Welding Question

nunyabinis · Nov 18, 2009

A while back I purchased a Millermatic 251 MIG welder that I run .045 flux-core wire through. I always grind/polish the area I intend to weld before laying a bead, however, I've noticed that on some brand new 1/4 inch steel I bought that the first bead always looks terrible with open "bubbles" that form once the weld hardens. I can go back over the same area a second time and the weld looks perfect. It's almost as if the first bead evaporates some sort of contamination and "prepares" the metal for the second pass.

Is there some sort of contamination on the surface of the metal that I'm not completely removing when I grind/polish the metal? The metal has some sort of think oily coating on it that I assume is supposed to keep it from rusting. What's the best way to clean that off before I lay a bead?

Thoughts?

jjcc246 · Nov 18, 2009

there are a lot of oils on new metal. i always gring new metal to a shiny surface before welding. you'll see the differance immediatly.

nunyabinis · Nov 18, 2009

jjcc246 said:
there are a lot of oils on new metal. i always gring new metal to a shiny surface before welding. you'll see the differance immediatly.

As I noted above, I always grind the surface before I run a bead but on this new metal I'm wondering if I need to clean the surface with some sort of degreaser before I grind it. Grinding alone certainly hasn't worked so far. I ground the bejesus out of the last piece I welded and it STILL created those open "bubbles" on the first pass.

I'm thinking that perhaps I'm just spreading the oily film with the grinder instead of getting it all off.

bobodu · Nov 18, 2009

Can't say I've had that problem.....but I arc weld!!

towmotor · Nov 18, 2009

The presence of oil in the pores of the metal is evident in the fact that your second pass is successful.

If that's what you're noticing with a particular batch of metal, consider buying a can of inexpensive brake cleaner.
A shot of that (not on hot spots though

) and a quick wipe with a clean rag will help eliminate the porosity in your root pass.

Page2 · Nov 18, 2009

Flux core wire will do that sometimes, not so much with stick welding, thicker flux I guess. Yes, you can try wiping the metal down first - lacquar thinner, mineral spirits, probably even diesel fuel would do it. Just let it dry out before welding.

J_J · Nov 18, 2009

I second the brake cleaner, but use a stainless brush to loosen it up, and then spray brake cleaner again so the brake cleaner flows off, not just dry in place.

Egon · Nov 18, 2009

If the metal is ground down before welding wiping the mill scale on the surface might not really help much.

firedog · Nov 18, 2009

How soon after the first pass are you making the second.
May just be that the first preheats the metal for the second.

nunyabinis · Nov 18, 2009

firedog said:
How soon after the first pass are you making the second.
May just be that the first preheats the metal for the second.

Good point. I usually let loose a few cuss words, brush the slag off and immediately weld back on top of the first crappy weld but I'm pretty sure that I've let a couple sit for many minutes before welding the second pass.

I'll have to run a little test.