Source: http://www.google.com/patents/US5582687?dq=7,339,580
Timestamp: 2013-12-11 17:36:43
Document Index: 609584239

Matched Legal Cases: ['art 10', 'art 10', 'art 51', 'art 51', 'art 51', 'art 51', 'art 51', 'art 10', 'arts 33', 'art 10', 'art 41', 'arts 73']

Patent US5582687 - Web former for a paper machine - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Sign inAdvanced Patent SearchPatentsThe invention relates to a twin-wire web former for a paper machine wherein a covering wire and a carrying wire form a twin-wire forming zone between them. A method for dewatering a web is also disclosed. In the invention, water is drained out of a web running through the twin-wire zone through both...http://www.google.com/patents/US5582687?utm_source=gb-gplus-sharePatent US5582687 - Web former for a paper machinePublication numberUS5582687 APublication typeGrantApplication numberUS 08/342,869Publication dateDec 10, 1996Filing dateNov 21, 1994Priority dateJan 17, 1992Fee statusLapsedAlso published asCA2087043A1, CA2087043C, DE69308904D1, DE69308904T2, EP0552139A1, EP0552139B1, US5395484, US5536372Publication number08342869, 342869, US 5582687 A, US 5582687A, US-A-5582687, US5582687 A, US5582687AInventorsJouko Aula, Pekka Evasoja, Jyrki Jaakkola, Michael OdellOriginal AssigneeValmet CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (25), Referenced by (3), Classifications (9), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetWeb former for a paper machineUS 5582687 AAbstract The invention relates to a twin-wire web former for a paper machine wherein a covering wire and a carrying wire form a twin-wire forming zone between them. A method for dewatering a web is also disclosed. In the invention, water is drained out of a web running through the twin-wire zone through both of the wires. After the twin-wire zone, the web is separated from the covering wire and is transferred on the carrying wire to a pick-up point. In hybrid formers, after an initial single-wire forming zone preceding the twin-wire zone, and in gap formers, after a curved forming zone placed directly after a forming gap, there is a forming shoe provided with a ribbed deck and arranged inside one of the wire loops. This forming shoe is followed by dewatering and web forming units which include forming ribs and are placed inside both of the wire loops. At least one of the dewatering and web forming units is loaded by means of a pressure-hose arrangement.
We claim: 1. A web former in a paper machine including a headbox for feeding a pulp suspension jet, comprisinga carrying wire and a covering wire defining a twin-wire forming zone in which a web is dewatered, the pulp suspension jet being fed from the headbox onto a loop of said carrying wire, the web being separated from said covering wire after said twin-wire zone and transferred on said carrying wire to a pick-up point, and guide rolls and web-forming rolls for guiding said covering wire in a loop, said twin-wire zone beginning on or after a first one of said guide rolls arranged inside said loop of said covering wire, said twin-wire zone includinga first forming shoe provided with a ribbed deck and arranged inside a loop of said covering wire or inside a loop of said carrying wire, a dewatering unit comprising forming ribs and arranged inside said loop of said covering wire or inside said loop of said carrying wire, a web forming unit comprising forming ribs and arranged opposite said dewatering unit inside the other of said loops from said dewatering unit, loading means for loading said forming ribs in at least one of said dewatering unit or said web forming unit, said loading means comprising a pressure-medium hose arrangement, and a spring blade wire loading device arranged after said first forming shoe and inside a loop of one of said wires, said spring blade wire loading device comprising a frame part, a flexible plate-shaped spring blade having a dragging area structured and arranged to drag against an inner face of said one of said wires and to follow variations in the thickness of the web, said spring blade being attached from outside its dragging area to said frame part, and spring blade loading means arranged in association with said spring blade for deflecting said spring blade into a curved profile to produce the dragging area and to apply an intensive pressure pulse to the web. 2. The web former of claim 1, wherein the linear load of the pressure pulse applied by said spring blade is from about 0.2 kN/m to about 3 kN/m, and/or wherein the length of the pressure pulse applied by said spring blade in a machine direction is from about 2 mm to about 10 mm.
3. The web former of claim 1, wherein said wire loading device is arranged in an area in which the dry solids content of the web is from about 1.2% to about 3% such that by means of the pressure pulse applied by said spring blade in said wire loading device, the formation of the web is improved and the dewatering of the web is promoted.
4. The web former of claim 1, wherein the linear load of the pressure pulse of said spring blade is adjustable in a cross-machine direction in order to control profiles of dewatering of the web, distribution of fillers in the web, formation of the web, and/or retention of water in the web in the cross-machine direction.
5. The web former of claim 1, wherein said ribbed deck is a curved ribbed deck having a radius of curvature in a range of about 3 m to about 8 m.
6. The web former of claim 1, wherein said first forming shoe and said wire loading device are arranged inside said loop of said carrying wire.
7. The web former of claim 1, further comprising a second forming shoe arranged after said dewatering unit and said web forming unit in the running direction of the web, said second forming shoe having a ribbed deck for guiding said twin-wire zone along a curved path.
8. The web former of claim 1, wherein the web former is a hybrid former and said covering wire is arranged above said carrying wire, said loop of said carrying wire having a substantially horizontal initial part after said headbox, said first forming shoe and said web forming unit being arranged inside said loop of said carrying wire, further comprisingdewatering members arranged in said initial part of said carrying wire for draining water from the web through said carrying wire, and a foil rib for removing water from the web through said covering wire, said dewatering unit comprising a first suction box having an associated drain duct, said foil rib being connected to said first suction box through said drain duct and being arranged after said first forming shoe in the running direction of the web and inside said loop of said covering wire. 9. The web former of claim 8, further comprisinga first open-faced forming roll arranged inside said loop of said covering wire and after said first suction box in the running direction of the web, said first forming roll having a sector arranged such that said twin-wire is curved upward on said sector, a curved-faced forming shoe arranged inside said loop of said carrying wire and after said first forming roll in the running direction of the web, a second forming roll arranged inside said loop of said carrying wire and after said curved-faced forming shoe in the running direction of the web, said second forming roll arranged to curve said twin-wire forming zone downward, and a second one of said guide rolls arranged inside said loop of said covering wire and after said second forming roll in the running direction of the web, the web being separated from said covering wire at or before said second guide roll and passed on said carrying wire onto a pick-up fabric. 10. The web former of claim 8,wherein said forming ribs in said web forming unit are arranged after said wire loading device in the running direction of the web and said loading means load said forming ribs in said web forming unit, further comprising a second suction box connected to a suction pump via a suction duct, and wherein said forming ribs in said dewatering unit are arranged inside said loop of said covering wire and operate against said covering wire, a first one of said forming ribs in said dewatering unit being arranged to operate in an area of a loading zone of said spring blade, said forming ribs in said dewatering unit defining gaps therebetween which communicate with said second suction box. 11. The web former of claim 10, wherein said forming rib and said loading ribs are structured and arranged to dewater the web before said first forming roll such that the dry solids content of the web after said forming rib and said loading ribs is from about 3% to about 5%.
12. The web former of claim 11, wherein said forming rib and said loading ribs are structured and arranged to dewater the web such that the dry solids content of the web is about 3.5%.
13. The web former of claim 10, wherein said first suction box comprises a first suction duct which connects said first suction box to a blower such that negative pressure prevailing in said first suction box is maintained at a level from about 0 mH.sub.2 O to about 2 mH.sub.2 O, and said second suction box comprises a second suction duct which connects said second suction box to a vacuum pump such that the level of negative pressure prevailing in said second suction box is maintained at a level from about 0.4 mH.sub.2 O to about 4 mH.sub.2 O.
14. The web former of claim 9, wherein said twin-wire zone has a substantially straight run between said second forming roll and said second guide roll, further comprising suction flatboxes arranged in said carrying wire for applying suction to the web.
15. The web former of claim 1, wherein said twin-wire zone is substantially horizontal.
16. The web former of claim 1, wherein said spring blade has a length and a thickness, the ratio of the length to the thickness of said spring blade being from about 10 to 1000.
17. The web former of claim 1, wherein said spring blade loading means comprise a loading hose positioned against said spring blade at a location between said frame part and a tip of said spring blade.
18. The web former of claim 1, wherein the ratio of the length of said spring blade to the thickness of said spring blade is from about 10 to about 1000.
19. A hybrid web former in a paper machine including a headbox for feeding a pulp suspension jet, comprisinga carrying wire and a covering wire defining a twin-wire forming zone in which a web is dewatered, the pulp suspension jet being fed from the headbox onto a loop of said carrying wire, said loop of said carrying wire having a substantially horizontal initial part after the headbox, the web being separated from said covering wire after said twin-wire zone and transferred on said carrying wire to a pick-up point, said covering wire being arranged above said carrying wire, dewatering members arranged in said initial part of said carrying wire for draining water from the web through said carrying wire, guide rolls and web-forming rolls for guiding said covering wire in a loop, said twin-wire zone beginning on or after a first one of said guide rolls arranged inside said loop of said covering wire, said twin-wire zone includinga first forming shoe provided with a ribbed deck and arranged inside a loop of said carrying wire, a dewatering unit comprising forming ribs and arranged inside said loop of said covering wire, a web forming unit comprising forming ribs and arranged opposite said dewatering unit inside said loop of said carrying wire, and loading means for loading said forming ribs in at least one of said dewatering unit or said web forming unit, said loading means comprising a pressure-medium hose arrangement, a foil rib for removing water from the web through said covering wire, said dewatering unit comprising a first suction box having an associated drain duct, said foil rib being connected to said first suction box through said drain duct and being arranged after said first forming shoe in the running direction of the web and inside said loop of said covering wire, a first open-faced forming roll arranged inside said loop of said covering wire and after said first suction box in the running direction of the web, said first forming roll having a sector arranged such that said twin-wire is curved upward on said sector, a curved-face second forming shoe arranged inside said loop of said carrying wire and after said first forming roll in the running direction of the web, a second forming roll arranged inside said loop of said carrying wire and after said curved-faced second forming shoe in the running direction of the web, said second forming roll arranged to curve said twin-wire forming zone downward, and a second one of said guide rolls arranged inside said loop of said covering wire and after said second forming roll in the running direction of the web, the web being separated from said covering wire at or before said second guide roll and passed on said carrying wire onto a pick-up fabric. 20. A twin-wire zone in a wire section of a paper machine defined by a pair of wires between which a paper web is carried, comprisinga first forming shoe including a curved ribbed deck and arranged inside a loop of a first one of said wires, web forming means comprising forming ribs and arranged inside said first wire loop, dewatering means arranged opposite said web forming means inside a loop of a second one of said wires, said dewatering means comprising a first and second suction box, forming ribs and a foil rib, said foil rib being arranged after said first forming shoe and before said web forming means in a running direction of the web, said foil rib removing water from the web through said second wire and causing the removed water to be passed into said first suction box, loading means for loading said forming ribs in at least one of said dewatering means and said web forming means, a first forming roll arranged inside said second wire loop after said dewatering means in the running direction of the web, said first forming roll curving said twin-wire in a first direction of curvature, a second forming shoe arranged inside said first wire loop and after said first forming roll in the running direction of the web, a second forming roll arranged inside said first wire loop and after said second forming shoe in the running direction of the web, said second forming roll curving said twin-wire zone in a second direction of curvature opposite to said first direction, and a guide roll arranged inside said first wire loop and after said second forming roll in the running direction of the web, the web being separated from said second wire at or before said guide roll and being passed on said first wire onto a pick-up fabric. 21. A twin-wire zone in a wire section of a paper machine defined by a pair of wires between which a paper web is carried, comprisinga first forming shoe including a curved ribbed deck and arranged inside a loop of a first one of said wires, web forming means comprising forming ribs and arranged inside said first wire loop, dewatering means arranged opposite said web forming means inside a loop of a second one of said wires, said dewatering means comprising a first and second suction box, forming ribs and a foil rib, said foil rib being arranged after said first forming shoe and before said web forming means in a running direction of the web, said foil rib removing water from the web through said second wire and causing the removed water to be passed into said first suction box, loading means for loading said forming ribs in at least one of said dewatering means and said web forming means, and a spring blade wire loading device arranged after said first forming shoe and inside said first wire loop, said spring blade wire loading device comprising a frame part, a flexible plate-shaped spring blade having a dragging area structured and arranged to drag against an inner face of said first wire and to follow variations in the thickness of the web, said spring blade being attached from outside its dragging area to said frame part, and spring blade loading means arranged in association with said spring blade for deflecting said spring blade into a curved profile to produce the dragging area and to apply an intensive pressure pulse to the web. 22. The twin-wire zone of claim 21, further comprisinga first forming roll arranged inside said second wire loop after said dewatering means in the running direction of the web, said first forming roll curving said twin-wire in a first direction of curvature, a second forming shoe arranged inside said first wire loop and after said first forming roll in the running direction of the web, a second forming roll arranged inside said first wire loop and after said second forming shoe in the running direction of the web, said second forming roll curving said twin-wire zone in a second direction of curvature opposite to said first direction, and a guide roll arranged inside said first wire loop and after said second forming roll in the running direction of the web, the web being separated from said second wire at or before said guide roll and being passed on said first wire onto a pick-up fabric. 23. A method for dewatering a web in a web former comprising the steps of:forming a web in a twin-wire forming zone between a carrying wire and a covering wire guided in separate loops by guide rolls and web-forming rolls, the twin-wire zone beginning on or after a first one of the guide rolls arranged inside the loop of the covering wire, draining water out of the web through both the carrying wire and the covering wire, arranging a first forming shoe in an initial portion of the twin-wire zone and inside the loop of the carrying wire or inside the loop of the covering wire, providing the first forming shoe with a ribbed deck, arranging a dewatering unit after the first forming shoe in the running direction of the web inside the same wire loop as the first forming shoe, arranging a web forming unit opposite the dewatering unit inside the other of the wire loops from the dewatering unit, providing the dewatering and web forming units with forming ribs, loading the forming ribs in at least one of the dewatering unit and the web forming unit by means of pressure-medium hose arrangements, separating the web from the covering wire after the twin-wire zone so that the web runs on the carrying wire, and transferring the web on the carrying wire to a pick-up point where the web is detached from the carrying wire, arranging a spring blade wire loading device after the first forming shoe in the running direction of the web, said spring blade wire loading device comprising a frame part and a flexible plate-shaped spring blade having a dragging area structured and arranged to drag against an inner face of one of said wires and to follow variations in the thickness of the web, said spring blade being attached from outside its dragging area to said frame part, and applying a pressure pulse to the web by loading the spring blade to defied said spring blade into a curved profile to produce the dragging area such that the formation of the web is improved and the dewatering of the web is promoted. 24. The method of claim 23, further comprising adjusting a linear load of the pressure pulse applied by the spring blade in a cross-machine direction in order to control profiles of dewatering of the web, distribution of fillers in the web, formation of the web, and/or retention of water in the web in the cross-machine direction.
25. The method of claim 23, further comprising arranging the first forming shoe and the wire loading device inside the loop of the carrying wire.
26. The method of claim 23, further comprisingarranging a second forming shoe after the dewatering and web forming units in the running direction of the web, providing the second forming shoe with a ribbed deck, and guiding the twin-wire zone along a curved path formed by the ribbed deck. 27. The method of claim 26, further comprisingproviding the first and second forming shoes with suction boxes connected to a source of negative pressure, providing the dewatering and web forming units with suction boxes connected to a source of negative pressure, and controlling the dewatering of the web by adjusting the level of negative pressure in the suction boxes in the forming shoes and dewatering and web forming units. 28. The method of claim 23, further comprising arranging the web former as a hybrid former byfeeding a pulp suspension jet from a headbox onto a loop of the carrying wire, providing the carrying wire with a substantially horizontal initial part, draining water from the web through the carrying wire in the initial part by means of dewatering members, arranging the first forming shoe inside the loop of the carrying wire, removing water from the web through the covering wire by means of a foil rib connected to a first suction box through a drain duct, arranging the foil rib after the first forming shoe in the running direction of the web and inside the loop of the covering wire, arranging the spring blade wire loading device inside the loop of the carrying wire and after the foil rib in the running direction of the web, dewatering the web by means of ribs arranged in the loop of the covering wire and the loop of the carrying wires, and arranging one of the ribs to operate in an area of a loading zone of the spring blade. 29. The method of claim 28, further comprisingarranging a first forming roll inside the loop of the covering wire, curving the twin-wire zone upward by means of a curved sector on the first forming roll, arranging a curved-faced second forming shoe and thereafter a second forming roll inside the loop of the carrying wire, curving the twin-wire zone downward by means of a curved sector on the second forming roll, then separating the web from the covering wire at or before a second one of the guide rolls arranged inside the loop of the covering wire direction of the web, and passing the web on the carrying wire onto a pick-up fabric. Description
DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a hybrid web former is illustrated comprising a headbox 110 having a slice 112 through which a pulp suspension is fed onto a substantially horizontal initial part 10a of the former formed by a lower wire 10. In the initial part 10a, a breast board 12 and foil ribs 13 are arranged. The passage of the lower run of the lower wire 10 is guided by guide rolls 19. The former includes an upper-wire unit 50 having a frame part 51, 52 on which rolls 21, 22, 23, 24 are mounted. Rolls 21, 22, 23, 24 determine the run of a loop of an upper-wire 20. Rolls 21 and 22 of the upper-wire unit 50 and suction boxes 53 and 54 are connected to frame part 51. Frame part 51 is connected to the rest of the frame part of the upper-wire unit 50 from above a forming shoe 14 by means of horizontal articulated joints or linkages 51b. At an opposite end from linkages 51b, the frame part 51 is connected to lifting devices 51a. By means of lifting devices 51a, the frame part 51 of the upper-wire unit, together with the connected devices mentioned above, can be raised to an upper position, for example, for maintenance work.
In the web former illustrated in FIG. 1, a twin-wire dewatering and forming zone starts at line V.sub.1 on a curved box or forming shoe 30 and ends at line V.sub.2 on the roll 23. According to FIG. 1, the forming shoe 30 is arranged inside a loop of the lower-wire 10 in the twin-wire zone after the guide roll 21 of the upper wire 20. The forming shoe 30 has a ribbed deck 31 which curves downwards with a curve radius R.sub.1. After the forming shoe 30, there is a dewatering foil 55 arranged inside the upper-wire loop 20 as shown in FIGS. 3 and 4. A draining duct 56 is placed in front of the dewatering foil 55 and communicates with a suction box 53.
Forming unit 32 and suction box 54 are followed by sector a of the forming roll 22, on which sector the run between the upper wire 20 and lower wire 10 turn upwards. After the forming roll 22, there is a short straight joint run of the wires 10 and 20 leading to a forming shoe 14. Forming shoe 14 is followed by a short straight joint run of the wires 10 and 20 and thereafter, forming roll 15 arranged inside the lower-wire loop 10. On a sector b of forming roll 15, the run of the wires 10, 20 turns downwards to become a straight run. In this straight run, there are suction flatboxes 16 arranged inside the loop of the lower wire 10 so that by means suction through flatboxes 16, the web W will be directed to follow the lower wire 10. The web W is thereafter separated from the lower wire 10 on the run between rolls 17 and 18 on a suction sector 60a of a pick-up roll 60. At the pick-up point 60, the web W is transferred onto a pick-up fabric 61 and then passed to the press section (not shown).
As illustrated in FIGS. 1, 3 and 4, the initial portion 10a of the twin-wire forming zone V.sub.1 -V.sub.2 of a hybrid former includes an important feature of the present invention. According to FIG. 3, the web W.sub.0 is couched in the single-wire initial part 10a so that its dry solids content k.sub.0 is in the range of about 1.5% to about 2.5%.
The first guide roll 21 placed inside the upper-wire loop 20 is not a forming roll proper, rather it is preferably a smooth-faced and solid-faced roll. Guide roll 21 is followed by the first forming shoe 30 placed inside the lower-wire loop 10, which forming shoe has a ribbed deck having a large curve radius R.sub.1 which curves the twin-wire zone downward. The curve radius R.sub.1 of the shoe 30 is generally in the range of about 3 m to about 8 m, preferably R.sub.1 is about 5 m. In some applications of the present invention, the forming shoe 30 can be replaced by pre-loading members, such as in a MB-former.
After the forming shoe 30 or equivalent forming member, the web forming unit 32 is arranged inside the lower-wire loop 10 and attached to fastening parts 33 of side frames of the former by means of fastening devices 35. In this manner, the position of the forming unit 32 can be adjusted substantially in the horizontal direction S--S. Two subsequent draining boxes 53 and 54 are arranged inside the upper-wire unit 50, facing the forming shoe 30 and the forming unit 32. These draining boxes 53, 54 are connected to sources of negative pressure by means of ducts 53b and 54b, respectively. At a rear edge of the first draining box 53, a foil rib 55 is arranged having a tip 55a which removes water through the upper wire 20 in the direction of the arrow S.sub.1 denoted in FIG. 4.
Water is removed from the web W through the upper wire 20 and passes in the direction of the arrow S.sub.1 along an upwards inclined duct 56 into the first suction box 53 by the effect of the kinetic energy of the draining water and the effect of the suction of the negative pressure present in the box 53. From the first suction box 53, the water drained from the web W is removed to one side of the former through a draining duct 53a.
According to FIGS. 3 and 4, a second draining box 54 operates and is arranged facing the forming unit 32 and inside the upper-wire loop 20. A bottom face of the second draining box 54 consists of a plurality of subsequent loading ribs 56a, 56b, 56c . . . , preferably between three and five, which are attached to fastening ribs 57 by means of dovetail grooves 58 in the loading ribs 56a, 56b, 56. In this manner, the loading ribs are replaceable quickly by pulling them to the side of the machine and removing them from the web former.
In the area of the ribs 37, 38a, 38b, 56a, 56b and 56c, the run of the twin-wire zone is very gently wave-formed with a low amplitude. This wave shape promotes the dewatering and the formation of the web and reduces the tendency of wrinkle formation in the wires 10, 20. The spaces between the ribs 56a, 56b and 56c connect to the negative pressure present in the suction box 54. The level of negative pressure present in the first suction box 53 is in the range of about 0 mH.sub.2 O to about 2 mH.sub.2 O. In the second suction box 54, the level of negative pressure is higher, generally in the range of about 0.4 mH.sub.2 O to about 4 mH.sub.2 O. To achieve this level of negative pressure in the second suction box 54, the second suction box 54 is connected to a suction pump which handles smaller quantities of air than a blower connected to the first box 53 through duct 53b.
In order to regulate the dewatering and optimization of the web formation, the positions of the ribs 37, 38a, 38b, 56a, 56b, 56c in the machine direction and the position of the spring blade 45 of the wire loading device 40 can be adjusted. The length L.sub.0 of the dragging area of the loading ribs 37, 38a, 38b, 56a, 56b, 56c in the machine direction is preferably about 30 mm, and the distance L.sub.1 between the ribs in the machine direction is preferably about 25 mm. After the loading area of the blade of the loading device 40, the dry solids content of the web W at the maximum k.sub.max is about 4%.
In the area before the forming roll 22 provided with an open hollow face 22', the dry solids content (k.sub.2) of the web W placed between the wires 10 and 20 is in the range of about 3% to about 5%. In such a situation, this level of dry solids content indicates that there is almost no more freely moving water remaining in the web W by whose means the formation could be affected. Thus, the formation is produced primarily by means of the single-wire initial part 10a of the dewatering zone together with the dewatering and forming members 30, 32, 55, 56a, 56b, 56c, 53, 54. It is characteristic of the construction described above that, by its means, it is possible to remove quite a large proportion of water expressly through the upper wire 20 and thereby compensate for the unevenness of the distribution of fines and fillers that have been produced by the one-sided draining through the lower wire 10 taking place in the single-wire zone 10a.
On the sector a of the open face 22' of the forming roll 22 shown in FIG. 1, the dewatering occurs upwards through the upper wire 20 because of the open face 22' of the roll 22 by the effect of compression between the wires 10 and 20. This upward-directed draining takes place on the curved-faced forming shoe 14 as a result of the dewatering that takes place upwards by the effect of the centrifugal force produced by the curve form R.sub.2 of the forming shoe 14 and also by the effect of the tension between the wires 10 and 20.
On the sector b of the smooth-faced forming roll 15, the pressure of the dewatering that takes upwards is increased substantially. This is achieved so that the radius of the roll 15 can be selected substantially smaller than, for example, the curve radius R.sub.2 of the curved forming shoe 14. On the sector b of the roll 15, the pressure of draining of the water through the upper wire 20 has been dimensioned in maximum proportions so that the radius of the roll 15 determines the dry solids content of the web W. Therefore, suction flatboxes 16 are used to the extent that is necessary to achieve this purpose. However, it is an important principle of the present invention that attempts are made to use a minimum number of suction flatboxes 16, or even to omit them completely when possible, because these dewatering members consume a relatively large amount of energy.
FIGS. 2 and 2A show a gap former in accordance with the invention, whose twin-wire forming zone runs vertically upwards. The carrying wire 10 and the covering wire 20 are guided by their guide rolls 11, 22A and form a forming gap G between them. A pulp suspension jet J is fed out of a discharge opening 111 of a headbox 110 into this forming gap G. At the end of the forming gap G, the twin-wire zone is curved on sector a.sub.0 of the forming roll 22A. The magnitude of sector a.sub.0 is generally from about 20 zone is separated from the forming roll 22A and continues its run guided by a ribbed deck 31 of a forming shoe 30A arranged inside a loop of the carrying wire 10.
In accordance with the invention, FIGS. 2 and 2A, a wire loading device 40 is arranged after the forming shoe 30A and inside the loop of the covering wire 20. A spring blade 45 in the wire loading device 40 produces a strong pressure pulse against an inner face of the covering wire 20. This pressure pulse is effective at the latest at a first loading rib 84 of an MB-unit 80 arranged inside the loop of the carrying wire 10.
After the MB-units 70, 80, the twin-wire zone proceeds as a vertical run on which a suction flatbox 85 is arranged. Water is sucked out from the web W through the carrying wire 10 and removed through gaps in the ribbed deck 86 of the flatbox 85. The vertical run of the twin-wire zone is curved on a suction zone 15a of the second forming roll 15A. Thereafter, the web W is detached from the covering wire 20 and is guided on the carrying wire 10 to the pick-up point (not shown).
In FIGS. 1-4 and mainly in FIG. 4, the details of the construction and the operation of the wire loading device 40 are illustrated. The loading device 40 comprises a thin plate-like spring blade 45 having a tip 45a which may be rounded. The spring blade 45 extends as a unified construction across the entire width of the web W and the wires 10, 20. The area of the tip 45a of the spring blade 45 may be provided with perforations. The spring blade 45 loads and drags against the inner face of the wire 10; 20 by means of its wide side. At its opposite edge, the spring blade 45 is attached to a frame part 41 of the loading device 40 by means of a fastening piece 42 and a screw 43. The blade 45 operates as a plate spring so that when it is loaded by one edge and becomes curved, a dragging and loading pressure is produced against the wire 10. The blade 45 is stationary and drags "with the fur" against the wire 10 that it loads. In this manner, the spring blade follows the variations in the thickness of the web transmitted through the wire.
In the web formers illustrated in FIGS. 5 and 6, the twin-wire zone has a short straight run after the forming roll 22A. The straight run is followed by a forming shoe 30A provided with a ribbed deck 31 similar to what has been described above with respect to FIGS. 2 and 2A. The suction box 32 of the forming shoe 30A communicates with a source of negative pressure, such as a suction pump, which is illustrated by arrow S.sub.0. The ribbed deck 31 of the forming shoe 30A has a curve radius R.sub.1 is about 3 m to about 8 m, preferably R.sub.1 is about 5 m.
The suction box of the forming shoe 30A is directly connected with a first suction box 89 in the MB-unit 80A. The first suction box 89 is connected to a source of negative pressure as illustrated by arrow S.sub.2. The suction box 89 is provided with a ribbed deck 81 which has an initial portion which guides the twin-wire zone along a straight run D.sub.1 up to the forming rib 81A. The forming rib 81A is placed substantially in the middle of the suction box 89. Ribs on the ribbed deck 81 are mounted in such a way that, with respect to a first straight run D.sub.1, the twin-wire zone will be guided along a second straight run D.sub.2. Between the straight runs D.sub.1, D.sub.2, there is a small deflection angle of a few degrees, whose "tip" is placed facing the rib 81A so that the twin-wire zone has a non-linear path in its entire run through the MB-unit 80A.
Suction box 89 of MB-unit 80A is followed almost immediately by or connected to a second forming shoe 30B, whose suction box 33 communicates with a source of negative pressure illustrated by arrow S.sub.3. Ribs 31 on a guide deck of the second forming shoe 30B are placed so that the forming shoe 30B guides the twin-wire zone with the curve radius R.sub.3, which has the same direction as the curve radius R.sub.1 of the first forming shoe 30A. The curve radius R.sub.3 is selected substantially equal to, or somewhat larger than, the curve radius R.sub.1. Opposite to MB-unit 80A on the other side of the twin-wire zone, MB-unit 70A is arranged inside the loop of the covering wire 20. Suction box 78 in MB-unit 70A is connected to and communicates with a source of negative pressure illustrated by arrow S.sub.4.
In the MB-unit 70A, the ribs 71, 72 operate against the inner face of the wire 20 and are loaded by pairs of pressure medium hoses 75a, 75b. The ribs 71, 72 are also interconnected in pairs by means of intermediate parts 73 in the manner shown in more detail in FIG. 2A. The operation of the MB-unit 80A, 70A is, in other respects, similar to that described above in relation to FIGS. 2 and 2A.
According to FIG. 5, the second forming shoe 30B is followed by a suction flatbox 79 arranged inside the loop of the covering wire 20 and, thereafter, by two suction flatboxes 85a and 85b arranged inside the loop of the carrying wire 10. After suction flatboxes 85a, 85b, the construction and the run of the web W are similar to that described in relation to FIG. 1. In FIGS. 5 and 6, the directions and routes of dewatering of the web are illustrated by arrows WA.
Referring to FIG. 7, in a preferred embodiment, the area of the spring blade 45 that will load and drag against the wire 10; 20 can be provided with a wear piece or a wear-resistant coating, e.g. with a ceramic layer. This wear-resistant coating is represented by the dashed line denoted with reference numeral 115 and is arranged on the spring blade 45 over a length of the loading area A.sub.0 of the blade in the longitudinal direction of the blade.
Other features of the spring blade are described at length in U.S. Ser. No. 07/829,953, the specification of which is incorporated herein. In certain preferred embodiments, the spring blade is a Sym-Pulse commercially available from Valmet Paper Machinery Inc.
This is a continuation of U.S. patent application Ser. No. 08/006,372, filed Jan. 19, 1993, now U.S. Pat. No. 5,395,484.
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