mig welding question

A gunsmith in So. Cal asked me to check out an old cheapy Mig welder that he had traded for a new rifle scope. Branded Silver Beauty, with
small 25/75 argon tank. Looks a lot like an Esab 110 volt joby. Typical HI/Lo and 1/2 switches. Seems to be built well enough. Tank has a regulator marked " Preset for 30lbs"
The roll of .023 wire was badly rusted and would hang in the liner, so I bought him a new 2lb roll yesterday and last night fired it up.
Ive never migged with gas before. Shrug. So I putzed around for a bit getting it dialed in, was even able to run a bead on some very thin galvanized sheetmetal without burning through as long as I kept the speed up and the power down to lo/1. It was nice to see a shiney bead, rather than the cruddy looking surprise package I get using my HF flux core machine (which will not go low enough to weld that same sheetmetal, no matter how fast I go)
Im curious though..when welding on a chunk of mystery steel (likely 12L something) I was getting a brown layer of soot on the work area. What is it? What was causing it? I recall something about that in a post before..but cannot find the reference. The tank was filled in 1992, and is about the size of a large thermos bottle. Says 25% /75% on the sticker. Unknown how much is really in there. Shrug.
I was also getting an unstable arc much of the time. Good ground, wire wheeled the work piece. Wire feed seems to be pretty consistant. When pressing the trigger, could clearly hear the gas at the nozzle end. I could get it to stablize a bit by welding closer to the workpiece, but ran the risk of welding the wire to the tip (which I did at least once)
As a control, I ran the same beads with my HF flux core machine, and got a better weld, and one that didnt stand quite so proud of the metal, like it was hotter and was getting better penetration.
Ill be returning this thing to the gunsmith this coming week, but would like to be able to give him a heads up on its shortcomings etc.
Thanks
Gunner
That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there.         - George Orwell
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I have been told that leaded steels are very difficult to weld. Perhaps that has something to do with it?
Regards,
Robin
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This one? http://groups.google.com/groups?selm=l069st0cg0559v1bbevkra1r2qkdj3libk%404ax.com "If you are welding hot rolled metals/A36 (like angle iron) and do not remove mill scale there is a substance which looks like rust where the parent and weld metals join. The shielding gas will also sometimes a brownish dust around the weld."
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wrote:

Ayup..the brownish dust thingy. Thanks!
Gunner
That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there.         - George Orwell
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<snip>

<snip> One thing that would have an effect is that the polarity used for FC it opposite to that used for gas and just happens to be the way round that puts more heat into the work. I came across this one when trying out a reel of FC wire with my (usually gas loaded) buzz box. I was shocked to see the angle iron I was using glowing orange!
Mark Rand RTFM
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You should grind it till its shiny.
Wire feed seems to be pretty consistant.

There are a lot of things that cause unstable arc in a mig. Insufficent shielding gas, too low of heat setting, to fast wire speed, to fast travel, dirty work piece, or a worn contact tip.
If your using solid wire it has a nickname(hardwire). It is very hard as deposited. It is difficult to drill and usually has to be ground. It doesn't like contaminated metal paint , rust ,dirt ect. If your welding rusty dirty stuff the inner shield works much better and if you get really tricky you can use gas with the inner shield and acheive good results. 75-25 is usually used for welding light gauge metals because it isn't as hot and the heating zone is not as wide. Straight CO2 is used when welding heavier materials its cheaper and you get good penetration.
Charlie
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"Charlie" wrote: (clip) if you get really tricky you can use gas with the inner shield and acheive good results.(clip) ^^^^^^^^^^^^ What polarity should one use?
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Straight polarity. Charlie
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