Effect of preheat temperature on the location of the minimum state of cure in a molded component

The distribution of state of cure in a molded rubber component is usually nonuniform due to the slow heat transfer processes involved in the molding-cooling cycle. The minimum in the distribution usually occurs in the center of the rubber section. For large components, one method of reducing molding time is to preheat the uncured rubber prior to molding, thus carrying out a portion of the required heat transfer in a more favorable geometry than the molded shape. In this work, computation of the state of cure distribution in preheat-molding-cooling cycles for one-dimensional rectangular geometry shows that as the preheat temperature is increased, the locus of the minimum state of cure will move outward from the center toward the surface of the component. This has important implications for the range of cure states existing in an article and calls into question the convention of removing samples for state of cure tests from the center of the component. The variables considered in this work are the preheat temperature, the component thickness, and the target state of cure of the rubber compound. A design curve is developed whereby the preheat temperature to optimize distribution of the cure can be established.