机械工程专业英语课件--L09.ppt

EnglishforMechanicalEngineering,机械工程专业英语,Slottedconepointedsetscrew.Hexnut.Slottednut.Brightwasher.Springwasher.Tabwasher锥端紧定螺钉六角螺母六角槽形螺母平垫圈弹簧垫圈外舌止动垫圈,Hexagonheadbolt.Stud.Slottedcheeseheadscrew.Slottedpanheadscrew.Slottedcountersunkscrew.Hexagonsocketcap六角头螺钉双头螺柱头圆柱头螺钉盘头螺钉沉头螺钉圆柱头内六角螺钉,Typesofscrewfasteners螺纹紧固件的种类,Partswiththreadsusedforjoiningandfasteningarecalledscrewfasteners.Themostwidelyusedcomponentsasscrewfastenersarebolts,doublescrewbolts-stud,screws,nutsandwashers。用螺纹联接并起紧固作用的零件称为螺纹紧固件。常用的螺纹紧固件有螺栓、双头螺柱、螺钉、螺母、垫圈等。,Lesson19Screws,fastenersandjoints,机械工程专业英语,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,Boltedjointsareoneofthemostcommonelementsinconstructionandmachinedesign.Theyconsistofcapscrewsorstudsthatcaptureandjoinotherparts,andaresecuredwiththematingofscrewthreads.Therearetwomaintypesofboltedjointdesigns.Inonemethodtheboltistightenedtoacalculatedclampload,usuallybyapplyingameasuredtorqueload.Thejointwillbedesignedsuchthattheclamploadisneverovercomebytheforcesactingonthejoint(andthereforethejoinedpartsseenorelativemotion).Theothertypeofboltedjointdoesnothaveadesignedclamploadbutreliesontheshearstrengthoftheboltshaft.Thismayincludeclevislinkages,jointsthatcanmove,andjointsthatrelyonlockingmechanism(likelockwashers,threadadhesives,andlocknuts).,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,Boltedjoint,Screwjoint,Studjoint,Bolt螺栓,Theboltassemblyisusedwhenjointpartsarenottoothicktodrillthroughholes.螺栓用于联接二通孔薄件,Stud双头螺柱,Studareusedinsituationswhereapartwithathroughholeandapartwithblindtappedhole.双头螺柱用于联接一通孔薄件和一盲孔厚件。,Screw螺钉,Screwsaremostlyusedforthecaseswithsmallbearingforces.suchasinspectioncoverswhichhavetoberemovedfrequently.螺钉多用于用于受力不大需要经常拆卸的情况,Nut螺母,Nutareusedtomatchtheotherscrewfasteners.螺母与其他螺纹件配合使用,Washer垫圈,弹簧垫圈平垫圈,Washerareusedtomatchtheotherscrewfasteners.垫圈与其他螺纹件配合使用,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,TheoryTheclampload,alsocalledpreload,ofacapscrewiscreatedwhenatorqueisapplied,andisgenerallyapercentageofthecapscrewsproofstrength.Capscrewsaremanufacturedtovariousstandardsthatdefine,amongotherthings,theirstrengthandclampload.Torquechartsareavailablethatidentifytherequiredtorqueforcapscrewsbasedontheirpropertyclassorgrade.Whenacapscrewistighteneditisstretched,andthepartsthatarecapturedarecompressed.Theresultisaspring-likeassembly.Externalforcesaredesignedtoactonthepartsthathavebeencompressed,andnotonthecapscrew.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,TheoryTheresultisanon-intuitivedistributionofstrain;inthisengineeringmodel,aslongastheforcesactingonthecompressedpartsdonotexceedtheclampload,thecapscrewdonotseeanyincreasedload.Thismodelisonlyvalidwhenthemembersundercompressionaremuchstifferthanthecapscrew.Thisisasimplifiedmodel.Inrealitytheboltwillseeasmallfractionoftheexternalloadpriortoitexceedingtheclampload,dependingonthecompressedpartsstiffnesswithrespecttothehardwaresstiffness.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,TheoryTheresultsofthistypeofjointdesignare:Greaterpreloadsinboltedjointsreducethefatigueloadingofthehardware.Forcyclicloads,theboltdoesnotseethefullamplitudeoftheload.Asaresult,fatiguelifecanbeincreasedor,ifthematerialexhibitsanendurancelimit,extendedindefinitely.Aslongastheexternalloadsonajointdontexceedtheclampload,thehardwaredoesntseeanymotionandwillnotcomeloose(nolockingmechanismsarerequired).Inthecaseofthecompressedmemberbeinglessstiffthanthehardware(soft,compressedgasketsforexample)thisanalogydoesntholdtrue.Theloadseenbythehardwareisthepreloadplustheexternalload.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,TheoryTheresultsofthistypeofjointdesignare:Greaterpreloadsinboltedjointsreducethefatigueloadingofthehardware.Forcyclicloads,theboltdoesnotseethefullamplitudeoftheload.Asaresult,fatiguelifecanbeincreasedor,ifthematerialexhibitsanendurancelimit,extendedindefinitely.Aslongastheexternalloadsonajointdontexceedtheclampload,thehardwaredoesntseeanymotionandwillnotcomeloose(nolockingmechanismsarerequired).Inthecaseofthecompressedmemberbeinglessstiffthanthehardware(soft,compressedgasketsforexample)thisanalogydoesntholdtrue.Theloadseenbythehardwareisthepreloadplustheexternalload.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,ThreadstrengthNutthreadsaredesignedtosupporttheratedclamploadoftheirrespectivebolts.Iftappedthreadsareusedinsteadofanut,thentheirstrengthneedstobecalculated.Steelhardwareintotappedsteelthreadsrequiresadepthof1.5threaddiametertosupportthefullclampload.Ifanappropriatedepthofthreadsisnotavailable,orthethreadsareinaweakermaterialthanthecapscrew,thentheclampload(andtorque)needstobederatedappropriately.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,FailuremodesThemostcommonmodeoffailureisoverloading.Operatingforcesoftheapplicationproduceloadsthatexceedtheclamploadandthejointworksitselfloose,orfailscatastrophically.Overtorquingwillcausefailurebydamagingthethreadsanddeformingthehardware,thefailuremightnotoccuruntillongafterward.Undertorquingcancausefailuresbyallowingajointtocomeloose.Itmayalsoallowthejointtoflexandthusfailunderfatigue.Brinellingmayoccurwithpoorqualitywashers,leadingtoalossofclamploadandfailureofthejoint.Corrosion,embedmentandexceedingtheshearstresslimitareothermodesoffailure.,机械工程专业英语,预备知识,一、Backgroundinformation,Lesson19Screws,fastenersandjoints,Notes:Brinellingreferstoamaterialsurfacefailurecausedbycontactstressthatexceedsthemateriallimit.Thisfailureiscausedbyjustoneapplicationofaloadgreatenoughtoexceedthemateriallimit.Theresultisapermanentdentorbrinellmark.Embedmentisaphenomenoninmechanicalengineeringinwhichthesurfacesbetweenmechanicalmembersofaloadedjointembed.Itcanleadtofailurebyfatigueasdescribedbelow,andisofparticularconcernwhenconsideringthedesignofcriticalfastenerjoints.,机械工程专业英语,预备知识,一、预备知识,Lesson19Screws,fastenersandjoints,1、基本类型普通螺栓联接：被联接件上通孔和螺栓杆间留有间隙，故精度低、结构简单。铰制孔用螺栓联接：孔和螺栓杆多采用基孔制过渡配合（H7/m6、H7/n6）,精确固定被联接件的相对位置，并可承受横向载荷。双头螺栓联接：被联接件之一太厚或经常拆装螺钉联接：不用螺母，比双头螺柱简单，用途相似，多用于受力不大、不需经常拆装的场合紧定螺钉联接：固定两零件的相对位置，可传递不太大的扭矩和力螺栓的类型：六角头螺栓和双头螺栓螺钉的类型：半圆头、平头、六角头、圆柱头、沉头,机械工程专业英语,预备知识,一、预备知识,Lesson19Screws,fastenersandjoints,2、螺纹的预紧预紧的目的：增强联接的可靠性、紧密性，防止受载后被联接件间出现缝隙或发生相对滑移。选用较大的预紧力可提高联接的可靠性和疲劳强度预紧应力不超过其材料的屈服极限的80%。控制预紧力的方法：1）借助测力矩扳手或定力矩扳手2）测定螺栓伸长量,机械工程专业英语,预备知识,一、预备知识,Lesson19Screws,fastenersandjoints,3、螺纹的防松螺纹升角小于螺旋副的当量摩擦角：自锁性好螺母与螺栓头部等支承面上的摩擦力摩擦防松：锁紧螺母、弹簧垫圈、自锁螺母机械防松：开口销与槽形螺母、止动垫圈铆冲防松：端铆、冲点,词汇,二、词汇,screw螺钉、螺纹bolt螺栓nut螺母studbolt双头螺栓washer垫圈thread螺纹,机械工程专业英语,Lesson19Screws,fastenersandjoints,课文分析,机械工程专业英语,Lesson19Screws,fastenersandjoints,Typicalmethodsoffasteningandjoiningpartsincludetheuseofsuchitemsasbolts,nuts,capscrews,setscrews,rivets,lockingdevicesandkeys.Partsmayalsobejoinedbywelding,brazing,orclippingtogether.Studiesinengineeringgraphicsandinmetalprocessesoftenincludeinstructiononvariousjoiningmethods,andthecuriosityofanypersoninterestedinengineeringnaturallyresultsinacquisitionofagoodbackgroundoffasteningmethods.,Typicalmethodsoffasteningandjoiningpartsincludetheuseofsuchitemsasbolts,nuts,capscrews,setscrews,rivets,lockingdevicesandkeys.,课文分析,典型的紧固件和联接件包括诸如螺栓、螺帽、有头螺钉、紧定螺钉、铆钉、锁紧装置和键。,Partsmayalsobejoinedbywelding,brazing,orclippingtogether.,零件联接也可以用熔焊、铜焊和夹紧的方法。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Studiesinengineeringgraphicsandinmetalprocessesoftenincludeinstructiononvariousjoiningmethods,andthecuriosityofanypersoninterestedinengineeringnaturallyresultsinacquisitionofagoodbackgroundoffasteningmethods.,课文分析,在工程图和金属加工工艺研究中常常包括关于各种联接方法的说明，在工程上对此很感兴趣的，求知欲强的任何人自然会获得关于固紧方法上良好的基础知识。,机械工程专业英语,Lesson19Screws,fastenersandjoints,课文分析,机械工程专业英语,Lesson19Screws,fastenersandjoints,Ifanuninformedpersonwereaskedtochoosethedullestandmostuninterestingsubjectinmechanicaldesignthathecouldimagine,hemightwellchoosethesubjectoffasteners,thatis,nutsandbolts.Infact,theterm“nutsandbolts”issynonymouswithhardandmonotonouswork,necessarybuttotallyuninterestingtasks.Couldoneseriouslyimagineagroupofnutandboltmanufacturersorganizinganassociationandgettingtogetherforannualmeeting?Whatsubjectcouldpossiblybeofanyinterest?,Ifanuninformedpersonwereaskedtochoosethedullestandmostuninterestingsubjectinmechanicaldesignthathecouldimagine,hemightwellchoosethesubjectoffasteners,thatis,nutsandbolts.,课文分析,如果让一个对紧固件不甚了解的人去选择他能想象的机械设计方面最枯燥无味的学科的话，那么他就会选择紧固件学科，即螺栓和螺帽。,Infact,theterm“nutsandbolts”issynonymouswithhardandmonotonouswork,necessarybuttotallyuninterestingtasks.,事实上，术语“螺栓和螺帽”是与艰苦、单调的工作同义，乏味但必须的工作。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Couldoneseriouslyimagineagroupofnutandboltmanufacturersorganizinganassociationandgettingtogetherforannualmeeting?Whatsubjectcouldpossiblybeofanyinterest?,课文分析,可以认真地设想有一群螺栓螺帽制造者组成一个协会并在一起召开年会吗？那么还有什么学科不能让人感兴趣呢？,Inspiteofthistaint,thesubjectisoneofthemostinterestingintheentirefieldofmechanicaldesign.,尽管存在这一偏见，但是这一学科在机械设计整个领域中却是最使人感兴趣的学科之一。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Thenumberofnewinventionsinthefastenerfieldoveranyperiodyoumightcaretomentionhasbeentremendous.,课文分析,在紧固件领域新发明的数目巨大超过你能注意到的任何时期,Thereisanoverwhelmingvarietyoffastenersavailableforthedesignersselection.,数不胜数的紧固件可供设计者任意选择使用。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Anotherthing:didyouknowthatagoodboltmaterialshouldbestrongandtough,butagoodnutmaterialshouldbesoftandductile?,课文分析,还有，你知道吗？好的螺栓的材料应该是坚固而有韧性，而好的螺帽的材料应该是软而有塑性的。,Ordidyouknowthattherearecertainapplicationswhereyoushouldtightentheboltastightlyaspossibleand,ifitdoesnotfailbytwistingtheboltintwoduringtightening,thereisaverygoodpossibilitythattheboltneverwillfail?,或者你知道吗?在某些应用中你应该尽可能地把它们旋紧，如果在上紧过程中，由于旋紧这螺栓过程中而未发生失效现象，那么螺栓将可能永远不会失效。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Inthematerialtofollowyouwilldiscoverthewhyofthesequestions.Youwilllearnwhyanutorboltloosensandwhatyoumustdotokeepittight.,课文分析,在下面的文字中你将发现这些问题的原因。你将掌握螺栓、螺帽为什么会松动和你必须怎样令它保持旋紧状态。,Methodsofjoiningpartsareextremelyimportantintheengineeringofaqualitydesign,anditisnecessarytohaveathoroughunderstandingoftheperformanceoffastenersandjointsunderallconditionsofuseanddesign.,联接件的联接方法在保证工程设计质量方面是极端重要的。在设计和使用的各种情况下，充分了解紧固件和联接件的性能那是必要的。,机械工程专业英语,Lesson19Screws,fastenersandjoints,JumbojetssuchasBoeings747andLockheeds1011requireasmanyas2.5millionfasteners,someofwhichcostseveraldollarsapiece.,课文分析,大型喷气发动机客机像被音747和洛克希德1011，需要250万个紧固件，有些每个要花数美元。,The747,forexample,needsabout70,000titaniumfasteners,costingabout$150,000inall;400,000otherclose-tolerancefasteners,costingabout$250,000;and30,000squeezerivetspricedat50centseach,installed.,例如波音747，大约需要装70000个钛合金紧固件，全部大约要花150000美元；400000个具有精密公差的其他紧固件，大约要花250000美元；和30000个挤压用铆钉，安装后每个价值50美分。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Tokeepcostdown,Boeing,Lockheed,andtheirsubcontractorsconstantlyreviewnewfastenerdesigns,installationtechniques,andtooling.,课文分析,为了降低成本，波音、洛克希德和他们的承包商不断重新审查紧固件的设计、安装和切削加工。,Cost-savingdesignsandtoolingwillfindareadymarket,whichwillgrowinvalueasjumbojetsproliferate.,节省的设计和加工成本将开发一个畅销市场，增长的价值那将像坐上喷气式飞机一样。,机械工程专业英语,Lesson19Screws,fastenersandjoints,pru5lifreitvi.激增;繁殖;增生,Fastenersarenamedaccordingtohowtheyareintendedtobeusedratherthanhowtheyareactuallyemployedinspecificinstances.,课文分析,紧固件是根据将如何使用他们来命名的，而不是根据其在具体例子中的实际应用命名的。,Ifthisbasicfactisremembered,itwillnotbedifficulttodistinguishbetweenascrewandabolt.,如果记住了这个基本事实，就将不难区别螺钉和螺栓。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Ifaproductisdesignedsothatitsprimarypurposeisassemblyintoatappedhole,itisascrew.Thusascrewistightenedbyexertingtorqueonthehead.Ifaproductisdesignedsothatitisintendedtobeusedwithanut,itisabolt.,课文分析,如果所设计的产品其主要目的是把它装入到已攻丝的螺纹孔中，那就是螺钉。这样螺钉是要在螺钉头上施加扭矩来旋紧的。如果所设计的产品打算跟螺母配合使用，那就是螺栓。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Aboltistightenedbyexertingtorqueonthenut.Astudresemblesathreadedrod;oneendassemblesintoatappedhole,theotherendreceivesanut.,课文分析,螺栓是靠在螺母上施加扭矩来旋紧的。双头螺栓就像刻了螺纹的杆，一端旋入螺纹孔中，另一端再装上螺帽。,Itistheintent,ratherthantheactualuse,whichdeterminesthenameofaproduct.,因而根据使用的目的来确定产品名称，并不是根据其实际使用来命名的。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Thusitmaybedesirableonvariousoccasionstouseadrilltodrillaholethroughtwosheetsofsteel,say,andjointthemusingascrewandanut.,课文分析,这样，在各种场合用钻头给两块钢板钻通孔，人们就会用螺栓和螺帽来连接它们，这可能是人们所希望的。,Therearefourformsofheadmostcommonlyusedwithcapscrew:hexagonhead,fillisterhead,flatheadandhexagonsockethead.,有帽螺钉最常用的四种螺钉头的形式是：六角头，槽头，平头和内六角沉头。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Whenaconnectionisdesiredwhichcanbedisassembledwithoutdestructingthepartsassembledandwhichisstrongenoughtoresistbothexternaltensileloadandshearload,oracombinationofthese,thenthesimpleboltedjointusinghardenedwashersisagoodsolution.,课文分析,当需要一个螺纹联接即可以拆开又不破坏被联接件，而且这个联接又要有足够的强度以承受外拉力和剪力或这两种力的合力时，使用带淬火垫圈的简单螺栓联接是一个很好的解决方法。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Insuchajointthebolthasfirstbeentightenedtoproduceaninitialtensilepreload,afterwhichtheexternaltensileloadandtheexternalshearloadareapplied.,课文分析,在这种螺纹联接中，首先把螺栓上紧以产生一预紧载荷初拉力，而后施加外拉力载荷和剪切载荷。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Theeffectofthepreloadistoplacethepartsincompressionforbetterresistancetotheexternaltensileloadandtocreatefrictionbetweenthepartstoresisttheshearload.,课文分析,预载荷的作用是使被连接件处于压应力状态以更好地抵抗外部拉伸载荷和产生摩擦力以抵抗剪切载荷。,Theimportanceofpreloadingofboltscannotbeoverestimated.Ahighpreloadimprovesboththefatigueresistanceofaboltedconnectionandthelockingeffect.,螺栓预加载荷的重要性不能被过高地估计。较高预载荷即提高螺栓联接的抗疲劳能力又改善锁紧作用。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Havinglearnedthatahighpreloadisverydesirableinimportantboltedconnections,wemustnextconsidermeansofassuringthatthepreloadisactuallydevelopedwhenthepartsareassembled.,课文分析,已经知道：高预载荷在重要的螺栓联接中是非常希望的。下一步我们要考虑的是，当要装配零件时，如何确保设计情况下该预载荷的产生。,机械工程专业英语,Lesson19Screws,fastenersandjoints,IftheoveralllengthLofaboltwithcrossareaAcanactuallybemeasuredwithamicrometerwhenitisassembled,theboltelongationdduetothepreloadFcanbecomputedusingtheformulad=FL/AE,whereEisthemodulusofelasticityoftheboltmaterial.,课文分析,如果横截面积为A、总长度为L的螺栓装配时，实际上是可以用千分尺来测量的，由于预载力F的作用而使螺栓伸长量为d，d可以利用公式dFLAE来计算，式中E是螺栓材料的弹性模量。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Thensimplytightenthenutuntiltheboltelongationthroughthedistanced.Thisassuresthatthedesiredpreloadhasbeenattained.,课文分析,那么只要旋紧螺母直至使螺栓伸长达到d。这就保证了已经达到了所希望的预紧载荷。,However,theelongationofascrewcannotusuallybemeasuredbecausethethreadedendmaybeinablindhole.,然而，螺钉的伸长量通常是不能测量的，因为螺钉端部可能是在盲孔内。,机械工程专业英语,Lesson19Screws,fastenersandjoints,Itisalsoimpracticalinmanycasestomeasureboltelongation.Insuchcasesthewrenchtorquerequiredt