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Slide1(Introduction)

A belt is a loop of flexible material used to link two or more rotating shafts

mechanically.Beltsmaybeusedasasourceofmotion,totransmitpowerefficiently,

ortotrackrelativemovement.Beltsareloopedoverpulleys.Inatwopulleysystem,

the belt can either drive the pulleys in the same direction, or the belt may becrossed, so that the direction of the shafts is opposite. As a source of motion, aconveyorbeltisoneapplicationwherethebeltisadaptedtocontinuallycarryaload

betweentwopoints.

Advantagesofbeltdrives

Beltshavemany advantages overotherpower transmissionmethods.One of the

most important is overall economics. The efficiency and reliability of belts as a

power transmission medium is well recognized. Belts are clean and require no

lubrication. Belts can transmitpowerbetween shafts spacedwidely apartwith a

wideselectionofspeedratios.

Wherebeltsareused

When the desired speed of the driven shaft is the same as the driver, directconnectionisthemostcommonandeconomicmethod,sometimesthroughflexible

couplings.Whenthespeedofthedrivenshaftmustbeinexactrelationshipwiththedriver,gearsorchainsaremostfrequentlyused.However,synchronousbeltshave

gainedwideusageinthisrelativelylimitedfield,primarilyduetoeconomics,lackof

lubricationrequirements,andveryhighpowerdensityofmoderncurvilinearbelts.Byfarthemostnumeroustypeofdriveiswheresynchronizationisnotrequired,

driveranddrivenspeedsaredifferent,andtheprimemoveranddrivenmachinery

areseparatedbysomedistance.Thistypeofdrivelendsitselfideallytotheuseofthevariouskindsofbeltsthatexisttoday.Beltshaveanextremelybroadapplication

rangethatmakethemidealforvirtuallyanyapplication.

Slide2(Frictionversuspositivebeltdrives)

Allpowertransmissionbeltsareeitherfrictiondriveorpositivedrive.Frictiondrive

belts rely on coefficient of friction to transmit the power and require tension to

maintainthecoefficientoffriction.Flatbeltsarethepurestformofafrictiondrive

whileV-beltsandV-ribbedbeltsrelyoncoefficientoffrictionbuthaveamultiplying

effectthroughtheVorwedgingcharacteristic.

Positivedrivebeltsrelyontheengagementofteethonthebeltwithgroovesonthe

pulley.Therecanbenorealslipwiththiskindofbelt,shortofanactualratcheting

action.

Slide3(Flatbelts)

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Flatbeltsarethesimplestandgenerallyleastexpensivetypeofbelt.Theyaremade

of leather, plastic, solid rubber, or rubber reinforced with fabric tensile cords.Reinforcedflatbeltsarecapableoftransmittinghighpower-upto500hpifwide,

flatbeltsareusedonlargepulleys.Suchdrivesaredemanding,however,andflat-belt drives have largely been replacedbymore compact V-belt andsynchronous

drives.

Modernflat-beltdrivesaregenerallyusedforapplicationswherehighspeedismore

importantthanhigh-powertransmission.

Advantages:Withtheirthinsections,flatbeltsalsodeveloplessbendingtensionas

theyflexaroundthepulley,especiallyonsmall-diameterpulleys.Becausebending

tension detracts from drive tension, flat belts offer advantages on drives with

pulleysthatmaybetoosmallforV-belts.

Disadvantages:Flatbeltsdependonhightensionstomaintaintractionandmustbe

designed to prevent high wear rates or early failure when coupled with rugged

shafts andbearings. Alignmentalsomust be controlled closely because flat beltshaveatendencytotrackofftheirpulley.

Slide4(Typesofbeltcrosssections)

Variousbeltcrosssectionsareusedonindustrialdrives.Theheavy-dutyindustrial

V belts (classical and narrow) are used on large industrial drives, usually inmatchedsets.Synchronousbeltsareusedwhereexactspeedrelationshipmustbe

maintainedbetweenthedriveranddrivesshafts(theyarealsousedfortheirlow

maintenancerequirementsandforenergyefficiencybenefits).TheV-ribbedbelts

are typically used where high-speed ratio and small diameters are encountered,

such as on clothes dryers. The light-duty belts are used in the lawn and garden

implementmarketandtodriveamultitudeofsmallmachinery.

Coggedbeltshaveslotsthatreducebendingresistanceofthebelt.

Slide5

V-belt(trapezoidal)

The most familiar and widely used type of belt in the industry is the V-belt ortrapezoidal belt. These belts have theirname from the general trapezoidal orV-

shaped.There arethreemajor categoriesor industrialtrapezoidal belts: classical,

narrowandlight-duty.

V- and V-ribbed belts are capable of handling large load fluctuations and have

excellentshock-absorbingabilities.

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Light-dutyindustrialbelts

Light-dutyindustrialapplicationsaregenerallylessthan5hpinloadandfrequently

runlessthan8hoursperday(smallfansandmachinetools).Light-dutyV-beltsare

similar to classic V-belts except that they are designed for more flexibility and

lighterloads.Thus,theyaremoreadaptabletothesmallsheavediametersfoundonlight-duty,fractional-horsepowerdrives.

JoinedindustrialV-belts

ClassicalandnarrowV-beltsareavailableinthejoinedconfiguration,whereseveral

beltstrandsareconnectedbyatiebandacrossthetopofthebelts.Thetieband

improveslateralstabilityandsolvestheproblemsofbeltsturningoverorcoming

offthesheaves.Thetiebandridesabovethesheave,soitdoesnotinterferewiththe

wedgingactionoftheindividualbeltstrands.

Heavy-dutyindustrialbelts

ThesebeltsaretypicallyhigherHPapplication(above5hp)andrun8-24hperday(fans, industrialaircompressors, androckcrushers).Many industrialdriveshave

loadandreliabilityrequirementsthatcannotbemetbysingleV-beltinstallations.

Therefore,2to12(ormore)industrialV-beltsarenormallyusedtogether.Multiple-beltdrivesdeliveruptoseveralhundredhorsepowercontinuouslyandcanadsorb

reasonableshockloads.

Slide6(V-ribbedandcoggedbelts)

Shallow ribs on the underside of the V-ribbed belts mate with corresponding

groovesinthepulley.Thismatingguidesthebeltandmakesitmorestablethana

flatbelt.SomedesignsofV-ribbedbeltsresultinthecompletefillingofthepulley

grooves.Becauseoftherelativelysmallribs,oftencombinedwithfilledgrooves,V-

ribbedbeltsdonothaveasmuchwedgingactionasV-beltsand,consequently,must

operateathigherbelttension.

V-ribbed belts have higher lateral stability than flat belts because of the mating

grooves. In fact, they have the stability advantages approaching that of joined V-beltsondriveswhereindividualbeltswhipandturnoverorcomeoffthesheave.

WhileV-ribbedbeltsmaynotbeasflexibleasflatbelts,theypreformwellonsmall-

diameterpulleys.

Cogged(Variable-speed)V-belts

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Withincertainlimits,V-beltsarewellsuitedforapplicationswherethedrivenspeed

must vary in relationship to the driver speed. Grooves decrease the bendingresistance.

Slide7

Roundbelts

Theyhaveacircularcrosssectionthatmatesinasemisphericalsheave.

Roundbeltscanbemadetolength(endless),ortheproperlengthcanbecutfrom

rolls of belting and spliced with a metal hook to form an endless product. The

present-day use of round belts is rather limited, primarily for agricultural

machinerydrivesandsomelight-dutyorappliancedrives,suchasvacuumcleaners.

Slide8

Splicedbelting

Sliced belting comes invarious forms. A type ofbelting ismade of several smallsegmentslinkedtogethereithermechanicallyorthroughintertwiningtheindividual

componentstoformcontinuousV-belt.AconventionalappearingV-beltlinkedwith

mechanicalsplicesthatareattachedtoeachendofthebelt.Oftensplicedbeltingisused inan emergency, asit isrelativelyeasy tomanufacture andinstalla spliced

beltonthedrivetokeepthewheelsturninguntilamorepermanentrepaircanbemade.

Heavy-dutyindustrialdoubleV-belts

DoubleV-belts(orhexagonalbelts)arecommonlyusedinmultiple,andareusedin

applicationswhere the drive geometry requires that power be transmitted from

bothsidesofthebelt.ThesebeltsoperateinthesamesheavesareregularclassicV-

belts.

Slide9(Synchronousbelts)

Synchronousbelts(timingbelts)weredevelopedtotransmitpowerindriveswhere

exact synchronization was required. These belts transmit power through thepositiveengagementofbeltteethwithpulleyteeth.Thus,precisespeedratiosand

synchronizationarepossible insuchapplications asmachine-tool indexingheads,automotivecamshafts,officemachines.

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Advantages: Synchronousbeltdrives have anadvantage overgearsandchains in

that they transmit reasonably high loads with relatively low noise and withoutlubrication. The shock-absorbing characteristics of the rubber teeth against the

metalpulleyalsocanbehelpful.Becauseoftheirhightensilemodulus,thesebeltsrequiremoreaccuratealignmentthanV-beltsbutaremoretolerantthangears.

SynchronousbeltshaveseenincreasinguseinapplicationwhereV-beltsandchainwereusedinthepast.Thisisprimarilydueto3significantcharacteristics.

1. They require lessmaintenance.BothV-beltsandchain stretchandrequireperiodictake-ups.Inaddition,chainrequireslubrication.

2. Theyareextremelyenergyefficient.3. Modern belts have high power density (high horsepower ratings with

relativelysmallpackagesizes).

Slide10(chaindrives)

Chainsarecomposedofaseriesoflinkspinnedtogether,inaformofflexiblegear

connecting 2 toothed sprocket wheels mounted on parallel shafts. Their main

advantagesarethattheyareasflexibleasbelts,theyareaspositiveasgears,theyprovide excellent design flexibility, convenience, and resistance to shock loading,

they operate satisfactorily inadverse surroundings, they canbemanufactured invariousspecialsteelstoresistspecificenvironments,andtheyhaveunlimitedshelf

life, simplicity installation and general economy. Mechanical efficiency, in

comparison to gear and belt drives, is favorable. Chains operating under idealconditionscanhaveefficienciesashighas97to99%.

Standardrollerchainconstruction

Roller chain is a series of connected journal bearings, assembled with alternate

roller linksandpin links.Eachroller linkconsistsof2 bushings, rollers,and link

plates.Rollersareslippedontothebushings;thenthebushingsarepress-fittedinto

thesideplatestocompleteasinglerollerlinksection.Therollerhassufficientside

clearancetopermitfreemovementandlubricantaccess.Thesesamerollerlinksare

usedforsingleandmultiplestrandedrollerchains.

Pinlinkshave2pinspress-fittedinto2linkplates,andwhenassembled,the2pins

slip intobushingsof adjacentroller links.The sideplate(linkplate)ona pin linksectionisheldinplacebywayofthepinbeingrivetedontheends.

Slide11(Standardprecisionrollerchains)

Singleorbasepitchrollerchains

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Outofallthemanystylesofchainsthatareavailable,themostwidelyusedforbasic

transmission of power are the precision roller chains. Their operation is offundamentalconsideration.Therollers(shockabsorbersthatreducetheeffectsof

impact)engageandbearagainstthesprocketteeth.Bushingsareaccuratelypress-fitted into the linkplatesso that theydonotturn.Whenengagingsprockets, the

rollersrollintomeshwiththeteethandsetatthebottomofthespacebetweentheteethtoprovideapositivegrippingaction.Theloadisdistributedoveranumberofteethtogivesmooth,uninterruptedtransmissionofpower.

Double-pitchpowertransmissionrollerchains

Double-pitchrollerchainsareparticularlyapplicableonpowerdriveswherespeeds

areslowtomoderate,loadsaregenerallymedium-type,orcenterdistancesbetween

sprocketsarerelativelylong.Double-pitchtransmissionserieschainshavetwicethe

distance between rollers of corresponding standard roller chains. Since double-

pitchchainscontainonlyhalfasmanyrollers,bushingsandpins,theyhavealighterweightandoffergreatereconomythancomparablestandardrollerchains.

Slide12

Double-pitchconveyorrollerchains

The conveyor series roller chain is available in 2 styles: those with standard or

regulardiameterrollers,inwhichbothpinlinkplatesandrollerlinkplatesareof

consistentheight,sothatwhentheyareemployedinhorizontalconveyorruns,they

canbesupported,byrailsor tracks (thisis the chiefreasonfor the straight-sidedparallellinkplates).

In the second style, thosewith large-diameteror carrier rollers, rollers larger in

diameterthattheheightofthelinkplatesareadvantageous,soastoproviderolling

action or support along a desired conveyor path, generally horizontal In theory,

rollingfrictionistypicallyhalf,orevenless,thanthelevelofslidingfriction.Hence,

it ispractical touse a large-diameterroller series chain, soas tominimizechain

workingloadonlongorroughconveyorpaths.

Slide13(Engineering-classchains)

Steeldetachable-linkchain

Steeldetachable-linkchainisanassemblyofidenticalone-pieceformed-steellinks

thathookandinterfittogether,soastoformacontinuouschain.Thisdesignallows

theendbarofonelinktofreelyarticulateinsidethehookoftheadjacentlink.

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Detachable chain is easy to assemble and to disassemble. Individual links are

insertedfromoneside,attheproperangle(generallyperpendicular).

Detachable-link chains have been used for many years for drive, conveyor, and

elevatorapplicationswhereloadsare lightandwithoutintermittedshocks,speeds

areuniform,andconditionsofoperationaregenerallynonabrasive.Undoubtedly,the largest users of this type of chain throughout the years have been theagriculturalandlumberindustries.

Leafchain

Leafchaingenerallyhasgreatertensilestrengththanstandardrollerchainsandis

thereforeideallyusedfortensionlinkageapplications.Leafchainisconstructedof

figure-8-shapedinterlaced linkplates held togetherbyrivetedpins.Thereare no

bushingsorroller incorporated in this design. Linkplatesare generallymedium-

carbonsteel,heat-treated,andpinsarecase-hardenedfortoughness.

Leaf chain is not usually applied in endless strands, as it has no provision for

sprockettoothengagementbutratheritschangesofdirectionarticulateoverplainsheaves pulleys. They are designed for practically any application requiring a

strong, flexible linkage for transmitting reciprocating motion or lift, rather thanrotativepower.Leafchainsareespeciallywellsuitedforuseonhydraulicfork-life

trucks, ascounterweightchains formachine tools, elevators,andovendoors, and

othersimilarliftingorbalancingapplications.

Slide14

Heavy-dutyoffset-sidebarrollerchain

Offset drive chains are designed for the heaviest applications requiring power

transmission such as construction machinery, conveyors, and power drives; and

theyoperateunderthemostsevereconditionsatmoderatelyhighspeeds.Offset-

sidebarpower-transmissionrollerchainisanassemblyofidenticalinterfittinglinks

withheavilywalledorextra-thicksidebars,whichareformedsoastoprovideone

wideendandonenarrowend(offset)foreachlink.

Theserugged,all-steel chains are suitableforawidevarietyofdrive applications

wheredifficultoperatingconditionsprevail,suchasforthepropelandcrowddrives

oncranesandpowershovels,fordrumdrivesontransitmixertrucks.

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Combinationchain

Thesechains are constructedofan alternating assemblyof cast one-piece center

links(innerblocklinks),andouterlinks (pin links), thataremodeofsturdysteel

sidebars(hencethetermcombinationchain).

Combination chains are extensively used for conveyor and elevator applicationswhereawidevarietyofabrasiveandnonabrasivematerialsmustbehandled.

Slide15

Steel-bushedrollerlesschain

Steel-bushedrollerlesschainisusedinconveyingandelevatingoperations,rather

thaninpowerdrives.

Drop-forgedrivetlesschain

Drop-forgedrivetlesschainisgenerallyregardedasoneofthestrongestchainsever

developed. This chain ismade upofanalternating assemblyofa single innerorcenterloop-typelinkandtwoseparateouterlinksorsidebars,coupledtogetherby

symmetricallyforgedT-headedpinsthatlockintothesidebarstopreventrotation.

Thesimplicityofdesignpermitseasyassemblyordismantlingofthechainwithouttheuseoftools.

Rivetless chainis ideallyadapted togeneralservicein longconveyorruns,where

chainweight is of prime consideration. Also, its design permits extensive use ofoverhead trolley conveyorapplications where service over irregular routes, both

horizontallyandvertically,demandsthatthechainflexintransverseormultiplane

operation.

Slide16

Self-lubricatingrollerchains

The heavy-walled, oil-impregnated, sintered-steel bushings replace the

conventional bushings of roller chains. This porous bushing material functionssomewhatasasponge,withthelubricantretainedinthevoids(20%ofthevolume).

While in operation, the lubricant contained within the oil-impregnated bushing

flowsoverallvitalsurfaces.Whenthedrivestops,thelubricantisreabsorbedbythe

bushing.Thiscyclecontinuesthroughoutthechainsservicelife.

Mainadvantagesnotfoundinconventionalchain:

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1. Oil-impregnated bushing: a protective film ofoil completely lubricates thelive bearing area between pin and bushing,minimizingwear by reducingmetal-to-metalcontactandinternalrustingofpinandbushingsurfaces.

2. Thepositiveclearancebetweenpinlinkplateandrollerlinkplatecreatesaself-cleaningactiontoeliminatebuild-upofdust,dirtandcorrosion.

Applications:timingandindexingdrives,farmequipment,foodprocessing,baking,printing, textile machinery, chemical processing, materials handling, packing

machinery.

Extra-clearancerollerchain

Theyaresometimesreferredtoasside-bowrollerchain,aredesignedtopermit

sideflexingandtwistingnottoleratedbyconventionalrollerchains(chainjoints).

They are combined with special pin links designed to allow greater clearance

betweenthepinsandbushings,andbetweentherollerlinkandpinlinksideplates.Extra joint and transverse clearances allow the chain to accommodate several

inchesoflateraldisplacement,andarealsowellsuitedtotransmitloadsoperating

inastraightline.Thisflexiblerollerchainpermitstwistsof8degrees.

Slide17

Hollow-pinrollerchains

They allow unusual flexibility for conveyor applications. The hollow pin feature

providesunlimiteddesignversatility.

Corrosion-resistantrollerchains

Roller chains that must operate in conditions involving water, acids or high

temperatures are known as noncorrosive and heat-resistant roller chains. These

includerollerchainsthatareanassemblyofstainlesssteel(almostallcomponents)

andthosethatareanassemblyofplatedcomponents.

Stainlesssteelchainsaremadefromacombinationofmaterialstogivelongservice

life.

Platedrollerchainsarepreferredwhenchainsoperateinmildlycorrosive

environmentsorfordecorativeapplications.Theyprovidegreatercorrosionresistancethantheircounterpartcarbon-steelchain.