GB959951A - Apparatus for the two-dimensional stretching of films and other sheets of organic polymeric materials - Google Patents

Abstract

959,951. Film - stretching apparatus. BADISCHE ANILIN-&-SODA FABRIK A.G. Nov. 25, 1960 [Nov. 27, 1959], No. 40539/60. Heading B5B. An apparatus for stretching fibres of synthetic thermoplastic polymeric organic material simultaneously in the longitudinal and transverse directions comprises four endless conveyer belts 1 (Figs. 1 and 2) arranged in pairs which are symmetrically disposed with respect to the longitudinal axis of the film. The filmgripping runs of the belts are guided by a number of vertical profiled guide pulleys 2 in such a way that they follow curved paths having a radius of curvature which continually increases in the direction of travel of the film, the paths becoming straight towards the outlet end of the apparatus. At the ends of the paths defined by the guide pulleys 2, the conveyer belts pass upwards over the vertical driven pulleys 3 on the shaft 6 and the return runs of the belts then travel via the horizontal guide pulleys 4 to and round the vertical pulleys 5. The runs of the conveyer belts which are in frictional contact with the edges of the film lie in the planes of travel of the upper and lower surfaces of the film, the belts of each pair of belts (of which, in Fig. 1, the upper belt of the left-hand pair of belts is shown) being arranged so that the edge of the film is gripped between the lower run of the upper belt and the upper run of the lower belt. The guide pulleys 2 urge the belt gripping runs of one or both belts into contact with the edges of the film. The guide pulleys for the lower run of the upper belt 1 are superposed on the corresponding guide pulleys for the upper run of the lower belt (Figs. 2, 3 and 4). As shown in Fig. 3, the upper pulley 2 is mounted on a support which is pivotally mounted at 10 on the support 11 of the lower pulley 2 and which is urged by a spring 12 downwards so that the upper pulley 2 is urged towards the lower pulley 2. As shown in Fig. 4, the two guide pulleys 2 are inclined to each other in order to counteract more readily the lateral pull acting on the beltgripping runs of the pair of conveyer belts as a result of the transverse tension applied to the film. The support 14 of the upper pulley is arranged to function as a spring, urging the upper pulley downwards. The curves along which the belt gripping runs of each pair of belts travel are concave with respect to the longitudinal axis of the film. The angle # at any point of each curve between the tangent and a straight line passing through the point and at right angles to the longitudinal axis of the film continually increases in the direction of travel of the film and finally becomes a right angle. The longitudinal stretching of the film is effected by the continual increasing of the angle #. The film is continuously withdrawn from the stretching zone by the draw-off roller 7. The apparatus may comprise at least eight conveyer belts arranged in pairs, all pairs of belts being driven at the same speed or individual pairs of belts being driven at speeds increasing in the direction of travel of the film.