The invention relates to a pair of rolls which are defined in the preamble of Patent Claim 1 and form an extended press nip.

Pairs of rolls forming extended press nips are used in paper and board machines during pressing and calendering, among other things. The extended nip is formed between a shoe roll and a mating roll. The shoe roll has a stationary support structure, an elastic tubular sleeve rotating around the latter, a sliding shoe moving against the inner surface of the tubular sleeve and loading elements which are supported on the support structure and with which the sliding shoe and the tubular sleeve are loaded against the mating roll. The sliding shoe preferably extends in the axial direction over the shoe roll. In this arrangement, an extended- nip pressing zone is formed between the sliding shoe of the shoe roll and the mating roll.

Finnish utility model FI-2674 by the applicant describes an extended-nip press from the prior art which can be used in paper or board machines. In this solution, the loading elements have two essentially parallel rows of loading cylinders in which the pressures on the loading cylinders of at least one row can be controlled individually or in pressure-distributing blocks.

Finnish Patent Specification FI-100264 by the applicant describes a shoe-loaded, deflection-compensated roll which has a stationary spindle and a tubular roll sleeve rotating around the latter. Fixed between the roll sleeve and the roll spindle are loading shoes which act, in the nip plane, against the inner surface of the roll sleeve, are supported on the spindle and are loaded by a pneumatic pressure medium. By controlling the pressure of the pressure medium which is conducted into the loading shoes, the press-nip pressure can be profiled in the direction of

the roll spindle. The roll sleeve is produced from fibre-reinforced composite material, specifically in such a manner that the roll sleeve has good dimensional stability in the circumferential direction and low stiffness in the axial direction.

The specification also explains a preferred pressure-medium-feeding arrangement in a situation in which the roll which is explained in the specification is used as a mating roll for the extended press nip. The hydraulic arrangement has a pressure- medium container from which the hydraulic pump removes the pressure medium and feeds it into the loading sleeve of the roll serving as the mating roll and into the loading shoe of the extended-nip press roll. After the hydraulic pump the pressure medium is conducted into parallel control valves. Departing from convention, the pressure channel emerging from the respective control valve is divided into two strands, specifically in such a manner that the one strand leads to the loading shoe of the extended-nip roll and the other strand to the loading shoe of the mating roll. The pair of loading shoes located at a corresponding point on both sides of the extended nip is therefore controlled by the same control valve.

Finnish Patent Specification FI-964262 by the applicant presents a deflection- compensated roll which has a stationary support structure and a sleeve rotating around the latter. The ends of the sleeve are mounted on the support structure using hydraulic sliding bearings which are arranged on the nip plane and on a plane at right angles to the nip plane. The sleeve is also supported on the support structure by hydraulic loading elements which act in the main loading direction and with which the nip profile can be controlled in the axial direction. The sleeve which is supported by the abovementioned, hydraulic sliding bearing can be offset with respect to the support structure, for example for the purpose of closing and opening the nip. A pressure medium generating the loading pressure is fed into these sliding bearings, and the medium used for lubricating the sleeve and the medium used for lubricating the sliding bearings are separated from each other.

This enables lubricant to be fed the whole time at constant pressure between the sliding bearing and sleeve even though the pressure which generates the loading pressure and/or the through flow of the medium is/are controlled for the purpose of offsetting the sleeve with respect to the support structure.

Finnish Patent Specification FI-980491 by the applicant explains an extended-nip press roll and a press section, which uses the latter, of a paper machine. The extended-nip press roll has a stationary central spindle and a loading shoe and also hydraulic loading elements which are present between the stationary spindle and the loading shoe. By means of the loading elements, the active end surface of the loading shoe is pressed against the inner surface of the elastic tubular sleeve of the extended-nip press roll, which results in the generation of the pressing pressure in the extended-nip pressing zone formed by the tubular sleeve and mating roll. The loading shoe, the loading arrangements of the loading shoe and the oil-removing arrangements of the loading shoe, which arrangements have oil-removing grooves made within the tubular-sleeve loop on both sides of the loading shoe, and oil- removing pipelines connected to the said grooves, are essentially symmetrical to the axial central plane of the extended-nip press roll. By means of this symmetrical loading arrangement, the extended-nip press roll operates independently of the direction of rotation of the tubular sleeve, and the extended- nip press roll can be used as such both as an upper roll and as a lower roll.

The invention is based on the object of providing a simple extended-nip loading arrangement.

The essential characteristic features of the simple extended-nip loading arrangement are defined in the characterizing part of Patent Claim 1.

By means of the novel pair of rolls forming the extended nip a situation is created in which the support structures of the upper roll and the lower roll of the extended nip and the loading arrangements connected to the support structures are identical.

The advantages in terms of synergy are increased by the solution according to the invention because a large number of identical parts can be used in the rolls forming the extended nip. This results in turn in cost savings.

With the invention, use can also be made of a simple hydraulic circuit and a simple control circuit for loading the loading elements, resulting in additional savings in equipment, maintenance and repair costs.

The invention is described in the following with reference to the figures of the attached drawing, but the invention is not to be narrowly restricted to the details thereof.

Fig. 1 shows, as a schematic cross section, part of the support structure of the extended-nip press roll according to the invention and the loading arrangement in a situation in which the extended-nip press roll is used as the lower roll of the press nip.

Fig. 2 shows, as a schematic cross section, part of the support structure of the mating roll according to the invention and the loading arrangement in a situation in which the mating roll is used as the upper roll of the press nip.

Fig. 3 shows, as a schematic cross section, a variant of the embodiment shown in Fig. 1 of the extended-nip press roll.

Fig. 4 shows, as a schematic cross section, a pressure-medium-feeding arrangement for the extended-nip press roll and mating roll according to the invention.

Fig. 5 shows, as a schematic cross section, a variant of the pressure-medium- feeding arrangement illustrated in Fig. 4.

The extended-nip press roll 10 shown in Fig. 1 has a stationary, cross-sectionally essentially I-shaped support structure 11, only part of which is illustrated, and an elastic belt-type sleeve 12 rotating around said support structure in the clockwise direction S. The belt-type sleeve 12 is supported by its inner surface 12'on the support structure 11 via at least one hydraulically loaded loading shoe 13 with which the belt-type sleeve 12 can be loaded against the sleeve 112 of the mating roll 100, which is shown in Fig. 2 and forms the extended nip together with the extended-nip press roll 10. The loading shoe 13 is supported in the radial direction by a plurality of cylinder-piston elements 14,15 arranged at a distance from one another in the axial direction. The loading shoe 13 is also supported in the direction of rotation S of the belt-type sleeve 12 against a supporting part 18 which is fastened to the support structure 11 and absorbs the viscosity forces which are directed towards the loading shoe 13 and run in the direction of the machine. The cylinder-piston element 14,15 which is used for loading the loading shoe 13 is formed from a cylinder 14, constructed on the support structure, and a piston 15 which is mounted thereon. The loading pressure medium is conducted by a loading-pressure-medium-feeding channel 16, constructed in the support structure 11, into the base of the cylinder 14. The piston 15 is sealed with respect to the cylinder 14 by a seal 17, specifically in such a manner that the loading pressure medium cannot leak into the interior of the roll 10.

The upper surface 13"of the loading shoe 13 is concave and thus essentially corresponds to the curvature of the outer surface 112"of the sleeve 112 of the mating roll 100 shown in Fig. 2. A lubricant is fed between the loading shoe 13 and belt-type sleeve 12 by lubricant compartments 19 opening into the upper surface 13"of the loading shoe 13. From the lubricant compartment 19 there is a connection to the axial lubricant-feeding channel 20 [sic] via lubricant channels 20 which are constructed in the loading shoe 13 and run in the radial direction.

The lubricant is therefore fed entirely separately from the loading-pressure- medium supply.

In a corresponding manner, the mating roll 100 (shown in Fig. 2) of the extended- nip press roll 10 has a stationary, cross-sectionally essentially I-shaped support structure 111, only part of which is illustrated, and a sleeve 112 which rotates in the anticlockwise direction S'around the said support structure and is supported by its inner surface 112'on the support structure 111 via at least one hydraulically loaded loading shoe 113 with which the sleeve 112 can be loaded against the

loading shoe 13 of the extended-nip press roll 10. The construction of the mating roll 100 differs from the construction of the above-explained extended-nip press roll 10 only with regard to the position of the sleeve 112, of the loading shoe 133 [sic] and of the supporting part 118. Instead of the elastic belt-type sleeve 12 used on the extended-nip press roll 10, a relatively stiff steel or composite sleeve 112 is used as the sleeve for the mating roll 100. The upper surface 113"of the loading shoe 113 used on the mating roll 100 is convex and therefore corresponds to the curvature of the inner surface 112'of the sleeve 112 of the mating roll 100, and the lubricant channel 120 opens directly into the convex, upper surface 113"of the loading shoe 113. Since the direction of rotation S'of the sleeve 112 of the mating roll 100 serving as the upper roll runs in the anti-clockwise direction, the supporting part 118, which supports the loading shoe 113, is offset to the other side of the loading shoe 113 in comparison with the position of the supporting part 18 of the loading shoe 13 of the extended-nip press roll 10.

Also drawn in Figs 1 and 2 are the nip plane Y-Y and the plane X-X which is at right angles to the nip plane Y-Y and with respect to which the support structures 11; 111 of the rolls 10; 100 and the loading arrangements 14,15,16 ; 114,115,116 connected to the said support structures, and also the lubricant-feeding arrangements 20,21; 120,121 are mirror-inverted. The direction of action of the roll 10 shown in Fig. 1 proceeds upwards S10, and the direction of action of the roll 100 shown in Fig. 2 proceeds downwards S 100. Taking into account the direction of action of the rolls 10; 100, the constructions of the rolls 10 ; 100 are identical with the exception of the loading elements 13 ; 113 and the position of the supporting parts 18; 118. The diameters of the cylinders 14; 114 and the diameters of the pistons 15; 115 mounted on the latter are the same. Also, the loading- medium-feeding channels 16; 116, which are constructed on the support structures 11; 111, have an identical cross section and their course in the support structures 11 ; 111 is identical.

Fig. 3 shows a variant of the embodiment shown in Fig. 1 of the extended-nip press roll. The essentially I-shaped support structure 11 is illustrated here in complete form. In this embodiment, the loading shoe is symmetrical to the gap plane Y-Y and so the lubricant compartment 19 is also symmetrical to the nip plane Y-Y. In this case, the direction of rotation of the roll 10 can run in the clockwise direction S or counter to the clockwise direction S'. The loading shoe 13 is therefore supported here on both vertical sides by supporting parts 18a, 18b which are fastened to the support structure 11 and absorb the viscosity forces directed towards the loading shoe 13. The belt-type sleeve 12 is normally also supported at supporting points of the support structure 11, which points lie outside the loading shoe 13. This can also be realized, for example, with supporting devices 30 which are supported on the support structure 11 and with which the belt-type sleeve 12 is kept circular.

The principle which is illustrated in Fig. 3 and according to which the loading shoe 13 is symmetrical to the nip plane Y-Y and the lubricant compartment 19 is also symmetrical to the nip plane Y-Y may, of course, also be applied to the mating roll 100. In this case, the loading shoe 113 of the mating roll 100 is supported in a corresponding manner on both vertical sides against the viscosity forces by supporting parts 118 which are fastened to the support structure 11.

Fig. 4 schematically illustrates a loading-pressure-medium-feeding arrangement for the extended-nip press roll 10 and mating roll 100. The rolls 10; 100 and the pressure-medium-feeding arrangement are only shown in part. The feeding arrangement has a pressure-medium container 200 from which the feed pump 201 feeds the pressure medium to the loading elements 15a, 15b of the loading shoe 13 of the extended-nip press roll 10 and to the loading elements 115a, 115b of the loading shoe 113 of the mating roll 100. The feeding channel 202 on the delivery side of the feed pump 201 is divided into parallel strands 203,204, each strand 203,204 having a control valve 205,206. Following the control valves 205,206, each parallel strand 203,204 divides further into two strands 203a, 203b and 204a,

204b, the first strand 203a, 204a leading to the loading elements 15a, 15b of the loading shoe 13 of the extended-nip press roll 10, and the second strand 203b, 204b leading to the loading elements 115a, 115b of the loading shoe 113 of the mating roll 100. The pressure-medium return line 210 of the extended-nip press roll 10 and the pressure-medium return line 211 of the mating roll 100 are directed into the pressure-medium return line 212 leading to the common pressure-medium container 200. Here, therefore, on both sides of the extended nip, the loading elements 15a, 115a and 15b, 115b present at the corresponding location are controlled by the same control valve 205,206.

Fig. 4 only shows two strands 203,204 of the strands of the delivery-side feeding channel 202 of the feed pump 201, but in reality exactly as many strands are present as opposite loading elements 15a, 115a ; 15b, 115b forming pairs in the rolls 10; 100 are present; etc.

With the pressure-medium-feeding arrangement shown in Fig. 4, the same pressure can be conducted into each identical loading element 15a, l 15a ; 15b, l 15b which form a pair, thereby automatically resulting in a stable equilibrium of forces between the extended-nip press roll 10 and the mating roll 100.

Fig. 5 shows a variant of the pressure-medium-feeding arrangement shown in Fig. 4. In this embodiment, the delivery-side feeding channel 202 of the feed pump 201 leads directly to the control valve 205, after which the feeding channel 202 divides into a strand 202a leading to the loading elements 15a, 15b of the loading shoe 13 of the extended-nip press roll 10, and a strand 202b leading to the loading elements 115a, 115b of the loading shoe 113 of the mating roll 100. The loading elements 15a, 115a ; 15b, 115b both of the extended-nip press roll 10 and of the mating roll 100 therefore controlled by one control valve 205.