The expanded polypropylene foam beads (EPP) production process, which consists of steaming, depressurizing, cooling and ageing processes, was simulated by a mathematical model. The model was developed by extending Yang and Lee's ageing model of extrusion foam products in terms of fundamental aspects of evaporation, condensation of blowing agents and heat conduction phenomena during the steam chest molding. The governing equations were established by coupling the mass transfer equation of steam and air at the interfoam cell walls, constitutive equation of evaporation and condensation in each cell, equation of heat conduction from the mold to foams, with mechanical force balances equation on the cell walls. The model could simulate the stress exerted to the foaming mold and expansion behavior of the cells in the EPP foam board.
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