In the lost wax casting process, where it is necessary to produce cavities in the finally cast object, it is common practice to use a ceramic core round which metal is cast, and which is subsequently leached or otherwise removed from within the solidified metal to leave the cavity having the same shape as the core. These cores are usually made of ceramic materials which withstand the high temperatures involved but which may be removed from the final casting without damaging the metal. These cores are commonly manufactured by an injection moulding technique in which shaped dies are used to define the form of the core.
A more recent development involves the use of disposable pieces in the manufacture of cores which have internal cavities within themselves. In this technique, sometimes known as the cored-core technique, the disposable piece is first made by an injection moulding technique and is placed in the die cavity when the core itself is injection moulded. The disposable piece is subsequently removed from the completed core so that it leaves the cavity therein which will be filled with metal when the core is used in the lost wax casting technique.
Problems arise because of the low strength of the materials used in these techniques. Thus the disposable piece or disposable core part must be strong enough to withstand the hydraulic pressures which act upon it during the injection moulding cycle for the core proper. Similarly, the ceramic core itself must be strong enough to withstand damage not only during the pouring of the metal plus the casing process (i.e. high temperatures for long periods) prior to this stage.