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Gold Porosity Problems


#1

Dear Members,

I am doing torch centrifugal gold casting for years,I have managed
to minimize porosity almost to zero but I can avoid little holes
appearing upon sanding ,finishing with tripoli or magnetic tumbling?

What causes these tiny holes and how can be avoided?

Thank you
Desperately waiting for your help
Thank You

Sheitanis Eleftherios
Y&A Jewellery Manufacture and Model making
Cyprus


#2

Hello Sheitanis!

Your description of your casting problem is clear enough to make a
reasonable guess. I am going to suggest you reduce your flame
temperature. It sounds like you may be overheating the metal.
Improper spruing can also cause problems. Your description however
sounds like overall, fine porosity. Improper spruing usually
manifests near the sprues, and/or localized in the thinner areas.

It is common practice to melt with a hotter flame; and when the metal
is molten, to then reduce the flame temperature by turning down the
oxygen. The extra time should be taken to melt the metal with a good
reducing to neutral flame. This will alleviate overheating. Of course
I could be way off base and totally misdiagnosed your problem! Hope
it helps. Good luck!

Tim