WO2008040842A2

WO2008040842A2 - Quick opening of a set of rolls of a multi-roll calender

Info

Publication number: WO2008040842A2
Application number: PCT/FI2007/050505
Authority: WO
Inventors: Keijo Laaksonen
Original assignee: Metso Paper, Inc.
Priority date: 2006-10-06
Filing date: 2007-09-24
Publication date: 2008-04-10
Also published as: FI20065641A0; FI121082B; CN101522988A; FI20065641A; DE112007002325T5; CN101522988B; WO2008040842A3

Abstract

This specification describes a method and an arrangement for quick-opening a set of rolls in a multi-roll calender (10), in which a paper or board web (W) to be cal- endered is passed through calendering nips (N1-N9) formed by a deflection- compensated upper roll (13), a deflection-compensated lower roll (14) and two or more intermediate rolls (15-22) arranged between the upper and lower rolls (13, 14), which rolls (13-22) are arranged as a set of rolls (12) and in which calender the intermediate rolls (15-22) are carried by hydraulic relief cylinders (155-225) for relieving nip load caused by the masses of the bearing housings (151-221) of the intermediate rolls (15-22) in question and auxiliary devices (154-224) related to them. For opening the calendering nips (N1-N9) in the quick opening of the set of rolls (12), the hydraulic load pressures of the deflection-compensated rolls (13, 14) of the set of rolls are discharged, the shell of the lower roll (14) of the set of rolls is lowered downwards, and the relief pressures of the relief cylinders (155-225) of the hydraulic relief devices of the intermediate rolls (15-22) and the load cylinders (143; 146) of the lower roll (14), which are conventional basic hydraulic cylinders without separate quick-opening cylinders, are relieved totally or partly. In the method and the arrangement, the use of both a cutting blade (230) and a cut-off blow (231) can be utilised.

Description

Quick opening of a set of rolls of a multi-roll calender

The present invention relates to the multi-roll calenders of fibre -web machines and similar types of roll machines. The invention relates to a method and an arrangement for quick-opening a set of rolls in a multi-roll calender in which a paper or board web to be calendered is passed through calendering nips formed by a deflection-compensated upper roll, a deflection-compensated lower roll and two or more intermediate rolls arranged between the upper and lower rolls, which rolls are arranged as a set of rolls and in which calender the intermediate rolls are carried by hydraulic relief cylinders for relieving nip load caused by the masses of the bearing housings of the intermediate rolls in question and auxiliary devices related to them.

Calenders require the quick opening of a set of rolls for preventing the cover damages of rolls in a situation in which a web-break occurs. Because of the break, bundles of paper, which can mark soft roll covers, are accumulated in the nip between the rolls. During the break, no fibre web passes in the nip between the rolls which would carry heat and prevent the excess heating of the soft cover of the roll adjacent the hot roll. Typically in calenders, there can be thermo rolls hot of their surface, e.g. even 250⁰C, beside polymer-coated rolls the momentary temperature resistance of which can be e.g. about 150⁰C. In a break situation, it is important to be able to perform threading as soon as possible and to make the web pass again through closed nips as soon as the set of rolls has been cleaned of foreign objects.

In the web-break situation, it is important to get the nips of the set of rolls open quickly so that quick opening starts rapidly and the nip gaps increase to adequate size rapidly. Thus, bundles of paper are not able to become thick before ending up in the area of the nips. The cutting of the web and the following cut-off blow cause such a punch to the web that it is not possible to know what kind of paper and bundles there are in each area of the set of rolls during quick opening. As known, an adequate quick opening time has been considered about 0.5 seconds which is the time from the break signal to the moment in which there are 5 -mm gaps in the nips. Said 5-mm gap in quick opening has been required on the paper rolls of supercalenders because of the problem of marking.

The set of rolls of a multi-roll calender, e.g. a supercalender or a calender of the types marketed by the applicant with the trademarks of OptiLoad, TwinLine, conventionally comprises several rolls which are arranged on top of each other as a set of rolls. The overlapping rolls are in nip contact with each other and the paper or board web or equivalent to be calendered is arranged to pass through the nips between the rolls.

The rolls are rotatably bearing-mounted into bearing housings which e.g. in supercalenders can be, for their part, fastened to base parts which are slidingly ar- ranged on vertical conduits in the calender frame. The base parts are suspended via stopper parts on lifting spindles in the calender frame the purpose of which spindles is then to function as guides for keeping the rolls of the set of rolls in a correct position. Thus, the rolls of the set of rolls are not rigidly fastened at their bearing housings in the calender frame, but the rolls are able to move in the verti- cal direction.

The masses of the bearing housings of the rolls and of the auxiliary devices fastened to them, such as fly rolls, are quite large, which caused in e.g. conventional supercalenders the considerable disadvantage of said masses causing distortions in the linear-load distributions of the nips. Because of this, multi-roll calenders, e.g. supercalenders, started to employ relief devices which were, on one hand, supported on the base parts of the rolls and, on the other hand, on the spindle nuts in the lifting spindles so that the distortions of linear-load profiles between the rolls caused by the weight of the bearing housings of the rolls and the auxiliary devices fastened to them were relieved by means of relief devices. Such an arrangement was previously disclosed, inter alia, in US patent 4901637. Also, the use of relief devices is previously known from conventional machine calenders in which attempts are made to eliminate the above-described effect of point loads caused by the bearing housings and auxiliary devices of the rolls particularly by means of hydraulic relief cylinders.

Patent specification EP 0 842 324 Bl describes a method in quick opening a set of rolls of a calender, particularly a supercalender, and a hydraulic system for the set of rolls of a calender, particularly a supercalender. The purpose of this known method and hydraulic system was to provide such a method and a system by means of which it is possible to open the nips of the set of rolls in quick opening controllably and desirably in a chosen order, most advantageously so that the nips open simultaneously in the quick opening.

A disadvantage of such quick opening is its unnecessarily expensive technique.

Furthermore, the momentary free fall of the set of rolls has caused additional indirect costs as the overdimensioning of structures, such as e.g. the stroke caused by quick opening can have required more massive foundings. When performed with quick-opening cylinders, quick opening caused by a fault situation during run can cause about double load for the foundings compared with usual load during run. In addition to the costs related to the frame of the multi-roll calender, costs were also increased by the stronger structures and possibly more expensive materials of pivots and levers used in supporting the rolls. Furthermore, the heavier dimensioning of the fly rolls has resulted in more expensive roll change tools and longer roll change time. Also, the roll change time is long due to bolting the set of rolls with more bolts.

A problem of the quick-opening chambers of the relief cylinder of multi-roll calenders known from prior art has been the breakdown of the oil removal system of the quick-opening chamber, which has been caused by the oil-removal hose of the quick-opening chamber being located outside the relief-cylinder structure, because the hose has to be located so that it enables a large arm movement. Thus, said oil- removal hose has been exposed to damages caused by external factors.

An object of the present invention is to provide a novel and inventive method for quick opening a set of rolls in a multi-roll calender, by means of which above- described problems and disadvantages related to quick opening the set of rolls of the multi-roll calender can be eliminated or at least minimised.

A further object of the present invention is to provide a novel and inventive ar- rangement for quick opening a set of rolls in a multi-roll calender, by means of which above-described problems and disadvantages related to quick opening the set of rolls of the multi-roll calender can be eliminated or at least minimised.

To achieve the above-mentioned objects and those that come out later, the method according to the invention is mainly characterised by what is presented in the characterising part of claim 1 and the arrangement according to the invention is mainly characterised by what is presented in the characterising part of claim 8.

The quick opening of a set of rolls implemented according to the invention with basic cylinders of the relief devices of a multi-roll calender and the load cylinders of the rolls without separate quick-opening cylinders provides a possibility to make more cost-effective arrangements, but still the set of rolls can be opened in about 0.5 seconds, in other words, the load of the rolls can be discharged and the opening of each nip gap can be arranged to have started in about 0.5 seconds.

The quick opening of the set of rolls of a multi-roll calender according to the invention using the basic hydraulic cylinders of the relief devices enables an easier and thus cheaper layout design, part deliveries, workshop assembly, installation and commissioning of the multi-roll calender. The other characteristic features and advantages of the present invention are depicted in the following description and dependent claims.

The invention will now be described in more detail by means of exemplifying embodiments with reference to the accompanying schematic figures.

Fig. 1 shows a side view of a multi-roll calender applying the method and arrangement according to the invention.

Fig. 2 is a partly sectional schematic side view of an alternative arrangement for moving and loading the lower roll of a multi-roll calender.

Fig. 3 shows in a schematic view the principle of alternative ways for arranging a reversing nip of a multi-roll calendar.

The quick opening of the set of rolls of a multi-roll calender, such as a multi-roll calender known with trademark Optiload, which is implemented solely with relief and load cylinders, i.e. without separate quick-opening cylinders, will be described in the following.

Fig. 1 shows a multi-roll calender 10 which comprises a calender frame 11 in which is installed a set of rolls 12 consisting of several rolls. The set of rolls 12 includes an upper roll 13, a lower roll 14 and several intermediate rolls 15-22 arranged on top of each other between the upper roll and the lower roll, which all rolls are arranged so that they are in nip contact in the running situation. Fig. 1 shows the set of rolls 12 of the multi-roll calender in the running position. In the example shown by the figure, a paper or board web W is guided via a spreader roll 133 and a fly roll 134 into an upper nip Nl and further through other nips N2-N8 of the multi-roll calender and finally out of a lower nip N9. Between the nips N1-N9, the paper or board web W is taken off the surface of the rolls by means of fly rolls 154, 164, 174, 184, 194, 204, 214, 224. As shown in Fig. 1, the fly rolls are located alternately "out- side" (fly rolls 164, 184, 204, 224) and "inside" (fly rolls 154, 174, 194, 214) of the set of rolls in relation to the calender frame 11. According to one aspect the invention, a set of rolls of a multi-roll calender 10 comprises at least one intermediate roll and/or four deflection-compensated rolls.

The upper roll 13 of the multi-roll calender in Fig. 1 is a deflection-compensated roll bearing housings 131 of which are in the embodiment of the figure fastened directly and rigidly in the multi-roll calender frame 11. The shaft of the deflection- compensated upper roll 13 is installed in said bearing housings 131 and the roll is in a normal way provided with inner load devices by means of which the deflection of the roll shell can be adjusted as desired. The upper roll 13 is a so-called soft roll and it is provided with a flexible polymer coating.

In Fig. 1, the lower roll 14 of the multi-roll calender is correspondingly a deflection- compensated roll the roll shell of which is rotatably installed on the shaft of the roll and which roll 14 is provided with inner load devices by means of which the deflection of the roll shell is adjustable as desired. The shaft of the lower roll 14 is installed in Fig. 1 in bearing housings 141 which in the embodiment of the figure are installed on load arms 144 which are pivotedly fastened by means of pivots 145 to the multi- roll calender frame 11. Between the frame 11 and the load arms 144 are installed first lower cylinders 143 by means of which the lower roll 14 can be transferred vertically. Fig. 2 shows an alternative way for moving and loading the lower roll 14 in the multi-roll calender 10, in which between the multi-roll calender frame 11 and the bearing housings 141 of the lower roll 14 are advantageously installed hydraulic second lower cylinders 146 for moving and loading the lower roll 14 in the load direction of the set of rolls 12. The loading of the nips N1-N9 of the set of rolls 12 can thus be implemented by means of the first lower cylinders 143 of Fig. 1 and, by means of the first lower cylinders 143, the set of rolls 12 can be opened when required; or alternatively the loading of the nips N1-N9 of the set of rolls 12 can be implemented by means of the second lower cylinders 146 of Fig. 2 and, by means of the second lower cylinders 146, the set of rolls 12 can be opened when required. In Fig. 2, the same reference numbers are used of the same or corresponding parts as in Fig. 1. Also load devices inside the upper roll 13 can participate in loading the nips N1-N9 of the set of rolls 12. Because of the deflection-compensated lower roll 14, it is possible to keep linear-load profiles uniform in the nips N1-N9 of the set of rolls 12. In the example of the figure, also the lower roll 14 is provided with a polymer coating corresponding the one of the upper roll 13.

In Fig. 1, the intermediate rolls 15-22 of the set of rolls 12 consist alternately of hard- and soft-surfaced rolls so that apart from the middle nip N5 of the set of rolls 12 in all other nips there are a hard-surfaced roll as the second roll and a soft- surfaced roll as the roll forming a nip with it. The middle nip N5 of the set of rolls 12 is a so-called reversing nip in which both the rolls forming the nip are soft-surfaced rolls. Thus, because the upper roll 13 of the set of rolls is a soft-surfaced roll, the upmost intermediate roll 15 is a hard-surfaced roll. Correspondingly, the second up- most intermediate roll 16 is a soft-surfaced roll provided with a flexible polymer coating and further the next i.e. the third upmost intermediate roll 17 is a hard- surfaced roll. As previously stated, the rolls 18 and 19 forming the middle nip N5 are soft rolls provided with a flexible polymer coating, whereby the next lowest roll 20 is a hard-surfaced roll. The second lowest intermediate roll 21 is a roll provided with a polymer coating and the lowest intermediate roll 22 is a hard-surfaced roll.

The schematic figure of Fig. 3 shows the principle of alternative ways for arranging a reversing nip of a multi-roll calender similar to the one described above. In the set of rolls 12 of the multi-roll calender, the reversing nip can be located in different points according to the example of Fig. 3. Fig. 3 shows soft-surfaced rolls as darkened circles and hard-surfaced rolls as delineated circles in the set of rolls 12 comprising ten rolls. In the left-hand set of rolls 12 of Fig. 3, the reversing nip is the middle nip such as in Fig. 1, i.e. using the designation of Fig. 1, the nip N5; in the middle set of rolls 12, the reversing nip is the third lowest nip, i.e. using the designa- tions of Fig. 1, the nip N7; and in the right-hand set of rolls 12, the reversing nip is the third upmost nip, i.e. using the designations of Fig. 1, the nip N3. Correspond- ingly, the reversing nip can be located in different points in sets of rolls comprising e.g. six, eight or twelve rolls.

In the multi-roll calender according to Fig. 1, bearing housings 151, 161, 171, 181, 191, 201, 211, 221 of each intermediate rolls 15-22 of the set of rolls 12 are installed in arms 152, 162, 172, 182, 192, 202, 212, 222 which are rotatably pivoted in the multi-roll calender frame 11 by axial pivots 153, 163, 173, 183, 193, 203, 213 and 223 of said rolls. The arms 152, 162, 172, 182, 192, 202, 212 and 222 are provided with relief cylinders 155, 165, 175, 185, 195, 205, 215 and 225 of the relief devices which are hydraulic cylinders which are fastened from their one end in the arms of said intermediate rolls 15-22 and from their opposite ends in the multi-roll calender frame 11. By means of the relief devices in question, it is possible to relieve loads caused by the bearing housings of the intermediate rolls 15-22 and the auxiliary devices fastened in the bearing housings. Required relief forces are of different size on different intermediate rolls 15-22, because, as already described above, the fly rolls which are fastened in the bearing housings of the intermediate rolls 15-22 are located alternately inside and outside of the nip level in relation to the multi-roll calender frame 11, whereby the load caused by them in the relief cylinders of the relief devices is of different size.

In a quick-opening situation of the set of rolls, it is possible to make the rolls 13-22 of the set of rolls break away from each other so that each of the nips N1-N9 opens or at least the load from each nip is discharged and the opening of each nip has started.

In a multi-roll calender, there can be several soft-surfaced deflection-compensated rolls in one set of rolls 12, whereby between two of such deflection-compensated rolls there can be a hard-surfaced thermo roll. In a quick-opening situation, the load of deflection-compensated rolls, such as rolls known with trademark Sym- Roll, is discharged i.e. their hydraulic pressures are decreased as described above, from which is caused a short-term delay, e.g. about 0.15 seconds, after which at least the nips in connection with the deflection-compensated rolls of the set of rolls start to open at the earliest after a web break signal.

In one set of rolls of the multi-roll calender, there can be even three sets of rolls similar to trademark OptiGloss on top of each other, whereby in each of these "sectional sets of rolls" there is a hard-surfaced thermo roll between two flexible- covered deflection-compensated rolls. Then, one to two cut-off blows can be arranged into connection with each sectional set of rolls of said OptiGloss type.

According to an embodiment of the invention, the set of rolls 12 of the multi-roll calender 10 comprises at least one cutting device known as such, such as a cutting blade 230, the location of which in Fig. 1 is chosen as an example. According to another embodiment of the invention, the set of rolls 12 of the multi-roll calender 10 comprises at least one cutting device, such as a cutting blade, for each sectional set of rolls comprising two nips. According to other embodiments, it is advantageous that the paper or board web W is cut in the set of rolls 12 of the multi-roll calender 10 with at least one cutting device, such as a cutting blade, into pieces the length of which is at the most from three to five nips.

According to an embodiment of the invention, it is further advantageous that paper or board web W to be cut in the set of rolls 12 of the multi-roll calender 10 is blown with at least one cut-off blow 231 known as such the location of which in Fig. 1 is chosen as an example. Then, one cut-off blow 231 can be arranged per each sectional set of rolls comprising e.g. three rolls, i.e. two nips.

It is advantageous according to the invention that the quick opening of the set of rolls 12 is started after the break signal so that the load of the deflection-compensated upper roll 13 and the deflection-compensated lower roll 14 of the set of rolls is discharged and, if any, the load of the deflection-compensated rolls of each above- mentioned sectional set of rolls is discharged. In other words, in the case of the set of rolls 12 of the figure in which such a deflection-compensated roll is used as the lower roll in which the roll shell is able to move radially for its whole length in relation to the shaft of the roll, pressures are relieved from the load elements of the roll shell 14 so that the roll shell substantially moves in relation to the shaft of the roll, whereby the intermediate rolls of the set of rolls or the sectional set of rolls are able to "fall" for a determined distance downwards with the roll shell of the lower roll. If the lower roll is not provided with loadable load elements, pressure is relieved from the lift cylinder 143 of the lower roll for achieving a corresponding effect.

In quick opening, the speed of the movement of the lower cylinder 143; 146 of the multi-roll calender can be the same as in normal opening i.e. about 25 mm/s and the movement of the intermediate rolls 15-22 of the multi-roll calender is stepped so that the set of rolls 12 opens fan- like. The movements of the intermediate rolls can be adjusted so that in 0.5 seconds the gap has started to form in all the nips. In the upmost nips, the gap between the rolls is smaller than in the lower end of the set of rolls 12 but from the upper nips the web has in any case exited because of the speed of the web W. It should be noted that there is no need to form a gap of similar size between the rolls, i.e. the opening of the nips of the set of rolls is not simultaneous, but the opening of the set of rolls 12 of Fig. 1 starts from the upmost nip Nl continuing as a successive occurrence towards the lowest nip N9.

In a case in which there are several sectional sets of rolls on top of each other in the set of rolls 12 as described above, advantageously the opening of the set of rolls in each sectional set of rolls starts from the upmost nip continuing as a successive occurrence towards the lowest nip of this sectional set of rolls.

There is no need for the opening distances be considerable, because polymer- surfaced rolls are used today as soft rolls the resistance of marking of which has improved.

As known, an adequate quick opening time has been considered about 0.5 seconds which is the time of the web-break signal to the moment in which there are 5 -mm gaps in the nips. Said 5-mm gap in the quick opening was earlier required on the paper rolls of supercalenders because of the problem of marking. Today, the impact and heat resistance of the polymer rolls has improved due to introducing new covers so a smaller than said gap in the quick opening can be accepted.

Thus according to the invention, the quick-opening time of 0.5 seconds of quick opening implemented with basic cylinders of the set of rolls of the multi-roll calender is determined to be the time spent in discharging the load of the set of rolls, such as the load of deflection-compensated rolls, and the start of the opening of the nip gaps. A danger caused by paper has exited within this time from the nips by means of cutting devices, such as cutting blades, and blows, such as cut-off blows, and due to the speed of the web.

With current paper speeds of about 2,000 m/min, the web W moves about 5 me- tres in 0.5 seconds. In a break situation, cutting blades possibly located in several points in the set of rolls cut the web immediately after the break signal, from which follows that the web W cut in the quick-opening time (about 0.5 seconds) has passed at least part of the nips or even all the nips N1-N9.

The wrapping of paper around the roll is prevented with cut-off blows of which in the set of rolls 12 can be arranged several as described above, whereby the length of the web wrapping around the roll after the cut-off blows is 5-10 m which is about three cycles of the web around the roll with typical roll diameters. Wrapping in this extent does not cause thermal problems for the polymer surface, be- cause the bundle will not become tight. Situations in which the bundling of the roll has occurred have mostly been caused by insufficient break monitoring or when cutting the web with cutting blades has not occurred as desired. With known quick opening, which is implemented by means of separate quick-opening cylinders, it would not have been possible to prevent bundling in these cases. The paper W possibly damaging the cover during quick opening according to the invention, which is implemented without separate quick-opening cylinders, is able to exit at least partly from the nips, namely with multi-roll calenders operating with the web speed of 1,000 m/min (16.7 m/s) depending on the functioning of the cutting blade and cut-off blows from almost all of the nips, and multi-roll calenders functioning with the web speed of 2,000 m/min (33.3 m/s) from all of the nips. The length of the web from the cutting blade to the last nip is about 15-20 m depending on the size of the set of rolls and the number of the rolls. Advantageously, there is at least from one to two cut-off blows in the set of rolls.

The invention was described above by way of examples with reference to the enclosed figures. The invention is not, however, limited to what is presented in the figures, but different embodiments of the invention can vary within the scope of the inventive idea presented in the enclosed claims.

Claims

1. A method for quick-opening a set of rolls in a multi-roll calender (10), in which a paper or board web (W) to be calendered is passed through calendering nips (N1-N9) formed by a deflection-compensated upper roll (13), a deflection- compensated lower roll (14) and two or more intermediate rolls (15-22) arranged between the upper and lower rolls (13, 14), which rolls (13-22) are arranged as a set of rolls (12) and in which calender the intermediate rolls (15-22) are carried by hydraulic relief cylinders (155-225) for relieving nip load caused by the masses of bearing housings (151-221) of the intermediate rolls (15-22) in question and auxiliary devices (154-224) related to them, characterised in that the method comprises the following steps for opening calendering nips (N1-N9):

- discharging the hydraulic load pressures of the deflection-compensated rolls (13, 14) of the set of rolls in the quick opening of the set of rolls (12), - lowering the shell of the lower roll (14) of the set of rolls downwards, and

- relieving the relief loads of the relief cylinders (155-225) of the hydraulic relief devices of the intermediate rolls (15-22) and the load cylinders (143; 146) of the lower roll (14), being conventional basic hydraulic cylinders without separate quick-opening cylinders, totally or partly.

2. A method according to claim 1, characterised in that the lower roll (14) of the set of rolls is lowered downwards by means of the lower cylinders (143; 146) of the multi-roll calender (10).

3. A method according to claim 1, characterised in that the shell of the lower roll (14) of the set of rolls is lowered downwards by means of load devices inside the lower roll so that the roll shell of the lower roll substantially moves downwards in relation to the shaft of the lower roll.

4. A method according to any one of claims 1-3, characterised in that the paper or board web (W) is cut in the set of rolls (12) by at least one cutting device, such as a cutting blade (230), into pieces the length of which corresponds at most five nips.

5. A method according to any one of claims 1-3, characterised in that the paper or board web (W) is cut in the set of rolls (12) by at least one cutting device, such as a cutting blade (230), into pieces the length of which corresponds at most four nips.

6. A method according to any one of claims 1-3, characterised in that the paper or board web (W) is cut in the set of rolls (12) by at least one cutting device, such as a cutting blade (230), into pieces the length of which corresponds at most three nips.

7. A method according to any one of claims 1-6, characterised in that the piece of the paper or board web (W) to be cut is blown with at least one cut-off blow

(231).

8. An arrangement for quick-opening a set of rolls in a multi-roll calender (10), in which a paper or board web (W) to be calendered is passed through calendering nips (N1-N9) formed by a deflection-compensated upper roll (13), a deflection- compensated lower roll (14) and two or more intermediate rolls (15-22) arranged between the upper and lower rolls (13, 14), which rolls (13-22) are arranged as a set of rolls (12) and in which calender the intermediate rolls (15-22) are carried by hydraulic relief cylinders (155-225) for relieving nip load caused by the masses of the bearing housings (151-221) of the intermediate rolls (15-22) in question and auxiliary devices (154-224) related to them, characterised in that the arrangement for quick opening the set of rolls (12) comprises

- hydraulic load cylinders of the deflection-compensated rolls (13, 14),

- a shell of the lower roll (14) to be lowered downwards, and - relief cylinders (155-225) of the intermediate rolls (15-22) and load cylinders (143; 146) of the lower roll (14), being conventional basic hydraulic cylinders without separate quick-opening cylinders.

9. An arrangement according to claim 8, characterised in that the set of rolls (12) comprises at least one cutting device, such as a cutting blade (230), for each sectional set of rolls comprising two nips.

10. An arrangement according to claim 9, characterised in that the set of rolls (12) comprises one cut-off blow (231) for each sectional set of rolls comprising three rolls.