FI92940C - Method in a paper machine for controlling the transverse fiber orientation profile of a paper web and a control arrangement implementing the method - Google Patents

Description

92940

Method in a paper machine for controlling the transverse fiber orientation profile of a paper web and a control arrangement implementing the method For the control of the paper web in the control of the paper web 5 The profile of the fiber center in the paper web is also adjusted for the genomics of the paper web

The invention relates to a method on a paper machine for controlling the transverse fiber orientation profile of a paper web, in which method water is removed from the paper web by pressing between two forming wires using dewatering and / or forming strips.

The invention further relates to a control arrangement for controlling the transverse fiber orientation profile of a paper machine to be made on a paper machine, the paper machine comprising a wire section having opposite strips in the two-wire zone pressed against each other, the wire section comprising a beam having a wall above the beam 20 there is a deflection compensating beam or the like, to which the circulation of the heating medium can be guided or a corresponding compensating arrangement, and the control arrangement comprises a paper web basis weight | for machine headbox lip strip profiling devices, and the control arrangement comprises a headbox lip profile measurement arrangement from which the measurement signals are derived to the control unit.

As is well known, the headbox of a paper machine has a lip channel which is generally bounded at the bottom by a stationary lower lip beam and on the other side by an upper lip beam fixed by a horizontal joint for pivoting in connection with the upper lip structures. The front edge of the upper lip bar has a tip strip that determines the exact profile of the lip opening in the transverse direction of the machine. As is known per se, the top strip has adjustment devices with which the profile of the lip opening is fine-tuned. As is already known, the upper lip beam is supported from above by several support arms, usually 4-6. The aim has been to arrange this support in such a way that the inclination of the upper lip beam 92940 2 is as small as possible and the fine adjustment of the lip opening profile is usually handled by an adjustable tip strip.

Headboxes are also known in which the upper lip beam 5 is supported on the arms at both ends, in addition to which various support and deflection compensation solutions, for example operating with hydraulic pressure chambers or hoses, have been used in connection therewith.

The aim is to design known headboxes in such a way that paper homogeneous in weight, shape and strength properties can be produced over the entire width of the web, from which as little as possible would have to be cut off from the edges of the web. To achieve said objects, it is already known to use different additional or exhaust flows on each side wall of the headbox lip channel at both sides, for which reference is made to the applicant's FI patent 75,377 (cf. U.S. Pat. No. 4,687,548).

A particularly important requirement, especially for fine paper, is that the major axes 20 of the orientation distribution of the fiber network of the paper coincide with the directions of the major axis of the paper and that the orientation be symmetrical with respect to these axes. For example, in copy papers, it is important that their top and bottom surface orientations are substantially the same. Sufficiently accurate implementation of the above requirements over the entire width of the web is often not possible with the above solutions. The diagonal curvature of the sheet and the "fall" of the form stack have been particularly awkward and causing complaints.

The above issues have been thoroughly investigated by the applicant. In this case, it has been shown that the required symmetry of the fiber orientation requires that at no point in the finished web, depending on the jet / wire speed ratio used in the lip jet, a transverse velocity higher than about 1-3 cm / s is exceeded, which is sufficient to pour the fibers in the main web. -20 ° to deviate from the machine direction, causing the above-mentioned "crash" and curvature-35 mismatch problems. Since the transverse velocity is already generated in the lip channel with the damping of the uneven main flow profile, the main attention must be paid to the uniformity of the velocity velocity profile after the 92940 3 turbulence generator.

One systematic cause of the transverse velocity in the lip channel is the effect of slowing down the machine direction flow of friction caused by the vertical side walls of the lip-5 channel. Another systematic effect is the spillage or spreading of the stock on a portion of the flat wire in the edge areas of the wire as the 10-30 mm thick layer self-levels. To compensate for these effects, the previously known additional side flow feeds (FI-10 pat. 75 377) are excellently suited.

In the previously known headboxes, the cross-section of the lip channel is measured to be uniform in the transverse height, and it is also known to use, in particular, the upper lip beam deflection adjusting devices so that the lip channel 15 is as constant as possible in the transverse direction.

When the paper web is dried, it shrinks less from the center of the web than from the edge areas, with shrinkage generally being about 4% in the middle and about 5-6% at the edge areas. Said shrinkage profile causes a change in the corresponding basis weight cross-sectional profile of the web 20 so that due to the shrinkage, the dry basis weight profile of a flat web having a basis weight transverse change during drying so that both edge regions have a slightly higher basis weight than the middle region. Due to the impact of the web drying, the already commonly used automatic basis weight profile adjustment automation sets the headbox top rail more open from the center area than from the edge areas. In addition, when the lip channel is known to be rectangular in the transverse direction, transverse currents are thus generated in the lip jet from the edges to the center, because the pulp suspension flowing from the edge areas of the lip channel is forced to move towards the center of the web.

This is adversely manifested in the so-called fiber orientation angle profile. S-form. Attempts have been made to control this problem by adjusting the profile of the top strip straighter, but in this case the uniformity of the basis weight profile has had to be compromised.

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With regard to the state of the art related to the present invention, reference is further made to U.S. Patent 4,769,11 to A. Ahlström Corporation, Applicant's FI Patent Application No. 885609, and Valmet-Ahlström Inc.'s F1 Patent Applications Nos. 885606 and 885607, which disclose trademarks. "MB-former" marketed formers. In addition, reference is made to the applicant's FI patent applications Nos. 904489, 911281, 913112 and 920228, which disclose various combination concepts of the above-mentioned MB former units and hybrid and kit formers. It is therefore an object of the present invention to further develop applications of the previously known 10 MB units.

The object of the invention is to provide such a method and adjustment arrangement by which the above-mentioned S-shape or other profile deviation of the fiber orientation profile can be corrected efficiently and using simple method operations and adjustment arrangements.

The object of the invention is to provide such a method and adjustment arrangement for a paper machine in which the so-called The S-shape correction can be carried out without at least substantially compromising the straightness of the other profiles of the paper 20, in particular the basis weight profile.

It is a further object of the invention to provide a method and control arrangement which is simple and inexpensive to implement, so that it is possible to make quite extensive use of the control arrangements already present in the paper machine as well as the forming members and their deflection compensation devices.

It is a further object of the invention to provide a control arrangement which can advantageously be integrated in an existing process control and regulation system in a paper machine so that the control loop required by the control arrangement according to the invention does not interfere with or cause instability in the other control system.

In order to achieve the above and later objects, the method of the invention is essentially characterized in that the method 92940 5 adjusts the transverse deflection of the web of the dewatering and / or forming strip or strips and thus affects the transverse retention profile of the web. 5 controls the lip opening profile of the headbox also to be substantially even in its edge areas so that a transverse flow rate which substantially skew the fiber orientation profile is not generated in the mass flow.

The control arrangement according to the invention is mainly characterized in that said control unit is arranged to control a controller for adjusting the heating arrangement of said compensating beam so that the transverse deflection of said strip web can be controlled to set the transverse retention profile of the track.

According to the invention, when the transverse retention profile of the track is controlled by existing dewatering and / or formation strips and their deflection compensation devices, no special actuators are required for this purpose.

The control arrangement according to the invention can advantageously be integrated into an already existing control system of the papermaking process, which measures the transverse basis weight profile of the paper web with a drying section and adjusts the profile of the headbox top strip based on said measurement result. The new control loop according to the invention is substantially slower in time constants than the control loop based on the measurement of the basis weight profile described above, so that the control arrangement according to the invention does not interfere with or cause instability in the existing control system.

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

35 92940 6

Figure 1 shows the beginning of the forming zone of a two-wire former, in which the method according to the invention is applicable.

Fig. 2A shows the former of Fig. 1 in a machine direction vertical cross-section in the plane II-II shown in Fig. 1 with the deflection of the MB beam compensated straight.

Fig. 2B shows the same as Fig. 2A with the MB beam bent upwards from the center.

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Fig. 2C shows, in a manner similar to Figs. 2A and 2B, a situation in which the MB beam is bent downward from the center.

Figure 3A schematically illustrates a prior art paper machine process control system.

Fig. 3B shows, in a manner similar to Fig. 3A, a process control system in which a control arrangement according to the invention is integrated.

The invention will first be described with reference to Figures 1 and 2A

MB formatter as a background and application environment for the invention. Figure 1 is shown very schematically and not on a scale of the so-called a guitar former into which the pulp suspension jet J of the headbox 30 is fed into a converging groove G between the forming wires 11 and 21, the geometry of which is determined by the forming and chest rollers 12 and 22.

immediately followed or relatively short by the dewatering and forming members is an MB unit 50 with a cross-machine housing beam 10 inside the loop of the upper wire 11. Said beam 10 is bounded by machine direction vertical end walls 10a and 10b and cross-direction. .30 full vertical walls 10c and bottom wall 10d. The beam 10 delimits a dewatering chamber 13 to which a dewatering channel 13a is connected, preferably only on the operating side of the machine. In connection with the lower wall 10d of the beam 10, fixed support and forming strips 14 are supported, through the slit gaps 14R of which the water leaves the web W in the direction of the arrows F through the suction deflector channel 35 16 inside the chamber 13 and further through the channel 13a to the paper breaker side. The interior of the chamber 13 is connected to a vacuum px, which enhances said dewatering.

Above the beam 10 there is a compensation beam 5 15 of its width and length, which is bounded on the beam 10 side by a horizontal partition wall 15b and above it by a corresponding outer wall 15a and an end wall 15c. The compensation beam 15 is passed into the (Vin) from the inlet pipe 17a and the valve 16 through the temperature Tx of the fluid flow is provided, preferably a water stream which is removed from the circuit 15 kompensointipalkin second end 15c are connected through the pipe 10 in the direction of arrow V out.

Inside the lower wire loop 21 there is a load unit 20 of the MB unit 50, comprising a support structure 23 and load strips 24 arranged transversely to the slots 14R of the support and forming strips 14 at 15R. The strips 24 of the unit 20 are loaded with pressure medium pressures pk applied to the hoses 25, and thus the wires 11,21 are pressed between the strips 14,24 and thus dewatering pressure and strip pulses are provided in the web W. The main direction of travel of the wires 11,21 and the web W past the strips 14,24 may be straight or curved with a relatively large radius of curvature.

According to Fig. 2A, the temperature Tx of the water fed into the interior of the compensation beam 15 is always known to be substantially equal to the temperature T2 of the water leaving the drainage chamber 13, the surface of which is marked with SH, T2. In this case, there is no deflection in the walls 15a, 15b, 10d of the beams 10 and 15, and the forming and supporting strip 14 supported by the wall 10d is completely straight in the transverse direction, as shown in Fig. 2A. As is already known, the compensating beam 15 is precisely designed to compensate for the deflection of the load and support strips 14, i.e. the strips 14 are "straightened" as straight as possible so that the wires 11,21 and the web W formed between them pass through the strips 14,24 in the transverse plane.

35 In the following, with reference to Fig. 3A, a prior art control system for the basis weight and fiber orientation profile of a paper machine and a fiber orientation profile will be described with reference to Fig. 3A. According to Fig. 3A, a pulp jet J is fed from the lip opening A of the headbox 30 between the wires 11,21. After the lip portion and the forming crystal G, the two-wire zone passes through the wire portion 50 and further to the press section 41. At the wire section 50 5 and the press section 41, the web W is mechanically dried, after which the web W is transferred to a drying section 42 where it is evaporatively dried. According to Figures 1 and 3A, the tip strip 33 and the lip opening A are profiled by a control system comprising a series of control rods 32 attached to the tip strip 33, which rods 33 are controlled by a series of actuators 31. The profile control devices 31,33 receive their control signal from the Sp process control system 100. The measurement arrangement of the transverse basis weight profile of the web W located on the drying section 42 provides a series of measurement signals in the web W, the most uniform basis weight profile in the transverse direction is realized.

As stated above, when drying, the web W shrinks in the middle region 20 less than in the edge regions with a shrinkage in the middle of -4% and in the edge regions of -5-6%, resulting in a corresponding increase in dry matter content in the edge regions of the web W. The adjustment system according to Fig. 3A seeks to compensate for this increase by adjusting the profile of the tip strip 33 so that the width of the flow opening A in the edge regions of the web W is smaller, as illustrated in Fig. 3A by the profile pa. This adjustment, in turn, results in the skew of the fiber orientation profile described above. The structures and method measures described above in connection with Figures 1,2A and 3A are known per se and are described only in connection with the application environment and background of the present invention and the problems solved by the invention. . . 30 m to understand.

As described above, there has always been an attempt to keep the gap between the strips 14 and 24 of the MB unit 50 as constant as possible in the transverse direction, especially to keep the retention in the transverse direction 35 as flat as possible. Retention, i.e. holding, means the retention of the solid in the mass path W between the wires 11,221 by retaining the wires 11,21.

At the beginning of the MB unit 50, the web consistency is typically of the order of 5 k1 «1.3% ... 2.5% and after the MB unit k2 * 3% ... 5%. In this case, the fibrous layer retaining the fines and fillers of the pulp, in particular against the inner surface of the upstream 11, has not yet been felted, so that the retention can be easily influenced in the strip zone 14,24, which is exploited in the invention. In the following, the invention will be described mainly with reference to Figures 2B, 2C and 3B.

According to Figure 3B, the invention seeks to ensure that, in normal operation, the cross-sectional profile of the headbox lip opening A is always as flat as possible. For this purpose, the profile of the lip opening A is measured in both edge regions with sensors 36a and 36c and in the central region with sensor 36b. The sensors 36 provide measurement signals A} ^ and Clt which are fed to a control unit 35 which controls the actuator 16a of the valve 16 as shown in Fig. 3B so that if Aj + Cx> 2BX actuator 20a adjusts the valve 16 open and if Ax + Cx <2BX closes . The valve 16 can be, for example, a three-way valve which mixes two different temperatures of water, or a supply water at a constant temperature T0 (T0> Tj) can be used, whereby the temperature 16 inside the compensation beam 15 can be influenced by the valve 16.

When Tx> T2 according to Fig. 2B, the walls 15a, 15b and 10d of the beams 15,10 bend so that in the transverse vertical plane the centers of their radii of curvature Rb1, Rb2 are on the side of the lower wire loop 21. In this case, the wall lOd. The forming and supporting strips 14 attached to the strips are bent accordingly, whereby the wires 11,21 are formed between the strips 14 and 24 and the web W has a larger gap in the middle than in the edge areas. In the situation of Figure 2C, where Tx <T2, the deflection of the walls 15a, 15b and 10d is opposite, whereby the gap between the strips 14,24 is smaller in the middle than in the edge-35 regions. In this case, the centers of the radii of curvature Rc1 and Rc2 of the walls 15a, 15b, 10d are on the side of the upper wire loop 11.

92940 10

The present invention actively utilizes the deflection control of the support and forming strips 14 as follows.

The adjustment arrangement 16, 16a, 35, 36a, 36b, 36c according to the invention is integrated into the process control system 100 so as to obtain the profile of the tip strip 33 and the cross-section profile p ,, of the pulp suspension jet as smooth as possible. . In the invention, by adjusting the deflection of the compensation beam 15, the cross-section of the forming and supporting strips 14 is affected, whereby according to Fig. 2B the distance Tx> T2 and the strips 14,24 is smaller in the edge regions of the web W than in the central region. In this case, the retention in the edge region of the web W also becomes smaller than in the middle region of the web W, because the retaining fiber layer 15 has not yet been felt against the outer surface of the upper wire 11. Thus, in the case of Fig. 2B, more fines and fillers are removed from the web W in the edge regions, whereby the basis weight of the web W correspondingly decreases, which is later compensated by the above-average effect of drying weft on the basis weight profile.

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For the reasons given above, the headbox lip profile adjustment system does not need to compensate, at least as much as before, for the increase in basis weight caused by drying shrinkage in the edge areas of the web W, so the machine can be run with an even smoother tip profile pb.

If, on the other hand, the situation were the opposite, i.e. it would be necessary to increase the retention in the edge regions of the web W above average, the arrangement according to Fig. 2C (Tx <T2) with a difference between the strips 14,24 would be used. . The gap 30 is larger in the edge regions of the web W than in the center region of the web W.

In preliminary experiments it has been found that the control of the fiber orientation profile according to the invention utilizing the deflection control of the dewatering and forming strips 14 or similar dewatering elements 35 according to the invention and the retention profile adjustment thus carried out does not prevent the good 92940 11 wind formation and ash profile.

The control loop 36a, 36b, 36c, 35,16a, 16,17a, 15,10,14, W according to the invention is integrated in the already existing control loop W, 43, nip, 100, Sp, 31,32,33, J of the paper machine. W so that the adjustment loops do not interfere with each other and cause instability. This is achieved above all by the fact that the new control loop according to the invention is lower in the control hierarchy and slower in time constants than the previously known control loop that already belongs to the paper machine.

The invention can be implemented in many other ways than those described above. Instead of or in addition to the fixed forming and support strips 14, load strips 24 or other opposing elements 15 can also be profiled, which can affect the transverse retention profile of the web W, so that the essential aim of the invention is to make the transverse fiber orientation profile more uniform. , that the headbox can be driven with a substantially more even lip opening profile.

The following claims set forth within the scope of the inventive idea, 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 (11)

92940 12 Patent suction s A method on a paper machine for controlling the transverse fiber tation profile of a paper web (W), wherein the paper web (W) 5 is dewatered by pressing between two forming wires (11, 21) utilizing dewatering and / or forming strips (14,24), characterized in that the method adjusts the transverse deflection of the web (W) of the dewatering and / or forming strip (s) (14, 24) and thus affects the transverse retention profile of the web (W) and that said retention profile is set such that the papermaking process control system (100) controls the profile of the lip opening (A) of the headbox (30) also substantially uniform in its edge areas so that no transverse flow rate is created in the mass flow which substantially skews the fiber orientation profile. 15 A method according to claim 1, characterized in that the method measures the width of the lip opening (A) of the headbox in both edge regions and the central region of the web (W) and adjusts the compensation bar (15) at the beginning of the wire section 20 on the basis of said measurement results. ) or the deflection of the drainage and / or support strips (14) supported by the corresponding and associated housing beam (10) or the like. A method according to claim 1 or 2, wherein the profile of the headbox (33) is adjusted on the basis of measuring the transverse basis weight profile (43, mp) of the dried paper web (W) by the papermaking process control system (100), characterized in that the retention level of the web ( W) the edge regions are reduced by adjusting the deflection of said dewatering and / or forming strip or strips (14) relative to the average retention level so that when drying the web (W) the increase in square weight due to greater than average shrinkage of its edge regions is substantially compensated. the lip opening (A) is profiled to be substantially uniform in width also at its edge areas. 35 92940 13 Method according to one of Claims 1 to 3, characterized in that the method uses an initial part of a two-wire zone (11, 21) in which the consistency of the web is in the range from 1 to 1.3%. (11,21) and the mass path (W) formed between them is guided past opposite strips (14, 24), one of which strips (24) presses the forming wires (11,21) and the fixed mass path (W) between them against the strips (14) that said strips (14, 24) of said strips (14,24), preferably said fixed top strips (14), are attached to a transverse support beam (10,15) of the track 10, the deflection of which is arranged to be adjustable and that said deflection adjustment affects the deflection of the strips (14) attached to said beam (10, 15) and thus affects the transverse retention profile. Method according to claim 4, characterized in that the method uses a transverse beam (10) arranged inside the upper wire loop (11), above which a compensating beam (15) is placed, said compensating beam (15) being provided with heating devices for adjusting its transverse deflection, 20 preferably a heating medium flow (Vin-Vout). A method according to claim 4 or 5, characterized in that a dewatering chamber (13) is arranged inside said beam (10), into which the water coming through the slit gaps • 25 (14R) of the strip (14) below the beam (10) is directed through the suction deflector channel (16). and from which the water is further led to the side of the paper machine, preferably only on the machine side, and that the ends (15c) of the compensation beam (15) arranged above said dewatering chamber (13) are led through the control valve (16) in volume and / or temperature (T0) controlled water or other similar heating medium and that the temperature Tx of said compensation beam (15) is arranged to be adjusted so that Tj> T2, where T2 is the temperature of the water continuously leaving through the underwater drainage chamber (13), the lower wall of said beam (10) (10d) and associated drainage and / or formation strips (14) bend so that the retention becomes lower than average at the edge regions of the web (Figure 2B). 92940 14 A control arrangement for controlling the transverse fiber orientation profile of a paper machine (W) made on a paper machine, the paper machine comprising a wire section (50) having opposite strips (14, 24) in the two-wire zone (11, 21) pressed against each other, the wire section comprising a beam (10) , to the wall of which, preferably to the lower wall (10d), one of said strips (14) is attached, and above the beam (10) there is a compensating beam (15) or the like for adjusting the deflection of the heating medium (Vin-Vout) or having a corresponding compensating system-10 ly, the control arrangement comprising a paper web (W) basis weight profile measuring arrangement (43) in connection with or after the paper machine drying section (42), which provides a measurement signal (nip) to the process control unit (100), which in turn provides a control signal (Sp) paper machine headbox lip (A) tip strip (33) pr (31,32), which control arrangement comprises a headbox lip profile measurement arrangement (36a, 36b, 36c) from which measurement signals (Ai.Bi.Ci) are derived to a control unit (35), characterized in that said control unit (31 35) is arranged to control an adjuster (16a) for adjusting the heating arrangement of said compensation beam (15) so that the transverse deflection of the web of said strip (14) is controllable for setting the transverse retention profile of the track (W). Control arrangement according to claim 7, characterized in that said compensation beam (15) is a hollow housing beam, the walls (15c) of which have inlet and outlet connections (17a, 17b) for heating medium, preferably heating water, and that the arrangement comprises a heating medium control valve (16) controlled by an actuator (16a) for adjusting the temperature (Τ :) of said compensation beam (15). 30 Adjustment arrangement according to Claim 7 or 8, characterized in that the measuring devices for the cross-sectional profile of the headbox lip opening (A) comprise measuring sensors (36a, 36c) arranged on both edge areas of the lip opening (A), from which measuring signals (Aj and Gx) and 35 are obtained. that in connection with the lip (A) of the headbox there is one or more lip (A) measuring sensors (36b) located in the middle of the paper web (W), 92940 15 from which a measuring signal (Bx) is obtained, which measuring signals (A ^ B ^ Ci) are fed to said control unit ( 35) for comparison and for providing a control signal to said actuator (16a). Control arrangement according to any one of claims 7 to 9, characterized in that said beam (10) is located at a point in the two-wire zone where the consistency of the web (W) is in the range k1-k2 ~ 1.3% to 5% and that said the support and forming strips (14) connected to the beam (10) have a controllable retention profile of the web (W) in such a way that the increase in basis weight due to the greater than average shrinkage of the edge areas of the web (W) in the drying section is mainly compensated for, and the papermaking process control system (100) adjusts the profile (pj,) of the tip strip (33) of the lip opening (A) of the headbox lip portion to a substantially uniform width 15 also at the edge areas of the web (W). Adjustment arrangement according to one of Claims 7 to 10, characterized in that a previously known control loop based on the measurement of the dry basis weight profile and the profiling of the tip strip (33) belonging to the paper machine is integrated in the control loop (36a, 36b, 36c, 35,16a). 16,15,10,14) such that the time constant of the latter control loop is substantially greater than that of the former control loop. 25 92940 16