FI90672B - Web forming method in paper or cardboard machines - Google Patents

Description

90672

In the forming process for a paper or board machines Banformningsförfarande i paper or kartongmaskiner 5 The invention relates to a paper or board machines, a web forming method, comprising the paper machine headbox slice channel is supplied to the pulp suspension forming wire or forming, wires to limit the forming throat and the headbox slice channel of the stock suspension flow is generated in the cross direction speed syöttä-10 by the pulp suspension to the slice channel of the to the second edge region more than to its opposite edge region so that the average of the edge currents substantially corresponds to the average flow in the lip channel.

Depending on its structure 15, previously known paper or board machines have either a smaller or greater tendency to direct the fibers in the direction of web production, i.e. in the machine direction. In addition, all machines have the possibility of emphasizing or reducing said tendency by adjusting the speed difference between the headbox lip jet and the forming wire or wires as necessary. For hybrid and especially guitar formers, said orienting effect is often detrimental, although they often have a beneficial effect on sheeting in other respects. Such advantageous factors are e.g. small variation in basis weight and flatness of formation and low one-sidedness of the paper produced.

25 The headboxes of paper machines use a variety of turbulence generators and diffusers to provide a level of diffusion and turbulence suitable for lip flow and lip jet, which is important to achieve good paper formation and a sufficiently low draw ratio (machine direction / cross direction - MD / CD). Headboxes are most commonly used to provide turbulence to produce turbulence, mainly due to frictional velocity differences in the flow direction, which transversely affect the mass flow rate, consistency and turbulence intensity profiles and the fiber orientation profiles. As is known, a series of vortex flows is generated adjacent to said walls 35 so that the vector defining the vortices is perpendicular to the direction of flow.

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In the lip channel of the headbox of a paper machine, individual vortices in the pulp suspension are difficult to detect because the flow is completely turbulent. However, it is obvious that the direction of the plane of vortices is important for the orientation of the fibers of the pulp suspension. The pulp suspension vortices provided by the previously known 5-plane walls, the vector of which is perpendicular to the main direction of flow, cannot be said to affect the fiber orientation on the forming wire.

The disadvantage of strong fiber orientation often manifests itself as impaired 10-sheet dimensional stability in the transverse direction of the machine. When a sheet gets wet or dry due to a change in air conditioning or is heavily and unilaterally heated, for example in a copier, its dimensional changes in the transverse direction lead to deviations from flatness, cupping or warping. The strong fiber orientation is also adversely reflected by a reduced reduction in the CD / MD strength of the transverse CD and the machine direction MD.

As is known, the direction of the fiber orientation of the paper is mainly determined by the direction of the relative velocity vector between the pulp suspension layer being felted and the forming wire. The strength of the fiber orientation, on the other hand, is determined by the absolute value of that relative velocity vector. As is known, the fiber orientation is controlled by a paper machine by adjusting the average magnitude of said velocity vector during dewatering, which control is usually achieved by adjusting the headbox pressure.

25 The essential difference in the orientation adjustment result of the known flat wire machines and gutter formers is due to the fact that the speed difference with the gutter former changes much more in the dewatering zone without said change being affected. Thus, the average value of the speed difference in both machine types can be set to zero if desired to minimize the orientation. Since the range of speed differences is larger in known gutter formers than in flat wire machines, the felted nonwoven mat has layers with a very strong orientation and the result is on average a much stronger orientation in the paper driven by the gutter formers. Known hybrid formers are positioned between the planar wire and the kitaformer-35 in order to achieve a minimum orientation.

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It is an object of the present invention to provide new solutions to the problems discussed above.

It is an object of the present invention to reduce the fiber orientation, i.e. to increase the relative proportion of fibers in the cross direction of the machine and the sheet at the expense of the machine direction fiber portion, especially in a kit-type former.

The object of the invention is to provide a method by which a tensile strength ratio MD / CD in the range MD / CD <2.0 can be obtained.

In order to achieve the above and later objects, the invention is mainly characterized in that the non-uniform velocity difference distribution AU - SW - F (Z) (S - mass jet velocity and W - wire of the non-uniform velocity distribution prevailing in the Z-direction of the track formed together at said transverse velocity). the fiber orientation of the web to be formed so that the web fibers are turned from the machine direction to the cross-machine direction, the method sets the transverse flow rate and the speed difference AU - SW distribution F (Z) so that in both surface layer regions of the web to be made in opposite directions from the machine direction to the transverse direction, and further, the fiber orientation of the inner layers of the web is reversed in the opposite direction from the machine direction 25 to the direction of the reversal of the fiber surface orientation of the nearest surface layer.

In headbox structures in which the converging lip channel is divided into two or more channels by uniform headbox-wide partitions, the transverse flow described above can also be controlled so that it is in opposite directions in adjacent channels.

According to the invention, the control of the fiber orientation takes place by changing the orientation angle of the orientation in a controlled manner. When the direction of the major axis of the ellipse, which well describes the orientation distribution of the orientation, is turned away from the machine direction, the ratio of the machine direction to the transverse radius vector of said ellipse is understandably reduced. The inversion of the ellipse is based on the fact that the tangent of the orientation angle is always the ratio of the transverse velocity component of the suspension to the relative (suspension / wire) velocity in the machine direction.

In addition to the transverse flow component mentioned in the invention, it is used that the velocity difference AU - S-W - F (Z) (S - pulp suspension jet velocity, W - wire velocity) varies in the forming zone, i.e. is not uniform in the Z-direction (thickness direction) of the forming web. In general, the situation is such that said speed difference AU is positive and substantially equal to the lower surface and the upper surface of the web to be formed and approximately equally negative in the middle of the web from which the water is last drained. Said velocity distribution is influenced by the gravitational force and the overpressure prevailing in the wire ridge. When the above-mentioned Z-direction velocity distribution is applied in conjunction with the transverse velocity component 15, a web is obtained which is symmetrical with respect to its central plane, i.e. in the opposite direction, 20 according to the direction angle rule above.

By bringing a uniform sufficient transverse velocity across the web in accordance with the method of the invention, the average of the absolute values of the orientation angles prevailing in the various fiber layers can be increased by several tens of degrees while the average orientation angle still remains parallel to the machine. The effect is larger the smaller the above-mentioned range of the machine direction speed difference (suspension / wire) and the closer to zero the machine direction average speed difference is set. In practice, it is possible to achieve an average orientation distribution that is wider in the transverse direction than in the machine direction.

The invention is particularly suitable for use with guitar formers, but also with other formers. Thanks to the invention, the tensile strength ratio MD / CD is generally obtained in the range MD / CD <2.0. Said tensile strength ratio range also meets the requirements for fine papers, which have the greatest dimensional stability requirement because they are exposed to large changes in temperature and humidity during copying or printing processes.

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The paper produced according to the method of the invention can increase its transverse strength and reduce the MD / CD tensile strength ratio, which is an important quality property of fine paper (dimensional stability). The often feared risk of warping (especially diagonal warping) is prevented by the fact that the paper can be oriented equally strongly on both surfaces by the method, by adjusting the horizontal movement of the upper lip and spraying at a suitable angle of impact with respect to the lower wire. A system operating on the basic idea described above is best suited for a guitar former. In addition, there is the advantage that the web drying with the -10 part shrinks less in the transverse direction and especially in the edge areas. This increases the production of the machine and facilitates all kinds of profile management.

Based on the above, in accordance with the invention, in order to reduce the fiber orientation 15, a uniform, sufficient and adjustable transverse speed of the stock is produced for the wire. The background factors of the invention have been studied by the applicant for years and it has been shown by both calculations based on flow mechanics and measurement results that an uneven stock flow fed by a turbulence generator generates a transverse flow component for 20 wires. Thanks to the invention, it is possible to aim for a uniform transverse flow and to calculate what kind of generator supply flow must be in order to achieve the result.

:'·· Flows of different magnitudes are fed to each edge region of the headbox, the average of which essentially corresponds to the magnitude of the main flow. 25 The transverse flow is almost linearly dependent on the edge flow. difference from the average flow. The effective term is speed difference x speed difference channel width. Since large speed differences easily generate disturbing turbulence, the edge channels have to be made moderately wide, and / or the smoothing speed difference has to be staggered into a multi-zone. If a very large transverse flow is desired and the maximum edge flow is to be increased more than twice its average value, the minimum flow at one edge must be negative, ie the mass must be removed from the edge. Flow control of the edge areas can be implemented with suitable pump and / or valve-35 solutions. The same solutions can also be applied to the embodiment in which the converging lip channel is divided into two overlapping zones by means of a spacer.

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.

Figure 1 schematically shows a machine direction vertical cross-section 10 of a headbox in connection with which the web-forming method according to the invention can be applied.

Figure 2 schematically illustrates a method of the invention seen from the front edge of a turbulence generator.

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Figure 3 shows the velocity profile of the transverse flow generated in the headbox mouth channel to implement the method of the invention.

Figure 4 shows a top view of the velocity distribution of the lip channel flow at the trailing edge of the generator section.

Figure 5A shows the placement of the additional feed to the second edge region of the turbulence generator when applying the invention.

Fig. 5B shows plugged turbulence generator tubes in accordance with Fig. 5A as viewed from the equalization chamber side toward the turbulence generator.

Fig. 6 shows in principle the variation of the orientation angle Θ of the orientation of a split web made with a guitar-30 former using the method of the invention in the paper thickness direction Z.

Figure 7 shows schematically a vertical cross-section of a lip section of a headbox according to the invention.

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Fig. 8 schematically shows the starting edge of the lip part with a spacer plate according to Fig. 7, which is at the same time the trailing edge of the turbulence generator.

Fig. 9 shows in the solution according to Figs. 7 and 8 a valve system arranged on each side of the headbox turbulence generator.

Fig. 10 illustrates the distribution of special mass feeds in the edge regions of the turbulent-10 generator, which is feasible with the valve arrangement according to Fig. 9.

Fig. 11 shows a valve arrangement according to Fig. 10 implementing the distribution of special mass feeds.

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Fig. 12 shows another distribution of the special feeds of the mass of the turbulence generator, which can be implemented with the valve arrangement according to Fig. 13.

Fig. 1A shows an alternative distribution of the special feeds of the mass of the edge areas of the turbulence generator.

The headbox according to Figure 1 is placed in connection with a double-wire former. Figure 1 shows the breast rollers 10 and 12 and the forming wires 11 and 13 passing over them 25, which delimit the forming bar G. Between the lip channel 15 of the headbox, a pulp suspension jet J is fed through the lip opening delimited by the tip strip 19 to limit the forming bar G.

The headbox comprises a pulp suspension flowing in the flow direction F, a manifold 24, a manifold 23, a compensating chamber 22, a turbulence generator 20 and a lip channel 15 with a septum plate 30 as a septum. The septum divides the lip channel 15 into two converging portions 15a and 15b. The lip channel 15 is bounded by a fixed lower lip wall 16 and an upper lip wall 17 pivoting about a horizontal joint 17a. The upper lip beam 28 and with it the upper lip wall 17 are arranged to be pivoted about said joint 8 90672 17a by means of a screw gear 27. The tip strip 19 delimiting the lip opening 18 from above is adjusted by a series of adjusting spindles 25 and a series of adjusting gears 26.

Instead of the perforated plate 20 with flow openings 21 shown in Fig. 1, other turbulence generators can also be used in the invention, e.g. turbulence generators

The headbox shown in Fig. 1 is largely known from the prior art and is described in this connection only as one of the implementation environments of the invention described, for example, in the following.

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According to Figures 2, 3 and 4, a transverse flow is generated in the lip channel 15 of the headbox from the trailing edge 20 'of the turbulence generator 20, the velocity vector of which is denoted by vo. Figure 3 is a cross flow velocity distribution in the cross-direction 20 and the drive side KP from the service side HP. In the edge regions R, the transverse flow rate v increases from the side walls 16a and 16b of the headbox from 0 to v0.

Said transverse flow is obtained by feeding the turbulence generator 25 in the second edge region 20A of the mass flow at velocities U. higher than the average main direction velocity U0 (Fig. 4) and U.2 than in the opposite edge region 20B, where the respective velocities Uw and Ub are average velocities U0 smaller.

The velocity distribution of the main flow of the lip channel 15 in the lip channel 15 is shown in Figure 4, where said flow profile is marked with U. In the central region E, the velocity U is constant U - U0. Due to the velocity difference between the edge regions 20A and 20B, a velocity vector field V with the transverse component v0 discussed above is generated in the main flow of the mass. Flows through pipes 32a and 32b are fed to the edge channels 21a 35 and 21b. These

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9 90672 backwaters (speeds Utl, UK) are controlled by valves 33a and 33b or equivalent control pumps.

Although the edge areas near the vertical side walls 5 of the lip channel 15 shown in Figures 3 and 4, with a width R <= 10-15 cm, cause anisotropy to the edge areas of the web, the web edges are in any case cut off at least said width R before the press pick-up roll. , so the edge areas R do not cause unevenness in the cross section of the track.

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Instead of the additional pulp feeds 32a, 32b shown in Fig. 4, the transverse flow v can also be provided by reducing the turbulence generator in the second edge region 20B of the turbulence generator, e.g. by plugging the edge region turbulence tubes 21c according to Fig. 5B. The corresponding figure 15 is shown in Fig. 5A by the edge regions 20C of the turbulence generator 20, between which there is an additional supply region 20D.

With a headbox operating on the basic idea described above, paper can be driven close to the so-called effective level. This means that when calculating the integral of the orientation angles of the different layers in the Z-direction of the paper 20, the result is = 0. This requires that the speed of the lip jet J at the outlet of the lip opening 18 is higher than the speed of the wires 11,13. Due to the deceleration of the jet J, some of the layers of paper seep in the underside situation despite the overdrive. Thus, the paper forms a 25-layer network structure and the net orientation angle = 0.

If the sheet of the kit former were to be split into several layers when running in the manner according to the invention, it would be observed that the main direction of orientation varies from one layer to another. Figure 6 shows schematically the observed result. Figure 6, the surface of the paper layer between each of the upper side and the underside of the AP YP (A-B and E-D) of the paper sheet is oriented in the same direction notwithstanding the direction of travel. In this range, the speed of the suspension is higher than the speed of the wire (S> W). At points B and D, the suspension is slowed to the speed of the wires 11,13 and a maximum orientation angle of 0 to 90 ° is reached. As the suspension slows even slightly from this, the direction angle jumps 180 ° to -90 ° and as the suspension continues to decelerate, the direction angle O begins to approach zero between B-C and D-C. The directional angle right in the middle of the web as the free suspension layer approaches zero is indeterminate because it has both a machine direction and a transverse relative velocity approaching zero.

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With further reference to Fig. 6, it can be seen that the sheet orientation structure formed according to the invention is generally mainly characterized by: the sheet orientation distribution is substantially symmetrical with respect to the center plane of the sheet (see Fig. 6), the sheet surface AB, DE and the center layer BD in different directions (transverse) to the machine direction, - the average net direction of the orientation remains completely or almost in the machine direction, 20 - the average level of the orientation has decreased significantly due to the transverse speed applied according to the invention.

Due to the mentioned properties, the following should be noted in relation to the other properties of the sheet: - since the average orientation skew is almost zero, the straight angle of the sheet is not deformed in the heat drying. The laser printability of the paper is good, and the so-called stacking occurs, 30 - as the relative proportion of fibers in the transverse direction is increased, the dimensional stability of the sheet is improved and its transverse strength is increased and thus the sheet is more square with respect to strength, - due to better dimensional stability also transverse drying-35 90672 - due to the symmetry of the orientation distribution of the sheet with respect to the median plane, the tendency of the sheet to bump or warp when experiencing climate change or heat drying is reduced, due to the 5 - sheet laminated structure, its bulkiness is increased and bending stiffness is transverse.

It is often necessary to drive the paper far away due to formation and other reasons. effective rudder position on either the lower or upper 10 side. In this case, the paper on average and the majority of its layers may be oriented in the same direction with respect to the direction of travel, causing a disadvantage to, for example, laser capability. By placing a rigid hetero plate 30 in the lip cone as shown in Figures 1, 7 and 8, the flow can be divided into channel portions 15a and 15b in the upper and lower portions. Hetula 30 prevents mixing of the partial flows 15 at the beginning of the lip channel 15.

Hetula 30 prevents flows in the direction of the arrows P shown in broken lines in Fig. 8. In Fig. 8, the areas marked (+) and (-) operate according to the normal additional supply, the areas operate according to the so-called negative additional supply, i.e. the mass flow takes place in the turbulence generator 20 backwards. In practical implementations, a pulp discharge pipe (not shown) is led from the edges of the equalization chamber 22 to a wire well. In the embodiment of Figures 7 and 8, the lip jet J has different transverse velocities on opposite surfaces, corresponding to the mutually opposite transverse velocities v2 and v1 of the channel parts 15a and 15b. In this way, the web structure already described in the basic idea is created when driving far away from the screed situation. The method according to the embodiment shown in Figures 7 and 8 is suitable for a hybrid former with all jet ratios and for a guitar former when driving with a strong under or overhead.

By arranging on each side of the headbox turbulence generator 20 the valve system according to Fig. 9 with the necessary piping, the desired layering can be formed in the lip channel 15 with the rigid spacer 30 and in the lip jet J. discharged therefrom. Instead of one spacer 30, two or more spacer plates 12 90672 may be used to divide the lip channel 15 into more than two overlapping wedge-shaped channel portions.

Figures 9-14 show one spacer baffle 30 dividing the lip-5 channel 15 into two overlapping channel portions 15a and 15b, to each of which the pulp supply tubes 32a and 32b are led in both edge regions of the turbulence generator 20. To said pipes 32a and 32b, the pulp is led from the headbox manifolds 24 through pipes 34a and 34b, through which additional pulp flows Fa and Fb are fed to the headbox edge regions 10 to provide said transverse flows in the lip channel.

According to Figures 9, 11 and 13, bypass pipes 36a, 36b with valves 35a, 35b are provided from the pulp supply pipes 32a and 32b. Through said pipes 36a, 36b, bypasses Fa1 and FbM can be fed to the wire well.

Fig. 10 shows a flow distribution achievable with the pipe and valve arrangement according to Fig. 9, in which the transverse velocities v, and v, on the different channels 15a and 15b of the intermediate light 30 30 are parallel. The flow arrangement according to Fig. 10 can be implemented e.g. with the settings of the different valves shown in Fig. 11.

. ·. Within the scope of the invention, a special flow distribution according to Fig. 12 is possible, where on the upper channel 15b side an additional feed takes place in both edge regions 20A and 20B of the turbulence generator 20, while on the lower channel 15a side an additional feed and a second negative area "negative feed" . The special flow distribution according to Fig. 12 can be implemented with the settings of the valves 30 according to Fig. 13.

With the piping and auxiliary supply arrangements described above, very different cross-flow combinations can be realized with different valve settings using a hetero partition 30. If necessary, more than one hetero partition 30 can also be used. By adjusting differently the (+) and (-) - I! The efficiency of the edge regions 20A and 20B is adjusted e.g. to the position according to Fig. 16, in which the upper channel 15b has a very high transverse velocity v1, which is substantially higher than the transverse velocity v2 prevailing in the lower channel 15b, the direction of which can vary.

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When applying the method according to the invention, it is also possible to reduce the swelling of the headbox mass flow due to the fact that the discharge vanes of the turbulence piping are not sufficiently mixed and which vanity occurs in the track by the pipeline division of the turbulence pipeline.

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When applying the method according to the invention, the transverse flow velocity v can be adjusted within quite wide limits so as to obtain the just desired effect on the distribution of the fiber orientation. Preliminarily, said transverse velocity will generally be in the range 0 <v <1 m / s.

Other speed ranges can be used if required. The appropriate speed can be determined by performing test runs on a paper machine or test machine, in which the transverse speed v is varied and 20 on-line orientation distributions are measured from the paper web, or similar measurements are performed on paper samples.

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

Claims (11)

A web forming process for paper or cardboard machines, in which method through the lip channel (15) in the inlet carriage of the paper machine, feeds a pulp suspension beam (J) into a forming wire or forming gap (G) which is limited by forming wires (11,13 ) and generating transverse velocity (v) in the pulp suspension stream in the lip channel (15; 15a, 15b) of the inlet carriage by feeding more pulp suspension to one edge region of the lip channel (15; 15a, 15b) than to the opposite edge region ρ means that the mean value of the edge currents substantially corresponds to the average current in the lip channel, characterized in that with said unidirectional velocity (v) together with the uneven distribution AU - SW - F (Z) (the S velocity of the pulp jet and the W velocity of the wire in the forming region) in velocity difference that travels in the Z direction of the web being formed affects the fiber orientation of the web formed so that For the web fibers to pivot from the machine direction to the transverse direction, in the method, the transverse flow velocity (v) and the distribution F (Z) are set in velocity difference AU - SW in such a way that the fiber orientation is swung in the two surface layer regions (ΑΡ). ) of the web to be produced in the same or in opposite directions from the machine direction to the transverse direction, and furthermore, the fiber orientation of the inner layers of the web is pivoted in the opposite direction in the pivotal direction of the fiber orientation of the surface layers (ΑΡ, ΥΡ) from the machine direction. transverse direction. 2. A method according to claim 1, characterized in that in the method the transverse flow velocity (v) and the distribution F (Z) are set in velocity difference AU - SW in such a manner as to provide such a path with the method whose structure in Z - the direction is essentially symmetrical in relation to the center plane. 3. A method according to claim 1 or 2, characterized in that the additional feed of pulp is applied in the turbulence pipes 35 (21a, 21b) of the edge region of the turbulence generator which precedes the lip duct or in corresponding flow channels. is 90672 4. A method according to claims 1,2 or 3, characterized in that, on one edge region of the inlet carriage, extra mass is fed into the stream of the inlet carriage and on the opposite edge area, pulp is removed from the stream of the inlet carriage which is led into a wire well or counter. - 5 being. 5. A method according to any of claims 1-4, characterized in that the extra feed of mass to the edge areas of the inlet carriage is taken from the distribution boom (24) of the inlet carriage and that the flow rate of the extra feedings is controlled by valves (33a, 33b) and / or control pumps. Method according to any of claims 1-5, characterized in that the profile of the transverse flow velocity (v) of the lip channel is arranged to be substantially equal except for the edge areas (R) of the lip channel (15) (Figure 3). . Method according to any of claims 1-6, characterized in that in the process the lip channel is divided by one or more intermediate discs (30) into two or more sub-channels (15a, 15b) one after the other and to the sub-channels ( 15a, 15b) separate the additional feed pipes for the pulp suspension as well as any outlet pipes (Figures 1, 9-14). 25 8. A method according to claim 7, characterized in that transverse currents (v) having the same or different directions are arranged on the sub-channels of the lip channel (15). 30 Method according to Claim 7 or 8, characterized in that on one edge region (20A) of the lip channel (15), additional feeds of pulp are provided for both or all the sub-channels (15a, 15b) and from the edge region (20B) of the opposite In the turbulence generator, the outflows (Fbout) are taken from the inlet carriage (Figures 9, 10 and 11). II is 90 672 Method according to any of claims 7-9, characterized in that the method uses valve and pipe systems for both edge regions (20A.20B) of the turbulence generator through which an optional flow of mass on the edge regions of the patch channel (15) of the inlet port and / or an outflow to a wire well or the like (Figs. 11-16). Method according to any of claims 1-10, characterized in that the velocity (v) of the transverse flow used in the method is in the range 0 <v <1 m / s.