Patent GB-713841-A (GB)
Title: Improvements in or relating to the production by extrusion of thin-walled seamless tubes of thermoplastic materials
Inventor: BERRY WILLIAM
IPC: B29C48/10
Filed: 1951-03-30
Abstract: <PICT:0713841/IV (a)/1> Apparatus for the extrusion of thin-walled seamless tubing of thermoplastic material comprises an extrusion die provided with a flexible circular external lip, a pin substantially coaxial with the hole of the die and provided with a rigid circular internal lip, the flexible and rigid lips bounding the annular extrusion orifice formed therebetween, and contour-adjusting means for the flexible external lip, the contour-adjusting means operating between the flexible lip and a rigid reaction member mounted on the die.  The pin together with the rigid internal lip may be moved relative to the die, e.g. by means of adjusting bolts in opposed pairs at right-angles, for effecting coarse adjustment of the orifice.  The contour-adjusting means may comprise bolts, preferably capable of fine adjustment, arranged around the outer edge of the flexible external lip.  Alternatively, thrusting rods controlled by electrical solenoids, or hydraulic means comprising pistons actuated by controlled water-pressure, may be used.  The extruded tube of molten thermoplastic material may be inflated before it has solidified and it may be maintained in the expanded condition until it has solidified.  Driven nip-rolls may enclose an elongated bubble of compressed fluid inside the extruded tube between the die and the nip.  The flexible lip may be a replaceable strip of springy metal, e.g. nickel-plated spring steel.  The extruded tube may be caused to pass over a fluid-cooled mandrel, mounted co-axially with the orifice and having a larger diameter than that of the orifice.  The mandrel may be hollow and may be cooled by the circulation therethrough of water or other fluid.  It may be ring-shaped, cylindrical or conical, and it may be supported directly from the pin.  A blast of cold air may be directed on to the outside of the extruded tube.  The thermoplastic material from which the tube is made may be cellulose acetate or other cellulose ester, polyethylene, polyvinyl chloride, a vinylidene chloride/vinyl chloride copolymer, a styrene/isobutylene copolymer, a polyamide such as polyhexamethylene adipamide or a polyester such as poly-ethylene glycol terephthalate.  As shown, the molten film-forming material is forced through the annular orifice 1 in die 2, which is provided with a flexible circular lip 3, a pin 4 and a rigid circular internal lip 5.  Bolts 6 are arranged at regular intervals around the outer edge of lip 3 for adjusting the contour of the wall of the tube which is being extruded.  The bolts 6 operate between the lip and the rigid reaction member 7.  The hot extruded tube is passed over the water-cooled mandrel 9.  Water inlet and outlet conduits 11, 12 pass through pin 4.  The tube 8 is inflated by air supplied by tube 10.  By adjusting bolts 6, the contour of the lip 3 is adjusted so that tube 8 has a substantially uniform wall-thickness at all points of its periphery.  Tubes having a wall-thickness after solidification of 0.02 inch down to 0.0015 inch or less may be obtained.