Properties of Gypsum-bonded Investment for Quick Heating of 20-Minute Type

Abstract

Properties of new gypsum-bonded investments for the quick heating method which could be heated at 20 minutes after the start of mixing were evaluated.The setting reaction of these investments was faster than that of gypsum-bonded investments used in the quick heating method heating at 30 minutes after mixing ; however, the setting expansion continuously increased for more than 20 minutes after tha start of mixing when the investment could be placed into a furnace for heating. Obvious casting defects were observed when the new investments were employed. Dimensional accuracies of castings obtained from these investments were stable with changes in the timing of mold heating up to 60 minutes after the start of mixing ; however, casting demensional accuracies were slightly greater than that obtained from a conventional gypsum-bonded investment. The surface roughness of castings obtained from the new investment was not significantly different from that obtained from the conventional gypsum-bonded investments.