英语专业英语书籍强烈推荐.docx
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英语专业英语书籍强烈推荐.docx
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英语专业英语书籍强烈推荐
焊接专业本科生用
1WHATISWELDING?
Weldingtechniqueshavebecomesoversatilethatitisdifficultnowadaystodefine“welding”.Formerlyweldingwas“thejoiningofmetalsbyfusion”,thatis,bymelting,butthisdefinitionwillnolongerdo.Eventhoughfusionmethodsarestillthemostcommon,theyarenotalwaysused.Weldingwasnextdefinedasthe“joiningofmetalsbyheat”,butthisisnolongeraproperdefinitioneither.Notonlymetalscanbewelded,socanmanyoftheplastics.Furthermoreseveralweldingmethodsdonotrequireheat.Everymachinistisfamiliarwithheatlesswelding.Whenthechipslidesoverthecuttingtoolonalathe,itoftenleavesabuilt-upedgeofchipmaterialweldedtothetopofthecutterbit.Thisiscoldpressurewelding,whichunderothercircumstancesisproperproductionweldingmethod.Besidespressurewelding,wecanweldwithsoundandevenwithlightfromthefamouslaser.Facedwithadiversityofweldingmethodsthatincreaseyearbyyear,wemusthereadoptthefollowingdefinitionofwelding.“weldingisthejoiningofmetalsandplasticsbymethodsthatdonotemployfasteningdevices”.
Thejoiningofmetalsbymethodsthatdonotemployfasteningdevicesisanartasoldasblacksmithing.Neverthelessweldingasamanufacturingprocessmustbeconsideredadevelopmentofthetwentiethcentury.Inthe1880’scarbonarclampswereusedforstreetlighting.Atthattimeitwasnotedthatthecarbonarclamp,likealllamps,producedmoreheatthanlight,andthefirstattemptsweremadetousethisheatforweldingmetals.Thusthefirstweldingmethodofthosestillinusewascarbonarcwelding,perfectedabouttheturnofthecentury.Stickelectrodesandoxyacetyleneweldingalsoappearedabout1900.weldingwasgenerallyusedonlyforrepairandmaintenanceuntilthe1920’s.X-rayexaminationofweldscamesoonafterwardanddidmuchtodevelopconfidenceinweldedjoints.Themiddleofthe20thcenturysawgreatdevelopmentinweldingaswellasinothertechniques.Italsogaveus,amongotherthings,inertgaswelding.Sincethenweldinghasprogressedatatremendousrate.Ithelpsdevelopscienceandtechnology,includingtheelectronictechnique.Atthesametime,thetechnologyofweldingembracesawidearea.Manyelectroniccircuitsarerequiredtocontrolthemoreintricateweldingmachines.Evenradiofrequencieshavetheirapplicationsinwelding,ininductionbrazingandtheultrasonictestingofwelds.PhotographyisalsodrawnintothescopeofweldingforX-rayandγ-rayphotographyisusedintheexaminationofweldedjoints.Weldinghasmadeimportantcontributionstothemodernizationofournationaldefenceindustry,suchasthemakingofnuclearreactorsandman-madeearthsatellites,forbothareweldments.Ontheothersideofthecoin,thoseproductsofthenuclearreactors,radioisotopesarefamiliararoundweldingshopsintheirfunctionofweldingtesting.Alltheseandotherdevelopmentsshowthatweldingisnolongerwhatitwasintimepast,thesimplematterofrunningaheadwithagasflameorastickelectrode.
Theoperatorofthemodernautomaticwelderwearsneitherweldinghelmetnorgoggleswhenweldingtheheavy-walledpressurevessel.Butdepositingweldmetalisaboutfifteentimesfasterthanbymanualmethods.Hisweldingrodsarethetwolargecoilsofwireatthetopoftheweldingmachine,andtheseareautomaticallyfedintotheweld.Thearcisnotvisibleinthismethodofwelding,andsonohelmetisrequired.Theweldingcontrolsaregroupedoperator.ThisisUnionmeltsubmergedarcwelding,acommonlyusedweldingmethodthatcaninanhourdepositweldmetalequalinweighttothatoftheoperatorhimself.Attheoppositeextremeismicrowelding,inwhichtheoperatormayneedamicroscopetoseewhathehaswelded.Betweenthesetwoextremesinsizeandweldingcapacityareperhapsfivedozenotherweldingmethods.
2ClassificationofWeldingProcesses
Mostweldingprocessesrequiretheapplicationofenergy(heatorpressure)toproduceasuitablebond.Thereforeweldingprocessesmaybeclassifiedandnamedaccordingtobythetypeofenergysourceemployed.Ifincludingbrazing,theclassificationofweldingprocessesislistedbelow
(1)Fusionwelding
1Oxyacetylenewelding(OAW)
2ArcWelding
Shieldedmetalarcwelding(SMAW)orManualmetalarcwelding(MMAW)
Gasmetalarcwelding(GMAW),includes:
metalinertgasesarcwelding(MIG)andmetalactivegasesarcwelding(MAG)
Gastungstenarcwelding(GTAW)ortungsteninertgasarcweldng(TIG)
Fluxcoredarcwelding(FCAW)
Electrogaswelding(GMAW-EG;FCAW-EG)
Plasmaarcwelding(PAW)
Submergedarcwelding(SAW)
3Electroslagwelding(ESW)
4Thermitwelding(TW)
5Laserbeamwelding(LBW)
6Elecrtonbeamwelding(EBW)
(2)Pressurewelding(resistancewelding)
1Spotwelding
2Seamwelding
3Buttwelding
4Coldpressurewelding
5Frictionwelding
6Ultrasonicwelding
7Explosionweldinginvacuum
8Diffusionwelding
9Highfrequencywelding
(3)Brazingwelding
Thiswayofclassifyingweldingprocessesiscalledfamily-treemethod.Infact,thereisnouniformmethodofnamingweldingprocesses.Manyprocessesarenamedaccordingtotheheatsourceorshieldingmethod,butcertainspecializedprocessesarenamedafterthetypeofjointproduced.Examplesarestud,spotandbuttwelding.Anoverallclassificationcannottakeaccountofthisbecausethesametypeofjointmaybeproducedbyavarietyofprocesses.Studweldingmaybedonebyarcorprojectionweldingandspotweldingbyelectricresistance,arcorelectron-beamprocesses.Buttweldingmaybyresistance,flashoranyofanumberofothermethods.Althoughincommonusagemanyprocesseshaveabbreviatednames,thefullnamesoftenfollowthepattern:
first,astatementofthetypeofshielding;secondly,thetypeofheatorenergysource;thirdly,thetypeofjoint(wherethisisofspecificandnotgeneralimportance).
Itisoftennecessarywhenreferringtoprocessestomentionthewaytheyareused,particularlywhethertheoperationismanualorautomatic.Thepracticaloperationofweldingcanbedividedintothreemainparts:
(a)Thecontrolofweldingconditions,particularlyarclengthandelectrodeorfiller-wirefeedrateandtime.
(b)Themovementandguidingoftheelectrode,torchorweldingheadalongtheweldline.
(c)Thetransferorpresentationofpartsforwelding.
Processesaredescribedasmanual,semi-automatic,orautomatic,dependingontheextenttowhichthepartsmentionedaboveareperformedmanually.Manualweldingisunderstoodbethatinwhichtheweldingvariablesarecontinuouslycontrolledbytheoperatorandmeansforweldingheldintheoperator’shand.Semi-automaticweldingisthatinwhichthereisautomaticcontrolofweldingconditionssuchasarclength,rateoffiller-wireadditionandweldtime,butthemovementandguidingoftheelectrode,torchorweldingheadisdonebyhand.Withautomaticweldingatleastparts(a)and(b)oftheoperationmustbedonebythemachine.
3.METALSANDFERROUSMETALS
Metalsaredividedintotwogeneraltypes-ferrousandnonferrous.Ferrousmetalsarethosewhichcontainiron.Nonferrousmetalsarethosewhichdonotcontainiron.However,somenonferrousmetalsmaycontainasmallamountofironasanimpurity.
Steelandcastironarethemostcommonferrousmetalsingeneraluse.Steelisanalloycontainingchieflyiron,carbon,andcertainotherelementsinvaryingamounts.Awiderangeofphysicalpropertiesmaybeobtainedinsteelbycontrollingtheamountofcarbonandotheralloyingelementsandbysubjectingthesteeltovariousheattreatments.
Plaincarbonsteelsusuallycontain,besidesironandcarbon,smallamountsofsilicon,sulphur,phosphorous,andmanganese.Alloysteelsareformedbytheadditionofoneormoreofthefollowingelements:
nickel,chromium,molybdenum,vanadium,tungsten,manganese,silicon,andsmallamountsofotheralloyingelements.
Carbonisbyfarthemostimportantalloyingelementinsteel.Itistheamountofcarbonpresentwhichlargelydeterminesthemaximumhardnessobtainable.Thehigherthecarboncontent,thehigherthetensilestrengthandthegreaterthehardnesstowhichthesteelmaybeheat-treated.
Low-carbonsteelsareusuallyusedforlow-strengthpartsrequiringagreatdealofforming.Medium-carbonsteelsareusedforforgingsandotherapplicationswhereincreasedstrengthandacertainamountofductilityarenecessary.High-carbonsteelsareusedforhigh-strengthpartssuchassprings,tools,anddies.Thefollowinglistisaclassificationofferrousmaterialsaccordingtotheircarboncontent.
FerrousMaterialCarbonContent
WroughtironTraceto0.08%
Low-carbonsteel0.04to0.30%
Medium-carbonsteel0.30to0.60%
High-carbonsteel0.60to1.70%
Castiron1.70to4.50%
Wroughtironisalmostpureiron.Itisnotfrequentlyfoundintheschoolshopbecauseofitshighcost.Itforgeswell,caneasilybebenthotorcold,andcanbewelded.
Carbonsteelsareclassifiedbytheamountofcarbontheycontain.Thisamountisgiveninpoints(100pointsequals1percent)orbypercentage.
A.Low-carbonsteel,oftencalledsoftormildsteel,contains0.04to0.30percentcarbon(4to30points).Thistypeofsteelisavailableasblack-ironsheet,bandiron,barsandrods.Becauseitiseasilywelded,machined,andformed,low-carbonsteelissuitableforproductsandprojectsinwhichaneasilyworkedmetalisneeded.
B.Medium-carbonsteelhas0.30to0.60percentcarbon(30to60points).Itisusedformanystandardmachineparts.Intheschoolshopitisusedforprojectslikehammerheadsandclampparts.
C.High-carbonsteelcontains0.60to
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