Manufacturing machine and manufacturing method for the production of a filter for a tubular element

Abstract

Manufacturing machine (8) and manufacturing method for the production of a filter (2) for a tubular element (1) for a smoking article. The following are provided: a folding drum (16) which rotates around a rotation axis (17) to move, along a circular folding path (P) at least one holding head (18) designed to accommodate a sheet (4) having an inner portion (5) and an outer portion (6); a feeding station (S2) where the holding head (18) receives the sheet (4) and engages the sole outer portion (6) of the sheet (4) leaving the inner portion (5) of the sheet (4) free; an insertion station (S1) where the holding head (18) releases the sheet (4) having the inner portion (5) folded like a bellows; and a folding device (25) which is arranged along the folding path (P) between the feeding station (S2) and the insertion station (S1) and is configured to fold the inner portion (5) of the sheet (4) like a bellows. The holding head (18) is mounted on the folding drum (16) so as to radially translate outwards in the feeding station (S2) to receive the sheet (4) and so as to radially translate outwards in the insertion station (S1) to release the sheet (4).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority from Italian patent application no. 102024000000786 filed on January 17, 2024, the entire disclosure of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to a manufacturing machine and to a manufacturing method for the production of a filter for a tubular element.

[0003] The present invention has an advantageous application in the manufacture of a filter for a tubular element with a truncated cone shape that is subsequently used for the manual manufacture of a cigarette, to which the description that follows will refer explicitly, but without thus losing its general nature.PRIOR ART

[0004] Tubular elements with a truncated cone shape, partially empty, and provided at one end with a filter, have recently been proposed on the smoking articles market, which are used for the manual manufacture of a cigarette; in particular, a user no longer needs to roll a paper manually (a lengthy and complex operation and one that requires a good manual dexterity to obtain an even only acceptable quality result), but simply has to fill a preformed tubular element with tobacco through the open end.

[0005] Patent application WO2021156818A1 describes a manufacturing machine for the production of a filter for a tubular element and comprising: a folding conveyor that moves along a folding path at least one pocket apt to accommodate a sheet of card stock having an inner portion and an outer portion; a feeding station where the pocket receives the sheet of card stock and engages only the outer portion of the sheet of card stock, leaving the inner portion of the sheet of card stock free; a folding station where the inner portion of the sheet of card stock left free by the first pocket is folded like a bellows; and an insertion station where the pocket releases the sheet of card stock having the inner portion folded like a bellows.DESCRIPTION OF THE INVENTION

[0006] The object of the present invention is to provide a manufacturing machine and a manufacturing method for the production of a filter for a tubular element, said manufacturing machine and manufacturing method allowing high levels of productivity to be reached, guaranteeing high quality standards and, at the same time, being easy and economical to manufacture.

[0007] In accordance with the present invention, a manufacturing machine and a manufacturing method for the production of a filter for a tubular element are provided, as claimed in the appended claims.

[0008] The claims describe preferred embodiments of the present invention and form an integral part of this description.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will now be described with reference to the appended drawings, which illustrate a non-limiting embodiment thereof, wherein: Figure 1 is a prospective view of a tubular element with a truncated cone shape intended for the manual manufacturing of a cigarette; Figure 2 is a plan view of a wrapping sheet used to obtain the tubular element of Figure 1; Figure 3 is a plan view of a spread-out sheet of card stock used to manufacture a filter of the tubular element of Figure 1; Figure 4 is a prospective view of the sheet of card stock of Figure 3 partially folded on itself; Figure 5 is a front view, and with parts removed for clarity, of a manufacturing machine that produces the tubular element of Figure 1; Figure 6 is a perspective view of the manufacturing machine of Figure 5; Figure 7 is a perspective view of a detail of Figure 6; Figure 8 is a perspective view of a further detail of Figure 6; Figure 9 is a perspective view of a magazine of sheets of card stock of the manufacturing machine of Figure 5; and Figures 10 and 11 are two different perspective views and with parts removed for clarity of a folding drum of the manufacturing machine of Figure 5. PREFERRED EMBODIMENTS OF THE INVENTION

[0010] In Figure 1, the reference number 1 denotes, in its entirety, a tubular element with a truncated cone shape, partially empty, and provided at one end (the narrowest) with a filter 2. The tubular element 1 is intended for the manual manufacturing of a cigarette, being filled through the open end with tobacco.

[0011] The tubular element comprises a wrapping sheet 3 (shown spread out in Figure 2) with a trapezoidal shape that is wrapped in a tube shape on itself until one end is superimposed on the other end; in particular, a permanent, vinyl-based glue is interposed between the two superimposed ends and keeps the two superimposed ends joined together, stabilising the tube-shaped folding of the wrapping sheet 3.

[0012] According to what is shown in Figures 3 and 4, the filter 2 is formed by folding on itself a sheet 4 of card stock (having a much higher grammage than the wrapping sheet 3). In particular, the sheet 4 comprises an inner portion 5 that has a set of pre-weakened folding lines 7 and (as shown in Figure 4) is folded like a bellows (zigzag, concertinaed) along the pre-weakened folding lines 7 to form an inner body of the filter 2; furthermore, the sheet 4 comprises an outer portion 6 that is contiguous to the inner portion 5 and is folded in a tube (i.e. is wrapped) around the inner body formed by the inner portion 5 folded like a bellows (as shown in Figure 4) to form an outer casing of the filter 2.

[0013] In Figure 5, the number 8 denotes, in its entirety, a manufacturing machine (only partially shown) for the production of the tubular elements 1 described above and provided with the filters 2. The manufacturing machine 8 has an intermittent movement, i.e. its conveyors cyclically alternate the motion phases and the stop phases.

[0014] According to what is shown in Figures 5 and 6, the manufacturing machine 8 comprises an insertion station S1 at which a filter 2 is inserted inside a corresponding tubular element 1. At the insertion station S1 an inserting device 9 is arranged that is adapted to insert a filter 2 into a tubular element 1 carried by a pocket 10 standing still at the insertion station S1. The inserting device 9 comprises a tubular inserting body 11 with a truncated cone shape that is adapted to be inserted inside a tubular element 1 and therefore to receive inside itself a filter 2, which is pushed along the entire inserting body 11 until it exits from the inserting body 11 and stops inside the tubular element 1 that surrounds the inserting body 11. In other words, the inserting body 11 is arranged inside the tubular element 1 (and / or the tubular element 1 is arranged outside the inserting body 11) so that a wider (larger) entry end of the inserting body 11 is arranged at the wider (larger) end of the tubular element 1 and a narrower (smaller) exit end of the inserting body 11 is arranged inside the tubular element and in proximity to the narrower (smaller) end of the tubular element 1 (i.e. where the filter 2 must be positioned). Once the inserting body 11 has been arranged inside the tubular element 1 (or the tubular element 1 is arranged outside the inserting body 11), the filter 2 is pushed along the entire inserting body 11 by entering from the wider (larger) entry end of the inserting body 11 and exiting from the narrower (smaller) exit end of the inserting body 11: when the filter exits from the narrower (smaller) exit end of the inserting body 11, it is located inside the tubular element 1 in its definitive position and, expanding due to springback (as it is no longer radially compressed by the inserting body 11), it is positioned (stably) through interference inside the tubular element 1.

[0015] The inserting device 9 comprises a pushing element 12 that pushes the filter 2 along the entire inserting body 11 by entering from the wider (larger) entry end of the inserting body 11 and exiting from the narrower (smaller) exit end of the inserting body 11. In accordance with a further embodiment, the pushing element 12 could enter from the wider (larger) entry end of the inserting body 11 and arrive at the narrower (smaller) exit end of the inserting body 11; in other words, in said embodiment it is only the filter 2 that exits from the inserting body 11.

[0016] According to a preferred embodiment shown in more detail in Figure 7, the pushing element 12 causes the filter 2 to rotate on itself (i.e. rotates the filter 2 around a longitudinal rotation axis coaxial to the tubular element 1 of the inserting body 11). In particular, the pushing element 12 comprises a gripper 13 provided with two opposing clamps 14 that are closed against each other to grip one end of the filter 2; the two clamps 14 have an elongated shape (i.e. a long and narrow shape) so as to be able to enter with a small amount of clearance inside the inserting body 11. Furthermore, the pushing element 12 comprises an actuator 15 that longitudinally translates the gripper 13 and, at the same time, rotates the gripper 13 around a longitudinal rotation axis. According to a preferred embodiment, each filter 2 is gripped by the gripper 13 with the outer portion 6 still spread out (i.e. not wrapped around the inner portion 5 folded like a bellows) and the rotation of the gripper 13 wraps the outer portion 6 of the filter 2 around the inner portion 5 folded like a bellows; for this purpose, a fixed tile is coupled to one end of the inserting body 11 and causes wrapping of the outer portion 6 of the filter 2 around the inner portion 5 folded like a bellows before inserting the filter 2 inside the inserting body 11 (i.e. rotation of the gripper 13 brings the outer portion 6 of the filter 2 against the fixed tile that causes folding of the outer portion 6).

[0017] According to what is shown in Figures 5 and 6, the manufacturing machine 8 comprises a folding drum 16 that is arranged vertically and mounted rotating in a stepped manner around a horizontal rotation axis 17; in other words, the folding drum 16 is made to rotate with an intermittent motion, i.e. a non-continuous motion that provides for a cyclic alternation of the motion phases, in which the folding drum 16 is in movement, and stop phases, in which the folding drum 16 stops. The folding drum 16 supports two holding heads 18, each of which is apt to retain a corresponding sheet 4 of card stock; according to a different embodiment not shown, the folding drum 16 supports a different number of holding heads 18 (for example, three, four, five, six, eight, etc., holding heads 18). At each rotation step, the folding drum 16 rotates by 180° around the rotation axis 17 to reverse the position of the two holding heads 18.

[0018] Each holding head 18 is adapted to retain a corresponding sheet 4 of card stock by engaging the corresponding outer portion 6 and leaving the corresponding inner portion 5 free; i.e. the inner portion 5 of the sheet 4 of card stock exits cantilevered from the holding head 18 to be folded like a bellows. In particular, according to what is shown in Figure 8, each holding head 18 has a support body 19 with an approximately parallelepiped shape in which a sucking seat 20 is obtained that reproduces, in negative, the shape of the outer portion 6 of a sheet 4 of card stock; i.e. the sucking seat 20 is provided with a set of small holes that are connectible to a suction source to apply a pneumatic vacuum that retains the outer portion 6 of a sheet 4 of card stock in contact with the sucking seat 20.

[0019] Each holding head 18 is mounted on the folding drum 16 to rotate together (solidly constrained to) the folding drum 16 around the rotation axis 17 and to translate linearly and radially (i.e. perpendicularly to the rotation axis 17) with respect to the folding drum 16. In particular, the folding drum 16 comprises two linear guides 21 (shown in Figure 11) which are oriented radially and along which two respective slides 22 (shown in Figure 11) slide; each slide 22 supports the support body 19 of a corresponding holding head 18 by means of an arm 23 (shown in more detail in Figure 8) and is pushed forwards and backwards along its own linear guide 21 by an actuation device 24 (shown in Figure 11).

[0020] According to what is shown in Figure 5, rotation of the folding drum 16 around the rotation axis 17 cyclically moves each holding head 18 along a circular folding path P that initially crosses a feeding station S2, in which the folding head 18 receives a sheet 4 of card stock, and subsequently the insertion station S1, in which the filter 2 being formed (i.e. the sheet 4 of card stock with the inner portion 5 folded like a bellows) is released to the pushing element 12. In other words, at the end of each rotation step of 180°, a holding head 18 is located at the insertion station S1, while the other holding head 18 is located at the feeding station S2.

[0021] Coupled to the folding drum 16 there is a fixed folding device 25 (i.e. one without moving parts) which is shaped as a circumferential arc (to follow the course of the folding path P) and is arranged along the folding path P between the feeding station S2 and the insertion station S1; in particular, the folding device 25 comprises a set of folding helices (profiles) that are shaped to fold like a bellows (as shown in Figure 4) the inner portion 5 of a sheet 4 of card stock. In use, the movement of each holding head 18 along the folding path P causes the inner portion 5 of the sheet 4 of card stock retained by the holding head 18 to cooperate with the folding device 25 in order to be folded like a bellows (as shown in Figure 4).

[0022] When the folding drum 16 is at a standstill, each holding head 18 is moved radially towards the outside of the folding drum 16 (i.e. moving away from the rotation axis 17) in order to go and pick up a new sheet 4 of card stock (the holding head 18 which is located at the feeding station S2) and, at the same time, in order to release the sheet 4 of card stock picked up previously (the holding head 18 which is located at the insertion station S1); subsequently, each holding head 18 is moved radially towards the inside of the folding drum 16 (i.e. approaching from the rotation axis 17) to allow the folding drum 16 to make a rotation step.

[0023] According to what is shown in Figure 9, the manufacturing machine 8 comprises a feeding system 26 provided with a horizontal hopper 27 that accommodates a series of stacks of sheets 4 of card stock (in accordance with other embodiments not shown, the hopper 27 could be arranged in a different manner, i.e. not horizontal). In particular, the hopper 27 is shaped like a "cartridge belt" and has a support drum 28 that is mounted so as to rotate, in a stepped manner, around a horizontal rotation axis 29, and has a series of horizontal channels 30, which are evenly distributed around the rotation axis 29 and are each shaped so as to accommodate a stack of sheets 4 of card stock positioned horizontally. Rotation of the support drum 28 around the rotation axis 29 cyclically causes a channel 30 to be aligned with the feeding station S2 at which the two holding heads 18 of the folding drum 16 alternately pick up the sheets 4 of card stock from the start of the stack of sheets 4 of card stock. The feeding system 26 comprises one pushing element 31 that is aligned with the feeding station S2 and is movable horizontally to push the stack of sheets 4 of card stock that is located in the channel 30 aligned with the feeding station S2 towards the feeding station S2 (i.e. towards the two holding heads 18 of the folding drum 16); the function of the pushing element 31 is to always keep at the feeding station S2 the start of the stack of sheets 4 of card stock that is located in the channel 30 aligned at the feeding station S2 progressively as the stack of sheets 4 of card stock is depleted. When a stack of sheets 4 of card stock is completely depleted, the support drum 28 rotates by one step around the rotation axis 29 to cause a new channel 30, and therefore a new stack of sheets 4 of card stock, to align with the feeding station S2.

[0024] According to what is shown in Figure 10, the folding drum 16 is integral to a main shaft 32 that is mounted rotating around the rotation axis 17 and causes rotation of the folding drum 16; in particular, the main shaft 32 is rotated by a main electric motor.

[0025] As shown in Figure 11, the actuation device 24 comprises a secondary shaft 33 that is mounted rotating around the rotation axis 17, is coaxial to the main shaft 32, is inserted inside the main shaft 32 and is rotated by a secondary electric motor that is separate and independent from the main electric motor. The secondary shaft 33 terminates with a pinion 34 that engages with two racks 35 that are arranged at opposite ends of the pinion 34 and are integral with the slides 22; in this manner, rotation of the secondary shaft 33 (i.e. rotation of the pinion 34) imparts to the two slides 22 two equal and contrary translations (i.e. in opposite directions).

[0026] Functioning of the manufacturing machine 1 with reference to the formation of a single filter 2 starting from a respective sheet 4 of card stock and with reference to manufacturing of the filter 2 is described below.

[0027] Initially, a holding head 18 that is at a standstill in the feeding station S2 moves radially outwards to pick up a sheet 4 of stock card from the channel 30 of the hopper 27 aligned with the feeding station S2 and therefore to retain the sheet 4 of stock card through suction; subsequently, the holding head 18 moves radially inwards (i.e. it returns towards the starting position) taking with it the sheet 4 of stock card retained through suction.

[0028] At this point, rotation of the folding drum 16 around the rotation axis 17 moves the holding head 18 from the feeding station S2 to the insertion station S1, where the holding head 18 is at a standstill; between the feeding station S2 and the insertion station S1, the inner portion 5 of the sheet 4 of card stock is folded like a bellows by the folding device 25.

[0029] When the holding head 18 is at a standstill in the insertion station S1, the holding head 18 moves radially outwards to release the partially folded sheet 4 of card stick (i.e. with the inner portion 5 folded like a bellows) to the gripper 13 of the pushing element 12, which grips with its clamps 14 the inner portion 5 folded like a bellows. As already stated, the filter 2 (formed of the folded sheet 4 of card stock) is gripped by the gripper 13 with the outer portion 6 still spread out (i.e. not wrapped around the inner portion 5 folded like a bellows) and rotation of the gripper 13 wraps the outer portion 6 of the filter 2 around the inner portion 5 folded like a bellows.

[0030] Once the holding head 18 that is in the insertion station S1 has released the partially folded sheet 4 of card stock to the gripper 13, the holding head 18 moves radially towards the inside (i.e. it returns towards the starting position).

[0031] When the pocket 10 supporting a tubular element 1 is at a standstill in the insertion station S1, the pocket 10 translates to couple with the inserting body 11; in this manner, the inserting body 11 enters into the pocket 10 and then enters into the tubular element 1 accommodated in the pocket 10.

[0032] Simultaneously, the pushing element 12 rotates and pushes a filter 2 along the entire inserting body 11 until the filter 2 exits from the narrower (smaller) exit end of the inserting body 11 (as described above) and therefore the filter 2 is positioned (stably) through interference inside the tubular element 1. When insertion of the filter 2 inside the tubular element 1 is terminated, the pocket 10 translates to extract the tubular element 1 from the inserting body 11.

[0033] According to a possible embodiment, once again only a single filter 2 is arranged in the inserting body 11 and is pushed by the pushing element 12 to completely cross the inserting body 11 with a single stroke; i.e. the same filter 2 engaged by the pushing element 12 completely crosses the inserting body 11 from one side to side so as to enter into a corresponding tubular element 1. According to an alternative embodiment, a series of filters 2 are arranged in the inserting body 11 so that a new filter 2 entering into the inserting body 11 pushes another filter 2 out on the opposite side of the inserting body 11; i.e. inside the inserting body 11 there is a row of filters 2 in which the previous filter 2 pushes the subsequent filter 2; this embodiment has the advantage of limiting the length of the stroke that must be performed by the gripper 13 of the pushing element 12, therefore reducing the accelerations to which the gripper 13 is subject in use.

[0034] The embodiments described here can be combined with each other without deviating from the scope of protection of the present invention.

[0035] The manufacturing machine 8 described above has numerous advantages.

[0036] In the first place, the manufacturing machine 8 described above allows high hourly productivity rates to be reached, while still guaranteeing a high quality standard (i.e. guaranteeing the formation of perfectly shaped filters 2 without more or less accentuated crushing or deformations). This result is obtained, among other things, thanks to a particularly gentle, but still highly effective and efficient, treatment of the sheets 4 of stock card, which are never excessively mechanically stressed and at the same time always have a known and certain position.

[0037] Furthermore, the manufacturing machine 8 is particularly compact and allows an operator who is positioned close to the manufacturing machine 8 to reach with their hands all the various parts of the manufacturing machine 8 without having to make unnatural movements.

[0038] Lastly, the manufacturing machine 8 is relatively simple and economical to manufacture.LIST OF REFERENCE NUMBERS OF THE FIGURES

[0039] 1tubular element 2filter 3wrapping sheet 4card stock sheet 5inner portion 6outer portion 7pre-weakened folding lines 8manufacturing machine 9inserting device 10pocket 11inserting body 12pushing element 13gripper 14clamps 15actuator 16folding drum 17rotation axis 18holding heads 19support body 20sucking seat 21guide 22slide 23arm 24actuation device 25folding device 26feeding system 27hopper 28support drum 29rotation axis 30channels 31pushing element 32main shaft 33secondary shaft 34pinion 35rack Pfolding path S1insertion station S2feeding station

Claims

1. A manufacturing machine (8) for the production of a filter (2) for a tubular element (1), in particular for a smoking article; the manufacturing machine (8) comprises: a folding drum (16), which rotates around a first rotation axis (17) to move, along a circular folding path (P), at least one holding head (18) designed to accommodate a sheet (4), preferably made of card stock, having an inner portion (5) and an outer portion (6); a feeding station (S2), where the holding head (18) receives the sheet (4) and engages the sole outer portion (6) of the sheet (4), leaving the inner portion (5) of the sheet (4) free; an insertion station (S1), where the holding head (18) releases the sheet (4) having the inner portion (5) folded like a bellows; and a preferably fixed folding device (25), which is arranged along the folding path (P) between the feeding station (S2) and the insertion station (S1) and is configured to fold the inner portion (5) of the sheet (4) like a bellows; the manufacturing machine (8) is characterised in that the holding head (18) is mounted on the folding drum (16) so as to radially translate outwards in the feeding station (S2) to receive the sheet (4) and so as to radially translate outwards in the insertion station (S1) to release the sheet (4).

2. The manufacturing machine (8) according to claim 1, wherein the folding drum (16) supports two and precisely two holding heads (18) and, with every rotation step, the folding drum (16) rotates around the first rotation axis (17) by 180° so as to switch the position of the two holding heads (18).

3. The manufacturing machine (8) according to claim 2, wherein, when the folding drum (16) is standing still, a holding head (18) in the feeding station (S2) is radially moved towards the outside of the folding drum (16) so that it can retrieve a new sheet (4) and, at the same time, the other holding head (18) in the insertion station (S1) is radially moved towards the outside of the folding drum (16) so that it can release a previously retrieved sheet (4).

4. The manufacturing machine (8) according to claim 2 or 3, wherein the folding drum (16) comprises: two linear guides (21), which are radially oriented; two slides (22), each sliding along a respective linear guide (21) and supporting a respective holding head (18); and an actuation device (24), which pushes the slides (22) back and forth along the respective linear guides (21).

5. The manufacturing machine (8) according to claim 4, wherein the actuation device (24) comprises: a secondary shaft (33), which is mounted so as to rotate around the first rotation axis (17); a pinion (34) integral to the secondary shaft (33); and two racks (35), which mesh with the pinion (34), are arranged at opposite ends of the pinion (34) and are integral to the corresponding slides (22).

6. The manufacturing machine (8) according to claim 5 and comprising a main shaft (32), which is mounted so as to rotate around the first rotation axis (17), is coaxial to the secondary shaft (33), is arranged around the secondary shaft (33) and determines the rotation of the folding drum (16).

7. The manufacturing machine (8) according to claim 6 and comprising: a main electric motor, which causes the rotation of the main shaft (32); and a secondary electric motor, which causes the rotation of the secondary shaft (33) and is separate from and independent of the main electric motor.

8. The manufacturing machine (8) according to one of the claims from 1 to 7, wherein the holding head (18) has a support body (19), where there is obtained a sucking seat (20), which reproduces, in negative, the shape of the outer portion (6) of the sheet (4).

9. The manufacturing machine (8) according to one of the claims from 1 to 8 and comprising a feeding system (26) provided with a preferably horizontal hopper (27), which accommodates a series of stack of sheets (4).

10. The manufacturing machine (8) according to claim 9, wherein the hopper (27) has a support drum (28), which is mounted so as to rotate, in a stepped manner, around a second rotation axis (29) and has a series of preferably horizontal channels (30), which are evenly distributed around the rotation axis (29) and are each shaped so as to accommodate a stack of sheets (4).

11. The manufacturing machine (8) according to claim 10, wherein the rotation of the support drum (28) around the rotation axis (29) cyclically causes a channel (30) to be aligned with the feeding station (S2).

12. The manufacturing machine (8) according to claim 11, wherein the feeding system (26) comprises a pushing element (31), which is aligned with the feeding station (S2) and is horizontally movable so as to push the stack of sheets (4) located in the channel (30) aligned with the feeding station (S2) towards the feeding station (S2).

13. The manufacturing machine (8) according to one of the claims from 1 to 12 and comprising: a tubular inserting body (11), in particular with the shape of a truncated cone, which is arranged in the area of the insertion station (S6) and is shaped so as to be inserted into the tubular element (1); and a pushing element (12), which is designed to push the filter (2) along the entire inserting body (11) until it comes out of the inserting body (11), so as to insert the filter (2) into the tubular element (1) surrounding the inserting body (11).

14. The manufacturing machine (8) according to claim 13, wherein the pushing element (12) is configured to place a row of filters (2) inside the inserting body (11) so that a new filter (2), by entering the inserting body (11), pushes out another filter (2) on the opposite side of the inserting body (11).

15. A manufacturing method for the production of a filter (2) for a tubular element (1); the manufacturing method comprises the steps of: moving, by means of a folding drum (16), which rotates around a first rotation axis (17), along a folding path (P), at least one holding head (18) designed to accommodate a sheet (4), preferably made of card stock, having an inner portion (5) and an outer portion (6); inserting, in a feeding station (S2), the sheet (4) into the holding head (18), which engages the sole outer portion (6) of the sheet (4), leaving the inner portion (5) of the sheet (4) free; transferring, in an insertion station (S1), the sheet (4) having the inner portion (5) folded like a bellows from the holding head (18); and folding the inner portion (5) of the sheet (4) like a bellows by means of a folding device (25) arranged, preferably in a fixed manner, along the folding path (P) between the feeding station (S2) and the insertion station (S1); the manufacturing method is characterised in that the holding head (18) is radially translated outwards in the feeding station (S2) to receive the sheet (4) and is radially translated outwards in the insertion station (S1) to release the sheet (4).

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