Anisotropic Expansion in Gypsum-bonded Cristobalite Investment Mold

Expansion of a gypsum-bonded investment mold was investigated using a fused quartz tube pattern. Two hours after mixing, a fusible alloy was cast into the space around the pattern induced by setting expansion. The other molds were heated up to 700 degrees C, then a dental silver alloy was cast into the space around the pattern induced by total expansion of the mold. Thickness of the castings was measured at every thirty degrees on seven cross-sections. The setting expansion was almost uniform, but the total expansion was not. Especially, a large amount of total expansion was produced toward the open ends of the casting ring and toward a seam of the asbestos liner. The thermal expansion of the mold was anisotropic because the investment was a mixture of calcium sulfate and silica, and was affected considerably by its environment.