The strength of the ceramic shell mold used in the Investment Casting Industry is one of the most measured attributes of a mold. Investment casting companies and material suppliers quantify shell strength to insure that the molds can withstand the stresses that are placed upon them during the process. The most common measurement of shell mold strength is in the green or unfired state. Green strength historically has been the measurement of shell strength during construction and dewaxing of the mold.

Recently, alternative methods for measuring and interpreting shell strength have been presented that indicated how shell materials may behave differently in traditional steam autoclaves. Measuring the shell strength in a “wet” condition can indicate that there are differences in the material properties in this state.

This paper will evaluate the methods that are used to characterize the strength of shell molds in the green, or prefired, condition. It will also look at various shell material components and how they impact the results of the various test methods that have been used or proposed. The authors will relate the scientific strength measurement techniques to practical tests and experiences so that conclusions can be drawn regarding the various test methods and how they predict how a shell material will perform in the process, especially the autoclave dewax process.

Various shell materials and components will be analyzed for this paper.