DEVICE FOR PRODUCING A FIBROUS WEB

[0001] This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2023/083641, filed on Nov. 30, 2023 and which claims benefit to German Patent Application No. 10 2022 131 868.0, filed on Dec. 1, 2022. The International Application was published in German on Jun. 6, 2024 as WO 2024/115620 A1 under PCT Article 21 (2).

[0002] The present invention relates to a device for producing a fibrous web, the device having a headbox which comprises a mixing chamber. The mixing chamber comprises an outlet which is provided for discharging a fibrous material suspension.

[0003] Devices for producing a fibrous web are known from the prior art. Headboxes comprising mixing chambers with outlets for discharging a fibrous material suspension are found, for example, in paper machines. The mixing chamber is typically supplied with the fibrous material suspension via a central distributor, a transverse distributor, or other feeds. The mixing chamber is used to transfer the fibrous material suspension to a subsequent machine portion for further processing. It is conceivable that the fibrous material suspension is diverted by the mixing chamber so that the mixing chamber thus changes a flow direction of the fibrous material suspension. It is further conceivable that the fibrous material suspension is mixed in the mixing chamber. A fibrous material suspension within the meaning of the present invention is a mixture having fibers and a liquid, for example, an aqueous foam and/or water.

[0004] It has surprisingly been found that the flow behavior of the fibrous material suspension after leaving the outlet and prior to application onto the screen belt is of great importance for the construction of the fibrous web. It is thus possible, for example, to influence the homogeneity of the fiber distribution in the fibrous web through changes in the flow properties of the fibrous material suspension between the outlet and application onto the screen belt. The homogeneity of the fiber distribution, in particular the homogeneity of the orientation of the fibers in the fibrous material suspension, may be used to adjust the strength in the MD and CD directions and also the stretch behavior in the MD and CD directions of the fibrous web.

[0005] An aspect of the present invention is to provide a device which makes it possible to selectively influence the flow properties of the fibrous material suspension after it has passed through the outlet.

[0006] In an embodiment, the present invention provides a device for producing a fibrous web. The device includes a screen belt, a mixing chamber, an apron, and a panel. The mixing chamber comprises an outlet which is configured to discharge a fibrous material suspension onto the screen belt. The outlet comprises an outflow gap. The apron is arranged in a vertical direction between the outlet and the screen belt. The panel is configured to adjust the outflow gap of the outlet and to be the displaceable in the vertical direction.

[0013] An apron is provided between the outlet and the screen belt. An apron within the meaning of the present invention is also known to a person skilled in the art by the German term “Siebleder” [screen apron]. An apron in this case can, for example, be a planar structure, such as a plate, which partially covers the top of the screen belt. Provision can, for example, be made for the apron to rest on the screen belt. The apron prevents the fibrous material suspension in the region of the apron from coming into contact with the screen belt. If suction is to be provided through the screen belt, this suction acting on the fibrous material suspension through the screen belt, for example, for dewatering, in particular makes possible that the fibrous material suspension is prevented from being drawn onto the screen belt in the region of the apron.

[0014] The device also has a panel for adjusting an outflow gap of the outlet. The panel may, for example, be a planar structure, in particular a plate, which projects into the outlet and narrows the cross section of the outlet. The remaining cross section of the outlet, through which the fibrous material suspension may issue from the mixing chamber, is referred to as the outflow gap in the context of the present invention.

[0015] To adjust the region in which there is no direct contact between the fibrous material suspension and the screen belt, provision is made for the apron to be displaceable along the direction of travel of the screen belt. Provision is thus in particular made for the distance, in the direction of travel of the screen belt, from the outlet to the point at which the fibrous material suspension comes into contact with the screen belt for the first time and, consequently, suction acts on the fibrous material suspension for the first time, to be adjustable. This achieves a high degree of flexibility when adjusting the flow characteristics of the fibrous material suspension after it issues from the mixing chamber. The apron can, for example, be displaceable so that it extends 50 mm to 400 mm, for example, 80 mm to 350 mm, and in particular 150 mm to 250 mm, from the mixing chamber in the direction of travel of the screen belt. The extent of the apron from the mixing chamber in the direction of the screen belt is also referred to as the insertion depth within the meaning of the present invention. It is conceivable that the apron is produced from a metal. It is, however, also conceivable that the apron is produced from a plastic material or a composite.

[0016] Provision can, for example, be made for the ratio of the speed of the screen belt and the speed, parallel to the direction of the screen belt, at which the fibrous material suspension contacts the screen belt, to be adjustable. It is thus advantageously possible to influence the arrangement of the fibers in the fibrous material suspension on the screen belt. It is conceivable that the ratio of the speed of the screen belt and the speed, parallel to the direction of the screen belt, at which the fibrous material suspension contacts the screen belt, to be adjustable between 1/0.5 and 1/2, for example, between 1/0.8 and 1/1.2.

[0017] Alternatively or in addition to the displaceable apron, provision is made for the panel to be displaceable along the vertical direction. Provision can, for example, be made for the panel to be displaceable along the vertical direction so that a hydraulic jump of the fibrous material suspension is produced. The displaceability of the panel along the vertical direction advantageously makes it possible to influence the flow behavior of the fibrous material suspension after it issues from the outlet. This in particular allows the formation of the hydraulic jump to be controlled. A hydraulic jump of the fibrous material suspension within the meaning of the present invention is a sudden change in the flow direction of at least a portion of the fibrous material suspension, i.e., at least a partial flow, without the sudden change being caused by an apparatus situated downstream of the abrupt change. This is also known as a backward-facing step. It is conceivable that only the partial flow undergoes the sudden change in flow direction. The partial flow may be a small portion of the entire flow of the fibrous material suspension, in particular less than half of the entire flow of the fibrous material suspension. The partial flow may, however, also be more than half of the entire flow of the fibrous material suspension. It is, however, also conceivable that the entire flow of the fibrous material suspension undergoes the sudden change in the flow direction. This advantageously generates vortices which influence the orientation of the fibers in the fibrous material suspension. One or more non-laminar dominant vortices are typically formed, and these in turn form a plurality of non-dominant vortices. The swirling of the fibers by the dominant, and in particular non-dominant, vortices causes the orientation of the fibers to be randomized.

[0018] Provision is in particular made for the partial flow in a hydraulic jump to run, for example, in an initially straight manner and then suddenly, i.e., all of a sudden, run upward, wherein the change in flow direction from straight onward to upward is initiated prior to the hydraulic jump. The portion of the fibrous material suspension which is not part of the partial flow is referred to hereafter as the main flow. There is in this case no change, or only an insignificant or minimal change, in the flow direction of the main flow.

[0019] A hydraulic jump is produced, for example, as a result of an abrupt deceleration of a flow, in this case the fibrous material suspension. To achieve this, the panel is displaced in the outlet so that the size of the outflow gap is greatly reduced and the fibrous material suspension is accelerated as a result. After the outlet, the fibrous material suspension suddenly slows down, thereby causing a hydraulic jump. Displacing the panel in the vertical direction narrows or widens the outflow gap, making it possible to adjust the desired flow behavior of the fibrous material suspension after the outflow gap.

[0020] The hydraulic jump within the meaning of the present invention is similar to a water jump, as is known from the field of the hydromechanics of open channels and incompressible liquids. The hydraulic jump within the meaning of the present invention may, however, also be achieved with fiber foams, i.e., compressible fluids.

[0021] Provision is in particular made for the panel to be pushed along the vertical direction into the outlet toward the screen belt. In other words, the panel can, for example, be arranged on the side of the outlet opposite the apron. This results in a hydraulic jump away from the apron or screen belt. It is, of course, also conceivable that the panel is pushed along the vertical direction into the outlet away from the screen belt. In other words, the panel is in this case arranged on the side of the outlet adjacent to the apron. This results in a hydraulic jump toward the apron or screen belt.

[0022] The vertical direction within the meaning of the present invention describes a direction which is arranged orthogonally to the flow direction of the fibrous material suspension in the outflow gap. It is conceivable that the vertical direction is arranged orthogonally to the machine direction. The direction of travel of the screen belt may be arranged parallel to the machine direction. The direction of travel of the screen belt may, however, also be arranged at an angle to the machine direction. This is in particular the case if the screen belt is an inclined screen belt. The phrase “displaceable along the vertical direction” does not restrict displaceability to the effect that the panel is only displaceable parallel to the vertical direction. Along the vertical direction within the meaning of the present invention also includes displaceability comprising only one direction component parallel to the vertical direction, wherein the displaceability of the panel encloses an angle of less than 90° to the vertical direction.

[0023] If the device has both an apron which is displaceable in the direction of travel of the screen belt, and a panel which is displaceable along the vertical direction, it is advantageously possible to alter the geometry of the device so that the hydraulic jump can be formed in a highly effective, reliable, and selective manner. It is thus in particular possible to take into account varying basis weights, production speeds, or fiber consistencies and, on this basis, to adjust the geometry of the device so that a hydraulic jump is reliably achieved.

[0024] It is most advantageous if the geometry of the device is such that the hydraulic jump forms a vortex which allows the fiber suspension to flow partially counter to the machine direction. In the absence of any particular measures when the fibrous material suspension is deposited onto the screen belt, the fibers tend to be arranged in the MD direction. If a vortex is generated by the partial flow of the hydraulic jump, the vortex traps fibers of the fibrous material suspension in a localized manner for a certain period of time, wherein the fibrous material suspension of the vortex remains largely within the vortex. The fibrous material suspension in the vortex only leaves the vortex at a defined rate. In the area of contact between the vortex and the partial flow, an interaction takes place between the partial flow and the vortex. This changes the orientation of the fibers in the partial flow. If the geometry of the device is adjusted so that the hydraulic jump, with the associated vortex, is arranged shortly in the machine direction or, for example, at the end of the apron, the ratio of the orientation in the MD/CD directions can be adapted. It is thus possible to adjust MD/CD ratios of 0.8 to 1.8. It is also possible to adapt the MD/CD ratio for tensile strength and the MD/CD ratio for stretch behavior by adjusting the MD/CD ratio.

[0025] The geometry of the device is furthermore most advantageous if a hydraulic jump with a vortex and a further vortex is formed. Such a hydraulic jump comprises a first change in flow direction in a first direction at a first point, and a second change in flow direction counter to the first direction at a second point situated downstream of the first point, without the first change being caused by an apparatus situated downstream of the first point. In other words, in such a hydraulic jump, the flow runs, for example, in an initially straight manner, then runs upward and finally downward, wherein the change in the flow direction from straight onward to upward is initiated prior to this hydraulic jump. The first change in flow direction produces a vortex with a direction of rotation. The second change in flow direction causes a further vortex, the direction of rotation of which is counter to that of the vortex.

[0026] MD direction within the meaning of the present invention is the direction in the machine direction. CD direction within the meaning of the present invention is the direction transverse to the machine direction.

[0027] The fibrous material suspension may comprise fibers made from organic materials and/or inorganic materials, natural fibers, synthetic fibers, regenerated fibers (for example, rayon), viscose fibers, cellulose fibers, metallic fibers and also fibers made, for example, from graphite, granite, polymers (for example, polyester) and/or mixtures thereof. The fibrous material suspension may have pulp fibers.

[0028] The fibrous web may be a fibrous web for producing nonwoven articles. Non-woven articles comprise, by way of example and non-exhaustively, sanitary wipes, cosmetic wipes, wet wipes, dispersible wet wipes, wipes, diapers, filter fabrics, etc.

[0029] The device according to the present invention makes it possible to selectively influence the tensile strength, stretch properties, volume, thickness, density, and absorbency of the fibrous web.

[0030] In an embodiment of the present invention, provision can, for example, be made for the fibrous material suspension to be discharged and deposited onto the screen belt as a fiber foam. The use of a fiber foam enables the fibers to be deposited onto the screen belt in a highly uniform manner so as to produce a highly uniform fibrous web. A fiber foam within the meaning of the present invention is a fiber-water-air mixture. The air bubbles in the fiber foam act to space the fibers apart. The finer the fiber foam, the more effectively the individual fibers are separated from one another. A method for producing a fibrous web in which a fiber foam is laid on a screen belt is also known as the foam-laying method.

[0031] The advantage of the foam-laying method is that flocculation is prevented by the separation of the fibers with the aid of the air bubbles. This makes it possible to use much higher fiber concentrations than in the known wetlaid method. Considerably less circulating water is furthermore used compared with known wetlaid methods, which drastically reduces the energy requirements of the device.

[0032] Further advantages of a device for producing a fibrous web via the foam-laying method are: significantly reduced water consumption, the option of using different combinations of fiber types, and a considerably higher dry content of the fibrous web, which saves energy when drying the fibrous web.

[0033] It is conceivable that the fiber foam has a density of 150 g/l to 700 g/l, for example, from 275 g/l to 375 g/l. It is conceivable that the fiber foam has an air volume of approximately 45% to 60%.

[0034] In an embodiment of the present invention, provision can, for example, be made for the mixing chamber to have a vortex chamber, in particular for the mixing chamber to be a vortex chamber. A vortex chamber within the meaning of the present invention is formed so that the fibrous material suspension is swirled as it passes through the vortex chamber. This has the advantage that the fiber foam is less susceptible to collapse. If the fiber foam is not swirled, the fiber foam breaks down over time. Relatively large foam bubbles are then formed which reduces the homogeneity of the distribution of the fibers in the fiber foam. The use of a vortex chamber therefore has a direct, positive influence on the homogeneity of the fiber distribution in the fibrous web.

[0035] The use of a vortex chamber has an advantageous effect on the distribution, along the CD direction, of the speed of the fiber foam issuing from the outlet in the MD direction, this distribution being rendered highly uniform with deviations of, for example, less than 5%, for example, less than 2.5%. A deviation of the speed within the meaning of the present invention is calculated as follows: (maximum speed-minimum speed)/average speed. An isotropic fiber orientation in the outlet is also particularly advantageous.

[0036] For this purpose, provision can, for example, be made for a shear rate of at least 10 1/sec, for example, at least 50 1/sec, to be generated within the entire vortex chamber. This provides an optimal consistency and concentration of the fibrous foam as it issues from the vortex chamber.

[0037] It is conceivable that the vortex chamber has at least one inlet on an upper side of the vortex chamber for introducing a fiber foam into the vortex chamber. The fiber foam is introduced into the vortex chamber as a flow, i.e., the fiber foam introduced flows into the vortex chamber. The fiber foam can, for example, be introduced into the vortex chamber along an inflow direction. Provision can, for example, be made for the upper side of the vortex chamber to be arranged at an angle of 45° to 135° to the inflow direction. A directing side is arranged opposite or obliquely to the upper side of the vortex chamber. The vortex chamber can, for example, be constructed so that the flow of the fibrous material suspension is directed by the directing side along the upper side of the vortex chamber, and along a lower side of the vortex chamber opposite the upper side of the vortex chamber, to the outlet. The directing side can, for example, be at least partially curved to divert the fiber foam to the upper side of the vortex chamber and to the lower side of the vortex chamber.

[0038] Provision can, for example, be made for the screen belt to be an inclined screen belt or a horizontal screen belt. Provision can, for example, be made for the inclined screen belt to be arranged at an angle of 20° to 50°, for example, 30°, to the horizontal. It is conceivable that a suction box is provided beneath the screen belt for dewatering the fibrous material suspension. Provision can, for example, be made for the suction capacity of the suction box to be adjustable. It is conceivable that the suction box is arranged so that dewatering takes place in a forming zone on the screen belt. Provision is in particular made for dewatering to take place only in a portion of the forming zone. Provision can, for example, be made for 70% of the dewatering to take place within the first third of the length of the forming zone.

[0039] In an embodiment of the present invention, provision can, for example, be made for the device to have a front wall following the outlet in the direction of travel of the screen belt. After discharge, the fibrous material suspension is arranged between the screen belt and the front wall in the vertical direction. The distance between the front wall and the screen belt can, for example, be adjustable. Provision can, for example, be made for the distance between the front wall and the screen belt to be adjustable independently of one another at an end located at the front in the direction of travel of the screen belt, and at an end located at the rear in the direction of travel of the screen belt. This makes it possible to further advantageously alter the geometry of the device for selectively generating a hydraulic jump. The distance between the front wall and the screen belt at the end located at the front in the direction of travel of the screen belt is also referred to as the roof height within the meaning of the present invention. The embodiment with a displaceable apron, displaceable panel, and adjustable distance between the front wall and the screen belt in particular offers excellent flexibility, so that the hydraulic jump can, for example, be optimally adjusted and the ratio of the orientations of the fibers in the MD/CD directions can be controlled.

[0040] Provision can, for example, be made for the roof height to be greater than the distance between the front wall and the screen belt at the end located at the rear in the direction of travel of the screen belt.

[0041] In an embodiment of the present invention, provision can, for example, be made for the panel to be displaced so that a Froude number of 15 to 35, for example, 20 to 30, is achieved in the outflow gap. The Froude number is calculated by dividing the flow speed in the outflow gap by the root of the product of the gravitational acceleration and the gap height of the outflow gap. An outflow gap adjusted in this manner provides optimal conditions for a hydraulic jump.

[0042] For the reliable formation of a hydraulic jump, provision can, for example, be made for the gap height to be between 20% and 80%.

[0043] To adjust the optimal geometry of the device, provision can, for example, be made for the insertion depth of the apron to be adapted depending on the gap height. The insertion depth of the apron can, for example, be adapted depending on the gap height and the flow speed of the fibrous material suspension in the outflow gap.

[0044] In an embodiment of the present invention, provision can, for example, be made for the device to have a first elevating screw for displacing the apron and/or a second elevating screw for displacing the panel. Provision is in particular made for the first elevating screw to be provided for displacing the apron along the direction of travel of the screen belt, and for the second elevating screw to be provided for displacing the panel along the vertical direction. Provision can, for example, be made for the device to have a third elevating screw for adjusting the distance between the front wall and the screen belt at the end located at the front in the direction of travel of the screen belt, and, for example, a fourth elevating screw for adjusting the distance between the front wall and the screen belt at the end located at the rear in the direction of travel of the screen belt. This advantageously makes it possible to adjust the apron and/or the panel and/or the front wall in an exact and precisely reproducible manner. Provision is in particular made for the device to have the first elevating screw and a further first elevating screw for displacing the apron and/or the second elevating screw and a further second elevating screw for displacing the panel. Provision can, for example, be made for the device to have the third elevating screw and a further third elevating screw for adjusting the distance between the front wall and the screen belt at the end located at the front in the direction of travel of the screen belt, and, for example, the fourth elevating screw and a further fourth elevating screw for adjusting the distance between the front wall and the screen belt at the end located at the rear in the direction of travel of the screen belt. This makes it possible to adjust the geometry of the device exactly, even if the device is very wide. The first elevating screw and the further first elevating screw and/or the second elevating screw and the further second elevating screw and/or the third elevating screw and the further third elevating screw and/or the fourth elevating screw and the further fourth elevating screw in this case form elevating screw pairs.

[0045] In an embodiment of the present invention, provision can, for example, be made for an inlet lip of the mixing chamber to rest on the apron during operation of the device, wherein the apron rests on the screen belt during operation of the device. This provides that the device functions in an optimal and stable manner.

[0046] To further improve the flow of the fibrous material suspension out of the outlet, provision can, for example, be made for a lower side of the panel to be arranged in a downwardly inclining manner, i.e., a converging manner along the direction of travel of the screen belt, at an angle between 0° and 30°. The angle is understood in this case to be the angle enclosed by the lower side of the panel and a plane which is oriented parallel to the plane opposite the lower side of the panel. This may, for example, be the apron, if the lower side of the panel is arranged opposite the apron. It is, however, also conceivable that the lower side of the panel is, for example, arranged opposite the lower side of the vortex chamber. The angle would in this case relate to the lower side of the panel and a plane which is arranged parallel to the lower side of the vortex chamber. This results in a significant improvement in the flow of the fibrous material suspension along the panel through the outflow gap, and the formation of the hydraulic jump is assisted.

[0047] Further details, features and advantages of the present invention are apparent from the drawings and the following description of embodiments with reference to the drawings. The drawings thereby only illustrate example embodiments of the present invention which do not restrict the concept of the present invention.

[0048] FIGS. 1-5 each show a schematic view of a device 1 according to an embodiment of the present invention. The device 1 is a device 1 for producing a fibrous web 2. The fibers of the fibrous web 2 may, for example, comprise organic and/or inorganic fibers. For example, natural fibers, regenerated fibers, synthetic fibers and other fibers not listed here are conceivable.

[0049] The device 1 shown in this case has a headbox 16 with a mixing chamber 3 comprising a vortex chamber 3.2. The mixing chamber 3 is provided to supply a fibrous material suspension 10 to a screen belt 5. The mixing chamber 3 has an outlet 4 therefor. The fibrous material suspension 10 flows out of the mixing chamber 3 through the outlet 4.

[0050] The screen belt 5 is designed as a screen belt, in this case an inclined screen belt 5. A suction device, which dewaters the fibrous material suspension 10 laid on the screen belt 5, is arranged beneath the screen belt 5.

[0051] In the vertical direction H, an apron 6 is arranged between the outlet 4 and the screen belt 5. The apron 6, which is also known to a person skilled in the art by the German term “Siebleder” [screen apron], is a planar structure and can be manufactured, for example, from a metal or a plastic material. The apron 6 is displaceable along the direction S of travel of the screen belt 5 by a first elevating screw 6.1. This makes it possible to adjust the insertion depth A of the apron 6 and thus the point at which the fibrous material suspension 10 comes into direct contact with the screen belt 5 and at which suction acts on the fibrous material suspension 10 for the first time. During operation of the device 1, an inlet lip 3.1 of the vortex chamber 3.2 rests on the apron 6, and the apron 6 in turn rests on the screen belt 5.

[0052] The device 1 has a panel 7 at the outlet 4. The panel 7 is connected to a second elevating screw 7.1, which allows the panel 7 to be displaced along the vertical direction H. The gap height B of an outflow gap 8 formed by the panel 7 can therefore be adjusted. Displacement of the panel 7 along the vertical direction H relates not only to displacement of the panel 7 parallel to the vertical direction H, as shown in FIG. 1, but also along a direction having a direction component in the vertical direction H, as shown in FIGS. 2 and 4. In other words, the panel 7 need not be oriented exactly in the vertical direction H and its displacement need not exactly follow the vertical direction H. The panel 7 may also be slightly tilted relative to the vertical direction H.

[0053] In the machine direction M, a front wall 9 is arranged following the panel 7. After being laid on the screen belt 5, the fibrous material suspension 10 transported in the direction of travel S of the screen belt 5 is arranged between the screen belt 5 and the front wall 9. The front wall 9 is attached, both at the front end 9.1 located at the front in the direction S of travel of the screen belt 5 and at the rear end 9.2 located at the rear in the direction S of travel of the screen belt 5, to a third elevating screw 9.3 and to a fourth elevating screw 9.4, respectively, which can be used to adjust the distance between the ends 9.1, 9.2 of the front wall 9 and the screen belt 5.

[0054] The panel 7 is guided along the vertical direction H on a vertical boundary 9.5, arranged in the vertical direction H, of the front wall 9. A bolt 7.3 is provided therefor which is guided along the vertical direction H in a slot (not shown in this case) in the vertical boundary 9.5. The bolt 7.3 reaches through the panel 7 and the vertical boundary 9.5. A clamping element 7.4, for example, here a spring element, pretensions the panel 7 and the vertical boundary 9.5 counter to the machine direction M and therefore prevents an undesired movement of the panel 7 and the front wall 9. It is also conceivable, however, that the panel 7 and the vertical boundary 9.5 are clamped hydraulically or pneumatically.

[0055] The third elevating screw 9.3 is connected via the vertical boundary 9.5 to the front end 9.1, located at the front in the direction S of travel of the screen belt 5, of the front wall 9. The device 1 has an articulation 9.6 between the front end 9.1, located at the front in the direction S of travel of the screen belt 5, of the front wall 9 and the vertical boundary 9.5 therefor.

[0056] In addition to the first elevating screw 6.1, a further first elevating screw (not shown in this case) is provided. The first elevating screw 6.1 and the further first elevating screw form an elevating screw pair for displacing the apron 6. In addition to the second elevating screw 7.1, a further second elevating screw (not shown in this case) is provided. The second elevating screw 7.1 and the further second elevating screw form an elevating screw pair for displacing the panel 7. In addition to the third elevating screw 9.3, a further third elevating screw (not shown in this case) is provided. The third elevating screw 9.3 and the further third elevating screw form an elevating screw pair for adjusting the distance between the screen belt 5 and the end 9.1, located at the front the direction of travel S of the screen belt 5, of the front wall 9. In addition to the fourth elevating screw 9.4, a further fourth elevating screw (not shown in this case) is provided. The fourth elevating screw 9.4 and the further fourth elevating screw form an elevating screw pair for adjusting the distance between the screen belt 5 and the rear end 9.2, located at the rear the direction of travel S of the screen belt 5, of the front wall 9. The elevating screws 6.1, 7.1, 9.3, 9.4 and the further elevating screws are located at a distance from one another along a transverse direction which is orthogonal to the machine direction M and orthogonal to the vertical direction H, to form the elevating screw pairs.

[0057] The vortex chamber 3.2 is constructed so that the fibrous material suspension 10 flowing into the vortex chamber 3.2 is always in motion in the vortex chamber 3.2. In the vortex chamber 3.2, no dead spaces are formed in which the fibrous material suspension 10 has a low speed or even comes to a standstill. This is achieved by the fibrous material suspension 10 flowing in through an inlet 3.3 of the vortex chamber 3.2 in the direction of a curved directing side 3.4 of the vortex chamber 3.2. At the directing side 3.4, the flow of the inflowing fibrous material suspension 10 divides and runs along a lower side 3.5 of the vortex chamber 3.2 comprising the inlet lip 3.1, and along an upper side 3.6 of the vortex chamber 3.2 to the outlet 4 and to the outflow gap 8.

[0058] The device 1 is intended to use a fibrous material suspension 10 in the form of fiber foam. The specific construction of the vortex chamber 3.2 promotes a high degree of homogeneity of the fiber foam at the outlet 4 of the vortex chamber 3.2. Since the fiber foam in the vortex chamber 3.2 does not come to a standstill, the fiber foam does not disintegrate and the fibers of the fiber foam remain homogeneously spaced. For this purpose, provision is made for a shear rate of at least 10 1/sec, for example, at least 50 1/sec, to be generated within the entire vortex chamber 3.2.

[0059] When issuing from the mixing chamber 3 through the outlet 4, the fibrous material suspension 10 passes through the outflow gap 8. The outflow gap 8 represents a narrowing, which greatly accelerates the fibrous material suspension 10 in the outflow gap 8. For this purpose, the gap height B of the outflow gap 8 is adjusted by displacing the panel 7 so that a Froude number of 15 to 35, for example, 20 to 30, is achieved in the outflow gap 8. A lower side 7.2 of the panel 7 is arranged in a parallel or, for example, in a downwardly inclining manner in the direction of travel S of the screen belt 5 at an angle of between 0° and 30°. In other words, the outflow gap 8 becomes narrower in the direction of travel S of the screen belt 5. After the outflow gap 8 in the direction of travel S of the screen belt 5, the cross section of the volume available to the fibrous material suspension 10 suddenly increases, which likewise suddenly reduces the flow speed of the fibrous material suspension 10. To improve the homogeneity of the fiber distribution of the fibrous web 2, the panel 7 along the vertical direction H, the apron 6 along the direction of travel S of the screen belt 5, and the distance between the front end 9.1, located at the front in the direction of travel S of the screen belt 5, of the front wall 9 and the screen belt 5, also referred to as the roof height C, are adjusted so that a hydraulic jump 11 of the fibrous material suspension 10 is formed. The options for adjusting the panel 7, apron 6, and front wall 9, allow a hydraulic jump 11 to be produced with different parameters with regard to the fibrous material suspension 10, the speed of the screen belt 5, and the flow speed of the fibrous material suspension 10 into the vortex chamber 3.2.

[0060] FIGS. 2 and 3 show devices 1 in which the hydraulic jump 11 and the effects produced thereby are illustrated by way of example. The hydraulic jump 11 in this case generates a vortex 12 which guides a portion of the fibrous material suspension 10 counter to the machine direction M. In the shown hydraulic jump 11, a partial flow 15 of the fibrous material suspension 10 abruptly changes direction, thereby producing the vortex 12. This influences the orientation of the fibers in the fibrous material suspension 10. There is no change, or only an insignificant change, in the flow direction of a main flow 14 of the fibrous material suspension 10.

[0061] The hydraulic jump 11, and thus also the vortex 12, are arranged at the end of the apron 6, i.e., where the fibrous material suspension 10 contacts the screen belt 5 for the first time and suction acts on the fibrous material suspension 10. Adjusting the hydraulic jump 11, and thus the vortex 12, makes it possible to control the MD/CD ratio of the arrangement of the fibers in the fibrous material suspension 10 upon application onto the screen belt 5.

[0062] FIGS. 4 and 5 show devices 1 in which the geometry of the device 1 is adjusted in each case so that the vortex 12 and a further vortex 13 are generated by the hydraulic jump 11. The flow direction of the fibrous material suspension 10 initially changes so that the fibrous material suspension 10 flows in the direction of the front wall 9. This generates the vortex 12, which guides a portion of the fibrous material suspension 10 back in the direction of the outlet 4 counter to the machine direction M. The flow direction of the fibrous material suspension 10 changes again downstream. The fibrous material suspension 10 flows from the front wall 9 in the direction of the screen belt 5. This generates the further vortex 13, which has a direction of rotation counter to the direction of rotation of the vortex 12. This configuration allows for highly precise adjustment of the MD/CD ratio of the arrangement of the fibers in the fibrous material suspension 10 upon application onto the screen belt 5.

[0063] The present invention is not limited to embodiments described herein; reference should be had to the appended claims.

• • [0064] 1 Device
  • [0065] 2 Fibrous web
  • [0066] 3 Mixing chamber
  • [0067] 3.1 Inlet lip
  • [0068] 3.2 Vortex chamber
  • [0069] 3.3 Inlet
  • [0070] 3.4 Directing side
  • [0071] 3.5 Lower side (of the vortex chamber)
  • [0072] 3.6 Upper side (of the vortex chamber)
  • [0073] 4 Outlet
  • [0074] 5 Screen belt
  • [0075] 6 Apron
  • [0076] 6.1 First elevating screw
  • [0077] 7 Panel
  • [0078] 7.1 Second elevating screw
  • [0079] 7.2 Lower side (of the panel)
  • [0080] 7.3 Bolt
  • [0081] 7.4 Clamping element
  • [0082] 8 Outflow gap
  • [0083] 9 Front wall
  • [0084] 9.1 Front end
  • [0085] 9.2 Rear end
  • [0086] 9.3 Third elevating screw
  • [0087] 9.4 Fourth elevating screw
  • [0088] 9.5 Vertical boundary
  • [0089] 9.6 Articulation
  • [0090] 10 Fibrous material suspension
  • [0091] 11 Hydraulic jump
  • [0092] 12 Vortex
  • [0093] 13 Further vortex
  • [0094] 14 Main flow
  • [0095] 15 Partial flow
  • [0096] 16 Headbox
  • [0097] A Insertion depth
  • [0098] B Gap height
  • [0099] C Roof height
  • [0100] S Direction of travel (of the screen belt)
  • [0101] H Vertical direction
  • [0102] M Machine direction