AUTOMATIC WRAPPING MACHINE FOR PACKAGING PRODUCTS, PARTICULARLY PALLETIZED UNITS, TO BE WRAPPED WITH A THERMORETRACTIBLE TUBULAR FILM

Abstract: An automatic wrapping machine for packaging products, mate­ rials and palletized units, to be wrapped with a thermoretractible tubu­ lar film, comprises a casing (1), at the centre of which the material to be packaged is positioned in order to receive a wrapping of thermoretracti­ ble tubular film formed as a bag with bottom at the top, and is equipped with heating means to carry out the thermoretraction of said film after the material has been wrapped therewith. According to the invention, said machine is provided with a plurality of movable gripper members (6), by means of which said film wrap­ ping is picked up in the form of a bag at the side of said casing, is lifted, is opened and is transferred into said casing above the material to be packaged, as a prismatic bag, being then lowered so as to wrap said material. Said gripper members consist of pairs of grippers which grip the folded tubular film on four edges. The machine also provides for the reel (B) feeding the thermo­ retractible tubular film to be rotatably supported between two end cones (10) suspended by means of flexible elements (9) to the machine casing. Further­ more, said heating means to carry out the thermoretraction of the film consist of a ring furnace (8).

Description: The present invention concerns an automatic wrapping machine for packaging products and materials, particularly palletized units, which makes use of a tubular film of thermoretractible, respectively thermoshrinkable plastic material, folded flat and rolled up on a respective feeding reel. More precisely, the invention relates to a machine of the type described in the introductory part of Claim 1. An automatic wrapping machine is described for example in DE-B-1 940 783, wherein the material to be wrapped, loaded on a pallet, is positioned at the centre of the base of a tall casing; the reel of film is placed on the top part of said casing, and the film is unrolled from said reel in a flat condition and is guided up to a pair of feed rollers arranged at the centre of said top part. The film is then moved by said rollers in a vertical direction, by guiding its four folding edges into four gripper guides. Said guides then grip the four edges and move, first sideways - to open the tubular film into an upside-down bag - and then downwards, to cause the film to envelop the material loaded on the pallet. Once the material has been enveloped, the pallet is shifted towards a further working station, where the packaging is completed by shrinking the film under heat treatment, carried out for instance into a suitable furnace. Machines of this type suffer however from the following drawbacks, tied to their specific structure: they are extremely oversized in height, due to the presence of the casing supporting the feeding reel on top of it, and taking into account that said reel is quite large and heavy; consequently, they cannot be fully assembled in the factory and then be transported ready for use, but they have to be transported in parts and then be assembled on the site of use, thereby evidently raising the capital costs and often creating problems of space on the sites of use; finally, they are not easy to use because of the difficulty in carrying the feeding reel up to the top of the casing and mounting it in a correct position; this operation normally requires the use of a traveling bridge crane, since a lift truck is not sufficiently high. To overcome this known drawback, the DE-C-20 26 860 proposes by disclosing an automatic wrapping machine as mentioned in the introductory portion of claim 1 to mount the feeding reel close to the base of the casing and to provide or means carrying the. film to the tory and then guiding it again downwards, over the load, using the same method described in DE-B-1 940 783. Also this technique involves however some drawbacks: in fact, the film follows a path unwinding through several transmission rollers and this can - as also described in DE-C-32 34 929 - cause cinchings which are harmful for the correct feeding and opening of said film. In order to overcome also this drawback, the DE-C-32 34 929 thus proposes to still position the feeding reel at the bottom of the casing, but to reverse the actual feeding system by moving the film from the bottom towards the top (instead of feeeding it from the top towards the bottom, as in previous technique). For this purpose, the DE-C-32 34 929 provides for the use, in combination with the conventional vertical gripper guides already used in previous technique: of means to draw a film length from the bottom to towards the top, and of a pair of cantilevered horizontal rails, along which said vertical gripper guides can be moved from position to the side of the pallet towards a position above the pallet. Similarly to the DE-C-32 34 929, also the EP-A1-0 076 867 describes a machine wherein the film is fed laterally of the load by gripping means which draw it from the bottom towards the top. These same means then perform a complicated movement, along an overturned U trajectory, in order to lift a length of film and simultaneously open it into bag, then carry it over an operating unit and finally fit it, from the top towards the bottom, over the load on the pallet. As it appears evident on reading said documents, the main object of these known machines is to form an overturned bag starting from a tubular film, and fit said bag over the load on the pallet, but none of them deals with the problem of providing for heating means to cause the shrinkage of the film bag. In fact, according to known technique, this oration is carried out in a successive working step by transferring the pallet with the enveloped load into a separate machine or furnace. The object of the present invention is to realize a machine apt to carry out both the operation of applying the film bag over the load and the oration of film thermoshrinkage. This object is reached - in a machine of the type described further above with reference to DE-C-20 26 860 - thanks to the characteristics pointed out in the characterizing part of Claim 1. The combination of a machine to apply a film wrapping over a palletized unit with a ring furnace causing the thermoshrinkage of said film - according to the teaching of the present invention - would have been possible neither in DE-B-1 940 783 or DE-C-20 26 860, in that the reel or film positioned at the top of the casing would be damaged by the heat rising from the ring furnace, nor in DE-C-32 34 929, in that the arms which grip, transfer and apply the film over the load would be interfering with the structure of the ring furnace. Whereas, the machine according to the present invention allows to surprisingly carry out ail these orations of gripping the film, pulling out a length thereof, transferring said film length and applying it over the palletized unit while moving inside the. ring furnace, by adopting a single system of grippers mounted on movable vertical bars in a simple but very efficient way. The accompanying drawings show a preferred embodiment of the wrapping machine according to the invention, which is now described in further detail. In said drawings: Figs. 1 to 7 are diagrammatic perspective views of the machine assembly according to the invention, schematically illustrating the different working steps thereof; Figs. 8 and 9 show some main components of the movable gripper members of the machine according to the invention, fig. 8 illustrating the vertical movements and fig. 9 the horizontal movements of said members; Figs. 10, 11, and 12, 13, are respectively side views and top plan views of the grippers carried by the movable gripper members, in two different working steps; Fig. 14 is a sectional view of one of the welding and cutting bars of the machine according to the invention; Figs. 15 and 16 diagrammatically illustrate the control means for said welding and cutting bars, in two different working steps; and Figs. 17, 18 and 19 are, respectively, a side, a front and a top plan view of the improved feeding section of the machine according to the invention. With reference to the drawings, the wrapping machine according to the invention comprises (fig. 1) a working section L and a section A feeding the tubular film PT. The working section L comprises a stout metal casing 1 with four uprights 2, at the centre of which the palletized unit UP (fig. 4) - or other material or product, or group of products - to be wrapped with the thermoshrinkable tubular film PT is positioned for packaging purposes. The four uprights 2 of the casing 1 are connected in twos by means of upper cross members 3, parallel one to the other and strongly projecting from the casing 1 towards the section A feeding the thermoshrinkable film PT. Along each of the cross members 3 of the casing 1 there is slidably mounted a carriage 4 carrying pairs of vertical bars 5, movable both horizontally - so that their position and reciprocal distance along said cross members depends on the position of the carriage 4 - and vertically, said bars being equipped with pairs of grippers 6, one pair at the lower end and the other higher up, designed to grip the section of tubular film PT with which the material being packaged has to be wrapped. The working section L of the machine according to the invention is completed with a pair of bars 7, for cutting and welding the film, and with a ring furnace 8. The feeding section A comprises means for simply suspending a reel B of thermoshrinkable tubular film PT, consisting of two flexible elements as chains 9 (or possibly ropes or cables) hanging from the free end of each cross member 3 of the casing 1, and of two supporting cones 10 into which are rotatably mounted the ends of the shaft 11 (fig. 18) of the reel B on which the film PT is wound up. The feeding section A also comprises an element, consisting for example of an idle roll 12, to support and guide the reel B, and three idle guide rollers to deviate the unreeled film, of which a movable roller 13 and two fixed and coupled rollers 14, parallel and close to the base of the machine. Going into further details for what concerns the working section L, the movements of the carriage 4 along the cross members 3 are directed (fig. 8) by guides 15 and controlled by a fluid pressure cylinder 16. The carriage 4 consists of two elements 17 and 18, each carrying one of the two pairs of vertical bars 5 of said carriage. The element 18 carries an idle sprocket 19 engaging with a toothing 20 fixed to the casing 1 and with a toothing 21 projecting from the element 17. The piston rod 16A of the cylinder 16 is connected to the element 18 of the carriage 4. In this way, the movements of the elements 17 and 18 of the carriage 4, controlled by the cylinder 16, take place with different laws and, in practice, the pairs of vertical bars 5, carried by said elements, draw close when the carriage travels towards the centre of the casing 1, and move apart when the carriage travels towards the feeding section A. The movements of the vertical bars 5 in the vertical direction are in turn directed (fig. 9) by pairs of rollers 22, 23, and controlled by bidirectional electric motors 24, 25, through toothed belts 26, 27, which wind onto driving sprockets 28 and guide rollers 28A, 28B, and which are fixed to the upper ends of said bars 5, said motors and rollers being carried by the elements 17 and 18 of the carriage 4. The grippers 6 are mounted at the lower ends of the vertical bars 5, and about half way along their length, so as to grip the section of tubular film PT allowing to wrap the palletized unit UP (or other material to be packaged). One of said grippers is shown in detail in figs. 10 to 13. It comprises a pair of jaws 29 reciprocally pivoted, about a vertical axis 30, onto a lever 31 which is in turn pivoted on the bar 5 about a horizontal axis 32. The jaws 29 of the gripper are kept open by a pair of springs 33, while their closing is controlled by a lever 34, fulcrumed horizontally in 35 on the bar 5 and operated by the piston of a fluid pressure cylinder 36, and by a connecting rod 37 which connects the lever 34 to the lever 31. Furthermore, an element 38 is provided to stop the movement of the lever 34. The cutting and welding bars 7 form part of a more complex device shown in detail in figs. 14 to 16. These bars comprise (fig. 14) a pair of longitudinal clamping shoes 39, pressed one towards the other by springs 40 and, fixed to said shoes, two resistor heating elements 41 and a cutting blade 42. The bars 7 are each carried (figs. 15 and 16) by two saddles 43, 44, movable along the cross members 3 under the control of leverages operated by a fluid pressure cylinder 45 and comprising two sets of three levers 46, 47, 48, of which, the end levers 46 are controlled by the cylinder 45, the end levers 48 control the saddles 43, 44, while the intermediate levers 47 are pivoted to an end of the casing 1. The ring furnace 8 is of a substantially conventional type, being formed as a large square metal frame, moving vertically inside the casing 1 and housing heating means, preferably in the form of gas flames to direct the heat towards the inside of said frame, and thus towards the palletized unit UP or other material to be packaged, designed to be fully and closely enveloped by said frame. The working of the wrapping machine described heretofore and shown on the accompanying drawings shall now be briefly illustrated. Considering first of all the feeding section of the machine, it should be noted that it is most important for the thermoshrinkable tubular film PT to be unreeled with the least lateral deviation, so as to make sure that the film is wrapped around the product being packaged without exceeding in size, as far as possible, the perimeter of said product. The solutions adopted so far, in order to obtain these conditions, are conceived with devices to shift axially the reel shaft, centering manually the film each time a new reel is mounted. It is however possible that, in a same reel, the film may not be wound perfectly straight, there being lateral deviations between the turns. Whereas, the solution adopted in the machine according to the invention makes it easier to center the reel B each time a new reel is mounted, but above all it allows to keep the reeled film centred while being unrolled. In fact, the mounting of the reel by suspension with flexible elements allows to easily and promptly move said reel in the axial sense, as may be required by the unevenness of its winding up, while the lateral shoulders of the reel keep the tubular film guided in the wanted position. The tubular film PT, emerging - flattened and with inwardly folded sides - from the idle roll 12 supporting the reel B, winds onto the vertically moving roller 13 and onto the two fixed bottom rollers 14. To feed the film PT to the working section L of the machine, the roller 13 of the feeding section A moves first upward, unrolling said film from the reel B of which it causes the rotation (while, downstream, the film is kept stationary as seen hereinafter), and then downward when the film PT, drawn by the machine, starts moving. The feeding to the working section L of the machine thus takes place without the reel B being dragged into rotation with negative stresses due to inertia. At the start of the working cycle, the film is positioned as shown in fig. 1, still substantially flattened and closed at its free end, at the top of the machine, by the transversal welding performed in the previous cycle, while strikers (not shown) act on its lateral folds, below said free end, to hold it in position. The roller 13 is in top position. The cycle starts with the downward movement of the four bars 5 (fig. 1), while the carriages 4 are positioned in correspondence of the portion of the cross members 3 projecting from the casing 1 and said bars 5 are drawn close. With the bars 5 in this position, the grippers 6 (fig. 1) - with open jaws and spaced from the folded tubular film PT (as shown in figs. 10 and 11) - are operated so as to grip the edges of said film in correspondence of eight points, two for each bar 5. This is obtained (figs. 10 to 13) by downstroke of the piston of the cylinder 36, and by anticlockwise rotation of the lever 34 and - thanks to the connecting rod 37 - of the lever 31; the grippers 6 - with the jaws kept open by the springs 33 - move from the position (figs. 10 and 11) far from the film, to the position (figs. 12 and 13) close to the edges of the film, and in this position the lever 31 stops against the element 38. The lever 34 continues to rotate, controlled by the further downstroke of the piston 36, and thus overcomes the resistance of the springs 33, causing the closing of the jaws 29 of the grippers 6, which hence grip in correspondence of eight points (fig. 1) the edges of the thermoshrinkable tubular film PT, thereby opening it slightly. The bars 5 are then caused to move upward by operating the electric motors 26 (fig. 9) while the carriages 4 are still stationary. The film (fig. 2) moves to the top, while being kept still folded but slightly open at the edges. At the same time, the roller 13 of the feeding section L moves downward to shift forward the film without causing the rotation of the reel B, which remains still. The cutting and welding device now starts to operate: the cylinder 45 causes, through the already described leverage, the mutual approach of the cutting and welding bars 7, until (fig. 3) the shoes 39 clamp the folded tubular film, the heating elements 41 provide for the welding thereof, and the blade 42 provides to cut said film above the welding point. In this way, the section of tubular film PT, already gripped by the grippers 6, takes up the configuration of a bag - open at the bottom and closed at the top - positioned in the upper part of the machine and apt to wrap the material to be packaged, but still folded (fig. 3). At the same time, the end of the tubular film coming from the feeding section A is clamped and closed at the top. The aforementioned bag must now be carried over the material to be packaged: this is obtained through a horizontal movement of the carriage 4 caused by operating the fluid pressure cylinders 16 (fig. 8). The elements 17 and 18 of the carriage 4, carrying the bars 5, are moved - as seen - with different laws, so that the two front bars 5 move away from the rear ones causing the opening of the bag formed by the film PT, the opening being completed when said bag is positioned - taking up a prismatic square shape SP - at the centre of the casing 1, above the material UP to be wrapped (fig. 4). During this step, the roller 13 of the feeding section is slowly moved upward from the previously reached lowered position. Since the free end of the folded tubular film is still clamped - and thus prevented from moving - by the shoes 39 of the welding and cutting bars, the upward movement of the roller 13 allows to unroll new film from the reel B - slowly caused to rotate - so as to form the bag for the successive cycle. At this point, the bars 5 are moved downward (fig. 5) by operating the motors 26 in a reversed sense from the previous one (fig. 9); the palletized unit UP is then wrapped with the bag SP formed by the thermoshrinkable tubular film PT. At the same time, the ring furnace 8 moves down, while the welding and cutting bars 7 (fig. 5) draw apart. The jaws 29 of the grippers 6 are now opened and the bars 5 are again moved upward (fig. 6), thereby releasing the palletized unit UP finally wrapped with the thermoshrinkable tubular film formed as a prismatic bag. The ring furnace 8 is turned on, while being in its lowest position, and is then slowly moved upward (fig. 7) at a speed allowing to obtain the desired degree of retraction of the film wrapping the unit UP. The machine ends its working cycle with the return of the carriage 4, and thus of the bars 5, into the initial position in which said bars are drawn close, next to the feeding section A of the machine (fig. 1). The heretofore described and illustrated machine - as well as for the reduced height of its structure, allowing it to be transported in fully assembled conditions - clearly differs from those of prior art in various respects, both as far as construction and as far as operation: to start with, for the first time one is able to draw - next to the material to be packaged - from a reel of tubular film (welded at the top in the previous working cycle), the desired amount of film to form the bag with which said material has to be wrapped, and to positively open said bag by means of grippers so as to give it a prismatic shape. It should be noted that, while in the solutions of known technique the positioning of the bag on the material to be wrapped involves the risk that the tubular film (which takes up a substantially circular shape due to the air being blown inside the bag) may interfere with the edges - at times sharp - of the product being wrapped, and thus break, the solution adopted in the machine according to the invention prevents this risk because, thanks to the grippers, the top part of the bag takes up a prismatic shape of rectangular or square section SP, and is kept in that shape. It is understood that there may be other embodiments of the invention, differing from that described and illustrated, but still falling within the scope of the invention itself. For example, the movement of the two elements 17 and 18 of the carriage 4 could be obtained (instead of using the aforedescribed and illustrated toothing and sprocket system) by means of two fluid pressure cylinders, suitably offset in operation, while the cutting system of the bars 7 could have a different configuration. Furthermore, in the case of a limited inertia in unwinding the reel B, the feeding section A of the machine could be simplified by eliminating the movable guide roller 13.

Claims: Automatic wrapping machine for packaging products and materials, particularly palletized units, to be wrapped with a tubular film of thermoshrinkable plastic material, of the type comprising: a casing (1), at the centre of which the material (UP) to be packaged is positioned in order to receive a wrapping of thermoshrinkable tubular film (PT); a feeding reel (B), on which said tubular (PT) is rolled up, folded flat; means (9, 10, 11) to support said reel (B) in a feeding section (A), external and close to the base of the casing (1); and means to cut out a length of film (PT), to weld the upper end thereof, and to form a bag with bottom at the top, said means comprising: a plurality of grippers (6) to grip the film (PT) in correspondence of its four longitudinal folding edges; and means (4, 5) to move said plurality of grippers (6) both horizontalwise, so as to open the length of film (PT) in an overturned bag position, and verticalwise, so as to transfer said overturned bag above the material (UP) to packaged; characterized in that it comprises: a pair of horizontal cross members (3, 15) projecting from the top of the casing (1) as far as above the feeding section (A); gripper members consisting of two carriages (4; 17, 18) sliding horizontally along said pair of cross members (3, 15), of four vertical bars (5) sliding up and down on the respective carriages (4; 17 or 18), and of at least two of said grippers (6) mounted on each bar (5); and a ring furnace (8), mounted vertically slidable inside said casing (1); the arrangement being such that the four vertical bars (5), together with the respective grippers (6), can move up and down inside the casing (1), within the space defined by the inner contour of the ring furnace (8). Machine as in claim 1), wherein said two carriages are movable horizontally along said cross members with different laws, said pairs of bars drawing close when the carriage moves towards the feeding section and drawings apart when the carriage moves towards the casing. Machine as in claim 2), wherein the horizontal movements of said carriages are controlled by at least one fluid pressure cylinder. Machine as in claim 1), wherein the vertical movements of said bars (5) are controlled by bidirectional electric motors (26) through driving sprockets, toothed belts an guide rollers. Machine as in claim 1), wherein the grippers carried by said bars (5) comprise a pair of jaws (29), kept open by springs (33) and normally spaced from the film (PT) to be gripped, and leverages controlled by a fluid pressure cylinder so as to draw said jaws close to said film (PT) and tighten them onto its edges. Machine as in claim 3), wherein said means to cut out a length of film (PT) comprise clamping shoes, heating elements (41) and a cutting blade (42), all carried by saddles normally spaced one from the other and drawn close by operating a fluid pressure cylinder through leverages. Machine as in claim 2), wherein said feeding section comprises a reel (B) of thermoshrinkable tubular film, wound onto a shaft rotatably supported between two end cones (10) suspended by means of flexible elements to the ends of the portion of said cross members (3,15) projecting from said casing (1), a roll (12) to support said reel (B), and idle guide rollers (13,14). Machine as in claim 7), wherein said cones (10) are suspended by means of the flexible elements (9) to the free end of cross members (3,15) of the casing (1) of the wrapping machine, projecting from the casing (1) itself. Machine as in claim 7), wherein said flexible elements (9) are chains. Machine as in claim 7), wherein said flexible elements are ropes or cables. Machine as in claim 7), wherein said element supporting the reeled film (PT) is an idle roll (12). Machine as in claim 7), wherein at least one of said idle guide rollers (13) is apt to perform a vertical rectilinear reciprocating motion. Machine as in claim 1), wherein the ring furnace (8) serves to carry out the thermoshrinking of the film (PT), with which the material (UP) to be packaged has been wrapped.

Inventors: TACCHINI, FRANCO
Applicants: OFFICINA MECCANICA SESTESE S.P.A.
Application year: 1990
Main classification: B65B9
IPC codes: B65B9