MIXING SECTION FOR A PLASTIC EXTRUSION SCREW

摘要

An mixing section for an extrusion screw has an inlet end and an outlet end as well as alternating wiping lands and barrier lands. The wiping lands have a greater helix angle than the barrier lands. The wiping lands and the barrier lands define inlet channels which narrow toward the outlet end and outlet channels which widen toward the outlet end. A helical pattern of mixing channels is cut into the wiping lands and the barrier lands. The mixing channels may be oriented generally at approximately right angles to the wiping lands and the barrier lands. A portion of the extrudate encounters the inside wall surfaces of the mixing channels and changes direction which improves the mixing of the extrudate.

主权项

1. A mixing section for an extrusion screw, comprising:
(a) an inlet end for receiving extrudate and an outlet end for discharging extrudate, (b) alternating wiping lands and barrier lands extending between the inlet end and the outlet end, both the wiping lands and the barrier lands having a positive helix angle and the wiping lands having a greater helix angle than the barrier lands, the wiping lands and the barrier lands defining inlet channels which decrease in cross sectional area from the inlet ends to the outlet ends thereof, the barrier lands and the wiping lands also defining outlet channels which alternate with the inlet channels and which increase in cross section area from the inlet ends toward the outlet ends thereof, (c) mixing channels cut into the wiping lands and the barrier lands, the mixing channels presenting inside wall surfaces common to the wiping lands, the mixing channels arranged to define a negative helix angle which is offset at least substantially 90 degrees from that of the wiping lands, whereby, a portion of extrudate flowing from the inlet end to the outlet end changes direction when the portion of the extrudate encounters the inside wall surfaces of the mixing channels.