Heat Transfer and Property Development in Liquid Silicone Rubber Molding

摘要

Molding of liquid silicone elastomers is much simpler and more energy efficient than the conventional method, since the low viscosity reactants, monomers or prepolymers, can be easily injected into the mold without having high injection and clamping forces. The liquid reactants inside the mold, however, have to react to the solid state such that the parts can be ejected with a desirable mechanical strength. As these materials polymerize they form complex branched molecules. These polymerizations are usually thermally activated. Since the degree of cure, polymerization shrinkage, internal thermal stress, material physical properties, surface quality, and also the demolding time are largely dependent on thermal changes inside the mold, heat transfer is one of the most important steps in the liquid silicone rubber molding. The purpose of this work is to propose a theoretical model which can predict the property development for curing in liquid silicone rubber molding. The purpose of this work is to propose a theoretical model which can predict the property development for curing in liquid silicone rubber molding. This study has used a heat transfer model to describe the cure of liquid silicone rubbers. The model shows that cure always starts from the wall and will continue during cooling. Thick parts may not be totally cured upon demolding, although the material near the wall has reached a desirable mechanical strength. Since silicone rubbers gel fast at high temperature, mold filling problems may occur for the thin and long molds, especially at high mold temperatures.