Cure analysis of 'fast-cure' Sheet Molding Compounds (SMC)

In this study, the cure behavior of fast-cure SMC (Sheet Molding Compound) is analyzed by a series of experiments and model simulation. A model was used that assumed that the SMC reaction can be described as a combination of three steps: initiation, inhibition, and propagation. Reaction starts only after the number of initiator radicals created is equal to the effective number of inhibitor molecules initiatlly present. It was found that a SMC compound must be designed in such a way that no cure reaction may occur during mold filling. During mold filling, heat transfer from the mold to the charge may result in a non-uniform temperature distribution which in turn may generate a non-uniform consumption of inhibitors at different locations. This can be readily analyzed by incorporating the decomposition rate of curing agents in the flow simulation and calculating the distributions of temperature and curing agents concentration during mold filling. The results at the end of mold filling can be used as the initial conditions for the cure analysis.