输送机英语文献原文

1原文：CONVEYORSYSTEMSConveyorsareusedwhenmaterialmustbemovedinrelativelylargequantitiesbetweenspecificlocationsoveraffixedpath.Thefixedpathisimplementedbyatracksystem,whichmaybein-the-floor,above-the-floor,oroverhead.Conveyorsdivideintotwobasiccategories:(1)poweredand(2)no-powered.Inpoweredconveyors,thepowermechanismiscontainedinthefixedpath,usingchains,belts,rotatingrolls,orotherdevicestopropelloadsalongthepath.Poweredconveyorsarecommonlyusedinautomatedmaterialtransportsystemsinmanufacturingplants,warehouses,anddistributioncenters.Innon-poweredconveyors,materialsaremovedeithermanuallybyhumanworkerswhopushtheloadsalongthefixedpathorbygravityfromoneelevationtoalowerelevation.TypesofConveyorsAvarietyofconveyorequipmentiscommerciallyavailable.Inthefollowingparagraphs,wedescribethemajortypesofpoweredconveyors,organizedaccordingtothetypeofmechanicalpowerprovidedinthefixedpath.RollerandSkateWheelConveyors.Theseconveyorshaverollsorwheelsonwhichtheloadsride.Loadsmustpossessaflatbottomsurfaceofsufficientareatospanseveraladjacentrollers.Pallets,totepans,orcartonsservethispurposewell.Thetwomainentriesinthiscategoryarerollerconveyorsandskatewheelconveyors,picturedinFigure10.6.Inrollerconveyors,thepathwayconsistsofaseriesoftubes(rollers)thatareperpendiculartothedirectionoftravel.Therollersarecontainedinafixedframethatelevatesthepathwayabovefloorlevelfromseveralinchestoseveralfeet.Flatpalletsortotepanscarryingunitloadsaremovedforwardastherollersrotate.Rollerconveyorscaneitherbepoweredornon-powered.Poweredrollerconveyoraredrivenbebeltsorchains.Non-poweredrollerconveyorsareoftendrivenbygravitysothanthepathwayhasadownwardslopesufficienttoovercomerollingfriction.Rollerconveyorsareusedinawidevarietyofapplications,includingmanufacturing,assembly,packaging,sortationanddistribution.Skate-wheelconveyorsaresimilarinoperationtorollerconveyors.Insteadofrollers,theyuseskatewheelsrotatingonshaftsconnectedtoaframetorollpalletsortotepansorothercontainersalongthepathway.Thisprovidestheskatewheelconveyorw2ithalighterweightconstructionthantherollerconveyor.Applicationsofskate-wheelconveyorsaresimilartothoseofrollerconveyors,exceptthattheloadsmustgenerallybelightersincethecontactsbetweentheloadsandtheconveyoraremustmoreconcentrated.Becauseoftheirlightweight,skatewheelconveyorsaresometimesbuiltasportableequipmentthatcanbeusedforloadingandunloadingtrucktrailersatshippingandreceivingdocksatfactoriesandwarehouses.BeltConveyors.Beltconveyorsconsistofacontinuousloop:Halfitslengthisusedfordeliveringmaterials,andtheotherhalfisthereturnrun.Thebeltismadeofreinforcedelastomer(rubber),sothatitpossesseshighflexibilitybutlowextensibility.Atoneendoftheconveyorisadriverollthatpowersthebelt.Theflexiblebeltissupportedbyaframethathasrollersorsupportslidersalongitsforwardloop.Beltconveyorsareavailableintwocommonforms:(1)flatbeltsforpallets,individualparts,orevencertaintypesofbulkmaterials;and(2)troughofbeltsforbulkmaterials.Materialsplacedonthebeltsurfacetravelalongthemovingpathway.Inthecaseoftroughofbeltconveyors,therollersandsupportsgivetheflexiblebeltaV-shapeontheforward(delivery)looptocontainbulkmaterialssuchascoal,gravel,grain,orsimilarparticulatematerials.ConveyorsDrivenbyChainsandCables.Theconveyorsinthisgrouparedrivenbyapoweredchainorcablethatformsanendlessloop.Insomecases,theloopformsastraightline,withapulleyateachend.Thisisusuallyinanover-and-underconfiguration.Inotherconveyors,theloophasamore-complexpath,withmorethantwopulleysneededtodefinetheshapeofthepath.Wediscussthefollowingconveyorsinthiscategory:(1)chain,(2)slat,(3)in–floortowline,(4)overheadtrolley,and(5)power-and-freeover-headtrolley.Chainconveyorsconsistofchainloopsinanover-and-underconfigurationaroundpoweredsprocketsattheendsofthepathway.Oneormorechainsoperatinginparallelmaybeusedtoformtheconveyor.Thechainstravelalongchannelsinthefloorthatprovidesupportfortheflexiblechainsections.Eitherthechainsslidealongthechannelortheyrideonrollersinthechannel.Theloadsaregenerallydraggedalongthepathwayusingbarsthatprojectupfromthemovingchain.Theslatconveyorsuesindividualplatforms,calledslats,connectedtoacontinuouslymovingchain.Althoughthedrivemechanismisapoweredchain,itoperatesmuchlikeabeltconveyor.Loadsareplacedontheslatsandaretransportedalongwiththem.Straightlineflowsarecommoninslatconveyorssystems.However,becauseofthec3haindriveandthecapabilitytoalterthechaindirectionusingsprockets,theconveyorpathwaycanhaveturnsinitscontinuousloop.Anothervariationofthechainconveyoristhein-floortowlineconveyor.Theseconveyorsmakeuseoffour-wheelcartspoweredbymovingchainsorcableslocatedintrenchesinthefloor,asinFigure10.8.Thechainorcableiscalledatowline;hence,thenameoftheconveyor.Pathwaysfortheconveyorsystemaredefinedbythetrenchandcable,andthecableisdrivenasapoweredpulleysystem.Switchingbetweenpoweredpathwaysispossibleinatowlinesystemtoachieveflexibilityinrouting.Thecartsusesteelpinsthatprojectbelowfloorlevelintothetrenchtoengagethechainfortowing.(Gripperdevicesaresubstitutedforpinswhencableisusedasthepulleysystem,similartot