EP4302985B1 - Device and method for producing hollow pipes - Google Patents

Description

The invention relates to a device for producing hollow tubes, in particular drinking straws or products of the tobacco processing industry, comprising a formatting device which is designed to form a first material strip and a second material strip into a two-layer hollow tube during conveyance through the formatting device, wherein a material strip feed device is provided which is designed to feed the first material strip and the second material strip to the formatting device, wherein a cutting device is provided for longitudinally axially cutting a base material strip into the first material strip and into the second material strip.

• Fördern eines Basismaterialstreifens in längsaxialer Förderrichtung,
• längsaxiales Schneiden des Basismaterialstreifens in einen ersten Materialstreifen mit einer ersten Breite und einen zweiten Materialstreifen mit einer zweiten Breite,
• Zuführen des ersten Materialstreifens und des zweiten Materialstreifens zu einer Formatvorrichtung,
• Formen des ersten Materialstreifens und des zweiten Materialstreifens in der Formatvorrichtung zu einem Hohlrohr.

The invention further relates to a method for producing hollow tubes, in particular drinking straws or products of the tobacco processing industry, comprising the following method steps:

• Conveying a base material strip in the longitudinal axial conveying direction,
• longitudinally cutting the base material strip into a first material strip with a first width and a second material strip with a second width,
• Feeding the first material strip and the second material strip to a format device,
• Forming the first material strip and the second material strip in the formatting device into a hollow tube.

When manufacturing hollow tubes, for example to produce straws or recess filters or heat-not-burn products in the tobacco processing industry, it is important to produce hollow tube cross-sections that are as consistent as possible in order to ensure that the hollow tubes have the most consistent quality possible.

EP 3 033 952 A2 discloses a device and a method for producing hollow tubes from which small tubes are cut to length at the end. The device has a material strip feed device and a cutting device for longitudinally cutting a base material strip into a first material strip with a first width and a second material strip with a second width, a gluing device by means of which the first and/or second material strips can be glued, a joining device by means of which the first and second material strips are brought together for gluing so that the first and second material strips lie offset from one another, and a formatting device in which a tubular strand is produced from the joined first and second material strips. In this case, two first and second material strips cut from the base material strip are placed offset from one another and connected to one another in order to enable edges to lie abutting in the hollow tube produced at the end. Paper webs are suitable as material webs, for example. The base material strip is usually pulled off a reel.

EP 3 332 655 A1 discloses a similar apparatus and method, specifying dimensions of the material strip thicknesses, widths and amount of adhesive.

WO 2021/185486 A1 also discloses a device for producing hollow tubes, in which a first formatting device is provided which is designed to convey a first material strip longitudinally axially and to form it into a first hollow tube during the conveying, wherein a second formatting device is provided which is arranged behind the first formatting device in the conveying direction and is designed to wrap a second material strip around the first material strip during longitudinal axial conveying of the second material strip, so that a double-layered hollow tube is formed which has the first hollow tube on the inside and the second material strip on the outside. This improves the quality of the hollow tubes produced, in particular drinking straws, whereby hollow tubes or drinking straws which are free of waves or smooth in particular can be produced. The first formatting device for forming has a formatting chamber which does not require a formatting belt, so that inner hollow tubes which have a constant diameter are reliably formed over very long periods of operation of the device.

Due to wear of the format belt used in the formatting device, the diameters of the hollow tubes produced can change over time. Wear is relatively high when producing hollow tubes because there is a relatively high slippage between the format belt and the material strip or the hollow tube.

It is the object of the present invention to provide a device and a method for producing hollow tubes, in particular drinking straws or products of the tobacco processing industry, which enable a very stable production process for hollow tubes, in particular reliable operation is possible when forming the hollow tubes from first and second material strips. In particular, safe production of hollow tubes should also be possible in the event that a connection point is present in the material strip.

This object is achieved by a device for producing hollow tubes, in particular drinking straws or products of the tobacco processing industry, comprising a format device which is designed to form a first material strip and a second material strip into a two-layer hollow tube during conveyance through the format device, wherein a material strip feed device is provided which is designed to feed the first material strip and the second material strip to the format device, wherein a first web tensioning device is provided for the first material strip and a second web tensioning device is provided for the second material strip, wherein upstream of the first web tensioning device and the second web tensioning device a cutting device for longitudinally axially cutting a base material strip into the first material strip and into the second material strip is provided.

The invention is based on the idea that by providing two web tensioning devices, one of which is provided for each cut strip of material, even with different friction differences in the paths of the two strips of material, fewer conveying problems occur than when guiding the two strips of material via a common web tensioning device.

Preferably, the second web tensioning device comprises a pneumatically deflectable deflection device. The pneumatically deflectable deflection device makes it possible for a tension to be present in the material strip that is guided around the pneumatically deflectable deflection device, which tension is sufficiently high but not too high. This is particularly advantageous if the other material strip experiences high friction during formation in the formatting device, so that very little tension is transferred to the associated web tensioning device via this material strip.

A maximum tensile stress can be set using the pneumatically deflectable deflection device. A minimum tensile stress can also be set using this. The pneumatically deflectable deflection device is preferably provided for the second material strip and, during operation, leads to a deflection or movement of the deflection device, which changes the conveying path or the length of the conveying path of the second material strip. For example, if the tensile stress in the second material strip drops too much, the conveying path can be extended, resulting in a higher tensile stress.

The second web tensioning device preferably has a deflection roller arranged on a compressed air cylinder. The deflection roller serves to deflect the second material strip. By changing the position of the deflection roller using the compressed air cylinder, preferably by linearly deflecting the compressed air cylinder, the deflection roller can be brought into a predetermined position by means of which a length of the conveying path of the second material strip is specified.

Preferably, the length of the conveying path or the conveying path is varied, controlled, regulated and/or adjusted depending on the stability of the first and/or second material strip by means of the pneumatically deflectable deflection device.

Alternatively or in addition to varying the distance or length of the conveying path of a feed path of the second material strip, the pressure in the pneumatically deflectable deflection device can also be changed.

Preferably, the pressure in the pneumatic cylinder is adjusted depending on the Stability of the second strip of material varies.

Preferably, the web tension devices are web tension control and/or regulation devices. The first web tension device can be a dancer. Such dancers are known in the tobacco processing industry, for example from EP 2 702 881 A1 , the EP 3 434 406 B1 and the WO 2019/211157 A1 , known.

The compressed air cylinder can preferably be deflected linearly. The deflectability can preferably be between 40 mm and 120 mm, in particular preferably between 60 mm and 100 mm and in particular preferably between 70 mm and 90 mm. As a result, when the second material strip is deflected by up to 180°, twice the path or twice the distance can be used to extend the path of the second material strip.

Preferably, the pressure in the compressed air cylinder is varied, particularly preferably depending on the stability of the second material strip. The overpressure in the compressed air cylinder can be between 0.5 bar and 10 bar, preferably up to 8 bar, particularly preferably up to 6 bar.

If, for example, a strip of material is pulled off a reel and the paper is further processed from this reel, the pressure in the compressed air cylinder can be at the upper value, for example 6 bar. This moves the deflection roller into a position that serves to extend the length of the conveying path of the second strip of material as much as possible. If a reel change takes place, i.e. a strip of material from a first reel is connected to the strip of material from a second reel, the tensile stability of this connection point is not as high as the tensile stability of the strip of material itself. In this case, the pressure in the compressed air cylinder is preferably reduced in order to keep the tensile stress in the strip of material low until the connection point has passed through the formatting device. For example, the overpressure in the compressed air cylinder can then be 0.5 bar. Preferably, the lower value is a value that is less than 1 bar, in particular less than 0.8 bar, in particular less than or equal to 0.6 bar and preferably greater than 0.2 bar, preferably greater than 0.4 bar.

Preferably, the first web tensioning device is a material strip tension control and/or regulation device which comprises a pivotable deflection roller, as disclosed in the above-mentioned prior art. The pivoting can be spring-loaded or pivoting can be provided by means of an electric motor.

Preferably, the cutting device for longitudinally axially cutting a base material strip into the first material strip and into the second material strip is provided immediately upstream of the first web tensioning device and the second web tensioning device. The cutting device preferably comprises a pulling cutting roller and a cutting blade acting therewith.

Typically, the first strip of material after cutting has a slightly different width than the second strip of material, since the first strip of material preferably serves to form an inner tube and the second strip of material preferably serves to form an outer tube of the two-layer hollow tube. In order to produce both tubes in a butt-joint manner, the width of the strip of material of the inner tube is necessarily smaller than the width of the strip of material of the outer tube.

Preferably, the first web tensioning device is designed to control and/or regulate a conveying speed of the base material strip. In this case, a basic conveying speed is preferably specified by a machine control system, which preferably depends on the conveying speed of the hollow tube to be produced. The first web tensioning device can then serve to adjust the basic conveying speed, in particular depending on the tension in the first material strip. This allows consistently high-quality hollow tubes to be produced.

The formatting device is preferably format-belt-free. A formatting device that is format-belt-free and serves to form a two-layer hollow tube has its own inventive content. The use of a formatting device that is format-belt-free to produce hollow tubes from a first material strip and a second material strip has the advantage that the diameter of the hollow tube produced remains constant. This means that wear on a formatting belt that would otherwise be used does not affect the diameter of the hollow tube, which would be the case if a formatting belt were used to form the hollow tubes in a formatting device. The hollow tube is formed completely from the two material strips in the formatting device.

Preferably, a pulling formatting device with a formatting belt is provided for conveying the material strips, which is arranged downstream of the formatting device in the conveying direction. The pulling formatting device then pulls the hollow tube produced in two layers.

The formatting device preferably has a heating device. Since the formatting device is free of format tape, it is possible to provide a heating device at this point. In particular, a heating device is provided from below in a sub-format. This allows the adhesive used to connect the material strips to harden early and quickly.

In order to reduce the friction of the material strips in the formatting device, an air flow is introduced from the outside to the inside of a formatting chamber of the formatting device. This creates an air cushion between the inner wall of the formatting chamber of the formatting device and the material strip, so that the friction is reduced. For this purpose, one or more holes can be provided in the formatting device, in particular through the cover strip. In addition, a A compressed air supply device can be provided which conveys compressed air through the bore or bores. The compressed air supply device can also be a compressed air reservoir. Alternatively, a pump can be provided.

Preferably, the formatting device comprises a first formatting chamber and a second formatting chamber, wherein the first formatting chamber is designed to convey the first material strip in a longitudinal axial direction and to form it into a hollow tube during the conveying process, wherein the second formatting chamber is arranged behind the first formatting chamber in the conveying direction and is designed to wind the second material strip around the first material strip in a longitudinal axial conveying process, so that a double-layered hollow tube is formed, which has the hollow tube on the inside and the second material strip on the outside. This is a configuration that is essentially the same as that shown in the WO 2021/185486 A1 Here, the second format chamber can be provided with a format belt or preferably without a format belt. Preferably, the first and second format chambers are free of format belts. The first format chamber and the second format chamber are part of the format device.

• Fördern eines Basismaterialstreifens in längsaxialer Förderrichtung,
• längsaxiales Schneiden des Basismaterialstreifens in einen ersten Materialstreifen mit einer ersten Breite und einen zweiten Materialstreifen mit einer zweiten Breite,
• Zuführen des ersten Materialstreifens über eine erste Bahnspannungsvorrichtung und des zweiten Materialstreifens über eine zweite Bahnspannungsvorrichtung zu einer Formatvorrichtung,
• Formen des ersten Materialstreifens und des zweiten Materialstreifens in der Formatvorrichtung zu einem Hohlrohr.

The object is further achieved by a method for producing hollow tubes, in particular drinking straws or products of the tobacco processing industry, with the following process steps:

• Conveying a base material strip in the longitudinal axial conveying direction,
• longitudinally cutting the base material strip into a first material strip with a first width and a second material strip with a second width,
• Feeding the first material strip via a first web tensioning device and the second material strip via a second web tensioning device to a format device,
• Forming the first material strip and the second material strip in the formatting device into a hollow tube.

Preferably, the first material strip and the second material strip are in direct or immediate contact with each other at least in the format device.

Preferably, by means of the second web tensioning device, a conveying path of the second material strip is changed depending on the stability of the first and/or second material strip.

Alternatively or additionally, instead of changing the conveying path or the length of the conveying path, the tensile stress of the second material strip is controlled or regulated.

Preferably, the first web tensioning device controls or regulates a feed of the base material strip or a conveying speed of the base material strip.

If the change in the conveying path or the length of the conveying path of the second material strip preferably takes place via a pneumatic deflection of a deflection device of the second web tensioning device, a very safe process can be made possible, whereby on the one hand a sufficient tensile stress is provided in the second material strip and on the other hand this tensile stress can be sufficiently reduced when changing the bobbin.

Preferably, the pneumatic pressure is changed if the stability of the first material strip and/or the second material strip changes. This is particularly the case if the connection point is conveyed through the material strip path when changing the reel. becomes.

Preferably, the first material strip and the second material strip are formed in the formatting device without a formatting belt. This allows the diameter of the hollow tube produced to be kept very constant. Preferably, a pulling formatting device with a formatting belt is provided for conveying the material strips, which is arranged downstream of the formatting device in the conveying direction.

Preferably, the material strips are heated in the formatting device.

Furthermore, in order to reduce the friction between the material strip and the inner surface of the format chamber or the format chambers of the format device, an air cushion is preferably created between the first material strip and/or the second material strip of at least one inner wall of the format device.

Preferably, the first material strip and the second material strip are brought together offset from one another in front of the formatting device so that they are placed on top of one another, or the first material strip is conveyed longitudinally axially through a first formatting chamber of the formatting device, whereby a first hollow tube is formed from the first material strip and then the second material strip of a second formatting chamber of the formatting device is wound around the first hollow tube to form a two-layer hollow tube. Thus, two alternative processes are preferably carried out, namely in the first process that the two material strips are brought together offset from one another before forming in the hollow tube, whereby an adhesive is then applied between the two material strips in order to then be conveyed together through the formatting device in order to produce the hollow tube or, as a second variant, first forming the inner tube in a first formatting chamber of the formatting device and then wrapping the second material strip around the outside. to wrap around, whereby an adhesive was applied to connect the two strips of material before wrapping.

Fig. 1

eine schematische Darstellung eines Materialstreifenlaufs gemäß der Erfindung,

Fig. 2

eine schematische Darstellung einer erfindungsgemäßen Formatvorrichtung in einer ersten Ausführungsform und

Fig. 3

eine schematische Darstellung einer erfindungsgemäßen Formatvorrichtung in einer zweiter Ausführungsform.

They show:

Fig. 1

a schematic representation of a material strip run according to the invention,

Fig. 2

a schematic representation of a format device according to the invention in a first embodiment and

Fig. 3

a schematic representation of a format device according to the invention in a second embodiment.

Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

In the drawings, identical or similar elements and/or parts are provided with the same reference numbers, so that a repeated presentation is dispensed with in each case.

Fig. 1 shows a schematic representation of a material strip run for Production of two-layer hollow tubes 10 in a material strip feed device 23 according to the invention. A base material strip 20, for example made of paper, is pulled off a reel 19 by a cutting device 37. The cutting device 37 can be a pull cutting device. In the prior art, for example in the EP 3 332 655 A1 the first material strip 21 and the second material strip 22, which is cut from the base material strip 20, are diverted via a common dancer, and later the material strips 21, 22 are conveyed via other paths. The dancer serves to control the tensile stress of the material strip webs. However, if excessive friction loss occurs in one of the two material strips 21, 22 during the formation of the hollow tubes 10, it may be that the propulsion of the base material strip 20 is determined or co-determined by this material strip alone, so that the tensile stress in the other material strip is greatly reduced, which can lead to problems in production.

The invention now provides in particular for the two material strips 21 and 22 to run over two separate web tensioning devices 31 and 32. In the embodiment of the Fig. 1 the first material strip 21 is allowed to run over a first web tensioning device 31, for example a dancer, i.e. over the deflectable, in particular pivotable, deflection roller 36, and the second web tensioning device 32 is allowed to run over a deflection device 33, comprising a deflection roller 35, which is arranged on a compressed air cylinder 34. The deflection device 33 can thus be moved over a distance, as the arrows indicate. This allows a sufficiently high or low force or tensile stress to be maintained in the second material strip 22. This is done by moving the compressed air cylinder 34 and/or the deflection roller 35, which is arranged on the compressed air cylinder 34, in a direction that lengthens or shortens the path of the second material strip 22.

In the usual production case of the hollow tubes 10, for example, a Compressed air cylinder 34 is subjected to a predeterminable pressure, such as 6 bar in this embodiment. This exerts a force on the second material strip 22 that is greater than the force on the first wrapping material strip 21 that is caused by the friction losses of the first material strip 21. This causes the deflection roller 35 to reach the position shown in Fig. 1 shown upper stop. In the event of a reel change, a connection point is provided in the material strips, which reduces the stability of the first material strip 21 and the second material strip 22. In this case, the pressure in the pneumatic cylinder 34 is reduced to 1 bar or lower, thereby reducing the force in the second material strip 22, so that the deflection roller 35 moves downwards, as also shown by the downward arrow. As soon as the change point or connection point of the material strips 21, 22 has arrived in the format device 11, the pressure in the pneumatic cylinder is increased again to 6 bar, causing the deflection roller 35 to move upwards again to the end position. In this way, even with high friction losses, seams or change points of material strips 21, 22 can be operated in continuous operation. High friction losses occur in particular when there is a large seam offset, in particular a seam offset greater than 82°, in particular greater than 100°, in particular greater than 110°, in particular greater than 120°, in particular greater than 130°, in particular greater than 140°, in particular greater than 150°, in particular greater than 160°, in particular greater than 170°, in particular with a seam offset of 180°

In this embodiment, the first material strip 21 passes after the first web tensioning device 31 via a deflection roller 17, a flat guide 14, three further deflection rollers 17, a further bolt guide 16, by means of which in particular the edges of the first material strip 21 are guided, and a further deflection roller 17 to the first format chamber 51 of the format device 11. In the first format chamber 51, the hollow tube 10 is formed, preferably with the seam at the bottom. The first format chamber 51 can comprise a middle finger. For this purpose, the WO 2021/185486 A1 referred to.

The path of the second material strip 22 runs after the second web tensioning device 32 over a deflection roller 17 past a flat guide 14 over further deflection rollers 17 to another flat guide in order to provide a film gluing 15, which provides a full-surface or almost full-surface gluing of the second material strip 22. Almost full-surface gluing is considered to be a gluing of at least 80% of the surface of the second material strip 22, in particular of at least 90%. The second material strip 22 then reaches another deflection roller 17 in order to be guided more precisely in the transverse axial position by a bolt guide 16. The bolt guide 16 has, for example, two edges that guide the edges of the second material strip 22. The second material strip 22 then passes via a deflection roller 17 into the second format chamber 52 of the format device 11, in which the second material strip 22 is wound around the inner hollow tube 10 formed from the first material strip 21.

In Fig. 1 A pulling formatting device 41 is also shown, which has a formatting belt and pulls the produced two-layer hollow tube 10 in the conveying direction 12. At the end, a hollow tube 10 comes out of the pulling formatting device 41, which can be cut to the desired length.

The guides for the material strips can of course also be designed differently. For example, more or fewer guides and/or more or fewer deflection rollers can be provided.

Fig. 2 shows schematically a format device 11 according to the invention, which has two format chambers 51, 52, wherein the process can be designed as in Fig. 1 is described. Here, an inner tube 10 is first formed from the first material strip 21, in order to then wrap the second material strip 22 around the formed inner tube 10. In order to reduce the friction in the first format chamber 51, a bore 54 is shown into which an air stream 55 can be introduced by a compressed air device 53. This is shown very schematically.

An air flow 55 can also be introduced into the second format chamber 52 or several air flows can be introduced into the format chambers 51, 52. In addition, Fig. 2 schematically shows a heating device 13 which serves to heat the hollow tube 10 formed from two material strips 21, 22 in order to provide early setting of the adhesive or glue.

The formatting device 11 is followed in the conveying direction 12 by a pulling formatting device 41. The pulling formatting device 41 has a formatting belt 40 which runs as usual in the pulling formatting device 41 and is wound at least partially around the double-layer hollow tube 10 in order to pull it in the conveying direction 12.

Fig. 3 shows schematically another embodiment of a format chamber 11 according to the invention. Here, the first material strip 21 and the second material strip 22 are placed one above the other in an offset manner and only then are they introduced into the format device 11. A double-layered or two-layered hollow tube 10 is then formed in the format chamber 51 of the format device 11. This hollow tube formed there is pulled through the subsequent pulling format device 41 in the conveying direction 12. In this case too, the pulling format device 41 is provided with a format belt 40 which runs through the pulling format device 41. In both embodiments of the Fig. 2 and 3 The respective format devices 11 are format tape-free. In addition, Fig. 3 A heating device 13 is also shown, which heats the material strips 21, 22 from below.

The provision of a format belt-free format device 11 for forming of the two-layer hollow tubes 10 leads to very uniformly produced diameters of the hollow tubes 10. If format belts 40 are used for forming, the diameters of the produced double-layer hollow tubes 10 would continuously increase over the course of use of the format belts 40, since the format belts become thinner due to wear. This is prevented by format devices 11 without format belts.

Preferably, the format chamber 51, 52 or the format chambers 51, 52 of the format device 11 are metallic and in particular the surfaces that come into contact with the material strips 21, 22 are friction-reduced. This can be made possible by a friction-reducing coating or by very smooth, in particular polished, surfaces. Format devices 11 that are free of format belts mean that the format belts 40 in the pulling format device 41, which are only used for conveying, can be used for longer, since they only have the function of pulling and no longer of forming. This reduces wear and tear on the one hand and on the other hand the format belts 40 can also be used for pulling if they have become too thin for forming.

list of reference symbols

10

hollow tube

11

format device

12

conveying direction

13

heating device

14

flat guide

15

film gluing

16

bolt guide

17

pulley

19

bobbin

20

base material strips

21

first strip of material

22

second strip of material

23

material strip feed device

31

first web tensioning device

32

second web tensioning device

33

deflection device

34

pneumatic cylinders

35

pulley

36

pulley

37

cutting device

40

format tape

41

train format device

51

first format chamber

52

second format chamber

53

compressed air device

54

opening

55

airflow

56

conveyor line

Claims (15)

1. A device for producing hollow tubes (10), in particular drinking straws or products of the tobacco processing industry, comprising a formatting device (11) which is configured to shape a first material strip (21) and a second material strip (22) during the conveying process through the formatting device (11) into a two-layer hollow tube (10), wherein a material strip feed device (23) is provided, which is configured to feed the first material strip (21) and the second material strip (22) to the formatting device (11), wherein a first web tensioning device (31) is provided for the first material strip (21) and a second web tensioning device (32) is provided for the second material strip (22), wherein a cutting device (37) for cutting a base material strip (20) in a longitudinally axial direction into the first material strip (21) and into the second material strip (22) is provided upstream of the first web tensioning device (31) and the second web tensioning device (32).
2. The device according to Claim 1, characterized in that the second web tensioning device (32) comprises a pneumatically redirectable deflecting device, wherein the second web tensioning device (32) in particular has a guide roller (35) arranged on a compressed air cylinder (34), wherein the pressure in the compressed air cylinder (34) is in particular varied as a function of the stability of the second material strip (22).
3. The device according to Claim 1 or 2, characterized in that the first web tensioning device (31) is a material strip traction control and/or regulating device which comprises a pivotable guide roller (17).
4. The device according to Claim 1 or 2, characterized in that the cutting device (32) is arranged immediately upstream of the first web tensioning device (31) and the second web tensioning device (32).
5. The device according to any one of Claims 1 to 4, characterized in that the first web tensioning device is configured to control and/or to regulate a conveying speed of the base material strip.
6. The device according to any one of Claims 1 to 5, characterized in that the formatting device (11) does not have a garniture tape, wherein a traction formatting device (41) having a garniture tape (40) is in particular provided for conveying the material strips (12, 22), which traction formatting device is arranged downstream of the formatting device (11) in the conveying direction (12).
7. The device according to any one of Claims 1 to 6, characterized in that the formatting device (11) has a heating device (13).
8. The device according to any one of Claims 1 to 7, characterized in that an airflow (55) is admitted in a formatting chamber (51, 52) of the formatting device (11) from the outside in.
9. The device according to any one of Claims 1 to 8, characterized in that the formatting device (11) comprises a first formatting chamber (51) and a second formatting chamber (52), wherein the first formatting chamber (51) is configured to convey the first material strip (21) in a longitudinally axial direction and to shape it into a hollow tube (10) during the conveying process, wherein the second formatting chamber (52) is arranged behind the first formatting chamber (51) in the conveying direction (12) and is configured to wind the second material strip (22) around the first material strip (21) in a longitudinally axial conveying process, so that a double-layer hollow tube (10) is formed, which has the hollow tube (10) inside and the second material strip (22) externally.
10. A method for producing hollow tubes (10), in particular drinking straws or products of the tobacco processing industry, having the following method steps:

    - conveying a base material strip (20) in a longitudinally axial conveying direction (12),

    - cutting the base material strip (20) in a longitudinally axial direction into a first material strip (21) having a first width and a second material strip (22) having a second width,

    - feeding the first material strip (21) via a first web tensioning device (31) and the second material strip (22) via a second web tensioning device (32) to a formatting device (11),

    - shaping the first material strip (21) and the second material strip (22) into a hollow tube (10) in the formatting device (11).
11. The method according to Claim 10, characterized in that a conveying section (56) of the second material strip (22) is altered as a function of the stability of the first and/or second material strip (21, 22) by means of the second web tensioning device (32), wherein the first web tensioning device (31) in particular controls or regulates a feed rate or a conveying speed of the base material strip (20), wherein the conveying section (56) of the second material strip (22) is in particular altered via a pneumatic redirection of a deflecting device (33) of the second web tensioning device (32), wherein the pneumatic pressure is in particular altered provided that the stability of the first material strip (21) and/or of the second material strip (22) changes.
12. The method according to Claim 10 to 11, characterized in that the shaping of the first material strip (21) and of the second material strip (22) in the formatting device (11) takes place without a garniture tape, wherein a traction formatting device (41) having a garniture tape (40) is in particular provided for conveying the material strips (12, 22), which traction formatting device is arranged downstream of the formatting device (11) in the conveying direction (12).
13. The method according to any one of Claims 10 to 12, characterized in that the material strips (21, 22) are heated in the formatting device (11).
14. The method according to any one of Claims 10 to 13, characterized in that an air cushion is generated between the first material strip (21) and/or the second material strip (22) and at least one inner wall of the formatting device (11).
15. The method according to any one of Claims 10 to 14, characterized in that the first material strip (21) and the second material strip (22) are merged offset with respect to one another before the formatting device (11), so that these are placed one above the other, or in that the first material strip (21) is conveyed in a longitudinally axial direction through a first formatting chamber (51) of the formatting device (11), wherein, as a result, a first hollow tube (10) is formed from the first material strip (21) and subsequently the second material strip (22) is wound around the first hollow tube (10) in a second formatting chamber (52) of the formatting device (11), in order to form a two-layer hollow tube (10).

Images