EP2129830A1

EP2129830A1 - Structural element for a functional member of a headbox in a web-manufacturing machine, functional member and headbox made thereof, and associated methods

Info

Publication number: EP2129830A1
Application number: EP08712750A
Authority: EP
Inventors: Ulf Haraldsson
Original assignee: Metso Paper Karlstad AB
Current assignee: Valmet AB
Priority date: 2007-03-01
Filing date: 2008-02-29
Publication date: 2009-12-09
Also published as: CN101622399A; EP2129830A4; CN101622399B; WO2008105714A8; WO2008105714A1

Abstract

The present invention relates to a structural element (17A, 17B, 17C) for a functional member (11) in a headbox of a web-manufacturing machine, the structural element comprising an integral block (1) comprising therein a plurality of channels (2) defining flow channels for a paper stock, said stock flow channels extending through the integral block from a first upstream end (1A) to a second downstream end (1B) of the block. According to the invention, the structural element comprises at least one gap-forming element (13) which is arranged to ensure a gap (14) of a predetermined width between the block of the structural element and a neighbouring element.

Description

STRUCTURAL ELEMENT FOR A FUNCTIONAL MEMBER OF A HEADBOX

IN A WEB-MANUFACTURING MACHINE, FUNCTIONAL MEMBER AND

HEADBOX MADE THEREOF, AND ASSOCIATED METHODS

The present invention relates to a structural element for a functional member in a headbox according to the preamble of claim 1 and a headbox comprising such a functional member. The invention also relates to structural element for a headbox according to the preamble of claim 17 and a method for manufacturing such a structural element.

As known in the art, in a papermaking machine or other types of web-manufacturing machines, a stock or fibre suspension is commonly fed to a headbox from a stock header or stock headers directly or by a number of separate conduits leading the fibre stock flow and connected to an upstream end of the headbox. Then the stock is discharged in the form of a jet from a slice chamber of the headbox through a slice lip opening situated on a downstream end of the headbox onto a forming wire so that a paper web is formed on the wire.

The papermaking machines can manufacture a single layer paper or board web consisting of the only one type of cellulose fibres and thus such machines have a single-layer headbox.

Alternatively, the machine can manufacture a multi-layer paper or board web, where the web consists of different layers having different types of fibres, and therefore such machines can be provided either with a plurality of the single-layer headboxes delivering the single-layer webs on the top of each other in order to form a multi-layer web consisting of different layers of fibres, or the paper machine can be equipped with a multi-layer headbox providing a multi-layer paper web formation.

A conventional headbox as disclosed in PCT-publication WO 99/36613 (Beloit) having a stock supply manifold connected directly to a headbox housing on its upstream end. A stock is introduced from the manifold into a tube bank or so called turbulence generator, consisting of an array of tubes arranged in rows for feeding the stock further to a slice chamber of the headbox. The stock supplied to the slice chamber passes therethrough and is ejected from a slice opining onto a forming wire. The tube bank comprises an array of the tubes formed of six rows of a few hundred tubes extending in the cross-machine direction. This arrangement is rather heavy and requires many working hours for assembling and manual welding of the tube bank.

An alternative design of the headbox for a multi-layer paper web is disclosed in US- patent US 4,376,014, wherein two stock manifolds are also connected directly to the turbulence generator of the headbox, said turbulence generator comprising a plurality of tubes for generating a fine scale turbulence in the stock. This design also has the drawback as mentioned above.

Still another conventional type of a multi-layer headbox has a number of conduits connecting the corresponding stock manifolds with the corresponding tube rows of the headbox turbulence generator as is disclosed in patent EP 0 912 797Bl (Metso Paper Karlstad AB).

Still another patent EP 0 939 842B2 (Metso Paper Karlstad AB) illustrates in Fig. 1 that the stock manifolds can be connected to a primary tube bank, and then the stock flow continues from the primary tube bank into a secondary tube bank or so called turbulence generator connected to the primary tube bank and further to the slice chamber to be ejected onto the forming wire. This design requires a lot of manual assembling work and welding of hundreds of the tubes in both primary - and secondary tube banks.

One still another type of the headbox disclosed in US 3,923,593 (Beloit). This headbox has a number of stock-providing chambers on its inlet end and a number of pressure equalising chambers situated after a turbulence generator consisting of a plurality of tubes and prior to a slice chamber of the headbox.

Therefore, generalising all the headboxes types discussed above, one can say that any headbox for delivering the fibre stock in the papermaking machine has a number of functional members comprising the pressure equalising chambers and/or the tube packages connected sequentially to each other in the fibre stock flow direction.

The conventional turbulence generator is made as a set of plurality of steeliness steel tubes attached together by welding and forming a tube bundle or tube bank of a number of tube rows across the width of the headbox. The inner surface of the tubes must be very smooth in order to avoid fibre sediments or friction of the flow and therefore should be carefully worked and subjected to an electrolyte process. This rather difficult and demanding work requires many work hours and increases price of the equipment.

Usually the tubes are made of stainless steel and are manually welded together to form the turbulence generator or the tube bank, which, consequently, is a rather bulky and heavy functional member of the headbox. Conventional papermaking machines vary in width from 60 cm up to 8 meters or more, which means that the turbulence generator or tube bank of the corresponding headbox of the paper machine are dimensioned accordingly and can be very big and heavy. The weight and size of such a tube bank creates difficulties when the headbox is to be manufactured, transported and assembled.

US 4,895,624 discloses an alternative construction of a turbulence generator. The turbulence generator is formed by one or a plurality of plastic beams. The beams are apertured or perforated such that flow ducts are formed. The face surface or wall of each flow duct is made of a synthetic or ceramic material which forms a hard, smooth and dense surface which prevents absorption of water by the material of the plastic beam. The portions between the walls are cast of a suitable plastic material such as polyurethane. The surface material of the flow ducts are chemically bond to the raw material of the beam such that the bodies of the beams and the coating of the surfaces of the flow ducts constitute a united entity of two synthetic and/or ceramic materials which are tightly bond together. The turbulence generator can be divided into the perforated beam either in a direction transverse to the longitudinal direction of the generator or in a plane parallel with the axis of the flow ducts. Thus, US 4,895,624 discloses that two plastic beams can be arranged one beside the other to form a functional member, e.g. a turbulence generator, in a headbox.

However, a problem associated with such a side-by-side arrangement of the plastic beams of US 4,895,624 is that stresses, e.g. thermal stresses or dynamic stresses due to a fluctuating stock flow pressure in the stock flow channels, that can deform the individual plastic beams and disturb the formation of the paper. Accordingly, it is an objective of the invention to compensate for such possible deformation and to simplify the structure of the functional members of a headbox and reduce their price, weight and assembling time while maintaining or improving the paper web formation.

The structural element according to the invention is characterised by features according to the characterising part of claim 1.

The gap-forming element of the structural element according to the invention ensures that there are gaps between the individual structural elements that make up the mixing unit, the equalising chamber unit, the primary tube unit, the turbulence generation unit or the other functional members of the headbox. Such gaps, in turn, ensure that there is room for the individual blocks to expand, whereby deformation of the stock flow channels is avoided.

The invention allows an essential reduction of the price, assembling time and the weight of the functional member.

Also, the invention allows an essential reduction of the price, assembling time and the weight of the entire headbox and accompanying framing and equipment and simplifies the mounting and control of the headbox during its operation.

The invention also provides a more efficient method of manufacturing the functional members of the headbox by allowing assembly of at least two structural elements according to the invention in an adjacent relationship.

The invention also provides a more efficient and simplified method of assembling the entire headbox by allowing assembly of a plurality of the structural elements into a package of a predetermined dimension, said package defining at least one of the functional members, wherein the structural elements are spaced from each other by a gap and sealed therebetween by a sealing element, disposing at least one of the functional member upstream in the stock flow direction to the slice chamber into the headbox housing and connecting the functional member to each other and/or to the headbox housing.

Thus, the structural element according to the invention allows simpler and faster manufacture and assembly of any of the different functional members of the headbox, reducing the amount of required steeliness steel and minimises the work hours for assembling the functional members and the entire headbox.

The functional member such as the turbulence generator unit assembled from the structural elements according to the invention has only half the weight of the conventional steel turbulence generator unit of the same dimension, type and model, and is much easier to assemble into the headbox.

Similarly, the other functional members of the headbox, such as the stabilising and/or pressure equalising chamber(s) and the primary tube bank, can be also assembled from the structural element(s) according to the invention and mounted into the headbox.

It is to be understood that the proposed improvement in the headbox is not limited only to the turbulence generator unit per se.

The headbox comprising housing, a slice chamber and at least one functional member disposed in said housing upstream of said slice chamber in a stock flow direction, wherein the functional member comprises at least one structural element according to the invention.

Depending on a size and type of the headbox, a plurality of structural elements according to the invention can be assembled together providing a required dimension of the turbulence generator unit or the other headbox functional member and necessary amount of the passage channels for the stock flow. The structural element defining the stock flow passage channels can be moulded, pressed, injected or extruded using a suitable polymer material, such as for example, polyurethane, polyurethane foam, PVDF-plastic, C-PVC, polypropylene, polyethylene-HDPE, Noryl®, polyacetal (PA), epoxies, phenolix resin, vinyl ester or the like, composite material or other suitable materials or technologies could be used. Alternatively, the channels could be drilled or bored into a solid block of the suitable material.

These manufacturing processes will save investment costs, saving steeliness steel, the turbulence generator section and/or other sections of the headbox will have much lighter weight, which will in its turn decrease the weight of the entire headbox.

The moulding process for manufacturing one structural element according to the invention takes approximately 15-20 minutes while the welding of the corresponding conventional tube bank takes more then one hour. The material saving costs depend on the headbox width: for a headbox of about 60 cm width the cost saving is about 20-30% comparing to a conventional tube bank; for a headbox of about 3 m width, the saving will be about 30-40% and for the headbox of 5.5 m - the costs will be only 50-60% of the conventionally manufactured tube bank. The weight of the turbulence generator or the tube bank will be reduced up to 50 %. The reduced weight of the headbox allows reducing the dimension of the headbox carrying framing and accompanying equipment.

The decreasing of the weight and dimensions of the headbox will simplify the mounting and control of the position of the headbox in the papermaking machine.

As the different profiles of the channels into the structural element can be chosen for the different purposes (such as the stock flow acceleration or expanding or controlling in any appropriate way) the stock flow channels can have different cross sections along their length such as circular, rectangular, oval, polyhedral of the same or the different geometric shape and the same area for the stock flow or, alternatively, the different stock flow areas or cross sections. This can be achieved during manufacturing much easier by the proposed above technologies than by usage of the conventional steeliness steel tubes.

The invention now will be described in more detailed with reference to the accompanying drawings.

FIG. 1 is a longitudinal section of a structural element according to a first embodiment of the invention. FIG. 2 is a longitudinal section of a structural element according to a second embodiment of the invention with a threaded insert shown in the enlarged view in Fig. 2A.

FIG. 3 is a longitudinal section of a structural element according to a third embodiment of the invention with a pressured insert shown in enlarged view in Fig. 3 A.

Fig.3B illustrates cross section views I-IV of the structural element according to Fig. 3, showing different cross section shapes of the stock flow channels provided in the structural element.

FIG. 4 is a longitudinal section of a structural element for a first functional member according to the invention in the form of a turbulence generator unit and an upstream structural element of a second functional member in the form of a primary tube unit connected to the turbulence generator unit.

FIG. 5 is a longitudinal section of a downstream structural element of a first functional member in the form of a turbulence generator unit connected to an upstream primary tube unit.

FIG. 6 is a longitudinal section of a headbox comprising three different functional members in the form of an equalising chamber unit, a primary tube unit and a turbulence generator unit, the turbulence generator unit is being assembled from a number of structural elements according to the invention.

FIG. 7 is a longitudinal section of a headbox comprising two different functional members in the form of an equalising chamber unit and a turbulence generator unit connected directly to the equalising chamber unit and assembled from a number of structural elements according to the invention.

FIG. 8 shows a turbulence generator unit assembled from a plurality of the structural elements according to the invention, gaps being provided between the structural elements and sealed by strips as shown in the enlarged view in Fig. 8A. FIG. 9 shows a longitudinal section of a headbox comprising two different functional members in the form of a mixing unit and a turbulence generator unit assembled from a number of structural elements according to the invention.

FIG. 10 shows a longitudinal section of the mixing unit according to Fig. 9.

FIG.l 1 shows a cross section view of the mixing unit according to Fig. 9.

Fig.l. shows in a longitudinal section a structural element 17 according to a first embodiment of the invention. The structural element 17 comprises a solid integral block 1 having a plurality of channels 2 going through the block 1 from an upstream end IA to a downstream end IB of the of the structural element 17. The channels 2 define flow paths for a paper stock and are arranged in rows and columns. For example, the block 1 may comprise four rows of channels 2 having three channels in each row, as is disclosed in Fig. 3 and Fig. 3B.

The structural element 17 is designed to be a part of a turbulence generator unit, e.g. as is disclosed in Fig. 8. In Fig. 8 three structural elements 17A, 17B and 17C of the type disclosed in Fig. 1 are arranged side by side in order to form a turbulence generator unit 11 in a headbox 10. The structural elements 17 A, 17B and 17C are arranged such that the upstream ends IA and the downstream ends IB of the structural elements 17 A, 17B and 17C coincide. Each structural element 17A, 17B and 17C comprises six rows of channels 2 with three channels in each row. Thus, in total the turbulence generator unit 11 comprises six rows of channels having nine channels in each row. However, the dimensions and number of the structural elements forming the turbulence generator unit 11 can of course be chosen in accordance with the required dimensions of the headbox 10.

The type of paper fibre stock, e.g. the consistency, fibre composition etc. of the stock, transported by each row of channels 2 can vary and as a result a multi-layer paper web can be formed. For example, if the embodiment of Fig. 8 is to be used in a three layer headbox, the two uppermost rows of channels are used for a fist type of stock, the two rows of channels in the middle are used for second type of stock and the two lowermost rows of channels are used for a third type of stock..

Preferably, the block 1 is manufactured from high performance polyurethane by molding, but any other polymer, such as polyurethane foam, PVDF-plastic, C-PVC, polypropylene, polyethylene-HDPE, polyacetal, epoxies, phenolix resin, vinyl ester and/or composite material, having the required properties, or light metal, or metal powder, or ceramics and the appropriated methods of manufacturing could be used.

When manufactured from high performance polyurethane elastomers, the block 1 is preferably made by moulding in a moulding form in a computer controlled casting machine. The polymer is pumped directly from the machine into a forming tool. The forming tool is normally made from machined aluminium. After a prescribed period of time, e.g. approximately 1 hour, the tool is opened and the block is demoulded, i.e. removed from the forming tool. The moulded block 1 is then placed in an oven for post curing, e.g. at 100 ° C for 16 hours. Excess flashing is then removed from the block 1 by means of a sharp knife or a scalpel. The hardness, porosity and other relevant parameters and also the general appearance of the block 1 is then checked to ensure that the quality of the block conforms to set up requirements. Retained samples from the cast may also be sampled for later quality control at a testing facility. Finally, inserts, e.g. metal inserts, may be fitted, e.g. push fitted or screwed, into the channels of the block (see Fig. 2) such that the final structural element is formed.

Of course, alternatively other known suitable manufacturing methods or technologies can be used.

Due to the above-described manufacturing method, the inner surface of the channels can be made very smooth and therefore the channels do not need any inner lining or additional working like the inner surface of the corresponding conventional steel tubes of conventional turbulence generator, for instance. Preferably, the dimension of a block is chosen such that the block is easy to mould and also easy to assemble into a tube unit. The size, form and number of channels in the block are adopted to the type of tube unit of which the block is going to be a part.

The material of the block should withstand the pressure of the stock flow. Thus, the required wall thickness between adjacent rows of channels and between adjacent rows in each channel will depend on the material used for the block. The dividing walls of adjacent channels in a block made of polyurethane should preferable be at least 2.0 mm in order to be able to withstand the pressure of the flow into the channels without substantial deformation. However, it is to be understood that the wall thickness or the distance between the neighbouring channels may vary if other material is used for manufacturing of the blocks 1. Generally, the preferred thickness of the walls between neighbouring channels 2 is may vary from 0.2 mm up to 50 mm depending on the chosen block material.

The channels 2 can have any desired shape or profile. They can be of a cylindrical shape such that the cross section area and the shape of each channel 2 are the same from an inlet opening 2 A at the upstream end IA of the structural element to an outlet opening 2B at the downstream end IB of the structural element. Alternatively, the area and/or the shape of the cross section of each channel 2 can vary along the length of the channel such that, for instance, combined cylindrical and conical shapes are obtained as is illustrated in Fig. 1.

Preferably, the structural element 17 comprises attachment means, e.g. recesses 6, for mounting the structural element into a headbox 10 housing 12 or for arranging the structural element together with other functional members or structural elements within the headbox 10.

On the downstream end IB of the structural element 17 and between neighbouring stock flow channels 2, there are recesses 4 for mounting vanes 5, either stock dividing vanes or so called wedges and/or turbulence vanes as known in the art. When a plurality of structural elements 17A, 17B, 17C are assembled into a turbulence generator unit 11 as shown in Fig. 8, the recesses 4 of the structural elements form grooves at the downstream end IB, which grooves run in a cross machine direction and in which the vanes 5 can be inserted as is illustrated in Fig. 2.

In order to connect to an upstream functional member, the structural element 17 may comprise inserts or insertions 3 arranged in the upstream part of the channels 2. Fig. 2 illustrates a longitudinal section of a structural element 17 comprising insertions 3 at its upstream end IA in the form of metal bushings or other suitable connecting elements for connecting the channels 2 of the structural element to tubes T of a conventional primary tube unit 7. The insertions 3 are threaded into the channels 2 as illustrated in the enlarged view in Fig. 2 A, and the tubes T are inserted into the insertions 3. In this embodiment, the channels 2 are made equally converging over the entire length of the block 1, while the geometrical shape of the cross section of the channels 2 can be varied as desired, for instance, circular, oval, rectangular form, etc.

While only four rows of channels are illustrated here, it is to be understood that the number of rows of channels in the block 1 can vary from 1 to 9 or more, and the number of channels in each row can vary from 1 to 8 or more.

The converging form of the channels 2 of the block 1 allows stock flow acceleration.

Preferably, the cross section area of the downstream end of the tubes T is less than the cross section area of the upstream end of the channels 2. The difference in cross section area causes a sudden expansion of the flow channel of the stock and thus improves re- flocculation of the paper fibres and creates a micro-turbulence in the flow. In this embodiment, the insertions 3 with the inserted tubes 7', which have a smaller open cross section area for the stock flow than the upstream part of the channels 2, provide for a sudden expansion of the stock flow channels and, therefore, causes the fibre flocks in the stock flow to break-up.

It is to be understood that the differences in the cross-section flow areas between different headbox functional members or units could be arranged in many different ways, for instance, as illustrated in Fig. 2 or in Fig. 7, by inserting any appropriate insertions 3, 3' into the channels 2, and is not to be limited only to the use of the insertions 3, 3'. As illustrated in Fig. 3, the insertions 3 can alternatively be pressed into the upstream openings 2 A of each of the channels 2 as illustrated in the enlarged view in Fig. 3A.

The form of the inlet openings 2A and the outlet openings 2B of the channels 2 could widely vary in the shape as illustrated in Fig. 3B, in cross sections I-IV, being circular, oval, rectangular, polygonal and other chosen form. The shape of the openings 2 A and 2B on the upstream end IA and the downstream end IB could be identical or different and are chosen depending on the parameters to be achieved for the stock flow within these channels.

Fig. 4 illustrates still another embodiment of a headbox 10 according to the invention, where at least two structural elements 17, 18 according to the invention, in this case a turbulence generator unit 11 and a primary tube unit 15, are mounted in sequence one after the other in a housing 12 of a headbox 10. The turbulence generator unit 11 comprises one structural element 17 or a plurality of structural elements 17 mounted one beside the other in the cross direction of the headbox 10. Likewise, the primary tube unit 15 comprises one structural element 18 or a plurality of structural elements 18 mounted one beside the other in the cross direction of the head box 10. Each structural element 17, 18 comprises a block made of high performance polyurethane elastomers which is moulded in accordance with the method described above.

It is to be understood that the shape and/or area of the cross section of the channels in the primary tube unit 15 also can vary like the shape and/or area of the cross section of the channels of the turbulence generator unit 11.

The blocks of the structural elements 17, 18 are fabricated such that they comprise cooperating attachment means 6, e.g. protrusions and recesses, for enabling precise positioning of the structural elements 17, 18 such that corresponding channels 2 fit to each other. Preferably the structural elements 17, 18 are fixedly enclosed in a housing 12 of the headbox 10, whereby there is no need for the above-described inserts in order to connect the primary tube unit 15 to turbulence generator unit 11. Fig. 5 illustrates still another embodiment of a structural element 17 according to the invention forming a secondary tube unit or turbulence generator 11 in a headbox 10. Primary tubes T of a conventional primary tube unit 7 are inserted into inserts 3 at the upstream end IA of the channels 2 of the structural element 17 in the same way as described above. However, in this case there are no dividing vanes or wedges mounted at the downstream end IB of the structural element 17.

Thus, when assembling a headbox 10 according to Fig. 5, a functional member 11 in the form of a secondary tube unit need to be fabricated. This is done by moulding blocks 1 and inserting inserts 3 in the upstream end IA of the channels 2 of the blocks 1, as has been described above, forming a structural element 17. Thereafter, a plurality of such structural elements 17 are arranged one beside the other as is shown in Fig. 8, i.e. such that gaps 14 are arranged in-between neighbouring structural elements, forming the functional member 11. Thereafter, the functional member 11 is arranged in a housing 12 of the headbox 10 such that gaps are arranged in-between the blocks 1 of the structural elements 17 of the functional member 11 and the housing walls. Thereafter, tubes 7' of a primary tube unit 7 are connected to the inserts 3 such that a fluid communication between the channels 2 of the blocks 1 and a upstream situated functional member, e.g. a mixing unit 23 of the type shown in Figs. 9-11, is provided. Optionally, stock dividing vanes 5 may be mounted at the downstream end IB of the blocks 1, such is shown in Fig. 2. Of course, the order of these steps may vary.

Fig. 6 illustrates a headbox 10 according to the invention comprising a housing 12 and the different functional members 8, 7, 11 and 9 spaced within the housing 12. The member 8 comprises a number of stabilising and/or equalising flow pressure chambers 8'. The stock flow is fed into the chambers 8' by a header or headers, or a plurality of manifolds (not shown). Then the flow continues into the primary tubes or channels 7'of the member 7 (as illustrated in Fig. 4 and Fig. 5) and explained above. From the functional member 7 the stock flow is fed into the turbulence generator unit 11 (the function of which also has been explained above) and further into a slice chamber 9, where the stock flow continues to the slice opening on the downstream end of the housing 12. From the slice opening the stock is being delivered onto the forming wire (not shown). The slice chamber 9 can comprise at least one dividing vane 5 mounted on the downstream end IB of the turbulence generator unit 11 and dividing the different stock flows within the slice chamber 9. Alternatively, at least one turbulence vane 5' can be mounted between the dividing vanes 5 within the same stock flow for promoting micro-turbulence and improving formation of the paper web.

As illustrated here, two rows of tubes T transport the same paper stock from the each equalising chamber 8' to the next turbulence generator unit 11.

Still another embodiment of an entire headbox 10 according to the invention is illustrated in FIG. 7. The headbox 10 comprises the housing 12 and different functional members, such as the equalising chamber unit 8 connected directly to the turbulence generator unit 11 and followed by the slice chamber 9, all these functional members 8, 9 and 11 being spaced within the housing 12. When the primary tubes are not used in the headbox 10, the sudden expansion of the flow into the secondary tubes channels 2 (or into the turbulence generator unit 11) can be provided by other known means, for instance by inserting the tubes or insertions into the turbulence generator channels as described below.

The functional member 8 comprises a number of stabilising and/or equalising stock flow pressure chambers 8'. Instead of the primary tube unit a number of insertions 3' in the form of metal tubes or, alternatively, long bushings are inserted into the channels 2 of the turbulence generator unit 11 for connecting the equalising chamber unit 8 with the turbulence generator unit 11. The upstream ends of these insertions 3' have a smaller open area for the stock flow as compared to the chambers 8, which provide a resistance to the stock flow. The downstream ends of the insertions 3' provide a step in the channels 2, as the channels 2 have a larger diameter then the open area for the stock flow within the insertions 3', and thus, the expansion of the channels 2 occurs and a pressure drop and a stabilised stock flow within the turbulence generator unit 11 is achieved which improves fluidising of the stock flow and provides a better formation.

Therefore, the primary tube unit or functional member 7 could be substituted by the insertions 3' or other appropriate means. The insertions 3' could be pressed or threaded into the channels 2 of the structural element lor fixed by other means known in the art. In this embodiment both or at least one of the functional members, the unit 11 and the unit 8, could be manufactured from structural elements according to the invention.

Fig. 8 illustrates the turbulence generator unit 11 of a headbox 10 assembled from a plurality of structural elements 17A, 17B and 17C, each comprising an integral block 1 according to the invention. Alternatively, other sections such as the functional members or units 7 and 8 can be assembled similarly. As the material of the blocks 1 can have some thermal expansion, and the structural elements 17 A, 17B and 17C can be subjected to temperatures of about 20 ° C to 55 ° C, the blocks 1 should be mounted with some gaps 14 there between. Preferably, the gaps 14 have a width of at least about 0.2 to 0.7 mm. However, due to the different temperature coefficients of different materials, the width of the gaps 14 may vary and may be different for different materials used for manufacturing the integral blocks 1. The gap 14 between two neighbouring blocks 1 is ensured by at least one gap-forming element 13. Preferably, the element 13 is arranged such that it simultaneously seals the gap 14 preventing the paper stock or other fluid or gas, e.g. air, to flow in-between neighbouring blocks. Thus, the element 13 can act as a sealing element as well as a gap-forming element. The elements 13 can be arranged at one or a plurality of the outer surfaces of each block 1. The elements 13 can be integrated with the block 1, i.e. manufactured as an integral part of the block 1, as is shown in Fig. 8A. The sealing element 13 can be formed as at least one strip 13 stepping out or protruding from the block 1 surfaces on the side 22, on the top 20 and on the bottom 21 of the block 1, approximately perpendicular to the stock flow direction. Alternatively, these sealing strips 13 or other sealing elements may be situated on the structural element side 22, be inclined relative to the stock flow direction. Preferably, the strips 13 of the block 1 are positioned such that strips 13 of neighbouring block surfaces cooperate and interconnect as is illustrated in the enlarged view of Fig.8A, wherein a single strip is arranged on one surface of the block 1 and a double strip is arranged on an opposite surface of the block 1, which strips are arranged such that the singe strip fit in between the double strip of a neighbouring block 1 of the same type. Alternatively, only one element or strip 13, having a height approximately as the gap 14, can ensure the gap 14 existence and at the same time seal the gap 14. The height of the strip 13, which preferably is moulded or manufactured by other means simultaneously with the block 1, is about the size of the chosen gap 14. Alternatively, the strip or sealing elements 13 of two neighbouring blocks can be arranged opposite each other such that each element is in contact with the element of the opposite block. In such an arrangement, the height of each element need only be half the width of the gap. Instead of being made as integral parts of the block 1, the strip or sealing elements 13 can be fixed to the block 1, e.g. by glue or other appropriate means, after the block as such has been manufactured. Alternatively, the strip or sealing elements 13 can be positioned between neighbouring block and/or between the blocks and the housing 12 when the headbox 10 is assembled, in which case the strip or sealing elements 13 may not have to be glued to the block surfaces, but may be held in place by the confining forces of the housing 12.

Thus, the gap-forming elements 13 can be arranged to abut the gap-forming element or the surface of a neighbouring block or the or the surface of the housing 12 of the headbox 10. The gap-forming elements 13 can have any suitable cross-section form, i.e. a semicircle as is shown in Fig. 8A. Preferably, the gap-forming elements 13 are elongated and continuous such that they run along the entire length or width of a block surface.

Figs. 11 shows yet another embodiment of a headbox according to the invention. The headbox 10 comprises a secondary tube unit or turbulence generator 11 comprising a plurality of structural elements 17 according to the invention arranged side by side. Upstream the turbulence generator 11 the headbox 10 comprises a primary tube unit 7 which comprises a plurality of metal tubes which are attached to inserts in the channels of the turbulence generator 11. Upstream the primary tube unit 7, the headbox 10 comprises a mixing unit 23. Upstream the mixing unit 23, the headbox 10 comprises a manifold 24 for supplying paper stock to the mixing unit 23.

The mixing unit 23 comprises a plurality of structural elements 25 arranged one beside the other in the cross direction of the headbox 10. Figs. 12 and 13 show such a structural element 25 in more detail. The structural element 25 comprises a block 1 in which a plurality of through channels 26 are arranged to lead paper stock from the manifold 24 to mixing chambers 27.The channels 26 are divided into two groups, each group of channels leading to a separate mixing chamber 27. Also, a supply channel 28 leads to each mixing chamber 27. The supply channels 28 are arranged for feeding a mixing fluid containing paper stock additives into the mixing chambers 27, which mixing fluid is arranged to mix with the paper stock in a fashion which is known per se in the art of paper making.

The structural element 25 also comprises a tube like insert 29, preferably a metal tube, fitted into each channel 26 such that they end inside the mixing chambers 27, as is shown in Fig. 9. Thus, when the mixing unit 23 is mounted on the primary tube unit 7, the inserts 29 end just short of the tubes T leaving a narrow opening for the paper stock to mix with the mixing fluid.

The blocks 1 of the structural elements 25 are preferably moulded from high performance polyurethane elastomers as has been described above. Also, preferably, the inserts 29 are fitted into the channels 26 as has been described above.

A headbox having functional members comprising structural elements according to the invention can be used in any type of web-manufacturing machine, e.g. a conventional paper, board or tissue manufacturing machine.

It is to be understood that the invention is not limited to the embodiments shown and should be interpreted in the spirit of the invention. The invention is applicable to any one of the functional members or units in the headboxes used in paper manufacturing machines.

Finally, it is to be understood that structural elements made from structural elements according to the invention could be used in new headboxes as well as when re-building or retrofitting existing headboxes.

Claims

1. A structural element (17, 18, 25, 30) for a functional member (11) in a headbox (10) of a web-manufacturing machine, the structural element (17, 18, 25, 30) comprising an integral block (1) comprising therein a plurality of channels (2) defining flow channels for a paper stock, said stock flow channels (2) extending through the integral block (1) from a first upstream end (IA) to a second downstream end (IB) of the block (1), characterised in that the structural element (17, 18, 25, 30) further comprises at least one first gap- forming element (13) which is arranged to ensure a gap (14) of a predetermined width between the block (1) of the structural element (17, 18, 25, 30) and a neighbouring element.

2. The structural element (17, 18, 25, 30) according to claim 1, characterised in that said neighbouring element is a housing (12) of the headbox (10).

3. The structural element (17A) according to claim 1, characterised in that said neighbouring element is another structural element (17B).

4. The structural element (17, 18, 25, 30) according to any one of claims 1-3, characterised in that said at least one first gap-forming element (13) is arranged on a first surface of the block (1).

5. The structural element (17, 18, 25, 30) according to claim 4, characterised in that the structural element (17, 18, 25, 30) further comprises at least one second gap-forming element (13) being arranged on a second surface of the block (1), which second surface is opposite to the first surface.

6. The structural element (17, 18, 25, 30) according to claim 5, characterised in that the first gap-forming element (13) comprises a single strip and the second gap-forming element (13) comprises a double strip, said strips being arranged such that the singe strip fit in between the double strip of a neighbouring block (1) of the same type.

7. The structural element (17, 18, 25, 30) according to any one of claims 4-6, characterised in that the gap-forming element or elements (13) are attached to the surface or surfaces of the block (1).

8. The structural element (17, 18, 25, 30) according to any one of claims 4-6, characterised in that the gap-forming element or elements (13) are made as integral parts of the block (1).

9. The structural element (17, 18, 25, 30) according to any one of claims 7 and 8, characterised in that the gap-forming element or elements (13) are continuous.

10. The structural element (17, 18, 25, 30) according to claim 9, characterised in that the gap-forming element or elements (13) are arranged to seal the gap or gaps (14).

11. The structural element (17, 18, 25, 30) according to any one of claims 1-10, characterised in that the block (1) is made from one of polymer, composite material, metal powder, light metal and ceramics.

12. The structural element (17, 18, 25, 30) according to claim 11, characterised in that the polymer is one of polyurethane, polyurethane foam, plastic, polypropylene, polyacetal, epoxies, phenolix resin and vinyl ester.

13. The structural element (17, 18, 25, 30) according to any one of claims 1-12, characterised in that the block (1) is manufactured by one of moulding, casting, injection, extrusion and pressing.

14. The structural element (17, 18, 25, 30) according to any one of claims 1-13, characterised in that the shape and/or area of the cross section of the channels (2) of the block (1) vary along the length of the channels (2).

15. The structural element (17, 18, 25, 30) according to any one of claims 1-14, characterised in that the wall thickness between two adjacent channels (2) of the block (1) is at least 2 mm.

16. The structural element (17, 18, 25, 30) according to any one of claims 1-15, characterised in that inserts (3, 3') are arranged in the channels (2) of the block (1).

17. A functional member (8, 11, 15, 23) for a headbox (10) for a papermaking machine, said functional member (8, 11, 15, 23) comprising a first structural element (17, 18, 25, 30) according to any one of claims 1-16.

18. The functional member (8, 11, 15, 23) according to claim 17, wherein said functional member (8, 11, 15, 23) in addition to said first structural elements (17B) further comprises at least one second structural element (17A, 17C) according to any one of claims 1-16, which first and second structural elements (17A, 17B, 17C) are arranged one beside the other such that the upstream ends (IA) and the downstream ends (IB) of the blocks (1) of the structural elements (17A, 17B, 17C) coincide, characterised in that the gap-forming elements (13) of said structural elements (17A, 17B, 17C) are arranged in- between neighbouring structural elements for ensuring a gap (14) of a predetermined width between the neighbouring structural elements (17A, 17B; 17B, 17C).

19. The functional member (11) according to claim 18, characterised in that said gap- forming elements (13) comprise strips being arranged between the blocks (1) of said neighbouring structural elements (17A, 17B; 17B, 17C).

20. The functional member (11) according to claim 19, characterised in that said strips are attached to the surfaces of the blocks (1) of said neighbouring structural elements (17A, 17B; 17B, 17C).

21. The functional member (11) according to any one of claims 18-20, characterised in that the gap-forming elements (13) are continuous and arranged to seal the gaps (14).

22. The functional member (11) according to any one of claims 18-21, characterised in that the gap or gaps (14) are sufficient to allow thermal expansion of the blocks (1) of said neighbouring structural elements (17A, 17B; 17B, 17C).

23. The functional member (11) according to claim 22, characterised in that the gaps (14) have a width of at least 0.2 to 0.7 mm.

24. The functional member according to any one of claims 17-23, characterised in that the functional member is any one of a mixing unit (23), an equalising chamber unit (8), a primary tube unit (15) and a secondary tube unit (11).

25. A headbox (10) for a papermaking machine, wherein the headbox (10) comprises a housing (12) and a first functional member (8, 11, 15, 23) according to any one of claims 17-24, characterised in that some of the gap-forming elements (13) of the structural elements (17, 18, 25, 30) of the first functional member (8, 11, 15, 23) are arranged to ensure a gap (14) of a predetermined width between the blocks (1) of the structural elements (17, 18, 25, 30) of the first functional member (8, 11, 15, 23) and the housing (12).

26. The headbox (10) according to claim 25 wherein the headbox (10) further comprises a second functional member (8, 11, 15, 23) according to any one of claims 17-24, wherein some of the gap-forming elements (13) of the structural elements (17, 18, 25, 30) of the second functional member (8, 11, 15, 23) are arranged to ensure a gap (14) of a predetermined width between the blocks (1) of the structural elements (17, 18, 25, 30) of the second functional member (8, 11, 15, 23) and the housing (12), and wherein the first and second functional members (8, 11, 15, 23) are arranged in the headbox (10) one upstream of the other in the direction of the stock flow.

27. A method of manufacturing a structural element according to claim 8, characterised by the steps of: pumping high performance polyurethane elastomers from a computer controlled casting machine into a forming tool in order to mould the block (1), the block being moulded such that said at least on gap-forming element (13) is formed on one of the surfaces of the block (1), removing the moulded block (1) from the tool after a prescribed period of time, placing the block (1) in an oven for post curing at a prescribed temperature for a prescribed period of time, and, optionally, fitting inserts (3, 3') into the channels (2) of the block (1).

28. The method according to claim 27, wherein the prescribed period of time after which the moulded block (1) is to be removed from the tool is approximately 1 hour, and wherein the prescribed temperature and time for post curing of the block (1) is approximately 100°C for approximately 16 hours.

29. A method of assembling a functional member (11) according to any one of claims 18-23, characterised by the steps of: arranging a plurality of structural elements (17 A, 17B, 17C) according to any one of claims 1-16 one beside the other such that the upstream ends (IA) and the downstream ends (IB) of the blocks (1) of the structural elements (17A, 17B, 17C) coincide; arranging gap-forming elements (13) of the structural elements (17A, 17B, 17C) between each neighbouring structural elements (17A, 17B; 17B, 17C); and forming gaps (14) of a predetermined width between neighbouring structural elements (17A, 17B; 17B, 17C).

30. A method of assembling a headbox (10) according to claim 25, characterised by the steps of: arranging a first functional member (11) according to any one of claims 17-24 in a housing (12) of the headbox (10); connecting tubes (7') of a primary tube unit (7) to the upstream end of the structural elements (17) of the first functional member (11) providing a fluid communication between the channels (2) of the first functional member (11) and second functional member (23) arranged upstream of the first functional member (11); and, optionally mounting stock dividing vanes (5) at the downstream end (IB) of the blocks (1) of the structural elements (17) of the first functional member (11).