i do production casting small scale, 500-1000 pieces of sterling per
week, 10-20 pieces of gold . 10 years of wholesale manufacturing. i
use oxy-acetelyene, kerr long arm centrifical, i cast 250-350 grams
per flask. i have had problems over the years, but porosity was never
the problem. seems like there is a tendency for the inexperienced to
worst case senerio avoid a problem you heard about but have not
experienced, throw money at it hoping to avoid the learning curve.
one of the problems i had, cracking of ring shanks right where the
sprue attached, i called precious metals west, swest, kerr, rio
grande, i sent samples even. no one diagnosed my problem. no one
suggested i was casting at too high a temperature. i have a
kilnminder and pyrometer. they all asked what the flask temp was,but
i was told sprue attachment, type of gas, metal temp, quench time.
one day out of frustration i called sunwest silver and was fortunate
to be able to talk to one of the casters, he suggested lowering my
flask temp, the one thing i had been paranoid to do, fear of little
pieces not filling out. 50 degrees made the difference. problem gone
not returned, happy, happy, happy. hydrogen melts faster, is cleaner,
and costs much more. richard in denver, hope to see you at snag
conference here in june!