strand to prevent material

passing between pulleys and the belt.9. Rip detection devices installed ahead of load point and

immediately after discharge point.10. If tramp iron is a hazard the belt may be protected by short

feeder belt incorporating an overbelt magnet to remove theiron.


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Belt tracking basics:! The belt will ALWAYS move to aposition which will equalisetension distribution.

! Displacement from the horizontal causes a resultant forceacting outwards.

A horizontal troughed idler set causes

equal and opposite resultant forcesacting outwards.

Non horizontal idler set causesunequal resultant forces. A greaterresultant force acts on the higher side.

! Non parallel idlers steer the belt. ! Non parallel pulley displaces the belt.


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Aids for checking alignment of idlers andstructures

!!!!!!!How to establish if a belt splice is true

Procedure for tracking a newly installed belt

Optical idler alignment instrument.Theodolite.

Spirit level.Plumb bob.Fish line.Measuring tape.Idler profiling jig.

1. Remove the idlers for 6 -10 metres on either side of the beltsplice.

2. Lay the belt flat on boards supported on the conveyorstringers. There must be no wavy edge as this indicatesthat the belt is not lying straight on the flat surface. (It isnormal for the belt edges to curl up from a flat surface but

pressing the edge down should cause the belt edge to layflat without any waviness.)3. Construct belt centre lines on either side of the splice

from a splice extremity to about 5 metres distance from thesplice.

4. Stretch a fish line from the furthest points of these centrelines, across the splice. The splice is true if the fish lineruns on the two centre lines along the entire length of thecentre lines.

1. Check structural steel alignment. Even in the case of oldconveyor structures, the alignment must be periodicallychecked and should always be checked when the belt is

replaced.2. Using the procedure described above, check that all

splices are true.3. Make sure that there are no obstructions to the belt along

the entire conveyor length and that no foreign materialshave been left on the belt.

4. Position the belt centrally in the structure and check that itclears the conveyor structure at all points along the length.

5. Check that the belt has been correctly reaved.6. Make sure that belt alignment switches are active.7. Position observers at critical points such as the pulleys,

loading chutes and any other points of least clearance.8. It will prove convenient to mark the belt on both surfaces at

each of the belt splices. Each splice should be uniquelymarked.9. Start the belt and while running empty observe the

tracking.9.1. Allow two to three complete revolutions beforemaking any initial adjustments. During this timedetermine the general tracking characteristics toascertain that all points along the belt length have asimilar tracking position at a particular point of theconveyor. The general tracking characteristics arebest observed at the lowest tension pulley.9.2. Start immediately behind the drive pulleyand check alignment along the return run of theconveyor, working toward the tail pulley.9.3. Do not adjust any of the pulleys which must

always be perpendicular to the belt centre line,central and horizontal.9.4. If the belt runs out at any position.

9.4.1. Double check the horizontal alignment ofthe idlers in the vicinity of the belt run out andadjust if necessary. The belt will move towardthe high side of idlers that are not horizontal.9.4.2. Adjust the idlers preceding the point of runout to steer the belt back to the centre. Makesmall adjustments to a few idlers and wait for afew minutes or a complete belt revolution beforemaking further adjustment.

10. Do the same to the carry side of the conveyor.Commencing at the tail pulley and working toward thehead pulley.

11. When the empty belt runs true a load can be applied.Commence with a small percentage of the design capacityand check that the belt alignment does not alter. Thenincrease the load in gradual increments checking for truebelt alignment after each increment. If the belt runs out oftrue when material is loaded then adjustments to the loadchutes are necessary to ensure that the load is placedcentrally on the belt.


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Material build up on return idlers

Too much lateral movement of take-upcarriage

Tension unevenly applied by take-up

Wind influences belt tracking

Material loaded off centre

Belt bowed

Mis-aligned splice

Plough steers belt to one side

Unevenly worn pulley lagging

Build up on pulleys

Install belt scrapers or improve cleaning efficiency by adjustment ofinstalled scrapers.Replace worn or damaged scraper blades.Replace belt fasteners with splices to improve efficiency of belt scrapers.High pressure sprays can be used in conjunction with belt scrapers toimprove cleaning efficiency.Install idler rolls that have shells with a low coefficient of friction to assistin preventing material adhering to the shell. The shell can be painted withlow coefficient paint or rolls manufactured of HDPE or having HDPEsleeves help prevent material build up.

Replace worn guiding components or install new components with lowerclearance tolerances

For a vertical gravity take-up system.Distribute the take-up ballast evenly across the width of the take-up

ballast box.Clean the take-up guides.Replace worn guide system components.

For horizontal gravity take-up system.Replace worn sheave wheels.Adjust rope to ensure that forces are evenly applied about the centreline of the take-up pulley.Clean take-up guide system.Replace worn guide system components.

Install sheeting along the length of the conveyor at a depth at least equalto the idler trough depth.

Install deflector plates in the chute to centralise the load.

Replace bowed section of belt.

Replace splice.The splice can become mis-aligned through belt damage or due to abreak down of adhesion within the splice.

Install vee plough which applies even force across the width of the beltand has central steering effect.

Replace worn pulley lagging.Install belt scrapers or improve cleaning efficiency by adjustment ofinstalled scrapers.Replace worn or damaged scraper blades.Replace belt fasteners with splices to improve efficiency of belt scrapers.High pressure sprays can be used in conjunction with belt scrapers to

improve cleaning efficiency.

Clean pulley surfaces. Lag pulley with soft rubber which helps prevent abuild up of sticky materials.Install efficient belt scrapers or adjust installed scrapers to provide moreefficient cleaning.Replace worn or damaged scraper blades.Replace belt fasteners with splices to improve efficiency of belt scrapers.High pressure sprays can be used in conjunction with belt scrapers toimprove cleaning efficiency.If build up occurs on pulleys in contact with the non-carry side of the belt.Install belt ploughs to clean the return belt or renew worn components ofan installed plough.Rebate belt fasteners into the carry side cover and cover the fastenerswith a rubber cover strip or polyurethane paste to prevent fine material

spilling through to the return belt.Replace worn skirt seals to prevent spillage.Install longer skirts at the loading points to prevent spillage.Install deeper troughing idlers at the loading points to prevent spillage.

Trouble Factor

Factors which influence belt training

Remedy


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Remedy

Section 4

Conveyor belt service difficulties

Typical service difficulties that can be experienced withconveyor belts are tabled below. This table lists possible causesof the difficulty in order of precedence with the most likely cause

having the highest precedence. Diagnosis criteria are givento help determine which cause is responsible for theparticular difficulty.

Replace worn skirtboard sealing material.Install wider skirtboard sealing material ormore efficient skirtboard seals so thatpressure can be reduced for the samesealing efficiency. Increase gap between

skirtboard and belt surface. Increasetension applied by the take-up to reducesag between the idlers at the loadingpoint.

Reduce the incline angle at the loadingpoint. Split the material feed so that finematerial is fed onto the conveyor first.

Alter gap between skirtboards and belt toprevent material entrapment. Increaseinter-skirt board width. Install garlandimpact idlers at the loading point. Installwider skirtboard sealing material or moreefficient skirtboard seals.

Increase the ground or floor clearance ofthe conveyor. Most commonly theproblem is associated with a low groundclearance at the tail pulley. Replace wornskirtboard sealing material. Increasetroughing angle at the loading points.Extend the length of the skirtboards.Improve house keeping.Install blocked chute detector with alarmcondition and belt tr ip. Increaseclearances in the discharge chute. If theconveyor discharges to another conveyorinstall interlock between the two.Install efficient belt scrapers at all

discharge points. Replace worn beltscraper blades. Adjust belt scraper toimprove cleaning efficiency.

Ad ju st be lt sc rape r to meet themanufacturer's specifications. Replaceworn scraper blades. Clean accumulatedmaterial from the belt scraper blades andblade mounting bracket. Replace faultytorsion mountings.Replace seized idler rolls. Replace orrepair idler brackets or frames that causeidler rolls to jamb. Locate idler rollscorrectly in the idler brackets or frames.

Align return idlers as described insection 3.Ratio of top to bottom cover thicknessshould not be greater than 3 to 1.

Relatively narrow strips of wearoccur along line of skirt seals incontact with the belt.

Wear is concentrated in the centreof the belt. Material accumulates atthe loading point. Little or nomaterial velocity in the direction ofbelt travel.Cover cut and gouged at line ofskirt- board contact with belt.

Wear occurs across the full width ofthe belt. Longitudinal cuts andgouges into the cover. Very oftenmore severe wear and damage tocover occurs nearer belt edges.Material accumulated under theconveyor to the extent that it makescontact with the return belt.

Longitudinal cuts and gougesacross the full belt width. Cover tornfrom the belt carcass.

Material build up on return idlers

and pulleys in contact with the carryside of the belt. Piles of materialaccumulate under return idlers.

Sinusoidal wear pattern. Width ofwear pattern related to the width ofthe scraper blades.

Longitudinal wear coinciding withposition of faulty idler rolls. Insevere cases the idler shell is wornthrough resulting in cutting of thecover.

Even wear across the width of thebelt. Poor tracking of the return belt.Belt curls up at edges. Top coverwears near edge because ofconcentration of weight at the edge.

Excessive pressurebetween skirtboardseals and the belt.

Loading conveyor at toosteep an angle.

Material trappedbetween skirtboardsand belt.

Material spillage fallingunder the conveyor.

Blocked dischargechute.

Excessive material

carry back on the returnside.

Poorly adjusted beltscraper or belt scraperincorrectly installed.

Seized or jammedreturn idler rolls

Badly aligned returnidlers.

Excessively high ratiobetween thickness oftop\and bottom covers.

Worn CoversTop Cover wearsout quicker thanpredicted by theDunlop belt wearformula.

Difficulty Causes Diagnosis


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RemedyDifficulty Causes Diagnosis

Cover swelling.

Soft and stickyrubber cover.

Cracks in the beltcover.

Belt carcassdamage.

Ply separation

Oil, grease or solventcontamination.

Belt fouls with beltstructure or chutes.

Belt slip on a pulley.

Badly adjusted beltscraper. Pressurebetween scraper bladeand belt too high.

Material conveyed isexcessively hot.

Prolonged exposure tosunlight.

Exposure to ultra-violetlight.

Exposure to ozone.

Impact of large materials.

Material trapped betweenbelt and pulley.

Short transition distance.

Belt fouls with the conveyor structure

Vertical alignment of idlersvaries excessively.

Spacing of idlers inconvex curve too large.

Belt carcass too light foradequate load support.

Soft cover in the area of the swelling.Belt curl induced by the coverswelling.Relatively high belt speed. Distinctivesmell of 'burning rubber'.Most commonly on drive pulley duringstarting but can also result from a

jammed pulley. Loud screechingnoise. Intermittent areas of soft coveron surface in contact with pulley.

Top cover smeared with soft, stickyrubber. Often smear occurs alongwidth coinciding with width of singlescraper blade.

Embrittlement of the cover rubber.Non heat resistant cover compound or

material temperature exceedstemperature rating of SBR heatresistant cover compound.

Fine surface cracks.

Fine surface cracks.

Fine surface cracks. Belt left standingin the same position for long periods.

Cuts andgouges in topcover.Material

flow path directly onto idler roll or impact bar. Materials loaded onto the

belt have a high vertical velocity

component.

Most commonly associated with the

tail pulley and material spillage at the

load point.High modulus belt carcass.

Punctures in the cover which is in

contact with theoffendingpulley face.

Carcass breaks at the edges. Rapidwear of pulley lagging where the beltedges contact thepulley.

Ply se parationconfine d to belt edges.Coverseparated from the carcass atthe belt edges. Edges badly worn. Inmost i nstances there will be sectionswhere the covers have been torn fromthe carcass.

Ply separation coincides with theidlerjunctions.

Ply separation coincides with the idlerjunctions.

Ply separation coincides with the idlerjunctions.

Remove the source of contamination orchange belt to a type that is not affected bythe contaminant.Provide sufficient clearance between thebelt and conveyor structure.

Rectify jammed pulley. Increase take-upforce toprevent belt slipduring starting.

Adjust scraper blade pressure. Replaceblades thathave worn.Ensure evencontactpressure acrossthe beltwidth.

Changebelt specificationto onethat is moreappropriatefor the temperature.

Protect thebeltfrom direct sunlight.

Screen the belt against exposure to ultra-violetlight.

During storage ofthe belt keep changing itsposition and rotate the roll at regularintervals. While on the conveyor the beltshould be turnedregularly.

Reduce vertical fall in the loading chute or

break the fall with drop boxes in the loadchute. Alter position of idlers in the loading

area. Increase thickness of top cover.

Reduce number of plies in the belt carcass

or increase the belt class. Increase the cord

diameter if thebelthas a steelcord carcass.

Install or adjust vee return plow to prevent

material carryback.

Reduce the troughing angle of the idlers inthe transition zone. Increase the distancebetween terminal pulley and the closesttroughing idler.

Remove obstructions to the belt path.Correct beltalignment.

Profile idlers to within a 3 mm verticalalignment tolerance.

Check that all idler sets are in place.Decrease idler spacing in the convex curve

so that maximum change of angle at anyparticular idleris withinspecification.

Replace belt with a construction thatprovides adequate load support. This is

normally achieved by increasingthe numberofpliesor increasing thebeltclass.


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RemedyDifficulty Causes Diagnosis

Section 5

ChutesThe primary purpose of chutes are to:1. Deposit the material centrally and evenly on the receiving

conveyor at a velocity approaching the belt velocity.2. Receive the material from the discharge point of a conveyor

and direct it to the required location.

Well designed chutes meet the following requirements:1. All chute openings are large enough to provide unrestricted

flow of the material.2. Material degradation is minimised3. The discharge chute collects all the material including that

which is removed by the belt scraper.4. Conveyor loading chutes direct the material at an angle and

velocity which minimises belt wear.

Factors effecting rate of wear of the covers of a rubbercovered conveyor belt.Velocity difference between the material and the belt has aprofound effect on the rate of wear of rubber compounds.Typically the rate of wear is proportional to the magnitude of thevelocity difference squared.

Angle of impingement of the material with the belt cover also

effects the rate of wear of the cover. A critical angle occurs atabout 22 where the wear rate is up to 100 times greater than anangle of 0 or 90 .

Pulley diameter smallerthan required minimum.

Oil, grease or chemicalcontamination.Conveyor structure mis-aligned.

Belt join mis-aligned.

Build up on pulleys.

Belt bowed.

Ply separation across full width ofbelt. Belt splices fail regularly.

Rubber soft and swollen in thevicinity of ply separation.

All sections of the belt run off at themisaligned section of the conveyor.Belt runs off in close vicinity of the

join at all points of the conveyorstructure.

Belt runs off in the vicinity of thepulley.

One section of belt runs off at allpoints of the conveyor.

Replace all pulleys that are smaller thanthe recommended minimum. Reduce thenumber of plies to suit the installed pulley

diameters checking first that thereplacement belt will provide adequateload support.

Remove source of contamination.

Correct alignment of conveyor structure.

Replace the belt join.

Clean the pulley face. Soft rubber pulleylagging (40 shore hardness) will assist inprevention of build up on pulleys.

Avoid stor ing belts in telescopedcondition. In some instances the bowedsection of belt can be straightened byapplying additional force in the take-up.Beware of exceeding the pulley shaft andbearing load capabilities.

Belt mis-tracking

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Magnitude of Velocity Difference

10

0

20

30

40

50

60

70

RateofWear

Rate of Wear vs Velocity Difference

Grade M rubber

Grade N rubber

Fire resistant or heatresistant rubber


0

Angle of Impingement

0

20

40

60

RateofWear

Rate of Wear vs Angle of Impingement

Grade M rubber

Grade N rubber

Fire resistant or heatresistant rubber


80

100

120

10 20 30 40 50 60 70 80 90

Documents

Care of Belting