PROCESS FOR WRAPPING LOADS AND RELATIVE SYSTEM

Technical Field

The present invention refers to a process and a system for wrapping loads with a covering sheet in plastic film subject to pre-stretching. Background art

As is common knowledge, the palletised loads consist of one or more goods distributed in a more or less orderly manner on a pallet so it can be moved and transported in a practical and easy way.

The palletised loads are normally covered with a stabilising wrap that immobilises the loads on the pallet so they can then be transported without any risk of falling or tipping over.

To make such a stabilising covering the usual way is to tightly wrap the sides of the load and pallet with a plastic covering film that is unwound from a dispensing reel. Wrapping is normally done by means of either automatic or semi automatic wrapping stations, which use one or more machines, intended to move a wrapping head which supports the reel of plastic film.

The moving machine is normally composed of a jointed robot arm that, to wind the covering film around the load to wrap, operates the wrapping head with a lifting and rotating motion around the palletised load which, on the contrary, substantially remains still.

Alternatively, the moving machine works by moving the wrapping head vertically, simultaneously winding the plastic film around the palletised load that turns on a rotating platform. The reel is mounted on the wrapping head in a rotating way around its own axis and, while wrapping, is kept substantially vertical and parallel to the lateral sides of the load to wrap.

The plastic film which unwinds from the reel, therefore, has two opposing longitudinal edges, one top and one bottom, which extend crosswise to the axis of the reel.

During wrapping, the palletised load is wound with several layers of covering, each one composed of one spiral winding of the plastic film until a wrap is

obtained where the bottom longitudinal edge of one winding and the top longitudinal edge of the adjacent winding overlap together in order to stabilise the windings one against the other.

Before the sheet of plastic firm is applied around the load to wrap it is normally subject to pre-stretching.

To do this operation, the known type of wrapping heads has a pair of pre- stretching rollers between which the plastic film unwound from the reel passes. The roller located downstream with respect to the feeding direction of the plastic film is made to turn at a peripheral speed higher than that of the roller upstream which, thanks to the friction between the surfaces of the rollers and the plastic film, generates an elongation of the film beyond the elastic limit resulting in pre-stretching of the film before being applied around the load to wrap. This operation, on one hand, allows to save a certain quantity of material used for wrapping and, on the other hand, allows to weaken the plastic film and to improve its resistance properties, increasing in particular its resistance to traction, with the possibility of binding the load in a stronger way and/or to increase its rigidity so that even particularly soft loads can be wrapped effectively without excessive residual elasticity of the material deforming them to an extent that cannot be tolerated.

Therefore, once the plastic film has passed through the pair of pre-stretching rollers, it exits the wrapping head to be wound around the palletised load. The wrapping of the palletised load usually starts by the pallet, around which the plastic film is wound several times. To increase the adhesion force of the plastic film on the pallet the wrapping head usually has specific devices arranged downstream from the two pre- stretching rollers and suitable for rolling up, folding and winding the bottom longitudinal edge of the pre-stretched plastic film on itself as it exits the wrapping head. Due to the effect of this rolling up, the bottom longitudinal edge increases in thickness until a proper seam is obtained that has considerable resistance to traction and can be wound around the pallet without breaking.

The traditional wrapping systems and processes do, however, have several drawbacks.

In fact, they do not allow the plastic film to be fully exploited which comes close to its breaking point due to the risk of tearing. In actual fact, in the case of excessive pre-stretching the plastic film normally tears at the top and/or bottom longitudinal edge in the section of film that extends between the two pre-stretching rollers.

Such tearing can subsequently spread from the longitudinal edges until involving the rest of the plastic film and leading to its complete breakage. If the plastic film tears completely, the system has to be stopped and then restarted after someone has freed the wrapping head by removing the piece of plastic film that has wound around the pre-stretching rollers and which did not reach the load to wrap. Furthermore, in these cases it is often necessary to start all over again packing the load that was not finished.

To overcome such drawbacks, users take precautional measures that avoid having to stop the system and which translate in the use of a degree of pre- stretching of the plastic film well below the maximum theoretical value, resulting in a reduction in sheet resistance and stiffness and an increase in reel consumption.

The total consumption of plastic film, therefore, is very high in relation to what could be obtained with a higher degree of pre-stretching. Also note that the need to overlap the spiral windings of the covering sheet with one another during wrapping negatively affects the total consumption of plastic film.

To ensure the necessary stability of the final wrap and protection of the goods, in fact, the bottom longitudinal edge of a winding and the top longitudinal edge of the adjacent winding are overlapped and left at a relative distance which, in some cases, can be as much as 150 í 200 mm. This means that a very large area in proximity of the longitudinal edges of the covering sheet is inconveniently destined to overlap other portions of the same sheet in order to give rigidity to the wrap and protect the wrapped goods.

Object of the Invention

The main aim of the present invention is to provide a process and a system for wrapping loads that allow to wrap the palletised loads in a practical, easy and functional way and, at the same time, that allow to operate in complete safety with high pre-stretching values, close to the theoretical ones of the material used and, however, well above the pre-stretching values actually applied in the known technique under safe conditions so as to increase the yield of the plastic film.

A further object of the present invention is to reduce the frequency of machine downtimes and to consequently increase the overall production output of the system.

Another object of the present invention is to provide a process and a system for wrapping loads that allow to overcome the mentioned drawbacks of the known technique as part of a simple, rational, easy, effective use and low cost solution The objects mentioned above are achieved by this process for wrapping loads which comprises the following steps: provide a covering sheet for wrapping at least one load; apply a certain pre-stretching elongation to said covering sheet; wind said pre-stretched covering sheet around said load; characterised in that before and/or during said application it comprises the following step: roll both longitudinal edges of said covering sheet up on themselves to form two opposite reinforcement borders.

The objects listed above are also achieved by this system for wrapping loads, comprising at least one wrapping head that has at least a first pre-stretching roller and a second pre-stretching roller for pre-stretching a covering sheet suitable for wrapping at least one load, said first and second roller being arranged upstream and downstream respectively in relation to the feeding direction of said covering sheet, characterised in that said wrapping head comprises rolling up means for rolling up said covering sheet, which are located upstream and/or immediately downstream from said first roller and are suitable for rolling both longitudinal edges of said covering sheet up on themselves to

form two opposite reinforcement borders.

Brief Description of the Drawings

Further characteristics and advantages of the present invention will appear even more evident from the description of a preferred, but not exclusive, embodiment of a system for wrapping loads, illustrated by way of non limiting example in the accompanying drawings, wherein: figure 1 is an elevated side view, schematic and partial, of the wrapping head of the system according to the invention; figure 2 is a plan view, schematic and partial, of the system wrapping head of the system according to the invention; figure 3 is an elevated side view, schematic and partial, of the system according to the invention; figure 4 is an enlarged view, schematic and partial, of a detail of figure 3.

Embodiments of the Invention With special reference to such figures, by 1 has been globally designated a system for wrapping loads, of the pallet type or the like, by means of a covering sheet 2 in plastic film subject to pre-stretching.

In the embodiment illustrated in the figures, the load to wrap consists of a palletised load C ₅ made up of a pallet B on which the goods M to wrap are loaded; it cannot be ruled out, however, that the present invention can be used also for wrapping loads that are not on pallets.

The system 1 has a rotating platform 3 to rotate the palletised load C and a machine 4 arranged in proximity of the rotating platform 3 and suitable for moving a wrapping head 5. The machine 4 consists of a jointed robot arm at the free end 4a of which the wrapping head 5 is mounted.

The jointed robot arm 4, in effect, is suitable for working together with the rotating platform 3 to move the wrapping head 5 in a vertical direction so the covering sheet 2 can be wound around the palletised load C which rotates on the rotating platform 3.

As an alternative, it is possible to operate the wrapping head 5 with a helicoidal movement around the palletised load C kept substantially still.

The covering sheet 2 is initially wound around itself on a dispensing reel 6 mounted on the wrapping head 5.

While the palletised load C is being wrapped, the dispensing reel 6 is kept substantially vertical. Inside the wrapping head 5 are arranged a first pre-stretching roller 7 and a second pre-stretching roller 8, substantially arranged parallel to the axis of the dispensing reel 6.

The covering sheet 2 is placed in contact around the rollers 7 and 8 and pulled forward. With regard to this, the fact is underlined that the rollers 7 and 8 are coated with a substance, rubber or the like, that exerts a high force of friction on the covering sheet 2 which, as a result, is kept substantially adhered to them.

The first and second rollers 7 and 8 are arranged upstream and downstream respectively in relation to the feeding direction of the covering sheet 2; with regard to this, it must be pointed out that in this dissertation, whenever it is stated that an element in contact with the covering sheet 2 is either upstream or downstream with respect to the other, it is meant that said relative arrangement is evaluated with reference to the feeding direction of the covering sheet 2.

In addition, the two rollers 7 and 8 are driven by electric motors 9 and 10 which work at different speeds.

In particular, the speed of the second roller 8 is faster than that of the first roller

7, thus imparting to the covering sheet 2 the desired pre-stretching in the section

2a that extends from the first roller 7 to the second roller 8.

Usefully, the wrapping head 5 has rolling up means 11 of the covering sheet 2 which are suitable for rolling both the bottom longitudinal edge 12 and the top longitudinal edge 13 of the covering sheet 2 up on themselves.

The rolling up of the longitudinal edges 12 and 13, in particular, is such to allow the formation of two opposing reinforcement borders 14 and 15 that are thicker than the normal thickness of the covering sheet 2 and allow to prevent the breakage of the longitudinal edges 12 and 13 during pre-stretching.

In this particular embodiment of the invention illustrated in the figures, the rolling up means 11 are positioned immediately downstream from the first roller

7 and, in particular, are inserted along the section 2a of the covering sheet 2 which extends from the first roller 7 to the second roller 8 (figure 2). However, other alternative embodiments of the present invention cannot be ruled out wherein the rolling up means 11 are positioned upstream from the first roller 7 and, in particular, are inserted along the section 2b of the covering sheet 2 which extends from the dispensing reel 6 to the first roller 7. The rolling up means 11 are composed of, for example, reciprocal approaching means of the longitudinal edges 12 and 13 which, in detail, comprise two contrast elements 16 and 17 that can be positioned in contact against the longitudinal edges 12 and 13 and suitable for pushing each longitudinal edge 12 and 13 towards each other.

The contrast elements 16 and 17, in particular, consist of a pair of wheels that can rotate around the rotation axis A at right angles to the surface on which the covering sheet 2 is placed. In addition, the reciprocal approaching means 11 comprise two guide elements 18 and 19 which extend along a direction of approach and moving away with respect to the longitudinal edges 12 and 13, direction which is substantially parallel with the dispensing reel 6 and rollers 7 and 8. The wheels 16 and 17 are engaged along the guide elements 18 and 19 and, by means of them, are movable between a move away configuration, wherein the wheels 16 and 17 are distanced from the longitudinal edges 12 and 13 and the covering sheet 2 unwinds from the dispensing reel 6 substantially without folds and a close up configuration, wherein the wheels 16 and 17 are in contact against the longitudinal edges 12 and 13 and substantially keep them folded. Advantageously, the wrapping of the palletised load C is carried out with the process according to the invention with consists in the following steps: provide the covering sheet 2 by unwinding the dispensing reel 6; apply a certain pre-stretching elongation to the covering sheet 2, making it pass between the first roller 7 and the second roller 8; - wind the pre-stretched covering sheet 2 around the palletised load C.

If, as illustrated in the figures, the wheels 16 and 17 are arranged along the section 2a of the covering sheet 2 which is between the rollers 7 and 8, in effect,

the rolling up of the longitudinal edges 12 and 13 and the formation of the two reinforcement borders 14 and 15 occurs at the beginning of the pre-stretching application phase and simultaneously with it.

Alternatively, if the wheels 16 and 17 are arranged in the space between the dispensing reel 6 and the first roller 7 the rolling up phase takes place immediately before the pre-stretching application phase.

In both cases, the function exerted by the wheels 16 and 17 remains the same, that is, forcing the longitudinal edges 12 and 13 to fold over and wind around themselves, leading to the formation of the reinforcement borders 14 and 15, with an increased thickness, able to support the high pre-stretching degrees imposed by the rollers 7 and 8 without breaking.

Advantageously, the total width of the covering sheet 2, that is, the distance between the bottom longitudinal edge 12 and the top longitudinal edge 13, is more than 400 mm. Preferably, such a total width is equivalent to 1000 mm but, alternatively, it can be equal to about 750 mm or 500 mm.

The width of the covering sheet 2 dedicated to forming each reinforcement border 14 and 15, instead, is comprised between 30 mm and 150 mm and, preferably, is equal to 100 mm. This means that the remaining width of the covering sheet 2, that is, the part that extends between the two reinforcement borders 14 and 15, is sufficiently wide to allow the spiral winding of the covering sheet 2 around the palletised load C.

With regard to this, the fact is underlined that the presence of the reinforcement borders 14 and 15, besides imparting the covering sheet 2 with greater resistance to tearing and, therefore, allowing particularly high pre-stretching degrees to be reached, also makes the wrapping phase of the palletised load C easier.

As illustrated in detail in figure 4, in fact, during the spiral winding of the covering sheet 2 around the palletised load C, the bottom reinforcement border 14 of a winding overlaps the top reinforcement border 15 of the adjacent winding, or vice versa, so as to stabilise one winding with respect to another.

Under such circumstances, the particular resistance to traction and the increased

thickness of the reinforcement borders 14 and 15 impart considerable adherence and stability to the adjacent windings and, therefore, it is unnecessary for the relative distance between the bottom reinforcement border 14 of a winding and the top reinforcement border 15 of the adjacent winding to be very big and, likewise, may only be, for example, 40 mm.

Also note that the position of the wheels 16 and 17 along the guide elements 18 and 19 can be conveniently adjusted at will, either manually or automatically, to form the reinforcement borders 14 and 15 that are more or less thick according to the degree of pre-stretching wanted, of the type of goods M to wrap and/or to other factors peculiar to wrapping operations.

With regard to this, for example, note that at the beginning of the wrapping phase, when the covering sheet 2 has to be wound around the pallet B ₅ the wheel 16 arranged at the bottom can work to form a reinforcement border 14 that is thicker than the reinforcement border 15 positioned at the top. In this way, the bottom reinforcement border 14 can be wound firmly around the pallet B without breaking and, once the beginning of the wrapping phase is completed, its thickness can be reduced and brought to the thickness of the top reinforcement border 15 to finish wrapping the palletised load C. However, alternative embodiments of the present invention cannot be ruled out wherein the wheels 16 and 17 always work in exactly the same conditions to form reinforcement borders 14 and 15 with the same thickness and wherein a device of the traditional type is provided arranged downstream from the rollers 7 and 8 and destined to thicken the bottom reinforcement border 14 when, at the beginning of the wrapping phase, it is necessary to stabilise the covering sheet 2 on the pallet B.

It has in practice been found how the described invention achieves the intended objects.

To this end, it should be noted that the particular expedient of forming the reinforcement borders before and during the pre-stretching phase, allows to subject the covering sheet to a high degree of pre-stretching significantly reducing the risk of tearing or breaking. Furthermore, in view of the higher pre-stretching values and of the possibility to

reduce the areas of the covering sheet that are overlapped with each other when winding around the load, the fact is underlined that this invention allows a big reduction in the overall consumption of plastic film and in the frequency of machine downtimes due to the total breakage of the film. The invention thus conceived is susceptible of numerous modifications and variations, all of which falling within the scope of the inventive concept.

Furthermore all the details may be replaced by other elements which are technically equivalent.

In practice, the contingent shapes and dimensions may be any according to requirements without because of this moving outside the protection scope of the following claims.