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Casting billets


#1

Hi folks

I need some help with casting rectangular billets. The project is to
make a solid bangle out of square 14kt gold material rougly 5mm wide.
I melt the gold in a ladle and pour it into the steel crucible, but
I’m getting impressions in the gold filled with borax. I think I’m
using too much to try to clean the junk out of the gold as these
"inverted bubbles" are too big to try to roll out. They are rougly
1mm wide and about 1/2 mm deep. How much borax should I use? Any
other tips/tricks?

-Stanley


#2

Hi Stanley,

I have had trouble with sterling billets (small round bars), but
with 18ct gold I have had no troubles at all. When the metal first
becomes liquid I add a small pinch of borax. Literally a half pinch.
I mix the metal with a carbon rod, and most of the borax sticks to
the rod. I heat until the metal will remain molten for a second after
the heat is removed. I tend to pour the through the torch flame into
the mould. I make round billets (19g, 3 inches long) and then use the
rolling mill to make them square. Now I don’t get borax includions
very often, but when I do, they all roll out in the mill, but as I
said I’m going from round to square, so by the time I have the
largest square billet, I have flattened all of the surfaces.

I used to get borax inclusions for 2 reasons. Firstly, I was using
too much borax, and secondly I didn’t stir the molten metal with a
carbon rod. Now on the borax note, when I was using too much borax,
most of it would solidify in the crucible, and so I had to chip out
most of it before the amount of borax added to the melt mattered at
all to the inclusions in the cast.

Brian

P.S. I offer these sugestions as an amateur and have no professional
training whatsoever in this art…