evfreek Posted March 28, 2012 Posted March 28, 2012 This might be a good idea if there is some galvanized steel that you want to work on that is a little too beefy to work cold. I wanted to bend a 1/4" thick bracket from an old trailer bar to use as an anvil hold down. It was a little bit too thick for bending cold. I got out a couple of firebricks and a MAPP torch and heated it up until it barely showed color. This is about at the low end of warm forging, and steel has about half the yield stress that it has at room temperature. The difference was quite amazing. It was pretty straightforward to bend and chamfer the bracket. As I was heating and hammering, I noticed some white flakes coming off the metal. This stuff was galvanized! But, at the warm temperature, it was not fuming off into htat sickening white smoke. Instead it was flaking off as the metal was being deformed. It brushed off easily with a wire brush and fell straight down, due to the flaky rather than powdered nature. Very interesting. At the warm temperatures, hammer marks in the metal are sharper, especially if you hit away from the warm areas. Also, no dinging of even a softer anvil, since the warm steel is appreciably softer. If you have to do it, warm forging might be a less risky alternative for working galvanized steel. Quote
bigfootnampa Posted March 28, 2012 Posted March 28, 2012 FAR BETTER to pickle the part in vinegar which will remove the galvanizing overnight! Then no safety issues! The galvanizing will not survive your warm forging anyway... so why take risks with it? After forging you can coat with a cold galvanizing paint or tin the piece or just prime and paint for weather protection. Quote
ThomasPowers Posted March 28, 2012 Posted March 28, 2012 I agree with bigfootnampa; why try to find an "OK method" for a task that shouldn't be done? I don't keep galvanized metal in my scrap pile and if something needs it I'll have it done *after* any hot working. Quote
Francis Trez Cole Posted March 28, 2012 Posted March 28, 2012 after all the warnings about galvanized metal why would any one want to mess with it at all. I guess some people have to learn the hard way. I have had to weld some galvanized metal in the past and I will pass on future jobs with its nasty stuff leave it alone. Quote
Jeff Seelye Posted March 28, 2012 Posted March 28, 2012 Sorry Evfreek, I'm with the others. Galvanized metal will get you if you heat it or grind it, it all goes into the air and we breathe it. I occasionally have to weld it on my regular job and I use a respirator and smoke sucker, wipe it down, vacuum what I can see and then I run the exhaust fans when I am done. If the shape is what you desire but it is galvanized, then acid bath it overnight. I would look for another piece without it. Quote
pkrankow Posted March 28, 2012 Posted March 28, 2012 Vinegar overnight, muriatic acid for a minute or two, problem no more! Phil Quote
Steve Sells Posted March 28, 2012 Posted March 28, 2012 do have any idea of what temperature zink vapourizes? Quote
Frosty Posted March 28, 2012 Posted March 28, 2012 Steve: Zinc ignites in the mid orange heat and it's easy to see, it burns with a bluish green flame. Correct brazing temp is below zinc's ignition temp but if anyone has done much brazing you've seen it burn by overheating the joint. It's part of the learning curve. It doesn't actually "vaporize," it oxidizes when it's hot enough to burn, the smoke is bluish white and looks like a solid (it is) floating in hung together lace/string/ etc. It's the same look as the smoke from an oxy acet torch lit with the acet turned down too low only bluish white. It's well worth NOT breathing it at all, breathing the smoke is the origin of the "blue flu" for the color residue the stuff leaves on everything like dust. It leaves a guy feeling punky and usually tops out the next day but exposing yourself for a few days seems to get it out of you and you don't feel punky. Over dosing on it can kill you dead but for different reasons than intuition tells us. I used to know but my memory isn't good enough to go into details on what it really does to a person other than to say it's B-A-D. Frosty The Lucky. Quote
Wesley Chambers Posted March 28, 2012 Posted March 28, 2012 around 900ºc or 1650ºf http://en.wikipedia.org/wiki/Metal_fume_fever Quote
Ramsberg Posted March 28, 2012 Posted March 28, 2012 Melting temp 787 F. 419 C. boiling point 1,665 F. 907 C. If the zinc melts off of the metal and runs into or onto the forge then it WILL reach the boiling point. Caleb Ramsby Quote
pkrankow Posted March 28, 2012 Posted March 28, 2012 http://en.wikipedia.org/wiki/Triple_point the triple point of zinc is about 787F, at a near vacuum, coincidentally the same as the melting point. It is probably safe to assume there is vapor present at that temperature at 1 atm. Phil Quote
evfreek Posted March 29, 2012 Author Posted March 29, 2012 Size does matter. Zinc fume is easily carried away by air currents. The zinc "scale" that forms during warm forging is not. It goes straight down, not into my forge, since the forge is too hot for just warming up steel. It falls off when hammering and wire brushing. It lands around the base of my RR track anvil (only hot metal is allowed on the good anvil). This is the first time I have tried this, and it was a surprise. I have also tried the muriatic acid for removing galvanization. It works well on clean metal. It does not work well on rusty or painted metal. The first time I tried that, there was a piece that the acid did not get to. But the heat found it. Fancy that. Who would thunk???!?!?!? Anyway, that was the last time I trusted the muriatic acid for dirty metal. It is unreliable. I do agree that zinc is dangerous. But it is OK to cold forge, solder with, use in the chloride form as flux. I have even heated zinc plated pennies to make brass plated pennies. This is a neat trick, by the way. Squeeze the "toothpaste" out of an alkaline battery, and spread it on the penny. Somehow, zinc plates on to the surface if heated. Then, heat the silver penny in a gas flame and it will turn gold. It will not fume, as long as it doesn't get too hot. This is also dangerous. But the sharp edges of the battery case and the corrosive potassium hydroxide electrolyte are much more dangerous than the zinc or the flame. Quote
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