Effect of Firing Temperature and Duration on Fused Silica Investment Shell Strength at Room Temperature
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Fused silica is widely used in investment casting shell molds as flour, stucco and binder for its superior properties, such as low linear thermal expansion coefficient and high thermal shock resistance. Investment shell molds are usually fired after the de-wax process to remove the residue pattern material, and to improve shell strength through sintering. The firing temperatures are generally high enough to affect the phase constituent and microstructure of the shells, which further influences the shell strength. Firing duration at firing temperature is another important factor having an impact on the shell strength due to grain coarsening, but it is often overlooked by investment foundries. In this article, the room temperature moduli of rupture of investment shells fired at different conditions were determined. The crystallinity of fused silica shells was determined using X-ray diffraction. The differences on the shell strength were discussed and correlated with the microstructure and phase constitution in the shells after different firing processes.
Keywordsinvestment shell firing temperature firing duration modulus of rupture phase transformation
The authors would like to thank American Foundry Society for funding this project. The suggestion and input from the AFS investment casting technical committee and project steering committee are much appreciated. Joe Govro, Madison Wooly, Scott Vogel and Wayne Pugh are acknowledged for the assistance with sample preparation and testing.
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