Apparatus for extruding molecularly oriented pipe of thermoplastic resin

Claim 1

AN EXTRUSION HEAD FOR THE EXTRUSION OF MOLECULARLY ORIENTED THERMOPLASTIC PIPE COMPRISING A CIRCULAR DIE, MEANS TO COOL THE SAID DIE, A HOLLOW COMICAL MANDREL AXIALLY DISPOSED TO SAID DIE, SAID MANDREL HAVING AN OPEN AND WIDEST END LOCATED WITHIN THE SAID DIE AND PROTRUDING BEYOND THE SAID DIE TO A CLOSED AND NARROW END, SAID MANDREL HAVING A PLURALITY OF PERFORATIONS DISPERSED OVER THE CONICAL SURFACE OF THE MANDREL IN COMMUNICATION WITH THE INTERIOR THEREOF, MEANS COOPERATIVELY ASSOCIATED WITH THE MANDREL TO ROTATE THE SAID MANDREL ABOUT THE AXIS THEREOF, SAID DIE AND SAID MANDREL BEING CONSTRUCTED AND ARRANGED SUCH THAT WHEN MOLTEN THEROPLASTIC IS FORCED THROUGH SAID EXTRUSION HEAD A MINOR PART OF SAID MOLTEN THERMOPLASTIC FLOWS OUTSIDE SAID MANDREL TO FROM A SKIN DEFINING THE OUTER SURFACE OF SAID PIPE AND A MAJOR PART OF THE SAID MOLTEN THERMOPLASTIC FLOWS OUTWARDLY THROUGH THE PERFORATIONS OF THE SAID HOLLOW MANDREL.