Simulation of Foaming Process in Reaction Injection Molding

Abstract

This paper deals with a procedure to simulate the foaming process in RIM (Reaction Injection Molding). The process involves heat generation by chemical reaction, heat loss through the mold and local vaporization and condensation of the solvent that plays a blowing agent. In addition, the foaming pressure causes change in the condensation temperature of the solvent. To simulate this dynamic process, one dimensional cell model was proposed. Each cell contains a certain mass of the solvent, and the volume, temperature and the pressure of the solvent can be estimated by the quantity of heat which is generated and/or transferred in the cell, assuming that no pressure gradient exists and total of each cell's volume is constant. For a typical fast cure polyurethane RIM system, apparent density profiles were predicted theoretically, as well as chemical conversion, temperature and pressure profiles. An experimental run was carried out and the results were compared with the theoretical values. Rather good agreement between them was obtained, considering that the number of material and process parameters were many and no adjusting parameter was introduced. The procedure presented here can be usefull to developement of materials and process for RIM.