Effects of Elapsed Time and Heating Rate on Dimensional Change of a Gypsum-bonded Investment for Quick Heating

Abstract

This study investigated the effects of elapsed time and heating rate on dimensional change of a gypsum-bonded investment for quick heating by placing a mold directly in an electric furnace at 700℃.
The elapsed time after the start of mixing had no effect on thermal expansion. However, the setting expansion increased for 50 min, resulting in an increase in total expansion. The heating rate did not significantly affect either the thermal or total expansion at any elapsed time investigated.
In the case of quick heating, the expansion curve showed the dehydration of gypsum, the transformations of both cristobalite and quartz, and a plateau which indicated the completion of thermal expansion.