Although there are several different types of compression molds, the all utilize the same type of molding press, as shown in Figure 3. Figure 4 illustrates a typical positive type compression mold. Compression molding, which requires minimal material flow life during processing, generally uses stiff to medium flow compounds. A properly designed compression mold will produce parts of excellent overall mechanical properties. However, compared to other molding methods, compression molding will have a greater amount of flash at the parting line and holes, slower molding cycles, difficulties in molding side holes or sections, and problems molding in flash-free metal inserts.
Material fills the mold while it is in the closed position.
These have a vertical clamping unit and an injection unit that delivers the compound to the side of the mold instead of the center. As shown in Figure 7, the compound enters the mold on the parting line, with the nozzle of the injection unit retracting upon the opening of the mold. There is also an added benefit in cavity layout when molding long, narrow parts. A low melt-point alloy is used to form the core around which the thermosets can be molded. In a subsequent operation the alloy is melted out.