| A methodology is developed for the analysis of a class of problems in polymeric foam processing where mass, momentum and heat transfer interact. Low-pressure structural foam molding is the particular example belonging to this class that is considered for purposes of application and experimental verification of the model. However, the approach taken is general and adaptations to other specific industrial processes are discussed.;Controlled experiments are carried out with industrial injection molding equipment in order to measure the variation of foam bulk density with time during expansion as well as the final density of the solidified foam. Comparison of theoretical and experimental results leads to an assessment of the importance of certain factors (primarily elasticity and bubble coalescence) which were neglected in the analysis.;A cell model which accounts for the close proximity of the bubbles to one another constitutes the basic building block of the analysis. This microscopic model is incorporated within the framework of a macroscopic one which considers bulk foam flow, non-isothermality and gradual solidification. The resulting coupled conservation equations are solved numerically to obtain predictions of bubble size and foam density as a function of time. Characteristic time scales for mass, momentum and heat transfer, which show the relative importance of these transport phenomena are identified. The effects of these time scales, as well as of other parameters such as initial temperature and blowing agent concentration, on foam expansion are studied by means of computer simulations. |
