belt conveyor maintenance basics_tcm77-1305659

7/26/2019 Belt Conveyor Maintenance Basics_tcm77-1305659

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By John A. Koski

Belt conveyors are a mainstay inmost concrete plants. Theycarry sand and aggregates from

stockpile areas to the bins and silosthat feed the plants batching equip-ment. In design, they are mechanical-ly simple; basically consisting of am o t o r, a belt, and a few pulleys.Because of that, in many plants theyoften are given little attention or evenneglectedthat is, until a breakdown

occurs.Knowing the basics of belt conveyor

maintenance can go a long wayt o w a rd preventing costly bre a k-downs. In addition, a good preven-tive maintenance program can reduceplant operating costs by ensuring thatbelt conveyors have a long, trouble-free service life.

PREVENTIVE MAINTENANCE INSPECTIONSDaily inspections of conveyor belt

equipment can keep minor, easily cor-rected problems from turning intomajorand costlyheadaches.Follow these guidelines, as well asthose recommended by the convey-ors manufacturer, to ensure smooth,reliable operation:

1. Check that splices are in goodcondition and have no raised edgesthat could catch on and damage skirtseals, belt wipers, and other compo-nents.

2. Check chutes and skirtboards to

make sure that no holes have wornthrough them that might allow mate-rial to escape. A small hole in the sideof a chute can quickly grow larger asabrasive material flows through it.

3. Check the condition of wear lin-ers in chutes and along skirtboards. Acracked and loose liner along a skirt-board can quickly tear a belt to shredsif not replaced immediately. In addi-tion, a liner that becomes loose andfalls onto a belt can find its way into

other equipmentwhere it can domajor damage.

4. Check thatrubber sealingstrips alongs k i r t b o a rds arep roviding anadequate seal.Seals should bechecked whilematerial is trav-eling along the

belt because theposition of thesealing stripagainst the beltcan be dramati-cally diff e re n tbetween aloaded andunloaded belt.

5. Check thatall idlers androllers are turn-ing. The frictioncaused by atraveling beltagainst a frozenidler can quicklywear thro u g hthe idler. This can create a razor-sharpedge that can easily and quickly cut abelt.

6. Check the condition of the head,tail, bend, and take-up pulleys. Looseor worn rubber on a pulley can causea belt to slip or track to one side.

7. Check belt wipers or cleaners forwear and proper alignment. If a wiperwears away, the metal bracket it ismounted in can contact a belt andcause serious damage. In addition, anineffective wiper allows material tocollect in areas where it can createadditional problems.

8. Before starting the belt, cleanaccumulated material from walkwaysand from around idlers and pulleys.When using a water hose to remove

accumulated materials, be careful thatthe material isnt washed into the tailor take-up pulleys where it coulddamage both the belt and pulleywhen the belt is started.

9. Check that all safety devices arein good working order and are not

damaged. In particular, check thatemergency stop cords, located in allaccessible areas along the conveyor,are not frayed or loose.

ENSURE PROPER

BELT LOADINGOne of the major concerns with belt

conveyors of all types is preventingspillage. Even a small amount ofmaterial escaping from a belt canquickly add up to a major problem.

Bel t conveyor maintenance basi csRegular inspections and proper repair pro c e d u res help ensure that belt conveyors havea long, tro u b l e - f ree service life

Belt c onveyors are key components in many concrete plants. Knowing corre c trepair pro c e d u res an d havi ng a good prevent ive maint enanc e pro gram w ill helpkee p t hem tro u b l e - f ree and oper at ing at peak eff i c i e n c y.


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For example, if a conveyor belt run-ning 10 hours a day spills just oneshovelful of material per hour, thetotal loss per month is about 2 tons ofmaterial. This is material that must becleaned up from around the conveyor,usually by hand, front-end loader, or

both.Because most spillage occurs in the

area where material is loaded onto abelt, particular attention must be paidto the design of those areas. Design

considerations include: Uniformly load material onto thebelt

Centrally load the belt Load the belt after it has become

fully troughed after leaving the tailpulley

Reduce the impact of materialfalling on the belt

Load the belt in the direction ofbelt t ravel whenever possible; side-loading a belt is acceptable but canc reate more problems than in-line

loading does Deliver material to the belt at the

same speed as the belt is traveling Maintain a minimum inclination

angle at the loading point Provide proper spacing between

the skirtboard and belt to ensureeffective sealing by the sealing strips

Prevent rollback of material at theloading point by installing a sealingstrip that matches the contour of theloaded belt at the back of the loading

chute

SKIRTBOARD CONSIDERATIONS

As a rule of thumb, the height of as k i r t b o a rd should be about one-fifththe width of the belt for 20-degre eidlers and one-third the belt width for35- and 45-degree idlers. Skirtboard s ,which usually are constructed ofmetal, should not be allowed to con-tact the belt. Rather, the gap between

the skirtboard and belt should besealed with a strip of flexible ru b b e rclamped to the outside of the skirt-b o a rd. The clamps should allow thesealing strip to be adjusted easily.

G e n e r a l l y, the gap between the bot-tom of the skirtboard and the beltshould be as small as possible to pro-vide adequate sealing. However, dontinstall a skirtboard too close to a belt. A

belt that jumps suddenly could be tornby a too-low skirtboard. In addition, tohelp prevent material from wedging

between the skirtboard and belt, setthe back of the skirtboard 18 to 14 i n c hcloser to the belt than the front of thes k i r t b o a rd. To prevent chutes ands k i r t b o a rd assemblies from wearingout, most incorporate some type ofreplaceable metal liners.

REPAIRING CUTS AND TEARSDespite the best preventive mainte-

nance measures, conveyor belts dosometimes become torn or cut. Cutsin a belt that do not extend into thereinforcing fabric plies can often berepaired by coating them with rubber-ized belt-repair cement.

If a cut or tear extends through thefabric plies or the entire belt, effectiverepairs can be accomplished by usingmetal belt clips. Doing so closes thecut or tear and prevents it from grow-ing larger. Make sure, however, thatthe metal clips are free of projectionsand sharp edges before starting the

belt. Projecting bolt ends or unfiled

sharp edges can quickly damage pul-

A splice that is not square to the center line of the belt is one of the chiefcauses of belt misalignment. To ensure a square splice, the ends of the beltmust be cut square. Follow these guidelines to ensure a square cut:

1. Locate point A at the edge of the belt where it is to be cut.2. Locate points B1 and B2 by measuring an equal distance from each belt

edge to determine the center line of the belt. The distance between B1 and B2should be at least double the width of the belt.

3. Locate point C on the center line of the belt by measuring diagonallyfrom point A a distance equal to double the belt width.

4. Locate point D on the opposite side of the belt by measuring diagonallyfrom point C a distance double the width of the belt.

5. Draw a guideline between points A and D and cut the belt carefullyalong this line. This cut will then be square with the center line of the belt.

6. Use this same procedure on the other end of the belt.

Source: Abco Engineering Corp.

HOW TO MAKE A SQUARE CUT ON A CONVEYOR BELT

CONVEYOR BELT TERMINOLOGY


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leys and idlers.If a cut or tear is serious, a section of

belt may need to be cut out and a newsection of belt spliced in. Make sure,however, that the new section of beltis long enough so that no more thanone splice contacts a pulley at onetime. If both splices contact a pulleyduring belt operation, excess stress is

applied to both splices. This weakensthe splices and can lead to unexpectedtearing or premature splice failure.

The two most common methods ofbelt splicing are vulcanizing andmechanical splicing. Vulcanizing usu-ally is preferred because it creates astronger splice and has a longer ser-vice life. In addition, a properly madevulcanized splice will not interferewith pulleys, sealing strips, idlers,and belt cleaners. They also keep aconveyor belt cleaner by not allowing

fines to filter through the spliced area,something that can occur withmechanical splices. Some limitationsof vulcanized splices include higherinitial cost, the length of time requiredto make the splice, and greater instal-lation expertise. The two types of vul-canizing are hot and cold.

Hot vulcanizing involves strippingthe layers of the belt in stair-step fash-ion. The exposed layers are then over-layed with glue and ru b b e r. A c o o k e ror heated press then applies heat andp re s s u re to vulcanize the belt.

In cold vulcanizing, the layers of thebel t are coated with glue, clamped,and cured at room temperature. Ingeneral, a hot-vulcanized splice iss t ro n g e r, more reliable, and has alonger service life. It does, however,require more time to perform.

Mechanical splices generally con-sist of some type of metal clip. Oneside of the clip is placed on theunderside of the belt with the other

side placed on the top of the belt.Bolts are usually used to secure thetwo halves of the clips together.Mechanical splices are relatively easyto install, requiring little training orexperience. The main advantage ofmechanical splices is that they can beinstalled quickly and easily, allowinga conveyor to get back into servicef a s t e r.

After splicing a belt, check it fre-quently during operation to ensure

that it is running true at all times and

that the splice is not separating.

BELT LUBRICATION

Do not over grease idlers and bear-ings. Too much grease can damagebearing seals, allowing dirt to enterbearings; cause excessive resistancewithin a bearing, resulting in prema-t u re bearing failure; fall ontohandrails, walkways, or floors, mak-ing them slippery and hazardous; andcontact the belt causing it to deterio-rate due to chemicals in the greasethat are not compatible with the rub-ber compounds used in conveyorbelting.

On the other hand, if idlers andbearings do not receive suff i c i e n tg rease they can stop turning andcause heat buildup that can destroybearings and wear through the wallsof an idler. The heat generated alsocan cause a fire if flammable materialsare present.

TRAINING A BELTAllowing a conveyor belt to run toone side can greatly reduce its servicelife. Among other things, the belt cans t retch permanently; contact portionsof supporting framework, damaging

both the belt and framework; the beltcan fold over onto itself and beruined; and material can spill off thebelt, especially at loading points.

The problem of belt wanderingoften can be corrected by changing

how the material is fed onto the belt,

such as installing a baffle in a chute todirect the feed onto the center of thebelt.

Rollers that do not turn or turnslowly due to bearing failure or

because something has lodgedagainst the roll create drag on a beltthat can pull it toward the side wherethe drag occurs.

Idlers that are not square with theconveyor frame will steer the belttoward the side to which the idlers areturned. Head, tail, bend, or take-uppulleys that are not square with theirmountings also will steer a belt off toone the side.

To correct belt wander:1. Do not use the head, tail, bend, or

take-up pulleys to train the conveyorbelt. Doing so can permanentlys t retch the belt. Pulleys should beused only for adjusting belt tension.In addition, never train a belt bywiring a training idler into place.Doing so creates strain on both the

training idler and belt, leading todamage or failure of both.2. Check that the tail pulley is aligned

with the head pulley, bend, and take-up pulleys, and that all pulleys are setat 90 degrees to the center line of theconveyor stru c t u re. In addition, ensurethat all pulleys are level.

3. Start the conveyor to determinetoward which side the belt wandersand on which parts of the conveyor itwanders. Belt wander sometimes is

BELT WEIGHT OF MATERIAL HANDLED (LBS./ CU. FT. ) RETURN

WIDTH 30 50 75 100 150 200 IDLER

(IN. ) SPACING OF TROUGHING IDLERS (FT. ) SPACING (FT. )

18 5.5 5.0 5.0 5.0 4.5 4.5 10.0

24 5.0 4.5 4.5 4.0 4.0 4.0 10.030 5.0 4.5 4.5 4.0 4.0 4.0 10.0

36 5.0 4.5 4.0 4.0 3.5 3.5 10.042 4.5 4.5 4.0 3.5 3.0 3.0 10.048 4.5 4.0 4.0 3.5 3.0 3.0 10.0

54 4.5 4.0 3.5 3.5 3.0 3.0 10.060 4.0 4.0 3.5 3.0 3.0 3.0 10.072 4.0 3.5 3.5 3.0 2.5 2.5 8.0

Source: Martin Engineering Co.

RECOM MENDED IDLER SPACING


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isolated, occurring on only one sec-tion of a conveyor.

4. Stop the conveyor and lock it out.It is dangerous to adjust idlers withthe belt running. Doing so can cause aworker to get caught between a mov-ing belt and idler or to be snared by amechanical belt fastener or loosesplice.

5. Move the first idler behind thespot where the belt began to wanderby turning the idler in the directionopposite the wander. In other words,if you want the belt to move left, turnthe idler toward the left in the sameway you would steer a bicycle usingits handlebars. Idler mounting boltholes are slotted, which allows theidler to be turned from its normalposition at a right angle to the axis ofthe belt. Make sure that all bolts aretightened after making adjustments.

6. Restart the conveyor and recheckbelt wander. If the belt stills wanders,stop the conveyor, lock it out, andturn the next idler ahead of the oneyou just adjusted. Continue this pro-cedure until the belt tracks up the cen-ter of the idlers.

7. If the belt wanders on its return,adjust the return idlers in the samemanner as described above.

BELT TIGHTNESS

A belt should only be tight enoughto prevent slipping on the drive pul-ley and sagging between troughingidlers. Running a belt tighter than

necessary increases belt wear andallows it to be cut more easily. On

belts equipped with a weighted take-up pulley, make sure that the weightis free to move up and down as need-ed. Do not allow material to accumu-late under the weight, as this can pre-vent its downward movement whenneeded.

WELDING AND CUTTING

Be extremely cautious when weld-ing or flame-cutting on or near con-veyor belt equipment. Always have asecond person present to keep an eyeon the belt to ensure that it does notcatch on fire. Once a conveyor beltcatches on fire, it can quickly producethick, acrid smoke and intense flames.

PUBLICATION #J940305Copyright 1994, The A b e rdeen Gro u pAll rights re s e r v e d

belt conveyor maintenance basics_tcm77-1305659

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