A MODEL OF ADVANCING FLOW FRONT IN RIM

A two-dimensional model is developed for mold filling in Reaction Inje ction Molding using a Petrov-Galerkin finite-element method with free surface parameterization. Dependence of viscosity on the conversion an d temperature is represented by the Castro-Macosko function. The model predicts the velocity, pressure, temperature, and conversion distribu tions with time during the filling stage of a rectangular mold. No a p riori assumptions are made regarding the shape of the advancing flow f ront, or regarding any variables in the flow front region. The accurac y is further improved by using the Petrov-Galerkin formulation, rather than the Galerkin formulation. The results are presented for well-cha racterized polyurethane systems, for which reliable experimental data is available. The predictions of the model for the pressure rise are i n excellent agreement with the experimental data (1) even close to the gel point. These refined predictions are expected to assist in estima ting fiber orientation and bubble growth in the final RIM parts, in wh ich the flow front region plays the most important role. Characterizat ion of polyurethane/polyurea and polyurea materials is underway, and w ill be subsequently incorporated in the model.