FI20227069A1 - Fiber web production line for producing a multi-layer fiber web - Google Patents

Abstract

The invention relates to a fiber web production line (100) for producing a multi-layer fiber web (W), which fiber web production line (100) comprises a forming section (110), a press section (120) and a drying section (130), which forming section (110) comprises a headbox (30) and a twin-wire forming unit formed between a common run of a first, lower wire loop (10) and a second, upper wire loop (20), which press section (120) comprises three press nips and which drying section (130) comprises at least one drying group with a single-wire draw. The headbox (30) is a multi-layer headbox and draw of the multi-layer fiber web (W) from the press section (120) to the drying section (130) is a closed draw.

Description

Fiber web production line for producing a multi-layer fiber web

Technical field

The invention relates generally to producing of fiber webs. Particularly the invention relates to a fiber web production line for producing a multi-layer fiber web 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 . 25 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

N headbox comprises a slice opening, through which a slice jet of fiber

S suspension is fed onto a forming wire of a following forming unit.

N

= 30 The task of a forming unit is to remove water from fiber suspension fed by the > 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

N wires for starting the formation of the web. Fibers remain on the forming wire

N 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 quality 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 quality or the desired quality 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.

A commonly used method of making a multi-ply fiber web is based on the use of several separate web forming units in which the different layers of the web are caused to be drained in a layer-by-layer fashion either onto one another or onto separate wires, in which case they are combined with one another after partial dewatering. Typically in multi-ply / multi-layer fiber web production i.e. when producing a fiber web having more than one layers term “multi-ply” is » 25 used when the layers are formed separately in the forming section and term

N “multi-layer” is used when a multi-layer headbox is used for feeding suspension

N layers to the forming section even though these terms multi-ply / multi-layer

S are used very often synonymously and thus the difference can be defined by

N the context only.

E 30 o Fiber webs, especially paper and board are available in a wide variety of types

C and can be divided according to basis weight in two grades: papers with a

N single ply and a basis weight of 25-300 g/m? and boards manufactured in

N multiply technology and having a basis weight of 150-600 m/m?. It should be noted that the borderline between paper and board is flexible since board grades with lightest basis weights are lighter than the heaviest paper grades.

Generally speaking, paper is used for printing and board for packaging. The present invention relates especially to production of multiply board webs. In particular the invention relates to forming of folding box boards (FBB) and solid bleached (sulfate) boards (SBS). FBB is used for various types of packaging purposes, for example for packaging food, confectionery, cosmetics, pharmaceuticals. The basis weight of FBB is 160-450 g/m? and it has typically three layers, each surface layer typically has the basis weight of about 45 g/m?.

SBS is also used for various types of packaging purposes similar to those of the FBB, especially for chocolate and cigarettes. The production lines for FBB and SBS have typically a separate headboxes and forming units for each ply.

A disadvantage of three fourdrinier forming units is thus caused high energy consumption. The fourdrinier forming units have also relatively low running speed. The production line for FBB also typically has a MG dryer (Yankee cylinder) for surface smoothness and the production line for SBS is typically provided with a wet stack calender for smoothness but bulkiness is reduced simultaneously. Often in production of FBB or SBS multiply board grades problems exists as not strong enough bonding strength between the layers of the multiply board web, which have been tried to be solved by internal sizing with pulp size and by adding starch or other sizing agent between the layers.

An object of the invention is to create a fiber web production line for producing a multi-layer fiber web, in which the disadvantages and problems of the fiber web production lines known form the prior art are eliminated or at least minimized. ; 25

N An object of the invention is to create an improved fiber web production line for

N producing a multi-layer fiber web, in which by means of one forming section

S multi-layer fiber web products can be produced such, that bottom surface of

Q the fiber web is smooth and simultaneously in the forming section high water

E 30 removal capacity is achieved. 5

Summary

N

S

N In order to achieve the above-mentioned objects, the fiber web production line for producing a multi-layer fiber web according to the invention is mainly characterized by the features of the characterizing clause of the independent claim 1. Advantageous embodiments and features are disclosed in the dependent claims.

According to the invention the fiber web production line for producing a multi- layer fiber web comprises a forming section, a press section and a drying section, which forming section comprises a headbox and a twin-wire forming unit formed between a common run of a first, lower wire loop and a second, upper wire loop, which press section comprises three press nips and which drying section comprises at least one drying group with a single-wire draw, wherein the headbox is a multi-layer headbox and that draw of the multi-layer fiber web from the press section to the drying section is a closed draw.

According to an advantageous feature of the invention the forming section comprises as first water removal means inside the first wire loop arranged non- pulsating water removal unit and as second water removal means inside the second wire loop arranged a pulsating water removal unit.

According to an advantageous feature of the invention the forming section comprises a variable-curvature roll located inside the first wire loop and at a location opposite to the variable-curvature roll is located water removal means formed by a water collector.

According to an advantageous feature of the invention in the forming section beginning of the twin-wire forming part the run of the wires is inclined towards . 25 the inside of the second wire loop, the variable-curvature roll guiding the wires

N forms a turn and end of the twin-wire forming part the run of the wires is inclined

N towards inside of the first wire. <Q

Q According to an advantageous feature of the invention the forming section

E 30 comprises inside the first wire loop located a suction boxes. >

According to an advantageous feature of the invention in the press section first

N press nip is provided as a press nip formed between a suction roll and a

N deflection compensated roll, second press nip is provided as a nip formed between the suction roll and a center roll and third press nip is provided as a nip between the center roll and an extended nip roll.

According to an advantageous feature of the invention the press section comprises four press fabrics: as first and second press fabrics two press felts with a common run and as a third press fabric a metal belt or a transfer belt 5 and as a fourth press fabric a press felt with a common run followed by a one fabric run of the metal belt or the transfer belt.

According to an advantageous feature of the invention in the drying section the at least one drying group provided with the single-wire draw is a so-called normal group, in which drying cylinders are placed in an upper horizontal row and reversing rolls are placed in a lower horizontal row.

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.

According to an advantageous feature of the invention 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 element and that the belt loop is impermeable. ‘ 25

N By the fiber web production line for producing a multi-layer fiber web according

N to the invention many advantages are achieved: The inventive combination of

S the forming unit, the press section and the drying section provides for

N producing of multi-layer fiber web products with smooth bottom surface. z 30 Additionally, good water removal capacity is achieved. The non-pulsating > water removal in the beginning of the forming unit followed by the pulsating

S water removal combined with the water removal by the variable-curvature roll

N provides structurally good fiber web, in which fine substance remain, which

N has good strength properties and formation on good level.

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 fiber web production line of a multi-layer fiber web 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 figure some repetitive reference signs have been omitted for clarity reasons.

In figure 1 is shown an example of a fiber web production line 100 comprising a forming section 110, a press section 120 and a drying section 130 for producing a multi-ply fiber web W, in this example for a two-layer fiber web W.

The forming section 110 comprises a multi-layer headbox 30, from which the stock suspension M is fed 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 thus begins in the gap forming unit with the twin-wire part followed by and a one wire part on the first wire 10. » 25 The multi-layer headbox 30 in the example is a multi-layer headbox for two

N layers, which layers can be of same or of different stock. The multilayer

N headbox comprises headers 31, 32, from which the pulp suspensions for each

S layer of a multiply board web are fed to manifold tubes to an egualization

Q chamber and further via a turbulence generator to slice channels ending to a

I 30 slice opening in the multi-layer headbox 30. Advantageously, the header 31 > for the layer top of the multiply board web comprises a dilution control device

S 33. Also, the header 32 for the bottom layer of the multiply board web may

N comprise a dilution control. The multilayer headbox 30 is advantageously a so

N called Agua-headbox, of which one example is described in EP-patent publication 2784213. Agua-header 34 is connected to corresponding distribution header in the multi-layer headbox, which feeds white-water between the layers of the multiply board web for forming an Aqua-layer between the layers of the multiply board web. Additionally, the white-water may contain chemicals, fillers and/or fine substances. By the Aqua layer, the layer purity is improved. Additionally, the inner strength of the multiply board web can be improved ty the chemical, filler and/or fine substance additions between the layers of the multiply board web. The aqua layer is combined to the stock suspension after the separation elements and by that way white-water prevents mixing of the stock suspensions.

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 10-50 degrees. The fiber suspension is first fed into the gap formed between the first guide rolls 12A, 22A 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 14 inside the first wire loop 10 for removing water by non-pulsating water removal unit 14 so that water is removed through the first wire 10. The twin-wire part comprises as second water removal means 26 inside the second wire loop 20 for removing water by a pulsating water removal unit 26 so that water is removed through the second wire 20. There after a variable-curvature roll 15 is located inside the first wire loop 10. The variable-curvature roll 15 guiding the wires 10, 20 forms a turn and the run of the wires is thus inclined towards inside of the first wire 10. At » 25 the location opposite to the variable-curvature roll 15 is located water removal

N means 21 formed by a water collector. The variable-curvature roll 15 is a roll

N with decreasing radius, which comprises a stationary support shaft on which

S support element is supported, an impermeable belt loop which is led to circle

Q around the stationary support shaft supported by the support element. The z 30 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.

S The degree of curvature of the curve of the curvilinear dewatering zone

N increases in the travel direction of the belt such that increasing dewatering

N 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 2010/046527 and in applicants EP patent 2350385 B1. The variable-curvature roll 15 is followed by inside the first wire loop 10 located a suction boxes 16, 17 for removing water through the first wire 10. The twin-wire forming is followed by the one wire forming on the first wire 10. This kind of web layer combining arrangement is beneficial in the cases where quality of the bottom side of the fiber web W is significant, for example forms printing surface of the multi-ply board.

At the one wire part the fiber web W is further guided towards a pick-up roll 53 of the press section 120, whereby the fiber web W is transferred to a first press fabric 50 of the press section 120. The press section 120 comprises four press fabrics: as first and second press fabrics two press felts 40, 50 with a common run and thereafter as a third press fabric a metal belt 60 or a transfer belt 60 and as a fourth press fabric a press felt 70 with a common run followed by a short one fabric run of the metal belt 60 or the transfer belt 60. The press fabrics 40, 50, 60, 70 each comprises rolls 42, 52, 62, 72 for guiding and driving the fabrics 40, 50, 60, 70 as an endless loop. In case the metal belt 60 is used as the third press fabric it is advantageously heated by heating means (not » 25 shown). In the press section 120 first press nip is provided as the nip formed

N between a suction roll 55 and a deflection compensated roll 45, second press

N nip is provided as the nip formed between the suction roll 55 and center roll 65

S and third press nip is provided as the nip between center roll 65 and an

Q extended nip roll 75. Advantageously the center roll 65 is also deflection

I 30 compensated roll. Thus, in the press section the fiber web W is dewatered by > pressing it by means of three successive press nips. This type of press section

S 120 is beneficial in the cases where quality of the bottom side of the fiber web

N W is significant, for example forms printing surface of the multi-ply board as

N the bottom surface is in the press section against the transfer belt or metal belt 60.

After the press section 120 the fiber web W is guided to the drying section 130 to first pick-up suction roll 83 of a drying wire 80 of the drying section 130 as closed draw from the third press fabric 60 to the drying wire 80. In the figure only first drying group of the drying section 120 is shown. In addition the drying section 130 may comprise more drying groups, advantageously drying groups with single-wire draw, and/or other drying devices. The drying group is provided with single wire draw and is a so-called normal group, in which drying cylinders 85 are placed in an upper horizontal row and reversing rolls 84 are placed in a lower horizontal row. The drying wire 80 is guided by guide rolls 72. The drying wire 80 presses the fiber web W to be dried on the drying cylinders 85 against their heated surfaces, and on the reversing rolls 84 the fiber web W remains on the outer surface of the drying wire 80 at side of outside curve.

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 . 25 many modifications and alterations are possible within the invention.

N

O

N

LÖ

<Q

O

N

I

=

E

O

O

N

N

QA

O

N

Claims (10)

Claims

1. Fiber web production line for producing a multi-layer fiber web (W), which fiber web production line (100) comprises a forming section (110), a press section (120) and a drying section (130), which forming section (110) comprises a headbox (30) and a twin-wire forming unit formed between a common run of a first, lower wire loop (10) and a second, upper wire loop (20), which press section (120) comprises three press nips and which drying section comprises at least one drying group with a single-wire draw, characterized in that the headbox (30) is a multi-layer headbox and that draw of the multi- layer fiber web (W) from the press section (120) to the drying section (130) is a closed draw.

2. Fiber web production line according to claim 1, characterized in that the forming section (110) comprises as first water removal means (14) inside the first wire loop (10) arranged non-pulsating water removal unit (14) and as second water removal means (26) inside the second wire loop (20) arranged a pulsating water removal unit (26).

3. Fiber web production line according to claim 1 or 2, characterized in that the forming section (110) comprises a variable-curvature roll (15) located inside the first wire loop (10) and that at a location . 25 opposite to the variable-curvature roll (15) is located water removal N means (21) formed by a water collector (21). N

S 4. Fiber web production line according to claim 3, characterized in that N in the forming section (110) beginning of the twin-wire forming part I 30 the run of the wires (10, 20) is inclined towards the inside of the > second wire loop (20), that the variable-curvature roll (15) guiding S the wires (10, 20) forms a turn and that end of the twin-wire forming N part the run of the wires (10, 20) is inclined towards inside of the first N wire (10).

5. Fiber web production line according to any of the previous claims, characterized in that the forming section (110) comprises inside the first wire loop (10) located a suction boxes (16, 17).

6. Fiber web production line according to any of the previous claims, characterized in that in the press section (120) first press nip is provided as a press nip formed between a suction roll (55) and a deflection compensated roll (45), second press nip is provided as a nip formed between the suction roll (55) and a center roll (65) and third press nip is provided as a nip between the center roll (65) and an extended nip roll (75).

7. Fiber web production line according to any of the previous claims, characterized in that the press section (120) comprises four press fabrics: as first and second press fabrics two press felts (40, 50) with a common run and as a third press fabric a metal belt (60) or a transfer belt (60) and as a fourth press fabric a press felt (70) with a common run followed by a one fabric run of the metal belt (60) or the transfer belt (60).

8. Fiber web production line according to any of the previous claims, characterized in that in the drying section the at least one drying group provided with the single-wire draw is a so-called normal group, in which drying cylinders (85) are placed in an upper . 25 horizontal row and reversing rolls (84) are placed in a lower N horizontal row. &

S 9. Fiber web production line according to any of the previous claims 3- N 8, characterized in that the variable-curvature roll (15) comprises z 30 a stationary support shaft, an belt loop, which is led to circle around > the stationary support shaft, that the variable-curvature roll further S comprises at least one curvilinear dewatering zone consisting of at N least two partial curves such that the radius of curvature of a first N 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.Fiber web production line according to claim 9, characterized in that the variable-curvature roll (15) 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.

N QA O N LÖ <Q O N I Ao a o O O N N QA O N