melting fluxes for alum and brass?

HI all

What would be good homemade fluxes for these? I've read about crushed clear glass for brass. Someone told me borax would also work. Will these work for aluminium? One other thing is, when asked about green sand the counter guy at the foundyr supply said it can be made by mixing bentonite with sodium silicate. I assume the latter has to be in the powder form, as the liquid form is used for cores. Now what I had read was bentonite + silica sand. Since silica sand is used to make sodium silicate, is this usage appropiate?

Any advice thanked in advance

regards,

Mongke

Reply to
mongke
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No.

No again.

Correct.

No. The foundry supply advice is confused. Primitive green sand does not contain sodium silicate (water glass), just finely milled clay (such as bentonite) and sand (silica aka quartz), and moisture. Modern hi-tech formulations add surfactants to better chemically activate the clay bonding properties. Sodium silicate is used to cement rock-hard sand structures like the cores you mention, not for friable/reusable green sand. Cheap "furnace cement" is typically a blend of powdered clay and sodium silicate; this sets permanently.

Reply to
Richard J Kinch

- As for fluxes, nothing with aluminum is fine. If you have an argon or nitrogen cylinder you can bubble gas through the melt to degas it (aluminum likes to dissolve hydrogen). I haven't had a hydrogen problem in some time, and mind you my furnace exposes the melt quite directly to the major source of hydrogen, flame. Probably the worst offender for gas is disturbing the melt surface. The oxide layer on aluminum seals it in.

As for brass, they say a teaspoon of borax plus enough crushed glass to form a cover works good. Don't try to use borax on aluminum as it isn't hot enough to work well and only ends up sticking to it and making a horrible mess.

Tim

-- "I have misplaced my pants." - Homer Simpson | Electronics,

Reply to
Tim Williams

My only advice is to use flux only if absolutely necessary. Flux is very destructive of crucibles, particularly when fluorspar is a part of the fluxing agent. The damage doesn't stop at the crucible, for some of it ends up in the furnace eventually, and damages the lining.

Most small foundries I've ever visited melt and skim, but don't flux. As Tim suggested, bubbling nitrogen through aluminum is good for expelling hydrogen. I've seen that done.

Harold

Reply to
Harold & Susan Vordos

Borax makes a mess of LWI-26 (um, looks like perlite in a refractory cement matrix)... forge welding being how I know. Big black spots about 3/16" deep...

Tim

-- "I have misplaced my pants." - Homer Simpson | Electronics,

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Reply to
Tim Williams

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