One common request heard from foundries is the need for an improved shell system. The definition of improved shell performance may vary, some requesting improved rheology, fewer dips, improving tensile strength or shorter drying time to name a few. However, perhaps the most commonly requested characteristic is improved survivability in the autoclave. While many shell properties can be measured quantitatively, until now autoclave performance could only be measured qualitatively.

The objective of the present investigation is to develop a test method allowing rapid and quantitatively demonstrated improvements in autoclave crack resistance. This avoids the typical painstaking process of inspecting a select few shell types over many weeks, which is required to accumulate a sufficient baseline to compare to a new system.

The premise of the test is that (i) the part configuration is sensitive enough to differentiate between material and process variables, (ii) parts are easily assembled in sufficient quantities on wax trees and (iii) most importantly the tree, shell and results all be reproducible.

This test is a collaboration between PSU, Minco and Nalco. This investigation required a facility with (i) wax injection and (ii) capability for large quantity of wax tree assembly, (iii) multiple slurry pots, (iv) temperature and humidity control, and (v) an autoclave with pressure, temperature, and cycling rate comparable to those of industrial-scale autoclaves.