外文翻译--滚动轴承.doc -- 5 元

附录附录1英文原文RollingContactBearingsTheconcernofamachinedesignerwithballandrollerbearingsisfivefoldasfollowsalifeinrelationtoloadbstiffness,i.e.deflectionsunderloadcfrictiondwearenoise.Formoderateloadsandspeedsthecorrectselectionofastandardbearingonthebasisofloadratingwillbecomeimportantwhereloadsarehigh,althoughthisisusuallyoflessmagnitudethanthatoftheshaftsorothercomponentsassociatedwiththebearing.Wherespeedsarehighspecialcoolingarrangementsbecomenecessarywhichmayincreasefrictionaldrag.Wearisprimarilyassociatedwiththeintroductionofcontaminants,andsealingarrangementsmustbechosenwithregardtothehostilityoftheenvironment.Becausethehighqualityandlowpriceofballandrollerbearingsdependsonquantityproduction,thetaskofthemachinedesignerbecomesoneofselectionratherthandesign.Rollingcontactbearingsaregenerallymadewithsteelwhichisthroughhardenedtoabout900HV,althoughinmanymechanismsspecialracesarenotprovidedandtheinteractingsurfacesarehardenedtoabout600HV.Itisnotsurprisingthat,owingtothehighstressesinvolved,apredominantformoffailureshouldbemetalfatigue,andagooddealofworkisbasedonacceptedvaluesoflifeanditisgeneralpracticeinthebearingindustrytodefinetheloadcapacityofthebearingasthatvaluebelowwhich90percentofabatchwillexceedalifeofonemillionrevolutions.Notwithstandingthefactthatresponsibilityforthebasicdesignofballandrollerbearingsrestswiththebearingmanufacturer,themachinedesignermustformacorrectappreciationofthedutytobeperformedbythebearingandbeconcernednotonlywithbearingselectionbutwiththeconditionsforcorrectinstallation.Thefitofthebearingracesontotheshaftorontothehousingsisofcriticalimportancebecauseoftheircombinedeffectontheinternalclearanceofthebearingaswellaspreservingthedesireddegreeofinterferencefit.Inadequateinterferencecaninduceserioustroublefromfrettingcorrosion.Theinnerraceisfrequentlylocatedaxiallybyabuttingagainstashoulder.Aradiusatthispointisessentialfortheavoidanceofstressconcentrationandballracesareprovidedwitharadiusorchamfertoallowspaceforthis.Wherelifeisnotthedeterminingfactorindesign,itisusualtodeterminemaximumloadingbytheamounttowhichabearingwilldeflectunderload.Thustheconceptofstaticloadcarryingcapacityisunderstoodtomeantheloadthatcanbeappliedtoabearing,whichiseitherstationaryorsubjecttoslightswivelingmotions,withoutimpairingitsrunningqualitiesforsubsequentrotationalmotion.Thishasbeendeterminedbypracticalexperienceastheloadwhichwhenappliedtoabearingresultsinatotaldeformationoftherollingelementdiameter.Thiswouldcorrespondtoapermanentdeformationof0.0025mmforaball25mmindiameter.Thesuccessfulfunctioningofmanybearingsdependsuponprovidingthemwithadequateprotectionagainsttheirenvironment,andinsomecircumstancestheenvironmentmustbeprotectedfromlubricantsorproductsofdeteriorationofthebearingdesign.Moreover,sealswhichareappliedtomovingpartsforanypurposeareofinteresttotribologistsbecausetheyarecomponentsofbearingsystemsandcanonlybedesignedsatisfactorilyonthebasisoftheappropriatebearingtheory.Notwithstandingtheirimportance,theamountofresearcheffortthathasbeendevotedtotheunderstandingofthebehaviorofsealshasbeensmallwhencomparedwiththatdevotedtootheraspectsofbearingtechnology.LathesLathesarewidelyusedinindustrytoproduceallkindsofmachinedparts.Somearegeneralpurposemachines,andothersareusedtoperformhighlyspecializedoperations.EngineLathesEnginelathes,ofcourse,aregeneralpurposemachineusedinproductionandmaintenanceshopallovertheworld.Sizesrangefromsmallbenchmodelstohugeheavydutypiecesofequipment.Manyofthelargerlathescomeequippedwithattachmentsnotcommonlyfoundintheordinaryshop,suchasautomaticstopsforthecarriage.TracerorDuplicatingLathesThetracerorduplicatinglatheisdesignedtoproduceirregularlyshapedpartsautomatically.Thebasicoperationofthislatheisasfallows.Atemplateofeitheraflatorthreedimensionalshapeisplacedinaholder.Aguideorpointerthenmovesalongthisshapeanditsmovementcontrolsthatofthecuttingtool.Theduplicationmayincludeasquareortaperedshoulder,grooves,tapers,andcontours.Worksuchasmotorshafts,spindles,pistons,rods,caraxles,turbineshafts,andavarietyofotherobjectscanbeturnedusingthistypeoflathe.TurretLathesWhenmachiningacomplexworkpieceonageneralpurposelathe,agreatdealoftimeisspentchangingandadjustingtheseveraltoolsthatareneededtocompletethework.Oneofthefirstadaptationsoftheenginelathewhichmadeitmoresuitabletomassproductionwastheadditionofmultitoolturretinplaceofthetailstock.Althoughmostturretshavesixstations,somehaveasmanyaseight.Highproductionturretlathesareverycomplicatedmachineswithawidevarietyofpoweraccessories.Theprincipalfeatureofallturretlathes,however,isthatthetoolscanperformaconsecutiveserialsofoperationsinpropersequence.Oncethetoolshavebeensetandadjusted,littleskillisrequiredtorunoutduplicateparts.AutomaticScrewMachinesScrewmachinesaresimilarinconstructiontoturretlathes,exceptthattheirheadsaredesignedtoholdandfeedlongbarsofstock.Otherwise,thereislittledifferentbetweenthem.Botharedesignedformultipletooling,andbothhaveadaptationsforidenticalwork.Originally,theturretlathewasdesignedasachuckinglatheformachiningsmallcastings,forgings,andirregularlyshapedworkpieces.Thefirstscrewmachinesweredesignedtofeedbarstockandwireusedinmakingsmallscrewparts.Today,however,theturretlatheisfrequentlyusedwithacolletattachment,andtheautomaticscrewmachinecanbeequippedwithachucktoholdcastings.Thesinglespindleautomaticscrewmachine,asitsnameimplies,machinesworkononlyonebarofstockatatime.Abar16to20feetlongisfedthroughtheheadstockspindleandisheldfirmlybyacollect.Themachiningoperationsaredonebycuttingtoolsmountedontheturretandonthecrossslide.Whenthemachineisinoperation,thespindleandthestockarerotatedatselectedspeedsfordifferentoperations.Ifrequired,rapidreversalofspindledirectionisalsopossible.Inthesinglespindleautomaticscrewmachine,aspecificlengthofstockisautomaticallyfedthroughthespindletoamachiningarea.Atthispoint,theturretandcrossslidemoveintopositionandautomaticallyperformwhateveroperationsarerequired.Afterthemachinedpieceiscutoff,stockisagainfedintothemachiningareaandtheentirecycleisrepeated.Multiplespindleautomaticscrewmachineshavefromfourtoeightspindleslocatedaroundaspindlecarrier.Longbarsofstock,supportedattherearofthemachine,passthroughthesehollowspindlesandaregrippedbycollets.Withthesinglespindlemachine,theturretindexesaroundthespindle.Whenonetoolontheturretisworking,theothersarenot.Withamultiplespindlemachine,however,thespindleitselfindexes.Thusthebarsofstockarecarriedtothevariousendworkingandsideworkingtools.Eachtooloperatesinonlyoneposition,butalltoolsoperatesimultaneously.Therefore,fourtoeightworkpiecescanbemachinedatthesametime.VerticalTurretLathesAverticalturretlatheisbasicallyaturretlathethathasbeenstoodonitsheadstockend.Itisdesignedtoperformavarietyofturningoperations.Itconsistsofaturret,arevolvingtable,andasideheadwithasquareturretforholdingadditionaltools.Operationsperformedbyanyofthetoolsmountedontheturretorsideheadcanbecontrolledthroughtheuseofstops.MachiningCentersManyoftodaysmoresophisticatedlathesarecalledmachiningcenterssincetheyarecapableofperforming,inadditiontothenormalturningoperations,certainmillinganddrillingoperations.Basically,amachiningcentercanbethoughtofasbeingacombinationturretlatheandmillingmachine.Additionalfeaturesaresometimesincludedbymanufacturerstoincreasetheversatilityoftheirmachines.NumericalControlOneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrolNC.PriortotheadventofNC,allmachinetoolsweremanuallyoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationof