WO2013024205A1

WO2013024205A1 - Headbox and method for a paper or cardboard machine

Info

Publication number: WO2013024205A1
Application number: PCT/FI2012/050788
Authority: WO
Inventors: Matti Luukkanen
Original assignee: Paperharju Oy
Priority date: 2011-08-17
Filing date: 2012-08-16
Publication date: 2013-02-21
Also published as: FI20115805A0; FI122799B

Abstract

The invention relates to a headbox for a paper or cardboard machine. The headbox (10) includes a flow channel (13), delimited by an internal wall (19) of the headbox (10) and a roll (11) arranged to rotate, which narrows in the flow direction. The roll (11) is arranged to act as a feed roll (12) and the axis of rotation of the feed roll (12) is arranged to be able to be moved radially, in order to alter the size and shape of the flow channel (13) and thus to control the headbox (10). The invention also relates to a method for a paper or cardboard machine.

Description

HEADBOX AND METHOD FOR A PAPER OR CARDBOARD MACHINE

The present invention relates to a headbox for a paper or cardboard machine, which headbox includes a flow channel, delimited by an internal wall of the headbox and a roll arranged to rotate, which narrows in the flow direction. The invention also relates to a. method for a paper or cardboard machine . In recent years, production amounts and speeds in paper and board manufacturing processes have increased rapidly. This has caused great technical challenges, particularly in the headbox. Paper and board manufacturing processes have become difficult to control and the headbox has become massive in size and expensive in price. The large flow quantities and their control require complex runnability components, which further increases costs. The pumps and screens connected to headboxes are also specially manufactured according to the requirements of the headbox. In addition, the headboxes of paper and board machines must be dimensioned for a narrow flow range., which is also referred to as the running window. This restricts the operating range of paper and board machines, making it impossible to use the same machine to produce the entire grammage range required. These factors increase investment costs and reduce the pro- cess's operating range. The narrowness of the operating range is a problem especially with board machines, for which the desired grammage range is often very wide. For different cardboard, the grammage range can vary, for example, from 120 to 380 g/m². In order to save costs, attempts have, been made to manufacture board from several layers, in such ,a way that surface layers are manufactured on either side of a core layer. For example,, in thick three-layer cardboard, it would be in principal advantageous to manufacture a thick core layer and thin surface layers, using, for example, a composition of 40 + 300 + 40 g/m². However, in practice this has proved impossible, so that the thickness of the surface layers has had to be increased, which has raised the production costs significantly, because the raw material of the surface layers is more expensive than that of the core layer. At the same time, this goes outside the running window of the headbox, leading to problems in the process itself and in the quality values of the finished product .

With existing headboxes, a low fibre-suspension consistency must be used, to achieve sufficient flow and mixing. The conventional consistency is 0.5 - 1.0 %. The operation of the headbox requires a specific minimum flow to create the necessary shear force and thus to homogenize the fibre suspension. The dimensioning of the entire wet end has proved difficult, even within the normal consistency range. The operation of existing headboxes is based on pressure and pressure loss, which makes headboxes heavy pressure vessels. Operationally, the headbox is a turbulence generator. This in turn demands a high manufacturing precision in the flow channels, which in turn increases costs. The existing production process is sensitive to pulsation and the air content of the fibre suspension, which detrimentally affects runnability and the quality of the finished product. The adjustability of headboxes is also limited in terms of the quality values of the finished product. Such values are, for example, formation, various strength values, the orientation ratio, and the relationships between the various values.

The manufacturing-precision requirements of existing headboxes have increased in step with the increase in flow quantities and production. In existing headboxes, the energy is pressure and thus headboxes have become pressure vessels in terms of construction. It has been necessary to raise the counter- pressure of the headbox to a high level to avoid flow disturbances and create shear forces, which leads to a narrow operating range. In practice, a headbox has a single optimum flow, which limits implementing grammage ranges of the grades being run by paper and cardboard machines. Adjustment of the quality values of the finished product is also limited with existing headboxes. Particularly with board machines, it is difficult to optimize the strength values and functional adjustments are lacking. Deviation from the narrow operating range immediately weakens the quality values of the finished product. The headbox's consistency too is in a narrow range and, in addition to everything else, the consistency is low, being about 0.5 %. This increases the flow quantities to a high level with large production quantities and makes them difficult to control. The large flow quantities also determine the sizes of the rest of the process equipment and some of it must be of specialist manufacture. Controlled running of the process also requires runnability components. This leads to high investment and operating costs.

Attempts have also been made to develop a headbox, in which a fibre suspension with a higher consistency than previously could be used. Such a headbox is disclosed in European patent number 2215305. The headbox includes a flow channel delimited by an internal wall of the headbox and a roll arranged to rotate, which narrows in the flow direction. In the narrowing flow channel, the rotating roll is used to create mixing and turbulence in the fibre suspension. Despite the roller, this is a so-called pressure headbox, which is powered by an external pump. Thus, the outflow speed of the fibre suspension and its regulation are based on the said pump. In other words, the operation of such a hydraulic headbox is based on a large pressure loss.

The invention is intended to create a new type of headbox for a paper or cardboard machine, which operates over a wide grammage and consistency range. The invention is also intended to create a new type of method for a paper or cardboard machine, by means of which the process, and thus the properties of the finished product, can be regulated not only more precisely than previously, but also more easily than previously. The characteristic features of the headbox according to the present invention are stated in the accompanying Claim 1. Correspondingly, the characteristic features of the method according to the invention are stated in the accompanying Claim 10. The new type of headbox operates in a surprising manner, permitting precise adjustability. Control of the production process and flows is thus better than before, so that control of the quality values of the finished product is also better than before. The new type of operating principle and construction permits part of the operations of the short circulation and forming section to be included in the headbox. Thanks to the method, the wet-end process is simple and, if necessary, a fibre suspension with a higher consistency that previously can be used. At the same time, the process can be used over a wide grammage range .

The wider operating area than previously and the adjustability permit several product grades to be produced by the same headbox, so that it is possible to speak of a multi-grade headbox. The headbox based on the flow principle acts itself as a kind of continuously operating, impeller-less, lightweight- construction feed pump. The pressure levels are then lower than before, making it possible to use lightweight structures. In addition, the operating range of the headbox is wide in terms of both flows and consistencies. In the headbox according to the invention, the final flow of the fibre suspension, more exactly the exit-flow velocity, is regulated by the speed of rotation of the feed roll. In addition, the headbox operates in the consistency range 0.5 - 5.0 %.

The construction and operation of the new type of headbox eliminates the problem of a small slice when using a high- consistency fibre suspension. At the same time, the formation of boundary-layer turbulence and slice-geometry disturbances are avoided. Also, fibre suspensions with a higher consistency can be used at lower grammages than previously. As is known, the flow properties of a fibre suspension change significantly when its consistency increases. This mainly due to the floccu- lation time of the fibre suspension, which diminishes rapidly as a function of consistency. A short flocculation time also signifies an increase in flocculation sensitivity. During flocculation, local variations, such as floes and voids, form in the fibre suspension. In other words, the fibre suspension has a non-homogeneous structure, which leads to runnability problems and quality deviations. In order to keep a viscous fibre suspension homogeneous, shear stresses exceeding the elastic limit must be caused in the liquid phase. The stresses required increase to the cube of the consistency and depend, in addition, on the length and longitudinal mass of the fibres. At the same consistency, long and flexible fibres will require a high shear stress, whereas a fibre suspension formed of short and stiff fibres will homogenize at a lower shear stress.

In the headbox according to the invention, the fibre suspension is homogenized by a rotating feed roll, which together with the internal wall of the headbox delimits a narrowing flow channel. In addition, the size of the flow channel can be altered and adjusted by moving the feed roll. Homogenization is based on two physical phenomena, which can be depicted using two dimensionless quantities, the so-called π number. These quantities are the Reynolds number Re and the Taylor number Ta. The Reynolds number Re depends on the flow gap d, the feed roll's angular velocity Ω=2πί, in which f is the number of revolutions, and the radius R of the feed roll, as well as the kinematic viscosity v of the pulp. The viscosity can be defined for the stretching flow and the shear flow and it increases as the fibre-length/width ratio increases. The Reynolds number Re can be written in the form Re=Q*R*d/v. When the Reynolds number Re increases, the shear stresses increase and finally the flow

Ta = Ω R^w x.d^w7;v=Rex-(d/R)^v becomes turbulence. The Taylor number Ta depends on the same factors and can be written in the form

As the Taylor number increases, at a specific stage vortices in the flow direction arise in the fibre suspension, which have an excellent ability to disperse floes and to separate the pulp component containing air from the fibre suspension. If the Taylor number is increased further, the flow finally becomes turbulent and the stable vortices disappear.

In the headbox according to the invention, the fibre suspension is guided into a narrow flow channel, in which a rotating feed roll causes a strong shear force in the fibre suspension. Initially, the shear gives rise to boundary-layer turbulence, which causes strong Reynolds stresses in the fibre suspension. If the fibre suspension further accelerates in the flow channel, vortices arise and finally the entire flow in the flow channel becomes turbulent. This flow sequence ensures that the exit jet from the headbox is homogeneous. If the radius of the feed roll and the viscosity of the fibre suspension are assumed to be fixed, the free parameters remaining being the radial dimension of the flow gap, as well as the width d of the flow gap and the lap of the feed roll, which in this headbox are adjustable. The final layer thickness coming from the slice is determined according to the bypass-circulation or overflow ratio, which will be explained later in greater detail. The bypass-circulation or overflow ratio is thus also an important adjustment parameter. The boundary-layer turbulence can be further boosted by means of the construction of the internal wall of the headbox. The shear stresses thus created exceed the elastic limit of the fibre suspension. In addition, the wall structure can be used to adjust the location at which the entire flow of the flow channel becomes turbulent. The shear forces act on the fibre suspension in the flow channel right up to the formation zone. This is achieved by means of a continuous but small acceleration of the flow, so that a stretching flow is created. However, the acceleration is kept low enough to prevent laminarization of the boundary layer. Formation takes place over a short distance and in a stretching flow, thus preventing the formation of floes. In the water-removal zone after the headbox an even and floc-less fibre suspension is maintained the whole time, which produces a good structure in the finished product. In the following, the invention is described in detail with reference to the accompanying drawings depicting some embodiments of the invention, in which

Figure la shows a cross section of the headbox according to the invention,

Figure lb shows schematically the control circuit of the headbox,

Figure 2 shows a second embodiment of the headbox according to the invention, in the same way as Figure la, Figure 3 shows one embodiment of a concept equipped with the headbox according to the invention,

Figure 4 shows one embodiment of a short circulation connected to a headbox according to the invention. Figure 1 shows the headbox 10 according to the invention, which is of a lightweight construction and thus has lower investment costs than known headboxes. The headbox can be lightened, because the flow velocity of the fibre suspension exiting the headbox, and the headbox pressure corresponding to this, can be as much as halved using the angular velocity of the feed roll. Thus, the operation of the headbox is based on the exploitation of kinetic energy, in which the roll is precisely a feed roll. Thus, the roll 11 according to the invention is arranged to act as a feed roll 12. In addition, the axis of rotation of the feed roll 12 is arranged to be moveable radially, in order to alter the size and shape of the flow channel 13 and thus to control the headbox 10. The adjustment of the headbox will be explained later in greater detail.

Figure la shows only the headbox 10 which is fitted into the throat formed by two rolls 14 and 15. The forming wires 16 and 17 travel through the rolls 14 and 15, with the fibre suspension being fed between them to form the web. From the short circulation, the fibre suspension is distributed to the headbox 10 through an inlet header 18. In the inlet header there is a circulation, in which there is control in order to regulate the pressure of the front and rear panels of the inlet header. The internal wall 19 of the headbox 10 and the feed roll 12 arranged to rotate delimit the flow channel 13, which narrows in the direction of flow. The fibre suspension is directed from the inlet header 18 to the flow channel 13, which is thus formed of the rotating surface of the feed roll 12 and the curved internal wall 19 of the flow channel 13. An interchangeable shape plate 20 can be fitted to the curved internal wall 19, by means of which the shear stresses are increased and thus the flow is homogenized. This is particularly important when running at the highest consistencies. The shape plate can be changed, thus making it possible to find the desired level of shear force. The position and attitude of the shape plate can be altered during production. The shape plate is used to affect the flow in the headbox and the boundary-layer turbulence required by the flow. The level of strength of the turbulence and the need for it are largely determined according to the raw-material base, the consistency in the headbox, and the grade being run. A high grammage and headbox consistency will increase the need for turbulence in order to achieve a homogeneous web, in which case the shape plate may be required. The shape plates can also be of different lengths over their active parts and the patterning on the active part can also vary. The shape plate can be exchanged and both its shape and model can be chosen freely. The shape plate can be surfaced with, for example, Teflon, in order to keep it clean. A discharge chamber, which is based on a rotational motion (not shown) , can be used in front of the inlet header. In this case, the rotational motion should be in the same direction as that of the feed roll.

At low consistencies, the shape plate can be smooth, or need not be installed in the headbox. Despite the shape plate or lack of it, the flow channel narrows in a controlled manner. This creates a low acceleration in the flow of the suspension and maintains the effect of the shear forces. This ensures that the fibre suspension remains homogeneous. At the circumferential velocity of the feed roll 12 as much as half of the exit-flow velocity is achieved in the headbox. The headbox also includes a bypass-flow channel 21, which is on the opposite side of the feed roll 12 relative to the flow channel 13, and which is delimited on one side by the feed roll 12. When the bypass flow increases, the effect of the feed roll on the flow velocity decreases. Some of the fibre suspension fed to the headbox is then recirculated through the bypass flow. The bypass flow can be regulated and the bypass flow can be used to ensure that the feed pressure is the same on both sides of the inlet header. Fibre suspension containing air is also removed along with the bypass flow. The centrifugal pressure of the liquid phase displaces air from the outer circumference of the flow channel and air collects on the surface of the feed roll precisely due to the rotational motion. The air is lighter than the liquid phase and separates onto the surface of the feed roll, from where it can be removed to the bypass-flow channel using a small bypass flow. The diameter and speed of rotation of the_. feed roll can thus also be used to influence the air removal. This is of great importance in simplifying the process, as air-removal equipment becomes unnecessary. The construction of the feed roll can also be used to affect the air removal. If the feed roll is made from micro-lamellas, the air removal can be made even more efficient. The lamellas result in the formation of micro-scale grooving in the machine direction on the surface of the feed roll, which improves the air removal without affecting the forming..

The motor 22 rotating the feed roll is equipped with a fre- quency converter 50, so that the speed of rotation of the feed roll and thus its circumferential velocity can be adjusted steplessly from zero as desired (Figure lb) . Thus, the feed roll can be used to regulate steplessly the exit-flow velocity of the fibre suspension of the headbox, and thus to control the jet ration and the machine-direction/transverse-direction orientation ratio. The circumferential velocity of the feed roll can also be used to vary and adjust the z-direction distribution of the web being formed, and thus permit, for example, adjustment of the quality and strength values, the formation, and the warping of the finished product. The aforementioned values are also affected by the shear force of the shape plate. The variations and pulsations caused by the short circulation, mainly the pumps and screens, are small and are attenuated, because only part of the headbox' s exit-flow velocity and the pressure acting on the headbox comes from the pump feeding the fibre suspension. The pressure level is in any event small, being only a small part of the pressure level of existing headboxes. The rotation of the feed roll creates a small centrifugal force in the fibre suspension, which separates the free air in the fibre suspension. This air collects on the surface of the feed roll 12, and is rotated along the surface of the feed roll 12 and away through the bypass-flow channel 21. In this way, detrimental air is removed immediately before the formation of the web. At the same time, the previously essential massive air-removal equipment can be eliminated from the short circulation. Air removal can be made more efficient by giving the surface of the feed roll a lamella construction, in which there are micro-grooves (not shown) . For the adjustment of the transverse profile of the web, there is dilution regulation 23 in the headbox, by means of which dilution water is fed to the flow channel 13 before the shape plate 20. As additional adjustment for correcting the flow profile, small alterations can be made to the diameter of the feed roll, which affect the 5 circumferential velocity of the feed roll in, a focussed manner in the transverse direction. There is often a need to adjust the flow velocity at both edges of the web, because the edges, for example, dry and shrink differently to the central areas of the web. The location of the feed roll can be altered, for 10 example, with the aid of eccentric bearings. The change affects the size and shape of the flow channel and thus the flow of the fibre suspension.

The flow channel 13 and the aforementioned bypass-flow channel 15 21 are separated by means of a divider table 24 arranged to be moveable. The divider table can be moved in both the vertical and horizontal directions. In addition, as a continuation of the flow channel 13, there is a slice channel 25, the initial part of which is determined by the divider table 24. In that 20 case, the narrowing angle of the slice channel and the slice opening can be altered, if desired, by adjusting the divider table. The attitude of the divider table is also used to define the size of the bypass-flow channel. In addition, the feed roll 12 is equipped with a high-pressure jet 26, which has a small 5 amount of water and a sharp jet. The jet is used to keep the feed roll clean and guide the pulp containing air away. The headbox is equipped with an opening cover 27, through which the headbox can be serviced and the feed roll and shape plate changed when required.

0

Figure 2 shows a variation of the headbox 10 according to the - invention. In this case, the upper slice of the slice channel 25 has been removed and replaced by a vacuum shoe 28, through which the upper formation wire 17 of the formation section 5 runs. In other words, the vacuum shoe 28 delimits the slice channel 25 from above. Web-forming then starts already in the slice channel of the headbox. This simplifies the formation process, makes water removal more efficient, and improves process control. The structures of the headbox and the forming section also become simpler, reducing purchase and operating costs. At the same time, operation of the process at a high consistency becomes possible and an even web forming is achieved with the headbox. The replacement of the top slice with a vacuum shoe prevents boundary-layer turbulence from arising. At the same time, the previous slice-jet problems are eliminated and the amplification of possible vertices is prevented. The vacuum shoe also permits the use of a higher consistency than usual, as the headbox lacks the traditional slice, so that the problems arising from a small slice and top- slice lip are avoided. Most of the water exits over a distance of about twenty centimetres in the area of the vacuum shoe. In connection with the vacuum shoe may also be a baffle, by the length of which the operating range of the vacuum shoe may be defined. In the location of the top-slice lip, it is also possible to use a control fin, which can be changed. Thus, the headbox can be assembled from modules, so that the desired properties of the headbox can be obtained while at the same time maintenance operations are facilitated.

Figure 3 shows a concept equipped with a headbox according to the invention, which is suitable for both paper and board machines. In this case, the headbox 10 according to Figure 2 is applied, which has a vacuum shoe 28 integrated in the formation section 29. In the formation section 29 shown, there is two- sided water removal, which is implemented with three water- removal elements 30, 30', 30", in addition to the vacuum shoe 28. The formation section is short and an expensive vacuum roll is unnecessary. Thus the forming section is vacuum-less, so that the temperature of the formed web remains high right up to the press section. For example, when producing a thin grade with a high consistency of, for example 3 %, after the forming section the solids content is already so high that a pre-press can be used. The pre-press gives planar strength, i.e. so- called spring force, which is very important in cardboard, but for the adjustment of which there have previously been no means. In this case, the forming wire 16 and the press fabric 32 are arranged to travel through the same pre-press 31. After this, due to the high solids content, even a single shoe press 33 is sufficient in the press section. This shortens the press section and simplifies its construction. The press section equipped with a pick-up roll 34, together with a high solids content ensure good runnability and permit the use of weaker raw materials. The pre-press makes compaction of the web more effective and increases strengths.

Figure 4 shows a short circulation operating at a headbox consistency of 0.2 - 5.0 %, preferably 1.0 - 3.5 %. Air-removal equipment is lacking entirely from the short circulation. The massive air-removal equipment, which consumes a great deal of energy, has been eliminated as unnecessary, because the fibre suspension containing air is removed by the bypass-flow channel. The so-called wire drain and the traditional head feed pump, which, especially in high flows, is of special manufacture and expensive, have also been eliminated. As such, the headbox can be combined even with known forming sections. The short circulation includes a machine tank 35 for the fibre suspension, as well as a mixing pump 36 and a pressure screen 37. In this case, the mixing pump 36 is arranged directly between the machine tank 35 and the pressure screen 37 and is arranged to feed fibre suspension directly to the headbox 10. More specifically, the fibre suspension is led to the mixing tank 38, in which there is consistency control. From the mixing tank 38, the fibre suspension is pump to the machine tank 35. In the machine tank 35, there is consistency measurement and control. From the machine tank 35, the fibre suspension is pumped through the pressure screen 37 to the headbox 10 by a mixing pump 36, which in this case is also the functional head feed pump. The consistency and flow amount of the fibre suspension coming from the machine tank are measured and these data are utilized when regulating the process. From the inlet header of the headbox 10, a circulation line 39 is arranged back to the suction side of the mixing pump 36. The reject 42' of the pressure screen 37 is led to the reject tank 40, from where there is pumping to the reject screen 41. The fraction accepted by the reject screen 41 is return to the suction side of the mixing pump 36 and the reject is led in a diluted form to the cyclone cleaner plant 42. The reject is diluted to a consistency of less than 1 %, so that the cyclone cleaner plant can operate. From the forming section 29, the circulation water goes to the lock-water drain 44 through adjustable suction feet 43. From the lock-water drain 44, there is an overflow to the circulating-water tank 45, from which there is a connection 46 for the consistency-regulation water to the suction side of the mixing pump 36. From the circulating-water tank, the excess fines water is pumped to the fines-water tower (not shown) . The fraction accepted by the cleaner plant is led to the input pulp of the mixing tank, so that the diluted pulp coming from the cleaner plant will not disturb the process.

Additional adjustments can also be included in the headbox. The feed roll according to the invention is a lightweight-construc- tion roll, which can be surfaced with the desired material. The roll can be manufactured from, for example, a fibre-reinforced plastic composite. This will avoid heavy and demanding structures. The feed roll is dimensioned in such a way that bending and torsional vibrations will be avoided, despite the high speed of rotation. The material and shape of the surfacing can be used to affect the behaviour and adjustments of the flow. The surface of the feed roll can also be made from lamellas, which will improve the air removal from the fibre suspension. The feed roll can be shaped as desired, so that the flow profile can be adjusted in the cross direction by altering the diameter of the feed roll locally. For example, it is often necessary to alter the flow in the edge areas of the web, because the edges behave differently to the centre part of the web. The diameter can be altered, for example, by grinding. In the new operating principle, a certain part of the total flow of the fibre suspension is implemented using a pump and the remainder by the speed of rotation of the feed roll. The ratio between these can be altered steplessly. The final precise exit-flow velocity can be adjusted by means of the speed of revolution of the feed roll. The exit-flow velocity from the slice channel is measured for the adjustment using ultrasound measurement. One ultrasound sensor is shown in Figure la. Figure lb shows schematically the control circuit of the headbox. On the basis of the ultrasound sensor 47, the machine control system 48 controls the feed-roll motor 22 and the mixing-pump 36 motor 49, with the aid of freguency converters 50 and 51. Thus, on the basis of the signal obtained from the measurement, the speeds of revolution of both the mixing pump and the feed roll are adjusted. In the headbox, there can also be other adjustment and/or control means, in order to achieve precise controllability. In addition to the exit-flow velocity, the speed of revolution of the feed roll also affect the web's quality values, such as formation, strengths, and their relationships, as well as the orientation relation. The diameter of the feed roll is determined by the wrap requirement, which is about 1500 mm. The exit-flow velocity of the headbox it determined by the machine speed and the speeds are largely the same. The speed of the feed roll is selected on the basis of the desired quality values of the finished product.

The headbox according to the invention has a wide operating range. Production at consistencies of 0.5 - 5.0 % is possible, because the boundary-layer turbulence of the headbox can be adjusted using the speed of revolution of the feed roll, the size and shape of the flow channel, and the construction of the internal wall of the flow channel. The exit flow of the fibre suspension can then be kept reliably homogeneous and even. The headbox according to the invention also permits the implementation of a new type of integrated process for manufacturing paper and board. The total process can be constructed around the headbox by exploiting its wide operating range in terms of consistency and flow. Thus, by using one and the same headbox, different qualities and grades of paper and board can be manufactured flexibly.. The headbox includes part of the operations of the short circulation, such as pumping and air removal, as well as operations of the forming section, such as water removal and web formation. The headbox according to the invention permits a wide grade and grammage range to be run using the same process. Thanks to the invention, investment, energy, and operating costs can be reduced- significantly in paper and board manufacture. The headbox according to the invention is clearly simpler in construction than known headboxes. In addition, the process is sure and reliable. The reduction in the amount of equipment and the increase in the consistency level reduce pumping, which in turn saves energy. At the same time, the amount of fresh water used decreases. Energy consumption is directly proportional to the amount of water used and affects right up to the treatment of water. The headbox according to the invention is also very suitable for paper or board-machine rebuilds, as an increase in production will succeed without an increase in the amount of electricity and water required, or an increase in the building space required. The web formation is controlled and the quality values of the finished product can be optimized. In addition, the same headbox can be used to manufacture different grades. For example, using the same headbox it is possible to manufacture three-layer cardboards with a middle layer with a minium grammage of 40 g/m² and a maximum of 320 g/m².

Claims

1. Headbox for a paper or cardboard machine, which headbox (10) includes a flow channel (13), delimited by an internal wall (19) of the headbox (10) and a roll (11) arranged to rotate, which narrows in the flow direction, characterized in that the roll (11) is arranged to act as a feed roll (12) and the axis of rotation of the feed roll (12) is arranged to be able to be moved radially, in order to alter the size and shape of the flow channel (13) and thus to control the headbox (10) .

2. Headbox according to Claim 1, characterized in that on the opposite side of the feed roll (12) relative to the flow channel (13) there is a bypass-flow channel (21), which is delimited on one side by the feed roll (12) .

3. Headbox according to Claim 2, characterized in that the flow channel (13) and the bypass-flow channel (21) are separated from each other by a divider table (24) , which is fitted moveably to the headbox (10) .

4. Headbox according to Claim 3, characterized in that there is a slice channel (25) as a continuation of the flow channel (13) , the starting part of which is determined by the divider table (24) .

5. Headbox according to Claim 4, characterized in that the headbox (10) includes a vacuum shoe (28), which is arranged to delimit the slice channel (25) from above.

6. Headbox according to Claim 4 or 5, characterized in that ultrasound measurement is connected to the outlet of the slice channel (25) and is arranged to be the controlled variable for a mixing pump (36) belonging to the paper or board machine, and for a motor (22) arranged to rotate the feed roll

(12) .

7. Headbox according to any of Claims 4 - 6, character- ized in that the slice channel (25) is delimited by a forming wire (17) belonging to a formation section (29) belonging to the paper or board machine.

8. Headbox according to any of Claims 1 - 7, character- ized in that a shape plate (20) , the position and attitude of which are arranged to be adjustable and the pattern of which is arranged to be changeable, is arranged to the detachably attached to the internal wall (19) .

9. Headbox according to any of Claims 1 - 8, characterized in that the headbox (10) is equipped with a cover (27) that can be opened.

10. Method for a paper or cardboard machine, in which method a headbox (10) is used, which includes a flow channel

(13) , delimited by an internal wall (19) of the headbox (10) and a roll (11), which narrows in the flow direction, and which roll is rotated, characterized in that the roll (11) is arranged to act as a feed roll (12) and the axis of rotation of the feed roll (12) is moved radially, when the size and shape of the flow channel (13) is altered and thus the headbox (10) is controlled.

11. Method according to Claim 10, characterized in that the flow of the headbox (10) is regulated by altering the speed of rotation of the feed roll (12) .

12. Method according to Claim 10 or 11, characterized in that fibre-suspension containing air is removed from the surface of the feed roll (12) .

13. Method according to any of Claims 10 - 12, characterized in that a fibre suspension, the consistency of which is 0.2 - 5.0 %, preferably 1.0 - 3.5 %, is fed to the headbox (10) .

14. Method according to any of Claims 10 - 13, characterized in that a web, the grammage of which is 40 - 320 g/m², is formed by means of the headbox (10) .

10 15. Method according to Claim 14, characterized in that the web with a grammage of 40 - 320 g/m² is arranged to be the middle layer of three-layer cardboard.