Flux for copper forge welding

[Rainier]

I need thick copper bars, 1/8" thick, for electrical purposes. I've been to the local scrap metal yard & they don't have them in those thickness. I do, however, have a copper pipe with 1/16" thickness. I would like to flatten & forge this pipe to be the bar that I require.

I figured I need a flux the inside of the pipe that would weld together. I flatten the pipe slightly to make the inside narrower (noting how soft hot copper actually is). Then I filled the inside with hydrous borax. I heated this to a propane torch until the borax got glassy & added more until I thought I had all the inside covered with glassy anhydrous borax. Then I heated it red hot & quickly hammered the pipe. I expected the borax to shoot out & the copper to weld. But, it didn't do it. Immediately, I had to stop, as with those few hits, I was already making the copper too thin, about 3/32".

What am I doing wrong? Maybe I should have added more borax until it was a big goop? Or, maybe I was wrong in thinking I could forge weld copper?

[Irondragon Forge ClayWorks]

Welcome from the Ozark Mountains.

I'm not sure but to forge weld copper it would have to be just under the melting temperature. I've never heard of that being done. I would think soldering the pipe would work.

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus

 

[Frosty]

The problem is pretty basic. Forge welding copper is pretty easy but certainly not by putting so much of the wrong kind of flux between the joint surfaces they can NOT make contact.

The proper approach is buy 1/8" bus bar. Copper pipe isn't the right kind of copper, it WILL work but it's not the right stuff. 

It's fun to be able to make do and in many cases necessary but not this one, this is what Dad would've called, "Penny wise and Dollar foolish." Don't take offense, Dad said that about me all the time. I sure miss the old man. <sigh>

Frosty The Lucky. 

 

[George N. M.]

I did some research and the copper used in plumbing applications can be different than the copper used in electrical applications, with some over lap.  Most electrical applications use C11000 alloy while plumbing can use that alloy and a number of other alloys as well.  A common plumbing alloy is C12200 which has some (0.04%) Phosphorus in the alloy which makes it somewhat less electrically conductive.  All of them are 99.9% Cu.

I have no idea if the small chemical variations in the Cu alloys will make any practical difference in forge welding them together but if I had to guess I would say that it wouldn't be enough to notice if there is any difference. The choice may be what is available and its cost.

Since copper is less chemically reactive than iron I would think that flux is less important in welding copper than it is in forge welding steel but I don't think I'd not flux at all. 

"By hammer and hand all arts do stand."

[Mike BR]

You can see the fire scale on copper disappear in a reducing atmosphere, which may suggest you don’t need flux to dissolve it. 

[Frosty]

It's neither Mike, in a reducing atmosphere copper will diffusion weld effortlessly, often when you don't want or expect it to. If you're using a propane forge, toss a piece of charcoal in a few (say 5-10 seconds) before doing the final heat. 

Making copper jewelry you can get lots of very cool colors with a soft flame and smoke.

Frosty The Lucky.

[SubterraneanFireForge]

I forgewelded some copper pipe. 
I closed one end put a bit of borax in the other hammer it almost shut. Kinda like how you did it Rainier. 
then I stuck it in my forge got it almost molted then tapped it together and some borax squeezed out. Then I stuck back in kinda melted some of it which stuck to the bottom of my forge and hammered it again Less lightly. 
put some more borax on and started folding it over. Again got it really hot hammered it shut and repeats the process. My gas pressure gage on my refrigerator is broken so I don’t know the gas pressure but it felt pretty high and my oxygen valve was pretty closed. 
 

this worked pretty well in the middle but I had trouble getting the ends mostly the front end hot enough without actually melting the copper in the center of the forge. 
 

I havet tried with out borax