EP1631437A1

EP1631437A1 - Drive device for a transverse drawing system for films made from a non-synthetic material

Info

Publication number: EP1631437A1
Application number: EP04767195A
Authority: EP
Inventors: Moreno Innocente Marchante; Gilbert Trivero
Original assignee: Darlet Marchante Technologie SA
Current assignee: Andritz Biax SAS
Priority date: 2003-06-02
Filing date: 2004-05-27
Publication date: 2006-03-08
Also published as: JP2007526965A; FR2855452A1; WO2004108395A1; JP2012096547A; FR2855452B1; US7322078B2; JP5559137B2; US20060180437A1

Abstract

The invention relates to drawing systems using a series of jaws for the support, transport and drawing of the film (2), which are supported and guided by rails and driven by endless chains (3), connecting the jaws between the above. Each chain (3) is driven by two toothed wheels (6, 7) of large diameter (D), one wheel (6) located at the beginning of the forward run (4) and the other wheel (7) located at the rear end of the return run (5) of the chain (3). Each wheel (6, 7) is provided with motorised rotational drive means, said means being synchronised with each other. Such a drive device finds application in high speed drawing machines.

Description

Drive device for transverse stretching system for plastic films

The present invention relates, in general, to the technical field of stretching films of synthetic material. This invention relates, more particularly, to a motorized drive device for a transverse stretching system for plastic films, of the type of those using, for holding, transporting and stretching the film, grippers successive supported and guided by rails, and driven forward by endless chains connecting the clamps. Thus, the invention relates, even more particularly, to a device which, in this context, ensures the forward drive of the chains provided with clamps.

Bi-oriented synthetic material films are obtained from an extruded ribbon, after melted material has been deposited on a cooled casting drum so as to slow down the crystallization of the film and allow it to be stretched. ulterior.

The extruded ribbon then passes through a longitudinal stretching machine, in which the stretching is carried out on the principle of a speed differential between different successive cylinders. The ribbon then passes through a transverse drawing machine, in which the ribbon is held by clamps mounted on chains, the spacing of which gradually increases.

This type of stretching, called sequential stretching, is perfectly suitable for films made of many synthetic materials such as polypropylene, polyester, and it is therefore widely used in industry. Another important step in the process for manufacturing bi-oriented synthetic material films is the so-called transverse stretching phase which occurs inside a large oven. In this oven, two chains equipped with clamps and guide members move on side rails, first, in parallel and until the film has reached the desired temperature, then, thanks to an adjustment of the guide rails, moving away from each other symmetrically so as to ensure a transverse stretching of the film. After stretching, the guide rails again become parallel or slightly convergent, so as to allow either the crystallization of the stretched film, or, possibly, its thermal relaxation. It is obvious that in order to reach an acceptable profitability target that meets market requirements, the unit throughput of the machines must be increased, which has the effect of proportionally reducing the amount of investment per kilogram of film produced, as well as energy consumption. This increase in capacity can obviously be done only by increasing the width of the films or by increasing the production speed.

Until recent times, it has been the increase in width of the films which has been favored due on the one hand to the limitations inherent in the maximum displacement speeds of the clamp and rail systems previously developed, and on the other hand to the fact that it is economically less expensive to design a larger machine, the expensive mechanical components remaining identical, whatever the width of the machine.

It is for this reason that the widths of the machines for producing bi-oriented film which did not exceed, ten years ago, 5 to 6 meters, now now routinely reach widths of 8, 9, and even 10 meters.

It is hardly conceivable that this trend continues to be favored, because beyond such widths arise difficult problems of supply and installation of surface treatment systems, winding, or simply handling problems sheets of synthetic material.

For this reason, the trend is now again towards increasing the production speed of the machines. This trend is greatly facilitated by the appearance on the market of so-called continuous rail devices and clamps, such as those which have been the subject, for example, of French patent N ° 2686041 in the name of the Applicant.

Indeed, the implementation of continuous guide means, combined with systems of moving chain or sliding elements as described in this patent, currently allows production speeds of between 300 and 500 to be obtained. m / min. These devices therefore mechanically allow the design and production of efficient production machines combining a large width of film, namely 7, 8, 9 or even 10 meters, with a high mechanical production speed capable of exceeding 500 or even 600 m / minute. It is however obvious that if an additional requirement is that the quality of the films produced on high speed machines is at the less comparable or equivalent to that of machines of previous generations of lower speed, it is then necessary that the length of the transverse drawing furnace is increased. Indeed, the important and incompressible parameters of the process are for example the residence times in the preheating zone of the oven necessary for the film to be heated to the core, and therefore stretches homogeneously, which requires the elongation of the preheating zone, or the progressiveness of the stretching which requires that the stretching zone be lengthened, and finally the maintenance, at a higher production speed, of a heat-stabilization time sufficient to ensure complete crystallization and therefore the stability of the films produced, which requires the elongation of the heat-stabilization zone.

It follows from this set of considerations that high-speed transverse drawing machines must be able, thanks to the quality of components such as rails and clamps, in particular to operate at high mechanical speeds, but also that the corresponding length of the associated machines and ovens should be increased.

The extension here desirable of the transverse stretching machines is not without posing many problems which are mainly of double nature: The drive of the chains which ensure the synchronization of the clamps on the guide elements is traditionally done from toothed wheels driven by suitable reducers by a motorized shaft located on the side of the outlet of the machine, the return of the mobile assembly consisting of the chain and clamps being made at the entrance of the oven by another toothed wheel not driven allowing the return of the chain / clamps, that it again enters the oven ensuring the transport of the film.

The driven toothed wheel located at the outlet of the oven must therefore ensure the drive of the assembly consisting of the chain and the clamps, not only for the strand which is inside the oven, but also for the return strand , or over a length approximately twice that of the machine concerned. This toothed wheel must therefore transmit a driving force to the chain, the result of which is a tension on the chain which must be greater than the forces opposing this movement, which are the mechanical frictions as well as the stretching forces of the film. . These efforts are particularly significant on high-speed machines during the speed-up and speed-reduction phases, and the resulting tensions on the chain in certain cases become unacceptable or too close to the resistance limit of the chains, which results in very serious production incidents such as frequent breakage or derailment of the chain / pliers assembly.

This increase in chain tension is damaging not only for the chain itself, but also and above all for self-lubricating rings which, more and more commonly, are used on high-performance machines so that it is there is no need to ensure, during the operation of the machine, its lubrication, this being ensured over a period of several years by self-lubricating rings. These rings ensure perfect functioning of the systems provided that the friction surfaces are not subjected to too high a specific pressure which tends to crush the lubricant product and damage it irreversibly. However, the specific pressure at the rings is directly proportional to the operating tension of the chains.

The increase in the running speeds of a chain driven by a toothed wheel rapidly reveals significant vibrations resulting from the so-called polygon effect, a well-known effect which results from the complex kinematics located in the area in which the chain comes into contact with the drive gear.

The only way to oppose this polygon effect is either to reduce the pitch of the chain, which has a significant impact on the price of the machine, or to increase the diameter of the gear wheels to reduce the so-called polygon effect. .

This increase in diameter is not without problems because the diameters of toothed wheels, necessary for a reduction to an acceptable rate of the polygon effect, become for current production speeds, greater than values of 1 meter or 1 , 5 meter.

The increase in the diameter of the toothed wheels beyond these values and which remains desirable for a machine operating at high speed poses problems of manufacturing the toothed wheel and of the flatness of the guide, and moreover requires the presence between the toothed wheels. and the driving element of a reduction gear whose reduction ratio must be more and more important, since the larger the diameter of the toothed wheel, the more as important is the relative difference between the speed of rotation of the toothed wheel and the speed of rotation of the motor shaft.

In the case of US Patent No. 3276071 or French Patent No. 1318130, these are simultaneous, i.e. longitudinal and transverse stretching machines, with link chains of variable length, which must be driven at low speed. These documents are therefore not concerned with the aims of the present invention. In addition, they do not provide any indication regarding the size of the wheels on which the chains pass. The objective of the present invention is to overcome this set of drawbacks and to allow the production of rail systems, clamps and chains operating satisfactorily at high speed, specifically for transverse drawing machines.

To this end, the subject of the invention is a drive device for a transverse stretching system for plastic films, of the kind indicated in the introduction, which is essentially characterized in that it comprises, for driving each endless chain connecting the clamps, at least two large-diameter drive gear wheels, ie a drive gear wheel located at the front end of the "go" strand of the chain, and another drive gear wheel located at the rear end of the "return" strand of the chain, with each toothed wheel being associated with motorized means for driving this wheel in rotation, and the motorized drive means associated respectively with the two toothed wheels being synchronized with each other . Also, a first arrangement at the base of the invention consists in using large gear wheels, much larger than the current dimensions which are diameters from 1 meter to 1.5 meters, the gear wheels driving the chains of the device object of the invention having a diameter greater than 1.5 meters. A second basic arrangement of the invention consists in using, for a chain, two toothed drive wheels, either a wheel located at the inlet of the transverse stretching system, and a wheel located at the outlet of the same system. of stretching, the two toothed wheels being driving, since each of them has its own rotational drive means. These drive means are in particular, for each drive gear, a servo electric motor, the two associated motors respectively with the two toothed wheels being synchronized in speed, and controlled so that the torque necessary for driving the chain is distributed substantially equally between the toothed wheel located at the entry of the transverse drawing system and the gear wheel located at the exit of the transverse stretching system.

This design makes it possible to ensure that each strand of the chain, namely the "go" strand and the "return" strand, is driven directly by one of the two toothed wheels, which is assigned to it, unlike the current devices in which the assembly of the two strands, therefore the "go" strand and the "return" strand, is usually driven by a single toothed wheel, the other wheel or wheels being only return wheels.

Thus, the drive device, object of the invention, makes it possible to halve the tension to which the chain is subjected. The transverse drawing machine can therefore be used at high speed, keeping the classic design of the chain / clamps assembly.

The solution according to the invention also makes it possible to use, on such high-speed stretching machines, self-lubricated chains, without the pressure force at the rings, resulting from the tensioning forces of the chain, exceeds acceptable constraints. According to another aspect of the invention, each large toothed drive gear consists of an outer ring, with teeth adapted to the chain to be driven, and a fixed support part, the crown and said support part finding themselves linked to each other by a set of balls or rollers ensuring rotational guidance of the outer crown, while the support part is fixed horizontally to a frame. Thanks to this arrangement, the support part being fixed perfectly horizontally to a rigid frame, it is ensured that the outer ring of the wheel, which guides and drives the chain, is also held in a perfectly plane horizontal, despite a large diameter.

According to an advantageous embodiment, the outer ring of each large-diameter drive gear has internal teeth, of diameter close to the external diameter of said wheel, teeth with which a relatively small diameter drive pinion engages, itself driven in rotation from the motor means associated with the toothed wheel considered. This mode of drive, by a motor pinion engaged with an internally toothed ring, has the additional advantage of producing a speed reducer, the reduction ratio of which is all the greater as the diameter of the toothed wheel drive is large, and that the diameter of the motor pinion is on the contrary small. Thus, the drive pinion rotates at relatively high speed, so that it can either be driven in rotation directly by the output shaft of the engine associated with the wheel in question, or be driven in rotation by means of a reduction gear, with or without angle gear, reducer which is relatively small. The invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of example, an embodiment of this drive device for transverse stretching system for films of material. synthetic:

Figure 1 is a very schematic overview, in plan from above, of a drawing machine provided with the device object of the invention;

Figure 2 and a perspective view of a toothed wheel and its rotational drive device;

Figure 3 is a vertical sectional view of this drive device. Figure 1 gives a very schematic overview of a transverse film stretching machine. In such a machine, the film 2 to be stretched is transported along the arrow F, so as to pass successively through the successive zones (here not detailed) of an enclosure, regulated in temperature, in which the longitudinal and then transverse stretching takes place of the film 2. To maintain and transport the film 2, it is held, by its two opposite edges, by means of pliers whose structure is known and can, in particular, be in accordance with that described in the aforementioned French patent No. 2 686 041. These clamps are carried by two endless chains 3, arranged symmetrically with respect to the longitudinal axis of the drawing machine, and driven along arrows respectively F1 and F2. Each endless chain 3 has an active part, which is its inner strand 4, the return of the chain 3 being provided by its outer strand 5. The two inner strands 4, belonging respectively to the two chains 3, in particular have divergent parts which correspond to the transverse stretching zone of the film 2. We are concerned here, more particularly, with the device which ensures the drive of the two endless chains 3. This drive device is describes, in what follows, for only one of the two chains 3, taking into account the perfect symmetry of the system.

The drive device comprises two toothed drive wheels 6 and 7, of vertical axis A and B respectively, therefore located themselves in a horizontal plane, that is:

- A first toothed wheel 6 located at the outlet of the drawing machine, in other words at the front end of the inner strand or "go" strand 4;

- A second toothed wheel 7 located at the entrance to the stretching machine, in other words at the rear end of the outer strand or "return" strand 5. The two drive toothed wheels 6 and 7 have a large diameter D , greater than 1.5 meters, and whose order of magnitude is for example from 1.5 meters to 2.5 meters.

Referring to Figures 2 and 3 we will now describe the structure and the rotational drive means of one of the toothed wheels 6, the other toothed toothed wheel 7 having a structure and similar drive means.

The toothed wheel 6 proper comprises an outer ring 8, provided with an external toothing 9 adapted to the characteristics of the endless chain 3 to be driven, which chain passes over this external toothing 9. The external crown 8 is integral with a flange central 10.

Beneath the outer ring 8 is concentrically mounted a ring 11 with internal toothing 12, serving to drive the wheel 6 in rotation.

The assembly constituted by the two concentric rings 8 and 11 is mounted rotating by means of a set of balls 13, carried by a horizontal support 14 belonging to a fixed frame 15, the set of balls 13 also holding the wheel tooth 6 in a horizontal plane.

The frame 15 supports an electric servo motor 16, the output shaft 17 of which is arranged horizontally drives a gear reducer 18, with angle gear. The vertical output shaft 19 of the reduction gear 18 carries a motor pinion 20 of relatively small diameter, which engages the internal toothing 12 by forming an additional reduction stage, for the rotational drive of the toothed wheel 6 from servo motor 16.

Again considering the whole stretching machine, on each side of the latter the endless chain 3 is driven by the two toothed wheels 6 and 7, motorized as just indicated, the servo motors respective 16 of the two wheels 6 and 7 being synchronized. The first toothed wheel 6 thus pulls the "go" strand 4 of each endless chain 3, while the second toothed wheel 7 pulls the "return" strand 5 of this chain 3.

Claims

1. Drive device for transverse stretching system for plastic films, of the type of those using, for holding, transporting and stretching the film (2), successive clamps supported and guided by rails, and driven forward by endless chains (3) connecting the clamps together, characterized in that it comprises, for driving each endless chain (3) connecting the clamps, at least two toothed drive wheels (6,7) of large diameter (D), either a toothed drive wheel (6) located at the front end of the "go" strand (4) of the chain (3), and another toothed wheel of drive (7) located at the rear end of the "return" strand (5) of the chain (3), with each toothed wheel (6,7) being associated with motorized means (11 to 20) for driving in rotation of this wheel (6, 7), and the motorized drive means associated respectively with the two toothed wheels (6,7) being synchronized in be them.

2. Drive device according to claim (1), characterized in that the toothed drive wheels (6,7) of the chains (3) have a diameter (D) greater than 1.5 meters.

3. Drive device according to claim 1 or 2, characterized in that the motorized rotary drive means are, for each drive toothed wheel (6,7), a controlled electric motor (16), both motors (16) associated respectively with the two toothed wheels (6,7) being synchronized in speed, and controlled so that the torque necessary for driving the endless chain (3) is distributed substantially equally between the cog wheel (7) located at the inlet of the transverse drawing system and the cog wheel (6) located at the outlet of the transverse drawing system.

4. Drive device for transverse stretching system of synthetic material films, in particular according to one of claims 1 to 3, characterized in that each toothed drive wheel (6, 7), of large diameter (D ), is constituted by an external crown (8), with a toothing (9) adapted to the chain (3) to be driven, and a support part (14) fixed, horizontal, the crown (8) and said support part (14 ) being linked to each other by a set of balls (13) or rollers ensuring guidance in rotation of the outer ring (8), while the support part (14) is fixed horizontally to a frame (15).

5. Drive device according to claim 4, characterized in that the outer ring (8) of each toothed drive wheel (6,7) of large diameter (D) carries an internal toothing (12), of close diameter the outside diameter (D) of said wheel, toothing (12) with which engages a motor pinion (20) of relatively small diameter (d), itself driven in rotation from the motor means (16) associated with the wheel considered.

6. Drive device according to claim 5, characterized in that the motor pinion (20), in engagement with the above-mentioned internal toothing (12), is rotated directly by the associated motor output shaft (16) .

7. Drive device according to claim 5, characterized in that the driving pinion (20), in engagement with the above-mentioned internal toothing (12), is rotated by means of a reduction gear (18) with or without angle gear, reducer (18) which is relatively small.