Compression molding is cost effective and highly efficient. The rubber material is placed in an open mold which has been pre-heated to a temperature that achieves vulcanization. Then the mold is closed, typically under hydraulic pressure, forcing the rubber completely into the mold cavities. Overflow, if any, is captured in channels referred to as “flash grooves.” The mold is opened when vulcanization is complete, parts are removed, and the process is repeated.
Compression molding's cost advantage is because molds are fairly inexpensive to produce while high throughputs are achieved through high cavity density and low changeover times. The biggest downside in compression molding is flash. Without proper monitoring, flash is difficult to control. Compression molding also typically involves longer in-press cure times. Finished parts exhibit the least tolerance control of the other molding techniques.