STENTER FRAME CLIP CHAIN ASSEMBLY

Abstract: Stenter frame apparatus for stretching film comprises clip chain assemblies adapted to grip opposite edge of the film. Each chain assembly includes a plurality of chain units (5) which are movable on a double track rail system (3, 4). Each chain unit 5 carries a series of rollers wherein rollers (10a, 10b) with a horizontal axis run on an edge of a track (4) for chain weight support while a plurality of vertical axis rollers (7a, 7b, 8, 9, 12) engage side surfaces of the track assembly to resist horizontal loading. A further roller (11) serves to prevent uplift of the chain assembly. The chain units (5) are linked by articulating link means comprising spaced link plates (21, 22) pivotally carried by link pins (23) in the chain units, each link pin additionally serving to support a drive roller (15). A film clip (6) is located on each chain unit (5) and above the articulating link means. Preferably the tracks (3, 4) are spaced vertically.

Description: SIi IER_FRAME_CLIP_CHAIN_ASSEMBLY i DESCRIPTION. This invention relates to an improved form of sten- ter frame clip chain assembly and, in particular, to those utilizing rollers for the clip chain running on substan¬ tially continuous tracks. In one known design of stenter frame clip chain assmebly described in British Patent Specification 1 504 450 the assembly ncludes a laminated track strip carried by a support casting. On the vertical faces of the track strip, vertical axis rollers catering for the horizontal loads run on the face adjacent to the film clip and on the side remote from the film clip. These rollers provide horizontal guidance for the chain, the components of the chain tension arising at convex and concave curves and, in the case of the latter rollers, addi ti ona 11 ly the film stretching load. The weight of the chain and the clip s taken by a s ngle horizontal axis roller running on the top edge of the track strip and any tendency to upward drift of the chain is resisted by a further roller contacting the bottom edge of the track strip. In this arrangement there are six track lines on which rollers run from which the clip chain is constrained and guided. In this prior construction the complete clip is mounted on the film side of the chain such that the distance be¬ tween the gripping line and the vertical centre line of the chain is considerable. An alternative design of stenter frame clip chain assembly incorporates a vertical track member and a horizontal track member disposed on the side of the vertical track member remote from the film clip. The general chain guidance forces and tension force compon¬ ents are contained by vertical axis rollers, one roller located below the chain line and on the film clip side while two rollers are located in line with film stretch- ing load and on the side remote from the flim clips. Chain weight is taken by a single horizontal axis roller running on the horizontal back track. The couple pro¬ duced by clip chain weight tends to keep the vertical axis rollers in contact with the vertical track member. The clip is mounted above the chain such that the distance between the gripping line and the vertical centre line of the chain is minimal and a fraction of that described above. In high speed stenters the rollers carrying the chain weight have an arduous duty due to the imprecise running surface of the laminated strip of the above des¬ cribed first design and the horizontal track of the second design which required great accuracy in the manufacturing methods of the clip chain base and the joints of the track. The first design has the comparative advantage of being constrained against upward movement by the bottom rollers but has the disadvantage of having the weight carrying rollers above the film line. thus the rollers with the most arduous duty and having a greater need for surface lubricant are these rollers above the line of the film clip and film such that exposure to contamination from lubricant and related detritus is thereby increased. An additional contamination hazard in the first design arisen from the locating of the top strand of the duplex drive chain above the film clip level. Further, in the first design the distance between the gripping line and the vertical centre line of the chain is considerably greater than that in the second design. This results in a greater tendency for film splits to arise from longitudinal stretching of the film edge between adjacent clips when the chain articulates in passing around the first significant point of track divergence when, for example, entering the stretching zone This tendency to split may be reduced by thickening the edges of the film at the casting process but this causes excessive losses during subsequent trimming when the thickened bead and attendent non-uni formly stretched edge is removed from both sides of the web. In the second design the film and film clip does not have the same exposure to contaminant because the weight carrying roller is located well to the rear and at a lower level than the film clip but the design provides a less effective method of controlling any; tendency to upward clip drift. In thin film high speed applications, the major load on the system is very often the weight of the clip chain assembly itself. A disadvantage common to both the above prior art designs is that the chain weight is carried by a single roller in each chain unit. The combination of running speed and load may result in premature failure of a single roller and/or accelerated wear of the track in contact with the roller. Accurate alignment of adjacent film clip gripping surfaces is necessary for the successful operation of thin film stenters at high speeds. During operation there are a number of multi-directional forces acting on the clip chains which tend to misalign the gripping surfaces . A further disadvantage common to both above des¬ cribed prior art designs is the inherent instability in the longitudinal horizontal plane due to a clip chain assembly which has only a single weight carr ing roller on each chain unit. In both designs, stability of the chain assembly is dependent on the accuracy of the devices linking the individual chain units together and the degree of misalignment of the film gripping surfaces is related to the amount of wear in the link assembly. It is an object of the present invention to obtain a preferential disposition of rollers, chain and clips which will substantially reduce the individual disadvant¬ ages noted above of contamination from exposed position of rollers, reduced efficiency by undesired longitudinal stretching between adjacent clips in combination with a roller system providing full three di ensional stability. According to the present invention a stenter frame clip chain assembly comprises chain means including chain units, a rail to movably support said chain units, film clips supported by the chain units, a support structure for said rail, a plurality of rollers carried by each chain unit and engaging said rail and chain link means adapted for driving engagement by drive means for driving the chain means assembly. wherei n the rail comprises a twin track assembly including two separate tracks, and the rollers include vertically spaced vertical axis rollers engaging said track assembly to restrain horizontal forces and horizontally spaced horizontal axis rollers engaging a surface of said track assembly for weight support and a further horizontal axis roller engagable with a surface of the track assembly to restrict upward lift of the chain unit, the surfaces engaged by the horizontal axis rollers being located between the levels of the vertically spaced vertical axis rollers, and where¬ in the chain link means is located substantially underneath the fli clip. Preferably said chain link means comprises a roller link adapted for engagement with a toothed drive sprocket wheel for driving of the chain assembly. In one preferred embodiment the track assembly comprises a vertically spaced pair of opposed but aligned vertical tracks, the vertical axis rollers running on side surfaces of the tracks and the horizontal axis rollers running on the opposed edge surfaces of the tracks. In an alternative embodiment the split track assembly comprises a spaced parallel pair of vertical tracks, a longer one of the tracks providing side surfaces for eng¬ agement by the vertical axis rollers while the other shorter track provides edge surfaces for the horizontal axis rollers. Preferably the stenter film clip comprises a base body part, and the film clip included a film gripping platform and a co-operating gripping lever, the film gripping platform being an upper horizontal surface. of the base body part. The present invention is also a stenter frame clip chain assembly comprising chain units, rail means to movably support said chain units, and fi lm clips carried by said chain units, said rail means comprising a twin track assembly with two separate tracks arranged in vert- ical spaced relationship, each chain unit rotatably supporting horizontally spaced horizontal axis rollers engaging a surface of one of said tracks for weight support, and first and second vertically spaced vertical axis rollers engaging side surfaces of respective upper and lower tracks to restrain horizontal forces. Preferably a further horizontal axis roller is provided engaging one of the tracks of the track assembly to restrict upward lift of the chain unit. Preferably further, said vertically spaced tracks are aligned vertically. Embodiments of the present invention will now be described by way of example with reference to the accom¬ panying drawings in which:- Fig. 1 shows a cross-sectional side elevation of a stenter frame clip chain assembly through section A-A in Fig. 2 and according to a first embodiment of the present invention; Fig. 2 shows a front view of the clip of Fig. 1 looking in direction of arrow C in Fig. 1; Fig. 3 shows a similar view as in Fig. 1 but of a modified stenter film clip chain assembly; and Fig. 4 shows a cross-sectional side view of a stenter film clip chain assembly according to another embodiment of the present i vention. Referring to Figs. 1 and 2, stenter apparatus for stretching film comprises opposed stenter clip chain ass- emplies movably carried by respective rails 2 and which chain assemblies serve to grip opposed longitudinal edges of the film and cause appropriate stretching of the film on chain movement. Each rail 2 comprises a double-track rail assembly having vertically spaced tracks 3, 4 with one track located directly above the other, and each track 3, 4 is supported by a respective flange 1A, 1B of a rail support structure which includes articulations (not shown) to facilitate changes in the path of the chain assembl es. Each clip chain assembly includes chain units 5 which are supported and guided by the tracks 3, 4 through rollers ( Later described) on the units 5, the tracks 3, 4 pre¬ senting a continuous surface to the rollers of the units 5 except at the zone of a chain tensioning device (not shown). Each track 3, 4 is of rectangular cross-section and for convenience may be of jointed construction. Each chain unit 5 comprises a chain base part 5a in the form of a casting and on the base part 5a are rotatably mounted vertical axis rollers 9, 12 which can engage vertical walls 4b, 3b respectively of tracks 4, 3. Further, the base part 5a includes projecting arms 5b, 5c rotatably carrying vertical axis rollers 7a, 7b which engage an outer side wall 3c of track 3, and an addition- al lower arm 5d rotatably supporting vertical axis roller 8 engaging outer side wall 4c of track 4. The base part 5a also rotatably carries horizontal axis rollers 10a, 10b and 11. As can be seen in ig. 3, the rollers 7a and 7b are laterally spaced on either side of roller 12, while the rollers 10a, 10b are laterally spaced on either side of roller 8, 9. The various rollers are rotatably supported via shafts 13 pinned into bores in the base part 5a. The fi lm load (stretching) is essentially transmitted to the tracks 3, 4 through the rollers 7a, 7b and these rollers in combination with the rollers 8, 9 and 12 also bear the chain tension force components which arise at concave and convex curves in the path of the rai l assemblies. It wi ll be noted that the rollers 7a, 7b are closely adjacent the fi lm level L "for effective operation. The horizontal axis rollers 10a, 10b transmit the chain (and clip) weight to the upper surface 4a of track 4 and any tendency for the clip chain- to drift upwards is prevented by the horizontal axis roller 11 contacting the lower edge 3a of track 3: since roller 11 wi ll be subject to less loading than the rollers 10a, 10b the roller 11 can be of smaller diameter than the rollers 10a, 10b. In the front view of Fig. 2, rollers 7a, 7b are vertically arranged above rollers 10a, 10b with the remaining rollers 8, 9, 11 and 12 located therebetween and in vertical alignment. The base part 5a supports a fi lm clip 6 which includes a fi lm gripping platform 6a and a co-operating gripper lever 6b which together define the fi lm level L and the fi lm grip ' line 6c, the fi lm clip 6 being located on an upper horizontal surface of the base part 5a by dowel pins 14. The clip 6 addit onally includes a lever arm 6d operable by cam surfaces (not shown) for movement of the gripper lever 6b to and from the film gripping posi t i on. The chain units 5 are pivotally linked together by means of upper and lower chain link plates 21. 22 which are located by chain pins 23 in the base part 5a, the pins 23 having end necks to receive the links whi le each pin 23 is removably located by means of an upper circlip 24 and a lower nut 25 on a threaded neck portion of the pin. As can be seen in this embodiment, the link plates 21, 22 are positioned externally of the base part 5a and are consequently widely spaced. Since the link plates 21, 22 are displaced at a substantial vertical dimension, these plates 21, 22 provide increased stability in the chain assembly at the points of rail divergence (for film stretching) and at the chain turnaround at each end of the machine. The pin 23 is journalled in separate journal bearing bushes 26, 27 in the base part 5a and a chain link roller 15 is journalled on a further bearing bush 29 on the pin 23. A toothed drive sprocket (not shown) engages the rollers 15 for driving of the chain assembly. The three separate journalled bushings 26, 27, 29 serve to reduce the need for external lubrication and to maximise the life of the chain assembly. The upper and lower bushes 26, 27 also serve to facilitate chain articulation while the separate central bush 29 enables free rotation of the roller 15. The embodiment shown in Fig. 3 is similar to that of Figs. 1 and 2 except that the link plates 21, 22 are incorporated in a link assembly located within the base part 5a . Fig. 4 shows a chain clip unit of a stenter clip chain assembly, according to another embodiment of the present invention and also includes a double track 3, 4 but in this case the vertical track parts 3, 4 are in spaced parallel relationship, being spaced by spacer plate 20 and secured to body member 1 by screws 21. The longer track 3 provides side surfaces for the vertical axis rollers 7a, 7b, 8, 9 and 12 while the track 3 of lesser vertical extent provides the edges surfaces for the horizontal axis rollers 10a, 10b amd 11. Otherwise it is felt the arangement of Fig. 4 will be fairly self- explanatory and is similar in operation to the embodiments of Figs. 1 to 3: like parts carry like reference numerals. In all of the embodiments it will be noted that the surface 4a for supporting rollers 10a, 10b is located intermediate the levels of rollers 7a, 7b and rollers 8, 9. The stenter clip chain assemblies of Figs. 1 and 4 provide particular benefits in the high speed production of extremely thin polyester film where clean and contin¬ uous operation is essential, such as in the production of polyester film for electrical recording applications. In contrast with the single track arrangement shown in U.K. Patent 1504450, the use of a separate double-track rail assembly as in the above described embodiments provides economies since if wear occurs in the tracks of the rail assembly it may be necessary only to adjust the vertical spacing between spaced tracks 3 and 4 (Fig. 1) or to replace only one of the tracks 3, 4 (or part there¬ of ) . More especially, there are particular advantages in the double-track arrangement of Figs. 1 to 3 viz. All rollers and chain link parts are located sub¬ stantially below the level of the film and this has the benefit of minimising contamination of the film by track wear debris and surface lubricants. Two horizontal axis rollers (i .e. 10a, 10b) provide stablity in the longitudinal direction and take the weight of the clip chain assembly which is the major life reduc¬ ing force in a high speed thin film stenter chain. The horizontal dimension (i.e. distance X) from the gripping line to the centre of chain articulation is maintained at a inimum to reduce the degree of machine drawn orientation in the film when the chain is at the first divergence point of the track system.

Claims: AMENDED CLAIMS [received by the International Bureau on 10 March 1986 (10.03.86); original claim 9 cancelled; claim 8 amended; other claims unchanged (2 pages)] characterised in that the split track assembly (2) comprises a spaced parallel pair of vertical tracks (3, 4 Fig. 4), a longer one (3) of the tracks providing surfaces for engagement by the vertical axis rollers while the other shorter track (4) provides edge surfaces for the horizontal axis rollers. 5. A chain assembly as claimed in claim 2, character¬ ised in that the chain link means (21, 22, 23 ) include link plates (21, 22) for linking successive chain units (5) and in that said link plates (21, 22) are carried by a link pin (23) supported in the chain unit ( 5 ) , said link pin (23) rotatably carrying the link roller (15) which engages the toothed drive sprocket. 6. A chain assembly as claimed in claim 5, character- ised in that transversely spaced link plate pairs (21, 22) are provided, said link plate pairs (21, 22 ) being located externally of a base part (5a) of the chain unit ( 5). 7. A chain assembly as claimed in claim 5 or 6, characterised in that separate bearing bushes (26, 27, 29 ) are provided between the link pin (23) and the chain unit (5) and between the link roller (15) and the link pin (23). 8. A stenter frame clip chain assembly comprising chain units, rail means to movably support said chain units, each chain unit rotatably supporting rollers which run on surfaces of the rail means to support the weight of the chain assembly and to resist lateral film stretching forces, and film clips carried by said chain units, characterised in that the rail means (2) comprises two individual rails (3, 4) (Fig. 1) arranged in verti cal spaced relationship, and in that a pair of horizontally spaced horizontal axis rollers (10a, 10b) rurf on an inner edge (4a) of the lower rail (4) for chain weight support, while pairs of vertical axis rollers (7a, 7b, 8, 9, 12) engage opposite side surfaces (3b/c, 4b/c) of the rails (3, 4) to resist horizontal forces. 9. A chain assembly as claimed in claim 8, character- ised in that a further horizontal axis roller (11) engages the inner edge (3a) of the upper rail (3 ) to resist upward lift of the chain unit (5). 10. A chain assembly as claimed in claim 8 or 9, characterised in that the vertically spaced rails (3, 4) are aligned vertically. 11. A chain assembly as claimed in any one of the pre¬ ceding claims, characterised in that at least one vertical axis roller (7a, 7b) engages a side surface ( 3c) of a substantially on a level with film gripped by the film clip (6) and serves to resist film stretching forces . 12. A chain assembly as claimed in any of the preceding claims, characterised in that the chain unit (5) includes a base part (5a), and in that the film clip (6) includes a film gripping platform (6a) and a co-operating gripping lever (6b), the film gripping platform (6a) being located on an upper horizontal surface of said base part (5a) .

Inventors: CUNNINGHAM WALLACE, GREEN GRAHAM, SCLATER ALEX, CUNNINGHAM, WALLACE, GREEN, GRAHAM, SCLATER, ALEX
Applicants: PROCTOR & SCHWARTZ LTD, PROCTOR & SCHWARTZ LIMITED
Application year: 1985
Main classification: B29C55
IPC codes: B29C55, B65H20