FI86085C - Method of removing water from a web which is being shed, especially a paper web - Google Patents

Description

86085

Method for removing water from a web, in particular a paper web For the purpose of removing water from a web, in particular 5 paper rolls, especially in the form of papers

The invention relates to a method for removing water from a web 10, in particular a paper web, by which method a dewatering pressure is provided in the web forming section of a paper machine or the dewatering pressure otherwise provided is enhanced, and which method uses a magnetic field or fields to provide a dewatering-promoting force.

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As is already known, in the initial stage of web web formation, water is removed from the paper web either by gravity, by deflectors or the like, in suction boxes or in two-wire formers in inter-wire compression. A layer of felt-20 foam is then leached and felted against the forming wire, which causes a considerable increase in the dewatering resistance. On the other hand, increasing paper machine speeds have led to reduced dewatering residence times.

An increasingly burning problem in web formation has been recognized in that it has not been possible to apply sufficiently high dewatering forces and accelerations to the water layer to be removed by known means. On the other hand, it is recognized that if the percentage of dry matter of the web after the forming section before the press section could be increased by 1%, this would mean a reduction in the need for dewatering in the press section by about; An increase of 8% and 3% of the dry matter in the forming section means a reduction of about 1 to 30% in the amount of water removed by the press section. 1 above. This example is calculated at a machine speed of 1200 m / min and a paper weight of * * 48.8 g / m2. Em. the increase in dry matter could be utilized, for example, as a reduction in one or even more nips of the press section and / tni *: 35 as a reduction in the compression pressures.

It is an object of the present invention to provide a new method for providing or enhancing dewatering with a paper machine forming part 2 86085 in order to achieve the above objects and to avoid said drawbacks.

Applicant's FI patent applications 885736 and 890934 disclose a method 5 in the web forming section of a paper machine for enhancing dewatering. Em. In the inventions according to the FI applications, it has been considered substantially new that a magnetic field or magnetic fields are applied to the water-fiber layer being formed, by means of which the electrically conductive layer causes a dewatering-promoting force effect due to its speed.

According to equation 1 of FI application 890934, the force effect on the web W due to the effect of the magnetic field D per unit volume 15 Fz - σ v Bz Bx where a - conductivity of the web W v - speed of the web W

Bx - magnetic field B web W

20 directional component

Bz - a component 25 Em perpendicular to the direction of travel of the web W of the magnetic field B. According to the FI applications, said force effect is specifically directed to the moving mass and the force effect is based specifically on the speed of the web and the mass. If the methods according to the above-mentioned FI applications were to increase the force effect, the speed of the web or its: · .: mass conductivity must be increased, where, however, in practice there will be no-; * · *; 30 soon against the cross.

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The main object of the present invention is to provide such -. a method based on the use of a magnetic field or fields to provide a dewatering force or pressure and / or to enhance dewatering so as to provide sufficient force effects for the intended effects without the necessary need to increase web speed or pulp conductivity such that 3 86085 otherwise suitable line speeds and mass conductivities may be used.

In order to achieve the above objects, the method of the invention is mainly characterized in that a force is applied to the electrically conductive wire by means of a magnetic field or field and that said force creates a pressure field removing water from the web between two opposite wires.

In the following, the invention will be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 schematically shows the physical basis of the invention and a simple embodiment of the invention in connection with a double wire former 15.

Figure 2 shows another embodiment of the invention in which the magnetic field is produced by permanent magnets.

Figure 3 shows areas of application of the invention in a prior art kit.

Figure 4 shows an embodiment of the invention in a hybrid former.

According to Figure 1, the initial fibrous web W, which has a consistency of e.g. in the range of 4-20%, preferably in the range of 7-15%, passes between the wires 10. According to the invention, a magnetic field B is applied to the web W, which according to the figure is produced by a current conductor 11 in a direction perpendicular to the direction x of travel of the web W: The conductor 11 can be made e.g. of a high temperature superconductor. There may be several conductors in parallel to amplify the magnetic field.

Consider, according to Figure 1, a mass 35 moving in the x-direction at a velocity v with a conductivity of σ. We assume that the mass is either such a poor conductor or that it is so small that the eddy currents induced in it do not substantially change the magnetic field. The currents and forces induced in the mass and induced by the inhomogeneous magnetic field B - B (x, z) are studied; By - 0, and 3B / 3y - 0. Such a field can be generated by the y-axis current conductors 11 shown in Fig. 1.

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In the coordinate system of a moving mass, the magnetic field is of the form B -B (u, z), where u - x-vt.

The starting point is Maxwell's two equations: $ 10 x E - 3B / 3t (1) 15 V x B - 0 (2)

When 3B / 3y - 0, we get from the equation 2: 20 3Bx / 3x - -3Bz / 3z (3)

Equation 1 again gives: -3Bz / 3t - 3Ey / 3Ex - 3Ex / 3y - 3Ey / 3x. (4) 25

Since 3Bx / 3t - (3Bz / 3x) (3x / 3u) (3u / 3t) - -v3Bz / 3x, then v3Bx / 3x - 3Ey / 3z, (5): which gives: 30 Ey (x, z) - J? EfEy / 3xdx - v J? E 3Bz / 3xdx - vBz (x, z) (6); Force on the volume element AV - ΔχΔyAz 35 AF - j x B AV - 3E x BAV, (7). . so the normal force per unit area, i.e. the pressure, is afz ::: P -......- σνΒζΒχνζ (8) 40 AxAy where Az is the thickness of the mass layer.

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Example: σ- 1 O "1 ™ '1, v - 20 m / s, B, - B, - 1 T, Δζ - 1 mm. Then P - 0.02 N / m2.

Higher forces and pressures are achieved when the conductivity of the moving mass is increased.

The conductivity of copper is about 6 x ΙΟ7: '1 ™ "1; If the conductor of the previous example were replaced by copper, the pressure from the above formula would be P - 1.2 x 106 N / m2, or about 12 bar. However, the initial assumption of poor conductivity of mass 10 is not no longer true, but the magnitude is correct.

Increasing the conductivity of pulp is cumbersome and can only be done within certain limits. According to a first embodiment of the invention, conductive e.g.

braids made of copper and / or the wire or wires 10 are made of an electrically conductive plastic material so as to have a sufficiently strong magnetic field according to the invention to press the opposite wires 10 against each other and, if necessary, against a compression response such as a suction box cover or a curved dewatering pressure is created. In this case, a dewatering force is also generated in the mass W of the web itself due to the magnetic field, if the mass is conductive but this force is relatively small compared to the magnetic force applied to the wires 10. However, the magnetic field applied to the mass and the water therein may have a greater effect on dewatering other than by force, because the magnetic field changes the molecular structure of the water and thus the viscosity of the water decreases, which enhances the dewatering. This additional *. however, the mode of action is not necessary in this invention.

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When the field is generated by a single straight mass flow corresponding to a perpendicular line 11 at a distance of 5 mm from the copper braid of the wire cloth and carrying a current of 1000 A, the field is of the order of magnitude B

I .. * - 0.04 T, for direct line field B - p0I / (2irR). If the thickness of the copper braids 10 of the wire or wire 35 is now 1 mm, the pressure according to formula (8) is P - 0.12 bar. However, the pressure of this example is obtained in a rather small range, and in practical applications it is advantageous to use large multilayer coils and / or permanent magnets, which will be described in more detail below with reference to Figure 2. Figure 2 schematically shows the use of permanent magnets to generate forces on the moving wires 10 and the web W mass. Above the web W between the wires 10 and 5, an air gap is placed to separate the permanent magnets 12 in two rows 13 and 14 so that the flow lines F circulate through the guide 10. The flux above the magnets 12 is closed, for example, by a plate 15 of ferromagnetic material. The arrows indicate the direction of the flux lines and magnetization 10 of the magnetic field.

Figure 3 shows an example of a kit former in which the invention can be advantageously applied. The twin-wire gutter former comprises a support wire 20 and a cover wire 21. The headbox 26 feeds a pulp suspension jet J to the forming roll in connection with the forming roll 22, from which a web W begins to form in the two-wire zone between the rollers 22,23. By means of the suction zone 23a or the like 23, the web W is detached from the covering wire 21 so that it follows the carrier wire 20, from which the web W is detached by the suction zone 28a of the pick-up roll 28 at an oblique run between the guide rollers 25 and transferred to the pick-up felt 27 takes the web W to the press' part (not shown).

According to Figure 3, a first magnetic device 101 according to the invention is arranged in the vicinity of the wires 20 and 21 opposite the suction zone of the suction roll 22. The second magnetic device 102 of the invention is located in a cover! . inside the loop of the wire 21 opposite the suction box 34 or the corresponding curved-shaped forming shoe before the upper forming roll 23.

The third magnetic device 103 according to the invention is placed against the forming roll.

ί Figure 4 shows the first magnetic device 101 for placement. a forming shoe 36 opposite the loop of the upper wire 21 inside. Still. Fig. 4 shows a wire 21 covering two magnetic devices 102: inside the loop after the forming roll 31 opposite the suction boxes 32.

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With respect to the different magnetic devices 101, 102 and 103 shown in Figures 3 and 4, it should be noted that not all of them are always needed at the same time, but Figures 3 and 4 are only intended to illustrate some preferred magnetic device placement -5 options in different web forming parts. Opposite the magnetic devices 101,102,103 shown in Figures 3 and 4, forming rollers 22,23, suction boxes 32,34 and a forming shoe 36 are shown, the dewatering and forming members acting as a abutment surface against which the wires 20,21 are pressed so as to magnetically create pin W dewatering pressure.

In Fig. 4, it is sufficient to arrange the covering wire 21 to be electrically conductive, whereby the force exerted by the magnetic devices 101 and 102 is applied only to the covering wire 21. The covering wire 21 15 is pressed against the forming shoe 36 and the cover of the suction boxes 32.

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 (4)

1. A method for removing water from a web (W) which is poured to form, in particular a paper web, by which method a dewatering pressure in the web forming portion of the paper machine or a dewatering pressure obtained otherwise is effected and by which method using one or more magnetic fields (B), with which a force effect is obtained which promotes the dewatering of the web (W), characterized in that a force effect is directed by means of the magnetic field (B) or fields. against the conductive wire (10; 20,21) and with said force effect a pressure field is created between two opposite wires (10; 20,21) which remove water from the web (W). 15 2. A method according to claim 1, characterized in that at least the side tissue (10,21) which is on the side of the magnetic device (101,102,103) is arranged to be electrically conductive. Method according to claim 1 or 2, characterized in that in the method the forming wire (10; 21) is at least on the side of the magnetic device (101,102,103), a tissue made essentially of conductive material, such as conductive plastics and / or the network of tissue made twists or the equivalent of conductors, for example copper. 25 Method according to claims 1-3, characterized in that said magnetic field (B) is provided by systems of permanent magnets (12,13,14,15) (Fig. 2). 30