I got a good owner 50lb CO2 bottle, exchanged it for a full one and have been using it on my Millermatic 185. Before I had been using flux cored wire. I've read on and off about mixed gas for MIG. What would be gained and which mix should I get once I deplete this bottle of CO2?
Common MIG (MAG , really) gases are Argon 75%/CO2 25% (or C25 for short), straight CO2 for steel. Aluminum MIG can use straight Argon and Argon/Helium mixes and there are other fancy Tri-mixes for stainless.
CO2 is cheap, gives high penetration (hotter arc), but tends to give lots of spatter. You can also dispense beer with it.
C25 is more expensive, but runs cleaner on mild steel. Not quite as much penetration as straight CO2. Really nice welds when the box is dialed in though.
Unfortunately, you're pretty much stuck with straight CO2 unless you trade for, or buy a new cyclinder. This is because CO2 cylinders hold liquid CO2 and the pressure inside is whatever the vapor pressure of CO2 is for a given temperature (my gauge usually reads 600ish psi).
Argon doesn't liquify, so it is present as a high pressure gas in order to fit a useful amount in a bottle. Pressure of full cyclinder ~2200psi.
In short, you can only put CO2 in your cylinder. I'll bet it lasts a while though...
My bad. At absolute zero, Argon will even solidify.
However for practical purposes, it is a gas at room temperature and 2200psi.
We have cryo tanks at work that hold liquid nitrogen and I know local glassblowers that go through enough oxygen to use LOX cryo tanks.
Those tanks are *HUGE* though. I haven't seen too many cryo tanks with liquid Argon though. Many of the shops that I've been in use the 330 cubic foot size GAS cylinders. They go through enough that the gas company is happy to pick up / deliver the cylinders.
Even though I proofread my posts I still get busted sometimes :)