Setting expansion of investment and accuracy of castings

Abstract

Setting expansion of 4 phosphate-bonded investments was measured under 3 different conditions: a hygroscopic condition, a condition using a ring lined with a wet liner and a condition using a ring lined with a dry liner. Accuracy of castings of a Ni−Cr alloy made in each of the 4 investments in rings lined with a wet liner was measured. One investment exhibited negative potential for hygroscopic expansion. Expansion of all investments in wet-lined rings was not significantly different from their expansion under the hygroscopic condition. There was no significant difference in setting expansion between the investments when a wet liner was used. Significant differences in accuracy existed between castings produced in the different investments using a wet liner. The correlation between the setting expansion of the investments using a wet liner and the accuracy of castings produced using a wet liner was not high and was not significant. Comparison between investments with regard to their ability to produce accurate castings in terms of mould expansion by measurement of setting expansion is of no value.