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Posted by David Sherman [24.32.202.83] on Tuesday, February 09, 2010 at 19:07:01 :
In Reply to: No flux, uses gas. posted by Chriscase [76.201.18.146] on Tuesday, February 09, 2010 at 17:45:18 :
As near as I can tell, it's 30% nickel, 70% copper, plus definite trace amounts of other stuff. Definitely no zinc to boil out. Gas or not, it seems like you'd still need flux to cut through the oxide layer on the base metal, unless the heat is sufficient to actually melt the base metal slightly and alloy the filler into it, rather than just braze it on top of it.
I expect you're right about brazing cast iron. I've always done it with a torch and felt the key was to either let the whole thing cool slowly, or have an arrangement like a break crosswise in a long piece, where the piece can freely expand and contract away from the work area without stressing anything. I've seen a fair bit of heavy castings on machinery "farmer-welded" with some sort of SS rod, but most of the time, there's a new crack right next to the one he fixed.