THE SOLIDIFICATION OF LARGE SECTIONS IN CERAMIC INJECTION-MOLDING .1. CONVENTIONAL MOLDING

A well-characterized alumina-polypropylene suspension was injection molded as cylinders of 20 and 40 mm diameter. A finite difference method was used to calculate the temperature distributions in the cylinders and in the sprue during solidification which incorporated the enthalpy of crystallization. The times at which pressure in the cavity began to decay, the calculated sprue solidification time, and the calculated time at which pressure in the center of the cavity reached zero were compared as a function of hold pressure. The resulting solidification-induced defects were revealed by radiography and sectioning and explained in terms of the kinetics of solidification.