[Jewelry making - Article 01039] - [Orchid] Hot Mix Investment for High Altitude Casting

[Hoover and Strong]

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Hot Mix Investment for High Altitude Casting
by Torry Hoover

    1. Calculate investment and water requirements. Use a ratio of
    water/powder of 44\100 for gypsum based investments, ie. 44g (or ml)
    water to 100g powder. For any flask of diameter (D) and height (H),
    calculate investment requirement as: Investment (grams) = 20 D^2H
    Water (ml) = .44 Investment (grams} 

    2. Weigh investment with accurate scales. 

    3. Measure water in graduated container. 

    4. Investment should be room temperature of 78F (25C). Measure
    with accurate thermometer. Water should be 110F (44C). Mix hot and
    cold to achieve this temperature. 

    5. Always add the investment powder to the water . 

    G. Mix with electric mixer at high speed for 6 minutes. 

    7. Vacuum in mixing bowl for 20 seconds after boiling starts. 

    8. Pour investment into flasks. 

    9. Vacuum the investment in the flasks for 60 seconds after boiling
    starts. 

    10. Cap off flasks with investment to bottom edge of flask.
    Carefully move flasks to setting area and do not disturb while
    investment is setting up which should be less than 3 minutes. Mark
    identification numbers on investment to identify flask when cast. 

    11. Then carefully remove sleeves. Place flask on floor with base
    down between feet. Use feet to hold collar and lift sleeve off-
    Remove any investment on collar seal surface and sides with wet rag.
    Remember, any investment on collar will prevent proper vacuum.
    Investment on collar surface will damage gaskets. Excess investment
    on the outside of the flask will fall into the vacuum chamber. 

    12. Remove sprue base. Gently load into oven. Load oven so that
    flasks to be cast at highest temperatures are cast first. 

    13. This procedure is especially useful at high altitudes where
    achieving good vacuum is difficult. It produces good results at all
    altitudes because it is less viscous than normal investment mix due
    to additional water and higher temperature. This gives it the
    capability of reproducing a better surface finish. The price paid for
    this is cleaning the bell jar because the hot mix boils much more. 

Hoover and Strong
http://www.hooverandstrong.com

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