Method and apparatus for extruding polytetrafluoroethylene tubing

Claim 1

EXTRUSION APPARATUS PARTICULARLY ADAPTED FOR PRODUCTION OF THIN-WALL TUBING OF TETRAFLUOROETHYLENE RESIN COMPRISING IN COMBINATION A HOLLOW MANTLE AND A DIE CONSTITUTING A CONTINUATION OF SAID MANTLE, SAID DIE HAVING A FIRST TAPERED CIRCULAR INNER SURFACE, A SECOND TAPERED CIRCULAR INNER SURFACE MERGING INTO THE SMALLER END OF SAID FIRST TAPERED SURFACE, AND A CYLINDRICAL INNER SURFACE MERGING INTO THE SMALLER END OF SAID SECOND TAPERED CIRCULAR INNER SURFACE AND COMPRISING A CYLINDRICAL NOZZLE, A MANDREL CENTRALLY LOCATED WITHIN SAID MANTLE AND DIE AND SPACED APART THEREFROM, SAID MANDREL HAVING AN OUTER TAPERED CIRCULAR SURFACE MERGING INTO AND TERMINATING IN AN OUTER CYLINDRICAL SURFACE AT THE SMALLER END THEREOF, SAID TAPERED CIRCULAR OUTER SURFACE OF SAID MANDREL LOCATED OPPOSITE SAID SECOND TAPERED CIRCULAR INNER SURFACE OF SAID DIE AND SAID CYLINDRICAL OUTER SURFACE OF SAID MANDREL LOCATED WITHIN SAID CYLINDRICAL NOZZLE OF SAID DIE AND SPACED APART THEREFROM TO DEFINE AN ANNULAR OPENING IN SAID NOZZLE, SAID SECOND TAPERED CIRCULAR INNER SURFACE OF SAID DIE AND SAID TAPERED CIRCULAR OUTER SURFACE OF SAID MANDREL HAVING HELICAL GROOVES WHICH PROGRESSIVELY DECREASE IN DEPTH TOWARD THE SMALLER ENDS OF SAID TAPERED SURFACES, THE DEPTH OF SAID GROOVES IN SAID MANDREL AND DIE BEING FROM ABOUT 2 TO ABOUT 5 TIMES THE DISTANCE BETWEEN SAID TAPERED SURFACES MEASURED AT OPPOSING LANDS AT EACH POINT ALONG THE AXIS OF SAID MANDREL AND DIE, SAID GROOVES AND LANDS BETWEEN SAID GROOVES HAVING SMOOTH CURVED SURFACES, SAID GROOVES IN THE CIRCULAR TAPERED SURFACE OF SAID MANDREL HAVING A DIRECTION OF ROTATION OPPOSITE TO THAT OF SAID GROOVES IN THE SECOND TAPERED CIRCULAR INNER SURFACE OF SAID DIE, THE CROSS-SECTIONAL AREA OF THE ANNULAR SPACE BETWEEN SAID TAPERED CIRCULAR INNER SURFACE OF SAID DIE AND SAID TAPERED CIRCULAR OUTER SURFACE OF SAID MANDREL DECREASING OVER THE GROOVED PORTIONS THEREOF WITH DISTANCE TOWARD THE SMALLER ENDS OF SAID TAPERED CIRCULAR SURFACES BY FROM ABOUT 50 TO ABOUT 95 PERCENT, A RAM CAPABLE OF RECIPROCATION WITHIN SAID HOLLOW MANTLE AND SURROUNDING SAID MANDREL, AND MEANS FOR PROVIDING SAID RAM WITH RECIPROCATING MOVEMENT.