Dual contact system for folding in a concertina-fashion

[0001] The subject of the invention is a device for wrapping, preferably covering a unit product on a pallet in a sleeved or hooded stretch film, having the features according to the preamble of claim 1, and a corresponding method with the features according to the preamble of claim 14.

[0002] Units for wrapping unit goods, as regards their basic components, are usually made as the apparatus described in European patent application 0 344 815 A1. They usually consist of a body on which the lifting frame can move up and down (approximately in the vertical direction). Typically, folding yokes are supported on the lifting frame, which can move transversely to the lifting frame (and thus approximately in the horizontal direction) to flexibly stretch the stretch film laterally when applied to the folding yoke. Usually the horizontal or lateral flexibility is from 10% to well above 50% with respect to the dimensions of the non-stretched transverse stretch film. Folding yokes can be shaped differently. It can be a very simply shaped finger yoke, but also yokes designed for stronger stretching, which are often T-shaped. In the latter case, the folding yoke consists essentially of a vertically extending shaft taking up the folded stretch film and a segment, which is essentially horizontally extending therein and made with a curvature of a certain radius, which segment rounds the respective corners of the film under tension on the folding yokes. To fold the sleeve or hood stretch film, the folding yokes are usually inserted into the inner bottom end of this sleeve or hood stretch film. Then, by means of folding devices, a section of stretch film is applied to the yokes, which is later to cover the lateral surfaces of the packaged load.

[0003] In this context, a folding device is understood to be the part of the device that comes into contact with the stretch film during its folding and, by means of its drive, transfers forces to this stretch film in an appropriate manner, whereby the stretch film is introduced onto the folding yokes overcoming resistances friction occurring on these folding yokes and is folded into a harmonica. Usually, a folding device in the form of a motor-driven folding roller is associated with each folding yoke. The folding device can, as a rule, be moved against a given folding yoke, so that the folding roll using the folding yoke as a resistance is pressed against the stretch film and pulls the stretch film onto the folding yokes using the existing friction forces and can fold it. The folded stretch film is then deposited on the folding yokes in said accordion folds.

[0004] The ready-folded stretch of stretch film is then stretched by a suitable method in the transverse direction of the folding yokes, i.e. generally in a generally horizontal direction. At the same time, all folds and in particular the mentioned folding folds are tightly pressed together. Therefore, two or more heavily compressed layers of stretch film overlap in several places - when viewed in the horizontal direction - and thus folds form, which can be referred to as "folds".

[0005] The coefficient of friction "film on film" is generally smaller than the coefficient of friction "film on folding yoke". When pulling stretch films from corrugated yokes (during stretch foil covering operations), moving and sliding along the corrugated yokes have ideally a tendency to straighten when slipping on these yokes, so that such a fold is removed before it reaches the upper edge of the respective folding yoke. However, it may happen that some folds do not straighten quite quickly and jump down without smoothing from the folding yoke. In this case, the fold fold is impacted, whose individual layers are no longer frictional pressed together when the fold folds off the folding yoke. As a result, this often leads to thin film stretching and breaking of the stretch film.

[0006] In addition, in the case of modern folding yokes, the film may break even when the fold fold only approaches the upper edge of the folding yoke on the pull side and only then is it straightened. This is because modern folding yokes are shaped such that the highest load on the foil hood occurs within the upper edge of the folding yoke on the pull side.

[0007] Various proposals for solving this problem are already known from practice.

[0008] Thus, a solution is known in which the folding yokes, when viewed in a vertical direction, are of sufficient length and folding folding devices with their driven folding rollers acting on the folding yokes act on the film almost in the middle of the folding yokes or at a sufficient distance from the upper edge of the folding yokes on the pull side, so below the folding rollers the stretch film is arranged in a harmonica, and above the folding rollers, depending on their tractive force, the foil hood adheres smoothly on a not very short section to the elongated part of the folding yoke. However, such oversizing of folding yokes is not desirable. This entails additional construction costs, in particular the devices have an increased overall height and, above all, the path which the folding yoke or the lifting frame supporting them must vertically travel during each packing operation. This adversely affects the speed of the device, which is of great importance.

[0009] Furthermore, devices are known in practice that achieve the desired end result by the fact that the folding rollers causing folding to folding yokes move at the end of the folding operation in a translational movement towards the upper edge of the folding yokes on the pull side. Such a movement results in the fact that the stretch film on a given folding yoke is stretched smoothly or spread evenly over a certain section, so that lateral folds form lateral stretching only at a distance from the end of the folding yokes on the pull side. This type of additional movement of the folding rollers at the end of the folding operation is an additional technological operation when preparing the stretch film for covering the load, which causes unnecessary waste of time, especially for high-performance devices . In addition, the additional progressive movement of the corrugating rollers increases construction costs, and thus costs, as well as being an additional source of possible defects. Besides, it is not always possible to provide smoothing in this way.

[0010] Furthermore, in the prior art, for example in the preamble of claims 1 and 14 of the corresponding description DE 40 37 105 C1, a solution has already been proposed in that pairs of rollers or rollers are arranged on the longitudinal sides of the folding frame, which - when the folding frame is in the position of sliding the foil hood - they serve as a pair of rollers extending this hood in its longitudinal direction, wherein during the folding operation of the stretch film for the folding fingers all the rollers work at the same circumferential speed and rotate in the same direction. When pulling or covering the packaged goods with a foil hood, the rollers are driven in the opposite direction than when folding, whereby the rollers are driven with different circumferential speed to pull, to ensure even and undisturbed removal of the stretch film.

[0011] Therefore, at the heart of the invention is the task of creating this type of device and method, ensuring that folding stretch of stretch film wraps around the side surfaces of the load is folded and fastened by simple means, so that when the stretched film is removed, the danger of lap folds getting into the critical zone of the folding yokes is significantly reduced and the stretch film in this zone does not undergo thin film stretching or damage.

[0012] The device-related part of this task is solved according to the invention by means of a device with the features according to the preamble of claim 1, wherein each folding device has folding tools with which it can act on the stretch film at least temporarily simultaneously in two zones spaced apart in the direction of the folding, the stretch film section between the two zones is placed overlapped on the respective folding yokes. In this case, each folding device has at least one first folding roller and a second pull roller further down in the direction of folding, wherein, while the device is operating in the folding mode, the folding roller on its circumference in contact with the stretch film has a lower circumferential speed than the pull roller, the stretch of stretch film between the folding roller and the pull roller is stretched, preferably it is flexibly stretched and positioned without overlaps on the corresponding folding yokes. Possible folds getting into the area between these zones are smoothed in this area both for folding and for pulling.

[0013] In this way, it is ensured that the stretch film at the beginning of the main coating operation is smooth on a certain, not very short section (hereinafter the "smooth section") in front of the upper edge of the folding yoke on the pull side, and thus lies on the folding yokes without folds lap. All pleat folds, which during the covering of the packaged load with stretch foil are possibly pulled off from the harmonica supply of the stretch foil and initially slide on the appropriate folding yokes, are therefore located at a defined, greater distance from the critical area near the upper edge of the folding yoke on the side pull, but these folds should generally not get into this critical area. It is thus ensured that any fold fold that is not straightened immediately when being pulled from the harmonica stock of the stretch film must first slide over a specific section along a given folding yoke before it reaches the critical area of ​​this folding yoke. In the course of this slip over a longer section, most of the folds are straightened before they reach the critical area. Thus, the risk of disturbances caused by thin-film stretching or rupture of the stretch film, which occurs especially when hoods are first formed, is significantly reduced.

[0014] Preferably, both said zones are spaced apart such that these folds are reliably straightened. Only in a few cases do folds persist between these zones and they can get into the critical area. This effect is advantageously obtained both when folding the film on the folding yokes, as well as when pulling the film from these yokes.

As already mentioned, the folding devices are shaped such that each such device has two driven folding tools arranged in a folding direction, which are formed as rollers, namely as a first folding roller and a second pull roller arranged behind it. the distance can be advantageously adjusted.

[0016] The device is shaped so that the folding roll, i.e. the roll to which the film first comes at the beginning of the folding operation, has a lower circumferential speed on its perimeter in contact with the stretch film than the second, i.e. the next pull roller, so that the film section the stretch between these rollers is stretched or wrinkled during folding. Such stretching (without significant elongation of the film) causes unfailing straightening of the folds that possibly get when folding the hood in the area between the two rollers.

[0017] Preferably the device is shaped such that the stretch film during operation of the device at least in one place on an imaginable straight line connecting said zones does not come into contact with the folding yokes or the folding devices. Thanks to this, during folding and tightening, it is particularly effective to straighten and smooth the folds reaching the area between the two rollers. Folds that possibly get into this area can be easily straightened with this configuration because there is no friction between the individual layers of the film within the folds when the given fold on the straight line connecting said places does not come into contact with the folding yokes or the folding devices. Any forces perpendicular to the fold that could hold this fold by friction are eliminated.

[0018] Particularly preferred is the configuration of the device in which one of the two rollers during operation of the device presses the stretch film against the elastically resilient portion of the respective folding yoke. This ensures particularly effective interaction of both rollers and eliminates overloading of the film in the area between two rollers, because within the roll pressing the film to this elastically resilient fragment, slip (if necessary) may occur between the film and the roll. Preferably, the elasticity of this portion can be adjusted to determine exactly when the slip occurs.

[0019] It is good if at least one of the two rollers, preferably a pull roller, is profiled so that when rolling over the stretch film it does not contact the stretch film constantly. This helps to straighten the folds that hit the fold between the rollers. The same applies to the profile of flexible transverse ribs.

[0020] When the device is shaped such that both rollers of each folding device are driven by one motor during operation of the device, the construction effort is particularly low. In this case, it is also advantageous if one of the two rollers, in particular the pull roller, is equipped with a low-speed mechanism that allows free rotation in the download direction to ensure that the film is pulled off easily from the folding yokes. It is also conceivable that separate drive motors are provided for these rollers, which, thanks to individual control, allow the rollers to be accelerated or delayed to achieve, for example, a braking effect.

[0021] The device can be further simplified when only the pull roller is operated in folding, i.e. drive, and the folding roller is retrograde driven, i.e. braked, during operation of the device. Also then, a tensile stress arises between the two rollers, thanks to which folds are reliably straightened during folding, which hits the area between the two rollers. [0022] In addition, it is possible to imagine for each of these rollers its own independent motor drive and / or independent infeed devices. However, the following is simple in construction and reliable solution shown in the embodiment in the figures, which under certain conditions is even suitable for use in existing devices, because the piston rod of the infeed device only needs to install a tandem roller instead of the existing single folding roller with its motor, which is a tandem of rollers, thanks to a chain or belt transmission, it is also driven by only one folding motor and therefore no major changes to the machine's control are needed.

[0023] This invention is particularly important for this type of packaging machine which works not only with high horizontal stretching, but also provides a significant vertical stretching of about 10% to 50%, in particular over 50%, compared to the unstretched state in a vertical direction , because when processing stretch film subjected to such a biaxial stress of high value, it is necessary to prevent cracks caused by slipping folds.

[0024] The method-related part of the invention is solved by the method according to claim 14, wherein the folding film is folded by folding devices by two spacing tools folding at least temporarily at the same time in two zones spaced apart in the direction of folding, so that after folding, a stretch of stretch film between these two zones is placed without overlaps on a given folding yoke. During tightening, folds that possibly get into the area between these zones are also smoothed, so they cannot enter the critical area of ​​the upper edge of the folding yoke.

[0025] The embodiment of the invention is explained below based on the drawings in which:

Fig. 1 shows the main fragment of the device according to the invention, namely the folding yoke and the folding device assigned thereto, Fig. 2 a side view of the main fragment of the device according to the invention during folding of the film into the folding yokes before transverse stretching and Fig. 3 a side view of the main fragment devices according to the invention before removing the transversely stretched film from the folding yokes.

[0026] The device according to the invention, which is not shown in its entirety, consists essentially of known main assemblies, already mentioned at the beginning in connection with discussing the state of the art, which can be shaped in different ways or in different variants. Add to this other known assemblies needed in each case to implement the entire type of packaging process discussed here.

[0027] Fig. 1 shows one of the most common four - sometimes six or eight - folding yokes 1, and the folding device 2 assigned to it. The folding yoke 1 is intended to be mounted on a drive that can move it in a reciprocating horizontal direction marked with arrow S. The folding device 2 consists of a feed device 4, here preferably in the form of a pneumatically moved feed cylinder, a folding device consisting of a folding roller 5a and a pull roller 5b, a folding motor 3 driving both of these rollers and a chain or belt transmission 6 providing the necessary gear . The feed device 4 is properly controlled and ensures that the folding roller 5a and the feed roller 5b are brought into their working position, and at a given time can withdraw them from this position by moving left or right in accordance with the arrow V. The feed device 4 is usually mounted with its plinth 7 on the same power unit, which also moves the folding yoke 1 according to the arrow S. In this way, it is ensured by simple means that when the folding yoke propagates to transversely stretch the stretch film, the folding device 2 moves away with the folding yoke 1. [0028] As can be seen in Fig. 2, the folding yoke 1 at its upper edge on the side the download area has a critical zone K. Only a few may reach this critical zone K when removing the stretch film from the container 8 of the folded stretch film, preferably no folds should occur. This is because in this critical zone K the cross section of the yoke changes significantly. As can be seen in Fig. 1, the folding yoke tapers locally in the constriction zone 9, while within the upper part 10 of the yoke it stretches the film even more. When the film slides along this zone K, its load changes rapidly. For this reason, overlap folds should not reach this area as much as possible, since under the influence of these rapid load changes the danger of thin film stretching or tearing increases. The critical K zone in the usual devices used in practice is located within the upper edge of the folding yoke. However, as an alternative one can imagine the use of almost smooth from top to bottom folding yokes without major changes in cross section, whereas in such shaped folding yokes it is only necessary to prevent "folding" of folds from folding yokes.

[0029] At the beginning of each folding operation, the folding devices are retracted according to the arrow V, so that there is a significant gap between the given folding yoke 1 and the rollers 5a and 5b. The folding yoke 1 and other (not shown) folding yokes are inserted a little into the sleeve of the stretch film, most often with the help of additional auxiliaries, preferably at such a distance that the bottom edge of this sleeve just covers the low-speed roller 11 fixed on the folding yoke 1. With due to the relatively short path required, the position of the folding yokes in the sleeve of the stretch film should be adjusted quickly.

[0030] Next, folding devices are provided, the stretch film being held between the low-speed roll 11 and the folding roller 5a by friction. The folding motor 3 is started, after which the stretch film is pulled down on the folding yoke 1 as a result of frictional contact with the folding roller 5a. After a short time, the lower end of the stretch foil sleeve is also gripped by friction by the below mounted pull roller 5b. Thus, the stretch film is acting by a corrugating roller 5a in the first contact zone (zone Z1) and a pull roller 5b in the second contact zone (zone Z2). The chain or belt transmission 6 interlocking both rollers 6 in this embodiment is designed so that the lower bearing roller 5b rotates faster than the folding roller 5a, so that the stretch film between the two rollers 5a and 5b is stretched in the area between the contact zones (Z1 and Z2) and depending on the difference in rotational speed of both rollers 5a and 5b, it is even temporarily stretched to a certain extent. [0031] As can be seen in fig. 1 and 2, the lower pull roller 5b in its operating position preferably does not rest directly on the rigid portion of the folding yoke 10, but cooperates with the bow 12, which - when viewed in the horizontal direction - is fastened with a screw 14 and springs in the horizontal direction under the action of a compression spring by means of a screw 13, in this way pressure of the bow 12 against the pull roller is caused. Instead of such, preferably unsteady bearing, the bow 12 can also be elastically-pivotably mounted. The bar 12 limits the force that the pull roller 5b can transfer to the film. Thus, friction forces transferred by the pull roller 5b to the film are also limited. Before the film overloads during folding between the slower folding roll 5a and the faster running pull roller 5b, there is slip between the film and the pull roller 5b. Advantageously, the force of the spring holding the bow 12 can be adjusted, which is not shown here.

[0032] Especially when folding the film hoods formed of stretch film sleeves, it is not possible to avoid the folds of the film sometimes passing through the folding roller 5a during folding and getting into the area between the two rollers 5a and 5b. They are effectively stretched there due to the fact that the faster rotating pull roller 5b stretches the film and these folds lose contact with the folding yoke in the zone between the low speed roller 11 and the bow 12.

[0033] The pull roller profile 5b also has a great effect to eliminate folds or improve smoothness. This profile is made of individual, circumferentially flexible ribs 17, between which there are wide gaps (profile gaps). As a result, there are advantageously rapid load changes outside and inward stretching the film between both rollers 5a and 5b, which optimizes the result.

[0034] This arrangement of the folding device with at least two rollers 5a and 5b seated separately along the vertical axis of the folding yoke 1, i.e. in the folding direction, ensures at the end of the folding that between the critical zone K and the zone ZH visible in Fig. 2, whose 8 foil stock is arranged in a harmonica, there is a fairly long zone G, in which the stretch foil remains virtually constantly smooth. The boundaries of zone G in the folding and withdrawal direction are defined by zones Z1 and Z2, i.e. the zones in which the folding roller 5a presses the film against the slow-speed roll 11 and the pull roller 5b presses the film against the roll 12, thus entering frictional contact with the film.

[0035] The skilled person can easily determine the vertical size of the G zone needed in a particular case. It depends on the parameters determined by the device and the films used (friction coefficient between the folding yoke and film, between the film and the film, speed of pulling the film onto the load, geometry of the given folding yoke, degree of horizontal and possibly vertical stretching and so on), as well as from required reliability, i.e. the degree of certainty with which the specialist wants to prevent the folds from entering the critical zone K. As a rule, an optimal compromise is obtained between the required compactness of the folding yoke and sufficient certainty to avoid the presence of folds in the critical zone K. Preferably, the zone G is between the critical zone K and the zone ZH, in which the supply of 8 foils is arranged in a harmonica. To set the size of the G zone or ZH zone, you can adjust the height position, i.e. in the vertical direction, of the bow 12 mounted on the folding yoke 1, while the roller spacing 5a, 5b can additionally or alternatively be adjusted.

[0036] The result described above can be obtained under certain conditions also due to the fact that the pull roller 5b is mounted, for example, pivotably, and only just before the end of the folding process it is separately added so that it cooperates with the folding roller 5a. However, the preferred solution looks as shown in the figures illustrating the preferred embodiment. In this embodiment, low construction effort is sufficient, and the danger that the subsequent delivery of the pull roller 5b could cause undesirable stacking of the film or a similar undesirable phenomenon is adversely affected.

[0037] Furthermore, the rollers 5a and 5b, when viewed in the folding direction, need not be positioned with high accuracy. Some reciprocal lateral displacement of both rollers 5a and 5b, which does not disturb their operation, is allowed.

[0038] As can be seen further in Fig. 3, the film loosely laid after folding on the folding yokes is stretched in a substantially horizontal direction due to the folding yokes and folding devices moving away by a distance that depends on the width of the packaged goods. At the same time, the pulling force of the stretched film, which is generated during this retraction, which acts in a generally horizontal direction, causes the overlapping folds 18 overlapping in the ZH zone during folding 18 of the loosely stored supply of stretch film to adhere tightly to the folding yokes under significant tension in the ZH zone.

[0039] During the stretch film coating operation of the packaged load, the whole device performs a vertical movement, wherein the film is pulled from the folding yokes. Due to the advantageous configuration of the device described and illustrated in Fig. 1, it is ensured that at the beginning of the stripping operation the stretch film adheres smoothly, i.e. without folds to the folding yokes in the smoothing zone in front of the upper edge of the folding yoke 1 on the pull side. All pleat folds, which during possible coating with stretch foil of the packaged load are removed from the harmonica and 8 under high tension foil stock and then initially slide along a given folding yoke 1, are located at a defined, greater distance from the critical zone K, however, these folds preferably do not typically penetrate this critical zone. It is therefore ensured that any fold fold that is released when being pulled out of the harmonica stock 8 of the stretch film must first slide over a specific section along the respective folding yoke before it reaches the critical zone K of this yoke 1. During slipping in this section between zones Z1 and Z2, most of the folds in zone G are removed before they reach critical zone K. As a result, the risk of disturbances caused by thin-film stretching or breaking of the stretch film is significantly reduced, which occurs especially when hoods are first formed from the stretch film.

[0040] During the pull operation, the pull roller 5b in its operating position still rests - looking in the horizontal direction - on the unstably mounted bow 12 so that the smoothing effect in zone G between zones Z1 and Z2 is maintained. In this case, the lower pull roller 5b in its operating position preferably rests on the roll bar 12, which, when viewed in the horizontal direction, is secured by a screw 13 and under the action of the pressure spring held by the screw 13 spring in the horizontal direction, so that the roll roll 12 is pressed against the pull roller. As already mentioned, instead of such an advantageously unstable bearing, the bow may also have an elastically pivotable bearing.

[0041] In zone G, between zones Z1 and Z2, in particular, the film could pile up during its removal due to the different circumferential speed of both rollers 5a and 5b. To avoid this, it is preferable to shape the bearing or drive of the pull roller 5b so that it is properly driven in the folding direction by the motor 3 during the folding operation to provide a difference in peripheral speeds of both rollers 5a and 5b and thereby achieve the desired smoothing in zone G . However, in addition, the bearing or drive of the pull roller 5b is additionally equipped with a low-speed mechanism, which during pulling operation allows the free running of the pull roller 5b together with the film in the pull direction. Thus, during the pull operation, the folding roller 5a and the pull roller 5b have almost the same peripheral speed. There is no need for friction-free, costly to implement, slow running, because it is desirable to have frictional drag on the roller or in the free-running mechanism, which cause a slight braking effect of the film, favoring its smoothing during the pulling operation. An alternative solution would be adequate braking of the low-speed lead roller or - in a device equipped with two drives - driving the lead roller at a lower speed to also achieve the desired effect.