EXTENDED-NIP PRESS

Abstract: Extended-nip press for dewatering of a paper or board web, comprising a counter-member (10), which forms an extended press zone (S) together with a press-glide shoe (33) and a glide belt (40) running around the shoe. Through said zone (S), at least one dewatering fabric (50) and the web (W) from which water is removed and which is sup­ ported by said fabric are passed. The glide belt (40) is passed over a leading and tensioning member (43;70), and the closed loop of the glide belt (40) is guided around its leading and tensioning member (43;70) so that, between said leading and tensioning member (43;70) and the glide shoe (33) and its possible guide parts (33a,­ 33b), if any, the glide belt (40) has, as a rule, substantially straight runs (40a,40b). The space enclosed by the glide belt (40) and susceptible of oil splashes is closed at both of the end areas of the loop of the glide belt (40) by means of wall constructions (42a,42b), which may, if necessary, be provided with expansion joints (61) fitted in such a way that movements of the glide shoe (33) and of the leading and tensioning member (43;70) for the glide belt (40) in relation to one another are possible.

Description: The invention concerns an extended-nip press for dewatering of a paper or board web, comprising a counter-member, most appropriately a press roll, which forms an extended press zone together with a press-glide shoe and a glide belt running around the shoe, through which said zone at least one dewatering fabric and the web from which water is removed and which is supported by said fabric are passed, and which said glide belt is passed over a leading and tensioning member. In prior art, extended-nip presses are known wherein the press zone is formed between a revolving belt mantle provided with a stationary core and a counter-roll. As is well known, in the stationary roll core hydraulically or hydrodynamically loaded pressure shoes are used, by whose means, by the intermediate of the revolving mantle, a compression pressure is applied to the web towards the counter-roll. The counter-roll may be either an ordinary smooth-faced or hollow-faced press roll, a variable-crown roll, or a belt mantle provided with a hydraulic glide shoe. As an example in respect of the prior-art extended-nip press described above, reference is made to the GB Patent Application No. 2,057,027 as well as to the published Patent Application WO 82/02567. In the patent applications mentioned above, no satisfactory solution has been suggested for the construction of the ends of the roll provided with a stationary core and with a revolving belt mantle. The object of said sealed ends is to prevent access of oil out of the interior of the roll mantle, e.g., to spoil the paper web. Lubrication fluid is needed in the lubrication between the inside face of the revolving mantle and the glide shoe or shoes that guide the mantle in considerable amounts. In this respect, reference is made to the US Patent 3,804,707, wherein an extended-nip press is described in which said roll ends are stationary and provided with resilient seal rings that rub against the inner face of the flange in the area of the ends of said roll mantle. Since the roll mantle has to alter its shape from the circular shape during each round of its rotation especially in the nip zone, this causes a considerable fatiguing and wearing load on said seal rings. In respect of the prior art related to the present invention, reference is made further to the FI Patent Applications 821503 and 850213, to the FI Patent 66,932, to the DE Published Pat. Appl. 3,239,954, and to the US Patent 4,584,059. One drawback, e.g., in the extended-nip presses known from the publications cited above is the lateral wandering of the belt mantle, because the prior-art devices have lacked efficient guide means for the belt mantle to keep the belt stably in its place laterally. The press forces employed in extended-nip presses are of an order of 10⁷ N, in which case a fully carrying lubricant film must be provided between the glide shoe and the belt mantle. In such a case, water is not adequate as a lubricant, but it is necessary to use different lubrication oils and hydrodynamic or hydrostatic lubrication chambers, the pressure level employed in said chambers being of an order of 4...8 MPa. The thickness of the belt mantles used is about 3...6 mm. This is why they can be guided exclusively by drawing, which also causes its problems in the guiding of the belts. Long belt mantles are preferable to short circular hose mantles in the respect that their service life is considerably longer and the standstills resulting from replacement of belt mantle are less frequent. Thus, one object of the present invention is to make the intervals between said standstills longer. An object of the present invention is to combine the good properties of a belt-mantle construction closed at its ends and of an open belt. An object of the invention is to provide such an extended-nip press belonging to the species concerned wherein the opening gap of the nip can be made sufficiently large, as a rule about 30...50 mm, so that the glide belt and the press felts can be replaced as quickly as possible. The main object of the present invention is to provide an extended-nip press belonging to the species defined at the beginning which is also suitable for thin paper qualities and for high machine speeds. The employment of the prior-art extended-nip presses of the sort concerned at high running speeds and with thin qualities has been prevented completely or at least restricted, e.g., by the following circumstances. In a construction with an open long glide belt, oil leakages and oil mist are increased as the speed becomes higher. In stead, the glide belt has a relatively good service life (up to 6 months), because its bend-loading situation is favourable. Leakages of oil in a belt-mantle construction closed at the ends are little, even though this construction is not fully sealed either. The service life of the belt mantle is a problem even at lower speeds, because the bend-loading situation of the belt mantle is difficult. The mantle has to bend to a "concave" shape in the area subjected to nip load as well as to a "convex" shape in the end area constituting an extension of the nip. Moreover, the circumferential dimension of the belt mantle is little, and the frequency of load alternation becomes high. The object of the present invention is to avoid the drawbacks that have come out above and to provide an extended-nip press construction wherein a closed construction is combined with a good loading situation of the press belt also when a relatively long glide belt is used. In view of achieving the objectives stated above and those that will come out later, the invention is mainly characterized in that the closed loop of said glide belt is guided around its leading and tensioning member so that, between said leading and tensioning member and the glide shoe and its possible guide parts, if any, the glide belt has substantially straight runs most appropriately parallel to one another, and that the space enclosed by said glide belt and susceptible of oil splashes is closed at both of the end areas of the loop of the glide belt by means of wall constructions. In the invention, in said wall constructions, there are preferably expansion joints arranged in such a way that movements of the glide shoe and the glide-belt leading and tensioning member in relation to one another are possible. Said expansion joints are, however, not always necessary if the resilience of the sealing members is sufficiently high in view of opening of the nip and even in view of tensioning of the belt. In the invention, the press shoe, which may be hydrodynamic or hydrostatic or a combination thereof, also forms the counter-face of one end area of the cycle of running of the glide belt, whereas the other end area consists of a roll or of a corresponding glide-shoe arrangement, which, at the same time, acts as a tensioning member. The latter roll or equivalent is preferably grooved. In the invention, in the running area of the of the glide belt in the press shoe, there may be low-pressure hydrostatic pressure chambers to ensure the lubrication and to lower the friction force. In the invention, the aligning of the glide belt takes place by means of an alignment roll against a belt-guide roll or by means of an alignment roll against a support plate placed inside the belt loop. The alignment roll may consist of narrow resilient-faced "wheels". According to the invention, prevention of leakage of the lubrication oil placed inside the belt loop takes place, e.g., by means of hose-loaded lubricated seal ribs, which are placed preferably at both sides of the glide belt. By means of the invention, the objectives as set above are achieved, and by its means a number of advantages important in practice are accomplished, which will be discussed below in more detail. Since, in the invention, the diameter of the glide-belt guide roll or equivalent is equal to the belt-running width on the press shoe, tensioning and guiding of the belt do not cause problems of sealing at the ends. In the invention, a length-variation joint of the seal ribs and a length-variation joint of the end plates of the belt loop are used. These joints can be arranged favourably without problems. The extended-nip press in accordance with the invention for thin paper is preferably a single-felt press, whereby the opposite roll is a smooth roll that transfers the paper web, and the hollow face may consist most appropriately of grooves, blind-drilled bores, or equivalent in the glide belt. Since the press for thin paper is most appropriately a single-felt press, the pressing result can be intensified by heating the press roll, e.g., by means of induction heating or IR-heating. The paper web and/or the press felt may also be heated by means known in prior art, such as by means of a steam box, an IR-heater, or a high-frequency heater. The extended-nip press in accordance with the invention is also advantageous with thin paper qualities when the pressure level is sufficient, i.e. about 7 MPa, which can be achieved. Further advantages include more efficient dewatering, whereby the number of nips can be lowered, low level of oscillations, and possibilities of improving the properties of quality of the paper. Even though, in the following, the invention will be described with reference to such an exemplifying embodiment only wherein the glide-belt/press-shoe device forms an extended nip with a counter-roll, it should be emphasized that the scope of the invention also includes extended-nip presses in which the counter-member consists of a member other than a press roll, e.g. a press-shoe device or a second glide-belt/press-shoe device or equivalent. In the following, the invention will be described in detail with reference to some exemplifying embodiments of the invention illustrated in the figures in the accompanying drawing, the invention being by no means strictly confined to the details of said embodiments. Figure 1 is a side view of a first embodiment of the invention as a partial vertical sectional view in the machine direction. Figure 2 shows a transverse vertical section II-II in Fig. 1. Figure 3 shows a section III-III in Fig. 1. Figure 4 is a vertical sectional view of the nip zone in the machine direction on an enlarged scale. Figure 5 shows a section V-V in Fig. 1. Figure 6 shows a second, alternative embodiment of the invention in a way corresponding to Fig. 1. The extended-nip press shown in Fig. 1 and having a wide press zone S comprises an upper counter-roll 10, which is provided with a mantle 11 revolving around a stationary central axle 12 on bearings 18a and 18b, said mantle 11 having a smooth outer face 11' and a smooth inner face 11''. The counter-roll 10 is a variable-crown roll provided with a journalling that withstands high loads and that consists of loading shoes 13 provided with loading members 14 and of liquid chambers 13a. A tubular roll journalled at its ends is also possible as a counter-roll 10. As is shown in Fig. 2, the counter-roll 10 is attached to its bearing supports 17a and 17b by its axle journals 15a and 15b, said bearing supports being provided with spherical bearings 16a and 16b. Figs. 1 and 2 show an extended-nip construction provided with one press felt 50, wherein the counter-roll 10 is a smooth-faced 11', preferably metal-faced roll, which permits heating of the roll face, e.g., by means of induction heating devices 10A. It is also possible to use infra-heating devices or flame heaters. Heating that takes place from inside the roll 10 is also possible, when a variable-crown roll is used, e.g., by means of hot-oil heating and, when a tubular roll is used, by means of steam, induction heater, IR-heaters, or equivalent. Also, it is possible to employ simultaneous heating of the counter-roll 10 from inside and from outside as well as various combinations of the different modes of heating described above. As is shown in Figs. 1 and 2, as an essential component the extended-nip press comprises a glide belt 40, which forms a closed belt mantle and which is preferably provided with an outside hollow face 40a in the construction which is shown in Figs. 1 and 2 and which uses one press felt 50. As is seen best from Fig. 3, the hollow face 40a of the belt 40 is placed at the side of the press felt 50. The hollow face 40a in the belt 40 has been produced by means of grooves, blind-drilled bores, by means of a coarse wire-like fabric placed on the outer face of the belt 40, or as a combination thereof. The outer face of the belt 40 may also be smooth, but than requires intensified dewatering of the press felt 50, e.g. an increased number of felt absorbers 53. Before the felt absorbers 53, there are water spraying devices 54. The loop of the felt 50 is guided by guide rolls 51. The glide belt 40 is preferably a polyurethane belt provided with a polyamide frame fabric. Moreover, the belt 40 may be made of a number of different composite materials. Inside the loop of the belt 40, a transverse beam 30 is fitted, which is provided with closed ends 30a and 30b. Loading cylinders 31 are supported on the top side of the beam 30, and by means of the piston rods 32 of said loading cylinders forces are applied to the glide shoe 33 by whose means the compression pressure dewatering the web W is produced in the press zone S formed together with the counter-roll 10. The glide belt 40 has a tensioning roll 43, which is supported on the bearing supports 41a and 41b by its axle journals 43a and 43b by means of bearings 56a and 56b. The bearing supports 41a and 41b are supported on the bottom side of the beam 30 by means of power units 57a,58a and 57b,58b so that, by means of said power units, the belt 40 can be tensioned while the sealing of both of its ends 42a and 42b remains good. The belt 40 tensioning roll 34 is most appropriately provided with grooves 43c. The tensioning roll 43 may also be provided with an auxiliary drive, in which case it can be driven by means of the axle journal 43d. The bearing housings 41a and 41b, which move during the tensioning, are sealed against the end plates 42a and 42b. The beam 30 is passed through the end plate 42a and 42b at both of its ends and, to prevent leakages of lubricant, the beam is also sealed against the end plates 42a and 42b. At both ends 42a and 42b, underneath the beam 30, there are length-variation joints 61, which permit movements of the tensioning roll 43 and the glide shoe in relation to one another, as well as an opening movement of the nip zone, which is about 30...50 mm. Said joints 61 are formed, for example, between wall portions 61a attached to the bottom side of the beam 31, the wall portion 61b placed at a distance from said wall portions 61a, and the edge portion 61c of the wall which can move as sealed between said wall portions. The latter portions 61c are attached in connection with the bearing supports 4la,41b of the guide roll 43. The side plates 42a and 42b are preferably attached by means of screws, so that, when the glide belt 40 is being replaced, the side plates 42a at the service side HP, and so also their seals 48a,49, can be detached rapidly. The operation side of the frame is denoted with KP. In Fig. 2 the leakage oil pipe 75 is shown, through which the lubricant can be passed in the direction of the arrow O out of the sealed box back to circulation. Moreover, Fig. 2 is a schematical illustration of the drive gearbox 80 of the counter-roll 10, of which said gearbox, e.g., the housing is not shown. As is shown in Figs. 1 and 2, the counter-roll 10 forms an extended press zone S together with the press shoe 33, which is hydrodynamic, hydrostatic, or a combination thereof. The press shoe 33 has a concave glide face 35 facing the counter-roll 10. The closed loop of the impervious press belt 40, which is guided over the glide face 35 of the press shoe 33, is passed over the tensioning roll 43. The diameter D of the guide roll 43 and the total width L of the glide face 35 and of the guide faces of the extension parts 33a and 33b placed at both sides of said glide face 35 are equally large as compared with one another (D = L). In view of the circulating running of the press belt 40 and in view of the sealing of the lubricant, it is preferable that, at both sides of the press zone of the press shoe 33, as fixed and continuous extensions of the glide face 35, there are convex guide parts 33a and 33b at both of its sides, said guide parts being preferably made of one piece with the press shoe 33. Said guide parts 33a and 33b and their glide faces are provided with glide portions consisting of hydrodynamic or hydrostatic lubricant chambers. Within the scope of the invention, in stead of a combination construction 33,33a,33b, a mobile press shoe and stationary belt-circulation glide shoes separate from it are also possible. In view of sealing of the lubricant, a press shoe 33 and belt 40 guide parts 33a,33b integrated with each other are preferable. In the invention, in addition to the length-variation and expansion joint 61 in both of the end walls 42a,42b, another essential feature is that the overall width L of the glide shoe 33,33a,33b is equal to the diameter D of the leading and tensioning roll 43. In such a case, the glide belt 40 can be arranged sufficiently long and in such a way that it has runs 40a and 40b parallel to each other, which runs are easy to seal and owing to which the expansion joint 61 can be arranged easily. As is shown in Fig. 1, substantially in the same plane with the tensioning roll 43, there is a belt 40 alignment roll 44, the direction of the axis of said alignment roll 44 being turnable in relation to the direction of the axis of the tensioning roll 43, whereby the belt 40 can be guided to run in the middle and its transverse wandering can be prevented. The alignment roll 44 is most appropriately a roll of one piece and of a length substantially equal to the length of the tensioning roll 43. The alignment roll 44 may also be composed of a few component rolls attached to the same axle. The alignment roll 44 is preferably coated with a resilient coating 44a, which is, e.g., made of rubber. The coating 44a may be provided with grooves, which increase the resilience of the face of the alignment roll 44, in order that the alignment roll 44 should contact the belt 40 better over its entire length even when the roll 44 has been turned slightly diagonally, by means of which turning an aligning effect is produced. Fig. 1 shows lubricant doctor devices 66, in whose connection there is a lubricant drain pipe 64. As is seen best from Figs. 2 and 3, at both of the end plates 42a and 42b there are inside projection parts 45, between which there are loading members 48a,49a and 48b,49b for the resilient seals 46. According to Fig. 3, said loading members are hoses loaded by means of a pressure medium, but corresponding bellows constructions may also be used. In the resilient seals 46, there are lubricant grooves 47 inside. The seals 46 glide, one opposite the other, against the lateral areas of the belt 40 and seal any oil leakages. By altering the pressure passed into the loading members 48,49, it is possible to adjust the sealing pressure against the inner face of the belt 40. The glide faces 46a of the seals 46 are, e.g., of plastic, whose wear can be reduced by means of lubricant fed into the lubricant grooves 47. From Fig. 5, which is a sectional view taken along the line V-V in Fig. 1, the joint of the seals 46 is seen, which joint permits movements of the glide shoe 33 and of the tensioning roll 43 relative one another in a plane parallel to the parallel (L = D) straight runs 40a and 40b of the glide belt 40. At both sides of the seals 47 there are glide pieces 59, which are placed facing the expansion joints 61 in the end plates 42a and 42b. According to Fig. 1, heating devices 55 are placed at the inlet side of the paper web W in before the press zone S. By means of the devices 55, the heating can be carried out, e.g., as steam heating, IR-heating, or as high-frequency heating. A raised temperature in the paper web W intensifies the dewatering in the press zone S, where the dewatering can be intensified further, e. g., by means of ultrasonic oscillations. Thus, in Fig. 4, an ultrasonic oscillator 63 is shown, which is placed centrally in the pressure chamber 34 of the glide shoe 33. From the oscillator 63, the ultrasonic field is passed to proceed through the glide belt 40 and the press fabric 50 into the paper web W in which is in the press zone S. Thereby, the face 11' of the mantle 11 of the counter-roll 10 acts as a reflector for the ultrasonic oscillations and improves the efficiency of the ultrasonic treatment. When a steam box is used as the heater 55, it is possible to use a suction device 65 inside the loop of the press fabric 50, opposite the steam box 55, which said suction device intensifies the absorption of the steam into the paper web W. After the press zone S, the web W departs from the press fabric 50 and follows the mantle face 11', whose surface is smoother than that of the press fabric, from which said mantle face 11' the web W is detached and passed over the paper guide roll 21 and from which the web W is passed onto the drying wire 23, which runs over the drying-wire guide roll 22 and carries the web W out to the drying section (not shown). After the drying-wire guide roll 22 there is a suction device 24, which helps the paper web W out to adhere to the drying wire 23. Fig. 6 shows such a variation of the invention wherein two press fabrics 50 and 60 are used, between which the web W is passed through the press zone S. In such a case, the mantle of the counter-roll 10 is provided with an outside hollow face 11a, which is, e.g., a grooved or blind-drilled face. In Fig. 6, after the press zone S, the web W is detached from both of the press fabrics 50 and 60 as soon as possible to avoid rewetting, being passed to the drying section (not shown). A second difference in the construction shown in Fig. 6, compared with Fig. 1, is that the glide-belt tensioning roll 43 shown in Fig. 1 has been replaced by a convex tensioning glide shoe 70, which is provided with hydrodynamic glide faces or hydrostatic lubricant chambers 71. Since the glide shoe 70 is displaceable in connection with tensioning of the belt 40, the end portions extending beyond its ends 42a and 42b must be sealed relative the end plates 42a and 42b so that movement is permitted. In Fig. 6, the diameter D of the glide shoe 70 is equally large as the overall width L of the press-glide shoe 33,33a,33b, so that the glide belt 40 can be made sufficiently long and the bending radii of the glide belt 40 can be made sufficiently large in view of bending strains applied to the glide belt 40. Moreover, the glide belt 40 can be arranged so that it has opposite straight runs 40a and 40b parallel to one another between the glide shoe 33,33a,33b and the glide shoe 70. In such a case, the sealing between the glide belt 40 and the end walls 42a,42b and the expansion joint 61 in the end walls can be arranged advantageously in the way described above, so that the box defined by the glide belt 40 and by the end walls 42a,42b becomes sufficiently oil-tight in all situations of operation, and so that the glide belt 40 can be replaced quite rapidly. When a glide belt 40 in accordance with the invention, similar to a crawler mat, is used, which has quite long opposite parallel straight runs 40a and 40b, the glide belt 40 can be made sufficiently long so that its resistance to wear and the intervals of its replacement become sufficiently large. The glide belt 40 is dimensioned, e.g., so that its length is within a range of 3...10 m, whereby the interval of its replacement becomes about 2...6 months. Besides an alignment roll 44, an alternative mode in the guiding of the glide belt 40 consists thereof that one edge of the belt 40 is tensioned more than the other edge by means of the tensioning roll 43 or a corresponding glide shoe 70. In the other respects, the construction illustrated in Fig. 6 is similar to that described above in relation to Figs. 1 to 5. In the following, the patent claims will be given, whereby the various details of the invention may show variation within the scope of the inventive idea defined in said claims and differ from the details described above for the sake of example only.

Claims: Extended-nip press for dewatering of a paper or board web, comprising a counter-member, most appropriately a press roll (10), which forms an extended press zone (S) together with a press-glide shoe (33) and a glide belt (40) running around the shoe, through which said zone at least one dewatering fabric (50) and the web (W) from which water is removed and which is supported by said fabric are passed, and which said glide belt (40) is passed over a leading and tensioning member (43;70), characterized in that the closed loop of said glide belt (40) is guided around its leading and tensioning member (43;70) so that, between said leading and tensioning member (43;70) and the glide shoe (33) and its possible guide parts (33a,33b), if any, the glide belt (40) has substantially straight runs (40a,40b) most appropriately parallel to one another, and that the space enclosed by said glide belt (40) and susceptible of oil splashes is closed at both of the end areas of the loop of the glide belt (40) by means of wall constructions (42a,42b). Extended-nip press as claimed in claim 1, characterized in that both of said wall constructions have expansion joints (61) arranged so that movements of the glide shoe (33) and of the glide-belt (40) leading and tensioning member (43;70) in relation to one another are possible. Extended-nip press as claimed in claim 1 or 2, characterized in that the entire circumference of both of the lateral areas of the glide belt (40) is provided with sealing members, most appropriately with sealing members both inside and outside the glide belt (40), said sealing members being attached to the wall parts (42a,42b) that close both ends of the glide belt (40), or to parts connected with said wall parts. Extended-nip press as claimed in claim 3, characterized in that said sealing arrangement, which is fitted in both of the lateral areas of the circumference of the loop of the glide belt (40), comprises two tubular and/or bellows-like loading members (48a,49a and 48b,49b) or equivalent loaded by means of a pressure medium, said members comprising sealing ribs (46) whose glide face (46a) rubs against the lateral areas of the glide belt (40), and said sealing ribs (46) being preferably provided with inside lubricant grooves (47). Extended-nip press as claimed in any of the claims 1 to 4, characterized in that the concave press-glide face (35) of the press-glide shoe (33) is connected with convex glide-belt (40) guide faces (33a,33b), which constitute smooth direct extensions of the press-glide face (35) and which said guide faces (33a,33b) are hydrodynamically and/or hydrostatically (36) lubricated, and that the width (L) of said combined press and guide shoe (33,33a,33b) is equal to the diameter (D) of the guide member (43;70) placed inside the loop of the glide belt (40). Extended-nip press as claimed in any of the claims 1 to 5, characterized in that the loop of the glide belt (40) is guided to run around a frame beam (30), that in connection with one side, preferably the upper side, of said frame beam (30) there are the hydraulic loading members (31) for the press-glide shoe (33), several loading members being preferably arranged in the transverse direction in view of controlling the transverse profile of distribution of the compression pressure, and that in connection with the opposite side, preferably the lower side, of said frame beam (30), hydraulic or equivalent loading members (57a,58a,57b,58b) are provided, by means of which the position of the glide-belt (40) leading and aligning member (43;70) can be regulated for the purpose of regulation of the tension of the glide belt (40) and possibly for the purpose of aligning the glide belt (40). Extended-nip press as claimed in any of the claims 1 to 6, characterized in that the glide-belt (40) leading and aligning member is a tensioning roll (43), which is most appropriately provided with a grooved face (43a), the diameter (D) of said roll being equal to the width (L) of the combined press and guide shoe (33,33a,33b). Extended-nip press as claimed in any of the claims 1 to 6, characterized in that the glide-belt (40) aligning member is a hydrodynamically and/or hydrostatically lubricated glide shoe (70), whose guide and glide face has a substantially crescent-shaped vertical section. Extended-nip press as claimed in any of the claims 1 to 8, characterized in that for transverse alignment of the glide belt (40) an outside alignment roll (44) is used, which is preferably placed at the proximity of an inside tensioning roll (43) or a corresponding glide shoe (70) of the glide belt (40), and that said alignment roll (44), or a corresponding alignment member consisting of a number of component rolls, is provided with a resilient coating (44a) or equivalent. Extended-nip press as claimed in any of the claims 1 to 9, characterized in that the press felt (50) of the extended-nip press is guided into contact with the glide belt (40) and that, in the press, the counter-member is a smooth-faced (11') press roll or that, in a two-felt press section, the web (W) is passed through the extended press zone (S) between two felts (50,60), in which case the counter-roll (10) is a hollow-faced (11a), preferably variable-crown, roll (Fig. 6). Extended-nip press as claimed in any of the claims 1 to 10, characterized in that the press is a single-felt press and comprises a smooth-faced (11'), preferably variable-crown (13,13a, 14), counter-roll (10), and that, in order to intensify the pressing result, in connection with said roll an induction and/or IR-heater is fitted and/or that the web to be pressed and/or the press felt (50,60) are arranged to be heated by means of a steam box (55), an IR-heater, and/or by means of a high-frequency heater.

Inventors: LAAPOTTI, JORMA
Applicants: VALMET PAPER MACHINERY INC.
Application year: 1990
Main classification: D21F3
IPC codes: D21F3