GB744768A - Apparatus for stretching webs - Google Patents

Abstract

<PICT:0744768/IV(a)/1> <PICT:0744768/IV(a)/2> <PICT:0744768/IV(a)/3> A machine for simultaneously stretching synthetic web material in both lateral and longitudinal directions comprises, on each side of the feed axis A-A of the material W, Fig. 1, web grippers mounted on regularly spaced pins 18 of a pin-and-link extensible chain 12, a sprocket 19 of maximum pitch and a sprocket 20 of minimum pitch engaged by the pins and pivoted on a bedplate 1, 2 the position of which is angularly adjustable about a pivot 4 with respect to axis A-A, and an adjustable guide rail 30 incorporating a cam surface 36 with which the links 14 of the chain co-operate to control the degree of pivot and the distance apart of the links. The link pins 18 are guided, as they travel between sprocket 20 and a guide roller 21, between a guide plate 35 carried by rail 30 and a guide rail 29 fixed to the bedplate. Rails 30 are <PICT:0744768/IV(a)/4> pivoted to the bedplate at 31. By operating a lead-screw 8, the divergence of rails 29 can be adjusted to control the degree of lateral stretch imparted to the web. By operating screws 32, the divergence of each cam surface 36 from the corresponding rail 29 can be adjusted to control the degree of expansion of the chain links and hence the degree of longitudinal stretch of the web. As shown, Figs. 2-4, each chain is constructed as described in Specification 744,805, [Group XXV], and consists of flat links 14 arranged in rows both above and below guides 29, 35 and pins 18, each of which passes through a pivot hole 15 in one link and a slot 16 in an adjacent link, each link having both a pivot hole and a slot. The slot is inclined at an angle F to the length of the chain in its closed position, so that tension of the chain will tend to expand the links from a minimum pitch of x to a maximum pitch of nx. The tip 17 of each link is shaped to coact with cam surface 36 which thereby controls the degree of pivoting of the links. The divergence of rails 29, 30 ensures that the links are continuously expanded between sprocket 20 and roller 21. A linkrealigning unit 38 is located between sprocket 19 and sprocket 20 and has a converging cam surface for contracting the chain links. The chains may be driven through their sprockets 19 alone, or sprockets 20 may be driven also through suitable gearing. Each web-gripper comprises a gripper arm 23 and a base-plate 27 carried by a bracket 22 mounted on a link-pin 18 and is kept in alignment by engagement of a slot 26 in bracket 22 with an adjacent pin. The bottom of each arm 23 may be rounded as shown or the arm may be fitted with an elongated flat plate provided with pins to pierce the web. Cam surfaces 42, 37 are provided for raising the arms, whech engage the webs by gravity or under the action of similar cam surfaces. The links 14 in each row may be stacked in pairs, or in units of three or four, the slot 16 in each link may be curved, instead of straight, so as to provide a constant angle of inclination to the line joining the pins and hence a constant link-expanding force. The web material may consist of a film of polyethylene terephthalate, nylon, polyethylene, vinyl resins, cellulose derivatives, rubber hydrochloride or polystyrene. By adjusting the bedplates 1, 2 so that the path of pins 14 is parallel to the sides of the web, longitudinal stretching only may be accomplished.