Weldingandcuttingofmetals

Weldingisaprocesswhichusesheatand/orpressuretojoinmetals.
Arcweldingisbyfarthemostcommonlyusedoneinconstruction.Moltenmetalfromthe
workpieceandafillermetalfromanelectrodeformacommonpuddlewhich
coolstoformaweld.
Flamecuttingisanalliedprocessthatrequirestheuseofatorch,fuelgas,andoxygen
tocutmetalsprimarilysteel.
ShieldedMetalArcWelding(SMAW)isthemostcommonarcweldingprocessin
construction.
SMAWusesashortlengthofconsumableelectrodewhichmeltsasitmaintainsthearc.
Meltedmetalfromtheelectrodeiscarriedacrossthearctobecomethefiller
metaloftheweld.
Theelectrodeiscoatedwithacomplexmixofchemicalsthatreleaseashieldinggas
suchascarbondioxidetokeepairoutofthearczoneandprotecttheweldfrom
oxidation.Thecompositionofthecoatingvarieswiththemetalbeingwelded.
GasMetalArc(GMAW)orMetalInertGasWelding(MIG)usesanuncoatedconsumable
wirethatisfedcontinuouslydownthemiddleoftheweldingtorch.Aringliketube
aroundthewiretransportsaninertgassuchasargon,helium,orcarbondioxidefroman
outsidesourcetothearczonetopreventoxidationoftheweld.
FluxCoredArcWelding(FCAW)isavariationofMIGwelding.Itusesahollow
consumablewirewhosecorecontainsvariouschemicalsthatgenerateshieldinggases
tostrengthentheweld.
GasTungstenArcWelding(GTAW)orTungstenInertGasWelding(TIG)
usesanonconsumabletungstenelectrodethatmaintainsthearcandprovidesenough
heattojoinmetals.Fillermetalisaddedintheformofarodheldclosetothearc.The
rodmeltsanddepositsfillermetalattheweld.Shieldinggasesmayormaynotbeused,
dependingonthemetalbeingwelded.
OxyacetyleneWeldingandCuttingburnsamixtureofgasesoxygenandacetylene
togenerateheatforweldingmetals.
Itsthemostcommonfuelgascuttingandweldingusedinconstruction.Theprocess
mayalsoemploytheuseofafillermetal.
ACETYLENE
Acetyleneisamixtureofcarbonandhydrogen.Itsstoredenergyisreleasedasheat
whenitburns.Whenburnedwithoxygen,acetylenecanproduceahigherflame
temperature(3,300C)thananyothergasusedcommercially.Thewideflammablerange
ofacetylene(2.5%to81%inair)isgreaterthanthatofothercommonlyusedgases,with
consequentlygreaterhazard.
OTHERFUELGASES
Fuelgasesforweldingareusedaloneorwithoxygen.Examplesincludepropane,
propylene,andnaturalgas.
Exposuretoultraviolet(UV)radiationcanresultdirectlyfromthearcorfromareflection
offbrightobjectssuchasshinymetalorwhiteclothing.Itcancausearceyewhen
sightisnotadequatelyprotected.Eyesbecomewateryandpainfulanywherefrom2to24
hoursafterexposure.Theconditionmaylast15daysbutisusuallyreversiblewithno
lastingeffects.However,repeatedexposuremayresultinscartissuethatcanimpair
vision.UVexposuremayalsocauseatemporarylossofvisualsharpnesscalled
fluorescence.
Skinreddening,commonlyknownassunburn,isanotherhazardofUVexposure.
Blisteringmayoccurinextremecases.AlthoughexcessiveexposuretoUVradiation
fromthesunhasbeenlinkedtoskincancer,therearenoreportsofincreasedskin
cancerratesfromweldingexposure.
TheintensityofUVradiationvarieswiththetypeofwelding.Generally,thehigherthe
temperatureoftheweldingprocessthehighertheUVradiation.
Infraredradiationishazardousforitsthermalorheatingeffects.Excessiveexposureto
theeyemaycausedamage.
Visiblelightisreleasedathighintensitybywelding.Shorttermexposurecanproduce
flashblindnessinwhichvisionisaffectedbyafterimagesandtemporaryblindspots.
Repeatedexposuretohighintensityvisiblelightcanproducechronicconjunctivitis,
characterizedbyred,tearfuleyes.
Xraysandgammaraysareinvisibleformsofionizingradiationusedtoinspectwelds
andcanbeextremelydamagingtounprotectedpartsofthebody.Keepwellawayfrom
anyareawherethistypeoftestingisunderway.Xraysarealsoproducedduring
electronbeamwelding.Theweldingchambermustbecompletelyshieldedtoconfine
thexraysandprotecttheoperator.
ExtremeTemperatures
Veryhightemperaturesarecausedbytheweldingprocess.Gasflamesmayreach
3,300C.Metalsmeltinarangefrom260Cto2,760C.Weldedmaterials,thework
environment,andweathermayallbesourcesofexcessiveheatwhichcancausemuscle
cramps,dehydration,suddencollapse,andunconsciousness.
Weldersmaysufferfrostbiteandhypothermiawhenworkinginextremecoldclimatesor
withweldinggasesstoredattemperaturesaslowas268C.Exposureto
freezingtemperaturescanleadtofatigue,irregularbreathing,loweredbloodpressure,
confusion,andlossofconsciousness.Heatstressandcoldstressarebothlife
threateningand,ifnottreatedintime,canbefatal.

WeldingandcuttingofmetalsCourse