SMAW Basci Concept Dox

8/16/2019 SMAW Basci Concept Dox

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CHAPTER 2

SHIELDED

PREPARED BY ACOMMITTEE CONSISTINOF:

D. R . Amos, Chair manW e st in g hou se E l ectric C or

D. A. Fink Lincol n E l ect r ic Co.

J. R . Hannahs

METAL ARCWELDING

Midmark C orpor at ion

R. W. Heid N ewport News S hipbuild

A. R. Hollins Duke P ower Co.

J. E. MathersW el d in g C onsul t ant s , nc.

L. C. Northar d*! enne s see " a # $ e % &ut hor it %

M. Parek h 'obart (rothers Co.

A. Pollack

)))))))))))))))))))))))))))))) C onsul t ant

M. S. Sier dinsk i

*****************************) &llo % +od s Co.

Fundamentals of the Pr ocess 44 M. !. "omsic P l a st r onic nc.

EquipmentWELDING HANDBOOKCOMMITTEE MEMBER :

###########�################## D.R .Amos

Mater ials52 W e st in g hou se E l ect ric C or

-----------------------------

- * Deceased

Applications 56

Joint Design and Preparation 57

Welding Pr ocedur es 61

ualit! of the Weld 68

"afet! #ecommendations 70

"upplementar ! #eading List 71

47


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44 "$%ELDED ME& A

A#' WELD%()

, CHAPTER 2

SHIELDED METALARC WELDING

FUNDAMENTALS OF THE PROCESS

DEFINITION AND GENERAL DESCRIPTIONSH$E%DED ME"A% ARC &eldin' (SMAW) is an arc &eldin'

*rocess in &hich coalescence o+ metals is *rodced - heat+rom an electric arc that is maintained -et&een the ti* o+ aco/ered electrode and the sr+ace o+ the -ase metal in the

0oint -ein' &elded."he core o+ the co/ered electr ode consists o+ either a

solid metal rod o+ dra&n or cast material or one +a -r icated - encasin' metal *o&ders in a metallic sheath. "he cor erod condcts the electric cr r ent to the arc and *ro/ides+iller metal +or the 0oint. "he *r imar +nctions o+ the elec1trode co/erin' are to *ro/ide arc sta -ilit and to shield themolten metal +rom the atmos*here &ith 'ases created as

the coatin' decom*oses +rom the heat o+ the arc."he shieldin' em*loed, alon' &ith other in'r edients

in the co/erin' and the core &ire, lar 'el controls themechanical *ro*erties, chemical com*osition, and metal1lr 'ical strctr e o+ the &eld metal, as &ell as the arc char 1acteristics o+ the electrode. "he com*osition o+ the elec1trode co/erin' /aries accordin' to the t*e o+ electrode.

PRINCIPLES OF OPERATIONSH$E%DED ME"A% ARC &eldin' is - +ar the most &idelsed o+ the /arios arc &eldin' *rocesses. $t em *los theheat o+ the arc to melt the -ase metal and the ti* o+ aconsma-le co/ered electrode. "he electrode and the&ork are *art o+ an electric cir cit illstr ated in Fi'r e 2.3."his circit -e'ins &ith the electr ic *o&er sor ce and in1cldes the &eldin' ca-les, an electrode holder, a &or k 1 *iece connection, the &ork*iece (&eldment), and an arc&eldin' electr ode. 4ne o+ the t&o ca-les +rom the *o&er sorce is attached to the &ork. "he other is attached to theelectrode holder .

Weldin' commences &hen an electr ic arc is strckt&een the ti* o+ the electr ode and the &ork. "he inteheat o+ the arc melts the ti* o+ the electrode and the+ace o+ the the &ork close to the arc. "in 'lo-les o+ mten metal ra*idl +orm on the ti* o+ the electrode, ttrans+er thro'h the arc stream into the molten & *ool. % $n this manner, +iller metal is de *osited5 as the etrode is *ro'ressi/el consmed. "he arc is mo/ed o/er&ork at an a * *ro*r iate arc len'th and tra/el s *eed, meland +sin' a *ortion o+ the -ase metal and continoaddin' +iller metal. Since the arc is one o+ the hottest o+commercial sor ces o+ heat 6tem *er atr es a-o/e 788(:8889C) ha/e -een measred at its center !, meltin' o+ -ase metal takes *lace almost instantaneosl *on arc

tiation. $+ &elds are made in either the +lat or the hor ital *osition, metal trans+er is indced - the +orce o+ 'it, 'as e; *ansion, electric and electroma'netic +orces,sr +ace tension. For &elds in other *ositions, 'ra/it &oa'ainst the other +or ces.

"he *rocess re


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" $ % ELD E D M E & A L A # ' W E L D % ( )

A' ,# D' P,WE# ",#'E A(D ',(,L"

ELE',DE $,LDE#

W,#P%E'E LEAD I ELE',DE LE AD

W,#

Figure 2.1-Ee!e"#$ %& ' T()i*' We+i"g Cir *ui# &%r S,ie+e+ Me#' Ar* We+i"g

C%-ere+ Ee*#r %+e$$N ADD$"$4N "4 esta-lishin' the arc and s**lin' +iller metal +or the &eld de *osit, the electr ode introdces other materials into or arond the arc, or -oth. De*endin' *onthe t*e o+ electrode -ein' sed, the co/erin' *er +or msone or more o+ the +ollo&in' +nctionsB

(3) Pro/ides a 'as to shield the arc and *re/ente;cessi/e atmos*heric contamination o+ the molten +iller metal.

(2) Pro/ides sca/en'er s, deo;idiers, and +l;in' a'entsto cleanse the &eld and *r e/ent e;cessi/e 'rain 'ro&th inthe &eld metal.

() Esta-lishes the electrical char acter istics o+ theelectr ode.

(>) Pro/ides a sla' -lanket to *rotect the hot &eld metal+rom the air and enhance the mechanical *ro*erties, -eadsha *e, and sr+ace cleanliness o+ the &eld metal.

(:) Pro/ides a means o+ addin' alloin' elements tochan'e the mechanical *ro*erties o+ the &eld metal.

Fnctions 3 and > *r e/ent the *ick* o+ o;'en andnitro'en +rom the air - the molten +iller metal in the ar cstr eam and - the &eld metal as it solidi+ies and cools.

"he co/erin' on shielded metal arc electrodes is a **lied - either the e;trsion or the di**in' *rocess. E;trsion ismch more &idel sed. "he di**in' *rocess is sed *ri1maril +or cast and some +a-ricated core rods. $n either case, the co/erin' contains most o+ the shieldin', sca/en'1in', and deo;idiin' materials. Most SMAW electrodesha/e a solid metal core. Some are made &ith a +a-ricatedor com*osite core consistin' o+ metal *o&ders encasedin a

metallic sheath. $n this latter case, the *r*ose o+ somee/en all o+ the metal *o&ders is to *rodce an allo &de *osit.

$n addition to im*r o/in' the mechanical *ro*erties the &eld metal, electrode co/erin's can -e desi'ned &eldin' &ith alternatin' crrent (ac). With ac, the &eldarc 'oes ot and is r eesta -lished each time the crrent /erses its dir ection. For 'ood arc sta -ilit, it is necessarha/e a 'as in the arc stream that &ill remain ionied dreach re/ersal o+ the cr r ent. "his ionied 'as makes *o -le the rei'nition o+ the arc. ases that readil ionie

a/aila-le +rom a /ariet o+ com*onds, incldin' ththat contain *otassim. %t is the incor *or ation o+ thcom*onds in the electr ode co/erin' that ena-les the etrode to o*erate on ac.

"o incr ease the de*osition rate, the co/erin's o+ socar-on and lo& allo steel electr odes contain ir on *o&"he ir on *o&der is another sorce o+ metal a/aila-le de*osition, in addition to that o -tained +rom the cor ethe electrode. "he *resence o+ iron *o&der in the co/eralso makes more e++icient se o+ the arc ener'. M *o&ders other than ir on are +re


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*/ " $ % E L , E D M E & A L A # ' W E L D % ( )

$ron *o&der electr odes &ith thick co/erin's redce thele/el o+ skill needed to &eld. "he ti* o+ the electrode can -e dra''ed alon' the sr +ace o+ the &ork &hile maintain1in' a &eldin' arc. For this reason, hea/ ir on *o&der elec1trodes +re


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"$%ELDED ME& AL A#' WELD%()

E/UIPMENT

POWER SOURCES

T()e %& Ou#)u# Cur r e"#E$"HER A%"ERNA"$N CGRREN" (ac) or direct crrent (de)ma -e em*loed +or shielded metal arc &eldin', de *end1in' *on the crrent s**lied - the *o&er sorce and theelectrode selected. "he s*eci+ic t*e o+ crr ent em *loedin+lences the *er+ormance o+ the electrode. Each cr r entt*e has its ad/anta'es and limitations, and these mst -econsidered &hen selectin' the t*e o+ crrent +or a s *eci+ica**lication. Factor s &hich need to -e considered are as+ollo&sB

0%#'ge Dr%). ?olta'e dro* in the &eldin' ca-les islo&er &ith ac. "his makes ac more sita-le i+ the &eldin'

is to -e done at lon' distances +rom the *o&er s**l.Ho&1 e/er, lon' ca-les &hich carr ac shold not -ecoiled -e1 case the indcti/e losses encontered in schcases can -e s -stantial.

L%1 Cur r e"#. With small diameter electrodes and lo&&eldin' cr r ents, de *ro/ides -etter o *er atin' character is1tics and a more sta-le arc.

Ar* S#'r#i"g. Strik in' the arc is 'enerall easier &ithde, *articlarl i+ small diameter electrodes are sed. Withac, the &eldin' crrent *asses thro'h ero each hal+ ccle,and this *resents *ro-lems +or arc star tin' and arc sta -ilit.

Ar* Le"g#,. Weldin' &ith a short arc len'th (lo& ar c/olta'e) is easier &ith de than &ith ac. "his is an im*or tantconsider ation, e;ce *t +or the hea/ ir on *o&der elec1trodes. With those electrodes, the dee* crci-le +ormed -the hea/ co/er in' atomaticall maintains the *ro*er ar clen'th &hen the electrode ti* is dra''ed on the sr+ace o+ the 0oint.

Ar* %1. Alternatin' crrent rarel *r esents a *r o -1lem &ith arc -lo& -ecase the ma'netic +ield is constantlre/ersin' (328 times *er second). Arc -lo& can -e a si'ni+i1cant *ro-lem &ith de &eldin' o+ +erritic steel -ecase o+ n-alanced ma'netic +ields arond the arc.2

We+i"g P%$i#i%". Dir ect crr ent is some&hat -etter than ac +or /ertical and o/erhead &elds -ecase lo&er am1 *era'e can -e sed. With sita-le electrodes, ho&e/er, sat1is+actor &elds can -e made in all *ositions &ith ac.

2. "he in+lence o+ ma'netic +ields on arcs and arc -lo& is discssed inCha*ter 2, @Phsics o+ Weldin',@ " e # d ing 'andbook, ?ol.3, th ed., **.>#>7.

Me#' Ti*"e$$. oth sheet metal and hea/ stions can -e &elded sin' de. "he &eldin' o+ sheet me&ith ac is less desira-le than &ith de. Arc conditions at lcrrent le/els re


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> " $ % E L D E D M E & A L A # ' W E L D % ( )

100 ',("&A(& 0,L&A)E PE#F,#M A('E

80 2�32.3 45

IJ........ K, 45

- - - ',("&A(& '##E(& PE#F,#M A('E

K, 45

en I@#J.. 2 -545

� 2 6�................ 45 2

-5 45-5

L #, K, K,40

22 2 7-5 -5J 2 2 #,

2

20 22

J2

2 2

00 100 200 300 400 500 600

'##E(&. A

Figur e 2.3-T()i*' 0%#-A!)er e Cure$ &%r C%"$#'"# Curr e"# '"+ C%"$#'"# 0%#'geP%1er S%ur *e$

SO and 388 ?, &hereas arc /olta'es ar e -et&een 3and

>8 ?. "he o*en cir cit /olta'e dro*s to the arc /olta'e&hen the arc is strck and the &eldin' load comes on themachine. "he arc len'th and the t*e o+ electrode -ein'sed determine 0st &hat this arc /olta'e &ill -e. %f the ar cis len'thened, the arc /olta'e &ill incr ease and the &eldin'cr r ent &ill decrease. "he chan'e in am*era'e &hich achan'e in ar c len'th *rodces is deter mined - the slo*e o+ the /olt#am*er e cr/e &ithin the &eldin' ran'e.

Some *o&er sor ces do 3not *ro/ide +or control o+ theo*en circit /olta'e -ecase this control is not needed +or all &eldin' *rocesses. %t is a se+l + eatr e +or SMAW, et itis not necessar +or all a **lications o+ the *rocess.

P%er S%ur*e See*#i%"SE?ERA% FAC"4RS NEED to -e considered &hen a *o&er sor ce +or SMAW is selectedB

(3) "he t*e o+ &eldin' cr r ent r e


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" $ % E L D E D M E & A L A # ' W E L D % ( )

A s**l o+ *rimar *o&er is needed. %f line *o&er isa/aila-le, it shold -e deter mined &hether the *o&er issin'le#*hase or three#*hase. "he &eldin' *o&er sor cemst -e desi'ned +or either sin'le# or three#*hase *o&er ,and it mst -e sed &ith the one it &as desi'ned +or . %f line

*o&er is not a/aila-le, an en'ine#dri/en 'enerator orI alter 1nator mst -e sed.

899

M A: %M-M ,'0

ACCESSOR3 E/UIPMENT

Ee*#r%+e H%+er

AN E%EC"R4DE H4%DER is a clam*in' de/ice &hich allthe &elder to hold and control the electrode, as sho&Fi're 2.:. $t also ser/es as a de/ice +or condctin'

&;


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+9 " $ % E L D E D M E &A L A # ' W E L D % ( )

Figur e 1.+-Welding a "tr uctur e With the "hielded Met�% Arc Welding Pr ocess


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"$%ELDED ME& AL A#' WELD%() :2 " $ % E L D E D M E & A L A # ' W E L D % ( )

&eldin' cr r ent +rom the &eldin' ca-le to the electr ode.An inslated handle on the holder se*arates the &elder Ishand +rom the &eldin' cir cit. "he crrent is trans+ er r edto the electrode thro'h the 0a&s o+ the holder . "o assr eminimm contact resistance and to a/oid o/erheatin' o+ the holder, the 0a&s mst -e ke*t in 'ood condition. 4/er 1heatin' o+ the holder not onl makes it ncom+orta-le +or the &elder, -t also it can case e;cessi/e /olta'e dro* inthe &eldin' cir cit. oth can im*air the &elderIs *er +or 1

mance and redce the = m) (>= to =3 m)

= 1

288 to 2:8(=3 to = m

8

* Gse t&o 3/0 ca-les in ar allel.

180 20-30 > > 2 8200 60 2 2 2 3 1/0200 50 = 1 8 1/0250 30 2 3 1/0300 60 1/0 1/0 1/0 2/0 3/0400 60 2/0 2/0 2/0 3/0 4/0500 60 2/0 2/0 3/0 3/0 4/0600 60 2/0 2/0 3/0 4/0 *


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sed. Alminm ca-le re) Cast irons (dctile and 'r a)(:) Alminm and alminm allos(=) Co**er and co**er allos() Nickel and nickel allos

Electrodes are a/aila-le +or a**lication o+ &ear, im *act,

Helmets are 'enerall constrcted o+ *ressed +i-e+i -er 'lass inslatin' mater ial. A helmet shold -e li'h&ei'ht and shold -e desi'ned to 'i/e the &elder the 'est *ossi-le com+or t. "he &elder in Fi're 2.: has a heon. "he o-ser/er is sin' a hand shield.

Mi$*e'"e%u$ E6ui)!e"#

C%EA N%$ NESS $S $MP4R "A N" in &eldin'. "he sr+aces o+&ork*ieces and the *re/iosl de*osited &eld metal m

-e cleaned o+ dirt, sla', and an other +orei'n matter&old inter + er e &ith &eldin'. "o accom*lish this,&elder shold ha/e a steel &ire -rsh, a hammer, a chand a chi**in' hammer . "hese tools are sed to r emdirt and rst +rom the -ase metal, ct tack &elds, andsla' +rom the &eld -ead.

"he 0oint to -e &elded ma re


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" $ % ELD E D M E & A L A # ' W EL D % ( ):> "$%ELDED ME& AL A#' WELD%()

the E desi'nates an electrode. "he +irst t&o di'its (=8) si'1ni+ the minimm tensile str en'th o+ the ndilted &eldmetal in ksi, in the as#&elded condition. "he third di'itr e *r esents the &eldin' *osition (3, in this case, r e+ er s to all

*ositions). "he last di'it re+ers to the co/erin' t*e andt*e o+ crrent &ith &hich the electrode can -e sed.

"here are t&o stren'th le/els o+ car-on steel electrodesBthe =8 series and the 8 series. "he minimm allo&a -letensile stren'th o+ the &eld metal +or the =8 series is =2 ksi(>2 MPa), altho'h additional elon'ation ma allo&some o+ these to 'o as lo& as =8 ksi (>3> MPa). For the 8series, it is 2 ksi (>7= MPa) and, a'ain, some o+ these ma'o as lo& as 8 ksi (> MPa), &ith additional elon'ation.Ma;imm chemical com*osition limits +or si'ni+icant ele1ments are *ro/ided &ithin the a**lica-le AWS s *eci+ ica1tions +or most electrode classi+ications. Char* ?#notchimlQact re8 toMPa) minimm tensile stren'th, in 38 ksi (8 MPa) inments. %n this s*eci+ication, &eld metals that are cmonl sed in the as#&elded condition are classi+ied on

-asis o+ their *ro*erties in that condition. Similarl, ththat are commonl sed in the str ess#r elie/ed condiare classi+ied on the -asis o+ their *ro*erties a+ter a strelie+ heat tr eatment.

%n this connection, it shold -e noted that the strelie+ called +or in A NS$HAWS &S.S consists o+ holthe test assem-l at tem*eratre +or one hFa-ricators sin' holdin' times that are si'ni+icadi++ er ent +rom one hor at tem*eratre ma ha/e tomore selecti/e in the elec1 trodes the se, and mare


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#3 indicates that the electrodes are sa-le in all *ositionsthro'h :H 2 in. (> mm) diameter . "he nm-er : indicatesthat the electr odes are sita -le +or se &ith dcr* (electrode *ositi/e). "he nm-er = means that electr odes are sita -le+or either ac or dcr* (electrode *ositi/e). Electrodes o/er : H 2 in. (> mm) diameter are +or se in the +lat andhori1ontal *ositions.

"he s *eci+ication does not descr i -e the co/erin' in'r e1die

nts, -t #3: co

/er i

n's sall c

ontain a lar

'e *r o*

or tio

no+ limestone (calcim Icar -onate). "his in'r edient *r o/idesthe C4 and C82 that are sed to shield the arc. "he -inder &hich holds the in'r edients to'ether in this case is sodimsilicate. "he #3= co/er in' also contains limestone +or ar cshieldin'. $n addition, it sall contains considera-le tita1nia (titanim dio;ide) +or arc sta -ilit. "he -inder in thiscase is likel to -e *otassim silicate.

Di++ er ences in the *ro*ortion o+ these in'r edients resltin di++erences in arc char acter istics. "he #3: electr odes(lime t*e co/erin's) tend to *ro/ide a more *enetr atin'arc and to *rodce a more con/e; and coarsel r i * *led -ead. "he sla' solidi+ies relati/el ra*idl so that theseelectrodes o+ten are *r e+ er r ed +or ot o+ *osition &or k ,

sch as *i*e &eldin'. 4n the other hand, the #3= co/er in's(titania t*e) *rodce a smoother arc, less s *atter , and amore ni+orm +inel ri**led -ead. "he sla', ho&e/er, ismore +lid, and the electrode sall is more di++iclt tohandle in ot#o+ # *osition &or k.

Stainless steels can -e se*ar ated into three -asic t*esBastenitic, martensitic, and + er r itic. "he astenitic 'r o *(2 and ) is, - +ar, the lar 'est one. Normall, thecom*osition o+ the &eld metal +rom a stainless steel elec1trode is similar to the -ase metal com*osition that theelectrode is desi'ned to &eld.

For astenitic stainless steels, the com*osition o+ &eldmetal di++ers +rom the -ase metal com*ositions sli'htl inorder to *rodce a &eld de*osit &hich contains +er r ite

(i.e., &hich is not +ll astenitic) to *r e/ent +issrin'or hot crackin' o+ the &eld metal. "he amont o+ +er r ite common to the /ar ios &eldin' electrodes isdiscssed in A NS$H AWS A:.> in some detail. $n'eneral, a minimm +errite content in the ran'e o+ to + er rite nm-er is s++ i1 cient to *r e/ent crack in'. Fer ritecontent as hi'h as 28 F N ma -e acce *ta -le +or some&elds &hen no *ost&eld heat treatment is em*loed. "heSchae+ +ler dia'ram, or the De1 lon' modi+ication o+ a *or tion o+ that dia'ram, can -e sed to *redict the+ er rite content o+ stainless steel &eldmetals. Ma'netic instrments are a/aila-le to make dir ectmeasr ements o+ the +er r ite content o+ de*osited &eldmetal. (See A NS$HAWS A>.2, S t and ar d Procedures $ or C al *ibrating Magnetic n st rument s to M ea sur e Delta / err it eC ont ent o $ &u st enit ic Stainless Steel W el d M et al . 0

Cer tain astenitic stainless steel &eld metals (" *es 38,28, and 8, +or e;am *le) do not +orm + er r ite -ecasetheir nickel content is too hi'h. For these mater ials, the

*hos*hors, sl+r, and silicon content o+ the &eld metalis limited or the car-on content incr eased as a means o+ minimiin' +issrin' and cr ack in'.

A**ro*riate &eldin' *rocedres can also -e sed to dce +issr in' and cr ack in'. %o& am*era'e, +or e;am*le -ene+icial. Some small amont o+ &ea/in', as a means *r omotin' celllar 'rain 'ro&th, ma -e hel*+l. Pro * *rocedres in terminatin' the arc shold -e sed to a/ocrater cracks.

A NS$HAWS &S .* contains t&o co/ered electrode clas+ications +or the str ai'ht chromim stainless ste(>

series). 4ne contains 33 to 3.: *ercent chromim, tother , 3: to 3 *er cent. "he car -on content o+ -oth is 8 *ercent ma;imm. oth &eld metals are air hardenin' atheir &eldments re


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" $ % EL D E D M E & A L A # ' W E L D % ( )&eldin' o+ alminm -ase metals. "hese classi+ications ar e -ased on the mechanical *ro*erties o+ the &eld metal inthe as#&elded condition and the chemical com*osition o+ the core &ire. 4ne core &ire is commerciall *re almi1nm (3388), and the other is an alminm#+i/e *er cent sili1con allo (>8>). oth electr odes are sed &ith dcr* (elec1trode *ositi/e).

"he co/erin' on these electrodes has three +nctions. $t *ro/ides a 'as to shield the arc, a +l; to dissol/e the

almi1 nm o;ide, and a *rotecti/e sla' to co/er the &eld -ead. ecase the sla' can -e /er corrosi/e to alminm,it is im *or tant that all o+ it -e remo/ed *on com*letiono+ the &eld.

"he *resence o+ moistr e in the co/erin' o+ these elec1trodes is a ma0or sorce o+ *orosit in the &eld metal. "oa/oid this *orosit, the electrodes shold -e stored in aheated ca-inet ntil the are to -e sed. "hose electrodesthat ha/e -een e;*osed to moistr e shold -e r econdi1tioned ( -ak ed) -e+ore se, or discar ded.

4ne di++iclt &hich ma occr in &eldin' is the +sin'o+ sla' o/er the end o+ the electrode i+ the arc is -r ok en. $norder to restrike the arc, this +sed sla' mst -e r emo/ed.

Co/ered alminm electrodes are sed *rimaril +or

noncritical &eldin' and re*air a**lications. "he shold -e sed onl on -ase metals +or &hich either the 3388 or >8> +iller metals are recommended. "hese &eld metals donot res*ond to *reci*itation hardenin' heat treatments. %f the are sed +or sch mater ial, each a**lication shold -ecare+ll e/alated.

C%))er '"+ C%))er A%( Ee*#r %+e$

A NS$H AWS &S.2, S peci $ icat ion $ or C o-er ed Copper and Copper &llo% &r c W el d in g E l ect r od e s , classi+ies co**er andco**er allo electrodes on the -asis o+ their all#&eld#metal *ro*erties and the chemical com*osition o+ their ndi1lted &eld metal. "he desi'nation sstem is similar to that

sed +or nickel allo electr odes. "he ma 0or di++ er ence isthat each indi/idal classi+ication &ithin a 'ro* is identi1+ied - a letter. "his letter is sometimes +ollo&ed - a nm1 -er, as in ECAl#A2, +or e;am*le. "he 'ro*s areB CSi +or silicon -rone, CSn +or *hos*hor -rone, CNi +or co *1

*er#nickel, and CAl +or alminm -rone. "hese elec1trodes, 'enerall, are sed &ith dcr* (electr ode *ositi/e).

Co**er electr odes ar e sed to &eld nalloed co * *er and to re*air co**er claddin' on steel or cast iron. Silicon -rone electrodes are sed to &eld co**er#inc allos,co**er, and some ir on -ase mater ials.I "he are also sed+or sr +acin' to *ro/ide corrosion r esistance.

Phos*hor -rone and -rass -ase metals are &elded &ith *hos*hor -rone electrodes. "hese electrodes are also

sed to -rae &eld co**er allos to steel and cast iron. "he *hos*hor -rones are rather /iscos &hen molten, -ttheir +lidit is im*r o/ed - *reheatin' to a-ot >889F(2889C). "he electrodes and the &ork mst -e dr.

Co**er#nickel electrodes are sed to &eld a &ideran'e o+ co**er#nickel allos and also co * *er #nick el

claddin' on steel. $n 'eneral, no *reheat is necessarthese materials.

Alminm -rone electr odes ha/e -road se +or &in' co**er -ase allos and some dissimilar metal com -tions. "he are sed to -rae &eld man + er ros metalsto a**l &ear and corrosion resistant -earin' sr +aWeldin' is sall done in the +lat *osition &ith s *r eheat.

Ee*#r %+e$ &%r C'$# Ir %"A NS$HAWS &S.3, S peci $ icat ion $ or W el d in g E l ect rand +ods $ or Cast ron, classi+ies co/ered electrodes&eldin' cast ir on. "he electrodes classi+ied in &S.3nickel, nickel#iron, nickel#co**er allos, and one steelo. Preheat is recommended &hen &eldin' iron cast *articlarl i+ the steel electrode is sed. "he s*eci+ic *eratre de*ends on the sie and com*le;it o+ the caand the machina-ilit re


14/30

:= " $ % E L D E D M E & A L A A ' W E L D % ( )

Sr +acin' &ith co/ered electrodes is sed +or claddin', -tterin', -ild*, and hard sr +acin'. "he &eld de *ositin these a**lications is intended to *ro/ide one or mor eo+ the +ollo&in' +or the sr+aces to &hich the are a*1 *liedB

(3) Corrosion r esistance;1 Metallr 'ical contr ol;= Dimensional control; Wear r esistance;+ $m *act r esistance

Co/ered electr odes +or a *articlar sr +acin' a **licationshold -e selected a+ter a car e+l r e/ie& o+ the r e


15/30

"$%ELDED ME& AL A#' WELD%()

+or /ertical and o/erhead &eldin' ma -e di++erent +r omthose sita -le +or +lat *osition &eldin'.

LOCATION OF WELDING

"HE S$MP%$C$"U 4F the e in. (= mm) and then onl &hen the 0oint is

to -e &elded in the +lat *osition +rom -oth sides. "he o+ material to -e &elded is also a consideration.

When thicker mem-ers are to -e &elded, the ed'eeach mem-er mst -e *re*ared to a contor that &ill mit the arc to -e directed to the *oint &here the &metal mst -e de*osited. "his is necessar to *ro/ide

sion to &hate/er de*th is r e


16/30

: " $ % E L D E D M E & A L A # ' W E L D % ( )

For t*es o+ -ackin' are commonl sedB

(3) ack in' stri *(2) ackin' &eld() Co**er -ackin' -ar (>) Nonmetallic -ack in'

.'*i"g S#r i)

* * +.* P,

8A9 ACING STRIP 8:9 STRUCTURE

.AC7ING

A ACN $ N S"R $P is a str i * o+ metal *laced on the -ack o+ the 0oint, as sho&n in Fi'r e 2.=(A). "he +ir st &eld *ass ties -oth mem-ers o+ the 0oint to'ether and to the -ack in'stri*. "he str i * ma -e le+t in *lace i+ it &ill not inter +er e&ith the ser/icea -ilit o+ the 0oint. 4ther&ise, it shold -eremo/ed, in &hich case the -ack side o+ the 0oint mst -e

accessi-le. $+ the -ack side is not accessi -le, some other means o+ o -tainin' a *r o*er root *ass mst -e sed.

"he -ackin' str i * mst al&as -e made o+ a mater ialthat is metallr 'icall com *ati -le &ith the -ase metal andthe &eldin' electrode to -e sed. Where desi'n *er mits,another mem-er o+ the strctr e ma ser/e as -ackin' +or the &eld. Fi're 2.=() *ro/ides an e;am*le o+ this. $n allcases, it is im *or tant that the -ackin' str i * as &ell as thesr +aces o+ the 0oint -e clean to a/oid *orosit and sla'inclsions in the &eld. $t is also im *or tant that the -ack in'stri* +it *ro*erl. 4ther&ise, the molten &eld metal canrn ot thro'h an 'a * -et&een the stri* and the -asemetal at the root o+ the 0oint.

C%))er .'*i"g .'r

A C4PPER AR is sometimes sed as a means o+ s**or tin'the molten &eld *ool at the root o+ the 0oint. Co**er is

. sed -ecase o+ its hi'h ther mal condcti/it. "his hi'hcondcti/it hel*s *r e/ent the &eld metal +rom +sin' to

the -ackin' -ar. Des*ite this, the co**er -ar mst ha/es++icient mass to a/oid meltin' dr in' de *osition o+ the+ir st &eld *ass. $n hi'h *r odction se, &ater can -e *assedthro'h holes in the -ar to remo/e the heat that accm1lates drin' continos &eldin'. Re'ardless o+ the methodo+ coolin', the arc shold not -e allo&ed to im *in'e on theco* *er -ar, +or if an co**er melts, the &eld metal can -ecome contaminated &ith co **er . "he co **er -ar ma -e 'roo/ed to *ro/ide the desired root sr+ace contor and r ein+or cement.

Figure 2.6-Fu$i5e Me#.' '*i"g &%r ' We+

R e+r actor t*e -ack in' consists o+ a +le;i-le, sha *e+or m that is held on the -ack side o+ the 0oint - clam*s o - *r essre sensiti/e ta *e. "his t*e o+ -ackin' is somtimes sed &ith the SMAW *rocess, altho'h s*ecial &eldin' techni


17/30

" $ % E L D E D M E &A L A # ' W E L D % ( )=8 " $ % E L D E D M E & A L A # ' W EL D % ( )

those o+ the SMAW &eld metal. "he -ackin' &eld mst -e lar 'e eno'h to s**ort an load that is *laced on it."his is es*eciall im *or tant &hen the &eldment mst -er e *osi1 tioned a+ter the -ackin' &eld has -een de*ositedand -e1 +ore the 'roo/e &eld is made.

FIT-UP

J4$ N" F$"#GP $ N?4%?ES the *ositionin' o+ the mem-ers o+ the 0oint to *ro/ide the s*eci+ied 'roo/e dimensions andali'nment. "he *oints o+ concern are the root o*enin' andthe ali'nment o+ the mem-ers alon' the root o+ the &eld.oth o+ these ha/e an im *or tant in+lence on the


18/30

rx)' J3B>H t :1 *+�f63Ar 8 I8/ &, =IM

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19/30

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Figure 2.:-8C%"#i"ue+9- T()i*' 4%i"# Ge%!e#rie$ &%r S,ie+e+ Me#' Ar* We+i"g %& S#ee


20/30

"$ %E L DE D ME& A L A#' WELD%() /1 " $ % E L D E D M E & A L A # ' W E L D % ( )

RUNOFF TA.S

$N S4ME APP%$CA"$4NS, it is necessar to com *letel +ill otthe 'roo/e ri'ht to the /er ends o+ the 0oint. $n sch cases,rno++ ta-s are sed. "he, in e++ ect, e;tend the 'r oo/e

-eond the ends o+ the mem-ers to -e &elded. "he &eld iscarried o/er into the ta-s. "his assres that the entir elen'th o+ the 0oint is +illed to the necessar de*th &ithsond &eld metal. A t*ical rno++ ta- is sho&n in Fi're

2.7. Rno++ ta-s are e;cellent a**enda'es on &hich tostar t and sto * &eldin'. An de+ects in these star ts andsto*s are located in areas that later &ill -e discar ded.

Selection o+ the mater ial +or rno++ ta-s is im *ortant."he com*osition o+ the ta-s shold not -e allo&ed to ad1/ersel a++ ect the *ro*erties o+ the &eld metal. For e;am1

*le, +or stainless steel &hich is intended +or corrosion ser 1/ice, the rno++ ta-s shold -e o+ a com*ati-le 'rade o+ stainless steel. Car-on steel ta-s &old -e less costl, -t+sion &ith the stainless steel +iller metal &old chan'e thecom*osition o+ the &eld metal at the 0nction o+ the car 1

-on steel ta- and the stainless steel mem-ers o+ the 0oint."he &eld metal at this location *ro-a-l &old not ha/eade


21/30

WELDING CURRENTSH$E%DED ME"A% ARC &eldin' can -e accom*lished &itheither alternatin' or dir ect crrent, &hen an a * *ro *r iateelectrode is sed. "he t*e o+ &eldin' crrent, the *olar 1it, and the constitents in the electrode co/erin' in+l1ence the meltin' rate o+ all co/ered electr odes. For an'i/en electr ode, the meltin' rate is dir ectl related to the

electrical ener' s**lied to the arc. Part o+ this ener' issed to melt a *ortion o+ the -ase metal and *art is sed tomelt the electr ode.

Dire*# Cur r e"#D$REC" CGRREN" A%WAUS *ro/ides a steadier arc andsmoother metal trans+er than ac does. "his is -ecase the

*olar it o+ de is not al&as chan'in' as it is &ith ac. Mostco/ered electr odes o*erate -etter on re/erse *olarit (elec1trode *ositi/e), altho'h some are sita -le +or (and e/enare intended +or ) strai'ht *olarit (electrode ne'ati/e). R e1/erse *olarit *rodces dee*er *enetration, -t strai'ht *olarit *rodces a hi'her electrode meltin' rate.

"he de arc *rodces 'ood &ettin' action - the molten&eld metal and ni+orm &eld -ead sie e/en at lo& am *er 1a'e. For this reason, de is *articlarl sited to &eldin'thin sections. Most com-ination ac#dc electrodes o *er ate

-etter on de than on ac, e/en tho'h the are desi'ned too*erate &ith either t*e o+ crr ent.

Dir ect cr r ent is *re+erred +or /ertical and o/er head&eldin' and +or &eldin' &ith a short arc. "he de arc hasless tendenc to shor t ot as 'lo-les o+ molten metal ar etrans+erred across it.

Arc -lo& ma -e a *ro-lem &hen ma'netic metals (ironand nick el) are &elded &ith de. 4ne &a to o/ercome this *ro-lem is to chan'e to ac.

A#er"'#i"g Cur r e"#F4R SMAW, A%"ERNA"$N cr r ent o++ers t&o ad/anta'eso/er de. 4ne is the a-sence o+ arc -lo& and the other is thecost o+ the *o&er sor ce.

Withot arc -lo&, lar 'er electrodes and hi'her &eldin'crrents can -e sed. Certain electrodes (s *eci+icall, those&ith ir on *o&der in their co/erin's) are desi'ned +or o *er 1ation at hi'her am*era'es &ith ac. "he hi'hest &eldin's*eeds +or SMAW can -e o-tained in the dra' techni


22/30

" $ % E L D E D M E &A L A # ' W E L D % ( )" $ % E L D E D M E &A L A # ' W E L D % ( )

11 5

10 i- E7024

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E6010 (de) E6013

E

21

125 175 225 200 250 300 225 275 325 200 250 300

WELD%() '##E(&5 A

Figure 2. 116 i". 8?.: !!@ Di'!e#er C'r5%" S#ee Ee*#r %+e$

For do&nhand &eldin', *articlarl &ith hea/ elec1trode co/erin's, the ti* o+ the electrode can -e dra''edli'htl alon' the 0oint. "he arc len'th, in this case, is ato1maticall determined - the coatin' thickness and themeltin' r ate o+ the electrode. Moreo/er, the arc len'th isni+orm. For /ertical or o/erhead &eldin', the arc len'th is'a'ed - the &elder. "he *ro*er arc len'th, in sch cases,is the one that *ermits the &elder to control the sie andmotion o+ the molten &eld *ool.

For +illet &elds, the arc is cro&ded into the 0oint +or

hi'hest de*osition rate and -est *enetr ation. "he same istre o+ the r oot *asses in 'roo/e &elds in *i *e.When arc -lo& is encontered, the arc len'th shold -e

shortened as mch as *ossi-le. "he /arios classi+ icationso+ electrodes ha/e &idel di++ er ent o*eratin' char acter is1tics, incldin' arc len'th. %t is im *or tant, there+ore, +or the&elder to -e +amiliar &ith the o*eratin' char acter istics o+ the t*es o+ electrodes the &elder ses in order to r eco'#

nie the *ro*er arc len'th and to kno& the e++ ect o+ di+ent arc len'ths. "he e++ ect o+ a lon' and a short arc on -a**earance &ith a mild steel electrode is illstrated inres 1.88;D and ;E.

TRA0EL SPEED

"RA?E% SPEED $S the r ate at &hich the electrode moalon' the 0oint. "he *ro*er tra/el s*eed is the one &h *rodces a &eld -ead o+ *ro*er contor and a * *earaas sho&n in Fi're 2.ll(A). "r a/el s*eed is in+lencedse/eral +actor sB

(3) " *e o+ &eldin' crrent, am*era'e, and *olar it(2) Position o+ &eldin'() Meltin' rate o+ the electrode(>) "hickness o+ material(:) Sr+ace condition o+ the -ase metal

�

345

#

�


23/30

=>=> " $ % E L D E D M E & A L A # ' W E L D % " $ % E L D E D M E &A L A # ' W E L D % ( )(=) " *e o+ 0oint() Joint +it# *() Electrode mani *lation

When &eldin', the tra/el s *eed shold -e ad 0sted sothat the arc sli'htl leads the molten &eld *ool. G* to a

*oint, incr easin' the tra/el s *eed &ill narro& the &eld -ead and incr ease *enetration. eond this *oint, hi'her tra/el s*eeds can decrease *enetration, case the sr +ace o+

the -ead to deter ior ate and *rodce ndercttin' at theed'es o+ the &eld, make sla' remo/al di++ iclt, and entra *'as ( *orosit) in the &eld metal. "he e++ ect o+ hi'h tra/els *eed on -ead a**earance is sho&n in Fi'r e 2.33 ().With lo& tra/el s*eed, the &eld -ead &ill -e &ide andcon/e; &ith shallo& *enetration, as illstrated inFi're2.33 (F). "he shallo& *enetr ation is cased - the ar cd&ellin' on the molten &eld *ool instead o+ leadin' it andconcentr atin' on the -ase metal. "his, in trn, a++ ects dil1tion. When diltion mst -e ke*t lo& (as in claddin'), thetra/el s *eed, too, mst -e ke*t lo&.

"ra/el s *eed also in+lences heat in*t, and this a++ ectsthe metallr'ical strctr es o+ the &eld metal and the heat#

a++ ected one. %o& tra/el s*eed incr eases heat in*tthis, in tm, incr eases the sie o+ the heat#a++ ected oneredces the coolin' rate o+ the &eld. For&ard tra/el s *eenecessaril redced &ith a &ea/e -ead as o**osed tohi'her tra/el s *eed that can -e attained &ith a str in'er -eHi'her tra/el s*eed redces the sie o+ the heat#a++ econe and incr eases the coolin' rate o+ the &eld. "hecrease in the coolin' rate can incr ease the stren'th and haness o+ a &eld in a hardena-le steel, nless *reheat o+ a l

s+ +icient to *re/ent hardenin' is sed.

ELECTRODE ORIENTATIONE%EC"R4DE 4R$EN"A"$4N, W$"H r es *ect to the &orkthe &eld 'roo/e, is im*ortant to the


24/30

! r a-el angle is the an'le less than 78 de'rees -et&een theelectrode a;is and a line *er*endiclar to the &eld a;is, ina *lane determined - the electrode a;is and the &eld a;is.W or k angle is the an'le less that 78 de'rees -et&een a line *er*endiclar to the ma0or &ork*iece sr +ace and a *lanedetermined - the electrode a;is and the &eld a;is. Whenthe electrode is *ointed in the direction o+ &eldin', the

$ or ehand techni9ue is -ein' sed. "he tra/el an'le, then, iskno&n as the push angle. "he backhand techni9ue in/ol/es *ointin' the electrode in the direction o**osite that o+ &eldin'. "he tra/el an'le, then, is called the drag an g le."hese an'les are sho&n in Fi're 2.32.

" *ical electr ode or ientation and &eldin' techni


25/30

P"$ A()LE F,#

F,#E$ A(D WELD%()D#A) A()LE

F,# H A'$ A(D

WELD%()

I

A:%" ,F WELD 8A9 GROO0E WELD

P"$ A()LE F,#

F,#E$ A(D WELD%()

D# A) A()LE F,#

H A'$ A(D WELD%()

89 FILLET WELD

Figure 2. 12-


26/30

and entra**ed sla' are a/oided. "his techni


27/30

/ " $ % E L D E D M E & A L A # ' W ELD % ( ) " $ % E L D E D M E &A L A # ' W E L D % ( )

Arc -lo& can r eslt in incom *lete +sion and e;cessi/e&eld s *atter and ma -e so se/ere that a satis+actor &eldcannot -e made. When &eldin' &ith ir on *o&der elec1trodes and electrodes &hich *rodce hea/ sla', +or&ar d

-lo& can -e es*eciall tro-lesome. $t *ermits the moltensla', &hich normall is con+ined to the ed'e o+ the cr ater ,to rn +or&ard nder the arc.

"he -endin' o+ the arc nder these conditions is cased - the e++ ects o+ an n-alanced ma'netic +ield. When ther eis a 'reater concentr ation o+ ma'netic +l; on one side o+ the arc than on the other , the arc al&as -ends a&a +r omthe 'r eater concentration. "he sor ce o+ the ma'netic +l;is indicated - the electr ical rle &hich states that a con1dctor carrin' an electric cr r ent *rodces a ma'netic+l; in circles arond the condctor . "hese circles are in

*lanes *er*endiclar to the condctor and are center ed onthe condctor .

%n &eldin', this ma'netic +l; is s*er im *osed on thesteel and across the 'a* to -e &elded. "he +l; in the *latedoes not case di++iclt, -t ne) Position the electrode so that the arc +orce cont

acts the arc -lo&.(:) Gse the shor test *ossi-le arc consistent &ith 'o

&eldin' *ractice. "his hel*s the ar c +orce to conteractarc -lo&.

(=) Redce the &eldin' cr r ent.() Weld to&ard a hea/ tack or rno++ ta -.() Gse the -ack ste * se


28/30

/ " $ % E L D E D M E & A L A # ' W ELD % ( ) " $ % E L D E D M E &A L A # ' W E L D % ( )

(3) Por osit $ncom *lete +sion ma -e cased - +ailre to raise(2) Sla' inclsions -ase metal ( or the *re/iosl de*osited -ead o+ &() $ncom*lete +sion metal) to the meltin' tem*eratre. $t ma also -e cased(>) Gnder ct +ailre to dissol/e, -ecase o+ im*ro*er +l;in', an o;i(:) Cr ack s or other +orei'n mater ial that mi'ht -e *resent on the s

+aces &hich mst +se &ith the &eld metal.

POROSIT 3"H$S "ERM $S sed to descri-e 'as *ockets or /oids in the&eld metal. "hese /oids reslt +rom 'as that +orms +r omcertain chemical r eactions that take *lace drin' &eldin'."he contain 'as rather than solids, and, in this r es *ect,the di++ er +rom sla' inclsions.

Porosit sall can -e *re/ented - sin' *ro*eram *er 1

a'e and holdin' a *ro*er arc len'th. Dr electrodes arealso hel*+l in man cases. "he deo;idiers &hich aco/er ed electrode needs are easil lost drin' de*osition&hen hi'ham*era'e or a lon' arc is sed. "his lea/es a s**l &hichis ins++ icient +or *ro*er deo;idation o+ the molten metal.

SLAG INCLUSIONS

"H$S "ERM $S sed to descri-e the o;ides and nonmetallicsolids that sometimes are entr a * *ed in &eld metal, -e1t&een ad 0acent -eads, or -et&een the &eld metal and the

-ase metal. Drin' de*osition and s-se


29/30

8 " $ % E L D E D M E &A L A #' W ELD % ( )the cracks shold -e remo/ed *rior to +rther &eldin', -ecase &eld metal de*osited o/er a crack can reslt incontination o+ that crack into the ne&l de *osited &eldmetal.

Hot crackin' is a +nction o+ chemical com*osition."he main case o+ hot crackin' is constitents in the &eldmetal &hich ha/e a relati/el lo& meltin' tem*eratre and&hich accmlate at the 'rain -ondaries dr in' solidi+i1cation. A t*ical e;am*le is iron sl+ide in steel. "he cr ack sare inter 'r anlar or inter dendr itic. "he +orm as the &eld

metal cools. As solidi+ication *ro'resses in the coolin'&eld metal, the shrink a'e str esses incr ease and e/entalldra& a*art those 'rains &hich still ha/e some li to > hors. Gn *r otected sk in, e;*osed to the

() Chan'in' the &eldin' techni7.3, S a $in W el d in g and C utt ing , *-lished - the American Win' Societ.

From time to time drin' &eldin', s*arks or 'lo-lesmolten metal are thro&n ot +rom the arc. "his is al&a

*oint o+ concern, -t it -ecomes more serios &hen &ein' is *er+ormed ot o+ *osition or &hen e;tremel h&eldin' cr r ents are sed. "o ensre *rotection +r o -rns nder these conditions, the &elder shold &e+lame#r esistant 'lo/es, a *rotecti/e a*ron, and a 0ack et (

Fi'r e 2.:). $t ma also -e desira-le to *rotect the &elde5 ankles and +eet +rom sla' and s *atter . C++less *ants ahi'h &ork shoes or -oots are r ecommended.

"o a/oid electric shock , the o*erator shold not &&hile standin' on a &et sr+ace. E


30/30

SUPPLEMENTAR3 READING LIST

"$ %E L DE D ME& AL A#' WELD L() >

American Societ +or Metals. @Weldin', -r ain', and Sol1der in'.@ Metals ' and book , ?ol. =, 7th Ed., :#7:. Met1als Park, 4hioB American Societ +or Metals, 37.

ar -in, L. M. @"he ne& moistr e r esistant electrodes.@W el d ing :ournal :=()B 3:#3RJl 37.

Che&, . @Moistre loss and 'ain - some -asic +l; co-*ered electrodes.@ W el d in g :ournal ::(:)B 32s#3>sMa 37=.

re'or, E. N. @Shielded metal arc &eldin' o+ 'al/aniedsteel.@ W el d ing ;ournal >()B =3#= A'st 37=7.

Jackson, C. E. @Fl;es and sla's in &eldin'.@ lletin 378. Ne& Uor k B Weldin' Research Concil, Decem-er 37.

%incoln Electr ic Com *an. !he pr oced ur e handbook o $ awel d ing , 32th Ed. Cle/elandB %incoln Electr ic Com*an37.

Sil/a, E. A. and Halett, ". H. @Shielded metal arc &eldi

nder&ater &ith ir on *o&der electrodes.@ W el d i :ournal :8(=)B >8=s#>3:s Jne 373.

Stot, R. D., and Dot, W. D. W e # d abilit % o $ S t eel s , 2nEd., Ed. E *stein, S., and Somer s, R . E. Ne& Uor k B Welin' Research Concil, 373.

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