Weld contamination problem (1 Viewer)

[jblueridge]

Apart from my BJ74 my other project is my MGB. Some years ago I used a pinch welder on many of the flanged panels. In my haste to prevent rust, I sprayed Eastwood rust coating paint into the body cavities.

NOW that I have more experience I know those spot welds have poor penetration: the spot welder did it make enough amps.
I have recently drilled flat-bottomed holes through one or two panels leaving the innermost panel intact. I have then tried to plug weld these holes with my MIG. A small fire erupts as the panel's black e primer and the Eastwood stuff ignite. The welds look pretty dodgy and some bashing shows they are weak.
Would flux-cored wire help with this? Could I ever increase the shield gas enough to prevent fire? Straight argon or straight CO2?

Any help or info would be appreciated.
Thanks,
Jamie

 

[PAToyota]

You could try back purging the panel to keep it from igniting, but I’m not sure that would even work. The primer and paint are going to contaminate the welds whether it actually ignites or not.

 

[jblueridge]

Back purging
Please explain.

You are surely right that the coatings will mess things up anyway. Flame and soot make it worse.

 

[george_tlc]

^ back purging, he means to have a second cup/hose pushing gas into the back of the weld area to keep air out. But that's not likely your issue since you have not drilled through the back of the 2nd metal plate.

The real issue though is that you have coating that is going to melt/contaminate the weld pool. The key to a good weld (braze/solder/etc) is CLEAN metal to work with...

cheers,
george.

 

[jblueridge]

Anyone have experience with the flux-core MIG wire? I have not used it but maybe the flux could help here?

I also wonder if I can get a tank of argon or CO2, run a second gas line and try to block oxygen altogether.

Would it be worth a try?

 

[george_tlc]

^ flux core won't help, the issue as you describe it is that you have 'rust coating / paint' between the two metal pieces. That stuff will contaminate the weld area, doesn't matter if you are using C02, Ar, flux core, etc. I presume that coating is melting into the weld pool, so it's a contamination issue - which will be a problem whether it is catching on fire or not.

Maybe get a higher current spot welder...

cheers,
george.

 

[jblueridge]

Thanks George. I'll try most anything except taking everything apart.

 

[bobm]

You will not get a good weld or spotweld if you are welding over your 1st spotwelds. You will always have contamination. Try a different area 1/2 the distance away.

 

[jblueridge]

I am interspersing the new welds between the poor spot welds.
Thus there is e-primer and stuff there: I cleaned the places I spot welded a good bit.

 

[bobm]

Results?

 

[jblueridge]

mini-fires. crusty looking welds.
I have not yet tried flux-core wire. Worth a go anyway.

 

[Weber Sarge]

You'd almost have to dip the part to remove the coating to prevent contamination - this is why a lot of panel/door repairs end up failing later with rust and corrosion/cracking . No way you can weld or spot weld a panel that has a coating on the hidden side and get a decent weld...
Sarge

 

[jblueridge]

I can get some of it out of the way by drilling down to the last panel with a mini hole saw. I then use a small burr to clean off the coating that covers the bottom layer.
When I weld I can hit the upper panels where the saw cut thru. The bottom layer conducts well also. The crap comes from the coatings that are adjacent to the areas cut/cleaned.

 

[cruiserpilot]

Basically it seems you have contaminant contained in between the sheets, and its mucking up your welds.
Not much you can really do, if I understand you have a punched hole in top sheet with solid sheet underneath?
You could use fine wire brush wheel to clean as much out as you can.
I had some issues with my MIG when I did the rear quarter on my BJ74. The older metal under was thin,
and inconsistent as well.
What I recommend to try is turn your gas up, I have a scale on mine. Usually its around 10, I cranked it up to 25.
I used a low power setting in my welder; with a very high wire feed speed. Short duration tacks will reduce the
heat spread through the surrounding area.

 

[jblueridge]

Here's a picture to show the situation.
I like the idea of using more shielding gas.

 

[cruiserpilot]

I see what you are trying to do. Once you hit that with heat, the paints gonna burn. So long as
you get enough heat to join all the layers its going to be welded, but its not going to be pretty.
Only way around it is to completely separate all the layers, that doesn't seem plausible at this point.
I just reread what you're doing, how about seam welds along the edges, and just reinforce the
weaker spot welds.

 

[PAToyota]

Turning the shielding gas up really isn’t going to do anything in this situation. Shielding gas prevents atmospheric contamination, but you have physical contamination that is entering the weld puddle directly. As pilot says, about the only real solution is to separate the layers and clean the paint out. Barring that, you’ll just have to accept that the paint is going to contaminate the weld and go from there.

 

[Pin_Head]

Yes, flux will help to float some of the contamination out with the slag, but probably not all of it. A plug weld in sheet metal can tolerate some contamination and porosity. It beats separating the metal, cleaning it and starting over again.

 

[jblueridge]

I need to get my cruiser back together before Labor Day... No welding for a while.
I will crank up the flow of argon/co2 to limit the amount of oxygen getting to the flames.
I have some flux powder in a can. I might make a paste and pack the holes before welding.

Thanks for all the advice!