Continuous Compression Molding of Plastics

a method for the production of long items, such as pipes and rods, which consists in the pressing of a plastic through a heated compression mold with open entry and exit holes. The mold is set on a special horizontal press, the plunger of which performs a slow forward (compression) motion and then rapidly returns to the starting position. The entire batch of material is fed into the mold in one cycle; the heated plastic remaining from the previous load is mixed with a new portion, thus achieving a continuous process. The method is used primarily for working thermosetting plastics with a high volume fraction of filler, such as molding powders. It has been replaced almost entirely by extrusion in the production of items made from thermoplatics.

The processing cycle for thermosetting plastics includes softening of the material, consolidation to produce items with good mechanical properties (achieved by using compression molds in which the area of the plunger is several times greater than the area of the exit hole), and curing. The process is performed at pressures of 250–400 meganewtons per m² (2,500–4,000 kg-force per cm²) and temperatures from 65°–80°C in the loading chamber of the compression mold to 150°–200°C at the exit of the item from the mold channel. Productivity ranges from 2 to 20 m per hour.