[Jewelry making - Article 01184] - Re: [Orchid] Large silver cups casting

[LEESSILVER]

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    Mark, I sometimes vacuum cast very large objects that might be
    similar to your cups. I melt my silver in an electro melt furnace to
    about 1860 degrees and use a 60 new to 40 scrap ratio.  My mold
    temperature is set to 860 degrees.  Like you I usually sprue from
    the top edge and center of the vessel.  I like to have the metal
    flow down against the design in the mold surface rather then be
    lifted up against the design surface.  I do not run gates to the
    sprue end.  Here in Phoenix I can pull a healthy vacuum. 

    I use R & R investment which I believe it is slightly stronger than
    other products. 

    From you post I assume the bubbles are caused in the investment step
    not the casting step. You might try one of the debubblizers on the
    wax to eliminate the bubbles formed during the investment step.  I
    vacuum the mix for about 1 minute after the investment pancakes and
    about 1 minute after the first bubble appears in the investment in
    the flask.  

    You chance getting porosity in your castings if you mold temperature
    is too hot. Jim said it right, "You ideally want as cool a flask as
    will fill." 

    Mark, you might want a copy of my anti-fire scale vacuum casting
    procedure.  The process eliminates most fire scale formed during the
    cooling process.  Its a very simple process and the paper is free. 
    Send me your snail mail address if interested. 

Lee Epperson


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