Patent GB-1091971-A (GB)
Title: Web stretching apparatus
Inventor: NICHOLAS DONALD CAMERON
IPC: B29C55/16
Filed: 1963-08-28
Abstract: 1,091,971. Film stretching apparatus. BAKELITE XYLONITE Ltd. Aug. 28, 1964 [Aug. 28, 1963], No. 34121/63. Heading B5B. [Also in Division D1] Apparatus for stretching a moving web of material, especially plastics material, e.g. polythene and polypropylene, comprises in combination first and second stretching units 7, 8 (Fig. 2) disposed on opposite sides of the web and each comprising an endless articulated link chain, a plurality of web grippers (Fig. 4) mounted on the chain at intervals along the length thereof in such manner that the spacing between adjacent grippers varies according to the degree of folding of the chain links, means for guiding the link chain along a closed path having an entrance portion 9, a divergent portion 13 and an exit portion 10, pivotal connections between said portions 56, 58, in Fig. 3, or 83, 85 in alternative apparatus of Fig. 8, means for causing the web grippers to grip and hold said web at the commencement of the entrance portion and to release the web at the end of said exit portion (cam rail 42), drive means for progressing said link chain along said closed path (driving sprockets 24, 69) desirably including also means for maintaining the tension in the link chain at a predetermined value (guide tracks 25, 26 formed as grooves 30, 31 in the upper and lower plates 17 and 18, or tracks 81, 82 in the apparatus of Fig. 8) and drive means for moving the entrance and exit portions towards and away from the longitudinal axis of the web (leadscrews 20, 65). The means for guiding the link chains preferably includes a section located in the entrance portion which is movable relatively to said portion in such manner as to control the degree of folding of the chain links whilst being progressed along that portion (plates 48, 49, Fig. 6, containing guide tracks 45, 46 and operated by leadscrews 53). Such a movable section may be slidably mounted in slots on the spaced members forming the entrance portion. Alternatively or additionally, a similar movable section may be located in the exit portion (parts 87, 88, 88a of Fig. 8). As shown, the web grippers comprise a mounting bracket 27, upper and lower supporting rollers 29, 44 rotatably supported upon the bracket, and a web gripper lever 37 pivotally supported upon the bracket in such manner that the lever engages the web at a grip point which is substantially coincident with the axes of rotation of the rollers. In operation, the web is led from supply reel 1 (Fig. 1) through feed rolls (not shown) and station 3 where the web is heated and tensioned if necessary to the tenter frame 4 where it is stretched both longitudinally and transversely, thence to trimming station 5 and hence to the take-up reel 6. Axial stretching is effected by opening up the links of the chain, thus increasing the distance between the web holding devices (vide Fig. 3) and adjustment of axial stretching is effected by variation of the distance between the guide tracks in the entrance and/or exit portions of the chain path in the apparatus of Figs. 3 and 8, respectively, by the mechanism described above, which is operated by leadscrew mechanisms (Figs. 7 and 9, not reproduced). Transverse stretching is effected by the divergence of the chains with respect to the web, and adjustment thereof is effected by movement of the divergent portion of the track. Thus plates 57 are mounted on rollers 59 which move over support guideways 60 mounted upon the frame, and similarly the plates 84 are supported on rollers 85 which move over support guideways 86 similarly mounted. Adjustment of both axial and transverse stretching ratio may be made while the apparatus is in use.