Patent GB-1128081-A (GB)
Title: Bi-axial web stretching machine
IPC: D06C3/00
Filed: 1966-04-22
Abstract: 1,128,081. Film stretching apparatus. ESSO RESEARCH & ENG. CO. 22 April, 1966 [May 3, 1965], No. 17781/66. Heading B5B. [Also in Division D1] Clamping means 38 for use in a biaxial web stretching machine comprise a body portion (or clamp carrier) 40 arranged for moving along a guide means 18, 20 of the machine in a substantially fixed attitude relative to the guide means, engagement means 46 for engagement with means for moving the body portion along the guide means, a clamping portion pivotally mounted upon the body portion 40 for pivotal movement about an axis transverse to the plane of the web (clamp swivel 50, bushing 54, and bearing washer 56) and having a jaw portion 74 for clamping the edge of the web, and bearing means 48, 46 arranged to co-operate slidably with the guide means to maintain the body portion substantially at a fixed angle relative thereto. Preferably, the clamping portion 74 includes a movable jaw portion having serrations 80 on its web clamping surfaces the serrations being concavely curved with respect to the edge of the clamping surface which is innermost during use so that when the clamping means is in use the end portions of the serrations will be substantially tangential to the direction of stress in the region of the web adjacent the jaw portion. First and second leg portions 42, 44 extend outwardly from the body portion 40 of each clamping means 38, the first leg portion having a roller 46 at each end for rolling contact with one surface of said guide means, (18, 20) and the second leg portion having a roller 46 at each end for rolling contact with another surface of said guide means so that in use rotation of said clamping means about the guide means in an axis perpendicular to the pivotal axis of the clamping portion is prevented. The clamp swivel 50 may be made rotatable within predetermined angular limits relative to the carrier 40. Thus as shown in Fig. 7, the desired predetermined angular freedom of clamp swivel 50 relative to the stud portion 52 is selected to be through a total arc of 45 degrees, with 10 degrees freedom forward of the perpendicular to the tracks 18 and 20, and 35 degrees rearward of the track perpendicular. In Figure 7, pivot stud 52 includes a projecting dovetail stop plug 68 which engages a similarly shaped but larger arc recess 70 formed in swivel 50. Recess 70 extends through an arc of 135 degrees while stop plug 68 has a 90 degrees segment to produce the total of 45 degrees angular freedom between these respective pieces. In operation, web 16 is fed through feed rollers 12 into the parallel entrance portion 32. At this stage, the clamp assemblies are cammed to the open position by plate 77 and shortly thereafter as they advance are released so that serrations 80 tightly grip the edges of the web in a relationship initially perpendicular to the machine centre line. As the clamp assemblies continue their travel through the entrance portion 32 in a parallel path, they operate to pull the web through the machine and at the same time are free to pivot rearwardly to the axis of the web travel in any angular amount up to 35 (the amount of rearward freedom between stop plug 68 and recess 70). As the clamp assemblies 38 enter the stretching or diverging zone 34, they start their travel in an approximate angle of 20 degrees relative to the lengthwise axis of the web. This 20 degrees change in direction of each clamp assembly as it enters the stretching zone is readily compensated for by the ability of the clamp to pivot relative to its body portion 40. Thus as the clamp enters the divergent zone, no twisting of the edge of the web under the serration of the jaw is introduced. Further, the pivoted relationship of clamp swivel 50 relative to body portion 40 permits the clamp to lag or rotate as required a further 15 degrees to optimize and reduce stress concentrations along the edge of the film web. Thus in Fig. 6, clamp swivels 50 have assumed a lagging angle relative to their direction of travel along divergent guideways 18, 20. Fig. 6 also illustrates the optimized stress reduction accomplished by the curve serrations 80 on the jaws of the clamps, the scalloped edge of the web being seen to approach the serrations in a generally tangential direction at the edges of the jaw face. As the clamps travel along a curved path either in the stretching zone or outside thereof they tend to have uneven speeds and angles of tension relative to the edge of the web. Since all forces about each clamp jaw are in balance, the ability of each of the clamps to pivot relative to its body portion results in less chance of stress concentration and the possibility of tearing of the film sheet is reduced. Each body portion 40 of the clamp carrier includes a downwardly projecting portion mounting a roller 82 adapted to engage a spiral slot 84 in feed screw 86. Feed screw 86 is mounted upon a pivot shaft 88 and rotated conventionally to advance each of the individual clamp assemblies 38 along the length of the screw. Spiral slot 84 has a varying pitch so that the clamps advanced along the length thereof gradually become more and more separated to thereby advance and stretch the film or web in the lengthwise direction at the same time that it is being stretched in the transverse direction. In addition to the feed screw 86 which advances the individual clamp assemblies 38 through the divergent stretching zone of the machine, the clamping means 38 are advanced along their path by the combined action of an endless conveyer 106, and a pair of sprocket wheels at opposite ends of the guide path (104, 108).