Welding
Description
Oxyacetyleneor fusion welding is oneof the oldest methods of joining metal. Oxyacetylenewelding equipmentis very common inan automotive shopand hasmany uses.Itis most oftenusedto heat or cutseizedor rusted parts thatcannot beremoved inotherways, or to weldsmall, thin metalpieces suchasexhaust tubing and brackets.
LessonOutcomes
The student willbeableto:
•Safely inspectandlight,operateand shut down anoxyacetylene weldingtorch.
•Weld asimple joint and demonstrateheatingskillsusingthe equipment in the automotiveshop.
Assumptions
It is expected that the students will not havepreviously used oxyacetylenewelding equipmentandwillnothavepreviouslylearnedskills specific toitsuse.
Terminology
Acetylenecylinder:astrong, welded steel container that is speciallydesignedtostoreacetylene, a highly unstable and explosivegas. Acetylene cylinders mustbe keptupright wheninuse.
Acetyleneregulator:usedto regulate acetylenepressurefromthecylindertothe mixer handle.Theacetylene gas regulatoris usuallycolouredred.
Figure1—Typicalacetyleneregulator
Thisworkis licensedunder aCreativeCommonsAttribution-NonCommercial-ShareAlike4.0InternationalLicenseunlessotherwiseindicated.
“Beanie”:smallskullcap hat used toprotectthescalpfrom sparks
Coupon: typicallysmall,pre-cutpieces of metal (roughly the size andshapeof a“coupon”)usedforpracticewelds
Gashoses: connect theregulator tothe mixer handle
Goggles:speciallydarkened glassesused toprotect a welder’seyes from thewelding flame
Oxygencylinder:cylinder forgedfromasingle pieceof strong, high-carbon steel with walls atleast 6mm(¼") thick. Oxygen is storedin thesecylindersunder enormous pressure.
Oxygengasregulator:usedto regulate oxygenpressurefrom thecylinder tothe mixerhandle.Theoxygen gas regulatorisusually coloured green.
Figure2—Typicaloxygenregulator
Striker:the only approved means oflightingan oxy-fueltorch. Also knownas aflint lighter orsparklighter,thesteelcuptrapsthegas,andwhentheflint contacts the file segmentitproducesaspark thatignites the fuelgas.Themodelshownin Figure 3 is the most commontype, thoughpistolgrip strikers are also available.
Figure3—Striker
Tip cleaner:steel tip-cleaning needleswith tiny file-liketeeth, designedto loosen oxidesandslag from theweldingtip orifice
Torch handle:mixes andregulates theacetylene andoxygengas flowto thewelding tip.It alsohas athreaded endfor changing todifferent tips.Sometimes called themixerhandle.
Figure4—Combinationtorchhandle
Weldingapronorjacket: protective gearwornoverworkclothes topreventburns
Welder’s gloves: gloves designedtoprotectthe welder’s hands from burns, usually made fromsoft cowhide leather
Weldingcart:portablecart usedtostoreandtransportwelding cylinders. Thecart is designedtostore thecylindersuprightina stable and secure positionwhen stationary,andto rolleasilywhentilted back on its wheels.
Welding filler rod: asteelrodthat comes indifferentthicknesses to help weldthe piecestogether.
Weldingtip:screws onto thetorch handle. Itcomesindifferentsizesandischangeddependinguponthe thickness ofthemetal tobe welded or the areato be heated.
EstimatedTime
60–120 minutes
RecommendedNumberofStudents
20, based on the BC TechnologyEducators’ Best PracticeGuide
Facilities
A regularautomotive or weldingshop withvisesandmetal-top benches
Tools
Anoperationaloxyacetylene welding unit(preferably more thanoneunit),withattachmentsenablinguseofmorethan onetorch per unit.Installing equipmenttoaccommodatea“Y”formationallows for the useof twostationsper bottle.
Materials
•Sufficient lengthsof metalplates(coupons) foreachstudent to practice (⅛" × 2" ×4").Mildsteelflatbarworkswell.
•Two pieces ofexhausttubingcutinto1"slicesforeachstudentis sufficient forfirst-timepractice.
•Sufficient⅛" oxyacetylenewelding rods foreach student
•Oxyacetylene weldinggloves and glasses or shadedface shieldsfor each student
Resources
OxyacetyleneWelding(OAW)
PowerPoint presentationcreatedby theYork County Schoolof Technology.Once youclickonthe linkbelow,this resource should appear in yourdownloads folder.
Oxy-AcetyleneWeldingandCutting
Goodtechnicalinformation. Gearedmore toward instructorsthan students.
Oxy-AcetyleneWelding
SteveBiele’s instructionalvideo, available at lowcost
ESABTrainingVictorVideos
LightingProceduresHandout
SeethehandoutattheendofthisActivityPlan.
SafetyTests
Generic safety tests are availableintheHeads-Upfor Safety!resourcethat canbe foundat:
Anoxyacetylenesafetyinformationsheetcanbefoundonpage85ofthedocument;a quizisincludedonpage86.
Activity
1.Havethe studentswork in pairs to assist each other.Demonstratethe process ofsetting upandlighting thetorch andthen haveeach studentdisplaytheirability to dothe same.
2.Wheneachpairhas shownmasteryof lightingand shuttingthe torch down, the studentscanassisteachother or practise welding their pieces of pipe together.
3.When students arecomfortable withlightingand shuttingdownthe system andthe pipewelding component, they can move on tothe next stage. The teacher should demonstratechangingto thelargerheatingtip andshould showhow it operates.Thenhavestudentsdemonstrate.
4.Students canthen practiseheatingthe samples of metal (coupon) whiletheteachersupervises. The studentsshouldbe shownhow tobend themetal into proper90° angles.
5.Whenbothcouponsarebenttoform right angles,theycanthen bewelded together to forma boxwithboth ends open.This exercise willallow students to practiseaccuratelyattachingthepieces.
6.If anyvery rustypieces of metal boltedtogetherare available,theymakeexcellentdemonstration pieces forheating nutsand boltsto removeseized parts.
EvaluationGuidelines
•Proficiencyandsafeoperationoftheoxyacetyleneequipmentis a priority.
•Accuracyisalsoanessentialconsiderationwhenheatingandbendingmetalto specifiedangles.
Theinformation below explainshowvisual appearance canhelp determinethe qualityofpenetrationinaweld.
SpeedofTravelandMovement
Speedoftravel (rate of travel) is avery important factorinproducing goodfusion welds. Thespeedoftravel depends on thebase metalthickness,the weldingjointdesign andthe volume ofheat produced by the welding torch.
If yourspeedoftravelis too fast, the weld beadbecomes toonarrow and thebead ripplesbecome pointed. The heat has notpenetratedand theresult islack of fusion (Figure 5).
Figure5—Weld bead formedwhen speedoftravelwas toofast
If yourspeedoftravelis too slow,it will result in too muchpenetration and ascaly appearanceonthe weld bead (Figure6).
Figure 6—Weld bead formedwhen speedof travel was tooslow
If you allowtoo muchheattobuild up,themolten weldpool willcollapse throughto the bottomof the plate andleave holes (Figure7). The undersideof the weldmighthavemolten metalthathassolidified,forming icicle-like structures.
Figure 7—Weld bead formedwith toomuchheat
If you complete your weldproperly,it will have uniform bead ripples,even beadwidth and ashinysurface appearance (Figure8).
Figure8—Weld beadformedcorrectly
The movementof the torchisalsoextremely important.As soonasthereis asmall weldpool(poolofmoltenweld metal),startto move thetorch forwardwith aside-to-sideor circularmotion.Atthesametime, insert theendofthefiller rod intotheweldpool,dippingthe rod intoandoutoftheweldpool.Thefiller rod should be withdrawnjustenoughtoremoveit from theweldpool,butnotentirely from theflame,sinceitshouldnot be allowedtooxidize or cool.
Coordinatingthemotionofthefiller rod andthemotionoftheweldingtorchisan importantfactor inproducing aqualityweld.You willbecome better at thiswithcontinued practice.
OxyacetyleneLightingProceduresforWeldingMildSteel
LightingUpthe Torch
1.Ensure thetanksareupright and secure.
2.Checktheweldingareaforanyflammablesthatshould be removed(papertowel,spraycans,etc.).
3.Unravel the welding hoses.
4.Make sure the regulator T-handlesareturned out loose.
5.Opentheacetylenetank½–¾turn.
6.Openthe acetylene torch valve½turn.
7.Screwintheacetylene regulator T-handle adjusting valve toworking pressure.(Forwelding,always usetip size for pressure.) NEVERgo beyond15 psi. Thismakes theacetylene very unstableand potentiallyexplosive.
8.Turnoff the acetylene torchvalve.
9.Openthe oxygentankvalve all theway.
10.Opentheoxygentorch valve½turn.
11.Screwinthe oxygen T-handle adjusting valve to working pressure.(Forwelding,alwaysusetip size forpressure.)
12.Turnoff theoxygen torchvalve.
13.Ensure you arewearing all necessary safetyequipment(goggles,gloves,apron,etc.).
14.Open the acetylene torch valve ¼turn, then light theacetylene usingastriker.
15.Openuptheacetylene torch valve until most of the smoke/sootdisappears.
16.Slowlyopentheoxygentorchvalveuntil a neutralflameisachieved.
Figure9—Correctstrikerposition
ShuttingDownthe Torch
1.Close the acetylenetorch valve.
2.Closethe oxygentorch valve.
3.Close the acetylenetank valve.
4.Closethe oxygentankvalve.
5.Back out theacetyleneregulator T-handle until loose.
6.Opentheacetylene torch valve to drainthe pressure. Boththe tank pressureand linepressureregulatorgaugesshould read 0.
7.Close the acetylenetorch valve.
8.Back out theoxygenregulator T-handleuntil loose.
9.Opentheoxygen torch valve todrainthe pressure. Both thetankpressureandlinepressureregulatorgaugesshould read 0.
10.Closethe oxygentorch valve.
11.Wrap upthe welding hoses.
12.Cleanthe welding area.