Extruder providing radial and axial melt removal

Claim 1

An extruder having a rotatable screw and a barrel enclosing said screw; said screw comprising a core and a thread so interrelated in shape as to define a continuous spiral channel, and a melt section including a substantial portion of the length of the channel to terminate adjacent a front or material-discharging end of the screw; said thread and core being shaped through said melt section in the direction of material advancement to progressively decrease the depth of said channel without substantial change in its width and to define a progressive corresponding decrease in transverse cross section of said channel, said channel terminating adjacent a peripheral end sUrface of the screw having an annular clearance with the barrel; said thread having throughout said melting section of the extruder a rearside portion of full thread radius and a leading side portion of smaller radius between which a groove is formed; said screw having an interior axially-extending passageway and a series of openings extending radially from the groove to the passageway, said openings being distributed along the full length of the melting section to provide free flow of material from the groove to the passageway; said clearance of the end surface of the screw with the barrel being of a smallness as to force passage of substantially all flowable thermoplastic material from a high pressure region within said channel to a low pressure region within said groove and outwardly of the screw through said openings and said passageway.