8 Consumables 309-320

7/30/2019 8 Consumables 309-320

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8Consmabls

309AU : IPRM 2007 : SectIon 8 : conSUMAbleS

WARnInG Wlding can giv ris to lctric shock, xcssiv nois, y and skin brns d to th arc rays, and a potntial halth hazard i yo brath in th mittd ms and gass.Rad all th manactrr’s instrctions to achiv th corrct wlding conditions and ask yor mployr or th Matrials Saty Data Shts. Rr to www.boc.com.a or www.boc.co.nz

Fundamentals of

Manual Metal Arc(MMA) Welding

Wdig thiqu

Sccssl MMA wlding dpnds on th ollowing actors:

Slction o th corrct lctrod

Slction o th corrct siz o th lctrod or th job

Corrct wlding crrnt

Corrct arc lngth

Corrct angl o lctrod to work

Corrct travl spd

Corrct prparation o work to b wldd.

erd Si

As a gnral rl, th slction o an lctrod is straight orward,in that it is only a mattr o slcting an lctrod o similarcomposition to th parnt mtal. Howvr, or som mtals thris a choic o svral lctrods, ach o which has particlarproprtis to sit spcic classs o work. Otn, on lctrod inth grop will b mor sitabl or gnral applications d to its allrond qalitis.

Th tabl blow shows jst a w o th wid rang o lctrodsavailabl rom BOC, with thir typical aras o application.

For xampl, th avrag wldr will carry ot most abricationsing mild stl and or this matrial has a choic o variosstandard BOC lctrods, ach o which will hav qalitis

sitd to particlar tasks. For gnral mild stl work, howvr,BOC Smootharc 13 lctrods will handl virtally all applications.BOC Smootharc 13 is sitabl or wlding mild stl in all positionssing AC or DC powr sorcs. Its asy striking charactristics andth tolranc it has or work whr t-p and plat sracs ar notconsidrd good, mak it th most attractiv lctrod o its class.Continos dvlopmnt and improvmnt o BOC Smootharc13 hav providd in-bilt oprating qalitis, which appal to thbginnr and xprincd oprator alik. For rthr advic on thslction o lctrods or spcic applications, or to obtain a copyo th ‘Wlding Consmabls: Slction Chart’, contact yor localBOC rprsntativ on 131 262.

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Electrodes and Typical Applications

NamAWSClassication Application

BOC Smootharc 13 e6013 A prmim qality lctrodor gnral strctral andsht mtal work in allpositions, inclding vrtical-down sing low carbon stls

BOC Smootharc 24 e7024 An iron powdr lctrodor high spd wlding orH-V llts and fat btt joints.Mdim to havy strctral

applications in low carbonstls

BOC Smootharc 18 e7018-1 A prmim qality, allpositional hydrogncontrolld lctrod orcarbon stls in prssrvssl applications andwhr high intgrity wldingis rqird; and or r-machining stls containingslphr

BOC Smootharc S 308L e308L Rtil basic coatd lowcarbon lctrods or wldingastnitic stainlss stlBOC Smootharc S 316L e316L

BOC Smootharc S 309L e309L Rtil basic coatd lowcarbon lctrod or wldingmild stl to stainlss stland diclt to wld matrial

erd Siz

Th siz o th lctrod gnrally dpnds on th thicknss o th sction bing wldd, and th thickr th sction th largr thlctrod rqird. In th cas o light sht, th lctrod siz sdis gnrally slightly largr than th work bing wldd. This mansthat, i 2.0 mm sht is bing wldd, 2.5 mm diamtr lctrod isth rcommndd siz.

Th ollowing tabl givs th maximm siz o lctrods that mayb sd or varios thicknsss o sction.

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310 AU : IPRM 2007 : SectIon 8 : conSUMAbleS


Fndamntals o Manal Mtal Arc (MMA) Wlding

Recommended Electrode Sizes

Avrag Thicknss o Plat orSction

Maximm Rcommnddelctrod Diamtr

1.5–2.0 mm 2.5 mm

2.0–5.0 mm 3.2 mm

5.0–8.0 mm 4.0 mm

≥8.0 mm 5.0 mm

Wdig curr

Corrct crrnt slction or a particlar job is an important actorin arc wlding. With th crrnt st too low, diclty is xprincdin striking and maintaining a stabl arc. Th lctrod tnds to stick to th work, pntration is poor and bads with a distinct ronddprol will b dpositd.

excssiv crrnt is accompanid by ovrhating o th lctrod.

It will cas ndrct and brning throgh o th matrial, andwill giv xcssiv spattr. Normal crrnt or a particlar jobmay b considrd as th maximm, which can b sd withotbrning throgh th work, ovr-hating th lctrod or prodcinga rogh spattrd srac (i.. th crrnt in th middl o thrang spcid on th lctrod packag is considrd to b thoptimm).

In th cas, o wlding machins with sparat trminals ordirnt siz lctrods, nsr that th wlding lad is connctdto th corrct trminal or th siz lctrod bing sd. Whnsing machins with adjstabl crrnt, st on th crrntrang spcid. Th limits o this rang shold not normally bxcdd. Th ollowing tabl shows th crrnt rangs gnrally

rcommndd or BOC Smootharc 13.

Generally Recommended CurrentRange for BOC Smootharc 13

elctrod Siz (mm) Crrnt Rang (Amp)

2.5 60–95

3.2 110–130

4.0 140–165

5.0 170–260

Ar lgh

To strik th arc, th lctrod shold b gntly scrapd on thwork ntil th arc is stablishd. Thr is a simpl rl or thpropr arc lngth; it shold b th shortst arc that givs a goodsrac to th wld. An arc too long rdcs pntration, prodcsspattr and givs a rogh srac nish to th wld. An xcssivlyshort arc will cas sticking o th lctrod and rogh dpositsthat ar associatd with slag inclsions.

For downhand wlding, an arc lngth not gratr than th diamtro th cor wir will b most satisactory. Ovrhad wldingrqirs a vry short arc, so that a minimm o mtal will b lost.Crtain BOC lctrods hav bn spcially dsignd or ‘toch’wlding. Ths lctrods may b draggd along th work and aprctly sond wld is prodcd.

erd Ag

Th angl that th lctrod maks with th work is important tonsr a smooth, vn transr o mtal.

Th rcommndd angls or s in th varios wlding positionsar covrd latr.

crr trav Spd

Th lctrod shold b movd along in th dirction o th jointbing wldd at a spd that will giv th siz o rn rqird. Atth sam tim, th lctrod is d downwards to kp th corrctarc lngth at all tims. As a gid or gnral applications, th tablblow givs rcommndd rn lngths or th downhand position.

Corrct travl spd or normal wlding applications varis btwnapproximatly 100 and 300 mm pr mint, dpnding on lctrodsiz, siz o rn rqird and th amprag sd.

excssiv travl spds lad to poor sion, lack o pntration tc,whil too slow a rat o travl will rqntly lad to arc instability,slag inclsions and poor mchanical proprtis.

Run Length per Electrode – BOC Smootharc 13

elctrod Siz(mm)

elctrodLngth (mm)

Rn Lngth (mm)

Minimm Maximm

4.0 350 175 300

3.2 350 125 225

2.5 350 100 225

crr Wrk Prparai

Th mthod o prparation o componnts to b wldd willdpnd on qipmnt availabl and rlativ costs. Mthods mayincld sawing, pnching, sharing, machining, fam ctting andothrs.

In all cass dgs shold b prpard or th joints that sit thapplication.Th ollowing sction dscribs th varios joint typsand aras o application.

typs f Jis

bu Wds

A btt wld is a wld mad btwn two plats so as to givcontinity o sction.

Clos attntion mst b paid to dtail in a btt wld to nsr thatth maximm strngth o th wld is dvlopd. Failr to proprlyprpar th dgs may lad to th prodction o alty wlds, ascorrct maniplation o th lctrod is impdd.

Butt Welding

Weld FaceReinforcement

Root FaceRoot Gap


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Two trms rlating to th prparation o btt wlds rqirxplanation at this stag. Thy ar:

Root Fac: th proportion o th prpard dg that has notbn bvlld (Land).

Root Gap: th sparation btwn root acs o th parts to b

joind.

Varios typs o btt wlds ar in common s and thir sitabilityor dirnt thicknss o stl ar dscribd as ollows:

Square Butt Weld

Th dgs ar not prpard, bt ar sparatdslightly to allow sion throgh th ll thicknsso th stl. Sitabl or plat p to 6 mm inthicknss.

Single ‘V’ Butt Weld

This is commonly sd or plat p to 16 mm

in thicknss and on mtal o gratr thicknsswhr accss is availabl rom only on sid.

Double ‘V’ Butt Weld

usd on plat o 12 mm and ovr in thicknsswhn wlding can b applid rom both sids.It allows astr wlding and gratr conomyo lctrods than a singl ‘V’ prparation onth sam thicknss o stl and also has lsstndncy to distortion as wld contraction canb qalisd.

Butt Weld with Backing Material

Whn sqar btt wlds or singl ‘V’ wldscannot b wldd rom both sids, it is dsirablto s a backing bar to nsr complt sion.

Single ‘U’ Butt Weld

usd on thick plats as an altrnativ to a singl‘V’ prparation. It has advantags in spd o wlding. It taks lss wld mtal than a singl ‘V’,thr is lss contraction and thr is, thror,a lssnd tndncy to distortion. Prparationis mor xpnsiv than in th cas o a ‘V’, asmachining is rqird. This typ o joint is mostsitabl or matrial ovr 40 mm in thicknss.

Double ‘U’ Butt Weld

For s on thick plat that is accssibl orwlding rom both sids. For a givn thicknss itis astr, nds lss wld mtal and cass lssdistortion than a singl ‘u’ prparation.

Horizontal Butt Weld

Th lowr mmbr in this cas is bvlld toapproximatly 15° and th ppr mmbr 45°,making an incldd angl o 60°. This prparationprovids a ldg on th lowr mmbr, whichtnds to rtain th moltn mtal.

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Gra ns bu Wds

Th rst rn in a prpard btt wld shold b dpositd with anlctrod not largr than 4.0 mm. Th angl o th lctrod or thvarios rns in a btt wld is shown blow.

It is ncssary to maintain th root gap by tacking at intrvals or by

othr mans, as it will tnd to clos dring wlding.

All singl ‘V’, singl ‘u’ and sqar btt wlds shold hav a backingrn dpositd on th ndrsid o th joint, othrwis 50% may bddctd rom th prmissibl working strss o th joint.

Bor procding with a rn on th ndrsid o a wld, it isncssary to back-gog or grind that sid o th joint.

Btt wlds shold b ovrlld to a crtain xtnt by bildingp th wld ntil it is abov th srac o th plat. excssivrinorcmnt, howvr, shold b avoidd.

In mlti-rn btt wlds, it is ncssary to rmov all slag andsrpls wld mtal bor a start is mad on additional rns. This isparticlarly important with th rst rn, which tnds to orm sharp

cornrs that cannot b pntratd with sbsqnt rns. elctrodslargr than 4.0 mm ar not gnrally sd or vrtical or ovrhadbtt wlds.

Th diagrams blow indicat th corrct procdr or wldingthick plat whn sing mltipl rns.

Bead Sequence for 1st and 2nd Layers

WELD BEADS

LAYERS

Bead Sequence for Subsequent Layers

WELD BEADS

LAYERS

Welding Progression Angle

3

81

74

6

2

1 Wld Mtal

2 Workpic

3 elctrod

4 Slag

5 Wlding Dirction

6 70–85° Angl

7 Arc

8 Wld Pool

5


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Fi Wds

A llt wld is approximatly trianglar in sction, joining twosracs not in th sam plan and orming a lap joint, t joint orcornr joint. Joints mad with llt wlds do not rqir xtnsivdg prparation, as is th cas with btt wldd joints, sinc th

wld dos not ncssarily pntrat th ll thicknss o ithrmmbr. It is, howvr, important that th parts to b joind bclan, clos tting, and that all th dgs on which wlding is to bcarrid ot ar sqar. On shard plat, it is advisabl to ntirlyrmov any ‘als ct’ on th dgs prior to wlding.

Fillt wlds ar sd in th ollowing typs o joints:

‘T’ Joints

A llt wld may b placd ithr onon or both sids, dpnding on thrqirmnts o th work. Th wld mtalshold s into or pntrat th cornrormd btwn th two mmbrs. Whr

possibl, th joint shold b placd in scha position as to orm a ‘Natral ‘V’ llt’sinc this is th asist and astst mthodo llt wlding.

Lap Joints

In this cas, a llt wld may b placdithr on on or both sids o th joint, dpnding on accssibility and thrqirmnts o th joint. Howvr, lap joints, whr only on wld is accssibl,shold b avoidd whr possibl andmst nvr constitt th joints o tanksor othr abrications whr corrosion islikly to occr bhind th lappd plats. Inapplying llt wlds to lappd joints, it isimportant that th amont o ovrlap o th plats b not lss than v tims ththicknss o th thinnr part. Whr it isrqird to prsrv th otsid ac orcontor o a strctr, on plat may b joggld.

Corner Joints

Th mmbrs ar ttd as shown, lavinga ‘V’-shapd groov in which a llt wldis dpositd. Fsion shold b compltor th ll thicknss o th mtal. Inpractic, it is gnrally ncssary to hav

a gap or a slight ovrlap on th cornr.Th s o a 1.0–2.5 mm gap has thadvantag o assisting pntration at throot, althogh stting p is a problm. Thprovision o an ovrlap largly ovrcomsth problm o stting p, bt prvntscomplt pntration at th root andshold thror b kpt to a minimm(i.. 1.0–2.5 mm).

Th ollowing trms and dnitions ar important in spciying anddscribing llt wlds.

lg lgh

A sion ac o a llt wld, as shown blow. In Astralia and NZ,spcications or llt wld sizs ar basd on lg lngth.

thra thikss

A masrmnt takn throgh th cntr o a wld rom th rootto th ac, along th lin that biscts th angl ormd by thmmbrs to b joind. Many contris s throat thicknss rathrthan lg lngth.

ectiv throat thicknss is a masrmnt on which th strngtho a wld is calclatd. Th ctiv throat thicknss is basd on amitr llt (Concav Fillt Wld), which has a throat thicknss qalto 70% o th lg lngth. For xampl, in th cas o a 20 mm llt,th ctiv throat thicknss will b 14 mm.

cvx Fi Wd

A llt wld in which th contor o th wld mtal lis otsida straight lin joining th tos o th wld. A convx llt wld o spcid lg lngth has a throat thicknss in xcss o th ctivmasrmnt.

Convex Fillet Weld

1

2 3

4

4

5

5

6

1 Actal Throat2 ectiv Throat

3 Convxity

4 Lg

5 Siz

6 Thortical Throat

cav Fi Wd

A llt in which th contor o th wld is blow a straight lin joining th tos o th wld. It shold b notd that a concav lltwld o a spcid lg lngth has a throat thicknss lss than thctiv throat thicknss or that siz llt. This mans that, whna concav llt wld is sd, th throat thicknss mst not b lssthan th ctiv masrmnt. This ntails an incras in lg lngthbyond th spcid masrmnt.

Concave Fillet Weld

1 23

6

54

5

4

1 Actal Throat

2 ectiv Throat

3 Concavity

4 Lg

5 Siz

6 Thortical Throat


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Th siz o a llt wld is actd by th lctrod siz, wldingspd or rn lngth, wlding crrnt and lctrod angl. Wldingspd and rn lngth hav an important ct on th siz and shapo th llt, and on th tndncy to ndrct.

Inscint spd cass th moltn mtal to pil p bhind th arc

and vntally to collaps. Convrsly, xcssiv spd will prodca narrow irrglar rn having poor pntration, and whr largrlctrods and high crrnts ar sd, ndrct is likly to occr.

Fi Wd Daa

Nominal FilltSiz (mm)

Min.ThroatThicknss (mm)

Plat Thicknss(mm)

elctrodSiz (mm)

5.0 3.5 5.0–6.3 3.2

6.3 4.5 6.3–12 4.0

8.0 5.5 8.0–12 and ovr 5.0

10.0 7.0 10 and ovr 4.0

Slction o wlding crrnt is important. I it is too high, th wldsrac will b fattnd and ndrct accompanid by xcssivspattr is likly to occr. Altrnativly, a crrnt which is too lowwill prodc a rondd narrow bad with poor pntration at throot. Th rst rn in th cornr o a joint rqirs a sitably highcrrnt to achiv maximm pntration at th root. A short arclngth is rcommndd or llt wlding. Th maximm siz lltwhich shold b attmptd with on pass o a larg lctrod is8.0 mm. eorts to obtain largr lg lngths sally rslt in collapso th mtal at th vrtical plat and srios ndrctting. Forlarg lg lngths, mltipl rn llts ar ncssary. Ths ar biltp as shown blow. Th angl o th lctrod or varios rns in a

downhand llt wld is also shown.Recommended Electrode Angles For Fillet Welds

1st Run 2nd Run

3rd Run Multi-run Fillet

Mlti-rn (mlti-pass) horizontal llts hav ach rn mad singth sam rn lngths (Rn Lngth pr elctrod Tabl). each rnis mad in th sam dirction, and car shold b takn with thshap o ach, so that it has qal lg lngths and th contor o thcompltd llt wld is slightly convx with no hollows in th ac.

Vrtical llt wlds can b carrid ot sing th pwards ordownwards tchniq. Th charactristics o ach ar: upwards – crrnt sd is low, pntration is good, srac is slightly convxand irrglar. For mltipl rn llts, larg singl pass waving rnscan b sd. Downwards – crrnt sd is mdim, pntration ispoor, ach rn is small, concav and smooth.

Th downwards mthod shold b sd or making wlds on thinmatrial only. elctrods largr than 4.0 mm ar not rcommnddor vrtical-down wlding. All strngth joints in vrtical plats10.0 mm thick or mor shold b wldd sing th pwardtchniq.This mthod is sd bcas o its good pntration andwld mtal qality.Th rst rn o a vrtical-p llt wld sholdb a straight saling rn mad with 3.2 mm or 4.0 mm diamtrlctrod. Sbsqnt rns or larg llts may b ithr nmrosstraight rns or svral wid waving rns.

Corrct slction o lctrods is important or vrtical wlding.

In ovrhad llt wlds, carl attntion to tchniq is ncssaryto obtain a sond wld o good prol. Mdim crrnt is rqirdor bst rslts. High crrnt will cas ndrctting and badshap o th wld, whil low crrnt will cas slag inclsions. Toprodc a wld having good pntration and o good prol, a shortarc lngth is ncssary. Angls o lctrod or ovrhad llts isillstratd blow.

Recommended Electrode Angles for Overhead Fillet Welds

30˚

15˚45˚


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Fndamntals o Manal Mtal Arc (MMA) WldingFndamntals o Manal Mtal Arc (MMA) Wlding

Manal mtal arc wlding, lik othr wlding procsss, has wldingprocdr problms that may dvlop and which can casdcts in th wld. Som dcts ar casd by problms with th

matrials. Othr wlding problms may not b orsabl and mayrqir immdiat corrctiv action. A poor wlding tchniq andimpropr choic o wlding paramtrs can cas wld dcts.

Dcts that can occr whn sing th shildd mtal arc wldingprocss ar slag inclsions, wagon tracks, porosity, wormholporosity, ndrctting, lack o sion, ovrlapping, brn throgh,arc striks, cratrs and xcssiv wld spattr. Many o thswlding tchniq problms wakn th wld and can cascracking. Othr problms that can occr and which can rdcth qality o th wld ar arc blow, ngr nailing and improprlctrod coating moistr contnts.

Dfs causd y Wdig thiqu

Sag Iusis

Slag inclsions occr whn slag particls ar trappd insid th wldmtal, which prodcs a wakr wld. Ths can b casd by:

rratic travl spd

too wid a waving motion

slag lt on th prvios wld pass

too larg an lctrod bing sd

ltting slag rn ahad o th arc.

This dct can b prvntd by:

a niorm travl spd

a tightr waving motion

complt slag rmoval bor wlding

sing a smallr lctrod

kping th slag bhind th arc, which is don by shortning tharc, incrasing th travl spd or changing th lctrod angl.

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Wag traks

Top View Thru Transparent Bead

Wagon tracks ar linar slag inclsions that rn th longitdinal axiso th wld. Thy rslt rom allowing th slag to rn ahad o thwld pddl and by slag lt on th prvios wld pass. Ths occrat th to lins o th prvios wld bad.

Prsiy

Porosity is gas pockts in th wld mtal that may b scattrd

in small clstrs or along th ntir lngth o th wld. Porositywakns th wld in approximatly th sam way that slaginclsions do.

Porosity may b casd by:

xcssiv wlding crrnt

rst, gras, oil or dirt on th srac o th bas mtal

xcssiv moistr in th lctrod coatings

impritis in th bas mtal

too short an arc lngth, xcpt whn sing low-hydrogn orstainlss stl lctrods

travl spd too high, which cass rzing o th wld pddlbor gass can scap.

This problm can b prvntd by:

lowring th wlding crrnt

claning th srac o th bas mtal

rdrying lctrods

changing to a dirnt bas mtal with a dirnt composition

sing a slightly longr arc lngth

lowring th travl spd to lt th gass scap

prhating th bas mtal, sing a dirnt typ o lctrod,or both.

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Wdig Dfs ad Prms

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Wrmh Prsiy (Pipig Prsiy)

Wormhol porosity is th nam givn to longatd gas pockts.Th bst mthod o prvnting this is to lowr th travl spd toprmit gass to scap bor th wld mtal rzs.

Udruig

undrctting is a groov mltd in th bas mtal nxtto th to or root o a wld that is not lld by thwld mtal. undrctting cass a wakr joint andit can cas cracking. This dct is casd by:

xcssiv wlding crrnt

too long an arc lngth

xcssiv waving spd

xcssiv travl spd.

On vrtical and horizontal wlds, it can also b casd by too largan lctrod siz and incorrct lctrod angls. This dct can. bprvntd by:

choosing th propr wlding crrnt or th typ and siz o lctrod and th wlding position

holding th arc as short as possibl

pasing at ach sid o th wld bad whn a waving tchniqis sd

sing a travl spd slow nogh so that th wld mtal cancompltly ll all o th mltd ot aras o th bas mtal.

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lak f Fusi

Lack o sion is whn th wld mtal is not sd to th bas mtal.This can occr btwn th wld mtal and th bas mtal orbtwn passs in a mltipl pass wld. Cass o this dct can b:

xcssiv travl spd

lctrod siz too larg

wlding crrnt too low

poor joint prparation

ltting th wld mtal gt ahad o th arc.

Lack o sion can sally b prvntd by:

rdcing th travl spd

sing a smallr diamtr lctrod

incrasing th wlding crrnt

bttr joint prparation

sing a propr lctrod angl.

ovrappig

Ovrlapping is th protrsion o th wld mtal ovr th dg orto o th wld bad. This dct can cas an ara o lack o sion

and crat a notch, which can lad to crack initiation. Ovrlapping isotn prodcd by:

too slow a travl spd, which prmits th wld pddl to gtahad o th lctrod

an incorrct lctrod angl.

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lgd Wdig Psii Arviais

Symbol Abbrviation Dscription

F Flat

H/V-FILLeT Horizontal-Vrtical Fillt

H Horizontal

V Vrtical

V-DOWN Vrtical-Down

OH Ovrhad

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It is th composition o th coating that dirntiats on typ o lctrod rom anothr and, to a dgr, what typ o applicationit can b sd or. MMA lctrods, with a solid wir cor, ar

gnrally catgorisd by th typ o fx coating thy mploy.Thr ar thr main grops o lctrod coating: rtil, basic andclllosic, pls a lss-widly-sd acid typ. Th nam o ach gropis a dscription o th main constitnt o th coating. Althogh notstrictly a coating typ, iron-powdr lctrods ar otn considrdas a sparat grop.

elctrods or ctting, grooving and goging, pls thos or hard-sracing, inclding tblar MMA lctrods, ar not classid bycoating typ.

Rui erds

Rtil lctrods hav a coating that contains abot 50% rtil sand(a pr orm o titanim dioxid), pls additions o rro-mangans,

minral carbonats and silicats, hld togthr with approximatly15% sodim silicat, also known as watrglass. Th rtil’scharactristics incld asy striking, stabl arc, low spattr, goodbad prol and, gnrally, asy slag rmoval rom th lctrod.

Th lctrod can oprat on both AC and DC crrnts andcan oprat in all positions i th ormlation o th coating isso dsignd.

On ngativ aspct o ths lctrods is that thy prodc a highlvl o hydrogn, typically gratr than 15ml / 100g o dpositdwld mtal. This cannot b avoidd, bcas thy rly on a crtainamont o moistr bing prsnt in th coating to oprat proprly.I th lctrods ar drid too mch, thy will ail to nctionproprly.

Rtil-coatd lctrods ar manactrd or wlding mild andlow-carbon stls. In this contxt, thy ar otn rrrd to asgnral-prpos or GP lctrods. Som low-alloy grads alsos rtil coatings. Rtil-typ coatings, which ar modicationso thos sd or rritic stls, ar also sd on many astniticstainlss stl lctrods.

basi erds

Basic, or low-hydrogn, lctrods contain calcim carbonat andcalcim forid in plac o th rtil sand and minral silicats. Thismaks thm lss asy to strik and mor diclt to r-strik, dto th vry dp cp ormd at th tip dring opration. Thy alsohav a poorr, mor convx bad prol than rtil lctrods. Th

slag is mor diclt to rmov than th rtil typs, bt thy dogiv bttr wld mtal proprtis than rtil typs, with a highrmtallrgical qality.

Basic lctrods ar capabl o bing sd on AC or DC crrntsand can b sd in mlti-pass wlds on matrials o all thicknsss.

Basic lctrods do not rly on moistr to nction proprly, andor th mor critical applications shold b sd compltly dry. Itis important to not that basic lctrods ar only low-hydrognlctrods i thy hav bn corrctly drid bor s. Thisconvntionally involvs r-drying in ovns on sit in accordancwith manactrrs’ rcommndations. Drying can rdc wldmtal hydrogn to lss than 5ml / 100g, as can vacm-packing thlctrods. Ths can b sd straight rom th packs withot any

orm o drying rqird. BOC Smootharc 16 and 18 lctrods arspplid in hrmtically sald containrs, which nsrs that thymt th H4 grad.

Basic-typ lctrods or rritic stls, with low-alloy additions toth coatings or th cor wir, allow a mch widr s, incldingsb-zro and lvatd-tmpratr application. Basic coatings ar

also widly sd or lctrods or wlding stainlss stls, nicklalloys, cast irons, coppr and alminim alloys, and or hard-acingapplications.

cusi erds

Clllosic lctrods contain a high proportion o organic matrial,rplacing all or som o th rtil sand. This prodcs a rc, dppntrating arc and a astr brn-o rat. Clllosic lctrods armor pron to spattr than rtil typs. Only carbon and somlow-alloy stls ar mad with a clllosic coating and most rnonly on DC+ polarity, bt som ar mad that will also opraton AC and DC-. Thy ar trly all-positional lctrods in all sizsand vn largr diamtrs p to 6 mm will oprat vrtical-down.Clllosic lctrods ar sd or root passs and piplin wlding.

It shold b notd that clllosic lctrods gnrat high amontso hydrogn. This prsnts a risk o hydrogn-indcd cracking i corrct wlding procdrs ar not ollowd.

Aid erds

Acid lctrods or mild stls hav bn largly rplacd by rtiltyps, bt som ar still prodcd by a w manactrrs. Thslctrods contain high amonts o iron oxid, ar rlativly asyto s and giv a volminos glassy slag that dtachs asily. Thyar lowr-strngth prodcts, so thy ar connd to s on non-strctral componnts.

Acid-rtil lctrods or stainlss stl ar now rplacing

convntional rtil typs. Thy ar highr in silicon, which givsimprovd oprating and wtting charactristics, and thy ar mchmor wldr-rindly. Thy strik and r-strik radily and willoprat on AC and DC crrnt. Thy prodc low spattr lvlsand an asily rmovd slag. Howvr, thy ar pron to ‘startporosity’ and nd r-drying bor s to avoid this.

Ir-pwdr erds

Iron-powdr lctrods ar otn considrd an indpndnt gropo consmabls. As thir nam sggsts, ths lctrods containhigh lvls o iron powdr hld within th coating – as th coatingmlts, th iron powdr crats mor wld mtal. This ctivlyimprovs th prodctivity rom th lctrod, allowing ithr largror longr wlds to b cratd rom a singl rod. Th amont o iron

powdr addd dpnds on th consmabl bing prodcd, bt it isnot ncommon or 75% o th cor wight to b addd.

Th addition o th iron powdr to th coating has th ct o incrasing th ovrall diamtr o th lctrod and rdcing thamont o fxing agnt prsnt in th coating. With lss fxingagnt availabl, th slag coating tnds to b thinnr, so many o thMMA lctrod’s positional wlding charactristics ar lost. Thismans that many o th lctrods can only b sd in th fat orhorizontal-vrtical (H-V) positions.

Coatings or iron-powdr lctrods may b basd on ithr thrtil or basic systms.

caig typs

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8




Praia csidrais

Srag ad R-dryig

MMA lctrods shold b stord in dry, wll-vntilatd andprrably hatd stors. For critical applications it is alsorcommndd that thy b hld in tmpratr and hmiditycontrolld conditions, maintaining hmidity blow 60%RH (RlativHmidity) and a tmpratr abov th dw point to avoidmoistr condnsing onto th lctrods. elctrods hld in dryconditions will rmain in prim condition or svral yars, bt i thcoating absorbs moistr, this will lad to a gradal dtrioration.evidnc o dtrioration inclds th prsnc o whit powdryaras on th srac o th coating, cracks in th coating or missingpics o coating.

elctrods with rtil or clllosic coating rqir som moistr inth coating to oprat proprly and shold not b r-drid. I rtillctrods gt wt, r-drying at abot 80°C is all that is ndd.Clllosic lctrods mst not b drid. In som hot nvironmntsthy may nd wtting to nction cintly.

Basic coatd lctrods nd to b dry to giv low-hydrogn wldmtal. Bor s, ths lctrods shold b r-drid accordingto manactrrs’ rcommndations, pt in holding ovns andthn transrrd to th workstations in hatd qivrs ntilndd. Vacm-packd basic lctrods can b sd straight romth packt.

elctrods or non-rros alloys and stainlss stl always nd tob compltly dry bor s and shold b tratd in accordancwith manactrrs’ rqirmnts.

Wdig Paramrs

Som lctrods will oprat satisactorily on AC or DC crrntand, or AC opration, manactrrs will rcommnd a minimmOCV (Opn Circit Voltag) to initiat a wlding arc withth lctrod.

car ad cdiiig f csumas

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8 Consmabls



Fundamentals of Metal

Inert Gas (MIG) Welding

Wdig thiqu

Sccssl wlding dpnds on th ollowing actors:

Slction o corrct consmabls

Slction o th corrct powr sorc

Slction o th corrct shilding gas

Slction o th corrct application tchniqs:a Corrct angl o lctrod to work Corrct lctrical stick-ot Corrct travl spd

Slction o th wlding prparation.

Si f rr sumaschmia mpsii

As a gnral rl, th slction o a wir is straightorward, in thatit is only a mattr o slcting an lctrod o similar compositionto th parnt matrial. Howvr, thr ar crtain applicationsor which lctrods will b slctd on th basis o mchanicalproprtis or th lvl o rsidal hydrogn in th wldmtal. SolidMIG wirs ar all considrd to b o th ‘low hydrogn typ’consmabls.

Th ollowing tabl givs a gnral ovrviw o som o thBOC rang o MIG wirs or th most common matrials. Mordtaild slction charts or spcic matrials can b ond in thappropriat matrials sctions.

Matrial Pag No

Mild and Alloy stl 351

Qnch and tmprd stls 353

Frritic matrials 352

Stainlss stl 406

Alminim 425

1�

2�

3�

4�

5�

Common Materials Welded with BOC MIG Wire

Matrial BOC MIG Wir

AS2074 C1, C2, C3, C4-1,C4-2, C5, C6

BOC Mild Stl MIG Wir

AS/NZS 3678-9 250, 300, 350, 400 BOC Mild Stl MIG Wir

AS1548-430, 460, 490 BOC Mild Stl MIG Wir

ASTM A36, A106 BOC Mild Stl MIG Wir

Stainless Steel

Grad 304 BOC Stainlss Stl 308LSi

Stainless to Carbon-Mn steels

Grad 316 BOC Stainlss Stl 316LSi

Aluminium

1080 BOC Alminim MIG 1080

6061, 3004 BOC Alminim MIG 4043

5005 BOC Alminim MIG 5356

Physia dii

Srac condition.

Th wlding wir mst b r rom any srac contamination,inclding mchanical damag sch as scratch marks.

A simpl tst or chcking th srac condition is to rn th wirthrogh a cloth that has bn dampnd with acton or 20sc. I a black rsid is ond on th cloth, th srac o th wir is notproprly cland.

Cast and Hlix.

Th cast and hlix o th wir has a major infnc on thdability o MIG wir.

Cast

Helix

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8



Fndamntals o Mtal Inrt Gas (MIG) Wlding

Cast – Diamtr o th circl

Hlix – Vrtical hight

I th cast is too small, th wir will dip down rom th tip. Thrslt o this is xcssiv tip war and incrasd war in th linrs.

I th hlix is too larg, th wir will lav th tip with a corkscrwct and cas ding problms.

Si f h crr Pwr Sur

Powr sorcs or MIG / MAG wlding is slctd on a nmbr o dirnt critria, inclding:

Maximm otpt o th machin

Dty cycl

Otpt control (voltag slction, wir d spd control)

Portability

Th ollowing tabl givs an indication o th oprating ampragor dirnt siz wirs

Wir Siz Amprag Rang (A)

0.8 mm 60–180

0.9 mm 70–250

1.0 mm 90–280

1.2 mm 120–340

A BOC powr sorcs slction chart is containd in th arcqipmnt sction o this manal (s pags 240–241).

Si f h crr Shidig Gas

Th slction o th shilding gas has a dirct infnc on th

apparanc and qality o th wldbad.

Th typ and thicknss o th matrial to b wldd will dtrminth typ o shilding gas that is slctd. As a gnral rl, ththickr th matrial (C-Mn and Alloy Stls), th highr thprcntag o CO2 in th shilding gas mixtr.

1�

2�

3�

4�

Dirnt grads o shilding ar rqird or matrials sch asstainlss stl, alminim and coppr.

Th ollowing tabl givs an indication o th most commonshilding gass sd or carbon mangans and alloy stls:

Matrial thicknss Rcommndd shilding gas

1–8 mm Argoshild Light

5–12 mm Argoshild univrsal

>12 mm Argoshild Havy

Mor dtaild slction charts, inclding rcommndations orwlding paramtrs (voltag, amprag, lctrical stick-ot, travlspd and gas fow rat) can b ond in th ollowing sctions:

Matrial Pag

C-Mn and Alloy Steels

Argoshild Light 60Argoshild univrsal 61

Argoshild Havy 62

Argoshild 52 63

Stainless Steel

Stainshild 65

Stainshild Havy 65

Aluminium

Argon 54

Alshild Light 67

Alshild Havy 67

Copper

Spcshild Coppr 80

Undercutting and burnback

No working condition

Dip Transfer (Steel Thickness (mm))

Spray Transfer (Steel Thickness (mm))

0

0 1 2 3 4 5

1 2 3 4 5

Burnback and arc instability

Spray Transfer

Optimum Parameters

DipTransfer

Optimum Parameters

Defect Free Zone

Defect Zone

Electrode (wire) stubbing and spatter

Current (A)

Wire Operating Limits

V o l t a g e ( V )

35

30

25

20

15

10

50 50 100 150 200 400250 300 350

1.0mm 1.2mm

0.8mm0.9mm 1.0mm

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8

320


Fndamntals o Mtal Inrt Gas (MIG) Wlding

crr Appiai thiqus

Diri f wdig

MIG wlding with solid wirs taks plac normally with a pshtchniq. Th wlding gn is tiltd at an angl o 10° towards thdirction o wlding (psh tchniq).

Th infnc o changing th torch angl and th wlding dirctionon th wld bad prol can b sn blow

Torch prpndiclar to workpic Narrow bad width withincrasd rinorcmnt

10°

Torch positiond at a drag angl o 10° narrow bad with xcssivrinorcmnt

90° 90°

0–15°

Torch position or butt welds

Whn wlding btt wlds, th torch shold b positiond within thcntr o th groov and tiltd at an angl o ±15° rom th vrticalplan. Wlding is still prormd in th psh tchniq

Torch position or fllet welds

Whn wlding llt wlds, th torch shold b positiond at anangl o 45° rom th bottom plat, with th wir pointing into thllt cornr. Wlding is still prormd in th psh tchniq

eria sik-u1 Gas Nozzl

2 Contact Tb Stback

3 Consmabl elctrod

4 Workpic

5 Stando Distanc

6 Contact Tb

7 Visibl Stick-ot

8 Arc lngth

9 elctrical Stick-ot

1

2

3

5

6

7

8

9

4

Th lctrical stick-ot is th distanc btwn th nd o thcontact tip and th nd o th wir. An incras in th lctricalstick-ot rslts in an incras in th lctrical rsistanc. Thrsltant incras in tmpratr has a positiv infnc in thmlt-o rat o th wir that will hav an infnc on th wldbadprol

Short Normal Long

Infnc o th chang in lctrical stick-ot lngth on thwldbad prol

trav spd

Slow Normal Fast

Th travl spd will infnc th wldbad prol and thrinorcmnt hight.

I th travl spd is too slow, a wid wldbad with xcssivrollovr will rslt. Convrsly, i th travl spd is too high, anarrow wldbad with xcssiv rinorcmnt will rslt.

Rcommndations or travl spd ar containd in th dtaildgass datashts ond in pags 58–68 o this manal.

8 Consumables 309-320

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