Manufacture of plastic tubular film

Abstract

Abstract A METHOD OF FORMING AN EXTRUDED TUBE OF PLASTIC MATERIAL COMPRISING EXTRUDING THE MATERIAL IN A SEMI-MOLTEN STATE AS A TUBULAR FILM, HAVING A WALL OF GREATER THICKNESS THAN THAT OF THE FINISHED TUBE, LOCATING A FIRST FORMER WITHIN THE TUBE NEAR THE EXTRUSION POINT, PASSING THE FILM OVER THE FACE OF THE FORMER IN CLOSE PROXIMITY THERETO, LOCATING A SECOND FORMER AT A POINT MORE REMOTE FROM THE EXTRUSION POINT, PASSING THE FILM OVER THE FACE OF THE SECOND FORMER IN CLOSE PROXIMITY THERETO, DIRECTING A HIGH VELOCITY STREAM OF AIR AGAINST THE INNER FACE OF THE FILM FROM BELOW THE FIRST FORMER AND CREATING A FURTHER HIGH VELOCITY STREAM OF AIR AGAINST THE INNER FACE OF THE FILM AND BETWEEN IT AND THE SECOND FORMER, EXTRACTING AIR FROM THE SPACE BETWEEN THE TWO FORMERS TO MAINTAIN THE AIR PRESSURE IN SAID SPACE BETWEEN THE FORMERS AT OR BELOW ATMOSPHERIC PRESSURE, SAID STREAMS OF AIR MOVING AT A VELOCITY SUFFICIENT TO PREVENT ACTUAL CONTACT BETWEEN THE FILM AND THE FORMERS, AND ARRANGING THAT THE FREEZE ZONE OF THE FILM IS IN THE REGION OF MAXIMUM DIAMETER OF THE SECOND FORMER AND PREFERABLY BETWEEN THE POSITION OF MAXIMUM DIAMETER AND THE DOWNSTREAM END THEREOF. THE DIAMETER OF THE TUBE BEING EXTRUDED CAN BE VARIED BY VARYING THE DIAMETER OF THE SECOND FORMER. IN ORDER TO OBTAIN STILL GREATER SPEEDS OF EXTRUSION EXTERNAL COOLING CAN BE APPLIED.

Inventors

• 👤 Bernard K Bigland

Bibliographic Details