外文翻译齿 轮.doc外文翻译齿 轮.doc

收藏

编号:201311171440036638    类型:共享资源    大小:165.50KB    格式:DOC    上传时间:2013-11-17
  
5
关 键 词:
专业文献 学术论文 精品文档 外文翻译
资源描述:
附录1GEARSpurandhelicalgears.Agearhavingtoothelementsthatarestraightandparalleltoitsaxisisknownasaspurgear.Aspurpaircanbeusedtoconnectparallelshaftsonly.Parallelshafts,however,canalsobeconnectedbygearsofanothertype,andaspurgearcanbematedwithagearofadifferenttype.(Fig.1.1).Topreventjammingasaresultofthermalexpansion,toaidlubrication,andtocompensateforavoidableinaccuraciesinmanufacture,allpower-transmitting,gearsmusthavebacklash.Thismeansthatonthegear,andviceversa.Oninstrumentgears,backlashcaneliminatedbyusingagearsplitdownitsmiddle,onehalfbeingrotatablerelativetotheother.Aspringforcesthesplitgearteethtooccupythefullwidthofthepinionspace.Helicalgearshavecertainadvantages;forexample,whenconnectingparallelshaftstheyhaveahigherloadcarryingthanspurgearswiththesametoothnumbersandcutwiththesamecutter.Becauseoftheoverlappingactionoftheteeth,theyaresmootherinactionandcanoperateathigherpitch-linetotheaxisofrotation,helicalgearscreateanaxialthrust.Ifusedsingly,thisthrustmustbeabsorbedinthesameblank.Dependingonthemethodofmanufacture,thegearmaybeofthecontinuous-toothherringbonevarietyoradouble-helicalgearwithaspacebetweenthetwohalvestopermitthecuttingtooltorunout.Double-helicalgearsarewellsuitedfortheefficienttransmissionofpowerathighspeeds.Helicalgearscanalsobeusedtoconnectnonparallel,non-intersectingshaftsatanyangletooneanother.Ninetydegreesisthecommonestangleatwhichsuchgearsareused.Wormandbevelgears.Inordertoachievelinecontactandimprovetheloadcarryingcapacityofthecrossed-axishelicalgears,thegearcanbemadetocurvepartiallyaroundthepinion,insomewhatthesamewaythatanutenvelopsascrew.Theresultwouldbeacylindricalwormandgear.Wormgearsprovidethesimplestmeansofobtaininglargerationsinasinglepair.Theyareusuallylessefficientthanparallel-shaftgears,however,becauseofanadditionalslidingmovementalongtheteeth.Becauseoftheirsimilarity,theefficiencyofawormandgeardependsonthesamefactorsastheefficiencyofascrew.Single-threadwormsoflargediameterhavesmallleadanglesandlowefficiencies.Multiple-threadwormshavelargerleadanglesandhigherefficiencies(Fig.1.2)Fortransmittingrotarymotionandtorquearoundcorners,bevelgearsarecommonlyused.Theconnectedshafts,whoseaxeswouldintersectifextended,areusuallybutnotnecessarilyatrightanglestooneanother.Whenadaptedforshaftsthatdonotintersect,spiralbevelgearsarecalledhypoidgears.Thepitchsurfacesofthesegearsarenotrollingcones,andtheratiooftheirmeandiametersisnotequaltothespeedConsequently,thepinionmayhavefewteethandbemadeaslargeasnecessarytocarrytheload.Theprofilesoftheteethonbevelgearsarenotinvolutes;theyareofsuchashapethatthetoolsfortheteethareeasiertomakeandmaintainthaninvolutecuttingtools.Sincebevelgearscomein,aslongastheyareconjugatetooneanothertheyneednotbeconjugatetoothergearswithdifferentbothnumbers.1EarlyHistoryofGearingTheearliestwrittendescriptionsofgearsaresaidtohavebeenmadebyAristotleinthefourthcenturyB.C.IthasbeenpointedoutthatthepassageattributedtoAristotlebysomewasactuallyfromthewritingsofhisschool,in“MechanicalProblemsofAristotle”(Ca.280B.C).Inthepassageinquestion,therewasnomentionofgearteethontheparallelwheels,andtheymayjustaswellhavebeensmoothwheelsinfrictionalcontact.Therefore,theattributionofgearingtoAristotleis,mostlikely,incorrect.TherealbeginningofgearingwasprobablywithArchimedeswhoabout250B.C.inventedtheendlessscrewturningatoothedwheel,whichwasusedinenginesofwar.Archimedesalsousedgearstosimu-earlyformsofwagonmileageindicators(odometer)andsurveyinginstruments.Thesedeviceswereprobably“thought”experimentsofHeronofAlexandria(ca.A.D.60),whowroteonthesubjectsoftheoreticalmechanicsandthebasicelementsofmechanism.TheoldestsurvivingreliccontaininggearsistheAntikytheramechanism,sonamedbecauseoftheGreekislandofthatnamenearwhichthemechanismwasdiscoveredinasunkenshipin1900.ProfessorPriceofYaleUniversityhaswrittenanauthoritativeaccountofthismechanism.Themechanismisnotonlytheearliestrelicofgearing,butitalsoisanextremelycomplexarrangementofepicyclicdifferentialgearing.Themechanismisidentifiedasacalendricalcomputingmechanismforthesunandmoon,andhasbeendatedtoabout87B.C.TheartofgearingwascarriedthroughtheEuropeandarkagesafterthefallofRome,appearinginIslamicinstrumentssuchasthegearedastrolabeswhichwereusedtocalculatethepositionsofthecelestialbodies.Perhapstheartwasrelearnedbytheclock-andinstrument-makingartisansoffourteenth-centuryEurope,orperhapssomecrystallizingideasandmechanismswereimportedfromtheEastafterthecrusadesoftheelevenththroughthethirteenthcenturies.ItappearsthattheEnglishabbotofSt.Alban’smonastery,bornRichardofWallingford,inA.D.1330,reinventedtheepicyclicgearingconcept.Heappliedittoanastronomicalclock,whichhebegantobuildatthattimeandwhichwascompletedafterhisdeath.AmechanicalclockofaslightlylaterperiodwasconceivedbyGiovannideDondi(1348-1364).Diagramsofthisclock,whichdidnotusedifferentialgearing,appearinthesketchbooksofLeonardodaVinci,whodesignedgearedmechanismshimself.In1967twoofdaVinci’smanuscripts,lostintheNationalLibraryinMadridsince1830,wererediscovered.Oneofthemanuscripts,writtenbetween1493and1497andknownas“CodexMadridI”,contains382pageswithsome1600sketches.IncludedamongthisdisplayofLenardo’sartisticskillandengineeringabilityarehisstudiesofgearing.Amongthesearetoothprofiledesignsandgearingarrangementsthatwerecenturiesaheadoftheir“invention”.2BeginningofModernGearTechnologyIntheperiod1450to1750,themathematicsofgear-toothprofilesandtheoriesofgearedmechanismsbecameestablished.AlbrechtDureriscreditedwithdiscoveringtheepicycloidalshape(ca.1525).PhilipdelaHireissaidtohaveworkedouttheanalysisofepicycloidsandrecommendedtheinvolutecurveforgearteeth(ca.1694).LeonardEulerworkedoutthelawofconjugateaction(ca.1754).Gearsdeignedaccordingtothislawhaveasteadyspeedratio.Sincetheindustrialrevolutioninmid-nineteenthcentury,theartofgearingblossomed,andgeardesignssteadilybecamebasedonmorescientificprinciples.In1893WilfredLewispublishedaformulaforcomputingstressingearteeth.Thisformulaisinwideusetodayingeardesign.In1899GeorgeB.Grant,thefounderoffivegearmanufacturingcompanies,published“ATreatiseonGearWheels”.Newinventionsledtonewapplicationsforgearing.Forexample,intheearlypartofthiscentury(1910),parallelshaftgearswereintroducedtoreducethespeedofthenewlydevelopedreactionsteamturbineenoughtoturnthedrivingscrewsofocean-goingvessels.Thisapplicationachievedanoverallincreaseinefficiencyof25percentinseatravel.Theneedformoreaccurateandquiet-runninggearsbecameobviouswiththeadventoftheautomobile.Althoughthehypoidgearwaswithinourmanufacturingcapabilitiesby1916,itwasnotusedpracticallyuntil1926,whenitwasusedinthePackardautomobile.Thehypoidgearmadeitpossibletolowerthedriveshaftandgainmoreusablefloorspace.By1937almostallcarsusedhypoid-gearedrearaxles.Speciallubricantantiwearadditiveswereformulatedinthe1920swhichmadeitpracticaltousehypoidgearing.In1931EarleBuchingham,chairmanofanAmericanSocietyofMechanicalEngineers(ASME)researchcommitteeongearing,publishedamilestonereportongear-toothdynamicloading.Thisledtoabetterunderstandingofwhyfaster-runninggearssometimescouldnotcarryasmuchloadasslower-runninggears.High-strengthalloysteelsforgearingweredevelopedduringthe1920sand1930s.Nitridingandcase-hardeningwasintroducedin1950.Extremelycleansteelsproducedbyvacuummeltingprocessesintroducedin1960haveprovedeffectiveinprolonginggearlife.Sincetheearly1960stherehasbeenincreaseduseofindustrialgasturbinesforelectricpowergeneration.Intherangeof1000to14000hp,epicyclicgearsystemshavebeenusedsuccessfully.Pitch-linevelocitiesareform50to100m/s(10000to20000ft/min).Thesegearsetsmustworkreliablyfor10000to30000hpbetweenoverhaule.In1976bevelgearsproducedtodriveacompressorteststandranstandransuccessfullyfor235hat2984kwand200m/s.formallindicationsthesegearscouldbeusedinanindustrialapplicationifneeded.Areasonablemaximumpitch-linevelocityforcommercialspiral-bevelgearswithcurvedteethis60m/s.Gearsystemdevelopmentmethodshavebeenadvancedinwhichlightweight,
  人人文库网所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。
关于本文
本文标题:外文翻译齿 轮.doc
链接地址:http://www.renrendoc.com/p-96638.html

当前资源信息

4.0
 
(2人评价)
浏览:27次
淘宝运营上传于2013-11-17

官方联系方式

客服手机:17625900360   
2:不支持迅雷下载,请使用浏览器下载   
3:不支持QQ浏览器下载,请用其他浏览器   
4:下载后的文档和图纸-无水印   
5:文档经过压缩,下载后原文更清晰   

精品推荐

相关阅读

人人文库
关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服客服 - 联系我们

网站客服QQ:2846424093    人人文库上传用户QQ群:460291265   

[email protected] 2016-2018  renrendoc.com 网站版权所有   南天在线技术支持

经营许可证编号:苏ICP备12009002号-5