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7/30/2019 Care of Belting Rev 01
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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
Correct Storage Procedures
Section 2
Protection of Conveyor Belting Section 3
Conveyor Belt Training
Section 4
Conveyor belt service difficulties
Section 5
Chutes
Care of
Conveyor 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 iscontinually subjected to varying degrees of human abuse. Whatare the effects of these on the life of the rubber conveyor belts?
The presence of ozone is predominant in the atmosphere whereelectrical 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 manifestsitself 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 tominimise the problem Dunlop Belting Products incorporate anti-oxidants and anti-ozonants into the rubber compound which actas a barricade against attack. The user can also assist by storingthe belting in a position well sheltered from direct sunlight andsources of ozone such as operating electric motors and arcwelding equipment.
Rubber compounds are degraded by heat. Some polymerswithstand the effects of heat better than others but all are
degraded. Additives can be added to the cover rubber of conveyor 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 hotenvironment as it will seriously effect the life expectancy. Idealstorage temperature for conveyor belting is between 10C and25C.
As is the case for heat resistant belting, specially formulated oilresistant compounds are available. These oil resistingcompounds are based on synthetic polymers. Standard Grade Nand M rubber covers (which have a very high Natural rubber content) are readily attacked by oils causing swelling andreduction of physical properties.
One of the most common enemies of the conveyor belt is abuseof one kind or another. Abuse arises either through ignorance or the desire for ever increasing achievement. The consequencesof abuse are vast. Between 80% and 90% of all belts arereplaced due to physical damage before they have worn out.
The correct way to lift rolls of belting is with a bar passed throughthe centre core, then depending on the width and weight, the rollmay be lifted by a fork lift truck or crane. If chains or slings areused on the bar at each side of the roll, a spreader bar should beused 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 thebelt 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. If storage 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 or pulleys.
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 for straight 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 become
jammed 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 andimmediately after discharge point.
10. If tramp iron is a hazard the belt may be protected by shortfeeder belt incorporating an overbelt magnet to remove theiron.
DUNLOP BELTING PRODUCTS
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DUNLOP BELTING PRODUCTS
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Belt tracking basics:! The belt will ALWAYS move to a
position 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 greater resultant force acts on the higher side.
! Non parallel idlers steer the belt. ! Non parallel pulley displaces the belt.
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DUNLOP BELTING PRODUCTS
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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 conveyor stringers. 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 isreplaced.
2. Using the procedure described above, check that allsplices are true.
3. Make sure that there are no obstructions to the belt alongthe 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 of the 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 of true 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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DUNLOP BELTING PRODUCTS
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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 of installed 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 lower clearance tolerances
For a vertical gravity take-up system.Distribute the take-up ballast evenly across the width of the take-upballast 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 of installed 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 of an 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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DUNLOP BELTING PRODUCTS
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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 or more 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 of the 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 trip. Increaseclearances in the discharge chute. If theconveyor discharges to another conveyor install 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 ra pe r to me et th emanufacturer's specifications. Replaceworn scraper blades. Clean accumulatedmaterial from the belt scraper blades andblade mounting bracket. Replace faultytorsion mountings. Replace seized idler rolls. Replace or repair 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 wear occur 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 of belt travel. Cover cut and gouged at line of skirt- board contact with belt.
Wear occurs across the full width of the 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 of wear pattern related to the width of the 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 cover wears near edge because of concentration 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 scraper incorrectly installed.
Seized or jammedreturn idler rolls
Badly aligned returnidlers.
Excessively high ratiobetween thickness of top\and bottom covers.
Worn Covers Top Cover wearsout quicker thanpredicted by theDunlop belt wear formula.
Difficulty Causes Diagnosis
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RemedyDifficulty Causes Diagnosis
Bottom cover worn.
Damaged or worn belt edges.
Cut Cover.
Material build up on deckplates.
Material trappedbetween belt and apulley in con- tact withthe bottom cover.
Seized or jammed carryidler rolls.
Slip on the drive pulley.
Misaligned idlers or pulleys.
Misaligned belt join.
Misaligned belt structure.
Material impinging withbelt at a critical angle.
Inadequate clearancebetween skirtboard andbelt.
Worn idler roll shell.
Loaded material fallsdirectly over an idler roll.
Large material trappedat the loading point.
Excessive materialturbulence at load point.
Replace worn skirtboard sealingmaterial. Increase troughing angle at theloading points. Extend the length of the
skirtboards. Increase tension applied bythe take-up to reduce sag between carryidlers at the loading point. Improve housekeeping. Install vee return scrapers to preventmaterial carry back into pulleys. Adjustscraper blades of existing vee returnscrapers. Replace worn vee returnscraper blades.
Replace seized idler rolls. Removematerial that may cause idler rolls to
jamb. Replace or repair idler frames thatcause idler rolls to jamb. Locate idler rollscorrectly in the idler frames. Lag drive pulleys or replace worn drivepulley lagging. Use grooved pulleylagging if water is present. Increase forceapplied by the take-up. Ensure that thetake-up pulley moves freely along itstravel length.
Align idlers and pulleys as described inSection 3. Replace the affected belt join.
Correct the alignment of the conveyor
structure.
Alter the load chute angle. Increase thevertical velocity of material through theload chute thereby increasing theeffective angle of impingement.
Increase gap between skirtboard and thebelt surface.
Replace worn idler rolls. Removematerial causing idler roll jambs. Replaceor repair idler brackets which have poor clearance between idler roll and bracket.
Alter position of idlers at the load point inrelation to the material flow path.Increase spacing of idlers at the loadpoint.
Alter arrangement at the load point.Increase gap between skirtboards andimpact bars. Skirtboard gap mustincrease in direction of belt travel.
Alter angle of material feed to reducevelocity difference between belt andmaterial.
Wear in centre third of belt width.Longitudinal cuts and gouges in thecover. Material spillage at loading
point.
Punctures into the cover. Wear across the full belt width. Excessivenoise in vicinity of pulley.
Wear coincides with position of theseized or jammed idler rolls. Insevere cases the idler shell is wornthrough resulting in cutting of thebottom cover. Cover worn across the full beltwidth. Very often this is anintermittent problem resulting inintermittent wear along the beltlength.
Belt fouls the conveyor supportstructure.
Belt in close proximity to a join, foulsthe conveyor support structure.
Belt fouls the conveyor structure at
the position of misaligned structure. Effective angle of impingement withthe belt cover between 18 and 28 .Material cuts the cover as it strikesthe belt. Many random cuts in thecentre third of the belt width. Beltsurface takes on an appearancesimilar to a well used choppingboard.
Longitudinal cuts in top cover alongline of skirtboard contact with thebelt.
Seized or jammed idler rolls. Cuts incover coincide with seized idler rolls.
Large material lump size. Materialflow path directly onto an idler roll.Insufficient idler spacing toaccommodate material lump size atthe loading point. Impact bars installed at load pointhaving insufficient clearance toprevent entrapment of material.
Large material lump size. Largevelocity difference between beltand material being loaded.
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RemedyDifficulty Causes Diagnosis
Cover swelling.
Soft and stickyrubber cover.
Cracks in the belt cover.
Belt carcassdamage.
Ply separation
Oil, grease or solventcontamination.
Belt fouls with beltstructure or chutes.
Belt slip on a pulley.
Badly adjusted belt scraper. Pressure between scraper blade and belt too high.
Material conveyed is excessively 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 convey or structure
Vertical alignment of idlers varies excessively.
Spacing of idlers in convex curve too large.
Belt carcass too light for adequate load support.
Soft cover in the area of the swelling.Belt curl induced by the cover swelling. 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 cover on 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. Rapid wear of pulley lagging where the beltedges contact thepulley.
Ply se parationco nfine d to belt edges.Cov er separated from the ca rcass atthe b elt edges. Edge s ba dly worn. Inmost i nstances there will be sec tionswhe re the covers have been torn fromthe carcass.
Ply separation coincides with theidler junctions.
Ply separation coincides with the idler junctions.
Ply separation coincides with the idler junctions.
Remove the source of contamination or change belt to a type that is not affected bythe contaminant. Provide sufficient clearance between thebelt and conveyor structure.
Rectify jammed pulley. Increase take-up force to prevent belt slipduring starting.
Adjust scraper blade pressure. Replaceblades that have worn.Ensure evencontactpressure across the beltwidth.
Changebelt specificationto onethat is more appropriatefor the temperature.
Protect thebeltfrom direct sunlight.
Screen the belt against exposure to ultra- violetlight.
During storage of the belt keep changing itsposition and rotate the roll at regular intervals. While on the conveyor the beltshould be turned regularly.
Reduce vertical fall in the loading chute or break the fall wi th drop boxes in the load chute. 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 steel cord carcass.
Install or adjust vee return plow to prevent material carryback.
Reduce the troughing angle of the idlers in the transition zone. Increase the distance between terminal pulley and the closest troughing idler.
Remove obstructions to the belt path.Correct belt alignment.
Profile idlers to within a 3 mm vertical alignment tolerance.
Check that all idler sets are in place.
Decrease idler spacing in the convex curve so that maximum change of angle at any
particular idleris withinspecification.
Replace belt with a construction that provides adequate load support. This is
normally achieved by increasingthe number ofplies or 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 rubber covered 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 smaller than 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 of belt. 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 conveyor structure.
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 belt s in te lescopedcondition. 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
R a t e o f
W e a r
Rate of Wear vs Velocity Difference
Grade M rubber Grade N rubber Fire resistant or heatresistant rubber
DUNLOP BELTING PRODUCTS
0
Angle of Impingement
0
20
40
60
R a t e o f
W e a r
Rate of Wear vs Angle of Impingement
Grade M rubber Grade N rubber Fire resistant or heatresistant rubber
DUNLOP BELTING PRODUCTS
80
100
120
10 20 30 40 50 60 70 80 90