Manufacture of plastic film and tubing

Claim 1

IN APPARATUS FOR PRODUCING SYNTHETIC RESINOUS THERMOPLASTIC TUBING AND SHEETING, AN EXTRUDER FOR EXTENDING HEATED SYNTHETIC RESINOUS THERMOPLASTIC TUBING IN NONSELF-SUSTAINING CONDITION, A HOLLOW FORMER OF HEAT CONDUCTIVE MATERIAL TO RECEIVE TUBING WHEN ENTRUDED WHILE IN NON-SELF-SUSTAINING CONDITION IN DIRECT CONTACT WITH THE FORMER AND WITHOUT INTRODUCING FLUID BETWEEN FORMER AND TUBING, CONDUITS FOR CIRCULATING A GAS UNDER PRESSURE WITHIN SUCH TUBING TO EXPAND SUCH TUBING TO THE INTERNAL SIZE OF THE FORMER, THE SURFACE OF THE FORMER IN CONTACT WITH SUCH TUBING WHEN BEING EXTRUDED IN NON-SELF-SUSTAINING CONDITION BEING DISCONTINUOUS, AND CONDUITS FOR CIRCULATING IS A PIPE OF COPPER COIL HAIVNG A NUMBER OF TURNS IN SUBSTANTIAL SIDEWISE CONTACT WITH ONE ANOTHER, THE ENDS OF THE COIL SERVING AS INLET AND OUTLET RESPECTIVELY FOR A FLUID CIRCULATED INTERNALLY THROUGH THE COIL.