The invention relates to a method according to the preamble of claim 1.

As known in the prior art, the nip of a soft calender is formed of at least one roll with a soft cover and of a heatable hard roll. There exist also applications in which a soft calender is formed of two rolls with soft covers. Soft calenders usually comprise either one calendering nip or several calenderinag nips one aRer the other. In connection with replacement of a roll in calendes, the calender must be stopped, which means that costly running time and production are lost.

It is an object of the invention to provide a method for replacing a roll in a calender, which method, when applied, enables production also during roll replacement.

In view of the above-noted object, the invention is mainly characterized in that which is stated in the characterizing part of claim 1.

In accordance with the invention when a roll/rolls in a calender, in particular in a soft calender, is/are replaced, the web is run through the calender with the nip open and by means of a roll situated before or after the nip, for example, by means of an alignment or a spreader roll the web is pressed or lifted into contact with the calender nip roll which is not replaced or the web is moved out of contact with the surface of the roll, in which connection a paper web can be passed through the calender-without a shutdown, for example, for purposes in which it is not required that the paper web is calendered in the calendering nip in question.

When the method according to the invention is applied, no production is lost during replacement of a roll in a calender because the rolls are replaced during ruining and the uncalendered web is used for another suitable purpose.

When the calender is operated with the nip open, the web shall be well supported and the free draws shall be preferably as short as possible in order that the web shall not flutter to avoid web breaks. Thus, in accordance with the invention, an alignment/spreader roll situated before a calendering nip or an alignment/spreader roll situated after it or both is/are displaced such that the web runs only via the roll not to be replaced. Moreover, in accordance with an advantageous feature of the invention the alignment roll is placed as close to the calender as possible.

The invention can be applied both in on-line calenders and in off-line calenders.

The invention is particularly suitable for use in connection with soft calenders with one nip and with two nips.

In the following, the invention is applied in more detail with reference to the figures in the appended drawing, to the details of which the invention is, however, not intended to be narrowly confined.

Figures 1A-1C schematically show one application of the method according to the invention.

Figures 2A-21) schematically show one application of the invention.

In the situation shown in Fig. I A there is a normal running situation in which a web W is run through a calendeming nip N formed by rolls 11 and 12. An alignment or a spreader roll 17 has been positioned before the calendering nip N and another alignment or spreader roll 14 has been positioned after the nip N. The running direction of the web has been denoted with reference arrow S.

In the stage shown in Fig. 1B there is replacement of the lower roll 11 of the calendering nip N, in which connection the calendering nip N has been opened and the alignment/spreader roll 17 situated before the calendering nip N has been displaced to an upper position as shown by arrow S 17, so that the web W runs via the upper roll 12 not to be replaced.

Fig. 1 C schematically shows a situation in which replacement of the upper roll is earned out, ;. in which connection the calendering nip N has been opened and the alignment/spreader roll 14 placed after the calendering nip has been displaced downwards as shown by arrow S 14, so that the web W runs via the lower roll 11 not to be replaced.

Thus, in the applications illustrated in Figs. IB and 1C, the calender nip N is opened by means of actuators known in themselves, which actuators can also be used, for example, to open the nip N in threading and web break situations, and the alignment/spreader roll 14, 17 is displaced by means of an actuator, for example, a pneumatic motor, to a position for replacement of a calender roll such that the web W is arranged to ran via the calender roll not to be replaced and the calender roll to be replaced is moved out of its place and a new roll is brought to its place.

In the application shown in Fig. 2A, a web W nms through a nip N without any contact with rolls 21, 22. In this calender, the nip gap is narrow and the web W is well supported and free draws, i. e. the distance between the calendering nip N and a roll 17, 14 provided before/after the nip has been made as short as possible in order that the web shall not nutter, hi this application, the alignment roll 24 after the calender has been positioned so close to the calender as possible. The length of the free draw is 0.5-4 m, preferably 1. 3-2 m.

In the situation shown in Fig. 2B, : (or the purpose of replacing the upper roll 22, the stopped rolls 21, 22 of the calender have been separated from each other by

detaching screws 23 which attach them, and the upper roll 22 has been lifted by a crane (not shown) on support of a frame post SO so as to be hanging therefrom without uncoupling drives, hoses and cables. The web W has been passed to run via the lower roll 21. It is also possible to replace the upper roll 22 directly, in which connection no support stage on the frame post is needed.

In Fig. 2C, the web W has been lifted up so as to run via the upper roll 22 by means of the alignment roll 24 situated after the calender, said alignment roll being provided with a displacement apparatus 30 comprising, for example, a lever 31 and synchronized gears 32 or guides and synchronized gears, by means of which both ends of the alignment roll 24 can be lifted simultaneously and to an equal extent sufficiently accurately and slowly so that the web W remains under control. When the web W has been lifted high enough, the lower roll 21 is lifted by means of a jack provided in transfer carriages 25 so that the lower roll 21 is lifted out of contact with wedges.

Fig. 2D shows a situation in which the lower roll 21 is pulled to the aisle by means of the transfer carnages 25, wherefrom it can be talcen away by means of a hall crane.

Rolls are put in place in an order opposite to that described in connection with Figs. 2B and 2C.

Above, the invention has been described with reference to some of its preferred applications only, to the details of which the invention is not by any means intended to be narrowly confined.