EP1022378A2 - Headbox - Google Patents

Abstract

The stock inlet for a papermaking machine, with a pulp feed and a turbulence generator, has a path section (I) where the free cross section steadily decreases towards the outlet which is directly followed by a second path section (II) with a steady and continuous expansion to the outlet. The second path section (II) with a flow expansion can be followed by a third path section with a steady and decreasing free flow cross section. The third path section length L3 is shorter than the second (II) length L2, which is shorter than the length L1 of the first path section (I). The structure of the path lengths is expressed as L2<0.3> L3 L2<0.7> and L1<0.1> L2 L1<0.3>. The first path section (I) starts directly after the turbulence generator. The total crosssection of the stock inlet jet is formed by a single suspension flow channel (4) at least over part of the length of the stock inlet jet. Or a number of suspension flow channels are over at least part of the stock inlet jet length of the total cross section of the stock inlet jet, formed by at least one divider between the two limit walls. Without exception, all the suspension flow channels have the same cross section pattern, in a shape which covers each other. The rate of divergence at the second path section (II) is identical for all the suspension flow channels. The dividers form a point towards each other at the second path section (II), each with the same degree of convergence at the ends of their surfaces. The alignment of the upper (1) and/or lower (2) wall of the stock inlet, at least in the second path section (II), is in a mirror image to the line of the adjacent divider in relation to the surfaces in contact with the suspension flow. The turbulence generator has a number of diffusion tubes, arranged in rows across the machine width. The dividers start between the rows of diffusion tubes. The upper and lower walls of the stock inlet have the same length. The ratio of the change in the reducing cross section height in the flow direction to the flow path length in the first path section (I) is 0.3-40.0 % and preferably 10-30%. The ratio of the increasing cross section height in the flow direction to the flow path length in the second path section (II) is 0.1-20.0% and preferably 2-12%. The ratio of the change in the reducing crosssection height in the flow direction to the flow path length in the third path section is 1-400% and preferably 10-200%. The first path section (I) has a length of 250-1000 mm and preferably 400-800 mm. The second path section (II) has a length of 20-150 mm. The length of the third path section is 0.5-300.0 mm and preferably 1-100 mm. The smallest cross section height of the first path section (I) is 10-500 mm, and preferably 15-150 mm, and 30-200 mm at the second path section (II), and 5-80 mm in the third path section.

Description

The invention relates to a headbox Paper machine with at least one System suspension supply system, at least one subsequent area for turbulence generation and one Headbox nozzle with a first and a second machine-wide boundary wall, with the headbox nozzle has a first path I, in which the Total cross section (= total free suspension flowed through Cross-sectional area) of the headbox nozzle continuously and continuously decreased, immediately following the first route I a second, shorter route II connects.

A headbox is according to the preamble of claim 1 known from the applicant's US patent US 5,599,428. In this patent, different variants of Multi-layer headboxes described in the nozzle area are equipped with separating blades of different types.

Papers made by these headboxes have the problem of insufficient transverse stiffness SCT _across , which can lead to malfunctions when used in modern copying systems or printers with automatic paper feed, for example. It would also be advantageous if the tear length ratio L / Q (L = longitudinal in the machine direction, Q = transverse to the machine direction) could be reduced after the sheet formation - if possible into a range of values from 0.6 to 1.0.

It is therefore the object of the invention to provide a headbox describe the transverse stiffness of the manufactured Improved paper, where possible that too Tear length ratio L / Q should be reduced.

The inventors have recognized that the transverse rigidity of the Paper significantly improved, if by an appropriate Shape of the headbox nozzles - especially in the end area the headbox nozzle - ensure that the in the stock of fibers in the end area of the Nozzle reinforced in the perpendicular to the leaf surface z direction and if possible also stretched.

To realize this basic idea, they propose Inventor before, the known headbox of a paper machine with at least one material suspension supply system, at least one subsequent area for Turbulence generation and a headbox nozzle with a first and a second machine-wide boundary wall develop, the headbox nozzle a first Has path I in which the total cross section - that is, the total free suspension Cross-sectional area of the headbox in the respective Machine section - the headbox nozzle continuously and continuously decreased, immediately following the first route I a second, shorter route II connects. The further development of the Headbox is that the second leg II a continuously expanding overall cross-section has, which extends to the end of the headbox nozzle extends. With this extension a Flow delay in the end area of the headbox nozzle causes, but no significant turbulence arises. Due to the speed profile created here Fibers that are within the stock suspension in stretched the z-direction of the suspension layer and it is created an improvement in the transverse stiffness of the finished paper. An additional positive side effect of this influence the stock suspension is that also Tear length ratio L / Q reduced and values between 0.6 to Can assume 1.0.

According to the basic idea of the invention is also a Improvement of a headbox possible, the additional has a third route III, which follows the second route II connects and to the end of Headbox nozzle is sufficient. The improvement is here in that the second route II is a continuous widening overall cross section and the Total cross section of the third route III is stepless and continuously decreased. It is advantageous here if the length L3 of the third distance is shorter than that Length L2 of the second route and length L2 of the second The distance is shorter than the length L1 of the first Distance. By choosing the appropriate ratio the path lengths to each other can promote transverse rigidity Effect can be increased or decreased, taking the path length route III should remain shorter than the route length the route II. By this aspect ratio prevents that reached in the second way Alignment of the fibers does not occur again in the third route is overcompensated. Favorable ratio values are in the Subclaims specified.

An advantageous embodiment of the invention Headbox provides that the first route I starts immediately after the turbulence generating area. It is also proposed that at least part of the Headbox nozzle length of the total cross section of the Headbox nozzle through a single suspension channel is formed. That means there are none in this area Separating elements - for separating individual layers - available are. This reduces edge effects, and the on one piece of available amount of Flow cross section corresponds to the total cross section, resulting in better alignment of the fibers in the z direction can be achieved.

Especially when the headbox is a multi-layer headbox is used, it can be advantageous if the total cross section of the headbox nozzle, at least over part of the headbox nozzle length, several Has suspension channels through at least one machine-wide separating element are formed, the at least one separating element between the first and the second boundary wall is arranged. Here it is particularly advantageous if all without exception Suspension channels have the same cross-sectional shape, so that the same acceleration and delay ratios for the running suspension given are. In addition, it is advantageous if without exception all suspension channels are congruent - also mirror image congruent - have shape. Hereby is achieved not only the amount of acceleration and delay in the suspension channels is the same, but also that the vector field in each suspension channel is identical over the entire length.

Another advantageous embodiment provides that the degree the divergence in the area of the second route II for everyone Suspension channels is the same.

The divergence of the individual suspension channels can for example with internal separators achieved that the separating elements in the area of the second Route II have a taper. Here it is advantageous if the degree of convergence of the surfaces of the tapered ends of all separators is the same to flow conditions as uniform as possible over the To reach cross-section of the headbox.

It is also advantageous if the course of the top wall and / or the lower wall at least in the second area II with respect to the area in contact with the suspension as a mirror image of Course of the surface of the adjacent separating element is trained. This ensures that the external suspension channels as identical as possible to the Interior are designed.

Another advantageous embodiment of the invention Headbox provides that the headbox has a Turbulence generator with a variety of diffusion tubes has, the diffusion tubes in machine width trending rows are arranged and the dividing elements start between the rows of diffusion tubes.

Especially with a headbox for a GAP former is provided, the top and bottom wall of the Headbox be of equal length.

It is understood that the above and Features of the invention not yet to be explained below only in the specified combination, but also in other combinations or used alone, without leaving the scope of the invention.

Further features and advantages of the invention result from the subclaims and the description below preferred embodiments with reference to the Drawings.

Figur 1:

Stoffauflaufdüse ohne Trennelemente

Figur 2:

Stoffauflaufdüse mit Trennelementen, ausschließlich im konvergierenden Bereich

Figur 3:

Stoffauflaufdüse mit Trennelementen, die in den divergierenden Bereich ragen

Figur 4:

Stoffauflaufdüse ohne Trennelemente mit kurzem divergierenden und anschließend konvergierenden Bereich

Figur 5:

Stoffauflaufdüse mit einem Trennelement

Figur 6:

Stoffauflaufdüse mit Trennelementen mit verstärkter Endkonvergenz

Figur 7:

Stoffauflaufdüse mit Trennelementen mit verstärkter Endkonvergenz und parallel verlaufender Ober- und Unterwand im Bereich verstärkter Endkonvergenz

Figur 8:

Stoffauflaufdüse mit Trennelementen mit verstärkter Endkonvergenz und parallel verlaufender Ober- und Unterwand im Bereich verstärkter Endkonvergenz und anschließend stark konvergierender Ober- und Unterwand

Figur 9:

Faser im Endbereich einer Stoffauflaufdüse mit zwei Momentaufnahmen

Figur 10:

Darstellung der Faser im Endbereich einer Stoffauflaufdüse mit zwei Momentaufnahmen aus Figur 10 im z/x-Koordinatennetz

The invention will be explained in more detail below with reference to the drawings. They represent:

Figure 1:

Headbox nozzle without separators

Figure 2:

Headbox nozzle with separators, only in the converging area

Figure 3:

Headbox nozzle with separators that protrude into the diverging area

Figure 4:

Headbox nozzle without separators with a short diverging and then converging area

Figure 5:

Headbox nozzle with a separating element

Figure 6:

Headbox nozzle with separators with increased final convergence

Figure 7:

Headbox nozzle with separating elements with increased final convergence and parallel top and bottom wall in the area of increased final convergence

Figure 8:

Headbox nozzle with separating elements with reinforced end convergence and parallel top and bottom wall in the area of reinforced end convergence and then strongly converging top and bottom wall

Figure 9:

Fiber in the end area of a headbox nozzle with two snapshots

Figure 10:

Representation of the fiber in the end region of a headbox nozzle with two snapshots from FIG. 10 in the z / x coordinate network

Figures 1 to 8 show to illustrate the Invention concept highly schematic longitudinal sections in Machine direction through a headbox nozzle, following a turbulence generating area up to the outlet gap of the Headbox.

Figure 1 shows the simplest variant of a Nozzle area of a headbox according to the invention an upper wall 1 and an opposite lower wall 2, between which a suspension channel 4 is formed. The Headbox nozzle has two paths I and II with fundamentally different flow situations. The Route I represents the route in which the entire free cross section for the material suspension flow itself continuously reduced to the end of the route and thus an acceleration of the stock suspension in Flow direction causes. Subsequent to the first Route I follows the second route II, in which one Reversal of the acceleration, i.e. a flow deceleration takes place, due to the divergent form of Suspension channel in this area an alignment of the Fibers that are in the stock suspension in the z direction is effected.

FIG. 2 shows a headbox nozzle with the top wall 1 and the lower wall 2, the course of which is shown in FIG. 1 corresponds, in addition, between the top wall 1 and Two dividing elements 3.1 and 3.2 inserted in the lower wall 2. The Separating elements 3.1 and 3.2 also show one in Flow direction converging arrangement, so that three Suspension channels 4.1 to 4.3 arise, on the one hand via the entire route I each converge, on the other hand also in the sum of the available ones Cross sections (total cross section) over the entire distance I show convergence. Subsequent to route I follows the separator-free route II, through the here divergent top and bottom wall 1 and 2 formed and thus a delay in the material suspension flow effected on this second route II. It will be on it noted that all areas of the invention Headbox in which there is a delay in the stock suspension is caused are designed such that no additional Turbulence caused by paragraphs occurs only in this way an orientation of the fibers of the stock suspension in the z direction is achieved.

FIG. 3 shows a variant of the headbox nozzle from the Figure 2 shown, the difference to Figure 2, the two separators 3.1 and 3.2 in the area of the second Project route II. The separators 3.1 and 3.2 can be trained very flexibly, so that an adaptation of the lamella shape to the divergence of the second Area II results, and thus due to the total in downstream enlarging cross-section also Cross-sectional profile of the individual substance suspension channels 4.1 to 4.3, which expands downstream. Through the Continuation of the separating elements 3.1 and 3.2 in the divergent area of the second route II is brought about that the targeting effect of the flow retardant Area is reduced, as in each suspension channel Available space conditions are somewhat smaller and full height only in the end area of the second route II is available.

FIG. 4 shows a continuation of the headbox nozzle of Figure 1. There are none in this embodiment Partitions between the top and bottom walls 1 and 2 available. The first and the second route I and II correspond to the version from Figure 1. Following the route II is arranged a third route III, in which a short convergent line is appended, the is used only for beam stabilization, but due to their significantly shorter exposure time - in contrast to second route II - the originally existing aligning effect of the fibers in the z direction from the second Route II not fully compensated.

While shown in Figures 2 and 3 separators whose thickness and therefore stability is small, Figure 5 shows a headbox nozzle in its shape corresponds to the headbox nozzle of Figure 1, being inside the headbox nozzle has a relatively solid separating element 3 is arranged. The separating element 3 points from the beginning of the Route I to a continuous and even taper up to the slat end, which is behind the nozzle outlet gap is arranged on. The degree of rejuvenation of this Separating element 3 is chosen such that the convergence between top and bottom wall 1 and 2 in the area of the first Path I turns out larger than the convergence of the Separator element surfaces, so that a total of two Suspension channels 4.1 and 4.2 arise, which cover the entire first path I experience convergence. Subsequent to the route I follows the divergent route II, the is generated by the top and bottom walls on this part the headbox are designed to diverge.

However, there is also the possibility of the top and Bottom wall 1 and 2 in the area of the second route II to run in parallel so that the divergence of the two Suspension channels and thus also the total cross section only due to the taper of the separating lamella 3 in this area is generated.

FIG. 6 shows a headbox nozzle with an upper and bottom wall 1 and 2 shown in their shape of Headbox nozzle from Figure 1 corresponds. In addition there are two massive dividing elements 3.1 and 3.2 between the top and Bottom wall 1 and 2 arranged, the three suspension channels 4.1 to 4.3 form. The separators 3.1 and 3.2 have the entire area of the first path I the same thickness on and are arranged converging overall. To this In this way, three suspension channels 4.1 to 4.3 emerge, which the entire length of the first path converge. in the subsequent area of the second route II have the two separating elements on the opposite one another Surfaces a kink with a subsequent taper on, while the outwardly facing surfaces of the Separating elements have a linear linear course.

A similar design of the headbox nozzle is in the Figure 7 shown. The difference to Figure 6 is that that here the two separators 3.1 and 3.2 in the course of second route II are tapered on both sides. The history the top and bottom wall 1 and 2 of the headbox nozzle is in second area II executed in parallel, so that the divergence of the fabric suspension channels 4.1 to 4.3 exclusively through the tapering of the separating elements 3.1 and 3.2 arises.

Figure 8 shows a headbox in its Execution over the first and second routes I and II Headbox from Figure 7 corresponds, but is additional a subsequent route III available, in the Stabilization of the free jet a short-term strong Contraction of the stock suspension jet by one another tapering sections of the top and bottom wall 1 and 2 is produced.

Figures 9 and 10 illustrate the effect a flow delay on the orientation of a fiber F, which extends between the two points A and B, affects.

FIG. 9 shows two snapshots at time t ₁ and at time t ₂ for a fiber F which changes from a continuous flow into a divergent, braked flow. At time t ₁ , the two boundary points A and B of the fiber F have a uniform speed V _a1 and V _b1 , the speed vector of which is directed exclusively towards the front. At time t ₂ , in which this fiber is located in the divergent part of the flow, the flow has additional speed components in the z direction due to the divergent course, while the speed of the fibers is also greatly reduced in accordance with the continuity equation due to the larger cross section available becomes. In the end, points A and B are brought closer together in terms of their distance in the direction of flow, while points A and B drift apart in the z direction. This type of movement creates an extension and orientation of the fiber F between the points A and B in the z direction. This leads to an improvement in the transverse stiffness of the paper produced.

FIG. 10 shows the same situation again on a coordinate cross with the x and z axes, the snapshots at time t ₁ and t _{2 being} shown in each case.

It should also be noted that in the illustrated Embodiments additionally at the downstream end of the Additional top and bottom wall of the headbox the known aperture for setting the Outlet cross-section and thus influencing the Basis weight cross section can be provided without the Leave the scope of the invention. However, care should be taken be ensured that the interference caused by this Apertures have little impact on the uniformity of the Current.

Reference list

1

Top wall

2nd

Bottom wall

3rd

Separating element

3.1 - 3.2

Separating element

4th

Fabric suspension channel

4.1 - 4.3

Fabric suspension channels

A, B

Endpoints of a fiber

V

Speed vector

t

time

Claims (24)

Headbox of a paper machine with at least one stock suspension supply system, optionally with at least one area for turbulence generation and a subsequent headbox nozzle with a first and a second machine-wide boundary wall, the headbox nozzle having a first path I in which the total cross-section (total suspension-flowed free cross-sectional area) of the Headbox nozzle continuously and continuously reduced, with a second, shorter path II directly adjoining the first path I, characterized in that the second path II has a - preferably continuously - widening overall cross section which extends to the end of the headbox nozzle. Headbox according to the preamble of claim 1, with a second path III immediately following the second path II, which extends to the end of the headbox nozzle, characterized in that the second path II has a continuously expanding total cross-section and the total cross-section of the third path III is continuously and continuously reduced. Headbox according to the preceding claim 2, characterized in that the length L3 of the third path III is shorter than the length L2 of the second path II and the length L2 of the second path II is shorter than the length L1 of the first path I. Headbox according to the preceding claim 3, characterized in that: L2 * 0.3 <L3 <L2 * 0.7 and L1 * 0.1 <L2 <L1 * 0.3. Headbox according to one of the preceding claims, characterized in that the first path I begins immediately after the turbulence-generating area. Headbox according to one of the preceding claims, characterized in that the total cross section of the headbox nozzle is formed by at least part of the headbox nozzle length through a single suspension channel. Headbox according to one of the preceding claims, characterized in that at least over a part of the headbox nozzle length the total cross section of the headbox nozzle has a plurality of suspension channels which are formed by at least one machine-wide separating element, the at least one separating element being arranged between the first and the second boundary wall. Headbox according to the preceding claim 4, characterized in that all suspension channels without exception have the same cross-sectional profile. Headbox according to one of the preceding claims 7-8, characterized in that, without exception, all suspension channels have a congruent shape. Headbox according to one of the preceding claims 7-9, characterized in that the degree of divergence in the region of the second path II is the same for all suspension channels. Headbox according to one of the preceding claims, characterized in that the separating elements have a taper in the region of the second path II. Headbox according to the preceding claim 11, characterized in that the degree of convergence of the surfaces of the tapered ends of all separating elements is the same. Headbox according to one of the preceding claims, characterized in that the course of the upper wall and / or the lower wall, at least in the second area II, is designed as a mirror image of the course of the surface of the adjacent separating element with respect to the area in contact with the suspension. Headbox according to one of the preceding claims, characterized in that the headbox has a turbulence generator with a plurality of diffusion tubes, the diffusion tubes being arranged in machine-wide rows and the separating elements beginning between the rows of the diffusion tubes. Headbox according to one of the preceding claims, characterized in that the top and bottom walls of the headbox are of the same length. Headbox according to one of the preceding claims, characterized in that the contraction ratio .DELTA.H / .DELTA.L (change in the cross-sectional height becoming smaller in the flow direction to the path length) in the region of the first path section I is between 0.3% and 40%, preferably between 10% and 30% . Headbox according to one of the preceding claims, characterized in that the divergence ratio ΔH / ΔL (change in the cross-sectional height increasing in the direction of flow to the path length) in the region of the second path II is between 0.1% and 20%, preferably between 2% and 12% . Headbox according to one of the preceding claims, characterized in that the contraction ratio .DELTA.H / .DELTA.L (change in the cross-sectional height becoming smaller in the flow direction to the path length) in the region of the third path III is between 1% and 400%, preferably between 10% and 200%. Headbox according to one of the preceding claims, characterized in that the first path I is 250 mm to 1000 mm, preferably 400 mm to 800 mm long. Headbox according to one of the preceding claims, characterized in that the second path II is 20 mm to 150 mm long. Headbox according to one of the preceding claims, characterized in that the third path III is 0.5 mm to 300 mm, preferably 1 mm to 100 mm long. Headbox according to one of the preceding claims, characterized in that the smallest overall cross-sectional height of the first path I is 10 mm to 500 mm, preferably 15 mm to 150 mm. Headbox according to one of the preceding claims, characterized in that the largest overall cross-sectional height of the second path II is 30 mm to 200 mm. Headbox according to one of the preceding claims, characterized in that the smallest overall cross-sectional height of the third path III is 5 mm to 80 mm.

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