The Stovebolt Site Forums The Shop Area Paint and Body Shop ? about copper backing

I have read it here many times about using copper as a backing for welding up holes. I have tried it but my welds tend to stick to the copper. I am using a flux core wire welder and was wondering if this could be the reason the weld is sticking to copper?
Yes, I know the mig is best for sheet metal work but I don't have the bucks for that so I just use what I have. It works pretty good, just have a little more cleanup (grinding) to finish off.

I dunno, that's a good question. I have a roll of flux core wire in case I'm outside, but I haven't tried it yet.

Ralph,

My guess would be that it's the molten flux that is actually sticking to the copper.


Stuart

NO. 1: Make sure it is copper not brass or a plated thing. NO. 2: it will stick a little but I've always been able to gently break it loose. this is on gas though. Some say brass and aluminum work also. Copper water tubing, flattened, is good.

Got me a little mixed up there Ralph, you say your using "flux core"? So you must have a MIG welder (Metallic Inert Gas) flux core is a MIG wire. Then you say you don’t have the bucks for a MIG welder in the next sentence. Do you mean that your using a little AC stick welder and rods with flux around the outside????
I think Stu is correct, probably just the flux sticking to the copper. Don’t use anything but copper, the thicker the better, if it’s to thin then you can melt it and it will stick. The reason copper is used for a back up is that it conducts the heat much more rapidly than the mild steel, the heavier the copper the better the heat sink! Use enough heat for the thickness of material and you certainly can melt copper. I’ve welded copper many times as an instrument welder at a National Accelerator Laboratory. Flattened copper pipe will work for small holes but it’s relatively thin and if you filling a large hole and have a small piece of tubing you can melt it. Once again, remember, you want a “heat sink”, the thicker the better, the larger the area the better!
Brass---Not good, it contains low melting temperature alloys.
Aluminum---Not good, much lower melting temperature than the mild steel parent metal.
Denny Graham
Sandwich, IL

Nah, Denny he prolly has the small machine w/no gas, ya gotta buy a kit(solenoid, etc)+bottle of gas ta make them work MIG. Technicaly a MIG, but not really

Although FCAW is technically different from GMAW, to the guy pulling trigger on the welder with the spool of wire on it, they can both be called MIG and only get into trouble when the technicians show up.

Ralph is using a machine that feeds wire off a spool, through a gun and onto the piece being welded...he isn't using shielding gas, but instead is using tubular wire that contains its own flux/shielding system. To most commoners, he's MIG welding..to the techies, he's Flux Core Arc Welding. As Red58 once told me, Stu, it's semantics.

Stuart

If understand correctly, the flux "burning" creates the gas while welding

Brian,

You understand correctly...

Stuart

Good, that means the old grey matter is still working sometimes

Wire welding????

I use brass which is 70% copper and never had anything stick

Keith

You guys are good. Yes, it is a 'mig' welder without the shielding gas. I just use the flux core wire since I don't have the money for the upgrade.
From some of the responses here, I believe it may be a combination of the molten flux and too thin of a heat sink. Perhaps I can find something a little thicker that will work better. Thanks for the help.