Press body, and paper machine comprising such a press body

Abstract

The present invention relates to a press body for a paper machine having an extended nip formed between the press body and a counter-pressure member, wherein the press body (50) is elastically deformable and comprises a working surface (15), and wherein the press body comprises a first pressure chamber (51) and a second pressure chamber (52) that are arranged inside the press body (50) and separated from each other by a partition wall (55), which pressure chambers (51, 52) are configured to be pressurized such that the press body (50) expands for pressing the working surface (15) towards the counter-pressure member, and wherein the first pressure chamber (51) has a first height (h1) and the second pressure chamber (52) has a second height (h2), and wherein the first height (h1) is larger than the second height (h2) The invention also relates to a paper machine comprising such a press body.

Description

[0001] PRESS BODY, AND PAPER MACHINE COMPRISING SUCH A PRESS BODY

[0002] TECHNICAL FIELD

[0003] The present invention relates to a press body for a paper machine having an extended nip formed between the press body and a counter-pressure member, said press body comprising internal pressure chambers. The invention also relates to a paper machine with such a press body.

[0004] BACKGROUND

[0005] In a paper machine, an extended press nip is generally used for pressing water out of a newly formed wet fibrous web but an extended nip may also be used for other purposes, e.g. calendering. Although extended press nips were first introduced for heavy grades such as paperboard, they have also come to be used for lighter grades such as printing paper and even for tissue paper. When making tissue paper, the extended press nip is often formed by an extended nip roll and a Yankee drying cylinder that acts as a counter-pressure member for the extended nip roll.

[0006] An extended press nip, especially in a machine for making tissue paper, is typically formed by an extended nip roll that comprises a support body with a working surface that is pressed against the counter roll by pressurized chambers inside or below the support body acting to push the support body in a first direction towards the counter-pressure member. The purpose of the extended press nip is to dewater a fibrous web during production of paper.

[0007] Within the art, rigid support bodies typically made from metallic materials are known but since they are inflexible it is difficult to achieve a desired pressure profile in the extended nip and this prevents an efficient dewatering of the fibrous web as well as causing excessive wear on components of the extended press nip such as the extended nip roll and the fabric used to transport the web through the nip.

[0008] Softer, more flexible support bodies that are elastically deformable are therefore a preferred choice and significantly improve dewatering by enabling a desired pressure profile against the counter-pressure member. Flexible support bodies typically comprise at least two pressure chambers housed inside the support body, and by pressurizing the pressure chambers the working surface is pressed against the counter-pressure member.

[0009] However, one area of difficulty when designing and operating flexible support bodies is to achieve high pressure in the nip with a desired pressure profile. This is particularly challenging when at least two pressure chambers are provided inside the press body since an increased pressure in the pressure chambers will not only cause deformation towards the nip but also internal deformation of partition walls between the pressure chambers and / or of outer walls. Due to the flexible material, the support body tends to deform in unexpected ways and thereby distort the pressure profile so that dewatering efficiency is decreased. There is also a risk of plastic deformation due to excessive pressure in one or more of the pressure chambers so that the support body is destroyed.

[0010] There is therefore a need for improvements within this area.

[0011] SUMMARY

[0012] The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a press body for a paper machine, and by a paper machine comprising such a press body according to the appended independent claims.

[0013] The press body according to the invention is suitable for use in a paper machine having an extended nip formed between the press body and a counter-pressure member. The press body is elastically deformable and comprises a working surface and also comprises a first pressure chamber and a second pressure chamber that are arranged inside the press body and separated from each other by a partition wall. The pressure chambers are configured to be pressurized such that the press body expands for pressing the working surface towards the counter-pressure member. The first pressure chamber has a first height and the second pressure chamber has a second height wherein the first height is larger than the second height. That the first pressure chamber has a larger height than the second pressure chamber is advantageous in enabling better control of the pressure profile in the nip as well as improved pressure distribution inside the press body. When the pressure chambers are pressurized the expansion of the press body takes place by the partition wall and outer walls of the press body stretching, and the resulting elongation of the walls will depend on their unstretched length. Also, depending on the height of the chambers the thickness of the material of the press body above the pressure chamber, i.e. between the pressure chamber and the working surface will differ. As a result, providing pressure chambers with different heights enables a greater control of the pressure distribution in the nip and thereby adjusts the pressure profile in the nip.

[0014] Suitably, the first pressure chamber and second pressure chamber are configured to be individually pressurized independently of each other. Also, the first pressure chamber may comprise a support element for supporting the partition wall, said support element having a support height that corresponds to the first height of the first pressure chamber. The support element provides support to walls of the first pressure chamber to prevent deformation that could otherwise occur if the pressure difference between the first and second pressure chambers is large.

[0015] Also, the first height is suitably at least equal to a sum of the second height and the maximum stroke length of the press body. Thereby, the first height is larger than the second height by at least the maximum stroke length. This ensures that the second pressure chamber is prevented from expanding beyond the first pressure chamber even when the press body is at its maximal elongation. In particular for embodiments that comprise the support element, this is advantageous since the risk of deformation of the partition wall is decreased or even minimized.

[0016] Suitably, a first bottom of the first pressure chamber and a second bottom of the second pressure chamber are at a bottom height from a bottom of the press body. Thereby, the pressure chambers are arranged at a common bottom level but extends to different heights in the press body. This is advantageous in providing a smaller distance in the press body from the first pressure chamber to the working surface as compared with a larger distance from the second pressure chamber to the working surface. Where the distance is larger the pressure is distributed more evenly in the material of the press body, thereby further adjusting the pressure profile in the nip.

[0017] Alternatively, the bottom of the first pressure chamber is at a first chamber bottom height in the press body and the bottom of the second pressure chamber is at a second chamber bottom height in the press body, wherein the second chamber bottom height is equal to or larger than a sum of the first chamber bottom height and the maximum stroke length. This ensures that the second pressure chamber is not able to expand downwards beyond the bottom of the first pressure chamber, even at the maximal expansion of the press body.

[0018] In some embodiments, a first top of the first pressure chamber and a second top of the second pressure chamber are each at a top height from the bottom of the press body. Thereby, the pressure chambers are arranged at a common top level but extend to different depths in the press body. This is advantageous in enabling the different heights of the pressure chambers while still holding both pressure chambers at equal distance from the working surface so that the press body provides similar deformation above both pressure chambers when expanded.

[0019] Alternatively, the top of the first pressure chamber is at a first chamber top height in the press body and the top of the second pressure chamber is at a second chamber top height in the press body, and the first chamber top height is equal to or larger than a sum of the second chamber top height and the maximum stroke length. This ensures that the second pressure chamber is not able to expand upwards beyond the top of the first pressure chamber when the press body is expanded.

[0020] Suitably, the maximum stroke length is at least 1 mm, preferably at least 4 mm and more preferably at least 7 mm. Thereby, the press body is able to expand to fit the requirements of the paper machine in which it is arranged. Also, the expansion of the press body can take place by the partition wall between the pressure chambers stretching due to the increased pressure inside the pressure chambers without risking plastic deformation or rupture of the partition wall due to excessive stretching.

[0021] In some embodiments, the maximum stroke length is at least 15 mm, preferably at least 20 mm and more preferably at least 30 mm. Thereby, very large strokes are achieved, and the partition wall is configured to be able to stretch to accommodate this. It is highly advantageous that stretching the partition wall to extend the press body takes place without undue absorption of energy to ensure that the desired pressure profile is achieved in the extended nip.

[0022] Suitably, the first pressure chamber has a first cross-sectional area, and the second pressure chamber has a second cross-sectional area, wherein the first cross-sectional area differs from the second cross-sectional area. Thereby, different volumes of the first pressure chamber and second pressure chamber are achieved, which enables different pressure into the nip even when the first pressure chamber and second pressure chamber are pressurized from the same source of pressurized fluid.

[0023] Alternatively, the first cross-sectional area is substantially equal to the second cross-sectional area. Thereby, width of the first pressure chamber and second pressure chamber are different so that the second pressure chamber is longer in the machine direction than the first pressure chamber, which provides improved control over the pressure profile in the nip.

[0024] Suitably, the press body comprises a third pressure chamber arranged inside the press body and configured to be pressurized such that the press body expands, wherein the third pressure chamber has a third height that differs from at least one of the first height and the second height. Thereby, the pressure profile in the nip can be controlled in even more detail than using only two pressure chambers. Suitably, the press body may comprise at least one additional pressure chamber arranged inside the press body and configured to be pressurized such that the press body expands, wherein each of the at least one additional pressure chamber has a height that differs from at least one of the first height and the second height. Thereby, the pressure profile in the nip can be controlled in more detail since the number, dimensions and pressurization of the additional pressure chambers can be selected to fit the particular requirements for any given application.

[0025] The invention also comprises a paper machine with at least one press body according to any embodiment of the invention.

[0026] Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.

[0027] DRAWINGS

[0028] The invention will now be described in more detail with reference to the appended drawings, wherein

[0029] Fig. 1 discloses a schematic cross-sectional view of an extended press nip of a paper machine, in which the extended nip is formed between a press body and a counter-pressure member;

[0030] Fig. 2 discloses a schematic cross-sectional view from the side of a press body according to a first embodiment of the invention;

[0031] Fig. 3 discloses a schematic cross-sectional view from the side of a press body according to a second embodiment of the invention;

[0032] Fig. 4 discloses a schematic cross-sectional view from the side of a press body according to a third embodiment of the invention;

[0033] Fig. 5 discloses a schematic cross-sectional view from the side of a press body according to a fourth embodiment of the invention; Fig. 6 discloses a schematic cross-sectional view from the side of a press body according to a fifth embodiment of the invention; and

[0034] Fig. 7 discloses a schematic cross-sectional view from the side of a press body according to a sixth embodiment of the invention.

[0035] All the figures are schematic, not necessarily to scale, and generally only show parts which are helpful to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated.

[0036] DETAILED DESCRIPTION

[0037] When referring to a “paper machine” herein, this is to be understood as a machine suitable for producing paper from a pulp. The machine may be configured to produce tissue paper but may alternatively be configured to produce writing paper or paperboard. In the following, references are made to the production of tissue paper but this is to be seen as an example only and not as limiting to the scope of the present invention.

[0038] When terms such as “upper”, “lower”, “top” and “bottom” are used in the following this is to be understood as being in relation to a first direction D that may be seen as a direction upwards. Thus, an upper side is a side that faces in the first direction D whereas a lower side faces in a direction opposite to the first direction D. Also, an upper part and a bottom part differ from each other in a movement towards the first direction D first passing the bottom part before passing the upper part.

[0039] It is to be noted that all dimensions given herein are to be understood as being within manufacturing tolerances or at least not differing more than 10 %. Also, when it is stated that a feature is equal, substantially equal, constant, substantially constant, uniform or substantially uniform to another, this is also to be understood as being equal, constant or uniform within manufacturing tolerances or at least not differing more than 10 %. Fig. 1 discloses an extended press nip of a paper machine 1 according to the invention, in which the extended nip N is formed between a press body 50 according to any embodiment of the invention and a counter-pressure member 7.

[0040] A paper machine comprising such an extended nip N with a press body 50 according to the invention will now be described, focusing on the extended nip N as such and mentioning other sections of the paper machine only briefly.

[0041] Thus, as is well known in the art, a paper machine generally comprises a forming section in which a head box is arranged to inject stock in a gap between a forming fabric and a felt 33. The forming fabric would typically be a foraminous wire. The felt is configured to pass over a forming roll and the felt and the forming fabric are guided in loops by guide rolls.

[0042] From the forming section, a newly formed wet fibrous web is transported by the felt 33 to the extended press nip N shown in Fig. 1 formed between an extended nip roll 5 and a counter-pressure member 7. The extended nip roll 5 comprises a press body 50 according to the present invention as will be described in more detail further below. The counter-pressure member 7 may suitably be a Yankee drying cylinder, but in some embodiments the extended nip may be arranged between the extended nip roll 5 and another counterpressure member 7 before being passed to a Yankee drying cylinder.

[0043] In the press nip N between the extended nip roll and the counter-pressure member 7, water is pressed out of the web W and absorbed by the felt 33 which is water-receiving. The web W then passes over the Yankee drying cylinder 7 and is dried by heat propagated from the Yankee drying cylinder 7 to the web W. The Yankee drying cylinder 7 is typically heated to reach a temperature on a surface that contacts the web W of about 95 - 100 °C. A dry solids content of the web W as it reaches the extended press nip N may vary considerably but is in typical applications in a range 18 - 30 %. After the extended press nip N, the web W may have a dry solids content of 40 - 55 %, depending on factors such as linear load in the nip, the temperature of the counter-pressure member 7 and the dry solids content of the web W before it reaches the extended press nip N.

[0044] The web W is typically doctored from the Yankee drying cylinder 7 by a doctor blade and is passed in the form of a ready-dried web to a reel-up.

[0045] What is said above is to be regarded as a general description of the paper machine 1 , but it is especially to be noted that the press body 50 according to the present invention may be used with various kinds of paper machines as long as they have the extended press nip between a press body and a counterpressure member.

[0046] The extended press nip N will now be described in more detail with reference again to Fig. 1, showing the extended nip roll 5 to comprise a flexible jacket 10 with an interior surface 11 and an exterior surface 12. The flexible jacket 10 typically comprises polyurethane and is shaped as a tube that extends in a cross-machine direction, said cross-machine direction being a direction that is perpendicular to a machine direction MD (see Fig. 2) defined as a direction from the forming section to the reel-up, i.e. a main direction of travel of the web W.

[0047] Thus, the flexible jacket 10 has an axial direction that coincides with the cross-machine direction and at its axial ends the flexible jacket 10 is normally connected to end walls that are rotatably arranged about and axis so that the extended nip roll 5 is able to rotate. Suitably, the extended nip roll 5 may be connected to a source of pressurized air so that an enclosed space formed by the flexible jacket 10 and the end walls may be filled with pressurized air.

[0048] Inside the extended nip roll 5, a support 21 is mounted and holds the press body 50 according to the present invention such that an upper surface 14 of the support body 50 is pressed against the interior surface 11 of the flexible jacket 10. On the upper surface 14 is a working surface 15 (see Fig. 2 onwards) that forms the extended press nip N by being pressed against the flexible jacket 10 so that the web W is in turn pressed against the counter-pressure member 7. The press body 50 is elongated and extends along the interior surface 11 of the extended nip roll 5 in a direction transversal to a direction of rotation of the extended nip roll 5 in order to be able to press against an entire width of the web W in the extended press nip N. For this purpose, the press body 50 may have a length that is equal to or larger than an intended width of the web W, but in some embodiments the press body 50 may instead have a length that is shorter than the intended width of the web W.

[0049] The working surface 15 is a surface that acts to form the extended press nip N. The shape of the working surface 15 may be adapted to form a desired press profile with the counter-pressure member 7, as is well known within the art. One prior art technology that deals with the design of a working surface is US 2009 / 0173465 (Metso paper). Although the working surface 15 is shown schematically as a flat surface in Fig. 2 onwards, it is to be noted that any shape and design of the working surface is suitable for use with the press body 50 of the present invention.

[0050] The press body 50 will now be described in detail, starting with a first embodiment shown in Fig. 2. For other embodiments of the invention, they will be described mainly in those features that differ from each other to avoid repetition. Therefore, it is to be understood that all features not specifically stated as differing from one embodiment to another are to be seen as similar or identical. Also, features from one embodiment may freely be incorporated into another embodiment where technically feasible.

[0051] The press body 50 comprises a first pressure chamber 51 and a second pressure chamber 52 that are separated from each other by a partition wall 55. Each of the first and second pressure chambers 51, 52 is configured to be pressurized by being fluidly connected to a source of a pressurized fluid as is already known in the art. The pressurized fluid is suitably a hydraulic fluid (e.g. oil) but may in some embodiments instead be other fluids.

[0052] The press body 50 is made from elastically deformable material, so when the first and second pressure chambers 51, 52 are pressurized, this causes the press body 50 to expand. Since the press body 50 is mounted in the support 21 when in use (see Fig. 1), the press body 50 is able to expand mainly in a first direction D upwards in Fig. 2. This expansion causes the working surface 15 on the upper side 14 of the press body 50 to be pressed towards the counter-pressure member 7, thereby forming the nip N. The partition wall 55 between the first and second pressure chambers 51, 52 suitably has a wall thickness t of 1 mm - 20 mm.

[0053] The first pressure chamber 51 has a first height h 1 and the second pressure chamber 52 has a second height h2, with the first height hl being larger than the second height h2. Also, the first pressure chamber 51 has a first cross- sectional area Al and the second pressure chamber 52 has a second cross- sectional area A2. In the first embodiment, the first cross-sectional area Al differs from the second cross-sectional area A2 by being larger, but in other embodiments this can be reversed with the first cross-sectional area Al being smaller. Alternatively, the cross-sectional areas Al, A2 can instead be equal (see Fig. 6).

[0054] Preferably, the press body 50 is elastically deformable by being made from a material having a Shore A hardness of of 50 - 100, preferably a Shore A hardness of 80 - 100 and more preferably a shore A hardness of 90 - 95. When referring to a Shore A hardness herein, this is to be understood as according to ASTM D2240. The press body 50 may also comprise more than one material, where at least one has a Shore A hardness as stated above. One suitable material is polyurethane.

[0055] When in use, the first pressure chamber 51 and the second pressure chamber 52 are pressurized to cause an expansion of the press body 50. In the first embodiment of Fig. 2, the first and second pressure chambers 51, 52 are configured either to be pressurized individually to different pressures or together to similar or identical pressure.

[0056] When the press body 50 expands, the partition wall 55 is stretched as a height of the first and second pressure chambers 51, 52 increases. Depending on the material or materials used in the press body 50, the thickness of the partition wall 55 and on the pressure inside the chambers, the partition wall 55 as well as sidewalls 57 at outer ends of the press body 50 in the machine direction MD stretch to accommodate the expansion. Dimensions of the partition wall 55 are selected so as to be able to stretch to a maximum stroke length SL of the press body 50 into the nip N, and also to give stability to the press body 50. In particular where the first pressure chamber 51 and the second pressure chamber 52 are individually pressurized to different pressures, there is a risk that the partition wall 55 could deform and protrude into the pressure chamber with lower pressure.

[0057] The pressure inside the first pressure chamber 51 may be equal to the pressure inside the second pressure chamber 52 or may alternatively differ. Depending on a specific pressure profile is desired in the nip N, it is advantageous to have a lower pressure in the first pressure chamber 51 and a higher pressure in the second pressure chamber 52. The press body 50 is then arranged to have the second pressure chamber 52 after the first pressure chamber 51 in the machine direction MD, so that the web W when moving through the nip N is subjected to a lower pressure from the first pressure chamber 51 before being subjected to a higher pressure from the second pressure chamber 52.

[0058] In embodiments of the invention where the first pressure chamber 51 and second pressure chamber 52 are individually pressurized, they can be referred to as a low-pressure chamber and a high-pressure chamber, respectively.

[0059] Fig. 3 discloses a second embodiment of the press body 50 that comprises a support element 54 that is arranged inside the first pressure chamber 51. The support element 54 has a support height SH that corresponds to the first height hl of the first pressure chamber 51 so that the support element 54 extends all the way from a bottom to a top of the first pressure chamber 51. In Fig. 3, the support element 54 is shown only along the partition wall 54, but in some embodiments the support element 54 can instead have other shapes and designs as long as it is able to support the partition wall 55 and prevent stretching or deformation in other directions than the first direction D (see e.g. Fig. 4). The support element 54 is advantageous in preventing such deformation in particular where the first and second pressure chambers 51 , 52 are individually pressurized so that the first pressure chamber 51 is at a lower pressure than the second pressure chamber 52. In such situations, the partition wall 55 would otherwise risk being deformed in a sideways direction from the second pressure chamber 52 towards the first pressure chamber 51 , i.e. a direction parallel to the machine direction MD and perpendicular to the first direction D. When using the press body 50, the expansion due to the pressurized pressure chambers 51, 52 should take place only in the first direction D, and the support element 54 ensures that this is the only available direction when the press body 50 is placed in the holder 21 of the paper machine 1.

[0060] Furthermore, in the second embodiment of Fig. 3, the first height hl is at least equal to a sum of the second height h2 and a maximum stroke length SL of the press body 50. This means that the press body 50 is able to expand its maximum stroke length SL in the first direction D without the second pressure chamber 52 extending beyond the first height h 1 , and since this corresponds to the height of the support element 54 there will be support for the partition wall 55 even at the maximum stroke length SL. This is highly advantageous in protecting the partition wall 55 and thereby increasing the lifetime of the press body 50 as well as decreasing the need for maintenance.

[0061] In the second embodiment, the first pressure chamber 51 has a first bottom b 1 that is at a first chamber bottom height bh 1 in the press body 50 and the second pressure chamber 52 has a second bottom b2 of the second pressure chamber 52 that is at a second chamber bottom height bh2. The second chamber bottom height bh2 is equal to or larger than a sum of the first chamber bottom height bh 1 and the maximum stroke length SL. This means that in situations where the expansion of the press body 50 causes the second pressure chamber 52 to expand at the bottom b2, the support element 54 will be able to support the partition wall 55 and prevent deformation into the first pressure chamber 51.

[0062] The first chamber bottom height bh 1 and the second chamber bottom height bh2 are determined in relation to a press body bottom B of the press body 50. Also, the first pressure chamber 51 has a first top tl and the second pressure chamber 52 has a second top t2 that are at a substantially equal top height TH from the press body bottom B.

[0063] For all embodiments of the invention, it is advantageous for the support element 54 to have a shape that corresponds to a shape of the partition wall 55 since this allows for a reliable support of the partition wall 55.

[0064] Fig. 4 shows a third embodiment that differs from the second embodiment by the top 11 of the first pressure chamber 51 being at a first chamber top height thl in the press body 50 and the top t2 of the second pressure chamber 52 being at a second chamber top height th2 in the press body 50. The first chamber top height th 1 is equal to or larger than a sum of the second chamber top height th2 and the maximum stroke length SL. This provides different material thickness between the first pressure chamber 51 and the working surface 15 as compared to between the second pressure chamber 52 and the working surface 15. It also means that in situations where the expansion of the press body 50 causes the second pressure chamber 52 to expand at the top t2, the support element 54 will be able to support the partition wall 55 and prevent deformation into the first pressure chamber 51.

[0065] In the third embodiment, the first bottom b 1 and the second bottom b2 are at a substantially equal bottom height BH from the bottom B of the press body

[0066] 50.

[0067] The third embodiment also shows a different design of the support element 54 to further increase stability at the partition wall 55 by extending both along the partition wall 55 and along an opposing wall of the first pressure chamber

[0068] 51 , and by spacing elements maintaining the support element 54 along both these walls at a fixed distance from each other. This is advantageous in maintaining alignment of the support element 54 along the partition wall 55 despite any movement of the partition wall 55 as the press body 50 expands.

[0069] The main difference between the second and the third embodiments, apart from the design of the support element 54, is the placement of the first and second pressure chambers 51, 52 in relation to each other. Depending on whether elongation of the partition wall 55 takes place at the top tl, t2 of the pressure chambers 51, 52 or at the bottom bl, b2, the embodiments of Fig. 3 and 4 are able to prevent sideways deformation of the partition wall due to the difference in height between the first and second pressure chambers 51, 52 and their arrangement in relation to each other.

[0070] Fig. 5 discloses a fourth embodiment where the advantages of the second and third embodiments are combined, i.e. where the difference in height between the first and second pressure chambers 51, 52 is such that the first height h 1 is at least equal to the sum of the second height h2 and twice the maximum stroke length SL. This means that elongation or stretching of the partition wall 55 can take place either at the top or the bottom or both, without risking deformation of the partition wall 55 into the first pressure chamber 51 since the support element 54 will be able to cover the elongation or stretching. Furthermore, by arranging at second pressure chamber 52 without aligning with either the first top 11 or the first bottom b 1 of the first pressure chamber 51, a greater freedom is achieved in selecting the placement of the second pressure chamber 52 to control the desired pressure profile in the nip N.

[0071] The maximum stroke length SL for all embodiments of the invention is at least 1 mm, to ensure that the press body 50 is able to expand into the nip N as desired. Preferably, the maximum stroke length SL is at least 4 mm and more preferably at least 7 mm. To provide a larger maximum stroke length increases the versatility of the press body 50 since it may be designed for use in different paper machines where different grades of tissue or paper is produced. In some applications of the invention, the maximum stroke length is at least 15 mm, more preferably at least 20 mm and even more preferably at least 30 mm. This ensures that the press body 50 can be used in a wide variety of paper machines for producing any kind of web from a lignocellulosic material.

[0072] The design of the press body 50 to enable the longer maximum stroke length SL is achieved through selecting dimensions of the first and second pressure chamber 51, 52 to ensure that the partition wall 55 is able to stretch the desired maximum stroke length without being damaged. By pressurizing the first and second pressure chambers 51, 52, the desired stroke is then achieved when the press body 50 is in use in the paper machine 1.

[0073] Fig. 6 discloses a fifth embodiment of the press body 50, where a third pressure chamber 53 is added inside the press body 50. Similarly to the first and second pressure chambers 51, 52, the third pressure chamber 53 is configured to be pressurized either individually or together with at least one of the first and second pressure chambers 51, 52 to cause expansion of the press body 50. The third pressure chamber has a third height h3 that differs from at least one of the first height hl and second height h2. In Fig. 6, the third pressure chamber 53 is shown with the third height h3 substantially equal to the first height hl. Also, the partition walls 55 on either side of the third pressure chamber 53 can be dimensioned as suitable to enable stretching to the desired maximum stroke length SL, while at the same time providing stability to decrease deformation when the pressure chambers 51, 52, 53 are pressurized individually. The third pressure chamber 53 may also comprise at least one support element 54 to support one or both of the adjacent partition walls 55 during expansion.

[0074] In the fifth embodiment, the first cross-sectional area Al of the first pressure chamber 51 is substantially equal to the second cross-sectional area A2 of the second pressure chamber 52. The third pressure chamber 53 has a third cross-sectional area A3 that may be substantially equal to the first cross- sectional area Al or that may differ as desired. Also, even though the third pressure chamber 53 is shown with its top and bottom on substantially equal heights as the first top 11 and the first bottom b 1 , this may also be varied as desired.

[0075] Fig. 7 discloses a sixth embodiment of the press body 50 that comprises the third pressure chamber 53 and an additional pressure chamber 56 with an additional height ha that differs from at least one of the first height hl and the second height h2. This is to show how the number of pressure chambers 51, 52, 53, 56 can be selected to include any suitable number in order to achieve greater control over the pressure profile of the nip. Dimensions of the partition walls 55 can also be selected as desired depending on the number of pressure chambers 51, 52, 53, 56 and the pressure during use, so that both the flexibility required for stretching and the stability required for minimizing deformation are achieved. Also, although only the third pressure chamber 53 is shown with a support element 54 in the sixth embodiment, it is to be noted that support elements 54 can be provided as required in any or all of the pressure chambers 51, 52, 53, 56.

[0076] It is to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

CLAIMS1. A press body for a paper machine having an extended nip formed between the press body and a counter-pressure member, wherein the press body (50) is elastically deformable and comprises a working surface (15), and wherein the press body comprises a first pressure chamber (51) and a second pressure chamber (52) that are arranged inside the press body (50) and separated from each other by a partition wall (55), which pressure chambers (51, 52) are configured to be pressurized such that the press body (50) expands for pressing the working surface (15) towards the counter-pressure member, and wherein the first pressure chamber (51) has a first height (hl) and the second pressure chamber (52) has a second height (h2), and wherein the first height (hl) is larger than the second height (h2).

2. A press body according to claim 1, wherein the first pressure chamber (51) and second pressure chamber (52) are configured to be individually pressurized independently of each other, and wherein the first pressure chamber (51) comprises a support element (54) for supporting the partition wall (53), said support element (54) having a support height (SH) that corresponds to the first height (hl) of the first pressure chamber (51).

3. A press body according to claim 1 or 2, wherein the first height (hl) is at least equal to a sum of the second height (h2) and the maximum stroke length (SL) of the press body (50).

4. A press body according to any of claims 1-3, wherein a first bottom (bl) of the first pressure chamber (51) and a second bottom (b2) of the second pressure chamber (52) are each at a substantially equal bottom height (BH) from a bottom (B) of the press body (50).

5. A press body according to any of claims 1-3, wherein the bottom (bl) of the first pressure chamber (51) is at a first chamber bottom height (bhl)in the press body and the bottom (b2) of the second pressure chamber (52) is at a second chamber bottom height (bh2) in the press body (50), and wherein further the second chamber bottom height (bh2) is equal to or larger than a sum of the first chamber bottom height (bhl) and the maximum stroke length (SL).

6. A press body according to any of claims 1-3 or 5, wherein a first top (tl) of the first pressure chamber (51) and a second top (t2) of the second pressure chamber (52) are each at a substantially equal top height (TH) from the bottom (B) of the press body (50).

7. A press body according to any of claims 1-5, wherein the top (tl) of the first pressure chamber (51) is at a first chamber top height (th 1) in the press body (50) and wherein the top (t2) of the second pressure chamber (52) is at a second chamber top height (th2) in the press body (50), and wherein further the first chamber top height (th 1) is equal to or larger than a sum of the second chamber top height (th2) and the maximum stroke length (SL).

8. A press body according to any of claims 3-7, wherein the maximum stroke length (SL) is at least 1 mm, preferably at least 4 mm and more preferably at least 7 mm.

9. A press body according to claim 8, wherein the maximum stroke length (SL) is at least 15 mm, preferably at least 20 mm and more preferably at least 30 mm.

10. A press body according to any previous claim, wherein the first pressure chamber (51) has a first cross-sectional area (Al) and the second pressure chamber (52) has a second cross-sectional area (A2), and wherein the first cross-sectional area (Al) differs from the second cross-sectional area (A2).

11. A press body according to any of claims 1-9, wherein the first cross- sectional area (Al) is substantially equal to the second cross-sectional area (A2).

12. A press body according to any previous claim, further comprising a third pressure chamber (53) arranged inside the press body (50) and configured to be pressurized such that the press body (50) expands, wherein the third pressure chamber (53) has a third height (h3) that differs from at least one of the first height (hl) and the second height (h2).

13. A press body according to claim 12, further comprising at least one additional pressure chamber (56) arranged inside the press body (50) and configured to be pressurized such that the press body (50) expands, wherein each of the at least one additional pressure chamber (56) has a height (ha) that differs from at least one of the first height (hl) and the second height (h2).

14. Paper machine comprising at least one press body (50) according to any previous claim.

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