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  • Investment casting

    I did investment casting more than 50 years ago in making custom jewelry. I modeled my designs in wax and used the refractory compound to make the mold, which was put in a burn out oven to get rid of the wax. Back then, it was standard procedure to line the flask with a strip of asbestos mat or paper. I want to get back into doing some lost wax casting and I watched a gem and mineral club member invest a wax model in a flask. He did not line it with anything. Can some of you guys doing lost wax casting tell me about the purpose of the asbestos liner? Was it necessary? Has the investment material changed?

    Jim

  • #2
    I think it was to make cleaning the flask easier. When I was in school, we just dropped the whole thing into water after casting and most of the investment would flake off.

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    • #3
      When I did some Lost Wax work in the early 1960's I was told the Asbestos was used because of the differing expansion rates of the flask and the investment.

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      • #4
        As stated, a liner is supposed to function as a cushion and to help remove the investment but I don't use them and don't notice any problems. Some people have also gone to perforated flasks and those are not typically lined.

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        • #5
          As was said, it was a thermal expansion solution that was carried over for many years.
          I have done well over 100 investment flasks, all without a liner and never had the investment crack---which is the concern in not using a liner as well as removal of the investment after casting.
          Using an electric furnace helps immensely. Direct flame impingement onto the flask with a gas furnace most likely needs such a intermediate barrier

          A word of caution . I have a huge disagreement with all books and publications that use the term " Wax Burnout" when you heat the flask to 1200-1400 degrees F.
          That is just completely bogus and wrong !
          Yes, you need to heat the mold to the desired temperature, but not for the wax !
          The high temperature is needed to convert the investment material from a plaster like material into a heat tolerant ceramic type material and has nothing to do with wax removal . At about 1100 degrees the investment starts to change structure and actually gives off water in doing so.
          I know because I lost hundreds of hours trying to solve a casting problem and have made "lost wax molds" without using wax.Most waxes have a vapor point well under 200 degrees (F) and evaporate early ( sublimation ) . I have observed water vapor being issued from a mold at 1200 degrees which signify's a chemical transition/action and change in structure . This mold was in a 350 degree oven for 72 hours just prior, and had no wax.

          Rich

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          • #6
            Thanks guys for the reply. As soon as I can get all of my stuff unpacked from the move to Florida, I will try to get sorted out and do some more casting. I will not use the asbestos liner.

            I found a new video by Paul Hamler in which he presents his techniques in doing investment casting. I found the video very informative. You can find it by going to Paul Hamler Videos, looking for the one on casting.

            Jim

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