Measurement of autoclave thermal profiles during high pressure steam de-waxing of investment shells Part 1 - Vessel profiles

Abstract

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. To metaphorically ‘see’ inside the vessel would allow the factors controlling de-wax to be characterised and controlled. This paper contains results obtained at The University of Birmingham using a specially instrumented steam autoclave that 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 inside the vessel body are presented and implications of these results upon the mechanism of wax removal and the effect upon ceramic shells are discussed.