Importance

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Abstract

An axially elongated extruder screw includes a screw body having an axially extending extruding portion defined by a feed section at an inlet end of the screw, a metering section at an outlet end of the screw and a barrier section between the feed and metering sections. At least one helical primary flight extends about and is coaxial with the screw body. The primary flight and the screw body cooperate to form a channel in the feed section for conveying resinous material to the barrier section. The barrier section includes at least one helical secondary flight extending from the primary flight about the screw body which in turn defines a first surface of revolution between the primary and secondary flights. At least one helical tertiary flight is positioned between the primary and secondary flights and also extends about the screw body which defines a second helical surface of revolution between the secondary and tertiary flights. A third surface of revolution is formed between the primary and tertiary flights and extends axially along the barrier section. A series of circumaxially contiguous cam-like forms are created by a second and third surfaces of revolution, each cam-like form being defined by a segment of the screw having a root, a crest, a first surface portion extending radially outwardly from the root to the crest in the direction of screw rotation, and a second surface portion extending radially inwardly from the crest to the root.

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First Claim