FI100810B - Paper machine two-wire guitar former - Google Patents

Description

5 100810

Paper machine double wire gunformer Gapformare med dubbel vira i en pappersmaskin

The invention relates to a two-wire web-forming part of a paper machine comprising a cover wire guided by guide rollers and a load-bearing wire guide guided by guide rollers, from which the formed web is removed to pick-up fabric or the like, and which web-forming part comprises a tuft to which the headbox lip can be fed determined by rollers within the loops of said wires and bounded by two wires having at least two successive pressure-loaded dewatering and forming units, each comprising 15 support strips and an opposing load strip, the strips being provided with water strips and opposite pressure strips - and the forming units comprise a vacuum box or boxes into which the vacuum can be applied and in which the forming part has successive dewatering and the vacuum boxes of the forming units are arranged inside opposite different wire loops and the first dewatering and desoldering unit is located substantially immediately or at a short distance from the forming crystal so that on the inlet side of said first unit the mass of xx in the two-wire zone ... 2.5%.

As the speeds of paper machines increase, several problems in web formation have become even more pronounced. In the forming part of the paper machine, the phenomena affecting the fiber network and in connection therewith, which are still relatively free but water, e.g. centrifugal forces, are generally intensified in proportion to the square of the web speed. Most of the current pa-. · The maximum track speeds of hatcheries are in the order of 1500 m / min. However, you plan to have machines that aim for a track speed of up to about 1700 m / min.

With regard to the state of the art related to the present invention, reference is made to U.S. Patent 4,769,11 to A. Ahlström Corpr, Applicant's FI Patent Application No. 885609, and Valmet-Ahlström Inc.'s FI Patent Application Nos. 885606 and 885607, which disclose the applicant's formers marketed under the trademark "MB-formeri".

In addition, reference is made to the applicant's FI patent applications Nos. 904489, 911281, t 5,913112, 920228, 920863 and 932264, which disclose various combination concepts of the above-mentioned MB-former units and hybrid and other formers.

In the above-mentioned dock formers, the pulp suspension is passed from the headbox to a form formed by a forming roll and two wires, after which both wires and the mass layer between them follow the curvature of the forming roll, leaving most of the water through the wires. The required dewatering pressure is provided by the tension of the outer wire, which generates a pressure in the pulp layer which is directly ver- 15 to the tension of the wire and inversely proportional to the radius of curvature of the forming roll. In the ridge, part of the kinetic energy of the mass jet is converted into pressure energy and the jet speed decreases accordingly. Dewatering through the outer wire away from the forming roll is enhanced by centrifugal force. The dewatering towards the forming roll can be enhanced by the vacuum of the forming zone.

Applicant's FI patent application 904489 discloses a dock former in which it is considered new that said dewatering unit or units comprise a stationary compression support unit which guides the incoming wire against it in a substantially straight flow, and that said dewatering unit or units comprise / comprise a dewatering apparatus with suction and foil equipment opposite said pressing and support unit, which removes a substantial amount of water from the web.

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One significant problem that occurs in prior art gutter formers with a previously known MB unit or units in the two-wire zone is the one-sidedness of the paper to be produced, especially in terms of fine and filler distribution. This disadvantage is due to the fact that the sensitive moving fillers in the two-wire zone tend to accumulate on the side of the wire through which the vacuum acts.

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In known MB units, the negative pressures of successive suction boxes usually appear on the wire side of the word.

The above-mentioned one-sidedness also adversely affects other properties of the web 5, such as the smoothness of the paper surfaces and the oil absorption of the paper. The above drawbacks are due in part to the fact that in the prior art guitar formers the MB unit has generally been located in an area where the consistency of the resulting mass layer has been decisively higher than the headbox consistency, i.e. clearly greater than about 1.5%, so that in the MB unit - and the distribution of fillers could no longer be greatly influenced.

The main object of the present invention is therefore to develop the state of the art which appears from the above-mentioned publications in such a way that the drawbacks discussed above can be substantially eliminated.

In order to achieve the above and later objects, the invention is mainly characterized in that in the second dewatering and forming unit the fixed support strips are inside the same wire 20 loop as the corresponding support strips of the first dewatering and forming unit and that the second dewatering and forming unit load unit is preferably so that water escapes from the space or spaces between the load lists of said load unit with the aid of a vacuum of the suction box.

In the former according to the invention, the MB unit is located in a double-wire zone in an area where the consistency of the formed mass layer is considerably lower than in the corresponding known formers, generally said consistency in the invention is in the range kj »0.5 ... 2.5%. close to headbox consistency. In this case, the fillers and fines are still relatively mobile in the mass layer formed in the region of the MB units, so that their distribution can still be effectively influenced by the opposite arrangement of the vacuum pressures of the suction zones of the MB boxes according to the invention. In addition, by adjusting the vacuum levels of successive MB boxes, the main amounts of the invention can be achieved with different pulp qualities and a sufficiently wide range of web speeds, even at high speeds of the order of 1500-1700 m / min. The formation of the web and the intensity of dewatering can also be effectively influenced by the vacuum, and in particular the load pressures applied to the load-5 hoses or the like of the compression unit. Thus, the invention provides versatile control parameters with which the web formation and dewatering process can be efficiently and expediently controlled.

In the former according to the invention, the two-wire zone is not necessarily vertical, but a two-wire zone running diagonally or even horizontally can also be used, although water treatment is not as easy as in the most preferred vertical model according to the invention, where the gravitational field similarly affects the two opposite wires.

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

Figure 1 shows a schematic side view of a most preferred embodiment of a former according to the invention.

Figure 2 shows the initial part of a two-wire zone according to the invention in a machine direction vertical cross-sectional pattern.

Figure 1 shows a guitar former according to the invention, the two-wire zone of which is flowing substantially vertically upwards. The covering wire 10 and the supporting wire 20, under the guidance of the rollers 11,21, form a gap. a pulp suspension jet J is fed into this forming ladder G. From the lip of the headbox 32 a pulp suspension jet J. After the bottom of the forming ladder G, the two-wire zone curves in the sector a of the forming roll 21, which is generally in the range a == 0 ... 600, preferably a »10 ... 45 °. After the sector, the running of the wires 10,20 differs from the forming roll 21 and 5 100810 continues to run under the deflector strip 13 arranged inside the covering wire 10.

The two-wire zone has two successive MB units 40 and 50. In Fig. 5, after the deflector strip 13 according to the invention, an MB box 15 of the first MB unit 40 with a support strip 16 and a preceding support strip 14 is arranged inside the loop of the covering wire 10. the box 15 is connected to a vacuum source 15a, which causes the vacuum px to act inside the MB box 15. Opposite the support 16 of the support box 10 of the MB box 15, inside the loop of the load-bearing wire 20, there is a load list 26, the lists of which are in the middle of the spaces between the support lists 16. The load strips 26 are pressed against the inner surface of the loop of the supporting wire 20 at a pressure pL of the load hoses 24c (Fig. 2) obtained from the pressure source 24.

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After the first MB box unit 40, the two-wire zone has a second MB unit 50 with a fixed support strip 17 inside the loop of the covering wire 10, which is opposed by an MB box 29 inside the loop of the supporting wire 20. This MB box 29 is connected to a sub-20 pressure source 29a so that there is a vacuum p2 inside the MB box 29. Inside the MB box 29, at the centers of the intervals between the support strips 17, there are load strips 27 which are loaded by the load hoses 24d (Fig. 2) with pressures transmitted from the overpressure source 24 via the connections 24b.

After the box 29 of the latter MB unit 50, inside the loop of the support wire 20, there is a second forming roll 23, the vacuum zone 23a of which partially removes water through the carrying wire 20 and helps to ensure that at the guide roll 12 'the web W follows exactly 30 supporting wires. 23, the web W passes on the load-bearing wire 20 over the suction zone 22a of the suction roll 22 to the pick-up point P, where the web W is transferred to the pick-up fabric 30 with the aid of the vacuum zone 31a of the pick-up roll 31, which takes the web W further to the paper machine press section ( not shown). The guide rollers 35 of the covering wire 10 are indicated by reference numeral 12 and the guide rollers of the supporting wire 20 are indicated by reference numeral 22, respectively.

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In Fig. 1, the first lower forming roll 21 has a suction zone 21a, the size of a sector a of which corresponds to the curved sector of the two-wire zone on the forming roll 21. The size of said sector 21 in Fig. 1 is about α <60 °. In sector a, water is discharged outwards, assisted by centrifugal forces, outwards mainly through the covering wire 10 due to the tightening pressure of the wire 10, and this dewatering is promoted and controlled by the deflector strip 13 and its subsequent water guide plate 13a. The deflector strip 13 is followed by a direct run of the two-wire zone to the support strip 14 at the front edge of the first MB unit box 15, the pulse im-10 of which removes water through the covering wire 10 and these waters are further guided by the dewatering plate 14a. In the first MB unit 40, the load strips 26 provide pressure to the two-wire zone between the strips 16,26 and at the same time dewatering is promoted towards the MB box 15 by the vacuum px prevailing inside it. Correspondingly, the next 15 MB unit 50 provides compressive pressure between the wires 10,20 against the support strips 17 by the load strips 27, and drainage through the dewatering wire 20 is promoted by the vacuum p2 inside the box 29 of the second MB unit.

Figure 2 shows in more detail the structure of the beginning of the two-wire zone according to Figure 1. Fig. 2 differs from Fig. 1 in that the first forming roll 21 has a rather small curved sector a of the two-wire zone, which in Fig. 2 is of the order a ~ 5 ... 10 °. The first forming roll 21 is not necessarily a suction roll, but can also be a solid-shell groove roll 25, a blind-drilled roll or even a roll with a smooth surface 21 '.

As the pulp suspension path W0 formed between the wires 10,20 reaches the leading edge of the first MB unit 40, its consistency is generally of the order of 30 ki = 0.5 ... 2.5%. In this case, the fillers and fines of the pulp web * W0 formed in the region of the MB unit 40 are still quite free-moving and their transfer towards the wire 10 is facilitated in the region of the MB unit 40 by the vacuum p: of its box 15. As the mass path W0 enters the region of the second MB unit 50, the vacuum p2 of the MB box 29 is promoted through its dewatering wire 35 20 in the opposite direction to the vacuum px of the first MB unit 40. When in the region of the inlet edge of the second MB unit 50 the dry matter content k2 of the pulp track W0 is generally of the order of k2 <2.5 ... 5%, then in the region of the second MB unit 50 the fines and fillers of the pulp track W0, especially on the side of the supporting wire 20 on the part of the pulp web W0 are still able to move, and thus are transferred to the filler-5 and the fines-carrying wire 20 by the vacuum p2 and at the same time promote the mutual symmetry of the fines and filler distribution of the web W and its different surfaces.

Figure 2 shows in more detail the load unit 10 of the first MB unit 40, to which the load strips 26 are attached. Said unit 25 is loaded by load hoses 24c against the wire 20 from the support response 24e. A similar structure is inside the box 24 of the second MB unit 50, comprising a load unit 28 to which load strips 27 are attached and which unit 28 is loaded against the inner surface 15 of the wire 20 resting on the abutment portion 24e. When the pulp track W0 leaves the second MB unit 50, its dry matter content is usually in the range k3 * 4 ... 8%.

The first forming roll 21 may also have a hollow surface jacket such as a grooved or blind drilled jacket. The load units 25 and 28 of the successive MB units 40 and 50 20 are located on the same side of the formed mass path W0. The structure according to Figures 1 and 2 has the advantage that with the second MB unit 40 the relatively wide (lj) support strips 17 interfere as little as possible with the felted web W0 on the outer surface of the covering wire 10. Thus, the width lx in the direction of travel 1 25 of the wires 10,20 of the support strips 17 is considerably larger than the corresponding width 12 of the load strips 16, 17a. Said widths lj and 12 are generally selected from the areas lx »25 ... 75 mm and 12« 10 ... 50 mm .

The space 25a between the load strips 26 30 of the load unit 25 of the first MB unit 40 is preferably closed so that dewatering towards this space 4 is substantially prevented so that at this point the water escapes mainly through the covering wire 10. In the figures, the space 28a between the load lists 27 of the load unit 28 inside the MB box 50 of the second MB unit 50 is, on the other hand, open to the size 29 of the MB box 35 so that in said space 28a there is a vacuum p2 of 100810 8 MB box 29 and in this space 28a water can escape through the carrier wire 20, which is promoted by the vacuum p2.

The vacuum levels px and p2 in the MB boxes 15 and 29 are generally selected from the range 5 to 2 ... 15 kPa, preferably from the range 2 to 10 kPa. The vacuum level is preferably arranged to rise in the direction of travel of the web W so that the difference P2> Pi and the difference Δρ - p2 - px of said vacuum pressures is preferably selected from the range Δρ * 1 ... 5 kPa.

With regard to the dimensioning of the two-wire zone of the forming part according to the invention, the diameter D of the first forming roll 21 is preferably selected from the range D to 1.2 to 1.6 m and the diameter of the second forming roll 23 is chosen to be substantially equal. The lengths Lx and L2 of the MB units 40 and 50 in the direction of travel of the web are preferably selected so that Li “L2 s 200.. .600 mm.

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 (8)

100810 9 Patent suction e A two-wire web forming section of a paper machine, comprising a cover wire (10) guided by guide rollers (12) and a support wire (20) guided by guide rollers (22), from which the formed web (W) is removed to the pick-up fabric (30). or the like, which web-forming part comprises a forming crystal (G) into which a pulp suspension jet (J) can be fed from the lip of the headbox (32) and which forming crystal (G) is guided by rollers 10 (11,21) inside the loops of said wires (10, 20) and the wires (10,20) delimit a two-wire zone with at least two successive pressure-loaded (pL) dewatering and forming units (40.50), each comprising a support strip (16,17) and an opposing load strip (26,27) ), the strips of which can be provided with a load pressure against said wires 15 (10,20) and which the dewatering and forming units (40.50) comprise a vacuum box (15.2 9) or boxes to which the reduced pressures (Pi, P2) i can be applied and in which the vacuum boxes (15, 29) of successive dewatering and forming units (40.50) are arranged in the forming part by means of opposite different vii-20 ras loops (10.20 ) and the first dewatering and forming unit (40) is located substantially immediately or at a short distance from the forming crystal (G) so that the consistency ki of the pulp track (W0) formed in the two-wire zone on the inlet side of said first unit (40) is only substantially in the range kj * 0, 5 ... 2.5%, characterized in that in the second dewatering and forming unit (50) the fixed support strips (17) are inside the loop of the same wire (10) as the corresponding support strips of the first dewatering and forming unit (40) (16) and that the load unit (28) of the second dewatering and forming unit (50) is arranged inside the suction box (29) 30 of the second unit (50), preferably so that said load water is removed from the space (28a) or spaces between the load lists (27) of the suction unit (28) with the aid of a vacuum (p2) of the suction box (29). A web-forming section according to claim 1, characterized in that the first dewatering and forming unit (40) has fixed support strips (16) in connection with its suction box (15), preferably inside a loop of a covering wire (10), and that inside the loop of the opposite wire (20) there is a pressure-loaded (pL) load unit (25) of the first unit (40), the intermediate space or spaces (25a) of the load list (25) of which no substantial dewatering takes place. Web-forming section according to Claim 1 or 2, characterized in that the consistency k2 of the pulp web (W0) formed after the first dewatering and forming unit (40) is arranged in the range k2 <2.5 ... 5% and in that the second dewatering and supporting unit 10 The consistency k3 of the mass path (W0) formed after (50) is arranged in the range k3 ~ 4 ... 8%. Web-forming section according to one of Claims 1 to 3, characterized in that after the second dewatering and forming unit (50) 15 there is a second forming roll (23) inside the loop of the supporting wire (10), the suction zone (23a) of which ensures that the web (W ) follows the load-bearing wire (20) after the two-wire zone. Web-forming section according to one of Claims 1 to 4, characterized in that the region of the forming crystal (G) has a first forming roll (21) under the control of which the two-wire zone curves in a certain sector α = 0 to 900, preferably in sector α <10. ..45 °. Web-forming part according to one of Claims 1 to 5, characterized in that the pouring sector a of the first forming roll (21) or substantially thereafter has a dewatering felt (13) and / or that the front edge of the first dewatering and forming unit (40) has, preferably fixed , drainage strip (14) or similar suction deflector. Web-forming part according to one of Claims 1 to 6, characterized in that the vacuum levels of the suction boxes (15, 29) of said dewatering and forming units (40.50; 40.50A) are arranged to be adjustable or set in the range from 2 to 15 kPa. , preferably in the range of 2 to 10 kPa, and that the vacuum level (px) of the first unit (40) is suitably higher than the vacuum level (p2) of the latter unit. 100810 11 Web-forming section according to one of Claims 1 to 7, characterized in that the two-wire zone is substantially vertically rising from the forming roll (G) to the second forming roll (23). 5 100810 12