[Jewelry making - Article 00153] - Re: [Orchid] 2 Hour Casting

[Peter W . Rowe]

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Fred,

>     Does anyone reading this have any technical data on how long the
>     flask core should be at maximum temperature? I am not referring the
>     holding time for the oven since the core temperature obviously lags
>     behing the oven temperature. 

    I doubt you can come up with any real hard and fixed times here. It
    will vary according to how much carbon needs to be oxidized in the
    investment (how much wax was in the flask, and how much of it soaked
    into the investment instead of melting and flowing out). And it will
    then vary according to both the size of the flask and thickness of
    investment through which oxygen must travel to do that job, and
    finally, and perhaps even harder to quantify, the amount of oxygen
    available to the investment, which will depend on the amount of
    ventillation in the oven, as well as air flow patterns. Even the way
    the flasks are placed and supported will affect this. It's important
    since if you're burning out without oxygen, the carbon won't burn
    away at all. One reason some casters find differences in performance
    between electric and gas fired burn out ovens is precisely this, that
    the gas fired furnaces have greater rates of ventillation, even
    though much of the oxygen in the furnace is being burned by the fuel
    gas. And it's also one of the reasons why some small furnaces,
    enamelling and PMC types especially, may not be suited to casting
    burnout, if they lack sufficient ventillation to allow an adequate
    inflow of oxygen and gas circulation to carry that oxygen to the
    investment. 

    With all that said, of course, one certainly can come up with times
    required for typical burnouts in most situations. For small flasks,
    usually a hold time of around an hour is sufficient. Given that this
    is with the usual slow burnout, it probably is is close to the time
    the flask core is at these temps too. Larger flasks with more waxes,
    need more. Steam dewaxing reduces the times needed. 

    Trial and error may be the best way. Easy enough for a caster to
    keep notes and find the best times for their own burnout method. 

    Great little book you've got there, by the way... Well done indeed. 

Peter Rowe


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