Re: casting brass, using flux
> Message 1[As others have told you, the smoke you noticed is the zinc burning off.
> From: "ojr52us" ojr52us@...
> Date: Sat May 6, 2006 6:51am(PDT)
> Subject: casting brass
> I tried to make brass ingots the other night and something must have
> gone terribly wrong. I don't have a pyrometer and was watching the
> melt fairly closely but it suddenly began to smoke violently, I turned
> down the heat and went to skim the dross, what a mess, when I finally
> did get to the pour the ingots resemmbled something other than metal.
> i need a little help was I to hot? do I need to use a fluxing
> material? or is this the nature of the beast? I sliced one of the
> ingots and inside they are solid and appear to be ok. In the future I
> have plans to cast some brass parts, have aleady made up molds and
> done them in aluminum, they came out really good, but this little
> adventure the other night scared me
Brass is composed largely of zinc, and at a certain temperature it combines
with atmospheric oxygen to form zinc oxide. This burning-off can be
minimized by using a protective layer of flux on top of the melt. Borax is
traditional (20 Mule Team is one famous brand, sold in the laundry aisle)
but there are also proprietary flux mixtures that work as well or better.
You sprinkle it on at an early stage in the melt, when the metal is hot
enough for the flux to stick and not fly off. It rises to the top and forms
an oxygen-proof barrier over the metal. If you can't find any flux, a few
pieces of broken glass are better than nothing. When you've removed the
crucible from the furnace, skim it off and pour quickly. You'll notice white
zinc smoke as soon as you do this - avoid breating it as it's toxic, and
will cause the flu-like symptoms of zinc fume fever. Milk is supposed to be
an antidote to some degree, but avoiding it in the first place is better. If
it's not essential to make these parts in brass, try switching to silicon
bronze, which is much cleaner-melting and is more or less self-fluxing.]