FI86444C - Use of an inlet box for feeding thick mass - Google Patents

Description

! 86444

Use of a headbox for feeding thick pulp - Användning av en inloppsläda för matning av tjock massa

The present invention relates to the use of a headbox 5 for feeding a pulp with a consistency of 6 to 15% from the headbox pressure chamber to the web forming section of a paper machine.

The object of the invention is to apply structurally to a certain extent a previously known headbox to the web of the pulp 10 so that it is suitable for use for 6 to 15%, in particular 8 to 12% pulp.

The problem with thick pulping has been how to break up a dense and strong fibrous web so that a separate web can be formed from the individual fibers. The fluid sonication of the pulp is one solution to this problem. However, fluidizing a 6-15% pulp requires more than a hundred times more power than fluidizing a dilute mass of about 1%. If large volumes of 20 have to be fluidized at the same time, the advantage of reducing the use of water in the transition from 1% to 10% of the pulp is lost. In this case, the use of a thick mass has no practical significance. The thick pulp box must therefore be implemented in such a way that the fluidization is applied only to a small space. . 25 and even then in just the right and necessary place. The method and apparatus for feeding pulp to a web forming apparatus according to the invention meet the above requirements. 1 2 3 4 5 6

At present, a web-forming method is generally used, in which pulp is dispensed from 2 headboxes through a narrow gap extending over the entire width of the machine 3 as a jet onto the forming wire 4: or between the forming wires. To achieve a satisfactory web- 5. ···. In order to obtain this, the mass jet must be uniform in thickness and direction and homogeneous. With a low consistency, up to about 1%, this does not cause problems, but with a higher consistency, where the fibers tend to flocculate, the situation is different.

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Applying the thick mass to a flat web is very difficult because, for example, the mass in the 10% consistency range is so solid that it can form a "snowball". 5 The number of bonds in a pulp mixture is directly proportional to the consistency of the pulp. The shear stress required to release the bonds increases according to the following equation (Gullichsen & Härkönen, Tappi Pulping Conference, 1980): 10 = kC *, where k and oc. are constants specific to each mass quality.

Under certain conditions, the thick mass can be momentarily made to have water-like flow properties. This phenomenon is called fluidization.

In fluidization, energy is introduced into the pulp to break the bonds between the fibers. The energy required is proportional to the consistency of the pulp and the number of bonds between the fibers.

The thick mass flocculates and easily clogs the flow channel as it flows in tapered conical structures. 25 In this respect, the thick mass differs in its flow properties from water and dilute masses. For water and dilute masses, the flow loss due to the tapered cone is small compared to the losses due to large changes in cross-sectional areas. In tapered cones, the fibers of the thick mass 30 are densely packed, whereby the flow is easily blocked and the flow channel is blocked. Leaching is the result of condensation of “flow lines” without turbulence.

It is known from Finnish patent 51116 that if a thick mass is subjected to high shear forces, an even distribution of the fibers over the entire width of the machine can be achieved.

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A device is known from Finnish patent application 1284/73, in which a fiber suspension with a high consistency is divided into several parallel channels and injected at a high speed into a chamber in which the direction of flow is suddenly changed.

Swedish Offenlegungsschrift 7807097-6 discloses a method and apparatus for forming a web of fibrous suspensions, in particular high consistency pulp suspensions, in which the suspension is made to flow in parallel jets tangentially into a mixing chamber having a rotationally promoting cross-section and from which the suspension exits 90-180 °.

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The above-mentioned devices, in which the fiber suspension, after flowing through the chamber, is led to the forming wire through the outflow channel in which the cohesive fiber network is formed, are usable for a mass of up to 6%.

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Previously known are structures in which there is a transverse, rotating member of the machine inside the headbox. In these structures, the thick mass is not fluidized, but the flocs in the dilute mass are broken or turbulence is added to it. With thick masses, the perforated rollers easily become clogged and thus make web formation more difficult. Examples of such structures are referred to in the patent publications mentioned below. 1 2 3 4 5 6 DE 1,058,355 discloses an apparatus 2 by means of which some of the water molecules contained in the pulp are displaced by means of compressed air and a rotary mixer 4. The rotational speed of the stirrer must be so low that no phase separation occurs. The high rotational speeds 6 required for fluidization would be detrimental to the operation of the device described in the publication, as they could separate the compressed air from the rest of the mass, so that no benefit would have been obtained from the addition of compressed air.

* 86444 DE-A-2,239,080 discloses a paper machine headbox with a circular, narrow channel inside. The center of the channel is formed by a transverse-5, movable roller of the machine. According to the publication, a turbulent state can be obtained by feeding the mass into a narrow annular channel, where it is divided into two parts so that the mass flows from two sides into the lip channel.

10 DE-publication 1.294.177 discloses a headbox,

Inside is a transverse, fixed perforated roller in front of the lip opening. The mass is fed into a channel inside the perforated roll, from where it is distributed into the lip opening. Inside the bore roll there is a rotating, conically expanding shaft 15 to equalize the flow out of the headbox. The perforated roller filters the non-flocculating fibers to the lip. The conically expanding shaft constricts the flow channel. Conical tapered structures are not suitable for 6 - 15% thick mass. In addition, the holes of the hole roll 20 are easily blocked in this consistency range.

Also known is the device disclosed in FI application 843463, in which a transverse, conically expanding shaft of the machine is arranged in front of the elongate opening, where .25 is a feed screw. The core of the screw and the sheath wall of the screw end delimit a space with an annular cross-sectional area which decreases continuously in the screw feed screw. The present invention is not concerned with fluidization or even breaking the blocks, but with a feed screw unit which pushes up to 9-12% of the mass out of the elongate opening. Thus, the resulting web is not uniform or controlled in quality. The basic precondition for the creation of a smooth and controlled web is that the fiber network is disintegrated and the fibers can be loosely formed in the new web in the emerging web and that the formed web can flow forward. A conically tapering flow channel cannot be used for thick mass flow.

U.S. Patent No. 5,864,453 to U.S. Patent No. 5,864,853 discloses a method of applying a headbox flow to a web-wide flow. The object of the invention is to provide a smooth, wide and calm flow by means of rotating members and volume changes of the channel. The rotating members are transverse to the machine. The organs do not fluidize the mass.

U.S. Patents 3,119,734 and 3,255,074 have a cross-machine rotating member inside the headbox. In U.S. Patent 10 3,119,734, the rotating member is a roll having circumferentially mounted thin, toothed plates obliquely to the center of the shaft. The purpose of the structure is to control the input current background and distribute the mass evenly. The mass flows to the lip along a conically tapering channel. It is an object of the invention disclosed in U.S. Patent 3,255,074 to minimize flocculation. The device disclosed in this patent, like the previous one, is intended as an alternative to a perforated roll.

Johan Gullichsen has presented (Tappi Pulping Conference, 20 1980) a schematic diagram of a headbox with a consistency of about 10%. Inside the headbox there is a large machine direction roll for fluidizing the mass in the flow channel formed by the roll and the headbox before it is fed out of the headbox through a narrow gap to 25 wires or between two wires. The thick pulp forms a strong and uniform fibrous network. Breaking this fiber network requires significantly more power than breaking up the fiber flocs in the dilute pulp. Fluidizing the entire headbox with 30 large rollers proposed by Gullichsen in a large factory machine using a roller with a diameter of more than 0.5 m consumes a lot of electrical power. A solution in which the entire volume of the headbox is fluidized and the mass is directed into the lip channel is too expensive.

. 35 Structures with an oscillating defloculator inside the headbox are also known. Such have been presented e.g. in U.S. Pat. No. 3,562,108 and 6,864,444 CA 1,173,681. In the headbox, the oscillating member is able to break up flocs in a dilute mass, but causes harmful pulses.

The invention is characterized by the use of a headbox consisting of a chamber having an adjustable flow gap with a wide width of the web to be formed and a rotating roller forming at least one interface of the gap to feed 6 to 15% pulp from the headbox pressure chamber to the web forming section of the paper machine.

The invention will now be described with reference to the accompanying drawings, in which Figure 1 shows a vertical section of 15 headboxes according to an embodiment of the invention, Figure 2 shows a section along the line A-A in Figure 1 and Figure 3 shows a partial section of a headbox according to another embodiment.

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In the embodiment shown in Figures 1 and 2, the headbox comprises a chamber 1 into which pulp is fed and in which the desired pressure is maintained in a manner known per se, not shown in more detail. The chamber has a transverse roll 25 in the machine direction 25. An inclined plate 3 is arranged in the headbox under the roll. The upper surface 4 of the plate and the outer circumference 5 of the roll. . delimit a downwardly expanding gap 6 in the width of the web to be formed. The plate through which the pulp can be discharged from the headbox can be adjusted in a manner known per se, not shown in more detail, so that its position relative to the roll can be changed so that the gap height and plate inclination change. . The lower edge of the plate is arranged close to the surface of the wire 8 passing over the roll 7 below the roll 2. There is a seal 10, ..: 35 between the chamber wall 9 and the roll, the purpose of which is to prevent the pulp from escaping from other than through the gap 6. In the lower part of the chamber, near the upper end of the plate 3, there is a second rotatable roll 11 formed of radial, flat bars 12 intended to move the mass and feed the mass into the slot 6. This roll is useless when the mass can otherwise be used by the roll 2. drain into the gap 6.

At the narrower point of the gap 6, the mass is subjected to high shear forces between the moving surface 5 of the rotating roll 2 and the stationary surface of the plate 3 so that it fluidizes and flows out. In the narrow gap, the fluidization can be brought to a very far, almost fiber-10 fiber level due to high shear forces. Advanced fluidization is limited to a small volume, i.e. a narrow gap, so the power requirement is small. In the expanding part of the gap, as soon as the effect of the shear forces ceases, a cohesive fiber network is formed, in which the fibers are evenly distributed over the entire width of the machine. The formed web slides along the inclined plate 3 onto the wire 8, where water is removed from it in a manner known per se.

Figure 3 shows another embodiment of the invention 20 in which in the headbox chamber 21 a roll 22 is arranged on the forming cylinder 20 so that the outer circumference 25 of the rotating roll and the forming cylinder surface 24 delimit a space 23 where the mass is subjected to shear forces between two moving narrow surfaces. In the narrow position 23, the fluidization can be brought very far to the near or fiber-to-fiber level due to the high shear forces. The wall 26 of the chamber, at the lower end of which a guide plate 27 is to be set, and the outer circumference of the roll form a flow channel 28 leading to the space 24 as the rollers - 30 rotate in opposite directions. The flow of pulp in the channel 28 is facilitated by the rotational movement of the roll 22. The position of the guide plate determines the size of the gap 29 between the roll 22 and the guide plate and the gap 30 between the forming cylinder 20 and the guide plate. At the lower end of the second wall 31 of the chamber there is a second adjustable guide plate - 35 32, which forms a seal between the forming cylinder and the chamber. The distance between the roll and the forming cylinder can be changed by moving the chamber, whereby the fluidization level in the gap can be adjusted as desired.

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The rotating roll feeds the pulp into the space between the roll and the forming cylinder, a portion of which, when fluidized, flows into the gap between the guide plate and the forming cylinder and forms a web in which the fibers are evenly distributed. The remaining part of the pulp is led back to the chamber 21 under the control of the channel 33 between the wall 31 and the roll 22. The flow in the channel 33 is facilitated by the rotational movement of the roll 22.

As the rotating roll and the web-forming cylinder rotate in the same direction, the pulp is introduced into the web-forming space 23 along the channel 33. In this case, the channel 28 operates in a return channel, the flow of which may be zero, when the return flow is set to zero on the control plate 27. The surface of the rotating roll 15 may be smooth or grooved.

The device according to the invention is suitable for different pulps and can be used over a wide range of consistency.

The invention is not limited to the embodiments shown in the examples, but can be modified within the scope of the inventive idea defined by the claim.

Claims (3)

9 86444 PATENT CLAIM Use of a headbox consisting of a chamber (1, 21) with an adjustable flow gap (6, 23) having a width of the web to be formed and a rotating roller (2, 22) forming at least one interface (5, 25) of the gap (6, 23) to feed a pulp having a consistency of 6 to 15% from the headbox pressure chamber to the web forming section of the paper machine. claim 1. Användning av en inloppsläda, som bestär av en kammare (1, 21) försedd med en regullerbar strömningsslits (6, 23) 15 av samma bredd som banan som skall bildas och roterande Vals (2, 22) som bildar ätminstone den ena in the case of slitsens (6, 23) gränsytor (5, 25), för matning av mass with en consistency of 6 -15% frän en inloppslädas tryckkammare account en pappersmaskins banformningsanordning. 20