FI129446B

FI129446B - Forming section of a fiber web production line

Info

Publication number: FI129446B
Application number: FI20205551A
Authority: FI
Inventors: Antti Poikolainen
Original assignee: Valmet Technologies Oy
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2022-02-28
Also published as: DE102021113491A1; FI20205551A1

Abstract

The invention relates to a forming section of a fiber web production line, which comprises a headbox (30) having a slice opening with a slice lip (32) configured to feed a slice jet (M) of a fiber suspension to the forming section, and a forming unit formed as a gap forming unit formed between a first wire (10) and a second wire (20), in which forming section the forming unit has first a twin-wire forming part formed between the first and the second wire (10,20) comprising inside a second wire loop (20) formed of the second wire (20) as a first dewatering element a fixed forming shoe and comprising a variable-curvature roll (50) inside a first wire loop (10) formed of the first wire (10). The headbox (30) slice opening slice lip (32) is on the side of the second wire loop (20).

Description

Forming section of a fiber web production line Technical field The invention relates generally to producing of fiber webs. Particularly the invention relates to a forming section according to the preamble of the independent claim 1.

Background As known from the prior art in fiber web production machines, especially in paper and board machines, the fiber web is produced and treated in an assembly formed by a number of apparatuses arranged consecutively in a process line. A typical fiber web production and treatment line comprises a forming section comprising a headbox and a forming unit and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a size press, a calender, a coating section. The production and treatment line also comprise typically at least one winder for forming customer rolls as well as a roll packaging apparatus. The task of the headbox is to supply fiber suspension for the fiber web production into the forming unit. In a multilayer headbox more than one fiber N suspension flows are discharged from the headbox via flow channels for pulp N suspension layers, each for forming one layer of a multiply fiber web. The S headbox comprises a slice opening, through which a slice jet of fiber 8 suspension is fed onto a forming wire of a following forming unit. z 30 - The task of a forming unit is to remove water from fiber suspension fed by the io headbox. When the web is manufactured of watery fiber stock, water in the S stock is removed on the forming section through a forming wire or forming wires for starting the formation of the web. Fibers remain on the forming wire or between the forming wires moving together. Depending on the grade of the web being manufactured, different types of stocks are used. The volume for which water can be removed from different stocks for achieving a web of good quality is a function of many factors, such as e.g. a function of the desired basis weight of the web, the design speed of the machine, and the desired level of fines, fibers and fill materials in the finished product. Many types of water removal devices are known on the forming unit such as foil strips, suction boxes, turning rolls, suction rolls, and rolls provided with an open surface, which have been used in many different arrangements and arrays when trying to optimize the volume, time and location of water being removed when forming the web. The manufacturing a high-quality end-product of desired grade is a function of the volume of dewatering, the dewatering method, the duration of dewatering, and the location of dewatering. When it is desired to improve the water removal capacity and to maintain or improve the guality of the end-product, many times unforeseeable problems are created as the result of which either the water removal volume has to be decreased for maintaining the desired guality or the desired guality has to be sacrificed for achieving the greater water volume. Additionally, it is important to make sure that fine substances etc. of the fiber suspension remain in the fiber suspension during the water removal.

In the gap forming units known form prior art there is typically combined a forming roll with small wrap angle and a long pulsating forming shoe, which provides for good water removal but has high energy consumption. During the in the beginning non-pulsating water removal with the forming roll filtrates the fiber web so much that the static forming element can improve fiber web formation and removes water from the fiber web.

N N The forming sections are sometimes, for example during beginning stages of S producing of a fiber web, run only in “water-run” i.e. no fiber suspension is fed S from the slice opening of the headbox to the forming unit. In prior art E 30 arrangements this has required dimensioning of the first water removal means - such that the first water removal means are able during water-run to deal with 2 entire slice jet of the headbox being water.

S N The forming units of the forming sections often reguire a lot of space due to need of space for wire-loop runs, different types of water removal means and other eguipment.

In patent publication EP1543194B1 is disclosed a twin-wire forming section of a paper or board machine, including forming wires formed as wire loops with the aid of guiding rolls, breast rolls and hitch rolls and/or other such structures, and in the area of the forming wires are arranged at least two successive dewatering zones, whereby at least a part of the first dewatering zone in machine direction is formed with the aid of at least one fixed forming shoe provided with a deck having a curved surface, against which forming shoe one of the forming wires is supported while the opposite forming wire is unsupported in the area of the forming shoe and whereby the latter, that is, the second dewatering zone in machine direction is formed by fixed dewatering blades, which are arranged on one side of the forming wires, are located in the cross-machine direction and are supported against the fibrous stock located in between the forming wires, and in between the dewatering blades there are gaps, and on the other side of the forming wires by dewatering blades, which can be loaded in a controlled manner against the fibrous stock located between them at the gaps in between the fixed dewatering blades in order to cause pulsating dewatering in the fibrous stock in the second dewatering zone, wherein the forming wires are guided from the beginning of the twin-wire forming section into the area of the fixed forming shoe of the first dewatering zone, and the fixed forming shoe is provided with an essentially open surface and it is constructed under the effect of under-pressure arranged under the forming shoe to cause essentially non-pulsating dewatering in the fibrous stock travelling in between the forming wires, which dewatering is applied to the fibrous stock in the area after the leading edge of the forming shoe, wherein N the forming section is a hybrid former and is formed with the aid of a fourdrinier N wire being the opposite forming wire and a former unit fitted on top of the S fourdrinier wire, wherein to a gap, formed between the fourdrinier wire and the 8 one of the forming wires being a wire of the former unit forming a twin-wire z 30 former unit gap, the fibrous stock is taken on the fourdrinier wire, wherein a - first dewatering element of the twin-wire forming section includes the lo underpressurized fixed forming shoe, and the wire of the former unit is in S contact with the fixed forming shoe.

O

N In patent publication EP2350385B1 is disclosed a forming section comprises a first and a second wire loop which form a twin-wire zone, which comprises and in which are arranged at least one dewatering element by means of which initial dewatering is performed from pulp suspension fed by the headbox, and at least one dewatering device following said at least one dewatering element in the travel direction of the web, which dewatering device comprises a stationary support shaft on which support elements are supported at a distance from each other, an impermeable belt loop which is led to circle around the stationary support shaft supported by said support elements, wherein said at least one dewatering device further comprises at least one curvilinear dewatering zone over which the wires are led to travel supported by the belt loop, whereby the degree of curvature of the curve of the at least one curvilinear dewatering zone increases in the travel direction of the belt such that increasing dewatering pressure is applied to the pulp suspension travelling between the wires on said at least one curvilinear dewatering zone, which increasing dewatering pressure is dependent on a tension of the wires and a radius of curvature of said at least one curvilinear dewatering zone, wherein the at least one curvilinear dewatering zone is preceded by two dewatering zones prevailing in opposite directions. An object of the invention is to create a forming section, in which the disadvantages and problems of the forming sections known form the prior art are eliminated or at least minimized. An object of the invention is to create an improved forming section comprising at least one a gap-type forming unit.

N Summary

N S In order to achieve the above-mentioned objects, the forming section 8 according to the invention is mainly characterized by the features of the z 30 characterizing clause of the independent claim 1. Advantageous embodiments = and features are disclosed in the dependent claims. 2 S According to the invention the forming section of the fiber web production line N comprises a headbox having a slice opening with a slice lip configured to feed a slice jet of a fiber suspension to the forming section, and a forming unit formed as a gap forming unit formed between a first wire and a second wire,

in which forming section the forming unit has first a twin-wire forming part formed between the first and the second wire comprising inside a second wire loop formed of the second wire as a first dewatering element a fixed forming shoe and comprising a variable-curvature roll inside a first wire loop formed of 5 the first wire, wherein the headbox slice opening slice lip is on the side of the second wire loop. According to an advantageous feature of the invention a very short open slice jet is provided, advantageously 150-250 mm measured from the point at which the slice jet detaches the slice opening to the point at which the slice jet meets the first wire. According to an advantageous feature of the invention the slice jet fed from the slice opening of the headbox is configured to first meet the first wire.

According to an advantageous feature of the invention the slice jet is guided directly in between the first and the second wire. According to the invention the forming unit of the forming section comprises first water removal means, the first water removal means inside the second wire loop of the twin-wire forming part of the forming unit comprises a first and a second suction chamber, the first suction chamber comprises non-pulsating foil lists and the second suction chamber comprises pulsating foil lists. According to an advantageous feature of the invention outer ends of foil lists N of the first and the second suction chamber form a curved surface against the N second wire and are configured to guide the first and the second wire along a S curved run. 3 z 30 According to an advantageous feature of the invention the forming unit of the - forming section comprises first water removal means, the first water removal lo means inside the first wire loop of the twin-wire forming part of the forming unit S comprises a first and a second suction chamber, the first and the second suction chamber comprises non-pulsating shoe lists.

According to an advantageous feature of the invention outer ends of shoe lists of the first suction chamber form a straight surface against the first wire and are configured to guide the first wire along a straight run and outer ends of shoe lists of the second suction chamber form a curved surface against the first wire and are configured to guide the first and the second wire along a curved run. According to an advantageous feature of the invention beginning of the twin- wire forming part the run of the wires is horizontal or vertical or slightly inclined towards the inside of the second wire loop the inclination being at most 30 degrees or inclined towards the inside of the second wire loop the inclination being 20-50 degrees. According to an advantageous feature of the invention the variable-curvature roll comprises a stationary support shaft, an belt loop, which is led to circle around the stationary support shaft, that the variable-curvature roll further comprises at least one curvilinear dewatering zone consisting of at least two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of belt loop. Advantageously the variable-curvature roll comprises a support element supported on the stationary support shaft, that the belt loop led to circle around the stationary support shaft is supported by the support elements and that the belt loop is impermeable. According to an advantageous feature of the invention the twin-wire forming N part comprises as the first dewatering element the fixed forming shoe in the N twin-wire forming part inside the second wire loop.

S S By the forming section according to the invention many advantages are E 30 achieved: During water-run of the forming section the invention provides that - the dimensioning of the first water removal means without special lo requirements as the first water removal means are able during water-run to S deal with the entire slice jet of the headbox being water. The inventive combination of the gap forming unit with foils and the variable-curvature roll provides for the possibility of a compact over all structure and thus space is saved. Additionally, good water removal capacity is achieved. The non-

pulsating water removal in the beginning of the forming unit by the forming shoe followed by the pulsating water removal by the foils combined with the water removal by the variable-curvature roll provides structurally good fiber web, in which fine substance remain, which has good strength properties and formation on good level. The invention also provides energy savings as required power for using the wires of the forming section is significantly decreased due to the possibility of using more water, which “lubricates” the run of the wires during formation, and which is effectively removed by the variable- curvature roll. As the slice lip of the headbox and the first water removal means of the twin-wire zone are on the same side a significantly shortened open slice jet is achieved, advantageously length of open the slice jet is 150 - 250 mm, as in forming sections known from prior art is 400-500 mm. This further decreases the effect of any mistakes in the slice jet to affect the structure of the fiber web. Combination of short open slice jet, non-pulsating water removal in the beginning of the forming section and variable-curvature roll ensures high quality (formation, strength properties etc.) in manufactured fiber web. Brief description of the drawings In the following the invention is explained in detail with reference to the accompanying drawing to which the invention is not to be narrowly limited. In figure 1 is shown schematically an advantageous example of a forming section according to the invention.

N N In figure 2 is shown schematically another advantageous example of a forming S section according to the invention. 3 z 30 In figure 3 is shown schematically an advantageous example of a beginning = part of a forming section according to example of figure 1 or 2. 2 S In figure 4is shown schematically yet an advantageous example of a forming N section according to the invention.

In figure 5 is shown schematically an advantageous example of a beginning part of a forming section according to example of figure 4. In figure 6 is shown schematically further an advantageous example of a forming section according to the invention.

In figure 7 is shown schematically further another advantageous example of a forming section according to the invention.

Detailed description During the course of the following description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous examples.

In the figures some repetitive reference signs have been omitted for clarity reasons.

In figure 1 is shown an example of a forming section comprising a headbox 30, from a slice opening of which a fiber suspension is fed as a slice jet M to a gap between first guide rolls 12A, 22A of a twin-wire forming unit formed between a first, lower wire 10 and a second, upper wire 20 and in which the forming of the fiber suspension fed from the headbox 30 thus begins in the gap forming unit with the twin-wire part followed by and a one wire part on the first wire 10. In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening.

The twin-wire forming part comprises the first wire 10 and the second wire 20, each comprising rolls 12A, 22A; 12, 22 for guiding and N driving the wires 10, 20 as an endless loop.

In the beginning of the twin-wire N forming part the run of the wires 10, 20 is horizontal or slightly inclined towards S the inside of the second wire loop 20. The inclination is at most 30 degrees. 8 The fiber suspension is first fed into the gap formed between the first wire 10 z 30 and the second wire 20 forming the twin-wire part of the forming unit.

The twin- - wire part comprises first water removal means 26 inside the second wire loop lo 20 for removing water by suction so that water is sucked through the wire 20. S There after a variable-curvature roll 50 is located inside the first wire loop 10. The variable-curvature roll 50 guiding the wires 10, 20 to form a turn towards at the location opposite to the variable-curvature roll 50 located water removal means 27 formed by a water collector.

The variable-curvature roll 50 is a roll with decreasing radius, which comprises a stationary support shaft on which support element is supported, an impermeable belt loop which is led to circle around the stationary support shaft supported by the support element.

The variable-curvature roll further comprises at least one curvilinear dewatering zone via which the wires 10, 20 are led to travel supported by the belt loop.

The degree of curvature of the curve of the curvilinear dewatering zone increases in the travel direction of the belt such that increasing dewatering pressure is applied to the stock suspension travelling between the wires 10, 20 on said at least one curvilinear dewatering zone.

Radius of curvature of the curvilinear dewatering zone consists of at least two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop.

Radius of curvature of the curvilinear dewatering zone can contain several curves such that the radius of curvatures decreases in the running direction of the wires 10, 20. The variable-curvature roll is for example described in more detail in applicant's WO patent application publication WO 2010/046527 and in applicant's EP patent EP2350385B1 mentioned before.

The variable-curvature roll 50 is followed by inside the first wire loop 10 located a foil//foils 16 for supporting the run of the wire 10. The twin-wire forming is followed by the one wire forming on the first wire 10, during which the fiber web has a substantially horizontal run.

At the one wire part the fiber web is further guided towards a pick-up roll 31 of a press section, where the fiber web is transferred to the press section.

Thus, in this first advantageous example of figure 1 of a foil gap former type of a forming section the slice jet M from the headbox is guided into the converging gap between the two wires 10, 20. The N slice jet M first hits the first wire 10, in the figure the lower wire 10 and thereafter N the second wire 20, in the figure the upper wire, is brought to contact with the S first wire 20 or the slice jet M is guided directly in between the two wires 10, 8 20. During the twin-wire forming between the two wire 10, 20 first water z 30 removal means 26 are inside the second wire loop 20 and also a slice lip 32 - guiding the slice jet M of the slice opening of the headbox is on the side of the lo second wire loop 20. By this a very short open slice jet M is provided, S advantageously 150-250 mm measured from the point at which the slice jet M detaches the slice opening to the point at which the slice jet M meets the wire.

In this example the water run can be accomplished well as the water passes directly through the first wire 10.

In figure 2 is shown an example of a forming section comprising a headbox 30, from a slice opening of which a fiber suspension or water in the water-run is fed as a slice jet M to a gap between first guide rolls 12A, 22A of a twin-wire forming unit formed between a first, lower wire 10 and a second, upper wire 20 and in which the forming of the fiber suspension fed from the head box 30 thus begins in the gap forming unit with the twin-wire part followed by and a one wire part on the first wire 10. In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening.

The twin-wire forming part comprises the first wire 10 and the second wire 20, each comprising rolls 12A, 22A; 12, 22 for guiding and driving the wires 10, 20 as an endless loop.

In the beginning of the twin-wire forming part the run of the wires 10, 20 is inclined towards the inside of the second wire loop 20. The inclination is advantageously 20-50 degrees.

The fiber suspension is first fed into the gap formed between the first wire 10 and the second wire 20 forming the twin-wire part of the forming unit.

The twin-wire part comprises first water removal means 26 inside the second wire loop 20 for removing water by suction so that water is sucked through the wire 20. There after a variable-curvature roll 50 is located inside the first wire loop 10. The variable-curvature roll 50 guiding the wires 10, 20 to form a turn towards at the location opposite to the variable-curvature roll 50 located water removal means 27 formed by a water collector.

The variable-curvature roll further N comprises at least one curvilinear dewatering zone via which the wires 10, 20 N are led to travel supported by the belt loop.

The degree of curvature of the S curve of the curvilinear dewatering zone increases in the travel direction of the 8 belt such that increasing dewatering pressure is applied to the stock z 30 suspension travelling between the wires 10, 20 on said at least one curvilinear - dewatering zone.

Radius of curvature of the curvilinear dewatering zone lo consists of at least two partial curves such that the radius of curvature of a first S partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop.

Radius of curvature of the curvilinear dewatering zone can contain several curves such that the radius of curvatures decreases in the running direction of the wires 10,

20. The variable-curvature roll is for example described in more detail in applicants WO patent application publication WO 2010/046527 and in applicants EP patent EP2350385B1 mentioned before.

The variable- curvature roll 50 is followed by inside the first wire loop 10 located a foil//foils 16 for supporting the run of the wire 10. The twin-wire forming is followed by the one wire forming on the first wire 10, during which the fiber web has a substantially horizontalrun.

Atthe one wire part the fiber web is further guided towards a pick-up roll 31 of a press section, where the fiber web is transferred to the press section.

Thus, in this first advantageous example of figure 2 of a blade gap former type of a forming section the slice jet M from the headbox is guided into the converging gap between the two wires 10, 20. The slice jet M first hits the first wire 10, in the figure the lower wire 10 and thereafter the second wire 20, in the figure the upper wire is brought to contact with the first wire 20 or the slice jet M is guided directly in between the two wires 10, 20. During the twin-wire forming between the two wire 10, 20 first water removal means 26 are inside the second wire loop 20 and also a slice lip 32 guiding the slice jet M of the slice opening of the headbox is on the side of the second wire loop 20. By this a very short open slice jet M is provided, advantageously 150-250 mm measured from the point at which the slice jet M detaches the slice opening to the point at which the slice jet M meets the wire.

In this example the water run can be accomplished well as the water passes directly through the first wire 10. In figure 3 is shown an example of the beginning part of the forming section N according to examples of figures 1 and 2. The beginning of the forming section N comprises the head box 30, from the slice opening of which the fiber S suspension or water in the water-run is fed as the slice jet M to the gap between 8 the first guide rolls 12A, 22A of the twin-wire forming unit formed between the z 30 first, lower wire 10 and the second, upper wire 20 and in which the forming of - the fiber suspension fed from the head box 30 thus begins in the gap forming lo unit, in which the gap is converging in the running direction of the wires 10, 20. S In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening.

The twin-wire part comprises the first water removal means 26 inside the second wire loop 20 for removing water by suction so that water is sucked through the wire 20. The first water removal means 26 in the example of the figure 3 comprises two suction chambers 26A, 26B under under- pressure.

In the first suction chamber 26A the foil lists 26A1 are advantageously non-pulsating i.e. they do not affect the fiber suspension with substantial pressure pulses.

The non-pulsating effect is provided by using thin foil lists 26A1 and shorth distances between the thin foil lists 26A1. The width of the foil lists 26A1 is advantageously 5-15 mm in running direction of the wires 10, 20 and the distance between two next to each other located foil lists 26A1 in the running direction of the wires 10, 20 is on 5-15 mm.

The second suction chamber 26B comprises pulsating foil lists 26B1 by which pressure pulses are affected to the fiber web and simultaneously water is removed by suction caused by the under-pressure in the suction chamber 26B.

The outer ends of foil lists 26A1, 26B1 of the two suction chamber 26A, 26B of the first water removal means 26 form a curved surface against the wire 20 and thus guide both wires 10, 20 along a curved run, which enhances the attachment of the wires 10, 20 to the foil lists 26A1, 26B1. In figure 4 is shown an example of a forming section comprising a headbox 30, from a slice opening of which a fiber suspension or water in the water-run is fed as a slice jet M to a gap between first guide rolls 12A, 22A of a twin-wire forming unit formed between a first, lower wire 10 and a second, upper wire 20 and in which the forming of the fiber suspension fed from the head box 30 thus begins in the gap forming unit with the twin-wire part followed by and a one wire part on the first wire 10. In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening.

The twin-wire forming part comprises the first wire 10 and the second wire 20, each comprising rolls 12A, N 22A; 12, 22 for guiding and driving the wires 10, 20 as an endless loop.

In the N beginning of the twin-wire forming part the run of the wires 10, 20 is horizontal S or slightly inclined towards the inside of the second wire loop 20. The 8 inclination is at most 30 degrees.

The fiber suspension is first fed into the gap z 30 formed between the first wire 10 and the second wire 20 forming the twin-wire - part of the forming unit.

The twin-wire part comprises first water removal means lo 17 formed of a forming shoe 17 inside the first wire loop 10 and second water S removal means 26 inside the second wire loop 20 for removing water by suction so that water is sucked through the wire 20. The second water removal means 26 are according to the figure 3 description.

There after a variable- curvature roll 50 is located inside the first wire loop 10. The variable-curvature roll 50 guiding the wires 10, 20 to form a turn towards at the location opposite to the variable-curvature roll 50 located water removal means 27 formed by a water collector. The variable-curvature roll 50 is a roll with decreasing radius, which comprises a stationary support shaft on which support element is supported, an impermeable belt loop which is led to circle around the stationary support shaft supported by the support element. The variable-curvature roll further comprises at least one curvilinear dewatering zone via which the wires 10, 20 are led to travel supported by the belt loop. The degree of curvature of the curve of the curvilinear dewatering zone increases in the travel direction of the belt such that increasing dewatering pressure is applied to the stock suspension travelling between the wires 10, 20 on said at least one curvilinear dewatering zone. Radius of curvature of the curvilinear dewatering zone consists of at least two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop. Radius of curvature of the curvilinear dewatering zone can contain several curves such that the radius of curvatures decreases in the running direction of the wires 10,

20. The variable-curvature roll is for example described in more detail in applicants WO patent application publication WO 2010/046527 and in applicants EP patent EP2350385B1 mentioned before. The variable- curvature roll 50 is followed by inside the first wire loop 10 located a foil//foils 16 for supporting the run of the wire 10. The twin-wire forming is followed by the one wire forming on the first wire 10, during which the fiber web has a substantially horizontal run. At the one wire part the fiber web is further guided towards a pick-up roll 31 of a press section, where the fiber web is transferred N to the press section. Thus, in this first advantageous example of figure 4 of a N blade gap former type of a forming section the slice jet M from the headbox is S guided into the converging gap between the two wires 10, 20. The slice jet M 8 first hits the first wire 10, in the figure the lower wire 10 and thereafter the z 30 second wire 20, in the figure the upper wire is brought to contact with the first - wire 20 or the slice jet M is guided directly in between the two wires 10, 20. lo During the twin-wire forming between the two wire 10, 20 first water removal S means 26 are inside the second wire loop 20 and also a slice lip 32 guiding the slice jet M of the slice opening of the headbox is on the side of the second wire loop 20. By this a very short open slice jet M is provided, advantageously 150-250 mm measured from the point at which the slice jet M detaches the slice opening to the point at which the slice jet M meets the wire. In this example the water run can be accomplished well as the water passes directly through the first wire 10.

In figure 5 is shown an example of the beginning part of the forming section according to example of figure 4. The beginning of the forming section comprises the headbox 30, from the slice opening of which the fiber suspension or water in the water-run is fed as the slice jet M to the gap between the first guide rolls 12A, 22A of the twin-wire forming unit formed between the first, lower wire 10 and the second, upper wire 20 and in which the forming of the fiber suspension fed from the headbox 30 thus begins in the gap forming unit, in which the gap is converging in the running direction of the wires 10, 20. In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening. The twin-wire part comprises the first water removal means 17 formed by the forming shoe 17 inside the first wire loop 10 for removing water by suction so that water is sucked through the wire 10. The first water removal means 17 in the example of the figure 5 comprises two suction chambers 17A, 17B under underpressure. In the first and second suction chamber 17A, 17B the shoe lists 17A1, 17B1 are advantageously non- pulsating i.e. they do not affect the fiber suspension with substantial pressure pulses. The non-pulsating effect is provided by using thin shoe lists 17A1, 17B1 and shorth distances between the thin shoe lists 17A1, 17B1. The width of the shoe lists 17A1, 17B1 is advantageously 5-15 mm in running direction of the wires 10, 20 and the distance between two next to each other located foil lists 17A1, 17B1 in the running direction of the wires 10, 20 is on 5-15 mm. N The outer ends of foil lists 17A1 of the suction chamber 17A, of the first water N removal means 17 inside the first wire loop 10 form a straight surface against S the wire 10 and thus guide wire 10 along a straight run. The outer ends of foil S lists 17B1 of the suction chamber 17B of the first water removal means 17 E 30 inside the first wire loop 10 form a curved surface against the wire 10 and thus - guide wire 10 along a curved run R, which enhances the attachment of the 2 wires 10, 20 to the shoe lists 17B1.

S N In figure 6 is shown an example of a forming section comprising a head box 30, from a slice opening of which a fiber suspension or water in the water-run is fed as a slice jet M to a gap between first guide rolls 12A, 22A of a twin-wire forming unit formed between a first wire 10 and a second wire 20 and in which the forming of the fiber suspension fed from the head box 30 thus begins in the gap forming unit with the twin-wire part followed by and a one wire part on the first wire 10. In the headbox slice opening is a slice lip 32, which is advantageously above the slice opening.

In the beginning of the twin-wire forming part the run of the wires 10, 20 is vertical or slightly inclined towards the inside of the second wire loop 20. The inclination is at most 30 degrees.

The twin-wire part comprises first water removal means 26 inside the second wire loop 20 for removing water by suction so that water is sucked through the wire 20. Inside the first wire loop 10 loading lists 18 are located, by which an adjustable load toward the wires 10, 20 is affected at the area of the first water removal means 26 inside the second wire loop 20, at points between the foil lists of the first water removal means 26. There after a variable-curvature roll 50 is located inside the first wire loop 10. The variable- curvature roll 50 guiding the wires 10, 20 to form a turn towards at the location opposite to the variable-curvature roll 50 located water removal means 27 formed by a water collector and further the variable-curvature roll 50 turns the running direction of the wires 10, 20 downwards.

The variable-curvature roll 50 is aroll with decreasing radius, which comprises a stationary support shaft on which support elements are supported at a distance from each other, an impermeable belt loop which is led to circle around the stationary support shaft N supported by the support elements.

The variable-curvature roll further N comprises at least one curvilinear dewatering zone via which the wires 10, 20 S are led to travel supported by the belt loop.

The degree of curvature of the 8 curve of the curvilinear dewatering zone increases in the travel direction of the z 30 belt such that increasing dewatering pressure is applied to the stock - suspension travelling between the wires 10, 20 on said at least one curvilinear lo dewatering zone.

Radius of curvature of the curvilinear dewatering zone S consists of two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop.

Radius of curvature of the curvilinear dewatering zone can contain several curves such that the radius of curvatures decreases in the running direction of the wires 10, 20. The variable-curvature roll is for example described in more detail in applicant's WO patent application publication WO 2010/046527 and in applicant's EP patent EP2350385B1 mentioned before. The variable-curvature roll 50 is followed by inside the first wire loop 10 located a foil//foils 16 for supporting the run of the wire 10. The twin-wire forming is followed by the one wire forming on the first wire 10, during which the fiber web has a substantially horizontal or slightly downwards inclined run. At the one wire part the fiber web is further guided towards a pick-up roll 31 of a press section, where the fiber web is transferred to the press section. Thus, in this first advantageous example of figure 6 of a blade gap former type of a forming section the slice jet M from the headbox is guided into the converging gap between the two wires 10, 20. The slice jet M first hits the first wire 10 and thereafter the second wire 20, in the figure the upper wire is brought to contact with the first wire 20 or the slice jet M is guided directly in between the two wires 10, 20. During the twin-wire forming between the two wire 10, 20 first water removal means 26 are inside the second wire loop 20 and also a slice lip 32 guiding the slice jet M of the slice opening of the headbox is on the side of the second wire loop 20. By this a very short open slice jet M is provided, advantageously 150-250 mm measured from the point at which the slice jet M detaches the head opening to the point at which the slice jet M meets the wire. In this example the water run can be accomplished well as the water passes directly through the first wire

10. In figure 7 is shown an example of a forming section comprising a head box N 30, from a slice opening of which a fiber suspension or water in the water-run N is fed as a slice jet M to a gap between first guide rolls 12A, 22A of a twin-wire S forming unit formed between a first wire 10 and a second wire 20 and in which 8 the forming of the fiber suspension fed from the head box 30 thus begins in z 30 the gap forming unit with the twin-wire part followed by and a one wire part on - the first wire 10. In the headbox slice opening is a slice lip 32, which is lo advantageously above the slice opening. The twin-wire forming part comprises S the first wire 10 and the second wire 20, each comprising rolls 12A, 22A; 12, N 22 for guiding and driving the wires 10, 20 as an endless loop. In the beginning of the twin-wire forming part the run of the wires 10, 20 is vertical or slightly inclined towards the inside of the second wire loop 20. The inclination is at most 30 degrees.

The twin-wire part comprises first water removal means 17 formed of a forming shoe 17 inside the first wire loop 10 and first water removal means 26 inside the second wire loop 20 for removing water by suction so that water is sucked through the wire 20. There after a variable-curvature roll 50 is located inside the first wire loop 10. The variable-curvature roll 50 guiding the wires 10, 20 to form a turn towards at the location opposite to the variable-curvature roll 50 located water removal means 27 formed by a water collector and further the variable-curvature roll 50 turns the running direction of the wires 10, 20 downwards.

Radius of curvature of the curvilinear dewatering zone can contain several curves such that the radius of curvatures decreases in the running direction of the wires 10, N 20. The variable-curvature roll is for example described in more detail in N applicants WO patent application publication WO 2010/046527 and in S applicants EP patent EP2350385B1 mentioned before.

The variable- 8 curvature roll 50 is followed by inside the first wire loop 10 located a foil//foils z 30 16 for supporting the run of the wire 10. The twin-wire forming is followed by - the one wire forming on the first wire 10, during which the fiber web has a lo substantially horizontal or slightly downwards inclined run.

At the one wire part S the fiber web is further guided towards a pick-up roll 31 of a press section, where the fiber web is transferred to the press section.

Thus, in this first advantageous example of figure 7 of a foil gap former type of a forming section the slice jet M from the headbox is guided into the converging gap between the two wires 10, 20. The slice jet M first hits the first wire 10, in the figure the lower wire 10 and thereafter the second wire 20, in the figure the upper wire is brought to contact with the first wire 20 or the slice jet M is guided directly in between the two wires 10, 20. During the twin-wire forming between the two wire 10, 20 first water removal means 26 are inside the second wire loop 20 and also a slice lip 32 guiding the slice jet M of the slice opening of the headbox is on the side of the second wire loop 20. By this a very short open slice jet M is provided, advantageously 150-250 mm measured from the point at which the slice jet M detaches the slice opening to the point at which the slice jet M meets the wire. In this example the water run can be accomplished well as the water passes directly through the first wire 10.

In the description in the foregoing, although some functions and elements have been described with reference to certain features and examples, those functions and elements may be performable by other features and examples whether described or not. Although features have been described with reference to the certain examples, those features may also be present in other examples whether described or not.

Above only some advantageous examples of the inventions have been described to which examples the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

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Claims

1. Forming section of a fiber web production line, which comprises a headbox (30) having a slice opening with a slice lip (32) configured to feed a slice jet (M) of a fiber suspension to the forming section, and a forming unit formed as a gap forming unit formed between a first wire (10) and a second wire (20), in which forming section the forming unit has first a twin-wire forming part formed between the first and the second wire (10,20) comprising inside a second wire loop (20) formed of the second wire (20) as a first dewatering element a fixed forming shoe and comprising a variable-curvature roll (50) inside a first wire loop (10) formed of the first wire (10), characterized in that the headbox (30) slice opening slice lip (32) is on the side of the second wire loop (20), that the forming unit of the forming section comprises first water removal means (26), that the first water removal means (26) inside the second wire loop (20) of the twin-wire forming part of the forming unit comprises a first and a second suction chamber (26A, 26B), that the first suction chamber (26A) comprises non-pulsating foil lists (26A1) and that the second suction chamber (26B) comprises pulsating foil lists (26B1).

2. Forming section according to claim 1, characterized in that a very short open slice jet (M) is provided, advantageously 150-250 mm measured from the point at which the slice jet (M) detaches the slice opening to the point at which the slice jet (M) meets the first wire (10).

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3. Forming section according to claim 1 or 2, characterized in that in the S slice jet (M) fed from the slice opening of the headbox (30) is configured 8 to first meet the first wire (10). z 30 -

4. Forming section according to claim 1 or 2, characterized in that the 2 slice jet (M) is guided directly in between the first and the second wire 3 (10, 20).

5. Forming section according to claim 1, characterized in that outer ends of foil lists (26A1, 26B1) of the first and the second suction chamber (26A, 26B) form a curved surface against the second wire (20) and are configured to guide the first and the second wire (10, 20) along a curved run.

6. Forming section according to any of the previous claims, characterized in that the forming unit of the forming section comprises first water removal means (17), that the first water removal means (17) inside the first wire loop (10) of the twin-wire forming part of the forming unit comprises a first and a second suction chamber (17A, 17B), that the first and the second suction chamber (17A, 17B) comprises non- pulsating shoe lists (17A1; 17B1).

7. Forming section according to claim 6, characterized in that outer ends of shoe lists (17A1) of the first suction chamber (17A) form a straight surface against the first wire (10) and are configured to guide the first wire (10) along a straight run and outer ends of shoe lists (17B1) of the second suction chamber (17B) form a curved surface against the first wire (10) and are configured to guide the first and the second wire (10, 20) along a curved run (R).

8. Forming section according to any of the claims 1-6, characterized in that in beginning of the twin-wire forming part the run of the wires (10, 20) is horizontal or vertical or slightly inclined towards the inside of the N second wire loop (20) the inclination being at most 30 degrees or N inclined towards the inside of the second wire loop (20) the inclination S being 20-50 degrees.

3 z 30 9. Forming section according to any of the previous claims, - characterized in that the variable-curvature roll (50) comprises a lo stationary support shaft, an belt loop, which is led to circle around the S stationary support shaft, that the variable-curvature roll (50) further comprises at least one curvilinear dewatering zone consisting of at least two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of belt loop.

10. Forming section according to claim 9, characterized in that the variable-curvature roll (50) comprises a support element supported on the stationary support shaft, that the belt loop led to circle around the stationary support shaft is supported by the support element and that the belt loop is impermeable.

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