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1、附录二外文原文和翻译Shafts、couplingsandrollingcontactbearingskeywords:shafts、couplings、bearingsVirtuallyallmachinescontainshafts.Themostcommonshapeforshaftsiscircularandthecrosssectioncanbeeithersolidorhollow(hollowshaftscanresultinweightsavings).Rectangularshaftsaresometi
2、mesused,asinscrewdriverblades,socketwrenchesandcontrolknobstems.Ashaftmusthaveadequatetorsionalstrengthtotransmittorqueandnotbeoverstressed.Italsobetorsionallystiffenoughsothatonemountedcomponentdoesnotdeviateexcessivelyfromitsoriginalangularpositionrelativetoase
3、condcomponentmountedonthesameshaft.Generallyspeaking,theangleoftwistshouldnotexceedonedegreeinashaftlengthequalto20diameters.Shaftsaremountedinbearingsandtransmintpowerthroughsuchdevicesasgears,pullerys,camsandclutches.Thesedevicesintroduceforceswhichattempttoben
4、dtheshaft;hence,theshaftmustberigidenoughtopreventoverloadingofthesupportingbearings.Ingeneral,thebendingdeflectionofashaftshouldnotexceed0.01in.perftoflengthbetweenbearingsupports.Inaddition,theshaftmustbeabletosustainacombinationofbendingandtorsionalloads.Thusa
5、nequivalentloadmustbeconsidered14whichtakesintoaccountbothtorsionandbending.Also,theallowablestressmustcontainafactorofsafetywhichincludesfatigue,sincetorsionalandbendingstressreversalsoccur.Fordiameterslessthan3in.,theusualshaftmaterialiscold-rolledateelcontaini
6、ngabout0.4percentcarbon.Shaftsareeithercold-rolledorforgedinsizesfrom3in.to5in.,shaftsareforgedandmachinedtosize.Pleasticshaftsarewidelyusedforlightloadapplications.Oneadvantageofusingplasticissafetyinelectricalapplications,sinceplasticisapoorconductorofelectrici
7、ty.Componentssuchasgearsandpulleysaremountedonshaftsbymeansofkey.Thedesignofthekeyandthecorrespondingkeywayintheshaftmustbeprperlyevaluated.Forexample,stressconcentrationsoccurinshaftsduetokeyways,andthematerialremovedtoformthekeywayfurtherweakenstheshaft.Ifshaft
8、sarerunatcirticalspeeds,severevibrationscanoccurwhichcanseriouslydamageamachine.Itisimportanttoknowthemagnitudeofthesecriticalspeedssothattheycanbeavoided.Asag
