EP1881106B1 - Headbox of a machine for producing a sheet of fibrous material - Google Patents

Abstract

The nozzle includes a combination of longer plates (11.1, 11.2) and shorter plates (11.3, 11.4). The longer plates are associated with the nozzle wall (5) which includes the aperture plate (13). The longer plates have a length (LL) of 80% - 120% of the length (LD) of the nozzle. At least some plates, preferably all of them, are adjustable in length. Plates have only two different lengths. All plates have an at least locally-textured surface. The nozzle wall (6) which is free of plates, has an adjustable overhang (L) of up to 20 mm. The nozzle wall (6) has an adjustable projection (V) to gap height ratio of preferably 1 : 5. The aperture plate (13) has a main surface (17) in contact with the fibrous suspension, which runs parallel to the inner surface (18) of the associated nozzle wall. A variant of the nozzle design includes a central separating wedge between longer and shorter plates, pointing in the flow direction. The nozzle feeds a gap former between two recirculating, continuous sieve belts in a web-forming and dewatering arrangement. The nozzle wall with the aperture plate is arranged on the same- or the opposite side as the former. The former is a forming roller or a forming shoe, and is complemented by a breast roller.

Description

The invention relates to a headbox for a machine for producing a fibrous web from a pulp suspension, having a headbox having an upper nozzle wall and a lower nozzle wall and two side walls, tapering to a gap and a flowed through by the pulp suspension nozzle headbox, wherein the nozzle space of the headbox at least partially divided by a plurality of slats extending from the inlet end in the flow direction end of the nozzle into the nozzle chamber, and wherein on the upper nozzle wall outlet side a positionable and extending over the machine width aperture is arranged.

The fibrous web formed from the pulp suspension may in particular be a paper, board or tissue web.

Such a headbox is for example from the European patent applications EP 1 452 640 A2 and EP 1 489 224 A1 known. Its asymmetrical headbox nozzle leads to a more or less pronounced two-sidedness of the so-called layer orientation between the top and bottom of the finished fibrous web. A layer here is a height range of a finished fibrous web formed from a pulp suspension partial flow. Due to the flow conditions in the headbox and the shear forces in the former, a certain orientation of the fibers contained in the pulp suspension forms in the layer. The orientation of the fibers (layer Orientation) is defined by the ratio of machine direction orientation (MD) and cross machine direction (CD) orientation. The layer orientation can be determined either optically or by the ratio of the layer strength (MD) and the layer strength (CD). The different layer orientation leads, in particular in the production of wood-free fibrous webs, to sometimes serious problems during further processing. By way of example, the curl can be cited for copying papers which may no longer be usable, that is to say salable, due to too great a curl tendency.

The reason for the asymmetry of the layer orientation is seen in professional circles in the asymmetric structure of conventional headbox nozzles, since in the flow deflection at the aperture used, the fibers contained in the pulp suspension are increasingly aligned in the machine direction. On the opposite, glare-free lower nozzle wall, which protrudes beyond the diaphragm, is an alignment in the machine direction by increased microturbulence in the pulp suspension, due, inter alia, by a wall friction at a high speed level, but not or only limited instead.

It has been tried, as in the already mentioned European patent application EP 1 452 640 A2 or in the German Offenlegungsschrift DE 103 18 035 A1 set forth to provide a symmetrical nozzle structure in a headbox. However, due to spatial conditions, it is often not possible to attach a positionable aperture that extends over the width of the machine to both nozzle walls on the outlet side. Moreover, the attachment of such a second panel requires additional expenditure on acquisition and operating costs. And finally, such a second panel must also be maintained and renewed if greater damage or signs of wear are present.

Another possibility for producing critical wood-free fibrous webs is the use of a known to those skilled in and in the German Offenlegungsschrift DE 102 11 178 A1 shown multi-layer casserole with at least one solid separating wedge. In this case, in addition to the symmetrical headbox nozzle, the layer orientation can additionally be counteracted by different flow velocities in the individual layers of a two-sidedness. However, such a multi-layer casserole has several disadvantages: it is on the one hand very complex in its construction and operation, on the other hand, it requires the presence and operation of a technically sophisticated constant part, including accompanying stock preparation.

It is therefore an object of the invention to improve a headbox of the type mentioned in such a way that on the one hand, the two-sidedness of the layer orientation between the top and bottom of the fibrous web can be selectively influenced and on the other hand sheet disturbances, for example in the form of white spots, improved can be avoided.

This object is achieved in a headbox of the type mentioned in the present invention that the non-dazzle further nozzle wall - seen in the flow direction of the pulp suspension - a preferably adjustable supernatant in the range of 0 to 20 mm, preferably in the range of 0 to 10 mm, relative to the diaphragm and that a combination of at least one longer lamella and at least one shorter lamella is provided, wherein the respective longer lamella of the aperture having upper nozzle wall is associated.

The object of the invention is completely solved in this way.

Experiments carried out have shown that the arrangement of the lamellae in the headbox nozzle can directly influence the velocity profile in the z-direction (height direction) of the pulp suspension jet. Thus, for example, by the targeted use of at least one longer lamella in one half of the headbox nozzle, the speed in this half can be reduced by increased friction between the at least one longer lamella and the pulp suspension. These Reduced speed with simultaneously increased microturbulence in the pulp suspension promotes non-orientation of the fibers in the machine direction in the pulp suspension.

Thus, in spite of the presence of an orifice and the associated flow deflection of the pulp suspension, orientation of the fibers contained in the pulp suspension virtually does not take place when using the head box according to the invention. As a result, the two-sidedness of the layer orientation is significantly reduced, ideally even completely avoided.

Due to the inventive advantage that the two-sidedness of the layer orientation between the top and bottom of the fibrous web can be selectively influenced, the headbox, and even the machine can be adapted to the requirements of different wood-free fibrous webs.

In the present case, the term "assignment" describes the spatial position of a lamella within the headbox nozzle. The headbox nozzle of a Einschichtenstoffauflaufs can basically be divided into two halves, wherein one half is disposed adjacent to the nozzle wall having the aperture. The "assignment" of a lamella to the diaphragm having the upper nozzle wall thus means that it is spatially arranged in the upper nozzle wall of this adjacent half of the headbox nozzle.

With regard to the practical application, the headbox according to the invention thus has at least two groups of lamellae, a first group with longer lamellae, which is associated with the upper nozzle wall having the diaphragm, and at least one further, in particular a second group with shorter lamellae, the facing away from the aperture upper nozzle wall.

In a first preferred embodiment, it is provided that all the longer lamellae are associated with the upper nozzle wall having the orifice. Thus, the two-sidedness of the layer orientation can effectively be counteracted due to the velocity profile prevailing in the headbox nozzle.

The respective longer lamella preferably has a lamella length in the range of 75 to 130%, preferably in the range of 80 to 120% of the length of the headbox nozzle. Should this particular longer lamella be beyond the aperture, it should not exceed a protrusion of 0 to 20 mm from the headbox to avoid leaf disturbances, for example in the form of white spots. By contrast, the respective shorter lamella preferably has a lamellar length in the range of ≦ 80%, preferably ≦ 75%, of the length of the headbox nozzle. In this case, in a further embodiment, at least some, preferably all slats have an adjustable slat length. Corresponding devices for adjusting slat lengths are known to the person skilled in the art from a large number of publications.

In view of a high degree of standardization and low storage levels are provided in a further favorable embodiment slats with only two different slat lengths. This also provides the advantage of improved interchangeability of lamellae.

Furthermore, at least some, preferably all lamellae are preferably provided at least in regions with a structured surface. This structured surface may, for example, be a downstream and structured lamella tip, wherein the structure may take the form of grooves of rectangular and / or wedge-shaped and / or parabolic and / or round shape with constant and / or different depth. This proposed geometry results in the advantage of the availability of stable flow conditions even with asymmetric flow channels and the best possible flow of the structured downstream fin end with respect to a vortex avoidance.

In general, the iris-free lower nozzle wall-viewed in the flow direction of the pulp suspension-can have a preferably adjustable board from projection to gap height in the range from 0 to 10, preferably in the range from 1 to 5, since in this area the influence of the iris-free lower nozzle wall on the layers Orientation can be minimized in an excellent way.

Moreover, it may be advantageous if the diaphragm has a main surface touched by the pulp suspension which runs parallel to the inner surface of the associated upper nozzle wall. This provides a fluidically optimal design of the end region of the headbox, in particular the aperture for reducing the jet contraction.

In a machine for producing a fibrous web from a pulp suspension, the headbox according to the invention can also be followed by a gap former with two endless sieves, each forming a sieve loop, of which the first sieve is guided via a forming device with a curved support surface and the second sieve over a further element is passed, the two sieves thereafter together to form a wedge-shaped material inlet gap which receives the fibrous suspension directly from the headbox according to the invention, converge in the region of the former or after the expiration of the two sieves of the respective element and then form a Doppelsiebstrecke.

In this case, the aperture upper nozzle wall may be the same or mutually arranged the forming device. In the case of a mutual arrangement obtained by the centrifugal forces a stronger drainage on the outer side, in addition, the jet velocity profile, ie the effect of the longer slats used there, immediately frozen. A similar result is also achieved when the shutter and the curved support surface of the former are on the same side.

The shaping device preferably has at least one forming roller or a forming shoe from a technological point of view, whereas the further element may comprise at least one breast roll.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

Figur 1

eine schematische und geschnittene Seitenansicht eines stromabwärtigen Teils einer Stoffauflaufdüse eines erfindungsgemäßen Stoffauflaufs, und

Figuren 2 und 3

zwei schematische und geschnittene Seitenansichten eines stromabwärtigen Teils von zwei weiteren Ausführungsformen einer Stoffauflaufdüse eines erfindungsgemäßen Stoffauflaufs mit nachgeordnetem Spaltformer.

Show it

FIG. 1

a schematic and sectional side view of a downstream part of a headbox of a head box according to the invention, and

FIGS. 2 and 3

two schematic and sectional side views of a downstream part of two further embodiments of a headbox of a headbox according to the invention with downstream Spaltformer.

The FIG. 1 shows a schematic and sectional view of a headbox 1 for a machine for producing a merely schematically indicated fibrous web 2 from a pulp suspension 3. The fibrous web 2 formed from the pulp suspension 3 may in particular be a paper, board or tissue web.

The headbox 1 has an upper nozzle wall 5 and a lower nozzle wall 6 and two side walls 7, 8, not shown, tapering to a gap 9 and a flowed through by the pulp suspension 2 nozzle chamber 10 having headbox 4.

The nozzle chamber 10 of the headbox nozzle 4 is at least partially divided by a plurality of fins 11.1 to 11.4, which extend starting from the flow direction R (arrow) inlet side nozzle end 12 into the nozzle chamber 10.

Further, a positionable and over the machine width B (arrow) extending aperture 13 is arranged on the outlet side of the upper nozzle wall 5. The aperture 13 is, for example, of several, across the machine width B (arrow) Distributed and not shown adjusting devices (arrow 14), in particular spindle drives, for the purpose of their positioning applied.

It is a combination of two longer slats 11.1, 11.2 and two shorter slats 11.3, 11.4 provided, wherein the respective longer slat 11.1, 11.2 of the diaphragm 13 having upper nozzle wall 5 is assigned. In short, there are two groups 11.A, 11.B provided by lamellae 11.1 to 11.4, a first group 11.A with longer lamellae 11.1, 11.2, which is associated with the diaphragm 13 having the upper nozzle wall 5, and a second group 11th .B with shorter lamellae 11.3, 11.4, which faces away from the diaphragm 13 having the upper nozzle wall 5. In this case, the slats 11.1, 11.2 (panel 13) should be longer in total than the slats 11.3, 11.4.

The respective longer lamella 11.1, 11.2 has a lamella length LL in the range of 75% (representation) to 130% (dashed line), preferably in the range of 80 to 120% of the length LD of the headbox nozzle 4. By contrast, the respective shorter lamella 11.3, 11.4 has a lamellar length LL in the range of ≦ 80%, preferably ≦ 75%, of the length LD of the headbox nozzle 4. So there are slats 11.1, 11.2 and 11.3, 11.4 provided with only two different slat lengths LL. At least some, preferably all slats 11.1 to 11.4 can have an adjustable slat length LL.

Furthermore, at least the longer fins 11.1, 11.2 are provided at least in regions with a structured surface 15. The structured surface 15 forms a downstream and structured fin tip 16, which structure may be in the form of grooves of rectangular and / or wedge-shaped and / or parabolic and / or round shape with constant and / or different depths.

The iris-free lower nozzle wall 6 - seen in the flow direction R (arrow) of the pulp suspension 3 - has a preferably adjustable supernatant L in the range of 0 to 20 mm, preferably in the range of 0 to 10 mm, relative to the diaphragm 13 on. The adjustability of the supernatant L is indicated by a double arrow E. Basically, the iris-free lower nozzle wall 6 - seen in the flow direction R (arrow) of the pulp suspension 3 - a preferably adjustable board V of supernatant L to gap height s in the range of 0 to 10, preferably in the range of 1 to 5, on. With regard to the further embodiment of the preferably adjustable board V of the lower nozzle wall 6 is on the German Offenlegungsschrift DE 103 24 711 A1 directed.

The orifice 13 of the headbox 1 may moreover have a main surface 17 which is in contact with the pulp suspension 3 and runs parallel to the inner surface 18 of the upper nozzle wall 5. With regard to the further embodiment of this "parallel diaphragm" 13 is based on the German patent application DE 10 2004 047 879 A1 directed.

And ultimately, in the FIG. 1 the velocity profile G in the z-direction (height direction, double arrow) of the pulp suspension jet formed from the pulp suspension 3 is shown. This velocity profile G has due to the asymmetric arrangement of the slats 11.1, 11.2 and 11.3, 11.4 as well as a clear asymmetry. The beam is significantly slower on the upper side, ie on the side with the longer fins 11.1, 11.2.

The FIG. 2 shows a schematic and sectional side view of a downstream part of a first embodiment of a headbox 4 of a headbox 1 according to the invention with downstream Spaltformer 200th

The gap former 200 has two endless sieves 201, 202, each forming a sieve loop 203, 204, of which the first sieve 201 is guided via a forming device 205 with a curved support surface 206 and the second sieve 202 is guided over a further element 207. Thereafter, the two screens 201, 202 together to form a wedge-shaped material inlet gap 208, which receives the fibrous suspension 3 directly from the headbox 1 according to the invention. Subsequently, the two sieves 203, 204 with the introduced pulp suspension 3 form a twin-wire section 209.

The former 205 is configured as a forming roller 210, whereas the other member 207 is configured as a breast roller 211. The shaping device 205 can also be designed as a forming shoe in a further embodiment.

With regard to the basic structural design of the headbox 1 together with slats 11.1 to 11.4 is based on the description of the trained as a single-layer headbox headbox 1 of FIG. 1 directed.

The aperture 13 having the upper nozzle wall 5 is mutually arranged in the present embodiment of the former 205. The lower nozzle wall 6, however, is glare-free.

The FIG. 3 shows a schematic and sectional side view of a downstream part of a second embodiment of a headbox 4 of a head box 1 according to the invention with downstream Spaltformer 200th

Since this embodiment is similar to that in the FIG. 2 is only in the embodiment of the nozzle walls 5, 6 different, is in terms of their general description to the description of the in the FIG. 2 referenced embodiment.

In this embodiment, the aperture 13 having the upper nozzle wall 5 is arranged on the same side of the former 205. The lower nozzle wall 6 is again glare-free.

In summary, it should be noted that the invention a headbox of the type mentioned is further developed such that on the one hand, the two-sidedness of the layer orientation between the top and bottom of the fibrous web can be selectively influenced and on the other hand leaf disorders, for example in the form of white spots, improved can be avoided.

LIST OF REFERENCE NUMBERS

1

headbox

2

Fibrous web

3

Fibrous suspension

3.1

Fibrous suspension

3.2

Fibrous suspension

4

headbox

5

Upper nozzle wall

6

Lower nozzle wall

7

Side wall

8th

Side wall

9

gap

10

nozzle chamber

11.1, 11.2

Longer lamella

11.3, 11.4

Shorter slat

11.A

fin group

11.B

fin group

12

nozzle end

13

cover

14

Control devices (arrow)

15

surface

16

lamella tip

17

main area

18

palm

200

gap former

201

First sieve

202

Second sieve

203

wire loop

204

wire loop

205

forming device

206

Curved support surface

207

element

208

Stock inlet gap

209

twin-wire

210

forming roll

211

breast roll

B

Machine width (arrow)

e

double arrow

G

velocity profile

L

Got over

LD

Length (headbox nozzle)

LL

lamellar length

R

Flow direction (arrow)

s

gap height

V

Board

z

Height direction (double arrow)

Claims (12)

1. Headbox (1) for a machine for producing a fibrous web (2) from a fibrous suspension (3), comprising a headbox nozzle (4) having an upper nozzle wall (5) and a lower nozzle wall (6) and also two side walls (7, 8), tapering to a slot (9), and a nozzle chamber (10) through which the fibrous suspension (3) flows, the nozzle chamber (10) of the headbox nozzle (4) being subdivided, at least in some regions, by a plurality of slats (11.1 to 11.4) which, starting from the nozzle end (2) on the inlet side in the flow direction (R), extend into the nozzle chamber (10), and there being arranged on the upper nozzle wall (5) on the outlet side a slice (13) that can be positioned and that extends over the machine width (B),
   characterized in that
   the lower nozzle wall (6) that has no slice - seen in the flow direction (R) of the fibrous suspension - has a preferably adjustable projection (L) in the range from 0 to 20 mm, preferably in the range from 0 to 10 mm, with respect to the slice (13), and
   in that a combination of at least one longer slat (11.1, 11.2) and at least one shorter slat (11.3, 11.4) is provided, the respective longer slat (11.1, 11.2) being assigned to the upper nozzle wall (5) having the slice (13).
2. Headbox (1) according to Claim 1,
   characterized in that
   all the longer slats (11.1, 11.2) are assigned to the upper nozzle wall (5) having the slice (13).
3. Headbox (1) according to Claim 1 or 2, characterized in that
   the respective longer slat (11.1, 11.2) has a slat length (LL) in the range from 75 to 130%, preferably in the range from 80 to 120%, of the length (LD) of the headbox nozzle (4).
4. Headbox (1) according to one of the preceding claims,
   characterized in that
   the respective shorter slat (11.3, 11.4) has a slat length (LL) in the region of ≤ 80%, preferably ≤ 75%, of the length (LD) of the headbox nozzle (4).
5. Headbox (1) according to one of the preceding claims,
   characterized in that
   at least some, preferably all, slats (11.1 to 11.4) have an adjustable slat length (LL).
6. Headbox (1) according to one of the preceding claims,
   characterized in that
   slats (11.1 to 11.4) having only two different slat lengths (LL) are provided.
7. Headbox (1) according to one of the preceding claims,
   characterized in that
   at least some, preferably all, slats (11.1 to 11.4) are provided with a structured surface (15), at least in some regions.
8. Headbox (1) according to one of the preceding claims, in particular according to Claim 7,
   characterized in that
   the lower nozzle wall (6) that has no slice - seen in the flow direction (R) of the fibrous suspension (3) - has a preferably adjustable forward protrusion (V) from projection (L) to slot height (s) in the range from 0 to 10, preferably in the range from 1 to 5.
9. Headbox (1) according to one of the preceding claims,
   characterized in that
   the slice (13) has a main surface (17) which is touched by the fibrous suspension (3) and which runs parallel to the inner surface (18) of the associated upper nozzle wall (5).
10. Machine for producing a fibrous web (2) from a fibrous suspension (3), comprising a headbox (1), downstream of which in the machine running direction there is arranged a gap former (200) having two endless wires (201, 202) each forming a wire loop (203, 204), of which the first wire (201) is led over a forming device (205) having a curved supporting surface (206), and the second wire (202) is led over a further element (207), the two wires (201, 202) thereafter run together in the region of the forming device (205) after the two wires have run off the respective element, forming a wedge-shaped stock inlet gap (208) which picks up the at least one fibrous suspension (3) directly from the headbox (1), and then form a twin-wire section (209),
    characterized in that
    the headbox (1) is formed in accordance with one of Claims 1 to 10, and in that the upper nozzle wall (5) having the slice (13) is arranged on the opposite side or the same side as the forming device (205).
11. Machine according to Claim 10,
    characterized in that
    the forming device (205) has at least one forming roll (210) or a forming shoe.
12. Machine according to Claim 10 or 11, characterized in that
    the further element (207) has at least one breast roll (211).

Images