Measurement of autoclave thermal profiles during the high pressure steam de-waxing of investment casting shells: Part II Wax body profiles

Investment casting research is being carried out by the University of Birmingham, sponsored by EPSRC and a consortium of industrial companies. The programme is aimed at developing a fundamental understanding of the process, with a view to routinely producing sound, net shape castings. A key stage within the investment process is that involving the removal of wax from the unfired ceramic shell. This important process is carried out within the confines of a sealed pressure vessel, more commonly referred to as a Boilerclave*, with external pressure gauges as the only indication of what is actually happening inside the cavity. The de-wax stage is a key stage in the process as wax needs to be removed from a weak ceramic shell system without cracking or dimensional alterations, which would be reflected in out of tolerance casting scrap. Due to the nature of the process, wax removal is probably the least understood or controlled aspect of the whole investment sequence. The following paper is the second of two which contain results obtained at The University of Birmingham using a specially instrumented stream autoclave which allows visual data capture, thermal and steam pressure profiles within the chamber, and thermal instrumentation of waxes and shells to be obtained. Results of thermal and pressure profiles within individual wax components are presented and implications of these results upon the mechanism of wax removal and the effect upon ceramic shells are discussed.