Patent GB-1075704-A (GB)
Title: Process and apparatus for producing elastic memory articles
Inventor: WRAY PIERRE EDWARD
IPC: B29C48/90
Filed: 1964-09-07
Abstract: 1,075,704. Dimensionally heat - unstable hollow articles; moulding. RAYCHEM CORPORATION. Sept. 7, 1964 [Sept. 26, 1963], No. 36614/64. Headings B5A and B5B. Dimensionally heat-unstable hollow articles are made by (1) passing a tube of crystalline or cross - linked crystalline polymeric material through a heating zone open to the atmosphere to heat the tube to a temperature equal to or above its crystalline melting temperature or range, (2) while the tube is at this temperature, passing the tube through a zone of partial vacuum to impart a pressure differential between the inside and outside of the tube, the pressure differential being insufficient to bring about a change of dimensions of the tube equal to the desired predetermined change of dimensions while the tube is at a temperature greater than the crystalline melting temperature or range, but being sufficient to cause a predetermined dimensional change when the tube is cooled through the crystalline melting range of the polymer, and (3) passing the tube through a cooling zone, while maintaining the pressure differential so as to cool the tube below the crystalline melting temperature or range, and to set the tube at its changed and predetermined dimensions. Superatmospheric pressure may be applied to the interior of the tube throughout the process. The crystalline polymer, e.g. polyvinyl chloride, polyethylene, polytetrafluorethylene, neoprene or silicone rubber, may be cross-linked by irradiation of at least 2 x 10<SP>6</SP> rads or by chemical means equivalent to such an irradiation dose. The polymer may be blended with an elastomer to produce an elastomeric tubing. Apparatus for use on the process comprises means for supplying heat to the tubing while the external surface thereof is subjected to substantially atmospheric pressure, a chamber provided with inlet and outlet means, and means for cooling the tubing passing through the chamber, the interior of which is adapted to be maintained at a pressure substantially different from atmospheric, the arrangement being such that the tubing is raised to a desired temperature before passage through the chamber. In one embodiment (Fig. 1), irradiated polyethylene tubing 11 is continuously fed into tank 15 containing heated oil. The tube, into the interior of which air under pressure is continuously fed from tank 70, then enters expansion assembly 25, the interior of which is maintained under reduced pressure. As the tube passes through the expansion assembly, it expands as it cools to the final predetermined diameter 11a when the tube contacts the inside surface of cooling die 35. The expanded tubing then passes through final cooling and rinsing bath 60 and reeled at 66. The speeds of capstans 12 and 64, and rolls 20, 21 are adjusted so that the speed of the unexpanded tube in tank 15 ahead of roll 21 is sufficiently greater than that of the tube between roll 21 and capstan 64 so that no tension is applied to the unexpanded tube in tank 15. Expansion differential pressure is controlled by valve 51a. The expansion assembly (Fig. 3) comprises a cylinder 26 having end wall 27 provided with a removable sealing die 29. Mounted within the cylinder is a piston member 32 comprising ring 33 secured to cylindrical wall member 34 and to cooling die 35 comprising cylinder 36, end wall 37, rear wall 38, and inner cylinder 39 of a diameter equal to the desired final diameter of the tube. Coolant chamber 40 is supplied through inlet 41 and outlet 42. The spacing between member 32 and wall 27 may be adjusted by means of screw assemblies 47, and the partial vacuum in chamber 50 is imposed by vacuum line 51. The end wall 38 of the cooling chamber is sealed by rubber diaphragm 160.