[Jewelry making - Article 00736] - Re: [Orchid] Casting reheating investment molds

[T R. Hawkinson, Ltd.]

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    Dear John, Rick & All, This happens at school all the time. If a
    student doesn't show up we pull the flask and try either the next day
    or the next week depending on class schedule. You can leave the flask
    at the casting temperature for quite a long time. I've had flasks at
    casting temperature for two or three days and still cast
    successfully. However, if they cool down to room temperature you do
    have more concerns. Reheating smaller flasks spin casting give the
    best results. Larger flasks (one & a half pounds of investment and
    up) vacuum casting is very very risky. If you try with the vacuum, as
    soon as you put the vacuum on, listen for a popping sound. If you
    hear it, the flask has just blown out. This will leave an open path
    for the molten metal to go through the flask and either into the
    vacuum line, flask chamber or even vacuum pump. Most of the time the
    molten metal just gets to the brass vacuum table fittings and freezes
    up. All in all a lot of work. Not only lost metal but rebuilding a
    vacuum system can be time consuming and expensive. Most of the stuff
    we cast at school comes from molds so if we sacrifice a flask or two
    to the casting Gods we can always do them again. 

Best Regards,
Todd Hawkinson
T.R. the Teacher
www.trhawkinson.com
www.ajt-online.com
www.mctc.mnscu.edu/jewelry

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