Pre-stretching group

Abstract

A pre-stretching unit (10), suitable for being installed on an apparatus for wrapping loads with a film (F), in particular an extendible film (F) or other sheet material, comprises support means (11) for a reel (B) of the film (F), a pair of pre-stretching rollers (13,14) that are rotatable around respective axes (X1,X2) and a rapid insertion device (30) for inserting a head strip of the film (F) between the rollers of the pair of pre-stretching rollers (13,14); the rapid insertion device (30) comprises a flexible dragging element (17), configured for advancing along a path that extends between, and partially around, the axes (X1,X2), so as to drag the head strip of the film (F) through the rollers of the pair of pre-stretching rollers (13,14), and connecting means (20), provided on the flexible dragging element (17), for connecting the head strip of the film (F) to the flexible dragging element (17), the pre-stretching unit (10) is further provided with height adjusting means (21,22) so as to adjust the height of the flexible dragging element (17).

Description

Background of the invention

[0001] This invention relates to a pre-stretching unit for wrapping film, or other sheet material intended, in particular, to be installed on an apparatus for wrapping loads in an extendible film.Prior art

[0002] Systems are known for wrapping loads in an extendible film in order to simplify the storage and transport of goods. For example, the use of pallet wrappers is known in order to wrap goods placed on a pallet in an extendible film in order to stabilize the collection.

[0003] US4747254 A discloses a device for threading a leading end of a web through a web path between a series of rollers that includes a leader line for attachment to the leading end of the web and for drawing the web through the web path. There is also a leader path on a side of the series of rollers that is generally parallel to but beside to the web path to support the leader line means and confining the lateral movement of the leader line means, permitting the longitudinal movement of the leader line means and of the leading end of the web in the direction that is generally parallel to but beside of the web path. The leader path includes pulleys mounted on the roller shafts that freely rotate relative to the respective rollers. The leader line means includes a proximal end portion by means of which the leader line means is engaged and drawn, a distal end portion and a loop intermediate the proximal and distal end portions for fixing the web of the leader line means.

[0004] US2013 / 227919 A1 discloses a stretch wrap assembly comprising a base, a turntable mounted on the base, a column that extends upwards from the base and a carriage that is vertically movable upon the column, the carriage having a housing that is configured to have stretch wrap move therethrough for wrapping a product on the turntable. The housing comprises a plurality of rollers extending between a bottom of the housing and a top of the housing, the plurality of rollers rotating about roller axes, a wrap surface of the stretch wrap engaging exterior surfaces of the rollers as the stretch wrap moves therethrough. The housing comprises a threading assembly for moving a front end of the stretch wrap through the housing during initiation of installation of the stretch wrap through the housing. The threading assembly includes a manually movable system moving the front end of the stretch wrap. The manually movable system includes a rotating handle, an endless link having a hook and a plurality of rotary members supporting the endless link at a plurality of locations.

[0005] US2004 / 163364 A1 discloses a stretching device for a wrapping machine comprising a support structure and a film support for rotatably holding a roll of stretchable film. First and second rollers are rotatably mounted on the support structure. The stretching device includes a take-off device for supporting the film as it is fed from the stretching device. A power drive assembly comprising a motor is configured for rotating the first and the second rollers to stretch a film between the rollers. The stretching device further includes an elongated flexible member forming a loop and having a connector adapted for securing the stretchable film. A guide assembly that is adjacent to the first ends of the first and of the second rollers movably supports the elongated flexible member for guiding the stretchable film through the stretching device. A disengageable drive is operably coupled to the elongated flexible member to provide powered movement of the elongated flexible member. The stretching device can be used with wrapping machines having a rotatable base or a turntable, or with wrapping machines of the type having an arm that rotates for wrapping film about packages. The stretching device may include a tensioning device that tensions the chain.

[0006] Before being wrapped around the load, the extendible film is subjected to a pre-stretching operation so as to be yielded, thus obtaining a significant percentage elongation and in this manner cutting the costs of the material used in the wrapping process.

[0007] The pre-stretching operation, in particular, is entrusted to a pre-stretching unit, and more in particular to two driven rollers, said pre-stretching rollers being arranged alongside one another and rotating at different speeds; in detail, the percentage elongation that has been obtained is a function of both the distance between the two rollers and the difference between the rotation speeds of the rollers.

[0008] Before driving the pre-stretching unit, however, the extendible film has to be inserted inside the two aforesaid rollers. In particular, a specialized operator manually slides the extendible film between, and partially around, the two pre-stretching rollers. Insertion can, however, be rather complicated and time-consuming also for an expert operator, because the distance between the two rollers is only a few millimetres, a condition that is necessary for ensuring the maximum possible percentage elongation.

[0009] In order to overcome this drawback, some pre-stretching units have been developed that in addition to the two pre-stretching rollers also have an idling roller positioned on a closable door; in this case, the distance between the two pre-stretching rollers has been increased so as to allow the insertion of the idling roller between the two pre-stretching rollers when the door is shut (operating condition). In this manner, the operator does not have to insert the extendible film manually between the two pre-stretching rollers because closing the door causes the idling roller to be positioned against the extendible film so as to tension the latter, at the same time enabling the extendible film to slide between the two pre-stretching rollers.

[0010] Nevertheless, this solution is not only unable to ensure a satisfactory percentage elongation (which is in particular less than the aforesaid first type of pre-stretching unit), but it is also more expensive and structurally more complex. Further, the door mechanism requires frequent maintenance also to avoid minimum positioning errors: in fact, even small imprecisions in closing the door may compromise the performance of the pre-stretching unit. In other words, the idling roller takes part actively in the delicate process of pre-stretching and is thus a critical component in this type of machine.

[0011] An improvement of current pre-stretching units for pre-stretching extendible films would thus be desirable, and thus also an improvement of current apparatuses for wrapping loads with an extendible film. In particular, it would be desirable to provide a solution that is able to facilitate and accelerate the insertion of the extendible film inside the pre-stretching unit without affecting the performance thereof and which is at the same time cheaper and such as to reduce maintenance works drastically.Objects of the invention

[0012] One object of this invention is to improve current pre-stretching units for apparatuses for wrapping loads with a film.

[0013] Another object of this invention is to provide a pre-stretching unit that is such as to facilitate and speed up insertion of the film and is simultaneously advantageous from the economic point of view.

[0014] A further object of this invention is to provide a pre-stretching unit that facilitates and speeds up inserting the film by at the same time ensuring high performance of the pre-stretching unit itself.

[0015] Another further object of this invention is to propose a pre-stretching unit that facilitates and speeds up inserting the film and is at the same time able to limit the periodic maintenance works.

[0016] Another still further object of this invention is to propose a fast and easy method for inserting films into a pre-stretching unit.Brief description of the invention

[0017] The objects listed above and yet other objects and advantages are achieved by a pre-stretching unit and an insertion method according to what has been defined in the appended claims.Brief description of the drawings

[0018] The invention can be better understood with reference to the attached drawings that illustrate an embodiment thereof by way of non-limiting example, in which: Fig. 1 is a perspective view of a pre-stretching unit according to the invention; Fig. 2 is a detail of the pre-stretching unit of Fig. 1; Fig. 3 is a top view of Fig. 1; Fig. 4 is a top section view of the pre-stretching unit of Fig. 1 with a film inserted; Fig. 5 is a further top section view of the pre-stretching unit of Fig. 1. Detailed description of the invention

[0019] With reference to the attached Figures, a pre-stretching unit 10 is disclosed below that is suitable for being installed on an apparatus for wrapping loads with a film F, or other sheet material like paper or another material suitable for wrapping loads (shown in Figure 4), for example, on an apparatus for wrapping pallets. In particular, the pre-stretching unit 10 can operate with films F of extendible or elastic type. Further on in the description, reference will be made in a non-limiting manner and only for the sake of simplicity of exposition, only to an extendible film F.

[0020] The pre-stretching unit 10, as visible in Fig. 1, comprises support means 11 for a reel B of the extendible film F, a pair of pre-stretching rollers 13,14, that are rotatable around respective axes X1,X2, and a rapid insertion device 30 for inserting a head strip of the extendible film F between the rollers of the pair of pre-stretching rollers 13,14. In the embodiment shown by way of example, the axes X1, X2 are parallel to one another.

[0021] In detail, each roller of the pair of pre-stretching rollers 13,14 is connected to a respective motor that controls the rotation speed thereof around the respective axes X1,X2. In fact, in order for the extendible film F to be yielded, the rollers of the pair of pre-stretching rollers 13,14 have to rotate at different speeds and have to have a side surface that is able to exert sufficiently great friction on the extendible film F, so as to ensure the necessary grip and ensure that the portions of extendible film F in contact with the respective rollers of the pair of pre-stretching rollers 13,14 advance at the same tangential speed as the rollers with which they are in contact.

[0022] In particular, with reference to Fig. 2, the rapid insertion device 30 comprises a flexible dragging element 17, configured for advancing along a path that extends between, and partially around, the axes X1, X2 so as to drag the head strip of the extendible film F through the rollers of the pair of pre-stretching rollers 13,14.

[0023] The rapid insertion device 30 comprises connecting means 20, provided on the flexible dragging element 17 itself, and configured for connecting the head strip of the extendible film F to the flexible dragging element 17.

[0024] In the embodiment shown by way of example in Fig.2, the connecting element 20 has recesses 26,27,28 that are suitable for enabling an operator to bind the extendible film F firmly to the connecting element 20.

[0025] The flexible dragging element 17 can be, for example, a cable, a rope, a string, or a belt, made of a flexible material. The flexible material can be chosen, for example, from a group comprising: polyvinyl chloride, polyester, polyamide, or polypropylene.

[0026] At a free end of the flexible dragging element 17, a gripping element 18 is provided such as a grip or handle, suitable for being grasped and pulled by an operator to make the flexible dragging element 17 advance along the path through the pair of pre-stretching rollers 13,14.

[0027] The pre-stretching unit 10 is, as visible in Figs 1 and 3, further provided with a return device 23, configured for returning the flexible dragging element 17 to a rest position; a blocking element 19 is provided that is suitable for restingly receiving the gripping element 18 when the flexible dragging element 17 is in the rest position.

[0028] More precisely, the return device 23 can comprise, for example, a return spring for rewinding the flexible dragging element 17 to the rest position that, in this case, comprises a wound rest position. Alternatively to the return spring of passive type, in one embodiment that is not part of the invention the return device 23 can comprise a return member of active type such as for example an electric winding motor, a unit of pneumatic or hydraulic type or another equivalent member of active type.

[0029] With reference to Figs 1, 3 and 5, each pre-stretching roller 13;14 of the pair of pre-stretching rollers 13,14 is provided with a disc element 24;25, each of which has a groove in which the flexible dragging element 17 slides. In particular, each disc element 24;25 with a groove is placed at one end of the respective pre-stretching roller 13; 14.

[0030] The disc elements 24;25 with a groove can be, for example, two pulleys.

[0031] The pre-stretching unit 10, as shown in Figs 1 and 3, is also provided with height adjusting means 21,22 so as to adjust the height of the flexible dragging element 17. This configuration permits greater design flexibility because it is not necessary for the flexible dragging element 17 to have a constant height along all the pre-stretching unit 10.

[0032] The height adjusting means 21,22 can comprise, by way of example, pulleys.

[0033] Lastly, with reference to Figs 1,3,4 and 5, the pre-stretching unit 10 is provided with entering film guide means 12 to guide the insertion of the extendible film F inside the pair of pre-stretching rollers 13, 14. The entering film guide means 12 being able to comprise, for example, an idling roller.

[0034] In the same manner, the pre-stretching unit 10 is also equipped with guide means 15,16 for guiding exiting film to guide the exit of the extendible film F from the pair of pre-stretching rollers 13,14. The guide means 15,16 for guiding exiting film can comprise, by way of example, idling rollers.

[0035] The operation of inserting the extendible film F inside the pre-stretching unit 10 according to the invention is disclosed below.

[0036] The reel B of the extendible film F is first inserted inside the support means 11 and the head strip of the reel B is unrolled to then be connected to the flexible dragging element 17 by the connecting element 20. For example, the head strip of the extendible film F can be bound firmly to the connecting element 20.

[0037] Subsequently, the operator grips and pulls the gripping element 18; in this manner, the flexible dragging element 17 advances along the path that extends between, and partially around, the axes X1,X2, dragging the head strip of the extendible film F through the rollers of the pair of pre-stretching rollers 13,14. During the advancement of the flexible dragging element 17, the reel B is unrolled and the extendible film F, pulled by the flexible dragging element 17, is induced to be inserted between the pair of pre-stretching rollers 13,14. The correct insertion of the extendible film F is promoted by the entering film guide means 12.

[0038] The operator continues with the pulling action until the connecting element 20 has overcome both rollers of the pair of pre-stretching rollers 13,14. Having reached this point, insertion of the extendible film F can be in fact considered to be concluded because the extendible film F now extends between, and partially around, the rollers of the pair of pre-stretching rollers 13,14.

[0039] Subsequently, the operator disconnects the head strip of the extendible film F from the flexible dragging element 17 and passes the head strip through the exiting film guide means 15,16 so that the head strip of the extendible film F is in the correct position to be used during the wrapping operation. At the same time, the return device 23 returns the flexible dragging element 17 to the wound rest position that will be maintained until a new insertion of an extendible film F by the blocking element 19.

[0040] Owing to the aforesaid features, the pre-stretching unit 10 enables the extendible film F to be inserted conveniently, easily and fast. The operator is no longer forced to perform the inconvenient task of trying to insert the head strip of the extendible film F, grasped directly with the operator's hands, into the narrow gap between the two pre-stretching rollers, even risking personal injury. Further, the rapid insertion device 30 according to the invention does not alter the general structure of the pre-stretching unit 10 (for example the distance between the rollers of the pair of pre-stretching rollers 13,14) so that the performance of the pre-stretching unit 10 is not affected and at the same time the cost of the pre-stretching unit 10 remains moderate, owing to the very simplified structural configuration of the rapid insertion device 30. Further, the rapid insertion device 30 according to the invention does not require frequent maintenance because the rapid insertion device 30 operates only during the step of insertion of the extendible film F; subsequently, during the pre-stretching process, it remains in the rest condition.

[0041] From what has been set out above, it is clear that the pre-stretching unit 10 according to the invention successfully attains the objectives mentioned previously.

[0042] What has been disclosed and shown in the attached drawings has been provided only by way of illustrative example of the pre-stretching unit 10.

Examples

Embodiment Construction

[0019]With reference to the attached Figures, a pre-stretching unit 10 is disclosed below that is suitable for being installed on an apparatus for wrapping loads with a film F, or other sheet material like paper or another material suitable for wrapping loads (shown in Figure 4), for example, on an apparatus for wrapping pallets. In particular, the pre-stretching unit 10 can operate with films F of extendible or elastic type. Further on in the description, reference will be made in a non-limiting manner and only for the sake of simplicity of exposition, only to an extendible film F.

[0020]The pre-stretching unit 10, as visible in Fig. 1, comprises support means 11 for a reel B of the extendible film F, a pair of pre-stretching rollers 13,14, that are rotatable around respective axes X1,X2, and a rapid insertion device 30 for inserting a head strip of the extendible film F between the rollers of the pair of pre-stretching rollers 13,14. In the embodiment shown by way of example, the a...

Background of the invention

[0001] This invention relates to a pre-stretching unit for wrapping film, or other sheet material intended, in particular, to be installed on an apparatus for wrapping loads in an extendible film.Prior art

[0002] Systems are known for wrapping loads in an extendible film in order to simplify the storage and transport of goods. For example, the use of pallet wrappers is known in order to wrap goods placed on a pallet in an extendible film in order to stabilize the collection.

[0003] US4747254 A discloses a device for threading a leading end of a web through a web path between a series of rollers that includes a leader line for attachment to the leading end of the web and for drawing the web through the web path. There is also a leader path on a side of the series of rollers that is generally parallel to but beside to the web path to support the leader line means and confining the lateral movement of the leader line means, permitting the longitudinal movement of the leader line means and of the leading end of the web in the direction that is generally parallel to but beside of the web path. The leader path includes pulleys mounted on the roller shafts that freely rotate relative to the respective rollers. The leader line means includes a proximal end portion by means of which the leader line means is engaged and drawn, a distal end portion and a loop intermediate the proximal and distal end portions for fixing the web of the leader line means.

[0004] US2013 / 227919 A1 discloses a stretch wrap assembly comprising a base, a turntable mounted on the base, a column that extends upwards from the base and a carriage that is vertically movable upon the column, the carriage having a housing that is configured to have stretch wrap move therethrough for wrapping a product on the turntable. The housing comprises a plurality of rollers extending between a bottom of the housing and a top of the housing, the plurality of rollers rotating about roller axes, a wrap surface of the stretch wrap engaging exterior surfaces of the rollers as the stretch wrap moves therethrough. The housing comprises a threading assembly for moving a front end of the stretch wrap through the housing during initiation of installation of the stretch wrap through the housing. The threading assembly includes a manually movable system moving the front end of the stretch wrap. The manually movable system includes a rotating handle, an endless link having a hook and a plurality of rotary members supporting the endless link at a plurality of locations.

[0005] US2004 / 163364 A1 discloses a stretching device for a wrapping machine comprising a support structure and a film support for rotatably holding a roll of stretchable film. First and second rollers are rotatably mounted on the support structure. The stretching device includes a take-off device for supporting the film as it is fed from the stretching device. A power drive assembly comprising a motor is configured for rotating the first and the second rollers to stretch a film between the rollers. The stretching device further includes an elongated flexible member forming a loop and having a connector adapted for securing the stretchable film. A guide assembly that is adjacent to the first ends of the first and of the second rollers movably supports the elongated flexible member for guiding the stretchable film through the stretching device. A disengageable drive is operably coupled to the elongated flexible member to provide powered movement of the elongated flexible member. The stretching device can be used with wrapping machines having a rotatable base or a turntable, or with wrapping machines of the type having an arm that rotates for wrapping film about packages. The stretching device may include a tensioning device that tensions the chain.

[0006] Before being wrapped around the load, the extendible film is subjected to a pre-stretching operation so as to be yielded, thus obtaining a significant percentage elongation and in this manner cutting the costs of the material used in the wrapping process.

[0007] The pre-stretching operation, in particular, is entrusted to a pre-stretching unit, and more in particular to two driven rollers, said pre-stretching rollers being arranged alongside one another and rotating at different speeds; in detail, the percentage elongation that has been obtained is a function of both the distance between the two rollers and the difference between the rotation speeds of the rollers.

[0008] Before driving the pre-stretching unit, however, the extendible film has to be inserted inside the two aforesaid rollers. In particular, a specialized operator manually slides the extendible film between, and partially around, the two pre-stretching rollers. Insertion can, however, be rather complicated and time-consuming also for an expert operator, because the distance between the two rollers is only a few millimetres, a condition that is necessary for ensuring the maximum possible percentage elongation.

[0009] In order to overcome this drawback, some pre-stretching units have been developed that in addition to the two pre-stretching rollers also have an idling roller positioned on a closable door; in this case, the distance between the two pre-stretching rollers has been increased so as to allow the insertion of the idling roller between the two pre-stretching rollers when the door is shut (operating condition). In this manner, the operator does not have to insert the extendible film manually between the two pre-stretching rollers because closing the door causes the idling roller to be positioned against the extendible film so as to tension the latter, at the same time enabling the extendible film to slide between the two pre-stretching rollers.

[0010] Nevertheless, this solution is not only unable to ensure a satisfactory percentage elongation (which is in particular less than the aforesaid first type of pre-stretching unit), but it is also more expensive and structurally more complex. Further, the door mechanism requires frequent maintenance also to avoid minimum positioning errors: in fact, even small imprecisions in closing the door may compromise the performance of the pre-stretching unit. In other words, the idling roller takes part actively in the delicate process of pre-stretching and is thus a critical component in this type of machine.

[0011] An improvement of current pre-stretching units for pre-stretching extendible films would thus be desirable, and thus also an improvement of current apparatuses for wrapping loads with an extendible film. In particular, it would be desirable to provide a solution that is able to facilitate and accelerate the insertion of the extendible film inside the pre-stretching unit without affecting the performance thereof and which is at the same time cheaper and such as to reduce maintenance works drastically.Objects of the invention

[0012] One object of this invention is to improve current pre-stretching units for apparatuses for wrapping loads with a film.

[0013] Another object of this invention is to provide a pre-stretching unit that is such as to facilitate and speed up insertion of the film and is simultaneously advantageous from the economic point of view.

[0014] A further object of this invention is to provide a pre-stretching unit that facilitates and speeds up inserting the film by at the same time ensuring high performance of the pre-stretching unit itself.

[0015] Another further object of this invention is to propose a pre-stretching unit that facilitates and speeds up inserting the film and is at the same time able to limit the periodic maintenance works.

[0016] Another still further object of this invention is to propose a fast and easy method for inserting films into a pre-stretching unit.Brief description of the invention

[0017] The objects listed above and yet other objects and advantages are achieved by a pre-stretching unit and an insertion method according to what has been defined in the appended claims.Brief description of the drawings

[0018] The invention can be better understood with reference to the attached drawings that illustrate an embodiment thereof by way of non-limiting example, in which: Fig. 1 is a perspective view of a pre-stretching unit according to the invention; Fig. 2 is a detail of the pre-stretching unit of Fig. 1; Fig. 3 is a top view of Fig. 1; Fig. 4 is a top section view of the pre-stretching unit of Fig. 1 with a film inserted; Fig. 5 is a further top section view of the pre-stretching unit of Fig. 1. Detailed description of the invention

[0019] With reference to the attached Figures, a pre-stretching unit 10 is disclosed below that is suitable for being installed on an apparatus for wrapping loads with a film F, or other sheet material like paper or another material suitable for wrapping loads (shown in Figure 4), for example, on an apparatus for wrapping pallets. In particular, the pre-stretching unit 10 can operate with films F of extendible or elastic type. Further on in the description, reference will be made in a non-limiting manner and only for the sake of simplicity of exposition, only to an extendible film F.

[0020] The pre-stretching unit 10, as visible in Fig. 1, comprises support means 11 for a reel B of the extendible film F, a pair of pre-stretching rollers 13,14, that are rotatable around respective axes X1,X2, and a rapid insertion device 30 for inserting a head strip of the extendible film F between the rollers of the pair of pre-stretching rollers 13,14. In the embodiment shown by way of example, the axes X1, X2 are parallel to one another.

[0021] In detail, each roller of the pair of pre-stretching rollers 13,14 is connected to a respective motor that controls the rotation speed thereof around the respective axes X1,X2. In fact, in order for the extendible film F to be yielded, the rollers of the pair of pre-stretching rollers 13,14 have to rotate at different speeds and have to have a side surface that is able to exert sufficiently great friction on the extendible film F, so as to ensure the necessary grip and ensure that the portions of extendible film F in contact with the respective rollers of the pair of pre-stretching rollers 13,14 advance at the same tangential speed as the rollers with which they are in contact.

[0022] In particular, with reference to Fig. 2, the rapid insertion device 30 comprises a flexible dragging element 17, configured for advancing along a path that extends between, and partially around, the axes X1, X2 so as to drag the head strip of the extendible film F through the rollers of the pair of pre-stretching rollers 13,14.

[0023] The rapid insertion device 30 comprises connecting means 20, provided on the flexible dragging element 17 itself, and configured for connecting the head strip of the extendible film F to the flexible dragging element 17.

[0024] In the embodiment shown by way of example in Fig.2, the connecting element 20 has recesses 26,27,28 that are suitable for enabling an operator to bind the extendible film F firmly to the connecting element 20.

[0025] The flexible dragging element 17 can be, for example, a cable, a rope, a string, or a belt, made of a flexible material. The flexible material can be chosen, for example, from a group comprising: polyvinyl chloride, polyester, polyamide, or polypropylene.

[0026] At a free end of the flexible dragging element 17, a gripping element 18 is provided such as a grip or handle, suitable for being grasped and pulled by an operator to make the flexible dragging element 17 advance along the path through the pair of pre-stretching rollers 13,14.

[0027] The pre-stretching unit 10 is, as visible in Figs 1 and 3, further provided with a return device 23, configured for returning the flexible dragging element 17 to a rest position; a blocking element 19 is provided that is suitable for restingly receiving the gripping element 18 when the flexible dragging element 17 is in the rest position.

[0028] More precisely, the return device 23 can comprise, for example, a return spring for rewinding the flexible dragging element 17 to the rest position that, in this case, comprises a wound rest position. Alternatively to the return spring of passive type, in one embodiment that is not part of the invention the return device 23 can comprise a return member of active type such as for example an electric winding motor, a unit of pneumatic or hydraulic type or another equivalent member of active type.

[0029] With reference to Figs 1, 3 and 5, each pre-stretching roller 13;14 of the pair of pre-stretching rollers 13,14 is provided with a disc element 24;25, each of which has a groove in which the flexible dragging element 17 slides. In particular, each disc element 24;25 with a groove is placed at one end of the respective pre-stretching roller 13; 14.

[0030] The disc elements 24;25 with a groove can be, for example, two pulleys.

[0031] The pre-stretching unit 10, as shown in Figs 1 and 3, is also provided with height adjusting means 21,22 so as to adjust the height of the flexible dragging element 17. This configuration permits greater design flexibility because it is not necessary for the flexible dragging element 17 to have a constant height along all the pre-stretching unit 10.

[0032] The height adjusting means 21,22 can comprise, by way of example, pulleys.

[0033] Lastly, with reference to Figs 1,3,4 and 5, the pre-stretching unit 10 is provided with entering film guide means 12 to guide the insertion of the extendible film F inside the pair of pre-stretching rollers 13, 14. The entering film guide means 12 being able to comprise, for example, an idling roller.

[0034] In the same manner, the pre-stretching unit 10 is also equipped with guide means 15,16 for guiding exiting film to guide the exit of the extendible film F from the pair of pre-stretching rollers 13,14. The guide means 15,16 for guiding exiting film can comprise, by way of example, idling rollers.

[0035] The operation of inserting the extendible film F inside the pre-stretching unit 10 according to the invention is disclosed below.

[0036] The reel B of the extendible film F is first inserted inside the support means 11 and the head strip of the reel B is unrolled to then be connected to the flexible dragging element 17 by the connecting element 20. For example, the head strip of the extendible film F can be bound firmly to the connecting element 20.

[0037] Subsequently, the operator grips and pulls the gripping element 18; in this manner, the flexible dragging element 17 advances along the path that extends between, and partially around, the axes X1,X2, dragging the head strip of the extendible film F through the rollers of the pair of pre-stretching rollers 13,14. During the advancement of the flexible dragging element 17, the reel B is unrolled and the extendible film F, pulled by the flexible dragging element 17, is induced to be inserted between the pair of pre-stretching rollers 13,14. The correct insertion of the extendible film F is promoted by the entering film guide means 12.

[0038] The operator continues with the pulling action until the connecting element 20 has overcome both rollers of the pair of pre-stretching rollers 13,14. Having reached this point, insertion of the extendible film F can be in fact considered to be concluded because the extendible film F now extends between, and partially around, the rollers of the pair of pre-stretching rollers 13,14.

[0039] Subsequently, the operator disconnects the head strip of the extendible film F from the flexible dragging element 17 and passes the head strip through the exiting film guide means 15,16 so that the head strip of the extendible film F is in the correct position to be used during the wrapping operation. At the same time, the return device 23 returns the flexible dragging element 17 to the wound rest position that will be maintained until a new insertion of an extendible film F by the blocking element 19.

[0040] Owing to the aforesaid features, the pre-stretching unit 10 enables the extendible film F to be inserted conveniently, easily and fast. The operator is no longer forced to perform the inconvenient task of trying to insert the head strip of the extendible film F, grasped directly with the operator's hands, into the narrow gap between the two pre-stretching rollers, even risking personal injury. Further, the rapid insertion device 30 according to the invention does not alter the general structure of the pre-stretching unit 10 (for example the distance between the rollers of the pair of pre-stretching rollers 13,14) so that the performance of the pre-stretching unit 10 is not affected and at the same time the cost of the pre-stretching unit 10 remains moderate, owing to the very simplified structural configuration of the rapid insertion device 30. Further, the rapid insertion device 30 according to the invention does not require frequent maintenance because the rapid insertion device 30 operates only during the step of insertion of the extendible film F; subsequently, during the pre-stretching process, it remains in the rest condition.

[0041] From what has been set out above, it is clear that the pre-stretching unit 10 according to the invention successfully attains the objectives mentioned previously.

[0042] What has been disclosed and shown in the attached drawings has been provided only by way of illustrative example of the pre-stretching unit 10.

Examples

Embodiment Construction

[0019]With reference to the attached Figures, a pre-stretching unit 10 is disclosed below that is suitable for being installed on an apparatus for wrapping loads with a film F, or other sheet material like paper or another material suitable for wrapping loads (shown in Figure 4), for example, on an apparatus for wrapping pallets. In particular, the pre-stretching unit 10 can operate with films F of extendible or elastic type. Further on in the description, reference will be made in a non-limiting manner and only for the sake of simplicity of exposition, only to an extendible film F.

[0020]The pre-stretching unit 10, as visible in Fig. 1, comprises support means 11 for a reel B of the extendible film F, a pair of pre-stretching rollers 13,14, that are rotatable around respective axes X1,X2, and a rapid insertion device 30 for inserting a head strip of the extendible film F between the rollers of the pair of pre-stretching rollers 13,14. In the embodiment shown by way of example, the a...

Claims

1. Pre-stretching unit (10) suitable for being installed on an apparatus for wrapping loads with a film (F), in particular an extendible film or other sheet material, comprising support means (11) for a reel (B) of said film (F), a pair of pre-stretching rollers (13,14) that are rotatable around respective axes (X1,X2), and a rapid insertion device (30) for inserting a head strip of said film (F) between the rollers of said pair of pre-stretching rollers (13,14), said rapid insertion device (30) comprising: - a flexible dragging element (17) configured for advance along a path that extends between, and partially around, said axes (X1,X2) so as to drag the head strip of said film (F) through the rollers of said pair of pre-stretching rollers (13,14), and - connecting means (20) provided on said flexible dragging element (17) for connecting the head strip of said film (F) to said flexible dragging element (17), said pre-stretching unit (10) being characterized by being further provided with height adjusting means (21,22) so as to adjust the height of said flexible dragging element (17).

2. Pre-stretching unit (10) according to claim 1, wherein at a free end of said flexible dragging element (17) a gripping element (18) is provided, such as a grip or handle, suitable for being grasped and pulled by an operator to make said flexible dragging element (17) advance along said path through said pair of pre-stretching rollers (13,14).

3. Pre-stretching unit (10) according to claim 1 or 2, further comprising a return device (23) configured for returning said flexible dragging element (17) to a rest position.

4. Pre-stretching unit (10) according to the preceding claim, wherein said pre-stretching unit (10) is provided with a blocking element (19) suitable for restingly receiving said gripping element (18) in said rest position.

5. Pre-stretching unit (10) according to claim 3 or 4, wherein said return device (23) comprises a return spring suitable for rewinding said flexible dragging element (17) to said rest position, said rest position comprising a wound rest position.

6. Pre-stretching unit (10) according to claim 3 or 4, wherein said return device (23) comprises a return member of active type chosen from a group comprising: an electric winding motor, a unit of pneumatic type, a unit of hydraulic type.

7. Pre-stretching unit (10) according to any one of the preceding claims, wherein each pre-stretching roller (13;14) of said pair of pre-stretching rollers (13,14) is provided with a disc element (24;25), each of which is provided with a groove in which said flexible dragging element (17) is slidable.

8. Pre-stretching unit (10) according to the preceding claim, wherein each disc element (24;25) with a groove is placed at one end of a respective pre-stretching roller (13;14).

9. Pre-stretching unit (10) according to any one of the preceding claims, wherein entering film guide means (12) is provided to guide the insertion of said film (F) inside said pair of pre-stretching rollers (13,14).

10. Pre-stretching unit (10) according to the preceding claim, wherein said entering film guide means (12) comprises an idling roller.

11. Pre-stretching unit (10) according to any one of the preceding claims, wherein exiting film guide means (15,16) is provided to guide the exit of said film (F) from said pair of pre-stretching rollers (13,14).

12. Pre-stretching unit (10) according to the preceding claim, wherein said exiting film guide means (15,16) comprises idling rollers.

13. Pre-stretching unit (10) according to any one of the preceding claims, wherein said flexible dragging element (17) is chosen from a group comprising: a cable, a rope, a string, a belt, which are made of a flexible material.

14. Pre-stretching unit (10) according to any one of claims 7 to 13, as claims 9, 11 and 13 are appended to claim 7 or 8, wherein the disc elements (24;25) with a groove comprise two pulleys.

15. Pre-stretching unit (10) according to any one of the preceding claims, wherein said height adjusting means (21,22) comprises pulleys.

16. Pre-stretching unit according to any one of the preceding claims, wherein said flexible dragging element (17) is made of a material chosen from a group comprising: polyvinyl chloride, polyester, polyamide, polypropylene.

17. Pre-stretching unit according to any one of the preceding claims, wherein said connecting element (20) has recesses (26,27,28) to enable the head strip of said film (F) to be bound firmly to said connecting element (20).

18. Method of inserting a film (F), or other sheet material, in particular an extendible film (F), between the rollers of a pair of pre-stretching rollers (13,14) of a pre-stretching unit (10) by a flexible dragging element (17), comprising the steps of: - connecting a head strip of said film (F) to said flexible dragging element (17) by connecting means (20) provided on said flexible dragging element (17), - gripping and pulling a gripping element (18), provided on said flexible dragging element (17), to advance said flexible dragging element (17) along a path that extends between, and partially around, said axes (X1,X2) so as to drag the head strip of said film (F) through the rollers of said pair of pre-stretching rollers (13,14), - disconnecting the head strip of said film (F) from said flexible dragging element (17) once said connecting element (20) has overcome both rollers of the pair of pre-stretching rollers (13,14); wherein said method is characterized in that it further comprises the step of: - adjusting the height of said flexible dragging element (17) by height adjusting means (21,22).

19. Method according to claim 18, wherein said connecting the head strip of said film (F) to said flexible dragging element (17) by connecting means (20) comprises tying said head strip firmly to said connecting element (20), and in which, after said disconnecting, said gripping element (18) is released to a blocking element (19) so as to return said flexible dragging element (17) to a rest position.

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