Patent GB-968878-A (GB)
Title: A method and apparatus for continuously stretching film
Inventor: LAURIE KENNETH SOMERVILLE
IPC: B29C55/16
Filed: 1961-03-14
Abstract: 968,878. Film stretching apparatus. JOHN DALGLISE & SONS Ltd. June 14, 1962 [March 14, 1961], No. 9212/61. Heading B5B. Apparatus for the simultaneous longitudinal an lateral stretching of a web of film includes successive pairs of drawing devices adapted to act on edge portions of the film fed thereto in a taut state, each pair of drawing devices comprising two devices mutually angled divergently in the direction of travel of the film, disposed one at each edge portion of the film and each consisting of an endless chain or belt extending around first and second lower wheels of which one is driven, and an upper wheel pressing downwards on the chain or belt so as to form a nip for the film edge portions, the interspacing between successive opposed pairs and their drawing speeds being progressively increased. As shown in Figs. 3 and 4, the first drawing stage consists of two interspaced and opposed sets of three wheels 2, 3, 4 and 5, 6, 7 one being located at each edge of the film 1. In each of the sets two wheels 2, 4 and 5, 7 lie below the film and are connected by a chain 8, and the single upper wheels 3, 6 are urged down on top of the chain 8 between the two lower wheels. As shown in Fig. 3, the wheels 2, 3, 4 and 5, 6, 7 diverge outwardly in the direction of travel of the film, thus causing the film to be stretched transversely simultaneously with the longitudinal stretching of the film. In the second drawing stage, in each set of three wheels, the first wheels 9, 12 of the lower wheels 9, 11 and 12, 14 are on the same shaft as the last wheels 4, 7 of the lower wheels in the first drawing stage, and the first wheels 9, 12 run idle on their shafts, being driven at second stage speed by their chains 8A. The upper wheels 3, 6 and 10, 13 in said stages bear with positive pressure on the two lower wheels 4, 7 and 11, 14 only, but are sufficiently close to the first wheels 2, 5 and 9, 12 and to the connecting chain 8A to engage the edges of the film 1. As shown in Fig. 1, three gear-boxes 15 are provided at each side of the apparatus and each gear-box drives three overlapping drawing stages and contains simple driving gear to give the longitudinal draw at each stage. All six gear-boxes 15 may be identical, with the drive to each pair different in ratio. Each gear-box is driven by a 1 H.P. Selsyn motor 16 and a worm speed reduction gear 17, a master Selsyn motor, not shown, being connected by a final drive to draw rolls 18 and wind-up roll 19. The construction of the gear-box is described. As shown in Fig. 7, a mounting for the set of wheels 2, 3, 4 comprises a frame 47 carrying the wheels 2 and 4 and posts 48, 49 on which a cross-bar 50 is slidably adjustable vertically and carries the wheel 3. The bar 50 rests on compression springs 51, 52 and is height adjustable by a screw-threaded rod 53 captive at its lower end in the bar 50 and passing through a tapped hole in a crossbar 54 resting on shoulders on the posts 48, 49 and held by nuts 55, 56. The chains and chain wheels in each set of wheels may be replaced by pulley wheels and rubber belts, and the upper wheel in each set may be rubber faced and may be separately driven through gearing.