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' ()N*)L (ET)L )RC +((),S()W-

• ost versatile welding techni-ue

• uitable for all thicknesses " t!pe of ferrous " nonferrous metals.

• an be carried out in all position and relativel! economicall!

• elding -ualit! ver! dependant to welder skill

• 4eat being provided b! electric arc which formed between a 5u6 " metal being weld

• 7verage temp around &8888 which is su9cient to melt the parent metal.

Powe e$uie"ent

• an be carried out either ac (ve polarit!# or dc(:ve polarit!#

•  The actual current form selected is dependant upon the composition of the electrode 5u6 coating" specic re-uirement of weld.

• 7 transformers are the most e)ective form of power suppl!.

• ;ower can be obtained from transformer, transformerrectier, generator or inverter.

•

egardless of t!pe, all welding plant must provide the following <1. drooping characteristic power source.2. a reasonable current must be available3. arc stabilit!$. a current which remain almost constant.

• )"pe#ge < the welding current , controls electrode burn o) and depth of penetration.

 Too low < slag incl, electrode freees to weld, arc strike Too high < e6cess pen, burn through, porosit!, spatter, high deposition, undercuts.

• Volt#ge < controls the weld pool 5uidit!.too low < poor pen, unstable arc, irregular root bead, fusion def, slag incl.too high < spatter, slag incl, ver! 5uid weld pool.

• Speed o t#.el < e)ect heat input therefore a)ects metallurgical and mechanical condition.

Cuent t/pe

•

DC electode positi.e1. 2'3 heat on elec " 1'3 on pm2. wide " shallow weld pool3. reduce possibilit! of 42 entrapment " brittle structure

• DC electode neg#ti.e1. 2'3 heat on pm2. narrow " deep weld pool3. ma! have 42 entrapment " susceptible of cracking.

• )C < = heat on pm = on electrode. 0)ects of e-ualiing due

to polarit! are reversing 188 times per second (%8 cps#. The weld one and mechanical characteristicare therefore midwa! between those produce b! > :ve " ve.

Consu"#%le Electodes

• Rutile < used mainl! for general purpose. 7 medium weight coating of TiO 2 : 5uorspar, made

5uid fast freeing slag. uitable for all position but not often in vertica down " ver! popular. ?lu6esshould kept dr! but never baked. The 5u6 contains of following <1. TiO2 (rutile# / slag former " secondar! ionier.2. cla! / binding agent3. @aiO2 / main ionier

• Cellulosic < designated indicates high cellulose content to produce large volume of gasin arc region. ;rinciples gas protection via gas shield consists of 42, O, O2 " 42O. ost important arewhich 42 e)ect of increasing the arc voltage " develops ver! forceful deepl! penetrating arc.apid burn rate, fast freeing " thin slag. uitable for vertical down " good -ualit! penetration beadsproduces.

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omplete weld have a rough appearance with course uneven ripples, spatter content is highercompare to other electrode t!pe. ?lu6es are h!droscopic " designated $+A moisture, kept dr! "never baked.

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?lu6 contain of following <1. cellulose (mainl! wool pulp# / gar former. 4igh 42 which increase arc voltage " overall power arc /

ma! detrimental some metal.2. TiO2 / slag former. 7 minor additional onl! / not enough to e)ect ioniation.3. @aiO2 / main ionier (> :ve#. BiO2 as an alternative to all current but e6pensive.

• 0#sic < have high limestone" 5uorspar content were to develop weld metal with a low 4 2

content. Cimestone has ver! good arc stabilier " produce O 2 gas shielding. Daked prior to used(%888# to drive o) moisture without damage occurring to the coating. Esed e6tensivel! because theirabilit! to weld low allo!, high, medium tensile steel, " steels with high content without an! realdanger of solidication cracking. educe possibilit! of 4F in weld " 47G, but this is dependant uponthem being properl! dried before used. T!pical precaution includes heated storages area, sealedcontainer, preissue ovens and -uiver for on site welding. D 0@ $HH starts with ma6imum 42 contentof 1%ml'188 g of weld metal deposite.

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(ET)L INERT&G)S 2 (ET)L )CTIVE G)SWELDING +(IG 2 ()G-

• a! consider together because all e-uipment are same, onl! its consumables and consumables

are di)er.

• Esed bare wire to provide arc " weld metal continuousl! fed from a coil through a speciall!

designated welding gun.

• Decause process 5u6less, it is necessar! to eliminate the possibilit! of atmosphere contaminationb! introducing a shielding gas.

• ?or some materials, 7r is an e9cient shielding gas, being inert, not chemicall! reacts with metal.

• hen inert gas using as a shield metal, the welding process known as 7I.

• hielding gas also changing the electrical properties of arc eg. not full! transfers if used 7r.

• can be transfer using O2 as shielding gas. Ft chemicall! reacts with the weld pool to producean o6ide.

• ain functions of shielding gases <1. to provide atm for electric arc2. to protect weld pool from atm contamination.

• ;ure 7r / 7l, u, HA @i

• O2 / with $A , low allow steel.

• ire used for welding should confprm to D 0@ $$8 " D 2H81 ;arts 2,3,$ " %

• Decause porosit! problem in 7I, full! deo6idied (killed# wire such as iliconanganese should be used.

• ode of transfer1. spra! or free 5ight2. dip transfer (semi short circuit arc#3. globular$. pulsed

• Sp#/ < used high current. 4igh welding deposition rates " deeps penetration, suitable for thickmaterials, accept for low allo! mats ma! onl! be used for horiontal welding position.

• Dip t#nse < low amp " low volt re-uired so that the consumables wire electrode touches the weldpool " short circuit. Decause produced a relativel! cool arc, it ca be used on thinner section " for allposition.

• Glo%ul# < intermediate range between spra! " dip. There is no manual application in FI'7I

welding and onl! limited on mechanied " auto setup.• Pulsed t#nse < modied from spra! transfer which e)ectivel! uses both the dip and spra! modes

in operation. ;ulses of high powered spra! transfer current are superimposed over a constant low semishort circuiting background mode.

• Powe Re$uie"ent < usuall! used constant voltage characteristic. This can be obtained fromgenerator of transformerrectier.

• J power sources must be used in combination with constant speed wire feeder.

)d.#nt#ged

• inimal wastages of consumables electrode

• @o fre-uentl! changing electrode

• Cittle or no interpass cleaning re-uired, no slag produced.

• 4eavier weld bead produced

• ?aster welding process

• Cow h!drogen content / preheat ma! not re-uired

Dis#d.#nt#ges

• Fncrease risk of porosit!

• ore maintenance of plant involve

• 4igh risk of CO?

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3 T*NGSTEN INERT G)S

• Eses of non /consumables tungsten electrode to provide arc.

• ire feed separatel!, 7r used as shielding gas where fed through welding gun. @o 5u6es are usedin this process.

• ore e6pensive " generall! used on when high metallurgical " mechanical properties arere-uired eg. in -ualit! root run in pipeline work.

• hen high -ualit! root runs are to be deposited, back purge is used to prevent o6idiing to weldmetal.

• hen access to weld area is di9cult, the tungsten stickout length can be increase providing agas lens is tted to prevent gas turbulence / to prevent weld metal o6idie.

• Ft is possible to automated TFI process.

Tungsten electodes

• ;lain (inactivated# tungstenan cause tungsten inclusion, suitable for lower -ualit! general purpose weld.

• 7ctivated tungsten

7dd thoria or irconia to the tungsten to increase electron emission for better arc striking, reignitionand stabilit!. >ecease possibilit! of tungsten inclusion14 T5oi#ted tungsten electode < used with electrode /ve dc for welding all metal e6cept lightallo!s.'4 T5oi#ted tungsten electode< as above but appl! for lower amp to improve arc stabilit!6iconi#ted tungsten electode < speciall! used for ac welding for light allo!.

Selection o cuent

• > /ve < narrow " deep pen, 2'3 heat on parent metal. Cow voltage (1$J# " suitable for all metalse6cept 7l, g and their allo!s.

• > :ve < wide " narrow pen. 1'3 heat on parent metal. 4igh voltage (2%J# " can cause overheating "melt the tips, globular in shape resulting of uncontrolled arc " possible tungsten inclusion.

• 7 < = heat on metal. edium of ve " :ve (28J#.

Potection o weld "olten pool

• 2 functions of gas shield, 1. provide suitable ioniable atm for electric arc " 2. to protect fromcontamination.

• Iases used are 7r, 4e " @2.

• 7r < ver! cheap. ;roduce smooth " -uiet arc with low arc voltage " improve cleaning when used ac onlight allo!s. 7ddition of 1%A active gas will improve penetration " welding speed due to increasing of voltage.

• 4e < lighter than 7r. e-uired higher 5owrate (22.% more than 7r#. reate higher voltage which usefulfor thick mats " metal with high thermal conductivit!. hen used with 7 on light allo!s, less cleaningcompare to 7r.

• @2 < inert in room temp. combine with O2 at arc temp become active. Ensuitable on most metal butgives good result on u as increase arc voltage which create more heat " far more cheaper than 7r "4e.

7ille "#tei#ls

• ?iller metal used must conform to D 0@ $$8 " D 2H81fller rods & wires or inert gas welding.

• Decause of porosit! problem in , killed wire as i'g'7l recommended.

Powe e$uie"ent

• 4igh OJ re-uired around H8volts to ensure stabilit!. To assist arc, prevent inclusion " damage toelectrode tips. 4igh fre-uenc! current is superimposed at the start at > operation.

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