Plastic extrusion and apparatus

Screw extruder apparatus for plasticizing thermoplastic material and issuing said material from an orifice comprising an elongated hollow barrel having an axial bore therein adapted to receive raw thermoplastic material from a source thereof and containing an axially disposed, rotatable extruder screw for plasticizing, advancing and melting thermoplastic material, a passage communicating with said bore and operatively connecting an exit orifice with said bore, said barrel having a low pressure end where raw thermoplastic material is received and a high pressure end from which plasticized melted material is delivered to said passage, said screw containing an elongated hollow internal axial cavity, bored through the end of the screw that is positioned in the high pressure end of said barrel and extending part way toward said low pressure end, seal means intermediate the ends of the hollow portion of the screw which prevents passage of plastic material across said seal means between said barrel and said screw, lateral passageways through the shaft of said screw, leading into said axial cavity from near the pushing side of the flights of said screw that are adjacent said axial cavity and are on the low pressure side of said seal means, the flights of said screw between said low pressure end and said seal means being pitched to advance plastic toward said seal and the flights of said screw that are on the high pressure side of said seal means being oppositely pitched to advance toward said seal means the material that issues through the end of the screw from said cavity, said passage connecting said bore and said orifice being located in the sidewall of said barrel near the high pressure side of said seal means.