IT201800010102A1 - Machine and method for hermetic packaging of food products - Google Patents

Description

DESCRIPTION

of the industrial invention entitled:

"Machine and method for the hermetic packaging of food products"

The present invention relates to the field of industrial packaging of food products.

In particular, the present invention relates to a machine and a method for the hermetic packaging of food products, in particular biscuits.

In order to pack flat or disc-shaped food products, as industrially produced biscuits typically appear, it is known to arrange these products in an ordered pile and subsequently wrap them with a wrapping.

In particular, the wrapping with the wrapping is carried out first by wrapping the wrapping around the lateral surface of the stack and sealing this wrapping along the direction of development of the same and subsequently closing the wrapping at the bases of the stack to obtain a package. hermetic that helps to preserve the properties and organoleptic characteristics of the product over time.

In this context, the technical task underlying the present invention is to propose a machine and a method for the hermetic packaging of food products capable of producing an alternative package with respect to the known art according to a different process.

The specified technical task and the specified purposes are substantially achieved by a machine and a method for the hermetic packaging of food products, comprising the technical characteristics set out in one or more of the appended claims. The dependent claims correspond to possible different embodiments of the invention. Further characteristics and advantages of the present invention will become clearer from the indicative, and therefore non-limiting, description of a preferred but not exclusive embodiment of a machine and method for the hermetic packaging of food products.

This description will be set out below with reference to the accompanying drawings, provided for indicative purposes only and, therefore, not limitative, in which:

Figure 1 shows a perspective view of a stack of food products packable by means of a machine object of the present description;

Figure 2 shows a schematic view of a machine for the hermetic packaging of food products object of the present description, arranged in a configuration according to a step of a method object of the present description;

Figure 3 shows a schematic view of the machine of Figure 2 in a different operating configuration, in accordance with a different one of a method object of the present description;

Figure 4 shows a schematic view of a machine for the hermetic packaging of food products object of the present description, arranged in a configuration according to a step of a method object of the present description;

Figures 5A to 5B show a schematic view of a detail of the machine of Figure 4 in accordance with subsequent steps of a method object of the present description;

Figure 6 shows a perspective view of a stack of food products packaged by means of a machine object of the present description.

With reference to the figures, a machine for the hermetic packaging of food products is generically indicated with 1 and will be referred to hereinafter with the abbreviated notation "machine 1". The machine 1 is configured for the packaging of flat, cylindrical, discoidal or parallelepiped shaped food products "A" in stacked arrangement. Preferably, these "A" food products are ready-to-eat foods, for example chocolates, candies, biscuits or snacks.

The machine 1 comprises a handling unit 10 having an input station configured to receive a plurality of food products "A", for example an upstream production line to which it is connected. Preferably, the handling unit 10 comprises a conveyor belt 12 suitable for receiving a plurality of food products "A" organized in stacks "P" arranged at the inlet station and for conveying such food products "A" from the inlet station to a subsequent transfer station "S2", maintaining its stacked configuration.

More in detail, each stack "P" looks like a packing of food products "A" ready for packaging and arranged along a stacking axis "X", as illustrated in figure 1.

Each pile "P" has a first and a second base surface "P1" and "P2" opposite and parallel to each other and a lateral surface "P3" interposed between them and defined by the cooperation of the lateral surfaces of the food products "A" .

For example, if the food products “A” are disc-shaped biscuits, the “P” stacks have a cylindrical side surface “P3”. To receive and maintain the stacks "P" of food products "A" in the stacked configuration during their handling, the conveyor belt 12 has a plurality of gripping teeth 13 arranged so as to define a plurality of housing seats 14 for the stacks "P". In particular, the housing seats 14 are configured to house the stacks "P" so that the first lower base surface "P1" of each of them rests on a flat surface of the conveyor belt 12 and the teeth 13 engage the surface lateral "P3" to maintain the arrangement along the stacking axis "X" of food products "A". Preferably, the teeth 13 leave the front and rear portions free with respect to the direction of movement of the conveyor belt 12 of the side surface "P3" of each stack "P".

The handling unit 10 also comprises a transfer member 16 configured to extract the stacks "P" of food products "A" from the housing seats 14 in the transfer station "S2" and transfer them to a subsequent withdrawal station "S3" .

Preferably, the transfer member 16 comprises gripper elements 17 configured to engage portions of the lateral surface "P3" of the stacks "P" not engaged by the teeth 13 of the conveyor belt 12, in particular to engage the front and rear described above, as shown in Figure 2.

The gripping portions 17 are configured to grip the stacks "P" firmly along their lateral surface "P3" and move them while maintaining their stacked configuration, preferably so as to maintain the aforementioned front and rear eastern portions according to the direction of movement of the respective stack "P".

In the preferred embodiment, the transfer member 16 is configured to move the gripping portions 17 both translationally and rotationally. In particular, the transfer member 16 is configured to move the stacks "P" away from the transfer station "S2" according to a translational movement along the stacking axis "X" to disengage the housing seats 14. Subsequently , the transfer member 16 is configured to move the stacks "P" transversely to the respective stacking axis "X" according to a rotary movement up to the withdrawal station "S3" so that said stacks "P" can be gripped by subsequent machinery, as shown in figure 3.

The machine 1 comprises a conveyor 20 configured to receive the stacks "P" of food products "A" from the handling unit 10, and in particular from the transfer member 16, and to move them along a predetermined advancement path between the pick-up station “S3” and an “S4” release station.

In the preferred embodiment, the conveyor 20 comprises a plurality of grippers 21 configured to grasp the stacks "P" and move them along this path of advancement transversely to the respective stacking axis "X", preferably so as to leave the front and rear portions free of the side surface "P3".

Each gripper 21 has a pair of jaws 22 arranged and / or configured to grip each stack "P" in correspondence with opposite portions of its side surface "P3" arranged laterally with respect to the direction of advancement of the stack "P" along the path of advancement, determined by the conveyor 20.

The jaws 22 have concave and counter-shaped gripping surfaces to the side surface "P3" of the "P" stacks, so as to adhere uniformly to the side surface "P3" of the "P" stacks and firmly support all food products "A "That compose them. Preferably these gripping surfaces are made of elastic and / or deformable material so as to adapt to the shape of the side surface "P3".

In the preferred solution, the conveyor 20 comprises a drum 24 rotatable around an axis of rotation "R" to which the pliers 21 are connected so as to define the aforementioned path of advancement according to a circular trajectory around the axis of rotation "R ".

In the preferred embodiment, the jaws 22 are configured to support the stacks "P" so as to orient and maintain the respective stacking axes "X" in a transverse direction and preferably incident to the rotation axis "R" along the path of advancement .

Furthermore, in the preferred embodiment, the jaws 22 are movable towards and away from each other along the rotation axis "R" of the drum 24 to grasp and release the piles "P" of food products "A".

The machine 1 also comprises application means 30, acting along the advancement path of the stacks "P" defined by the conveyor 20 to apply a sheet "F" of heat-sealable material and preferably rectangular or square in shape around each of the stacks "P ". More specifically, the application means 30 are configured to apply said sheet "F" around each stack "P" according to a "U" conformation, so that the first base surface "P1" of said stack "P" is in contact with a preferably central portion "F1" of this sheet "F".

In the preferred embodiment, the application means 30 comprise a support 32 arranged in a position adjacent to the advancement path of the stacks "P" and configured to position a sheet "F" along this advancement path so that the stacks "P" passing along it engages this sheet "F" in correspondence with its side surface "P3".

Preferably, the support 32 positions the sheet "F" along the path of advancement in such a way that a first lateral portion "F2" of the sheet "F" adjacent to the central portion "F1" abuts against a portion of the lateral surface "P3 "Of the respective stack" P "left free by the jaws 22 of the gripper 21 which supports and moves it, in particular the aforementioned front portion of the side surface" P3 ".

In a preferred embodiment the support 32 is connected to a cutting unit configured to cut the sheets "F" of the correct size according to the dimensions of the stacks "P" and feed these sheets "F" to the support 32 in synchrony with handling of the “P” piles.

Furthermore, the application means 30 comprise a plurality of retaining members 34 mounted on the conveyor 20 and movable, preferably around a hinge axis, between a holding position and a release position.

Preferably, the application means 30 comprise a retaining member 34 for each gripper 21 of the conveyor 20, each of which is associated with the respective gripper 21 and is configured to retain the first side portion "F2" of a sheet "F" in abutment against a respective “P” stack when placed in the holding position.

In the illustrated solution, each retaining member 34 comprises a movable hinged conveyor plate 20 and rotatably movable between the retaining position in which it abuts a portion of the conveyor 20, of the respective gripper 21 or of the stack "P", and the position of disengagement angularly spaced from the holding position. In practice, the operation of the machine 1 in the preferred embodiment provides that a stack "P" moved by the conveyor 20 along the described advancement path engages a respective sheet "F" supported by the support 32 and positioned preferably stationary along this path of advancement.

Subsequently, a movement of the holding member 34 from the release position to the holding position determines a constraint of the sheet "F" which is pressed between the holding member 34 and a surface of the respective stack "P" or of the respective gripper 21 .

The sheet "F" thus constrained is dragged by the movement imparted by the conveyor 20 to the respective stack "P" and is released from the support 32 following the movement of the stack "P" along its path of advancement.

Subsequently, a new sheet "F" is fed to the support 32 to repeat the operation with a subsequent stack "P".

The application means 30 also comprise a folder 36 arranged along the aforementioned path of advancement to intercept each sheet "F" held by the holding member 34 and moved by the conveyor 20 together with the respective stack "P".

More specifically, the folder 36 is arranged so as to intercept a portion of the sheet "F" protruding away from the stack "P" and to cause a first folding of this sheet "F" between the first side portion "F2" and the central portion "F1", so that the latter is arranged to cover the first base surface "P1" of the respective pile "P".

Preferably, the folder 36 is fixed and defined by a shoulder facing the path of advancement, while the aforementioned first folding is cushioned by the movement imparted by the conveyor 20 to the stack "P" with respect to the folder 36.

Preferably, the application means 30 further comprise a folding gripper 38 configured to cause a second folding of the sheet "F" to define this "U" shape of the same around the respective stack "P".

In the preferred solution, the folding pincer 38 is mounted on a mobile support 39 which can be moved away from and towards the conveyor 20 to feed each stack "P" and tap a second side portion "F3" of the sheet "F" onto the side surface " P3 ”of the same stack“ P ”to determine this second fold between the central portion“ F1 ”and the second lateral portion“ F3 ”.

This folding pincer is illustrated in Figures 2 and 3, in which it is represented in a hidden line in a first configuration of use away from the conveyor 20 and in a continuous line in a second configuration of use in which it rivets the second side portion "F3 ”Against the respective“ P ”stack.

Furthermore, the bending pincer 38 is preferably configured to pick up the stack "P" from the conveyor 20 in the release station "S4" and move it away from the same conveyor 20. In the preferred embodiment, the bending pliers 38 is configured to grip the stack "P" in the release station "S4" oriented according to a first orientation in which an upper opening of the sheet "F" folded into a "U" is facing the conveyor 20 and in particular towards the rotation axis "X "Of the drum 24 and to rotate the same stack" P "so as to arrange it according to a second orientation in which the upper opening is not facing the conveyor 20 and is preferably facing the subsequent processing means, as illustrated in figure 4 .

The machine 1 comprises welding means 40 acting on the sheet "F" wrapped in a "U" shape around the stacks "P" coming from the conveyor 20. The welding means 40 comprise a pincer welder 42 configured to perform a first reciprocal welding, preferably fin-shaped, of end flaps "F4" of each sheet "F" so as to transform its "U" configuration into a tubular configuration around the respective "P" stack of food products "A", illustrated in figure 4.

The end flaps "F4" are defined by the apexes of the "U" formed by the sheet "F" which are welded together in order to determine this first abutment weld on the second base surface "P2" of the pile "P". Preferably, the pincer welder 42 is configured to grip the end flaps "F4" during the first welding and is coordinated with the bending pincer 38 so as to receive the sheet "F" therefrom and, through it, the "P" battery.

Furthermore, the pincer welder 42 is movable and configured to move the sheet "F" and the stack "P", gripping the end flaps "F4", away from the bending pincer 38, preferably towards subsequent welding members , illustrated in Figure 4 with the generic reference 43 and in more detail in Figures 5A to 5C.

The sheet "F" folded into tubular form after the first welding is wound around the pile "P" and abuts against it in correspondence with the first and second base surfaces "P1" and "P2" and defines two opposite openings in correspondence of opposite sides of the lateral surface "P3" of the pile "P".

The welding means 40, and in particular the aforementioned successive welding members 43, comprise first and second welding members 44 and 46 configured to carry out respectively a second and a third welding, preferably fin-shaped, at these opposite sides of the surface. side “P3” of each stack “P” so as to occlude the two openings described above to define an airtight wrapping of the plurality of food products “A”.

Preferably, the first and second welding members 44 and 46 are configured to orient the second and third welds in a common plane parallel to the first and second base surfaces "P1" and "P2" and to the plane of the first weld. .

In a preferred embodiment solution, the welding means 40 are also configured to beat the fin flaps of the first, second and third welding against the body of the wrapping defined by the sheet "F".

The machine 1 also comprises pneumatic means 50 cooperating with the sealing means 40 to define an at least partial vacuum inside the hermetic wrapping defined by the sheet "F" and, preferably, to reintroduce a controlled atmosphere inside it. to favor the preservation of “A” food products, for example an atmosphere rich in nitrogen.

Preferably, the pneumatic means 50 comprise a suction tube 52 cooperating with the first sealing members 44 and configured to suck in air and translatable from an engagement position in which it is inserted in one of the openings of the sheet "F" folded in a tubular configuration and a disengagement position in which it disengages from the same opening. Preferably, the suction pipe 52 has an elongated shape in plan transversal to its internal opening.

This elongated shape is developed in the same direction of development as the second weld from whose opening, prior to the weld itself, the suction pipe 52 is configured to suck in air.

Furthermore, the suction tube 52 has recessed lateral recesses configured to favor a folding of the sheet "F" either before or during the second welding.

Preferably, the pneumatic means 50 comprise a shaping element, not shown, cooperating and coordinated with the first welding members 44 and with the suction tube 52.

To remove the air inside the hermetic wrapping, prior to the second welding, the suction tube 52 is introduced into one of the opposite openings of the tubular sheet "F".

The first welding members 44 are configured to abut above and below the sheet "F" to press it against the suction tube 52.

At the same time, the shaping element is configured to abut laterally against the sheet "F" to press it against the suction pipe 52.

Together, the first sealing members 44 and the shaping element allow to at least partially eliminate the clearances between the suction tube 52 and the openings in which it is inserted, so as to make effective the extraction of air from the wrapping for create at least partial air vacuum. Preferably, the shaping element has opposing and counter-shaped abutment surfaces to the side leads of the suction pipe 52 and is configured to determine, in cooperation with them, a fold of the sheet "F" preparatory to the welding of the opening.

Similarly, the first welding members 44 are configured to determine, before the second welding, a further fold of the sheet "F" preparatory to the welding of the opening.

To avoid or reduce unwanted air penetrations, the first welding members 44, the suction pipe 52 and the shaping element are movable in coordination with each other to carry out the second welding during or immediately after a movement of the suction pipe. 52 from the engagement position to the disengagement position. In the embodiment in which the machine 1 is configured to re-inject gases to form a controlled atmosphere inside the hermetic wrapping, the pneumatic means 50 comprise an inlet pipe 54 similar to the suction pipe 52 and configured to emit a gas through the other of the two openings.

In this solution, the second welding members 46 are similar to the first welding members 44 and the pneumatic means 50 comprise a further shaping element similar to the shaping element described above cooperating with each other and with the inlet pipe 54 in the same way with in which the first welding members 44, the suction tube 52 and the shaping element cooperate with each other.

A further object of the present description is a method for hermetic packaging of food products which can be implemented by means of the machine 1 described above.

The method in question comprises a preliminary step of preparing a plurality of food products "A" in a stack "P" configured as described above and illustrated in Figure 1.

Preferably, the stack "P" is arranged in a stacked configuration in a housing seat 14 of a conveyor belt 12 similar to that described above.

Subsequently, the stack "P" is advanced by means of the conveyor belt 12 maintaining the stacked arrangement of the food products "A", as illustrated in Figures 2 to 4.

Subsequently, in accordance with the method in question, the stack "P" is transferred from the conveyor belt 12 to a conveyor 20, preferably similar to the one described above, by means of a transfer member 16 of the type described above, as illustrated in Figures 2 and 3. Preferably, this transfer step is carried out in such a way that the gripper elements 17 of the transfer member 16 grasp the stack "P" in correspondence with portions of the lateral surface "P3" of the same arranged between successive pairs of teeth 13 of the conveyor belt 12, preferably defined by the front and rear portions already described above.

Subsequently, the method involves a phase of movement of the "P" stack along a path of advancement in a direction transverse to the "X" stacking axis. Preferably, this advancement path is circular.

Preferably, the movement step of the stack "P" is carried out by means of a conveyor 20 of the type described above, so that each gripper 21 of the conveyor 20 grasps a respective stack "P" in correspondence with opposite portions of its lateral surface "P3" . In addition, the grippers 21 of the conveyor 20 and the gripping devices 17 of the transfer member 16 grip the stacks "P" in correspondence with portions of their lateral surface "P3" which are different from each other.

More specifically, each gripper 21 of the conveyor 20 grasps the relative stack "P" so as to leave the front and rear portions of its lateral surface "P3" free.

During the handling phase of the "P" stack, the method involves a step of wrapping a sheet "F" of heat-sealable material, preferably similar to the one described above, around the "P" stack according to a "U" conformation, in so that the first base surface "P1" of the pile "P" is in contact with a central portion "F1" of the sheet "F", defining the lower horizontal portion of the "U" shape. This phase is illustrated in Figures 2 to 4.

The winding phase is performed by arranging side portions "F2" and "F3" opposite each other of the sheet "F", adjacent to its central portion "F1" against respective intermediate portions of the lateral surface "P3" of the stack "P" interposed between the grippers 21, preferably arranged at 90 ° with respect to the grippers 21 around the stacking axis "X".

Such intermediate portions are preferably defined as the front and rear portions described above.

Preferably, the wrapping step of the sheet "F" comprises the steps of preparing the same sheet "F" along the path of advancement of the stack "P", so that the front portion of the lateral surface "P3" comes into contact with the first lateral portion "F2" of sheet "F" and blocking of the first lateral portion "F2" abutting against said frontal position.

Preferably, the sheet "F" is kept in a predefined position along the advancement path by means of the support 32 described above. Furthermore, the blocking step is carried out by means of a retaining member 34 previously described.

In one embodiment, the method further comprises a step, preliminary to the winding step, of cutting the sheet "F" according to the desired dimensions and positioning the sheet "F" in the correct position along the path of advancement on the support 32.

Preferably, the wrapping phase of the sheet "F" includes the further steps of carrying out a first folding or re-tapping of the sheet "F" to arrange the central portion "F1" to cover the first base surface "P1" of the pile "P "And carrying out a second folding or re-hammering of the sheet" F "to arrange the second side portion" F3 "to cover the rear portion of the side surface" P3 "of the pile" P ", in order to obtain the" U "shape "Of sheet" F "described above.

Preferably the first folding is carried out by using a fixed folder 36 such as the one previously described arranged along the path of advancement of the stack "P".

Furthermore, the second folding is preferably carried out by folding the second lateral portion "F3" of the sheet "F" by means of the folding pincer 38 described above.

In the illustrated embodiment, stack "P" and sheet "F" reach the release station "S4" arranged so as to have the end flaps "F4" of sheet "F" facing the rotation axis "R" drum 24.

At the release station "S4", the method comprises a subsequent step of removing the sheet "F" and the relative stack "P" from the gripper 21 which moved them along the path of advancement. In the preferred solution, this removal step is carried out by means of the folding pincer 38, gripping the sheet "F" and the stack "P" during the second folding.

Preferably, the removal step is carried out with a rotary movement such that the end flaps "F4" of the sheet "F" are arranged and / or kept away from the folding clamp 38 to move them away from the clamp 21 (and from the axis of rotation "R") and preferably rotate them towards the pincer welder 42 previously described so as to offer them to a subsequent welding phase.

Subsequently, the method comprises a first step of welding the end flaps "F4" of the sheet "F" to define the tubular configuration around the stack "P" already described above, preferably carried out by means of the pincer welder 42. This step is illustrated in figure 4.

The first welding is carried out in correspondence with the second base surface "P2" of the pile "P". Furthermore, the first welding is a fin welding and involves a subsequent riveting of its edge against the rest of the sheet "F".

Preferably, this first welding step comprises grasping the end flaps "F4" by means of the pincer welder 42 to carry out the welding and subsequently moving the sheet "F" and the stack "P" by means of the pincer welder 42 gripping the edges of end “F4”, while the folding clamp 38 releases the sheet “F” and the stack “P”.

Subsequently, the method comprises a second and a third welding phase on opposite ends of the sheet "F" in a tubular configuration in such a way as to close its two openings and define a hermetic wrapping to obtain a complete sealing of the "P" stack of products food items “A” in sheet “F”, illustrated in figures 5A to 5C.

In particular, the second weld occludes a first of the two openings and the third weld occludes the second of the two openings.

Preferably, the second and third welding are carried out respectively by means of the first and second welding members 44 and 46 previously described.

The second and third welds are carried out in correspondence with the aforementioned opposite portions of the side surface "P3" of the stack "P" and are preferably oriented parallel to each other and perpendicular to the first weld.

Furthermore, the second and third welds are carried out and fin and preferably provide for a subsequent riveting of the respective edges. In the preferred embodiment solution, the method in question provides, between the second and third welding, an air intake phase through the second of the two openings to determine an at least partial vacuum effect in the hermetic wrapping.

Furthermore, after the air intake phase and prior to the third welding, the method in question preferably includes a phase of re-entering gas through the second of the two openings for the creation of a controlled atmosphere in the hermetic wrapping.

Preferably, the suction phase and / or the re-introduction phase are carried out by means of the pneumatic means 50 previously described, in coordination with the welding means 40.

Figure 6 illustrates the stack "P" wrapped with sheet "F" by the machine 1 following the method described above.

In a form not illustrated, the end flaps "F4" joined by the first weld could also be arranged in a different position from that shown in Figure 6, for example displaced laterally with respect to the second base surface P2. In this case the first base surface P1 of said stack P is in contact with a portion which will not be central to said U-folded sheet F, but will be in contact with a portion arranged more laterally than the sheet F itself.

The present invention achieves the proposed object by providing a machine and a method for making an alternative wrapping with respect to the known art.

Advantageously, the wrapping obtained is adherent to the product so as to create a pleasant aesthetic effect and with a total footprint of the final package that will be less than the known technique. This will also allow, along the wrapping line, to have multiple wrappers, composed of a plurality of individual wrappers of these packages, of smaller dimensions, thus offering greater manageability and a considerable saving of wrapping material, both for the wrapping single and for the packaging of multiple wrappers composed of a plurality of single wrappers. Furthermore, the arrangement of the second and third seals along portions of the lateral surface of the stack of food products determines a type of packaging suitable for new potential arrangements of the product in the relative package, in order to be able to offer a more effective presentation.

Claims (20)

CLAIMS 1) Method for the hermetic packaging of food products comprising the steps of: - arranging a plurality of food products (A) in a stack (P) ordered along a stacking axis (X), said stack (P) presenting a first and a second base surface (P1, P2) opposite each other and a lateral surface (P3) interposed between said first and second base surfaces (P1, P2) and defined by the cooperation of lateral surfaces of said stacked food products (A); - moving said stack (P) of food products (A) along a path of advancement transversely to said stacking axis (X) by means of a conveyor (20) equipped with grippers (21), each gripper (21) gripping a respective stack ( P) in correspondence with opposite portions of the lateral surface (P3) of the stack (P); - during said stack (P) handling step, wrap a sheet (F) of heat-sealable material around said stack (P) according to a "U" conformation, so that the first base surface (P1) of said stack (P) is in contact with a portion (F1), preferably central, of said sheet (F) folded into a "U"; - carry out a first mutual welding of the end flaps (F4) of said sheet (F) to define a tubular configuration of the sheet (F) around the stack (P) so that the sheet (F) overlaps both the first surface base (P1) than to the second base surface (P2) of said stack (P), said tubular configuration defining two openings at opposite sides of the lateral surface (P3) of said stack (P); - carrying out a second and a third sealing on opposite ends of said sheet (F) in a tubular configuration in such a way as to close said two openings of the tubular sheet (F) obtaining a complete sealing of said stack (P) in the sheet (F) of heat-sealable material in which said sheet (F) defines a hermetic wrapping of said plurality of food products (A). 2) Method according to claim 1, wherein the second weld occludes a first of said two openings and the third weld occludes the second of said two openings, said method comprising, between said second and third weld, a step of sucking air through said second opening to determine an at least partial vacuum effect in said hermetic wrapping. 3) Method according to claim 2, comprising, after the air suction phase and prior to the third welding, a gas re-entry phase through said second opening for the creation of a controlled atmosphere in said hermetic wrapping. 4) Method according to one or more of the preceding claims, in which the step of wrapping the sheet (F) of heat-sealable material around the stack (P) is carried out by arranging opposite lateral portions (F2, F3) of the sheet (F), adjacent to said central portion (F1) of the sheet (F), against respective intermediate portions of the lateral surface (P3) of the stack (P) interposed between said grippers (21), preferably arranged at 90 ° with respect to the grippers (21) around said stacking axis (X). 5) Method according to claim 4, wherein the step of wrapping the sheet (F) comprises the steps of: - arranging said sheet (F) along said advancement path so that a first of said intermediate portions of the lateral surface (P3) comes into contact with a first of said lateral portions (F2) of said sheet (F) during the handling of the stack (P); - locking said first lateral portion (F2) abutment with said first intermediate portion by means of a retaining member (34) movable together with the stack (P) of products. 6) Method according to claim 5, wherein the step of wrapping the sheet (F) comprises, after the step of locking the first side portion (F2) of the sheet (F), the steps of: - carrying out a first folding or re-folding of said sheet (F) to arrange the central portion (F1) of the sheet (F) to cover the first base surface (P1) of said stack (P) preferably by using a folder (36 ) fixed arranged along said path of advancement; - carrying out a second folding or re-hammering of said sheet (F) to arrange the second lateral portion (F3) of said sheet (F) against the second intermediate portion of the lateral surface (P3) of the stack (P) so as to obtain said conformation "U" shape of the sheet (F), said second folding being carried out by riveting said second lateral portion (F3) of the sheet (F) by means of a folding pincer (38). 7) Method according to claim 6, in which the second folding step is carried out by grasping said sheet (F) wrapped in a "U" shape around the stack (P) by means of said folding pincer (38), said method comprising a subsequent step of remove said sheet (F) and the relative stack (P) from the respective gripper (21) of the conveyor (20) by means of said folding gripper (38), in particular with a movement such that said end flaps (F4) are arranged and / or kept away from said bending pincer (38) to be offered to said first welding step. 8) Method according to one or more of the preceding claims, wherein said first welding step comprises a step of grasping said end flaps (F4) by means of a pincer welder (42), preferably said method comprising a subsequent step of moving said sheet (F) and said stack (P) by means of said pincer welder (42). 9) Method according to one or more of the preceding claims, in which the first welding is carried out at the second base surface (P2) of said pile (P), the second and third welding being carried out at said opposite portions of the lateral surface (P3) of said pile (P). 10) Method according to one or more of the preceding claims in which said first and / or second and / or third welding are carried out and preferably provide for a riveting of the respective edges. 11) Method according to one or more of the preceding claims comprising, following the preparation in stack (P) of the plurality of food products (A), a step of advancing said stack (P) by means of a conveyor belt (12) equipped with teeth ( 13) gripping on said lateral surface (P3) to maintain the stack arrangement (P) of the food products (A), said method comprising a step of transferring said stack (P) from the conveyor belt (12) to the conveyor (20) by means of a transfer member (16) equipped with pliers, said pliers of the transfer member (16) by grasping the stack (P ) in correspondence with portions of the lateral surface (P3) of the stack (P) arranged between relative pairs of teeth (13) and different with respect to the opposite portions gripped by the grippers (21) of the conveyor (20). 12) Machine (1) for the hermetic packaging of food products, comprising: - a handling unit (10) configured to advance a plurality of food products (A) arranged in stacks (P) arranged along respective stacking axes (X), each of said stacks (P) having two base surfaces ( P1, P2) opposite each other and a lateral surface (P3) interposed between said base surfaces (P1, P2) and defined by the cooperation of lateral surfaces of said stacked food products (A); - a gripper conveyor (20) configured to receive said ordered stacks (P) and move them transversely to the respective stacking axis (X) along a path of advancement; - application means (30), acting along said path of advancement to apply a sheet (F) of heat-sealable material around each pile (P) according to a "U" conformation, so that one of the base surfaces (P1) of said stack (P) is in contact with a portion (F1), preferably central, of said sheet (F) folded into a "U"; - welding means (40), configured to carry out a first welding at the other base surface (P2) of said stack (P), and a second and third welding respectively at opposite sides of the lateral surface (P3) of said pile (P) so that said sheet (F) defines a hermetic wrapping of said plurality of food products (A). 13) Machine (1) according to claim 12, comprising pneumatic means (50) configured to suck air from an opening of said wrapping to define an at least partial vacuum effect in said hermetic wrapping, said pneumatic means (50) also preferably being configured to re-introduce a dose of gas for the creation of a controlled atmosphere in said hermetic wrapping. 14) Machine (1) according to claim 12 or 13, wherein said conveyor (20) comprises a drum (24) rotatable around an axis of rotation (R) and defines said path of advancement according to a circular trajectory around said axis rotation (R), said conveyor (20) comprising a plurality of peripheral grippers (21) each of which having a pair of jaws (22) arranged and / or configured to grip each stack (P) at portions of the lateral surface (P3) of the stack (P) arranged laterally with respect to a direction of advancement of the stack (P) along said path of advancement, preferably said jaws (22) having concave gripping surfaces and counter-shaped to the lateral surface (P3) of said stacks ( P). 15) Machine (1) according to claim 14, wherein said handling unit (10) comprises: a conveyor belt (12) having a plurality of teeth (13), said teeth (13) being arranged so as to define a plurality of housing seats (14) for food products (A) in stacked configuration and said conveyor belt (12) being configured to move said plurality of food products (A) from an inlet station (S1) to a transfer station ( S2); and a transfer member (16), configured to extract said stacks (P) of food products (A) from said housing seats (14) in said transfer station (S2) and move the stacks (P) transversely to the respective axis stacking unit (X) up to a pick-up station (S3) to offer them to said gripper conveyor (20), said transfer member (16) comprising preferably gripper elements (17) configured to engage respective portions of the lateral surface (P3) of the stacks (P) not engaged by said teeth (13), preferably said gripping elements (17) engaging each stack (P) in correspondence with a front portion and a rear portion of the stack (P) with respect to a direction for advancing the stack (P) on said transfer member (16). 16) Machine (1) according to one or more of claims 12 to 15, wherein said application means (30) comprise: - a support (32) adapted to position said sheet (F) of heat-sealable material in a preferably stationary way along said advancement path so that a stack (P) moved by the conveyor (20) comes into contact with said sheet (F) , - a plurality of retaining members (34) mounted on the conveyor (20) and each of which is configured to retain a lateral portion (F2) of said sheet (F) abutting against a respective stack (P) to move said sheet (F ) together with the stack (P) along said path of advancement; - a preferably fixed folder (36), arranged along said advancement path to intercept said sheet (F), said folder (36) being configured to cause a first folding of said sheet (F) so that the central portion (F1) said sheet (F) is arranged to cover one of the base surfaces (P1) of said stack (P); - a folding gripper (38) configured to cause a second folding of said sheet (F) to define a "U" shape of said sheet (F) around the stack (P). 17) Machine (1) according to claim 16 in which said folding pincer (38) is mounted on a mobile support (39) and is configured to take said stack (P) from the pincer conveyor (20) from a first position in wherein said U-folded sheet (F) has a concavity facing towards said conveyor (20) and a second position in which said concavity faces towards said welding means (40). 18) Machine (1) according to one or more of claims 12 to 17, wherein said welding means (40) comprise a pincer welder (42) configured to weld together respective end flaps (F4) of said sheet (F ) folded in a "U" shape to define a tubular configuration of said sheet (F) around said stack (P). 19) Machine (1) according to claims 17 and 18, wherein said pincer welder (42) is configured to receive said stack (P) from the folding pincer (38) by grasping said end flaps (F4) of the sheet (F ) folded into a "U" and moving said sheet (F) and said stack (P) away from said folding pincer (38). 20) Machine (1) according to one or more of claims 12 to 19, in which said pneumatic means (50) comprise a suction tube (52) which can be moved from an engagement position in which it is inserted into one of said sheet openings (F) folded in a tubular configuration and a release position in which it disengages from said opening, and a shaping element having respective abutment surfaces opposite and counter-shaped to said suction pipe (52), said welding means (40) comprising movable welding members (44) in coordination with said suction tube (52) and / or said shaping element for carrying out said second and / or third welding during the extraction of the tube from the respective opening.