Web stretching apparatus

• Main Authors: NICHOLAS DONALD CAMERON, HEMPSTEAD JAMES WILLIAM
• Format: Patent
• Language: English
• Published: 18.09.1963
• Subjects: AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING; PERFORMING OPERATIONS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDEDFOR; SHAPING OR JOINING OF PLASTICS; TRANSPORTING; WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL

Apparatus for continuously stretching a moving web of material, particularly a web of film consisting of organic thermoplastic material, includes two endless articulated chains, means for guiding and driving each chain in a predetermined closed path, the guiding and driving means co-operating to ensure that in operation at the commencement of a working run of each chain the links thereof are folded in zig-zag fashion and are expanded in the course of their movement along said working run, the working runs of the two chains being positioned to extend along opposite sides of a moving web being stretched, and a plurality of web holding means mounted on each chain at intervals therearound so that the spacing of the holding means varies according to the degree of folding of the links of the chains, the holding means being actuable to hold the sides of a moving web at the commencement of said working runs and to release the moving web at the end of said runs whereby in operation the moving web is stretched as a result of the increase in the spacing of the holding means while they are holding the web consequent upon the expansion of the links of the chains in the course of their movement along said working runs. The chains may be disposed so that they diverge in the direction of travel of the web over at least a part of their working runs, as a result of which the web is simultaneously stretched in both the longtitudinal and the transverse directions. The chains may be arranged so that they are parallel over part of their working runs and this part of their working runs may follow the part of their runs over which they diverge. In the parallel part of their working runs the chains may be guided so that no further expansion of their links occurs. As shown in Figs. 1 and 2, the apparatus comprise a main frame 1 and a vertical frame 2 on which are mounted two chain units 3 and 4 in a vertical plane. The chain 6 (Fig. 3) of each chain unit mounts a plurality of holding means 5 which are carried around in a closed path by the chain and over the working run of the chain 6 hold an edge of the web 7 being stretched at spaced intervals. Opposite edges of the web 7 are held by the holding means 5 of the respective units 3, 4 and the working runs of the chains 6 diverge over part of their length and at the same time the spacing of individual holding means 5 increases as the result of which the web 7 is stretched both widthwise and lengthwise in its passage between the units 3, 4. The web 7 to be stretched is supplied from a supply roll 9 (Figs. 1 and 2) under tension and is passed successively over an idler roll 16, two heated rolls 17, 18 and idler roll 19 before passing between the units 3, 4. The rolls 17, 18 and the units 3, 4 are driven by a variable speed motor 35. The drive to roll 17 is by a belt and pulley drive 36 to a variable gear-box 37 and thence via a belt and pulley drive 38 including a jockey pulley 39. The drive to roll 18 is taken off a vertical shaft 40 via a bevel <PICT:0936965/IV(a)/1> <PICT:0936965/IV(a)/2> <PICT:0936965/IV(a)/3> <PICT:0936965/IV(a)/4> <PICT:0936965/IV(a)/5> <PICT:0936965/IV(a)/6> gear 44 and a gear train 45 to 48. The web 7 in leaving the units 3, 4 passes around rolls 20, 21 and in passing around roll 21 the edges of the web are trimmed by knives 25, 26. The web 7 is then drawn through mangle rolls 22, 23 and passes successively either around idler rolls 31, 32 and 33 to take-up roll 13 of unit 11 or around rolls 31, 32, 33 and 34 to take-up roll 12 of unit 10, the units 10, 11 being used alternately and being individually powered by variable speed motors 14, 15. Roll 22 is driven by a variable speed motor 24. Each chain unit 3, 4 is driven by an endless toothed driving chain 49 (Fig. 3) carried by two sprockets 50, 51 of which sprocket 50 is driven by drive shaft 40 (Fig. 2) through shafts 55, 54, flexible coupling 53 and shaft 52. The endless articulated chains 6 of the chain units 3, 4 are each mounted between parallel plates 57, 58 held apart by spacers 79 (Fig. 3) and the units are mounted by means of these plates respectively on opposite sides of the vertical frame 2 (Figs. 1 and 2). Each chain 6 is guided in a closed path (Fig. 3) having two generally parallel runs 59, 60 and two arcuate ends 61, 62. The greater part of the parallel run 59 constitutes the working run of the chain at the commencement of which the links of the chain are fully folded upon one another in zig-zag fashion and at the end of which the links are fully unfolded. The two first portions of the two working runs 59 of the two chains 6 diverge symmetrically from the central line of the web 7, while the two second portions are parallel. The chains 6 are disposed in planes parallel to the plane of the web 7 being stretched. Each link of each chain 6 has spaced elongate flat side members 63, 64 defining a slot between which the teeth 65 of the driving chain 49 can extend (Figs. 3 and 4). The pivotal connection between adjacent links of the chain 6 comprises a pivot pin 66 upon which a spacer sleeve 67 is rotatably mounted (Figs. 4 and 5). The sleeve serves to space the members 63, 64 apart and the inner pair of members 63, 64 at each pivotal connection are pivotally mounted respectively on reduced end portions of the sleeve. The outer pair of members 63, 64 at each pivotal connection engage bearing bushes 68 pivotally mounted on the pin 66 and abutting the ends of the sleeve 67. Each holding means 5 (Figs. 5 and 6) is carried by a mounting block 69 (Figs. 4 to 6) which is pivotally mounted by two spaced lugs 70, 71 at a pivotal connection between adjacent links of the chain for pivotal movement about the pivotal axis of that connection. The lugs 70, 71 respectively pivotally engage opposite ends of the pivot pin 66 of the connection. One such block 69 is mounted at alternate connections between the links and each block has two pins 72, 73 extending therethrough and disposed parallel to one another and to the pivot pin 66 of the pivotal connection. The ends of the pins 72, 73 mount ball races 74. The pivot pins 66 of the remaining alternate connections between the links also mount at both ends thereof ball races 75. In the inner surface of each of the parallel plates 57, 58 there are provided two separate endless grooves arranged opposite one another to provide two pairs of grooves 76, 77 in which run ball races 74 and 75 respectively so that the grooves and races constitute guiding means for the chain 6. At the upstream end run of the path of the chain the two pairs of guide grooves are spaced at their widest and consequently the links are folded. A rubber tyre 78 is mounted on a sleeve 80 freely journalled between the plates 57, 58 on a spacer 79 and is engaged around the end run 61 by those alternate pivotal connections between the links which are guided by the inner pair of grooves. Over the first portion of the working run 59 of the chain 6 the two pairs of guide grooves 76, 77 converge until, at the end of said portion, the links are fully expanded. Thereafter, over the second portion of the working run 59 of the chain 6, the two pairs of grooves 76, 77 run parallel and continue so over the downstream end run 62 and over the first portion of the return run 60, until over the second portion of the return run they diverge to contract the links preparatory to their engaging the rubber tyre 78. Each holding means 5 mounted on its block 69 comprises a fixed jaw 84 and a movable jaw 85 normally biased by a spring 86 into contact with jaw 84. Movable jaw 85 constitutes an arm mounted to be pivotable about the axis 87 and having on its extension 86a a roller 88 which serves as a cam follower. Two short cam plates 89, 90 are mounted on plate 58 one each at the end runs 61, 62 of the chain respectively adjacent the beginning and end of the working run 59 of the chain. These plates 89, 90 serve momentarily to open the jaws 84, 85 of the holding means as they are carried past by the chain 6 so that the web 7 is received between the jaws at the beginning of the working run and released at the end of the working run. Over the second or parallel portions of the working runs 59 of the chains no further stretching of the web takes place and in this zone the web may be allowed to cool without shrinkage if it has been stretched hot or may be annealed if it has been stretched cold.