Method for controlling a vacuum in a forming part and forming part having a control system for controlling a vacuum in a forming part

Abstract

The invention relates to a method for controlling a vacuum in a forming section (200) and a forming section with a control system for controlling a vacuum in a forming section, the forming section comprising at least one forming unit (250) comprising at least one fourdrinier wire (10) and an arrangement of several successive suction boxes (15A-15E) with controllable vacuum at the fourdrinier wire. The method comprises the following steps of: setting a running direction (S; s1) having a vacuum setpoint value for the last suction tank (15E) of a number of continuous suction tanks (15A-15E) with controllable vacuum; calculating a setpoint value of at least one consecutive suction tank (15A-15D) having a controllable vacuum prior to the last suction tank (15E) from the setpoint values of the succeeding suction tanks on the basis of the vacuum setpoint value of the last suction tank (15E); the vacuum setpoint value (Pi) of the preceding suction tank in the running direction of the forming unit is made smaller than the vacuum setpoint value (Pi + 1) of the succeeding suction tank.

Description

Technical Field

[0001] The present invention generally relates to producing a fiber web. In particular, the present invention relates to a method for controlling a vacuum in a forming section and to a forming section having a control system for controlling a vacuum in a forming section. Background Art

[0002] From the prior art it is known that in fiber web machines, especially paper and board machines, fiber webs are produced and processed in an assembly formed by a plurality of devices arranged in series on a production line. A typical production and processing line comprises: a forming section, including a headbox and a forming unit; a press section; and a subsequent drying section and a reel. The production and processing line may also comprise further devices and sections for finishing the fiber web, such as a size press, a calender, a coating section. The production and processing line also usually comprises at least one winder for forming customer rolls and roll packaging equipment.

[0003] The task of the headbox is to supply the fiber suspension for fiber web production to the forming unit. In a multi-layer headbox, more than one fiber suspension stream is discharged from the headbox through flow channels for a plurality of stock suspension layers, each of which is used to form one of the multi-layer fiber webs.

[0004] The task of the forming unit is to remove water from the fiber suspension supplied by the headbox. When the web is made from an aqueous fiber slurry, the water in the slurry is removed on the forming section by one or more forming wires used to start the forming of the web. The fibers remain on the forming wire or between the forming wires moving together. Different types of slurries are used, depending on the grade of the fiber web being manufactured. The amount of water that can be removed from different slurries in order to obtain a high-quality web depends on many factors (for example, on the desired basis weight of the web, the design speed of the machine, and the desired level of fibrous fragments (fines), fibers and fillers in the finished product). There are many types of devices known on the forming unit, such as forming shoes, foil boxes, suction boxes, turning rolls, suction rolls and rolls with open surfaces, which have been used in many different arrangements and arrangements when trying to optimize the amount, time and location of water removal when forming the fiber web. The production of a high-quality finished product of the desired grade depends on the amount of dewatering, the dewatering method, the dewatering duration and the dewatering location. When it is desired to increase water removal capacity and maintain or improve the quality of the finished product, many times unforeseen problems arise which result in having to reduce the amount of water removed in order to maintain the desired quality, or having to sacrifice the desired quality in order to obtain a greater amount of water.

[0005] Fiber webs, especially paper and board, are available in many types and can be divided into two product grades according to basis weight: single-ply paper with a basis weight of 25-300 g / m2 ; and paperboard manufactured by single-ply or multi-ply technology, with a basis weight of 80-600m / m 2 It should be noted that the boundary between paper and paperboard is flexible, as the paperboard product grade with the lightest basis weight is lighter than the paper product grade with the heaviest basis weight. Generally speaking, paper is used for printing and paperboard is used for packaging.

[0006] The stock suspension for producing fiber webs of different product grades varies depending on the fiber web grade to be produced, but usually at least a certain drainage level is reached in the forming section in order to form a fiber web suitable for processing in the press section of the fiber web production line, and water is further removed by pressing the fiber web in the press section. For some product grades, virgin fibers or recycled fibers are refined to very fine fibers, i.e., to highly refined stock for the required stock suspension. Some product grades may also have a high content of fibrous fragments. Highly refined stock and a high content of fibrous fragments reduce the dewatering properties of the stock suspension, for example, a wire sealing effect of the fiber web may occur, which may therefore lead to dewatering restrictions in the forming unit.

[0007] Furthermore, generally, as the forming process progresses, the vacuum required for water removal increases, and a higher vacuum is required in order to achieve a corresponding water removal efficiency. This usually leads to a considerable increase in energy consumption, so that the vacuum can only be used to a limited extent. When the same vacuum is used in several consecutive suction boxes, the efficiency of the first suction box is good, but then in the subsequent suction boxes the water removal efficiency decreases significantly, while the energy consumption remains approximately the same. Difficult dewatering situations may even lead to the need to use lower production run speeds, which naturally has a negative impact on cost-effectiveness.

[0008] Therefore, in view of the above, it is important to control the vacuum in an efficient and reliable manner in forming units and water removal devices that use vacuum to form a fiber web in a forming section and to remove water from the fiber web.

[0009] For example, it is known that on fourdrinier and multi-fourdrinier forming sections, each suction box (such as a vacuum foil box) of the fourdrinier (i.e., single wire section) has a dedicated automatic control valve to control its vacuum, in which the set point value is either set manually or according to a set point value dependent table for the fiber web grade. Therefore, each vacuum foil box also needs a dedicated control circuit with its set point value. This makes the control system for controlling the vacuum in the forming section complicated. In addition, this requires multiple selections and settings of the set point values. Therefore, the structure and operation of the control system are cumbersome.

[0010] It is also known, for example, to control the vacuum on the Fourdrinier wire and multi-Fourdrinier wire forming sections at the Fourdrinier wire, before the upper suction section of the Fourdrinier wire or multi-Fourdrinier wire forming section (i.e. before the twin wire section), and on the Fourdrinier wire section (i.e. on the single wire section), to control the vacuum based on the detected water removal of the vacuum forming shoe. Due to variations in the forming process in the machine direction, the amount of water removal also varies, which affects the connection consistency and other quality factors, such as scar-like marks, diagonal worm-like defects and gull-wing defects. Therefore, the water removal of the vacuum forming shoe is to be detected in short time intervals, for which purpose the vacuum control also requires continuous setting ups, which is time-consuming.

[0011] In patent application publication US2012145346A1, a forming section in a machine for producing a fiber material web is disclosed, the forming section comprising: at least one continuously rotating screen that at least indirectly supports a fiber slurry suspension; a compression zone; a plurality of dewatering units, at least two of the plurality of dewatering units being positioned in series and positioned successively to each other along the travel direction of the fiber slurry suspension in the compression zone; and a control and / or regulation system, comprising: a control and / or regulation device; at least one device for at least indirectly obtaining a value that at least indirectly represents a dryness of the web in a transfer area from the forming section to a subsequent functional unit, the control and / or regulation device and at least one device for at least indirectly obtaining a value that at least indirectly represents a dryness of the web in a transfer area from the forming section to the subsequent functional unit The invention relates to a device connected to at least one of the devices for measuring the value of the dryness of the web in the transfer area of ​​the continuous functional unit; a device for inputting a desired value of a target dryness, the control and / or adjustment device being connected to the device for inputting the desired value of the target dryness; a plurality of control elements, the control and / or adjustment device being at least indirectly connected to (a) the plurality of control elements of each of the plurality of dewatering units located before a dewatering unit among the last ones of the plurality of dewatering units; and (b) one of the plurality of control elements of the last dewatering unit of the plurality of dewatering units in the compression zone; and a device for creating a plurality of control variables to separately control each of the plurality of dewatering units.

[0012] In patent publication US 4466873A, a vacuum dual control system for a flat box section of a paper machine is disclosed, comprising: a plurality of vacuum boxes arranged in series; a header interconnecting the boxes; a vacuum pump operably connected to the boxes so that the vacuum applied to the boxes depends on the speed of the pump; a first control member for operating the pump at an initially substantially constant high speed to generate the vacuum required to dewater a web in an initial state; a member for passing the web to be dewatered through the box so that the suction applied by the pump running at its initially substantially constant high speed dewaters the web until the state of the web changes sufficiently to increase the vacuum in the last box to a predetermined maximum level; a second control member a control member having a set point adjustment member thereon so as to be able to select a predetermined set point corresponding to a predetermined maximum vacuum degree, the second control member being connected to the last tank and the vacuum pump and comprising a sensing member for sensing a predetermined maximum vacuum degree determined by a second control member predetermined maximum vacuum degree determined by the second control member predetermined set point, and being operable only in place of the first control member; and a member for terminating the operation of the first control member and starting the operation of the second control member in response to the detection member detecting that the vacuum degree has reached the maximum vacuum degree determined by the second control member set point, thereby correspondingly reducing the speed of the vacuum pump and maintaining the maximum vacuum degree.

[0013] In patent application publication WO2005068715A1, a double fabric hybrid forming section for a papermaking machine is disclosed, having a first forming fabric and at least one second forming fabric, so that: each forming fabric has a paper side and a machine side; the forming fabrics move in the machine direction together with the pulp layer sandwiched between them; the forming fabrics are supported by a series of fabric support elements, the fabric support elements are selected from the group consisting of rollers, static fabric support elements and both rollers and static fabric support elements, the machine side of each forming fabric passes through the fabric support elements in a sliding contact manner, the fabric support elements are supported on a series of dewatering boxes, the dewatering boxes have curved fabric support element support surfaces; and the dewatering boxes provide separate drainage areas, at least some of which are connected to a vacuum source to provide separate vacuum areas, and the forming area includes a portion of the forming section, which is located at the position where the forming fabrics come together to sandwich the pulp between them and the two The forming fabric is separated and the slurry continues to be located between positions on one of them; the dewatering box provides at least four separate and different vacuum zones in the forming section; either: the radius of curvature of the curved surface of the supporting fabric support element gradually decreases in the machine direction, or: the radius of curvature of the curved surface of the supporting fabric support element gradually decreases in the machine direction on the continuous support surface; or: the spacing of the fabric support elements in each vacuum zone is constant, and the spacing of the fabric support elements on consecutive vacuum zones decreases in the machine direction; or: the spacing of consecutive fabric support elements in each vacuum zone decreases in the machine direction; the dewatering boxes supporting the fabric support elements are constructed and arranged so that the fabric support elements contact the machine side of the first forming fabric and the machine side of the second forming fabric in alternating order in the machine direction; and on all dewatering boxes: either: all fabric support elements have the same width in the machine direction; or: all fabric support elements have different widths in the machine direction.

[0014] It is an object of the present invention to create a method for controlling a vacuum in a forming section, wherein the disadvantages and problems of the prior art are eliminated or at least minimized.

[0015] It is an object of the present invention to create a forming section with a control system for controlling the vacuum in the forming section, wherein the disadvantages and problems of the prior art are eliminated or at least minimized.

[0016] An object of the present invention is to create a method for controlling a vacuum in a forming section and a forming section with a control system for controlling a vacuum in a forming section, wherein the disadvantages and problems related to controlling a vacuum in a forming section known from the prior art are eliminated or at least minimized. Summary of the invention

[0017] In order to achieve the above-mentioned object, a method and a forming section according to the present invention are provided.

[0018] It has surprisingly been found that, considering the efficiency of water removal and considering the energy consumption regarding the provision of vacuum and drive output, the vacuum in the continuous suction boxes increases proportionally (advantageously evenly). Accordingly, the vacuum value of the last suction box in the continuous suction boxes set in the running direction of the forming section is set, and the setpoint values of the preceding suction boxes in the continuous suction boxes are calculated such that the setpoint value of the vacuum of the preceding suction box in the running direction of the forming unit is less than the setpoint value of the vacuum of the succeeding suction box in the running direction of the forming unit. The control system includes means for setting the vacuum setpoint value of the last suction box in the running direction of a forming unit having a plurality of continuous suction boxes with controllable vacuum and at least one controller configured to control the vacuum of at least one of the preceding continuous suction boxes with controllable vacuum based on the vacuum setpoint value of the last suction box, the setpoint value of the vacuum of the preceding suction box in the running direction of the forming unit being less than the setpoint value of the vacuum of the succeeding suction box in the running direction of the forming unit. In fact, if the last suction box vacuum setpoint value is decreased, this will decrease the vacuum setpoint value in the preceding suction box, and vice versa, if the last suction box vacuum setpoint value is increased, this will increase the vacuum setpoint value in the preceding suction box.

[0019] According to an advantageous aspect of the invention, when controlling the vacuum at the forming wire in a forming section having a plurality of continuous suction boxes, only the vacuum value of the last suction box is independently set, and the setpoint value of the preceding suction box is calculated based on the setpoint value of the succeeding suction box such that the setpoint value P of the vacuum of the suction box i is less than the setpoint value P of the vacuum of the succeeding suction box i+1 , where i is 1, 2, 3, 4,..... Thus, the formula for calculating the vacuum of a suction box in an arrangement of a plurality of continuous suction boxes is P i < P i+1 , and the vacuum value of the last suction box in the arrangement of the plurality of continuous suction boxes is set independently (e.g., manually), or set based on information in a stored data collection of setpoint values for different fiber web product grades, or set based on a calculated setpoint value calculated, for example, based on the measurement results of dewatering. Accordingly, the need to store data related to the setpoint values according to basis weight is avoided. The functional equation for calculating the vacuum of a suction box in an arrangement of a plurality of continuous suction boxes is advantageously P i = a * P i+1 , where a is a coefficient and 0 < a < 1, more advantageously 0.5 < a < 1.0. As long as P i < P i+1 , other functional forms are also possible. Thus, the formula for calculating the pressure is Pi >P i+1 , for example P i =-5kpa and P i+1 =-10 kPa. According to an advantageous example, the minimum vacuum is first set for the first suction box after the headbox, the maximum vacuum is set for the last suction box in the consecutively arranged suction boxes, and when the vacuum of the last suction box changes, based on the formula P i <P i+1 Calculate the vacuum of the preceding suction box.

[0020] According to an advantageous aspect of the invention, there is also provided a method for automatically controlling the vacuum of each of several consecutive suction boxes at the fourdrinier wire based on measurement data received from a measuring device in the fiber web production line (for example based on layer thickness measurement values) and / or based on the dewatering amount of the upper wire section of the twin-wire section following the fourdrinier wire section (for example based on dewatering data information received from at least one vacuum forming shoe located in the upper wire section of the twin-wire section following the fourdrinier wire section).

[0021] According to an advantageous aspect of the invention, when controlling the vacuum in a forming section with a Fourdrinier wire and a vacuum forming shoe, the control system is provided with an intelligent additional device configured to detect the amount of dewatering at the vacuum forming shoe and to control the vacuum at the Fourdrinier wire to keep the dewatering at the Fourdrinier wire at a desired level (dead zone). The vacuum at the Fourdrinier wire is controlled by controlling the vacuum of a water removal device positioned at the Fourdrinier wire. The vacuum at the Fourdrinier wire section is controlled by controlling the main vacuum so that the desired dewatering is achieved in the subsequent upper web section, i.e. the dewatering is controlled by controlling the vacuum at the Fourdrinier wire section, where sufficient water is removed. This provides a stable, operator-independent vacuum control, thereby reducing variations in production quality and achieving a good, stable quality level.

[0022] According to an advantageous aspect of the invention, when controlling the vacuum in a forming section with a Fourdrinier wire and a vacuum forming shoe, the control system is provided with an intelligent additional device configured to detect the amount of dewatering at the vacuum forming shoe and control the set point value of the main vacuum at the Fourdrinier wire to fix the amount of dewatering at the vacuum forming shoe to a selected range of the main vacuum at the Fourdrinier wire. Advantageously, the operator sets a set point value in terms of the amount of dewatering at a time interval (e.g. 1 / s), and the control is such that the amount of dewatering at a time interval is maintained within the set range (e.g. 10 l / s).

[0023] Advantageously, the forming section comprises an arrangement of several consecutive suction boxes at the Fourdrinier wire and its vacuum is controlled. According to an advantageous embodiment, the set point value of the vacuum of the last of the several consecutive suction boxes at the Fourdrinier wire is set based on the dewatering detected at the vacuum forming shoe.

[0024] In the present invention, the control system comprises means for setting the vacuum set point value of the last suction box and at least one controller, the controller comprising at least a processor and a memory and a computer code (e.g. a software application) to provide control instructions based on manually set data and / or at least measurements received from the forming section, optionally from the fiber web production line. Thus, the controller of the control system receives, collects, processes, stores and transmits data. The control system and the controller may be configured as one entity or it may be configured as separate units connected to each other by a data transmission connection. The control system and the controller are configured to provide control data to control the vacuum in the forming section. The control data are transmitted to control the vacuum in the forming section. The control data may be transmitted to a control unit of a part and / or a device and / or an element of the fiber web production line. The controller may be configured to provide automatic control and / or manual control of the vacuum of the forming section.

[0025] In the description and claims, the expression "control (and its derivatives)" refers to controlling at least one device and / or at least one element operatively connected to the forming section.

[0026] The controller of the control system advantageously comprises at least one processor and at least one memory comprising computer program code, which at least one memory and the computer program code are configured to, together with the at least one processor, generate a signal and transmit the signal as first control data to the forming section based on first information data received from the forming section, and / or based on second information data received from the fiber web production line and / or based on third data automatically and / or manually received as input values ​​from the data memory.

[0027] The method for controlling the vacuum of the forming section advantageously includes: receiving first and / or second and / or third information data; processing the received first and / or second and / or third information data according to a predetermined configuration; and based on the processed data, generating a signal according to a predetermined configuration to control the vacuum of the forming section.

[0028] By means of the method and forming section according to the invention, an optimal, uniformly increasing vacuum distribution in an arrangement of several consecutive suction boxes at the Fourdrinier wire can be provided, only by changing the set point value of the last of the several consecutive suction boxes in the arrangement. The invention also provides for a minimization of manual operations when controlling the vacuum in the forming section and thus a reduction in operator errors, since the vacuum circuits of the individual suction boxes of the arrangement of several consecutive suction boxes do not need to be set manually individually. Furthermore, the invention provides for an automatic control of the desired, increased vacuum distribution at the Fourdrinier wire, thereby achieving improved quality and runnability, e.g. providing a more uniform distribution of fibrous fragments. The solution according to the invention reduces the energy consumption of the fiber web machine, increases the lifetime of the forming section ceramics and fabrics and optimizes the properties of the fiber web. In this way, the fiber web can be dewatered, so that it is not compacted too early. It improves the glue penetration in the glue press and reduces the vacuum demand in the forming section. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the following, the invention is explained in detail with reference to the accompanying drawings, to which the invention is not restricted.

[0030] exist Figure 1 , schematically showing an advantageous example of a forming section with a vacuum control system according to the invention, and an advantageous example of a method according to the invention for controlling a vacuum in a forming section;

[0031] exist Figure 2 , schematically showing another advantageous example of a forming section with a vacuum control system according to the invention, and another advantageous example of a method according to the invention for controlling a vacuum in a forming section;

[0032] exist Figure 3 In the figure, an example of a vacuum setting diagram associated with an advantageous example of the present invention is schematically shown.

[0033] In the following description, the same numerals and symbols will be used to identify the same elements according to the different views showing the present invention and its advantageous examples. In the drawings, some repeated reference numerals may be omitted for clarity. DETAILED DESCRIPTION

[0034] exist Figure 1-Figure 2 In FIG. 1 , an advantageous example of a forming section 200 with a vacuum control system and an advantageous example of a method for controlling vacuum in a forming section are shown. Each forming section 200 comprises at least one headbox M1 , M2 for supplying a slurry suspension to a forming unit 250. The forming section 200 comprises a control system 100 for controlling the vacuum in the forming units 250 of the forming section 200. Figure 1In the example shown, there are examples related to the production of a single-layer fiber web W or to the production of a multi-layer fiber web W having multiple layers. Figure 2 An example related to the production of a double-layer fiber web W is shown in FIG. Figure 1 In the example of FIG. 2 , in addition to the forming section 200 , the start of the press section 300 after the forming section 200 is also shown.

[0035] exist Figure 1, an example of a forming section 200 is shown, which produces a single-layer fiber web W by means of a single-layer headbox M1 or a multi-layer fiber web W by means of a multi-layer headbox M1. The running direction is indicated by an arrow S. In this example, the forming section 200 comprises one headbox M1 and a forming unit 250, and the start of a press section 300 is also shown. In this example, the forming section 200 is therefore used to produce a fiber web W which may contain one or more fiber web layers. The forming section 200 comprises a headbox M1 from which a stock suspension is fed to a forming unit 250, which starts with a single-wire section (i.e., a Fourdrinier section) having a substantially horizontal run, comprising a first wire 10 for single-wire run and a second wire 20 for twin-wire run, to form a fiber web W. In the case of manufacturing a single-layer fiber web W, only one stock suspension is fed to the headbox M1, but in the case of manufacturing a multi-layer fiber web W, two or more equal or different kinds of stock suspensions are fed to the headbox M1. The stock suspension may differ due to the raw material, fiber length, fiber freeness or additives. Each wire 10, 20 comprises rollers 12, 22 for guiding, tensioning and / or driving the first wire 10 and the second wire 20 as endless (annular) first wire loop 10 and the second wire loop 20. The stock suspension from the headbox M1 is first supplied to the single wire run of the first wire 10, i.e. first supplied to the Fourdrinier wire 10, then the stock on the Fourdrinier wire 10 is guided through the inside of the loop of the first wire 10, at the start of its run there are located dewatering members 11A-11C, the dewatering members may be, for example, foil boxes and / or suction devices, then through the loop of the first wire 10 there are located suction boxes 15A-15E with controllable vacuum. During the run on the first wire 10, the fiber web dewatering is substantially horizontal. The first single-wire run is followed by a twin-wire run during which the fiber web runs between the two wires 10, 20 of the twin-wire section of the forming unit 250. During this twin-wire run, water is removed by controllable dewatering members 16A-16C, advantageously controllable vacuum forming shoes 16A-16B with optional adjustable loading blades P in the opposite first wire loop 10. The twin-wire run is followed by another single-wire run on which additional dewatering members 14A, 14B are positioned, which can also be used as supporting members to support the run of the fiber web W. After the forming section 250, the fiber web W is guided via a suction roll 13 of the forming unit 250, positioned inside the first wire loop 10, towards a pick-up roll 41 to transfer the fiber web to a first press fabric 40 of the press section 300. The press section further comprises a second press fabric 50 with a roll 51. The press fabric 40, 50 comprises rollers 42, 52 for guiding, tensioning and / or driving the fabric 40; 50 as an endless loop.In the press section, the fibrous web W is guided between a first press fabric 40 and a second press fabric 50 to a press nip formed between a first press roll 45 and a second press roll 55.

[0036] In Figure 1 the example of, a control system 100 for controlling the vacuum in the forming section 200 includes a member and a controller 150 for setting a vacuum setpoint value of the last suction box 15E, the controller being operably connected at the first wire 10 (i.e., the long wire 10) to a plurality of successive suction boxes 15A - 15E having controllable vacuum. Each of the successive suction boxes 15A - 15E includes control elements V5A - V5E (such as adjustable valves V5A - V5E) to control the vacuum of the corresponding suction box 15A - 15E. When controlling the vacuum in the forming section 200 (especially in the forming unit 250), the vacuum setpoint value of the last suction box 15E is set individually, and the setpoint values of the preceding suction boxes 15A - 15D are calculated based on the setpoint values of the subsequent suction boxes 15B - 15E, such that the setpoint value P i of the vacuum of the suction boxes 15A - 15D is less than the setpoint value P i+1 of the vacuum of the subsequent suction boxes 15B - 15E, where i represents the order of the suction boxes and is 1, 2, 3, 4,... where 1 is the position of the first suction box 15A in the running direction S, or in the example i is represented by the symbols A, B, C... Thus, the formula for calculating the vacuum of the suction boxes 15A - 15D in the arrangement of a plurality of successive suction boxes 15A - 15E is P i < P i+1 , and the vacuum setpoint value of the last suction box 15E in the arrangement of a plurality of successive suction boxes 15A - 15E is set individually, for example, manually, or based on information in a stored data set of setpoint values for different fibrous web product grades, or based on a calculated setpoint value calculated, for example, based on measurement results of dewatering. The functional equation for calculating the vacuum of the suction boxes 15A - 15D in the arrangement of a plurality of successive suction boxes 15A - 15E is advantageously P i = a * P i+1 , where a is a coefficient, and 0 < a < 1, more advantageously 0.5 < a < 1.0. As long as P i < P i+1, other functional forms are also possible. It can also be provided that the vacuum of each of several continuous suction boxes 15A-15E at the Fourdrinier wire 10 is automatically controlled based on data information received from measuring devices of the fiber web production line (e.g. based on layer thickness measurements) and / or based on dewatering data information received from the forming unit 250 (e.g. from at least one vacuum forming shoe 16A-16C located at the second wire 20 (i.e. the upper wire 20 in the upper wire section of the twin wire section after the Fourdrinier wire section). The control system 100 can also be provided with an intelligent additional device 110 configured to detect the amount of dewatering at the vacuum forming shoe 16A-16C and control the vacuum at the Fourdrinier wire 10 to keep the dewatering at the Fourdrinier wire 10 at a desired level (dead zone). The vacuum at the Fourdrinier wire 10 is controlled by controlling the vacuum of at least one of the dewatering devices 11A-11C, 15A-15E located at the Fourdrinier wire 10 (preferably the vacuum of the continuous suction boxes 15A-15E). Advantageously, the operator sets a set point value with the dehydration volume (e.g., 1 / s) of the first top suction unit suction box 15A of the continuous suction boxes 15A-15E, and the control keeps the dehydration volume of the time interval within the set range (e.g., 10 l / s). Alternatively, the operator can set a set point value with the dehydration volume (e.g., 1 / s) of the time interval of the last suction box 15E of the continuous suction boxes 15A-15E, and the control keeps the dehydration volume of the time interval within the set range (e.g., 10 l / s).

[0037] exist Figure 2, an example of a forming section 200 for producing a multilayer fiber web W having at least two layers is shown. The running direction for forming the first layer W1 is indicated by arrow S1, and the running direction for forming the second layer W2 and the combined layers W1, W2 is indicated by arrow S2. The forming section is provided with two headboxes M1, M2, one or both of which may be single-layer headboxes M1, M2 or multi-layer headboxes M1, M2. The forming section 200 in this example comprises two headboxes M1, M2 and a forming unit 250. In this example, the forming section 200 is used to produce a multilayer fiber web W, which may contain two or more fiber web layers W1, W2. The forming section 200 comprises one headbox M1, from which a stock suspension is fed to a forming unit 250 for forming a first layer of the fiber web W. The forming unit 250 starts with a single wire section (i.e., a Fourdrinier wire section) having a substantially horizontal operation, including a first wire 10 for single wire operation and a second wire 20 for twin wire operation to form a fiber web W. In the case where the first layer comprises only a single layer, only one kind of stock suspension is fed to the headbox M1, but in the case where the first layer of the multi-layer fiber web W comprises more than one layer, two or more equal or different kinds of stock suspensions are fed to the headbox M1. The stock suspensions may differ due to differences in raw materials, fiber length, fiber freeness, or additives. Each wire 10, 20 comprises a roller 12, 22 for guiding, tensioning, and / or driving the wire 10, 20 as an endless loop. The stock suspension from the headbox M1 is first fed onto the single wire run of the first wire 10, i.e. first fed onto the Fourdrinier wire 10, then the stock on the Fourdrinier wire 10 is led through the inside of the loop of the first wire 10, at the start of its run there are located dewatering members 11A-11C, which can be for example foil boxes and / or suction devices, then through the loop of the first wire 10 there are located suction boxes 15A-15E with controllable vacuum. During the run on the first wire 10, the fiber web is dewatered substantially horizontally. The first single wire run is followed by a twin wire run, during which the fiber web runs between the first wire 10 and the second wire 20 forming the twin wire part of the forming unit 250. During this twin wire run, water is removed by controllable dewatering members 16A-16C, advantageously the controllable vacuum forming shoes 16A-16B have optional adjustable loading blades P in the opposing wire loop 10. The twin wire run is followed by another single wire run on which additional dewatering members 14A, 14B are located, which may also serve as supporting members to support the run of the fiber web W. The forming section 200 further comprises another second headbox M2 from which the stock suspension is fed to a forming unit 250 to form a second layer of the fiber web W. The forming unit 250 for the second layer is a single wire section with a substantially horizontal run comprising a third wire 30 for forming the fiber web W.In case the second layer comprises only a single layer, only one kind of stock suspension is fed to the second headbox M2, but in case the first layer of the multi-layer fiber web W comprises more than one layer, two or more equal or different kinds of stock suspensions are fed to the headbox M2. The stock suspensions may differ due to differences in raw materials, fiber length, fiber freeness or additives. The third wire 30 comprises rollers 32 for guiding, tensioning and / or driving the wire 30 as an endless loop. The stock suspension from the second headbox M2 is fed to the single wire run of the third wire 30, and then the stock on the third wire 30 is guided through the inside of the first wire loop 10, at the start of which a dewatering member 31A-31F is provided, which may be, for example, a foil box and / or a suction device, and then the first and second layers are bonded to the multi-layer fiber web W at a bonding roller 17 located inside the first wire loop 10. The bonding roll 17 is followed by another single wire run on which additional dewatering members 34A-34B are located, which may be, for example, foil boxes and / or suction devices and may also serve as supporting members to support the run of multilayer fiber web W. After the forming section 250 the fiber web W is guided to a press section, as indicated by arrow 300.

[0038] exist Figure 2 In the example of , the control system 100 for controlling the vacuum in the forming section 200 includes a component for setting the vacuum set point value of the last suction box 15E and a controller 150, which is operably connected to several consecutive suction boxes 15A-15E with controllable vacuum at the first wire 10 (i.e., the fourdrinier wire 10). Each of the consecutive suction boxes 15A-15E includes a control element V5A-V5E (e.g., an adjustable valve V5A-V5E) to control the vacuum of the corresponding suction box 15A-15E. When controlling the vacuum in the forming section 200 (in particular, in the forming unit 250), the vacuum set point value of the last suction box 15E is set separately, and the set point value of the preceding suction box 15A-15D is calculated based on the set point value of the following suction box 15B-15E, so that the set point value P of the vacuum of the suction box 15A-15D is i Less than the vacuum set point value P of the subsequent suction boxes 15B-15E i+1 , where i denotes the order of the suction boxes and is 1, 2, 3, 4, ..., where 1 is the position of the first suction box 15A in the running direction S1, or in the example i is represented by the symbols A, B, C, .... The formula for calculating the vacuum of the suction boxes 15A-15D in an arrangement of several consecutive suction boxes 15A-15E is therefore P i <P i+1, and the vacuum setpoint value of the last suction box 15E in the arrangement of a number of consecutive suction boxes 15A - 15E is set and set individually, for example, set manually, or set based on information in a stored data set of setpoint values for different fiber web product grades, or set based on a calculated setpoint value calculated, for example, based on dehydration measurement results. The functional equation for calculating the vacuum of the suction boxes 15A - 15D in the arrangement of a number of consecutive suction boxes 15A - 15E is advantageously P i = a * P i+1 , where a is a coefficient and 0 < a < 1, more advantageously 0.5 < a < 1.0. As long as P i < P i+1 , other functional forms are also possible. It can also be provided that the vacuum of each of the number of consecutive suction boxes 15A - 15E at the long wire 10 is automatically controlled based on data information received from a measuring device of the fiber web production line (such as based on layer thickness measurements) and / or based on dehydration data information received from the forming unit 250 (such as from at least one vacuum forming shoe 16A - 16C at the upper wire 20 of the twin wire 10, 20 section (i.e., the upper wire 20 after the long wire 10 section)). The control system 100 can also be provided with an intelligent add-on device 110 configured to detect the amount of water removed at the vacuum forming shoes 16A - 16C and control the vacuum at the long wire 10 to maintain the dehydration at the long wire 10 at a desired level (dead zone). The vacuum at the long wire 10 is controlled by controlling the vacuum of at least one of the water removal devices 11A - 11C, 15A - 15E located at the long wire 10 (preferably, the vacuum of the consecutive suction boxes 15A - 15E). Advantageously, the operator sets a setpoint value for the amount of water removed (such as l / s) at the time interval of the first top suction unit suction box 15A of the consecutive suction boxes 15A - 15E, and the control causes the amount of water removed at the time interval to be maintained within a set range (such as 10 l / s). Alternatively, the operator can set a setpoint value for the amount of water removed (such as l / s) at the time interval of the last suction box 15E of the consecutive suction boxes 15A - 15E, and the control causes the amount of water removed at the time interval to be maintained within a set range (such as 10 l / s).

[0039] At Figure 1-Figure 2In an example, the control system 100 includes means for setting the vacuum setpoint value of the last suction box and at least one controller 150, which controller 150 includes at least one processor and a memory as well as computer code (such as a software application) to provide control instructions based on manually set data and / or measurements received at least from the forming section and optionally from the fibrous web production line. Thus, the controller 150 of the control system 100 receives, collects, processes, stores, and transmits data. The control system 100 and the controller 150 can be configured as one entity, or it can be configured as independent units connected to each other via a data transmission connection. The control system 100 and the controller 150 are configured to provide control data to control the vacuum in the forming section. The control data is transmitted to control the vacuum in the forming section 200. The control data can be transmitted to a part of the fibrous web production line and / or the control unit of a device and / or an element. The controller 150 can be configured to provide automatic and / or manual control of the vacuum in the forming section 200. The controller 150 of the control system 100 advantageously includes at least one processor and at least one memory including computer program code, which at least one memory and computer program code are configured to, together with at least one processor, generate a signal and transmit the signal as first control data to the forming section 200 based on first information data received from the forming section 200 and / or based on second information data received from the fibrous web production line and / or based on third data received automatically and / or manually from a data memory as input values. The method of controlling the vacuum in the forming section 200 advantageously includes: receiving first and / or second and / or third information data, processing the received first and / or second and / or third information data according to a predetermined configuration, and generating a signal according to a predetermined configuration based on the processed data to control the vacuum in the forming section 200.

[0040] Figure 3 Examples of vacuum set diagrams C1 - C3 are shown. The X-axis shows the successive suction boxes 15A - 15E, and the Y-axis shows the setpoint values of the corresponding vacuum boxes. As can be seen from the C1 - C3 diagrams, by changing only the setpoint value of the last suction box 15E, based on the formula P i = a * P i+1 (where a is a coefficient and 0 < a < 1, more preferably 0.5 < a < 1.0), controlling the vacuum in the preceding successive boxes 15A - 15D by controlling the vacuum as described above provides an optimal, uniformly increasing vacuum distribution. The setpoint value of the last one can be selected, for example, based on layer thickness measurements or based on the water removal amount related to the oncoming of the twin-wire section after the fourdrinier section. In the exemplary diagrams C1 - C3, the vacuum setpoint value of the last suction box 15E increases at selected intervals (for example, in steps of 2 kPa) within a vacuum value range (for example, 0 - 16 kPa), and the coefficient a value is 0.7.

[0041] In the foregoing description, although some functions have been described with reference to certain features and examples, these functions may be performed by other features and examples (whether described or not). Although features have been described with reference to certain examples, those features may also exist in other examples (whether described or not).

[0042] The above describes only some advantageous examples of the invention, to which the invention is not narrowly limited, and in which many modifications and variations are possible.

Claims

1. A method for controlling a vacuum in a forming section (200), the forming section comprising at least one forming unit (250), the forming unit (250) comprising at least one Fourdrinier wire (10) and an arrangement of several consecutive suction boxes (15A-15E) with a controllable vacuum at the Fourdrinier wire (10), the forming unit (250) further comprising a second wire (20) located after the Fourdrinier wire (10), the second wire forming together with the Fourdrinier wire (10) a twin-wire section, It is characterized in that The method comprises the following steps: - setting the vacuum set point value of the last suction box (15E) of a number of consecutive suction boxes (15A-15E) with controllable vacuum in the running direction (S; S1) of the forming unit (250), the last suction box (15E) being followed by the twin-wire section, and - based on the vacuum set point value of the last suction box (15E), the set point value of at least one consecutive suction box (15A-15D) with controllable vacuum before the last suction box (15E) is calculated from the set point value of the following suction box, so that the vacuum set point value (P i ) is less than the vacuum set point value (P) of the subsequent suction box in the running direction (S; S1) of the forming unit (250) i+1 ).

2. The method according to claim 1, characterized in that In the method, the formula for calculating the vacuum of the preceding suction box (15A-15D) in an arrangement of several consecutive suction boxes (15A-15E) is P i <P i+1 , where i is the sequence (1, 2, 3, 4, ...) of the suction boxes in the running direction (S; S1) of the forming unit (250).

3. The method according to claim 1 or 2, characterized in that: In the method, the formula for calculating the vacuum of the preceding suction box (15A - 15D) in the arrangement of a number of successive suction boxes (15A - 15E) is P i = a * P i+1 , where a is a coefficient and 0 < a < 1, more preferably 0.5 < a < 1.0, and where i is the order (1, 2, 3, 4...) of the suction boxes in the running direction (S; S1) of the forming unit (250).

4. The method according to any one of claims 1 to 3, characterized in that In the method, the set point value of the last suction box (15E) is set based on information in a stored data set of set point values ​​for different fiber web product grades or based on a calculated set point value advantageously calculated on the basis of measured results of dewatering in the forming section (200).

5. The method according to any one of claims 1 to 4, characterized in that In the method, the set point value of the last suction box (15E) is set based on the dehydration data information received from the forming unit (250), the forming unit also including at least one vacuum forming shoe (16A-16C) located at the second wire (20), and the dehydration data information is measured at the at least one vacuum forming shoe (16A-16C).

6. The method according to any one of claims 1 to 5, characterized in that In the method, the vacuum is controlled by a control system (100), the control system comprising at least one controller (150), the controller comprising at least one processor and memory and computer code, such as a software application, to provide control instructions based on manually set data and / or measurement results received from the forming section and, optionally, measurement results received from the fiber web production line.

7. A forming section having a control system (100) for controlling the vacuum in the forming section (200), the forming section comprising at least one forming unit (250), the forming unit (250) comprising at least one Fourdrinier wire (10) and an arrangement of several consecutive suction boxes (15A-15E) with a controllable vacuum at the Fourdrinier wire (10), the forming unit (250) further comprising a second wire (20) located after the Fourdrinier wire (10), the second wire forming a double wire section together with the Fourdrinier wire (10), characterized in that The control system (100) comprises: - means for setting the vacuum set point value of the last suction box (15E) of a number of consecutive suction boxes (15A-15E) with controllable vacuum in the running direction (S; S1) of the forming unit (250), the last suction box (15E) being followed by the twin-wire section, and - at least one controller (150) configured based on the vacuum set point value of said last suction box (15E) to control the preceding consecutive suction boxes (15A-15D) with controllable vacuum The vacuum of at least one of the forming units (250) is such that the vacuum set point value (P i ) is less than the vacuum set point value (P) of the subsequent suction box in the running direction (S; S1) of the forming unit (250) i+1 ).

8. The forming section according to claim 7, characterized in that The forming unit (250) further comprises at least one vacuum forming shoe (16A-16C) located at the second net (20), and the controller (150) is configured to define a set point value of the last suction box (15E) based on dehydration data information received from dehydration data information measured at the at least one vacuum forming shoe (16A-16C).

9. The forming section according to claim 7 or 8, characterized in that: The controller (150) comprises at least a processor and a memory and computer code, such as a software application, to provide control instructions based on manually set data and / or measurements received from the forming section and optionally from a fiber web production line.

10. The forming section according to claim 8 or 9, characterized in that: The control system (100) is provided with an intelligent attachment (110) configured to detect the amount of dewatering at the vacuum forming shoes (16A-16C) and control the vacuum at the Fourdrinier wire (10) to maintain the dewatering at the Fourdrinier wire (10) at a desired level.

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