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Gontent1 What is cast iron?'1.1 General'1.2 Grey casl iron1,3 White cast iron1.4 Ductilecastiron1 .5 Compacted graphjte cast iron (Cc_iron)1,6 Malleable cast iron1.7 Alloyed cast iron

2 Factors affecting weldability2.1 General2.2 Cooling sAess€s2.3 lrregularshap€2.4 HAZ snd Iusion line2.5 Carbon pick-up from base nE*al2.6 Otl impregnalion of lhe cast ron

3 How to confol these factors3.1 Cooling slres9es3.2 lrrogular shapes3.3 HAZ and tusion line3.4 Carbon pick-up from base metal3.5 Oilimpregnation ol cast iton

4 Welding procedures4.1 Cleaning4.2 JointPreparation4.3 Preheating4.3.t Preheatingmethods4,3.2 Preheating levels4,4 welding4.4.1 G€neral4.4.2 Buttering layers4,4.3 Single layerwelds4.4.4 Mlltilayerwelds4.5 Post weld heat treatrnent4.6 Cooling

5 Somecommonapplications5.1 Foundry d€Iecls5.2 R€pairs5,2.1 General5.2.2 Cracks (light stress)5.2.3 Frsctures (hlgh stress)5.2.4 Holloweddamages5.2.5 Burntcastings5.2.6 Thinsections

6 Consumables6.1 Gensral6-2 lron based sleclrodes6.3 Nickel based electrocles6.4 Copper based €l€ctrodes

I What is cast iron?1I GENEBALByaloying pure ironwithcarbonthe me ting pointcan be loweredfrom 1534 C (purelron)to 1147 C (4.3 % C).Th s reduct on is lsedindlsiria y to prodlce cast iron- Cast iron iherefore, has a highcarbon conient (betweef 2 and 5olo)which considerably afiecisiis weldab liiy.lf additionioih s phosphorusand sulphurcontentare usually higherthantorord nary steel, wh chfurtheraffectsiheweldabi l ty .Pure ron, alloyed primar lyw th2 5%carbonshows owduciillty,low hardness and low strength, and s on thewholeavery briitlemaierlal.To improvethese propedies (and to renderthe irofadd tlonalpropertes ike heai-, corfosion- and wear resistance),cast irons are oftef aloyed and/or heai treated.The numerousamount ofalloys so created may forconvenience be divded intoiheio l lowing groups.

Grey cast iron

Malleable cast ronDuctile casi ron

1,2 GREYGAST IRONGrcy cast ron is the most common type of cast iron (aro! nd 70 %ofa lcasl irons are grey).The microstruciure consisis ol graphitef akes dist buled n a matrix of ferite, peff ite o. boih Thegraphite possesses zero strength. and therefore ruprure walways appear in this phase. and since graphite is grey. thefracture surface will ook gre)l Thereby ihe n a,.ie. Grey non ! suallyconta ns upio4 a:o C a.d uoio3 i : S i . l i is madebyslow coo ingotihe casting. Some old r_!ps may coniain considerabeamo!nts oi sulphura.d phosphorus.which can makeweldingdlfiiculi Ho\lever o. modern casilngs ihis is seldomthe case,and welding is mosi ofien e..poyed wilhoutcomp ications,

1.3 WHITE CASTIRONWhite cast iron is evaluated on hardness/wear resistance andmostryusediorsuch purposes.ll is of s niilalcomposition to greyiron, butwith a owersillcon conieni. Sometimes t isa soalloyedwiih carbide siabilizers such as C[ Mo and V The m crostructurecor . is ls o ' cd lb dFs d st ib ' red i r a -E,1ers i . i . or pear r .r.atrx.The carbides are hard and br tt e, and render the Iraciuresurface a whiiislr colour. Thereby the nar.e. li s made by rapidcooling wilh 'chills". lt s to be considered as non wedable,aithough successf! wed surfacings have been achieved oncrlsherrolls us ng OKAutrod 12.51.The hardness was renderedthe m ld steelwed metalthrough carbon pick up from ihe whiteiron.Tojoin while non, however, welding is noi recommended.

1.4 DUCTILE CASTIRONDuctilecast i.on have sim ar composilion to grey iron, bLri usl]allyh gherpuriiy.Theadd t on ofsma amounts of mag nes um brjngsthegraphite into fornr ng spheroids, |]nilorm yclispersed through-out the structure! nsteadolfakes ikeingrey ron.Thiswill, niheanneaecl siate, renderdLrctile ron mechanical propefties similarto mild sieel-Welding istherefore seldom diJliculi w th these irons_Howeve[ the voent heaiireair.eni nvoved n weding, iogeihefw ih ihe d uiion fronr the casi ron, still ca ls for ihe lse oi specialo r . t rod6. ard cd.eJL p"1r19otr ' leprc.Fou," .

1.5 COMPACTED GBAPHTTE CASTTBON (CGtRON)Compacted graphltecast iron (CG-iron) may be considered asan:ntermediaie belween duci e and grey lron. lt s produced byadding controlled amounts ol magnesi!m, t ianium and cer Lrnr toa cornposition similallo grey iron. Weld ng should be pedormed

1.6 MALLEABLE CAST IRON[/alleable cast irons are produced by heattreatmeni of white casti ronstorenderihemmoreduct i ethan greyirons.Theyhavelowercarbon and silicon conteni than grey rons, io secLrre wh te konso difcaton.The microsiructure cons sls ofaggregated,somewhai irregular nodules ofgraphite distr buted n a mairix ollerrite, pearl ie ortempered martensite. L,lechan cal properiiesare similar to duci e iron. Wdd ng oi malleable iron may prod ucea ihin whlte iron zone in ihe weld and ihe podion ol lhe HMadjaceni iolhe weld meta.Th s ls notserous n manyappl ica-lions. However, parts produced io be welded are often render,adexcelleft wedabiliiy by a decarburizing heattreatment.

1,7 ALLOYED CAST IRONAlloying eementsare added io improve properties lke heat,corroson- and wearresistance and io increase sirength.Examples are "Ni resist" (corrosion resistance), "n crosilal'(heairesistance), and " meehanite ' (hig h iensle). These irons show aweldabi ty simi lar io duct ie i rons.However, one spec al type oi alloyed iron is "N hard", whjch smore ke a while ron and thereforeto be considered as non

2.3 IRBEGULAR SHAPElron castings are usually deslgned for rlgity. They are seldom ofuniform ih ckness, and genera ythey are of niricale shape wlthrapid changes ofseci lon.Thus, they wi l lno i readiy adjustthemse ves to local conlract on, and d Lre to their ow d uclil ty, newiractures are lableto occur. (SG iron, dueto its good ductilily, isnoi so sersilive in ihis respect).

2.4 HAZAND FUSION LINEThe heal afiected zone oflhe cast iron adiacent to the weld, w llbe hardened dur ng welding due to the high carbon conteni.The hardness oflhe non nrelted pad oflhe HAZ s ma ntydepending on cooling rate, and the width mainiy on apptied heai

2 Factors affecting weldability2.1 GENERALWhiie iron and "Ni-hard'Liypes, because oliheirexteme brittle-ness, genera lycrack when attempts are madeto weld ihem.Troube mayalso byexperienced when weldirg white-heartmalleabe cast iron, due io porostycaused by gas heid in thistype of ror. Othergrades of casi iron are being successfu ywelded every day, provided the correct procedLrre is empioyed.Successfulwe d ng of cast iron is ma nlydependlng on nrin nr z ngthe nf uence ofthe following:- Cooling stresses

rregular shape oiihe castingHardening of the HAZCarbor plck-upfrom the base metaiOil mpregnation of cast iron

2.2 COOLTNG STRESSESTheweld meialw llcontract upor coo ing. This contraclion issenerally largerihan ihe corresponding contraction ofthe casiron. Duetoihe briiileness ol casi iron,the resu t ngconiraciionaistresses mustbeaccomodated inthe we d meia ilcrackingisto

The portion ofthe HAZ c osesi to thefuson llne w lconta np d r i a l l y m e l . - d . c l e r a . - l _ " n i r o q f J L I L e o l t i ' T o ' l e c v e 1

Lomple. aro corsrs( : o lc n i ' 'J re o- mar le rs i le . cJs la ' r i loprimary carb de, and lederburite which surrounds pai(ialyd ssolved nod! es orflakes ofgraph te.This po,lion isihe hardesl

The extent and h ardness of this zone s ma nly depend ng onapplF. l ped. .e-oe ' r - i re . , leat , lpL la ' rd.ool 10 rdt 'd- r "o

weld ing. Sincethe peaktemperaiure is fa i ry equal n MMAweldlng, regardless ofconsumabe choice, the p.opeJlies wilalso here ma nly depend on heat input and cooling rate.

2,5 CARBON PICK-UP FROM BASE METALThedilltion wilh base rlralerial will calse caton pick-up n iheweld meta . t w ll a so cause lncreased weLd nreia conteni oisu phur and phosphorus ii s!ch are present in the casl ron

2.6 OIL IMPREGNATION OFTHE CASTIRONOilmay be absorbed n graphile and micropores, iherebypeneiraiing deep into the casi iron. Dur ng weding, thiso wevaporale and cause porosity in ihe weld meta.

3.2 IRREGULARSHAPESTo avod cracking in associated parts oithe casting dueiocontraci onalstresses caused by weld ng, t is often usefu toexpandihis pari by preheat ng in orderioba ancethese siresses-Th s lype oi preheat ng is commonLy named ndireci prehealrng.Flg I shows the application ofthis preheating, as agenera rule,

3 How io controlthese factors3I COOLING STRESSES

Using conect welding parameters.We d wth shortstringer beads, low am perage and plan the bead

The smaller the volume to cool, the smaller the cooling stresses.Consequently, shofi beads are preierred to long ones.Weav ng wl I resuli n arger pats of the weld io cool, thereby

c .d i r g coo 10 s l esses. Srr ropr b"dds dre Lte e 'o 'e o e_

In m ultilayer welding, subsequent ayers w I heat pfevioLrs layers,ihereby releas ng some of lhe stresses buit |]p dur ng wed ng oi

Toiur ther owerthe heat inpui , ln par t ic ! arwhen weld ing ih lnsecions, t has been proved usefu ioweld in thevertica downposton.Th s s possib le us ng ihe OK Selectrode 92.58.

Using consumablesthat provides a ductile weld metalRes d ual stress levels nwed meta areusually ntlrereg on oi tsy eld stress. Consequent y, to ower the res d ua stress levels orcooling stresses, weld metal w th low y e d slress are preierred iosuch wi ih h igh yed st ress.

Performing preheatingTheyield stress olanymaier a generaiy decreases wilh increas-lngremperalure. Consequent y, ii the conlraciional siressesorginai ng l rom weld ing could be fu ly accomodaied nthewedmelaiai a higher temperature than room iemperature, theres dualstress levelwo!ld be lower. Consequently preheatingmay lowerthe nf uence ofcoolifg siresses.

PeeningPeen ng w ntroduce compressve stresses in iheweld metainstead ofthe iensileslresses ftroduced during ihe wedingoperatlon. This s the mosi uselul method to avo d crack ng in casi

when lsing ih s proc3,r L:: r ls belter lo heai a large area io a lowtemperaiurethan 1o h:ai 2 s-a Larea to a high ter.peraiure.However. a high oca pr:h:a: in the o ni w sl I be necessary, iiasofi machineab elved is reor r3ci.When welding an ntncate casrii-o co lia n ng rap d changes oisect ion, lhe generalpreheai ing sho- ,c be oainta ned at atem perature jusl uder red hear. Where :f:s s .loi poss ble. manyrepairs can be madesaiisfactorilywrh ag.nera creheat to blackh e a t w i r t - a , o . a p r e h p d i o , r l e j o i r i . A p . . l e . o - ' o - t d b ecarred out s lowly lo a low a !n i form dls i r ibu i on o i heai io bui ldup in ihe casting. Genera preheal ng up to a remperaiu re oraround 600"C may be car ed olt in a suitab e m provised furnaceus ng gas heaUng orcharcoa.F naly, the more lntricaiethe shape. theqreaterlhe need iorevenly applied preheatlng.

3.3 HAZAND FUSION LINEThe hard ness of the HAZ maybe owered by p.eheat ng. However,to reach a substantial ha.dness reductio.. rr^e casting wouldneed io be preheated to around 500 CThe hardness ofthe part y rerne ied zone c ose io tire ius on linema) be lowered bv redL 9 t l p tm d ' L oecr te_ 0e dt - red!fing weLding (e.9. using oly amperager.

3.4 CABBON PICK-UP FROM BASE METALCarbon pick-upfrom base mefa w Laways occurin cast ironwe ding. In princ paL. there s lwo ways oi m nimizing the effects oi

1 us ing h igh preheal ing n comb nai ion wth s low cool ing, loavo d ihe detrimenta eflecis of the carbon pick-up- Th s isesseniialwhef using Fe based consurlrables.

2 Using consumableswherelhecarbon p ick up snotdetrmen-ial.This s bytarthe most used method, and the consumablesare mostly oi N 'based type.

3.5 OIL IMPREGNATION OFCASTIBONWhen oilhas penetrated deep intolhecast iron, t s imposs bleloremove by anydegreas ng agent, s nce this willaiiect only ihe

Instead the oilhas lo be burnt off by comparably long heattreatments al tem peraiures around 500'c. Norma heat ng time

On nrany appl ica i ionsih s ls not poss be, and forsuch, gaugingw th OK Selecirode 21.03 mayprovlde asu tab e enough so uiion.Should porosty st Llocc![ the best way to produce sound we dss to repeated y remove tlre we d meial by grlnding and rewe d tuntil no porosity occurs.

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Doired lnesshoweifecl IFS1 .opreheat sused

4 Welding procedures4I CLEANINGAll su rfaces musi be cleaned p or to welding. Casi iron itself, s ofsuch lowstr€ngth that it is unnecessary to lurther weaken thewelded jolnt by omitting ihis importantprecaution.

Oil, grease, eic.Surfaces sha be thorouqhly degreased chemically, otherwiseporosily will result.f ihe cast ron has long be€n in coniact with oil, (like gearsimmersed in oilorgear boxes holdlng oil), iheol may beabsorbed byihe graphite or micropores.This way ol carpenevaie deep intothe casting.To rcmove such oil, whichoiherwisewillevaporateduringwelding, chemica degreasingis not enough. Insiead thecasiing musi be heatedio burn oulthe oil.This js done at temperatures around 400-500'C for

li is obviousthatthis is notalways possible, and forsuchapplications, gauging w th OKSelectrode2l.03 often providesa suitable enough soluuon, by local burnoul ofihe oil. Inaddition io ihis, gauging wi lprovide ihe nrost suilablejo ntconiiguraiion

- Dirt, castskin, paint, etc.l lbelongsto normalwedingprocedlretoremovecontamina-tions like these priorio welding. However, the nickel basedconsumables normally used forthe welding of cast iron aremore sensitiveto contarnination irom th s than rnrld steel

So, besurcto makeaihorough cleaning. Generally ii isenoughto cleanlhe areawithin 20 mm from ihe weld.

4.2 JOII'ITPBEPARATION- Joint angles shou ld bewiderihan formild steel, around 80 90

- Allsharp edgesmlsl berounded ofi, to minir.ize heatconcen

- Generally u-grooves are prefeffed io v-lo nis. Th s is the pr mereason whygaug ng ls so beneficialin comparison with othermethods forprepalring casi iron joints.

- Cracks must befulyopened to a low accessability. However,leave 2--3 nrm onthe rootsideio alloweasyltting. UseOKSeleclrode 21.03 iorjo ni preparation on allcracks-

- Cavities lrkeblow holes, etc. must be opened and cleaned.

I

Joint preparation in Cast lron

60-75.

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Fig 2

4.3 PREHEATING

4.3.1 PreheatingmethodsA though asat siactoryjointcan be ach eved w thout preheating,

the risk of cracking due to ihe rigidity or ack of duciil ty espec allv

n comp caled shapes is considerably reduced by preheat ng.

Tlere arF tlree -ethods o'apply,ng preheat Io tl-e casl ,lgs'

Local preheating, to retard the raie of coo ng oi ihe weld joini-

General ireheating, to release interna locked_up stresses andto retard cool ng ofthewe d, ftheiemperaiure s ralsedtoabove450"C, a sLighi mprovement in ductilty occurs, which increaseswih flrrlher increase jn the iemperature. This allows for somesiress adlustmeni and grealLy reduces the d stortional ten dencresand the r isk of cracking in thejo int being welded aswel lasreducing the hardness ofthe wed deposiiand heal affecied

Indirect prehearing, which is oftenvaluab e, ifused with cauno.lorexpandlng an assoclated part oilhe casiing n orderioba ance contraclionaL stresses caused byweld ng

4.3.2 PreheatinglevelsAll eves ofpreheat ng is usually beneficja. Nowever there may

bea point n es iabl ish ing sonre 'key_ eves .- Ambienltemperature

Secur ng ihat lhecasi ng isofat leasta.nb ent iemperaturew r l

secLrfethai no air rno siure will condensate on its surtacea0-100"cPreheat ng io aro! nd 80 100'C will secure that al wet surlacesw Lldry thereby no hydrogen coniribulion fronr air hum dity

- 200-250'cPreheating to aro!nd 200-250'C is Lrsed on ducu e iron toprevenl madenslte formation n ihe HAZ.li is noi necessarvtopreheaithese irons to higher tem peraiures Sometimes it nrav

even be dangerous, s nce preheat ng ntheregionof300500'C may promote plec p tat on of proeuiecto d cemenite,which consderably owerstheir ducti tyUp to 500'CIndirect preheating is Lrsed at alltemperature evels uplo500'C. The h ghe[ ihe beiier, provded boih heaiing and

- 500-600"c500 600"C is used on grey and CG iron to achieve lowestpossible hardness n the HAZ.

4.4 WELDING

As mentioned above wed ng can be performed wth d fierentevels oi pr€heating.As ageneralrule, ihe higherlhe preheating

eve , the Loss r g d thewelding procedure.To facilitateihereconimendat ons, wew ll here work with th ree differentier.pera

Room temperature (cold welding)250"C (semi-hot weldins)

- 500"C (horweldins)Flrrther we need io diflerbetween three kinds o1welds:Butterin9 layersSingle layer welds

4.4.2 Buttering layersOn someweids lt is often beneficialto use a "buttering

techn que. Ln shorttlris means that one lor boih) ol the su{acesto

beweldecl, are surfaced priorto thejoin ng operation The

reasons for using thisiechn que may beerther melalurgrcalornrechanical. Fig 3A.

Metalurgic6lTo avoid lormalion ofbritle phases in dissLmildwelds

4

To allowfor coo ngs siressesto moreaffectthe ductile bulieringayerihan ihe br tt e HAZofihe basemateria. (Oicoursethe HAZofthe base meialwill be affected by cooling stresses lrom eachweld bead, bui they w I be spread out over a arger area an d thehard phases ofthe HAZw llbe annealed)Buttering is employed Pr marily on:Multilayer welds, to a ow lor l-"ss rg d wed ng proced!res onthef i l l runs.This is nrainlydueiotheiolowng:

- The contract onaLsiresses i'ori Ine cooling weld rneta insubsequent beads wil be accomodated in the butiering layer, !thereby owering lhe st.ess eve and ihe risk oicfack ng.

- The heai from subsequenr beads w Llannea the HAZ in thecast iron, and owerthe sness eve in previous beads

- No dillt on from thecasl ron wl occ|]r, dLretoihe insulatrngbuiiering ayer.

Welds between cast non and othermetals ike sieel, copperalloys or nickela Loys. to secure good wed bond.Rebuilding largersurface defects, resu t ng rrom overmach ning, casung operations or mechanica forces, eicThe idea here s io irame ihe defecl, us ng short stringer beadsfo lowed by immediaie peening.The resl oi ihe rebuildning canthen be commenced |]s ng a less rgld weld ng procedurewelds perforlned under heavily restrained conditions, e.g.rep acing a holowed damage wlh a milcl sieel plate.

Muliiayerwitir bLie..g i-.. qle

4.4.3 SinglelayerweldsOn s ngle ayerweds, allweld meta is in conlaci with the castiron. Further, no heat lreaiment ofthe HAZ by ihe welding oJsubsequent beads willoccur.This ca ls for parucularly r gidwedingproceduresand/orpreheai ing.

Cold weldingThehardnessof iheHMwi l ldependonthecool ins ra ie.Theonlyway to ower ih s wiihout preheating is to use a hig her heai inpui.Th is will, however, imply a larser weld poo and ihereby highercoolirg stresses, which is even more deirimerta ihan the HAZ

Therefore, do noi lse high heat inputlInstead ihe HAz zone sha lbe as th in as poss bLe io lmi t ihedangerousarea, and cooling siresses must be neuiralized. i isiherefore extremely importantlofo low below pfocedure recom-

- Weld w' ' r shor l srnngF'bFads (2 3cm..- Usethin gauge electrodes and weld with lowamperage.

Welding on DC negat ve wilresuli in lowerdiuiion from basemaieral, and may be benetcal, in particularwhen weldlng ongrey cast iron with pure nickel electrodes.

- The intermed iaie temperatu re shallbe kept below 100'C.. - Use he bac(-s leo iechr iqLe s l_ow1 1l igr ,| } F a m m e . l r e w e o s - i 3 c e w i r h a r o J r o e o r o o , p e e r n o )-

d 'ec lv ahe weld i rq.T"e r ro e l l^e wFd meia l sa lowedlocool, the greaterthe risk ol cracking due to cooling siresses.Thereforepeeningshould beperformedwhi le iheweldmeia l isst lred hot.lt s important nolto hammerperpendicu ariothewed bead, blt raiherfrom ihe end oiiheweld lowardsthestariing po ni-Th s sto avoid causlng cracks bythe peeningoperation itse f.

Semi-hotweldingThispreheat ng leveLis most y usedforthewelding ofducu e konand thereforethe below recommendatons are given forthis

Preheaiing as mentioned above will lower the cooLing raie, andtherebythe hardness ofthe HAZ. However, ihe reduction inhardness w llbe marg nalwith a preheat levelofonly 250"C, andtheref ore the procedure recommendauons given in section 3l areva d also here, ihough somewhat less rigid.- nterpass iemperaiure shal bekeptat250"C.- Shorr stringer beads sha Lbe used (no weavingl). N,4axjnr!rn

50 mm.The back-siep techniq're shown in fig 4 s preferred.

- Theamperage may be increased in re at onto cold weLding, bLrist lth n gauge elecvodes and moderate amperages musi be

- Peen ng shall be periormed (see seciion 3l ).- S low coolng is imperatvel

Hot weldingThispreheaiinglevelismosilyusedforsmallercaslings, becauseofthed filculiy nvolved in heaiing arge parls. H oi welding smostbenelicialon greyand CG kon. On Sc-iron, however, preheaiingsho!ld not exceed 350'C.

The weding may be carried out asfor normal steel welding,wth the exceptionihat peen ng should be performed.

- OKSelecirode 92.58 should be preferred to OKSelecvode9218, s nce this high preheating wil subsianta y ncreaseihedilutroa from base rnaterial, and OK92,58 is the mosttolerantof the lhree in ih s respect.Slow coo ing s mperativel

4.4.4 Multilayerwelds- Allbeads n phys ca coniaciwith the cast ron shal bewelded

according toihe proceduregjven fors ngle ayerweds-- The last bead musl noi bewelded direcily io the cast ron, but

on iop ofa prevoLrs welded bead.- The best results n multilayer weldlng on casi ron are aways

achieved usifg the buttering lechn que (seerig 3).

4.5 POSTWELD HEATTREATMENTThe mosi common heat treatment afterweld ng is stress-reliefanneal ng. i has been quest oned wheiher it w I mprove thepropert es of the we d or not, but jts use s w de yspread, and theovera experience seems to be good.Tempering to lowerihe hardressofihewe d rnayalso occur.Th sis pad cularly usefu when we ding wiih Fe-based consunrabes.

4.6 COOLTNGBecause ofihe low thermal expansion of casi lrons, (in compari-son with mostweld metas used), and because oltheoftenniricale shape of the castjngs, s ovi/ cooling is essenlial in al castron weld ng.Sow coo ing mayiake pace n a coveroisaw dust, vermiculiie,hot dry sand or in iheoven Lrsed forthe preheai ng operaton.

5 Some common aPPlications5I FOUNDRYOEFECTSThesedelectsaremainlycavitiesand blowholes- They mustl rst be opened up and ceaned of d ri ikeirapped

- Use OK Selectrode 9218 or92.58iof llthe caviv.

5.2 BEPAIBS

5.21 GeneralCast ircn repairscan genera Ly bec assed into two groups,lighilystressed app cations and heavily stressed appLicaionsWherethe delectve part is understress,lhe repa r normarrvconsisis of cutting and weding the defect ve nraierraLw thouiprovd ng add t onaL strengthening r.aterial-Wherethe defective part must be capable oltransm tung h gh

loads, the repa r s often ach eved wiih ihe aid ofmeclranicameans, because the iensile sirengih ofacast ron weld is:s!a \'

5.2.2 Cracks (lisht stress)

It ls essentia io detemineihe exaci lengih oia crack.Asaiegeneralrule s to cut oui more maiedala ong hs length ihan is

rea LV necessarylo ensure that tire whole ol the crack has been

The pract ce ol di ling a smallhole (-3 mm n d ametet accurately localed at either end ofthe crack, to preveni tirom

spread ng dLrring ihe repair !s often employed wth good res!lts.Where cLrtt ng out and welding do noi nvolve mLch work, ii s

oflen advisabeto free one end ofthe crack by cutung outto the

edge of the casting. Where the crack has already spread io an

edge, weldlng shou ld slart irorn the i xed end and trave outwarosThepointatwhichweld ingshouldcor imenceincasesother thanthe above musi be decided on the merlts of each repair Atyp caL

method o i repai rofa crack nthecentreofacast ingisshown nl s . 5 .

Alignment of workpieceA surfacesihat shallbe mechanlca y attached to anothersudace, must be fixed accurateLy in thai pos t on dunng weldinglfnoi, anymisfitbetweenthe surfacesw Llresult in crack ngwhenmounting lhe repa red Part.Oneverycommon exafap e ofih s, iscracked braces on eLeciricalengine housings (see fig 6). We d ng a broken brace wthouiproperfixing oflen results in ihe brace not being in plane Whentighien ng the boLls upon mounting the engine, a new crack willoccur due to the low duct ity of the cast iron

6

5.2.3 Fractures (high stress)FaiLure byfracture is usla ly due to asudden increase !n thework ng load, and the repalrmusi be capable of transmitting iheoad carried bythe parts in quesiion.This s ofien achieved bymechanical nreans whjch consislsof re nforcinq thelolni wlthsome form of coverslraps f xed by boLls, orpreferably byshrinklnq on a iroop or band to carrythe tensile load.Fractures which may coverareas in thln sections, such as water

tackets. are often bes: rapaired by removlng the deiective areaand weLding n a f;!c s:ee 3a:cn.Anoiher ioF ci r-.ca. x-rc^ is o.::si:n: ) successi'r yused.bui nor a tra-vs r.c.nran3:c. c..s:s:s ol s:!Cii.8 [lild steelsii-c s ar. ^se.e! Lni. :n.':c€s ri :n: ir:ci-.. an c we.ced io theces: 'o. ."ior::ie rainl.b ot \reLo ng Jpr.e o ni ls com-rerc,-c. : Ls essenia to iirread the studs and screwthem ilrmlyinio:ir: oareni melal.The us-aofstuds in buttwelds rs somewnalnef:crive whe.eiensile strcsses are involved, slnce wedingotienservesloloosenthesiuds- Forreinforcing broken gearieeih. however: where shearsiresses are involved, stldding s ausetu strengiheningdevoe.

5.2,4 Hollowed clamagesAhollowed damage in iron castings may be repaired intheiollow ng way:- Removea ldamaged niaterialfrom the cast iron (preierably bv

gr indlng) .- Round off allsharp edges.

Gr nd the edges oi ihe cast ron io around 45 degrees- Butter the edges ofthe cast iron w th OK Selecirode 92 58 or

9218.

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- Cut a mild steelplatetoft into the buttercd hollowed section,Because of the great difference in heat expansion betweensteel and cast iron, it is betterto use a steel plaie with about halftheihickness ot thecast imn-This will also lowerihe amount ofweld metal needed, thereby making it easier to limit ihe heairnput,

- Grind the edges of th€ mild steel to around 45 degrees. (Leave2 mm 'oor face to fucrlrtale fixng ot lhe two suriaces),

- Tack weld lhe steel olate in to the cast iron,- Weld with short srring€r b€ads usingthe back-siep technique.

Place the beacls one alter the other as in fig 8.- When peening, hammeriowards ihe weld bead ratherthan

perpendjcular to th€ weld surface, to avoid crack ng the weld.lf all pieces of broken cast iron are possible to use in the repairoperation, there is no need for a rn ild stee replacer. lt is ihen alsopossibleto weld without the buttering layei even though this stilwill provide a betier weld.

5.2.5 BurntcastingsTheterm "Burntcasi iron" generally describes a casl iron, whichisoxidized bolh on the surface aswellaswiihin the maiedal.Thisoxidation occurs whenthe cast ng has been exposed to hiqhservice temperatures, Depending on the alloying content t maystarl already at 400'C.Burnt cast iron is characterised by:1 A visible oxide-skin forming on ihe surface.

This oxide consists of Fer03, Fe304 and Fe0. Fer03 holds mostoxygen and willtherefore take the outer place of the three.Oxides of alloying components may of course atso be found inthis oxide conrp ex.

2 Internal oxidaiionOxygen penetratesquicklyinioihemater ialaongihegraphiteilakes- For thermodynamica reasons, the result is not onlyburning ofgraphileto COand CO,, but also the formation ofiron oxides.This iron oxide wilform in a zone surrounding thegraphiteflakes- lfexcess oxygen is sullavailable and thelernperature is righl, the graphite wi I be burnt off. The graphiteisthen replaced eitherwiih iron oxide or noi at al,leaving anempty space wiihin ihe siructure. Th is process is continuousand willcontinue untilthe materia is destroyed,The iron oxide is nrore voluminous ihan lrcn whlch causes a"swelling" of the casling.The presence of iron oxides will alsoresult in an increased hardness,

This, iogeth€rwiih the rough and dirtysurface, makes burntcastingsvery difiiculttowe d, urlessiheworn parts of thesurfaceare removed. Therefore, on such applications ii is always bestiogrind orgaugedownto sound metalbefore weld ng,However, praciice hasshownihai reasonable good welds can beachieved in sleel manufaciuring on riser planes and mou ds,using the OK Selectrode 91.00 with high amperages (380-600A).The reason seer.sto bethatthe high anrperage pemitsrheelectrodeto cutdeep jnlolhecasting, crealing a good bondtosound metal. Furthei much ofthe impurilies lend to rise to the

As an emergency solutior on smaller castings wth burni orconoded surfaces, thefollowing procedure mayhelpto create asuitable eno!gh bond.- Cean the surfacefrom al dusi and looseattached damaged

maierial.This maybe donewiih a stee brush orgrindins.- Use OK Selectrode 9T.58 to strike reDeatedlv overthe surface

in the same way as striking a match. This will cause some steelmetalfromiheelectrodetostickonthewornsu ace,providinga better bond du ng ihe actual welding,

- Use OK Se ectrode 92.58 ior the actual welding.Experience has shownthat OK Selectrode94.25 may providesuccessfulweldswhereNi basedelecirodes havefailed. So havefor insiance exhaust manifolds been successiullv welded on

5.2.6 Thin sectionsThinsectionsarefound in manycastings, such as engine blocks,cy inder heads, valves, etc.The main problem isto avoid app yingtoo much weld metalin orderio minimize ihe coolirg stresses.Therewillalso be difficulties n peening, sirceihe hammering iniiseif mav cfack the weld.The besi way to apply tust enough weld rneta is io weld in iheverticaldown position.This is possibe, using ihe OKSelecirode92.58, whlch has a specialcoating thatpermiis weding in thisPosition.To avoid breaking the casling during peening, it is better ioharnrnerin a45 degree angle iowards the welded bead, raiherihan perpendicularto the weld sudace.

Fig 7

Fig 8

6 Consumables6.1 GENERALElecirodes for cast iron welding:

OK SeLectrode 91-00 - Casi iron composiiion- oKSelecirode 91.58- Mild steel composiiion- OK Selectrode 9218-Pure nickelelecircde- oK Selecirode 92.58 NickeFiron compositron- OK Selectrode 94.25-Coppertin co..position

6.2 IRON BASED ELECTRODESOK Selectrode 91.00 is developed for the repair of hugh ironcastings, such as steel ingot moulds, botlom plates and slagpols.lt deposits aweld metalofcast iron composiiion glvingsimilarcoourand rusting properiies Theweld metal wi! befairlyhard when welding without preheatingOKSelectrode 91.58 is used lor refiLing of caviUes orsurfacedefects.Theweld metalwillbehard and briiiL€, and thereiore it rsnot recommended forjoining. Colour and rusting properties willbe simiarto cast iron. lt is also used to secure good bonding onburntcast iron, such as exhausi manifolds, doorsior martin and

6.3 NICKEL BASED ELECiRODESOK Selectrode 9218 is us€d for welding of all casi irons. The weldmeialisduciiie and very easily machineable.lt is recommendedfor refilling ot caviiies, general repair and where machinear'leweldsarereouired on cast ironwith hardnessesaround 150 HB ltmust not bewelded in more than two layers, so formultilayerwelds, use OK Selecirode 92.58 for the fill runs and OK Selectrodeg2lSforihecap runs.lt is not recommended on high sulphurorhigh phosphorus rons.OKSelectrode92.58 is usedforcold we ding of allcast irons. li isoarticula v useful for ductlle iron becauseofiis h igher strength. ltis recommended when machineable welds are requ red on castironswith hardnesses around 250 HB lt is more iolerant todiluiion with sulphurand phosphorusihan OK Selectrode 92.18

6.4 COPPER BASED ELECTRODESOK Selectrode 94.25 isorimarilvused for the welding of copperalloys. Howeve( experience has shownthat good results may beachleved usingthise ectrodeon high sulphurcasi irons. on someoccaslons it has also proved heLplulon burnt casl iron, whent\i based eleclrooes l^ave failed l l^e n aclira orliiy ' rol asqoodas for OK Selecirode 9218.

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