GB2120597A

GB2120597A - Stretching film longitudinally by tentering

Info

Publication number: GB2120597A
Application number: GB08215437A
Authority: GB
Inventors: Hans Rottensteiner
Original assignee: Lindauer Dornier GmbH
Current assignee: Lindauer Dornier GmbH
Priority date: 1982-05-26
Filing date: 1982-05-26
Publication date: 1983-12-07

Abstract

In a foil tentering apparatus, the tentering clips engage their driving member (which may be a sprocket chain) through a member, such as a sprocket wheel, which can be rotated to increase or decrease the separation of the clips in the longitudinal direction. The rotation is caused by activating members, such as sprocket chains 11, Fig. 1B or electrical contacts 29, Fig. 4 stationed along the path of the clips and engaging each clip as it passes. The invention is characterised in that the activating members are in segments, which follow one another without a gap so that their action is continuous. <IMAGE>

Description

SPECIFICATION Foil web stretching apparatus This invention relates to an apparatus for stretching a foil web, comprising drivable tentering means or clips travelling along two endless guide tracks, one at each of the two side edges of the web. The tentering means or clips have clamping elements for gripping the two side edges, in which the distance between individual tentering means or clips can be controlled as required for a longitudinal stretching ratio or possibly a longitudinal shrinkage ratio.

A foil stretching apparatus has been proposed in our co-pending application No. 82 05659, in which a drivable, endlessly revolving toothed traction or clip driving device is provided in each of the two guide tracks as carrier for the clips, the clips engaging the clip driving device by way of sprocket wheels and being displaceable in the longitudinal direction of the clip driving device by rotation of the sprocket wheels by associated displacement devices. The displacement devices are operable by control means arranged along the guide track and independent of the clips. Thus in this prior apparatus the tentering means or clips are not themselves joined together to form a chain but are carried and transported by an endlessly revolving traction or clip driving device, e.g. a conveyor chain.Sprocket wheels on the clips engage with a toothed system of the clip driving device and by being rotated they cause the clips to be displaced along the clip driving device.

The sprocket wheels are driven by the displacement devices, e.g. gears, which are associated with the clips and designed to be acted upon from outside. The distance between the clips on the clip driving device can thus be adjusted by means of an independent control device arranged outside the clip driving device. The main longitudinal forces act on the clip driving device which can be designed to take the full load.

The clip driving device is driven in known manner by deflecting and conveyor wheels engaging it, which are arranged at the beginning of a heating zone and at the end of a stretching or fixing zone. If the clips are displaced along and relatively to the clip driving device, there results a relative velocity between clip driving device and clip, which brings about longitudinal stretching of the foil web gripped by the clips at each side. In this prior apparatus, the individual clips are at least from time to time displaced at differing velocities so that the distance between them varies. Where no control means are present, the clips move at the basic velocity of the clip driving device and no longitudinal stretching of the web occurs at those locations.

Within individual treatment zones of the apparatus, the control means are sub-divided into part lengths which drive the clip displacement devices at different speeds for the appropriate lengths of time. Duration and speed are in each case adjusted to the particular treatment concerned. The distance between individual clips and hence the longitudinal stretching ratio or, where applicable, the longitudinal shrinkage ratio, can thus be readily adjusted and controlled.

For use as displacement device acting on the clips, it has been proposed to use transmission devices which engage with control gear elements along the guide track by way of a driving sprocket wheel, and are driven by them. It has been proposed to use fixed control gear systems or revolving control driving chains as control elements. The necessary speed of displacement of the clips and hence the longitudinal stretching ratio can be individually adjusted from case to case by appropriate choice of the driving speed of the control driving chains, bearing in mind the transmission ratio of the driving gear wheels or transmission, and may even be readjusted during operation.The apparatus is therefore versatile in use, e.g. for pure longitudinal stretching, or for transverse stretching, or for simultaneous biaxial stretching, of a foil web, and is independent of the particular means used for mounting and guiding the clips in the guide tracks.

The present invention relates to a development of the above discussed prior apparatus. In the prior apparatus, further requirements arise in operation since longitudinal stretching of the foil web should proceed as uniformly as possible. This requires not only fine sub-division of the part lengths of the control elements arranged along the guide track but smooth and uniform displacement of the clips on the clip driving device without jerky transitions.

According to the present invention there is provided apparatus for stretching a foil web, comprising drivable tentering means or clips travelling along two endless guide tracks, one at each of the two side edges of the web, the distance between individual tentering means or clips being controlled as required for a longitudinal stretching or shrinkage ratio by displacement devices associated with the tentering means or clips and acted upon by control elements arranged along the guide track, control by means of the displacement devices being achieved in that a drivable, endlessly revolving, toothed traction or clip driving device is provided for each guide track as carrier for the tentering means or clips which engage the driving device by way of rotatable means and are displaceable in the longitudinal direction of the clip driving device, the rotatable means being rotated by the associated displacement devices, wherein the control elements are subdivided into separate part lengths and the ranges of action of successive separate part lengths are without gaps in the direction of movement of the tentering means or clips.

The apparatus may be constructed not only for a mechanical drive by for example sprocket wheels and control driving chains in various forms, but may be modified for other forms of drive. Thus according to a further feature of the invention, electric motors supplied with current from control contact rails along the guide tracks by way of sliding contacts may be provided as the displacement devices for the clips. The control contact rails act as control elements which are independent of the clips and which are advantageously sub-divided into a plurality of sections following one upon the other along each guide track and electrically connected together, selectively either individually or groupwise. The sliding contacts may have a unipolar or a multipolar arrangement in several parallel rows insulated from each other.

The electric motors may be influenced or energized differently by the various sections of the control contact rails, e.g. by applying different voltages across the sections, so that the motors can be driven at different speeds along different sections, thereby producing different distances between clips.

Embodiment of the invention are described below by way of example, with reference to the accompanying diagrammatic drawings, in which:~ Fig. 1 A shows part of a clip displacement device with control driving chains; Fig. 1 B shows the arrangement of control driving chains of Fig. 1 A; Fig. 2A shows a modification of the construction of Fig. 1 A; Fig. 2B shows the arrangement of control driving chains of Fig. 2A: Figs. 3A, 3B show an electric driving device clip displacement, viewed in the direction of movement of the clips (Fig. 3A) and transversely thereto (Fig. 38); and Fig. 4 illustrates schematically a subdivision of control contact rails for the displacement device of Figs. 3A, 3B.

Referring to the drawings, the arrangement of the clip driving devices in the guide tracks and the arrangement of the clips on the clip driving devices are similar to those described in our co-pending Application referred to above and need not be described in detail. The same applies to the construction of the clips and of the transmissions used for displacing them.

Figs. 1A and 1 B show schematically a subdivision of control driving chains into part lengths. Subdivision into part lengths driven at differing, adjustable speeds is necessary, as briefly mentioned above, where a change in the distance between the clips is required, as for example in the stretching zone.

In Fig. 1 A, two coaxial driving sprocket wheels 12 and 12' are carried on a clip 10 (which is only shown in part). One sprocket wheel engages a control driving chain 11 and the other a control driving chain 1 a parallel to the chain 1 The two sprocket wheels 12 and 12' are mounted on a common shaft leading to the displacement device (not shown), e.g. a bevel gear.

The driving chains 1 1 and 11 a extend parallel to the direction, indicated by the arrow in Fig. 1 B, in which the clip driving device (not shown) is moved along the guide track 1.

In Fig. 1 B, the parallel arrangement of the part lengths of the control driving chains is seen from the side. As shown, the chains are arranged so that successive part lengths are situated alternately in a first and a second of two parallel rows extending along the guide track 1. The part lengths 11 and 1 1 of chains shown in solid lines and any further lengths lid, 1 If. . (not shown) are arranged in alignment along the guide track 1.

The part length 1 a shown in broken lines and any further parth lengths 1 c, ..... . (not shown) are arranged in alignment with each other in a second rod displaced from but parallel to the first.

As the clips move along the guide track in the direction of the arrow (Fig. 11 B), the driving sprocket wheels 12 and 12' mesh alternately with their associated part lengths of control driving chains 11, 11 b, etc. and 11 a, 11 c, etc. The separate part lengths are contiguous with each other. This arrangement provides for fine subdivision of the control driving chains with finely graded speeds of movement and hence virtually infinite adjustability of the speeds of displacement of the clips relative to the clip driving device. The changes in speed for displacement of the clips and hence longitudinal stretching or shrinking of the web therefore proceed virtually free from jerking.

The embodiment shown in Fig. 2A has only one driving sprocket wheel 12 but the driving chain parts 11, 11 a, 11 b, 11 c are in this case arranged at two different levels, alternatively above and below the sprocket wheel 12. Fig. 2B is again a side view showing the alternating arrangement of the chain parts 11, 1 a, 1 b and the transition of the sprocket wheel 12 from the driving chain part 11 tothepartlia.

Both embodiments show that there need not necessarily be any interruptions or substantial gaps between successive parts of control driving chains driven at different speeds but that these part lengths may be contiguous so that the clips may be displaced continuously on the clip driving device. The axes of rotation of the deflecting wheels for the individual part lengths of the driving chains, for example the deflecting wheel at the end of the length 1 1 and that at the beginning of the succeeding length 1 1 a, are arranged so that there are no gaps between the axes of rotation in the direction of movement of the clip driving device. In Fig. 1 b the axes of rotation of the two deflecting wheels belonging to adjacent part lengths are therefore coaxial, whereas in Fig. 2b the axes of rotation are situated one above the other in a common vertical plane. In sections where the clip is not acted upon by a control element, there is no relative displacement between the clip and the clip driving device, and in these locations the clip travel at the normal speed of the clip driving device and the instantaneous distance between two successive clips remains unchanged.

Another embodiment is shown in Figs. 3a and 3b, Fig. 3b being a simplified side view of Fig. 3a.

The displacement device in this case comprises one electric motor per clip. These two figures show part of a clip 10 with a transmission 13' which is driven by an electric motor 27. The current supplied to the motor 27 is obtained, for example, from control contact rails 29 along the guide track 1 by way of sliding shoes or contacts 28.

Insulation is indicated at 30. The sliding contacts need not necessarily be unipolar but may be multipolar, as indicated in broken lines, with the contact rails arranged in parallel rows along the guide track 1 and electrically insulated from one another.

In Fig. 4, the control contact rails 29 are subdivided into a large number of sections closely following one another. The control means is assumed for the sake of simplicity to be a voltage divider 31. The various sections of the control contact rails may be individually switched and connected at different points of the voltage divider 31, as for example the sections 29 and 29a, but they may also be connected together in larger or smaller groups, such as the groups 29b, 29c, 29d and 29e as and when.required. The electric motor 27 is energized or influenced differentially by the various sections of the control contact rails. This may be achieved, as indicated above, by applying different voltages. Different types of electric control for the motor may also be used.

The longitudinal stretching ratio can thus be adjusted quite individually from one case to another along a length of guide track. In this example it is also possible to achieve virtually jerk-free transition from one step of displacement speed of the clips to another, since the various separate sections of the control contact rails can follow each other so closely that the sliding contacts can be carried over them without interruption. This provides for a very smooth longitudinal stretching operation.

The control voltage applied, or the relative speed between clip driving device and control driving chain, whether this be a driven control driving chain or a rigid rack, determines the speed of displacement of the clips on the clip driving device and hence the longitudinal stretching ratio, taking into account also the transmission ratio of the transmission elements in the clips.

Claims

1. Apparatus for stretching a foil web, comprising drivable tentering means or clips travelling along two endless guide tracks, one at each of the two side edges of the web, the distance between individual tentering means or clips being controlled as required for a longitudinal stretching or shrinkage ratio by displacement devices associated with the tentering means or clips and acted upon by control elements arranged along the guide track, control by means of the displacement devices being achieved in that a drivable, endlessly revolving, toothed traction or clip driving device is provided for each guide track as carrier for the tentering means of clips which engage the driving device by way of rotatable means and are displaceable in the longitudinal direction of the clip driving device, the rotatable means being rotated by the associated displacement devices, wherein the control elements are subdivided into separate part lengths and the ranges of action of successive separate part lengths are without gap in the direction of movement of the tentering means or clips.

2. Apparatus according to claim 1, wherein the part lengths are each in the form of control driving chains endlessly revolving over deflecting wheels, and the axes of rotation of the deflecting wheels of two adjacent control driving chains, which wheels are situated at the beginning and at the end, respectively, of the forwardly moving part of the chain, are arranged without any space between them in the direction of movement of the tentering means or clips.

3. Apparatus according to claim 1 or claim 2, wherein the part lengths are arranged alternately in two parallel rows extending side by side along the guide track, and for each row there is a separate driving sprocket wheel engaging with the row and rigidly mounted on a shaft leading to the driving device.

4. Apparatus according to claim 1 or claim 2 wherein the part lengths are arranged alternately at two different levels in vertical longitudinal planes along the guide track, a single driving sprocket wheel, provided on a shaft leading to the displacement device, engaging alternately with a lower part length and an upper part length.

5. Apparatus according to claim 1 , wherein electric motors supplied with current from control contact rails situated along the guide track by way of sliding contacts are provided as displacement devices for the tentering means or clips.

6. Apparatus according to claim 5, having a plurality of sections of control contact rails following closely upon one another along the guide track and designed to be electrically connected together selectively either singly or in groups.

7. Apparatus according to claim 6, wherein the various sections of the control contact rails have differential action on the electric motors.

8. Apparatus according to claim 7 wherein the differential action is provided by differing potentials.

9. Apparatus according to any of claims 5 to 8, having a multipolar arrangement of sliding contacts in several parallel rows insulated from each other.

10. Apparatus for stretching a foil web constructed and arranged substantially as herein described and shown in the drawings.