NO315570B1 - Apparatus and method for generating turbulence in a blank in a section forming a fourdrinier - Google Patents

Abstract

A method and apparatus for generating turbulence in stock to deflocculate the stock in an open surface forming section of a paper making machine comprises a dewatering box (2) providing vacuum assisted drainage and which has a set of dewatering elements that impart turbulence into relatively thick stock layers carried at machine operating speeds of equal up to about 400 m/min, for the production of paper products having a basis weight generally in excess of about 160 gsm. Each set of elements includes a lead-in element (5), at least one intermediate element (6, 7), and a trailing element (8). The path of the forming fabric (13) is deflected downwardly as it passes over the intermediate elements, which are inclined at an angle of from about 0 DEG to about 10 DEG from a plane defined by forming fabric supporting surfaces on the lead-in and riser elements. This vertical movement initiates turbulence and agitation in the stock, which acts both to deflocculate the stock and to diminish the possibility of sheet sealing. The apparatus is useable in combination with other known formation and drainage devices which are located either upstream or downstream to augment their performance with thicker, slower moving stock layers.

Description

The invention relates to an apparatus and a method for generating turbulence in a blank in the forming part of the paper machine with an open surface. In particular, the invention relates to an apparatus and method for generating sufficient turbulence in the blank layer in an open surface forming section of a paper machine to assist in pulverizing a relatively thick blank layer carried on a relatively slow moving forming material. The invention thus finds application in the production of relatively heavy paper, pulp and board products. Furthermore, the device can be adjusted so that the amount of turbulence exerted in the workpiece layer can be regulated and optimized to adapt the product quality.

In a typical open surface forming section, aqueous stock containing both paper fibers and other paper constituents in amounts of between 0.1% to about 1.5% by weight is fed from a cleaning machine to a horizontally moving forming material. In such a forming section, the movable forming material, after receiving the blank from the cleaning machine, is carried by a forming table followed by a series of drying stations. The drying stations usually include dewatering devices, e.g. blades and foils mounted on the drying station touching the machine side of the forming material. Table rollers are still used in some modern low-speed machines as dewatering and turbulence-producing devices. The forming section can also include other devices that can produce at least some turbulence in the workpiece, e.g. formation showers. As the blank with the open forming material moves through the forming section, the water is removed from the blank until the paper tap contains about 75% to about 85% water. The rest of the water is removed in subsequent parts of the papermaking machine.

The thickness of the blank layer from the cleaning machine to the forming material is determined by the machine speed, the water content of the delivered blank from the cleaning machine and the basis weight of the paper or the sheet product being produced. Heavier products, e.g. lining boards, corrugated medium, market pulp grades and board products, require a greater blank thickness than lighter grades, e.g. newsprint.

In order to produce an acceptable paper product, it is important that the paper components, such as fibers, are thoroughly mixed and dispersed as randomly as possible in the blank after the cleaning machine. In practice, this is almost impossible to achieve: some of the paper fibers tend to flocculate in the blank and are placed as fluff on the forming material. Flocculation will continue in the blank on the forming material unless steps are taken to generate turbulence in the blank. After an initial paper cock is formed, it will be nearly impossible to disperse any remaining fluff. What thus occurs in the blank on the forming material to convert it from a diluted solution of fibers and other constituents to a paper tap is very important in papermaking.

Many methods have been proposed to disperse the fiber in the blank in the forming section. Most of these methods involve turbulence in the blank to disperse flocs. E.g. it is known to introduce a rapid transverse vibration against the forming material near the cleaning machine, in order to add a destructive cutting force to the tufts and thereby redistribute the paper fibres. Forming showers, table rollers and various air and water jets placed above and below the forming material have also been used to produce turbulence in the workpiece layer. The amount of energy required to cause the desired level of turbulence in the workpiece is generally a function of workpiece layer thickness, machine speed, and workpiece composition.

A common way of producing turbulence in the workpiece on an open forming material is to place dewatering elements (e.g. foils, agitator blades and the like) in bearing contact with the machine side of the moving forming material. Devices of this type are described by Wrist, US patent 2,928,456; Sepall, US 3,573,159; Johnson, US 3,874,998; Saad, US 4,420,370; Kallmes, US 4,687,549 and US 4,838,996; and Fuchs, US 4,789,433. Foils have a leading edge that scoops liquid from the forming material, the rear portion sloping downwards at an angle of about 1° to about 8° and serves to provide a suction action that sucks liquid from the blank and father material to deflect sufficiently to cause at least some turbulence in the blank.

Agitator blades are profiled so that some water is sucked out and then directed back through the forming material into the liquid blank layer. Carefully profiled directional channel is placed in the blade surface to achieve this and the water is thereby directed back through the forming material and produces turbulence in the blank on the material, which provides an anti-flocculation effect and serves to distribute the solids indiscriminately.

Another method of producing agitation is described by Johnson, US 4,140,573. In this device, at least one of the dewatering elements of a lava-kuum dewatering box is lowered slightly in relation to the other boxes on either side, so that the material passes over the row with elements and is pulled down slightly by the dewatering vacuum box and then released, causing some turbulence in the blank.

An alternative way of introducing workpiece turbulence is described by Cabrera y Lopez Caram, US 5 830 322.1 this device uses a pair of material carrying elements, a primary element with an inclined surface together with a rear element with a horizontal surface. Drainage of water from the workpiece is regulated by limiting the size of a drainage opening between the two elements. The inclined surface of the primary element is configured to introduce turbulence into the workpiece above the drainage opening without the forming material being deflected in the drainage opening, by means of blade profiles as substantially described by Fuchs, US 4,789,433 and by Kallmes, US 4,838,996. The apparatus uses fluid flow in and out of the drain opening and against the inclined surface of the primary element in the drain opening to cause turbulence in the blank after the fluid has been returned through both the forming element and any paper mat formed thereon to the blank.

Other subject agitating devices are described by Cowan, US 3,922,190; Marx, Jr., US 4,999,086; Hansen et al., US 5,011,577; Hansen, US 5,089,090; and Neun, US 5,681,430.

In situations where the manufactured paper product requires the forming material to move relatively slowly and carry a relatively thick blank layer, e.g. in the production of heavier products, it will be very difficult to generate desired turbulence levels in the workpiece. As the machine speed decreases and the workpiece thickness increases, when producing heavier products, it becomes increasingly difficult to produce the desired amount of turbulence in the workpiece and consequently improve the formation. It has thus been found that in open forming sections where the forming material moves at speeds of less than 400 m/min, and which carry blank layers whose thickness is greater than approximately 2.0 cm at the cleaning machine and which produce heavier products weighing over 160 gsm, there will still be a need for a device that can generate an effective level of turbulence in the blank that can at least cause some antiflocculation in the blank. It would also be an advantage if such a device could be easily adjusted so that the turbulence level could be adapted to the paper manufacturer's requirements.

Another problem can arise with blank compositions containing relatively short fibers or recycled materials. In these blanks, an almost impermeable mat can form on the paper side of the forming material surface which effectively seals the material and prevents satisfactory drainage of the blank, a phenomenon commonly called "sheet sealing". There is therefore a need for a dewatering device that at least improves the drainage that can occur in connection with this phenomenon.

The invention seeks to provide an apparatus and method for generating billet turbulence which can cause at least some billet pulverization and improve formation in an open paper machine forming section where the billet layer is relatively thick and where the forming material moves at a relatively low speed. The invention thus seeks to improve the formation in open paper machines used to produce relatively heavier products, e.g. cardboard and the like. The invention also seeks to reduce, if not eliminate, sheet sealing by generating sufficient turbulence in the blank to redistribute the fiber mat forming a more or less impermeable layer on the paper side of the forming material. The invention is therefore relatively suitable for use in blank compositions containing short fibers or recycled materials.

In a particular embodiment, this invention seeks to provide an adjustment device for generating an adjustable level of blank turbulence which causes at least some blank pulverization and improves formation in an open paper machine forming section where the blank layer is relatively thick and where the forming blank moves at a relatively low speed . In the invention, the term "relatively low speed" is intended to mean an open surface forming material that moves through the forming section at a linear speed of less than about 400 m/min. "Relatively heavier products" and a "relatively thick blank layer" are intended to include an open surface forming material matrix used to produce a product with a basis weight of about 160 gsm, which would generally require a blank layer of more than about 2.0 cm thickness near the border machine. It will also appear that although the invention relates to the production of products with a relatively high basis weight, it is not limited to this and under certain circumstances it is advantageous to have lighter products and higher machine speeds.

According to a first aspect of the invention, a device is provided for generating turbulence in the blank of a forming material in the forming section of an open surface paper machine, the forming section comprising a relatively slow moving forming material with a paper side and a machine side, a relatively thick blank layer on the machine side .

a substantially horizontal intermediate surface; and

an inclined end face;

(ii) a rising dewatering element with a material-bearing surface consisting in sequence of: a leading auxiliary edge;

an inclined surface;

an outgoing surface; and

a part comprising the connection between the inclined surface and the output surface; and

(iii) at least one intermediate dewatering element placed between the incoming dewatering element and the rising element and placed from every other dewatering element with a space, each intermediate element having a material-bearing surface which in turn consists of: a leading auxiliary edge;

an inclined surface; and

a trailing edge;

where:

(a) the portion of the rising element located at the junction between the inclined and exit surfaces is selected from a tip at the junction between the inclined surface and the exit surface, a short, substantially horizontal surface connecting the inclined surface and the exit surface, and a curved surface connecting the inclined surface and the exit surface; (b) the intermediate surface of the inlet dewatering element and the part of the riser element comprising the connection between the inclined surface and the output surface form a first plane; (c) the inclined rear surface of the input dewatering element and the inclined surface of each intermediate dewatering element form a second plane inclined at a certain downward rear angle relative to the first plane;

and

(d) the leading auxiliary edge of the ladder element is placed over the rear edge of the adjacent intermediate dewatering element, so that the movement of the forming material from the rear edge of the adjacent intermediate drainage element to the leading auxiliary edge of the ladder element leads to a vertical movement of the forming material, and of both the initial paper tap and the blank carried on the forming material.

Preferably, at least one intermediate dewatering element is placed between the incoming dewatering element and the riser element and placed from every other dewatering element by a space, adjustably attached to the dewatering box, so as to enable the placement of the inclined surface thereof in the desired, second plane, and the movement to another desired second plane . In this embodiment, as mentioned below, the angle between the first and second planes, instead of being determined by the angle at which the inclined surface of the intermediate element is cut, is determined by setting the adjustable attachment to the drainage box. In this embodiment it is preferred, since the input element is not adjustable, that its sloping rear surface is pointed.

In an alternative, preferred embodiment, the device further comprises a drainage-limiting element which is placed between the riser element and the nearby, intermediate element, which has a material-bearing surface which, in order, comprises:

a leading auxiliary edge; and

an upward inclined surface;

wherein the attachment of the drainage limiting element to the dewatering box is designed and arranged to place the upward inclined surface at an angle to the second plane, to produce a shallow "V" angle therebetween corresponding to the inclined surface of the riser element. In this embodiment, the attachment of the drainage limiting element to the dewatering box can be selected from the group consisting of a fixed element, an adjustable attachment and a second, adjustable attachment included in a first, adjustable attachment for the intermediate elements.

Preferably, all intermediate material-bearing elements have the same width in the machine direction. Alternatively, all intermediate material-bearing elements do not have the same width in the machine direction.

Preferably, each intermediate material-bearing element has a substantially flat inclined surface. Alternatively, at least one intermediate element has an agitator blade profile.

In an alternative aspect, the invention seeks to provide a method for producing the desired level of turbulence in a blank layer carried on a forming material in a forming section in an open surface paper machine which consists essentially of moving the forming material carrying the blank over at least one dewatering box carrying several material carrying elements under and in bearing contact with the forming material, and supply a controlled vacuum supply to produce a controlled, reduced pressure in the dewatering box, the load-bearing elements of the dewatering material consisting essentially of: (i) an incoming dewatering element with a material-bearing surface which, in order, consists of: a leading auxiliary edge;

a substantial horizontal middle overfiate; and

a sloping rear surface;

(ii) a rising dewatering element with a material-bearing surface consisting in sequence of: a leading auxiliary edge;

an inclined surface;

an output surface; and

a part consisting of the connection between the inclined surface and the output surface; and

(iii) at least one intermediate dewatering element placed between the incoming dewatering element and the riser element and placed from every other dewatering element by a space, the intermediate element having a material-bearing surface which, in order, comprises: a leading auxiliary edge;

an inclined surface; and

a trailing edge;

where:

(a) the part of the ladder element placed at the connection between the inclined surface and the exit surface is selected either as a tip at the connection between the inclined surface and the exit surface, a substantially horizontal surface connecting the inclined surface and the exit surface or as a curved surface connecting the inclined surface and the exit surface; (b) the intermediate surface of the inlet dewatering element and the part of the riser element comprising the connection between the inclined surface and the output surface forms a first plane; (c) the inclined rear surface of the incoming dewatering element and the inclined surface of each dewatering element form a second plane inclined at a certain downward rear angle relative to the first plane;

and

(d) the rear auxiliary edge of the riser element is located above the rear edge of the adjacent, intermediate dewatering element, so that the movement of the forming element from the rear edge of the adjacent, intermediate dewatering element to the leading auxiliary edge of the ladder element leads to a vertical movement of the forming material and of both the initial paper tap and the blank carried on the forming material.

Preferably, the desired turbulence level is produced and regulated by at least one adjustable, intermediate dewatering element placed between the incoming dewatering element and the riser element which is adjustably attached to the dewatering box and allows placement of the inclined surface thereof in the second plane; and the turbulence level is regulated by adjusting the adjustable, intermediate support element to a desired location on the second plane.

More preferably, the desired level of turbulence is produced by a device which further comprises a drainage-limiting element which is placed between the riser element and the nearby, intermediate element and which has a material-bearing surface which, in sequence, consists of:

a leading auxiliary edge; and

an upward inclined surface;

wherein the attachment of the drainage limiting member to the dewatering box is designed and arranged to place the upward sloping surface at an angle to the second plane, to produce a shallow "V" angle therebetween in accordance with the sloping surface of the riser member.

Most preferably, the desired level of turbulence is produced and regulated by:

(i) at least one adjustable, intermediate dewatering element placed between the incoming dewatering element and the riser element which is adjustably attached to the dewatering box and which enables the placement of each inclined surface thereof in the second plane; and (ii) a drainage limiting element which is placed between the riser element and the adjacent intermediate element, and which has a material-bearing surface consisting in sequence of:

a leading auxiliary edge; and

an adjustable, upward bevel;

where the turbulence level is regulated by:

(a) adjusting the intermediate support element to the desired second plane location; or

(b) adjusting the drainage limiting element to another location; or

(c) adjusting both the adjustable intermediate support member to a desired second plane location, and adjusting the drainage limiting member to another location.

Preferably, the angle between the first and second planes is from 0° to about 10°.

An advantage of the device according to the invention is that with relatively thick workpiece layers, as soon as a desired turbulence level has been introduced into the workpiece, it is less difficult to maintain the desired turbulence level further along the forming section. Although known devices are not able to generate an acceptable level of turbulence, they will be able to maintain the level of turbulence after it has been generated. The invention can thus be used to optimize the performance of these known devices.

As a result of this, the design of the exit surface of the riser blade will be determined by what follows after the dewatering device according to the invention in the forming section. If the e.g. is followed by a second set of the same elements, so that the ladder element is both the last element in a set and the first element in the next set, the output surface of the ladder blade will have the same shape as the corresponding part of the incoming element, so that it will have significant the same horizontal intermediate surface and an inclined rear surface in the same second plane as the following elements. If, however, it is followed by an undrained space or by a drainage box provided with foils, the exit surface of the riser blade will generally be designed as a foil blade with a foil angle generally between 0.5° to about 5°.

The invention will now be described with reference to the attached figures, where: Fig. 1 schematically shows a section in the machine direction of a workpiece turbulence generating unit according to a first embodiment of the invention; fig. 2, 3 and 4 show sections of the material-bearing elements used in fig. 1; fig. 5 and 6 show alternative elementary arrangements in relation to what is shown in fig. 1; fig. 7 schematically shows a section in the machine direction of a workpiece turbulence generating unit with two sets of material carrying elements; fig. 8 schematically shows an intermediate element with an agitator blade profile; fig. 9 and 10 show schematic partial sections of a subject turbulence generating unit according to a second embodiment of the invention; fig. 11 and 12 show details of the turning and adjusting device used in fig. 10 and 11; fig. 13 schematically shows a section of the unit in fig. 9-12; fig. 14 schematically shows a section in the machine direction of a workpiece turbulence generating unit according to a third embodiment of the invention; fig. 15 shows a section of the drainage limiting element shown in fig. 14; and fig. 16 shows alternative intermediate element arrangements that apply to fig. 1, 7 and 14 with agitator blade profiles for the intermediate elements.

In this invention, the following expressions have been given the meaning:

"machine direction" means the direction along a machine substantially parallel to the forming material travel direction;

"cross machine direction" means a direction substantially perpendicular to the machine direction, generally parallel to the plane of the forming material;

"upstream" means the direction near the cleaning machine for a given point in the machine direction;

"downstream" means the direction away from the cleaning machine in the machine direction;

"front" refers to an upstream element edge;

"rear" refers to a downstream surface or edge;

"paper side" refers to the side of the forming material on which the blank is brought, and the paper tap is formed; and

"machine side" refers to the side of the forming material that is in contact with the material-bearing elements and is thus the other side of the paper side.

In all the sections of the dewatering box shown in the figures, the material-bearing elements extend in the transverse machine direction in the entire width of the forming material. Furthermore, all the angles shown have been enlarged for clarity.

In fig. In is shown a first embodiment of the invention. Both in this figure and later figures, most of the other common parts of a forming section, e.g. the cleaning machine, roller, possibly forming table, forming shower and other drainage or forming devices, not shown. The workpiece turbulence generating device 1 comprises a dewatering box 2 which is provided with a hydraulic tight drain 3 at the bottom through which the water 3 A is emptied from the workpiece. The Awanningsbox 2 is attached by the pipe 4 to the vacuum source which provides a controlled, reduced pressure in relation to the ambient pressure of approximately 7.5 kPa below the ambient pressure.

The desired level of turbulence is generated in the blank by a set of material carrying elements 5, 6, 7 and 8 which are mounted on the top rail of the dewatering box 2 by means of a regular T-beam, as shown at 9A, 9B and 9C. Together, the spaces between the T-beams and the width of the elements determine the widths of the drainage spaces 10, 11 and 12. These spaces are sealed on the sides with end caps (not shown). In the embodiment shown, the spaces 10 and 11 have the same width and a space 12 is wider. The factors that influence the choice of gap width are described below. The elements 5, 6, 7 and 8 can be made of dense polyethylene with inserted ceramic wear surfaces or other material that is suitable for the production of the material bearing surfaces. Within the set of material-bearing elements, element 5 is the leading blade, element 8 is the riser blade and elements 6 and 7 are the intermediate blades.

The forming material 13 moves in the direction of the arrow A with its machine side in contact with the support elements 5-8. Above the gap 12, the forming material 13 rises from the last intermediate element 7 to the riser element 8. This vertical movement of the forming material and of the initial paper tap and the blank carried by it causes turbulence in the blank near and downstream of the exit surface of the riser element 8.

The cross-section of the leading element 5 is shown in fig. 2. This comprises a leading auxiliary edge 14, an intermediate surface 15 and an inclined end surface 16.1 In this embodiment, the end surface is substantially flat and has a slope a in relation to the surface 15. The element is mounted on the T-beam 9A, so that the surface 15 is substantially horizontal. The leading auxiliary edge 14 removes at least some of the water that has been drained through the forming material upstream of the leading element.

The cross-section of the ladder element 8 is shown in fig. 3. This comprises a leading auxiliary edge 17, an inclined surface 18, an outlet surface 19 and a part 20 which comprises a connection between the inclined and outlet surfaces. As shown, the part 20 is the tip at the junction between the two surfaces 18, 19 on each side. Alternative designs are a short horizontal surface and a curved surface. The underlying requirement for the part 20 of the ladder element is that it provides a continuation of the support for the forming material that bends over it and that together with the substantially horizontal surface 15 of the leading element it forms the first plane below which the material is deflected during its passage over the intermediate elements. The exact design of the part 20 is selected based on the construction materials used and desired lengths of the bevel surface 18 and outlet sleeper surface 19. The bevel surface 18 has an angle p which is measured between the bevel surface and the first plane defined by the surface 15 of the leading element, and the part 20 of the ladder element. The design of the outlet surface 19 is described below.

In fig. 1 shows two intermediate elements 6 and 7 which are generally the same. The cross-sections of these are generally similar and the section of the intermediate element 6 is shown in fig. 4. This comprises the leading auxiliary edge 21, an inclined surface 22 and a trailing edge 23. The set of three elements comprising the leading element and the two intermediate elements carried by the T-beams 9C are placed apart, so that the surface 16 and the two the surfaces 22 lie in a common, second plane at an angle a in relation to the first plane.

In the device in the embodiment of the invention as shown in fig. 1, the material 13 moves over the dewatering box 2, with the machine side of the material 13 first gripping the leading edge 14 of the leading element 5 which pushes liquid from the machine side onto the material 13. The forming material 13 continues downstream and eventually passes over the inclined surface 16, the space 10, the inclined surface 22 and the rear edge 23 of the intermediate element 6, the intermediate space 11, the inclined surface 22 and the rear edge 23 of the intermediate element 7, the intermediate space 12 and finally the leading edge 17 and the surfaces 18, 20 and 19 (in this order) of the ladder element 8. The material is drawn down to surface 16 and the two surfaces 22 respectively by the controlled, low vacuum in the dewatering box, to form a fluid seal on these surfaces. Finally, the forming material rises above the gap 12 and the surfaces of the ladder element 8. This upward movement generates turbulence in the workpiece near the ladder element 8.

In this embodiment, the value of the angle a is determined by the characteristics of the machine, which include the total separation of initial and ascending elements, the number of intermediate elements, the machine speed, the thickness of the workpiece layer and the desired level of turbulence in the product being produced. Accordingly, the value a determines the vertical distance through which the forming material must rise from the place where it loses contact with the last intermediate element, which is at the part near the rear edge 23 of this element, to the leading auxiliary edge 17 of the rising element. In general, a is in the range between 0.25° to about 10°. For most purposes a has been found to be less than 6° and often between 2° and 4°. The gap widths between each of the elements that make up the set, along with the applied vacuum and the characteristics of the blank and its ingredients, affect both the amount of drainage that occurs and the amount of turbulence that is generated. The level of applied vacuum together with the gap widths must be sufficient to ensure that the forming material is in hydraulic contact with the material-bearing surfaces for all the elements. The actual value of the supplied vacuum also affects the turbulence level since it affects the transition between the forming material from the last intermediate element to the riser element. At this point, the forming element has a shallow "V" shape that is sharper or flatter, depending at least in part on the applied vacuum. The actual values chosen for a and of the other identified variables are determined by the desired amount of turbulence in the workpiece at that point in the forming section. Some experimentation may be necessary to determine optimum values for a given set of papermaking conditions.

The shape of the outlet surface 19 of the riser element 8 depends to a large extent on what follows this element downstream in the forming section, where there are several things to choose from. The ladder element can e.g. followed by another identical blank turbulence generating unit, an uncontrolled drainage gap, by a set of foils, or by an Isoflo (trademark) drainage unit. When the next drainage unit is more or less identical to, or even mounted on the same drainage box as the preceding unit, the riser element becomes common to both units. The outlet surface of the ladder element is then profiled as if it were the leading element, so that it is equal to the selected value for a for the following unit, which need not be equal to the preceding unit. When the riser element is followed by a spacer or a foil unit, it may be sufficient to use an outlet surface that is substantially horizontal or slopes downwards at more or less the same angle used for a conventional foil blade, ie up to about 5°, without an intervening short horizontal surface.

The inclined surface of a ladder element, as at 18 in fig. 3, is generally a fairly steep angle, as it forms the path for the pitch shape of the material shown in FIG. 1. The angle P shown in fig. 3 will generally be between 0° and 30°. In practice, an angle between 10° and 20° will be sufficient. The magnitude of the angle p is determined by the vertical displacement of the forming material as it rises from the inclined surface 22 of the last intermediate element to the surface 20 of the riser element. The value of p should be chosen to minimize material deflection at low vacuum levels. If the material deflection becomes greater than this, it is found that the forming material still engages and follows the shape of this surface. However, some experimentation may be required to determine the optimum value of P for a given set of machine conditions.

Furthermore, it turns out that after a desired level of turbulence has been produced in the workpiece by the device according to the invention, it will be easier to cause turbulence in the workpiece downstream in the forming section and thus make it easier to use downstream generating devices for subsequent turbulence. This improves the operation of subsequent, conventional pulverizing and dewatering devices and improves the formation of the manufactured product. In a similar way, it has been discovered that the device according to the invention will improve a lower level of turbulence produced in the subject by an upstream device, e.g. a formation shower.

Although the above embodiment applies when the material speed is 400 m/min or less and the workpiece is relatively thick, e.g. 2.0 cm or more near the cleaning machine, for the manufacture of paper products whose basis weight is 160 gsm or greater, it is thought that the invention also has advantages in other conditions, e.g. at higher material speeds and/or thinner workpiece layers.

It has unexpectedly been discovered that after the material 13 has been run at machine speed over the dewatering box 1 under an applied vacuum, that it will often continue to follow the path defined by the supporting members 5, 6, 7 and 8, even as the vacuum is reduced . This makes it possible to reduce the amount of drainage above the dewatering box 2. This entails an additional advantage in that any tendency to sheet sealing is reduced.

In the embodiment shown in fig. 1, the shown unit 2 has intermediate dewatering elements 6 and 7. Depending on the characteristics of the machine and the product being produced, other configurations can also be used. Fig. 5 shows an intermediate drainage element 6 between a leading element 5 and a riser element 8 and fig. 6 shows a configuration with five intermediate elements 24, 25, 26, 27 and 28, where all five intermediate elements are arranged to be in the second plane at a common angle a in relation to the first plane. It is also shown in fig. 6 that the intermediate elements do not need to be of the same width.

It is also possible to utilize the invention with two dewatering units in succession, where the ladder element in the first unit also serves as the initial element in the second. This arrangement is shown in fig. 7. The first set of elements comprises a leading element 5 and two intermediate elements 29 and 30. The second set of elements again comprises two intermediate elements 32 and 33 and a ladder element 8. The central element 31 functions as a ladder for the first set and initial element for the second set. Its upstream beveled surface 18 is shaped to fit a riser member and its downstream beveled rear surface is shaped to match the leading member. This event can also be set up in two different ways:

(i) a single dewatering box 2 can be used with a single vacuum supply 4, which is essentially shown in fig. 1; or (ii) a dewatering box with two hydraulically separate rooms 2A and 2B, separated by wall 34, each having its own vacuum supply 4A and 4B, as shown in fig. 7.

In the latter arrangement, the vacuum supplied to the two chambers need not be equal. It is also possible that the angles ax and 0C2, where both are measured in relation to the first plane as shown in fig. 7, do not have to be the same, depending on the desired level of turbulence in each unit.

In the embodiments shown, the intermediate elements have essentially planar support surfaces for the forming material. In some cases, depending both on the characteristics of the machine, the properties of the workpiece and the product being manufactured, it has been found desirable to produce more turbulence in the workpiece than is provided by utilizing planar bearing surfaces for the forming material on the intermediate elements in the second plane. As shown in fig. 8, an intermediate element with a so-called agitator blade profile with a single channel 35 can be used to introduce additional turbulence. Agitator blades with such a described surface are described e.g. by Johnson in US 3874 998. Other profiles are known and used. It has been found that the agitator blade profile can improve the turbulence effects produced by the turbulence generating unit according to this invention.

In the same way, it is also envisaged in this invention that the dewatering device shares a common dewatering box with another dewatering device, e.g. an Isoflo (trademark), agitator blades or a set of foil blades.

In an experimental trial, a workpiece turbulence generating unit according to the invention was placed downstream of a forming shower in an open-surface forming section for a paper machine. The device used is as shown in fig. 7, but without the internal dividing wall 34 and only a single vacuum supply. Two suction boxes provided with covers substantially as described by Johnson in US 4,140,573 were placed immediately downstream of the unit. The machine speed in the forming section was about 320 m/min and the paperboard product had an average weight of about 299 gsm. The initial element was 38.1 mm wide with a beveled surface with a width of 8.5 mm. The two intermediate elements were the same in each pair and had an inclined surface width of 150.9 mm. The drainage gap between each of the elements was 9.5 mm, except for the gap downstream of the last intermediate elements, which was 12.7 mm. In both sets of elements, the value for a was 2°. The drainage element, which acted as a common inlet and riser element in the middle of the set, had a sloping surface that was 9.5 mm wide and the value for the angle a was 5°. The exit surface downstream of this common element was substantially flat and sloped downwards at 2° and thus equal to the value of a. The exit surface of the second riser blade was horizontal. All element widths and element separation gaps were measured in the machine direction.

During the experiment, the supplied vacuum level from the suction box was varied from ambient pressure to approximately 5 kPa below ambient pressure. It was found that when the upstream formation shower was turned off, as the billet was passed over the turbulence generating unit, there was no increased activity in the billet. However, it was found that both the drainage from the initial sheet and the quality of the resulting paper product, by its formation and smoothness, were improved compared to the quality before the device was installed. This shows that the device was effective in generating turbulence in the blank and in preventing sheet sealing, despite the formation shower being switched off.

When the formation shower was turned on, the appearance of the blank changed dramatically as it was passed over the blank turbulence generator, indicating increased levels of blank activity. This showed that the workpiece turbulence generating unit according to the invention is effective both by introducing turbulence into the workpiece to improve formation and prevent sheet sealing and to improve the performance of other drainage and turbulence generating devices.

In the embodiment described above, the location of the intermediate members is determined by fixed structures and the cross-sectional profile of the intermediate members determines the value of a. Since the value of a is never very high, this design requires accurate machining and installation of the intermediate members to produce a set of surfaces that are precisely located in the second plane.

In a second embodiment of the invention, each element is adjustably mounted on the construction of the dewatering box instead of mounting the intermediate element directly on the construction of the dewatering box. It then becomes possible to control the value of a by moving the entire intermediate element to a suitable angle of inclination for the inclined surface by adjusting the assembly, instead of constructing the element to the desired, fixed angle of inclination. In this embodiment, it is preferred, where more than one intermediate element is used, that all the intermediate elements are mounted on a single, adjustable assembly at the desired machine direction separated from their workpiece bearing surfaces in a common plane. The desired value of a is then obtained by adjusting the assembly or assemblies as required.

In addition to greatly simplifying the construction of the turbulence generating unit as all the intermediate elements can be manufactured in substantially the same size, this configuration has the advantage that the value of a can be easily changed to change the level of turbulence generated. This may be necessary for several reasons, e.g. a change in the product, a change in the processing of the product, and less than perfect mixing in the cleaning unit causing problems on the molding material. Thus, the embodiment of the invention provides, in addition to producing turbulence in the blank on the forming material, a device whereby the level of turbulence produced can be regulated and either improved or reduced as needed during paper production.

This embodiment of the invention is shown in fig. 9-13. In fig. 9-12, the forming material is omitted for clarity.

In fig. 9 and 10, showing partially cut away three quarters of the unit, the unit comprises a single drainage box 2 carrying a leading member 5, three intermediate members 35, 36 and 37, of which the middle one, 36, is narrower than the other two and a riser member 8. The leading element 5 and the ladder element 8 are supported by the T-beam structures 9A and 9B, both of which are directly supported by the frame 38 at the top of the dewatering box 2. The three intermediate elements are supported by the same T-beam structures 9C, each of which is mounted on a adjustable support frame 40. At the upstream end, the adjustable frame 40, close to the leading element 5, is carried by a swing assembly 41. At the downstream end, the adjustable frame 40 is provided with a vertically adjustable assembly 42 which in turn is controlled by the adjustment rod 43 which is moved in the directions shown by arrow B by means of the handle 44. The adjusting rod 43 is carried by suitable bearings (not shown) on the beam 45 carried by the support frame for the dewatering box at the top, as shown at 46.

The upstream pivot point is shown in detail in fig. 11. The frame 40 rotates through a small arc (providing sufficient angular movement to achieve the desired value for a) about the rod 47 which is supported by the wall of the dewatering box 2, as shown at 50. The frame 40 is attached to the rod 47 by means of an adjustable bearing block 58 carried by a bracket 49. The bearing block is held in place by the locking bolt 51 which passes through the opening 52. This form of attachment enables fine adjustment of the position of the element's surface 35 in relation to the inclined surface of the leading element 5. Fig. 12 shows only a pivot point assembly, as in practice there will be at least two and often more so that the upstream end of the frame 40 is satisfactorily supported in the entire width of the forming section.

The downstream vertical adjustment assembly is shown in detail in fig. 12. The vertical adjustment assembly 42 is attached to the downstream face of the frame 40 by bolts 53 and 54 which are provided with larger holes 53A and 54A. The assembly 42 also includes an angled slot 55 where a locking pin 56 is fitted. The outer end of the pin 56 engages the opening 57 in the adjustment rod 43. As a result, the horizontal movement of the rod 53 in the direction of the arrow B causes a vertical movement of the frame 40 in the direction of the arrow C directions. The enlarged holes 53A, 54A are provided to enable fine adjustment of the assembly 42 in relation to the frame 40, so that the same value of a is obtained over the entire width of the forming section. If desired, the rod 43 can be locked in a specific setting by using suitable locking mechanisms. Fig. 12 shows only one adjustment assembly, as in practice there will be at least two and up to several, so that the downstream end of the frame 40 is satisfactorily carried over the entire width of the forming section.

It is also contemplated that other vertical adjustment devices may be used: e.g. the adjustment rod 43 can be replaced by a screw that can be monitored, and the entire adjustment device can be replaced by a hydraulic or pneumatic system. If the vertical adjustment device is to be able to operate freely, care should be taken that it is placed in an environment where it can be clogged by components from the workpiece.

The section of figures 9-12 is shown schematically in fig. 13. The guide element and the riser element respectively 5 and 8 are carried by their T-beams 9A and 9B attached directly to the drainage box 38. The three intermediate elements 35, 36 and 37 are each carried by T-beams 9C carried on the subframe 40. The subframe 40 is carried at the upstream end of the rod 47 which it rotates to produce the desired value for a. At the downstream end it is carried by the adjustment assembly 42, regulated by the adjustment rod 43. The actual value of a is determined by the position of the adjustment rod 43 relative to the vertical adjustment assembly 42 .

Although the intermediate elements in this arrangement are adjustable to the desired value of a, the leading element is still fixed and cannot be adjusted, so that its sloping rear surface is at a constant angle. In some cases, it has been found that this can lead to deflection of the forming material over the rear end of the leading element, which is not desirable for several reasons. It is therefore preferred that in this arrangement, as shown at 70 (see also fig. 10), the leading element has a curved rear edge.

Thus, it will be seen that in this preferred embodiment, rather than adjusting each spacer individually to achieve the desired value of a, which requires either precise machining and installation, or precise individual vertical and angular adjustment, that the set of spacers is made equal and is mounted on the subframe, so that the entire gripping surface of the forming material is in a common plane which is essentially parallel to the frame itself. When the frame is installed, the desired value of a is obtained by moving the rod 43 to the desired position after any adjustment of the bolts 51, 53 and 54, which bevels the surfaces of the intermediate elements to the desired position to determine the second plane.

In another embodiment, a fourth drainage limiting element is included in the dewatering device and placed in the space between the riser element and the immediately preceding upstream intermediate element. In some configurations, especially where the intermediate element's space is chosen to be relatively large, or the value of a together with the length of the machine direction in the unit gives a relatively large vertical distance between the last intermediate element and the leading auxiliary edge of the ladder element, a significant amount of the forming material can be exposed for vacuum-assisted drainage between the point where the machine side of the forming material loses contact with the last intermediate element near its rear edge, and the leading auxiliary edge of the riser element. This makes it possible to suck out excess water from the workpiece at this point. This can be regulated by inserting a fourth drainage-limiting element in this space by a workpiece-bearing surface that is inclined upwards in bearing contact with the forming material, so that the bearing surface of the intermediate element and the bearing surface of the drainage-limiting element form a shallow "V" that supports the machine side of the forming material and limits the machine-side area of the forming material subject to vacuum-assisted drainage at this point.

There are several possibilities for constructing the additional drainage limiting element, for example: (a) it can be mounted without being adjustable, more or less as described above for the other elements; or

(b) it can be mounted adjustably; or

(c) it can be adjustably mounted on a sub-frame carrying a set of intermediate members.

For the same reasons as mentioned for the intermediate elements, it is preferred that the additional drainage limiting element is adjustable. More preferably, more or less the same subframe assembly is used as described for the intermediate members for the additional drainage limiting member.

In fig. 14 shows a schematic drawing with a drainage limiting element. The leading and ladder elements 5 and 8 are supported by their respective T-beams 9A and 9B. The three intermediate members 35, 36 and 37 are each carried by T-beams 9C carried on the first subframe 40. The first subframe 40 is carried at the upstream end of the rod 47 about which it rotates to provide the required value for a. The downstream end is carried of the adjustment assembly 42 and the adjustment rod 43. The actual value of a is determined by the position of the adjustment rod 43 relative to the vertical adjustment assembly 42. The drainage restrictor element 55 is supported by a T-bar 9D supported by a second subframe 56 which is rotatably supported at the downstream end (in much the same way as the first subframe 40) of the rod 57. The inclination of the drainage limiting element, designated by the angle y between the surface 61 and the first plane, is controlled by the vertically adjustable upstream assembly 58 of the second subframe 56. A similar arrangement as described for the first subframe may be suitably used. In the latter case [J and y will be more or less equal.

The cross-section of the drainage limiting element is shown in fig. 15. The upstream surface 59 comprises a leading auxiliary edge 60 which is followed by an upward sloping surface 61 which terminates in a trailing edge 62. The element is suitably supported by a T-beam as at 9D. The value of 5 is chosen to enable a value for the angle y which provides a smooth transition for the moving forming material from the point where it loses contact with the last intermediate element 37 to the inclined surface of the riser element 8. Depending on the mounting form used for the drainage limiting element, the angle 5 be quite small and can be zero, so that the upward inclined surface is substantially perpendicular to the upstream surface 59. As mentioned above, the point where the forming material loses contact with the element 37 depends, among other things, on the vacuum level supplied to the dewatering box.

Fig. 16 schematically shows alternative intermediate element profiles in relation to those shown in fig. 1,7 and 14. Fig. 16 shows a set of seven elements. The first set of elements comprises a leading element 5 and two intermediate elements 63, 64, each of which has an agitator blade profile. The smaller element 31 is both the ladder element for the first set and the leading element for the second set. The second set comprises two intermediate elements 65 and 66 followed by a ladder element 8. The elements 65 and 66 have a substantially flat surface. As shown, the two sets are placed above a split dewatering box 2 with separate drainage chambers 2A and 2B which can be supplied with the same or a different vacuum. It is also thought that the elements 63 and 64 can form the second set, while the elements 65 and 66 form the first set. From this it will appear that the combination of element profiles can be used to generate a desired level of turbulence in the subject.

The invention offers several advantages compared to prior art. The workpiece turbulence generation unit can be used to advantage to dewater and pulverize thick and or heavier workpieces with the supply of low vacuum pressure or in some cases a minimal vacuum after the section is started. The ability to reduce the applied vacuum level significantly reduces drainage and sheet sealing as the workpiece passes over the unit. The turbulence generated through the thickness of the blank can also be used to improve the uniform and efficient pulverization of the blank by other agitation devices located both upstream and downstream of the device.

Claims (15)

1. Apparatus for generating turbulence in the blank of a forming material in an open surface forming section for a paper machine, the forming section comprising a relatively slowly moving forming material with a paper side and a machine side, a relatively thick blank layer on the paper side, a dewatering box (2) which is placed under the forming material (13) connected to a controlled vacuum supply device (4) which can produce a reduced pressure in the dewatering box, and several supporting dewatering elements (5, 6, 7, 8) for the forming material (13) carried by the dewatering box (2) which essentially consisting of: (i) a leading dewatering element (5) with a material-bearing surface consisting in sequence of: a leading auxiliary edge (14); a substantially horizontal intermediate surface (15); and an inclined rear surface (16); (ii) a rising dewatering element (8) with a material-bearing surface comprising in sequence: a leading auxiliary edge (17); an inclined surface (18); an output surface (19); and a part (20) comprising the connection between the inclined surface (18) and the output surface (19); and (iii) at least one intermediate dewatering element (6, 7) placed between the leading dewatering element (5) and the riser element (8) and placed a distance from every other dewatering element (6, 7) at a space (10, 11, 12), wherein each intermediate element (6, 7) has a material-bearing surface which in turn comprises; a leading auxiliary edge (21); an inclined surface (22); and a rear edge (23); characterized by: (a) that the part (20) of the ladder element (8) which is placed at the connection between the inclined surface (18) and the output surface (19) is chosen either as a tip at the connection between the inclined surface (18) and the output surface (19) a short substantially horizontal surface connecting the inclined surface (18) and the output surface (19) or as a curved surface connecting the inclined surface (18) and the output surface (19); (b) that the intermediate surface (15) of the leading dewatering element (5) and the part (20) of the riser element (8) which comprises the connection between the inclined surface (18) and the output surface (19) form a first plane; (c) that the inclined rear surface (22) of the leading dewatering element (5) and the inclined surface of each intermediate dewatering element (6, 7) form a second plane which is inclined at a selected downward rear angle (a) in relation to the first plan; and (d) that the leading auxiliary edge (17) of the riser element (8) is placed over the rear edge (23) of the nearby intermediate drainage element (7), so that the movement of the forming material from the rear edge (23) of the nearby, intermediate drainage element (7) to the leading auxiliary edge (17) of the riser element (8) leads to a vertical movement of the forming material (13), and of both the initial paper tap and the workpiece carried on the forming material (13). 2. Apparatus according to claim 1, characterized in that at least one intermediate dewatering element (6, 7) placed between the leading dewatering element (5) and the riser element (8) and placed from every other dewatering element by a space (10, 11, 12) is adjustable attached (42, 43, 44) to the dewatering box (2) which enables placement of each inclined surface (35, 36, 37) thereof in the desired second plane and enables movement to another desired second plane. 3. Apparatus according to claim 1 or 2, characterized in that it further comprises a drainage-limiting element which is placed between the riser element (8) and the nearby intermediate element (37) and which has a material-bearing surface which consists in sequence of: a leading auxiliary edge; and an upward sloping surface (55); where the attachment (56, 57, 58) of the drainage limiting element to the dewatering box (2) is constructed and arranged to place the upward inclined surface at an angle (7) to the second plane, so that it forms a shallow "V" angle between them which corresponds to the inclined surface (18) of the ladder element (8). 4. Apparatus according to claim 1, 2 or 3, characterized in that the attachment (56, 57, 58) of the drainage limiting element to the dewatering box is selected from the group consisting of a fixed attachment, an adjustable attachment (42, 43, 44) and a second adjustable mount included in a first adjustable mount for the intermediate elements. 5. Apparatus according to claim 1, 2 or 3, characterized in that all the intermediate material-bearing elements (6, 7) have either the same width in the machine direction, or not all have the same width in the machine direction. 6. Apparatus according to claim 1, 2 or 3, characterized in that it or each of the intermediate material-bearing element(s) (6, 7) has a substantially flat inclined surface, or agitator blade profile (35). 7. Apparatus according to claim 1, 2 or 3, characterized in that the downward, rear angle between the first and second planes is between 0.25° and 10°. 8. Apparatus according to claim 1, 2 or 3, characterized by first and second turbulence-generating devices in sequence, where the output surface of the riser element in the first device provides the rear surface of the leading element for the second device, and comprises either a single dewatering box that carries both turbulence-generating devices , or a dewatering box with a first and second hydraulically separated compartment, each of which has its own vacuum supply, and where each of the compartments supports a turbulence generating device. 9. Apparatus according to claim 8, characterized in that the angle (a{) between the first and second planes in the first turbulence-generating device is equal to or different from the angle (a2) between the first and second planes in the second turbulence-generating device. 10. Apparatus according to claim 1, 2 or 3, characterized in that the forming material moves less than approximately 400 m/min. 11. Method for producing the desired level of turbulence in a blank layer carried on a forming material (13) in a forming section with an open surface in a paper machine which essentially consists of moving the forming material (13) which carries the blank over at least one dewatering box device' (1) which carries several material-bearing elements (5, 6, 7, 8) underneath and which are in supportive contact with the forming material (13) and which supply a controlled vacuum supply (4) to produce a controlled reduced pressure in the dewatering box (2), as the dewatering material's bearing elements essentially consist of: (i) a leading dewatering element (5) with a material-bearing surface which in turn consists of: a leading auxiliary edge (14); a substantially horizontal intermediate surface (15); and an inclined rear surface (16); (ii) a rising dewatering element (8) with a material-bearing surface consisting in sequence of: a leading auxiliary edge (17); an inclined surface (18); an output surface (19); and a part (20) comprising the connection between the inclined surface (18) and the output surface (19); and (iii) at least one intermediate dewatering element (6, 7) placed between the leading dewatering element (5) and the riser element (8) and placed from every other dewatering element (6, 7) by a space (10, 11, 12), each intermediate element (6, 7) has a material-bearing surface which, in order, consists of: a leading auxiliary edge (21); an inclined surface (22); and a rear edge (23); characterized by: (a) that the part (20) of the ladder element (8) which is placed at the connection between the inclined surface (18) and the output surface (19) is selected either as a tip at the connection between the inclined surface (18) and the output surface (19), a substantially horizontal surface connecting the inclined surface (18) and the output surface (19) or as a curved surface connecting the inclined surface (18) and the output surface (19); (b) that the intermediate surface (15) of the leading dewatering element and the part (20) of the riser element (8) which includes the connection between the inclined surface (18) and the output surface (19) form a first plane; (c) that the inclined rear surface (22) of the leading drainage element and the inclined surface of the or each of the intermediate drainage element(s) (6, 7) form a second plane which is inclined at a selected downward rear angle (a) in relation to the first plan; and (d) that the leading auxiliary edge (17) of the riser element (8) is placed over the rear edge (23) of the nearby dewatering element (7), so that the movement of the forming material from the rear edge (23) of the nearby intermediate dewatering element (7) to the leading auxiliary edge (17) of the riser element (8) leads to a vertical movement of the forming material (13) and of both the initial paper tap and the blank carried on the forming material (13). 12. Method according to claim 11, characterized in that the desired level of turbulence is produced and regulated by at least one adjustable intermediate dewatering element (6, 7) placed between the leading dewatering element (5) and the riser element (8) which is adjustably attached (42, 43, 44) to the dewatering box (2) and enables the placement of it or each of the inclined surfaces (35, 36, 37) thereof in the second plane; and the turbulence level is regulated by adjusting the adjustable intermediate support element to the desired second plane location. 13. Method according to claim 11 or 12, characterized in that the device further comprises a drainage limiting element (55) which is placed between the riser element (8) and the nearby intermediate element (37) and which has a material-bearing surface which in sequence consists of: a leading auxiliary edge; and an upward inclined surface; wherein the attachment of the drainage limiting element to the dewatering box (2) is designed and arranged to place the upward inclined surface (55) at an angle (7) to the second plane, to provide a shallow "V" angle between them in accordance with with the inclined surface of the ladder element. 14. Method according to claim 11, 12 or 13, characterized in that the desired level of turbulence is produced and controlled by: (i) at least one adjustable intermediate dewatering element (6, 7) placed between the leading dewatering element (5) and the riser element (8), which is adjustable attached (42, 43, 44) to the dewatering box (2) and enabling the placement of the or each of the inclined surfaces (35, 36, 37) thereof in the second plane; and (ii) a drainage limiting element which is disposed between the riser element and the adjacent intermediate element and which has a material bearing surface consisting in sequence of: a leading auxiliary edge; and an adjustable, upward bevel; wherein the turbulence level is controlled by: (a) adjusting the adjustable intermediate support element to a desired second plane location; or (b) adjusting the drainage limiting element to another location; or (c) adjusting both the adjustable intermediate support member to a desired second plane location and adjusting the drainage limiting member to another location. 15. Method according to claim 11 or 14, characterized in that said material moves at a speed equal to or less than approximately 400 m/min.