| 摘要 |
1,272,808. Making heat-shrinkable thermoplastic tubing. D. S. MURRAY. 25 Aug., 1969 [30 Aug., 1968], No. 42193/69. Heading B5A. Heat shrinkable thermoplastic tubing is made by advancing a thermoplastic tube along a path and maintaining therein a difference in internal pressure levels at adjacent portions of the path by means of a plurality of clamping means which successively engage the tube and move with it, one of the clamping means being in engagement with the tube at any instant. As shown, an extruded tube 4, internally supplied with air, is initially cooled in a liquid bath 7 and is then engaged by clamps 12, 13 on endless chain pairs 14, 15 and 17, 18 respectively, before passing to a heating and expansion zone and subsequent cooling zone within a chamber 24. Chamber 24 comprises a tubular sizing member, preferably perforated and preferably having a continuous belt passing therethrough which forms a sheath around the tubing. The upstream portion of the sizing member is enclosed in a hot air bath or is subjected to steam or radiant heating and expansion of the tubing may be assisted by applying a vacuum. The downstream portion is cooled, e.g. with water or brine, with or without the application of a vacuum. Pressures within the tubing are further controlled by plates 9 adjustable towards and away from each other, and draw-off rollers 25. Chain pairs 14, 15 and 17, 18 are adjustable transversely of the tubing by rotation of screw 23, see also Fig. 2 (not reproduced). In modifications, liquid bath 7 may be replaced by air cooling means, plates 9 may be replaced by rollers, and rollers 25 by caterpillar tracks. Clamps 12, 13 may be of rubber or felt, the sizing member belt of P.T.F.E.-coated fibre glass and the tubing may be of P.V.C. |
