Vallely wrote:
> > What type of gas do you use with your MIG? I have been using CO2 but
> > think Argon might make a difference. Got any helpful thoughts?
>
> I use 75% argon / 25% co2. My Lincoln instruction manual recommends pure
> co2, no reason given. The welding shop guy says the blend runs cooler.
> I've been satisfied, but am curious about whether the co2 would be any
> different/better. My guess is that the difference is not critical.
I would agree as well, the differences might not be
very critical. We all strive to be as good as we can be
but without welding eight hours a day it might be hard
to get so experienced that you can pick out the differences.
If you'd rather skip the long crap that follows here,
just buy 75% argon 25% CO2 and you'll be happy.
If you care about minutia, read on!
One of the choices in the gas type is CO2. This gas is
technically not inert, but under the heat of welding is
converted to carbon monoxide which is relatively
inert. However, the spare oxygen atom given off will
form O2 gas, then combine with other elements in the
air and form contaminants on the surface.
CO2 is probably the cheapest gas, it welds fast with
good penetration, but should probably only be used if
your wire has a deoxidizing agent in it to "catch" the
freed oxygen and keep it out of your welds.
Pure Argon is very good, and this is what you will use
for welding aluminum and other non ferrous metals. It
gives a very concentrated arc and good penetration.
Argon can be "tuned" by doping it with other gases. The
most common, and probably the "best overall" gas for welding
autobody is 75% argon 25% CO2. It's often called C-25, and
around here it's sold as "Argomix". It's cheap, welds with
less spatter than pure Argon, and produces cleaner welds
especially on metal that contains minor contaminants like
rust and scale.
There are some gases specifically for high volume bodywork,
one of them is called Argoshield which is argon with some
CO2 and oxygen. It produces the smallest weld beads which
require the least grinding after. Sounds encouraging, but
I've only read about it never tried it, so I have no
opinion.
For welding THICK metals, a gas that contains helium
or even that is mostly helium will give a hotter arc. Something
like 25% Argon 75% helium is used for welding thick
aluminum, like in a full race car frame. You won't
need this.
And finally, if you are welding stainless steel, a near-pure
mix of 90% helium plus argon/CO2 will give the hottest arc and
will make the hottest puddles. I haven't got experience with
welding stainless, but apparently the weld puddle on stainless
can be sluggish and hotter arcs help.
You also need to choose a bottle size. I have a 55 cu ft
bottle, and that seems like a good size. Not too cumbersome,
but enough to work a whole weekend without a refill. That is
important because most places to get the bottle exchanged
aren't open weekends.
It took me about two bottles to do the floors, sills, and
a fender or two on my B. At $27CDN per exchange, that's
fairly cheap. The bottle itself was $180CDN.
(if any of the above sounds familiar, I basically parotted
it out of my welding manuals. Don't call the copyright
cops on me!)
--
Trevor Boicey, P. Eng.
Ottawa, Canada, tboicey@brit.ca
ICQ #17432933 http://www.brit.ca/~tboicey/
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