Overview

Robert W. Bainbridge

Consultant

Occidental Chemical Corp.

Durez Resins & Molding Materials

North Tonawanda, New York

THERMOSET-MOLDING PROCESSES

Molding compounds of thermosetting materials, or thermosets, when subjected to heat and pressure within the confines of a mold, cure or set into an infusible mass. An irreversible chemical change, involving the cross-linking of molecules of the material, takes place, and a solid part is formed.

Three basic methods of molding may be selected to process thermosets: compression, transfer (pot or plunger), and injection molding. Compression molding is illustrated in Fig. 6.1.1.

Figure 6.1.1: Schematic illustration of compression molding. A preform of thermosetting material is placed in a mold cavity. Heat softens the preform, and the ram pressure forces the material into all portions of the mold cavity, where it takes the shape of the cavity. The material then sets into a solid part that can be removed from the mold.

The molding operation requires a press large enough to generate the required pressure and a mold mounted into the press and heated by steam, electricity, or hot oil to the recommended temperature. Auxiliary equipment, for preheating the molding compound, loading it,...