[Jewelry making - Article 01142] - Re: [Orchid] Steam de-waxer

[jesse Brennan]

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    I will start by listing the temperatures of condensing steam qt
    appropriate temperatures: 

        1 atmosphere ( 0 psig gage) 212 F
        5 psi gage 227 F
        10 psi gage 239 F
        15 psi gage 249 F
        100 psi gage 337 F

    Domestic pressure cookers may be capable of working to 5, 10 or 15
    psig maximum pressure. 

    Generally industrial de-waxing using ceramic shell investment can and
    will nominally run at about 100 psig. This industrial melt out can
    takes less than 30 minutes. 

    This is very effective at rapidly removing molding waxes and the
    harder waxes used for industrial parts These are similar to the
    machinable carving waxes. These temperature does not totally de- wax
    the mold. Efficiency depends on the actual mold configuration for
    fluid wax drainage. 

    Poor Sprue configurations can cause some wax to remain in trapped
    sections which may cause problems. Complete wax removal is conducted
    during burn out which ends with mold vitrification with ceramic shell
    investment. With ceramic shell temperature rise are very rapid.
    Gypsum plaster investments can not go this high and ass fast and high
    temperatures in burn out attempts are destructive too the mold. 

    Organic compounds generally decompose to carbon above about 450 F.
    Ray Bradbury's classic "Farhenheight 450" refers to this. To removing
    (burn out) of the carbon requires combustion with oxygen and molds
    can be very inefficient at getting air into the mold raising the
    temperatures increases burn rates but does not get oxygen to the
    right places quickly. Soaking time helps as air slowly diffuses thru
    the mold. Remember that combustion products fill the mold with oxygen
    poor gases. 

    Higher temperatures do not increase this very much. and can damage
    the mold surfaces. Many of the recommended practices tend to go too
    high too fast for gypsum based investments. Consider this if your
    practice gives difficulty. 1200 F is a recommended maximum finishing
    temperature and may be too high, soaking at 700- 900 F for a period
    with only a short finish at a higher temperature may work better for
    you. It definitely does on very large gypsum molds. Steam de-waxing
    helps by driving steam through the molds and greatly reduces wax
    absorption into the mold. Starting with a wet mold and slowly heating
    to above 450 F helps. In this regard initially de-wax above boiling
    water. when wax appears to be gone start with the final slow burn
    out. 

jesse
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