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Pulleys used in bulk materialhandling applications come in avariety of types and styles. A

glance in the conveyor componentssection of the DODGE® catalog revealspulley types that include the Heavy DutyDrum, Mine Duty Extra (MDX),Engineered Class, T-Section, and Wing.With so many options it’s sometimesdifficult to know where to begin theselection process. Perhaps the best placeto start might be a review of theadvantages of each pulley and how itmight perform in a given application.

The most popular and most basic pulleyis the Heavy Duty Drum pulley. This

Selecting the RightConveyor Pulley

pulley is designed to meet the load limitsset by the Conveyor EquipmentManufacturer’s Association (CEMA).These pulleys are used throughout theaggregate industry and in some lightmining applications. CEMA pulleys arewelded-steel construction and typicallyutilize flexible end discs. But how do youknow if you need more than a CEMApulley?

The end disc design is the mostcommon differentiator between a heavyduty or extra heavy duty construction.The limiting factor that preventsadditional load capacity in the pulley isthe heat-affected zone (HAZ) at the enddisc to hub weld. The heat-affected zoneis an area within the base metal that has

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its mechanical properties ormicrostructure altered by the heat of theweld itself (see head affected zonedrawing on page 30). These zonesbecome the weak link within the pulleyand therefore are the subject area forfatigue failure. Cracks in this area are themost common type of failure mode forCEMA pulleys.

Another factor to consider beforechoosing between a heavy duty or extraheavy duty pulley is the shaft size of theapplication. The stress increases in theend disc are a function of shaft size, so fora given load, the smaller the shaft, thegreater the shaft deflection at the hub.Higher shaft deflection at the hub willresult in more distortion within the enddisc. This distortion influences the stressin the end disc welds. As end disc stressincreases, so does the probability forpremature pulley failure, which can be

verified through finite element analysis(FEA). This type of failure will generallyoccur when pulley shafting is undersizedfor the tensions applied to the pulley.Basically the bending stress in the enddisc reaches such elevated levels that thematerial experiences fatigue failure in thearea similar to a paper clip bendingseveral times in your hand. Larger shaftswith less deflection will minimize theamount of stress in the end disc.

One way to eliminate this end discfailure is to increase the shaft size. Thelarger shaft will prevent excess deflection.This in turn willminimize the enddisc stress andprolong pulley life.Another option is tochoose a differentstyle of pulley

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altogether. TheDODGE MineDuty Extra (MDX)pulley has integralhubs within the enddiscs. The integralhub of the MDXeliminates the fatiguepoint in the heataffected zone andprovides muchgreater service factorto the pulley.

DODGEEngineered Classpulleys are usuallystronger than MDX

pulleys. Engineered pulleys are just that;they are custom designed to the tensions,bearing centers, and wrap angles of theapplication. CEMA or MDX pulleys mayqualify for the Engineered Class rating,provided they can meet the designrequirements for the application. It neverhurts to have Engineered Class pulleysquoted when tensions are known andpulley specifications are provided.

T-Section pulleys, which include SuperPulleys, are larger pulleys that aregenerally much more expensive. Theneed for these types of pulleys is generallybased upon enhanced reliability and/orelevated tension levels. T-Section pulleysare rare and will generally include SuperPulleys on large mining conveyors.

Wing pulleys are another offeringavailable for belt conveyors. Wing pulleysare essentially combination belt cleanersand belt supporters. Separate contactingsurfaces on the pulley beat the conveyorbelt through chordal action to removedirt and debris. As this debris falls off thebelt it is directed outward away from thepulley through angled spacer platesexisting within the wing pulley itself. Ifthe debris were not removed the belt anddrum pulleys would wear, resulting indecreased product life. Wing pulleys areavailable up to 350 PIW (pounds oftension per inch of belt width) and aretypically used as bend, snub or take-uppulleys.

HEAT AFFECTED ZONE

WELD ZONE

The heat affected zone (MA 2) caused fromwelding is normally the limiting factor to aconveyor pulley’s load transmitting capability. As aresult of the welding process, this area’smechanical properties and microstructure arealtered, weakening the parent material. Stressreduction in this area will prolong a conveyorpulley’s operating life; a design concept that isused by the engineers who design DODGEpulleys.

End disc design is the primarydifferentiator between conveyor drumpulleys. The welded design end disc isthe most common, with the integral huband T-section designs offering greaterservice factor within the application.

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Other Considerations before MakingFinal Selection

Most pulleys discussed in this article canalso be either a crown or straight-facedpulley. Crown faced pulleys are tapered tothe center of the pulley and aid with belttracking in applications where there is along unsupported span of belt. Crownfaced pulleys may also be a good choicefor applications where there are endpulleys on the return side of the belt, tailpulleys witnessing long unsupportedspans, and even short conveyors withwide belts. However, crown pulleys arenot recommended for tensions exceeding750 PIW or high-modulus belts.

Lagging, sometimes required forefficient long-term pulley operation, isanother option to consider when orderinga pulley. Particularly harsh environments,typically found in the aggregate andmining industries, may demandadditional protection provided by lagging.Lagging reduces the wear caused byabrasive materials and can be used toincrease the traction or griping capacityof drive pulleys to the conveyor belt. Thisadditional traction helps prevent slip andincreases the life of the pulleys and belts.Any pulley that will transmit torqueworks best if lagged. A layer of rubberlagging will also protect the rim fromwear and prevent catastrophic rim failureas the rim thickness decreases from thewear. If the rubber wears, it can be re-lagged at a much lower cost thancomplete replacement of the pulley.Many customers will specify lagging onall pulleys encountering the “dirty side”

of the belt. This would include snubpulleys and bend pulleys.

With so many types, styles, anddifferent options available today,choosing the right pulley foryour application can beconfusing. The bottom lineis to choose a pulley that hasbeen designed for yourparticular application. If youhave any doubts, or need anyhelp in making that decision,please contact the applicationengineering department at864.284.5700.

Finite element analysis (FEA) is often utilizedto control stress distribution in the pulley, alongwith shaft and rim deflection. The result is areliable DODGE pulley that offers many years ofdependable service.

TensionRange(PIW*)

AvailableBushings

Available as Wing?

End Disc

CEMA 0 – 750 HE, TL, QD Yes Welded Hub

MDX 0 – 750 HE Yes Integral Hub

Engineered Class 0 – 2,500+ HE, TL, QD, Keyless Yes Welded Hub or Integral Hub

T-Section / Super Pulley 2,500 – 10,000+ Keyless No Integral and Profiled

*PIW = Pounds per inch of belt width