FI121546B - Arrangement for forming gap in a double wire former - Google Patents

Description

Controlling the formation of twin-wire formers

FIELD OF THE INVENTION The present invention relates to a twin-wire forming machine forming system comprising a head box, a first wire loop containing a breast roll and a second wire loop having a dewatering element which closes the forming wire by aligning the flow of the second wire with the first wire. through the lip opening of the headbox so that the pulp hits the first wire when it is a support 10 mat.

In conventional gritformers, the fibrous mass is led from the headbox into an open jet in the order of 200-500 mm in length. The length of the free jet depends, among other things, on roller diameters, tissue running, 15 lip profiling devices, and headbox construction. A long flight will expose the jet to air currents in the kid, which may alter its point of impact or disintegrate its surface. Long free flight also increases fiber flocculation. The structure of the mass jet significantly influences the properties of the final product. A homogeneous and uniform surface mass jet produces higher quality paper than an inhomogeneous and non-uniform or rough surface jet. The importance of the roughness and stability of the mass jet increases as the speed increases.

For the properties of the paper, it would be advantageous to use a pulp jet as short as possible or even completely closed. However, the current structure of two-wire formers does not allow for such a solution due to lack of space. The trackformer has a large diameter forming roll over which the wires curve over the surface to produce a curved, converging, downwardly curved mandrel. The roller shaper has two parallel rollers, after which the wire runs are guided together by 30 rollers or the like. The fiber pulp may be fed to the forming spindle in a substantially jet pulp jet, or the pulp jet may be directed against 2 other wires at a low attack angle, whereby the unstable behavior of the unsupported wire may be a problem. Because of the large diameter of the breast and / or forming rolls, the geometry of the forming ridge is generally such that it is difficult to insert the head opening lip sufficiently deep into the forming sheath. The free travel of this mass jet from the lip opening of the headbox between the wires is generally long. Problems are especially pronounced when using a multilayer headbox.

WO 2004/018768 discloses a preamble design of a molded glass mold in which a mass jet discharging from the lip opening of the headbox hits a first wire as it passes from an unsupported breast roll to a forming shoe, thereafter the forming shoe closes the forming wire . Here again, a free mass jet is required, with the problems described above.

The object of the invention is to solve the problems of the prior art. Specifically, the object is to improve the supply of the pulp to form a twin-wire forming kit.

20

The forming crystal arrangement according to the invention is characterized by what is stated in the characterizing part of claim 1.

In the new kitformer, the lip opening of the headbox is brought into contact with the first wire at a point located between the first wire breast roll and the forming barrier dewatering element, whereby the pulp is introduced to the first wire without substantially free pulp jet.

By moving the two pre-forming rollers or, in the case of a track roller, the chest roll and forming roller sufficiently far apart, the headbox can be positioned between the rolls and its lip opening can be secured to the wire. In practice, it is advantageous to position the headbox so that the first lip limiting the lip opening in the upstream direction of the wire is in contact with the first wire and the second lip limiting the lip opening in the downstream direction is at a short distance from the first wire. Thus, the first lip seals the lip opening and provides 5 support points for the wire as it travels from the breast roll to the dewatering element. With the exception of this single support point, the wire proceeds without support throughout the distance from the breast roll to the dewatering element.

Preferably, the fibrous mass discharged from the lip opening of the headbox hits the first 10 wires at an angle of 5 to 25 °. Dewatering through the wire begins as soon as the pulp hits the wire. The mass jet stays well together and does not spread over a wide area.

The dewatering element that leads to the contact of the second wire with the fibrous mass layer on the first vii-15 may be a curved forming shoe provided with a tear-off lid for non-pulsed dewatering. Alternatively, the dewatering element may be a forming roll, on which a flow scanner combines the flows of the first and second wires.

Following the first dewatering element, there are further dewatering elements, preferably comprising at least one dewatering box with a cover lid, which can optionally be placed inside either the first or second wire mesh. Hereby, loading lists can be placed inside the opposing wire loop to provide effective pressure pulses that further enhance dewatering and improve web formation.

The solution of the invention is particularly well suited for multilayer striping using a multilayer headbox. In this case, the various layers of the web can be applied directly to the fabric, separated by a short distance, and the mixing of the layers is less than 30 mm than when using an open lip jet.

4

The stability of the pulp feed is increased when the free pulp jet is reduced or eliminated. As a result, the paper web profiles improve. The headbox pressure can be reduced when energy is not lost in the free mass jet. The space requirement of the forming member is reduced by the new geometry. Less air se-5 enters the web.

The invention will now be described with reference to the figures in the accompanying drawings, the examples of which, however, are not to be construed as limiting.

10

Fig. 1 shows a prior art arrangement for feeding a pulp of fiber into a forming wire for a two-wire forming machine.

Fig. 2 is a side view of a forming bar in which the pulp is led onto a wire without 15 free mass jets.

Fig. 3 is a side view of the twin-wire zone of a vertical gritformer.

Fig. 4 is a side view of a dockformer.

20

Fig. 5 is a side view of a horizontal gritformer in which the pulp is fed to the top wire without a free mass jet.

Fig. 6 is a side view of a kitformer equipped with a multilayer headbox. 25

Fig. 7 is a side view of the forming bar in which the pulp is led to the bottom wire without a free pulp jet.

Figure 8 is an enlarged view of the region of the forming barrier.

Figure 9 illustrates the supply of fibrous pulp to a flat wire.

30 5

Fig. 1 illustrates a prior art molded forming kit arrangement known from, for example, WO 2004/018768. The passage of the first wire 2 is guided by the first chest roll 4 and the passage 5 of the second wire 3 is guided by the second breast roll 5 so that a downwardly converging forming gasket G is left between the wires 2 and 3. G. Fiber pulp is fed from headbox 1 into a forming shoe G as an open pulp jet which hits the first wire 2 as it advances from the breast roll 4 towards the forming 10 shoe 6. The curved cover 7 of the forming shoe 6 guides the surface of the fiber web. The cover 7 is provided with openings 8 through which water is discharged from the fiber mass layer in the direction of the forming shoe 6 due to the tension of the outer wire 2 and the negative pressure in the forming shoe 6.

15

Because the breast rollers 4 and 5 are very close to each other, the headbox 1 has to be located far from the first wire 2, whereby the free travel of the mass jet J from the lip opening of the PCB 1 to the point of impact on the wire 2 is relatively long. The mass jet J has to pass the rotating rollers 4 and 5 in close proximity, thereby being exposed to interference from air flows. The wires 2 and 3 approach each other at a very small angle so that the pulp jet J also hits the wire 2 at a very small angle. There is a lot of air flowing into the wire cloth that needs to be removed.

Figure 2 shows a solution according to the invention. The first chest roll 4 in the first wire loop 25 2 and the second chest 5 in the second wire loop 3 are moved so far apart that the head box 1 can be inserted between the rolls 4 and 5 into the first wire 2. The fibrous mass discharges from the lip 9 of the head box 1 directly onto wire 2, whereby the free travel of the mass jet is very short or completely absent. The fibrous pulp discharged from the lip-30 from the lip 9 hits the wire 2 at an angle α of 5-25 °. The lip opening 9 is delimited by the first lip 10 on the inlet side 6 and the second lip 11 on the downstream side, respectively, viewed in the direction of the wire travel. The first lip 10 is brought onto the wire 2 so as to seal the area into which the pulp is applied. The surface facing the wire 2 of the first lip 10 is curved so that its radius of curvature R is 100 to 2000 mm. The second lip 11 is slightly si-5 weathered with respect to the first lip 10 such that there is a gap between the second lip 11 and the wire 2 through which the fibrous mass exits the area of the lip opening 9 with the moving wire 2.

The second wire 3 is guided to the surface of the fibrous mass layer 10 on the first wire 2 by means of a forming shoe 6 located inside the second wire loop 3. The forming shoe 6 has the same structure as the forming shoe 6 shown in Fig. 1, thus providing a substantially non-pulsed dewatering pressure. After the forming shoe 6, there is a dewatering box 12 within the second wire loop 3, the surface facing the wire 3 comprising a plurality of dewatering strips 13. The first wire loop 2 has loading strips 14 arranged opposite the slots between the drainage strips 13. Further, within the first wire loop 2, a preload strip 15 is located opposite the region between the forming shoe 6 and the dewatering box 13.

20 Figure 3 shows another vertical listakitaformeri, wherein the fiber pulp is fed into the headbox is shown between one of two breast roll 4, 5 into the forming gap G so that the fibrous material falls first of the first wire 2 to the wire leaves a large amount of water in the direction of arrow C, as shown. When the pulp hits the wire at an angle of 5-25 °, the amount of water exiting through the wire 2 can be up to 20-30% of the total amount of water in the headbox. The second wire 3 is guided to the surface of the partially drained fibrous mass layer on the surface of the first wire 2 by a forming shoe 6. After the forming shoe 6, within the first wire loop 2, there are two dewatering boxes 12, 16, the surface facing the wire 2 comprising a plurality of dewatering strips 13 guiding the wires 2, 3 through their vertical flow and 30 dewatering . Opposite to the dewatering strips 13, there is a plurality of loading strips 14 at the first dewatering box 7 12.

Fig. 4 shows a cathodicformer in which the headbox 1 is disposed between the first roller 2 guiding roller 4 and the second wire 3 forming roller 18 so that the fibrous mass discharged from the lip opening of the headbox 1 hits the first wire 2 substantially without free mass jet. The forming roll 18 guides the wires 2 and 3 together and thereby closes the forming bar G. In the curved sector of the forming 10 roll 18, the fibrous mass between the wires 2, 3 is dewatered by the tension of the outer wire 2 and the negative pressure on the forming roll 18. Following the forming roll 18, dewatering boxes 12 and 16 follow within the first wire loop 2 and loading strips 14 within the second wire loop 3. There are 15 suction rolls at the end of the two-wire zone 17.

Fig. 5 shows a horizontal strip formformer, in which the pulp is fed from the PCB box 1 to the lower surface of the upper fabric 2 and the lower fabric 3 is brought into contact with the fibrous mass layer 20 on the lower surface of the upper fabric 2. The breast roller 4 controlling the passage of the upper wire 2 and the breast roller 5 controlling the passage of the lower wire 3 are arranged so far away that the head box 1 can be brought into the upper wire 2. The curved cover 7 of the forming shoe 6 closes the forming bar G. The forming shoe 6 is provided with a vacuum and a cover structure 7 which together provide non-pulsed dewatering of the fibrous mass between the wires 2, 3. The distance from the discharge point of the pulp to the point where the lower wire 3 meets the pulp layer on the upper wire 2 is relatively short, up to 700 mm, preferably up to 200 mm. The first lip 10 defining the lip opening 9 in the direction of the wire 2 is curved in its face against the wire 2 and forms the only support point for the wire 2 as it otherwise runs unsupported braids 4 for the forming shoe 6. Following the forming shoe 6 it is possible to combine the vacuum with, for example, a dewatering box. At the corresponding point, within the bottom wire loop 3, there is a plurality of load strips 14 alternating with dewatering strips 13.

5

Figure 6 shows an embodiment suitable for making a layered fibrous web. The double-layered headbox 101 comprises first and second manifolds 102 and 103 for supplying pulp through the first and second manifolds and turbulence tubes 104, 105 to first and second lip openings 106 and 107. 10 The first layer of fibrous web is fed to the lower surface of upper fabric 2 through first lip opening 106; the first lip 108 defining the direction of the wire 2 being in contact with the wire 2. The second lip 109 separates the first lip 106 and the second lip 107. The second layer of fibrous mass is introduced through a second lip opening 107 defined by said second lip 109 and third lip 15 110. The radius of curvature R 1 of the first lip 106 is preferably 0.1 to 2 m and the radius of curvature R 2 of the second lip 107 is preferably 0.1 to 2 m.

The advantage over current layering technology is that inter-layer mixing is substantially reduced, thereby improving bed purity. This is a possible list of 20 because the drainage of the first layer can begin even before the second layer is imported onto it. Further, by changing the dimensions of the second lip 109 separating the lip openings 106 and 107, the time allowed for the first layer to drain before the second layer of fibrous pulp is applied thereto can be adjusted.

Figure 7 shows a horizontal gritformer in which the pulp is fed from the head box 1 to the upper surface of the bottom wire 2. The passage of the lower wire 2 is guided by the chest roll 4 and the passage of the upper wire 3 is controlled by the forming roll 18 which closes the forming bar G by guiding the run of the upper wire 3 to the run of the lower wire 2. The headbox 1 is disposed on the run of the lower wire 2 between the breast roll 4 and the forming roll 18. The lip opening 9 of the headbox 1 is brought so close to the bottom wire 2 that the fibrous mass can be fed from the lip opening 9 to the bottom wire 2 substantially without a free mass jet.

9

The headbox 1 is arranged in a position relative to the lower wire 2 such that the fibrous material hits the wire at an angle α of 5 to 25 °. Immediately after the point of impact, some of the water contained in the pulp is discharged downward through the wire 2. The forming roll 18 guides the upper wire 3 to the surface of the fibrous mass layer on the lower wire 2. After form roll 5 18, dewatering strips 13 are provided on bottom side 2.

Fig. 8 is an enlarged view of the mold gasket G of the mold, in which the lip 9 of the headbox 1 is inserted even deeper than the mold G of Fig. 7. This is possible especially when the forming roll 10 is replaced by a breast roll 5 and subsequent forming shoe (not shown) the dosing strain G by conducting the wires 2 and 3 together. The fibrous mass discharged from the lip opening 9 hits the wire at an angle α of 5-25 °. The first lip 10 defining the lip opening 9 on the inlet side of the wire 2 leans on the lower wire 2, sealing the area where the pulp hits the wire 2. The surface 15 touching the wire 2 of the first lip 10 is curved so that its radius of curvature R is 0.1-2 m. retracted with respect to the first lip 10 such that the second lip 11 is at a short distance d from the lower wire 2. Preferably, this distance d is 2 to 20 mm.

Figure 9 shows a solution corresponding to the invention applied to a flat wire section. The headbox 1 is arranged above the wire 2 behind the breast roller 4 in such a position that the fibrous mass discharges from the lip opening 9 of the headbox 1 to the wire 2 without substantially a free mass jet. The fibrous mass enters the wire at an angle of 5-25 °. The first lip 10 defining the lip opening 9 in contact with the wire 2 and the second lip 11 is in contact with the wire 2. The dewatering of the fibrous material 25 begins as soon as the pulp hits the wire and continues with the dewatering strips 13.

Many variations of the invention are possible within the scope defined by the following claims. It is also to be noted that the attached figures are for reference only and do not illustrate the details of the invention on a proper scale.

Claims (14)

An arrangement for a forming gap in a double-wire former in a paper machine, comprising an inlet carriage (1), a first wire loop (2), within which is arranged a chest roll (4), and a second wire loop (3), wherein in a forming gap (G) bounded by the first and second wires (2,3), fiber pulp is inserted through a lip opening (9) into the inlet carriage (1) in such a way that the pulp hits the first wire (2) while being unsupported , characterized in that within the second wire coil (3) is provided a dewatering element (6,18) which guides the second wire 10 (3) into contact with a fiber pulp layer on the first wire (2) and closes the forming gap (G) , and that the lip opening (9) of the inlet sled (1) is brought into contact with the first wire (2) at a location which lies between said breast roll (4) and said dewatering element (6,18), the fiber mass being carried on the first wire ( 2) substantially without any free pulp. 15 Arrangement for a forming gap according to Claim 1, characterized in that the lip opening (9) of the inlet carriage (1) is limited by a first lip (10) brought into contact with the first wire (2) and a second lip (11). ), which remains at a slight distance (d) from the first wire (2). 20 Arrangement for a forming gap according to claim 2, characterized in that the surface of the first lip one (11) which comes against the first wire (2) is curved in such a way that its radius of curvature (R) is 100-2000 mm. . Arrangement for a forming gap according to claim 2, characterized in that the distance (d) between the second lip (11) and the first wire (2) is 2-20 mm. Arrangement for a forming gap according to claim 1, characterized in that the fiber mass strikes the first wire (2) at an angle (a), the size of which is 5-25 °. Arrangement for a forming gap according to claim 1, characterized in that the distance from the place where the fiber pulp hits the first wire (2) to the place where the second wire (3) comes into contact with the fiber pulp layer on the first wire (2) ) is not more than 700 mm, advantageously not more than 200 mm. 5 Arrangement for a forming gap according to claim 1, characterized in that the dewatering element within the second wire loop (3) is a forming shoe (6) which has a curved lid (7) which guides the second wire (3) in contact with the fiber pulp layer. on the first wire (2). 10 Arrangement for a forming gap according to claim 7, characterized in that the forming shoe (6) is provided with underpressure and with a perforated lid structure (7) which together provide essentially pulsation-free dewatering of the fiber pulp layer between the wires (2,3). 15 Arrangement for a forming gap according to claim 1, characterized in that the dewatering element within the second wire coil is a forming roller (18) which controls the second wire (3) in contact with the fiber pulp layer of the first wire (2). 20 Arrangement for a forming gap according to any one of the preceding claims, characterized in that, after the dewatering element (6,18), an ethereal tone is provided with a dewatering drawer (12,16) provided with dewatering strips (13,16). within either the first or second wire loop (2,3). 25 Arrangement for a forming gap according to claim 10, characterized in that a plurality of load strips (14) arranged at the gaps which arise between the drainage strips (13) are arranged within the relative to the drainage drawer (12, 16) opposite the winding loop (2,3). 30 Arrangement for a forming gap according to claim 1, characterized in that the inlet carriage is a multilayer inlet carriage (101) having at least two lip openings (106,107) which are in contact with the first wire (2). Arrangement for a forming gap according to claim 12, characterized in that said at least two lip openings (106,107) are limited by at least three lips (108,109,110), of which at least the first lip (108) touches the wire (2) and is curved in such manner. , that its radius of curvature (R1) is 0.1-2 m. Arrangement for a forming gap according to claim 13, characterized in that also the second lip (108) located between the first and the second lip opening (106) is curved in such a way that its radius of curvature (R2) is 0.1-2. m.