Extrusion apparatus

An extruder screw for use in processing a thermoplastic resin, comprising a shaft having in sequence a feed section, a transition section, and a metering section, a screw flight beginning in said feed section and ending in said metering section, said screw flight being helically wound and attached to said shaft, the helix angle in the feed section of said screw flight being constant and between 10.degree. and 25.degree., the helix angle in the metering section being constant and between 25.degree. and 35.degree., the helix angle in the transition section varying from the helix angle of the feed section to the helix angle of the metering section.

An extrusion apparatus for processing a thermoplastic resin comprising a barrel portion with grooves within the feed section and an extruder screw extending the length of the barrel and having in sequence from the feed section end, a feed section, a transition section, and a metering section;

• the core of said screw being helically wound with a flight of constant helix angle in the feed section, the helix angle being between 10.degree. and 25.degree., the helix angle of the flight in the metering section being constant and between 25.degree. and 35.degree. and the helix angle in the transition zone constantly increasing from the helix angle of the feed section to the helix angle of the metering section;
• the length and number of the grooves in the metering section being determined to supply substantially the maximum feed rate of thermoplastic resin to the transition and metering sections without deflecting the extruder screw into the barrel.