Patent GB-1207918-A (GB)
Title: Film stretching
Inventor: ZYGAN HEIRONYMUS
IPC: B29C55/20
Filed: 1968-06-27
Abstract: 1,207,918. Stretching films. FARBENFABRIKEN BAYER A.G. 27 June, 1968 [4 July, 1967], No. 30687/68. Heading B5B. In apparatus for stretching. longitudinally and transversely, a beaded-edge thermoplastic synthetic resin film, the film 21 is held by a plurality of holding devices each of which comprises a driven contact pressure wheel 9 and a pair of driven, obliquely-positioned counter wheels 23, 24; means are provided for automatically adjusting the distance between wheel 9 and counter wheels 23, 24 according to the thickness of the beading, and for automatically adjusting the distance between counter wheels 23 and 24 according to the change in distance between wheel 9 and counter wheels 23 and 24. Thus the holding device of Fig. 1 comprises a first bearing member 2 supported on an arm 1 and a second bearing member 3 movable relatively to bearing member 2. Bearing member 3 carries a shaft 4 connected to the main drive (not shown), and bevel wheels 5 and 6. Wheel 6 is mounted near one end of shaft 8 which rotates in bearings 7 and carries at its centre contact pressure wheel 9. Gear-wheels 10, which mesh with gear-wheels 12 at the ends of shafts 11 are arranged at the ends of shaft 8. Grooves 13 in the form of circular arcs are formed in the bearing member 3, and have their centre of curvature Q on the mid-line of the width of the gear-wheels 12. Sliding arcs 14 of the slide members 15 which carry loose bearings 16 for the shafts 11 engage in the arcuate grooves 13. Each of the shafts 11 is also mounted by means of a fixed bearing 17 in slide members 18, which engage by means of sliding arcs 19 and corresponding circular arcuate grooves 20 of bearing member 2. The centre of curvature P of the circular arcuate grooves 20 and hence of the sliding arcs 18 must be situated outside film 21, substantially in the extension of the plane of the film, so that the obliquely set wheels 23 and 24 may adjust their distance a to each other automatically according to the thickness of the film at any given instant (Fig. 2), and the adjustment should be such that the distance a increases with an increase in the thickness b of the beading at the edge of the film. This automatic adjustment is effected in dependence upon the automatic adjustment of the distance between the wheels 23, 24 on the one hand and the contact pressure wheel 9 on the other as a result of the fact that these two adjustments are coupled together by the relative movement between the bearing member 2 arid the second bearing member 3. This coupling results from the fact that the shafts 11 are mounted both in the bearing member 2 and in the second bearing member 3. Spring 26 which is tensioned by a screw 25 acts on a lever mechanism 27, 28 to ensure that the obliquely set wheels 23, 24 and contact pressure wheel 9 will press sufficiently firmly against the surface of beading 22 which forms the edge of the film. The position of the different wheels in relation to each other is shown diagrammatically in Fig. 2, in which the distance between the centre of curvature or centre of rotation P of the circular arcuate grooves 19, 20 and the points at which the wheels 23, 24 touch the beading is indicated by reference c. Since the centre of rotation P of bearings 17 is not exactly at the mid-point of the shortest line joining the wheels 23 and 24 but is situated further out in the direction of the contact pressure wheel, displacement of the second bearing member 3 parallel with the first bearing member 2 causes the minimum distance a between the wheels 23 and 24 to increase because the parallel displacement causes a rotation of the slide members 18 and hence also of bearing 17. This distance a would remain constant only if P were situated exactly on the line connecting the two most closely adjacent points of the wheels 23 and 24. It is thus possible to adjust the distance a of each wheel pair 23, 24 as a function of the thickness b of the beading 22 existing at any particular moment at the position of this wheel pair 23, 24. The distance a is in this way not directly determined by the thickness of the film, but, since the reduction in thickness b of the beading progresses in parallel with the reduction in thickness of the film as the degree of stretching increases, the distance a necessary for the passage of the film is also a function of the thickness b, and the thickness of the beading is therefore suitable for adjusting the distance a indirectly. Since the bearings 16 for the shaft 11, although rotatable, are otherwise fixed in their connection with the second bearing member 3, gear-wheel pairs 10, 12 remain firmly in engagement with each other even when the beading at the edge of the film is thick, and merely undergo slight tiliting in relation to each other. In a preferred embodiment, the opening angle 2a of the wheel pair 23, 24 is about 6 degrees when the thickness of the beading is 0, and about 9 degrees when the thickness of the beading reached its greatest value of 10 mm. The holding device of Fig. 3 comprises a fixed bearing member 29 and a second bearing member 30 movable in relation to bearing 29. The driving force is transmitted from the main drive (not shown) to a gear-wheel 33, which is arranged on one end of the shaft 8 by way of a shaft 31 and a gear-wheel 32. Shaft 8 which carries contact pressure wheel 9 is rotatably mounted in a pivot bearing 34 in fixed bearing member 29. A gear-wheel 37, which is arranged at one end of a shaft 36 rotating in fixed bearings 35, meshes with the gear-wheel 33, whilst the other end of the shaft 36 carries the obliquely set wheel 23. The outer end of shaft 8 mounted in pivot bearing 34 on the second bearing member 30 which is made displaceable relatively to the first bearing member 29 by the spring 26 and the screw 25. Gear-wheel 10 meshes with gear-wheel 12 driving the shaft 11 which is loosely mounted in a pivot bearing 38. The second, fixed bearing 17 of shaft 11 is arranged on the slide member 18 which engages by means of the sliding arc 19 in the circular arcuate groove 20 in bearing member 20. The centre of curvature P of the arc and groove is situated outside the width of the film, substantially in the extension of the plane of the film. Using the apparatus of the invention, both the necessary width of the gap for the edge beading and the width of the gap for the film adjust themselves automatically so that disadvantages due to variations in film thickness are automatically avoided.