Patent Application
20180036987
The present invention relates to a method for producing bags according to which, from a tubular body including lines of transverse perforations delimiting the tabs of the future bag, two separation steps are carried out along the lines of perforations for separating the two consecutive bags, and a piece of waste remaining on one of the bags between the two tabs. It also relates to a machine implementing said method.
To produce bags industrially, particularly of paper, a technique is known consisting of forming a tubular body from a sheet of paper in rolls, separating the segments starting from this tubular body and closing one of the ends of the segment to form a bag. The tubular body can also be constituted with a portion made of plastic, transparent for example, assembled by gluing with the paper by covering the respective edges.
Document FR 786 579 shows several examples of this technique. It shows in particular, in
There exists a particular case of a bag without a rear tab for which the opening line crosses the entire paper strip and is offset from the central line.
The tubular body is formed by folding each edge over the central portion and gluing the two edges along a central junction between them. The tubular body thus formed passes between a pair of drive cylinders which drive the tubular body at a constant speed. The tubular body passes between a pair of separating cylinders rotating with a higher peripheral speed than that of the drive cylinders before being driven toward a folding device. One of the cylinders of the pair of separation cylinders is hollowed out over a large portion of its perimeter so as to come into contact with the other cylinder only intermittently. During this contact, which occurs between the opening line and the central line, the tubular body is put into tension between the drive cylinders and the separation cylinders so as to obtain the separation of a segment derived from the tubular body at the central line of perforation and the bottom lines. The front portion of the segment which was just separated is then grasped by the folding device which rotates with a greater peripheral speed than that of the pair of separation cylinders. The pair of separation cylinders holds the separated segment at this time between the central line and the bottom line, that is only the upper portion of the segment, so that the portion of the segment between the opening line and the bottom line is separated from the segment, forming a piece of waste. The piece of waste is driven downward by the lower cylinder of the pair of separation cylinders equipped for this purpose with spikes that plant themselves in the waste piece between the central line and the bottom line. A rear tab is thus formed on the segment, likewise a front tab at the end of the tubular body. This front tab will be found on the following segment. The front and rear tabs are situated on the same side of the segment, that is in the lower portion. The front tab is bonded and folded by the folding device to close the front portion of the segment.
The ratios of peripheral speeds between the drive cylinders, the separation cylinders and the folding device are generally determined in a fixed manner by mechanical drives from the same drive motor.
The grasping of the waste piece on the rear side imposes limitations on the operating speed of the machine. In fact, the front portion of the waste piece can turn over because it is not held. This phenomenon is particularly noticeable with a great length of the waste piece and with a high rate of production. When the front portion turns over, it can bring about the detachment of the waste piece, which then risks being jammed in its removal path.
Variants have been provided to this technique. Document DE 647 889 shows an identical technique wherein the central line is subdivided into two lines so that the waste piece forms a complete ring.
Document FR 829 591 proposes to add a pair of cylinders between the pair of separation cylinders and the folding device, so as to be able to accomplish the operation of separation in lieu of the folding device. This document also proposes to add a pair of auxiliary cylinders between the drive cylinders and the separation cylinders, by clamping the tubular body only during the tearing operation.
It has also been proposed to add a pair of retrieval cylinders positioned downstream of the pair of separation cylinders, driven at an over-speed with respect to the speed of the tubular body. This makes it possible to grasp the front end of the tubular body after separation and cause it to retrieve the possible delay that the end may have incurred due to retention by the pair of separation cylinders. However, once the retrieval is accomplished, the over-speed induces friction of the catch-up cylinders on the tubular body and the wear of said cylinders, which can be rapid.
Document FR 1 159 929 proposes to distinguish the two separation operations by providing two stations between which the separation between the segment and the tubular body occurs and two other stations between which the second separation between the tubular body and the waste piece occurs. This arrangement tends to make the production machine bulky and expensive due to the multiplication of the number of stations. It can apply only to a machine the dimensions whereof have been made sufficient to accommodate supplementary stations, which is not the standard case.
The invention aims to supply an alternative arrangement which simplifies the construction of the machine implementing the production method, which allows a compact machine and which facilitates the implementation of the method during adjustment depending on the format of the bags to be produced.
With these objectives in view, the invention has as its purpose a method for producing a bag according to which, starting with a tubular body including lines of transverse perforations delimiting a rear end of a first bag and at least one front tab of a second bag following the first between a central line and a bottom line, a first step occurs consisting of a separation of the first and of the second bag and, in a second step, separating a waste piece remaining on one of the bags between the rear end and the front tab, characterized in that the first and the second step are accomplished between, on the one hand, a first pair of separation cylinders and, on the other hand, a second pair of separation cylinders downstream of the first pair of separation cylinders with respect to the scrolling direction of the tubular body, the waste piece being clamped between the central line and the bottom line between the cylinders of the first pair during the first step to be retained on the second bag, then clamped and torn off by the second pair during the second step, the first pair of cylinders being driven with a lower peripheral speed than that of the second pair at least during the first and the second step.
The method according to the invention makes it possible to produce bags according to the same principle as in the prior art, but with only two pairs of separating cylinders, while the prior technique required at least one additional pair of cylinders to accomplish the second separation. The machine implementing the method according to the invention can thus be more compact because it uses the same two pairs of cylinders for accomplishing the two separation steps. For this reason it is less expensive due to the reduction in the number of pairs of cylinders and due to the reduction in the size of the machine. Another advantage is that the waste piece is carried at the front of the second bag, which makes it possible to grasp it by the front for its removal. Even if it is long, its removal is not affected, the long portion being located at the rear and not risking turning over or becoming detached. In fact, in the prior art, when the waste piece remains attached to the rear of the first bag, the only possibility for grasping it is the rearmost portion, and it becomes difficult to guide it during its removal, in particular in the case of a great length of the waste piece.
According to an original arrangement, the tubular body is driven upstream of the first pair of cylinders using a pair of drive rollers turning at a constant peripheral speed, called the reference speed, the peripheral speed of the first pair of cylinders being less than the reference speed during the first and the second step. During each step, the tubular body is thus retained by the first pair of cylinders, the portion of the tubular body between the pair of drive rollers and the first pair of cylinders being slackened and sometimes even temporarily forming a wave. This possible wave is absorbed thereafter when the first pair of cylinders no longer clamps the tubular body.
According to another arrangement, the speed of at least one of the cylinders of the first pair of cylinders is adjusted between the second and the first step so that the gripping of the waste piece between the cylinders of the first pair is synchronized with the gripping and the tearing off of the first bag by the second pair of cylinders. It must be possible to adjust the length of the bag on the machine. However, the length of the bag which runs between the clamping of the bag during the first, then during the second step, corresponds substantially to the distance between the first and the second pair of cylinders. In fact, during the first step the clamping by the first pair of cylinders takes place at the waste piece between the central line and the bottom line, to maintain it with the second bag. The clamping during the second step takes place when the waste piece maintained on the second bag is at the second pair of cylinders, hence after traveling a substantially fixed distance, which does not depend on the length of the bag. On the other hand, the interval between the gripping of the second step and that of the first step for the following bag depends on the length of the bag. It can therefore be advantageous to adjust the speed of rotation of the first pair of cylinders between the second and the first step to adapt the cycle to the length of the bag. The adjustment of the speed of rotation of the cylinders is accomplished for example by using a synchronous electric servo-motor. The means for adjusting the speed of the first pair of cylinders can also be utilized to adapt the peripheral speed during the first and the second step so as to limit the gap using the scrolling speed of the tubular body. Thus, the end of the tubular body has very little delay after the first separation step with respect to normal travel, and it is then not necessary to provide retrieval cylinders downstream of the first pair of cylinders. The speed gap can be adjusted for each type of production, depending on the format of the bags and the nature of the tubular body material.
Similarly, the speed of at least one of the cylinders of the second pair of cylinders is adjusted between the second and the first step so that the gripping of the first bag between the cylinders of the second pair is synchronized with the clamping of the waste piece by the first pair of cylinders. The peripheral speed of the second pair of cylinders is always greater than the peripheral speed of the first pair of cylinders during the first and the second step, but changes freely between the steps and could be more rapid or slower than the first cylinders and could be different depending on the format of the bags.
According to one application of the method, the lines of perforations also delimit a rear tab at the rear end of the first bag facing the front tab of the second bag.
The invention also has as its object a machine for producing bags including means for forming a tubular body including lines of transverse perforations delimiting a rear end of a first bag and at least one front tab of a second bag following the first, separation means for, in a first step, accomplishing a separation of the first and second bags and, in a second step, separating a waste piece remaining on one of the bags between the rear end and the front tab, the machine being characterized in that the separation means include a first pair of separation cylinders, driven by first drive means, and a second pair of separation cylinders, driven by second drive means, the separation means being configured to clamp the waste piece between the cylinders of the first pair during the first step and to retain it on the second bag while the second bag is clamped between the second pair of separation cylinders, the first and the second drive means conferring a peripheral speed to the first pair of cylinders that is less than that of the second pair, at least during the first and the second step.
According to a complementary feature, a principal cylinder of the second pair of separation cylinders includes grasping means for seizing the waste piece during the second step. The grasping means make it possible to carry away the waste piece in the rotation of the cylinder which includes these means. These are conventionally a line of spikes, but it can also be a suction cup or an adhering surface. Other means are provide for then withdrawing the waste piece from the grasping means.
According to a first arrangement, the principal cylinder of the second pair of separation cylinders includes a clip for clamping the tubular body, the grasping means being retractable so as to be retracted during the first step. The same clip carries out the gripping during the first and the second step, which necessitates that the grasping means are retracted during the gripping of the first step. This arrangement makes it possible to optimize bulk and to reduce the minimum size of the bags.
According to a second arrangement, the principal cylinder of the second pair of separation cylinders includes a first tear-off clip for clamping the tubular body during the first step and a second tear-off clip for clamping the tubular body during the second step, the grasping means being positioned in the environment of the second tear-off clip. Each of the clips is dedicated to one of the steps, which makes it possible to carry out the two steps during one cycle of rotation of the principal cylinder. Such an arrangement makes it possible to obtain high rates of production and makes it possible to dispense with the mechanism for retracting the grasping means.
According to another constructive arrangement, the principal cylinder of the second pair of cylinders includes at least two tear-off clips, the grasping means being positioned in the environment of all the tear-off clips or of one of two tear-off clip to clamp the tubular body during the first step with a clip not provided with a grasping device or the grasping device whereof is retracted, and a second tear-off clip with an operational grasping device for clamping the tubular body during the second step and grasping the waste piece. In this arrangement, it is possible, using second drive means, to accomplish clamping steps for the first step, either with the same clips or with different clips from those used during the second step. The two steps can be accomplished, depending on the adjustments selected, in less than one revolution of the principal cylinder, one revolution or even more than one revolution, which allows a high production rate over the entire range of formats. The tear-off clips can be positioned in a regular manner or variously offset.
According to one constructive arrangement, a principal cylinder of the first pair of separation cylinders includes a holding clip for clamping the tubular body during the first and the second step. Clamping on the clip is limited to the accomplishment of the separation steps, which leaves the possibility of conferring to the main cylinder which carries it or to the pair of cylinders an unconstrained rotation speed outside of these steps. The same clip is used for the first and for the second step, which allows a compact construction with a small diameter for the first pair of cylinders.
According to another constructive arrangement, a principal cylinder of the first pair of separation cylinders includes a first holding clip for clamping the tubular body during the first step and a second holding clip for clamping the tubular body during the second step. The two steps are accomplished during the same revolution of the principal cylinder, which allows a high production rate. The two holding clips can be positioned opposite one another or variously offset.
In one variant, a counter-cylinder of the first or of the second pair of cylinders includes an eroded zone, the corresponding drive means being configurable so that the first tear-off clip or the second tear-off clip faces the eroded zone intermittently during rotation of the principal cylinder. This thus offers many adjustment possibilities by making it possible to achieve at least one passage of one of the clips facing the counter-cylinder without it being active because it is not able to clamp the bag or the tubular body due to being facing the eroded zone. The eroded zone can take the form of a groove, a flat or any other shape locally reducing the radius of the cylinder, and extending along a generator of the cylinder. The counter-cylinder can include several eroded zones.
The invention will be better understood and other characteristics and advantages will appear upon reading the detailed description which follows, the description referring to the appended drawings wherein:
A machine conforming to an embodiment of the invention is shown schematically in
In
The second bag 28 includes a front tab 231 coming from the lower face 23 of the tubular body 20, and delimited by a central line 233 in the transverse direction and two diagonal lines 234 reaching the gussets 21. The gussets 21 and the upper face 22 are cut at the same transverse level as a bottom line 236 of which the front tab 231 projects forward. The portion of the tubular body 20 delimited between the diagonal lines 234 and between the bottom 236 and opening 235 lines on the upper face 22 forms the waste piece 26 which will be extracted. The rear tab 232 of the first bag 27 thus faces the front tab 231 of the second bag 28.
The perforation station 3 creates perforations on the entire width of the paper strip 2, at regular intervals. The perforations extend along the central line 233, diagonal lines 234, the opening line 235 and the bottom line 236 delimiting the bags on the upper face 22 and the gussets 21.
Referring to
The method implemented by the machine will now be described beginning with an arbitrary position, knowing that each position is found again in the following cycle. The method is a succession of cycles, one bag being produced for each cycle.
In the position shown in
The scrolling of the tubular body 20 and of the first bag 27 continues in the direction of the arrow F1 to the position shown by
The differential peripheral speeds of each pair of cylinders bring about tension between the waste piece 26 and the second bag 28 so as to obtain their separation along diagonal 234 and bottom 236 perforation lines, as shown in
Once the first bag 27 is separated from the tubular body 20, it is transferred to the folding device 6 which bonds, then folds over the front tab 231 over the upper face 22 so as to close the end of the bag. This device is conventional and is not described here in more detail.
Other than in the first and the second phase, the clips do not carry out clamping on the other cylinder of the pair. Thus, these periods without position constraints are used for accelerating or slowing down the rotation speeds of the cylinders so that the following clamping occurs at the chosen time with respect to the position of the tubular body 20 and to the desired speed. These adjustments in speed are adapted to each bag length.
Consider a machine the pairs of cylinders 51, 52 whereof rotate synchronously, at one revolution per bag produced. The cylinders of the first pair have a developed perimeter of 320 mm while those of the second pair have a developed perimeter on the order of 430 mm. The counter-cylinders are smooth while the main cylinder of each pair carries two diametrically opposed clips. The developed perimeter ratio determines in principle the speed ratio during the first and the second phase, so as to obtain the separation of the tubular body or the waste piece. With reference to
If the tear-off clips did not have a relative angular position identical to that of the holding clips, it would be necessary to cause the rotation speeds of each pair of cylinders to change independently.
In one variant, not shown, the cylinders in the lower portion turn at a constant speed, and only the speed of the cylinders carrying the clips are adjusted. The result is lower inertia of the movable portion which undergoes accelerations. It is however necessary to provide at least one other motor for the counter-cylinders.
The invention is not limited to the embodiment that has just been described. The clips can positioned by pairs on one and the other cylinders of the same pair. It is also possible to provide only one clip per pair of cylinders, the cylinders carrying out two rotations per cycle to accomplish clamping both in the first and in the second step. This solution can apply to one of the pairs of cylinders or to both. When it applies to the second pair of cylinders, it is necessary that the grasping means be retractable so as to be active only during the second step.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1462928 | Dec 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/080531 | 12/18/2015 | WO | 00 |
