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1、SolderingandWelding(钎焊和焊接)Thereareanumberofmethodsofjoiningmetalarticlestogether,dependinginthetypeofmetalandthestrengthofthejointwhichisrequired.1.SolderingandBrazingSolderinggivesasatisfactoryjointforlightarticlesofsteel,copperorbrass,butthestrengthof
2、solderedjointisratherlessthanajointwhichisbrazed,rivetedorwelded.Thesemethodsofjoiningmetalarenormallyadoptedforstrongpermanentjoint.Solderingistheprocessofjoiningtwometalsbyathirdmetaltobeappliedinthemoltenstate.Solderconsistsoftinandlead,whilebismutha
3、ndcadmiumareoftenincludedtolowerthemeltingpoint.Oneofthemostimportantoperationsinsolderingisthatofcleaningsurfacestobejoined,thismaybedonebysomeacidcleaner.Althoughtheoxidesareremovedbythecleaningoperation,anewoxidecoatingformsimmediatelyaftercleaning,t
4、huspreventingthesoldertounitewiththesurfaceofthemetal.Fluxisusedtobesoldered,allowingthesoldertoflowfreelyandunitewiththemetal.Zincchlorideisthebestfluxtouseforsolderingmostferrousandnonferrousmetals,forsolderingaluminumstearineorvaselineistobeusedasflu
5、xes.Thesolderingcopperisapieceofcopperattachedtoasteelrodhavingahandle.Solderingcoppersaremadeindifferentlengths,formsandweights.Thequalityofsolderingdependstoagreatdegreeontheformandsizeofthesolderingcopper.Twopartsmaybeperfectlysolderedonlywhenthesurf
6、acestobejoinedhaveabsorbedenoughheattokeepsoldermeltedforsometime.Insomecasesitmaybenecessarytoconnectmetalsurfacesbymeansofahardspeltersolderwhichfusesathightemperature.Thiskindofsolderingiscalledbrazing.1.WeldingWeldingisthejoiningoftwometalpiecesbyso
7、fteningwithheatandthenpressing,hammering,orfusingthemtogether.Manypartsofmachines,automobiles,airplanes,ships,bridges,andbuildingsarewelded.Oxyacetyleneweldingistheheatingoftwopiecesofmetalwithaflamewhichburnsamixtureofoxygenandacetylenegas.Theoxygenand
8、acetylenegasarekeptintwoseparatesteeltanksfromwhichtheyflowtoatorch;therethetwogasesmixandthenpassintotheflame.Itisthehottestflameknownforordinaryuse;itstemperatureisabout6300degreesFahrenheit.Theoxyacetyleneflamemaybeusedtocutir
