EP4606751A1

EP4606751A1 - Buffer unit of a web of packaging material for a packaging machine and packaging machine for forming sealed packages

Info

Publication number: EP4606751A1
Application number: EP25157848.0A
Authority: EP
Inventors: Gabriele Poletti; Marco Ricco'; Riccardo CASELLI
Original assignee: Tetra Laval Holdings and Finance SA
Current assignee: Tetra Laval Holdings and Finance SA
Priority date: 2024-02-23
Filing date: 2025-02-14
Publication date: 2025-08-27
Also published as: IT202400003910A1; WO2025176556A1

Abstract

There is described a buffer unit (10) of a web of packaging material for a packaging machine (1) comprising an accumulation space (BS) for buffering the web (3) of packaging material, an input roller device (16) configured to feed the web (3) of packaging material into the accumulation space (BS), a number of rollers (17) arranged within the accumulation space (BS) and configured to guide the web (3) of packaging material along a conveying path (P), wherein the rollers (17) are divided into a first group of rollers (17A) and a second group of rollers (17B) and wherein the second group of rollers (17B) is movable with respect to the first group of rollers (17A) from an accumulation position in which the distance between the first group of rollers (17A) and the second group of rollers (17B) is maximum and an emptying position in which the distance between the first groups of rollers (17A) and the second group of rollers (17B) is minimum, and a brake device (35) configured to block the second group of rollers (17B) in any position comprised between the accumulation position and the emptying position.

Description

TECHNICAL FIELD

The present invention relates to a buffer unit of a web of packaging material for a packaging machine. The present invention further relates to a packaging machine for forming sealed packages filled with a pourable product having a buffer unit of a web of packaging material.

BACKGROUND ART

As is known, many liquid or pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by sealing and folding laminated strip packaging material. The packaging material has a multilayer structure comprising a base layer, e.g. of paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of oxygen-barrier material (an oxygen-barrier layer), e.g. an aluminum foil, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, which advance a web of packaging material, normally provided in the form of a reel, along a conveying path. The web of packaging material is advanced through a sterilization apparatus for sterilizing the web of packaging material at a sterilization station and to an isolation chamber (a closed and sterile environment) in which the sterilized web of packaging material is maintained and advanced. During advancement of the web of packaging material through the isolation chamber, the web of packaging material is folded and sealed longitudinally at a tube forming station to form a tube having a longitudinal seam region, the tube being further fed along a vertical advancing direction.
For completing the forming operations, the tube is filled with a pourable product, in particular a pourable food product, and is transversally sealed and subsequently cut along equally spaced transversal cross sections within a package forming apparatus of the packaging machine during advancement along the vertical advancing direction. Pillow packages are so obtained, each pillow package has a longitudinal sealing band, a top transversal sealing band and a bottom transversal sealing band.
A typical packaging machine comprises a conveying device for advancing the web of packaging material, the sterilization apparatus for sterilizing the web of packaging material prior to its formation into the tube, a tube forming and sealing device configured to form the tube from the advancing web of packaging material and to longitudinally seal the tube, a filling device for filling the tube with the pourable product and the package forming apparatus adapted to form, transversally seal and cut individual packages from the tube of packaging material.
A packaging machine of the known type further comprises a splicing unit configured to splice a new web of packaging material to the web of packaging material in use when the web of packaging material in use is about to exhaust, preferentially without interrupting the production of the packaging machine. The end portion of the web of packaging material in use is arranged in a fixed position when it is spliced to the end portion of the new web of packaging material.
Hence, the packaging machine normally comprises a buffer apparatus arranged upstream of the tube forming and sealing device and downstream of the splicing unit along the conveying path and configured to buffer the web of packaging material. The quantity of the web of packaging material collected within the buffer apparatus is increased before splicing the new web of packaging material to the almost exhausted web of packaging material in use. In this way, during the activation of the splicing unit, the end portion of the web of packaging material arranged upstream of the buffer apparatus does not advance and can be spliced to the new web of packaging material while the portion of the web of packaging material arranged downstream of the buffer apparatus continues to advance to the tube forming and sealing device fed by the buffer apparatus without interrupting the production of packages.
Even though the buffer apparatuses of the known type provide for good results and work satisfactorily well, a need is felt within the industry to further improve the operation of the buffer apparatuses.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a buffer unit of a web of packaging material for a packaging machine addressing the drawbacks of the prior art and, in particular, being easy and economical to be manufactured.
A further object of the present invention is to provide a packaging machine for forming sealed packages having a buffer unit of a web of packaging material addressing the drawbacks of the prior art and, in particular, being easy and economical to be manufactured.
According to the invention there are provided a buffer unit of a web of packaging material for a packaging machine and a packaging machine for forming sealed packages having a buffer unit of a web of packaging material according to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

figure 1 is a schematic perspective view of a packaging machine having a buffer unit of a web of packaging material with parts removed for clarity;
figure 2 is a schematic side view of the packaging machine of figure 1;
figure 3 is a schematic perspective view of a magazine unit of the packaging machine of figure 1 with part removed for clarity;
figure 4 is a schematic perspective view of a buffer unit according to the present invention in a first configuration and with parts removed for clarity; and
figure 5 is a schematic perspective view of the buffer unit of figure 4 in a second configuration and with parts removed for clarity.

BEST MODES FOR CARRYING OUT THE INVENTION

Number 1 in figure 1 indicates as a whole a packaging machine for packaging pourable products, in particular pourable food products, such as milk, cream, yoghurt drinks, yoghurt, fruit juice, wine, tomato sauce, sugar, salt, emulsions, solutions containing solid particles (e.g. legumes), etc., into packages.
Advantageously, packages 2 are formed from a multilayer packaging material. The multilayer packaging material comprises at least a layer of fibrous material, such as e.g. a paper or cardboard layer, and at least two layers of heat-seal plastic material, e.g. polyethylene, interposing the layer of fibrous material in between one another. One of these two layers of heat-seal plastic material defines an inner surface of the packages 2 contacting the pourable product packaged within the packages 2.
According to some possible non-limiting embodiments, the multilayer packaging material comprises a layer of gas- and light-barrier material, e.g. aluminum foil or ethylene vinyl alcohol (EVOH) film, in particular being arranged between one of the layers of the heat-seal plastic material and the layer of fibrous material. Preferentially, the multilayer packaging material also comprises a further layer of heat-seal plastic material being interposed between the layer of gas- and light-barrier material and the layer of fibrous material. Preferentially, the multilayer packaging material is provided as an endless web 3 of packaging material.
Each package 2 comprises a longitudinal seal portion 4 and a pair of transversal seal portions 5, in particular a top transversal seal portion and a bottom transversal seal portion (i.e., one transversal seal portion 5 at an upper end of the package 2 and another transversal seal portion 5 at a lower end of the package 2).
With particular reference to figure 1, the packaging machine 1 comprises:

a conveying apparatus 6 for advancing the web 3 of packaging material along a conveying path P through guiding elements, in particular through a number of rollers 7, to a tube forming and sealing unit 8, configured to gradually fold the web 3 of packaging material into a tube 9, preferentially by overlapping opposite longitudinal edges of the web 3 of packaging material with one another, and longitudinally sealing the tube 9;
a buffer unit 10 configured to buffer the web 3 of packaging material;
a filling device 11 for filling the tube 9 with the pourable product; and
a package forming unit (not shown) arranged along the conveying path P downstream of the tube forming and sealing unit 8 and configured to form, transversally seal and cut the advancing tube 9 for forming packages 2.

The packaging machine 1 comprises an isolation chamber IC, preferentially delimiting an inner environment IE from an outer environment. Preferentially, the inner environment IE is a sterile (aseptic) environment, preferably containing a controlled atmosphere. Preferably, the tube forming and sealing unit 8 is at least partially arranged within the isolation chamber IC, in particular within the inner environment IE, and is configured to fold and longitudinally seal the tube 9 within the isolation chamber IC, in particular within the inner environment IE.
Preferentially, the packaging machine 1 also comprises a sterilizing unit STU arranged to sterilize the advancing web 3 of packaging material. The sterilization unit has a sterilizing bath, in which a chemical sterilizing agent is applied to the web 3 of packaging material. Advantageously, the chemical sterilizing agent comprises a hydrogen peroxide solution. Preferentially the sterilization unit STU is arranged upstream of the tube forming and sealing unit 8 along the conveying path P.
Advantageously, the tube forming and sealing unit 8 comprises at least two forming ring assemblies 12 configured to fold in cooperation with one another the web 3 of packaging material gradually into the tube 9. Furthermore, the tube forming and sealing unit 8 comprises a longitudinal sealing device SD being configured to longitudinally seal the tube 9 along a longitudinal seam region (which defines the seal portion 4 of the packages 2). In particular, the longitudinal sealing device SD may be of the kind operating by means of induction heating or by a stream of a hot fluid or by means of ultrasound. The longitudinal sealing device SD comprises a sealing head interposed between the forming ring assemblies 12.
The filling device 11 comprises a filling pipe 13 in fluid connection with a pourable product storage tank (not shown) for storing/providing for the pourable product to be packaged. The filling pipe 13 is at least partially arranged within the tube 9 and is configured to direct, in use, the pourable product into the tube 9.
The packaging machine 1 further comprises a splicing unit SU configured to splice a new web 3 of packaging material to the web 3 of packaging material in use. The splicing unit SU is arranged upstream of the buffer unit 10 along the web conveying path P. More in detail, the splicing unit SU is configured to splice the new web 3 of packaging material to the web 3 of packaging material in use when the web 3 of packaging material in use is about to exhaust, preferentially without interrupting the production of the packaging machine 1. Preferably, the end portion of the web 3 of packaging material in use is arranged in a fixed position when it is spliced to the end portion of the new web 3 of packaging material.
Advantageously, the packaging machine 1 comprises a magazine unit 14 having a number of support devices 30 each carrying a respective reel 15 of the web 3 of packaging material. With particular reference to figure 3, the magazine unit 14 comprises two support devices 30. More specifically, one support device 30 is configured to provide the web 3 of packaging material in use and the other support device 30 is configured to provide the new web 3 of packaging material. Advantageously, the two support devices 30 are arranged next to one another. More in detail, each reel 15 comprises a spindle 31 extending along a center axis C, the web 3 of packaging material being wound about the spindle 31. Each support device 30 is provided with a number of guide rails (not shown) configured to guide the respective spindle 31.
Advantageously, the buffer unit 10 is arranged upstream of the tube forming and sealing unit 8 and downstream of the splicing unit SU along the web conveying path P. In other words, the buffer unit 10 is interposed between the tube forming and sealing unit 8 and the splicing unit SU along the web conveying path P.
The buffer unit 10 comprises a buffer space BS delimiting an environment for buffering the web 3 of packaging material.
The buffer unit 10 further comprises an input roller device 16 configured to feed the web 3 of packaging material into the buffer space BS. The buffer unit 10 further comprises a number of convey rollers 17 configured to interact with the web 3 of packaging material 3 after entering into the buffer space BS and to convey the web 3 of packaging material along the conveying path P.
The input roller device 16 comprises a drive roller 23 and a number of counter rollers (not shown) configured to receive the web 3 of packaging material between the drive roller 23 and the counter rollers. Preferably, the input roller device 16 comprises an actuator device 24, in particular a motor, configured to actuate a rotation of the drive roller 23. More in detail, the actuator device 24 is configured to control an angular speed of the drive roller 23 so as to regulate an input speed of the web 3 of packaging material 3 entering the buffer space BS.
The convey rollers 17 are arranged downstream of the input roller device 16 along the conveying path P. The convey rollers 17 are at least partly arranged within the buffer space BS. The convey rollers 17 have respective rotation axes X, parallel one another. Preferably, each rotation axis X is arranged horizontally.
The convey rollers 17 comprise an output roller 18 configured to direct the web 3 of packaging material out of the buffer space BS. The outfeed roller 18 is configured to convey the web 3 of packaging material along the conveying path P downstream of the buffer unit 10. The portion of the web 3 of packaging material present, i.e. received, within the buffer unit 10 extends between the input roller device 16 and the output roller 18.
Advantageously, at least one convey roller 17 is interposed between the input roller device 16 and the output roller 18 along the conveying path P. Even more advantageously, a plurality of convey rollers 17 is interposed between the input roller device 16 and the output roller 18 along the conveying path P.
The convey rollers 17 are divided into a (first) group of upper rollers 17A arranged with the respective axes X parallel to one another and a (second) group of lower rollers 17B arranged with the respective axes X parallel to one another. In other words, the convey rollers 17 comprises a number of upper rollers 17A and a number of lower rollers 17B. Advantageously, the convey rollers 17 comprises a plurality of upper rollers 17A and a plurality of lower rollers 17B. The convey rollers 17 may comprise the same number of upper rollers 17A and of lower rollers 17B, i.e. the number of upper rollers 17A is equal to the number of lower rollers 17B. Preferably, the number of upper rollers 17A and lower rollers 17B is three or four. According to a preferred embodiment, the group of upper rollers 17A comprise the output roller 18.
The upper rollers 17A are aligned along a first alignment direction D₁. The first alignment direction D₁ is transversal, in particular perpendicular, to the rotation axes X.
The lower rollers 17B are aligned along a second alignment direction D₂. The second alignment direction D₂ is transversal, in particular perpendicular, to the rotation axes X.
Advantageously, the first alignment direction D₁ is parallel to the second alignment direction D₂.
The upper rollers 17A and the lower rollers D₂ are staggered along a positioning direction D parallel to the first alignment direction D₁ and the second direction D₂. In other words, each upper roller 17A is interposed between two consecutive lower rollers 17B along the positioning direction D, or each lower roller 17 B is interposed between two consecutive upper rollers along the positioning direction D.
The web 3 of packaging material enters the buffer space BS from the input roller device 16 and travels along the conveying path P moving alternately between an upper roller 17A and a lower roller 17B. Finally, the web 3 of packaging material exits the buffer space BS through the output roller 18.
The web 3 of packaging material creates a plurality of loops, in particular substantially vertical loops, arranged next to each other, each loop being defined by the portion of web 3 of packaging material interposed between, and partially wound around, two adjacent upper rollers 17A and a lower roller 17B arranged between the two adjacent upper rollers 17A, or by the portion of web 3 of packaging material interposed between, and partially wound around, two adjacent lower rollers 17B and an upper roller 17A arranged between the two adjacent lower rollers 17B.
In this way, the web 3 of packaging material is arranged along an accumulation path A so as to allow accumulation of the web 3 of packaging material within the buffering space BF. The length of the accumulation path A, and therefore the amount of web 3 of packaging material received in the buffering space BS, depends on the (variable) distance between the upper rollers 17A and the lower rollers 17B, as it will be better explained in the following.
The buffer unit 10 comprises a frame 19 for supporting the convey rollers 17 and the input roller device 16. In particular, the frame 19 comprises a fixed upright 20 supporting an upper crossbar 21 and a lower crossbar 22. The upper crossbar 21 is connected in a fixed manner to the upright 20. The lower crossbar 22 is connected in a non-fixed manner to the upright 20. In other words, the lower crossbar 22 is movable with respect to the upright 20.
The upper crossbar 21 is configured to support the input roller device 16 and the (first) group of upper rollers 17A. The input roller device 16 is connected in a fixed manner to the upper crossbar 21. The upper rollers 17A are rotatably supported by the upper crossbar 21 around the rotation axes X. The rotation axes X are arranged in respective fixed position with respect to the upper crossbar 21. In other words, the upper rollers 17A rotate with respect to the upper crossbar 21, but do not translate with respect to the upper crossbar 21.
The lower crossbar 22 is configured to support the (second) group of lower rollers 17B. The lower rollers 17B are rotatably supported by the lower crossbar 22 around the rotation axes X. The rotation axes X are arranged in respective fixed position with respect to the lower crossbar 22. In other words, the lower rollers 17B rotate with respect to the lower crossbar 22, but do not translate with respect to the lower crossbar 22.
The upright 20 comprises a guide 26 which is arranged in a fixed position and defines a sliding path R. The sliding path R extends in a substantially vertical direction. In particular, the guide 26 is formed by a fixed (i.e. without movement) rail, which is arranged along the sliding path R. In addition, the buffer unit 10 comprises a slide 27 (or carriage), which supports in a fixed manner the lower crossbar 22 and is coupled to the guide 26 to slide along the guide 26.
The slide 27 is configured to slide on the guide 26 between two end positions. The slide 27 is movable along the sliding path R from an accumulation position, in which a distance between the group of upper rollers 17A and the group of lower rollers 17B is maximum, to an emptying position, in which the distance between the group of upper rollers 17A and the group of lower rollers 17B is minimum, and vice versa from the emptying position to the accumulation position. In the emptying position the lower rollers 17B are arranged in proximity of and facing the upper rollers 17A.
In other words, the group of lower rollers 17B is movable with respect to the group of upper rollers 17A between an accumulation position in which a distance between the group of upper rollers 17A and the group of lower rollers 17B is maximum and an emptying position in which the distance between the group of upper rollers 17A and the group of lower rollers 17B is minimum.
The slide 27 is further configured to be arranged/stopped in any intermediate position between the emptying position and the accumulation position. The slide 27 is configured to be blocked, i.e. maintained, in a fixed intermediate position interposed between the emptying position and the accumulation position.
The loading level of the buffer unit 10 is measured as the quantity of web 3 of packaging material extending between the input roller device 16 and the output roller 18. The loading level of the buffer unit 10 is variable as a function of the position of the slide 27 along the sliding path R. In other words, the loading level of the buffer unit 10 depends on the distance between the (first) group of upper rollers 17A and the (second) group of lower rollers 17B.
More in detail, the buffer unit 10 is configured to be in an accumulation configuration, in which the maximum quantity of web 3 of packaging material is accumulated within the buffer space BS. The accumulation configuration is realized when the slide 27, i.e. the group of lower rollers 17B, is in the accumulation position.
The buffer unit 10 is further configured to be in an emptying configuration, in which the minimum quantity of web 3 of packaging material is accumulated within the buffer space BS. The emptying configuration is realized when the slide 27, i.e. the group of lower rollers 17B, is in the emptying position.
The buffer unit 10 further comprises a number of brake devices 25 which are configured to block the slide 27, i.e. the group of lower rollers 17B, in any (desired) intermediate position between the emptying position and the accumulation position along the guide 26, i.e. along the sliding path R. The brake devices 25 are mainly (but not exclusively) arranged to block the slide 27 in any intermediate position between the emptying position and the accumulation position along the guide 26 when the packaging machine 1 is not running. More in detail, the brake devices 25 are configured to block the slide 27 in any position along the sliding path R so as to avoid directly tensioning the web 3 of packaging material, especially when the packaging machine 1 is not running.
According to a first embodiment, the buffer unit 10 comprises a single brake device 25 configured to block the slide 27 supporting the lower crossbar 22 (and the group of lower rollers 17B) in any intermediate position between the emptying position and the accumulation position.
According to a second and preferred embodiment, the buffer unit 10 comprises a couple of brake devices 25 configured to block the slide 27 supporting the lower crossbar 22 (and the group of lower rollers 17B) in any intermediate position between the emptying position and the accumulation position. Two brake devices 25 are redundant and normally used to increase the safety conditions of the buffer unit 10.
Advantageously, the brake devices 25 are fluid brake devices 25 or air brake devices 25 or compressed air brake devices 25. A fluid is used to activate the fluid brake devices 25 in order to block the slide 27 in any position between the emptying position and the accumulation position.
According to a preferred embodiment, the buffer unit 10 comprises an imaging device (not shown). The imaging device comprises at least a sensor configured to frame the sliding path R. The sensor 35 is preferably a laser sensor or a camera. In particular, the imaging device is arranged in close proximity to the guide 26 and is configured to determine the position of the slide 27 along the guide 26 (i.e. along the sliding path R). The buffer unit 10 further comprises a control unit connected to the imaging device and configured to determine the loading level of the buffer unit 10 as a function of the position of the slide 27 along the guide 26.
It is important to highlight that the (second) group of lower rollers 17B is moved downwards along the sliding path R (exclusively) under the action of its weight. The (second) group of lower rollers 17B is moved upwards along the sliding path R (exclusively) due to the dragging action of the web 3 of packaging material wound around the convey rollers 17. The brake devices 25 avoid tensioning the web 3 of packaging material due to the weight of the (second) group of lower rollers 17B.
In the buffer unit 10 the slide 27 is arranged in a working position between the accumulation position and the emptying position during a normal operation condition of the packaging machine 1. The working position can be selected according to the working conditions of the packaging machine 1. During the normal operation condition, the distance between the group of upper rollers 17A and the group of lower rollers 17B is kept substantially constant.
The quantity of the web 3 of packaging material collected within the buffer space BS is increased before activation of the splicing unit SU, when the new web 3 of packaging material must be spliced to the almost exhausted web 3 of packaging material in use. In other words, when it becomes necessary (e.g. to prepare for splicing the two webs 3 of packaging material) to buffer the web 3 of packaging material within the buffer space SP, the slide 27 is arranged in the accumulation position, in particular by varying through the control unit the speed of the web 3 of packaging material in use and or the pulling action on the web 3 of packaging material in use. In this case, the upper crossbar 21 (i.e. the upper rollers 17A) and the lower crossbar 22 (i.e. the lower rollers 17B) are moved away from each other.
When the splicing unit SU is activated, the end portion of the web 3 of packaging material in use arranged upstream of the buffer unit 10 is fixed (i.e. it does not advance) and is spliced to an end portion of the new web 3 of packaging material. The portion of the web 3 of packaging material arranged within the buffer space BS and downstream of the buffer unit 10 continues to advance to the tube forming and sealing device 8 without interrupting the production of the packaging machine 1. Thus, when the splicing unit SU is activated the distance between the group of upper rollers 17A and the group of lower rollers 17B is progressively reduced.
Afterwards (e.g. once the splicing of the web 3 of packaging material in use with the new web 3 of packaging material 3 is completed), the buffer unit 10 is brought again to the configuration of the normal operation condition of the packaging machine 1, i.e. the slide 27 is moved back to the working position.
The buffer unit 10 according to the present invention has some advantages that are clear from the foregoing description. In particular, the buffer unit 10 is easy and economically convenient to be manufactured and the presence of the brake devices 25 enables to block the slide 27 in any position along the sliding path R thereby avoiding tensioning the web 3 of packaging material (especially when the packaging machine 1 is not running).

LIST OF REFERENCE NUMERALS

1: packaging machine
2: packages
3: web of packaging material
4: longitudinal seam portion
5: transversal seal portion
6: conveying apparatus
7: roller
8: tube forming and sealing unit
9: tube
10: buffer unit
11: filling device
12: forming ring assembly
13: filling pipe
14: magazine unit
15: reel
16: input roller device
17: convey roller
17A: upper roller
17B: lower roller
18: output roller
19: frame
20: upright
21: upper crossbar
22: lower crossbar
23: drive roller
24: actuator device
25: brake device
26: guide
27: slide
30: support device
31: spindle
P: conveying path
SD: sealing device
BS: buffer space
X: rotation axis
R: sliding path
IC: isolation chamber
IE: inner environment
STU: sterilizing unit
D1: first alignment direction
D2: second alignment direction
D: positioning direction
A: accumulation path
C: central axis

Claims

A buffer unit (10) of a web of packaging material for a packaging machine (1) comprising:
- an accumulation space (BS) for buffering the web (3) of packaging material;

- an input roller device (16) configured to feed the web (3) of packaging material into the accumulation space (BS);

- a number of rollers (17) arranged within the accumulation space (BS) and configured to guide the web (3) of packaging material along a conveying path (P); wherein the rollers (17) are divided into a first group of rollers (17A) and a second group of rollers (17B) and wherein the second group of rollers (17B) is movable with respect to the first group of rollers (17A) from an accumulation position in which the distance between the first group of rollers (17A) and the second group of rollers (17B) is maximum and an emptying position in which the distance between the first group of rollers (17A) and the second group of rollers (17B) is minimum; and

- at least a brake device (35) configured to block the second group of rollers (17B) in any position comprised between the accumulation position and the emptying position.
A buffer unit according to claim 1, and further comprising a slide (27) which supports the second group of rollers (17B) and is movable along a sliding path (R).
A buffer unit according to claim 2, wherein the sliding path (R) extends in a substantially vertical direction, from the accumulation position of the second group of rollers (17B) to the emptying position of the second group of rollers (17B).
A buffer unit according to claim 2 or 3, wherein the brake device (25) is configured to block the slide (27) in any intermediate position along the sliding path (R) between the accumulation position of the second group of rollers (17B) and the emptying position of the second group of rollers (17B).
A buffer unit according to any previous claims 2 to 4, and further comprising an imaging device configured to frame the sliding path (R) and to determine the position of the slide (27) along the sliding path (R).
A buffer unit according to any previous claim, and further comprising two brake devices (35) configured to block the second group of rollers (17B) in any position comprised between the accumulation position and the emptying position.
A buffer unit according to any previous claim, wherein the at least one brake device (25) is a (compressed) fluid brake device (25) wherein the fluid is used to activate the brake device (25).
A buffer unit according to any previous claim, wherein the number of rollers (17) comprises an output roller (18) configured to direct the web (3) of packaging material out of the accumulation space (BS).
A buffer unit according to any previous claim, wherein the input roller device (16) comprises a drive roller (23) and at least an actuator device (24) configured to control an angular speed of the drive roller (23) so as to regulate an input speed of the web (3) of packaging material entering the accumulation space (BS).
A packaging machine (1) for forming packages (2) from a web of packaging material (3) filled with a pourable product comprising:
- a conveying device (6) for advancing the web of packaging material (3) along a conveying path (P);

- a buffer unit (10) according to any one of the preceding claims;

- a tube forming and sealing unit (8) arranged downstream of the buffer unit (10) along the conveying path (P) and configured to form and longitudinally seal a tube (9) from the web of packaging material (3); and

- a filling device (11) configured to direct the pourable product into the tube (9).
A packaging machine according to claim 10, and further comprising a splicing unit (SU) configured to splice a new web of packaging material (3) to the web of packaging material (3) in use, wherein the splicing unit (SU) is arranged upstream of the buffer unit (10) along the conveying path (P).