Mixing extruder screw with long pitch channel of alternating twist - to promote mixing without inhibiting throughput

摘要

Screw for a compounding extruder has a conventional archimedean screw section followed by an odd number of zones each having groups of concave section channels having a helical pitch of between 1 and 10 times the screw dia. The first and last zones twist in the same direction as the preceding screw section, and alternate zones are of opposing twist. The concave section channels are in groups sepd. by a broad rib with just sufficient clearance from the barrel for effective lubrication without significant circumferential flow: adjacent channels are sepd. by a narrower crest having sufficient clearance for high shear cross-flow mixing between channels to occur. Suitable for blending or homogenising materials based on polyolefins, rubber-modified styrene or acrylonitrile polymers, PVC cpds. etc. Generates high shear forces for mixing without excessive back pressure to inhibit throughput.