FI83102C - Path forming part in paper machine - Google Patents

Description

83102 5

Paper machine forming part Banformningsparti i pappersmaskin

The invention relates to a web forming section of a paper machine comprising two wire loops, in which the dewatering of the fibrous suspension forming the web takes place in two directions through said wires 10 in their common run. and wherein the forming portion thereof has a two-wire web-forming zone comprising, from the forming ladder, the following special and separate forming members and dewatering zones in a sequential order (a) a first forming zone in the region of the first hollow-surfaced forming roll in two directions in both directions; (b) a second forming band defined by the curved cover portion of the stationary forming member; a zone curving in the opposite direction to the two-wire sector on the first forming roll; (c) a third forming zone controlled by the second forming roll, in the area of which the covering wire is separated from the dough formed between the wires, which then follows the carrier wire to a pick-up point or the like.

Numerous twin-wire web-forming components designed by various manufacturers over the past 20 years, an overview of which has been published, e.g., in Pulp & Paper, September 35, 1982. In addition to or in connection with the present references, reference is made to Applicant's U.S. Patents: 3,846,232, 3,941. 651, 3,997,390, 4,113,556, 4,154,645 and 3,996,098.

2 83102

Paper is known to be made from cellulosic fibers, most commonly derived from wood material. In the papermaking process, the fibers are usually slurried in about 100-300 times the amount of water as a fiber suspension, which is fed to a paper machine, its headbox, which has the task of providing these fibers in a continuous process with a uniform, desired width. The paper web. When the final dry matter content of the finished paper is about 95%, this means that the removal of water from the fiber suspension is an essential part of the operation of the paper machine. The bulk of this dewatering takes place as a kind of filtration process in the so-called through the wire fabric by the web-forming section of the paper machine, which may be either a single-wire fourdrinier or flat-wire section, the dewatering taking place substantially simultaneously through two wires, the common passage of which is then generally curvilinear.

15

In the mutual comparison of different types of two-wire web-forming parts, i.e. formers, they can be divided into main groups, for example, on the basis of how and at what stage dewatering takes place in them. Using this division criterion, it is possible to distinguish between "pure" two-wire formers and 20 ns. hybrid formers.

By hybrid formers is meant web-forming sections in which a substantial portion of the dewatering initially takes place over a relatively long section through only one wire, followed by the actual two-wire section.

In pure two-wire formers, the pulp is fed directly to the gutter or throat between the two wires in order to "freeze" from the outset the uniform fiber distribution provided by the headbox to the nonwoven mat or web formed between the two wires 30. These web-forming sections are referred to in the following representation as guitar formers. In addition, as an intermediate form between these and the hydride formers, there are web-forming sections in which the pulp is not fed directly into the inter-wire groove, but into a rather short, often dewatered, section supported by the wire table 35 immediately preceding the grout.

I; 3,8102 In connection with the present invention, attention should be paid to the technical terms 'formation' and 'retention'.

The term formation has two meanings in paper technology. It can mean the papermaking process as a broad concept, which includes both the formation of a nonwoven, i.e. the placement of the fibers on the wire of the forming part, and the simultaneous dewatering of this nonwoven. Then formation - web forming.

10 The term formation also refers to a property of the finished paper that can be detected by looking at a sheet or sample of paper against light. Paper formation is said to be poor if the fibrous material is unevenly distributed in the paper so that there are many larger or smaller cloud-like formations. Correspondingly, the formation is good if the surface of the paper through the distribution of the fibrous material is flat.

In the following, a forming member or forming surface means a structural member which in one way or another participates in the formation of the web 20, e.g. by influencing the intensity of dewatering or how the fibers are positioned relative to each other. If the forming zone has a wire flanking or guiding this roll, this usually only affects the dewatering, but not much of the formation as a property of the paper.

25 The forming surface may be a mere plate, but is preferably a cover part of a box-like structure followed by a wire. The forming surface may be solid, non-perforated, but most commonly has slits that are generally substantially transverse to the direction of travel of the wire. The slits can also be inclined with respect to the course of the web, e.g. in the form of a fishbone.

When the formulation surface is a cover in a box-like structure, this may be open or in contact with the external atmosphere, but it may also be closed and connected to a vacuum source and thus operate under vacuum. It has been found that such a slit-bearing forming member affects both the dewatering of the web formed and the properties of the finished paper.

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The term 'retention' refers to the ability of a paper web that is in the formation stage on a wire section during the dewatering process to retain in its structure the fine fibers and filler particles in the fiber suspension. Since said fines are important raw material components of paper, 5 which e.g. improve the printing properties of the finished paper, in various ways, for example in the production of newsprint and printing papers, the aim is to keep the retention as high as possible.

10 As the speeds of paper machines increase, several problems in web formation have become more pronounced. In the forming part of the paper machine, the phenomena affecting the fiber network and the water still relatively free in connection therewith, e.g. centrifugal forces, are usually intensified in proportion to the square of the web speed. The current web speeds of the current newspaper-15 paper machines are in the order of 1200 m / min. However, there are plans for newspaper machines aiming at a track speed of up to about 1,500 m / min. Said increase in speed causes several problems, which are discussed below.

20 The problem with hybrid formers as well as flat wire formers at high working speeds is that splashes occur on the free surface of the pulp in the single wire section. These splashes are generated when the pulp jet from the headbox collides with the wire supported by the chest, even at a small angle, whereby the pulp jet partially disintegrates. The bearing capacity of said splashes 25 in the direction of travel of the web is quite high and these splashes cause marks on the web to be formed and thus degrade the quality of the paper to be produced. On the other hand, in the flat wire section, the impulses caused by the foils used for dewatering increase at such high speeds that this also causes spattering which deteriorates the formation of the web. After all, foil pulsation is known to increase in the square of the velocity. In order to keep the pulsation below the spatter limit at high speed, the foil angles must be selected as small as possible (close to 0 °), but in this case sufficient dewatering power is not always achieved.

35 The disadvantage of the flat wire section is also that the transverse profile defects in the lip shower may still be accentuated by the flat wire e.g.

il 5 83102 due to oblique pulp slurry flow components (so-called plowing with wire) or due to the strengthening of the longitudinal vanes.

In general, it has been found that the variations in basis weight of the guitar formers remain smaller than with flat wire formers or hybrid formers, which may be due in part to the fact that the jet is fed directly to the groove where the pulp jet is immediately "frozen" between the two wires. .

10

As the speed of paper machines, especially newspaper machines, has increased, it has become clear that web smoothness is not only an important feature of paper quality but also increasingly a factor in paper machine runnability, as the weakest points in the web are usually the cause of breakage.

15

Against the background set forth above, it is an object of the present invention to provide a method and apparatus for forming a paper web suitable for high web speeds up to 1500 m / min and even higher.

20

The object of the invention is to provide a web-forming section suitable for a wide surface pressure range, which is suitable for the production of general printing papers such as newsprint and LWC paper as well as heavier SC and fine paper grades, especially with papers having a basis weight of between 30 g / m 2 and 100 g / m 2. However, the development is constantly taking square weights in a smaller direction, which makes the uniformity requirements of the paper even stricter.

It is a particular object of the present invention to provide a web-dosing portion which, however, achieves even better formation and sheet formation while at the same time achieving at least the same level of retention as is achieved with known retention formers.

Other objects of the invention are to provide a web-forming part which achieves an even distribution of fines and fillers so that the opposite surfaces of the web 6 83102 are as similar as possible, with low porosity (without so-called pinholes), with good printing and coating properties. and which achieves a sufficiently high dry matter content after the wire section.

In order to achieve the mentioned goals, the present invention is based on the so-called kitformer because, according to the most common experience and as shown above, it is best suited for high speeds-10 due to the uniformity of the basis weight and the elimination of splashes.

On the other hand, the invention seeks to avoid the disadvantages of several prior art guitar formers, namely poor formation and poor retention.

The object of the invention is to further develop the web-forming part disclosed in the applicant's U.S. Patent No. 3,996,098 on the basis of user experience of this structure both in its few commercial applications and in particular as a result of extensive test runs on the applicant's test paper machine. the effect of its components on the operation of the web forming section.

As disclosed in the specification of U.S. Patent 3,996,098, the various two-wire web-forming sections have the advantage that dewatering 25 is significantly more efficient and faster than conventional fourdrinier flat wire sections, and that the former formed paper web is more homogeneous in structure than the latter. In this context, the homogeneity of the structure of the web means that the fibrous material contained in the paper and the so-called the fillers are evenly distributed in the thickness direction of the web and that both surfaces of the paper are e.g. as similar in smoothness properties as possible. For example, paper intended for newspapers, magazines, etc. must generally contain as many fine fibers and fillers as possible, which give such papers 35 good printing properties.

7 83102

The experience gained with the web forming section of U.S. Pat. is not always satisfactory. The high retention rate is the result of a pulse-free dewatering method at the beginning of the web.

10

As a result of the test runs, it has been found that in order to control the formation of the paper to be produced, i.e. to influence the formation in the desired way, the web-forming part must have stationary forming members suitably located in addition to and / or instead of rotating wire furniture.

It is already known that solid flat wire towing so-called forming board structures or similar drainage and / or formation members of which a list / gap / list-type deck structure is an integral part. One example of this structure is the structure of Applicant's U.S. Patent No. 4,154,645. The principle of operation of the various arrangements for improving the formation is to apply a controllable and adjustable pulsating effect or series of pulses to the forming fiber web or web, as a result of which the fibers in the non-fibrous web move relative to each other to achieve the desired result.

Stationary so-called. the disadvantage of using wire furniture is its wire-consuming effect, which has been a major drawback, especially when using metal-30 linen fabrics. Plastic wires are less sensitive in this respect, but the use of stationary members has generally been kept to a minimum. However, as good formulation has become an increasingly important criterion for paper quality in modern high-speed large-format paper machines and thus requires some kind of fixed formation elements, their operation and operating conditions have been extensively studied by the applicant in connection with the present invention.

The even positioning of the fibers relative to each other in the fiber mat in the formation step 5 requires a certain freedom of movement for them, which is possible only if the non-fibrous water content is high enough to allow the fibers to move relative to each other.

This means that dewatering must not take place too quickly and must be controllable and adjustable in any case. Thus, with van-10 holli flat wire machines, the aim was to slow down the drainage by using closed-edged "forming boards" at the beginning of the wire run.

In order to be able to affect the formation mechanically, it has been found that the non-fibrous water content in the partial suspension form must then preferably be about 30- to 100-fold the amount of fiber. Such a high dilution of the suspension is also useful in that the formation of the nonwoven between the wires. . the water leaving during the step acts as an effective lubricant between the stationary forming elements and the wire and thus reduces the wear of the wire.

According to U.S. Pat. No. 3,996,098, dewatering in this web-forming section already takes place very efficiently in the inter-wire gutter and in the first web-forming roll in a sector of about 90 °, although this area forms only a small part of the total flow between the first wire and the second wire. is available for dewatering and generally web formation. The dewatering thus takes place mainly in this area, with the result that the nonwoven mat between the wires 30 has time to reach a dry matter content of 8-10% in the structure according to the reference patent already after the first web-forming roll. In such a consistency, the mutual position of the fibers with respect to each other, i.e. the formation of the resulting web, has already solidified after the forming roll, so that it is no longer possible to be influenced sufficiently effectively by the stationary members arranged after the forming roll. In addition, under these conditions, the wire-consuming effect of the stationary forming member becomes excessive.

The headform of the web forming section of the present invention feeds the pulp jet directly into the gap between the two wires. The fiber consistency of the pulp, i.e. the amount of weight of the paper fibers per corresponding unit volume of suspension, can at this stage be 0.3-0.5%, which means that the pulp contains 200-300 times the amount of water compared to the fibers. The pulp, i.e. the fiber suspension, generally also contains fillers 10 when making paper for printing. The amount of filler can be equal to the amount of fibrous material, in which case the total consistency of the pulp suspension will be of the order of 0.5-1.5%.

In order to achieve the above and later objects, the invention is mainly characterized in that the stationary forming member arranged inside the covering wire loop is a strip-shaped forming member arrangement, followed by a second forming member arranged inside the supporting wire loop before the second forming roll.

20

According to the invention, the formation of the web begins with a hollow-surface forming roll, in which, however, the dewatering takes place in both directions somewhat more away from the forming roll, i.e. through the covering wire. According to the invention, a strip-like or similar shoe-shaped forming member is arranged after the forming roll. It is essential in the invention that the main dewatering direction changes from the first forming roll when entering the strip shoe, so that in the area of the strip shoe the dewatering takes place in the direction of the slightly felted fibrous layer, i.e. through the supporting wire. Particularly from the point of view of formation, it is advantageous that the fiber layer is not felted too far when it comes to the stationary formation member. The water content of the fibrous layer coming to the molding shoe can be adjusted by means of the coverage angle of the first forming roll and the possible vacuum of the forming roll.

One object of the present invention is to improve the formation by limiting the dewatering with the first forming roll ίο 83102 only to the amount required to achieve a suitable dry matter content before the forming member.

The magnitude of the coverage angle α on the forming roll can be at least about 15 ° at the smallest and less than 90 ° at the largest. This angle of coverage can be adjusted, within desired limits, according to the type of paper to be made with the former in question by adjusting the position of the chest roll near the first forming roll and the first guide roll (prior to the forming roll) of the support wire. The position of the headbox can also be arranged to be adjustable so that the direction of the mass jet discharged from the headbox relative to the guitar formed together by the wires is as desired.

Experience gained in various ways with these types of web-forming parts has shown that in order to obtain a good or at least satisfactory formation 15, at least one fixed pulsating forming member with a sufficiently long range of action in the web direction must be placed in the dewatering zone following the first forming roll.

The arrangement and arrangement of the forming members and forming rolls according to the invention makes it possible that the formation and dewatering of the web can be controlled in several steps in the desired manner with a view to the highest possible retention level and simultaneous good formation and low porosity.

25

For example, a forming shoe disclosed in Applicant's U.S. Patent No. 4,154,645 may be used in the invention. Ko. the forming shoe is positioned on the common run of the covering and bearing wire in the web forming section so that the wires and the nonwoven mat therebetween side-30 the cover of this shoe, which consists of a plurality of strips substantially transverse to the direction of travel of the wire. Each strip and flange causes a certain hydraulic pulse on said nonwoven mat, which causes a certain rearrangement of the fibers in the fiber network forming the final web, which usually results in an optical formation. In the region of such a forming shoe, not only does the fibers move relative to each other, but also the removal of water from the pulp, the dewatering intensity of which depends on the radius of curvature of the wire guide shoe and whether the shoe's hollow surface is under pressure or vacuum.

5 In order for the forming surface formed by the cover of such a shoe or chamber and its possible moldings to function to improve the formation, the non-fibrous water content between the wires in the area of this surface must be high enough so that the fibers can still move relatively freely. This is particularly well achieved in the invention in that the dewatering in the region of the strip shoe takes place in the direction of the less felted pulp layer.

The dewatering in the area of the forming shoe is affected by certain structural features of the forming surface, such as its length in the direction of travel of the web, its radius of curvature, the number of strips therein and the size of the gaps between them. The fabric density and type of wires also have an effect on dewatering, as does the tension of the wires, which determines the compressive force applied to the nonwoven mat between the wires and which also contributes to the dewatering of the web.

The invention will now be described in detail with reference to an embodiment of the invention shown in the figure of the accompanying drawing, to which, however, the invention is not limited.

;: · 25

The figure shows a schematic side view of a web forming part according to the invention, comprising in its most essential parts a first wire loop 10 and a second wire loop 20 and a first web forming roll 21 and a second web forming roll 25 and 30 a chest roll 11. The web forming rollers 21 and 25 are both inside the wire loop 10 inside.

. "· The wire 10 is a so-called covering wire and a wire 20 a so-called load-bearing wire, followed by a web W after a two-wire forming zone. The lip portion of the headbox 40 of the paper machine directs the pulp jet 35 (arrow) 35 bounded by the wires 10 and 20 consisting of the rolls between 11 and 21, the position determined. Kitaa K restrict the other side of i2 831 02 a wire 20, which is closest to the guide roll 26 'of the control covers the first forming roll 21 and on the other side of the wire 10 which is passed rintate-salt 11 over the forming roll 21 to face the wire 20, though separated by a layer of fibers.

5

According to the invention, the forming roll 21 is a roll provided with a hollow surface 21 '. The cavities of the surface 21 'may be either circumferential grooves or holes drilled in the roll shell. The holes, in turn, can be so-called. blind holes or extend through the shell 21 of the roll. In the case 10 that the holes are drilled through, the roll 21 can be provided with a single or multi-compartment suction chamber 21a located inside its casing. The forming roll 21 is relatively large in diameter, preferably having a diameter D - 1500 to 2000 mm. The sector, which means the common coverage angle of the wires 20 and 10 in the region of the roll 21, is smaller than 15 °, preferably about 40 ° -60 °. The larger the diameter D of the roll 21, the smaller the sector a, i.e. the central angle corresponding to the wire coverage, can be.

Dewatering in the region of the forming roll 21 takes place in two directions, partly through the wire 10 away from the forming roll 21 and partly through the wire 20 either into the cavities of the surface 21 'of the roll 21 or into the suction chamber 21a inside the roll 21 shell.

The extent to which the dewatering in the region of the forming roll 21 is distributed on the one hand through the wire 20 and on the other hand through the wire 10 is influenced by many factors e.g. the distance between the breast roll 11 and the forming roll 21 and the type of the cavity surface 21 'of the forming roll 21 and the percentage surface area of the cavities. The intensity of dewatering can also be influenced by the density of the covering wire 10 and the supporting wire 20 in the castle.

The aim is to use the above-mentioned construction parameters and to apply the most careful initial dewatering in a controlled manner, which on the one hand contributes to the high retention of fines 35 and on the other hand leaves sufficient suspension water in the formed fibrous web, enabling the web formation to be affected. with respect to the prior art of the invention.

Between the first forming roll 21 and the second forming roll 25, a forming member 12 is formed inside the wire loop 10, which is formed by a chamber-like body part and a cover part 3 acting against the wire 10, which consists of a plurality of slats 13 'separated by slots. The cover part 13 of the forming member 12 is curved either so that the radius of curvature R is constant or so that the radius of curvature R of the curve 10 continuously or in suitable steps decreases in the direction of travel of the wires 10,20. The position of the forming shoe 12 can be made adjustable vertically and horizontally, and its position can be rotated, e.g., about an axis passing through its support points.

For the running of the wires 10,20 between the forming rollers 21 and 25 inside the wire loop 20, a suction box 24 or the like can be placed after the forming member 12, if necessary, to supplement the dewatering. The final dewatering on the two-wire section is achieved by a forming roll 25 mainly in sector b, after which the wires 20 and 10 20 differ from each other.

As the formed web W follows the carrier wire 20, which is ensured by suitable suction in the sector c of the roll 25, the web W advances in the support P of the wire 20 to a point P where it is detached from the wire 25 20 by the suction zone 30a of the pick-up roll 30 31, which takes the web W further to the press section of the paper machine (not shown).

At the forming shoe 12 shown in the figure, inside the wire loop 20 there is a water collecting trough (not shown) of a type known per se, which directs the water leaving through the wire 20 to the side of the paper machine. The guide rollers of the wire 10 are indicated by reference numerals 14 and 15, and the guide roller rollers of the wire 20 are indicated by reference numerals 26 and 26 '.

35 The operation of the former described above and its various variations are discussed below. It is essential in the invention that, as stated above, in the sector a of the first forming roll 21, dewatering takes place in both directions generally more through the wire 10. In this case, in sector a, a relatively dense fibrous layer is felted on the surface of the outer wire 10, while the fibrous layer 5 on the side of the opposite wire 20 is less felted. As a result, the radius of curvature of the cover 13 of the forming shoe 12 is opposite to the radius of curvature of the sector a. In this way, changing the dewatering directions has the advantage that the fibrous structure of the already partially felted pulp layer is not broken, so that an even wider range is available for all operating parameters.

In the sector a of the roll 21, the dewatering is limited so that the fiber suspension is not completely felted, but is passed for further dewatering to the cover part 13 of the forming shoe 12, the strips 13 'of which cause pulsation 15 in the dewatering pressure. In this case, water is removed mainly by the acceleration forces and tightening of the wires 10,20 in the region of the forming member 12 through the web W carrying the wire 20 and also through the wire 10 partially covering the web W, especially if the interior of the forming member 12 is connected to suction devices schematically shown in block 20.

The forming member 12 is followed by a suction box 24 acting against the support wire 20, which can be used, if necessary, to enhance dewatering. In some cases, the suction box 24 is unnecessary.

25

The second forming roll 25 is further dewatered to some extent by the vacuum in the suction zone 25. The suction zone 25b of the roll 25 is mainly intended to ensure that the web W detaches from the covering wire 10 and moves forward on the supporting wire 20 30.

The following describes the structural alternatives of the different members of the former according to the invention and the suitable ranges and limits of variation of the various parameters.

For the reasons set out above, the two-wire dewatering zone is preferably substantially vertical.

I i is 83102

It is essential in the invention that the first forming roll 21 in a relatively narrow sector carefully removes water in two directions, mainly for reasons related to porosity and formation. The size of sector a is 5 from about 15 ° upwards and at most sector a within the scope of the invention can be about 90 °. The diameter of the first forming roll 21 is preferably of the order of 1.5 m or more after sector a, the fiber density k of the pulp layer is generally about 2-3%. The radius of curvature R of the guide cover 13 of the forming member 12 is generally in the range of 2 m to 5 m and most preferably about 3 m. The fiber consistency k k after the member 12 is about 5-7% and the dry matter content k <about 15-20% after the suction roll 25.

The total length of the two-wire zone is generally of the order of 4-7 m, of which about 1 m becomes part of the cover 13 of the forming shoe 12.

15

One advantageous feature in the geometry of the vertical former of the figure is that the first forming roll 21 of the wires 10; The common coverage zone 20 is located on either side of the horizontal plane set through the central axis of the roll 21.

20

According to the figure, said second forming roll 25 is a suction roll with at least two suction zones 25a and 25b as described above, each of which is acted upon by a suitable vacuum. The cover sector b; of the cover wire 10 on said "I second forming roll 25" is preferably in the range of about 40 ° -120 ° and the corresponding cover sector c of the support wire 20 is preferably in the range of about 60 ° to 180 °.

The following are claims within the scope of which the various details of the invention may vary and differ from those set forth above.

Claims (6)

A web forming part of a paper machine comprising two wire loops (10.20) in which the web forming part dewatering from the fiber suspension 5 formed by the web (W) takes place in two directions through said wires (10.20) on their common course, in which forming part of the wire loops (10.20) consisting essentially of the first forming roll (21) and a chest roll (11) forming a tapered gap (K), in which the inlet sheet (40) of the paper machine feeds a pulp beam (J) and in which forming part its double forming web zone The wires comprise, from and with the forming gap (K), separate forming means and dewatering zones one after the other in presented order (a) a first forming zone in the area of the first forming roller 15 (21) with hollowed out surface (21 '), where the dewatering takes place. two directions through both wires (10, 20) in a sector (a) of no more than about 90 °, (b) a second forming zone determined by a curved (R) lid portion (13 ') of the stationary forming member (12) , which zone curves in the opposite direction In the double-wire sector (a) on the first forming roller (21), (c) a third forming zone (25a, 25b) controlled by the second forming roller (25), in an area of which zone, the covering wire (10) is separated from the web (W) formed between the wires (10, 20), which path follows the supporting wire (20) to the pick-up site (P) or the corresponding, characterized Therefore, a molding member arrangement (12) with molded lid functions as a stationary molding member which is arranged inside the loop of the supporting wire (10), followed by a second forming member arranged inside the supporting wire loop (24) before the other the forming roller (25). 2. Molding portion according to claim 1, characterized in that the radius of curvature (R) on the molding of said molding means (12) is within the range of about 2 m - 5 m, most preferably about 3 m. Molding portion according to claim 1 or 2, characterized in that the guide lid (13) in the stationary forming member (12), which is blended by strips (13 ') which are separated by each other by cracks, provides a pulsating dewatering pressure in the pulp layer which flows past this and that the inner space of said forming means (12) is, if necessary, joined by a source of negative pressure (27). 4. A molding portion according to any of claims 1-3, wherein the first and second forming rolls (21; 25) may be a suction roll. 5. Molding portion according to claims 1-4, characterized in that the width of the common tacking sector (a) on the first forming roller (21) is about 15 ° -19 °, most preferably about 40 ° -60 °. 15 6. A web forming portion according to any one of claims 1-5, characterized in that the various forming zones and the means therein are thus arranged so that the fiber density of the web or multilayer blended in the proportion of double wire develops as follows: first forming roll (a) k, - 2-3%; after the second forming zone as determined by the stationary forming member (12) kJ - 3-4%; after the second forming member (24) within the carrying wire coil (20) k4 - 5-7% and after the second forming roller (25) and any additional dewatering elements after this k5-15-20%. '25