[Jewelry making - Article 00942] - [Orchid] Rough surface on Sterling belt buckle casting

[ben's mail]

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    I have experienced casting defects and don't know the reason. 

    Using high grade investment purchased in 2003 and stored in
    carefully fastened plastic bag in a plastic pail bucket, the sterling
    belt buckle casting was defective. 

    The casting exhibits a rough texture on surfaces that should have
    been flat and smooth. 

    The molded investment surface seemingly broke down and the resultant
    casting surface is rough over 50% of the total surface. 

    The 38/100 mixing ratios were carefully followed measured to the
    gram. The water was pure rain water. The temperature was a little
    cool with investment setting time ~ 15 minutes in a 65 F room. 

    The flask was burned out completely with the opening being white
    with no trace of carbon. The flask was ramped to 300 f then 700 then
    1350 and cooled to 850 and soaked for half an hour. The total cycle
    was 5 hours. The burnout began approximately 16 hours after
    investing. The invested flask was stored at approximately 45 F
    overnight. 

    The flask was not dropped or jolted. The sprues were not tightly
    bent. The casting is 66% new metal. The flask was cast with a good
    solid 30 im on the vacuum gage 

    Although the soak temperatures are published, the ramp times are
    not. Heating too rapidly is a cause of defects. Are there suggested
    ramp times to 300, 700, 1350, cooling to 850? 

    Smaller castings with same investment and similar procedures but
    lacking the extensive flat surfaces of a buckle don't have the noted
    problems. 

    Orchidian thoughts as to cause for the defects would be appreciated.

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