An axially elongated extruder screw
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 respective one of the second or the third surfaces of revolution, each 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.
A single screw extruder having a screw body including an axially extending extruding portion defined by a feed section at an inlet end of said screw, a metering section at an outlet end of said screw and a barrier section between said feed and metering sections, at least one helical primary flight extending about and coaxial with said screw body, said primary flight and said screw body cooperating to form a channel in said feed section for conveying resinous material from said feed to said barrier section; said barrier section further comprising: at least one helical secondary flight extending from said primary flight about said screw body, said screw body defining a helical first surface of revolution between said primary and secondary flight at least one helical tertiary flight positioned between said primary and secondary flights and extending about said screw body, said screw body defining a second helical surface of revolution between said secondary and tertiary flights, and a third surface of revolution between said primary and secondary flights, said second and third surfaces of revolution extending axially along said barrier section; a respective one of said second and third surfaces of revolution defining a series of circumaxially contiguous cam-like forms, each cam-like form being defined by a segment of said screw having a root, a crest, a first surface portion extending radially outwardly from said root to said crest in the direction of screw rotation, and a second surface portion extending radially inwardly from said crest to said root; and wherein the other of said second and third surfaces of revolution and the first surface of revolution is substantially planar and free from any surface undulations.