SHOE PRESS

Abstract: A shoe press for paper or board machines comprises a press shoe (300) and a counter roll (312), which between themselves form an extended nip (N) for a paper or cardboard web (W) and for a circulated flexible belt (311); at least one hydraulic loading cylinder (310) with a working chamber (325) supplied with hydraulic fluid and adapted to press the press shoe against the counter roll; and a hydraulic fluid chamber (301) between the side of the press shoe facing the loading cylinder and the opposing side of the loading cylinder. The working chamber (325) and the hydraulic fluid chamber (301) do not communicate with each other and are arranged for hydraulic fluid supply independently of each other.

Description: SHOE PRESS The present invention relates to a shoe press for paper/board machines, comprising a press shoe and a counter roll, which between themselves form an extended nip for a paper or cardboard web and for a circulated flexible belt, at least one hydraulic loading cylinder with a working chamber supplied with hydraulic fluid and adapted to press the press shoe against the counter roll, and a hydraulic fluid chamber supplied with hydraulic fluid and positioned between the side of the press shoe facing the loading cylinder and the opposing side of the loading cylinder. DE-195 15 832 discloses a shoe press in which the supplying of the pressure chamber with hydraulic fluid is carried out via a throttle extended from the working chamber and arranged in the piston of the loading cylinder. A drawback of this known arrangement is that the ratio of the pressure in the working chamber to the pressure in the hydraulic fluid chamber is already locked at the construction stage. The object of the invention is to eliminate this drawback. The object is achieved by a shoe press according to claim 1. Advantageous embodiments have the characteristic features stated in the dependent claims. According to the invention, hydraulic fluid thus is supplied separately to the working chamber of the loading cylinder and to the hydraulic fluid chambers, whereby the pressure conditions of the working chamber and the hydraulic fluid chamber can be monitored and controlled separately, which ensures that the shoe is always able to move in relation to the loading cylinder, thereby eliminating the risk of the thermal expansion and motions of the shoe being transferred to lateral forces between piston and cylinder wall. The invention will now be described in more detail with the aid of two embodiments, both concerning the use of a shoe press according to the invention in the press section of a paper or board machine. Fig. 1 is a cross-sectional view of the first embodiment of the shoe press, and Fig. 2 is a cross-sectional view of the second embodiment of the shoe press. It is understood that the press shoe is made in a single piece and extends in the cross direction, whereas loading cylinders, hydrostatic compartments and pressure chambers can be several in number, distributed in the longitudinal direction of the press shoe (cross direction) . Reference is made to Fig. 1. The shoe press com- prises a press shoe 300 and a counter roll 312, which form a nip N between themselves. In the nip N run a paper web W which is to be dewatered, a circulated flexible press belt 311 and a press felt F. The press shoe is pressed against the counter roll 312 by means of a load- ing cylinder 310 with piston 330 and cylinder part 340. An O-ring seal therebetween is designated 380. The piston is attached to the horizontal beam 309 included in the frame system of the shoe press, by means of screws 350. The working chamber 325 of the loading cylinder 310 is supplied with hydraulic fluid by means of a horizontal duct 326 which is formed in the piston and which is shared by all the pistons, and a vertical duct 327 formed in the piston. A hydraulic fluid chamber 301 between the upper sur- face of the cylinder part 340 and the opposing side of the press shoe is delimited by an O-ring seal 336. The hydraulic fluid chamber 301 is supplied with hydraulic fluid through a duct 302 formed in the press shoe and having duct parts 302' and 302". The duct 302 receives the hydraulic fluid from a pipe 303 which extends in the longitudinal direction of the press shoe and is attached to one longitudinal side edge 304 (in this case, the ris- ing side) of the press shoe 300 by means of screws 305, which engage in threaded holes 305' in the press shoe. The duct or bore 306 of the pipe 303 communicates with the duct 302 by means of a throttle 308. The pipe 303 can be supplied with hydraulic fluid through its one end or both ends. The hydraulic fluid to the working chamber 305 and to the hydraulic fluid chamber 301 can have the same source, i.e. the ducts 306 and 326 can be branches of a common supply of hydraulic fluid (usually oil) and the fluid pressure in the working chamber 325 and the pressure chamber 311 can be controlled separately, for instance, by means of throttles and/or other known pressure control means, or different sources can be used for said hydraulic fluid supply. The hydraulic fluid chamber 301 has a slightly smaller area than the working chamber 325. The embodiment in Fig. 2 comprises the press shoe 400, the counter roll 312, the circulated press belt 311, the loading cylinder 410 with cylinder part 410A and piston 410B, a seal 480 arranged therebetween, and ducts 426 and 427 for supplying hydraulic fluid to the working chamber 425 of the loading cylinder. The hydraulic fluid chamber 301 is also in this case supplied with hydraulic fluid via ducts 402 with part 402" formed in the press shoe and receiving the hydraulic fluid from a pipe 403 attached to one longitudinal side edge of the press shoe, via a hole 408. The pipe is attached by means of screws 405 and screw holes 405'. The duct 402 opens into the hydraulic fluid chamber 301 by means of a throttle 402A. A feed pipe is designated 411. The shoe press in Fig. 2 also has a hydrostatic compartment 401 in its side facing the counter roll 312. This hydraulic fluid is supplied by means of a duct 402' branched off from the duct 402. The hole 408 in the pipe 403 in the form of a throttle delimits the hydraulic fluid flow to the compartment 401 to the desired level. The throttle 402A prevents the hydraulic fluid flow through the nip N from disappearing completely if the hydraulic fluid chamber 301 should leak. The hydraulic fluid chamber 301 has in this case a greater area than the working chamber 325. The pipes 303 and 403 are preferably made of aluminium, of which also the press shoe is usually made, and is manufactured by extrusion. By loosening the screw joints 305/305' and 405/405', the pipes 303 and 403 can be replaced with other pipes 303 and 403 having different dimensions, a different size of throttle etc. The inventive shoe press is applicable also to calendering operations in a paper or board machine.

Claims: CLAIMS 1. A shoe press for paper or board machines, com- prising a press shoe (300; 400) and a counter roll (312) , which between themselves form an extended nip (N) for a paper or cardboard web ( ) and for a circulated flexible belt (311), at least one hydraulic loading cylinder (310) with a working chamber (325; 425) supplied with hydraulic fluid and adapted to press the press shoe against the counter roll, and a hydraulic fluid chamber (301) between the side of the press shoe facing the loading cylinder and the opposing side of the loading cylinder, c h a r a c t e r i s e d in that the working chamber (325; 425) and the hydraulic fluid chamber (301) do not communicate with each other and are arranged for hydraulic fluid supply independently of each other. 2. A shoe press as claimed in claim 1, c h a r a c t e r i s e d by a duct (302; 402) formed in the press shoe (300; 400) and adapted to supply the hydraulic fluid chamber (301) with hydraulic fluid. 3. A shoe press as claimed in claim 2, c h a r a c t e r i s e d by a pipe (303; 403) attached to one longitudinal side edge of the press shoe (300; 400) and communicating with said duct (302; 402) via a hole (308; 408) formed in the pipe wall. 4. A shoe press as claimed in claim 3, c h a r a c t e r i s e d in that the hole (308; 408) forms a throttle . 5. A shoe press as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the duct (402) opens into the hydraulic fluid chamber (301) via a throttle (402A) . 6. A shoe press as claimed in any one of claims 1-5, a hydrostatic compartment (401) being formed in the surface of the press shoe facing the counter roll, c h a r a c t e r i s e d in that said duct (402) has a branch (402') to the hydrostatic compartment (401). 7. A shoe press as claimed in any one of claims 1-6, c h a r a c t e r i s e d in that the area of the hydrau- lie fluid chamber (301) is greater than that of the working chamber (425) . 8. A shoe press as claimed in any one of claims 1-6, c h a r a c t e r i s e d in that the area of the hydraulic fluid chamber (301) is smaller than that of the work- ing chamber (325) . 9. A shoe press as claimed in any one of claims 3-8, c h a r a c t e r i s e d in that the pipe is releasably attached to the press shoe (300; 400). 10. A shoe press as claimed in claim 9, c h a r - a c t e r i s e d in that the pipe (308; 408) is attached to the press shoe (300; 400) by means of screws (305; 405) and screw holes formed in the press shoe. 11. A shoe press as claimed in any one of claims 3-10, c h a r a c t e r i s e d in that the pipe (308; 408) is made of aluminium by extrusion.

Inventors: BROX ERIK, GUSTAVSSON LARS, NYMAN MIKAEL, PALMGREN JOAKIM, SAEFMAN NILS-ERIK, BROX, ERIK, GUSTAVSSON, LARS, NYMAN, MIKAEL, PALMGREN, JOAKIM, SAEFMAN, NILS-ERIK
Applicants: VALMET KARLSTAD AB, VALMET-KARLSTAD AB
Application year: 1998
Main classification: D21F3
IPC codes: D21F3