MIG with Powdercoat

Just thought I'd share this here in case it helps someone in the future.

I've found trying to MIG weld powdercoated steel a pretty dreadful experience. Grinding the weld area helps a bit, but the nearby melting coating seems to produce some gas or something that makes the arc go to hell, making a hissing sound and leaving a globby-looking bead.

The answer? Change the gas to straight CO2. Welds like a dream.

What gas mix were you running before the CO2 ?

Steve

Quote:

---

Originally Posted by OxxAndBert

What gas mix were you running before the CO2 ?

---

Speedgas MIG mix - 93% Ar 5% CO2 2% O2

My CO2 beer gas bottle is a throwback to before they had swap'n'go - I still use it for on-site work as the little D-size bottle is easy to move around, and it turns out there's certain things that weld much better with it.

you get more heat and better penetration with it. We were using it on heavy sections at work 20mm+, but after some testing decided it wasn't worth the trouble of keeping extra gas.

Allegedly, straight CO2 is actually MAG rather than MIG. It behaves better with gal, but in general the bead tends to have a more humped profile - not as nice as you get with conventional MIG gas. On the other hand, for short-circuit welding, CO2 is considerably quieter than MIG gas.

Quote:

---

Originally Posted by RustyArc

Allegedly, straight CO2 is actually MAG rather than MIG. It behaves better with gal, but in general the bead tends to have a more humped profile - not as nice as you get with conventional MIG gas. On the other hand, for short-circuit welding, CO2 is considerably quieter than MIG gas.

---

As in, the CO2 reacts with the weld metal in some way?

Quote:

---

Originally Posted by Pumpkinate

As in, the CO2 reacts with the weld metal in some way?

---

I believe that it does, but I've yet to find a really good explanation of what it actually means. All that's observable is the quieter arc, and it does produce more spatter than MIG gas.

Pretty sure I have read that the co2 does react with the base metal acting as a flux and provides some cleaning. OTOH, pure argon as used with tig, does not clean hence the need to preclean. (I was trying to understand why mig could weld any old rusty thing without prep)

I guess pure co2 takes this to another level.

Russ

I use CO2 for all my welding (gal, painted, black, thick sections and thin sheet). Works well in all situations and gives good penetration, however the bead isn't as neat (as MIG mix) and you do tend to get more spatter.