[Jewelry making - Article 00216] - Re: [Orchid] Investment inside casting pieces

[LEESSILVER]

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>     On occations we cast pieces that once almost finished we find that
>     they have rather large cavities that contain investment init. 

    I can think of two possible causes of your problem. 

    1. There are bubbles in your waxes. When the investment/wax is
    vacuumed the bubbles pop allowing investment to penetrate the wax
    design. You might want to vacuum the wax before investing. If there
    are bubbles under the wax they will show up after vacuuming. You
    might also want to hold the design up against a light. The bubbles
    will show up as lighter sections. The bubbles can be filled with wax
    before investing. 

    2. Portions of investment are breaking off from somewhere in the
    mold. The breakage can be caused by too fast of a temperature
    increase at the start of the burn out cycle or by the molten metal
    breaking of a thin section of investment as the metal is poured.
    This broken off piece of investment will float in the mold until the
    metal is poured. The weight of the molten metal will float the piece
    of investment up against the surface of the mold. The broken off
    piece of investment will become trapped in the metal. I can send a
    sketch of this problem if you contact me directly. You might want to
    shake the mold with the sprue end down as you remove it from the
    burnout oven before placing it on the vacuum table. This might case
    the broken off piece of investment to drop out of the mold. Try to
    sprue the model so that the molten metal as it is poured does not hit
    a thin section of investment.


 
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