< TWO STAGE BURNOUT
METAL CASTING
After the burnout/firing sequence has been completed, the investment mould can be removed from the kiln before filling with a metal charge. Larger PLASTER & GROG investments are allowed to cool in the kiln to a temperature that allows them to be handled; at which point they may be reinforced by wrapping around with a plaster and scrim binding or metal package strapping. Wrapping the mould with a bandage is done as close to the time of metal pouring as possible, because the wet bandage exposes the mould to moisture; fired grog investment is hygroscopic and will quickly absorb water content from the bandage into the mould wall, if left for a period of time a bandage dampened mould could damage the cast. Open core ceramic shell moulds are usually taken direct to the foundry floor and cast while the mould is still fairly close to kiln temperatures.
Small block moulds can be poured free standing, though it is usual to secure larger moulds within the confines of a sand pit or sand filled flask. HYBRID investments used in combination with a sand venting technique have flexible nylon tubing pushed into the mould’s drain holes. These tubes are then run to the top of the pouring cup’s lip and secured in place with duct tape. The mould and tubing is then enclosed in a flask and buried up to cup level in a hard setting sand (not the dry, free running sand usually used for supporting investment moulds), this provides the mould both with a means of venting to the atmosphere, and a hard jacket support.
OPEN CORE ceramic shell investments may also be poured with the mould left free stranding, though usually they are supported on some form of framework to prevent accidental toppling. Alternatively, the ceramic mould can be set in a flask and surrounded with a dry free running sand (after covering the cup with foil to prevent dust entering). Some ceramic shell foundries use a fluidised sand system for burying and supporting moulds during the pour, this method is described in more detail in the later section on vacuum casting.
MELTING & POURING METALS >
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