Extrusion

Abstract

The extruder, which offers the advantages of a completely versatile processing technique, is unsurpassed in economic importance by any other process. This continuously operating process, with its relatively low cost of operation, is predominant in the manufacture of shapes such as films, sheets, tapes, filaments, pipes, rods, and others. The basic processing concept is similar to that of injection molding (IM), in that material passes from a hopper into a cylinder in which it is melted and dragged forward by the movement of a screw. The screw compresses, melts, and homogenizes. When the melt reaches the end of the cylinder, it usually is forced through a screen pack prior to entering a die that gives the desired shape with no break in continuity (8–9, 85, 90–96, 100–106, 115–143) (Fig. 3–1).