Welding Question

[nunyabinis]

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]

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]

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]

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

 

[towmotor]

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]

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]

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]

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

 

[firedog]

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

 

[nunyabinis]

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.

 

[jimgerken]

If you upgrade your process by adding the CO2 tank and going with solid core wire your problem will dissappear. Your welds will also be much better.

 

[two_bit_score]

Grinding dirty or greasy metal can drive the contaminants down into the metal, so I am told by my friends who do body work. They always clean metal before they do any grinding.

 

[LD1]

If you upgrade your process by adding the CO2 tank and going with solid core wire your problem will dissappear. Your welds will also be much better.

I agree

 

[2manyrocks]

I think two of the posters already hit the nail on the head. Flux core creates its own shielding gas as you weld. When you start the first of the weld, there isn't any gas yet. So the porosity is a result of it being the first pass.

If you switch to tank shielding gas, you're going to get less smoke, less spatter, and a much cleaner weld. Once you switch, you aren't likely to go back to flux core unless you just flat run out of shielding gas on a project and have to use flux core to finish until you get another tank.

 

[nunyabinis]

If you upgrade your process by adding the CO2 tank and going with solid core wire your problem will dissappear. Your welds will also be much better.

I have a Lincoln 175 MIG welder that I run .030 solid wire with CO2/Argon for welding small stuff. And yes, it lays down a very nice weld.


I use the Millermatic 251 welder with the flux core for the thick stuff.


I'll try cleaning the metal BEFORE I grind it and see if that helps clean up the first weld. If that doesn't fix the problem I'll try heating the metal before the first weld and see what that does.


Thanks for the suggestions guys.

 

[gazoo1]

hey buddy i've had this happen also first i clean with commercial grade` degreeser works great then grind sorry i had it backwards good luck

 

[RPW]

If this is very thick metal you will get better welds if you pre-heat your metal to begin with. This can be done with a propane torch. You will only need to do this at the beginning. Al else is clean, clean, and clean.

Good luck.

 

[zman007007]

I just read a article about a week ago warning not to use brake cleaner on a part that you are going to weld on. It puts off poisonous gases,and it only takes a little whiff to make you very sick, so I would just use a degreaser on it. zman

 

[towmotor]

Just a minor point here:
Brake cleaner is degreaser, bottled up and pressurized in a convenient can.

About the only degreasing agent that I can think of, which won't offgas some nasty fumes is Simple Green; and it doesn't work as well as the alcohol/acetone/laquer thinner based stuff-plus it takes much longer to dry.

Toxic fumes you say?
ANY welding operation produces toxic fumes, and should be done with adequate ventilation.
If the toxic fumes put off by brake cleaner were the only thing to worry about, in terms of residual gasses when welding, then such a warning against it's use for pre-weld degreasing would be a major influence in the decision to use/not use it.

It makes me wonder how the Nervous Nellies who write these articles would actually degrease a brake rotor...
Same smelly stuff, same potential for heat input once dry and assembled...not to mention the possibility of inhaling asbestos brake lining dust, or even the non-organic linings now in use. They just don't know or haven't told us what that stuff will do to our lungs.

Bottom line?
You've got to use some common sense and basic safety measures when you're doing any sort of "build it yourself" project.
Otherwise, leave the keys in the garage office, wrap yourself in a blanket and wonder what eventually will kill you.

Sorry for the rant. I'm not attacking you zman, just your source. I've used brake cleaner for many different purposes, including pre-weld degreasing, with adequate ventilation.
Never got any sicker than I was when I started.

 

[Egon]

Wouldn't sandblasting before welding work?