毕业外文翻译--齿轮和齿轮传动

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1、兰州交通大学毕业设计（论文）GearsandgeardriveGearsarethemostdurableandruggedofallmechanicaldrives.Theycantransmithighpoweratefficienciesupto98%andwithlongservicelives.Forthisreason,gearsratherthanbeltsorchainsarefoundinautomotivetransmissionsandmostheavy-dutymachin

2、edrives.Ontheotherhand,gearsaremoreexpensivethanotherdrives,especiallyiftheyaremachinedandnotmadefrompowermetalorplastic.Gearcostincreasessharplywithdemandsforhighprecisionandaccuracy.Soitisimportanttoestablishtolerancerequirementsappropriatefortheapp

3、lication.Gearsthattransmitheavyloadsorthanoperateathighspeedsarenotparticularlyexpensive,butgearsthatmustdobotharecostly.Silentgearsalsoareexpensive.Instrumentandcomputergearstendtobecostlybecausespeedordisplacementratiosmustbeexact.Attheotherextreme,

4、gearsoperatingatlowspeedinexposedlocationsarenormallytermednocriticalandaremadetominimumqualitystandards.Fortoothforms,size,andquality,industrialpracticeistofollowstandardssetupbytheAmericanGearManufacturesAssociation(AGMA).ToothformStandardspublished

5、byAGMAestablishgearproportionsandtoothprofiles.Toothgeometryisdeterminedprimarilybypitch,depth,andpressureangle.Pitch：StandardspitchesareusuallywholenumberswhenmeasuredasdiametralpitchP.Coarse-pitchgearinghasteethlargerthan20diametralpitch–usually0.5t

6、o19.99.Fine-pitchgearingusuallyhasteethofdiametralpitch20to200.Depth:Standardizedintermsofpitch.Standardfull-depthhaveworkingdepthof2/p.Iftheteethhaveequaladdenda(asinstandardinterchangeablegears)theaddendumis1/p.Stubteethhaveaworkingdepthusually20%le

7、ssthanfull-depthteeth.Full-depthteethhavealargercontractratiothanstubteeth.Gearswithsmallnumbersofteethmayhaveundercutsothantheydonotinterferewithoneanotherduringengagement.Undercuttingreduceactiveprofileandweakensthetooth.Matinggearswithlongandshorta

8、ddendumhavelargerload-carryingcapacitythanstandardgears.Theaddendumofthesmallergear(pinion)isincreasedwhilethatoflarger9兰州交通大学毕业设计（论文）gearisdecreased,leavingthewholedepththesame.Thisformisknowasrecess-actiongearing.PressureAngle:Standardangles