A study of the dynamics of foam growth: Simplified analysis and experimental results for bulk density in structural foam molding

Abstract

Abstract A cell model describing the diffusion‐induced growth of closely spaced single bubbles developed in an earlier publication is now used as the microscopic building block of an analysis of low‐pressure structural foam molding. Heat transfer, solidification, and bulk flow of the foam in the mold cavity are included in this macroscopic analysis. An experimental method is described whereby the bulk density of an expanding thermoplastic polymeric foam is measured as a function of time when the expanding foam is prepared by the short shot injection molding process. Instantaneous and final bulk foam density data obtained for various values of the controlling process parameters are compared with the predictions of the model. These predictions are found to be in qualitative agreement with the experimental measurements reported here. However, quantitative differences exist between the two. These differences are explained mainly by the omission of melt elasticity and bubble coalescence in the model.