How to weld

THE FIRST IN A SE­RIES ON HOW TO WELD

The Shed - - Contents - By Greg Hol­ster Pho­to­graphs: Jude Wood­side

Part one of a seven-part se­ries: The ba­sics of arc weld­ing

The form of weld­ing com­monly known as ‘stick weld­ing’ or ‘man­ual arc weld­ing’ is the most ver­sa­tile and widely used weld­ing process in the world.

It can be used to weld most com­mon met­als and alloys and weld­ing mild steel —

low-car­bon steels with good weld­abil­ity — and this process is won­der­fully un­com­pli­cated. It can be used out­doors and it’s nor­mally por­ta­ble, es­pe­cially with the small pow­er­ful ma­chines on the mar­ket to­day.

A com­plete weld­ing set was first made by the Lin­coln brothers in 1909 and in 1911 Lin­coln Elec­tric in­tro­duced for sale the first vari­able-volt­age, sin­gle­op­er­a­tor, por­ta­ble weld­ing ma­chine. The world of weld­ing ma­chines has changed since then yet the ba­sics and the tech­niques re­main very much the same.

Arc weld­ing over the past few years has had a resurgence. It’s very cost-ef­fi­cient as well as sim­ple to do once the ba­sics are mas­tered. Suc­cess­ful arc weld­ing is essen­tially about good po­si­tion (it comes with prac­tice) and choos­ing the best of many types of elec­trodes to suit a mul­ti­tude of base ma­te­ri­als and uses.

For this ar­ti­cle on arc weld­ing — more cor­rectly, shielded metal arc weld­ing (SMAW) or man­ual metal arc weld­ing (MMAW) — I am deal­ing with the ba­sics.

Many peo­ple ask me what they are do­ing wrong when arc weld­ing but most prob­lems they en­counter are all re­lated to things not be­ing set up prop­erly or be­ing ig­nored.

How it works

The cur­rent flows from the ma­chine or power source through the elec­trode ca­ble to the elec­trode holder in the hand­piece, down through the elec­trode, and across the arc to the base metal. This com­monly is the pos­i­tive side.

On the work side of the arc, the cur­rent flows through the base ma­te­rial to the work clamp and back to the weld­ing ma­chine. This is usu­ally the neg­a­tive or earth side.

An arc oc­curs when the elec­trode comes in con­tact with the work­piece and com­pletes the cir­cuit … like turn­ing on a light. This elec­tric arc be­tween the end of the elec­trode and the work reaches tem­per­a­tures around 5500°C, which melts both the elec­trode and base metal.

Elec­trode

The elec­trode, with an in­ner core rod and a flux coat­ing, car­ries the weld­ing cur­rent and then be­comes part of the weld.

Most prob­lems they en­counter are all re­lated to things not be­ing set up prop­erly or be­ing ig­nored

The flux melt­ing forms a shield­ing gas that pre­vents ox­i­diza­tion and poros­ity in the weld pool. With­out this shield, we would end up with a very brit­tle weld– metal ma­trix. Chem­i­cals can be added to the flux to en­hance ten­sile strength, duc­til­ity, and user ap­peal.

As the core rod, flux coat­ing, and work­pieces heat up and melt, they form a pool of molten ma­te­rial re­ferred to as a ‘weld pud­dle’ or ‘weld pool’. The weld pool is what a welder watches and ma­nip­u­lates while weld­ing.

Slag

‘Slag’ is a com­bi­na­tion of the flux coat­ing and im­pu­ri­ties from the base metal that float to the sur­face of the weld. Slag quickly so­lid­i­fies to form a solid coat­ing, a bit like a mini lava flow.

Slag also slows the cool­ing rate of the weld while also in­hibit­ing sur­face ox­i­diza­tion.

Once the slag has so­lid­i­fied, you can chip it away and clean the weld with a wire brush. Some­times it will peel off by it­self, but if it looks a bit like bird poo it’s not go­ing to be too easy to chip. How easy it is to chip de­pends on how smooth or rough your fin­ished weld is. Of­ten it’s harder to ob­tain a good slag re­lease from the higher ten­sile or more spe­cial­ized elec­trodes. With stan­dard, gen­eral-pur­pose Easyarc­style elec­trodes, a half-de­cent weld should be easy enough to chip.

Power

Se­lect­ing the cor­rect am­per­age de­pends on elec­trode size and the size and thick­ness of the ma­te­rial. Thin met­als re­quire less cur­rent than thicker sec­tions and small-di­am­e­ter elec­trodes re­quire less power also.

De­pend­ing on the ac­cu­racy of your ma­chine, these set­tings will give you a rea­son­able start for a bead on a flat plate:

• 2.5mm thick = 85A

• 3.2mm thick = 120A

• 4mm thick = 150A.

If you can weld in the flat or hor­i­zon­tal po­si­tion it will make weld­ing a lot eas­ier. I have a rule of thumb that for ver­ti­cal-up weld­ing, drop the amps down 10–15A; for ver­ti­cal down, go up 15–20A.

Strik­ing an arc

This is the part that frus­trates most learn­ers. An arc is started and main­tained when the weld­ing cur­rent is forced across a gap be­tween the stick elec­trode and the base metal. But of­ten it doesn’t start; it just sticks to the plate.

There are ba­si­cally two meth­ods of strik­ing an arc us­ing a non–volt­age re­duc­tion de­vice (VRD) ma­chine:

• scratch­ing, and

• tap­ping.

Be sure to have your hel­met on and face shield down first. The ‘scratch’ start method is gen­er­ally con­sid­ered eas­ier for begin­ners and when us­ing some of the older AC ma­chines. It’s a bit like strik­ing a large match or swip­ing a smart­phone.

A sud­den burst of light will be pro­duced on con­tact with the plate. Use this burst of light to get your di­rec­tion and start po­si­tion. In the ‘tap’ start method, the elec­trode is moved down­wards to the base metal in a ver­ti­cal di­rec­tion. The prob­lem with this is ‘stick­ing’, or ‘freez­ing’. This is when the elec­trode fuses to the plate.

You can just about guar­an­tee that you will lift up your shield just in time to flash your­self as the rod breaks loose. So, with your shield down, tap and pull up, as once again the burst of light will show you the way. When restart­ing half-way through a weld, check the end of the elec­trode. You will no­tice the cen­tral rod will have burnt back up inside the flux, leav­ing a cone­shaped crater. With your glove on, break this flux off un­til the metal is show­ing. For the novice I would rec­om­mend the scratch tech­nique for a restart.

Ma­chines

Con­stant-cur­rent (CC) power sources are used in the man­ual arc weld­ing process. A CC power source is one in which cur­rent or am­per­age re­mains con­stant even as changes in weld­ing volt­age oc­cur with changes in ‘arc length’, the dis­tance be­tween the plate and the tip of the elec­trode. CC weld­ing ma­chines are ei­ther AC, DC, or AC/DC. Weld­ing po­lar­ity will de­pend on the po­lar­ity of the elec­trode (writ­ten on the packet) or the lim­i­ta­tions of the weld­ing power source.

The pop­u­lar mul­ti­pro­cess or threein-one weld­ing ma­chines can per­form many different weld­ing pro­cesses (i.e., stick, TIG, and MIG). The stick and

TIG modes are CC. The Pow­er­craft 180i (I used a 160 here) is a great ex­am­ple of this three-in-one as­pect.

Bead

The ‘bead’ of the weld is a con­tin­u­ous de­posit of weld metal formed by the arc on the sur­face of the base metal, cre­at­ing a fused mix­ture of base-ma­te­rial and filler-metal chem­istry. A smooth, uni­form weld bead in arc weld­ing in­volves mov­ing the elec­trode along the plate at the cor­rect speed while hope­fully achiev­ing ad­e­quate pen­e­tra­tion.

No­tice how the arc digs into the base metal for pen­e­tra­tion, how it fills the crater and builds up the bead shape.

Prac­tice will help you rec­og­nize the char­ac­ter of the slag and a good or bad bead while you are ac­tu­ally weld­ing it.

Keep your eye on the back of the weld pool as the arc trans­fers the weld de­posit and builds up the bead. You can then vary the arc length, elec­trode an­gle, or travel speed to cor­rect a poor weld-pool ap­pear­ance. A good arc length, which comes with prac­tice, should be slightly less than the di­am­e­ter of the elec­trode, usu­ally around 1.5 to 3mm. If the arc length is too long you will no­tice an in­crease in spat­ter, matched with a hiss­ing, spit­ting sound, not the nice, soft, even crackle that you should hear. Pen­e­tra­tion will be poor, you may have un­der­cut, and the slag will more than likely be dif­fi­cult to re­move. We have all suf­fered that prob­lem.

Too higher amps can do this too. So don’t be afraid to come down a bit if needed.

Travel speed

Travel speed af­fects the shape of the weld bead. Too fast and the bead will be thin and stringy, matched with poor pen­e­tra­tion. Too slow and the weld metal will build up and roll over with an ex­ces­sive over­lap. Get­ting it just right is a mat­ter of prac­tice. Ex­cess weld metal usu­ally means ex­cess heat. Ex­cess heat, par­tic­u­larly on thin­ner ma­te­ri­als, can make the par­ent ma­te­rial brit­tle and weak.

Pen­e­tra­tion

Just a quick note on pen­e­tra­tion. Usu­ally you will no­tice the arc dig­ging into the base plate. If you are not sure how much pen­e­tra­tion you are get­ting, do a short weld 25–35mm and break it open in the vice. If the toe of the weld has fused, pen­e­tra­tion has been achieved.

How to

To start, po­si­tion your work­piece flat on a metal table­top or plate and at­tach the clamp se­curely to the work (metal) or ta­ble. A good earth is im­por­tant. Check the con­di­tion of the clamp and fit­tings. Set the po­lar­ity and am­per­age on the ma­chine: DC+ (neg­a­tive earth), say 110–115A for the E6013 elec­trode. Place the bare end of the elec­trode in the holder so that it is gripped se­curely at a 90-de­gree an­gle to the jaws.

Buy de­cent elec­trodes and you might find you can weld bet­ter than you thought

Don’t for­get to turn the welder on. Make sure you are com­fort­able; get your­self into a nat­u­ral po­si­tion and grasp the elec­trode holder firmly but com­fort­ably by us­ing ei­ther one or both hands. Us­ing both hands helps to steady elec­trode and re­duce fa­tigue. To use both hands (as I do), rest your left el­bow on work ta­ble and, with the left hand, steady the right hand by hold­ing the right wrist. The op­po­site if you are left-handed.

Move the elec­trode down un­til it is about 25mm above the metal plate, ver­ti­cal to the plate, in­clined at an an­gle of 65–70 de­grees in the di­rec­tion of travel.

Place the shield down in front of your eyes — you may ask why I’ve both­ered to men­tion this: once you have flashed your­self a few times, you will know why. Strike the arc us­ing the scratch method. A sud­den burst of light will be pro­duced on con­tact with the plate.

Pre­pare

A good ex­er­cise is to get your­self a de­cent piece of plate, flat bar, tube, or an­gle iron, etc. Not too small if pos­si­ble.

Alert: the more you prac­tise, the hot­ter your weld piece be­comes and this af­fects your am­per­age set­tings.

Clean the base ma­te­rial by brush­ing the metal free of dirt and scale.

Set your ma­chine to 110–115A, which will prob­a­bly be a bit on the hot side, de­pend­ing on the type of ma­chine

you have, your power sup­ply, and how ac­cu­rate the dial/power in­di­ca­tor is. We can al­ways drop the power back if our arc is too fierce.

Get a 3.2mm 6012 or 6013 elec­trode, strike your arc us­ing the scratch start method, pull a long arc length for a sec­ond or two (6–10mm). This will help you get your bear­ings and avoids stick­ing or freez­ing.

Weld­ing

Be­gin weld­ing very slowly, keep­ing a close arc length, which as al­ready noted is the dis­tance the spark trav­els be­tween the end of the elec­trode and the base metal. Hold the elec­trode into the cor­ner and drag the elec­trode while touch­ing the par­ent metal. Let the weld pool build up be­hind you. Slowly speed up as the rod burns away.

If you find that you are mov­ing the elec­trode at a uni­form speed, you will also need to make sure you are feed­ing the elec­trode into the weld pool at a con­stant speed as it melts. This will come nat­u­rally.

The travel an­gle is 60–70 de­grees, give or take. Even­tu­ally you will see a nice-look­ing weld, with a nice bead

shape and the slag will de­tach more eas­ily. This won’t come straight away.

The rea­son I say to start out slowly is that most learn­ers/novices tend to start off go­ing far too fast. Stick weld­ing is cer­tainly not racey.

Prac­tise start­ing the arc, hold­ing it, and break­ing it un­til it is easy to strike an arc on the first try.

Begin­ners of­ten weld with a long arc length. This will pro­duce a rough bead shape and lots of spat­ter. So the tighter, con­trolled arc length will im­prove your bead ap­pear­ance, give a nar­rower, more uni­form bead, and hope­fully min­i­mize spat­ter.

End

When fin­ish­ing the weld and break­ing the arc, you may find you have a small crater. Good prac­tice at the fin­ish is to pause for a sec­ond or two. A slight back step with the elec­trode (12–15mm) at the end of the weld to fill in this crater is an­other op­tion. Large craters can be the cause of weld crack­ing.

Ver­ti­cal down

Ver­ti­cal-down weld­ing us­ing a gen­er­alpur­pose elec­trode will give you low pen­e­tra­tion, which is not good for weld­ing heavy sec­tions, but re­ally good for thin­ner, sheet met­als. Note, not all elec­trodes will run ver­ti­cal down. Check the packet, as nor­mally it will be stated here.

A fast-freez­ing elec­trode is ideal. The Easyarc 6012 and 6013 are excellent for up or down.

When weld­ing ver­ti­cal down on thin sheets, speed is im­por­tant. Move as fast as pos­si­ble while main­tain­ing a con­tin­u­ous bead. Use cur­rents in the higher por­tion of the range.

Ver­ti­cal up

Anyone who has tried ver­ti­cal-up weld­ing and made a mess of it will re­al­ize by now that grav­ity is not your friend. Every­one does this a bit dif­fer­ently but ends up with a sim­i­lar re­sult. So here is my ver­sion that I know works well.

Once you have struck the arc, let the rod burn for two or three sec­onds to build up a shelf at the bot­tom of the joint. Then add layer upon layer, us­ing a straight weave, paus­ing on each side for about two sec­onds. This will en­sure pen­e­tra­tion and proper wash-in.

Do not whip or take the elec­trode out of the molten pool. Point the elec­trode slightly up­wards so arc force as­sists in con­trol­ling the pud­dle.

Travel slowly enough to main­tain the shelf with­out spilling. The slag will run down each side of the elec­trode. But you should be con­cen­trat­ing on the weld pool. If the weld bead looks too con­vex, try paus­ing for three sec­onds on the side. Don’t stop in the mid­dle. Just con­cen­trate on the sides; the mid­dle will take care of it­self, trust me. Use cur­rents in the lower por­tion of the range.

Cover­ings

As stated ear­lier, gal­va­niz­ing, paint, and rust should all be re­moved. But for those of us who know bet­ter, try a lit­tle flick-for­ward tech­nique. As you are weld­ing, flick for­wards 3–4mm ev­ery sec­ond or so, as if you were sketch­ing with a pen­cil. This will burn a lit­tle bit of for­eign mat­ter as you go. This works re­ally well on gal­va­niz­ing pipe.

Strik­ing the arc

The weld pool

Prac­tice weld beads

Poor bead and spat­ter from too-high amps and too-long arc

Good prac­tice welds

Chip­ping off slag with ham­mer

About to strike an arc. Note sup­ported po­si­tion

Cone formed in used elec­trode

Slag lifts off good weld

… good fil­let weld

In­te­rior con­trols for hel­met

Clean­ing …

Ver­ti­cal weld

… weav­ing …

Ver­ti­cal weld­ing …

… from side to side

Weld pool

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