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外文翻译--轴和齿轮的设计及应用.doc

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外文翻译--轴和齿轮的设计及应用.doc

英文原文SHAFTANDGEARDESIGNAbstractTheimportantpositionofthewheelgearandshaftcantfalterintraditionalmachineandmodernmachines.Thewheelgearandshaftsmainlyinstallthedirectionthatdeliversthedintattheprincipalaxisbox.Thepassingtoprocesstomakethemcanisdividedintomanymodelnumbers,usedingformanysituationsrespectively.SowemustbethemultilayerstotheunderstandingofthewheelgearandshaftinmanywaysKeywordsWheelgearShaftIntheforceanalysisofspurgears,theforcesareassumedtoactinasingleplane.Weshallstudygearsinwhichtheforceshavethreedimensions.Thereasonforthis,inthecaseofhelicalgears,isthattheteetharenotparalleltotheaxisofrotation.Andinthecaseofbevelgears,therotationalaxesarenotparalleltoeachother.Therearealsootherreasons,asweshalllearn.Helicalgearsareusedtotransmitmotionbetweenparallelshafts.Thehelixangleisthesameoneachgear,butonegearmusthavearighthandhelixandtheotheralefthandhelix.Theshapeofthetoothisaninvolutehelicoid.Ifapieceofpapercutintheshapeofaparallelogramiswrappedaroundacylinder,theangularedgeofthepaperbecomesahelix.Ifweunwindthispaper,eachpointontheangularedgegeneratesaninvolutecurve.Thesurfaceobtainedwheneverypointontheedgegeneratesaninvoluteiscalledaninvolutehelicoid.Theinitialcontactofspurgearteethisalineextendingallthewayacrossthefaceofthetooth.Theinitialcontactofhelicalgearteethisapoint,whichchangesintoalineastheteethcomeintomoreengagement.Inspurgearsthelineofcontactisparalleltotheaxisoftherotationinhelicalgears,thelineisdiagonalacrossthefaceofthetooth.Itisthisgradualoftheteethandthesmoothtransferofloadfromonetoothtoanother,whichgivehelicalgearstheabilitytotransmitheavyloadsathighspeeds.Helicalgearssubjecttheshaftbearingstobothradialandthrustloads.Whenthethrustloadsbecomehighorareobjectionableforotherreasons,itmaybedesirabletousedoublehelicalgears.Adoublehelicalgearherringboneisequivalenttotwohelicalgearsofoppositehand,mountedsidebysideonthesameshaft.Theydevelopoppositethrustreactionsandthuscanceloutthethrustload.Whentwoormoresinglehelicalgearsaremountedonthesameshaft,thehandofthegearsshouldbeselectedsoastoproducetheminimumthrustloadCrossedhelical,orspiral,gearsarethoseinwhichtheshaftcenterlinesareneitherparallelnorintersecting.Theteethofcrossedhelicalfearshavepointcontactwitheachother,whichchangestolinecontactasthegearswearin.Forthisreasontheywillcarryoutverysmallloadsandaremainlyforinstrumentalapplications,andaredefinitelynotrecommendedforuseinthetransmissionofpowerThereisondifferencebetweenacrossedhelicalgearandahelicalgearuntiltheyaremountedinmeshwitheachother.Theyaremanufacturedinthesameway.Apairofmeshedcrossedhelicalgearsusuallyhavethesamehandthatis,arighthanddrivergoeswitharighthanddriven.Inthedesignofcrossedhelicalgears,theminimumslidingvelocityisobtainedwhenthehelixangleareequal.However,whenthehelixanglearenotequal,thegearwiththelargerhelixangleshouldbeusedasthedriverifbothgearshavethesamehandWormgearsaresimilartocrossedhelicalgears.Thepinionorwormhasasmallnumberofteeth,usuallyonetofour,andsincetheycompletelywraparoundthepitchcylindertheyarecalledthreads.Itsmatinggeariscalledawormgear,whichisnotatruehelicalgear.Awormandwormgearareusedtoprovideahighangularvelocityreductionbetweennonintersectingshaftswhichareusuallyatrightangle.Thewormgearisnotahelicalgearbecauseitsfaceismadeconcavetofitthecurvatureoftheworminordertoprovidelinecontactinsteadofpointcontact.However,adisadvantageofwormgearingisthehighslidingvelocitiesacrosstheteeth,thesameaswithcrossedhelicalgearsWormgearingareeithersingleordoubleenveloping.Asingleenvelopinggearingisoneinwhichthegearwrapsaroundorpartiallyenclosestheworm..Agearinginwhicheachelementpartiallyenclosestheotheris,ofcourse,adoubleenvelopingwormgearing.Theimportantdifferencebetweenthetwoisthatareacontactexistsbetweentheteethofdoubleenvelopinggearswhileonlylinecontactbetweenthoseofsingleenvelopinggears.Thewormandwormgearofasethavethesamehandofhelixasforcrossedhelicalgears,butthehelixanglesareusuallyquitedifferentThehelixangleonthewormisgenerallyquitelarge,andthatonthegearverysmallBecauseofthis,itisusualtospecifytheleadangleontheworm,whichisthecomplementofthewormhelixangle,andthehelixangleonthegearthetwoanglesareequalfora90deg.ShaftangleWhengearsaretobeusedtotransmitmotionbetweenintersectingshaft,someofbevelgearisrequired.Althoughbevelgearareusuallymadeforashaftangleof90deg.Theymaybeproducedforalmostanyshaftangle.Theteethmaybecast,milled,orgenerated.Onlythegeneratedteethmaybeclassedasaccurate.Inatypicalbevelgearmounting,oneofthegearisoftenmountedoutboardofthebearing.Thismeansthatshaftdeflectioncanbemorepronouncedandhaveagreatereffectonthecontactofteeth.Anotherdifficulty,whichoccursinpredictingthestressinbevelgearteeth,isthefacttheteetharetapered.Straightbevelgearsareeasytodesignandsimpletomanufactureandgiveverygoodresultsinserviceiftheyaremountedaccuratelyandpositively.Asinthecaseofsqurgears,however,theybecomenoisyathighervaluesofthepitchlinevelocityInthesecasesitisoftengooddesignpracticetogotothespiralbevelgear,whichisthebevelcounterpartofthehelicalgear.Asinthecaseofhelicalgears,spiralbevelgearsgiveamuchsmoothertoothactionthanstraightbevelgears,andhenceareusefulwherehighspeedareencountered.Itisfrequentlydesirable,asinthecaseofautomotivedifferentialapplications,tohavegearingsimilartobevelgearsbutwiththeshaftoffset.SuchgearsarecalledhypoidgearsbecausetheirpitchsurfacesarehyperboloidsofrevolutionThetoothactionbetweensuchgearsisacombinationofrollingandslidingalongastraightlineandhasmuchincommonwiththatofwormgearsAshaftisarotatingorstationarymember,usuallyofcircularcrosssection,havingmounteduponitsuchelementsasgears,pulleys,flywheels,cranks,sprockets,andotherpowertransmissionelements.Shaftmaybesubjectedtobending,tension,compression,ortorsionalloads,actingsinglyorincombinationwithoneanother.Whentheyarecombined,onemayexpecttofindbothstaticandfatiguestrengthtobeimportantdesignconsiderations,sinceasingleshaftmaybesubjectedtostaticstresses,completelyreversed,andrepeatedstresses,allactingatthesametimeThewordshaftcoversnumerousvariations,suchasaxlesandspindles.Anaxleisashaft,witherstationaryorrotating,norsubjectedtotorsionload.Ashirtrotatingshaftisoftencalledaspindle.Wheneitherthelateralorthetorsionaldeflectionofashaftmustbeheldtocloselimits,theshaftmustbesizedonthebasisofdeflectionbeforeanalyzingthestresses.Thereasonforthisisthat,iftheshaftismadestiffenoughsothatthedeflectionisnottoolarge,itisprobablethattheresultingstresseswillbesafe.ButbynomeansshouldthedesignerassumethattheyaresafeitisalmostalwaysnecessarytocalculatethemsothatheknowstheyarewithinacceptablelimitsWheneverpossible,thepowertransruissionelements,suchasgearsorpullets,shouldbelocatedclosetothesupportingbearings,Thisreducesthebendingmoment,andhencethedeflectionandbendingstress.AlthoughthevonMisesHenckyGoodmanmethodisdifficulttouseindesignofshaft,itprobablycomesclosesttopredictingactualfailure.Thusitisagoodwayofcheckingashaftthathasalreadybeendesignedorofdiscoveringwhyaparticularshafthasfailedinservice.Furthermore,thereareaconsiderablenumberofshaftdesignproblemsinwhichthedimensionareprettywelllimitedbyotherconsiderations,suchasrigidity,anditisonlynecessaryforthedesignertodiscoversomethingaboutthefilletsizes,heattreatment,andsurfacefinishandwhetherornotshotpeeningisnecessaryinordertoachievetherequiredlifeandreliabilityBecauseofthesimilarityoftheirfunctions,clutchesandbrakesaretreatedtogether.Inasimplifieddynamicrepresentationofafrictionclutch,orbraketwoinertias11and12travelingattherespectiveangularvelocitiesWlandW2,oneofwhichmaybezerointhecaseofbrake,aretobebroughttothesamespeedbyengagingtheclutchorbrake.Slippageoccursbecausethetwoelementsarerunningatdifferentspeedsandenergyisdissipatedduringactuation,resultinginatemperaturerise.Inanalyzingtheperformanceofthesedevicesweshallbeinterestedintheactuatingforce,thetorquetransmitted,theenergylossandthetemperaturerise.Thetorquetransmittedisrelatedtotheactuatingforce,thecoefficientoffriction,andthegeometryoftheclutchorbrake.Thisisprobleminstatic,whichwillhavetobestudiedseparatelyforeathgeometricconfiguration.However,temperatureriseisrelatedtoenergylossandcanbestudiedwithoutregardtothetypeofbrakeorclutchbecausethegeometryofinterestistheheatdissipatingsurfaces.Thevarioustypesofclutchesandbrakesmaybeclassifiedasfllows1.Rimtypewithinternallyexpandingshoes2.Rimtypewithexternallycontractingshoes3。Bandtype4.Diskoraxialtype5.Conetype6.MiscellaneoustypeTheanalysisofalltypeoffrictionclutchesandbrakesusethesamegeneralprocedure.Thefollowingsteparenecessary1.Assumeordeterminethedistributionofpressureonthefrictionalsurfaces2.Findarelationbetweenthemaximumpressureandthepressureatanypoint3.Applytheconditionofstaticalequilibriumtofindatheactuatingforce,bthetorque,andcthesupportreactionsMiscellaneousclutchesincludeseveraltypes,suchasthepositivecontactclutches,overloadreleaseclutches,overrunningclutches,magneticfluidclutches,andothers.Apositivecontactclutchconsistsofashiftleverandtwojaws.Thegreatestdifferencesbetweenthevarioustypesofpositiveclutchesareconcernedwiththedesignofthejaws.Toprovidealongerperiodoftimeforshiftactionduringengagement,thejawsmayberatchetshaped,orgeartoothshaped.Sometimesagreatmanyteethorjawsareused,andtheymaybecuteithercircumferentially,sothattheyengagebycylindricalmating,oronthefacesofthematingelementsAlthoughpositiveclutchesarenotusedtotheextentofthefrictionalcontacttype,theydohaveimportantapplicationswheresynchronousoperationisrequiredDevicessuchaslineardrivesormotoroperatedscrewdriversmustruntodefinitelimitandthencometoastop.Anoverloadreleasetypeofclutchisrequiredfortheseapplications.Theseclutchesareusuallyspringloadedsoastoreleaseatapredeterminedtoque.TheclickingsoundwhichisheardwhentheoverloadpointisreachedisconsideredtobeadesirablesignalAnoverrunningclutchorcouplingpermitsthedrivenmemberofamachinetofreewheeloroverrunbecausethedriverisstoppedorbecauseanothersourceofpowerincreasethespeedofthedriven.Thistypeofclutchusuallyusesrollersorballsmountedbetweenanoutersleeveandaninnermemberhavingflatsmachinedaroundtheperiphery.Drivingactionisobtainedbywedgingtherollersbetweenthesleeveandtheflats.TheclutchisthereforeequivalenttoapawlandratchetwithaninfinitenumberofteethMagneticfluidclutchorbrakeisarelativelynewdevelopmentwhichhastwoparallelmagneticplates.Betweentheseplatesisalubricatedmagneticpowdermixture.Anelectromagneticcoilisinsertedsomewhereinthemagneticcircuit.Byvaryingtheexcitationtothiscoil,theshearingstrengthofthemagneticfluidmixturemaybeaccuratelycontrolled.ThusanyconditionfromafullsliptoafrozenlockupmaybeobtainedIntroducitonofMachiningHaveashapeasaprocessingmethod,allmachiningprocessfortheproductionofthemostcommonlyusedandmostimportantmethod.Machiningprocessisaprocessgeneratedshape,inthisprocess,Driversdeviceontheworkpiecematerialtobeintheformofchipremoval.Althoughinsomeoccasions,theworkpieceundernocircumstances,theuseofmobileequipmenttotheprocessing,However,themajorityofthemachiningisnotonlysupportingtheworkpiecealsosupportingtoolsandequipmenttocomplete.Machiningknowtheprocesshastwoaspects.Smallgroupoflowcostproduction.Forcasting,forgingandmachiningpressure,everyproductionofaspecificshapeoftheworkpiece,evenaspareparts,almosthavetospendthehighcostofprocessing.Weldingtorelyontheshapeofthestructure,toalargeextent,dependoneffectiveintheformofrawmaterials.Ingeneral,throughtheuseofexpensiveequipmentandwithoutspecialprocessingconditions,canbealmostanytypeofrawmaterials,mechanicalprocessingtoconverttherawmaterialsprocessedintothearbitraryshapeofthestructure,aslongastheexternaldimensionslargeenough,itispossible.Becauseofaproductionofspareparts,evenwhenthepartsandstructureoftheproductionbatchsizesaresuitablefortheoriginalcasting,Forgingorpressureprocessingtoproduce,butusuallyprefermachiningStrictprecisionandgoodsurfacefinish,MachiningthesecondpurposeistheestablishmentofthehighprecisionandsurfacefinishpossibleonthebasisofManyparts,ifanyothermeansofproductionbelongingtothelargescaleproduction,WellMachiningisalowtoleranceandcanmeettherequirementsofsmallbatchproduction.Besides,manypartsontheproductionandprocessingofcoarseprocesstoimproveitsgeneralshapeofthesurface.Itisonlynecessaryprecisionandchooseonlythesurfacemachining.Forinstance,thread,inadditiontomechanicalprocessing,almostnootherprocessingmethodforprocessing.Anotherexampleistheblacksmithpieceskeyholeprocessing,aswellastrainingtobeconductedimmediatelyafterthemechanicalcompletionoftheprocessing.PrimaryCuttingParametersCuttingtheworkpieceandtoolbasedonthebasicrelationshipbetweenthefollowingfourelementstofullydescribethetoolgeometry,cuttingspeed,feedrate,depthandpenetrationofacuttingtool.CuttingToolsmustbeofasuitablematerialtomanufacture,itmustbestrong,toughhardandwearresistant.Toolgeometrytothetipplaneandcutteranglecharacteristicsforeachcuttingprocessmustbecorrect.Cuttingspeedisthecuttingedgeofworkpiecesurfacerate,itisinchesperminutetoshow.Inordertoeffectivelyprocessing,andcuttingspeedmust

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