Patent Publication Number: US-2017361956-A1

Title: Apparatus for wrapping products with film

Description:
The invention relates to apparatus for wrapping products with a plastic film and in particular relates to a wrapping apparatus that is associable with a heat-shrinkable plastic film packaging machine, in particular a bundling machine. 
     The known bundling machines allow wrapping groups of products of various shapes and dimensions, such as bottles, cans, jars, boxes, etc. with a film or pellicle made of heat-shrinkable plastic material, i.e. a material that is suitable to shrink or contract with heat, so as to wrap, compact and block each other the products. 
     The known bundling machines include a transporting system that moves the products to be packaged through a series of operating stations. 
     Downstream of a composing station, in which the products are divided and separated into groups of desired composition (for example in two or more side by side rows, each row including two or more products), a wrapping station is provided in which the groups of products are successively and individually wrapped with a portion of plastic film having a suitable length for forming respective bundles or packages. In a following heating station (shrinking tunnel or oven), the film portion wrapped around the products shrinks due to the heat so as to tightly wrap the products and carry out the final bundle or package. 
     The wrapping station includes a film feeding unit, which picks the film from a reel and cuts a film portion of suitable length, and a wrapping unit that picks and folds around the group of products said film portion that is obtained and dispensed by the feeding unit. 
     The feeding unit is positioned under a conveying or supporting plane of the bundling machine, on which the products are moved along an advancing direction. Through a first opening or slot of the conveyor plane, which is transverse to the advancing direction, the film portion is dispensed by the feeding unit so as to intercept the moving products. More precisely, a first front flap of the film portion is inserted under the group of moving products, which drag the film along the advancing direction. 
     The wrapping unit is provided with a plurality of wrapping transverse bars or crossbars, which are mobile longitudinally along a closed loop trajectory around the group of products, so as to pick, support and guide the film portion above and around the group of products. More precisely, once the group of products pass beyond the first transverse opening, a crossbar comes out from the conveyor plane through said first transverse opening so as to intercept and lift a rear flap of the film portion and fold the latter above the products, by moving along a first part of the closed loop trajectory. A second transverse opening, which is positioned downstream of the first transverse opening, allows the crossbar to entry under the conveyor plane and to insert the second rear flap of the film portion under the group of products, overlapping said second rear flap on the first front flap. The two overlapped flaps of film are blocked by the weight of products. Under the conveyor plane, inside the machine, the crossbar completes its closed loop trajectory by covering the second part thereof. Thus, the film that is unwound along the same longitudinal advancing direction wraps the products. 
     At the end of the wrapping, a bundle or package is obtained that leaves the group of products sideways open. 
     Different solutions are known for moving the crossbars for wrapping the film along the closed loop trajectory. 
     A first solution includes two driving chains, which are arranged parallel and opposite at both sides of the conveyor plane and provided with links to which the crossbars are fixed, suitably spaced. The motion trajectory of the crossbars coincides with the path of the chains. 
     In a second solution, the crossbar is cantilevered fixed to the end of an arm or rod, which is mounted on a hub around an axis that is horizontal and transverse to the conveyor plane so as to rotate on a substantially vertical plane. The motion trajectory of the crossbar that is fixed to the rotatable rod is circular or elliptical. 
     Generally, in the known wrapping units, the rod supports at the opposite ends two respective crossbars, whose distance is consequently fixed and equal to the length of the rod itself and to the distance between the two transverse openings of the conveyor plane. In some particular applications, one of the two crossbars can be dismounted. 
     A second rod, that is opposite to the first rod and parallel thereto, can be provided so as to support at both ends the crossbars and provide with greater stiffness and resistance the moving mechanism however without modifying the kinematics thereof. 
     In the bundling machines it is know the requirement of packaging products having different dimensions and sizes, for example bottles or cans or tins. 
     Products of different heights require modifying the position and/or the trajectory of the crossbars, in particular changing the distance thereof from the conveyor plane in order to correctly applying and folding the film. 
     Furthermore, in order to increase the production speed of the bundling machine in the case of small dimension products, it is necessary to modify also the packaging pitch, i.e. the distance between two successive groups of products and consequently between two successive crossbars. 
     In the wrapping units provided with chains for moving the crossbars it is possible to vary the height of the latter ones from the conveyor plane during the film wrapping (according to the height of product) and/or vary the pitch between the crossbars (according to the dimensions), by modifying the number of crossbars that are mounted along the path of the chain. 
     These wrapping units are therefore configurable according to the product or bundle size, but prevent the bundling machine to operate at high speeds, mostly because of the vibrations due to the mechanisms and to the operation of the chains moving the crossbars. For manufacturing high-speed machines, solutions are used in which the chains slides inside shaped channels, in these cases, however, being not possible to vary simply and quickly the trajectory of crossbars. 
     The wrapping units provided with rotating rods for supporting the crossbars have a simpler and cheaper construction and provide a greater precision of motion, but they do not allow modifying the angular distance between the crossbars (since only a configuration with two crossbars at 180° or with single crossbar is possible) and therefore to modify the pitch or distance between two groups of successive products. 
     There are wrapping units in which the rotating rod and the crossbars are connected and moved by motion adjusting means in such a way that the crossbars can move according to trajectories that are not circular, but arched and adjustable depending on the product size. More precisely, the crossbars are moved along an arched path with a distance from the conveyor plane that is variable and selectable. An apparatus of this type is disclosed in EP 1256519 of the same applicant. 
     However, these wrapping units with rotating rods for supporting the crossbars are complex and require, under the conveyor plane, sufficient room for rotating rod and crossbars in all the possible configurations. Furthermore, said wrapping units do not allow to modify the number of crossbars and the related angular distance in order to vary the pitch or distance between the products to be packaged. 
     An object of the invention is to improve the known wrapping units or apparatuses that are associable to packaging machines, in particular bundling machines, for wrapping a film made of heat-shrinkable plastic around groups of products to be packaged. 
     Another object is to carry out a versatile and flexible wrapping apparatus that allows to fold and wrap in a precise and efficient manner the film around products having different size and dimensions and/or to vary quickly and easily the packaging pitch, i.e. the distance between the products to be packaged, in particular for optimizing a production speed of the packaging machine. 
     A further object is to provide a wrapping apparatus having a structure that is simple, compact, with particularly small overall dimensions and at the same time having a precise and reliable operation. 
     Such objects and others are achieved by a wrapping apparatus according to one or more of the below disclosed claims. 
     The wrapping apparatus of the invention is associable with a packaging machine, in particular with a bundling machine, for wrapping a group of products with a film made of plastic material and includes conveyor elements for supporting and moving the products along a longitudinal advancing direction and forming a supporting plane for the products, a feeding unit of film that is arranged under the supporting plane for dispensing a film portion of defined length through a transverse opening of the conveyor elements so as to engage said products, and a wrapping unit for picking the film portion coming out from the transverse opening and wrapping the products with said film portion. 
     The wrapping unit includes a plurality of crossbars that are supported by respective rods and suitable to pick, support and guide respective film portions around the groups of products. The crossbars are transverse, in particular orthogonal, to the advancing direction and parallel to the supporting plane. 
     The wrapping unit also includes a hub arrangement that is rotatable around the rotation axis and slidably supports the rods so that the latter ones are mobile linearly and transversely to the rotation axis and rotatably about said rotation axis, the crossbars being so mobile along a closed loop wrapping trajectory. More precisely, the rods are coupleable in a removable manner to the hub arrangement so as to allow changing the number of said rods and of the respective crossbars and an angular distance between the rods around the rotation axis according to the dimensions of the groups of products and/or a pitch between the successive groups of products on the supporting plane. 
     The wrapping apparatus also includes guiding assembly engaged by the rods and/or the crossbars for guiding the latter ones along the wrapping trajectory by changing a distance of the crossbars from the rotation axis during a rotation of the respective rods. 
     Therefore, the wrapping trajectory of the crossbar is not a circular trajectory, but an arched and shaped trajectory that is defined by the guiding assembly, which can be easily replaced. More precisely, the guiding assembly is interchangeable, easily replaceable so as to change or modify the wrapping trajectory, in particular to change a first operating stretch of said trajectory that extends above the supporting plane. In this manner, it is possible to change displacement and position of the crossbar with respect to the supporting plane according to dimensions, or size, of the products to be packaged. 
     Products of great height, for example bottles for beverages, with respect to products of shorter height, such as cans or jars, require a film portion of bigger length, and consequently a first operating stretch of the wrapping trajectory of larger extension for wrapping, and a bigger distance of the crossbar from the supporting plane in said first operating stretch. 
     The operation of size change, i.e. the replacement of guiding assembly, is easy and simple and requires minimum downtime for the packaging machine. 
     It is also possible, by suitably choosing the guiding assembly, to create the wrapping trajectories that are most effective and appropriate for the products to be packaged according not only to dimensions and size, but also to the pitch between two successive groups of products. 
     The pitch of the products in the wrapping machine can be changed since the wrapping apparatus of the invention allows changing quickly and simply also the pitch, i.e. the angular distance, between two successive crossbars. In fact, the number of crossbars, i.e. the number of rods fixed to the hub arrangement, can be easily changed. More precisely, the supporting arms of the hub arrangement, which slidably support the rods, can be quickly mounted or dismounted to be angularly repositioned, in a smaller or larger number, so as to allow fixing a different number of rods and related crossbars. 
     Alternatively, the hub arrangement may include central bodies that are easily and quickly mountable and dismountable and interchangeable with a plurality of central bodies having a different number of supporting arms, so as to change the number of crossbars. 
     Therefore, by changing the number of crossbars and the related angular distance it is possible to change the pitch between the successive groups of products and thus increase or decrease the speed of the packaging machine according to the size of products. 
     Thanks to the wrapping apparatus of the invention, the packaging machine, which includes said apparatus, is suitable to package a wide range of products of different dimensions and s while optimizing the production speed or rate. More precisely, with small size product it is possible to reduce the pitch between the groups of products and increase the machine speed (up to values that are not suitable for large size products) so as to increase the productivity. 
     It should be noted that the wrapping apparatus of the invention has a simple and compact structure and further allows reducing and limiting the overall dimensions of the wrapping apparatus under the supporting plane, inside the packaging machine. This is made possible because the crossbars move separately and not in couple, since each crossbar is fixed to a respective rod, or a couple of opposite rods, and a second return stretch of the wrapping trajectory can be designed so as to be compact. On the contrary, in the known wrapping apparatuses, each rod supports at the opposite ends two separate crossbars and the trajectory of the crossbar under the supporting plane (second return stretch) is a consequence of the trajectory of the crossbar that moves above the supporting plane (first operating stretch) and that is imposed by the characteristics of the group of products to be wrapped. More precisely, in the wrapping apparatus of the invention, thanks to the rods that are slidably connected to the hub arrangement and thus during the rotation are mobile linearly and transversely, in particular orthogonally, to the rotation axis, the second return stretch of the wrapping trajectory can have a limited extension. In particular, the second return stretch can extend to a limited extent under the supporting plane since the rods are linearly displaced inwards along the respective supporting arms, towards the rotation axis. The overall dimensions of guiding assembly and rods under the supporting plane is therefore substantially defined by the length of the supporting arms of the hub arrangement, such length being much shorter than the summed length of supporting arms and rods in the maximum extension position in the first operating stretch of the wrapping trajectory. 
    
    
     
       The invention will be better understood and implemented with reference to the attached drawings, which illustrate an exemplifying and non-limiting embodiment, wherein: 
         FIG. 1  is a schematic perspective view of the wrapping apparatus of the invention installable on a packaging machine; 
         FIG. 2  is a side view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a section view along the line of  FIG. 2 ; 
         FIG. 4  is a schematic section view of the apparatus of  FIG. 1  associated to a group of products to be wrapped and in an operating step; 
         FIG. 5  is a perspective view of the wrapping apparatus of  FIG. 1 ; 
         FIG. 6  is a schematic section view of a different configuration of the apparatus of  FIG. 5  that is associated to a group of products to be wrapped and in an operating step. 
     
    
    
     With reference to  FIGS. 1 to 6 , the wrapping apparatus  1  of the invention is shown that is associated with a packaging machine  100 , in particular a bundling machine, for wrapping with a film  50  made of plastic material, in particular of heat-shrinkable type, groups  61  of products  60  so as to form respective bundles or packages of products. More precisely, the wrapping apparatus  1  can be used and installed in a wrapping station of the packaging machine  100 , interposed between a composing or forming station of groups of products to be wrapped, in which the products are divided and separated so as to form groups of desired composition, and a successive heating station, in which the film wrapped around each group of products  60  contracts and shrinks because of the heat so as to tightly wrap the products and carry out the bundle. 
     The composing station and the heating station are of known type and not illustrated in the figures. 
     The wrapping apparatus  1  includes conveyor elements  21 ,  22 ,  23  for supporting and moving groups  61  of products  60  along an advancing direction A, longitudinal and substantially horizontal, a feeding unit  2  of film  50  for dispensing film portions  51  of defined length, and a wrapping unit  3  suitable to pick the film portions  51  and wrap with the latter ones the groups  61  of products  60 . 
     With reference to the embodiment shown in the figures, the conveyor elements include three distinct conveyors or transporting belts that are arranged aligned and in succession along the advancing direction A. 
     A first conveyor  21  receives the group  61  of products  60  from the upstream forming station and transfers said group  61  of products  60  to a successive second conveyor  22  that moves the products  60 , while the latter ones are wrapped by the film portion  51 . A third conveyor  23  receives the group  61  of products  60  wrapped in the film  51  and moves said group  61  of products towards the successive heating station that is arranged downstream. The three conveyors  21 ,  22 ,  23  moving the products  60  along the advancing direction A at the same speed, have respective supporting surfaces that form a substantially horizontal supporting plane  20  for said products  60 . 
     The feeding unit  2 , of known type and not illustrated in detail in the figures, is positioned under the supporting plane  20  and includes means for unwinding the plastic film  50  from a reel and for cutting a portion  51  thereof having a suitable length and such as to allow wrapping the group  61  of products  60  properly and completely. The feeding unit  2  dispenses the cut film portion  51  through a transverse opening  24  of the conveyor elements  21 ,  22 ,  23  so as to catch and engage the products  60 . 
     More precisely, the feeding unit  2  dispenses the film portion  51  so that a first front flap thereof is inserted under the products  60  moving on the conveyor elements  21 ,  22 ,  23 . The transverse opening  24  is a slot or slit that is transverse, in particular orthogonal, to the advancing direction A, and separates the first conveyor  21  from the second conveyor  22 . A further transverse opening  25  is provided for separating the second conveyor  22  from the third conveyor  23 . The further transverse opening  25  is a respective slot or slit that is transverse, in particular orthogonal, to the advancing direction A. 
     The wrapping unit  3  includes a plurality of transverse bars or crossbars  4 , which are arranged transversely, in particular orthogonally, to the advancing direction A for picking, supporting and guiding respective film portions  51  around the groups  61  of products  100 . Each crossbar  4  is connected to an end portion  15  of a respective rod  5  that is mounted rotatable around a rotation axis X, which is substantially horizontal and transverse, in particular orthogonal, to the advancing direction A. In such manner, the rods  5  rotate on an almost vertical plane and the respective crossbars  4  are fixed to the rods  5  so as to be parallel to the rotation axis X and parallel to the supporting plane  20 . 
     In the embodiment shown in the figures, the wrapping unit  3  includes three crossbars  4  that are angularly spaced around the axis X, in particular by 120°, and connected to respective couple of rods  5 . More precisely, each crossbar  4  is supported and fixed at its opposite ends to two respective rods  5 , which are both rotatable around the axis X and arranged parallel and mutually facing at the two opposite sides of conveyor elements, in particular of the second conveyor  22 . The rods  4  of each side of the conveyor elements  21 ,  22 ,  23  are angularly spaced each other by 120° around the axis X. 
     Alternatively, the crossbars  4  can be cantilevered fixed to only one respective rod  5 , the rods  5  being in this case provided at only one side of the conveyor elements  21 ,  22 ,  23 . 
     During the rotation of rods  5  around the rotation axis X, the crossbars  4  are thus moved along a defined closed loop wrapping trajectory T, around the group of products  60  moving on the second conveyor  22  along the advancing direction A and through the transverse openings  24 ,  25  of the supporting plane  20 , as better explained in the description below. 
     The wrapping trajectory T of the crossbars  4  includes a first operating stretch T 1  extending above the supporting plane  20  and the products  60  and a second return stretch T 2  extending below the supporting plane  20 . 
     The wrapping unit  3  also includes a hub arrangement  8 , rotatable around the rotation axis X and slidably supporting the rods  5  so that the latter ones are mobile linearly and transversely to the rotation axis X, in particular orthogonally to the latter, and rotatably about the rotation axis X. 
     The apparatus includes a guiding assembly  6 ,  7  that is engaged by the rods  5  and/or by the crossbars  4  for guiding the latter ones along the wrapping trajectory T, changing a distance of the crossbars  4  from the rotation axis X during a rotation of rods  5 , i.e. during the movement of crossbars  4  along the wrapping trajectory T. 
     The rods  5  are coupleable in a removable manner to the hub arrangement  8  so as to change the number of rods  5  and of respective crossbars  4  and an angular distance between the rods  5  around the rotation axis X according to the dimensions of the groups  61  of products  60  and/or a pitch or distance p between two successive groups  60  of products  61  on the supporting plane  20 , as better explained in the description below. 
     More precisely, each crossbar  4  is fixed to the end portion  15  of the respective rod  5  that is removably connected to the hub arrangement  8  by means of a respective supporting arm  28  suitable to slidably support said rod  5  transversely, in particular orthogonally, to the rotation axis X. 
     The hub arrangement  8  includes at least a central body  27  that is rotatably connected to a frame  10  of the wrapping unit  3 , so as to rotate about the rotation axis X driven by actuating means  35 , including for example an electric rotary motor. In the embodiment shown in the figures, the hub arrangement  8  includes two central bodies  27  that are rotatably connected to the frame  10  at the opposite sides of conveyor elements  21 ,  22 ,  23  and are both driven by actuating means  35 . 
     Each central body  27  includes a fastening assembly  26  for removably fastening a desired number of supporting arms  28 . Each supporting arm  28  is arranged for slidably supporting a respective rod  5  that is linearly mobile along an adjusting direction, which is almost orthogonal to the rotation axis X. In particular, the supporting arms  28  are tangentially fastened to the central body  27 . Alternatively, the supporting arms  28  can be radially fastened to the central body  27 . 
     In the illustrated embodiment, the supporting arms  28  are provided with respective carriages  29 , for example provided with sliding rollers or spheres, which slidably engage and support the corresponding rods  5 , formed by suitable shaped rails. The linear coupling between the carriages  29  and the shaped rails of rods  5  guarantees the linear sliding of the latter ones along the adjusting direction and parallel to the supporting arm  28 . 
     The supporting arms  28  can be easily dismounted from the fastening assembly  26  of the central body  27  that includes fastening elements such as holes for screws, plugs and similar elements, so as to be angularly positioned in a smaller or larger number and enable to fix a different number of rods  5  and related crossbars  4 . More precisely, the fastening assembly includes a plurality of fastening elements  26  that are mutually angularly spaced around the rotation axis X, a supporting arm  28  being reversibly fastenable to a respective fastening element  26 . 
     As shown in  FIG. 4 , each fastening element  26  includes, for example, a group of fastening holes for screws, plugs and similar elements that are carried out on a wall of the central body  27 , said groups of fastening holes enabling to fasten to each central body  27  of the hub arrangement  8  three supporting arms  28  that are regularly angularly spaced from each other, in particular by 120° or, as shown in  FIG. 6 , two supporting arms  28 , regularly angularly spaced from each other, in particular by 180°. 
     The number and the angular distribution of the groups of fastening holes  26  on the central bodies  27  can however be such as to allow fastening a larger number of supporting arms  28 , i.e. of crossbars  4 , for example four or five. 
     The number of crossbars  4  can be chosen, in fact, according to the pitch p and the size of the groups  61  of products  60  to be packaged, for example can be increased for reducing the pitch p between two successive groups of products  60  so as to increase speed and productivity of the packaging machine  100 . 
     In a variant of the wrapping apparatus that is not illustrated in the figures, the hub arrangement  8  includes at least a central body  27 , more precisely two central bodies  27  that are arranged on opposite sides of conveyor elements  21 ,  22 ,  23 , each central body  27  being provided with a set number of supporting arms  28  for respective rods  5  and crossbars  4  and in this case fixed in a removable and reversible manner to the frame  10  and interchangeable with further central bodies  27  having different number of supporting arms  28 . In this case, the supporting arms  28  are fixed to, or carried out as a single body with, the central body  27 . The central body  27  can be disengaged, for example, along the rotation axis X. 
     The guiding assembly includes at least a guiding element  6  arranged on the side of the conveyor elements  21 ,  22 ,  23  and provided with an annular seat  11 , which extends along the wrapping trajectory T and is suitable to slidably receive a coupling element  14  that is fixed to each crossbar  4  or related rod  5 . More precisely and in the illustrated embodiment, the end  15  of each rod  5  includes a shaped portion, for example a lever shaped portion, to which the respective crossbar  4  and the respective coupling element  14  are fixed. Alternatively, the coupling element  14  can be directly associated to the crossbar  4 , fixed at one end thereof. 
     In the illustrated embodiment, the guiding assembly includes two guiding elements  6 ,  7  that are arranged facing, and fixed to the frame  10  at opposite sides of the conveyor elements  21 ,  22 ,  23 . In particular, the guiding assembly includes, in addition to the guiding element  6 , a further guiding element  7  provided with a further seat  12 , which is substantially specular to the seat  11  and arranged for slidably receiving the corresponding coupling elements  14  of rods  5 . 
     The two guiding elements  6 ,  7  support and guide the opposite ends of crossbars  4  and, more precisely, the ends  15  of the couple of rods  5  of each crossbar  4 . 
     Each guiding element  6 ,  7  includes, for example, a respective curvilinear shaped element, which forms a closed and shaped loop and is provided with an annular groove  11 ,  12  forming the seat suitable to receive the coupling elements  14  of the end portions  15  of rods  5 , said coupling elements  14  including, for example, respective rolls or wheels idly mounted on the end portions  15 . 
     Each guiding element  6 ,  7  is essentially a positive cam, or channel cam, that is provided with a respective groove or seat  11 ,  12  (channel) which the rolls  14  of the rods  5  engage. In this manner, during the rotation around the rotation axis X, each rod  5 , which is engaged with the end portion  15  by the respective roller  14  to the seat  11 ,  12  of the guiding elements  6 ,  7 , slides linearly and orthogonally to the rotation axis X, allowing the crossbar  4  moving along the wrapping trajectory T coinciding with the path or track of the seat  11 ,  12 . 
     Each guiding element  6 ,  7  includes a first upper portion  16 ,  17 , suitable to support and guide the crossbars  4  along the first operating stretch T 1  of the wrapping trajectory T, and a second lower portion  18 ,  19 , suitable to support and guide the crossbars  4  along the second return portion T 2  of the wrapping trajectory T. 
     The first upper portion  16 ,  17  is removably connected to the second lower portion  18 ,  19  for forming the respective guiding element  6 ,  7  and is interchangeable with one of a plurality of first upper portions having different respective annular seats  11 ,  12  so as to change or modify the first operating stretch Ti of the wrapping trajectory T and then a position of the crossbar  4  with respect to the supporting plane  20 , in particular according to a dimension or size of the products  60  to be packaged. 
     Also the second lower portion  18 ,  19  can be dismounted from the wrapping unit in order to modify the second return stretch T 2  of the wrapping trajectory T. 
     In a version of the apparatus  1  not shown in the figures, the first upper portion  16 ,  17  and the second lower portion  18 ,  19  are fixed so as to carry out a single body. In this case, the whole guiding element  6 ,  7  is fixed in a removable manner to the frame  10  of the wrapping unit  3  and is interchangeable with one of a plurality of guiding elements provided with respective different seats  11 ,  12  for changing and modifying the wrapping trajectory T. 
       FIG. 6  illustrates a different configuration of the wrapping apparatus  1  of the invention in which the wrapping unit  3  includes two crossbars  4  that are supported by two respective couple of rods  5 , angularly spaced by 180°. In this variant, two respective supporting arms  28  are fastened to the fastening assembly  26  of the two central bodies  27  of the hub arrangement  8 , and are tangentially fixed and angularly spaced by 180°. The two crossbars  4  are supported and guided at the respective ends by the two guiding elements  6 ,  7 . More precisely, the rolls  14  of the end portions  15  of rods  5  slide inside the seats  11 ,  12  of the guiding elements  6 ,  7  causing the rods sliding on the supporting arms  28  during the rotation around the axis X. 
     The different number of crossbars  4  and the related angular distance (180° allows increasing the pitch p between two successive groups  61  of products  60 , for example because the latter ones have larger dimensions. With respect to the configuration with close pitches that is illustrated in  FIG. 4 , the speed of the machine can be reduced in order to not destabilize the products  60  when moving. 
     The number of the crossbars  4  can be increased, according to pitch and size of the groups of products to be packaged for allowing reducing, in this case, the pitch between two successive groups of products  60  and increasing speed and productivity of the packaging machine  100 . 
     The operation of the wrapping apparatus  1  of the invention mounted on a packaging machine  100 , in particular in a wrapping station thereof, includes moving the groups  61  of products  60  coming from the forming station along the first conveyor  21  towards the second conveyor  22 , on the supporting plane  20 . At the transverse opening  24 , which is interposed between the first conveyor  21  and second conveyor  22 , a front or forward portion of the group of products catches a portion  51  of the film  50  of suitable length that is dispensed by the feeding unit  2 . More precisely, a first front flap of the film portion  51  is inserted under the moving group  61  of products  60  and dragged along the advancing direction A. 
     Once the group of products is transferred onto the second conveyor  22 , a crossbar  4  supported by a respective couple of rods  5  comes out from the supporting plane  20  through the transverse opening  24  so as to intercept and lift a second rear flap of the film portion  51  and fold the latter above, and longitudinally around, the group  61  of products  60 , moving along the first operating stretch T 1  of the closed loop wrapping trajectory T. 
     More precisely, the crossbar  4  is supported at the opposite ends and moved along the wrapping trajectory T by a respective couple of rods  5 , which are rotatable around the rotation axis X and linearly slidable orthogonally thereto. More precisely, the linear movement of rods  5  during the rotation is carried out by the coupling elements  14  slidably coupling with the seats  11 ,  12  of guiding elements  6 ,  7 . Basically, the guiding elements  6 ,  7  are two positive cams provided with respective grooves or seats  11 ,  12  in which said coupling elements  14  are engaged. 
     Continuing the movement along the wrapping trajectory T, the crossbar  4  returns under the moving plane  20  through the further transverse opening  25  so as to insert the second rear flap of the film portion  51  under the group of products  60 , overlapping the aforesaid second rear flap to the first front flap. The two overlapped flaps of the film portion  51  are blocked by the weight of the products. 
     Under the supporting plane  20 , inside the packaging machine  100 , the crossbar  4  completes the wrapping trajectory T by covering the second return stretch T 2 . 
     It should be noted that the wrapping trajectory T of the crossbar  4  is not a circular trajectory, but a shaped trajectory that is defined by the guiding assembly  6 ,  7  that can be easily replaced. More precisely, the upper portions  16 ,  17  of the guiding elements  6 ,  7 , which guide the rods  5  and then the crossbars  4  along the first operating stretch T 1 , are interchangeable, easily replaceable with first upper portions  16 ,  17  having different seats  11 ,  12  so as to change or modify such first operating stretch T 1 . In this manner, it is possible to change the displacement and the position of crossbar  4  with respect to the supporting plane  20  according to dimensions, or size, of the products  60  to be packaged. 
     Products of great height, for example bottles for beverages, with respect to products of shorter height, such as cans or jars, require a film portion  51  of bigger length and consequently a first operating stretch T 1  of larger extension for wrapping, and a bigger distance of the crossbar  4  from the supporting plane  20  in said first stretch T 1 . 
     The operation of size change, i.e. the replacement of first upper portions  16 ,  17  (or alternatively of the complete guiding elements  6 ,  7 ), is easy and simple and requires minimum downtime for the packaging machine  100 . 
     By suitably choosing the path of the seats  11 ,  12  of guiding elements  6 ,  7 , it is also possible to obtain the wrapping trajectories T that are more effective and appropriate for the products to be packaged according not only to dimensions and size, but also to the pitch p between two successive groups  61  of products  60 . 
     In fact, it is possible to change the pitch of the groups  61  of products  60  in the wrapping machine  100  since the wrapping apparatus  1  of the invention allows modifying in a fast and simple manner the number of crossbars  4 , i.e. of rods  5  fixed to the hub arrangement  8 . More precisely, the supporting arms  28 , thanks to the fastening assembly  26 , can be quickly and easily mounted on, or dismounted from, the central bodies  27  of the hub arrangement  8  so as to be angularly repositioned, in a smaller or larger number, and to enable to fix a different number of rods  5  and related crossbars  4 . 
     Therefore, by changing the number of crossbars  4  and the related angular distance it is possible to change the pitch p between two successive groups  61  of products  60  and then to increase or decrease the speed of the packaging machine  100  according to the product size. 
     Thanks to the wrapping apparatus  1  of the invention the packaging machine  100  can package a wide range of products  60  and groups  61  of products  60  having different dimensions and sizes, while optimizing the production speed or rate. More precisely, with small size products it is possible to reduce the pitch p between the groups of products and increase the machine speed (up to values that are not suitable for large size products) so as to increase the productivity. 
     Finally, it should be noted that the wrapping apparatus  1  of the invention has a simple and compact structure and further allows reducing and limiting the overall dimensions of the wrapping unit  3  under the supporting plane  20 , inside the packaging machine  100 . 
     Thanks to the rods  5 , which are slidably connected to the hub arrangement  8  and then linearly mobile during the rotation around the rotation axis X transversely, in particular orthogonally, to the latter, the second return stretch T 2  of the wrapping trajectory T can have a limited extension. More precisely, such second return stretch T 2  extends to a limited extent under the supporting plane  20 , since the rods  5  are linearly moved along the respective supporting arms  28  inwardly toward the rotation axis X, so that the end portions  15  are adjacent to the carriages  29 . The overall dimensions of the guiding assembly  6 , 7  and rods  5  under the supporting plane  20  is therefore substantially defined by the length of the supporting arms  28 , which is much shorter than the summed length of the supporting arms  18  and rods  5  in the position of maximum extension in the first operating stretch T 1 .