FI95293C - A paper machine hybrid former equipped with an MB unit - Google Patents

Description

95293

Paper machine hybrid formatter equipped with an MB unit Hybridformers in a paper machine with an MB unit 5

The invention relates to a hybrid former of a paper machine comprising a lower wire loop having a single-wire initial portion of the forming zone with dewatering elements inside the lower wire loop and then within the upper and lower wire loops wire guide and dewatering elements. on top of the pulp layer formed by the single-wire initial portion, and wherein the hybrid former has a dewatering and forming unit in the two-wire zone, comprising a loadable compression apparatus within opposite wire loops and a drainage chamber and support apparatus, the installations having mating stacks against each other.

15

It is a general object of the present invention to develop a new hybrid former structure

TM

in particular for the renewal of old flat wire sections and formers marketed by the applicant under the name SYM FORMER in order to improve the quality of the paper, expand the range of use and / or increase the speed of the paper machines. It should be emphasized, however, that the former according to the invention is intended to be suitable for use in completely new forming parts as well.

• · • Several different forming members are used in the web forming parts of a paper machine.

The main purpose of these members is to provide compression pressure and pressure pulsation to the resulting fibrous layer 25 to promote dewatering of the forming web while improving its formation. Said forming members include various forming shoes, usually with a curved strip cover, over which the overlapping forming wires and the web between them are curved. In the area of these forming shoes, water escapes through the wire on the outer curve side due to its tightening pressure 30, and this dewatering is further aided by a centrifugal force field.

Dewatering also takes place through a wire on the inner curve side, which is usually enhanced by the vacuum in the chamber of the forming shoe. The strip cover of the forming shoe 55293 2 provides a pressure pulsation which both promotes dewatering and improves web formation.

In addition, the so-called MB units through which pass, usually in a straight 5 run, two opposite wires. Inside the second wire loop of the known MB units there is a pressure loading device and inside the opposite second wire loop there is a dewatering device with a control and dewatering strip. As is known, this MB unit is generally placed on the flat wire section so that the MB unit is preceded by a substantially long single wire section with a substantial amount of dewatering before the web passes in a straight run in the plane of the flat wire through the MB unit. With regard to the structural details of the previously known MB units, reference is made as examples to the applicant's FI applications 884109 and 885607.

A variety of hybrid and twin wire formers with the MB unit or units 15 described above are already known. For these, reference is made to the following FI patent applications 884109, 885608, 904489, 905447, 920228, 920863, 924289, 930927, 931950, 931951, 931952, 932265, 932793 and 934999.

The inlet geometry of the initial portion of the two-wire forming zone has proven to be a very critical point when using MB forming units. The static forming shoes used at that inlet of the double-wire zone inside the lower wire loop may cause instability in the passage of the wires and thereby the aging of the finished paper. In addition, the initial portion of the two-wire zone of the MB unit has been found to have a significant effect on e.g. the porosity of the paper. The entry area of the two-wire zone 25 is problematic, especially because at this point the fiber structure of the pulp web "solidifies" when the upper wire comes into contact with the top surface of the pulp web, whereby said irregularities on the top surface of the pulp layer appear as vanity in the finished paper. Indeed, the pressure pulses of the static forming shoe cause a ripple on the upper surface of the track, which in its "solidifies-30 weather" appears as said vanity. In addition, the above-mentioned static forming shoes have a rather high friction as well as a wire-wearing effect.

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With regard to the state of the art most closely related to the invention, reference is made to the applicant's FI patent application 934999 (filed on 12 November 1993), according to which it is considered new to have a rotating guide and forming roll laterally inside the two-wire forming zone. 5 zones at a small angle α, the angle selected from the region a «0 ... 5 ° and followed immediately after the guide and forming roll by a dewatering and forming unit comprising said strips, in the area of which water exits mainly through the upper wire of the dewatering chamber or chambers of said unit assisted by vacuum.

10

Em. One disadvantage of FI application 934999 and other similar formers has been that at the beginning of the two-wire zone, the forming roll inside the lower wire loop restricts upward drainage through the upper wire and there is a risk, especially with thicker grades, that the track structure will break.

15 The obvious solution to this problem is to increase the diameter of the forming roll in question to ~ 2 m, which, however, makes the structure quite expensive. From the point of view of web formation and dewatering symmetry, it would be of paramount importance that in hybrid formers a two-wire forming zone could be started in an area where the web dry matter is 1.5-2%, with the surface of the fiber layer already felt to a suitable degree. . However, with previous former solutions, the two-wire zone has usually only been able to be started at a dry matter content of 2.5% • with a maximum layer thickness of about 5-6 mm. Even this has not been achieved with thicker grades of paper.

The object of the invention is therefore to provide a hybrid former in which the two-wire zone and the list pulse dewatering can be started in the dry matter as much as 1.5-2%, while before the corresponding process step has only been started in the dry matter by 3-4%.

It is therefore an object of the present invention to further develop the hybrid former and other similar formers disclosed in FI application 934999 30, in particular so that it is also suitable for use with thicker paper grades and / or higher web speeds 4 53293 and so that the above objectives and disadvantages are avoided. The invention is also intended to realize that the wires do not have to pass over a steep curvature immediately after the MB zone while the dry matter of the web is still relatively small.

5

It is a further object of the invention to provide a hybrid former in which even more water is removed upwards so that a more symmetrical sheet is realized and thus an even lower tensile strength ratio. The aim is to achieve a draw-to-hair ratio of about 1.5.

10

It is a further object of the invention to provide a hybrid former in which a fairly stable control of the wires can be realized in the two-wire MB zone.

In order to achieve the above and later objects, the invention is essentially characterized in that at the beginning of the two-wire forming zone there is a first load list traced inside the lower wire loop. followed by a loading and support apparatus with 20 opposing strips in the region of or after which the two-wire zone is curved with an opposite second radius of curvature towards the forming roll inside the lower wire loop, after which the paper web is detached from the upper wire and led to the lower wire pick-up.

A preferred embodiment of the invention is mainly characterized in that the two-wire zone inlet has an open-surface chest roll arranged in such a position that the area of the chest roll adjacent to the pulp web slightly presses the upper surface of the pulp web into the pit without substantially curving the lower wire. According to this embodiment, when a rather open chest roll is used at the entrance of the two-wire zone, which "weighs" and at the same time seals the upper surface of the pulp web, the quality and retention of the paper to be produced are improved at the same time. When the open chest roller compacts the mass path

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55293 5 upper surface, this ensures even better retention in the following dewatering strips for dewatering through the upper wire.

The open chest roll is typically placed in a position where it presses a depression of 5 ~ 2 mm on the upper surface of the pulp web. The open surface of the breast roll accounts for about 50-80% of the surface area of the active cylinder liner of the breast roll. The open chest roll is preferably arranged in a position where the consistency of the fibrous layer is of the order of ~ 0.7 to 1.7%.

The invention realizes several practical advantages over the prior art, which are briefly mentioned below. In the invention, the web can be moved to the beginning of a two-wire zone with a sufficiently low dry matter content. The former according to the invention can also be applied to thick grades without scraping problems. In the invention, a sufficiently large dewatering section can also be realized upwards, in part because the load-forming forming strips acting against the lower wire loop at the beginning of the two-wire zone curve the lower wire and the pulp path with a large radius of curvature downwards, thereby enhancing the upstream and suction deflector. An additional advantage is that the wires do not have to pass over a steep curvature immediately after the MB zone, while the dry matter content of the track is still relatively low.

20

Figure 1 shows a schematic side view of a first embodiment of the invention.

Figure 2 shows a second embodiment of the invention in a manner similar to Figure 1.

Figure 3 shows a third embodiment of the invention in a manner similar to Figures 1 and 2.

Figure 4 shows, on a larger scale, the inlet of the two-wire zone preferably used in the invention in a machine direction vertical cross-section.

30 Figures 1, 2 and 3 show a hybrid former with the basic structure of the applicant's trademark

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A component marketed by SYM FORMER. The forming part according to the figures is 95293 '1, 6

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it is also intended to be suitable for the replacement of old flat wire sections or SYM FORMER, in which case the lower wire loop 10 with its frame is an old structure and the former flat wire section has been renewed with a new upper wire unit built on the frame section. The formed shown in Figures 1, 2 and 3 can, of course, also be a new structure. The lower wire 10 is guided by rollers 11, 11a, 5b, 11c, 19, and a pulp suspension jet J is fed to the chest roll 11a through the headbox lip portion 12 at the beginning of the horizontal planar wire portion 10a. This portion 10a has dewatering elements (not shown) known per se. The two-wire zone bounded between the lower wire 10 and the upper wire 20 begins after the upper wire smooth surface chest roll 21a and the wedge-shaped groove G and in the region of the forming strip 13. The formation-10 strip 13 is followed in the two-wire zone by an MB unit 30 with a pressure loading apparatus inside the lower wire loop 10 and vacuum suction chambers 22b and 22c inside the upper wire loop 20. Below the chamber 22b there is a support strip 25 against which the load strip 15 of the pressure loading equipment loads the two-sided zone.

15

In Figures 1 and 3, the MB units 30 are substantially similar to each other, while in Figure 2 the MB unit 30 comprises only two successive dewatering chambers, namely a suction deflector chamber 22a and a latter dewatering chamber 22b, in which the same vacuum prevails.

20, in Figs. 1, 2 and 3, the upper wire 20 encounters the pulp layer W0 on the lower wire 10 with a dry matter content of 1¾ k 1.5-2.0%. The upper wire 20, the guide roll 21a in the direction of arrow A tracked asemaltaaan be adjustable so that the gap G jaw angle a can be adjusted as well as the twin-exact starting point. From the first fixed forming strip 13 in the region G of the bottom wire loop-25, the two-wire zone curves with a rather large radius of curvature Rq <5-10 m towards the bottom wire loop. The MB unit 30 has a first load list 15a inside the lower wire loop, e.g. two pairs of load lists, e.g. connected in pairs and which are load loads of 30 for the pressures of the medium to be introduced into the hoses 16.

· «55293 7

The first load list 15a is below the suction deflector chamber 22a and there are no fixed counter-strips opposite it. The first fixed forming strip 13 is preferably fixed and, together with the first strip 15a loaded with media pressures, guides the lower wire 10 and the upper wire guided thereon with the above-mentioned relatively large radius of curvature R0. When the first fixed forming strip 13 and the subsequent pressure-loaded loading strips 15a bend the lower wire and the mass path supported by it downwards, the dewatering through the upper wire 20 at this point is intensified, thereby promoting the symmetry of the dewatering. In this case, leave the water passing through the upper wire 20 imudeflektorikanavaan 24 and 10 by the arrow F direction of the first dewatering chamber 22a. Thus, dewatering can be initiated through the upper surface of the pulp layer W0 sufficiently efficiently but still carefully and without curating problems, even with thick qualities, in part because there is no fixed support list against the first strip 15a as in the next MB zone 15b, 25a.

15

The first load list 15 is followed by a second load list 15b, opposite which is a fixed support list 25a below the dewatering chamber 22b. The two-wire zone guided by the strips 15b and 25a is either straight (Figs. 1 and 3) or upwardly curved with a radius of curvature Rj as shown in Fig. 2. According to Fig. 1, said opposite strips 15b, 25a are followed by a stationary support strip 25b, which according to Figs. 1 and 3 is below the third dewatering chamber 22c 'without opposite load strips. The last strip 25b guides the two-wire zone upwards with a radius of curvature Rj ~ 3-5 m.

25 within the upper wire loop is the MB-unit 30 into the drain 22a, 22b and 22c, which has a water outlet channels 24. The drain channels 24 through leaving through the upper wire loop 20, the water is guided in the direction of the arrow F drainage channels 23, which is typically only on one side of the machine. The dewatering chambers 22a, 22b and 22c are connected to vacuum sources. The water inlet channels 23 are connected to suction feet 17a, 17b and 17c, the height of the water-30 of which is marked with WA. The load lists 15a and / or the environments 55293 8 can also be connected to vacuum sources. In the invention, about 30-50% of the total dewatering takes place in the dewatering chambers 22a, 22b, 22c under the influence of vacuum or pressures.

According to Fig. 1, after the MB unit 30, inside the lower wire loop, a forming roll 19 with a smooth surface 19 'follows, in the region of which the two-wire zone curves from top to bottom, then inside the top wire loop 20 there is a smooth surface forming roll 21b. The two-wire zone then continues as a horizontal zone with a suction box 30 inside the lower wire loop 10. At this point, the upper wire 20 is separated from the paper web W under the direction of the guide roll 21c The web W is detached from the lower wire 10 at the pick-up point P between rollers 11b and 11c not shown) with the aid of a suction zone for a pick-up fabric (not es.) which takes the web W to the press section (not es.).

Figures 1, 2 and 3 show a dewatering trough 32, 15 inside the lower wire loop 10, which is connected together 33 and via a channel 34 to a wire well (not shown). The embodiment shown in Figures 2 and 3 differs from that shown in Figure 1 in that there is a forming shoe 18 between the strip 25b and the forming roll 19. The forming shoe 18 has a strip cover 18a having a radius of curvature R3 ~ 2 ... 8 m, the slits of which can be connected to a vacuum source. After the strip cover 18a of the shoe 18, the two-wire zone 10,20 runs 20 in a horizontal run on a forming roll 19 with a diameter Dj <1.0 ... 1.5 m.

A preferred two-wire zone entrance having sysergic effects with the invention described above will now be described with reference to Figure 4. In the single-wire initial portion 10a of the lower wire 10, the layer Wh against the lower wire 10 of the pulp web W is felted to some extent by the inlet, but in the upper surface and layer Wy of the pulp web W0 there is still substantially headbox-thick pulp W at the bust roll 21A. The breast roll 21A is set and / or adjusted to precisely the height of the arrow A, in such a position that its lowest mantle portion is depressed into the pulp web W0 However, the lower wire 10 and 30 do not substantially curving. Said printing Ah is typically Ah <1-5 mm.

95293 9 In this way, the chest roll 30 felt the fibrous layer against the upper wire 20, as a result of which even better retention is achieved on the subsequent strips 15a, 15b, 25a, 25b.

As the breast roll 21A, a breast roll with a very open jacket 21C is used, the open surface 5 of which typically accounts for 50 ... 80% of the total active jacket surface. A suction roll perforated in the jacket 21C can also be used as the breast roll 21A. The diameter of the chest roll 21A is typically D <500 ... 1200 mm depending on the width of the machine. At the entry point bounded by the breast roll 21A, the average fiber density 1¾ of the pulp web W is 1¾ = 0.7 ... 1.7%, i.e. the breast roll 21A according to the invention can preferably be placed in a substantially lower fiber density area of other formers without the risk of breaking the pulp web structure W0. Due to the arrangement of the breast roll 21A according to the invention, no too abrupt dewatering pulse is generated in the area of the breast roll 21A, so the invention can also be applied to thicker species (basis weight> 170 g / m 2), where the thickness of the pulp web 15 is typically h <10 ... 25 mm.

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In the S YM FORMER renewals, it is possible to proceed so that the forming roll previously in the region of the groove G is transferred to the chest roll 21a; 21A of the upper wire loop 20. In the former according to Figures 2 and 3, in the case of a renewal of the forming part, an old forming shoe 18 is left in place 20.

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.

25 • ·

Claims (13)

A paper machine hybrid former comprising a lower wire loop (10) having a single wire initial portion (10a) of the forming zone having 5 dewatering elements inside the lower wire loop (10) and then wire guide and dewatering elements inside the upper and lower wire loops (10,20). which hybrid former comprises an upper wire unit having an upper wire (20) guided by rollers (21a, 21b, 21c), guided by a chest roll (21a; 21A) over a pulp layer (W0) formed by a single wire initial portion (10a) of the lower wire (10), and a hybrid former - and a forming unit (30) comprising load-bearing pressing equipment inside opposite wire loops (10, 20) and dewatering chamber and support equipment, which equipment have load-bearing strips (15a, 15b, 25a, 25b), characterized in that, that at the beginning of the two-wire forming zone there is a trace inside the lower wire loop (10) a first load list (15a) guiding the lower wire (10) and the upper wire (20) guided over the pulp layer (W0) thereon by a large first radius of curvature (Rq) centered on the side of the lower wire loop (10), and said first load list (15a) followed by a loading and support apparatus with opposing strips (15b, 25a) in the region of or after which the two-wire zone is curved with an opposite second radius of curvature (Rj) towards the forming roll (19) inside the lower wire loop (10), followed by a paper web .. (W) is detached from the upper wire (20) and led to follow the lower wire (10) up to the pick-up point (P). Hybrid former according to Claim 1, characterized in that the inlet of the double-wire zone has a chest roll (21A) with an open surface (21C) which is arranged in such a position that the area of the chest roll (2IA) adjacent to the mass path (W0) is slightly depressed. ) to the upper surface without substantially bending the lower wire (10). Hybrid former according to claim 2, characterized in that said printing depth of the upper surface of the mass track (W0) of the breast roll (2IA) is of the order Ah * 1-5 mm. 95293 11 Hybrid former according to Claim 2 or 3, characterized in that the breast roll (2IA) is a very open-shell (21C) breast roll with an open surface area of about 50 to 80% of the active surface area of the roll shell (21C). Hybrid former according to one of Claims 2 to 4, characterized in that the breast roll (2IA) is arranged in a position in which the fiber density of the pulp web (W0) is of the order of 1 to <0.7 to 1.7%. Hybrid former according to one of Claims 1 to 5, characterized in that the first radius of curvature R0 is selected from the range Rq 55-10 m and / or that the second radius of curvature R1 in the opposite direction is selected from the range Rt 3-55–5 m. Hybrid former according to one of Claims 1 to 6, characterized in that the loading and support unit (15b, 25a) is followed by a second support strip (25b) arranged inside the upper wire loop (20), which is preferably located in the third dewatering and forming unit (30). below the dewatering chamber (22c). Hybrid former according to any one of claims 1 to 7, characterized in that after said second turning strip (25b) the two-wire zone is guided in an upwardly sloping direction 20 on a forming roll (19) which is preferably smooth (19 ') and then the two-wire zone is guided in a downwardly sloping direction 20) on the inner roll (21b). Hybrid former according to any one of claims 1 to 8, characterized in that after said fixed support strip (25a, 25b) the two-wire zone is guided on a forming shoe (18) with a curved strip cover (18a), the center of curvature (R3) of the strip cover (18a) (10) side, after which the two-wire zone is guided to form a roll (19), which is preferably smooth-surfaced (19 '), and then the two-wire zone is guided as an oblique run to the roll (21b) inside the upper wire loop (20). 12 Cr907 s' U * _ s U Hybrid former according to Claim 8 or 9, characterized in that after the latter roll (21b) the two-wire zone is guided, preferably in a horizontal run, over a suction box (31) inside the lower wire loop (10), under which the paper web (W) is removed from the upper wire (20). ), after which the paper web (W) 5 is guided to follow the lower wire (10) up to the pick-up point (P). 10 9j293 Hybrid former according to one of Claims 1 to 10, characterized in that the two-wire zone first has a first strip (15a) which gently curves the two-wire zone towards the lower wire loop, then a substantially straight strip 10 (20) has a fixed strip (25b) inside which directs the two-wire zone to curve in the opposite direction to the first strip (Figures 1 and 3). Hybrid former according to one of Claims 1 to 11, characterized in that the first strip (15) is followed by opposite strips (15b, 25a), of which the strip (15b) inside the lower wire loop (10) is a load strip and the strip (20b) inside the upper wire loop (20). the list is a fixed support list and that in the latter list (15b, 25a) the two-wire zone is guided to curve upwards by a radius of curvature R1? which is selected such that the first radius of curvature Rq> (Fig. 2). 13 ςΓ993 / υ ί- ✓ W