[Jewelry making - Article 00569] - Re: [Orchid] Bronze casting porosity

[Volpe, Tino]

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    Carlos, Porosity, if it is shrinkage is caused by improper metal
    flow. It can also be worsened by casting at too high a system (
    flask + metal) t emperature. From what you describe the grain
    structure is dendritic. Try low ering your flask temperature until
    the piece won't fill. Then raise back to the last temperature that
    you gotr complete fill. This should be the coolest you can cast it.
    Better to raise the metal temp slightly and go with a lowe r flask
    temperature than the other way around. If your going to have porosit
    y, you want to drive it to the center of the piece where it won't be
    visible If possible try gating with a shepards hook to the middle of
    the piece. Th e more you improve your metal flow, the lower a system
    temperature you can c ast at, the better your casting quality. I'm
    casting sterling silver pieces at almost 200F flask temperature and
    the pieces come out great. Don't be afr aid to get nonfill, that
    condition gives you a better idea of where your sys tem temperature
    is at. 

Tino Volpe
Metallurgist, Technical Manager
Tiffany & Co.
300 Maple Ridge Drive
Cumberland, RI 02864-8707
401-288-0124


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