The dynamic curing behavior of sheet molding compound (SMC) has been investigated by using a cylindrical cure reactor. Both thermal and mechanical responses were determined for R‐25 SMC paste. The responses from this material were analyzed to determine the chemical and physical transformations that occur during the SMC molding process. The thermal response was obtained from a thermocouple placed along the centerline of the paste sample in the cure reactor. The thermal history at this location shows distinctive stages associated with heat transfer and crosslinking reactions during the cure cycle. The R‐25 paste has a precure time of 160 seconds, a reaction time of 25 seconds, and a temperature rise of 134°C. The mechanical response describes the volume change and the pressure of the paste. The displacement curve shows volume changes due to thermal expansion, cure shrinkage, and thermal contraction during the course of a cure cycle. We found a less than 1% shrinkage during the reaction of the R‐25 paste. The pressure response of the paste was found to parallel the volume transformation, although it also is strongly influenced by mechanical interactions between the press and the paste.
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H. T. Kau (1989) studied this question.
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