第6章 Machine Element.ppt

TEXTREADINGMATERIAL Unit6 TEXTMachineElementsHoweversimple anymachineisacombinationofindividualcomponentsgenerallyreferredtoasmachineelementsorparts Thus ifamachineiscompletelydismantled acollectionofsimplepartsremainssuchasnuts bolts springs gears camsandshafts thebuildingblocksofallmachinery Amachineelementis therefore asingleunitdesignedtoperformaspecificfunctionandcapableofcombiningwithotherelements Sometimescertainelementsareassociatedinpairs suchasnutsandboltsorkeysandshafts Inotherinstances agroupofelementsiscombinedtoformasubassembly suchasbearings couplings andclutches Themostcommonexampleofamachineelementisagear which fundamentally isacombinationofthewheelandthelevertoformatoothedwheel Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower dependinguponthenumberofteethonthebasicwheels Fig 6 1NutandboltFig 6 2Spring Fig 6 3Shaftandbearing Fig 6 4Clutch Otherfundamentalmachineelementshaveevolvedfromwheelandlever Awheelmusthaveashaftonwhichitmayrotate Thewheelisfastenedtotheshaftswithcouplings Theshaftmustrestinbearings maybeturnedbyapulleywithabeltorachainconnectingittoapulleyonasecondshaft Thesupportingstructuremaybeassembledwithboltsorrivetsorbywelding Properapplicationofthesemachineelementsdependsuponknowledgeoftheforceonthestructureandthestrengthofthematerialsemployed Manymachineelementsarethoroughlystandardized Testingandpracticalexperiencehaveestablishedthemostsuitabledimensionsforcommonstructuralandmechanicalparts Throughstandardization uniformityofpracticeandresultingeconomicsareobtained Notallmachinepartsinusearestandardized however Intheautomotiveindustryonlyfasteners bearings bushings chains andbeltsarestandardized Crankshaftsandconnectingrodsarenotstandardized LEARNTOSPEAKMr Liu Goodafternoon Mr Xie Mr Xie Goodafternoon Mr Liu Mr Liu MayIaskyouafewquestions Mr Xie Yes ofcourse Whataretheproblems Mr Liu Howmanykindsofgearsarethereincommonuse Mr Xie Therearefourkindsofgears Mr Liu Whatarethey Mr Xie Theyarespurgears helicalgears wormgears andbevelgears Mr Liu Aregearsimportantinnearlyallofmachinery Mr Xie Yes theyare Mr Liu Whatcanthespurgearsbeusedfor Mr Xie Spurgearsareusedtotransmitpowerandrotarymotionbetweenparallelshafts Mr Liu Howdoyoudistinguishthedrivingelement andthedrivenelement Mr Xie Thesmalleroftwogearsinmeshiscalleddrivingelement andtheotheriscalleddrivenelement Mr Liu Wherearethespurgearsusedfor Mr Xie Theyareusedforlowspeedapplicationsandthosesituationswherenoisecontrolisnotaproblem Mr Liu Andwherearethehelicalgearsusedfor Mr Xie Theyareusedforhighspeed largepowertransmission orwherenoiseabatementisimportant Mr Liu Thankyoufortellingmeaboutthese Mr Xie Notatall NEWWORDSANDEXPRESSIONScombination k mb ne n n 组合 组合物component k m p n nt n 元件 组件dismantle d s m ntl vt 分解 机器 拆开nut n t n 螺母 螺帽v 上 拧 装 螺母spring spr n 弹簧v 弹回cam k m n 凸轮 偏心轮machinery m i n r n 机器 机械perform p f m v 执行 完成 associate s et v 联合 结合key ki n 键subassembly s b sembl n 组合件 部件coupling k pl n 联轴节 联轴器clutch kl t n 离合器fundamentally f nd ment l adv 从 根本上hub h b n 轮毂evolve v lv v 进化 演变assemble semb l v 安装 装配n 组件 rivet r v t n 铆钉v 铆接 铆weld weld v n 焊接 熔焊adj 焊接的thoroughly r l adv 完全地 彻底地standardize st nd da z vt 标准化establish st bl vt 确定 建立dimension d men n n 尺寸v 标尺寸 uniformity ju n f m t n 均匀性 一致性obtain b te n v 获得automotive t m t v adj 自动的 汽车的distinguish d s t gw v 区别abatement be tm nt n 消除 referto指的是 称为combinewith与 相结合inotherinstances在其它情况下spurgear直齿轮drivingelement主动元件drivenelement被动元件 NOTES1 Thus ifamachineiscompletelydismantled acollectionofsimplepartsremainssuchasnuts bolts springs gears camsandshafts thebuildingblocksofallmachinery 因此 如果把机床完全拆开 就可以得到像螺母 螺栓 弹簧 齿轮 凸轮及轴等简单零件 这是所有机器的标准元件 if引导条件状语从句 表示如果 2 Themostcommonexampleofamachineelementisagear which fundamentally isacombinationofthewheelandthelevertoformatoothedwheel Therotationofthisgearonahuborshaftdrivesothergearsthatmayrotatefasterorslower dependinguponthenumberofteethonthebasicwheels 机械零件中最常见的是齿轮 它实际上是由轮子和杆组成的带有齿的轮子 装在轴套轮毂或轴上的旋转齿轮驱动其它齿轮做加速或减速转动 这取决于基准齿轮的齿数 which 引导非限制性定语从句 修饰 gear 不定式 toformatoothedwheel 作状语 表示结果 分词 dependingupon 作状语 3 Notallmachinepartsinusearestandardized however 然而 并不是所有已经使用的零件都是标准的 Notall 是不完全否定 其含义是 并非所有 句中 hower 的位置可以比较灵活 可以放在句首 也可以放在句子中间 还可以放在句子后面 EXERCISES1 DiscussthefollowingquestionsinEnglish 1 Whatismachineelement 2 Whatdotheboltsdo 3 Wherearethespringsused 4 Whichelementsareassociatedinpairs 3 Placea T aftersentencesthataretrueandan F afterthosethatarefalse 1 Gearsareusedasbuildingblocksfortheconstructionofmostdevices apparatus andmachinery 2 Apairofgearswithdifferentnumbersofteethwillrotateatdifferentspeeds 3 Themostcommonmachineelementisthegearfromwhichotherfundamentalmachineelementshavedeveloped 4 Acouplingisamachineelementwhichjoinstwoshafts 5 Allmachinepartshavebeendevelopedintostandardizeddesigns 4 Contextualreference 1 Insentencetwo thebuildingblocks refersto a machineelements b devices apparatusandmachinery 2 Insentence9 the it refersto a thebrake b theshaft c theclutch 3 Insentence11 the it refersto a thepulley b theshaft c thebelt 4 Insentence13 thesemachineelements refersto a boltsandrivets b wheels shafts bearings clutches couplings etc 5 Rephrasing 1 Themostcommonmachineelementisthegear whichcombinesfeaturesofthewheelandthelever 2 Thehardnessofageardeterminesitsabilitytoresistwear 3 Inthedesign calculationsmustmaketheforcesfitthematerialsinthesimplestconstruction 4 Manufacturingengineershavecenteredtheireffortsonthedevelopmentofstandardizedelements 5 Thesepartsareproducedinlargequantitieswithahighdegreeofperfectionatreducedcost READINGMATERIALGearsThetransmissionofrotarymotionfromoneshafttoanotheroccursinnearlyeverymachineonecanimagine Gearsconstituteoneofthebestofthevariousmeansavailablefortransmittingthismotion Agearisvirtualawheelwithveryaccuratelyshapedteeth Theseteethmeshwiththeteethofanothergear thusprovidingapositive motiondrive Thespeedratiobetweentheshaftscarryingapairofgearsdependsuponthenumberofteethinthegears Forexample ifa20 toothgeardrivesagearof50teeth thesmallergearwillhavetoturn21 2timestocausethelargeronetomake1turn Varioustypesofgearinghavebeendevelopedfordifferentpurposes Iftheshaftsareparallel anyofthreetypesmaybeused spur helical orherringbone Spurgearsarethesimplestandleastexpensivetype Theyaregenerallyusedondrivesrequiringmoderatespeeds Bevelgearsservetotransmitpowerbetweentwointersectingshafts Withaworm geardrive itispossibletoobtainlargespeedreductionataright angledrive Rack and piniondrivesareusedwhereitisdesirabletotransformtherotarymotionofonepartintolinearmotionfortheotherpart orviceversa asshowninFig 6 8 Fig 6 5SpurgearandpinionFig 6 6Bevelgears Fig 6 7WormgearandwormFig 6