The invention concerns a multi-nip calender in accordance with the preamble to Claim 1.

In state-of-the-art multi-nip calenders equipped with a single set of rolls, there has been no method with which to implement a separate soft/soft-matt nip independ- ently of the other roll set and with sufficient line loads. As is known in the state of the art, solutions have been attempted by over-dimensioning the calender's idle rolls, whereby it has been possible to raise the line load for matt grades (hard/soft nip), however, not sufficiently so. With the over-dimensioning of idle rolls, roll costs in deliveries have increased due to the larger diameters, and thus in multi- nip calenders of the state-of-the-art type it has not been possible to arrange any matt nip.

One objective of the invention is therefore to present a solution to the shortcom- ings mentioned above.

Known in the state of the art is a multi-nip calender, which comprises two sepa- rate roll sets, wherein the rolls are stacked on top of each other to form roll stacks.

One roll set is usually a roll set formed by several, usually at least three, rolls, and the other roll set generally comprises at least two rolls, preferably two standby rolls. One such arrangement is presented in FI Utility Model Registration 4460, wherein a calender is described having at least two separate groups of calender rolls located in the same frame, besides which the calender has varying routes to guide the web's leading roll's paper web to be calendered in such a way that at least one group can be passed by. One of the groups is a calender roll stack with at least five rolls and the other group is a group formed by one couple of rolls, and the top and bottom rolls of the mentioned at least five-roll calender roll stack are

variable crown rolls similar to one another and they are similar to the rolls of the roll couple.

The invention aims at presenting a multi-nip calender, which makes more versa- tile than before the multi-nip calender with two roll sets, for example, a calender of the type presented above, whereby it can be used for running different varia- tions.

The invention also aims at presenting a multi-nip calender, which is suitable for use both in connection with re-building of calenders and in connection with new calender investments.

In order to achieve the above-mentioned objectives and those emerging hereinaf- ter, the multi-nip calender according to the invention is mainly characterised by the features presented in the characterising part of Claim 1.

According to the basic idea of the invention, a multi-nip calender formed by two separate roll sets can first be provided so that it consists of a multi-nip set of rolls as one set of rolls and of a standby set of rolls formed by at least two, preferably two or three rolls, as the second set of rolls. According to the invention, the calen- dering method and arrangement of the type described above is made cost-effective in such a way that by utilising standby rolls it is possible in the main direction of travel of the web to arrange a separate matt nip in the first roll set, and by moving one roll or more rolls from the second roll set to the first roll set, whereby the two multi-nip roll sets of the calender can be used for different grades. In this way the invention makes possible a cost-effective solution, for example, for matt grades, because the calender's idle rolls need not be over-dimensioned for running meth- ods using a part of the nips. The invention allows modernisation of a multi-nip calender equipped with a matt nip to get a cost-effective calender having two roll sets and allowing different variations. With the aid of the invention a high capac- ity is also achieved with the calender by alternative web transfers. In the invention

it is possible to bypass rolls or roll sets and at the same time to exchange rolls of the roll set not in use.

The multi-nip calender according to the invention comprises two calender frames, which are joined together, or one frame, which makes it possible to place two roll sets therein. Thus, the calender also comprises two roll sets. In the first calender frame there are first the calender's standby rolls, preferably the two or three rolls of the calender's first roll set, for example, two standby rolls forming a matt nip, or, for example, two standby rolls and one standby thermo roll. In the first frame a releasably mounted intermediate piece is located, which is adapted to cover possi- ble places for idle rolls lacking in the roll stack in the first roll set. The second frame or the section of the frame's second roll set and the roll set are formed in such a way that the bottom-most and top-most rolls of the roll set most suitably are variable crown rolls similar to one another, and the idle rolls of the calender's roll stack comprise hard rolls, preferably thermo rolls, as well as in between them at least one roll having a soft surface.

According to the invention, when the calender is turned into a multi-nip calender having two roll sets, wherein several different grades can be run, one idle roll is removed from the second roll set in the web's main direction of travel, for exam- ple, the second idle roll, and at the same time the topmost roll/topmost rolls of the roll stack are lowered. When lowering the top roll/top rolls, an intermediate piece can be placed in the frame in the space remaining above it/them in between the frame and the top roll. The idle roll/idle rolls to be removed from the second roll set can be moved to the first roll set, and as required also more new idle rolls can be mounted therein. After the change, as the first roll set comes into constant pro- ductive use, the original standby rolls will form the rolls proper, whereby in this situation the calender must be provided with even more standby rolls as required.

In the following, the invention will be described in greater detail by referring to the figures in the appended drawing, but the intention is not to limit the invention narrowly in any manner to the details of the figures.

Figure 1 shows a multi-nip calender and Figure 2 shows the roll sets of the calen- der according to Figure 1 in one embodiment of the invention.

Figure 1 shows a calender 10, which comprises two frame parts 1,2 of the calen- der joined together and supporting the calender's rolls. In the first frame part 1 the calender's 10 first roll set 3 in the main direction of travel of web W is supported and in the second frame part 2 the second roll set 4 is supported. In the roll sets 3, 4 the calender rolls are stacked on top of each other. In the first roll set 1 there are two calender rolls 5,6 having a soft surface, for example, provided with a poly- mer surface coating, preferably standby rolls forming in between them a calender- ing nip N1. In the first roll set 3 there may be, besides the standby rolls 5,6, also other standby rolls, preferably, for example, one metal roll with a hard surface, for example, a thermo roll (not shown). In the second roll set 4 there are six calender rolls forming in between them five calendering nips N2, N3, N4, N5 and N6.

Of the calender rolls of the second calender roll set 4 the top roll (the topmost roll) 9Y is a variable crown roll, where the shape of its rotating shell is controlled by loading parts located inside the shell and supported against the fixed shaft. The roll surface is soft, for example, polymer-coated. The bottom roll 9A (the bottom- most roll) of the second calender roll set 4 has a structure similar to the top roll 9Y and it is a variable crown roll with a soft surface. The intermediate rolls 7,8 located in between the top and bottom rolls 9Y, 9A are ordinary calender rolls mounted in bearings to rotate in their supports. Some intermediate rolls 7,8 have a soft surface, for example, some rolls 8 have a polymer coating, while some are hard metal rolls 7 with a smooth surface. Of the roll set's 4 four intermediate rolls 7,8 the topmost and bottom-most calender roll 7 is a hard metal roll, preferably a heated so-called thermo roll. The most centrally located rolls 8 have a soft surface,

for example, they are rolls provided with a polymer coating, which form a so- called turning nip N4, where the web's W side to be calendered is exchanged.

Above the turning nip N4 the web W is calendered in such a way that on one side the web W is against a smooth and hard, heated roll in nips N2, N3 formed by a hard and a soft roll, while below the turning nip the opposite side of the web is against a smooth and hard, heated roll in corresponding nips N5, N6.

Figure 1 also shows different alternatives for taking the web W through the calen- der 10. According to the first alternative I, the web W is taken to the calender's second roll set 4 bypassing the first roll set 3 above and it is calendered in the nips N2, N3, N4, N5 and N6. In this situation, the calender is used as a multi-nip cal- ender, that is, it is used to perform multi-nip calendering. According to the second alternative II, the web W is guided into the first roll set 3 and it is calendered in nip NI. Whereupon the web W is guided to travel under the second roll set 4. In this situation, the calender is used as a matt calender.

According to Figure 2, a roll set formed by three rolls is changed to be the calen- der's 10 first roll set 3, of which three rolls two are preferably the calender's standby rolls 5,6 and between them is located an intermediate roll 7,8 transferred from the second roll set 4, preferably the upper intermediate roll 8 with a soft coating, or an intermediate roll/intermediate rolls from the second roll set 4 is lo- cated on top of the standby rolls 5,6. From roll set 4 a standby thermo roll may also be transferred to the first roll set 3, whereby a roll (not shown) with a soft coating remains as the standby roll. When needed, intermediate rolls 7,8 of the second roll set 4 may be transferred to the first roll set 3 as required, when the intermediate piece 11 visible in the presentation according to Figure 1 has been removed from the first frame part 1. Figure 2 shows an advantageous web trans- fer.

In the second roll set 4 there are now five rolls 9Y, 9A, 7,8 and the roll 9Y, which was earlier the topmost one, has now been lowered as has the roll 7 below it, and

an intermediate piece (not shown in the figure) is fitted in between the topmost roll 9Y and the roll body Z.

According to the invention, the initial situation may also be such that in the first roll set in the web's main direction of travel there are three rolls, the standby rolls and one standby thermo roll of the embodiment according to Figure 1, whereby the delivery contains, for example, 2 standby thermo rolls and 2 standby variable crown rolls.

In the foregoing, the invention has been described by referring only to some ap- plication examples of the invention, but the intention is not to restrict the inven- tion in any narrow manner to the details of those examples.