WO2000019010A1

WO2000019010A1 - Lubricating arrangement and method when impulse-pressing a fibre web

Info

Publication number: WO2000019010A1
Application number: PCT/SE1999/001655
Authority: WO
Inventors: Malin Kilian; Lars Gustavsson; Mikael Nyman
Original assignee: Valmet-Karlstad Ab
Priority date: 1998-09-25
Filing date: 1999-09-22
Publication date: 2000-04-06
Also published as: SE512792C2; SE9803291L; SE9803291D0

Abstract

The invention relates to a lubricating arrangement and a method when impulse-pressing a fibre web in presses having an extended press nip, such as shoe presses. The arrangement comprises a first press surface and a pressing member (5) arranged for forming an extended press nip through which a flexible belt travels when impulse-pressing. The arrangement is arranged for being able to generate an initial high pressure and a finishing lower pressure through the press nip in an effective pressure zone (7) delimited by two side borders (8, 9) extending essentially in the machine direction when impulse-pressing. The arrangement further comprises at least one supply area for lubricant with separate side supply areas (13, 14) and central supply areas (10, 11, 12), wherein the side supply areas (13, 14) are arranged for providing an improved edge lubrication between the pressing member (5) and the flexible belt within the effective pressure zone (7) in the proximity of the side borders (8, 9) when impulse-pressing. The invention can be applied when impulse-pressing in presses having an extended press nip with a decreasing pressure curve through the press nip, and is particularly advantageously practised when manufacturing liner, paperboard, fine paper, tissue paper, or other paper qualities.

Description

Title

Lubricating arrangement and method when impulse-pressing a fibre web.

Technical field

The present invention relates to a lubricating arrangement when impulse-pressing a fibre web in presses having an extended press nip, such as shoe presses. Thereby, impulse- pressing means that at least one press surface is heated to a temperature which considerably exceeds 100 °C.

The invention further relates to a lubricating method which utilises the arrangement according to the invention.

The invention can be applied for all impulse-pressing of fibre webs in presses having an extended press nip with a decreasing pressure curve through the press nip, i.e. a pressure curve with an initial high pressure and a finishing lower pressure. The present invention is particularly advantageous to apply when manufacturing liner, paperboard, fine paper, tissue paper, or other paper grades.

Background of the invention

A paper manufacturing process comprises a number of different steps such as stock preparation, sheet forming and dewatering, pressing and drying. Thereby, the function of the pressing is to dewater the paper sheet, which has been formed and dewatered on one or several wires, even further before the subsequent drying.

The pressing also significantly influences the physical properties of the the finished paper, such as density and strength properties. Normally, the pressing takes place in one or several press nips between pairs of press rolls, wherein the paper web usually is supported through the press nips by one or several water-absorbing press felts which pass through the press nip or the press nips together with the paper web. The nip pressure and the length and geometrical design of the press nip have a great influence on the pressing result, when the dryness of the pressed paper web, and the density and the strength properties of the finished paper are concerned.

It is previously known to extend a press nip by means of replacing one press roll in a pair of press rolls with a so-called shoe-press unit (extended nip press). A shoe-press unit extends the effective press nip and, accordingly, enables a high pressing impulse even if the maximum nip pressure is at a relativity low level. The use of a shoe-press unit provides a pressing which is more gentle towards the fibre web, but with a maintained dryness increase.

A conventional shoe-press unit comprises a concave, stationary surface, a so-called shoe. The concave surface is facing towards the counter roll in the pair of press rolls, wherein a flexible, endless belt travels in a loop around the shoe, so that the belt will pass between the shoe and the counter roll. Such a shoe-press unit also comprises a pressing device for pressing the shoe against the counter roll, and a support beam which supports the shoe.

Furthermore, a system for supplying a suitable lubricant between the stationary shoe and the movable belt is present. In some previously known shoe-press units, a solid counter roll is used, but it happens that also the counter roll is provided with one or several internal pressing members, such as a system with pressing shoes or hydraulic pressure zones, which are able to influence the geometrical shape and the pressure profile of the press nip across the machine direction.

EP 0224428 Al discloses a previously known shoe-press unit, which comprises a counter roll and an elongate shoe having a concave surface facing the counter roll in order to form an extended press nip when the shoe is pressed against the roll. Furthermore, the disclosed shoe-press unit comprises a belt running over the shoe and between the shoe and the counter roll. The edges of the belt are sealed by side walls, which enables a lubricant to form a wedge between the shoe and the belt. According to EP 0 224 428 Al, a flexible, radial connection, between the side walls and the edges of the belt, enables the belt to follow the curvature of the press nip beyond the ends of the shoe and to flex only in a single plane of the press nip. Furthermore, in US 5,167,768, a shoe-press unit comprising a shoe having a curved surface which is applied against a belt travelling through a high pressure zone between the shoe and a rotating backing roll is disclosed. The nip line of the most intense nip pressure along the shoe's contact zone over the backing roll can be placed in a desired position by means of pivotally supporting the shoe about two parallel axes, which in turn are a supported on separately controllable hydraulic pistons . The pressure profile of the nip pressure over the face of the shoe can also be altered by controlling the hydraulic pressure in the hydraulic pistons.

In EP 0 605 376 Al, a shoe in a shoe-press unit is disclosed, which is fitted to be placed in a nip between a back-up roll and a belt-mantle roll, wherein the shoe is placed inside the mantle. By means of an actuating means, which preferably is a cylinder device, the shoe is pressed against the back-up roll, while the paper web/felt or felts are placed between the back-up roll and the belt mantle. The shoe comprises at least one chamber for hydraulic fluid, into which chamber the fluid is passed through a duct. The shoe further comprises a first curved face, whose curve radius is substantially equal to the curve form of the backup roll, and a second face which forms a bottom of the chamber for hydraulic fluid. The second face is joined to the first face and has a larger curve radius than the first face. Thereby, according to EP 0 605 376 A 1, the tangents of the first and second faces are substantially the same at the joint between the first and the second face.

Previously, it has been thought that the pressure curve through the press nip of conventional shoe presses should be asymmetrical, in such a way that the pressure increases from the ingoing side to the outgoing side and reaches its maximum immediately before the point where the web leaves the nip. Such a pressure profile is desirable in order to make it possible to minimise the rewetting of the paper web.

However, US 5,302,252 discloses a shoe-press unit having a reversed, decreasing pressure curve through the press nip. The object is claimed to be to provide an apparatus for mechanical dewatering which provides a better drying result, and which at the same time prevents delamination of the fibrous web. This is reported to be achieved by means of an apparatus in which the fibrous web is passed between at least two press surfaces, which form a press gap and which exert a dewatering pressure on the fibrous web by means of one press surface being designed as an impermeable band which can be pressed against the other press surface by means of a hydraulic pressing element. A support pocket, located in the pressing element essentially in the region between the inlet end of the fibrous web and the centre of the pressing element, generates a hydrodynamic pressure field at the pressing element by setting a lubricant into circulation. The hydrodynamic pressure field provides the desired pressure characteristics as the paper web passes through the press zone. In this way, according to US 5,302,252, a pressure characteristic is achieved in the press nip which is characterised in a rapid pressure increase in the inlet zone, a constant pressure in the region of the supporting pocket, and a gradually decreasing pressure in the outlet zone, whereby the risk for delamination is eliminated.

Impulse-pressing is another previously known technique for dewatering paper webs. In principle, this technique implies that mechanical dewatering by means of pressing in a press nip is combined with heating of, for example, one of the press rolls. Since the heating takes place at the same time as the paper web is subjected to a very high pressure in the press nip, the heating temperature has to be substantially higher than 100 °C, and generally 150 - 400 °C.

It has been known for a long time that the heating of water in a fibre web results in a reduction of the viscosity of the water which facilitates the dewatering. When impulse- pressing, a particularly effective dewatering is obtained, which is thought to be a result of the above-mentioned viscosity reduction, that the water in the paper web is vaporised and forms a "front" which expels residual water, or that the high pressure in the press nip enables a superheating of the water in the paper web so that the water immediately is vaporised when the pressure decreases after the press nip. It is not completely clarified which of these mechanisms is/are the most prevailing, and it is conceivable that several of these mechanisms together contribute to the high efficiency of the impulse-pressing.

US 4,738, 752 discloses a previously known apparatus for impulse-pressing a fibre web.

The disclosed pressing apparatus comprises a press member and a blanket cooperating therewith, which together therebetween define an elongate press section, wherein the web is pressed between the press member and the blanket when passing through the pressing section. The blanket is urged against the pressing member such that fluid is pressed out from the web when the web passes through the pressing section. Thereby, a heating device is disposed adjacent to the press for transferring heat to the web such that, when the web passes through the pressing section, the web is subjected for an extended period to increased pressure and temperature, so that water vapour which is generated during the passage of the web through the pressing section forces the fluid in the liquid phase away from the fibre web.

Furthermore, US 4,324,613 discloses a method and an apparatus for impulse-pressing a moist, porous fibre web. Thereby, the web is guided through the nip between two rotatable rolls, wherein the surface of one roll is heated when it approaches the nip. One side of the web is in direct contact with the surface of the heated roll, and the other side faces a permeable surface. The rolls are pressed together under high pressure to transfer heat from the heated roll to the web compressed therebetween to dry the same. The roll surface can be heated by hot gases from a fuel burner or by a liquid. The dried and consolidated web can be removed from the heated roll by means of doctoring, or it can be conveyed further on from the nip between the rolls to an apparatus for processing the web further.

Even if the technique for impulse-pressing theoretically seems effective, it's commercialisation has been rendered difficult by certain technical problems occurring in practice. One such serious technical problem is that the pressed paper web can delaminate during the pressing. Delamination takes place when the pressure inside the paper web is built up to a very high level within the press nip, whereafter the paper web leaves the press nip and the surrounding pressure rapidly decreases. This causes the paper web to explode from inside and delaminate, something which strongly impairs the strength properties of the finished paper.

In order to enable the intended heat transfer to the fibre web to take place when impulse- pressing, a relatively long retention time in the press nip is required. Therefore, it has been suggested previously that pressing devices having an extended press nip should be utilised for impulse-pressing. In case one desires to utilise a pressing device having an extended press nip for impulse- pressing, for example a shoe-press unit, the normally "increasing" pressure curve through the press nip will make the delamination problem even worse. During such impulse- pressing, it is therefore convenient to turn the pressure curve through the press nip in the opposite direction, so that a decreasing pressure curve is obtained, where the maximum pressure prevails in the beginning of the press nip, in order to thereafter decrease against the end of the press nip.

Since the flexible belt of a shoe-press unit travels over the shoe and is pressed hard between the shoe and the counter roll, the shoe has to be lubricated continuously with a suitable lubricant in order to reduce the friction. The lubrication also provides a certain cooling of the flexible belt. When conventional shoe-press units having an increasing pressure curve through the press nip are concerned, the lubrication of the flexible belt has not been considered to be a particular problem. The increasing pressure curve through the press nip effectively presses out supplied lubricant also towards the edges of the shoe, which is the reason why the point of addition for lubricant is not critical. In conventional shoe-press units, the lubrication of the flexible belt is usually accomplished by means of supplying a lubricant oil to the inside of the belt immediately before the press nip, or by means of the central portion of the shoe being provided with a channel for supplying lubricant oil to the backside of the belt in the press nip.

Accordingly, in US 5,110,417 a shoe press with an extended press zone, having an increasing or level pressure curve through the press nip, is disclosed. The disclosed shoe press comprises a rotating press roll, a press shoe, and a slide band sliding along the surface of the press shoe, a web being passed between felts through the press in order to be pressed between the roll and the slide band. The press shoe, which is designed to operate hydrodynamically, has a surface provided with at pocket area formed by one or more pockets having a low average thickness. If required, pressurised lubricant can be introduced to the pocket area in order to achieve the desired press effect and speed. According to US 5 , 110,417, the pocket or pockets has/have a lubrication introduction area for introducing lubricant, communicating with at least one lubricant line, wherein the lubrication introduction area is formed by at least one lubrication introduction groove, which has a depth larger than the pocket or the pockets, and which extends in the axial direction of the press roll.

Furthermore, US 5,441,604 discloses an extended nip press apparatus for removing water from a web, wherein the pressure curve through the nip essentially is increasing. The apparatus includes a rotatable backing roll and an elongate shoe which cooperates with the backing roll for defining therebetween an extended nip for the passage of the web. A bearing blanket is movably disposed between the backing roll and the concave surface. The arrangement is such that the web is supported by the blanket with the web being disposed between the blanket and the backing roll. A lubricant is supplied between the concave surface and the blanket such that the blanket is slidingly supported by the concave surface during the passage of the felt through the extended nip. The concave surface encompasses a pocket which is defined by the shoe. The arrangement is such that the pocket is filled with lubricant flowing from the concave surface, so that in the event of a paper wad from the web entering into the extended nip, the wad is yieldingly received within the pocket and the damage caused to the blanket by the wad is minimised.

When impulse-pressing in shoe-press units having a decreasing pressure curve through the press nip, the previously known arrangements and methods for lubrication between the shoe and the flexible belt have proved to be unsatisfactory. Thereby, problems with insufficient lubrication, with resulting increased friction and temperature, have occured, in particular at the edges of the shoe. The raised temperature caused by increased friction leads to a viscosity reduction of the supplied lubricant, which in turn further impairs the lubrication. The reason for these problems is that lubricant, which is added in a shoe-press unit having a decreasing pressure curve, more willingly moves forwards in the machine direction than outwards towards the edges of the shoe, since the pressure forwards in the machine direction is lower than the pressure outwards against the edges of the shoe.

Insufficient lubrication at the edges of the shoe is not acceptable in a commercial shoe- press unit for impulse-pressing, since the lifespan of the flexible belt is reduced considerably, and the insufficient edge lubrication, in the worst case, results in the shoe- press unit becoming impossible to keep operating due to frequent belt breakdowns. Accordingly, it is most important to be able to solve the above-mentioned problem with the lubricant, which is added to a shoe-press unit having a decreasing pressure curve through the press nip, more willingly moving forwards in the machine direction than out towards the edges of the shoe, thereby causing an insufficient lubrication between the shoe (the pressing member) and the flexible belt in the proximity of the edges of the shoe.

Summary of the invention

Accordingly, the first object of the present invention is to provide a lubricating arrangement when impulse-pressing a fibre web in a pressing device having an extended press nip and a decreasing pressure curve through the press nip, which arrangement eliminates the above-mentioned problems with delamination and insufficient edge lubrication, and which ensures that a sufficient quantity of lubricant is supplied across the entire width of the flexible belt so that this is not worn out prematurely.

In accordance with claim 1, this first object is achieved by means of the arrangement comprising a pressing device having a first press surface provided with heating means adapted for heating to above 100 °C, a second press surface in the form of a flexible belt, and at least one pressing member. Thereby, the first press surface and the pressing member are arranged for forming a press nip through which the flexible belt travels when impulse- pressing, and for being able to generate, counted in the machine direction through the press nip, an initial high pressure and a finishing lower pressure in a pressure zone effective when impulse-pressing. Thereby, the effective pressure zone is delimited by two side borders extending essentially in the machine direction, and the arrangement further comprises at least one supply area for lubricant. According to the invention, the supply area or supply areas for lubricant comprise(s) separate side supply areas and central supply areas, wherein the side supply areas are arranged for providing an improved edge lubrication between the pressing member and the flexible belt within the effective pressure zone in the proximity of the side borders when impulse-pressing.

A second object of the present invention is to provide a lubricating method with the aid of the arrangement according to the invention. In accordance with claim 12, this object is achieved by means of a method utilising a pressing device having a first press surface which by means of heating means is heated to above 100 °C, a second press surface in the form of a flexible belt, and at least one pressing member. Thereby, the first press surface and the pressing member form a press nip through which the flexible belt travels, wherein an effective pressure zone is generated with, counted in the machine direction through the press nip, an initial high pressure and a finishing lower pressure, wherein the effective pressure zone is delimited by two side borders extending essentially in the machine direction, and lubricant is supplied via at least one supply area for lubricant. According to the invention, the supply area or supply areas for lubricant comprise(s) separate side supply areas and central supply areas, wherein the side supply areas provide an improved edge lubrication between the pressing member and the flexible belt within the effective pressure zone in the proximity of the side borders.

Accordingly, the present invention enables the problem of insufficient edge lubrication, in shoe-press units having a decreasing pressure curve through the press nip, to be eliminated when impulse-pressing.

By means of a reliable arrangement and a simple method, the present invention offers a number of further advantages. Amongst these, it can be mentioned that delamination of the pressed fibre web can be avoided, which provides an excellent quality, at the same time as the wear of the flexible belt is minimised and the machine efficiency can be improved. Furthermore, the invention can easily be applied on a number of different impulse pressing devices, having a decreasing pressure curve through the press nip, where problems with insufficient edge lubrication between an essentially stationary pressing member and a moving flexible belt or flexible shell can occur.

Brief description of the drawings

In the following, the invention will be described in greater detail with reference to the attached drawings, in which Fig. 1 schematically, in the form of a diagram, shows a typical decreasing pressure curve through a press nip of the type of pressing devices in question,

Fig. 2 shows a schematic side view of a pressing device comprising an arrangement according to a preferred embodiment of the invention,

Fig. 3 shows a schematic top view of a pressing member of the arrangement in

Fig. 2,

Fig. 4 shows a schematic sectional view through the section IN-IV in Fig. 3,

Figs. 5-9 show similar views as Fig. 3, but of pressing members according to alternative embodiments of the arrangement according to the invention, and

Fig. 10 shows a schematic perspective view of the pressing member in Fig. 3.

Detailed description of preferred embodiments

In the attached Fig. 1, a typical pressure curve through a press nip of the type of pressing devices for which the present invention is applicable is shown schematically in a diagram form. As is evident from the diagram, the pressure P rapidly increases to a high value X in the beginning of the press nip, in order to thereafter gradually decrease to lower and lower values Y towards the end of the press nip. In the diagram, the arrow denoted with MD indicates the machine direction, i.e. the direction in which the fibre web travels when impulse-pressing. When practising the invention, it is conceivable with a number of different pressure curves, as long as they exhibit a decreasing tendency towards the end of the press nip, something which it is necessary in order to avoid the above-mentioned problem that the paper sheet delaminates during the pressing when impulse-pressing with an increasing pressure curve through the nip.

In Fig. 2, a schematic side view of a pressing device 1, comprising an arrangement according to a preferred embodiment of the invention, is shown. Furthermore, in Figs. 3 and 4 detailed views of a pressing member 5, shown in fig 2, are shown, while Figs. 5-9 show pressing members of arrangements according to alternative embodiments of the invention.

The pressing device 1 has a first press surface 2 which is provided with heating means 3 adapted for heating to above 100 °C. In the described embodiment, the first press surface 2 is constituted of a cylindrical counter roll of a conventional type, while the heating means 3 is constituted of a device for heating by means of induction, according to previously known technique er se.

However, it is also conceivable with embodiments of the invention in which the first press surface is provided in the form of a counter roll comprising mechanical pressure shoes, hydraulic pressure zones, or similar devices, which for example give an opportunity to influence the press nip characteristics across the machine direction. The heating means does not necessarily have to be based on induction technique, but also other types of previously known heating means 3', such as oil or gas burners, or heated oil, can be utilised.

The pressing device 1 further has a second press surface in the form of a flexible belt 4 of a water impervious polymer material, of the type which previously is known for use in conventional shoe-press units. In the described embodiment, the flexible belt 4 consists of a weave-reinforced polyurethane film.

Furthermore, the pressing device comprises at least one pressing member 5, wherein the first press surface 2 and the pressing member 5 are arranged for forming a press nip 6 through which the flexible belt 4 travels when impulse-pressing, in a similar way as in a conventional shoe-press unit.

In the described embodiment, the pressing member is designed as a pressure shoe 5 having an essentially concave surface, which corresponds to the contact surface against the cylindrical counter roll 2. However, it is also conceivable with embodiments of the invention in which the pressing member is designed in another previously known way. In the described embodiment, the position of the pressure shoe 5 and therewith the position of the concave surface in relation to the first press surface 2 can be regulated by means of at least one pressing means (not shown in Fig. 2), acting on the pressure shoe 5, which in the described embodiment consists of a number of hydraulic pistons which are arranged so that the pressure shoe can be inclined/tilted both in the machine direction MD or, if desirable, across the machine direction. However, many other designs are conceivable, as long as they are able to give the formed press nip a decreasing pressure curve, and it is also conceivable with embodiments of the arrangement in which no pressing means is present and the pressure shoe is mounted in a fixed position.

In the described embodiment, the flexible belt 4 is arranged as an essentially cylindrical, endless shell around the pressure shoe 5 so that, seen from the outside, an essentially cylindrical press roll with suitably arranged gables is formed. When impulse-pressing, the cylindrical shape of the formed press roll is maintained by means of fans (not shown in the drawings), which in a previously known way blow air into the interior of the press roll so that a pneumatic over-pressure is created within the flexible belt 5 and the gables provided with sealings. However, it is conceivable with embodiments of the invention in which the flexible belt is guided around the pressure shoe in another way, for example around a number of suitably arranged leading rolls. In such embodiments, the above-mentioned fans are of course eliminated.

In the described embodiment, only the counter roll is provided with driving, but it is also conceivable with embodiments of the invention in which the driving is arranged in another way, for example by means of a suitably arranged leading roll driving the flexible belt.

The pressing member 5, and the first press surface 2, are arranged for generating an effective pressure zone 7 when impulse-pressing with, counted in the machine direction MD through the press nip 6, an initial high pressure X and a finishing lower pressure Y. The effective pressure zone 7 is delimited in the lateral direction by two side borders 8, 9, extending essentially in the machine direction MD. Accordingly, there is no pressure outside the side borders 8, 9 when impulse-pressing. The arrangement according to the invention further comprises at least one supply area for lubricant 10, 11, 12, 13, 14. According to the invention and the preferred embodiment, the supply areas comprise separate side supply areas 13, 14 and central supply areas 10-12, wherein the side supply areas 13, 14 are arranged for providing an improved edge lubrication between the pressing member 5; 505; 605; 705; 805; 905 and the flexible belt

4, in the preferred embodiment the shell, within the effective pressure zone 7 in the proximity of the side borders 8, 9 when impulse-pressing.

In the described embodiment, the side supply areas for lubricant, i.e. both the side supply areas and the central supply areas, are constituted of pockets 10- 14 in the concave surface of the pressure shoe 5, wherein the pockets 10-14 stand in connection with channels (not shown in the drawings) from a lubricant source (not shown), which in the described embodiment is a container for lubricant oil (not shown) of a suitable type with a suitably arranged pump (not shown). When impulse-pressing, the pockets 10-14 are intended to face towards the flexible belt 4 and, via a hydrostatic pressure which is generated in the lubricant supplied from the lubricant source, to exercise a pressure on the flexible belt 4. Furthermore, the supplied lubricant will provide a hydrodynamic lubrication within the effective pressure zone 7 outside the pockets 10-14. In the described embodiment, the side supply areas 13, 14, i.e. the side pockets, are arranged for creating a hydrostatic pressure between the shell 4 and the pressure shoe 5 , specifically at the edges of the shoe, by means of lubricant supplied from the source of lubricant, and also for providing a hydrodynamic lubrication within the effective pressure zone 7 outside the pockets, in order to thereby provide an improved edge lubrication and, furthermore, an improved cooling. In the described embodiment, the improved edge lubrication is achieved by means of the distance A, across the machine direction MD from the side borders 8, 9 of the effective pressure zone 7 to the closest supply area for lubricant, i.e. the side pockets 13, 14, being smaller than 50 mm.

In the preferred embodiment of the arrangement according to the invention, the side supply areas 13, 14, seen from above in relation to the machine direction MD, further have a smaller area than the central supply areas 10-12, wherein the side and central supply areas are arranged for receiving an essentially equal supply of lubricant when impulse-pressing. In this way, in this embodiment, an additional supply of lubricant per unit of width is obtained at the edges of the pressure shoe 5 and the flexible belt 4, wherein the risk of edge wear is reduced even further. However, a number of different embodiments of the arrangement are conceivable in which the same effect is achieved in another way, as long as the side supply areas 13 , 14 are arranged for receiving a larger quantity of lubricant per unit of width across the machine direction MD than the central supply areas 10-12. This can, for example, also be accomplished by means of arranging a separate, larger supply of lubricant to the side supply areas 13, 14.

In a further embodiment of the arrangement according to the invention, the side supply areas 513 , 514 are arranged for supplying lubricant within the effective pressure zone 507 in the proximity of the side borders 508, 509 and, counted in the machine direction MD, also before the high pressure X in the press nip when impulse-pressing. Since the supply of lubricant in this embodiment takes place already before the pressure in the press nip has been built up, the subsequent pressure increase through the nip will press the supplied lubricant out towards the edges by means of a similar mechanism described above in connection with the prior art. Accordingly, in this embodiment of the arrangement according to the invention, lubrication conditions which are more similar to the ones prevailing in an extended press nip having an increasing pressure curve are obtained.

In another embodiment of the arrangement according to the invention, both the central 10- 12; 510-512 and the side supply areas 13, 14; 513, 514 comprise pockets in the surface of the pressing member 5 ; 505. Thereby, the lubricant which is supplied via the pockets when impulse-pressing will exercise a hydrostatic pressure on the flexible belt 4 and, furthermore, provide a hydrodynamic lubrication within the effective pressure zone 7; 507 outside the pockets.

In an alternative embodiment of the arrangement according to the invention, see fig. 7, both the central supply areas 710, 711, 712 and the side supply areas 713, 714 comprise channel outlets 710-714 for supplying lubricant through the surface of the pressing member 705 when impulse-pressing. In contrast to the above-mentioned recessed pockets in the surface of the pressing member, the supply of lubricant through the channel outlets does not create any hydrostatic pressure, but instead provides a purely hydrodynamic lubrication between the pressing member 705 and the flexible belt. An advantage with this embodiment is that the supply of lubricant through the channel outlets 710-714 will not affect the pressure curve through the press nip, or the pressure profile across the machine direction MD, to any significant extent.

In another alternative embodiment of the arrangement, the central supply areas 610, 611, 612 comprise pockets in the surface of the pressing member 605 which via the supplied lubricant exercise a hydrostatic pressure on the flexible belt and, furthermore, provide a hydrodynamic lubrication within the active pressure zone outside the pockets when impulse-pressing, wherein the side supply areas 613, 614 comprise channel outlets for the supply of lubricant through the surface of the pressing member 605 when impulse- pressing, so that a purely hydrodynamic lubrication is provided between the pressing member 605 and the flexible belt at the two side borders 608, 609. Accordingly, this embodiment combines hydrostatic lubricant pockets and hydrodynamic lubrication in the central region with a purely hydrodynamic lubrication at the edges of the pressing member.

In still another alternative embodiment, the arrangement comprises applicator means 815; 913, 914 arranged for applying lubricant on the inside of the flexible belt, so that the lubricant is transferred further to the supply area or areas of the pressing member 805 ; 905 when impulse-pressing. Accordingly, in this embodiment, the lubricant is applied onto the flexible belt before it passes into the press nip with the aid of a distributing device outside the effective pressure zone, for example a spray pipe, a nozzle arrangement, or the like. This embodiment does not require any through channels in the pressing member.

According to another alternative embodiment of the arrangement, the applicator means 815 extends across essentially the entire width of the flexible belt across the machine direction MD, and is designed for being able to supply a larger quantity of lubricant per unit of width at the edges of the flexible belt for further transfer to the pressing member 805 at the two side borders 808, 809. In still another alternative embodiment, the arrangement comprises at least two separate side applicator means 913, 914 arranged for applying an additional quantity of lubricant at the edges of the flexible belt for further transfer to the pressing member 905 at the two side borders 908, 909 when impulse-pressing. This type of additional application of lubricant can advantageously be utilised in order to obtain an improved, purely hydrodynamic lubrication at the edges in combination with another type of lubrication according to the invention across the remainder of the width of the pressing member across the machine direction MD.

The arrangement according to the invention further comprises suitably arranged supporting means, electrical motors, electrical connections, and components included in a suitable control system. These components will not be described in greater detail herein, since they are well known to the skilled person from, for example, the above-mentioned prior art documents and, for example, from the brochure: "Sym-Belt™ - SHOE PRESSES THE VALMET WAY" from NALMET AB.

In the following, a preferred embodiment and a number of alternative embodiments of a method according to the invention will be described, wherein reference is made also to the description above of the arrangement according to the invention.

The method according to the invention and the preferred embodiment utilises a pressing device 1 having a first press surface 2 which by means of heating means 3, 3' is heated to above 100 °C, a second press surface in the form of a flexible belt 4, and at least one pressing member 5. Thereby, the first press surface 2 and the pressing member 5 form a press nip 6 through which the flexible belt 4 travels, and an effective pressure zone 7 is generated with, counted in the machine direction MD through the press nip 6, an initial high pressure X and a finishing lower pressure Y. The effective pressure zone 7 is delimited by two side borders 8, 9 extending essentially in the machine direction MD, and lubricant is supplied via at least one supply area for lubricant 10, 11, 12, 13, 14. According to the invention and the preferred embodiment, the supply area or supply areas for lubricant comprise(s) separate side supply areas 13, 14 and central supply areas 10, 11, 12, wherein the side supply areas 13, 14 provide an improved edge lubrication between the pressing member 5; 505; 605; 705; 805; 905 and the flexible belt 4 within the effective pressure zone 7 in the proximity of the side borders 8, 9.

In another advantageous embodiment of the method according to the invention, the first press surface is provided by a cylindrical counter roll 2 and the pressing member comprises a pressure shoe 5, having an essentially concave surface, which exercises pressure on the flexible belt 4, wherein the position of the concave surface in relation to the counter roll 2 is regulated by means of at least one pressing means acting on the pressure shoe. In this embodiment, the flexible belt 4 is arranged as an essentially cylindrical, endless shell around the pressure shoe 5, and the supply areas for lubricant 10-14 stand in connection with channels from a lubricant source. According to the described embodiment, the side supply areas 13, 14 create a hydrostatic pressure and/or provide a hydrodynamic lubrication between the shell 4 and the pressure shoe 5 by means of lubricant supplied from the lubricant source, and thereby provide the improved edge lubrication.

According to an alternative embodiment of the method, the side supply areas 13, 14 receive a larger quantity of lubricant per unit of width across the machine direction MD than the central supply areas 10-12.

In one advantageous embodiment of the method, the distance A, across the machine direction MD from each side border 8, 9 of the effective pressure zone 7 to the closest supply area for lubricant 13, 14, is smaller than 50 mm.

According to another, alternative embodiment of the method, the side supply areas 513, 514 supply lubricant within the effective pressure zone 507 in the proximity of the side borders 508, 509 and, counted in the machine direction MD, before the high pressure X in the press nip.

In still another alternative embodiment, both the central 10-12; 510-512 and the side supply areas 13, 14; 513, 514 comprise pockets in the surface of the pressing member 5;

505, wherein the lubricant which is supplied via said supply areas exercises a hydrostatic pressure on the flexible belt 4 and, furthermore, provides a hydrodynamic lubrication within the effective pressure zone 7; 507 outside the pockets.

In another embodiment of the method, both the central 710, 711, 712 and the side supply areas 713, 714 comprise channel outlets through which lubricant is supplied through the surface of the pressing member 705, so that the the lubricant provides a hydrodynamic lubrication between the pressing member 705 and the flexible belt.

In still another embodiment of the method, the central supply areas 610, 611, 612 comprise pockets in the surface of the pressing member 605 which via supplied lubricant exercise a hydrostatic pressure on the flexible belt and, furthermore, provide a hydrodynamic lubrication within the effective pressure zone outside the pockets, while the side supply areas 613, 614 comprise channel outlets through which lubricant is supplied through the surface of the pressing member 605, so that a purely hydrodynamic lubrication is provided between the pressing member 605 and the flexible belt at the two side borders 608, 609.

In still another alternative embodiment of the method, an applicator means 815; 913, 914 applies lubricant on the inside of the flexible belt, whereafter the lubricant is transferred to the supply area or supply areas of the pressing member 805; 905. Thereby, the applicator means 815 advantageously extends across essentially the entire width of the flexible belt across the machine direction MD and supplies a larger quantity of lubricant per unit of width at the edges of the flexible belt, whereafter the lubricant is transferred to the pressing member 805 at the two side borders 808, 809.

According to a particularly advantageous, alternative embodiment, the method utilises at least two separate side applicator means 913, 914, which apply an additional lubricant addition at the edges of the flexible belt, whereafter the additional addition is transferred to the pressing member 905 at the two side borders 908, 909.

The present invention should by no means be regarded as being limited to what has been described above in connection with the different embodiments, or to what is shown in the attached drawings, but the scope of the invention is defined by the attached claims. Accordingly, the lubricant utilised in the invention can be of any previously known type, preferably a lubricant oil with properties which are suitable for the application.

Furthermore, when impulse-pressing, the passage of the fibre web 16 through the press nip 6 of the arrangement according to the invention can be varied in different ways. As is indicated in Fig. 2 with dotted lines, the fibre web 16 is preferably supported through the press nip 6 on a suitable machine clothing of a previously known type, for example a water-absorbing press felt 17.

It should be noted that the attached figures 1-10 should be regarded as schematic.

Accordingly, for example the size of the above-mentioned channel outlets has been exaggerated in the figures for reasons of clarity. In reality, the channel outlets can have a diameter for example within the range of 0.8 - 3 mm.

Claims

1. A lubricating arrangement when impulse-pressing a fibre web, comprising a pressing device (1) having a first press surface (2) provided with heating means (3, 3') adapted for heating to above 100 °C, a second press surface in the form of a flexible belt (4), and at least one pressing member (5), wherein the first press surface (2) and the pressing member (5) are arranged for forming a press nip (6) through which the flexible belt (4) travels when impulse-pressing, and for being able to generate, counted in the machine direction (MD) through the press nip (6), an initial higher pressure (X) and a finishing lower pressure (Y) in an effective pressure zone (7) when impulse-pressing, wherein the effective pressure zone (7) is delimited by two side borders (8, 9) extending essentially in the machine direction (MD), and the arrangement further comprises at least one supply area for lubricant (10, 11, 12, 13, 14), c h ar a c t e r i s e d i n that said supply area(s) for lubricant comprise(s) separate side supply areas (13, 14) and central supply areas (10, 11, 12), and that said side supply areas (13, 14) are arranged for providing an improved edge lubrication between the pressing member (5; 505; 605; 705; 805; 905) and the flexible belt (4) within the the effective pressure zone (7) in the proximity of the side borders (8, 9) when impulse-pressing.

2. An arrangement according to claim 1, wherein the first press surface is provided by a cylindrical counter roll (2) and the pressing member comprises a pressure shoe (5) having an essentially concave surface intended to exercise pressure on the flexible belt (4), and the position of the concave surface in relation to the counter roll (2) can be regulated by means of at least one pressing means acting on the pressure shoe, wherein the flexible belt (4) is arranged as an essentially cylindrical, endless shell around the pressure shoe (5), and the supply areas for lubricant (10-14) stand in connection with channels from a lubricant source, c h a r a c t e r i s e d i n that the side supply areas (13, 14) are arranged for creating a hydrostatic pressure and/or providing a hydrodynamic lubrication between the shell (4) and the pressure shoe (5) by means of lubricant supplied from the lubricant source, and for thereby providing said improved edge lubrication.

3. An arrangement according to claim 1 or 2, characterised in that the side supply areas (13, 14) are arranged for receiving a larger quantity of lubricant per unit of width across the machine direction (MD) than the central supply areas (10-12) when impulse-pressing.

4. An arrangement according to claim 1, 2 or 3, characterised in that the distance (A) across the machine direction (MD) from each side border (8, 9) of the effective pressure zone (7) to the closest supply area for lubricant (13, 14) is smaller than 50 mm.

5. An arrangement according to any one of the preceding claims, characterised in that the side supply areas (513, 514) are aπanged for supplying lubricant within the effective pressure zone (507) in the proximity of the side borders (508, 509) and, counted in the machine direction (MD), also before the high pressure (X) in the press nip when impulse-pressing.

6. An arrangement according to any one of claims 1 to 5, characterised in that both the central (10-12; 510-512) and the side supply areas (13, 14; 513, 514) comprise pockets in the surface of the pressing member (5; 505) and are arranged so that the lubricant supplied via said pockets exercise a hydrostatic pressure on the flexible belt (4) and, furthermore, provides a hydrodynamic lubrication within the effective pressure zone (7; 507) outside the pockets.

7. An arrangement according to any one of claims 1 to 5, characterised in that both the central (710, 711, 712) and the side supply areas (713, 714) comprise channel outlets for supplying lubricant through the surface of the pressing member (705) when impulse-pressing, so that said lubricant provides a purely hydrodynamic lubrication between the pressing member (705) and the flexible belt.

8. An arrangement according to any one of claims 1 to 5, characterised in that the central supply areas (610, 611, 612) comprise pockets in the surface of the pressing member (605), which via supplied lubricant exercise a hydrostatic pressure on the flexible belt and, furthermore, provides a hydrodynamic lubrication within the effective pressure zone outside the pockets when impulse-pressing, and that the side supply areas (613,614) comprise channel outlets for supplying lubricant through the surface of the pressing member (605) when impulse-pressing, so that a purely hydrodynamic lubrication is provided between the pressing member (605) and the flexible belt at the two side borders (608, 609).

9. An arrangement according to any one of claims 1 to 5, characterised in that the arrangement comprises applicator means (815; 913, 914) arranged for applying lubricant on the inside of the flexible belt, so that the lubricant is transferred further to said supply area(s) of the pressing member (805 ; 905) when impulse- pressing.

10. An arrangement according to claim 9, characterised in that the applicator means (815) extends across essentially the entire width of the flexible belt across the machine direction (MD), and is designed for being able to supply a larger quantity of lubricant per unit of width at the edges of the flexible belt for further transfer to the pressing member (805) at the two side borders (808,

809).

11. An arrangement according to any one of the preceding claims, characterised in that the arrangement comprises at least two separate side applicator means (913,914) arranged for applying an additional lubricant addition at the edges of the flexible belt for further transfer to the pressing member (905) at the two side borders (908, 909) when impulse-pressing.

12. A lubricating method when impulse-pressing a fibre web, utilising a pressing device ( 1 ) having a first press surface (2) which by means of heating means (3 , 3 ') is heated to above 100 °C, a second press surface in the form of a flexible belt (4), and at least one pressing member (5), wherein the first press surface (2) and the pressing member (5) form a press nip (6) through which the flexible belt (4) travels, and an effective pressure zone (7) is generated with, counted in the machine direction (MD) through the press nip (6), an initial high pressure (X) and a finishing lower pressure (Y), wherein the effective pressure zone (7) is delimited by two side borders (8, 9) extending essentially in the machine direction (MD), and lubricant is supplied via at least one supply area for lubricant (10-14), characterised in that said supply area(s) for lubricant comprise(s) separate side supply areas (13, 14) and central supply areas (10, 11, 12), and that said side supply areas (13,14) provide an improved edge lubrication between the pressing member (5; 505, 605; 705; 805; 905) and the flexible belt (4) within the effective pressure zone (7) in the proximity of the side borders (8, 9).

13. A method according to claim 12, wherein the first press surface is provided by a cylindrical counter roll (2), and the pressing member comprises a pressure shoe (5) having an essentially concave surface which exercises pressure on the flexible belt (4), wherein the position of the concave surface in relation to the counter roll (2) is regulated by means of at least one pressing means acting on the pressure shoe, and the flexible belt (4) is arranged as an essentially cylindrical, endless shell around the pressure shoe (5), and the supply areas for lubricant (10-14) stand connection with channels from a lubricant source, characterised in that the side supply areas (13, 14) create a hydrostatic pressure and/or provide a hydrodynamic lubrication between the shell (4) and the pressure shoe (5) by means of lubricant supplied from the lubricant source, and thereby provide said improved edge lubrication.

14. A method according to any one of claims 12 or 13, characterised in that the side supply areas (13, 14) receive a larger quantity of lubricant per unit of width across the machine direction (MD) than the central supply areas (10-12).

15. A method according to claim 12, 13 or 14, characterised in that the distance (A) across the machine direction (MD) from each side border (8, 9) of the effective pressure zone (7) to the closest supply area for lubricant (13, 14) is smaller than 50 mm.

16. A method according to any one of claims 12 to 15, characterised in that the side supply areas (513, 514) supply lubricant within the effective pressure zone (507) in the proximity of the side borders (508, 509) and, counted in the machine direction (MD), before the high pressure (X) in the press nip.

17. A method according to any one of claims 12 to 16, characterised in that both the central (10-12; 510-512) and the side supply areas (13, 14; 513, 514) comprise pockets in the surface of the pressing member (5; 505), and that the lubricant which is supplied via said supply areas (10-14; 510-514) exercises a hydrostatic pressure on the flexible belt (4) and, furthermore, provides a hydrodynamic lubrication within the effective pressure zone outside the pockets.

18. A method according to any one of claims 12 to 16, characterised in that both the central (710, 711, 712) and the side supply areas (713, 714) comprise channel outlets through which lubricant is supplied through the surface of the pressing member (705), so that said lubricant provides a purely hydrodynamic lubrication between the pressing member (705) and the flexible belt.

19. A method according to any one of claims 12 to 16, characterised in that the central supply areas (610,611,612) comprise pockets in the surface of the pressing member (605), which via supplied lubricant exercise a hydrostatic pressure on the flexible belt and, furthermore, provide a hydrodynamic lubrication within the effective pressure zone outside the pockets, and that the side supply areas (613, 614) comprise channel outlets through which lubricant is supplied through the surface of the pressing member (605), so that a purely hydrodynamic lubrication is provided between the pressing member (605) and the flexible belt at the two side borders (608, 609).

20. A method according to any one of claims 12 to 16, characterised in that applicator means (815; 913, 914) apply lubricant on the inside of the flexible belt, and that said lubricant thereafter is transferred to said supply area(s) of the pressing member (805; 905).

21. A method according to claim 20, characterised in that the applicator means (815) extends across essentially the entire width of the flexible belt across the machine direction (MD) and supply a larger quantity of lubricant per unit of width at the edges of the flexible belt, and that the lubricant thereafter is transfeπed to the pressing member (805) at the two side borders

(808, 809).

22. A method according to any one of claims 12 to 21, characterised in that the method utilises at least two separate side applicator means (913,914), which apply an additional lubricant addition at the edges of the flexible belt, and that said additional addition thereafter is transferred to the pressing member (905) at the two side borders (908, 909).