Some thoughts on Arc Welding, or MMA (Manual Metal Arc) as its now called. The hand held masks are a bit of a pain, you really need 2 hands to control the torch and your work. Machinery Mart have a selection of flip down masks under £10, and they usually come right down so cover part of your chest, which is very useful. Its a pain if you get a red hot spark of molten metal down your teeshirt, you can't get the B*** out, and it still burns, oh yes!!
. Next thing is a good pair of Welders Leather Gauntlets. They don't cost a lot (£3?) but protect your hands, sleeves from sparks. They last a long time, mine are over 15 years old, so are a good investment. I also spashed out on a leather Bolero, which also covers my arms and chest, which is very useful if you are welding overheard. There is something pyschological about welding overhead watching the shower of sparks fall down, thinking "SH1T, these are all at 1100deg C, and may get down my teeshirt" !! :-? :-? :-?. The autodarkening helmets are very clever, but you may end up spending twice what the welder cost for safety equipment, which you may rarely use. Try a cheap flipdown, and if you want to progress get an auto darkening. The hand held mask is still useful, someone will invariably want to watch the pretty sparks. This is a
BAD IDEA, arc welding gives off intense UV, which dries out the cornea, and makes you feel as if someone has put a load of sand in your eye. Not nice. The effect usually wears off after a day, and there shouldn't be any permanent damage but.....
Now onto actual welding. The factors that affect the weld are : current, angle of torch, speed of travel, and clean work. If you can, get a piece of about 1.6mm steel, and 1.6mm electrodes. I chose 1.6mm steel because its about the optimum thickness for that size of electrode, also about the thinnest you can properly weld with that current. You can sometimes weld thinner, but its a bit difficult. Clip the earth electrode to the steel, clip an electrode in the torch, and set the welder to about 40A. Angle the electrode at about 45deg, and scratch it across the surface of the steel. This should start an arc. Remember not to stop, or the electrode will weld itself to the steel, and you will have to switch off or unclip the electrode and bend it to get it off. This will damage part of the flux covering, so the electrode will be a pain to use next time, it will tend to stick immediately. Keep trying this, and eventually you will get a good bead of weld on the surface. Once you have chipped off the slag look at the bead. It should be nice and even, between 1 and 2mm high. If much higher than this, you are not getting good penetration to the steel, so the current is a bit low, you are too slow, the angle is a bit high, or the surface dirty. Also as said by Hotel21, the slag should chip off easily. The idea is that the slag solidifies on the surface of the molten metal and protects it from oxidising when it is cooling. If it get mixed up in the weld metal, then the arc is jumping about, speed is slow, or the angle is too high. Having got this sussed, try increasing the current to say 80A and trying the same again. This is your doubling the heat input, the arc will sound much fiercer, the metal should start to glow red, and its poss you will blow a hole. Thats OK, try welding at a faster speed and see how it affects things. Thats the rule, if welding thin metal keep the current down, but watch out for incomplete penetration. If thick, turn it up, 'cause a lot of heat will be ducted away by the metal thickness.
Now try welding 2 pieces of steel together. put them apart about 1mm, and weld short blobs every 4 ins to keep them spaced that distance. When you weld, the heat will make the metal tend to bend away, so the gap may start at 1mm, but will soon become 2 or 3 or 4mm which will be a pain!. Using the 40A setting, start an arc at the top, still 45deg to the direction of travel, and weld down the job. When finished, chip off the slag and look at the weld from both sides. Ideally you should have a bead about 2mm high on top and about 0.5mm on the bottom, and there should be no sign of the metal edges underneath. This means that you have totally penetrated the thickness of the metal, and its well fused.
Sometimes you will do a brilliant weld and immediately pick it up to show someone how good you are. THIS IS NOT A GOOD IDEA. The metal has recently been at about 1100deg C, and will still be hot to the mortal hand for a long time. That is reason why the welding guantlets are a GOOD IDEA !. They are also handy, when welding thick metal (>6mm), I tend to use the left gloved hand to guide the electrode near the work. Try writing with a pencil 12" long, held from the blunt end.
The Nirvana of Arc Welding is when you finish a weld, flip the helmet up, you hear a slight crack from the cooling metal, and the slag curls off all by its self. This only happens rarely, but when it does, it means you have got all the parameters right, the slag has hardened and is protecting the steel, which is cooling and shrinking, and hence the flux peels off all by itself. I've only had it happen a few times, but its very satisfying when it does !!!!.
Best of luck
Ken
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Topic: Welding (Read 2251 times)