WO2012000690A2

WO2012000690A2 - Sheet-forming system for a machine for producing an at least single-layer fibrous material web

Info

Publication number: WO2012000690A2
Application number: PCT/EP2011/054324
Authority: WO
Inventors: Markus Häußler; Volker Schmidt-Rohr; Wolfgang Schwarz; Jürgen Prössl; Thomas RÜHL
Original assignee: Voith Patent Gmbh
Priority date: 2010-06-30
Filing date: 2011-03-22
Publication date: 2012-01-05
Also published as: DE102010030707A1; WO2012000690A3

Abstract

The invention relates to a sheet-forming system (1) for a machine (2) for producing an at least single-layer fibrous material web (3), in particular a paper, cardboard or packaging paper web, from at least one fibrous material suspension (4; 4.1, 4.2). The system comprises at least one single-layer headbox (5) and a twin wire former (6), which comprises two endless wires (7, 8), each revolving in a wire loop (7.1, 8.1). The first wire is a Fourdrinier wire (7), which, in a pre-dewatering section (9) downstream [or in the region] of the application of the at least one fibrous material suspension (4; 4.1, 4.2) in the form of a free fibrous material suspension jet (4.S) by means of the at least single-layer headbox (5), is guided over a wire table (10) that is stationary and preferably under suction, the surface (11) of which touching the Fourdrinier wire (7) is formed by a covering (12) having a plurality of foils (13) which are arranged in succession in the wire running direction (S) and extend in the transverse machine direction (CD) and have interposed free dewatering openings (14), and over a plurality of suction elements (15), in particular suction boxes (15.1). The second wire is a top wire (8), and the two wires (7, 8) together form, at least in sections, a twin wire zone (16) having a wedge-shaped infeed nip (17). In the twin wire zone (16), the top wire (8) guided over an infeed roller (18) runs over a plurality of rigidly arranged foils (19), which are arranged spaced with respect to each other at a dewatering box (20). The sheet-forming system (1) according to the invention is characterised in that the covering (12) of the stationary wire table (10) that is preferably under suction comprises at least two zones (10.Z1, 10.Z2), each having a plurality of foils (13), wherein the foils (13) arranged in the first zone (10.Z1) are arranged with an average spacing (10.Z1.TD) in the range between 20 and 70 mm, preferably between 20 and 40 mm, more particularly between 20 and 35 mm, and the foils (13) arranged in the second zone (10.Z2) are arranged with an average spacing (10.Z2.TD) in the range between 50 and 120 mm, preferably between 50 and 100 mm, more particularly between 50 and 80 mm.

Description

Sheet forming system for a machine for manufacturing

an at least single-layer fibrous web

The invention relates to a sheet forming system for a machine for producing an at least single-layer fibrous web, in particular a paper, cardboard or packaging paper web, from at least one pulp suspension, with an at least one-layer headbox and with a Doppelsiebformer, the two, in each case a loop loop endless screens comprising, wherein the first sieve is a wire, which in a Vorentwässerungsstrecke after or in the region of application of the at least one pulp suspension as a pulp suspension free jet by means of at least one-layer headbox via a stationary and preferably evershened Siebtisch, the longitudinal sieve-contacting surface of a coating with several in Sieblaufrich- direction successively arranged and extending in the cross-machine direction bars with intermediate drainage openings is formed, and a plurality of suction elements, in particular suction boxes g eführt, wherein the second sieve is an upper sieve, wherein the two sieves at least partially together form a wedge-shaped inlet gap having a double-wire zone, and wherein in the twin-wire guided over an inlet roller upper sieve over a plurality of rigidly arranged strips runs at a mutual distance to a Drainage boxes are arranged.

Sheet forming systems for machines for the production of fibrous webs, in particular paper, board or packaging paper webs, from at least one respective pulp suspension are previously known in a wide variety of designs from the prior art. Thus, such a sheet forming system for a machine for producing an at least single-layer fibrous web, in particular a paper, cardboard or packaging paper web, from at least one pulp suspension, for example from the document WO 2004/018768 A1 (EP 1 543 194 A1), in particular Figure 7 together Description of the figures known. In this case, the first dewatering element of the twin-wire zone is designed as a stationary and evacuated dewatering shoe. In this case, the drainage shoe is designed in such a way that a substantially pulsation-free drainage thereof takes place in the fibrous suspension guided between the two sieves.

Practice has shown for this dewatering element that it does not have the best suitability for producing a high quality fibrous web. Furthermore, drainage elements are known which have obliquely employed and coated with ceramic plates at an angle to the direction of the screen.

By obliquely employed plates, a transverse force component is generated, which shifts and upsets the screen in the cross machine direction. This enhances the wire ripple, which contributes to cross-profile quality degradation in the fibrous web to be produced. Furthermore, this embodiment also tends to produce strips in the longitudinal direction of the fibrous web to be produced. It is therefore an object of the invention to improve a sheet forming system of the type mentioned in such a way that the disadvantages of the prior art mentioned as far as possible reduced, preferably even completely avoided. In particular, an initial, that is to say initial stationary and preferably evacuated drainage element in an embodiment of a screening table for use in a sheet forming system should be specified, by means of which the at least one pulp suspension in a front drainage section of the drainage element at the same level of retention as at a For- merswalze a costly Spaltformers can be dewatered evenly across the width.

This object is achieved according to the invention in a sheet forming system of the type mentioned in that the covering of the stationary and preferably evacuated Siebtisches at least two, each having multiple strips comprising zones, wherein arranged in the first zone bars with an average pitch in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm, and wherein the strips arranged in the second zone have an average pitch in the range between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm, are arranged. The object of the invention is completely solved in this way.

As a result of the embodiment according to the invention having the strips arranged in the dividing region according to the invention, the pressure profile profile characterizing the dewatering pressure on the first initial dewatering element can be considerably smoothed in comparison to the embodiments of the prior art. Locally high variations of the amplitudes and strong gradients of the dewatering pressure are avoided. As a result, the retention can be significantly improved and adapted approximately to the level of a forming roller. The invention is also based on the finding that the pressure curve over a stationary, that is, in operation of the sheet forming system drainage with drainage holes depending on the geometry of different gradients, especially in terms of height and gradients occurring pressure peaks and their frequency may have. This different maximum pressure level decisively influences the retention. It has also been recognized that the vacuum pulses between the overpressure pulses, that is, the amplitudes and the gradients of these high vacuum values, can be decisively influenced by the number of drainage bars per unit length, that is to say by the division. Furthermore, the maximum flow velocity in the fiber mat and the compaction state are essential for the retention. By the vacuum pulses, the compression of the fiber mat generated by the pressure pulses is reversed again by the fiber mat is relieved by the reversal of the dewatering direction. With a reduction in the compression of the fiber mat, the retention deteriorates because the filter effect decreases. In order to still receive a high retention, therefore, the shortest possible discharge points along the drainage section should be present, which by the inventive design of the divisions in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm , or between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm, is achieved.

The respective average pitch in the individual zones defines the distance between two consecutive bars in the direction of the direction of the wire, each measured from the same reference edge on the individual bar. This can be described by the sum of the width of the drainage opening in the wire direction and the width of the strip on the surface. The term "average" is based on the well-known mathematical definition.

The strips forming the covering and arranged in a zone of the stationary and preferably evacuated screening table preferably have a respective division of pitch in the range from 50 to 120 mm, preferably from 50 to 100 mm, in particular from 50 to 90 mm.

The individual strips of the lining of the stationary and preferably vacuum-sieve can be used with a constant or approximately constant groin be arranged in at least a single zone of the lining of the stationary and preferably evacuated sieve or over the entire stationary and preferably evacuated sieve. Furthermore, the strips forming the covering and arranged in a zone of the stationary and preferably evacuated screening table preferably have a respective strip width of at least 3 mm, preferably of at least 10 mm, in particular of at least 15 mm, thereby providing adequate guidance and stabilization of the screen to ensure.

Furthermore, the individual strips of the stationary and preferably evacuated screening table can have a constant or approximately constant strip width in at least one individual zone of the lining of the stationary and preferably evacuated screening table or over the entire stationary and preferably evacuated screening table. In this case, very small partitions can be realized while maintaining a high drainage performance and a pressure curve free of large vibration amplitudes.

To achieve a high dewatering performance, in at least a single zone of the lining of the stationary and preferably evacuated screening table or over the entire stationary and preferably evacuated sieve table, the summed last width of the surface of the individual strips touching the sieve is preferably smaller than the summed opening width of the individual drainage openings.

Furthermore, in the first zone of the lining of the stationary and preferably evacuated sieving table, the summed opening width of the individual drainage openings preferably assumes a value in the range of 90 to 230% of the summed last width of the surface of the individual strips touching the four-wire sieve. And in the second zone of the lining of the stationary and preferably evacuated drainage element, the summed opening width of the individual drainage openings preferably has a value in the range of 100 to 400% of the summed last width of the cross-section touching surface of the individual strips. This embodiment causes in the initial region of the drainage of at least one introduced pulp suspension better and more effective extraction of air bubbles contained in it. This effectively prevents the formation of bright spots in the fibrous web to be produced.

Moreover, the surface of the lining of the stationary and preferably evacuated screening table is preferably curved at least in regions. In this case, at least one, the curvature of the surface of the covering of the stationary and preferably evacuated sieve table describing at least partially curvature radius preferably takes a value in the range between 0.3 and 5.0 m, preferably between 0.6 and 3.0 m, in particular between 1 , 0 and 2.0 m, on. The greater curvature allows a higher dewatering pressure on the at least one pulp suspension due to the acting screen tension to achieve the same dewatering performance as on a forming roll.

The radius of curvature of the surface of the first zone of the pad of the stationary and preferably evacuated screen may be smaller than the radius of curvature of the surface of the second zone of the pad of the stationary and preferably evacuated screen. The advantage of this design is that the dehydration of the at least one fibrous suspension with gentle dewatering is thereby gentler. The at least two zones covering of the stationary and preferably evacuated screening table may be zonal different in terms of design, arrangement and / or orientation of the individual strips and / or drainage openings. This makes it relatively easy to make adjustments to the specific application.

Furthermore, in the twin-wire zone, the wire mesh preferably runs over a plurality of strips which mutually rigidly arranged on the drainage box Bars are arranged, which are supported by means of resilient elements and which are pressed with a selectable force against the wire. This embodiment option has a positive effect on improving the formation in the fibrous web to be produced.

In a further preferred embodiment, the head box of the sheet forming system according to the invention is designed as a multi-layer headbox, in particular a two-headbox containing a headbox nozzle, the at least two across the width of the machine extending, separated by at least one separating element, during operation of the multilayer headbox , in particular of the two-layer casserole each having a pulp suspension as pulp suspension flow leading and converging nozzle chambers, which upstream each have a feed and downstream each having a width extending across the exit gap having a gap width. In this case, the two outer nozzle spaces on the outside each have an outer wall and the separating element has two during the operation of the multi-layer headbox, in particular the Zweilichtstoffauflaufs of the respective adjacent pulp suspension flow touched separator element surfaces.

Such a multilayer headbox for a machine for producing a multilayer fibrous web, in particular a multilayer paper or board web, from at least two fibrous stock suspensions is known, for example, from document DE 195 38 149 A1. In the case of the multi-layer casserole designed as a three-layer fabric casserole, the fiber suspension layers are kept separate from one another by rigid dividing elements, in particular partitions. At the downstream end, adjacent dividing walls are deformable differently perpendicular to the jet plane, so that both a good jet guidance is possible and the optimal connection of the suspension layers after the exit from the head box. The pulp suspensions will usually be suspensions of different pulps; but it can also be suspensions with the same fibrous materials, but with different physical properties. A physical property may be, for example, different pressures for setting different flow velocities in the respective pulp suspension stream.

The sheet forming system according to the invention with such a multi-layer head box, in particular two-layer headbox, preferably also has the following features:

the at least one separating element arranged in the headbox nozzle has a separating element projection in the range from 0.05 to 3.00, preferably from 0.10 to 2.00, in particular from 0.20 to 1.50, the largest individual gap width of the at least two Nozzle chambers on; and

- The pulp suspension free jet formed from the at least two pulp suspension streams has a free jet length in the range of 100 to 500 mm, preferably from 125 to 400 mm, in particular from 150 to 300 mm. The headbox of the multilayer headbox of the sheet forming system of the present invention thus constructed provides the advantage that the layer purity in the height direction can be markedly improved over known multilayer headboxes. This is in principle due to the fact that the pressure loss and thus the fluid wall friction on the separating element can be reduced by shortening the separating element projection. Associated with this is a reduction of the turbulence forming in the pulp suspension streams with concomitant improvement of the layer purity in the height direction. Also, the separating element of the multilayer headbox of the sheet forming system according to the invention which is designed in this way has the advantage that the layer purity in the height direction is better than known multilayer material. in turn noticeably improve. This is primarily due to the fact that the angle of incidence of the two pulp suspension streams is significantly reduced when they are merged at the separator end. This again involves a reduction of the turbulences forming in the pulp suspension streams with a concomitant improvement in the layer purity in the height direction.

The turbulence forming in the outer pulp suspension streams also substantially affects the coverage qualities of the outer pulp suspension layers. Now, if the turbulence is reduced, so also reduce the mixing zones within the pulp suspension jet in its height direction. And the reduced mixing zones, in turn, contribute significantly to improved coverage qualities of the outer pulp suspension layers.

Thus, in a fibrous web produced by means of the multilayer headbox according to the invention, both a high-grade layer purity in the height direction and a good optical cover quality of the outer fibrous stock suspension layers are achieved.

If the multi-layer casserole is designed as a three- or even four-layer casserole, the separator projections can have the same, approximately the same or even different values, depending on the application. The separating element of the multi-layer headbox may also comprise two separating element regions each having a separating element angle, an upstream separating element starting region and a downstream separating element end region. Furthermore, the two separating element angles of the two separating element regions of the multilayer headbox may assume different angular values, the separating element starting angle of the upstream separating element starting region preferably assuming a greater angle value than the separating element end angle of the downstream separating element end region. Furthermore, the said free jet length of the pulp suspension jet formed from the at least two pulp suspension streams still ensures a free-jet quality which is sufficient in terms of process technology. In the mentioned length range, the pulp suspension free jet still experiences no significant widening due to the air boundary layers forming on the two free-jet surfaces. Thus, by avoiding turbulence due to non-expansion of the pulp suspension jet, the layer purity of the pulp suspension streams in the height direction can be continued. The four mentioned features of the sheet formation system according to the invention ensure the continuous and process-reliable achievement of both a high-grade layer purity in the height direction and a good optical cover quality of the outer pulp suspension layers in a fibrous web produced therewith. The production of a multilayer fibrous web having a basis weight in the range of 20 to 60 g / m ² per pulp suspension layer at a production speed of over 900 m / min is also possible.

The at least one separating element arranged in the iris-free headbox nozzle preferably has a separating element supernatant in the range from 0.05 to 1.00, preferably from 0.10 to 0.95, in particular from 0.20 to 0.90, the largest single gap width the at least two nozzle chambers. In the case of this glare-free multi-layer headbox, the requirement is fulfilled that no diaphragm master requires only a small separating-element supernatant owing to the absence of a diaphragm.

The pulp suspension streams emerging from the headbox nozzle of the multi-layer headbox, in particular two-layer headbox of the sheet forming system according to the invention as a common pulp suspension jet, may moreover have different jet velocities. For example, the at least one difference in the jet velocities may have a value in the range from 10 to 60 m / min, preferably from 15 to 25 m / min, accept. This significantly reduces the spread of the mixing cone in the pulp suspension jet to the relevant pulp suspension layer. These requirements may also be dependent on the former concept in a known manner.

Furthermore, a preferably adjustable diaphragm with an aperture immersion depth is preferably arranged on at least one outer wall of the headbox nozzle and the at least one separator arranged in the headbox nozzle preferably has a separator projection in the range from 0.5 to 3.0, preferably from 0.6 to 2.0 , in particular from 0.7 to 1, 5, · the largest single gap width of the at least two nozzle chambers. Thus, in this multilayer material run, in particular two-layer bake, the requirement is met that a large baffle baffle requires a larger separation element projection. In the multi-layer casserole, in particular two-layer casserole of the sheet forming system according to the invention, it is of course also possible to arrange on both outer walls of the headbox nozzle a preferably adjustable aperture with an aperture immersion depth. The setting of the aperture can be done, for example, by means of a plurality of arranged over the width of the headbox adjusting units, in particular servomotors. This minimizes the pressure loss in the respective pulp suspension layer.

Furthermore, the aperture of the multi-layer headbox, in particular two-layer headbox of the sheet forming system according to the invention, can have a shallow immersion depth in the adjacent pulp suspension stream in the range of 1 to 30 mm, preferably in the range of 5 to 15 mm. This embodiment allows the generation of a minimum turbulence in the corresponding pulp suspension, but without equal to achieve the above-described disadvantageous turbulence level.

Furthermore, depending on the system requirement, at least one separating element can be used to separate two adjacent pulp suspension flows of the multilayer material. casserole, in particular Zweilichtstoffauflaufs the sheet forming system according to the invention rigid or by means of an upstream mounted hinge unit be arranged articulated in the headbox. These embodiments allow an optimal design of the multilayer headbox, in particular two-layer headbox of the sheet forming system according to the invention, to different operational system requirements.

In order for the two pulp suspensions guided in pulp suspension flows to undergo an optimum combination of process technology, the separating element end angle of the downstream separating element end region preferably has an angle value in the range from 1.5 to 8.0 °, preferably from 2.5 to 4.5 °. In addition, these angular ranges avoid adverse mixing of the two adjacent pulp suspensions. Furthermore, in view of a sufficient guide length for the two pulp suspension flows, it is advantageous if the downstream separating element end region of the separating element has a downstream separating element end length in the range from 10 to 150 mm, preferably from 15 to 75 mm, in particular from 25 to 50 mm and / or the downstream Trennelementendbereich of the separating element projects beyond the outlet gap of the headbox nozzle, preferably in a range of 10 to 25 mm.

And the mode of operation of the multi-layer headbox, in particular two-layer headbox of the sheet forming system according to the invention, can take place both in the overflow and underflow with the speed ranges 20 to + 80 m / min or 20 to -80 m / min.

Furthermore, with regard to a regulation of both the fiber orientation transverse profile and the basis weight cross profile of the multilayer fiber web, it may be advantageous if the multilayer headbox, in particular two-layer headbox, in another embodiment is provided with a dilution water control known from a large number of publications. For this purpose, at least one pulp suspension is a controlled feed stream, in particular a dilution water stream when generating a mixed stream with a mixed concentration fed. Furthermore, the separating element is preferably a flexible CFRP lamella which has a minimum rigidity both in the longitudinal direction and in the transverse direction, which assumes a value of at least 40 N / mm in some areas. Moreover, the separating element is preferably articulated by means of an upstream separating element holder and thus freely movable in the headbox nozzle. As a result of the upstream separating element receptacle of the separating element, a straight line, which is preferably aligned centrally in its longitudinal direction, runs by definition. Furthermore, the separation element may be provided in the embodiment of a flexible CFRP blade with a pointed Trennelementendbereich. The sheet forming system according to the invention can also be used in an outstanding manner in a machine for producing a fibrous web, in particular an at least one-layered paper, board or packaging paper web, from at least one fibrous stock suspension. The machine can be constructed according to the prior art and have all known machine areas.

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

Show it

Figure 1 is a schematic partial side view of a first preferred

Embodiment of the sheet forming system according to the invention;

Figure 2 is a schematic longitudinal partial sectional view of a first

Execution of a stationary and preferably evacuated drainage element of the sheet forming system according to the invention; FIG. 2A shows a bottom view of the first embodiment of a stationary and preferably evacuated drainage element of the sheet forming system according to the invention shown in FIG. 2. FIG. 3 shows a schematic longitudinal section of a second preferred embodiment of a stationary and preferably evacuated drainage element of the sheet forming system according to the invention;

FIG. 4 shows a first course of vibration in the pulp suspension produced with a known stationary and preferably evacuated drainage element on the basis of a diagram;

FIG. 5 shows a second oscillation profile in the pulp suspension produced with a known stationary and preferably evacuated drainage element on the basis of a diagram;

Figure 6 one with a stationary and preferably evacuated

Dewatering element of a sheet forming system according to the invention generated vibration waveform in the Faserstoffsuspen- sion on the basis of a diagram;

Figure 7 is a diagram of pitch width oscillation width for a stationary and preferably evacuated dewatering element of a sheet forming system according to the invention;

FIG. 8 is a schematic partial longitudinal section of a preferred embodiment

Embodiment of a sheet forming system according to the invention; and

9 shows a schematic longitudinal partial section illustration of an end region of a further preferred embodiment of a head box nozzle of a multi-layer headbox of a sheet forming system according to the invention.

1 shows a schematic partial side view of an embodiment of a sheet forming system 1 for a machine 2 not shown in detail for the production of a fibrous web 3 (dashed line) of at least one pulp suspension 4. In the produced fibrous web 3 (dashed lines) ment) may in particular be a paper, board or packaging paper web.

The sheet-forming system 1 has an at least one-layer headbox 5 and a twin-wire former 6, which comprises two endless wires 7, 8, each circulating in a respective wire loop 7.1, 8.1.

The first sieve is a four-wire sieve 7, which in a pre-dewatering section 9 after or in the region of application of the at least one pulp suspension 4 as a pulp suspension free jet 4.S means of at least one-layer headbox 5 via a stationary and preferably evacuated sieve 10, the surface of the wire 7 touching 1 1 of a covering 12 with a plurality in the wire direction S (arrow) arranged successively and in machine transverse direction CD (arrow) extending strips 13 is formed with intermediate drainage openings 14 therebetween, and a plurality of suction elements 15, in particular suction boxes 15.1 is performed.

The second sieve is an upper sieve 8. The two sieves 7, 8 at least in sections form a double-wire zone 16 having a wedge-shaped inlet gap 17, in the twin-wire zone 16 the upper sieve 8 guided via an inlet roller 18 runs over a plurality of rigidly arranged strips 19, which are arranged at a mutual distance on a drainage box 20.

The rigidly arranged strips 19 of the dehydration box 20 describe in the manner shown a running in the direction of wire direction S (Peil) curvature 19.K or they are arranged in a manner not shown along a direction extending in the wire direction S (arrow) straight line.

The two sieves 7, 8 with the at least one intervening fibrous suspension 3 are guided after the dewatering box 20 and within the twin-wire zone 16 via several dewatering elements known to the person skilled in the art and thus not explicitly shown. Then it will be in known The screen separation takes place, so that the fibrous web 3 to be produced (dashed line) on only one sieve of a press section, not shown, a machine for producing a fibrous web is fed. In an embodiment indicated only by dashed lines, in the twin-wire zone 16, the wire 4 can run over a plurality of strips 21 .1, which are mutually arranged on the strips 19 which are rigidly attached to the drainage box 20 and which are supported by resilient elements 22 and which can be selected with a selectable force 22 F (arrow) against the wire 7 are pressed. Also, in addition or alternatively, in the region of the wedge-shaped inlet gap 17, the wire 7 can run over at least one strip 21 .2 indicated only by dashed lines, which can be pressed against the wire 7 with a selectable force 22.F (arrow). Such embodiments are described in the German patent application DE 10 2009 027 432.4 dated 02.07.2009 (applicant's name: HPB14491 DE), the relevant disclosure of which is hereby made the subject of the present description.

The covering 12 of the stationary and preferably vacuum-sieve table 10 comprises two zones 10.Z1, 10.Z2 each having a plurality of strips 13. Of course, the pad 12 may include more than the two exemplified zones. In this case, the strips 13 arranged in the first zone 10.Z1 are arranged with an average pitch 10.Z1.TD in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm. On the other hand, the strips 1 3 arranged in the second zone 10. 2 are arranged with an average pitch 10.Z2.TD in the range between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm. see Figure 2).

2 shows a schematic longitudinal partial sectional view of a first embodiment of a stationary and preferably evacuated screening table 10 of the sheet forming system 1 according to the invention. The shown stationary and preferential Sifted sieve table 10 may for example be part of the sheet forming system 1 shown in FIG.

As already stated, the covering 12 of the stationary and preferably vacuum-sieve table 10 comprises two zones 10.Z1, 10.Z2 each having a plurality of strips 13. In this case, the strips 13 arranged in the first zone 10.Z1 are arranged with an average pitch 10.Z1 D in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm. On the other hand, the strips 13 arranged in the second zone 10.Z2 are arranged with an average pitch 10.Z2.TD in the range between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm.

On the underside, the stationary and preferably evacuated screening table 10 is provided with a closed box 23, which can be acted upon by preferably a single vacuum source, not shown in greater detail but known to a person skilled in the art, having a preferably controllable vacuum.

The individual strips 13 of the covering 12 of the stationary and preferably evacuated screening table 10 are in a constant or approximately constant strip division 10.T1, 10.T2 in at least one individual zone 10.Z1, 10.Z2 of the covering 12 of the stationary and preferably evacuated screening table 10 or over the entire screen table 10 away. In this case, the strips 13 of the stationary and preferably vacuumed screen table 10 have a respective strip width 10.T1, 10. T2 in the range from 50 to 120 mm, preferably from 50 to 100 mm, in particular from 50 to 90 mm.

The individual strips 13 are also inclined relative to the surface 11 of the covering 12 of the stationary and preferably evacuated screen element 10 which is contacted by the wire 4, ie they run obliquely to the same. The alignment is carried out at an angle in the direction of wire run S (arrow) in an alignment direction. angle α, which assumes a displayed constant or varying value in screen direction S (arrow).

In a further, but not explicitly illustrated embodiment, the surface 1 1 of the pad 12 of the stationary and preferably suctioned Siebtisches 10 may be curved at least partially. In this case, at least one, the at least partially curvature of the surface 1 1 of the pad 12 of the stationary and preferably evacuated Siebtisches 10 descriptive radius of curvature has a value in the range between 0.3 and 5.0 m, preferably between 0.6 and 3.0 m, especially between 1, 0 and 2.0 m, assume.

Further, the surface 7 touching the wire 7 of the individual and arranged in a zone 10.Z1, 10.Z2 strips 13 of the pad 12 of the stationary and preferably evacuated Siebtisches 10 has a respective strip width 13.B of at least 3 mm, preferably of at least 10 mm, in particular of at least 15 mm, on. It is constant or approximately constant in at least one individual zone 10.Z1, 10.Z2 of the lining 12 of the stationary and preferably evacuated sieving table 10 or over the entire sieve table 10. Also, in at least a single zone 10.Z1, 10.Z2 of the pad 10 of the stationary and preferably evacuated Siebtisches 10 or over the entire screen table 10 away the summed strip width 13th BS of the wire 7 touching surface 1 1 of the individual strips 13 smaller 14. Generally, in the first zone 10.Z1 of the lining 12 of the stationary and preferably evacuated screening table 10, the summed opening width 14.sub.BS of the individual drainage openings 14 has a value in the range from 90 to 230%. the summed strip width 13 BS of the wire 7 touching surface 1 1 of the individual strips 13 at. And in the second zone 10.Z2 of the lining 10 of the stationary and preferably evacuated sieving table 10, the summed opening width 14 BS of the individual drainage openings 14 takes a value in Range of 100 to 400% of the summed strip width 13 BS of the wire 7 touching surface 1 1 of the individual strips 13 at.

In principle, the covering 12 of the stationary and preferably evacuated screening table 10 comprising at least two zones 10.Z1, 10.Z2 can be zonal in terms of design, arrangement and / or orientation of the individual strips 13 and / or drainage openings 14.

FIG. 2A shows a bottom view of the first embodiment, shown in FIG. 2, of a stationary and preferably evacuated screening table 10 of the sheet forming system 1 according to the invention.

The drainage openings 14 of the covering 12 of the stationary and preferably evacuated screening table 10 extend essentially over the entire width 12.B of the lining 12, but at least over the effective width of the pulp suspension 10.B of the stationary and preferably evacuated screening table 10. The drainage openings 14 are preferably designed as slots. FIG. 3 shows a schematic longitudinal partial section illustration of a second embodiment of a stationary and, preferably, evacuated screening table 10 of the sheet forming system 1 according to the invention. The shown stationary and preferably evacuated screen table 10 may in turn be part of the sheet forming system 1 shown in FIG. 1, for example.

The lining 12 of the stationary and preferably vacuumed screening table 10 in turn comprises two zones 1, ZZ, 10.Z2 each having a plurality of strips 1 3. Here, the strips 13 arranged in the first zone 10. 1 are arranged with an average pitch 10.Z1 .TD in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm. On the other hand, the strips 13 arranged in the second zone 10.Z2 with an average pitch 10.Z2.TD are in the range between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm.

On the underside, the stationary and preferably evacuated screening table 10 is again provided with a closed box 23, which can be acted upon by preferably a single, not shown, known to those skilled in vacuum source with a preferably controllable / vacuum.

The individual strips 13 of the covering 12 of the stationary and preferably evacuated screening table 10 are also in a constant or approximately constant line division 10.T1, 10.T2 in at least one individual zone 10.Z1, 10.Z2 of the covering 12 of the stationary and preferably evacuated Sieving table 10 or arranged over the entire screen table 10 away. In this case, the strips 13 of the stationary and preferably suctioned Siebtisches 10 a respective strip pitch 10.T1, 10.T2 in the range of 50 to 120 mm, preferably from 50 to 100 mm, in particular from 50 to 90 mm on.

The individual strips 13 are also inclined relative to the surface 11 of the covering 12 of the stationary and preferably evacuated screen element 10 which is contacted by the wire 4, ie they run obliquely to the same. The alignment is carried out obliquely in the direction of wire direction S (arrow) in an alignment angle a, which assumes a displayed constant or varying value in the wire direction S (arrow). In a further, but not explicitly illustrated embodiment, the surface 1 1 of the pad 12 of the stationary and preferably suctioned Siebtisches 10 may be curved at least partially. In this case, at least one radius of curvature describing the at least partially curvature of the surface 11 of the lining 12 of the stationary and preferably evacuated sieving table 10 can have a value in the range between 0.3 and 5.0 m, preferably between 0.6 and 3.0 m, in particular between 1, 0 and 2.0 m, accept. Furthermore, the surface 7 contacting the wire 7 of the individual and arranged in a zone 10.Z1, 10.Z2 strips 13 of the pad 12 of the stationary and preferably evacuated Siebtisches 10 again a respective strip width 13.B of at least 3 mm, preferably of at least 10 mm, in particular of at least 15 mm. It is constant or approximately constant in at least one individual zone 10.Z1, 10.Z2 of the lining 12 of the stationary and preferably evacuated sieving table 10 or over the entire sieve table 10. Also, in at least a single zone 10.Z1, 10.Z2 of the pad 10 of the stationary and preferably evacuated Siebtisches 1 0 or over the entire screen table 10 across the summed strip width 13th BS of the wire 7 touching surface 1 1 of the individual strips thirteenth smaller than the summed opening width 14. BS of the individual drainage openings 14.

In addition, in the first zone 10.Z1 of the lining 12 of the stationary and preferably evacuated sieving table 10, the summed opening width 14.sub.BS of the individual drainage openings 14 takes a value in the range of 100 to 400% of the summed strip width 13.sub.BS of the long line 7 touching surface 1 1 of the individual strips 13. And in the second zone 10.Z2 of the lining 10 of the stationary and preferably evacuated screening table 10, the summed opening width 14 BS of the individual drainage openings 14 takes a value in the range of 90 to 230% of the summed strip width 13 BS of the surface 7 touching the surface 1 1 of the individual strips 13.

FIG. 4 shows a first oscillation profile V1 in the pulp suspension produced with a known sieve table 1 0.1 on the basis of a diagram. The abscissa of the diagram represents the dewatering path s, whereas the positive ordinate represents an overpressure Pü and the negative ordinate represents a negative pressure Pu, ie a vacuum. It is clearly a periodic or approximately periodic waveform V1 in the pulp suspension using a known screen table 10 with a variety of strips recognizable. The respective positive oscillation surface is a drainage region, the retention level of which can be set via the height of the oscillation amplitude. On the other hand, the respectively negative oscillation surface causes a loosening of the fiber mat forming from the at least one fibrous suspension as a result of the acting negative pressure. In addition, a worse filter effect is generated here.

FIG. 5 shows a second oscillation profile V2, V3 in the pulp suspension produced with a known sieve table 1 0.2 on the basis of a diagram.

The abscissa of the diagram in turn represents the dewatering section s, whereas the positive ordinate again represents an overpressure Pü and the negative ordinate again represents a negative pressure Pu, ie a vacuum.

Here, too, a repetitive oscillation course, which may optionally be subdivided into zones, in the pulp suspension can be discerned when using another known sieve table 10. The graph shown by a solid line shows the waveform V2 using a plurality of slats having drainage element, whereas the graph shown by a dashed line shows the waveform V3 using a known pulse-free Gleichdruckentwässerungselements. The second graph has a constant oscillation amplitude. FIG. 6 shows a vibration course V10 in the pulp suspension produced with a stationary and preferably evacuated screen table 10 of a sheet forming system 1 according to the invention on the basis of a diagram. Here again, the abscissa of the diagram represents the dewatering path s and the screen direction S (arrow), whereas the positive ordinate represents an overpressure Pü and the negative ordinate represents a vacuum Pu, ie a vacuum.

It can be clearly seen that the lining 12 of the stationary and preferably evacuated screening table 10 in at least two zones 10, Z1, Z0 each having a plurality of strips 13, oscillations S10 with different oscillation amplitudes S10.A in the at least one on the at least one Produced sieve introduced pulp suspension such that generated in the first zone 10.Z1 in the at least one fibrous suspension Schwingungsbrei- theses S1 OB of the vibrations S10 are smaller than the generated in the second zone 10.Z2 in the at least one pulp suspension oscillation widths S10.B the vibrations S10.

The oscillation amplitudes S10.A of the oscillations S10 generated in the first zone 10. Z1 of the lining 12 of the stationary and preferably evacuated sieving table 10 are in the range of 2 to 8 kPa, preferably of 4 kPa, and those in the second zone 10 Pads 12 of the stationary and preferably evacuated sieve table 10 produced vibration amplitudes S10.A the vibrations S10 are in the range of 5 to 20 kPa, preferably from 8 to 10 kPa.

The number of vibrations S10 generated in the at least one pulp suspension in the first zone 110 of the lining 10 of the stationary and preferably evacuated screening table 10 assumes a value in the range from 2 to 20, preferably from 4 to 10. On the other hand, the number of oscillations S1 0 generated in the at least one fibrous suspension in the second zone 10.Z2 of the lining 12 of the stationary and preferably evacuated sieving table 10 assumes a value in the range from 1 to 7, preferably from 2 to 3. Also, the vibration widths S10.B of the vibrations S10 generated in the at least one pulp suspension in the first zone 10. 1 are smaller than the vibration widths S10.B of the vibrations S10 generated in the second zone 10. Z2 in the at least one pulp suspension.

With regard to the process technology, it can be stated that the higher oscillation widths with high pressure pulses present in the first zone of the lining of the stationary and preferably evacuated drainage element cause the air bubbles to be pressed out of the at least one fibrous suspension. And the low oscillation width present in the second zone of the lining of the stationary and preferably evacuated drainage element causes a high retention in the at least one pulp suspension.

Finally, FIG. 7 shows a diagram of pitch width oscillation amplitude for a stationary and preferably evacuated drainage element of a sheet forming system according to the invention.

The abscissa of the diagram represents the pitch width TB at a constant ratio of opening width ÖB to pitch width TB, whereas the ordinate represents the vibration amplitude SA.

In this case, a dividing width TB is clearly visible, below which the preferred pitch width TB.Z1 for the first zone 10.Z1 of the lining of the stationary and preferably evacuated drainage element and above which the preferred pitch width TB.Z2 for the second zone 10.Z2 of the pavement the stationary and preferably evacuated Siebtisches is.

FIG. 8 shows a schematic longitudinal partial sectional illustration of the multi-layer casserole 5 of the sheet-forming system 1, wherein the multi-layer material feed is designed as a two-layer casserole 5. The illustrated sheet forming system 1 is a component of a machine 2 not shown in detail for producing Position of a multilayer fibrous web 3, in particular a multilayer paper or board web, of two pulp suspensions 4.1, 4.2.

The pulp suspensions 4.1, 4.2 will generally be suspensions with different pulps; but it can also be suspensions with the same fibrous materials, but with different physical properties.

The multi-layer headbox 5 designed as a two-way headbox comprises a headbox nozzle 24 which has two pulp suspension 4.1, 4.2, which extend across the width B (arrow) and are separated on the inside by a separating element 25, while the multi-layer headbox 5 is operating. , 4.20 (arrow) leading and converging nozzle chambers 26.1, 26.2. The two nozzle chambers 26.1, 26.2 have the same or approximately the same cross-sectional profiles. Furthermore, the respective nozzle chamber 26.1, 26.2 each upstream of a feed device 27.1, 27.2, not shown in detail, downstream each having a width B (arrow) extending exit gap 28.1, 28.2 with a gap width 28.1 .S, 28.2. s and on the outside each have an outer wall 29.1, 29.2. The separating element 25 has two separating element surfaces 25.0, 25, U which are touched during the operation of the multi-layer material casserole 5 by the respectively adjacent pulp suspension stream 4.10 (arrow), 4.20 (arrow).

The gap widths 28.1 .s, 28.2.S of the exit gaps 28.1, 28.2 are the same size in the illustrated embodiment; however, they can be different in size. The respective feed device 27.1, 27.2 not shown in detail in the illustrated embodiment, one of the headbox nozzle 24 directly upstream turbulence generator; However, it may also be arranged upstream of the headbox nozzle 24 indirectly and / or it may comprise a preferably machine-wide intermediate chamber or a pipe grid. These units are known to the person skilled in the art. The separating element 25 is a flexible CFRP lamella 25.3, which has a minimum rigidity M both in the longitudinal direction and in the transverse direction, which region assumes at least a value of> 40 N / mm. Moreover, in the present embodiment, the separating element 25 is articulated by means of an upstream separating element receptacle 30 and thus freely movable in the headbox nozzle 24.

The multi-layer casserole 5 is arranged directly downstream of the twin-wire former 6 shown in FIG. 1 with two continuous endless screens. The illustrated first wire 7, the wire, runs over the peripheral region 32 of a breast roll 31, before it then immediately the pulp suspension streams 4.10 (arrow) emerging with a free jet length 4.SL from the headbox nozzle 24 of the multi-layer headbox 5 as a common pulp suspension free jet 4.S. , 4.20 (arrow).

The pulp suspension streams 4.10 (arrow), 4.20 (arrow) emerging from the headbox nozzle 24 as a common pulp suspension free jet 4.S can have different jet speeds 4.10.V (arrow), 4.20.V (arrow). The difference in the jet velocities 4.10.v (arrow), 4.20.V (arrow) in particular assumes a value in the range from 10 to 60 m / min, preferably from 15 to 25 m / min.

The separating element 25 arranged in the headbox nozzle 24 now has a separating element protrusion 25. Ü in a range of 0.05 to 3.0, preferably from 0.1 to 2.0, in particular from 0.2 to 1, 5, · the largest Single gap width 28.1 .s of the two nozzle chambers 26.1, 26.2. The separating element protrusion 25.sub.U of the separating element 25 preferably assumes a value in a range of 10 to 25 mm. On the multi-layer headbox 5 shown in FIG. 8, a preferably adjustable diaphragm 33.1, 33.2 with an orifice immersion depth 33.1 .t, 33.2.t is arranged on both outer walls 29.1, 29.2 of the headbox nozzle 24. net. The respective orifice immersion depth 33.1 .t, 33.2.t into the adjacent pulp suspension flow 4.10 (arrow), 4.20 (arrow), assumes a value in a range of 1 to 30 mm, preferably in a range of 5 to 15 mm. The respective orifice immersion depth 33.1 .t, 33.2.t is by definition the vertical immersion depth of the respective orifice 33.1, 33.2 in the associated pulp suspension flow 4.10 (arrow), 4.20 (arrow). The adjustability of the corresponding aperture 33.1, 33.2 is indicated by a respective double arrow. Of course, it is also possible to arrange a preferably adjustable diaphragm with a diaphragm immersion depth only on an outer wall of the headbox nozzle.

Furthermore, the separating element 25 optionally consists of two separating element regions each having a separating element angle β, γ, an upstream separating element starting region 25.1 and a downstream separating element end region 25.2. The two separating element angles β, γ of the two separating element regions 25.1, 25.2 assume different angle values, the separating element initial angle β of the upstream separating element starting region 25.1 assuming a greater angle value than the separating element end angle γ of the downstream separating element end region 25.2. The Trennelementendwinkel γ of the downstream Trennelementendendbereichs 25.2 has an angular value in the range of 1, 5 to 8.0 °, preferably from 2.5 to 4.5 °.

Also, the downstream Trennelementendbereich 25.2 of the partition member 25 has a downstream Trennelementendlänge 25.2. L in the range of 10 to 150 mm, preferably from 15 to 75 mm, in particular from 25 to 50 mm.

Moreover, the pulp suspension free jet 4.S formed from the two pulp suspension streams 4.10 (arrow), 4.20 (arrow) has a free jet length 4.S.L in the range of 100 to 500 mm, preferably from 125 to 400 mm, in particular from 150 to 300 mm.

And finally, at least one pulp suspension can be a regulated feed stream, in particular a dilution water stream when a mixed feed stream is produced. Stream can be supplied with a mixed concentration. This allows a regulation of both the fiber orientation transverse profile and the basis weight cross profile of the multilayer fibrous web. FIG. 9 shows a schematic longitudinal partial section illustration of an end region of a further preferred embodiment of a headbox nozzle 24 of a multilayer headbox 5 of a sheet forming system 1 according to the invention. The basic structure of this headbox 24 essentially corresponds to the basic structure of the headbox nozzle 24 shown schematically in FIG. 8, so that reference is also made to this description of the figures.

In this figure, a multilayer headbox 5 is now shown with a blind-free headbox 24. The separating element 25 arranged in this iris-free headbox 24 in this case has a separating element projection 25. Ü in a range from 0.05 to 1.0, preferably from 0.1 to 0.95, in particular from 0.2 to 0.90 largest single gap width 28.1 .s of the two nozzle chambers 26.1, 26.2.

In summary, it should be noted that the invention provides a sheet forming system of the type mentioned that the mentioned disadvantages of the prior art as far as possible reduced, preferably even completely avoided. In particular, an initial, that is to say initial stationary and preferably evacuated drainage element is provided in an embodiment of a forming table for use in a sheet forming system, by means of which the at least one pulp suspension in a front dewatering section of the dewatering element at the same retention level as on a forming roll of a costly Spaltformers evenly over Width can be drained. LIST OF REFERENCE NUMBERS

1 foliation system

2 Machine for producing a fibrous web 3 fibrous web

4 pulp suspension

4.1 pulp suspension

4.10 Pulp suspension flow (arrow)

.10.v blasting speed (arrow)

4.2 pulp suspension

4.20 Pulp suspension flow (arrow)

.20.V blasting speed (arrow)

4.S pulp suspension free jet

4.S.L free jet length

5 headbox; Multi-layer headbox

6 twin wire formers

7 sieve; wire

7.1 (First) sieve loop

8 sieve; top wire

8.1 (Second) wire loop

9 pre-dewatering section

10 sieve table

10.1 Sieve Table (prior art)

10.2 Sieving Table (Prior Art)

10.B width

10.T1 First groin division

10.T2 Second groin division

10.Z1 First Zone

1 D Average division

10.Z2 Second zone

2.TD Average division

1 1 surface 12 topping

12. B width

13 bar

13.B last width

13.BS Total bar width

14 drainage opening

14.BS Total opening width

15 suction element

15.1 Suction box

16 twin-wire zone

17 inlet gap

18 inlet roller

19 bars

19.K curvature

20 drainage box

21 .1 bar

21 .2 bar

22 Resilient element

22.F Selectable force (arrow)

23 box

24 headbox nozzle

25 separating element

25.1 Separator start area

25.2 Trennelementendbereich

25.2. L Trennelementendlänge

25.3 Flexible CFRP lamella

25.O separator surface

25.U separator surface

25.Ü Separator overhang

26.1 nozzle chamber

26.2 nozzle chamber

27.1 feeder 27.2 feeder

28.1 exit slit

8.1 .S gap width

28.2 exit slit

8.2.S gap width

29.1 outer wall

29.2 outer wall

30 separating element holder

31 breast roll

32 peripheral area

33.1 aperture

33.1 .t Iris immersion depth

33.2 Aperture

33.2.t Iris immersion depth

B width (arrow)

CD cross machine direction (arrow)

M minimum stiffness

ÖB opening width

Pu negative pressure

Overpressure

S Sieve direction (arrow) s Drainage section

SA oscillation amplitude

S10 vibration

S10.A oscillation amplitude

S10.B oscillation width

TB pitch width

TB.Z1 pitch width

TB.Z2 pitch width

V1 vibration curve

V2 vibration curve Vibration curve Vibration curve

alignment angle

Separating element angle

Claims

Sheet forming system for a machine for producing an at least single-layer fibrous web. Claims

Sheet forming system (1) for a machine

(2) for producing an at least single-layer fibrous web

(3), in particular a paper, cardboard or packaging paper web, made of at least one fibrous suspension (4; 4.1, 4.2), with an at least single-layer headbox (5) and with a double wire former (6), which has two, each in a wire loop (7.1, 8.1) comprises rotating endless sieves (7, 8), the first sieve being a fourdrinier wire (7) which is in a pre-drainage section (9) after [or in the area of] the application of the at least one fibrous suspension (4; 4.1, 4.2). Fiber suspension free jet (4.S) by means of the at least single-layer headbox (5) over a stationary and preferably suctioned sieve table (10), the surface (1 1) of which contacts the fourdrinier wire (7) of a covering (12) with several in the direction of wire travel (S) successively arranged strips (13) extending in the machine transverse direction (CD) with free drainage openings (14) in between, and a plurality of suction elements (15), in particular suction boxes (15.1), are guided, the second sieve being a top sieve (8). , wherein the two sieves (7, 8) at least partially form a double sieve zone (16) with a wedge-shaped inlet gap (17), and in the double sieve zone (16) the upper sieve (8) guided over an inlet roller (18) is rigid over several arranged strips (19) run, which are arranged at a mutual distance on a drainage box (20),

characterized,

that the covering (12) of the stationary and preferably vacuumed sieve table (10) has at least two strips (13), each with several strips Zones (10.Z1, 10.Z2), the strips (13) arranged in the first zone (10.Z1) having an average pitch (10.Z1.TD) in the range between 20 and 70 mm, preferably between 20 and 40 mm, in particular between 20 and 35 mm, are arranged and the strips (13) arranged in the second zone (10.Z2) have an average

Pitch (10.Z2.TD) in the range between 50 and 120 mm, preferably between 50 and 100 mm, in particular between 50 and 80 mm, are arranged. 2. Sheet forming system (1) according to claim 1,

characterized,

that the strips (13) of the stationary and preferably suctioned sieve table (10) which form the covering (12) and are arranged in a zone (10.Z1, 10.Z2) have a respective strip division (10.T1; 10.T2) in the area of 15 to 120 mm, preferably from 50 to 100 mm, in particular from 50 to 90 mm.

Sheet forming system (1) according to claim 1 or 2,

characterized,

that the strips (13) of the stationary and preferably suctioned sieve table (10) which form the covering (12) and are arranged in a zone (10.Z1, 10.Z2) have a respective strip width (13.B) of at least 3 mm, preferably of at least 10 mm, in particular at least 15 mm.

4. Sheet forming system (1) according to one of the preceding claims,

characterized,

that in at least one individual zone (10.Z1, 10.Z2) of the covering (12) of the stationary and preferably vacuumed sieve table (10) or across the entire stationary and preferably vacuumed sieve table (10) the summed strip width (13. BS) the surface (1 1) of the individual strips (13) touching the sieve (7) is smaller than the summed opening width (14.B) of the individual drainage openings (14).

5. Sheet forming system (1) according to claim 4,

characterized,

that in the first zone (10.Z1) of the covering (12) of the stationary and preferably suctioned sieve table (10), the summed opening width (14.BS) of the individual drainage openings (14) has a value in the range of 90 to 230% of the summed bar width (13.B) the surface (1 1) of the individual strips (13) touching the fourdrinier sieve (7) and that in the second zone (10.Z2) of the covering (12) of the stationary and preferably vacuumed sieve table (10). summed opening width (14th BS) of the individual drainage openings (14) assumes a value in the range of 100 to 400% of the summed strip width (13th BS) of the surface (11) of the individual strips (13) touching the fourdrinier wire (7).

6. Sheet forming system (1) according to one of the preceding claims,

characterized,

that the surface (1 1) of the covering (12) of the stationary and preferably vacuumed sieve table (10) is at least partially curved and that at least one, the at least partially curvature of the surface (1 1) of the covering (12) of the stationary and preferably vacuumed The radius of curvature describing the sieve table (10) assumes a value in the range between 0.3 and 5.0 m, preferably between 0.6 and 3.0 m, in particular between 1.0 and 2.0 m.

7. Sheet forming system (1) according to one of the preceding claims,

characterized,

that in the double wire zone (16), the fourdrinier wire (7) runs over several strips (13), which are arranged opposite to the strips (19) which are rigidly arranged on the drainage box (20), which are supported by means of flexible elements (22) and which with can be pressed against the fourdrinier wire (7) with a selectable force (22. F).

8. Sheet forming system (1) according to one of the preceding claims, wherein the headbox is designed as a multi-layer headbox (5), in particular a two-layer headbox, which comprises a headbox nozzle (24) which is at least two across the width (B) of the machine ( 2) extending, separated from one another by at least one separating element (25), and during the operation of the multi-layer headbox (5), in particular the two-layer headbox, each carrying a fiber suspension (4; 4.1, 4.2) as a fiber suspension stream (4.10, 4.20) and converging towards one another (26.1, 26.2), which upstream each have a feed device (27.1, 27.2) and downstream each have an outlet gap (28.1, 28.2) extending over the width (B) with a gap width (28.1.s, 28.2.s), whereby the two outer nozzle spaces (26.1, 26.2) each have an outer wall (29.1, 29.2) on the outside and the separating element (25) touches two of the adjacent fibrous suspension stream (4.10, 4.20) during operation of the multi-layer headbox (5), in particular the two-layer headbox Has separating element surfaces (25.0, 25. U),

characterized,

that the at least one separating element (25) arranged in the headbox nozzle (24) has a separating element projection (25th Ü) in the range from 0.05 to 3.00, preferably from 0.10 to 2.00, in particular from 0.20 to 1 ,50, · the largest individual gap width (28.1.S) of the at least two nozzle spaces (26.1, 26.2) and that the fibrous suspension free jet (4.S) formed from the at least two fibrous suspension streams (4.10, 4.20) has a free jet length (4.S.L) in Range from 100 to 500 mm, preferably from 125 to 400 mm, in particular from 150 to 300 mm.

9. sheet forming system (1) according to claim 8,

characterized,

that the at least one separating element (25) arranged in the aperture-free headbox nozzle (24) has a separating element projection (25th Ü) in the range from 0.05 to 1.00, preferably from 0.10 to 0.95, in particular from 0.20 to 0.90, · the largest individual gap width (28.1.s) which has at least two nozzle spaces (26.1, 26.2).

10. Sheet forming system (1) according to claim 8,

characterized,

that a preferably adjustable diaphragm (33.1, 33.2) with a diaphragm immersion depth (33.1.t, 33.2.t) is arranged on at least one outer wall 29.1, 29.2) of the headbox nozzle (24) and that the at least one separating element arranged in the headbox nozzle (24). (25) a separating element projection (25th Ü) in the range from 0.5 to 3.0, preferably from 0.6 to 2.0, in particular from 0.7 to 1.5, · the largest individual gap width (28.1. S) which has at least two nozzle spaces (26.1, 26.2).

1 1 . Sheet forming system (1) according to claim 8, 9 or 10,

characterized,

that the separating element end angle (γ) of the downstream separating element end region (25.2) of the separating element (25) has an angle value in the range from 1.5 to 8.0°, preferably from 2.5 to 4.5°.

12. Sheet forming system (1) according to one of claims 8 to 11,

characterized,

that the downstream separating element end region (25.1) of the separating element (25) has a downstream separating element end length (25.2. L) in the range from 10 to 150 mm, preferably from 15 to 75 mm, in particular from 25 to 50 mm.

Sheet forming system (1) according to one of claims 8 to 12,

characterized,

that the downstream separating element end region (25.1) of the separating element (25) protrudes beyond the outlet gap (28.1, 28.2) of the headbox nozzle (24), preferably in a range of 10 to 25 mm. Sheet forming system (1) according to one of claims 8 to 13,

characterized,

that the separating element (25) is a flexible CFRP lamella (25.3) which has a minimum stiffness (M) in both the longitudinal and transverse directions, which in some areas assumes at least a value of > 40 N/mm.

Machine (2) for producing an at least single-layer fibrous web (3), in particular a paper, cardboard or packaging paper web, from at least one fibrous suspension (4; 4.1, 4.2),

characterized,

that it comprises at least one sheet forming system (1) according to one of the preceding claims.