EXPERIMENTAL STUDY OF MOLD FILLING FOR THE REACTION INJECTION MOLDING PROCESS.

The RIM process can be broken down into unit operations as shown schematically in figure 1. These include: component metering, either batch or continuous; intensive mixing to bring the reactants into intimate molecular contact within a time scale short compared to the process cycle time; flow into the final shape, such as filling a mold; reaction or curing in shape until the part is stiff enough to remove; and post curing, used to improve modulus and dimensional stability. The present work is a preliminary experimental study of the mold filling unit operation of the RIM process. More detailed experiments and mathematical modeling are in progress. It is shown that the pressure rise during filling for the RIM process is very low. For the thick mold if the filling time is shorter than the gel time, the pressure rise during filling can be predicted assuming Newtonian fluid with constant viscosity. For the thin mold, the pressure rise observed was in general less than expected. This could be due to viscous dissipation, since the viscosity of these materials are highly temperature sensitive. To obtain good surface finish, it is necessary for the filling time to be smaller than the gel time. The mathematical modeling of the filling stage and the subsequent foaming are in progress.