GB1434368A - Feed screws and apparatus such as extrusion machines especially fo working plastics materials - Google Patents

Abstract

1434368 Extruder screw K R MATTHEWS & CO (WORCESTER) Ltd 13 June 1973 [16 June 1972] 28257/72 Heading B5A An extruder screw comprises a melting zone Z in which particles of plastics are melted by conduction through the extruder barrel, with the melt being progressively transferred from a trailing portion t of the channel 22b, Fig. 6, which is of continuously decreasing depth, to a leading co-extensive portion l of the channel 22b which is of continuously increasing depth. The portions t and l are defined between medial channel locations Al, Bl, by a portion 20b of the screw thread 20, which is of a greater pitch than the thread portions 20a, 20c, upstream and downstream thereof, so that the boundary between the portions t and l is defined at the pitch of the portions 20a, 20c, and the portion t is of a width which is constant to a median channel location M and thereafter decreases to the location B1, and the portion l is of a width which decreases to the location M and is constant thereafter, the depths being equal at the location M and the channel 22b being of substantially constant cross-sectional area throughout the zone Z. The region Z is provided with intermediate feed and delivery regions X and Y, in which the threads 20a, 20c are of the same constant pitch and the screw channnels 22a, 22c are respectively of constant and decreasing channel depth. More than one zone Z may be provided along the screw, and a zone Z may be provided in a multiple thread screw. Heating and cooling means are provided for the extruder, and in the screw may be provided by fluid circulation through an axial passage or passages.