FI85888C - INLOPPSLAODA FOER BREDNING UT TJOCK MASS TILL EN BANA. - Google Patents

Description

1 85888

HEADBOX FOR SPREADING SAKE PULP INTO A WIND -INLOPPSLÄDA FÖR BREDNING UT TJOCK MASS TILL EN BANA

The present invention relates to the use of a headbox comprising a pressure chamber, one wall of which forms one or more flow openings which open into the chamber, for feeding a thick mass to a web-forming device.

The object of the invention is to provide a headbox for applying a thick mass 10 into a web, which headbox is suitable for use on a mass of 6 to 15%, in particular 8 to 15%.

Today, a web-forming method is commonly used in which pulp is dispensed from a headbox through a narrow gap extending over the entire width of the machine 15 as a jet onto or between the forming wires. In order to obtain a satisfactory web, the pulp 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, with the fibers tending to flocculate, the situation is different.

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 be formed into a "snowball" without removing water. The number of bonds contained in the 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, 30 1980): A- ^ = kC #, where k and (X are constants specific to each mass grade.

.35 For example, the shear stress required to remove bleaches from bleached pine sulphate fibers increases so that 10% of the pulp is required to remove 2 85888 fibers at the 100% pulp than to remove the fiber bonds at 1% of the pulp.

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. 15 In tapered cones, the fibers of the thick pulp pack densely, which easily obstructs the flow and clogs the flow channel. Leaching is the result of condensation of "flow lines" without turbulence. 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.

It is known from Finnish patent 51116 that if 25 thick pulps are subjected to high shear forces, an even distribution of the fibers over the entire width of the machine can be achieved.

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 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 from a fibrous suspension, in particular high-density pulp suspensions, in which the suspension is made in parallel jets 3 85888 jets tangentially to a mixing chamber having a rotation-promoting cross-section and after which the suspension is removed.

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

10 Known prior art are structures in which a transverse, rotating member of the machine is located inside the headbox. These structures do not fluidize the thick mass, but break the flocs in the dilute mass or add turbulence to it. With thick masses, the perforated rollers easily become clogged and thus make web formation more difficult.

Johan Gullichsen has presented (Tappi Pulping Conference, 1980) a schematic diagram of a headbox with a consistency of about 10%. Inside the headbox there is a large machine direction roll 20 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 the wire or between two wires. The thick pulp forms a strong and uniform fibrous network. The breakdown of this fibrous web requires much more power than the disintegration of the fibrous flocs in the dilute pulp, so that a large roll, which at its rotational speed has to fluidize a large volume of pulp before the lip channel, consumes so much power that such a solution is not feasible.

Also known are structures in which there is an oscillating deflocculator inside the headbox. Such have been presented e.g. in U.S. Pat. No. 3,562,108 and 35 CA 1 173681. In the headbox, the oscillating member is able to disintegrate flocs in a dilute mass, but causes harmful pulses. The oscillating defloculator is unable to transfer sufficient fluidizing energy to the mass path without causing excessive pulses.

Finnish patent application 2017/67 discloses a headbox of 5 paper machines with a machine-wide rotating chamber in which the formed flocs disintegrate and whose inlet is connected to a flow divider evenly distributing the pulp to the machine width and an outlet to the paper machine wire in a sloping outlet channel. The headbox is not suitable for thick pulp.

The fluidized state is a reversible state. The fluidized pulp thus quickly recovers into a dense fibrous web. For this reason, the locations and dimensions of the flow channel lengths must be carefully considered. It is also important in thick mass webing that the resulting web is smooth and in good shape. Thus, the web must be formed when the mass is fluidized. Fluidization and application of the pulp to the web 20 must be performed as close as possible. To achieve this object, the headbox according to the invention is provided with a pulp application section and a web-forming section. In the pulp application section, the pulp is fluidized to such an extent that it is caused to flow through holes or slits 25 into the web-forming section. In the web-forming section, the mass impinges on a moving surface where web-forming takes place in a closed chamber.

The invention is characterized by the use of a headbox comprising a pressure chamber adjoining the movable forming surface or surfaces of the web forming device 30, one wall of which forms one or more flow openings opening into said chamber from which pulp is fed to the web forming device.

5 85888

The invention will now be described with reference to the accompanying drawings, in which Figure 1 shows a headbox according to some embodiments 5 of the invention in vertical section, Figure 2 shows another embodiment of the invention and Figure 3 shows a third embodiment of the invention.

10

The headbox shown in Figure 1 comprises a pressure 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 pressure chamber may have a rotating or movable member 15 to keep the mass moving in the chamber and to equalize its flow, because the internal friction of the thick mass is so great that it does not flow easily. The vertical wall 2 running in the transverse direction of the machine at the bottom of the pressure chamber has several openings 3 in the horizontal row. A transverse collision barrier 4 is fastened to the lower part of the pressure chamber with 20 screws, the position of which in the horizontal plane is adjustable. A web forming device is arranged under the pressure chamber, which includes a suction roll 5 around which the wire 7 acting as a forming surface passes. By changing the position of the pressure chamber in the vertical plane, the gap 16 between the lower edge of the impact barrier and the wire can be adjusted to suit the formation of the web. A seal 6 is attached to the wall 2, which closes the gap between the lower edge of the wall 2 and the wire 7. A guide plate 8 is pivotally attached to the collision barrier.

30

A plurality of fluidizers with a rotating rotor 9 are arranged in the pressure chamber, which are arranged so that there is a fluidization rotor in front of each opening. The rotor is attached to a shaft 12 passing through the rear wall 11 of the pressure chamber 35, which is rotated by the motor 13. The position of the root troughs relative to the openings 3 can be adjusted by moving the fluidizers towards or away from the openings.

6 85888

The mass fed to the pressure chamber is fluidized by means of fluidization rotors with vanes or other protrusions in front of the openings and flows through the openings due to the high flow rate caused by the pressure difference. The pulp discharges from the openings as jets at high speed into the chamber 14 between the wall 2 and the impact barrier 4. The jets collide with the impact barrier counter surface 15, causing their direction to change sharply and the vortex flow formed to distribute the fibers into a flat web over the roll 7. The pulp is introduced from the chamber 14 immediately onto the wire through an opening 17 directed towards the wire between the wall 2 and the collision barrier 4 so that the fibers cannot flocculate before the web 15 is formed on the wire. The thickness of the web can be adjusted by changing the gap 16 between the lower edge of the impact barrier and the wire. The guide plate 8 is held substantially parallel to the wire 20 by means of a setting bar 18 restricting its movement against the wire and a spring compressing the web formed on the wire. The angle between the jet and the collision barrier can be changed by tilting the wall 4 to adjust the width of the jet.

In the embodiment shown in Figure 2, the headbox pressure chamber 25 has a transverse slot or row of holes 22 in the vicinity of the machine, in the vicinity of which a fluidizer 23 rotates, the axis of which is parallel to the slot or row of holes. The fluidizer fluidizes the pulp to such an extent that it flows out of the pressure chamber through the slot or holes into the web forming space 24 formed between the pressure chamber and the moving wire 25 of the web forming device arranged below it. Between the lower part of the pressure chamber and the forming surface, a transverse, adjustable seal 26 of the machine is arranged, which delimits the space 35 under the gap or holes 24 in the direction opposite to the direction of travel of the wire.

In the pressure chamber, the fluidizing power at the web-forming point on the wire must be made so high that the fibers loose 7 85888 are able to form a web-thick fiber network. The fluidizing energy is supplied by the mass jets or jets from the slit or holes into the web forming space 24 and the moving forming surface 25. The thickness of the web is determined by the size of the web forming space outlet, i.e. the gap 27 between the pressure chamber base 28 and the forming surface. The thickness of the track is adjusted by changing the height of this opening.

In the embodiment shown in Figure 3, the headbox pressure chamber 31 forms a web forming chamber 32 with two rotating rollers 33 and 34 and adjustable seals fitted between the rollers and the pressure chamber. The web is formed at the junction of the wires 35 and 36 passing over the rolls, and the thickness of the web is determined by the distance 37 between the wires between the rolls.

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

20

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)

8 85888 PATENT CLAIM A headbox comprising a pressure cannon (4) bounded by a movable forming surface (7) and / or movable forming surfaces of a web forming device (5, 7), one wall (2) of which forms one or more flow openings (3) opening into said chamber (4) , from which the pulp is fed to the web forming device (5, 7), to apply the pulp with a consistency of 6-15% to a flat web 10 to the web forming device. 1. An application in the form of an in-room test (7) or a ring-shaped arrangement (5,7) of a three-dimensional formation (4), in which case (2) a picture or an additional arrangement (3), in the case of this chamber (4), frän vilka 20 pappersmas mätäs account in banformningsanordning (5, 7), för att brreda ut massa med en consistence av 6 - 15% account en jämn bana pä banformningsanordningen.