[Jewelry making - Article 00724] - Re: [Orchid] Casting reheating investment molds

[John A. Henkel]

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    Hello Casters, I thought I should weigh in on this one. Over the
    years,  I too have had kiln failures during burnout. They can happen
    from switch, element, wiring or program failure, or even a power
    outage just before casting. However, it is possible to get perfect
    castings after an interrupted burnout or temp drop. There some things
    to watch for though. It is NOT a good idea to water soak an already
    burned out flask. The steam can break partially soaked investment.
    The most important thing to do is let the flask temp change as slowly
    as possible. Here's a possible scenario and solution; Your kiln quits
    at 900F on the way up and you don't decide to do anything until it's
    at 800F, you discover the problem was another appliance on the same
    circuit (not a good idea!) and you reset the circuit breaker. You can
    turn the heat back up and continue to the top of the cycle. Another
    possibility; The element has broken, the kiln you have doesn't have
    the element buried so you can see it right away. After some
    expressive words, you close the kiln, unplug it and wait until the
    next day. Carefully place the flask somewhere it won't be jostled or
    bumped, complete your kiln repair and start from the beginning with
    your burnout.  If this is going to be a week you can put the room
    temp flask in a plastic bag until you're ready to begin the second
    burnout. If you have an auxiliary kiln on the bench, it can take over
    after it has warmed up to the same temp as the flasks when they are
    switched. Re-burning your flasks can be done successfully with the
    flasks that were present during the problem run, but you should not
    add newly invested flasks to the re-burn. Excessive moisture from the
    newly introduced flasks can create some problems in the partially
    burned flasks. This is probably where the idea to soak the 2nd burn
    flasks came from. It is better to do a separate burnout for the new
    ones later. The most important thing to remember is to prevent
    thermal shock. Heating up or cooling down too fast will usually crack
    the flask. Remember that the christobalite and silica are expanding
    around 700F and need to hang out there for an hour or so, as with any
    burnout. And speaking of burnout...I hope you got all your jobs done
    and can relax and enjoy the celebration of our Saviors birth...Merry
    Christmas from all the jewelry elves up here in Maine (we're very
    close to the north pole!) John, J.A.Henkel Co. Inc., Moldmaking
    Casting Finishing, Producing Solutions for Jewelry Artists

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