Improvements in or relating to apparatus for stretching tubes

摘要

1,074,459. Tubular film stretching apparatus. GENERALE ALIMENTAIRE G.A.S.A. Sept. 30, 1964 [Oct. 3, 1963], No. 39784/64. Heading B5B. As depicted in Fig. 1 (not shown) an apparatus for stretching a tubular film simultaneously in the longitudinal and transverse directions in a continuous manner comprises a pair of driven feed rolls 3 for feeding a tubular film 1 into a stretching zone A and a pair of draw rolls 4 driven at a higher peripheral speed than the feed rolls 3 for stretching the film 1 longitudinally in the stretching zone A and withdrawing it from the zone. A frusto-conical core body or mandrel 5 coaxial with the tubular film travelling through the stretching zone A extends from the inlet to the outlet of the stretching zone and is " freely floating " within the film, not being attached to any body located outside the tubular film. The mandrel 5 comprises an axial stem 6 provided with a number of radial blades 7 the outer edges of which are inclined to the stem 6 and form the external surface of the mandrel 5. The tubular film 1 on entering the stretching zone A is drawn over a cylindrical extension 7 of the mandrel 5 which has the same cross-sectional area as the lower end of the mandrel. The upper end of the stem 6 extends at 61 beyond the upper ends of the radial blades 7 (which form the upper broader end of the frusto-conical mandrel and which coincide with the outlet from the stretching zone A) towards the draw rolls 4. To the upper end of the extended stem portion 61 is secured a thin plate 8 on opposite sides of which are mounted two freely rotatable rollers 9 and 91. The passage of the tubular film 1 over the floating mandrel causes the latter to tend to rise towards the draw rolls 4 and to urge the rollers 9 and 91 against the inner surface of the tube. The tube is thereby urged against the rollers 10 which are freely rotatable but fixed in position with respect to the draw rolls 4. Upward movement of the mandrel 5 is thereby restrained. Rollers 10 and 101 are spaced sufficiently far apart to permit the passage of the flattened tubular film 1 between them and an extension 81 of the plate 8. Heating means are provided in the zone A and the tube is spontaneously or artificially cooled during its passage through zone B.