Method and device for producing a fiber web

Abstract

A device (1) for producing a fibrous web is proposed, comprising a headbox (10) with a vortex chamber (3) and an equalizing device (11) for uniformly introducing a fibrous suspension into the vortex chamber (3), wherein the equalizing device (11) for introducing the fibrous suspension in a stream (A) has a plurality of hoses (9), pipes and / or bores of equal length, each with an inlet (8) on a feed side (4) of the vortex chamber (3), wherein a guide side (5) is arranged opposite the feed side (4) in such a way that a stagnation point flow of the stream (A) is created, wherein the stream (A) is divided into a partial stream (B) and a further partial stream (C). A method for producing a fibrous web is also proposed.

Description

[0001] The invention relates to a method and a device for producing a fiber web.

[0002] Methods for producing a fiber web are known from the prior art. The so-called wet-laid process is frequently used, in which an aqueous fiber suspension is laid to form a nonwoven web. A nonwoven within the meaning of the present invention is also referred to as a nonwoven. One difficulty in producing nonwoven webs from aqueous fiber suspensions is the occurrence of basis weight fluctuations due to local differences in the amount of laid fibers. Reasons for this can be, for example, pulsations from the headbox or uneven flow conditions. In particular, the piling of fibers to form fiber flakes in the fiber suspension and the deposition of the fiber flakes leads to poor formation values ​​of the end product, which is perceived by the customer as an uneven structure.

[0003] Considerable technical effort is required to prevent floc formation. Moving elements, such as perforated rollers, are used to break up fiber flocs. Stationary elements are also used for this purpose. For example, tube bundles with diffusers are provided, through which the fiber suspension flows. Strong turbulence with high shear rates develops within the tube bundles, leading to the fibers in the fiber suspension being separated. The fiber suspension is then accelerated in nozzles, which dampens the turbulent movement and thus produces a smoother fiber pattern in the final product.

[0004] A disadvantage of the state of the art is that the division of the flow of the fiber suspension caused by the tube bundles leads to an uneven basis weight distribution transverse to the flow direction of the fiber suspension, which is reflected as streaks in the final product.

[0005] It is an object of the present invention to provide a device and a method for producing a fiber web, by means of which the described disadvantages are prevented and which enable a very uniform deposition of the fibers of the fiber suspension, in particular while avoiding streak formation.

[0006] This problem is solved by the subject matter of claim 1 and by the subject matter of claim 15.

[0007] The device according to the invention for producing a fibrous web comprises a headbox with a vortex chamber. A homogenizing device of the device ensures uniform introduction of the fibrous suspension into the vortex chamber. The fibrous suspension is introduced into the vortex chamber in a stream via a plurality of preferably equally long hoses, pipes and / or bores, each with an inlet on an inlet side of the vortex chamber. The use of the homogenizing device in conjunction with the plurality of equally long hoses, pipes and / or bores ensures that the fibrous suspension is introduced into the vortex chamber in a manner that is disjoint in several parts but, on average, uniform over a relatively large distance transverse to the direction of the flow. A guide side of the vortex chamber is arranged opposite the inlet side. The inlets on the inlet side are arranged such that the flow is directed towards the guide side.This creates a stagnation point flow, dividing the flow into one sub-stream and another sub-stream. The transition into the vortex chamber and from the stream to the sub-streams introduces a high degree of kinetic energy into the fiber suspension, allowing the fibers to be separated by sufficiently high shear forces and turbulence, thus breaking up the geometric pattern initially introduced through the inlets. The movement of the fiber suspension appears mushroom-shaped in the area of ​​the stagnation point flow, ensuring good mixing and further homogenization. Typically, one or more laminar and non-laminar vortices form, which can extend dominantly across the entire width or length of the vortex chamber or be locally limited.The interaction of these vortices with each other and the resulting mixing of the fibers in the pulp suspension leads to a uniform fiber distribution. In particular, large-scale transverse vortices occur, which ensure a uniform fiber concentration in the transverse direction and thus prevent the formation of longitudinal stripes. The energy introduced into the pulp suspension corresponds at most to the Carnot shock loss during an abrupt transition of 90°.

[0008] In addition to the aforementioned advantages with regard to strip formation, a particularly advantageous feature of the device according to the invention is that it requires significantly fewer components than a conventional device for producing a fiber web, making it more cost-effective and less space-consuming. In particular, no diffusers or moving components for breaking up fiber flakes are required.

[0009] Preferably, the fiber suspension is introduced into the vortex chamber along an inflow direction. Preferably, the feed side is arranged at an angle of 45° to 135° to the inflow direction.

[0010] It is conceivable that the inlets have enlarged or reduced cross-sections. It is also conceivable that the inlets are chamfered. This makes it possible to adapt the flow velocity to the conditions in the vortex chamber and the physical parameters of the fiber suspension.

[0011] It is also conceivable for the headbox, especially the inlets, to have supply lines for diluting the fiber suspension. This advantageously makes it possible to locally adjust the fiber content of the fiber suspension and thus the basis weight.

[0012] Preferably, the fiber suspension comprises fibers made of viscose and / or lyocell and / or natural fibers and / or recycled fibers and / or synthetic fibers and / or inorganic fibers such as glass fibers and / or man-made fibers and / or fibers made of pulp, northern (bleached) softwood pulp, and / or southern (bleached) softwood pulp. It is conceivable that the fiber suspension comprises 10-100% man-made fibers.

[0013] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0014] According to a preferred embodiment of the present invention, a termination side is arranged between the feed side and the guide side. An outlet side for discharging the fibers from the vortex chamber is arranged opposite the termination side. This enables advantageous guidance of the partial flows through the vortex chamber to the outlet side.

[0015] Preferably, the leading side has a curved impact region for redirecting the flow and / or the terminal side is at least partially curved for redirecting the fiber suspension. The curvature forces movement of the fiber suspension in all directions. This generates high shear rates, resulting in excellent singulation and mixing of the fibers. In the context of the present invention, curved means that the surface is curved. The surface is in particular the surface of the leading side or terminal side facing the interior of the vortex chamber. Particularly preferably, the flow impacts the leading side or terminal side at a transition from a non-curved region of the leading side or terminal side to a curved region of the leading side or terminal side. This is particularly effective, increases the shear rates in the vortex chamber, and prevents dead spaces.

[0016] In particular, a partial flow is directed along the feed side to the outlet side. By splitting the flow of the fiber suspension opposite the feed side and diverting it along the feed side to the outlet side, dead zones in the vortex chamber and thus the formation of fiber flakes in the vortex chamber are avoided.

[0017] According to a further preferred embodiment of the present invention, a shear rate of at least 10 1 / sec and preferably at least 50 1 / sec and in particular at least 100 1 / sec is generated in the vortex chamber. This ensures optimal separation and mixing of the fibers upon exiting the vortex chamber. Furthermore, the distribution of the exit velocity of the fiber suspension in the MD direction along the CD direction is very uniform and has deviations of preferably less than 5% and particularly preferably less than 2.5%. A deviation in velocity within the meaning of the present invention is calculated as: (maximum velocity - minimum velocity) / average velocity. A particular advantage is also an isotropic fiber orientation upon exiting the vortex chamber.These advantages make it particularly easy to specifically adjust different strengths of the fiber web in the MD and CD directions. In particular, it is possible to achieve very high strengths in the CD direction.

[0018] MD direction in the sense of the present invention is the direction in the machine direction. CD direction in the sense of the present invention is the direction transverse to the machine direction.

[0019] According to a preferred embodiment of the present invention, the end side is at least partially curved. This allows the partial flow to be advantageously directed to the feed side. Sedimentation on the sides is thus avoided.

[0020] According to a further preferred embodiment of the present invention, the distance between the feed side and the guide side decreases toward the outlet side, or the feed side is at least partially arranged such that the distance between the feed side and the guide side decreases toward the outlet side. By reducing the distance, the fiber suspension is accelerated toward the outlet side, which promotes a particularly advantageous exit of the fiber suspension from the vortex chamber. Furthermore, the turbulence in the fiber suspension is dampened before deposition, resulting in a more stable structure in the final product.

[0021] Particularly preferably, the feed side and the guide side enclose a first chamber angle. The first chamber angle is between 10° and 45°, and preferably between 15° and 25°. This results in optimal outflow of the fiber suspension from the vortex chamber.

[0022] Furthermore, it is preferably provided that the feed side and the end side enclose a second chamber angle. The second chamber angle is between 90° and 150°, and preferably between 100° and 120°. This advantageously ensures high shear rates in the region of the end side.

[0023] It is conceivable for the headbox to have a rear wall, with an outlet gap being formed between an underside of the headbox and the rear wall. The underside preferably adjoins the guide side of the vortex chamber and is in particular arranged parallel to the guide side of the vortex chamber. However, it is also conceivable for the underside and the guide side to be arranged at an angle to one another. The rear wall is arranged directly adjacent to the feed side. Preferably, an outlet gap angle between the rear wall and the underside is adjustable. For this purpose, it can be provided that the rear wall is adjustable in its distance and / or angle to the underside, in particular rotatable about a pivot joint.

[0024] Furthermore, it is preferably provided that the fiber suspension leaves the outlet gap along an outlet direction, and that an angle between the outlet direction and a belt on which the fiber suspension is deposited is adjustable. For this purpose, it is provided, in particular, that the vortex chamber is rotatable with its underside, or that the underside is rotatable about an axis arranged orthogonally to the outlet direction.

[0025] According to a further preferred embodiment of the present invention, several inlets arranged in a row are provided on the feed side. Preferably, several inlets arranged in two rows are provided on the feed side. The fiber suspension is thus fed to the vortex chamber through several individual sections. It is conceivable that the inlets are connected to a circular distributor, central distributor, or cross-flow distributor via the hoses, pipes, and / or bores.

[0026] Preferably, the inlet has a diameter of 5 mm to 100 mm, preferably 10 mm to 60 mm, and in particular 15 to 25 mm. It is conceivable that each of the inlets has a diameter of 5 mm to 100 mm, preferably 10 mm to 60 mm, and in particular 15 to 25 mm.

[0027] According to a further preferred embodiment of the present invention, the headbox has no open edges, in particular no inlet openings for diffusers, perforated rollers, and / or louvres. This ensures that the device is very cost-effective, low-maintenance, and space-saving.

[0028] Alternatively, the headbox is preferably provided with a diffuser. This advantageously allows for multi-stage swirling of the fiber suspension.

[0029] According to a further preferred embodiment of the present invention, the device comprises a belt onto which the fiber suspension is deposited after passing through the vortex chamber. The belt is, in particular, a screen belt. Preferably, the device comprises means for dewatering the fiber suspension immediately after it has been deposited on the belt. The means for dewatering the fiber suspension can, for example, comprise suction boxes arranged beneath the belt and acting on the fiber suspension through the belt, and / or suction drums. It is further conceivable that the device comprises means for depositing a further fiber layer onto the belt, the headbox being arranged such that the fiber suspension is deposited onto the further fiber layer. It is conceivable that the further fiber layer comprises carded fibers.In particular, it is conceivable for the device to comprise a carding machine for carding the fibers of the additional fiber layer. It is also conceivable for the additional fiber layer to be wet-laid and for the device to have an additional headbox for this purpose. All features and details relating to the headbox also apply to the additional headbox.

[0030] In particular, the device is intended for use with an inclined screen, with the screen belt preferably encompassing the inclined screen. However, it is also conceivable that the device is intended for use with a fourdrinier screen.

[0031] A further object of the present invention to achieve the aforementioned object is a method for producing a fiber web, wherein a fiber suspension is introduced into a vortex chamber of a device according to the invention. The flow of the fiber suspension is divided in the vortex chamber into a partial flow and a further partial flow. The fiber suspension is then discharged at the outlet side of the vortex chamber.

[0032] In particular, it is intended that a shear rate of at least 10 1 / sec, preferably at least 50 1 / sec, and especially at least 100 1 / sec, is generated throughout the entire vortex chamber. This ensures optimal separation and mixing of the fibers of the fiber suspension upon exiting the vortex chamber.

[0033] Preferably, the fiber suspension is introduced into the vortex chamber in one stream, and the stream is divided into a partial stream and a further partial stream at the leading end and then redirected. The further partial stream flows along the leading end toward the outlet side, and the partial stream flows along the end side to the feed side and along the feed side toward the outlet side. This eliminates dead spaces. High shear rates prevail throughout the vortex chamber.

[0034] In particular, it is intended that the fiber suspension, after leaving the vortex chamber, is deposited on an inclined screen or a fourdrinier screen and / or on another fiber layer.

[0035] All details, features and advantages previously disclosed in connection with the device according to the invention also relate to the method according to the invention and vice versa.

[0036] Further details, features, and advantages of the invention will become apparent from the drawings and the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the scope of the invention.

[0037] They show: Fig. 1: a schematic view of a device according to an exemplary embodiment of the present invention and of a method device according to an exemplary embodiment of the present invention, Fig. 2: a schematic view of a detail of a device according to an exemplary embodiment of the present invention, Fig. 3: a schematic view of a detail of a device according to an exemplary embodiment of the present invention and Fig. 4: a schematic view of a detail of a device according to an exemplary embodiment of the present invention.

[0038] The Fig. 1, Fig. 2, Fig. 3 and Fig. 4 each show a schematic view of a device 1 according to an exemplary embodiment of the present invention and details of a device 1 according to an exemplary embodiment of the present invention in a schematic view. The device 1 is a device 1 for producing a fiber web (not shown) according to the wet-laying process. In the wet-laying process, a fiber suspension is deposited on a belt 13, for example a screen belt. This can happen directly, so that the fiber suspension lies directly on the belt 13. However, the fiber suspension can also be deposited on another fiber layer (not shown here), which is already lying on the belt 13.

[0039] The fiber suspension is a mixture of water and fibers, for example natural or synthetic fibers. Lying on the belt 13, the fiber suspension is dewatered using dewatering means 14, for example suction boxes. The fibers can consist of viscose and / or lyocell. It is conceivable that the fibers are natural fibers and / or recycled fibers and / or synthetic fibers and / or inorganic fibers such as glass fibers and / or man-made fibers and / or fibers from pulp, northern (bleached) softwood pulp and / or southern (bleached) softwood pulp. It is conceivable that the fiber suspension contains 10 - 100% man-made fibers.

[0040] The device 1 has a homogenizing device 11, from which the fiber suspension is fed to a vortex chamber 3 via a plurality of hoses 9 of equal length, alternatively or additionally via pipes or bores. The homogenizing device 11 can, for example, comprise a circular distributor, a central distributor, or a transverse distributor. The hoses 9 are each connected to the vortex chamber 3 via an inlet 8 such that the fiber suspension flows into the vortex chamber 3 in a stream A at an inlet side 4 of the vortex chamber 3. The inlets 8 are preferably connected in one or more rows (not shown), which here extend orthogonally to the plane of the page. The inlet 8 and preferably all inlets have a diameter of 10 mm to 100 mm.

[0041] A guide side 5 of the vortex chamber 3 is arranged opposite the feed side. The flow A is directed towards the guide side 5, so that a stagnation point flow occurs and thus a division of the flow A into a partial flow B and a further partial flow C.

[0042] When the fiber suspension enters the vortex chamber 3 and the flow A is divided, high shear forces and turbulence occur, which separate and mix the fibers of the fiber suspension. This breaks up fiber flakes, which leads to a more uniform basis weight of the fiber web. Furthermore, transverse turbulence occurs in the vortex chamber 3. The transverse turbulence mixes the fibers, particularly in the CD direction, thereby avoiding longitudinal stripes that would otherwise have been caused by the juxtaposition of the disjoint inlets 8.

[0043] To maintain high shear forces in the vortex chamber 3, the incoming stream A of the fiber suspension first encounters an impact area 5' of a guide side 5 opposite the feed side 4. At the impact area 5', the stream A is split into partial stream B and the further partial stream C and diverted. The guide side 5 and the feed side 4 are connected by a terminal side 6. The guide side 5 and / or the terminal side 6, preferably the guide side 5 and the terminal side 6, have a bend. Partial stream B flows from the impact area 5' along the bend past the terminal side 6. Subsequently, the partial stream B is directed along the feed side 4 to an outlet side 7. The outlet side 7 is arranged opposite the terminal side 6. High shear forces are maintained throughout the vortex chamber 3 so that the separated fibers do not form flocs again.For this purpose, the device 1 is designed to generate a shear rate of at least 10 1 / sec, preferably at least 50 1 / sec, and in particular at least 100 1 / sec, throughout the vortex chamber 3. Adjacent to the outlet side 7 is an outlet gap 16 formed by a rear wall 12 of the headbox 10 and a bottom side 15 of the headbox 10. The fiber suspension is deposited onto the belt 13 through the outlet gap 16.

[0044] The end face 6 is partially curved and connects with a flowing contour to the curved impact area 5' of the guide face 5. The feed face 4 and the guide face 5 are not arranged parallel to one another. Rather, the distance between the feed face 4 and the guide face 5 decreases towards the outlet face 7. The feed face 4 and the guide face 5 form a first chamber angle α of 15° to 25°. The reduction in the distance between the guide face 5 and the feed face 4 towards the outlet face 7 causes the fiber suspension to accelerate on its way to the outlet gap. To increase the shear rates, the feed face 4 and the end face 6 form a second chamber angle β of 100° to 120°.

[0045] The outlet gap, in particular an outlet gap angle γ between the rear wall 12 and the underside 15, is adjustable by connecting the rear wall 12 to a pivot joint 17. Using a rocker 18, the rear wall can be rotated on the pivot joint about a rotation axis, which is arranged orthogonally to the paper plane in this case. This allows the outlet gap angle γ, and thus the outlet gap, to be increased or decreased as required.

[0046] In its described configuration, the outlet gap 16 serves to dampen the turbulence generated in the vortex chamber 3. This makes it possible to achieve a very uniform fiber distribution in the produced fiber web. List of reference symbols: 1 device 3 vortex chamber 4 Feed side 5 Home page 5' impact area 6 Final page 7 Exhaust side 8 Entrance 9 Hose 10 Headbox 11 Harmonization device 12 Rear wall 13 volumes 14 Dehydrating agents 15 Bottom 16 Outlet gap 17 Swivel joint 18 swing A current BC partial flow further partial flow γ outlet gap angle

Claims

[1] Device (1) for producing a fiber web, comprising a headbox (10) with a vortex chamber (3) and an equalizing device (11) for uniformly introducing a fiber suspension into the vortex chamber (3), wherein the equalizing device (11) for introducing the fiber suspension in a stream (A) is provided with a plurality of hoses (9), pipes and / or bores, each with an inlet (8) on a feed side (4) of the vortex chamber (3), wherein a guide side (5) is arranged opposite the feed side (4) in such a way that a stagnation point flow of the stream (A) is created, wherein the stream (A) is divided into a partial stream (B) and a further partial stream (C). [2] Device (1) according to claim 1, characterized bythat a closing side (6) is arranged between the feed side (4) and the guide side (5), wherein an outlet side (7) for discharging the fiber suspension from the vortex chamber (3) is arranged opposite the closing side (6). [3] Device according to one of the preceding claims, characterized by that the guide side (5) has a curved impact area (5') for diverting the flow (A) and / or the end side (6) is at least partially curved for diverting the fiber suspension. [4] Device (1) according to one of the preceding claims, characterized by that a shear rate of at least 10 1 / sec and preferably at least 50 1 / sec and in particular at least 100 1 / sec is generated in the vortex chamber (3). [5] Device (1) according to one of claims 2 to 4, characterized by that the end side (6) is at least partially curved. [6] Device (1) according to one of claims 2 to 5, characterized by that the distance between the feed side (4) and the guide side (5) becomes smaller towards the outlet side (7) or that the feed side (5) is at least partially arranged such that the distance between the feed side (4) and the guide side (5) becomes smaller towards the outlet side (7). [7] Device (1) according to one of the preceding claims, characterized by that the feed side (4) and the guide side (5) enclose a first chamber angle (α), wherein the first chamber angle (α) is between 10° and 45°, wherein the first chamber angle (α) is preferably between 15° and 25° and / or that the feed side (4) and the end side (6) enclose a second chamber angle (β), wherein the second chamber angle (β) is between 90° and 150°, wherein the second chamber angle (β) is preferably between 100° and 120°. [8] Device (1) according to one of the preceding claims, characterized bythat a plurality of inlets (8) arranged in a row are provided on the feed side (4), wherein the inlets (8) are preferably spaced apart from one another by 20 mm to 100 mm, wherein a plurality of inlets (8) arranged in two rows are preferably provided on the feed side (4). [9] Device (1) according to one of the preceding claims, characterized by that the inlet (8) has a diameter of 5 mm to 100 mm and preferably of 10 mm to 30 mm and in particular of 15 mm to 25 mm. [10] Device (1) according to one of the preceding claims, characterized by that the headbox has no open edges, in particular no inlet openings of diffusers, perforated rollers and / or slats. [11] Device (1) according to one of claims 1 to 9, characterized by that the headbox (10) has a diffuser. [12] Device (1) according to one of the preceding claims, characterized bythat the device (1) has a belt (13) on which the fiber suspension is deposited after passing through the vortex chamber (3), wherein it is preferably provided that the device (1) has means for dewatering (14) the fiber suspension immediately after it has been deposited on the belt (13), wherein it is preferably provided that the device (1) has means for depositing a further fiber layer on the belt (13), wherein the headbox (10) is arranged such that the fiber suspension is deposited on the further fiber layer. [13] Device (1) according to one of the preceding claims, characterized by that the device (1) is intended for use with an inclined sieve (9). [14] A method for producing a fiber web, wherein a fiber suspension is introduced into a vortex chamber (3) of a device (1) according to one of the preceding claims, wherein the flow (A) of the fiber suspension is divided in the vortex chamber (3) into a partial flow (B) and a further partial flow (C), and wherein the fiber suspension is discharged at the outlet side (7) of the vortex chamber (3). [15] Method according to claim 14, characterized by that a shear rate of at least 10 1 / sec, preferably at least 50 1 / sec and in particular at least 100 1 / sec is generated in the entire vortex chamber (3). [16] Method according to one of claims 14 to 15, characterized bythat the flow (A) is divided and diverted on the guide side (5) into the partial flow (B) and the further partial flow (C), wherein the further partial flow (C) flows along the guide side (5) in the direction of the outlet side (7), wherein the partial flow (A) flows along the end side (6) to the feed side (4) and along the feed side (4) in the direction of the outlet side (7). [17] Method according to one of claims 14 to 16, wherein the fibrous suspension is deposited on an inclined screen or a fourdrinier screen or a fiber layer after leaving the vortex chamber (3).

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