EP3333315B1

EP3333315B1 - Forming section

Info

Publication number: EP3333315B1
Application number: EP16202857.5A
Authority: EP
Inventors: Antti Poikolainen; Teuvo Virkkunen
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2016-12-08
Filing date: 2016-12-08
Publication date: 2019-05-01
Anticipated expiration: 2036-12-08
Also published as: CN108179651A; CN108179651B; EP3333315A1

Description

The invention relates generally to producing fiber webs. Particularly the invention relates to a forming section according to the preamble of claim 1.
As known from the prior art in fiber web 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 production and treatment line comprises a forming section comprising a head box 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 comprises typically at least one winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by fiber webs are meant especially container-board or cartonboard webs.
The task of a forming unit is to remove water from fiber suspension fed by the head box. When the web is manufactured of watery fiber stock, water in the 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 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.
In patent application publication EP 1096067 A2 is disclosed a former for a fiber web machine, which former is constructed as a gap forming unit, in which stock suspension from the head bow is fed into a gap formed between two wire loops, in between of which wire loops a forming gap is formed. The gap forming unit comprises at least two, advantageously three rolls, which are at least partly in contact with both wires.
In patent publication US 4,209,360 is disclosed a forming section, in which pulp suspension is fed from a head box into a gap formed between two wire loops and in which at first is located a grooved forming roll and immediately after the forming roll on the other side of the wires a roll with a smooth surface is located.
In patent publication CA 1,156,080 is disclosed a forming section with two movable water pervious dewatering bands, a dewatering shoe and a dewatering cylinder arranged after the dewatering shoe and a deflection roll arranged after the dewatering cylinder.
In patent publication US 4,925,531 is disclosed a twin-wire former for a paper machine having a lower wire and an upper wire. The former has a twin-wire forming zone which has forming members and forming zones situated in a specific sequence as follows. A downwardly curved forming zone is conformed to a sector of a large-diameter forming roll mounted on a frame of a lower wire unit, the magnitude of this sector being within the range of <90°. A second forming roll then follows which is preferably provided with a hollow face and onto which the wires arrive from the first forming roll. The twin-wire forming zone is curved within a certain sector of less than 90° on the second forming roll so as to become horizontal. A forming shoe is provided with a ribbed deck and fitted after the second forming roll inside the lower wire loop, this forming shoe having a relatively large curve radius after which the twin-wire forming zone ends and the web is arranged to follow along with the lower wire.
In the twin-wire formers known form prior art there is typically combined a forming roll with large 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 condenses the fiber web so much that there is difficulties of achieving desired water removal without powerful and long lasting pulsating water removal.
These types of forming sections are typically high; about 10 meters, and thus expensive. The height of opening of the head box typically is at height level of about 8 meters, due to the large wrap angle of the forming roll and the long forming shoe. The height as such might not raise so many difficulties but this type of construction leads to in high locations rotating, heavy rolls, which tend to create vibration and thus the frame and support structures need to be dimensioned for heavy loads.
Especially when producing board webs problems occur due to low consistency of fiber stock in the head box, which leads to increased need of water removal in the forming unit, whereby in types of forming sections one disadvantage relating to optimizing water removal and desired quality of the board web. Typically this has been tried to solve by adding water removal devices of the forming unit, which naturally increases costs and complicates the construction of the forming section.
In patent application publication WO 2010046527 A1 is disclosed a forming section comprising two wire loops which form a twin-wire zone which comprises a dewatering element performing initial dewatering and a dewatering device following it. The dewatering device comprises a stationary support shaft on which are supported support elements around which circles an im-permeable belt loop. The dewatering device further comprises a curvilinear dewatering zone over which the wires 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 stock suspension travelling between the wires on the curvilinear dewatering zone. said at least one curvilinear dewatering zone of said at least one dewatering device, 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 web.
An object of the invention is to create a forming section, in which the disadvantages and problems of prior art are eliminated or at least minimized.
In particular an object of the invention is to provide a new type of forming section in which height of the forming section can be decreased.
In order to achieve the above mentioned objects the forming section according to the invention is mainly characterized by the features of the characterizing clause of claim 1. Advantageous embodiments and features are disclosed in the dependent claims.
According to the invention the forming section comprises a twin-wire forming unit formed between a lower wire and an upper wire, in which a first water removal means of the twin-wire forming unit is a forming roll with a wrap angle, wherein in the twin-wire forming unit following the forming roll there is a sleeve roll and the run between the forming roll and the sleeve roll is free of vacuumed dewatering i.e. between the forming roll and the sleeve roll no vacuumed dewatering is located.
According to the invention the sleeve roll comprises a stationary support shaft and a belt loop, which is led to circle around the stationary support shaft, the sleeve roll further comprising at least one curvilinear dewatering zone consisting 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.
According to an advantageous feature of the invention the sleeve roll comprises a support elements supported at a distance from each other on the stationary support shaft, the belt loop led to circle around the stationary support shaft is supported by the support elements and the belt loop is impermeable.
According to an advantageous feature of the invention distance between the forming roll and the sleeve roll is 0,2 - 2 meters, advantageously 0,3 - 1,5 meters, which distance is measured between the point at which the lower and upper wires wrap angle ends on the forming roll and the point at which the contact of the lower and upper wires on the sleeve roll begins.
According to an advantageous feature of the invention the forming unit comprises first a one wire part followed by the twin-wire part and advantageously the one wire part is substantially horizontal or inclined. According to an advantageous feature the one wire part comprises a forming shoe with a deck and suction openings in the deck.
According to an advantageous feature of the invention at a distance from the sleeve roll the twin-wire forming unit ends as the run of the upper wire turns away from the lower wire and the end part of the forming unit is formed as one wire part.
According to an advantageous feature of the invention the overall height of the forming section is less than 8 meters.
According to an advantageous feature of the invention the highest point of the sleeve roll is on a higher vertical position than the lowest point of the forming roll.
By the forming section according to the invention many advantages are achieved. The overall height of the forming section can be decreased even 2 - 3 meters and thus also the frame and support structures can be dimensioned for smaller loads. The overall height of the forming section is less than 8 meters. The properties, especially strength properties of the fiber web are improved as the amount of pulsating water removal is minimized. Further there is less contacting water removal means in the forming section, thus the life time of wires is increased as well as the power consumption is decreased. Also good strength properties of the fiber web are achieved as there is no vacuumed, pulsating dewatering between the forming roll and sleeve roll. Further savings in investment and use costs are achieved. Short distance from the forming roll to the sleeve roll enables manufacturing of packaging board grades with high quality, efficiency and capacity.
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.
In figure 2 is shown schematically an advantageous example of a forming section according to the invention.
In figures 3A - 3B is shown very schematically a forming shoe and a sleeve roll. 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, which is a twin-wire forming unit type forming section and begins with a twin-wire part. The forming section comprises a head box 30, from which the stock suspension M is fed to the forming unit formed as a twin-wire forming unit comprising a lower wire 10 and an upper wire 20, each comprising rolls 12, 22 for guiding and driving the wire as an endless loop. The stock suspension M is first fed into a gap formed between the lower wire 10 and the upper wire 20. The first water removal means is a forming roll 13 with a wrap angle 13V, which forming roll 13 is located inside the loop formed by the lower wire 10. The wrap angle 13V is advantageously 40-110 degrees for ensuring required water removal capacity. The forming roll 13 is advantageously a suction roll. The forming roll 13 is followed support foils 26 that support the lower wire 10 but do not participate in active dewatering, only remove water from the bottom surface of the wire 10 and support the run of the wires 10, 20 between the forming roll 13 and the sleeve roll 50. The support foils 26 do not deviate the run of the wires 10,20 and thus no dewatering pressure is effected to the fiber web between the wires 10, 20.The support foils 26 are followed by a sleeve roll 50, which is located inside the loop formed by the upper wire 20. The distance L between the forming roll 13 and the sleeve roll 50 is only about 0,2 - 2 meters. The distance is measured between the point in which lower and upper wires 10, 20 wrap angle 13V ends on the forming roll 13 and between the point in which lower and upper wires 10, 20 are in the contact on the sleeve roll 50 i.e. the point in which the contact of the lower and upper wires 10, 20 begins on the sleeve roll 50. According to the invention, there is no need to use suction boxes between the forming roll 13 and the sleeve roll 50. The support foils 26 can be also situated after the sleeve roll 50 for removing water from the surface of the wire 10. After the sleeve roll 50 the fiber web is further guided between the upper and the lower wire 20, 10 and at a distance towards the pick-up roll 31 transferring the fiber web to a press section the run of the upper wire 20 turns upwards away from the lower wire 10 and the end part of the forming unit is formed as a one wire part. Inside the loop formed by the lower wire 10 further water removal means 16 are located as shown in the example of the figure. The further water removal means 16 may comprise forming shoes and/or suction devices. For ensuring the low height of the forming section, the highest point of sleeve roll 50 is on the higher vertical position than the lowest point of the forming roll 13.
In figure 2 is shown an example of a forming section begins with a short one wire part followed by a twin-wire part. The forming section comprises a head box 30, from which the stock suspension M is fed to the forming unit formed as a twin-wire forming unit comprising a lower wire 10 and an upper wire 20, each comprising rolls 12, 22 for guiding and driving the wire as an endless loop. The stock suspension M is first fed onto the lower wire 10 and onto the area of a forming shoe 17 and thereafter the stock on the lower wire is guided into a gap formed between the lower wire 10 and the upper wire 20 forming the twin-wire part of the forming unit. The beginning of the forming unit with a short, substantially horizontal or inclined one-wire section comprising a forming shoe 17 removing water by suction provides for exact control of the head box flow, so that water is sucked through the lower wire 10 but stock suspension is not bouncing on the wire 10 as there is no pulsating water removal. The first water removal means in the twin-wire part is a forming roll 13 with a wrap angle 13V, which forming roll 13 is located inside the loop formed by the lower wire 10. Wrap angle 13V is advantageously 40-110 degrees for ensuring required water removal capacity. The forming roll 13 is advantageously a suction roll. The forming roll 13 is followed support foils 26 that support the lower wire 10 but do not participate in active dewatering, only remove water from the bottom surface of the wire 10 and support the run of the wires 10, 20 between the forming roll 13 and the sleeve roll 50. The support foils 26 do not deviate the run of the wires 10, 20 and thus no dewatering pressure is effected to the fiber web between the wires 10, 20. The distance L between the forming roll 13 and the sleeve roll 50 is only about 0,2 - 2 meters. The distance is measured between the point in which lower and upper wires 10, 20 wrap angle 13V ends on the forming roll 13 and between the point in which lower and upper wires 10, 20 are in the contact on the sleeve roll 50 i.e. the point in which the contact of the lower and upper wires 10, 20 begins on the sleeve roll 50. According to the invention, there is no need to use suction boxes between the forming roll 13 and the sleeve roll 50. After the sleeve roll 50 the fiber web is further guided between the upper and the lower wire 20, 10 and at a distance towards the pick-up roll 31 transferring the fiber web to a press section the run of the upper wire 20 turns upwards away from the lower wire 10 and the end part of the forming unit is formed as a one wire part. Inside the loop formed by the lower wire 10 further water removal means 16 are located as shown in the example of the figure. The further water removal means 16 may comprise forming shoes and/or suction devices. This kind of forming section is especially good for forming higher basis weight webs, because forming shoe 17 reduces the web layer thickness around 20 - 40% and web doesn't tend to extrude between the wires on the forming roll 13 area.
The forming sections of the examples of figures 1 and 2 comprise a twin-wire forming unit with a sleeve roll, in which the twin-wire forming unit is formed between the lower wire 10 and the upper wire 20. Due to the location of the sleeve roll following next the first forming roll 13 at a distance L of 0,2 - 2 meters, advantageously 0,3 - 1,5 meters, also the location height of the upper wire 20 can lowered and thus further the location of the head box and the forming unit can be lowered.
In figure 3A is schematically shown a forming shoe 17, in which the deck 18 comprises suction openings 19, through which a suction effect is created to remove water from the stock suspension and the formation of the stock suspension is improved. Advantageously deck 18 design does not cause pulsations to the web in the beginning forming shoe 17. The openings 19 are formed between foils, which foils have width of 5-15 mm located at a distance between 5-15 mm between each other and advantageously the forming shoe 17 is connected to a suction device.
In figure 3B is schematically shown a sleeve roll 50 with decreasing radius, which comprises a stationary support shaft 51 on which support elements 52 are supported at a distance from each other, an impermeable belt loop 53 which is led to circle around the stationary support shaft 51 supported by the support elements 52. The sleeve roll 50 further comprises at least one curvilinear dewatering zone K via which the wires 10, 20 are led to travel supported by the belt loop 53. The degree of curvature of the curve of the curvilinear dewatering zone K increases in the travel direction of the belt 53 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 K. Radius of curvature of the curvilinear dewatering zone K consists of two partial curves such that the radius of curvature K1 of a first partial curve is greater than the radius of curvature K2 of a second partial curve following the first partial curve K1 in the travel direction of belt loop 53. Radius of curvature of the curvilinear dewatering zone K can be contain several curves such that the radius of curvatures decreases in the running direction of the wires.
Above only some advantageous examples of the inventions has been described to which examples the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

Claims

Forming section comprising a twin-wire forming unit formed between a lower wire (10) and an upper wire (20), in which a first water removal means of the twin-wire forming unit is a forming roll (13) with a wrap angle (13V), in which twin-wire forming unit following the forming roll (13) there is a sleeve roll (50) comprising a stationary support shaft (51) and a belt loop (53), which is led to circle around the stationary support shaft (51), which sleeve roll (50) further comprises at least one curvilinear dewatering zone (K) consisting of two partial curves such that the radius of curvature (K1) of a first partial curve is greater than the radius of curvature (K2) of a second partial curve following the first partial curve (K1) in the travel direction of the belt loop (53), characterized in that the run between the forming roll (13) and the sleeve roll (50) is free of vacuumed dewatering i.e. between the forming roll (13) and the sleeve roll (50) no vacuumed dewatering is located.
Forming section according to claim 1, characterized in that the sleeve roll (50) comprises support elements (52) supported at a distance from each other on the stationary support shaft (51), that the belt loop (53)led to circle around the stationary support shaft (51) is supported by the support elements (52), and that the belt loop (53) is impermeable.
Forming section according to claim 1 or 2, characterized in that the distance (L) between the forming roll (13) and the sleeve roll (50), which distance is measured between the point at which the lower and upper wires (10, 20) wrap angle (13V) ends on the forming roll (13) and the point at which the contact of the lower and upper wires (10, 20) on the sleeve roll (50) begins, is 0,2 - 2 meters, advantageously 0,3 - 1,5 meters.
Forming section according to any of claims 1-3, characterized in that the forming unit comprises first a one wire part followed by the twin-wire part.
Forming section according to claim 4, characterized in that the one wire part is substantially horizontal or inclined.
Forming section according to any of claims 4 or 5, characterized in that the one wire part comprises a forming shoe (17) with a deck (18) and openings (19) in the deck (18).
Forming section according to any of claims 1-6, characterized in that at a distance from the sleeve roll (50) the twin-wire forming unit ends as the run of the upper wire (20) turns away from the lower wire (10) and the end part of the forming unit is formed as one wire part.
Forming section according to claim 3, characterized in that the overall height of the forming section is less than 8 meters.
Forming section according to claim 3, characterized in that the highest point of the sleeve roll (50) is on a higher vertical position than the lowest point of the forming roll (13).