GB1013627A - Improvements in and relating to apparatus for stretching sheet material - Google Patents

Abstract

1,013,627. Stretching sheet material. BAKELITE XYLONITE Ltd. Sept. 21, 1964 [June 19, 1963; June 2, 1964], Nos. 24487/63 and 22840/64. Heading B5B. Apparatus for stretching sheet material comprises two sets of grippers 1 mounted on endless guide tracks 2 below which is located driving means for the grippers comprising a rotatable frusto - conical member 3 (Fig. 1). Each gripper consists of a body 6 having a slot 7 in which a web is held by spring- loaded pin 9. The body 6, which may be straight (Fig. 4) or bent (Fig. 2) is mounted on bogie 12 provided with wheels 13-16 which engage rails 17 forming the guide tracks 2. Rotatable wheels 20 on each gripper are mounted so that their axes are neither parallel nor perpendicular to the direction of the rails 17, and the rails are so formed that the wheels contact the surface of the rotatable driving member 3 and make an acute angle with the direction of movement of its surface. In operation, a web 24 is fed to A where cams raise pins 9 and enable the edges of the web to be gripped. The grippers are urged along their tracks by a star-wheel or the like operating at A. At B, where the tracks 2 diverge, the angle between the axes of the wheels 20 and the direction of movement of the contacting rotating surface 3, the speed of which increases towards its larger diameter, causes the grippers to be accelerated towards the other end of divergent zone 5. Cams operating at C disengage the biaxially stretched web, which is then taken up on a roll. In one embodiment, the guide tracks run parallel so that the film is only longitudinally stretched. Acceleration of the grippers may be effected also by varying the angle of inclination of the axes of the wheels to the direction of movement of the rotating driving member, which in this case is a right cylinder, or by a combination of this with variation in the surface speed of the driving member. Heating means, e.g. an oven, air blower or radiator, may be provided in the stretching zone and cooling means may be provided for the stretched web. Return of the grippers to their starting point may be effected by gravity, hooked belts, or series of movable members operating in the same way as driving means 3. The grippers in each set may be disconnected or connected by a resilient material. An increased stretching force may be achieved by providing supplementary driving means, e.g. a rack and pinion, for the grippers. In other embodiments, the rotating frusto-conical driving member 3 is replaced by a rotating disc, series of endless belts or cylinders, driven at successively increasing speeds, or a series of interconnected frusto-cones (Fig. 8). Also, each set of grippers may be provided with its own driving surface or surfaces, which in one embodiment are located both above and below the grippers (Fig. 13). The degree of stretch of the web may be altered by moving the rotating driving surfaces in the direction of movement of the grippers, or by changing the rate of alteration of the angle of inclination of the wheel axes to the direction of movement of the surface of the driving member, or, when a series of discontinuous driving members are used, varying the speeds of each member relative to each other. Also, the guide tracks may be moved together or apart, and the angle between the divergent parts of the tracks may be varied. The guide tracks may also be of telescopic construction. The apparatus may be applied to the stretching of textile materials or films of polymeric material, e.g. polystyrene, polyvinylchloride, polyethylene terephthalate or polypropylene.