Extruder screw for efficient mixing - has start and end parts with concentric circular core profiles but asymmetrical intermediate length which is pref. polygonal

摘要

An extruder with planetary rollers or a single screw has a number of inlets arranged along the whole length of the barrel, each inlet being at a feeding part of the screw(s). Each such feed length of screw(s) has a core profile at the two ends which is circular and concentric with its axis of revolution; a centre part extending along at least half one pitch of each flight has a core profile however which is asymmetrical about the axis of revolution. In the figure the feeder section of the screw has a short start (16) long mid-section (17) and intermediate length end part (18). The screw flights (20,21) are unbroken along the three lengths (16,17,18). The screw has a circular core profile (24,25) at both ends (16,18) but it is asymmetrical (26,27) along the mid-section (17). The start (16) has a length which is half the pitch of the two screw channels (28) and (29) the intermediate part (17) extends along two complete channels (28,29) and the end part (18) covers a pitch of both channels (28,29). The core profiles (26 and 27) are best polygonal, both to produce and in their function. ADVANTAGE - The design has an efficient mixing effect, at least where different materials are brought together i.e. at the material feed inlets.