Hollow tube fabrication

Abstract

Method for producing hollow tubes for the tobacco processing industry or drinking straws, comprising the following process steps: - forming a hollow tube (10, 31) from two material strips (21.1, 21.2, 25, 26) by longitudinally conveying the material strips (21.1, 21.2, 25, 26) in a forming device (11, 12, 30), wherein the hollow tube (10, 31) has an inner material layer (63) and an outer material layer (64), the longitudinal axial edges (66) of which are butted together, defined by two butt areas (70, 71) that are offset from each other, - wherein the material strips (21.1, 21.2, 25, 26) are2, 25, 26) are bonded in a first area (81) with a first type of adhesive (61) and a second type of adhesive (62) is provided for bonding in at least a second area (82), wherein the second type of adhesive (62) is a hot melt adhesive and wherein the second area (82) is a butt joint area (70, 71), - wherein the hollow tube (10, 31) is cut into hollow tubes by means of a cutting device (38, 39), wherein the cutting device (38, 39) enters at an entry point (72) of the hollow tube (10, 31) and exits at another point, wherein the entry point (72) is provided in the second area (82) and / or the entry point (72) is clockwise between 180° and 20° in the conveying direction (20, 34) of the hollow tube (10, 31). 290° in front of the inner impact area (71) and / or the entry point (72) is located at an outer impact area (70).

Description

[0001] The invention relates to a method for producing hollow tubes for the tobacco processing industry or drinking straws, comprising the following process steps: Forming a hollow tube from two material strips during longitudinal axial conveyance of the material strips in a formatting device, wherein the hollow tube has an inner material layer and an outer material layer, wherein the longitudinal axial edges of one material layer are abutting and the other material layer is designed to overlap and be offset from the abutting longitudinal axial edges, or wherein the longitudinal axial edges of the inner material layer and the outer material layer each abutting, thereby defining two abutting regions that are offset from one another, wherein the material strips are glued in a first region with a first type of glue and in at least one second region a second type of glue is provided for bonding, wherein the second type of glue is a hot melt adhesive and wherein the second region is a butting region or a region in which the inner material layer (63) is designed to overlap,wherein the hollow tube is cut into hollow tubes by means of a cutting device, wherein the cutting device enters at one entry point of the hollow tube and exits at another point.

[0002] Furthermore, the invention relates to a stranding machine in the tobacco processing industry or the drinking straw industry for producing hollow tubes and to the use of a corresponding stranding machine.

[0003] WO 2021 / 185486 A1 discloses a device for producing hollow tubes, in particular drinking straws, comprising a first formatting device configured to convey a first material strip longitudinally axially and to form it into a first hollow tube during conveyance, wherein a second formatting device is provided, which is arranged downstream of the first formatting device in the conveying direction and is configured to wrap a second material strip around the first material strip during longitudinal axial conveyance 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. Such a device can be used to produce a double-layered tube by cutting the produced hollow tube into hollow tubes.Under certain circumstances, it may happen that the inner paper web, particularly in the inner seam area, i.e. where the edges of the inner material strip are opposite each other, can detach slightly during the cut, since there is no counter pressure there during the cut.

[0004] The object of the present invention is to produce high-quality hollow tubes which, in particular, have a low ovality.

[0005] This task is solved by a process for producing hollow tubes for the tobacco processing industry or drinking straws with the following process steps: Forming a hollow tube from two material strips during longitudinal axial conveyance of the material strips in a formatting device, wherein the hollow tube has an inner material layer and an outer material layer, wherein the longitudinal axial edges of one material layer are abutting and the other material layer is designed to overlap and be offset from the abutting longitudinal axial edges, or wherein the longitudinal axial edges of the inner material layer and the outer material layer each abutting, thereby defining two abutting regions that are offset from one another, wherein the material strips are glued in a first region with a first type of glue and in at least one second region a second type of glue is provided for bonding, wherein the second type of glue is a hot melt adhesive and wherein the second region is a butting region or a region in which the inner material layer is designed to overlap,wherein the hollow tube is cut into hollow tubes by means of a cutting device, wherein the cutting device enters at one entry point of the hollow tube and exits at another point, , which is further developed in that the entry point is provided in the second region and / or that the entry point is located in the conveying direction of the hollow tube in a clockwise direction between 90° and 290° in front of the inner joint region or the inner longitudinal axial edge of the inner material layer and / or that the entry point is located at an outer joint region.

[0006] A hollow tube can also be a drinking straw.

[0007] The method according to the invention produces high-quality hollow tubes. In particular, since the entry point is located in the second area, i.e., in the area where hot melt glue is applied, this area also being a joint area, the hot melt glue already setting during cutting, thus ensuring that the inner material strip is sufficiently firmly bonded to the outer material strip during cutting, there is no risk of the inner material strip detaching from the outer material strip.

[0008] In the variant in which the entry point is positioned between 90° and 290° in front of the inner joint area in the clockwise conveying direction, this ensures that the entry point of the cutting device has a counter-surface, namely the inner material not interrupted by edges. This advantage also applies if the entry point is located in an outer joint area, since the outer joint area is radially offset from the inner joint area.

[0009] According to the invention, the material strips formed into a hollow tube thus have edges arranged longitudinally axially and abutting against each other. The method according to the invention can be carried out, for example, by a device from WO 2021 / 185486 A1, if a knife device or a cutting device is arranged therein that cuts through the hollow tube from above, i.e., has an entry point arranged at the top of a hollow tube.

[0010] The edges of the material strips are butted. This results in a longitudinal axial extension of the butt edge along the manufactured tube and, after cutting to length, along the longitudinal extension of the hollow tube. The butt edges are radially offset from one another. The butt edges define a center point of a butt area. The butt area itself extends transversely to the butt edges over a predeterminable angular range of, for example, at least 10°, in particular at least 20°, in particular at least 30°, in particular at least 40°, in particular at least 50°, up to a maximum of 80° or a maximum of 90°.

[0011] Hot-melt adhesive can be applied between the material strips in one or both of the joint areas. The joint area(s) are preferably coated with hot-melt adhesive over the entire surface or almost the entire surface. Almost the entire surface is understood to mean a surface gluing coverage of at least 80%, particularly preferably at least 90%.

[0012] The other areas of the material strips that are not located in the butt area(s) are preferably coated with a first type of glue as a positional adhesive over their entire surface, but at least approximately over their entire surface. Approximately full-surface gluing means that this area is at least 80%, in particular at least 90%, offset with the first type of glue. The center of the butt areas, or alternatively, the butt edges of the inner material layer and the outer material layer, are preferably radially offset from one another.

[0013] Preferably, an inner joint of the edges of the inner material strip of 0.0 mm is provided and in the case of an outer joint, there are 0.0 mm to 0.4 mm between the edges of the outer material strip.

[0014] The entry point is preferably located between 110° and 270°, in particular 140° and 220°, in the clockwise conveying direction, from the inner butt region or the inner longitudinal edge of the inner material layer. The entry point is preferably located between 180° and 290°, in particular 180° and 270°, in particular 200° and 250°, in the clockwise conveying direction, from the inner butt region or the inner longitudinal edge of the inner material layer. These degrees and the degrees according to the invention are to be understood as the radial distance of the entry point to the inner butt edges or the center of the butt region or the inner edge of the inner material layer.

[0015] Preferably, the exit point of the knife, i.e., the point in the hollow tube that is cut last, is located between 160° and 280° from the entry point in the clockwise conveying direction. In particular, the radial distance is between 180° and 270°, especially between 190° and 260°, especially between 200° and 250°.

[0016] Preferably, the second region is an external butt joint. This ensures, in particular, that the cut begins in an external butt joint, so that the internal material is continuously exposed during the cutting process, thus providing a counter-bearing during the cutting process.

[0017] Preferably, the second area is cooled using a cooling device before cutting. This ensures that the hot melt glue has already set sufficiently by the time of cutting.

[0018] Preferably, hot melt glue is applied to each joint area, or to a joint area and an area where the material layer overlaps. This allows for the production of a very stable hollow tube.

[0019] It is particularly preferred if the hollow tube is reshaped by means of at least one guide roller after leaving the formatting device, in particular before cutting. The at least one guide roller is preferably arranged directly after the formatting device. This makes it possible to reduce the ovality, i.e., the difference between the maximum and minimum diameter of the hollow tube or pipe. Preferably, two or more forming rollers are provided.

[0020] Furthermore, preferably two opposing forming rollers are provided or more forming rollers are provided, which are arranged in particular symmetrically to one another.

[0021] If preferably the at least one forming roller is driven, in particular by a motor, the formatting belt of the formatting device can be protected, since the forming roller pulls on the product and thus relieves the load on the formatting belt.

[0022] Preferably, a forming roller with a concave guideway is provided and / or a guide roller with a flat guideway is provided. Preferably, two opposing forming rollers with a concave guideway are provided.

[0023] When multi-layer material strip tubes with a longitudinal seam are produced in a strand process, a perfectly round shape is usually not achieved. Depending on the seam position and predetermined components, the finished tube will still have slight kinks that affect the ovality. The use of guide rollers significantly improves this ovality. Previously, when the thickness of the format strip decreased or the production speed increased, shape-defining components such as cover strips or a cooling bar had to be repositioned to compensate for kinks. However, this resulted in greater wear on the format strip or a higher thermal load on the cooling bar.The concave forming roller, or preferably two opposing concave forming rollers, have a slightly larger forming radius than the product radius of the hollow tube relative to the concave guideway, but a slightly smaller distance than the product diameter, so that the hollow tube is slightly squeezed as it passes through the two concave forming rollers. This has made it possible to reduce the ovality from, for example, over 0.4 mm to under 0.2 mm. More than two forming rollers can also be arranged asymmetrically or symmetrically around the hollow tube. The rollers can be rotated passively, by friction with the hollow tube, or actively, for example, by a motor.

[0024] The pressure of the forming rollers is preferably set symmetrically to the product axis, i.e. set to the hollow tube axis. In addition, the structure of the surface of the forming rollers that come into contact with the hollow tube can be adapted. For example, it can be roughened, smoothed, perforated and / or slitted. By means of at least one forming roller or at the position of the forming roller, product properties such as the hardness of the hollow tube, the diameter of the hollow tube or an electrical resistance can also be measured. The forming rollers also serve in particular to steady the strand run or the hollow tube run and / or to remove the residual strand, preferably after a machine stop.

[0025] As a further embodiment, a forming roller can also be provided which has a concave running surface and a forming roller which has a flat running surface, for example in order to smooth out longitudinal kinks in the hollow tube, wherein these two forming rollers preferably have parallel axes of rotation.

[0026] The task is further solved by a stranding machine of the tobacco processing industry or the drinking straw industry for the production of hollow tubes, with a format arrangement for Forming a hollow tube from two material strips during longitudinal axial conveyance of the material strips in the format arrangement and with a cutting device for cutting the hollow tube into hollow tubes, wherein the cutting device enters at one entry point of the hollow tube and exits at another point, characterized in that the format arrangement has a first format device which is designed to convey a first material strip longitudinally axially and to form it into a first hollow tube during conveyance, and the format arrangement has a second format device which is arranged behind the first format device in the conveying direction and is designed to wrap a second material strip around the first material strip during longitudinal axial conveyance of the second material strip, so that a double-layer hollow tube is formed which has the first hollow tube on the inside and the second material strip on the outside,or that the format arrangement comprises a format device which is designed to form two material strips which are glued together and arranged offset from one another during longitudinal axial conveyance into a double-layer hollow tube.

[0027] If preferably a forming unit is provided for reshaping the hollow tube, wherein the forming unit is arranged downstream of the format arrangement and upstream of the cutting device, wherein in particular the forming unit is designed in the form of a forming roller or comprises at least one forming roller, the ovality of the hollow tube produced can be significantly improved.

[0028] Preferably, the forming unit comprises two forming rollers arranged opposite one another or more than two forming rollers, which are arranged in particular at the same or different distances from one another in the circumferential direction.

[0029] If preferably at least one forming roller is provided which can be driven in rotation, in particular by a motor, the conveyance of the hollow tube is supported so that particularly high-quality hollow tubes can be produced.

[0030] Preferably, a forming roller with a concave guideway is provided, in particular in the form of a circumferential groove with a rounded groove base, and / or a guide roller with a flat guideway, in particular in the form of a cylindrical roller or in the form of a roller with a circumferential groove with a flat, preferably planar, groove base. This measure enables the production of particularly precisely shaped hollow tubes with low ovality. In particular, the flat guideway can be used to smooth a seam area. A rounded groove base preferably serves to shape the other areas of the hollow tube where there is no seam as round as possible.

[0031] The object of the present invention is to enable a highly stable manufacturing process for hollow tubes, especially drinking straws, while improving the quality of the resulting drinking straws. In particular, the object is to produce hollow tubes or drinking straws that are free of corrugations or smooth.

[0032] One embodiment is a device for producing hollow tubes, in particular drinking straws, comprising a first formatting device which is designed to convey a first material strip longitudinally axially and to form it into a first hollow tube during the conveying process, wherein a second formatting device is provided which is arranged behind the first formatting device in the conveying direction and is designed to wind a second material strip around the first material strip during a longitudinal axial conveying of the second material strip, so that a double-layer hollow tube is formed which has the first hollow tube on the inside and the second material strip on the outside.

[0033] This device efficiently produces a double-layered hollow tube, from which drinking straws or hollow tubes, for example, can be cut to length. The hollow tubes produced in this way feature a longitudinal seam.

[0034] By using two formatting devices arranged one behind the other, a very stable production of hollow tubes with excellent properties is possible. Preferably, the first formatting device and the second formatting device partially overlap. Overlapping is understood in particular to mean that the two formatting devices overlap in the conveying direction, i.e., partially overlap or partially lie side by side. The outlet of the first formatting device is preferably located in the inlet area of the second material strip of the second formatting device.

[0035] Preferably, the first formatting device comprises a first formatting chamber and the second formatting device comprises a second formatting chamber, wherein the first formatting chamber and the second formatting chamber are aligned flush with one another, in particular collinear. This makes it possible in particular for the first material strip formed into a hollow tube to be applied to the second material strip without forming waves. The formatting chambers in the formatting devices are elongated and hollow and serve to accommodate the material strips and to form the material strips into a tube. For this purpose, internal walls are provided which have a decreasing radius of curvature in the conveying direction of the material strips. In this way, a flat or substantially flat material strip can nestle against the inner walls or against a formatting belt which bears against the inner walls and can be increasingly formed into a hollow tube in the conveying direction.

[0036] Preferably, a formatting belt is provided in the second formatting chamber, which runs through the formatting chamber from the beginning of the formatting chamber to the end of the formatting chamber. The first formatting chamber and / or the second formatting chamber preferably have a circular or elliptical cross-section. An elliptical cross-section is understood to mean a non-circular cross-section.

[0037] Preferably, the first formatting device is free of a formatting belt. The first material strip is conveyed by tension acting on the first material strip in the second formatting device. Preferably, each formatting device comprises a lower format and an upper format. The lower format is the part of the formatting device that first comes into contact with the material strip and performs a pre-forming operation. The upper format itself then closes the hollow tube. Thus, in conjunction with the lower format, it ensures complete hollow tube forming.

[0038] Closing the hollow tube specifically means that the two lateral edges of the material strip are placed abutting against each other. This results in a longitudinal axial extension of this butting edge along the finished tube.

[0039] Preferably, the diameter of the first format chamber is smaller than the diameter of the second format chamber, or the diameter of the first format chamber is as large as the diameter of the second format chamber. This refers in particular to the inside diameter, i.e., the diameter of the first format chamber and the diameter of the second format chamber, through which a format belt also runs, whereby the diameter is the diameter from the inside of the format belt to the inside of the opposite upper format.

[0040] This measure of adjusting the diameters ensures that the inner material strip, ie the first material strip, is fed with some tension to the outer material strip.

[0041] Preferably, the first formatting device is arranged with a mirror-image or rotational offset relative to the second formatting device. The rotational offset preferably involves a rotation of 180°.

[0042] For example, the first formatting device has the lower format on top and the upper format on the bottom, and the second formatting device has the lower format on the bottom and the upper format on top. In a mirror offset, the first formatting device is mirrored on a plane relative to the second formatting device. A rotational offset is a rotation. Furthermore, the formatting devices are linearly offset relative to one another, so that the first formatting device is arranged upstream of the second formatting device in the conveying direction of the material strips. In this case, a partial overlap of the formatting devices is preferably provided.

[0043] Preferably, the upper formats of the first format device and the second format device are arranged adjacent to each other.

[0044] Preferably, the contours of the first format chamber and / or the second format chamber are consistently symmetrical. The cross-section of the format chambers is thus symmetrical. This has the advantage that very high-quality hollow tubes can be formed. In particular, very high-quality double-layer hollow tubes can be formed.

[0045] Preferably, a pressing element is provided in the inlet area of the first formatting device, which is designed to press the first material strip into a groove of the first formatting device. The pressing element then presses the first material strip into the groove to preform the first material strip in the groove, which is arranged in the sub-format and belongs to the first formatting chamber. Preferably, the shape of the groove and the shape of the pressing element are complementary on the opposite or adjacent sides.

[0046] Preferably, a roller is provided that is designed to press the first hollow tube onto the second material strip, thus enabling a stable connection between the first material strip, formed into a first hollow tube, and the second material strip. Furthermore, the roller serves to improve the entrainment of the first material strip and the second material strip by the formatting belt in the second formatting device. This measure primarily ensures that the abutting edges of the first material strip remain closed in the first hollow tube.

[0047] Preferably, the first formatting device comprises an inner wall along which the first material strip is guided, wherein the inner wall has a porous structure through which the first formatting chamber of the first formatting device can be pressurized with compressed air.

[0048] The porous structure is in particular integrated into an inner wall of the first format chamber, in particular into an inner wall of the upper format and / or lower format. In particular, the first formatting device comprises an air chamber which supplies the porous structure with compressed air. The compressed air which escapes through the porous structure creates an air cushion between the inner wall and the first material strip. The air cushion significantly reduces the friction between the inner wall and the material strip guided along it. In addition, the material strip is better pre-formed and guided, no heat is generated due to friction, and dust adhesion in this area is reduced. The porous structure is particularly advantageous when the first formatting device is format-belt-free. The air cushion largely eliminates the frictional forces which occur during format-belt-free conveying.

[0049] Preferably, the device comprises a, in particular driven, grooved embossing roller and a pressure roller, which are designed to pass the first material strip between them and to provide it with, in particular longitudinal axial, grooves, wherein in particular a distance between the embossing roller and the pressure roller corresponds to one half to three quarters, in particular substantially two thirds, of a thickness of the first material strip.

[0050] Longitudinal grooves are grooves that extend parallel to the conveying direction of the first material strip. In particular, the embossing roller is arranged upstream of the first formatting device in the conveying direction. The grooves are formed into the first material strip by the embossing roller. The grooves reduce the bending back of the material strip, as the thickness of the material strip is reduced in the areas of the grooves, thus reducing rigidity. The grooves are formed into the material strip in such a way that the material strip is not completely cut through. The grooves facilitate better preforming of the first material strip.In addition, the tension of the first material strip in the first formatting device is supported by the additional drive of the embossing roller, since the first material strip in the first formatting chamber is not only driven by the support on the second material strip, but also by the embossing roller.

[0051] Preferably, a stranding machine for producing hollow tubes, in particular double-layered hollow tubes, in particular drinking straws, comprises a device according to the invention or a further development thereof, which is described above.

[0052] One embodiment discloses a method for producing drinking straws or hollow tubes with the following method steps: longitudinally axially conveying a first material strip through a first format chamber of a first format device, whereby a first hollow tube is formed from the first material strip, gluing a surface of a longitudinally axially conveyed second material strip with an adhesive, applying the first material strip formed into a hollow tube to the glued surface of the second material strip and wrapping the first material strip formed into a hollow tube with the second material strip, whereby the wrapping takes place during longitudinally axial conveyance of the material strips through a second format chamber of a second format device, whereby a double-layer hollow tube is formed, subsequently cutting the double-length hollow tube to length into drinking straws or hollow tubes.

[0053] The process according to the invention allows for the production of very high-quality drinking straws or hollow tubes. Furthermore, a very smooth surface is achieved on both the inside and outside of the straws. Since the second material strip has been previously glued or provided with adhesive, the two material strips are bonded together when the second material strip is wrapped around the first.

[0054] For the purposes of this invention, the terms hollow tube and drinking straw are to be understood as synonymous.

[0055] The second material strip is wound around the first material strip in the second formatting device. The second formatting device preferably has a cooled seam plate or a cooled upper format to enable faster setting of hot glue in the joint area, in particular the seam area, of the double-layer hollow tube. Preferably, the centers of the joint areas or the seam areas, i.e., the edges of the first material strip, are located opposite the edges of the second material strip. The seam areas are preferably offset from one another by 180°.

[0056] Preferably, the surface is glued over its entire surface or essentially over its entire surface, which enables a very reliable bond between the two material strips. Full-surface gluing specifically means that the second material strip is glued across its entire width. The gluing can be interrupted in a short section in the conveying direction to prevent a preferred cutting blade from becoming contaminated with adhesive when cutting the double-layered hollow tube into, for example, drinking straws or hollow tubes. The cutting area is, in effect, spared from the gluing.

[0057] To improve the quality of the produced hollow tube, especially a double-layer hollow tube, the first material strip can be preformed using an elliptical roller. The ellipse is provided in the cross-section of the roller.

[0058] If the first material strip has a first and a second edge that abut within the formed hollow tube, a very high quality of the resulting double-layered hollow tubes, especially drinking straws, is possible. The quality can be further increased if the second material strip has a third and a fourth edge that abut after the first material strip has been wrapped with the second material strip. Particularly stable hollow tubes or drinking straws are possible if the abutting areas of the first material strip and the second material strip are opposite each other.

[0059] The joint area of the first material strip is preferably located between a 4 o'clock and an 8 o'clock position, preferably at a 6 o'clock position. This fixes the edges or edge regions of the first material strip by gluing them to the second material strip at an early stage of the process. This enables the production of very stable hollow tubes or drinking straws. The radial angular distance between the joint areas of the second material strip and the first material strip is preferably 145° and 225°. A radial angular distance of 170° and 190° is preferably provided. A radial angular distance of 180° is particularly preferred.

[0060] The ratio of the width of the second material strip to the width of the first material strip is preferably between 52:48 and 50.5:49.5. The ratio of the widths of the material strips to one another can depend on the diameter of the hollow tube or drinking straw. For example, with an outer diameter of 4.5 mm, the ratio of the widths can be in the range of 51.5:48.5. With an outer diameter of, for example, 5.3 mm, this ratio can be 51.1:48.9, and with an outer diameter of 7.4 mm, this ratio can be 50.5:49.5. Preferably, an inner joint of 0.0 mm is provided between the edges of the first material strip, and an outer joint of 0.0 mm to 0.4 mm is provided between the edges of the second material strip.

[0061] Preferably, the weight of the first and / or second material strip, in the case of paper, is in a range from 27 g / m 2 to 160 g / m 2 , in particular from 120 g / m 2 to 140 g / m 2 . The weight is particularly preferably 130 g / m 2 .

[0062] The thickness of the first and second material strips is preferably in a range from 100 µm to 180 µm, in particular 135 µm to 175 µm, in particular 155 µm. The application thickness of the adhesive, also referred to as positional adhesive, is preferably in a range from 10 µm to 40 µm, in particular 15 µm to 30 µm.

[0063] The width of the material strips can range from 23 mm to 61 mm, depending on the format, and in particular from 24 mm to 48 mm. The material strips can be made of paper or cardboard of the appropriate thickness and weight as specified above. The paper can be colored on one or both sides; patches made of aluminum or other materials can be applied, for example, or the paper can be vapor-coated with a material, such as aluminum lamination. Embossing or printing can also be provided.

[0064] The adhesive can be one or more than one, for example, two types. In particular, a PVA adhesive (polyvinyl acetate adhesive) can be used, and optionally, an additional hot-melt adhesive.

[0065] The manufactured diameter of the double-layered hollow tube is preferably between 4 mm and 10 mm. Preferably, the thickness of the first material strip and the second material strip is between 0.1 mm and 0.18 mm, preferably between 0.15 mm and 0.16 mm. A cold glue or hot glue can be used as the adhesive.

[0066] In the context of the invention, abutting edges of the respective material strip section means that these edges abut one another or are a short distance apart.

[0067] Preferably, the longitudinal axial conveyance of the first material strip through the first formatting chamber and the second formatting chamber takes place in a straight line. A straight line refers to an aligned conveyance of the first material strip or a conveyance without kinks.

[0068] Particularly in the production of hollow tubes, especially drinking straws, the inner tube is formed in such a way that the finished inner tube is placed or inserted coaxially into the outer tube or coaxially onto the outer material strip. This means that the finished material strip of the inner hollow tube no longer needs to be deflected, so that no additional kinks or stresses occur in the material strip, e.g. paper. The contour of a formatting device or the formatting chamber of a formatting device is used to form the material strips. Two formatting devices and two formatting chambers are used here. The inner surface of the formatting chambers represents a transition from a straight line or essentially a straight line to a circle or an ellipse in the conveying direction.

[0069] The inner diameter of the format tube or the first format chamber of the first format device corresponds to the outer diameter of the shaped first hollow tube or inner hollow tube. This creates tension in the material strip, which causes the material strip to adhere to the inner wall of the first format chamber of the first format device and form a round circle or, if the format chamber has an elliptical shape, an ellipse. In the inlet area of the first format device for the inner hollow tube, a hold-down device or a pressing device or a pressing element serves to press the material strip against the wall of the first format chamber. The first and the second format device can be small if they are designed symmetrically, i.e. if the inner walls of the format chambers are symmetrical in cross-section, in particular continuously in cross-section.Symmetrical shaping is possible because the first material strip is not folded over during shaping, but the edges of the first material strip are formed butt-to-butt and preferably the second material strip is not folded over either, but the material edges there too are placed butt-to-butt.

[0070] To keep the first formatting device short, the second material web is preferably deflected by a deflection of a formatting belt of the second formatting device. The deflection can be a deflection roller for the formatting belt.

[0071] In order to improve the roundness of the manufactured inner hollow tube and the ultimately fully manufactured double-layer hollow tube, the first material strip can additionally be pre-formed with an elliptical roller. Preferably, provision is also made for the inner hollow tube to be pressed onto the outer material strip by means of a roller, which can also be designed as a roller, in order to improve the grip of the inner hollow tube. Alternatively, glue can be applied at the same point or in addition to this, using a nozzle, for example, to make the seam of the second material strip even more secure. The invention makes it possible for the inner material strip to not have to be twisted in order to achieve an equally smooth surface on the inside and outside. In addition, process stability, high roundness and a low amount of glue or adhesive are possible.

[0072] Preferably, the upper format of the first format device is divided into two in the longitudinal axial direction, so that two jaws are provided which form part of the first format chamber.

[0073] Preferably, cooling of at least part of the first format device is provided.

[0074] The invention also makes it possible to reduce the occurrence of paper jams during the production of hollow tubes, since the open strand forming areas can be kept short.

[0075] According to the invention, a stranding machine of the tobacco processing industry or the drinking straw industry is provided for producing hollow tubes, wherein the stranding machine is designed and configured to carry out an above-mentioned method according to the invention.

[0076] Preferably, this strand machine is used to carry out a method according to the invention.

[0077] Further features of the invention will become apparent from the description of embodiments of the invention together with the claims and the accompanying drawings. Embodiments of the invention may incorporate individual features or a combination of several features.

[0078] The invention is described below, without limiting the general inventive concept, using exemplary embodiments with reference to the drawings, whereby express reference is made to the drawings for all details of the invention not explained in more detail in the text. They show: Fig. 1 schematically shows a sectional view through a hollow tube to be cut, Fig. 2 a further schematic sectional view through a hollow tube to be cut, Fig. 3 yet another embodiment of a hollow tube to be cut in a schematic sectional view, Fig. 4 a schematic three-dimensional view of an extrusion machine according to the invention, Fig. 5 a further embodiment of an extrusion machine according to the invention, Fig. 6 a schematic three-dimensional view of two forming rollers and Fig. 7 a schematic view of two forming rollers in detail.

[0079] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

[0080] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a repeated presentation is omitted.

[0081] Fig. 1 shows schematically a hollow tube 10 to be cut and the cutting edge 39 which is used for this purpose. In the lower area of the hollow tube 10, i.e. at 6 o'clock, is the entry point 72 of the knife 39 of a cutting device 38. The hollow tube 10 is composed of a first material strip 21.1 and a second material strip 21.2, wherein the first material strip 21.1 is on the inside and the second material strip 21.2 is on the outside. The first material strip 21.1 has two edges 66 which are in abutting relationship and form an inner material layer 63. There is an outer material layer 64 made of the second material strip 21.2, whose edges 66 are also in abutting relationship, but in the Fig. 1 are shown at a distance for better display.

[0082] In the Fig. 1 also shown is a first butt area 71 for the seam area of the edges 66 of the inner material layer and a butt area 70, which is also referred to as the second area. In this area, a hot melt adhesive 62 is provided between the inner and outer material layers for bonding. In the entire first area 81, i.e. the complete circumference with the exception of the second area 82, a first adhesive, which can also be referred to as a positional adhesive 61, is provided. The butt edges in the butt area 71 are located approximately at 12 o'clock and the butt edges in the butt area 70 are located approximately at 6 o'clock. The inner material layer 63 is closed at 6 o'clock. The inner material layer 63 therefore represents a counter-bearing when cut by the knife 39 at the entry point 72, so that the material layers cannot separate from one another at this point.

[0083] In Fig. 2 a slightly different constellation is shown. In this case, the hollow tube itself was manufactured as in WO 2021 / 185486 A1, i.e. the abutting edges of the inner material layer 63 are at 6 o'clock and the abutting edges of the outer material layer are at 12 o'clock. The entry point is again at 6 o'clock. In contrast to WO 2021 / 185486 A1, however, a hot melt adhesive 62 is also provided in the abutting area 71, i.e. where the abutting edges of the inner material layer 63 are located, in addition to the hot melt adhesive 62 in the abutting area 70 at 12 o'clock. This ensures that the inner material layer in the abutting area adheres or sticks better to the outer material layer during cutting.

[0084] Fig. 3 shows yet another constellation. Here, the angle between the entry point 72 of the knife 39 and the butt area 71, i.e. where the edge area of the inner material layer 63 is located, is more than 180° apart, clockwise in the conveying direction. In this case, the angle is 270°. This also means that the inner material layer 63 will not detach from the outer material layer. In this case, a hot melt adhesive 62 is only provided in the butt area 70 of the outer material layer 64. Otherwise, a positional adhesive 61 is provided here. A positional adhesive 61 is also provided in the area of the butt area 71. Alternatively, a hot melt adhesive 62 can also be provided here.

[0085] Fig. 4 shows schematically a device according to the invention, which is slightly modified compared to WO 2021 / 185486 A1.

[0086] Fig. 4 shows a schematic three-dimensional representation of a device according to the invention. A first formatting device 11 is provided, followed by a second formatting device 12 in the conveying direction 20. The first formatting device 11 overlaps the second formatting device 12 in an overlap region 18. The first formatting device 11 has a lower format 50 and an upper format 51.

[0087] The sub-format 50 with the upper format 51 form a Fig. 4 not shown first format chamber 31, which in this embodiment has inner walls that form a circular contour at the latest at the exit of the first format device 11. The sub-format 50 is located in Fig. 1 above the upper format 51. The lower format 50 is divided in two lengthwise. In this embodiment, the upper format 51 is also divided in two lengthwise. The lower format 50 and the upper format 51 can also be formed as a single piece.

[0088] In the inlet area 13 of the first formatting device 11, i.e., where the first material strip 21.1 enters the first formatting device 11, a hold-down device or a pressing element 14 is provided, which presses the first material strip 21.1 into a groove of the upper format 51. There, the pressing element 14 is shown internally pressing on the first material strip 21.1.

[0089] The groove in the lower format 50 preferably begins with a flat surface for receiving the first material strip 21.1 and continuously forms in the conveying direction 20 in the direction of a partial circle or a semicircle. Accordingly, a groove is provided in the upper format 51, which takes up the deformation of the groove of the lower format 50 and forms a second semicircle or remaining partial circle at the end of the first formatting device 11 at the latest, so that the first formatting chamber 31 of the first formatting device 11 has a circular cross-section.

[0090] Alternatively, an elliptical shape can be provided here. With a circular cross-section, a first hollow tube 23 is formed that has a circular cross-section.

[0091] By providing the upper format 51 above the lower format 50, a first hollow tube 23 is formed, which has a lower first edge 41 and a lower second edge 42, which lie abutting.

[0092] The first wrapping material strip 21.1 is pulled through the first formatting device 11 by the latter resting on a second wrapping material strip 22 due to adhesion, preferably static friction or adhesive adhesion. The second wrapping material strip 21.2 is pulled through the second formatting device 12 by a formatting belt 54, which is deflected at the entrance of the second formatting device 12 via a deflection roller 19 and introduced into the second formatting device 12.

[0093] A second material strip 21.2 is thus placed on the formatting belt 54. The second material strip 21.2 is provided with adhesive on surface 16 so that a stable, double-layered hollow tube can be efficiently produced. In the inlet area of the second formatting device 12, the first hollow tube 23 is placed on the second material strip 21.2 and is pulled along in the conveying direction 20 by the conveyance of the second material strip 21.2 by means of the formatting belt 54.

[0094] The second formatting device 12 comprises a lower format 52 and an upper format 53. The lower format 52 is shown here as a single piece, and the upper format 53 as a two-piece piece. The two formatting devices 52, 53 overlap in the overlap area 18.

[0095] Adjacent to the second formatting device 12 may be a seaming plate or a heating device, or a cooling device, depending on the adhesive used. To ensure better grip of the first material strip 21.1, a roller 15, which may also be designed as a cylinder, can press the first hollow tube 23 onto the second material strip 21.2. This is shown in Fig. 2 shown schematically. The format band 54 is then removed (not shown) from the produced double-layer hollow tube 10 and returned to the deflection roller 19. The produced hollow tube 10 can then be cut or shortened into appropriately long hollow tubes. This allows drinking straws to be produced very efficiently.

[0096] In addition to WO 2021 / 185486 A1, the cutting device 38 with the blades 39 is now provided according to the invention to act from above on the hollow tube 10. This results in the constellation of Fig. 1 , namely an entry point 72 of the knife 39 in the region of the longitudinal seam of the outer material strip 61, ie, in the joint area 70 or second area 82.

[0097] Fig. 5 shows schematically another strand machine 5 according to the invention in a schematic view.

[0098] A correspondingly wide base material strip 24 is drawn off a reel (not shown) in the conveying direction 34 and guided over rollers 41. A cutting device 23 is connected to a material strip feed device 22. In the cutting device 23, the base material strip 24 is cut longitudinally. The cutting device 23 is a longitudinal cutter.

[0099] The cut material strips in the form of a first material strip 25 and a second material strip 26 are conveyed in parallel over a further deflection roller 41, and are then separated from each other by a cross conveyor 32 in the form of a deflection roller. After a further deflection, the second material strip 26 is essentially completely glued, at least over its entire length, by means of a gluing device 27'. This gluing device 27' can, for example, omit the area of a seam, but this is not necessarily required.

[0100] The first material strip 25 is conveyed separately from the second material strip 26 and offset transversely to the conveying direction by means of the offsetting device 29, so that in the pair of pull rollers 28, by means of which the first material strip 25 is joined to the second material strip 26, an offset lying of the material strips 25 and 26 is achieved. The material strips are arranged, for example, at this point as shown in Fig. 1 shown schematically.

[0101] Subsequently, a heating device 35 is provided, by means of which the applied glue or the applied adhesive 17 is pre-cured. In another embodiment, however, a cooling device (not shown here) can also be used if the setting of the glue or the adhesive 17 requires a reduction in temperature, for example when using hot melt glue. A variant without a heating device or cooling device is also possible. In the event that seam gluing has already taken place, the superimposed material strips 25 and 26 are fed to a formatting device 30. If the seam gluing has not yet taken place, this takes place by means of the seam gluing device 36, which is arranged between the heating device 35 and the formatting device 30.

[0102] In the formatting device, the inlet finger 44 presses the material strips downwards onto the formatting belt 43, which is guided endlessly through the formatting device 30 via corresponding deflection rollers 41.

[0103] In the formatting device, the material strips are formed into a round or oval shape in a known manner. The upper format is designed as a heated upper format 37 to further cure the glue or adhesive 17. In another embodiment, however, a cooled upper format can also be used if a temperature reduction is required for the curing of the glue or adhesive 17.

[0104] Subsequently, double-layered tubes of the desired length can be cut from the strand 31 thus formed by means of the cutting device 38.

[0105] The gluing device 27 and the seam gluing device 36 can be designed as flat nozzles, spin-spray nozzles, or according to EP 2 974 798 A1. Here, a flat application of adhesive or glue is preferably carried out.

[0106] The heating device 35 can be provided optionally. It essentially serves to precure or pre-harden the adhesive.

[0107] To precisely align the paper webs relative to each other, especially to set the correct offset across the width, appropriate sensors can be provided to detect the position of the edges of the material strips. Appropriate control mechanisms can then be provided to regulate the relative position of the material strips.

[0108] The gluing devices 27 and 27' can be offset from each other transversely axially in the conveying direction to allow different areas of the positional adhesive on the material strip 26. The gluing device 36 for the hot melt adhesive can also consist of two gluing devices or comprise two gluing devices in order to be able to apply hot melt adhesive at two different locations, for example, to glue two joint areas with hot melt adhesive.

[0109] The transverse adjustment device 60 can be arranged to produce a hollow tube 10 as shown in Fig. 3 is shown. Viewed in the conveying direction, the joint area 71 of the inner material layer 63 is at 3 o'clock and the joint area of the outer material layer 64 is at 12 o'clock.

[0110] In comparison to the prior art, viewed clockwise in the conveying direction, the joint area of the inner material layer is not located in front of the joint area of the outer material layer, but rather downstream, which in itself represents a preferred embodiment according to the invention.

[0111] Fig. 6 shows a schematic three-dimensional representation of the post-forming of the hollow tube 10 or 31. In this exemplary embodiment, two opposing forming rollers 90 and 91 are provided, each having a concave guideway 94. The radius of the concave guideway 94 is preferably slightly larger than the radius of the hollow tube 10 or 31. In addition, the distance between the forming rollers 90 and 91 or the guideways 94 at the apex is set such that it is slightly smaller than the diameter of the hollow tube 10 or 31. This enables post-forming.

[0112] Fig. 7 shows a schematic view of a section of a device by means of which the hollow tube 10 or 31 can be reshaped, especially when a longitudinal seam is arranged at the bottom. Fig. 7 from the direction in which the hollow tube 10 or 31 is conveyed. A forming roller 90 with a concave guideway 94 is provided at the top, and a forming roller 92 with a flat guideway 95 is provided below. This very efficiently smooths out a kink in the hollow tube 10 or 31. The forming rollers 90 and 92 are attached to the holder 93.

[0113] All mentioned features, including those revealed solely in the drawings as well as individual features disclosed in combination with other features, are considered essential to the invention, both individually and in combination. Embodiments according to the invention may be fulfilled by individual features or a combination of several features. Bezugszeichenliste

[0114] 5Strand machine 10Hollow tube 11First format device 12Second format device 13Starting area 14Pressing element 16Surface 18Overlap area 19Deflection roller 20Conveying direction 21.1First material strip 21.2Second material strip 22Material strip feed device 23Cutting device 24Base material strip 25First material strip 26Second material strip 27, 27`Gluing device 28Pair of pull rollers 29Offset device 30Formatting device 31Hollow tube 32Cross conveyor 34Conveying direction 35Heating device 36Seam gluing device 37Upper format 38Cutting device 39Knives 41Deflection roller 43Format belt 44Inlet fingers 50Lower format 51Upper format 52Lower format 53Upper format 54Format tape 59Edge sensor 60Cross adjustment device 61Position adhesive 62Hot melt glue 63Inner material layer 64Outer material layer 66Edge 70Joint area 71Joint area 72Entry point 81First area 82Second area 90Forming roller 91Forming roller 92Forming roller 93Bracket 94Guide track 95Guide track

Claims

1. A method for producing hollow tubes for the tobacco processing industry or drinking straws, comprising the following method steps: - forming a hollow tube (10, 31) from two material strips (21.1, 21.2, 25, 26) during a longitudinal axial conveyance of the material strips (21.1, 21.2, 25, 26) in a formatting device (11, 12, 30), wherein the hollow tube (10, 31) has an inner material layer (63) and an outer material layer (64), wherein the longitudinal axial edges of one material layer (63, 64) are in abutting relationship and the other material layer (63, 64) is designed to overlap and is offset from the abutting longitudinal axial edges, or wherein the longitudinal axial edges (66) of the inner material layer (63) and the outer material layer (64) are in abutting relationship, whereby two abutting regions (70, 71) are defined, which are offset from each other, - whereby the material strips (21.1, 21.2, 25, 26) are glued in a first region (81) with a first type of glue (61) and in at least one second region (82) a second type of glue (62) is provided for gluing, wherein the second type of glue (62) is a hot melt glue and wherein the second region (82) is a butt region (70, 71) or a region in which the inner material layer (63) is designed to overlap, - wherein the hollow tube (10, 31) is cut into hollow tubes by means of a cutting device (38, 39), wherein the cutting device (38, 39) enters at an entry point (72) of the hollow tube (10, 31) and exits at another point, . characterized in thatthe entry point (72) is provided in the second region (82) and / or that the entry point (72) is located in the conveying direction (20, 34) of the hollow tube (10, 31) clockwise between 90° and 290° in front of the inner butt region (71) or the inner longitudinal axial edge (66) of the inner material layer (63) and / or the entry point (72) is located on an outer butt region (70).

2. Method according to claim 1, characterized in that the second region (82) is an external impact region (70).

3. Method according to claim 1 or 2, characterized in that the second region (82) is cooled by means of a cooling device (37) before cutting.

4. Method according to one of claims 1 to 3, characterized in that hot melt glue (62) is provided in each joint area (70, 71) or in a joint area (70, 71) and an area in which the material layer overlaps.

5. Method according to one of claims 1 to 4, characterized in thatthe hollow tube (10, 31) is reshaped after leaving the formatting device (11, 12, 30) by means of at least one forming roller (90, 91, 92), this being done in particular before the hollow tube (10, 31) is cut into hollow tubes.

6. Method according to claim 5, characterized in that two opposing forming rollers (90, 91, 92) are provided or more than two forming rollers (90, 91, 92) are provided.

7. Method according to claim 5 or 6, characterized in that at least one forming roller (90, 91, 92) is or will be driven, in particular by a motor.

8. Method according to one of claims 5 to 7, characterized in that a forming roller (90, 91, 92) with a concave guide track (94) is provided and / or a guide roller (92) with a flat guide track (95) is provided.

9. A rod-making machine (5) of the tobacco processing industry or the drinking straw industry for producing hollow tubes, wherein the rod-making machine (5) is designed and configured to carry out a method according to one of claims 1 to 8.

10. Use of a strand machine (5) according to claim 9 for carrying out a method according to one of claims 1 to 8.

11. A rod-forming machine (5) of the tobacco processing industry or the drinking straw industry for producing hollow tubes, comprising a format arrangement (11, 12, 30) for - forming a hollow tube (10, 31) from two material strips (21.1, 21.2, 25, 26) with a longitudinal axial conveyance of the material strips (21.1, 21.2, 25, 26) in the format arrangement (11, 12, 30) and comprising a cutting device (38, 39) for - cutting the hollow tube (10, 31) into hollow tubes, wherein the cutting device (38, 39) enters at an inlet point (72) of the hollow tube (10, 31) and exits at another point, characterized in thatthe format arrangement (11, 12, 30) has a first format device (11) which is designed to convey a first material strip longitudinally axially and to form it into a first hollow tube during the conveying, and the format arrangement (11, 12, 30) has a second format device (12, 30) which is arranged behind the first format device (11) in the conveying direction and is designed to wind a second material strip around the first material strip during a 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, or that the format arrangement (11, 12, 30) has a format device (30) which is designed to form two material strips which are glued to one another and arranged offset from one another into a double-layered hollow tube during a longitudinal axial conveying.

12. Strand machine (5) according to claim 11, characterized in thata forming unit is provided for reshaping the hollow tube (10, 31), wherein the forming unit is arranged downstream of the format arrangement (11, 12, 30) and upstream of the cutting device (38, 39), wherein in particular the forming unit is designed in the form of a forming roller (90, 91, 92) or comprises at least one forming roller (90, 91, 92).

13. Strand machine (5) according to claim 11 or 12 characterized in that the forming unit has two forming rollers (90, 91, 92) arranged opposite one another or has more than two forming rollers (90, 91, 92), which are arranged in particular at the same or different distances from one another in the circumferential direction.

14. Strand machine (5) according to claim 12 or 13, characterized in that at least one forming roller (90, 91, 92) is provided so as to be rotatably driven, in particular by a motor.

15. Strand machine (5) according to one of claims 12 to 14, characterized in thata forming roller (90, 91, 92) with a concave guide track (94) is provided, in particular in the form of a circumferential groove with a rounded groove base and / or a guide roller (92) with a flat guide track (95), in particular in the form of a cylindrical roller or in the form of a roller with a circumferential groove with a flat, preferably planar, groove base.

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