FI119333B - Method in connection with a headbox of a paper or board machine and a lamella of a headboard of a paper or board machine - Google Patents

Description

119333

Method in connection with a headbox of a paper or board machine and a lamella of a headbox of a paper or board machine 5

The invention relates to a method according to the preamble of claim 1 in connection with a headbox of a paper or board machine.

The invention also relates to a headbox section of a paper or board machine according to the preamble of claim 2.

As is known in the art, lamellae, or lamellae, are used in the lip ducts of the headboxes to increase the tensile strength ratio of the paper or board web due to increased turbulence yield. The waves, or wedges, also reduce the scale of the resulting turbulence, because the waves provide: a small duct height because the lip duct is divided into layers vertically; increased boundary layer turbulence as lamellae increase the wall surface area; and a thin leaving end, because of the small area change over the lamellae walker and the small vortices caused by the lamella leaving end; and additionally, the waves allow • t · I * "to prevent mixing of currents from different rows of the turbulence generator.

• * * · * / Flats used in headboxes vibrate slightly during use as a result of the headstock flow in certain conditions. One problem when using the lamella fabric is that the vibration of the lamella creates a standing wave for the la-25 Melli, causing very regular transverse locking in the direction of the paper and cardboard web. For example, in a structure such as basis weight or fiber orientation stiffness, thus impairing the end-use properties of the product, the strength of the resulting phenomenon depends on the structure of the waves and on the running parameters Old / striped structures ··· * 30 they in the web are directly linked to the transverse periodic «• · · * · periodicity observed in water measurements, while this has been shown to be due to the flow 2,119,333 structure interaction where turbulence and periodic vortex detachment at the tail edge create a whirring in appropriate conditions. As a result of the resulting oscillation mode, the flow separation is further enhanced at certain transverse positions and attenuated in others, resulting in a secondary flow structure following the lamella, which forms old fibers in the flow.

This problem has not been satisfactorily solved by prior art solutions, but has had to compromise between the old-fashioned nature of the final product and some other feature, which has not been able to improve as much as possible in principle. Efforts have been made to solve the problem, for example, by making structural changes to the lamellae, for example by moving to a more rigid wedge-like structure. In addition, special materials such as titanium and carbon fiber have been introduced. However, this phenomenon has not been completely eliminated and, among other things, carbon fiber lamellae have been found to oscillate at high speeds, causing problems with fiber quality.

In addition, efforts have been made to solve the problem by using passive or active ['20 attenuation. One known refinement to effect passive damping is the laminating of the visco-elastic film to the surface of the lamella, which, according to measurements, has proven to be a strong secondary flow structure reduction in the van.

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However, one disadvantage of this ice sheet is that the damping material is then subject to process conditions, whereby the coating used has additional requirements. Tracking active damping along the lamella is, in turn, quite complicated and expensive.

• * • · ® ·· · • * · * .. * The cause of the problem, that is, the resonance of the lamella, is also influenced by the geometry of the lamella geometry, and the flow around the lamella. however, the problem cannot be solved either, because in practice changing the background state so much that the resonance of the lamella would disappear is limited because at the same time the properties of the final product would change too much.

In the prior art, reference may be made to U.S. Patent 4,566,945, which discloses a self-positioning lamella following the lip channel of a papermaking machine head machine, which is stiffer in the machine direction on the inlet side and in the transverse direction on the flow side. The lamella is preferably made of a plurality of layers laminated to one another. This known arrangement is problematic in that the blade tip is blunt, which causes a strong turbulence which is reflected in the web being manufactured.

The object of the invention is to provide a method in connection with a headbox of a paper or board machine and a headbox lamella in which the problems associated with the vibration of the lamella are eliminated or at least minimized.

In order to achieve the foregoing and further objects, the process according to the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The lamella according to the invention, in turn, is essentially characterized by the lamellae according to the invention. * as set forth in the characterizing part of claim 2.

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According to the invention, the vibrations of the lamellae in connection with the headbox of a paper or board machine are damped at least by minimizing the flow separation from the lamella. by adjusting the thickness of the lamellas' passageways to a thickness of less than 0.5 mm, preferably less than 0.1 mm, and at least one curved surface having a wrapping portion on the lamella surface length is at least 10 times greater than the thickness of the lamellae visitor, • · • · * "In this case, the vibration of the lamella of the headbox of a paper or board machine and consequent disturbance in the flow field as a result of the lamella tip • · * · T * · *: designed to prevent the build-up of vibration excitation, or regular vortex 4,119,333, and at the same time the tip of the blade is stiff enough to withstand flow deformations in the tip area, so that the blade's rigidity or structure is not thinned suffered, that is, preferably the lamella is thinned with the shortest possible mat-5, however, so that the flow release is controlled.

In accordance with the invention, a separate tip piece located in the region of the lamellar is used.

The invention can be applied to various types of lamella / wedge structures, for example, to hinged and fixedly attached lamella structures. Preferably, the lamella / wedge is tapered in the direction of flow.

The invention will now be described with reference to some preferred embodiments of the invention shown in Figures 15 of the accompanying drawings, to which the invention is, however, not intended to be narrowly limited.

Fig. 1 schematically illustrates a headbox structure in which the invention is applicable.

Fig. 2 schematically shows an embodiment.

Figure 3 schematically illustrates an embodiment of the invention.

Figure 1 schematically illustrates a headbox 10 comprising a mass distribution manifold, followed by a bellows 12 in the flow direction of the pulp suspension comprising a flow tube, · · · · · · · · · · from which the flow is conducted to the intermediate chamber 13. From the intermediate chamber 13, the flow is further directed to the turbulence generator 14 and through its turbulence tubes to the lip channel 15 and further to the forming wire (not shown). As shown in Figure 1, the mass flow from the manifold supports 11 is led through the inlet plate 11A to the barrel 12. After the air inlet plate 1Aa, there is a manifold plate 19. Both the inlet nozzle plate 1A and the manifold plate 5119333 19 comprising channels 21, 22 in vertical and horizontal rows communicating with one another via branch channels (not shown) .The channels 22 of the distributor plate 19 are connected to channels 23 at respective positions of the bellows 12, a dilution stream of preferably pure or fibrous water, 5 through manifolds 20 through channel 24 through inlet 1A channel 1 to valves 25 at various width positions of the paper machine / board machine head to adjust the basis weight of the web. to the turbulence generator 14 10 and further to the lip channel 15 of the headbox 10. The lip channel 15 of the headbox 10 comprises lamellae / wedges 16 extending across the width of the lip channel 15 of the headbox 10. According to the invention, the lamellae tips are thin and have a thickness D of less than 0.5mm and the lamina surface comprises a curved surface, a curved portion preferably disposed within the lamella tip region, whereby the lamellae tip is shaped such that no periodic flow separation occurs.

Fig. 2 shows an example showing a lamella 16 in the mouthpiece 15 of the headbox 10 having a thin tip, i.e., having a thickness D of less than 0.5 · · · * · * * mm and a curved area having a curved portion length is at least 10 times 20 greater than the thickness D of the blade tip 18. In the embodiment shown in the figure, the blade tip is made so that the blade tip region 17 is thinned towards the end * · ·, tapering as close to the tip 18 as the blade tip region 17. · * * * * "Such that the machine derivative of the thickness of the lamella has no discontinuity due to, for example, the beginning of the chamfer and the angle between the tangent 25 to the surface and the flow does not exceed 10 degrees. .t from the surface of the blade 16 before the tip 18 of the blade 26 by adding the radius of curvature of the tip area · · 17 is always on one or both surfaces of the lamella continuously or towards both ends, there is no blunt leaving edge of the lamina t · "which would cause the upper and lower surface boundary layers to be different • i«: * 30 points. The curved portion of the surface of the lamella 16 is preferably located at the edge of the lamella. Preferably, the curvature radius R of the curved portion of the surface of the lamella 16 is at least 6,119,333 100 times the thickness of the lamella tip. With the curved portion of the surface of the lamella 16, the angle between the tangent to the surface of the lamella and the flow is less than 10 degrees. Preferably, the lamellar thickness P prior to the start of the curved portion is at most 1.5 mm.

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The embodiment of the invention shown in Figure 3 corresponds substantially to the above and the like reference numerals denote corresponding parts. In the embodiment of the invention illustrated in this figure, the tip 16 of the blade 16 is made of a separate thin and 10 tip piece 41. The length L of the tip piece 41 is preferably 4-12 times greater than the height H of the trailing edge of the blade 16. adhere to the surface of the tip piece 41, but does not have time to stabilize as a boundary layer. The tip D 41 has a very small thickness D, preferably 0.1-0.3 mm. In the embodiment shown in the figure, the boundary layer flow 15 is detached from the surface of the lamina 16 in a controlled manner while ensuring that no absolutely unstable flow field is created. This is advantageously achieved, for example, by installing a tip piece 41 which acts as a stabilizing plate in connection with the rounded leaving edge of the lamella 16. The length L of the tip piece 41 is 4-12 ·· * • · «*. * * Times the height H of the leading edge 16 of the fin.

Although the invention described above with respect to the hinged lamella / wedge is applicable, the invention may also be used in connection with various types of lamella structures, e.g. therefore fixed in connection with lamellar structures.

• · * * * * ·., T 25 Paper or board machine also covers tissue machines.

The invention has been described above only with reference to some advantageous application examples thereof. (> 1 thus, the details of which, however, are not intended to be limited in any way. "1).

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Claims (5)

A method in connection with an inlet carriage in a paper or cardboard machine, in which method at least one lamella (6) is used in a lip channel (15) in the inlet carriage (10) to generate / maintain turbulence in the pulp suspension, in which method vibrations in the slat (16) are at least attenuated by loosening of the flow from the slat (16) in such a way that the thickness of the tip of the slat (16) is made tutin, below 0.5 mm, and that on the surface of the slat at least one curved surface is provided, the length of the curved section being at least 10 times greater than the thickness of the tip of the slat (16), characterized in that the vibrations in the slat (16) are attenuated in the process by the effective tip of the slat (16). ) is minimized by a thin tip piece (41) placed in connection with the rounded trailing edge of the lamella (16), the length (L) of the tip piece being 4-12 times greater than the height (H) of the rear edge of the lamella (16). 15 2. Slat of an inlet carriage in a paper or cardboard machine, said slat being located in a lip channel (15) of the inlet carriage (10), to attenuate vibrations in the slat (16) by minimizing the release of flow from the slat (16) thick · · · V; the clearance of the tip of the lamella (16) is less than 0.5 mm and the surface of the lamella (16) comprises at least 1 curved surface, the length of the curved section being at least 10 *. the thickness of the tip of the slat, characterized in that the curved portion of the surface of the slat (16) is positioned in a tip region (17) of the slat (1) and that the tip of the slat (16) is formed by a separate piece (41), the length (L) of the tip piece (41) being 4-12 times greater than the height (H) of the slat ( 16), .25 backside • · «• · · • · IM • · • · 3. A slab according to claim 2, characterized in that the radius of curvature R of the curved section of the surface of the slab (16) is at least 100 times greater than the thickness • 2 · · · · 1 (D) of the tip of the slat. • · • · · »• · · • · · 2 • 119333 ίο 4. A lamella according to claim 2 or 3, characterized in that on the curved section of the lamella surface, the angle between a tangent parallel to the lamella (16) surface and the flow is less than 10 degrees. 5 • · · • ♦ • · »t • · • · • · · •» t • · • · • · · • • t »·· • · t ··· • · · * · • · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·