外文翻譯--滾動(dòng)軸承.doc

附錄附錄1英文原文RollingContactBearingsTheconcernofamachinedesignerwithballandrollerbearingsisfivefoldasfollows:(a)lifeinrelationtoload；(b)stiffness,i.e.deflectionsunderload；(c)friction；(d)wear；(e)noise.Formoderateloadsandspeedsthecorrectselectionofastandardbearingonthebasisofloadratingwillbecomeimportantwhereloadsarehigh,althoughthisisusuallyoflessmagnitudethanthatoftheshaftsorothercomponentsassociatedwiththebearing.Wherespeedsarehighspecialcoolingarrangementsbecomenecessarywhichmayincreasefrictionaldrag.Wearisprimarilyassociatedwiththeintroductionofcontaminants,andsealingarrangementsmustbechosenwithregardtothehostilityoftheenvironment.Becausethehighqualityandlowpriceofballandrollerbearingsdependsonquantityproduction,thetaskofthemachinedesignerbecomesoneofselectionratherthandesign.Rolling-contactbearingsaregenerallymadewithsteelwhichisthrough-hardenedtoabout900HV,althoughinmanymechanismsspecialracesarenotprovidedandtheinteractingsurfacesarehardenedtoabout600HV.Itisnotsurprisingthat,owingtothehighstressesinvolved,apredominantformoffailureshouldbemetalfatigue,andagooddealofworkisbasedonacceptedvaluesoflifeanditisgeneralpracticeinthebearingindustrytodefinetheloadcapacityofthebearingasthatvaluebelowwhich90percentofabatchwillexceedalifeofonemillionrevolutions.Notwithstandingthefactthatresponsibilityforthebasicdesignofballandrollerbearingsrestswiththebearingmanufacturer,themachinedesignermustformacorrectappreciationofthedutytobeperformedbythebearingandbeconcernednotonlywithbearingselectionbutwiththeconditionsforcorrectinstallation.Thefitofthebearingracesontotheshaftorontothehousingsisofcriticalimportancebecauseoftheircombinedeffectontheinternalclearanceofthebearingaswellaspreservingthedesireddegreeofinterferencefit.Inadequateinterferencecaninduceserioustroublefromfrettingcorrosion.Theinnerraceisfrequentlylocatedaxiallybyabuttingagainstashoulder.Aradiusatthispointisessentialfortheavoidanceofstressconcentrationandballracesareprovidedwitharadiusorchamfertoallowspaceforthis.Wherelifeisnotthedeterminingfactorindesign,itisusualtodeterminemaximumloadingbytheamounttowhichabearingwilldeflectunderload.Thustheconceptof“staticload-carryingcapacity”isunderstoodtomeantheloadthatcanbeappliedtoabearing,whichiseitherstationaryorsubjecttoslightswivelingmotions,withoutimpairingitsrunningqualitiesforsubsequentrotationalmotion.Thishasbeendeterminedbypracticalexperienceastheloadwhichwhenappliedtoabearingresultsinatotaldeformationoftherolling-elementdiameter.Thiswouldcorrespondtoapermanentdeformationof0.0025mmforaball25mmindiameter.Thesuccessfulfunctioningofmanybearingsdependsuponprovidingthemwithadequateprotectionagainsttheirenvironment,andinsomecircumstancestheenvironmentmustbeprotectedfromlubricantsorproductsofdeteriorationofthebearingdesign.Moreover,sealswhichareappliedtomovingpartsforanypurposeareofinteresttotribologistsbecausetheyarecomponentsofbearingsystemsandcanonlybedesignedsatisfactorilyonthebasisoftheappropriatebearingtheory.Notwithstandingtheirimportance,theamountofresearcheffortthathasbeendevotedtotheunderstandingofthebehaviorofsealshasbeensmallwhencomparedwiththatdevotedtootheraspectsofbearingtechnology.LathesLathesarewidelyusedinindustrytoproduceallkindsofmachinedparts.Somearegeneralpurposemachines,andothersareusedtoperformhighlyspecializedoperations.EngineLathesEnginelathes,ofcourse,aregeneral-purposemachineusedinproductionandmaintenanceshopallovertheworld.Sizesrangefromsmallbenchmodelstohugeheavydutypiecesofequipment.Manyofthelargerlathescomeequippedwithattachmentsnotcommonlyfoundintheordinaryshop,suchasautomaticstopsforthecarriage.TracerorDuplicatingLathesThetracerorduplicatinglatheisdesignedtoproduceirregularlyshapedpartsautomatically.Thebasicoperationofthislatheisasfallows.Atemplateofeitheraflatorthree-dimensionalshapeisplacedinaholder.Aguideorpointerthenmovesalongthisshapeanditsmovementcontrolsthatofthecuttingtool.Theduplicationmayincludeasquareortaperedshoulder,grooves,tapers,andcontours.Worksuchasmotorshafts,spindles,pistons,rods,caraxles,turbineshafts,andavarietyofotherobjectscanbeturnedusingthistypeoflathe.TurretLathesWhenmachiningacomplexworkpieceonageneral-purposelathe,agreatdealoftimeisspentchangingandadjustingtheseveraltoolsthatareneededtocompletethework.Oneofthefirstadaptationsoftheenginelathewhichmadeitmoresuitabletomassproductionwastheadditionofmulti-toolturretinplaceofthetailstock.Althoughmostturretshavesixstations,somehaveasmanyaseight.High-productionturretlathesareverycomplicatedmachineswithawidevarietyofpoweraccessories.Theprincipalfeatureofallturretlathes,however,isthatthetoolscanperformaconsecutiveserialsofoperationsinpropersequence.Oncethetoolshavebeensetandadjusted,littleskillisrequiredtorunoutduplicateparts.AutomaticScrewMachinesScrewmachinesaresimilarinconstructiontoturretlathes,exceptthattheirheadsaredesignedtoholdandfeedlongbarsofstock.Otherwise,thereislittledifferentbetweenthem.Botharedesignedformultipletooling,andbothhaveadaptationsforidenticalwork.Originally,theturretlathewasdesignedasachuckinglatheformachiningsmallcastings,forgings,andirregularlyshapedworkpieces.Thefirstscrewmachinesweredesignedtofeedbarstockandwireusedinmakingsmallscrewparts.Today,however,theturretlatheisfrequentlyusedwithacolletattachment,andtheautomaticscrewmachinecanbeequippedwithachucktoholdcastings.Thesingle-spindleautomaticscrewmachine,asitsnameimplies,machinesworkononlyonebarofstockatatime.Abar16to20feetlongisfedthroughtheheadstockspindleandisheldfirmlybyacollect.Themachiningoperationsaredonebycuttingtoolsmountedontheturretandonthecrossslide.Whenthemachineisinoperation,thespindleandthestockarerotatedatselectedspeedsfordifferentoperations.Ifrequired,rapidreversalofspindledirectionisalsopossible.Inthesingle-spindleautomaticscrewmachine,aspecificlengthofstockisautomaticallyfedthroughthespindletoamachiningarea.Atthispoint,theturretandcrossslidemoveintopositionandautomaticallyperformwhateveroperationsarerequired.Afterthemachinedpieceiscutoff,stockisagainfedintothemachiningareaandtheentirecycleisrepeated.Multiple-spindleautomaticscrewmachineshavefromfourtoeightspindleslocatedaroundaspindlecarrier.Longbarsofstock,supportedattherearofthemachine,passthroughthesehollowspindlesandaregrippedbycollets.Withthesinglespindlemachine,theturretindexesaroundthespindle.Whenonetoolontheturretisworking,theothersarenot.Withamultiplespindlemachine,however,thespindleitselfindexes.Thusthebarsofstockarecarriedtothevariousendworkingandsideworkingtools.Eachtooloperatesinonlyoneposition,butalltoolsoperatesimultaneously.Therefore,fourtoeightworkpiecescanbemachinedatthesametime.VerticalTurretLathesAverticalturretlatheisbasicallyaturretlathethathasbeenstoodonitsheadstockend.Itisdesignedtoperformavarietyofturningoperations.Itconsistsofaturret,arevolvingtable,andasideheadwithasquareturretforholdingadditionaltools.