FI85524B - Method for producing paper of uniform quality, as well as the drying part for a paper machine intended to execute the method - Google Patents

Description

85524

The invention relates to a method for producing uniform paper using a paper machine after drying, mainly by evaporation from about 40-50% to about 90-100%, and in which method the transverse moisture profile of the web is controlled by using a drying section with wetting devices adjusting the transverse moisture profile of the web and / or controlling the cross-distribution of the drying power.

The invention further relates to a drying section of a paper machine for applying the method of the invention, which comprises a plurality of successive groups of drying cylinders using a single-wire outlet and / or a two-wire outlet.

It is known from the prior art to use a single-wire export and / or a two-wire export in the drying section of a paper machine. Single wire export, in which the drying wire also supports the web by tension between the rows of cylinders, is generally used. : at the beginning of the drying section. The single-wire outlet can also be used for the entire length of the drying section.

Recently, single-wire outlet drying parts have become more common, in which the upper cylinders are steam-heated drying cylinders, against which the web comes into direct contact when pressed by the drying wire, and the lower cylinders are cylinders with internal suction, e.g. "UN0-VAC" (trade mark) cylinders, ....: 35 through which a vacuum is applied through a perforated casing to a groove around the cylinder liner from inside the rotating cylinder. The purpose of said vacuum effect is to effectively hold the web in the drying groove when the web is brought to the outer curve by the lower turning cylinders 2 85524 and to prevent transverse shrinkage of the web as the drying progresses.

Typically, a multi-cylinder dryer has 5-8 wire groups and the groups at the beginning of the drying section are normally shorter than the groups at the end.

As is known, the edge portions of the paper web dry in the drying portion of the paper machine to be drier than the central region of the web. This moisture profile is generally corrected after said main drying step, either by further drying the central area with zone infrared radiators or by wetting the edges with zone-water spraying. Both of these known methods increase the relative looseness of the edges relative to the center portion.

15 When a paper machine dries the web unevenly in its transverse direction, this causes e.g. uneven tension in the web. An uneven tension profile means, for example, that the edge of the paper web made from the paper machine is looser than the middle part of the web, which is a common situation. It has been found by measurements that peaks and valleys also occur in the cross-sectional profile 20 of the stress, even in the middle parts of the web, i. tighter and looser zones.

In the post-paper machine web processing steps, the unevenness of the web tension profile may cause significant handling and driving difficulties, for example, in controlling the structure of the customer roll, in the form of wrinkles, breaks, and printing machine alignment problems.

The loose edge of the paper web can be explained by three known factors: first, in a conventional cylinder drying group, the edges of the web 30 dry faster than the center; second, the water-swollen fibers and paper web shrink as drying progresses. This shrinkage; '; is particularly strong in the dry matter range of about 65-95%; third, the deformation of the paper when wet is mainly plastic, while the force-elongation behavior of drier paper is largely elastic. Thus, the deformation caused to the wet paper, such as stretching, remains largely permanent at 3,85524, while the elongation of the drier paper largely recovers and disappears as the force is released.

The main object of the present invention is to provide new solutions to the problems discussed above and to provide a method for producing homogeneous paper and a drying section of a paper machine with a substantially more uniform cross-sectional tension profile than paper made by prior art methods and paper machines.

10

In order to achieve the above and later objects, the method of the invention is mainly characterized in that the transverse tension profile of the paper web to be dried is equalized by arranging the drying of the web and / or the transverse moisture profile of the web advancing through the drying section with devices affecting the transverse drying performance.

20

The drying section of the paper machine according to the invention, in turn, is essentially characterized in that inside the drying section those drying groups in which the dry matter content of the web is in the range of 65-95% are: V: arranged wetting devices for the web and / or drying felt or fabrics : 25 and / or similar blowing air or infrared drying devices for adjusting the drying efficiency in the transverse direction, with which the transverse dry matter content of the web can be set, controlled or adjusted so as to obtain a substantially uniform transverse tension profile on the web.

30

In the following, the invention and its background elements will be described in detail with reference to the inventions shown in the figures of the accompanying drawing. to some application examples of the invention, the details of which are not limited to the invention.

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Figure 1 shows the dependence of the length (shrinkage) of the free-drying paper on the dry matter content.

Figure 2 shows the force-elongation curves of the paper at different stages of drying 5 (at different dry matter contents) and the effect of removing the stretch.

Figures 3A, 3B, 3C and 3D show the relative cross-sections of the paper web at different stages of drying, Figure 3A shows the dry matter content of the paper web, Figure 3B the theoretical length of the free-drying web, Figure 3C the actual length of the web and Figure 3D the plastic deformation of the web in different steps 1-7.

Figure 4 schematically shows a drying section of a paper machine applying the method according to the invention.

Figure 5 shows the development of the dry matter content of the paper web in the drying section according to Figure 4.

Fig. 6 schematically shows, in machine direction, a vertical section of water jet systems with which the method of the invention can be implemented.

Fig. 7 schematically shows a second version of the invention in a manner corresponding to Fig. 6 in a machine direction vertical section of the machine.

--- Figure 8 shows spray devices applying the method of the invention as seen from the cross-machine direction.

Figure 1 shows the dependence of the length (shrinkage) of free-drying paper on the dry matter content. It can be seen from Figure 1 that the water-swollen fibers and with them the paper web shrink their. ···. as drying progresses, especially in the dry matter range of 65-95%. In Figure 1, the derivative of the curve illustrates the intensity of the shrinkage.

i.

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Figure 2 shows the force-elongation curve of the paper at different stages of drying in a paper machine and the effect of removing the stretch. Figure 2 shows the force corresponding to the AC elongation OC, the OB plastic deformation and the BC plastic recovery after the removal of the tensile force - EP. Figure 2 5 shows a swarm of force-curve curves with paper dry matter of 50%, 60%, 70%, 80% and 90%. It can be immediately seen from Figure 2 that EPgoz> EP70Z> EP5QZ. From Figure 2, it can be seen that the elongation caused by the wet paper remains largely permanent, while the elongation caused by the dry paper W largely disappears when the stretching exits 10 (EPgoz »EP50Z).

It can be assumed that the dry matter content of the paper web W ka (Figs. 4 and 5) is substantially uniform in cross-section after the press section at the beginning of drying. Figure 3A schematically shows the development of this dry-15 material profile during the previously known conventional cylinder drying. From Figures 1 and 2, it can be seen that a significant tendency to shrink drying begins to occur in the web W after a dry matter content of about 65%. Fig. 3B schematically shows the theoretical cross-sectional length profile of the free-drying web W, should this be allowed to change as the drying progresses. However, in practical papermaking, the web W is known to have to be pulled to a slight tension; in its longitudinal direction so that it generally remains straight, fluttering, bag-free and passes otherwise undisturbed through the drying section. So there is no difference in length between the edges of the web W::: and the center,

; 25 shown in Figure 3C. In previously known paper machines, the web W

this results in a permanent elongation at the edges, as illustrated in Figure 3D. As the central part of the web W, on the other hand, dries and tends to shrink the edges later, this naturally causes, on the basis of the above, that the edges of the web W remain looser or "longer" than the central part in the finished paper machine roll 30.

The basic idea of the invention is to make the drying proceed as uniformly as possible in the dry matter content front throughout the drying section, but especially in the range of 65-95%, where drying shrinkage is most strong. This is achieved by correcting the moisture profile of the web, not only after the actual drying, but specifically in the above-mentioned dry matter range of 65-95%, or before. The correction can theoretically be done in different ways. by locating the zone wetting devices at suitable locations in the drying section, thereby substantially reducing the different ("different pace") stretches and permanent deformations of the web edges and the center portion.

In addition to reducing edge looseness, the method shown can also be applied to the correction of machine direction tension differences caused by "moisture" and "dry spikes" of the web.

The presented relationships can be complicated and converted e.g. the fact that wetting of dry paper in particular may to some extent trigger internal stresses in the paper during drying. Another factor not analyzed above is the effect of web tension strength. However, these factors do not preclude the applicability of the inventive idea.

Figure 4 shows a typical multi-cylinder dryer with a single wire outlet, in which the method according to the invention is applied.

20 The drying section comprises seven successive wire groups R1..R7, all of which apply single wire export. The various drying groups R1 ... R7 have ..:: steam-heated drying cylinders 20 and reversing cylinders 21,: with a perforated and grooved jacket inside which a pressure of:::: exists.

25

According to Fig. 4, the paper web Win is introduced from the press section (not shown) to the drying wire 11 of the first group R1 for running after its guide roll 18a, and the web W is attached to the drying wire 11 by means of a vacuum field of the suction boxes 25. The dry matter content of the web W is generally in the range of 30% to 40% ... 45% as the web W enters the drying section and its first drying cylinder 20a. The web W leaving the dryer section: the last drying cylinder 20b in the direction of the arrow Wout is the kulva- kaout solid content - 91% ... 98%. The total length of the drying section is denoted by L. The length L is generally in the range L to 80 m ... 100 m. The group R5 is followed by an inverted group Rg, in which the turning cylinders 21 'are in the top row and the hot drying cylinders 20' in the bottom row. the opposite side comes against the heated surfaces of the cylinders 20 'compared to the web W of the previous groups Rj-Rs and the last group R7. The transfer of the web W between the normal group Rs and the inverted group R6 takes place in such a way that the web W leaves the wire 15 of the group R5 and follows the wire 16 of the inverted group R6 16 under the influence of the vacuum in the groove on the outer surface of the cylinder 21 '.

Fig. 5 schematically shows the development of the dry matter ka (L) of the web W as the web W progresses in the drying section through the cylinder groups RX ... R7 10. The above-mentioned dry matter range k0 to 65-95% thus extends, according to Figures 4 and 5, from the cylinder group R4 to the last group R7. In this range L0 it is most advantageous to apply the humidity profile control and correction according to the invention.

Figure 4 schematically shows some possibilities for implementing the method of the invention. According to Fig. 4, nozzle tubes 31 and 32 extending over the entire width of the paper web W are arranged in the wire groups R4, R5, R6 and R7, of which the spray and jet tubes 31 apply nebulizable and sufficiently fine water jets S20 across the entire transverse width of the drying fabric 15. The jet tubes 32 apply the adjustable water jets S directly to the outer surface of the web. Substantially immediately after or relatively close to the nozzle tubes 31,32, the moisture profile measuring sensors 41 of the web W are arranged, which are e.g. conventional traversing moisture sensors or: · 25 corresponding stationary sensor sets. These sensors 41 measure the transverse moisture profile of the web W inside the drying section.

The above spraying and the subsequent moisture profile measuring devices and the closed control loops formed by them can ensure that the moisture profile of the web remains constant as it passes through the drying section, especially in the above-mentioned dry matter range kQ to 65-95%.

According to Fig. 4, the moisture profile of the web Wout is also measured by the sensor 35 50 after the drying section, i.e. after the last drying cylinder 20b, and the series of measurement signals thus obtained are fed to the control system.

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Fig. 4 schematically shows control systems 40 by which a feedback signal of the control system 40 is generated from the sets of measurement signals M (mA) obtained from the humidity sensors 41, and control signals C (οΑ) are generated in the system 40 for controlling the water jet S (sk) of the jet pipes 5,32. Above, the index i refers to the measurement points in the transverse direction of the web W.

In the control system 40, it is essential that the transverse moisture profile of the web be measured not only after the drying section but also within the drying section, preferably substantially immediately after the spray tubes 31,32 or other similar wetting device. This guarantees the essential feature of the invention that the drying proceeds as evenly as possible in the dry matter front through the entire drying section. It should be emphasized, however, that the control system 40 described above is only one embodiment of the invention. The invention can therefore be applied in many other ways and with different control systems.

Figures 6, 7 and 8 show in more detail the implementation of the humidity profile control equipment. Shower pipe 31,32 introduced into water or another wetting agent 20, such as water vapor or water vapor and a mixture of different gas medium source 50 in the direction of the arrow Sin (Figure 8). A series of spray nozzles 33 with a nozzle hole 34 are connected to the jet pipes 31, 32 '. Each: the spray nozzle 33 is connected to a control valve 35, which according to the figure is a series of control valves 35A. 40 with the control signals cl given by the measuring device 41. The water jets controlled by the valves 35A can be used to control the moisture profile of the web in the transverse direction.

According to Fig. 6, water jets S are applied to the surface of the web W directly as the web W passes by the drying cylinders 21 'outside on the drying fabric 16. In addition to or instead of the direct moisture profile control of the web W of Fig. 6, wetting of the drying fabric can be used, as shown in Fig. 7.

In practice, it is not always necessary to extend the nozzles 31,32 with their control valves 35A over the entire transverse width of the web W, but may l! 9 85524 it is sufficient that the jets S are applied only to both edge areas of the web W.

The invention can also be implemented in part by adjusting the drying efficiency of the web in the cross-machine direction. This control can be implemented by various block controls known per se, such as block control devices for controlling the air volume and / or air drying efficiency of the blow pipes of the air conditioning and / or stabilizing devices of the drying section. Even then, it is essential that the control of these block control devices not only measure the moisture profile when the web leaves the drying section, but that the measurement is performed inside the drying section so that in all normal applications - 65-95%, where dehydration is most pronounced.

In all cases, it is not necessary to use active control devices to measure the transverse distribution of the dry matter content of the web, but the method of the invention can also be carried out by determining the wetting and / or drying efficiency settings inside the drying section with test runs of 20 paper machines and laboratory tests of the paper to be produced. using, for example, manual control, the parameters of which are changed, for example, when the quality of the paper to be produced or the running parameters of the machine are changed, taking advantage of the information obtained from experience and test runs.

The profile adjustment devices according to the invention can also be used to control the homogeneity of the paper to be produced in the machine direction, although this control is not actually within the scope of the present invention.

The following claims set forth within the scope of the inventive idea defined by the various details of the invention may vary and differ from those set forth above by way of example only.

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Claims (10)

1. Process for making uniform-quality paper on a paper machine, using a drying section, 5 pcs, which increases the dry matter content (ka) of the web (W) after drying is done by pressing mainly by evaporation from about 40-50% to about 90-100%, and in which method one checks the transverse moisture profile of the web (W) by using on the drying section humidifiers which regulate the transverse moisture profile of the web (W) and / or control devices or corresponding, which per section controls the transverse distribution of the drying effect, characterized in that the transverse stress profile of the paper web (W) to be dried is smoothed out by in the area of the drying portion where the web (W) strives to substantially shrink during drying, arranging the drying of the web (W) to progress in the transverse direction of the machine in the form of a substantially even front the dry matter content by controlling or adjusting the transverse moisture profile of the web (W) advancing through the drying portion with said wetting means and / or with devices affecting the transverse drying effect. 2. A method according to claim 1, characterized in that the settings, controls and / or controls of said transverse moisture profile are carried out within the drying section at sufficiently many places, especially within the range k "- 65-95% of the dry matter content of the web (W). , in which area the drying shrinkage of the web (W) ”- appears most strongly. 3. A method according to claim 1 or 2, characterized in that the method utilizes an active control of the transverse moisture profile of the web (W) by measuring the wetting devices or the corresponding, in the vicinity thereof. the transverse moisture profile of the web (W) with traversing humidity sensors or corresponding series of humidity sensors and with the thus measured signal series regulate the humidifiers and / or those of -____; sectional drying means of the web (W). 14 85524 4. A method according to any one of claims 1-3, characterized in that the method uses a direct wetting of the paper web (W) within the drying portion by spraying a series of scattered jets of moisture medium (Sj 2 -Sg), the distribution of which serle in the transverse direction of the path is set, controlled or regulated, most preferably with an interconnected control system. 5. A method according to any one of claims 1-4, characterized in that the method uses an indirect wetting of the paper web (W) by directing jets (S 2 S 2) of moisture medium to the drying tissue of the drying portion of the paper web, from which the moisture medium is transferred to the web (W), 6. A method according to claims 1-5, characterized in that humidifiers and / or control devices for the drying effect controlled per section are placed for application of the method over the entire width of the web (W) or only on both edge areas of the web. The drying portion of a paper machine intended to carry out the method according to any of claims 1-6, the drying portion comprising several groups of drying cylinders (R1 ... R7) on one another, using a single wire pull and / or double wire pull, k characterized in that in the drying groups (R4 ... R7) within the drying portion, in which the dry matter content of the web (W) is in the range of 65-95%, moisture devices for the web (W) and / or drying means are provided. the tissue or tissues and / or the corresponding blowing air or infrared drying devices which control the drying effect in the transverse direction, with which the transverse dry matter content of the web (W) can be set, controlled or regulated so as to obtain a substantially even ____ transverse stress profile for the web (W). Drying portion according to claim 7, characterized in that the device includes measuring devices (41) for the transverse moisture profile of the web (W), with whose measuring signals (M) controlling the profile control devices for the humidity and / or drying effect of ____ : banana (W). Il 15 85524 9. Drying portion according to claim 8, characterized in that said drying level measuring devices (41) are located substantially immediately after the humidifying devices and / or the drying devices are arranged in sections which are controlled by them in the direction of progress of the web (W). Drying portion according to any one of claims 7-9, characterized in that in the drying groups (R4-R6) in the at least the other half of the drying portion, injection pipes (31,32) extending in the transverse direction of the web (W ), which has a series of control valves (35 ±), through which scattered adjustable water jets are directed towards the web (W) and / or the drying tissue (16) or the tissues (Figures 6-8). • · ·