Extruder screw - in which multiple threads in fusion zone have twin flow paths where one has sickle shaped section

摘要

A multiple-thread extruder screw for thermoplastics/elastomers, with normal height crests, has at least one shear/ blending length with at least one pair of flow passages consisting of a spiral entry path and a parallel outlet path; these paths are separated by a normal height thread crest when viewed circumferentially and in the direction of screw rotation, or the entry path leads the outlet path when viewed against the rotation direction. The downstream end of the entry path and the upstream end of the outlet path are blocked where the gap between the blockage and barrel is at least equal to the gap between the normal height thread and barrel. The root of the entry path, viewed circumferentially agand against the rotation direction, is tapered to form a sickle-shaped cross-section between root and barrel, and its narrowest width is greater than the gap between the normal height crest and the barrel. Thermally and mechanically homogeneous extrusions are obtd. Low temp. and low pressure at the start of the fusion zone enable low flow resistance at transition to the entry zone.