[Jewelry making - Article 00310] - Re: [Orchid] Casting Fine Silver

[James Binnion]

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    Sprue placement and thickness is very critical in pure metal
    casting. Casting pure metals is different than alloys. The main
    reason is that there is no solidification range in pure metals, they
    transition instantly from liquid to solid. This means that as a
    casting cools it cannot draw molten metal from the sprues to fill in
    the shrinkage that occurs upon cooling like it can in an alloy where
    there is a range of temperature where the alloy is in a semi liquid
    state . This often results in large shrinkage porosity that is found
    near the sprue connection. The way to avoid or reduce this is to
    make the sprues thicker than the section of the item where they
    attach. Also make sure you are attaching the sprue to the heaviest
    area of the design. Ideally you want the thinnest sections farthest
    away from the pouring cup/button and the section of the casting to
    get progressively thicker as it gets closer to the pouring cup. This
    way the casting solidifies from the outside of the flask inward with
    the pouring cup/button being the last section to solidify. -- Jim
    Binnion 

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
http://www.mokume-gane.com
jbin AT mokume-gane.com
Member of the Better Business Bureau


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