Plastics extruder or injection screw and cylinder design has a reduced screw diameter below the feed opening

摘要

A screw section(9) in the material feed zone below the feed opening(5) has a reduced diameter(d) compared with the principal diameter(D) of the screw which fills the barrel or cylinder bore(4). The barrel or cylinder may have one or more multi-flight screws and the screw cross-section below the feed opening(5) may have a reduced number of screw flights. The cross-sectional area of the screw channel may also vary compared to a following screw section. Screw flight depth may also be reduced in the feed section(9). Screw root diameter(d') may also be reduced from the normal root diameter(D'). Axial length of the feed section is at least equal to an injection stroke length. Diameter reduction may be continuous or sudden. Screw diameter may increase to a maximum(D) on the downstream side of the feed opening. Additionally the screw root diameter in this section may also be a maximum giving a minimum channel depth. Barrel cross-section may vary to follow the reduced screw cross-section.