< KILN & CASTING INTRODUCTION
WAX REMOVAL & FIRING THE MOULD
Once the complete, the GREEN [unfired] investment mould is usually allowed to stand for a period under ambient conditions. Standing allows the mould to to air dry and can also improve the overall quality of the mould. The period of time allowed for standing varies according to the investment system used by the founder and the volume of refractory within the mould. CERAMIC SHELL investments tend to acquire a satisfactory GREEN STRENGTH more rapidly than PLASTER & GROG or HYBRID investments. In fact ceramic shell moulds can proceed to the wax burnout stage almost immediately after the application and drying of the final sealing coat (though some standing time is nearly always preferable).
Once the investment mould has air dried the wax assembly must be removed before a metal charge can be poured in to the evacuated air gap. In addition to removing wax contents, the mould materials must be fired to attain their full REFRACTORY properties.
During the initial stages of a combined burnout and firing process, the wax pattern and running system contained within the investment mould are flushed out. Continued firing modifies the chemical structure of the refractory materials used in the mould’s construction, enabling the mould to attain it’s maximum resistance to thermal exposure. The heat applied to the investment in the kiln also eliminates excess moisture, allowing the founder to pour molten metal into the mould without risking an explosion or damage to the cast due to steam reactions.
The wax burnout and mould firing process can be carried out either as a single, or a two stage procedure. Most art foundries use a single stage procedure, this method removes wax and fires the refractory in a continuous cycle of events.
SINGLE STAGE BURNOUT & FIRING >
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