PRESS DEVICE HAVING AN EXTENDED NIP FOR PRESSING A RUNNING PAPER OR PAPERBOARD WEB

Abstract: A press device having an extended press nip for pressing a running paper or paperboard web, comprising a press shoe (101) aligned across the machined direction, and a carrier (102) supporting the press shoe (101; 201) via a plurality of loading cylinders (103), out of which at least a few comprise a first cylinder member (104) having a first end (105) attached to or integrated in the press shoe (101), and a second cylinder member (106) having a second end (107) attached to or integrated in the carrier (102). The first (104) and the second (106) cylinder members are slidably coupled to each other by a coupling member (108), wherein the coupling member (108) and the first cylinder member (104) are displaceable in relation to each other with a first length of stroke (L1), while the coupling member (108) and the second cylinder member (106) are displaceable in relation to each other with a second length of stroke (L2). The coupling member (108; 208) is designed so that the first length of stroke (L1) runs closer to the carrier (102; 202) than the second length of stroke (L2). The press device can particularly advantageously be utilised for wet-pressing or calendering.

Description: Title Press device having an extended nip for pressing a running paper or 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 particularly, the invention relates to a shoe press of the type which comprises a carrier supporting a press shoe next to a counter roll or another counterstay in such a way that the press shoe and the counterstay form an extended nip between each other, and which furthermore comprises a hydraulic or pneumatic arrangement for urging the press shoe towards the counterstay for applying 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 moist paper or paperboard webs, but also for calendering and 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 or paperboard grades, primarily for wet- pressing intended to increase the dryness of the web, but also for calendering or other finishing intended to improve the surface properties or other physical properties of the web. Thanks to their extended press 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 which is more gentle to the sheet at a lower nip pressure but with retained dryness. The patent publication US 4,917,768 discloses a previously known shoe press device in which the press shoe is carried via tubular sleeves which are rigidly attached to and spaced apart along a carrier 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 towards or away from a counter roll, and the nip pressure to be varied. The disclosed shoe press comprises hydraulic jacks upstream and downstream the sleeves for urging the press shoe towards the counter roll, and for tilting the shoe about an axis across the machine in order to vary the nip pressure in the machine direction. Thereby, the sleeves have a somewhat loose fit within the recesses in the shoe, and an elastic seal encloses each sleeve in order to seal the boundary surface between the sleeve and the recess. Accordingly, the press shoe of the shoe press disclosed in US 4,917,768 can be tilted in relation to the carrier in order to vary the nip pressure in the machine direction. However, it has been found that shoe presses in accordance with the prior art can be associated with certain problems. Such a problem originates from the thermal expansion of the press shoe which results from the heat generated by friction against the belt running across the press shoe and which carries the paper or paperboard web trough the press, and by the hot hydraulic fluid which for different reasons is circulated through the shoe. The thermal expansion results in an extension in the cross-direction which in spite of elastic seals and the like still can give rise to high stresses in the supporting and hydraulic assemblies of the press shoe, something which of course is undesired. The European patent application No.0933471 discloses a shoe press which minimises the problems originating from the thermal expansion of the press shoe by means of having the ability to tolerate relatively large extensions 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 passing through the press, and a plurality of pivoted hydraulic loading cylinders supported by a carrier and spaced apart along the shoe. The loading cylinders define working chambers which can be pressurised by means of hydraulic fluid in order to get the cylinders to urge the press shoe away from the carrier and towards a counter roll or another counterstay for applying pressure onto the web which is carried through the nip defined between the shoe and the counterstay. Each loading cylinder comprises a piston member arranged within a cylinder member. Either the piston or the cylinder comprises a two-part member which has a first member fixated in relation to the press shoe and a second member fixated in relation to the carrier, while the remaining piston or cylinder comprises a connecting member. In a preferred embodiment of the shoe press according to EP 0 933 471, the two-part member consists of first and second cylinders, whereas the connecting member comprises a piston which is slidably received within the two cylinders. In an alternative, also preferred embodiment, the two-part member instead comprises first and second pistons, while the connecting member comprises a cylinder enclosing both pistons. The connecting member of the shoe press disclosed in EP 0 933 471 sealingly retains at least one of the members, so that the first member is urged away from the second member in a loading direction when pressurizing the working chamber in order to urge the press shoe towards the counterstay. In order to enable the loading cylinders to accommodate expansion of the press shoe across the machine direction, each connecting member retains the respective first and second members at seals which enable the connecting member to pivot in relation to the first and second members about axes which are parallel to the machine direction. Accordingly, the press shoe is free to expand thermally across the 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 0933471 also can move or be tilted in the machine direction in relation to the carrier, the shoe press comprises a stopping member which restricts the movement of the shoe forwards in the machine direction, Accordingly, the loading cylinders of the above-described types of shoe press devices have piston and cylinder members which can be tilted in relation to each other and/or in relation to the press shoe in order to accommodate movements of the press shoe in relation to the carrier across the machine direction, and also in the machine direction. Even if such tilting is necessary, in reality it is undesired since it can result in elastic seals of the loading cylinders being subjected to large stresses, or in very large forces being directed against the guiding or stopping means which in accordance with the present techniques are necessary for ensuring that the press force exercised by the press shoe is directed in the intended direction towards the counterstay when lengthening the loading cylinders. Therefore, it would be advantageous to be able to provide a press device having an extended nip with loading cylinders which when necessary allow but otherwise counteract a skewness between the in relation to each other slidable cylinder members included in the loading cylinder. 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 device the loading cylinders when necessary allow but otherwise counteract skewness between the included cylinder members, and which ensures that the lengthening force of the loading cylinders in all circumstances are directed in the intended direction, in order to thereby minimise the stresses acting on the elastic seals of the loading cylinders and the forces which during the pressing may come to be directed towards guiding or stopping means for the press shoe of the press device. 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 and arranged for forming an extended nip in cooperation with a counterstay for passage of the web during the pressing. The press device further comprises a carrier supporting the press shoe in an, in a direction towards the counterstay, displaceable way via a plurality of loading cylinders spaced apart along the press shoe for enabling application of pressure onto the web during the pressing. At least a few of the loading cylinders comprise a first cylinder member having a first end attached to or integrated in the press shoe, and a second cylinder member having a second end attached to or integrated in the carrier. The first and the second cylinder member are slidably coupled to each other by a coupling member, wherein the coupling member and the first cylinder member are displaceable in relation to each other with a first length of stroke, while the coupling member and the second cylinder member are displaceable in relation to each other with a second length of stroke. According to the invention, the coupling member is designed so that the first length of stroke runs closer to the carrier than the second length of stroke. Further objects of the present invention will become evident from the subsequent description, while the features enabling the further objects to be reached 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 in the machine direction, of a loading cylinder of a press device having an extended nip according to a preferred embodiment of the invention, without any skewness between the cylinder members, Fig. IB shows the loading cylinder in Fig. 1A, but when the press shoe has been displaced or has moved in relation to the carrier so that the cylinder members have been tilted in relation to each other, Fig. 2A shows a schematic sectional view, seen in the machine direction, of loading cylinder of a press device having an extended nip according to another advantageous embodiment of the invention, without any skewness between the cylinder members, and Fig. 2B shows the loading cylinder in Fig. 2A but when the press shoe has been displaced or has moved in relation to the carrier so that the cylinder members have been tilted in relation to each other. Detailed description of preferred embodiments The attached Figs. 1 A and IB show two different schematic sectional views seen in the machine direction, i.e. across the cross-direction CD indicated in the Figures, of a loading cylinder of a press device having an extended nip according to a preferred embodiment of the invention without, and with, skewness between the cylinder members. Figs. 2A and 2B show corresponding views as in Figs. 1A and IB, but of a press device having an extended nip according to another advantageous embodiment of the invention. Accordingly, Figs. 1 A - 2B show two different designs of loading cylinders included in the press device according to the invention, which is intended for pressing a running paper or paperboard web. When the remaining components of the press device according to the invention are concerned, these can be of types which are previously known per se, for example those which are disclosed in the above-mentioned EP 0 933 471. Now referring to Figs. 1 A and 2A, the press device according to the invention comprises a press shoe 101; 201, aligned across the machine direction, out of which only a minor portion is visible in the drawings. The press shoe is arranged for forming an extended nip (not shown), in cooperation with a counter stay (not shown in the drawings), for passage of the web (not shown) during the pressing. The press device according to the invention further comprises a carrierl02; 202 supporting the press shoe 101; 201 in an, in a direction towards the counterstay, displaceable way via a plurality of loading cylinders 103; 203 spaced apart along the press shoe 101; 201 for enabling application of pressure onto the web during the pressing. At least a few of the loading cylinders 103; 203 comprise a first cylinder member 104; 204 having a first end 105; 205 attached to or integrated in the press shoe 101; 201, and a second cylinder member 106; 206 having a second end 107; 207 attached to or integrated in the carrier 102; 202. The first 104; 204 and second 106; 206 cylinder member are slidably coupled to each other by a coupling member 108; 208, wherein the coupling member 108; 208 and the first cylinder member 104; 204 are displaceable in relation to each other with a first length of stroke LI , while the coupling member 108 ; 208 and the second cylinder member 106; 206 are displaceable in relation to each other with a second length of stroke L2. Thereby, according to the invention and the preferred embodiment, the coupling member 108; 208 is designed so that the first length of stroke LI runs closer to the carrier 102; 202 than the second length of stroke L2. Thanks to this feature, the loadings cylinders characteristic of the invention obtain "self-centering properties", i.e. when the cylinder members 104, 106; 204, 206, which are slidable in relation to each other, are tilted in relation to each other they will strive to return to their natural "position of rest" where no skewness occurs. The function of a loading cylinder included in the arrangement according to the invention can be compared to the function of a cardan joint axle suspended vertically from its upper end. In case the lower end of the cardan axle is displaced laterally, it will strive back towards the vertical position, in a way which on the whole can be compared to the self-centering properties of the loading cylinders included in the arrangement according to the invention. In one advantageous embodiment, one or several stopping means 109, 110, 111 ; 209, 210, 211 are arranged on the first cylinder member 104; 204 and/or on the coupling member 108; 208 in order to restrict the first length of stroke LI. In another embodiment, one or several stopping means 112, 113; 212, 213 are arranged on the coupling member 108; 208 and/or on the second cylinder member 106; 206 in order to restrict the second length of stroke L2. In the following, referring to Figs IB and 2B, the "self-centering" properties of a loading cylinder included in a press device according to an advantageous embodiment of the invention will be explained in greater detail. The self-centering properties exhibited by the loading cylinder 103'; 203' of the press device according to the invention can be explained in the following way. In case the coupling member 108'; 208' is tilted, surfaces X, X', Y, Y', Z, Z', W, W will be covered/exposed, something which will influence the equilibrium of forces. Starting from Fig. IB, it can be established that the coupling member 108' will pivot in counter clockwise direction (illustrated by the angle α between the central axes C 2 and C 3 ) when the first cylinder member 104' is displaced to the right in the Figure (with a displacement of its central axis a distance D). Thereby, the pressure on the surface X exposed within the working chamber 116' will generate a force via the coupling member 108' directed to the left in the Figure on the first cylinder member 104'. Therefore, the first cylinder member 104' will strive to return to its starting position. To sum up, it can be established that a relative displacement between the first 104' and second cylinder members 106 of the loading cylinder 103', belonging to the press device according to the invention cannot be achieved without performing a work. Accordingly, in one advantageous embodiment of the invention, particularly illustrated by Figs. IB and 2B, the coupling member 108'; 208' slidably couples the first cylinder memberl04'; 204' and the second cylinder memberl06; 206 to each other in a sealed way by means of contacting seals 114', 115'; 214', 215' in order to form at least one working chamber 116'; 216' 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 103'; 203'. In this embodiment, at least one first seal 114'; 214' bears against the first cylinder member 104'; 204' and the coupling memberl08'; 208' while at least one second seal 115'; 215' bears against the coupling memberl08'; 208' and the second cylinder member 106; 206. Thereby, the cylinder members 104'; 106; 204', 206, the coupling member 108'; 208' and the seals 114', 115'; 214', 215' are arranged in such a way that, in case of a displacement of the press shoe, the first cylinder member 104'; 204' is displaced in a direction in relation to the second cylinder member 106; 206, while a central axis C 3 of the coupling member 108'; 208' is tilted in relation to a central axis C 2 of the second cylinder member 106; 206, wherein the pressure acting on surfaces X; Z exposed within the working chamber 116'; 216' generates a force in a direction opposite to the direction of the displacement between the first 104'; 204' and second 106; 206 cylinder members. In still another advantageous embodiment, particularly illustrated by Fig. IB, the first seal 114' is constituted of a seal ring inserted into a groove extending along an outer circumference of the first cylinder member 104', while the second seal 115' is constituted of a seal ring inserted into a groove extending along an inner "circumference" of the second cylinder member 106. In another advantageous embodiment, particularly illustrated by Fig.2B, the first seal 214' is constituted of a seal ring inserted into a groove extending along an inner "circumference" of the coupling member 208', while the second seal 215' is constituted of a seal ring inserted into a groove extending along an outer circumference of the coupling member 208'. The above-mentioned counterstay (not shown in the drawings) of the press device according to the invention is particularly advantageously a rotatable counter roll, wherein a flexible belt (not shown), preferably in the form of a sleeve, is arranged in an endless loop for travelling between the press shoe 101, 101'; 201, 201' and the paper or paperboard web (not shown) during the pressing. The press device according to the invention is preferably intended for wet pressing or for calendering of a paper or paperboard web. The present invention should by no means be regarded as being limited to what has been disclosed herein in connection with the different embodiments, or to what is shown in the accompanying drawings, but the scope of the invention is defined by the following claims. As has become evident from the foregoing, mechanic and hydraulic, optionally pneumatic, components 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 described and illustrated in the above-mentioned EP 0933471. Within the scope of the invention, it is conceivable with embodiments where either the first or the second cylinder member is constituted of a substantially solid piston while the coupling member has the shape of a sleeve, but also embodiments where the first and second cylinder members and the coupling member all have the shape of a sleeve, Furthermore, it should be noted that the paper or paperboard web during the pressing preferably is carried through the press nip of the press device according to the invention by one or several pieces of water-receiving machine clothing, such as one or several press felts.

Claims: Claims 1. A press device having an extended press nip for pressing a running paper or paperboard web, comprising a press shoe (101; 201) aligned across the machine direction arranged for forming an extended press nip in cooperation with a counterstay for passage of said web during the pressing, a carrier (102; 202) supporting the press shoe (101; 201) in an, in a direction towards the counterstay, displaceable way via a plurality of loading cylinders (103; 203) spaced apart along the press shoe (101 ; 201) for enabling application of pressure onto the web during the pressing, wherein at least a few of said loading cylinders (103; 203) comprise a first cylinder member (104; 204) having a first end (105; 205) attached to or integrated in the press shoe (101; 201), and a second cylinder member (106; 206) having a second end (107; 207) attached to or integrated in the carrier (102; 202), and wherein the first cylinder member (104; 204) and the second cylinder member (106; 206) are slidably coupled to each other by a coupling member (108; 208), and the coupling member (108; 208) and the first cylinder member (104; 204) are displaceable in relation to each other with a first length of stroke (LI), while the coupling member (108; 208) and the second cylinder member (106; 206) are displaceable in relation to each other with a second length of stroke (L2), c h a r a c t e r i s e d i n that the coupling member (108; 208) is designed so that the first length of stroke (LI) runs closer to the carrier (102; 202) than the second length of stroke (L2). 2. A press device according to claim 1, c h a r a c t e r i s e d i n that one or several stopping means (109, 110, 111; 209, 210, 211) are arranged on the first cylinder member (104; 204) and or on the coupling member (108; 208) in order to restrict the first length of stroke (LI). 3. A press device according to any one of the preceding claims, c h a r a c t e r i s e d i n that one or several stopping means (112, 113; 212, 213) are arranged on the coupling member (108; 208) and/or on the second cylinder member (106; 206) in order to restrict the second length of stroke (L2). 4. A press device according to any one of the preceding claims, wherein the coupling member (108'; 208') slidably couples the first cylinder member (104'; 204') and the second cylinder member (106; 206) to each other in a sealed way by means of contacting seals (114', 115'; 214', 215') in order to form at least one working chamber (116'; 216') 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 (103'; 203'), wherein at least a first seal (114'; 214') bears against the first cylinder member (104'; 204') and the coupling member (108'; 208') and at least a second seal (115'; 215') bears against the coupling member (108'; 208') and the second cylinder member (106; 206), c h a r a c t e r i s e d i n that the cylinder members (104'; 106; 204', 206), the coupling members (108'; 208') and the seals (114', 115'; 214', 215') are arranged so that, in case of a displacement of the press shoe, the first cylinder member (104'; 204' ) is displaced in a d rection in relation to the second cylinder member (106; 206), while a central axis (C 3 ) of the coupling member (108'; 208') is tilted in relation to a central axis (C 2 ) of the second cylinder member (106; 206), wherein the pressure acting on surfaces (X; Z) exposed within the working chamber (116'; 216') generates a force in a direction opposite to the direction of the displacement between the first (104'; 204') and second (106; 206) cylinder members. 5. A press device according to claim 4, c h ar ac t e ri s e d i n that the coupling member (108'; 208') is designed so that the first seal (114'; 214) is situated closer to the carrier (102; 202) than the second seal (115'; 215'). 6. A press device according to claim 4 or 5, c h ar ac t eri s e d i n that the first seal (114') is constituted of a seal ring inserted into a groove extending along an outer circumference of the first cylinder member (104'), and that the second seal (115') is constituted of a seal ring inserted into a groove extending along an inner circumference of the second cylinder member (106). 7. A press device according to claim 4 or 5, characterised in that the first seal (214') is constituted of a seal ring inserted into a groove extending along an inner circumference of the coupling member (208'), and that the second seal (215') is constituted of a seal ring inserted into a groove extending along an outer circumference of the coupling member (208'). 8. A press device according to any one of the preceding claims, characterised in that the counterstay is a rotatable counter roll, wherein a flexible belt, preferably in the form of a sleeve, is arranged in an endless loop for travelling between the press shoe (101, 101'; 201, 201') and the paper or paperboard web during the pressing. 9. A press device according to any one of claims 1 to 8, characterised in that the press device is intended for wet-pressing of a paper or paperboard web. 10. A press device according to any one of claims 1 to 8, characterised in that the press device is intended for calendering of a paper or paperboard web.

Inventors: BROX ERIK, BROX, ERIK
Applicants: VALMET KARLSTAD AB, VALMET-KARLSTAD AB
Application year: 2001
Main classification: D21F3
IPC codes: D21F3