FI120747B - Paper or cardboard machine - Google Patents

Description

Paper ·· or board machine

The invention relates to a paper or board machine comprising a forming part 5 for forming a web from a fibrous slurry, a press section for dewatering the formed web and a drying section for drying the pressed web.

The press section of a paper machine has traditionally had at least two press nipples through which the web is carried supported by at least one press felt. The development of the Pit-10 nip presses has made it possible to introduce single nip press components, resulting in significant cost savings and reduced space requirement for the press member. The benefits of the solution are also its simplicity, closed exports and reduced paper bias.

Single-nip press sections are described, for example, in US 6638395 and WO

2006/018388 in which both webs are introduced into the press section with a dry matter content of at least 18% and are passed from the forming part to the drying section without open export. In US 6638395, the forming part has a pre-press nip j * \. to provide a sufficient solids content of the web before the press section. The first group of cylinders in the dry • · • * · »contains up to three drying cylinders, •«: · · which improves the possibilities to compensate the stretching of the web immediately upon drying.

: Initially by the difference in speed between the drying groups. WO

2006/018388 At the beginning of the drying section is an air blowing drying unit • # ». The forming component is a conventional dieformer.

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To achieve sufficient solids levels, more water removal capacity is required at high speeds and high density * * · * ·; · 'than one press *: ** · nip. This limits the use of the single nip press section. Also, precise control of the process and uniformity of the press felt are also required from the press, as unevenness in the pressed web can no longer be corrected · · · ·; ** and smoothed in subsequent press nipples.

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In addition, it has been found that known single nip press portions are not always able to provide sufficiently good transverse rigidity of paper. Good transverse rigidity is an important feature of copy paper, for example. The reason for the low transverse stiffness of the web 5 may be the anisotropic stretching and shrinkage of the web by the press section and the drying section.

The object of the invention is a paper or board machine capable of producing high quality paper or board with high production. A specific aim is to minimize known drawbacks associated with the manufacture of paper or board.

To achieve this and the following objects, the invention is characterized by what is set forth in claim 1.

The paper or board machine of the invention comprises a combination of a particular type of hybrid compactor and a single nip press. The two-wire portion of the hybridformerm begins with a forming shoe that leads to the surface of the downstream fiber slurry layer and provides non-pulsed dewatering. Such a hybrid j * former produces a web in which the fiber orientation and the resulting anisotropy is relatively low.

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• · · • · · ··; i '; Anisotropy of paper structure affects almost all physical properties of paper, but is particularly important for strength properties. Plane anisotropy occurs with different physical properties in the machine and transverse directions of the paper. Anisotropy occurs, on the one hand, as a result of the orientation stripping V · and, on the other hand, as a result of anisotropic dimensional changes occurring on the press and dryer section ··· • ',,, ί. Machine-made paper always contains more machine-directional than cross-directional fibers. The press ····· and the drying section exhibit machine-directional stretching and transverse shrinkage of the web.

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In most cases, low orientation indices are sought because the properties of the paper are almost the same in all directions of the plane. An indirect indicator of the orientation index can be the MD / CD ratio of tensile strengths or any other MD / CD ratio of physical properties (ratio of properties measured in the machine direction and transverse direction). Also important for the properties of the paper is the variation of the fiber orientation in the thickness direction of the web. The difference in orientation between the surface of the web and the inserts increases the stiffness of the paper, while the difference in orientation between the opposite surfaces of the web increases the tendency of the paper to warp.

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During the forming phase, several hydrodynamic forces affect the distribution of the fiber orientation in the paper. The most important factor is the speed difference between the lip jet and the wire. Other significant factors include acceleration and deceleration of the fiber sludge flow in the headbox and the wire section, and random variations due to turbulence. The fiber orientation of a paper made with a flat wire is clearly stronger on the wire side than on the upper side. The z-orientation orientation profile of the paper produced by Kitaformer is symmetric. Hybrid formers can be used to produce paper with a clearly lower orientation profile. Thus, the anisotropy of the physical properties of the paper produced by the hybridformer is generally less than 20 mm than that of the paper produced by the flat wire or kitformer.

: · * • «:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ! supported by the fence wire, into a two-wire zone where dewater 25 is discharged both through the fence wire and upwards through the upper wire. At the beginning of the double wire zone «·· V ·, the top wire is brought into contact with the fiber slurry layer on the bottom wire. In list hybrid formers (e.g. SymFormer MB, Duoformcr D, BelBond), r ♦; ··; the pin is removed at the beginning of the two-wire zone by pulsating dewatering, ·: ··: whereby the web is easily broken if the consistency of the web is too low. By replacing pulsed dewatering at the beginning of the two-wire zone with non-pulsed dewatering, dewatering pulses are avoided, which contributes to reducing fiber orientation and paper-level anisotropy.

When the biaxial zone begins with non-pulsatile dewatering, retention can be maintained good, since the fiber network formed on the surface of the fiber slurry layer is capable of retaining fine and filler in subsequent dewatering steps, where thereafter, the dewatering capacity will begin to decline despite the increase in vacuum 10. The deterioration in dewatering is probably due to the fact that as the vacuum increases, the surface of the fiber layer facing the wire is compacted, making dewatering through the surface layer more difficult. Therefore, the effect of the vacuum must sometimes be interrupted, whereby the thickness of the fiber layer is partially restored and the pore structure of its surface is opened. The relatively light pressure pulses are sufficient to open the surface structure of the fiber network 15 so that dewatering can continue. Pulse-dewatering dewatering is accomplished by dewatering moldings adapted to support the wires transverse to their direction of travel. The use of dewatering strips and opposing loading lists enhances dewatering and improves web formation, since pressure pulses produce shear forces in the fiber slurry layer that break the already formed Blocks, with water away from the surface layers of the web. Excessive pressure pulses increase the orientation of the fibers and thereby increase the paper

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· * ,,, · * strength difference between machine and transverse directions.

25 * ·· 5 In order to achieve good formation, it is essential that the fiber slurry layer reaches the loading zone of the dual wire zone at a sufficiently low consistency. ·; ··: This requirement easily results in high headbox flow, which is problematic with current technology *: * ·:. Problems may include, for example, the jumble of the pulp as it hits the wire (stock jump), difficult control of the orientation profile, and curling of the web at the beginning of the twin-wire portion.

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Headbox dilution control can significantly improve the orientation profile compared to conventional headbox tip adjustment.

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The mass jump or stock jump at the beginning of the flat wire section is a phenomenon in which liquid particles are released from the liquid stream as vertically moving droplets. Splashing is caused by bouncing or a change in the amount of movement when the lip spray hits the tissue or chest. As driving speeds increase, the problems caused by splashing 10 tend to increase. Splashing can be prevented, for example, by appropriate alignment of the chest roll and chest or by the use of a bevelled tip strip.

Curling of the web at the start of the twin-wire portion can be prevented by placing a stationary forming shoe at the top of the twin-wire portion that leads to the surface of the fiber slurry layer on the bottom wire.

The hybridformer described above already produces a very low tensile strength ratio of MD / CD-1 · 1, which substantially improves the transverse rigidity of the paper.

20 Adding shaking of the chest roller to the solution results in a tensile strength ratio; since its fall. Transverse oscillation of the thoracic roll reduces fiber stubble; : 1: Machine orientation.

F1 · t1 6 paper on a paper machine with lower manufacturing costs than traditional solutions. In addition, the solution of the invention enables papermaking with lower energy consumption.

5 As a long nip press, a shoe press or some other known press solution can be used which provides an extended stay in the press nip. The length of the Puris tinnip in the long nip is typically 30 to 450 mm. The web is passed through a nip between two press felts, which take up water from the web in the nip.

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The usability of the single-nip press section can be further improved by installing at least one over-blow dryer afterwards, which improves runnability and moisture profile control prior to cylinder drying. For example, blow-drying may be carried out in a manner known from WO 2005/068713.

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At high speeds, only the drying section containing the drying cylinders becomes long. Some of the drying cylinders can be replaced by blow dryers, especially at the beginning of the drying section, where full drying pressure cannot be applied to the drying cylinders because the web can stick to the surface of the cylinder. Space savings can be achieved by using a vertical blow-dryer with fans on each side of the web. Because the air is blown directly into the paper web, the drying air between the paper can be used to increase the blowing air temperature (250-700 ftC) to provide a very effective heating effect.

25 ·· * • ψ * 'The blow dryer comprises arrangements for supporting a paper web and a blowing chamber having openings on the web side for blowing hot air or other gas to the surface to be dried. The advantage of a vertical dryer is the saving of space. the paper machine is shortened when a part of the dryer of a paper machine based on the level of the lower or • j · 30 above. the advantage is also the fact that the force of gravity can not adversely affect the paper web ic spread flow. Efficient vertical impingement drying requires 7 that the opposite side of the web pre-dried the horizontal impingement-dryer. the horizontal esipäällepuhalluskuivain to heat the first side of the self before the second side of the web begins to dry in a vertical-plated lepuhalluskuivaimessa. two vertical impingement not the foot-5 ren space requirements, can not be installed in sequence. Preferably, the vertical over-Kui puhalluskuivain load the same side of the web as the subsequent drying cylinder group. It is advantageous to place the various drying units close together so that the web does not have time to cool down before moving to the next drying unit.

The running speed of a paper or board machine according to the invention is typically in the range of 600-1700 m / min, preferably 600-1,300 m / min, and can produce paper or board having a basis weight of 40-250 g / m 2. The solution according to the invention is particularly suitable for the production of fine paper.

In the following, the invention will be described with reference to the examples shown in the figures of the accompanying drawings, which, however, are not intended to be limited thereto.

Fig. 1 is a side view of a paper machine according to the invention.

Fig. 2 is a side view of a forming part of a papermaking machine according to the invention.

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ί, ί, ϊ Fig. 3 is an enlarged view of the front of the forming member.

Fig. 1 shows a paper machine according to the invention comprising a forming part 1, a press part 2 and a drying part 3. The forming part 1 is a hybridformer, ···: ... Σ press part 2 comprises only one press nip N and the dryer section 3 has overcoat: 23: 24 prior to the first cylinder group 25.

The forming part 1 of Figure 1 comprises a headbox 4, a lower wire 5 which forms an endless loop guided by a bobbin roller 6, a suction roller 7 and a guide roller 8, and an upper bar 8 which forms a guide roller 10 another endless loop. The lower wire 5 and the upper wire 9 define between them the double wire portion preceded by the flat wire portion on the lower wire 5. The fiber slurry is fed from the headbox 4 to the lower wire 5, with the flat wire portion thereof dewatering through the lower wire 5 by means of dewatering elements (not shown). At the beginning of the twin wire section, there is a dewatering box 11 with a curved lid inside the upper wire loop 9 which guides the upstream 9 to the surface of the fiber slurry layer on the lower wire 5.

In the example of Figure 1, the dewatering box 11 comprises three successive suction chambers 11a, 11b, 11e, each of which can be adjusted to a desired vacuum. The first suction chamber 11a is designed to provide non-pulsating dewatering, while the second and third suction chambers 11b and 11c provide a pulsating dewatering. Further, at the bottom of the second suction chamber 11b, there is a plurality of loading strips 12 on the underside of the wire 5, which provide 15 strong pulsations.

After the dewatering box 11, there is a transfer suction box 13 on the side of the lower wire 5, which · * ·,. ensuring that the web W follows the bottom wire 5 as the top wire 9 is guided apart from the bottom wire 5. Following the twin wire portion, there follows again the flat wire portion to dewater the dough W through the bottom wire 5 down dewatering steps (not shown). through. At the end of the flat wire section there is a suction roll 7 which turns! web W to run obliquely downwards. After the suction roll 7 follow the suction box · * ·!, „! 14, which raises the dry substance content of the web W before transferring it to the press section 2.

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After the suction box 14, the web W is moved from the underside portion of the lower fabric 5 to the upper felt 15 of the press section i by inserting a pick-up roll 16. The sole press nip * "*: pi N of the press section 2 is formed between two press rolls 18, 19, the upper being the shoe roll 18 30 and the lower counter roll. 19. The shoe roll 18 is provided with a static concave surface, · · · The web W is passed through a nip N between the upper felt 15 • * 9 and the lower felt 17, both of which receive water pressed out of the web. At the press team N, the counter roll 19 presses the fabrics 15, 17 and the web W against the concave surface a so-called long nip having a nip length greater than that of two hard surface rolls, followed by a suction roll 20 on the side of the lower felt 17, one function of which is to ensure that the web W follows the lower felt 17 during The web W is then transferred from the lower felt 17 by means of a transfer belt 21 to the first drying fabric 22 of the drying section 3.

Initially, the dryer section 3 comprises a horizontal blow dryer 23, followed by a vertical blow dryer 24 and at least one set of drying cylinders 25. The horizontal blow dryer 23 comprises a blow unit 26 and a dryer fabric 22 guided by the support rolls 27 to form an endless loop. From the blowing unit 26, heated air is blown towards the web W 15 as it passes under the blowing unit 26 supported by the drying fabric 22 and the supporting rollers 27, whereby the web W heats up and some water evaporates from its surface.

· * · ,. The web W is then transferred from the first dryer fabric 22 to the second dryer fabric 28, which conveys the web W through both the vertical over-blow dryer 24 and the first dryer cylinder group 25. Initially guided by the support rolls 29, the drying fabric jj '28 forms a vertical loop with two vertical sections fitted with blowing units 30 and 31. The first blowing unit 30 blows heated air to the surface of the web W as it passes 25 vertically downward and the second blowing unit 31 W against 11 «V · heated air as it travels back up.

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·: ··: After the vertical blow-blow dryer 24, the web W is led by a drying dryer:: ··: a winding path through a first drying group 25 30 comprising a plurality of steam-heated drying cylinders in the top row · ♦ ·! 32 and a plurality of turning rolls 33 in the bottom row. The first drying cylinder group 25 • '· 10 may be followed by one or more other drying cylinder groups, which may be single or double wire.

The web is carried as a closed export from the forming section 1 through the press section 2 5 to the beginning of the drying section 3, which prevents unnecessary stretching of the web and minimizes the number of breaks.

Figure 2 illustrates in more detail one forming unit 1 of a papermaking machine according to the invention. Fiber slurry is fed from headbox 4 over chest roll 6 to chest 10, the structure of which is explained in more detail in connection with Figure 3. After the breast table 34, there is a suction box 35 within the lower wire loop 5. At the beginning of the double wire zone 9, there is a dewatering box 11 whose curved lid 36 guides the partially woven web on the lower wire 5. The dewatering box 11 of Figure 2 comprises four successive suction 15 chambers 11a, 11b, 11c and 11d, each of which can be controlled with a different vacuum.

The cover 36 facing the top wire 9 of the first suction chamber 11a is designed to provide a non-pulsed, substantially constant dewatering pressure. Such a construction shoe structure is described in Example 2 **: ·. 20 in WO 2004/018768. The lid of the second, third and fourth suction chambers i.,, 1 Ib, Iloy 1 Id consists of dewatering strips 37 with gaps between them, · «« 2 ί. ·. through which the vacuum in the respective suction chamber 11b, 11c, 1 Id affects the web i ·· · • between the upper wire 9 and the lower wire 5. The dewatering strips 37 provide pressure pulses that enhance dewatering and improve web formatting. At the third suction chamber 11c there is a plurality of loading strips 12 inside the bottom wire loop 5, each of which is located at the gap between the two upper dewatering strips 37. This solution provides a highly pulsatile, alternating dewatering of the third suction chamber 1le.

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After the dewatering box 11, there is still a curved suction box 38 and a transfer suction box 13 inside the lower wire loop 5, after which the upper wire 9 is guided apart from the web W, which remains in the support of the lower wire 5.

Figure 3 shows the structure of the chest 34, and above it is a graphical representation of the dewatering pressure at various points on the chest. The chest 34 comprises two successive dewatering chambers 39,40 provided with different vacuum pressures and deck structures. The lid of the first suction chamber 39 has holes 41,42 which are disposed so that no pressure pulses are generated and the dewatering pressure 10 is substantially constant. The air through the first holes 41 is discharged through the wire 5 and the lip spray 45 and the subsequent holes 42 through the water. The lid of the second suction chamber 40 consists of dewatering strips 43 transverse to the machine direction, generating alternating pressure pulses P1, P2 and scraping water from the lower surface of the wire 5. Preferably, the front 44 of the chest is curved 15 in its surface before the lip jet 45 discharged from the headbox 4 hits the chest 34, which allows a smaller headbox lip 45 to hit the chest 34.

! * · “At the first suction chamber 39 of the chest 34, the dewatering is careful, whereby a thin layer of fiber capable of retaining the fine, filler material is felt against the wire 5. At the second suction chamber 40 of the chest 34, the dewatering strips 43 provide pressure pulses Pj, P2 which enhance dewatering, rigid fiber flocs, and improve formation.

· «· • * • 1 ··· 25 The aim is to track the delivery of fiber slurry from the headbox to the chest so that there is no stock jump at high speeds. This is achieved, for example, by positioning the chest roll in a position where its highest point * “* i is near the height of the lower lip of the headbox and the vertical plane passing through the center axis of the head roll *: ** ί is at a distance from the headbox. · * On the 30 side that a lip shower that can be discharged from the lip opening in the headbox can be provided · «·· · * · ,; to meet the planar wire substantially parallel to it or with a very low impact • • 12 mass either at the breast roll or in the trajectory direction of the web after the breast roll. One such solution is described in FI application 990432. Spattering can also be reduced by using a tip molded into the headbox.

Many modifications of the invention are possible within the scope defined by the following claims.

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• • · t t t + + + + + + + +: +::::::::::::::::: * · • · • · • «* ♦» ··· • · ···· * t · »··· ··· * I • · ·.

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Claims (11)

A paper or cardboard machine comprising a scoop portion (1) for scooping a web (W) of a fabric slurry, a pressing portion (2) for dewatering the shaped web (W), and a drying portion (3) for drying the web. the pressed web (W), comprising a portion (1) of an inlet carriage (4) for feeding fiber mud to a lower wire (5) and said pressing portion (2) comprising only one press nip (N) formed by a long nip, through which the web (W) is passed between two press tissues (15, 17), characterized in that the forming portion (1) comprises an initial single-wire dewatering section, followed by a double-wire section, at the beginning of which is provided a molding shoe (1a) which guides an upper wire (9) to the surface of a fiber mud layer on the lower wire (5), the forming shoe (11a) surface (36) being provided with dewatering openings which together with a molding shoe ( 11a) rescue suppression provides a pulsation-free dewatering from fiber mud the layer between the wires (5.9), and after which the forming shoe (11a) follows at least one dewatering element (1 lb, 1 le, 1 Id) which provides a pulsating dewatering from the fiber mud layer between the wires (5.9), the forming part (1 ) enables .. production of a web (W) having a low MD / CD tensile strength ratio. • · * · · ·· • · * · · I 20 Paper or cardboard machine according to claim 1, characterized in that ·· * *. * V inlet carriage (4) is a dilution inlet carriage. ♦ * * ··· · • · · • e * a. ···. 3, Paper or cardboard machine according to claim 1 or 2, characterized therein. In that the forming portion (1) comprises a chest table (34) to which the fiber mud 25 is measured from the inlet carriage (4), which chest table (34) comprises a first suction chamber ·; (39), which is provided with a lid construction, which, together with one in the form (M * - it] <; The suction chamber (39) rescuing negative pressure produces a pulsation-free dewatering pressure, and a second suction chamber (40), which is provided with a lid construction, which together with one in the second suction chamber (40). ) rescue suppression f * · ·; * · 30 produces a pulsating dewatering pressure. • · i • ♦ · * · ' 4. A paper or cardboard machine according to claim 3, characterized in that it comprises a breast roll (6) arranged before the breast table (34), said breast roll (6) being provided with means for effecting shaking of the breast roll (6). Paper or cardboard machine according to claim 3 or 4, characterized in that it comprises a breast roll (6) before the breast table (34), which breast roll (6) is positioned relative to the inlet carriage (4) in such a position that a protruding lip beam (45) projecting from the inlet tray (4) meets the lower wire (5) after the chest roll (6) substantially parallel to the lower wire (5). 10 Paper or cardboard machine according to any of the preceding claims, characterized in that the length of the initial dewatering section with single wire is at least 500 mm. 7. A paper or cardboard machine according to any of the preceding claims, characterized in that the long nip (N) is formed between a shoe roll (18) and a counter roll (19). ·· • · ϊ ** 8. A paper or cardboard machine according to any of the preceding claims, characterized in that the tap (W) is moved from the pressing portion (2) to the drying portion (3) at the end. 9. · Paper or cardboard machine according to any of the preceding claims, characterized in that the drying portion (3) comprises at least one dryer cylinder group, ·; * # 25 (25), which is preceded by at least one blow-drying dryer (23,24). A paper or cardboard machine according to claim 9, characterized in that the drying portion (3) comprises a vertical blow dryer (24). • · t ··· • ♦ • · ♦ * ·· • · 11. A paper or cardboard machine according to claim 10, characterized in that the dryer portion (3) comprises a horizontal blow dryer (23) arranged prior to the vertical blow dryer (24). 5 · 1 · 1 · 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · • · • · ··· i1 «• 1 1 *« · • M • · • 1 • f · '' · · · • · · MO · • · · * ·· * ·