Apparatus for forming thin plastic tubing

Claim 1

IN AN APPARATUS FOR FORMING FOLDED PLASTIC TUBING COMPRISING MEANS FOR VERTICALLY EXTRUDING A TUBULAR ELEMENT OF THIN PLASTIC MATERIAL AT A TEMPERATURE ABOVE ITS DEFORMATION TEMPERATURE AND BELOW ITS LIQUID PHASE TEMPERATURE, MEANS FOR INFLATING SAID TUBULAR ELEMENT WITH A GAS AT A PRESSURE ABOVE ATMOSPHERIC PRESSURE BEFORE SAID ELEMENT COOLS BELOW SAID DEFORMATION TEMPERATURE, A SIZING AND COOLING SLEEVE ADJACENT THE EXIT END OF SAID EXTRUDER MEANS AND SURROUNDING SAID EXTRUDED TUBULAR ELEMENT, SAID SLEEVE HAVING AN INNER SIZING AND COOLING SURFACE WITH A PERIPHERAL SHAPE CORRESPONDING TO THE DESIRED FINAL PERIPHERAL SHAPE OF SAID PLASTIC TUBING AND SAID SURFACE HAVING A LENGTH SUFFICIENT TO COOL SAID ELEMENT BELOW SAID PLASTIC DEFORMATION TEMPERATURE, SAID SLEEVE HAVING A COOLING CHAMBER IN HEAT EXCHANGE RELATIONSHIP WITH SAID INNER SURFACE, THE IMPROVEMENT COMPRISING: SAID SLEEVE BEING SPACED FROM SAID EXTRUDING MEANS BY A CHAMBER SURROUNDING SAID TUBULAR ELEMENT AND HAVING INNER DIMENSIONS GREATER THAN THOSE OF SAID SIZING SLEEVE, AND MEANS FOR FILLING SAID CHAMBER WITH A GAS AT A PRESSURE SUBSTANTIALLY THE SAME AS THE GAS PRESSURE USED TO INFLATE SAID TUBING.