A plasticating extruder screw
A plasticating extruder screw is provided with a wave section in which the depth of the material conveying channel varies cyclically over a plurality of cycles. The wave section as a whole provides good pumping performance for metering the extrudate at a uniform rate. The deep valley portions of the wave section minimize heat inputs to the material being fed, and the shallow ridge portions of the wave section assure repeated intensive mixing of the material for providing high quality polymer melts. The minimum channel depth portions are in a balanced relationship about the axis of the screw to avoid lateral thrust problems. Such balance may be achieved in successive cycles of a single channel or as between adjacent channels of a multiple channel screw. The wave may be in the metering section of a single stage screw or in any of the pumping sections of sheet production extruder
A screw for plastic working apparatus of the type in which a barrel having a cylindrical internal wall surface receives therein a rotatable screw having generally helical land portions cooperating with said wall surface to confine the plastic material in the generally helical channel portions between adjacent land portions and feed such material along said channel portions as said screw is rotated, said screw comprising a wave section in which a helical channel varies in depth cyclically along its length through at least three cycles, the minimum channel depth portions of said channel being disposed in angularly balanced relation about the screw axis.
A multiple stage screw for extruders comprising at least two pumping sections spaced apart along the length of the screw and having a vent section therebetween, said vent section having a helical material flow channel therein, at least one of said pumping sections having a helical channel which varies in depth cyclically along its length through at least three cycles with the maximum channel depth portion of each cycle being of less depth than the depth of said channel in said vent section. In a plastic feeding apparatus having a barrel provided with a generally cylindrical opening extending from a feed zone where solid material is supplied thereto to an outlet at an end of the barrel, an improved rotatable screw having generally helical channels defined by the screw root and adjacent land portions protruding radially into such close proximity to the wall of said cylindrical opening as to substantially preclude the flow of material thereover, said screw comprising a feed section of a first channel depth located in said feed zone and a metering section of sufficient length to provide an output rate generally proportional to the rotational speed of the screw and substantially insensitive to the back pressure at said outlet, at least a major portion of the length of said metering section being characterized by a wave channel the depth of which varies cyclically through maximum and minimum values for at least three cycles each of which has an angular extent about the axis of the screw from about 180° to about 1,080°, the maximum channel depth of said wave channel being less than said first channel depth of said feed section.