PRESS DEVICE HAVING AN EXTENDED PRESS NIP FOR PRESSING A TRAVELING PAPERBOARD WEB

Abstract: A press device having an extended nip comprising a press shoe (101) aligned across the machine direction (MD) and a support (105) which supports the press shoe via a plurality of loading cylinders (106) along the press shoe (101) in order to enable application of pressure on the web during the pressing. The loading cylinders (106) comprise a first cylinder member (107) attached to or integrated in the press shoe (101), and a second cylinder member (109) attached to or integrated in the support (105). The cylinder members (107, 109) are slidably connected by a connecting member (111), wherein the connecting member (111) and the first cylinder member (107) are movable in relation to each other with a first length of stroke (L1), while the connecting member (111) and the second cylinder member (109) are movable in relation to each other with a second length of stroke (L2), and the connecting member has a third length (L3). Thereby, the first length of stroke (L1) is smaller than the second length (L2) of stroke. The shoe press device can particularly advantageously be utilised for wet-pressing or calendering of paper or paperboard webs.

Description: Title Press device having an extended press nip for pressing a traveling paperboard web. Technical field The present invention relates to a press device having an extended nip intended for pressing a running paper or paperboard web. More specifically, the invention relates to a shoe press of the type which comprises a support which supports a press shoe adjacent to a counter roll or another backing member in such a way that the press shoe and the backing member form an extended nip between themselves, and which furthermore comprises a hydraulic or pneumatic arrangement for urging the press shoe toward the backing member in order to apply a pressure onto the web passing through the nip. The press device according to the invention particularly advantageously can be utilised for wet-pressing of moistpaper or paperboard webs, but also for calendering or other finishing of dried paper or paperboard. The press device according to the invention can also be utilised for other fibre webs than paper and paperboard. Background of the invention Since a long time, shoe press devices, i.e. presses having an extended nip, have been utilised when manufacturing different paper and paperboard grades, primarily for wet- pressing in order to increase the dryness of the web, but also for calendering and other finishing in order to improve surface properties or other physical properties of the web. Thanks to their longer nips, the previously known shoe press devices provide a number of advantages in comparison to conventional roll presses, such as a higher dryness at the same nip pressure, or a pressing at a lower at nip pressure but with maintained dryness which is more gentle to the sheet. The patent publication US 4,917,768 discloses a previously known shoe press device in which the press shoe is supported via tubular sleeves rigidly affixed to and spaced apart on a support in a direction across the machine direction. Thereby, the sleeves are received in cylindrical recesses in the press shoe in order to allow the press shoe to move toward or from a counter roll and the nip pressure to be varied. The disclosed shoe press comprises hydraulic jacks upstream and downstream the sleeves for forcing the press shoe against the counter roll and for pivoting the shoe around an axis across the machine in order to vary the nip pressure in the machine direction. Thereby, the sleeves fit somewhat loosely in the recesses in the shoe, and a resilient seal encircles each sleeve for sealing the interface between the sleeve and the recess. Accordingly, the press shoe of the shoe press disclosed in US 4,917,768 is capable of pivoting relative to the support for varying the nip pressure in the machine direction. However, it has been found that such shoe presses can be associated with certain problems. Such a problem originates from the thermal expansion of the press shoe, which is a result of the heat generated by friction against the belt which runs over the press shoe and carries the paper or paperboard web through the press and by the hot hydraulic fluid which for different reasons is circulated through the shoe. The thermal expansion of the press shoe results in an elongation in the cross direction which creates bending tensions in the support and hydraulic arrangement of the press shoe, something which of course is undesired. In EP 0 933 471, a shoe press is disclosed which reduces the problems originating from the thermal expansion of the press shoe, since it has the ability to tolerate relatively large elongations of the press shoe across the machine direction, and also other deformations of the press shoe. The disclosed shoe press comprises a press shoe extending in the cross- direction along the entire width of a web running through the press, and a plurality of articulated hydraulic loading cylinders supported by a support and spaced apart along the shoe. The loading cylinders define working chambers which are pressurizable by hydraulic fluid, so as to get the cylinders to urge the press shoe away from the support and toward a counter roll or other backing member for applying pressure to the web being carried through the nip defined between the shoe and the backing member. Each loading cylinder comprises a piston member disposed within a cylinder member. Either the piston or the cylinder comprises a two-part member having a first member relative the press shoe and a second member fixed relative to the support, while the remaining piston or cylinder comprises a coupler. In a preferred embodiment of the shoe press according to EP 0 933 471, the two-part member consists of first and second cylinders, while the coupler comprises a piston which is slidably received in the two cylinders. In an alternative, also preferred embodiment the two-part member instead comprises first and second pistons, while the coupler comprises a cylinder which surrounds both pistons. The coupler of the shoe press disclosed in EP 0 933 471 sealingly engages at least one of the members, so that the first member is urged away from the second member in a loading direction when pressurising the working chamber to cause the press shoe to be urged towards the backing member. In order to enable the loading cylinders to accommodate elongation of the press shoe across the machine direction, each coupler engages the respective first and second members at seals which enable the coupler to pivot relative the first and second members about axes parallel to the machine direction. Accordingly, the press shoe is free to expand thermally in the cross-machine direction without causing bending of any piston and/or cylinder members of the loading cylinders. Since the press shoe of the shoe press disclosed in EP 0 933 471 also can move or pivot in the machine direction relative to the support, the shoe press comprises a stopping means which restricts the movement of the shoe forward in the machine direction. In order to control the conditions in the nip of a shoe press, such as the pressure profile (curve) through the nip, it is usually desirable to be able to move to the press shoe forward or backwards in the machine direction in order to be able to influence the pressure profile through the nip so that the nip pressure is highest in the beginning and lower in the end of the nip, or vice versa. When performing such a regulation of the pressure profile through the nip, the press shoe, in principle, will follow an arc-shaped path with its centre in the central axis of the counter roll. This may result in a skewness in the machine direction between the parts included in the loading cylinders, i.e. between piston and cylinders or between pistons and cylinder. Such a skewness can generate forces both on the cylinder and on the shoe, which forces are directed in the machine direction or against the machine direction, depending on the direction of the skewness. If the skewness of the connecting member in a direction away from a possible stopping means (shoe support) is large enough, these forces may exceed the force directed towards the support, and resulting in instability. If the connecting member is tilted in a direction toward the shoe support, forces which are directed toward the shoe support are generated, something which increases the stresses on the shoe support. Also in case a paper lump or the like unintentionally enters the nip, similar skewnesses can be generated and cause stresses on a shoe support. Summary of the invention Accordingly, the first object of the present invention is to provide a press device having an extended nip for pressing a running paper or paperboard web in which the press shoe unintentionally or intentionally can be tilted/pivoted around an imaginary axis across the machine direction with minimum skewness between the parts included in the loading cylinders, and without generating any excessively large forces directed towards a possible shoe support or the press shoe becoming unstable if the forces are directed against the machine direction (away from a possible shoe support). In accordance with claim 1 , this first object of the present invention is achieved by means of a press device comprising a press shoe aligned across the machine direction arranged for forming an extended nip in cooperation with a backing member for passage of the web during the pressing, a support which supports the press shoe in a, in a direction toward the backing member, movable away via a plurality of loading cylinders spaced apart along the press shoe for enabling application of pressure on the web during the pressing. Each of the loading cylinders comprises a first cylinder member having a first cylinder end which is attached to or integrated in the press shoe, and a second cylinder member having a second cylinder end which is attached to or integrated in the support, which first and second cylinder members are slidably connected by a connecting member. The coimecting member and the first cylinder member are movable in relation to each other with a first length of stroke, while the connecting member and the second cylinder member are movable in relation to each other with a second length of stroke, and the connecting member has a third length. Thereby, according to the invention, the first length of stroke is smaller than the second length of stroke, whereby the above-mentioned first object is achieved. Further objects of the present invention will become apparent from the following description, while the features enabling the further objects to be achieved are defined in the dependent claims. 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. 1A shows a schematic sectional view seen across the machine direction of a shoe press device with its press shoe in a first position, intended to generate a substantially symmetrical pressure curve through the nip, Fig. IB shows the shoe press device in Fig. 1A with its press shoe intentionally moved into a second position, intended to displace the pressure maximum of the pressure curve toward the end of the nip in comparison to when the press shoe is in the first position shown in Fig. 1 A, Fig. 2A shows a similar view as in Fig. 1 A, but of a press device having an extended nip according to a preferred embodiment of the invention with its press shoe in a first position similar to the first position in Fig. 1 A, Fig. 2B shows the press device according to the invention in Fig. 2A, but now with its press shoe intentionally moved into a second position similar to the second position in Fig. IB, Fig. 3 schematically shows the motion pattern of the cylinder members and the coupling member belonging to a loading cylinder of a shoe press device when lengthening the loading cylinder with its first cylinder member tilted to a certain angle, and Fig.4 schematically shows the motion pattern of the cylinder members and the connecting member belonging to a loading cylinder of a press device according to the invention when lengthening the loading cylinder with the first cylinder member tilted to the same angle as in Fig.3. Detailed description of preferred embodiments For comparison, the attached figures 1 A and IB show two different schematic sectional views, seen across the machine direction MD, of a shoe press device which will be discussed further in the following description. In Figs. 2A and 2B, similar views as in Fig. 1A and IB are shown, but of a press device having an extended nip according to a preferred embodiment of the invention. The press device according to the invention is intended for pressing a running paper or paperboard web, and comprises apress shoe 101 aligned across the machine direction MD and arranged for forming an extended nip 103 in cooperation with abacking member 102 for passage of the web 104 during the pressing. The press device further comprises a support 105 which supports the press shoe in a, in direction toward the backing member, movable way via a plurality of loading cylinders 106 spaced apart along the press shoe 101 for enabling application of pressure on the web during the pressing. Each of the above-mentioned loading cylinders 106 comprises a first cylinder member 107 having a first cylinder end 108 which is attached to or integrated in the press shoe 101, and a second cylinder member 109 having a second cylinder end 110 which is attached to or integrated in the support 105. The expression "cylinder member", as used herein, should be understood as a functional part of the loading cylinder, which can be of a hydraulic or pneumatic type. Examples of such "cylinder members" comprise internally or externally substantially cylindrical sleeves which are open in at least one end, substantially cylindrical solid bodies or pistons, or substantially cylindrical recesses in the press shoe or in the support. The first and second cylinder members 107, 109 are slidably connected by a connecting member 111, wherein the connecting member 111 and the first cylinder member 107 are movable in relation to each other with a first length of stroke LI, while the connecting member 111 and the second cylinder member 109 are movable in relation to each other with a second length of stroke L2, and the connecting member has a third length L3. The expression "length of stroke", as used herein, should be understood as the maximum length of a cylinder member available for sliding displacement of a second, cooperating member in relation to said cylinder member. According to the invention and in the preferred embodiment, the first length of stroke LI is smaller than the second length of stroke L2. In a particularly prefened embodiment of the press device according to the invention, the first length of stroke LI is less than half of the second length of stroke L2. In another advantageous embodiment, the third length L3 is larger than both the first LI and the second L2 length of stroke, wherein the third length L3 particularly advantageously is larger than the first LI and the second L2 length of stroke together. In still another advantageous embodiment of the press device according to the invention, the connecting member 111 slidably connects the first 107 and the second 109 cylinder members in a sealed way by means of contacting seals 112, 113 in order to form at least one working chamber 114 within which the pressure of a pressurising medium, such as hydraulic oil or pressurised air, can be reduced in order to generate a shortening or increased in order to generate a lengthening of the loading cylinder 106. Thereby, the coimection is arranged in such a way that a central axis Cl of the first cylinder member 107 and a central axis C3 of the connecting member 111 can be tilted to an angle in relation to each other and to a central axis C2 of the second 109 cylinder member during an intentional or unintentional tilting of the press shoe 101 during the pressing. In this embodiment, the first LI and second L2 lengths of stroke, the third length L3, and the geometrical positions of the contacting seals 112, 113 are adapted in order to minimise the angle A2 between the central axis C3 of the connecting member and the central axis C2 of the second cylinder member during the tilting. Accordingly, the above-mentioned tilting either can be intentional or unintentional. The seals 112, 113 can advantageously be of the type disclosed in the above-discussed EP 0 933 471. As will become evident from the following description, also the connecting member can have different geometrical shapes. In still another advantageous embodiment of the press device according to the invention, particularly illustrated in Fig. 2B, a shoe support 115 is fixated to the support for receiving forces in the machine direction MD exercised by the press shoe 101 in contact with the shoe support during the pressing. In this embodiment, one or several stopping means 116 are arranged on the first cylinder member 107 and/or on the connecting member 111 , in order to restrict a maximum value of the first length of stroke LI, and thereby ensure a very low angle A2 between the central axes C3 and C2. In the press device illustrated in Figs. 2A and 2B, the stopping means 116 are constituted by a ring, screwed on the open end of the first cylinder member 107, and having a slightly smaller inside diameter than the diameter of the first cylinder member, wherein the ring 116 is intended to cooperate with the pro trading seal 112 enclosing the connecting member 111. However, it is also conceivable with embodiments of the shoe press device according to the invention in which the stopping means has/have another suitable design. In connection with this embodiment, it should be noted that the shoe press device illustrated in Figs. 1 A and B lacks stopping means for restricting the maximum value of its corresponding length of stroke 11. In still another advantageous embodiment of the press device according to the invention, the first cylinder member 107 comprises an open third cylinder end 116 opposite the above-mentioned first cylinder end 108, while the second cylinder member 109 comprises an open fourth cylinder end 117 opposite the above-mentioned second cylinder end 110. In this embodiment, the third 116 and fourth cylinder ends 117 encircle a respective end of the coimecting member 111 in order to form the working chamber 114 or several working chambers. Thereby, the connecting member 111 advantageously can be a substantially cylindrical sleeve, the interior of which constituting a part of the working chamber 114, as illustrated in Figs. 2A and 2B. In an alternative embodiment (not shown in the drawings), the connecting member instead is constituted of a solid, substantially cylindrical body, at each end of which a working chamber is fonned, wherein one or several channels advantageously but not necessarily can be ananged between the two ends for pressure connection between the formed working chambers. In still another alternative embodiment (not shown) of the shoe press device according to the invention, the first and second cylinder members are solid, substantially cylindrical bodies one end of which being enclosed by the connecting member in order to form the working chamber. Thereby, the sealing means should be arranged on the connecting member in order to make it possible to minimise its tilting/skewness in accordance with the invention. It is particularly advantageous with embodiments of the invention in which the backing member 102 is a rotatable counter roll, and where a flexible belt 118 is arranged in an endless loop for running between the press shoe 101 and the paper or paperboard web 104 during the pressing. Thereby, the flexible belt preferably has the shape of a sleeve. The press device having an extended nip according to the invention preferably is intended for wet-pressing, or for calendering a paper or paperboard web. In the following, some of the advantages which can be achieved by means of the present invention will be illustrated through an example. Fig. 1A shows a shoe press device with its press shoe in a first position, intended to generate a substantially symmetrical pressure curve through the nip. Fig. IB shows the shoe press device in Fig. 1 A, but now with its press shoe intentionally moved into a second position, which is intended to displace the pressure maximum of the pressure curve towards the end of the nip in comparison to when the press shoe is in the first position shown in Fig. 1 A. As is evident from Figs. 1 A and IB, the first length of stroke 11 of the illustrated shoe press device is larger than the second length of stroke 12. Accordingly, the intentional displacement of the press shoe 1 into the second position shown in Fig. IB is intended to displace the pressure maximum of the pressure curve towards the end of the nip, wherein the press shoe 1 and, consequently, the central axis cl of the therewith associated first cylinder member 7 will be tilted forwards in the machine direction MD to an angle al in relation to the central axis c2 of the second cylinder member 9. In connection with this, it should be noted that the angles shown in the drawings, for reasons of clarity, have been exaggerated. A large tilting of the connecting member (piston) 11 in direction towards the shoe support 15 results in the shoe support 15 being subj ected to large stresses during the pressing, since a force component is generated which will press against the first cylinder member 7 and, together with other forces directed forwards in the machine direction MD, will press the press shoe 1 against the shoe support 15. Figs. 2A and 2B instead illustrate a press device having an extended nip according to a preferced embodiment of the invention. Fig. 2A shows the press device with its press shoe in a first position similar to the first position in Fig. 1 A, while Fig. 2B shows the press device with its press shoe intentionally moved into a second position similar to the second position in Fig. IB. In Fig. 2B, the press shoe 101 has been intentionally tilted approximately as much as the press shoe 1 in Fig. IB in order to make it possible to obtain a higher nip pressure in the end of the nip than in its beginning. Accordingly, the angle Al between the central axis C 1 of the first cylinder member 107 and the central axis C2 of the second cylinder member 109 is approximately as large as the angle al in Fig. IB. As a result of the different parts of the loading cylinder 106 being arranged in accordance with the invention, the angle A2 between the central axis C3 of the coimecting member 111 and the central axis C2 of the second cylinder member 109 now becomes significantly smaller than the conesponding angle a2 between the central axes c2 and c3 in Fig. IB. Starting from the examples above, it should be evident to the skilled person that the minimization, i.e. reduction or even elimination, of the angle A2 which is achieved by means of the present invention reduces or even eliminates the force components in the machine direction MD, originating from pressurisation of the working chamber 114, which are exercised by the press shoe 101 on the shoe support 118. Fig. 3 schematically shows the motion pattern of the cylinder members 7', 9' and the connecting member 11' belonging to a loading cylinder 6' of a shoe press device when lengthening the loading cylinder with its first cylinder member tilted to a certain angle. In contrast, Fig. 4 schematically shows the motion pattern of the cylinder members 107', 109' and the connecting member 111' belonging to a loading cylinder 106' of a press device according to the invention when lengthening the loading cylinder with the first cylinder member tilted to the same angle as in Fig. 3. As is evident from Fig.4, the press device according to the present invention enables the connecting member 111 ' to move substantially linearly and in parallel to the lengthening direction of the loading cylinder 106, when lengthening (or shortening) the loading cylinder 106'. This minimises the stresses on a possible shoe support. During the lengthening (or shortening) of a loading cylinder 6' of the shoe press device shown in Fig. 3, the connecting member 11 ' instead will be tilted with different angles in relation to the lengthening direction of the loading cylinder 6' depending on how far the lengthening or shortening course has proceeded. This can generate very large stresses on a possible shoe support, or result in the press shoe becoming unstable in case the forces are directed towards the machine direction (backward in the machine direction). Furthermore, the frictional force between the press shoe and the shoe support will vary in a direction across the machine direction, depending on the larger deflection of the support (beam) in the middle (and resulting larger skewness of the piston). This can cause cross- machine variations in the machine-directional pressure curve of the shoe press. The present invention should by no means be regarded as being limited to what has been described in the foregoing 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 following claims. The mechanical and hydraulic, alternatively pneumatic, components which are in included in the shoe press device according to the invention have not been described in any greater detail herein, since such components should be well-known to the skilled person and also are disclosed and discussed in the above-mentioned EP 0 933 471. Furthermore, it should be noted that the paper web 104 preferably is carried through the nip 103 by one or several water receiving machine clothings, such as one or several press felts.

Claims: Claims 1. A press device having an extended nip for pressing a running paper or paperboard web, comprising a press shoe (101) aligned across the machine direction (MD) arranged for forming an extended nip (103) in cooperation with a backing member ( 102) for passage of said web (104) during the pressing, a support (105) which supports the press shoe in a, in a direction toward the backing member, movable way via a plurality of loading cylinders (106) spaced apart along thepress shoe (101) for enabling application of pressure on the web during the pressing, wherein each of said loading cylinders (106) comprises a first cylmder member (107) having a first cylinder end (108) which is attached to or integrated in the press shoe (101), and a second cylinder member (109) having a second cylinder end (110) which is attached to or integrated in the support (105), which first and second cylinder members (107, 109) are slidably connected by a connecting member (111), wherein the coimecting member (111) and the first cylinder member (107) are movable in relation to each other with a first length of stroke (LI), while the coupling member (111) and the second cylinder member (109) are movable in relation to each other with a second length of stroke (L2), and the connecting member has a third length (L3), c h a r a c t e r i s e d i n that the first length of stroke (LI) is smaller than the second length of stroke (L2). 2. A press device having an extended nip according to claim 1 , c h a r a c t e r i s e d i n that the first length of stroke (LI) is less than half of the second length of stroke (L2). 3. A press device having an extended nip according to claim 1 or 2, characterised in that the third length (L3) is larger than both the first (LI) and the second (L2) length of stroke. 4. A press device having an extended nip according to any one of the preceding claims, characterised in that the third length (L3) is larger than the first (LI) and the second (L2) length of stroke together. 5. A press device having an extended nip according to any one of the preceding claims, wherein the connecting member (111) slidably connects the first (107) and the second (109) cylinder members in a sealed way by means of contacting seals (112, 113) in order to form at least one working chamber (114) within which the pressure of a pressurizing medium can be reduced in order to generate a shortening or increased in order to generate a lengthening of the loading cylinder (106), and in such a way that a central axis (Cl) of the first cylinder member (107) and a central axis (C3) of the connecting member (111) can be tilted to an angle in relation to each other and to a central axis (C2) of the second (109) cylinder member during an intentional or unintentional tilting of the press shoe (101) during the pressing, characterised in that the first (LI) and second (L2) lengths of strokes, the third length (L3), and the geometrical positions of the contacting seals (112, 113) are adapted in order to minimise the angle (A2) between the central axis (C3) of the connecting member and the central axis (C2) of the second cylinder member during said tilting. 6. A press device having an extended nip according to any one of the preceding claims, wherein a shoe support (115) is fixated to the support for receiving forces in the machine direction (MD) exercised by the press shoe (101) in contact with the shoe support during the pressing, characterised in that one or several stopping means ( 116) are arranged on the first cylinder member (107) and/or on the connecting member (111) in order to restrict a maximum value of the first length of stroke (LI). 7. A press device having an extended nip according to claim 5 or 6, characterised in that the first cylinder member (107) comprises an open third cylinder end (116) opposite said first cylinder end (108) and the second cylinder member (109) comprises an open fourth cylinder end (117) opposite said second cylinder end (HO), wherein the third (116) and fourth cylinder ends (117) enclose a respective end of said connecting member (111) in order to fonn the working chamber (114) or several working chambers. 8. A press device having an extended nip according to claim 7, characterised in that the coimecting member (111) is a substantially cylindrical sleeve, the interior of which constituting a portion of the working chamber (114). 9. A press device having an extended nip according to claim 7, characterised in that the connecting member is a solid, substantially cylindrical body at both ends of which a working chamber is formed. 10. A press device having an extended nip according to claim 9, characterised in that the cylindrical body comprises one or several channels between the two ends for pressure connection between the working chambers. 11. A press device having an extended nip according to claim 5 or 6, characteri s ed i n that the first and second cylinder members are solid, substantially cylindrical bodies one end of which being enclosed by the connecting member in order to form the working chamber, wherein said sealing means are arcanged on said connecting member. 12. A press device having an extended nip according to any one of the preceding claims, characterised in that the backing member (102) is a rotatable counter roll, wherein a flexible belt (118), preferably in the fonn of a sleeve, is arranged in an endless loop for running between the press shoe (101) and the paper or paperboard web (104) during the pressing. 13. A press device having an extended nip according to any one of claims 1 to 12, characterised in that the press device is intended for wet-pressing of a paper or paperboard web. 14. A press device having an extended nip according to any one of claims 1 to 12, characterised in that the press device is intended for calendering of a paper or paperboard web.

Inventors: SNELLMAN JORMA, SNELLMAN, JORMA
Applicants: METSO PAPER INC, METSO PAPER INC.
Application year: 2000
Main classification: D21F3
IPC codes: D21F3