METHOD AND DEVICE FOR CALENDERING PAPER, COMPRISING A HEATABLE ROLL

Abstract: A method and a device for calendering paper in a calender which comprises at least one calender unit (10; 110) in which a first calendering nip (N1; N3) is formed between a heatable calender roll (16; 116) and an extended-nip roll (12; 112), which nip is an extended nip, through which a paper web (W) is guided to run in order to calender the paper on at least one side. In the calender unit (10; 110), a second calendering nip (N2; N4) is formed with the heatable calender roll (16; 116) and a third calender roll (17; 117), which nip is a roll nip, and the paper web (W) is guided to run through said roll nip (N2; N4) such that, in both calendering nips (N1, N3; N2, N4), the same side of the paper web (W) is in contact with the heatable calender roll (16; 116).

Description: METHOD AND DEVICE FOR CALENDERING PAPER, COMPRISING A HEATABLE ROLL The invention relates to a method for calendering paper in a calender which comprises at least one calender unit in which a first calendering nip is formed between a heatable calender roll and an extended-nip roll, which nip is an extended nip, through which a paper web is guided to run in order to calender the paper on at least one side. The invention also relates to a calender which comprises at least one calender unit which includes a calender frame and a heatable calender roll and an extended-nip roll mounted in the frame, which rolls form with each other a first calendering nip, which is an extended nip, through which a paper web is guided to run in order to calender the paper on at least one side. When the standard of calendering of a paper web is improved, with the conventional solutions, in actual fact, the only possibility in supercalenders has been to increase the number of calendering nips. This has resulted in a more complicated construction of the calender and in more difficult control and tail threading of the paper web. In the case of on-line machines in particular, it must be possible to solve the contradictions arising from high running speed and from threading at full speed. Attempts have been made to solve these problems, among other things, by means of various belt and shoe calenders by which the calendering nip is extended and, thus, the operation of the nip is made more efficient. Belt calenders have been described previously, among other things, in Finnish patents 95 061, 102 304 and 102 305. Technology relating to shoe calenders has in turn been described, for example, in DE publication 43 44 165 and US patent 5 163 364. Belt and shoe calenders, or more generally extended-nip calendering, provide a gloss that corresponds to that of a supercalendered quality or is at least fairly close to the gloss achieved by means of supercalendering, but it is difficult to achieve corresponding smoothness. The maximum pressure in the nip of a belt and a shoe calender remains, because of a wider nip, lower than in conventional nips formed between two rolls, for which reason extended-nip calenders are most suitable for paper grades in which bulk preservation is of high significance. Extended-nip calendering has been found to be particularly good in calendering of low-gloss (under 40 % Hunter) paper grades. If clearly higher gloss is desired and required, the nip pressure provided by an extended-nip calender is not in itself sufficient to form gloss. The aim of the present invention is to provide a new method and a new calender, by which method and calender the drawbacks associated with the state of the art are avoided and which method and device provide an improved calendering result with respect to the prior art. With a view to achieving this aim, the method according to the invention is mainly characterized in that, in the calender unit, a second calendering nip is formed with the heatable calender roll and a third calender roll, which nip is a roll nip, and the paper web is guided to run through said roll nip such that, in both calendering nips, the same side of the paper web is in contact with the heatable calender roll. The calender according to the invention is in turn mainly characterized in that a third calender roll has been fitted in the calender unit, which roll forms a second calendering nip with the heatable calender roll, which nip is a roll nip, in which connection the paper web is guided to run through said roll nip such that, in both calendering nips, the same side of the paper web is in contact with the heatable calender roll. The second calendering nip, or the roll nip, is formed in the calender unit on the side of the heatable calender roll opposite to the extended nip. The third calender roll, by means of which the second calendering nip is formed, is advantageously a deflection- compensated roll. Said third calender roll may be provided with a soft roll cover depending on the demands of the calendering process, in which connection the second calendering nip is a soft nip, or said roll may be a hard-surface calender roll, in which connection the second calendering nip is a hard nip. The invention provides a number of advantages over the prior art and of these advantages, for example, the following can be stated in this connection. The properties of an extended-nip calender and a conventional calender provided with a roll nip have been combined in the invention, with the result that, in particular when an extended and low-pressure nip is used as the first nip of the calender, such an extended and low-pressure nip makes it possible to heat, plasticize and suitably mould the paper before the subsequent roll nip. By this means, bulk of the paper can be preserved without compromising other quality characteristics. At the standard gloss level, a bulk saving of even about 7 % can be achieved as compared with conventional supercalendering. The achieved benefit is based on longer nip dwell time and on higher calendering temperatures. The calendering process is usually a rather "violent" operation towards the paper, but especially when a calendering nip extended in the manner according to the invention is used as the first nip of the calender in particular, it does not put so great stress on the paper as conventional roll nips, with the result that the structure of the paper does not suffer in calendering. The strength properties of the paper can be kept good. The arrangement according to the invention provides more forces parallel to the paper surface and, by the action of these forces parallel to the surface as well as by the action of plasticization of the web, the smoothness of the calendered paper also becomes better than that of the conventional standard. When compared with today ' s soft calendering in particular, improved microroughness and higher gloss in addition to bulk preservation can be considered to be benefits of the invention. In accordance with the invention, the calendering can also be performed such that a roll nip is used as the first nip and an extended nip is used only after it, if the process so requires. It is, of course, also possible to use the calender such that only one nip, either the extended nip or the soft nip, is in use. The caliper profiling of the web is, however, performed by means of the roll nip. The other advantages and characteristic features of the invention come out from the following detailed description of the invention. A further very fine advantage is also provided by the fact that replacement of the extended-nip roll is easy to accomplish in the calender because of the structure of the calender. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic side view of an embodiment of the calender according to the invention intended in particular for two-sided calendering. Figure 2 is a schematic side view of another embodiment of the calender intended for two-sided calendering. Figure 3 shows the calender of Fig. 2 in which the run of the web has been turned such that the side of the web opposite to that of Fig. 2 is calendered first. Figure 4 shows one calender unit of the calender shown in Figs. 2 and 3 with the nips opened for replacement of the extended-nip roll. The calender shown in Fig. 1 comprises two calender units 10, 110, which have been arranged one after the other with respect to the running direction of a paper web W. The calender comprising the two calender units 10, 110 shown in Fig. 1 is used in the case where the paper web W is calendered on both sides. Typically, papers of this kind to be calendered on both sides are, for example, fine papers intended for offset printing. Of course, the invention can also be applied to one-sided calendering of the paper web W, in which connection only one of the calender units shown in Fig. 1 is needed. Typically, papers of this kind to be calendered only on one side are, for example, label papers. The first calender unit 10 comprises a calender frame 11 in which an extended-nip roll 12, a heatable calender roll, i.e. a so-called thermo roll 16, and a third calender roll 17 have been fitted to form a stack. Said rolls 12, 16, 17 form with one another calendering nips N l 5 N 2 , of which the nip Nj between the extended-nip roll 12 and the heatable calender roll 16 is an extended nip and, in a corresponding way, the nip N 2 between the heatable calender roll 16 and the third calender roll 17 is a roll nip. In the illustration shown in Fig. 1 , the extended-nip roll 12 comprises a roll support 13, a belt shell 14 disposed on it, as well as a loading shoe 15 by means of which the belt shell 14 is loaded against the heatable calender roll 16 to form the extended nip Nj. The third calender roll 17 can be, as shown in the figure, a so-called soft roll which is provided with a soft roll cover 18, especially with a polymer cover. In this kind of case, the roll nip N 2 between the heatable calender roll 16 and the third calender roll 17 is a soft nip. On the other hand, if the paper that is being calendered so demands, the third calender roll 17 may be without a soft polymer cover so that the third calender roll 17 is a hard roll, in which connection the roll nip N 2 is also a hard nip. In the illustration of Fig. 1, the paper web W is passed, while guided by a spreader roll 20, first into the extended nip Nj of the calender unit 10. From the extended nip N] the paper web W is passed by means of a take-out roll 21 and a spreader roll 22 into the roll nip N 2 . From the second nip of the first calender unit 10, i.e. from the roll nip N 2 , the paper web W is passed, in the illustration of the figure, by means of guide and alignment rolls 23 - 27 to the second calender unit 110 of the calender. If the paper web W needs to be calendered only on one side, it is, of course, not passed to the second calender unit 110, but the paper web W can be passed after the second nip, i.e. the roll nip N 2 of the first calender unit 10 directly to further processing, for example, to a reel-up. As already stated above, the calender shown in Fig. 1 of the drawing also includes the second calender unit 110, the structure and the operation of which are similar to those of the first calender unit 10. Thus, in Fig. 1 , the frame of the second calender unit has been denoted by the reference numeral 111, the extended-nip roll fitted in the frame by the reference numeral 112, the heatable roll by the reference numeral 116, and the third calender roll by the reference numeral 117. Similarly to the first calender unit 10, the extended-nip roll 112 in the second calender unit 110 also comprises a roll support 113, a belt shell 114 disposed on the support, as well as a loading shoe 115 by means of which the belt shell 114 is loaded against the heatable calender roll 116 to form the first nip of the second calender unit 110, i.e. an extended nip N 3 . Further, similarly to the first calender unit 10, the third calender roll 117 forms with the heatable roll 116 the second nip of the calender unit, i.e. a roll nip N 4 . In this calender unit too, the third calender roll 117 may be a soft-surface roll provided with a soft roll cover, in particular with a polymer cover 118, but instead of this it is also possible to use a hard roll when the process so demands. As shown in Fig. 1 , the paper web W is passed, while guided by the guide and alignment rolls already previously mentioned as well as by a guide roll 119 and a spreader roll 120, from the first calender unit 10 into the first nip of the second calender unit 110, i.e. into the extended nip N 3 . From this extended nip N 3 the paper web W is passed, in the embodiment of Fig. 1 , by means of a take-out roll 121 and a spreader roll 122 into the second nip of the calender unit, i.e. into the roll nip N 4 . From the roll nip N 4 , the paper web W is passed to further processing, for example, to a reel-up. In the embodiment shown in Fig. 1, the paper web W is thus calendered on both sides, first by the extended nip N,, N 3 and after that by the roll nip N 2 , N 4 , which roll nip may be either a soft or a hard nip. Further, as described above, a considerable saving of bulk is achieved by using the extended nip N,, N 3 as compared, for example, with traditional supercalendering, and the calendering effect is enhanced by the roll nip N 2 , N 4 in order to provide sufficient gloss. The caliper profiling of the paper web is performed by means of the roll nip. The calendering can also be accomplished first by means of the roll nip N 2 , N 4 and only after that by means of the extended nip N, , N 3 , if the process demands this. In that connection, the run of the paper web W is opposite to that shown in the figure. With the calender shown in Figs. 2 and 3, calendering is performed just in the manner last described so that, at the first stage, calendering is performed by means of a roll nip and only after that by means of an extended nip. In the arrangements of Figs. 2 and 3, the paper web W is calendered on both sides, as also in the embodiment of Fig. 1 , and for this reason the calender shown in Figs. 2 and 3 comprises two calender units arranged one after the other, which units are generally denoted by the reference numerals 30 and 130. Thus, one side of the paper web W is calendered with the first calender unit 30 and the opposite side of the web is calendered with the second calender unit. However, as in the case of Fig. 1 , in this embodiment it is also possible to calender the paper web only on one side, in which connection only one calender unit 30 or 130 is needed for calendering. The illustrations of Figs. 2 and 3 differ from each other only as to from which side of the web W the calendering is started, and for this reason the structure of the calender is described more closely only in connection with Fig. 2, while with regard to Fig. 3 only the differences with respect to Fig. 2 are described. Thus, in the embodiment of Fig. 2, the calender comprises two calender units 30, 130 arranged one after the other, which both comprise an extended-nip roll 32, 132, a heatable calender roll, i.e. a thermo roll 36, 136, as well as a third calender roll 37, 137 mounted in a frame 31 , 131 of the calender to form a stack, which rolls form with one another calendering nips N,, N 2 and N 3 , N 4 . A roll nip N 2 is formed between the thermo roll 36, 136 and the third calender roll 37, 137 and, in a corresponding way, an extended nip N 1 ; N 3 is formed between the extended-nip roll 32, 132 and the thermo roll 36, 136. The arrangement of the rolls is advantageously just as shown in Fig. 2, i.e. the third calender roll 37, 137 is in the upper position, the thermo roll 36, 136 is the centre roll of the calender unit, and the extended-nip roll 32, 132 functions as the bottom roll. Most advantageously, the third calender roll 37, 137, i.e. the top roll, is a deflection-compensated roll, in which connection the caliper profile of paper can be corrected by means of the upper nip N 2 , N 4 . Further, when the arrangement is as shown in the figures, i.e. the rolls 32, 36, 37; 132, 136, 137 have been arranged on the same nip plane such that the top roll 37, 137 and the extended-nip roll 32, 132 are situated on the opposite sides of the thermo roll, the thermo roll 36, 136 situated in the middle can be supported by the upper nip N 2 , N 4 at the same time, in which connection by means of the extended-nip roll 32, 132 situated on the lowest level it is possible to apply a higher linear load to the thermo roll 36, 136 of the size in question. Advantageously, the top roll, or the third calender roll 37, 137, is provided with a soft roll cover, as already described in connection with Fig. 1. However, if the calendering process demands it, a hard roll can be used as the top roll. The rolls 32, 36, 37; 132, 136, 137 have been mounted in both calender units 30, 130 on support of bearing housings, from which they have been attached to one another by means of long attachment bolts 58, 158, in which connection the nip forces are mainly not transmitted at all outside the bearing housings to the frame structures 31 , 131 and the foundation of the calender. In Fig. 2, the bearing housings of the top roll, i.e. the third calender roll 37, 137, have been denoted by the reference signs 37a, 137a, the bearing housings of the thermo roll 36, 136 by the reference signs 36a, 136a, and the bearing housings of the extended-nip roll 32, 132 by the reference signs 32a, 33; 132a, 133. Thus, the bearing housings of the extended-nip roll 32, 132 are formed of two parts comprising an outer housing 32a, 132a and, inside it, an inner housing 33, 133 which has been movably fitted in the outer housing. Usually, in calender arrangements of this type there is a need to use high temperatures of the thermo roll 36, 136, in which connection the rolls are large because of sufficient heat transfer capacity and, for this reason, the unequalsidedness of loading may also be great. With the extended-nip roll 32, 132 it is possible to load even about 400 kN/m more than with the top roll. The construction shown in the figures, that is, placing the extended- nip roll 32, 132 in the bottom position in the calender is mainly due to safety reasons, but from the point of view of operation it is also possible to use an extended-nip roll in the upper position. As shown in Figs. 2 and 3, the paper web W is passed first into the upper nip N 2 of the first calender unit 30 formed between the top roll 37 and the thermo roll 36. The upper nip N 2 is thus a roll nip. In the illustration of Fig. 2, the web W is passed into the roll nip N 2 as guided by a guide roll 40 and a spreader roll 41 such that the top side of the web W is placed first against the thermo roll 36. From the roll nip N 2 the web W is passed by means of a take-out roll 42 and a spreader roll 43 into the extended nip N . From the extended nip Nj of the first calender unit 30 the web W is passed to the second calender unit 130, in which it is passed, while guided by a spreader roll 141, into the roll nip N 4 , which is formed between the top roll 137 and the thermo roll 136. As shown by Fig. 2, the side of the web W placed against the thermo roll 136 in the second calender unit 130 is opposite to that placed against the thermo roll in the first calender unit 30. From the upper nip N 4 the web W is passed further, while guided by a guide roll 142 and a spreader roll 143, into the extended nip N 3 between the thermo roll 136 and the extended-nip roll 132. Finally, the web W is taken out of the extended-nip N 3 and passed to further processing while guided by guide rolls 144, 145. The illustration of Fig. 3 differs from Fig. 2 only in that in this embodiment the web W is passed into the upper nip N 2 between the top roll 37 and the thermo roll 36 in the first calender unit 30 while guided by a spreader roll 41 such that the bottom side of the web W is placed first against the thermo roll 36. From the upper nip N 2 , which is thus a roll nip, the web W is passed by means of a take-out roll 42 and a spreader roll 43 into the extended nip N, formed by the thermo roll 36 and the extended-nip roll 32, from which nip the web W is passed further by means of a take-out roll 44 and guide rolls 45, 46 to the second calender unit 130. In the second calender unit 130, the web W is passed first by means of a spreader roll 141 into the extended nip N 3 between the thermo roll 136 and the extended-nip roll 132, and therefrom further by means of a take-out roll 142 and a spreader roll 143 into the roll nip N 4 between the thermo roll 136 and the top roll 137, and therefrom further by means of a take-out or guide roll 144 for further processing. The upper nip N 2 , N 4 is loaded by the movement of the shell of the top roll 37, 137 and the opening of the nip is accomplished solely by the movement of the shell. The lower nip, or the extended nip N N 3 , is loaded by the movement of the loading elements (not shown in the figures) of the bottom roll (extended-nip roll 32, 132), but the rather large opening of the nip required by the extended-nip roll 32, 132 of today's construction is provided by means of cylinders 54, 154 fitted inside the outer housing 32a, 132a, by which cylinders the extended-nip roll 32, 132 is lifted from the inner housing 33, 133 (support) against the bearing housing 36a, 136a of the thermo roll 36, 136. The lifting movement is guided by means of guide pieces 51, 151 fitted in the outer housing 32a, 132a of the extended-nip roll and disposed between the outer housing and the inner housing as well as by means of guide pins 59, 159. The outer housing 32a, 132a of the bearing housing of the extended-nip roll 32, 132 is fitted with movable support pieces 52, 152 as well as with horizontal cylinders 53, 153, by which said support pieces are moved. When the inner housing 33, 133 of the extended-nip roll and the bearing housing 36a, 136a of the thermo roll are together and in contact with each other, the support pieces 52, 152 are pushed under the inner housing 33, 133 by means of said horizontal cylinders 53, 153, and the inner housing is lowered so as to rest on the support pieces, in which connection loads will not be carried by the lower cylinders 54, 154 but the lower cylinders will carry only the weight of the extended-nip roll. When the extended-nip roll is lowered such that the inner housing 33, 133 will rest on the support pieces 52, 152, a small clearance (of the order of about 1 mm) remains between the inner housing and the bearing housing 36a, 136a of the thermo roll. However, such a clearance is not harmful from the point of view of operation, because the extended nip N,, N 3 is run only with high linear loads, as already explained above. The belt shell 34, 134 of the extended-nip roll 32, 132 can be replaced without detaching the roll from the machine. For replacement of the belt shell 34, 134, the inner housing 33, 133 is in its lower position, in which connection there remains a gap between the inner housing and the outer housing 32a, 132a, from which gap the replacement of the belt shell 34, 134 can be carried out. For the replacement, only the guide pieces 51, 151 have to be detached. The situation where the inner housing is in its lower position is shown in Fig. 4. Replacement of the entire extended-nip roll 32 is illustrated by means of Fig. 4, and it is accomplished in the following way. The extended-nip roll 32 is lowered to the lower position for replacement of the roll. The long attachment bolts 58 are loosened and turned to the side as shown in Fig. 4. The top roll 37 is lifted up for about 200 mm and, in this raised position, the bearing housings 37a of the top roll are fastened to side posts of the calender frame 31 such that the top roll hangs from its bearing housings 37a on support of the side posts. The centre roll, or the thermo roll 36, is lifted up, for example, for about half of the lifting distance of the top roll 37 (for example, about 100 mm) and the thermo roll is fastened from its bearing housings 36a to the side posts of the calender frame 31. In the calender frame 31 , under the outer housing 32a of the bearing arrangement of the extended-nip roll 32, there is a lifting cylinder 55 by means of which the outer housing can be raised relative to the frame. In the normal operating position, there are wedges (not shown) between the outer housing 32a and the frame 31, on support of which wedges the outer housing rests on the frame 31. In the calender frame 31 there are rails 57 extending in the axial direction of the rolls, and the outer housing 32a is provided with wheels 56 which, when the calender is in the operating position, have been lifted up such that they do not participate in carrying load. For replacement of the roll, the outer housing 32a is raised by the lifting cylinder 55 such that it lifts out of support of the wedges. The wheels 56 provided in the outer housing 32a are locked in the lower position by disposing intermediate pieces (not shown) above the wheels, after which it is possible to make a lowering movement by means of the lifting cylinder 55 such that the wheels 56 of the outer housing will be on the rails 57 and the outer housing rests on its wheels 56 on support of the rails 57. After that, the roll 32 can be pulled out along the rails 57. The roll is lifted by means of a hall crane such that the outer housing remains on the rails and the inner housing comes out with the roll. The fitting of the roll in place is performed in reverse order. The top roll 37 of the calender unit 30 is replaced directly upwards by means of a hall crane. The centre roll, or the thermo roll 36, is replaced directly upwards by means of the hall crane after the top roll 37 has been first taken away. Above, the invention has been described by way of example with reference to the figure in the accompanying drawing. However, the invention is not exclusively confined to the example shown in the figure, but the different embodiments of the invention may vary within the inventive idea defined in the accompanying claims.

Claims: Claims 1. A method for calendering paper in a calender which comprises at least one calender unit (10, 110; 30, 130) in which a first calendering nip (N t ; N 3 ) is formed between a heatable calender roll (16, 116; 36, 136) and an extended-nip roll (12, 112; 32, 132), which nip is an extended nip, through which a paper web (W) is guided to run in order to calender the paper on at least one side, characterized in that, in the calender unit (10, 110; 30, 130), a second calendering nip (N 2 ; N 4 ) is formed with the heatable calender roll (16, 116; 36, 136) and a third calender roll (17, 117; 37, 137), which nip is a roll nip, and the paper web (W) is guided to run through said roll nip (N 2 ; N 4 ) such that, in both calendering nips (N,, N 3 ; N 2 , N 4 ), the same side of the paper web (W) is in contact with the heatable calender roll (16, 116; 36, 136). 2. A method according to claim 1, characterized in that the second calendering nip (N 2 ; N 4 ) is formed on the side of the heatable calender roll (16, 116; 36, 136) opposite to the extended nip (N^ N 3 ). 3. A method according to claim 1 , characterized in that the second calendering nip (N 2 ; N 4 ) is formed by means of a deflection-compensated roll (17, 117; 37, 137) with the heatable calender roll (16, 116; 36, 136). 4. A method according to claim 1 , characterized in that the second calendering nip (N 2 ; N 4 ) is formed between a calender roll (17; 117) provided with a soft roll cover (18; 118) and the heatable calender roll (16, 116; 36, 136) such that said second calendering nip (N 2 ; N 4 ) is a soft nip. 5. A method according to claim 1 , characterized in that the second calendering nip (N 2 ; N 4 ) is formed between a hard-surface calender roll (17, 117; 37, 137) and the heatable calender roll (16, 116; 36, 136) such that said second calendering nip (N 2 ; N 4 ) is a hard nip. 6. A method according to any one of the preceding claims, characterized in that the paper web (W) is calendered in the calender unit (10, 110; 30, 130) first by means of the first calendering nip (N,; N 3 ) , i.e. an extended nip, and after that by means of the second calendering nip (N 2 ; N 4 ), i.e. a roll nip, and that, between the calendering nips, the paper web (W) is taken out of contact with the surface of the heatable calender roll (16, 116; 36, 136). 7. A method according to any one of claims 1 to 5, characterized in that the paper web (W) is calendered in the calender unit (10, 110; 30, 130) first by means of the second calendering nip (N 2 ; N 4 ) , i.e. a roll nip, and after that by means of the first calendering nip (N,; N 3 ), i.e. an extended nip, and that, between the calendering nips, the paper web (W) is taken out of contact with the surface of the heatable calender roll (16, 116; 36, 136). 8. A method according to any one of the preceding claims, characterized in that, in the calendering unit (10, 110; 30, 130), caliper profiling of the paper web (W) is performed by means of the roll nip (N 2 ; N 4 ). 9. A method according to any one of the preceding claims, characterized in that, in the calender, the paper web (W) is passed through two successive calender units (10, 110; 30, 130), between which the paper web (W) is turned such that, in the successive calender units, a different side of the paper web comes into contact with the heatable calender roll (16, 116; 36, 136) in order to calender the paper web (W) on two sides. 10. A calender which comprises at least one calender unit (10, 110; 30, 130) which includes a calender frame (11, 111; 31 , 131) and a heatable calender roll (16, 116; 36. 136) and an extended-nip roll (12, 112; 32, 132) mounted in the frame, which rolls form with each other a first calendering nip (N^ N 3 ), which is an extended nip, through which a paper web (W) is guided to run in order to calender the paper on at least one side, characterized in that a third calender roll (17, 117; 37, 137) has been fitted in the calender unit (10, 110; 30, 130), which roll forms a second calendering nip (N 2 ; N 4 ) with the heatable calender roll (16, 116; 36, 136), which nip is a roll nip, in which connection the paper web (W) is guided to run through said roll nip (N 2 ; N 4 ) such that, in both calendering nips (N l 5 N 3 ; N 2 , N 4 ), the same side of the paper web (W) is in contact with the heatable calender roll (16, 116; 36, 136). 11. A calender according to claim 10, characterized in that the third calender roll (17, 117; 37, 137) has been fitted on the side of the heatable calender roll (16, 116; 36, 136) opposite to the extended-nip roll (12, 112; 32, 132). 12. A calender according to claim 10, characterized in that the third calender roll (17, 117; 37, 137) is a deflection-compensated roll. 13. A calender according to claim 10, characterized in that the third calender roll (17, 117; 37, 137) is provided with a soft roll cover (18; 118) such that the calendering nip (N 2 ; N 4 ) between said third calender roll (17, 117; 37, 137) and the heatable calender roll (16, 116; 36, 136) is a soft nip. 14. A calender according to claim 13, characterized in that the roll cover (18; 118) of the third calender roll (17, 117; 37, 137) is a polymer cover. 15. A calender according to claim 10, characterized in that the third calender roll (17, 117; 37, 137) is a hard-surface calender roll such that the calendering nip (N 2 ; N 4 ) between said third calender roll (17, 117; 37, 137) and the heatable calender roll (16, 116; 36, 136) is a hard nip. 16. A calender according to any one of claims 10 to 15, characterized in that, in the calender unit (10, 110; 30, 130), the paper web (W) has been arranged to run first into the first calendering nip (Nf, N 3 ), i.e. an extended nip, after which the paper web (W) is guided out of contact with the surface of the heatable calender roll (16, 116; 36, 136), and after that into the second calendering nip (N 2 ; N 4 ), i.e. a roll nip. 17. A calender according to any one of claims 10 to 15, characterized in that, in the calender unit (10, 110; 30, 130), the paper web (W) has been arranged to run first into the second calendering nip (N 2 ; N 4 ), i.e. a roll nip, after which the paper web (W) is guided out of contact with the surface of the heatable calender roll (16, 116; 36, 136), and after that into the first calendering nip (N^ N 3 ), i.e. an extended nip. 18. A calender according to any one of claims 10 to 17, characterized in that the calender unit (10, 110; 30, 130) is provided with means for performing the caliper profiling of the paper web (W) by means of the roll nip (N 2 ; N 4 ). 19. A calender according to any one of claims 10 to 18, characterized in that the calender comprises two successive calender units (10, 110; 30, 130), through which the paper web (W) is passed so turned that, in the successive calender units, a different side of the paper web comes into contact with the heatable calender roll (16, 116; 36, 136) in order to calender the paper web (W) on two sides.

Inventors: KAARAKKA HEIKKI, LARES MATTI, PALONEN SEPPO, TIISTOLA VILLE, TORVI TIMO, KAARAKKA, HEIKKI, LARES, MATTI, PALONEN, SEPPO, TIISTOLA, VILLE, TORVI, TIMO
Applicants: KAARAKKA HEIKKI, LARES MATTI, METSO PAPER INC, PALONEN SEPPO, TIISTOLA VILLE, TORVI TIMO, KAARAKKA, HEIKKI, LARES, MATTI, METSO PAPER, INC., PALONEN, SEPPO, TIISTOLA, VILLE, TORVI, TIMO
Application year: 2001
Main classification: D21G1
IPC codes: D21G1