Thermosets are usually purchased as liquid monomer-polymer mixtures or as a partially polymerized molding compound. Starting from this uncured condition, they can be formed to the final shape in the cavity by polymerization. The polymerization is activated either by heat or by chemical mixing, with or without pressure.
In the Reactive Molding process, the temperature in the feed mechanism (the barrel) is only slightly increased, however, the cavity is usually hot enough to initiate chemical cross-linking. As the warm pre-polymer is forced into the cavity, heat is added from the cavity wall, from viscous (shear) heating of the flow, and from the heat released by the reacting components. The temperature of the part often exceeds the temperature of the mold. When the reaction is sufficiently advanced for the part to be rigid (even at a high temperature), the cycle is complete and the part is ejected.
The chemical reactions that occur during filling and curing add complexity to mold and process design for Reactive Molding processes. For example, slow filling may cause premature gelling, resulting in a short shot. Fast filling may induce turbulent flow, creating internal porosity. Improper control of the mold-wall temperature and/or inadequate part thickness will result in either moldability problems or scorching of the materials.
Reactive Molding analyses can help you avoid such problems, without costly and time-consuming trial and error debugging.