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United States Patent 5932159
Douris , ê et al.

Screw extruder with improved dispersive mixing

Rauwendaal August 3, 1999

Abstract

A screw extruder (10), including a barrel (18) having a bore (26) which defines an inner surface (24). At least one extruder screw (28) is positioned within the bore (26), each screw (28) further including a central shaft (34) and at least one screw flight (30). Each screw flight (30) further includes a front pushing face (36) and a rear face (38). The profile (40) of each front pushing face (36) acts with the inner surface (24) of the barrel (18) to form a progressively narrowing passage (46) through which material is forced into multiple regions of high elongational and shear stress (48) which act to break down agglomerates of material and thus dispersively mix the material. Also presented is a screw extruder (100) having a single screw (28) which includes dispersion disks (102) which are rotationally offset from one another and whose design is not constrained by interaction with a second disk, which provides improved distributive and dispersive mixing. Also presented is a method of extruding material using a screw extruder (10) having pushing face (36) profiles (40) which form progressively narrowing passages (46) in conjunction with the barrel (18) inner surfaces (24) to provide improved dispersive mixing.