Theoretical Study of the Flow of Highly Viscous Materials

Abstract

Injection molding of thermosetting elastomers has become an important processing technique within recent years. The material enters the injection head at a temperature below the vulcanization point. It is fed by a screw and injected with a ram-like action into a closed mold. Vulcanization of the rubber occurs in the heated mold. The elastomer must flow from the injection chamber into the closed mold through nozzles, channels, sprues, and gates. Pressure drops occur and the material temperature increases as heat is transferred from the mold walls and internal heat is generated by viscous shear. Analytical methods of describing this flow are useful in modifying the mold configuration to increase flow. The basic flow equations are discussed, simplifications are made and a numerical solution of the set of equations describing the flow of a highly viscous non-Newtonian fluid is outlined. Heat transfer from the wall and generation of heat due to viscous shear is considered. The mathematical model is used to generate the local temperature and velocity profiles in the fluid at typical molding conditions.