[Jewelry making - Article 00196] - Re: [Orchid] Investment inside casting pieces

[David L. Huffman]

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Hello Marco;

>     I have encounter a problem to which I can't figure out how to
>     solve 

    I'm not *the* expert on the subject of casting, here among our
    Orchid posters, but I immediately thought of what might be the cause
    of your problem. I have been casting for 30 some years, though, so I
    figured I'd throw out my idea in case nobody else here considers it. 

    Since you have covered all the considerations such as proper
    investment, burnout cycle, casting settings, and I'll assume you
    aren't banging the flasks around after they're burned out and before
    their cast with... you are careful with them, right? Investment is a
    little fragile when it's burned out. There are two other
    possibilities: 

    If the burnout schedule is ramping up too quickly in the beginning,
    and the designs are such that there are delicate configurations of
    investment left after the wax is gone, it could be the pressure of
    the expanding wax is breaking the plaster free in those areas. It's
    obvious the plaster is coming from somewhere in the design (although
    there is the possibility it's coming from irregularities in the sprue
    chamber). Study these castings when you find the these inclusions.
    There should be a corresponding area in your design that has filled
    with metal where it shouldn't have. If the area that is breaking free
    is too delicate, too long, or otherwise unable to support itself
    through the process of the metal entering the cavity, you'll have to
    change that somehow. Might there be certain designs you have this
    problem with more than others? Shoot some waxes and hold them up to a
    strong light. It's even possible there are bubbles within the wax
    that the investment is managing to fill during investment. Good luck. 


David L. Huffman
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