8/6/2019 Sif Tips 05 Aluminium Soldering Brazing

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Sifbronzewasestablishedin1925andisoneofthelastcompanieswhocontinuetomanufactureweldingconsumableshereintheUK.

InFebruary2008theybecameawhollyownedcompanywithintheWWSGroupandnowfeatureaspartofthecombinedWELDABILITY SIFproductrange.

Thecompanyhaskindlyofferedtoprovideaseriesoftechnicaladvicedocumentsfortheweldingsalesengineerand AWDmembers,followingthetraditionalSIFTIPSformatwhichwasoriginallystartedin1932.

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AluminiumSolderingandBrazing

SOLDERINGSIF555 AluminiumSolder

BRAZINGSifaluminNo16& AluminiumFlux

Historically,engineershaveconsideredthatweldingaluminiumpresentsarangeofproblems,duetoitssurfaceoxideandthatitdoesnotchangecolourwhenheated.WiththeadventofMIGand TIGwelding,itisnowregularlyweldedwithgreatsuccess.Certainalloyscanbegasweldedorbrazed,buttheremovaloffluxresidueismostimportant,asitscorrosiveactionwillcontinueafterthejointhasbeencompleted.

Thereisanotherlowtemperature process,whichiscalledsoldering,althoughtheworkpieceismelted. Thepartstobejoinedareheated(evenbyasmallpropaneburner)andtherodrubbedontheworksurface. Atthecorrecttemperature(370C),therodisseentomeltandcreatesanexothermicreactiongeneratingsufficientheattolocallymeltthealuminium. AnadvantageofthisprocessisthatfluxisNOT required.WerefertothematerialasSIF555 AluminiumSolder. Theproductgiveshighstrengthdepositsthatdonothavetheproblemofgalvaniccorrosionbetweenbasemetalandsolder. Thelowworkingtemperaturekeepsdistortionanddiscolorationoftheworktoaminimum.

Thisprocessiscommonlyusedbymanufacturersofaluminiumwindowsanddoors.Itisidealforrepairingandsealingdefectsinaluminiumboats,gutters,engineparts,castingsandsheets,beingespeciallyrecommendedforapplicationswherefluxresidueremovalisaproblem.

Thecorrectprocedureisasfollows;cracksandjointsshouldbebevelledtoa60to90Vee.Removealldirt,greaseandforeignmaterialfromthesurfacetobebonded.Forahigherstrengthbond,roughenthesurfacebeforeapplyingthealloy.Usingacarburizingflame,heatthepartbroadly. Asthetemperatureapproaches370C,rubtherodonthesurfacetobesoldered.Continueheatingbasemetaluntilenoughheatispresenttocausetherodtomeltoffwhenitisrubbedonthejoint.Donotoverheat,butbesuretheentirejointsurfaceistinnedbeforeaddingadditionalalloytomakeabuild-up. Tinningactionmaybeimprovedbyusingaclean,stainlesssteelwirebrushtobrushthroughthemoltenmetaltothebasemetalsurface. Allowparttocoolslowly.

TraditionallySifbronzereferredtothetechniqueasProcess36,butrecentlySifaluminNo36and AluminiumNo36fluxhavebeenreplacedbySifaluminNo16whichmeltsapprox.80Clowerthanpurealuminiumand AluminiumFlux.

Theprocessisapplicabletopurealuminiumandalloyswithupto2%magnesium.Otheralloyswillprovedifficult,especiallyifcontaininghigh%ofsilicon. Thejointdesignshouldbelaptypewithagoodmechanicalfit.Partsmustbethoroughlycleanedandifmagnesiumbearingwirebrushingisessential. Thebrazingoperationshouldbecarriedoutassoonaspossibleaftercleaning.

TheSIF Aluminiumfluxisusedasatemperatureindicatorandcanbeappliedviatherodorapplieddirecttotheworkpieceasapaste,madebymixingthefluxwithwater. Thewholeworkpieceshouldbepre-heatedwiththeblowpipemovingbackwardsandforwardsalongthejointline. Asthefluxmelts,therodisappliedtoflowfreelyalongandtroughthejoint.ItisimportanttoavoidoverheatingwhichcandestroythepropertiesofSifaluminNo16.

Aluminiumfluxishighlycorrosiveandtheresiduemustberemovedwithin30minutesofthebrazingoperation.Wherejointsareaccessible,wirebrushwithveryhotwaterorevenasteamjet,alternativelytreatmentwith5%nitricacidsolutionmayberequired.

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