Polarity for tig welding brass?

I thought I posted this earlier, but I guess not. I made a few attempts at welding brass and realized I didn't know which polarity to use. Both worked, but I had less porosity with AC than DC. Also noticed white smoke and the piece had a white film like what happens when you weld on galvanized steel. Should I be worried about the fumes? would I need a respirator or can I just set up an exhaust system? Haven't tried brazing or silver soldering the brass yet, will I get the same fumes and discoloration of the surrounding metal?

Jake


Rich Waugh's picture

Jake, Stick with the DC for

Jake,

Stick with the DC for TIG welding on brass. One trick is to start with a healthy stomp on the pedal, kind of like you do with aluminum, then quickly back down to the lowest amperage you can sustain a puddle with. No matter what, you're going to get that white film of zinc oxide residue from the zinc alloy in the brass boiling off. That causes the porosity, too. Brass can be tricky stuff, depending on the alloy. One more reason I prefer silicon bronze.

When brazing brass you shouldn't get as much zinc boil-off, but you'll still get some from the filler rod you get to melting point. Unfortunately, the melting point of the filler rod is so near the melting point for the brass itself that you can have a sudden collapse of the base metal. I usually wimp out and use Sil-Fos if I can stand the color mismatch.


Gene Olson's picture

this is where tig gets

this is where tig gets weird.

Go over to Metalmeet.com and check out the recomendations for welding odd brasses.

One olde guy that signed on gave us his secret of success.

When tig welding some brasses you need to stir the metal to get it to break surface tension and meld together. (oxides floating out)

This is especially important when welding lead filled stuff like architectural bronze and muntz.

stick the tungsten right into the puddle and stir.

(if I have to tell you that EXCELLENT vents and independent air supplies are good ideas here, then you probably just started this voyage.)

Gene Olson
Sculptor
Elk River, MN


visitor's picture

polarity

D.C. negative (straight polarity) Red tungsten works best(IMO) Frequent wire bushing to remove products of zinc outgassing. Preheating to about 300f helps reduce outgassing, but you don't want it too hot either.(cool between passes)Silicon bronze rods are best unless color is an issue.And like Rich said start with VERY high Heat then back way off. I actualy use a pulsing action with the foot petal or thumb control. Some people use the pulse setting on the machine if it has one. If you can figure out how to set the pulse properly, this really helps. Bronze is way easier to weld than most brasses. arftist@yahoo.com


eligius1427's picture

Thanks Rich, Gene, and our

Thanks Rich, Gene, and our visitor,

The welding has been going ok. I'm still getting a little porosity, but it's getting better. I seem to get less when I use a low fuming bronze brazing rod for filler, color match is pretty good too once you buff it out. I also seem to get better results at higher temps, probably because it's easier for the zinc to boil out, but that's just speculation. I'll keep you posted on any new outcomes. Thanks again.

Jake


visitor's picture

welding brass

White film is probably from zinc in the brass, which is why you might associate it with galv. Defianately worry about the fumes, they are caustic and over time can do damage.


Stephen Fitz-Gerald's picture

fumes

Stephen Fitz-Gerald

VERY VERY BAD FUMES Neil,
If you saw this white spider web type filament (which floats off the weldment in the air), under the microscope,you'd never weld it again. The shapes are called "spicules" and look like jacks from a child's game of "ball and jacks". They have what look like little barbs on them and if breathed in the lungs ,scarify on the bronchi villi and never come out...
it is the same for welding galvanize. It's the zinc that's the killer.
Definitely use a respirator with exhaust fan.