EP0270426B1 - Pass-through packaging method and machine - Google Patents

Description

The invention relates to a pass-through packaging method and machine for pre-stretched stretch film.

The pass-through packaging process and machine are intended for the packaging of palletized loads (front, side, rear vertical sides). A vertical transverse film curtain extending before the front face of the load is produced beforehand, from two film reels of fixed vertical axes placed on either side of a motorized conveyor on which the load rests, thanks to a transverse weld. We move the load towards the curtain. The curtain is deformed transversely in order to give it a generally U-shaped outline, to cover the front face and the side faces. The load is stopped when it has passed the coils. The curtain is transversely deformed on either side of the load in order to bring the film to the rear face, thus being closed in on itself. Thanks to cutting and welding jaws, a transverse cutting and double welding of the curtain is carried out in order to dissociate the packaged load from the film coming from the reels and, to reconstitute a film curtain for a following packaging cycle, for another charge.

These methods and machines were first used with heat-shrinkable films, the packaging proper being followed by heat-shrinking by means of an oven or the like (documents FR-A-2 212 263, US-A-3 514 920, US-A-3 640 048 and US-A-3 662 512).

These processes and machines were then used with stretch films. In a first technique (documents FR-A-2 243 113, US-A-3 672 116, US-A-4 -044 529), the stretching is carried out by braking the film reels. In a second technique, originally described in document FR-A-2 281 275, the film is pre-stretched: The film is stretched by means of pre-stretching before the film is applied to the load and independently of the load itself. The pre-stretching means comprise, for example, two rollers such that the downstream roller rotates with a greater circumferential speed than that of the upstream roller (with reference to the direction of advance of the film). In a particular embodiment - motorized pre-stretching - the two rollers are associated by pinions, a motor positively driving the rollers.

A development of the pass-through packaging process with motorized pre-stretching is described in document US-A-4 413 463 which provides a roller with a floating axis stressed by a spring, constituting a detector of the strength of the film carried by the load and control the motor of the pre-stretching means: gripper pads preventing the transverse cutting and welding being carried out on the film under tension, as also provided for in document US-A-3,672,116.

Another development is described in document FR-A-2 568 219 which provides that the machine is equipped with a pre-stretching system with speed gradient rollers. The announced objective is to obtain a substantially uniform film tension around the load. And, the technical means proposed is the presence of jaws with transverse displacement at the rear of the load combined with means for driving the film at relative speed relative to that of the appropriate jaws. However, this objective cannot be achieved for the entire film surrounding the front, side and rear faces of the load since the stretched film is applied to the load after a variable delay depending on the pre-stretching: long for the front face up to shorter for the back side; therefore the application of the stretched film to the load does not occur in the elastic return phase which immediately follows the pre-stretching phase. Likewise, the length of pre-stretched film before it is applied to the load varies widely. In addition, the film is welded in the stretched state which is not satisfactory.

Pass-through packaging machines with pre-stretching have certain advantages (notably automaticity) but pose certain problems which limit their use.

The first problem is obtaining a film clamping force on the load as constant as possible on the different faces of the load. Indeed, a simple control of the pre-stretching to the detected force of the film is not sufficient to obtain a sufficiently constant clamping force (document US-A-4,413,463). Likewise, an action on the film when covering the rear face does not allow an action on the entire film surrounding the load (document FR-A-2 568 219).

The second problem is the possibility of packing with the same machine and conveniently loads of different heights (spacing between the lower and upper faces), or of different widths, or even to locally reinforce the packaging, in particular in the part load height median.

The third problem is the possibility of depositing on the upper face of the load a plastic topsheet with the same machine and conveniently, mainly for loads of different heights.

The invention therefore aims primarily to solve these problems and, more generally, to provide a method and a pass-through packaging machine for pre-stretching the stretch film, remarkable for the quality of the packaging that they make it possible as well as for the automaticity which they guarantee and also the versatility of use which they present.

The invention relates to a method of pass-through packaging of a load with pre-stretching of the stretch film, according to which an initial film curtain is formed; the load is moved in the direction of the film curtain; the film curtain is deformed in order to cover the front face and the side faces of the load; we unwind the film coils and simultaneously it is pre-stretched by two pre-stretching means before applying it to the load, so that the film is applied to the load in the pre-stretched state; the movement of the load is stopped; the film curtain is deformed to bring it onto the rear face of the load; a transverse cutting and double welding of the film curtain is carried out (such a process is known from FR-A-2 568 219) by the fact that it starts from an initial position where the pre-stretching means are in a waiting position in front of the load, in which they are close to each other; then the pre-stretching of the initial film curtain is carried out and the pre-stretching means are moved transversely, ensuring the flow of pre-stretched film, to a spaced position close to the lateral faces of the load; then the film is pre-stretched for the side faces; then the film is pre-stretched for the rear face and the pre-stretching means are moved transversely to a close position while ensuring the necessary flow of pre-stretched film.

According to the invention, the pre-stretching means are maintained in the vicinity, in particular immediate of the face of the load on which the stretched film is applied. In addition, the speed of flow of the pre-stretched film is controlled as a function of the position of the load relative to the pre-stretching means so as to obtain clamping forces of the film on the different faces of the load which are equal. between them or close to each other.

According to another characteristic of the invention, the load is packaged in two successive passes, one where the film is attached to or adjacent to the lower face of the load and the other where the film is attached to or adjacent to its upper face .

A pass-through packaging machine according to the invention comprises a motorized conveyor on which the load can rest; and a pre-stretched film depositing assembly on the load comprising two film reel supports with generally vertical axes; pre-stretching means extending parallel to the film reels, two cutting and welding jaws movable transversely between two extreme positions, a spread position where the load can pass between them and a close position where they are applied one against the other (such a machine is known from FR-A-2 568 219) and is characterized in that two pre-stage means are mounted movable transversely between two positions, namely a separated position where the load can pass between them, and a close position close to each other on the path of the load carried by the conveyor.

Such a machine can also include two carriages which support the cutting and welding jaws and the pre-stretching means as well as,
respectively two guide rollers on which the film passes, the axes of the guide rollers and therefore the guide rollers themselves being movable between two extreme positions, an active projecting position and a retracted position, the guide rollers having the functions, in active projecting position, of preventing the friction of the film on the jaws and passing from the active projecting position to the position retracted (in position close to the carriages) to relax the film for transverse welding.

According to another characteristic, the machine can comprise two sets of film deposition respectively lower and upper and, optionally, integrated means of deposition on the upper face of the load of a topsheet in plastic material.

The inventor discovered, first of all, that the mastery of quality packaging, in particular with a film having a constant clamping force or varying little on the different faces of the load, was linked not only to the control of the pre stretching as is known but also and above all under the conditions in which the stretched film is applied to the load. After stretching, the stretch film subjected to itself tends, immediately afterwards, to see its tightening force decrease sharply while, simultaneously, its elongation rate decreases slightly (elastic phase of the hysteresis cycle). The inventor therefore developed the general concept that the control of the pre-stretch should be combined with an application of the pre-stretched film on the load as quickly as possible after the pre-stretch and in as constant a time as possible during the entire packaging cycle. The inventor also developed the particular concept that with the servo-control of the pre-stretching as a function of the strength of the film, as is known, it was preferable to replace a servo-function depending on the position of the load with respect to to the pre-stretching means.

The inventor also pointed out that in the case of a load of great height, it was preferable to substitute for a single curtain of film of large width, two curtains of weaker widths overlapping in the middle part of the load height.

These characteristics highlighted by the inventor are contrary to the teachings of document US-A-4 413463 in which the length of pre-stretched film before it is applied to the load is always large and varies greatly during a packaging cycle. In particular, due to the configuration of the machine, the length of pre-stretched film between the pre-stretching means is maximum when the film is applied to the rear face of the load. Likewise and consequently, the delay between the pre-stretching of the film and its application to the load is significant and also varies greatly during one packaging cycle. This results in particular from the existence of rollers for detecting the strength of the film, deflection rollers separating the film from the lateral faces of the load, from the length of the pre-stretched film as mentioned above, taking into account the position of the pre-stretching with respect to the load.

These characteristics are also contrary to those taught by document FRA-2,568,219, the object of which is, in fact, limited to the problem of covering the rear face of the load since then the latter is at rest.

The other characteristics and advantages of the invention will emerge from the description which follows with reference to the appended drawings in which:
Figure 1 is a schematic perspective view of a machine according to the invention, in a possible embodiment, the various parts of the machine being shown in a theoretical non-operating position for better understanding.

Figures 2A, 2B, 2C, 2D, 2E, 2F, 2G are seven schematic views from above illustrating the different stages of the method according to the invention for a film pass.

FIGS. 3A, 3B, 3C are three schematic views in cross section illustrating the jaws for cutting and transverse welding.

FIGS. 4A, 4B, 4C, 4D, 4E are five schematic side views illustrating the different stages of a method according to the invention with two passes, by means of the machine according to FIG. 1.

Figure 5 is a schematic side view illustrating the variant with the deposition of a topsheet on the load.

The invention relates to a method and a machine for pass-through packaging of a load 1, in particular palletized, by means of a film 2 in stretchable plastic, by the pre-stretching technique.

The load 1 has a parallelepiped shape delimited by a lower face 3, an upper face 4, horizontal, a front face 5, two lateral faces 6 and a rear face 7, vertical.

The load 1 may be in one piece or, made up of a plurality of elementary loads, the film 2 having the functions of ensuring the cohesion of the load 1 and, weather protection. The use of pre-stretching allows the packaging of loads 1 fragile or lacking in cohesion or having irregular or cutting shapes.

The film 2 is stretchable, that is to say having the properties of being able to be stretched between a few tens and a few hundred percent under the effect of a stretching force; to relax over time; to follow an elastic phase of the hysteresis cycle following its elongation; where appropriate, to follow a visco-elastic phase following the elastic phase; or if the film is blocked in elongation during the elastic phase to generate an increase in the clamping force. Such films are marketed in particular by the companies MOBIL, or EXXON. According to the invention, the concept of applying the film 2 to the load 1 in its elastic phase is implemented in order to increase the clamping force, once the film 2 is placed on the load 1. , the final objective being to obtain a clamping force as constant and as large as possible.

An initial film curtain 2 is formed beforehand, transverse in front of the front face 5, from two film reels 8 placed generally symmetrically with respect to a circulation path 9 (thanks to a motorized conveyor) of the load 1, thanks to a transverse weld 10: the load 1 is moved in the direction of the film curtain 2 (from upstream to downstream); the film curtain 2 is deformed transversely in order to give it a generally U-shaped outline so as to cover the front face 5 and the side faces 6: the film 2 is unwound from the reels 8 and simultaneously it is pre-stretched using two pre-stretching means 11 before applying it to the load 1, so that the film 2 is applied to the load 1 in the pre-stretched state; the movement of the load 1 is stopped when it has passed the film reels 8: the film curtain 2 is transversely deformed on either side of the load 1 in order to bring the film 2 to the rear face 7, the curtain of film 2 thus coming to be closed on itself: a transverse cut and double weld 10 of the film curtain 2 is carried out in order to separate the packaged load 1 from the film 2 coming from the reels 8 and to reconstitute an initial film curtain 2 for a next packing cycle, for another load 1.

The delay between the pre-stretching of the film 2 by the pre-stretching means 11 and the application of the pre-stretched film to the load 1 is particularly short as short as possible and varies only very slightly during a complete cycle of packaging. The film 2 is therefore applied to the load 1 in the pre-stretched state in the elastic return phase which immediately follows the pre-stretching phase.

To this end, the length of pre-stretched film 2 before its application to the load 1 is short, in particular as short as possible and varies only very slightly during a complete packaging cycle.

By delay between the pre-stretching of the film 2 and its application to the load 1 is meant the delay which elapses between the moment when the film 2 passes the pre-stretching means 11 and the moment when the film 2 is applied to the load 1. This delay is as short as possible because the pre-stretching means 11 are in the immediate vicinity of the load 1 and the path of the film 2 between the pre-stretching means 11 and the load 1 is as direct and short as possible.

For example, and without these values being limiting, this delay (pre-stretching-application on the load 1) is of the order of a few seconds, in particular 5 seconds, and the length of the pre-stretched film before its application to the load 1 is of the order of 50 cm.

In addition and in combination, the initial film curtain 2 is stretched immediately before applying it to the front face 5, unlike the prior art, in which the initial film curtain awaiting a operating cycle has already undergone stretching or pre-stretching.

The pre-stretching means 11 are permanently maintained in the vicinity, in particular immediate, of the face 5, 6, 7 on which the stretched film is applied, unlike the prior art where they are fixed and / or separated from the load 1.

This feature is implemented in three different ways. The first is that the pre-stretching means 11 are placed opposite, in front of and in the immediate vicinity of the front face 5 before applying the stretched film 2 to it. The second is that the pre-stretching means 11 are placed opposite, behind and in the immediate vicinity of the rear face 7 when the stretched film 2 is applied to it. The third is that the pre-stretching means 11 are located opposite and in the immediate vicinity of the side faces 6 when applying the stretched film 2 to them. The transverse displacement of the pre-stretching means 11 allows this immediate proximity, whatever the load 1.

In addition, the pre-stretched film 2 is applied directly to the load 1, in particular without passing the stretched film 2 through accumulator means or film strength detection means. It is therefore avoided, according to the invention, that the path of the film 2 between the pre-stretching means 11 and the load 1 is complex, indirect and therefore increased.

The application of the stretched film 2 to the load 1 occurs with a very short delay just after the pre-stretching, this delay being constant or varying only very slightly, for example of the order of a few%. The stretched film 2, at the time of its application on the load 1 is in the elastic phase of the hysteresis cycle which follows its stretching but close to the stretching point and the clamping force of the film 2 once on the load 1 is therefore increased.

This results in a clamping force of the film 2 on the load 1 varying little from one side to the other and a better pre-stretching yield.

According to another characteristic, under given conditions (linear speed of displacement of the load 1, characteristics of the film 2 and of the load 1 -dimensions, cohesion, brittleness, sharp edges or not, clamping force of film 2 on the load 1 after packaging) the speed of flow of the pre-stretched film 2 controlled by the pre-stretching means 11 of motorized type is controlled at the position of the load 1 relative to the pre-stretching means 11, so as to obtain film clamping forces on the different faces 5, 6, 7 of the load 1 which are equal to each other or close to each other. Such control is preferable to control over the strength of the film.

To this end, reference values of the speed of flow of the pre-stretched film are defined in phases of the cycle, namely: a first value V₁ for a first phase in which the initial stretching of the film curtain 2 is carried out : a last value V₄ for the phase in which the pre-stretched film 2 is applied to the rear face 7: at least one value V₂ intermediate in the phase in which the pre-stretched film 2 is applied to the side faces 6.

Preferably, at least two intermediate reference values V₂ and V₃ are defined, in particular corresponding respectively rather to the start and rather to the end of the application of the pre-stretched film 2 on the lateral faces 6.

The set values V₁, V₂, V₃, V₄ are calculated as a function of the geometry of the load assembly 1-pre-stretching means 11 and, of the general conditions under which the process.

The setpoints V₁ V₂, V₃ and V₄ take into account the fact that in the first phase of the cycle, the wire flow speed: pre-stretched can be constant. It is the same in the phase in which the wire: pre-stretched 2 is applied to the rear face 7. With regard to the side faces 6, the invention proposes a compromise with the determination of two set values corresponding to the two extreme positions of the load 1 relative to the pre-stretching means 11. However, it goes without saying that the invention could also operate with a single intermediate set value V₂ or even with a greater number of intermediate set values . In the first case, the clamping force will be less constant. In the second case, it will be more so.

The user can define one of the setpoint values, for example the first V₁ and the other values V₂, V₃ V₄ are set accordingly. The setting and implementation of the set values V₁ V₂ V₃ and V₄ allow the regulation of the pre-stretching means 11 without the need to measure the effective force of the film.

The implementation of the method may involve locating the position of the load 1 relative to the pre-stretching means 11 and, more particularly, locating the position of the front 5 and rear faces 7 so as to control the speed of the motor of the pre-stretching means 11. In general, the linear speed of movement of the moving load 1 is constant.

We start from an initial position (FIG. 2A) which is a waiting position, in which the two pre-stretching means 11 are close to each other, in particular at the right of the traffic path 9 of the load 1 The film curtain 2 between the pre-stretching means 11 is in the unstretched state. The load 1 is located opposite the film 2 and the pre-stretching means 11, its front face 5 facing and in the immediate vicinity of the film 2 and the pre-stretching means 11. Then and only at this time, (FIG. 2B) the initial stretching of the initial film curtain 2 is carried out and, for this purpose, the two pre-stretching means 11 are moved apart transversely while ensuring the necessary flow rate of pre-stretched film. The transverse spacing of the pre-stretching means 11 continues until a separated position where the pre-stretching means 11 are close to the lateral faces 6 while allowing the passage of the load between them. In general, the movement transverse spacing of the pre-stretching means 11 is produced at constant linear speed and to this speed corresponds a set value V₁ of the flow rate of film pre-stretched by the motorized pre-stretching means 11. During this movement of spacing of the pre-stretching means 11, the load 1 is stationary.

Then (Figures 2C and 2D) the load 1 is moved in translation from upstream to downstream, in particular at constant linear speed, and the film 2 is pre-stretched to apply it to the lateral faces 6, firstly to their area adjoining the front face 5 and finally for their area adjoining the rear face 7. As mentioned, preferably two set values V₂, V₃ corresponding to these two cases are fixed. In addition, the pre-stretched film 2 coming from the pre-stretching means 11 is preferably deformed with a view to being applied to the load 1, in particular by means of guide rollers described later.

Then (Figures 2E and 2F) the load 1 has exceeded the film reels 8 and then stops its translational movement. In this position of the load 1, the film 2 is pre-stretched for the rear face 7 and, for this purpose, the two pre-stretching means 11 are brought together transversely to a close position, ensuring the required flow of pre-stretched film and this as a function of the last setpoint V₄.

The pre-stretching means 11 are more spaced from one another in the standby position (FIG. 2A) than in the close position (FIG. 2E).

Then, once the pre-stretching means 11 are in this close position, the curtain is welded transversely film 2 (Figure 2F) immediately after pre-stretching and after stretching the film (Figures 2E and 2F). Finally, we return to the standby position (Figure 2G).

The carrying out of the transverse welding immediately after the pre-stretching results more especially from the fact that the pre-stretching means 11 are brought together so that the length of film between the pre-stretching means 11 and the solder 10 is very limited.

According to a variant, the film curtain 2 is applied adjoining or adjacent to the upper face 4 and, there is deposited on the latter a topsheet 12, of plastic material and its folded edges 13 are allowed to fall onto the faces 5, 6 and 7.

The topsheet 12 is a sheet of normal plastic or stretchable plastic or heat shrinkable plastic. In general, the topsheet 12 does not participate in the cohesion of the load 1 but only aims to protect it from the weather.

The establishment of the topsheet 12 is more particularly carried out in the following manner: first the folded edge 13 of the front sheet of the topsheet 12 is placed on the front face 5; then the film curtain 2 is applied to the front face 5 and to this folded edge 13 at the front so as to trap it securely. Then, gradually place on the side faces 6, first the folded edges 13 and, then, the film curtain 2. Then, finally, on the rear face 7 first place the folded edge 13 rear and then the film curtain 2.

Thus, the establishment of the topsheet 12 occurs simultaneously or, more precisely, slightly before, the establishment of the film curtain 2 around the load 1, so that the folded edges 13 of the topsheet 12 can be trapped by the film curtain 2 immediately before being put in place.

The invention also relates to a pass-through method of packaging a load 1 in which an initial curtain of film 2 is transversely formed before the front face 5; the load 1 is moved in the direction of the film curtain 2; the film curtain 2 is deformed so as to cover the front 5 and side 6 faces; the movement of the load 1 is stopped; the film curtain 2 is deformed transversely to bring the film 2 to the rear face 7; a transverse cut and double weld of the film curtain 2 is carried out and the load 1 is packaged in two successive and separate passes, one where the film 2 is attached to or adjacent to the underside 3 and the other where the film 2 is adjoining or adjacent to the upper face 4.

For this purpose, two films 2 are used, each of width less than the height of the load 1 between the faces 3 and 4, the sum of the two widths being greater than the height of the load 1 so that the two films 2 come to overlap, especially in the middle of the height of the load 1.

Preferably: the film adjoining the lower face 3 is first placed and then, in particular a short time after, the film adjoining the upper face 4. And two films with the same width and same characteristics are used.

A particular application of this method uses a stretch film 2 and the load 1 is packaged with pre-stretching of the stretch film, for each pass, by the method described above.

This two-pass process has the general advantage of allowing versatility of use for loads 1 of variable heights. The particular application of the two-pass process with pre-stretching has the additional advantages of avoiding the use of films of too large widths for loads 1 of great height and, also, of allowing a median reinforcement of the tightening.

The invention further relates to a pass-through packaging machine for a load 1 with pre-stretching of the stretch film 2 more specifically intended for the implementation of the process described, comprising a motorized conveyor 9 on which the load 1 can rest, defining a circulation path of the latter, placed generally horizontally, in particular a roller conveyor; and a pre-stretched film deposition assembly 2 on the load 1 comprising two reel supports 8 with generally vertical axes, symmetrical with respect to the conveyor 9; two pre-stretching means 11 extending parallel to the film reels 8 and also symmetrical with respect to the conveyor 9; two cutting and transverse welding jaws 14 of the film 2 also extending parallel to the film reels 8 and placed symmetrically with respect to the conveyor 9, movable transversely between two extreme positions, respectively spaced where the load 1 can pass between them and close together where they are applied against each other.

The two pre-stretching means 11 are mounted movable transversely between two extreme positions: a separated position where the load can pass between them and a close position close to each other.

The pre-stretching means 11 can also be in an intermediate position called the standby position located between the two extreme positions apart and close together and in which they are very close to one another.

In a preferred embodiment, the machine comprises two carriages 15 slidably mounted on a transverse support guide 16, in particular horizontal, supporting respectively the two cutting and welding jaws 14 and the two pre-stretching means 11 in close proximity to each other. others, respectively, in the transverse and longitudinal directions. The machine also comprises means for driving the carriages as well as means for controlling these driving means (not shown). The two carriages 15 are movable between two extreme positions, respectively spaced apart and approximated, corresponding to the two extreme positions of the pre-stretching means 11, and of the cutting and welding jaws 14.

The control means of the carriage drive means 15 are controlled as a function of the operation of the conveyor 9, under given operating conditions, so that in the initial position of a cycle the conveyor 9 is stopped and the two carriages 15 are in a standby position close to each other but more distant than in the close position. In this waiting position, the film 2 between the two pre-stretching means 11 is not stretched (FIG. 2A). Then, (FIG. 2B), the carriages 15 are brought into the separated position so as to allow the pre-stretching of the initial film curtain 2, the conveyor 9 remaining at a standstill. Then, (Figures 2C and 2D), the carriages 15 remain in their separated position during the operation of the conveyor 9 so that the load 1 is wrapped with the film curtain 2 as described in the operation of the method. Then, once the load 1 beyond the film reels 8, the conveyor 9 is stopped and the carriages 15 are brought into close position (Figures 2E then 2F). In this close position, the cutting and welding jaws 14 can be applied against each other and make the desired cut and welds 10 and, the pre-stretching means 11 are also closest to each other .

The carriages 15 also respectively support the two coil supports 8, the pre-stretching means 11 can then be placed in the immediate vicinity of the coils 8 and, overall, in a fixed fixed position relative to them .

In another embodiment, the axes of the film reels 8 remain fixed on either side of the conveyor 9 and the distance between the film reels 8 and the pre-stretching means 11 is reduced or increased depending on whether the carriages 15 are in the spread or close position.

The two carriages 15 also respectively support two guide rollers 17 over which the film 2 passes, after the presorting means 11, extending parallel to the coils 8, mounted with free pivoting around their axes, the axes of the two rollers -guides 17 being mobile and therefore the guide rollers 17 also being mobile as a whole between two extreme positions, an active projecting position (FIGS. 2C, 2D, 2E) and a retracted position (FIG. 2F). The two guide rollers 17 are, in the active projecting position, close to and inside the two cutting and transverse welding jaws 14, on the downstream side relative to the direction of advance of the conveyor 9. In the retracted position, the guide rollers 17 are at most coplanar with the two jaws 17 and on the upstream side.

The guide rollers 17 have the function, in the active projecting position, of preventing the friction of the film 2 on the jaws 14 and, passing from the projecting position to the retracted position, in the position close to the carriages 15, of relaxing the film 2, given that the length of the path between the pre-stretching means 11 and the jaws 14 is shorter when the guide rollers 17 are in the retracted position than when they are in the active projecting position.

In the active projecting position, and during the application of the film 2 to the side faces 6, the guide rollers 17 are located in the immediate vicinity of the side faces 6 and also have the function of deflecting the film 2 in order to bring it closer to them. ci and thus allow faster application of the pre-stretched film 2 on the side faces 6.

The existence of carriages 15 supporting the pre-stretching means 11, the jaws 14, the guide rollers 17 and, if necessary, the coils 8, also makes it possible to use the machine with loads 1 of different dimensions, the machine still adapted to the load 1, in particular the pre-stretching means 11 remaining at a constant and known distance from the side faces 6.

Preferably, the pre-stretching means 11 are of the motorized type, each comprising for example an upstream roller 18 and a downstream roller 19 connected together notably by pinions so that the downstream roller 19 rotates with a circumferential speed greater than that of the upstream roller 18. Such a pre-stretching assembly with two rollers with differential and motorized speeds is known per se and in particular generally described in French patent 2,281,275 of the applicant.

The motor means of the pre-stretching means 11 defining the speed of the stretched film flow are controlled - under given conditions of use - at the conveyor 9 and at the position of the load 1 carried by the conveyor 9 relative to the means of pre-stretching 11 so as to obtain clamping forces of the film 2 on the different faces 5, 6, 7 which are equal to one another or close to each other. However, preferably, this control does not involve any film force sensor or the like disturbing the operation of the machine and lengthening the path of the pre-stretched film 2.

In one embodiment, the machine comprises a lower assembly 20 for depositing film 2 pre-stretched on the lower part of the load 1, in particular adjoining the lower face 3, the pre-stretching means 11, the jaws 14 and the guide rollers 17 extending downward at least up to the plane of the conveyor 9, or even preferentially even lower than this plane by crossing the conveyor 9 transversely. In this case, the support guide 16 of the lower assembly 20 is preferably located below the conveyor 9. The carriages 15 have a longitudinal size (in the direction of advancement of the load 1 on the conveyor 9) of the order of magnitude of the diameter of the film reels 8. This size is that of all of the movable members associated with the film: jaws, coils, pre-stretching means. In addition, the conveyor 9 has a transverse passage 21 allowing the passage of the pre-stretching means 11, the jaws 14, the guide rollers 17 and, possibly, the carriages 15 and the coils 8.

This constructive arrangement is made possible because the longitudinal size of the lower assembly 20 is very limited because the circuit followed by the film 2 is direct and does not include any tormented path extending longitudinally from front to back or vice versa. As a result, the load 1 can cross the passage 21 without hindrance and while retaining the necessary stability.

In the embodiment where the carriages 15 support the film reels 8 (FIGS. 2A to 2G) a carriage 15 has, in elevation -that is to say seen from above- a generally rectangular shape. At the outer outer part is the film reel 8. Immediately near the film reel 8 are the pre-stretching means 11, the two rollers 18, 19 being offset in the longitudinal direction for reasons of space. . A roller 22 ensures the return of the film 2 upstream. At the inner end part and downstream the jaw 14 is mounted. On the carriage is also mounted the guide roller 17 carried at the end part of a lever articulated around an axis 23 located on the carriage 15 on the side downstream, towards the outside of the jaws 14, between the jaws 14 and the downstream roller 19.

Each jaw 14 (FIGS. 3A to 3C) comprises a U-shaped part 24 comprising two branches 25, 26 arranged transversely and spaced apart in the longitudinal direction from one another. These two branches 25, 26 constitute, with those of the jaw 14 facing the welding jaws and make it possible to produce two transverse welds spaced apart longitudinally from one another. In a free space between the two branches 25, 26 of one of the pieces 24 is located, on one of the pieces 24, a cutting heating wire 27 movable transversely by suitable drive means to pass from one of the pieces 24 to the other so as to ensure a cross section of the film 2 between the two welds performed.

In addition, the jaws 14 immediately comprise, on the downstream side of the parts 24, a clamp 28 capable of pinching the film downstream of the parts 24 so that, downstream of the clamp 28, the film is stretched against the rear face 7 of the load 1 and that, on the contrary, upstream of the clamp 28 the film 2 can be relaxed, for welding.

The two parts of the clamp 28 can be urged permanently by a spring or the like towards a projecting position relative to the parts 24 (FIG. 3B) and can be retracted while remaining applied against each other when the two parts 24 are applied one against the other (FIG. 3C), where they are then coplanar with the parts 24.

The clamp 28 is functionally combined with the guide rollers 17 which, in their projecting position project with respect to the two parts of the clamp 28.

The machine may include an upper assembly 29 for depositing pre-stretched film on the upper part of the load 2, in particular adjoining the upper face 4. The pre-stretching means 11, the jaws 14 and the guide rollers 17 s' extend upwards to the plane of the upper face 4.

The support guide 16 of the upper assembly 29 is located above the conveyor 9 and the load 1, being mounted to slide vertically and in an adjustable manner and being carried, for this purpose, by two support and guide brackets 30, generally placed vertically on either side of the conveyor 9, with which are associated drive means (not shown) allowing the drive of the support guide 16.

The lower assembly 20 and the upper assembly 29 are spaced longitudinally along the conveyor 9 by a distance at least equal to the spacing between the front 5 and rear faces 7. Optionally, the brackets 30 are also mounted longitudinally adjustable. so as to allow the adjustment of this spacing.

The upper assembly 29 has the same general characteristics as the lower assembly 20 already described, the film reels 8 and the associated movable members of the lower assembly 20 being directed upwards while the film reels 8 and the members associated mobiles of the upper assembly 29 are directed downwards.

It goes without saying that the movement of the two assemblies 20 and 29 is coordinated. To this end, the pre-stretching means 11 of the upper assembly 29 are in the standby position when the load 1 has exceeded the lower assembly 20 and the film of this lower assembly 20 is applied to the rear face 7 of the load.

In addition, the two assemblies 20, 29 have the same general structure, the same operation.

This constructive arrangement of the machine allows on the one hand the packaging of loads of different heights, without changing film reels. This arrangement is particularly important taken in combination with the fact that the pre-stretching means 11 are also adjustable in transverse spacing. In addition, it allows the constitution of a reinforced clamping band in the middle part of the height of a load 1. Finally, it avoids the use of film of too wide width, which is not desirable. in the case of pre-stretched stretch film.

The machine may include integrated means 31 for depositing on the upper face 4 of the load 1 a topsheet 12 of plastic material, comprising a film reel support 32 with generally horizontal, transverse and upper axis and means for cross section of this film. These means 31 are preferably carried by the support guide 16 of the upper assembly 29, on the upstream side. This constructive arrangement makes it possible to functionally combine the removal of the topsheet 12 and the removal of the film curtain attached to the upper face 4, in particular the height adjustment of the means 31.

Claims (19)

1. Method for pass-through packaging of a load (1) with pre-stretching of the stretchable film (2), in which an initial curtain of film (2) is formed, the load (1) is displaced in the direction of the curtain of film (2), the curtain of film (2) is deformed in order to cover the front face (5) and the lateral faces (6) of the load (1), the film (2) is unwound from bobbins (8) and simultaneously it is pre-stretched by virtue of two means of pre-stretching (11) before it is applied to the load (1), in such a manner that the film (2) is applied to the load (1) in the pre-stretched state, the displacement of the load (1) is stopped, the curtain of film (2) is deformed in order to bring it onto the rear face (7) of the load (1), and a transverse cut and double weld of the curtain of film (2) are made, characterised in that the starting point is an initial position in which the means of pre-stretching (11) are in a waiting position in front of the load (1), in which they are close to one another, the pre-stretching of the initial curtain of film (2) is then carried out and the means of pre-stretching (11) are separated transversely, while ensuring the delivery of pre-stretched film, as far as a separated position close to the lateral faces (6) of the load (1), then the pre-stretching of the film (2) for the lateral faces (6) is carried out, then the pre-stretching of the film (2) for the rear face (7) is carried out, while bringing near transversely the means of pre-stretching (11) as far as a brought-near position, while ensuring the necessary delivery of pre-stretched film (2).
2. Method according to Claim 1, characterised in that the film (2) is applied to the load (1) in the elastic return phase which follows the pre-stretching phase.
3. Method according to either one of Claims 1 and 2, characterised in that the stretching of the initial curtain of film (2) is carried out immediately before it is applied to the front face (5) of the load (1).
4. Method according to any one of Claims 1 to 3, characterised in that the pre-stretched film (2) is applied directly to the load (1) without making it pass through accumulating means.
5. Method according to any one of Claims 1 to 4, characterised in that, under given conditions (linear speed of displacement of the load (1), characteristics of the film (2), characteristics of the load (1), gripping force of the film (2) on the load (1) after packaging), the speed of delivery of the pre-stretched film (2) is controlled by the position of the load (1) in relation to the means of pre-stretching (11) in such a manner that the gripping forces of the film on the faces (5, 6, 7) of the load (1) are equal or close to one another.
6. Method according to Claim 5, characterised in that a first control value (V₁) is defined of the speed of delivery of pre-stretched film (2) in a first phase in which the pre-stretching of the initial curtain of film (2) is carried out, a final control value (V₄) in the phase of the cycle in which the pre-stretched film (2) is applied to the rear face (7), and at least one intermediate control value (V₂) in the phase of the cycle in which the pre-stretched film (2) is applied to the lateral faces (6).
7. Method according to Claim 6, characterised in that at least two intermediate control values (V₂ and V₃) are defined, which correspond respectively to the start and to the finish of the application of the pre-stretched film (2) to the lateral faces (6).
8. Method according to Claim 1, characterised in that the curtain of film (2) is applied adjoining or close to the upper face (4) of the load (1), and there is placed on the upper face (4) a top sheet (12) made of plastic material, the turned-down edges (13) of which are allowed to fall over the front (5), lateral (6) and rear (7) faces of the load (1), in such a manner that the turned-down edges (13) are trapped by the film (2).
9. Method according to Claim 1, characterised in that the load (1) is packaged in two successive and separate passes, one in which the film (2) is adjoining or close to the lower face (3) of the load (1) and the other in which the film (2) is adjoining or close to its upper face (4).
10. Method according to Claim 9, characterised in that use is made of films which are each of a width which is smaller than the height of the load (1) between the lower (3) and upper (4) faces, the sum of the two widths being greater than the height of the load (1), in such a manner that the two films come to overlap, in particular in the central part of the height of the load (1).
11. Machine for pass-through packaging of a load (1) with pre-stretching of the stretchable film, comprising a motorised conveyor (9), on which the load (1) can rest, and an assembly for application of pre-stretched film to the load (1), comprising two supports for film bobbins (8) having generally vertical axes, means of pre-stretching (11) extending parallel to the film bobbins (8), two cutting and welding jaws (14) which are movable transversely between two extreme positions, a separated position in which the load (1) can pass between them and a brought-near position in which they are applied against one another, characterised in that two means of pre-stretching (11) are mounted so as to be movable transversely between two positions, namely a separated position in which the load (1) can pass between them, and a brought-near position close to one another on the path of the load (1) carried by the conveyor (9).
12. Machine according to Claim 11, characterised in that it comprises two carriages (15) mounted so as to be sliding on a transverse, in particular horizontal, support guide (16), supporting respectively the two cutting and welding jaws (14) and the two means of pre-stretching (11), means of driving the carriages (15), and means of control of the driving means, the carriages (15) being movable between two extreme positions, separated and brought-near respectively.
13. Machine according to Claim 12, characterised in that the means of control of the means of driving the carriages (15) are operated according to the functioning of the conveyor (9), in such a manner that in the initial position the two carriages (15) are close in a waiting position, then the carriages (15) are brought into the separated position, then the carriages (15) remain in their separated position during the functioning of the conveyor (9), and then the carriages (15) are brought into the brought-near position.
14. Machine according to any one of Claims 11 to 13, characterised in that the two carriages (15) likewise support respectively two guide rollers (17), over which the film passes and which extend parallel to the film bobbins (8) and are mounted freely pivotably about their shafts, the shafts of the guide rollers (17) and the guide rollers (17) being movable between two extreme positions, a projecting active position and a retracted position, the two guide rollers (17) being, in the projecting active position, in the vicinity of and inside the two transverse cutting and welding jaws (14), on the downstream side in relation to the direction of advance of the conveyor (9), possibly in the immediate vicinity of the lateral faces (6) and, in the retracted position, at the most coplanar with the two jaws (14) and on the upstream side, the guide rollers (17) having the functions, in the projecting active position, of preventing the rubbing of the film on the jaws (14), possibly of diverting the film (2) in order to bring it near to the lateral faces (6), and, passing from the projecting active position to the retracted position, in the brought-near position of the carriages (15), of slackening the film (2) with a view to welding.
15. Machine according to any one of Claims 11 to 14, characterised in that the means of pre-stretching (11) are motorised, the motive means of the means of pre-stretching (11) which define the speed of delivery of stretched film being controlled by the conveyor (9) and by the position of the load (1) carried by the conveyor (9) in relation to the means of pre-stretching (11), in order to obtain forces for gripping the film on the various faces of the load (1) which are equal or close to one another.
16. Machine according to any one of Claims 11 to 15, characterised in that it comprises a lower assembly (20) for application of pre-stretched film to the lower part of the load (1), the means of pre-stretching (11), the jaws (14) and the guide rollers (17) extending downwards at least as far as the plane of the conveyor (9), or even preferably lower than this plane, passing transversely through the conveyor (9), and an upper assembly (29) for application of pre-stretched film to the upper part of the load (1), the means of pre-stretching (11), the jaws (14) and the guide rollers (17) extending upwards as far as the plane of the upper face, the lower assembly (20) and the upper assembly (29) being separated longitudinally by a distance which is at least equal to the separation between the front (5) and rear (7) faces.
17. Machine according to any one of Claims 11 to 16, characterised in that the conveyor (9) comprises a transverse passage (21) which allows the passage of the means of pre-stretching (11), of the jaws (14), of the guide rollers (17), and possibly of the carriages (15), this passage (21) having in particular a longitudinal dimension of the same order of magnitude as the bobbins (8).
18. Machine according to Claim 17, characterised in that the support guide (16) of the upper assembly (29) is situated above the conveyor (9) and the load (1), this guide (16) being mounted so as to be sliding vertically and in an adjustable manner and being carried to this end by two guiding support brackets (30) which are positioned vertically on either side of the conveyor (9) and with which driving means are associated.
19. Machine according to Claim 11, characterised in that it comprises integrated means (31) of application to the upper face (4) of the load (1) of a top sheet (12) made of plastic material, comprising a film bobbin support (32) having a generally horizontal, transverse and upper shaft, and means of transverse cutting of the film, carried in particular by the support guide (16) of the upper assembly (29) on the upstream side.

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