On-line multi-roll calender and a method for calendering fibrous web on an online multi-roll calender

FIELD OF INVENTION

The invention relates to improving the runnability of an on-line fibrous-web machine according to the preamble of claim 1. In an on-line multi-roll calender according to the invention, a paper or board web being calendered is arranged to be conveyed 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 roll stack and the intermediate rolls are arranged in relation to the calender body carried by means of hydraulic relief cylinders and levers for relieving nip load caused by the masses of bearing cups of the intermediate rolls in question and auxiliary devices related to them. A method according to the invention for the on-line multi-roll calender in accordance with claim 1 is presented in claim 11.

PRIOR ART

Calendering is generally carried out in order to improve the properties, such as smoothness and gloss, of a web-like material, such as a paper or board web. In a calender, nips are formed between a smooth-surfaced press roll, such as a metal roll, and a roll covered with flexible cover, such as a polymer roll. In calendering, the web is passed into a nip, i.e. calendering nip, formed between rolls being pressed against each other, in which nip the web becomes deformed from the effect of temperature, moisture and nip pressure. The roll with a flexible surface accommodates to the shapes of the web surface and evenly presses the opposite side of the web against the smooth-surfaced press roll.

The line between paper and board is flexible, and they may be divided in two classes according to their basis weight: papers which are single-layered with a basis weight of 25-300 g/m ² and boards which are manufactured by the multilayer technique with a basis weight of 150-600 g/m ² . As one notices, the line be- tween paper and board is flexible as the boards lightest of their basis weight are lighter than the heaviest papers. Usually, paper is used in printing and board in packing.

The next descriptions are examples of fibrous-web values used today and they may include considerable variation from given values.

Printing papers manufactured from mechanical pulp, i.e., wood-containing papers are newsprint, uncoated magazine paper and coated magazine paper.

Newsprint either totally consists of mechanical pulp or it may include little bleached softwood pulp (0-15%) and/or recycled fibre may replace some of the mechanical pulp. The following values may be considered common for newsprint: basis weight 40-^8.8 g/m ² , ash content 0-20%, PPS SlO roughness 3.0^.5 μm, Bendtsen roughness 100-200 ml/min, density 600-750 kg/m ³ , brightness 57-63% and opacity 90-96%.

Uncoated magazine paper (SC = supercalendered) usually includes mechanical pulp 50-70%, bleached softwood pulp 10-25% and fill materials 15-30%. Typical values for calendered SC paper (including inter alia SC-C, SC-B and SC- A/A+) are basis weight 40-60 g/m ² , ash content 0-35%, Hunter gloss <20-50%, PPS SlO roughness 1.0-2.5 μm, density 700-1 ,250 kg/m ³ , brightness 62-70% and opacity 90-95%.

Coated magazine paper (LWC = light-weight coated) includes mechanical pulp 40-60%, bleached softwood pulp 25-40% and fill and coating materials 20-35%.

The following values may be considered common for LWC paper: basis weight

40-70 g/m ² , Hunter gloss 50-65%, PPS SlO roughness 0.8-1.5 μm (offset) and 0.6-1.0 μm (roto), density 1,100-1,250 kg/m ³ , brightness 70-75% and opacity 89-94%.

The following values may be considered common for MFC (machine finished coated) paper: basis weight 50-70 g/m ² , Hunter gloss 25-70%, PPS SlO roughness 2.2-2.8 μm, density 900-950 kg/m ³ , brightness 70-75% and opacity 91- 95%.

The following values may be considered common for FCO (film coated offset) paper: basis weight 40-70 g/m ² , Hunter gloss 45-55%, PPS SlO roughness 1.5- 2.0 μm, density 1,000-1,050 kg/m ³ , brightness 70-75% and opacity 91-95%.

The following values may be considered common for MWC (medium weight coated) paper: basis weight 70-90 g/m ² , Hunter gloss 65-75%, PPS SlO roughness 0.6-1.0 μm, density 1,150-1,250 kg/m ³ , brightness 70-75% and opacity 89- 94%.

The basis weight of HWC (heavy weight coated) paper is 100-135 g/m ² and it can be coated even more frequently than twice.

Wood-free printing papers manufactured of pulp, i.e., fine papers are uncoated and coated pulp-based printing papers in which the part of mechanical pulp is less than 10%.

Wood- free uncoated (WFU) printing papers include bleached birchwood pulp 55- 80%, bleached softwood pulp 0-30% and fill materials 10-30%. The values of WFU vary considerably: basis weight 50-90 g/m ² (even 240 g/m ² ), Bendtsen roughness 250^00 ml/min, brightness 86-92% and opacity 83-98%.

In wood-free coated (WFC) printing papers, coating amounts vary considerably according to requirements and intended use. The following are typical values for once- or twice-coated wood-free printing paper: for once-coated, basis weight 90 g/m ² , Hunter gloss 65-80%, PPS SlO roughness 0.75-2.2 μm, brightness 80-88% and opacity 91-94%; and for twice-coated, basis weight 130 g/m ² , Hunter gloss 70-80%, PPS SlO roughness 0.65-0.95 μm, brightness 83-90% and opacity 95- 97%.

The basis weight of release papers varies in the range of 25-150 g/m ² .

Other fine papers are, inter alia, sackkraft papers, tissue papers and wallpapers.

Chemical pulp, mechanical pulp and/or recycled pulp are used in the manufacture of board. Boards may be divided, inter alia, in the following main groups accord- ing to their intended use: corrugated board with a surface layer (liner) and fluting board box board of which are manufactured boxes, cartons, inter alia, liquid packaging boards (FBB, WLC, SBS) graphic boards, inter alia, cards, files, screens, casings, covers etc. - wallpaper bases.

Multi-nip on-line calendering is on-line calendering in a calendering unit in which nips are formed between a smooth-surfaced press roll, such as a metal roll, and a roll covered with flexible cover, such as a polymer roll, alternately following each other. A multi-roll calender usually includes 5-1 1 nips i.e. 6-12 rolls of which 2- 5 are thermo rolls and 4-7 polymer-covered rolls. A multi-nip on-line calender unit can include e.g. 8 rolls and 7 nips. A multi-nip calender is required in manufacturing e.g. fibrous-web grades more demanding of their weight properties and extremely glossy paper, such as magazine paper.

The calender can be a fixed part of the fibrous-web or coating machine, whereby

it is an on-line calender. Onto the on-line calender, the fibrous web is guided from the drying section of the fibrous-web or coating machine. If the calender is a separate unit, it is called an off-line calender onto which the fibrous web is conveyed from a reeler.

Linear load increases in multi-nip calenders from the upper nip to the lower nip due to gravitation. In multi-nip calenders presently in use, roll relief compensating for gravitation carried out by a cylinder and lever mechanism is used for eliminating this downwards-increasing linear load, for monitoring the deflection line of the roll and, also, for quick opening of the roll stack. A such relief system of rolls exists in OptiLoad™ and TwinLine™ calenders.

The OptiLoad™ multi-roll calender is suitable for manufacturing almost all paper grades. It is particularly suitable for calendering glossy and smooth paper grades. OptiLoad includes 6-12 rolls. It can be located into connection with the fibrous- web machine as an on-line calender or it can be a separate unit.

The calendering technique of choice is more and more often on-line calendering, because higher run speeds are required of fibrous-web machines. Simultaneously, of the on-line calender of the fibrous-web machine is required accommodation ability for producing several different fibrous-web grades with the same roll stack of the calender, whereby the role of on-line runnability diagnostics is emphasised in the multi-roll calender. In such an on-line run situation of the calender implemented with high run speeds, when the on-line fibrous-web machine can option- ally produce many different fibrous- web grades, the control of the geometry of the nips of the roll stack of the on-line calender i.e. the nip profile and of the geometry of each fibrous web being calendered has to be optimised fibrous-web-grade- specifically (grade-to-grade optimised calender stack operation).

The object of the invention is to improve the runnability of the on-line multi-roll calender which on-line multi-roll calender can be used e.g. as an on-line multi-roll calender of some above-mentioned fibrous-web types and fibrous web grades.

SUMMARY OF INVENTION

According to the invention, in an on-line multi-roll calender

- all intermediate rolls with a hard surface of the roll stack are forged thermo rolls manufactured of steel - all intermediate rolls with a soft surface of the roll stack are, advantageously composite-structured, polymer-surfaced calendering rolls for which is arranged a system for balancing their temperature there are fly rolls for guiding the web inside the nip and out from it at least one of which is provided with a flexible one-piece composite shell - there are web break detection means which include optical web break observation means, means for cutting the web into pieces and means to prevent the wrapping of the web in the roll stack

- the web being calendered is arranged extra wide so that, during run, the web is wider than the end area of the shell of the hot thermo roll of which a considerable amount of heat can be conducted or emitted into the cover of the adjacent polymer roll there are first actuators providing the offset of the polymer-surfaced calendering roll and first mechanisms for transferring the polymer-surfaced calendering roll during run sideways in relation to the press plane of the roll stack, and there are second actuators providing a change of distance of the fly roll with a composite shell from the adjacent thermo roll and second mechanisms for increasing or decreasing the distance of the fly roll with a composite shell from the adjacent thermo roll during run so that the length of the web in the roll stack changes accordingly.

In the method for on-line calendering a fibrous web on the on-line multi-roll calender by means of which it is possible to calender optionally several fibrous-web grades on-line, there are the following steps: the real-time state of the on-line multi-roll calender during run is moni- tored by measuring means and diagnostic means the measuring means measure at least the vibration of the calender body or at least the vibration of one roll

- measurement data is analysed by first diagnostic means pre-processed data is communicated to an upper-level automation system which as second diagnostic means in real-time runnability diagnostics analyses at least pre-processed vibration measurement; and

- after the vibration has increased to a preset reaction limit, one of the following two steps or both following steps is/are implemented: controlling the first actuators providing the offset of the polymer- surfaced calendering roll during on-line calendering so that the polymer-surfaced calendering roll is transferred sideways in relation to the press plane of the roll stack,

- after the vibration has increased to a preset reaction limit, controlling the second actuators providing a change of distance of the fly roll with a composite shell from the adjacent thermo roll during online calendering so that the distance of the fly roll with a composite shell from the adjacent thermo roll increases or decreases, whereby the length of the web in the roll stack changes accordingly.

The arrangement according to the invention is suitable for minimising and eliminating the runnability problems of on-line fibrous-web machines, such as on-line multi-roll calenders. By means of the invention, it is possible to optimise the geometry of the nips, i.e. the nip profile, of the on-line multi-roll calender roll stack and the geometry of each fibrous web being calendered fibrous-web-grade - specifically. In this context, on-line also particularly refers to the control of runnability occurring during a run situation so that no breaks are created in the web

but the fibrous web can be produced continuously without stopping the fibrous- web machine or slowing the speed e.g. to creeping speed.

The other characteristic features and advantages of the invention are depicted in the following description and claims.

BRIEF DESCRIPTION OF FIGURES

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

Fig. 1 schematically shows an example of an on-line multi-roll calender and the advantageous positions of forged steel thermo rolls T with a hard surface, of advantageously composite-structured, polymer-surfaced calendering rolls C with a soft surface, and of composite-structured fly rolls F arranged in it.

Fig. 2 schematically shows active run components and built-in run features arranged for improving the runnability of the on-line multi-roll calender.

Fig. 3A shows a bearing and a joint allowing rotation of the thermo roll T and lubrication and cooling arrangements implemented in them.

Fig. 3B shows a thermal insulation arrangement of a shaft at the end of the thermo roll.

Fig. 4 shows a structure of an advantageously composite-structured polymer roll and a diagram of a temperature balancing system of such a calendering roll.

Fig. 5 shows a fly roll F which is provided with a flexible one-piece composite shell supported from the middle.

Fig. 6 shows a taper of the polymer roll, an extra wide web and an insulation tube of the thermo roll.

Fig. 7 shows a structure suitable for real-time offset of the roll.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

In on-line multi-roll calenders, calender-roll nips are being formed between adjacently positioned calender rolls, whereby the stack of rolls i.e. the roll stack formed by the adjacent calender rolls can be located in a vertical position or in an oblique position in relation to a vertical position. The web being calendered travels on-line by twists and turns via the above-mentioned nips so that it is conveyed into the roll stack e.g. from the start of the roll stack and it leaves the roll stack at its end.

Fig. 1 schematically shows an on-line fibrous-web machine 10 in which there are eight nip rolls 1 1-18 and seven nips N1-N7. The on-line multi-roll calender 10 of Fig. 1 will be used in the following description as an example of an on-line fibrous-web machine, in which a paper or board web W to be calendered is passed through calendering nips N1-N7 formed by a deflection-compensated upper roll 1 1 , a deflection-compensated lower roll 18 and two or more intermediate rolls 12- 17 arranged between the upper and lower rolls 11, 18, which rolls 11-18 are arranged as a roll stack and in which the intermediate rolls 12-17 are carried in relation to the calender body R by means of hydraulic relief cylinders 29a and a sup- port and load arm 29b for relieving nip load caused by the masses of bearing cups of the intermediate rolls in question and auxiliary devices related to them, whereby the roll stack includes as an intermediate roll with a hard surface one or more forged thermo rolls T, 12, 15, 17 manufactured of steel and as an intermediate roll with a soft cover one or more polymer-surfaced calender rolls C, 13, 14, 16 which roll is advantageously composite-structured.

In Fig. 1, the roll stack of the multi-roll calender 10 includes the upper roll 1 1 and the lower roll 18 and six intermediate rolls 12-17 arranged between the upper and lower rolls, whereby the upper, lower and intermediate rolls form the nip rolls 1 1- 18 of the roll stack. The intermediate rolls 12-17 are bearing-mounted to the body of the multi-roll calender e.g. by means of the support and load arms 29b rotating around a pivot. The body R is shown with a dashed line, the pivots and arms are only schematically shown in connection with one intermediate roll. In the multi- roll calender 10 shown in the figure, there is a vertical roll stack, but the roll stack or a part of the roll stack can as well be a set of rolls different from a vertical stack for implementing the invention.

The thermo rolls with a hard surface used in the on-line multi-roll calender of Fig. 1 are all forged thermo rolls T manufactured of steel, whereby it is also possible to implement the highest temperatures designed in on-line calendering. The forged thermo rolls have excellent dynamic properties in a calendering situation because, even as a basic material, steel can be obtained homogenous of its structure. The surface of the thermo rolls T is advantageously induction-hardened or made hard with some other heat treatment or covering, whereby the surface wears evenly without roughening of its surface quality. Actual grinding is required if one wishes to change the profile of the thermo roll T. For several grindings, it is advantageous to arrange a hard surface layer the thickness of which is 5-8 mm.

It is advantageous to balance the thermo rolls used in high temperatures when hot for observing their dynamic operation in the run situation in the best possible way.

The soft calendering rolls used in the on-line multi-roll calender of Fig. 1 are all polymer rolls C which can advantageously be composite-structured. This enables the use of rolls smaller of their dimensioning which, for its part, decreases the mass of the rolls. Decreasing the mass of the rolls gives an opportunity to use smaller bearings and otherwise improve the lifetime of the bearings, the cheaper price of the components and the structure also naturally being an advantage.

In the schematic side view of the example of Fig. 1 , the fibrous web W is calendered in the roll stack of the on-line multi-roll calender 10 in all nips between the calender rolls, the web draw being downwards from the top. It is not necessarily required to calender the web in all nips but, in some run situations, it can be advantageous to guide the web through an open nip without calendering the web and, in some run situations, it can be advantageous to arrange the draw of the web partially outside the roll stack thus enabling e.g. partial nip run. Thus, it is possible to arrange the web to totally bypass one or more nips, e.g. by means of fly rolls. In Fig. 1, the web W is guided via a fly roll 21, F advantageously provided with a flexible composite shell into the upper nip Nl and further through the other nips N2-N6 and finally out of the lower nip N7. Between the nips N1-N7, the web W is taken off the surface of the rolls by means of fly rolls 22, 23, 24, 25, 26 and 27.

In the on-line multi-roll calender 10, all of the fly rolls are fly rolls F provided with a one-piece composite shell supported from the middle, one of which is shown in more detail in Fig. 5. For clarity, the support devices of the fly rolls F in connection with the bearing cups of the rolls or in connection with the calender body R are not shown. After the roll stack, the fibrous web W can be further guided, according to requirements, e.g. with the roll 28.

Fig. 1 shows a solution to prevent barring by roll offset RO, whereby thus one or more of the rolls in the roll stack is/are transferred away from a line passing through the central axis of the rolls of the roll stack. Such an offset is usually of the order of some dozens of millimetres. The lateral shift i.e. offset of the polymer-surfaced calendering roll C, 13 advantageously being third in the upper position in the roll stack in relation to the press plane of the roll stack is described in more detail in connection with Fig. 7.

Fig. 1 shows another solution to prevent barring by the change of the distance WS of the fly roll F with a composite shell from the adjacent thermo roll T. Said change of distance is provided by second actuators and second mechanisms for increasing or decreasing the distance of the fly roll F with a composite shell from the adjacent thermo roll real-time during run so that the length of the web W in the roll stack changes accordingly. The distance of the fly roll F, 22 with a composite shell adjacent the thermo roll T, 12 advantageously second in the upper position in the roll stack is changed WS in relation to said thermo roll.

The on-line multi-roll calender 10 comprises a doctor arranged for at least one calendering roll.

The on-line multi-roll calender 10 comprises an on-line roll cleaning device arranged for at least one calendering roll which enables the cleaning of coating, glue material or dirt accumulated on the surface of the roll. With the roll cleaning device the surface or cover of the roll, cost savings are accrued when there is no need to stop the calender nor cool the hot rolls for the time of cleaning. Thus, there is no need to run broke due to stopping the calender, which accumulates savings especially in the on-line run of the fibrous- web machine. Further savings are accrued from the increase of lifetime of the rolls in the calender as the cleaning of the roll can be performed on-line and there is no need to remove the rolls from the calender for the time of cleaning.

The on-line multi-roll calender 10 utilises the quick opening of the roll stack to prevent 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 fibrous 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 250°C, beside polymer-covered rolls the momentary temperature resistance of which can be e.g. about 150°C. In a web

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 roll stack has been cleaned of foreign objects.

The on-line multi-roll calender 10 comprises web break detection means which include optical break observation means, means for cutting the web into pieces, and means to prevent the wrapping of the web in the roll stack. The optical break observation means comprise a pair of photocells before the roll stack and a pair of photocells after the roll stack and two pairs of photocells in the roll stack. The means for cutting the web advantageously into several short pieces comprise at least one cutting device, such as a cut-off knife 230, which is advantageously arranged before the first nip Nl of the roll stack. The means to prevent the wrapping of the web comprise at least one cut-off blow 231 in the roll stack. Web break detection is an important feature from the viewpoint of the runnability of the on- line multi-roll calender because, as the web exits from the hot nips, the soft roll covers can be damaged from the effect of the heat of the thermo rolls. The cut-off blow 231 is used to prevent the wrapping of the web around the calendering roll, because especially a web wrapped around a polymer-covered roll can prevent the exit of extra heat from the cover and result in damaging the cover.

By means of the web break detection system, it is possible to quickly recover from the situation after the break in the web, whereby naturally it is possible to escape unnecessary work stages and the number of damaged components can be diminished. This same object is aimed at with quick-opening cylinders 29a ena- bling the simultaneous quick opening of the nips of the roll stack of the on-line multi-roll calender 10 in about 0.5 seconds which cylinders include hydraulic damping for the soft landing of the intermediate rolls. Quick opening cylinders of said type are known e.g. from specification EP 0842324B1.

Fig. 3A shows a bearing 32, 33 and a joint 34 allowing rotation of one end of the thermo roll T and lubrication and cooling arrangements implemented in them. In

the shell part 30 of the thermo roll T is fastened a shaft end 31 for which is arranged a bearing 33 located inside the bearing cup 32. The lubrication and cooling of the bearing 33 is implemented with a first circulating lubricating-oil flow an inflow channel of which into the bearing cup 32 is designated with 3.1 in and an outflow channel 3.1 out. The inflow channel 3.1 in consists of a flow channel formed in the bearing cup which guides the first lubrication-oil flow into rolling elements of the bearing 33. The first lubrication-oil flow exiting from the rolling elements of the bearing due to flow, by means of gravity and centrifugal force exits through channels formed in the bearing cup into the outflow channel 3.1 out. The heating of the shell 30 of the thermo roll T is implemented with a second circulating oil flow an inflow channel of which is designated with 3.2 in and an outflow channel with 3.2 out in the rotary joint 34. The rotary joint 34 is fastened at the end of the shaft end 31 , and the flow channels of the second heating oil flow are arranged inside the shaft end e.g. in a way shown in Fig. 3B. The cooling and lubrication of the rotary joint 34 itself are implemented with a third circulating oil flow the temperature of which can be adjusted, and the inflow channel of which third oil flow is designated with 3.3 in and the outflow channel with 3.3 out. The circulating flow media are advantageously oils suitable for heat transfer in connection with the high temperatures of the shell of the thermo roll but naturally also other than oil-bearing heat-transfer media can be used.

Fig. 3B shows a heat insulation arrangement of the shaft 31 at the end of the shell part 30 of the thermo roll T, the aim of which is to diminish the increase of the temperature of the bearing arranged on the shaft and thus decrease the amount of heat transferring from the thermo roll in the structure surrounding the calender. The inflowing oil of the second heating-oil flow 3.2b in centrally flowing inside the shaft 31 and the outflowing oil of the second heating-oil flow 3.2b out are separated from each other by a wall 35 of the inner tube which is shown in the enlarged detail of Fig. 3B. The thermal insulation of the heating oil flow channels 3.2b in and 3.2b out outwards in the radial direction are formed by a surrounding vacuum insulation 36 arranged outside the heating oil flow oil 3.2b out and a sur-

rounding air insulation 37 arranged outside the vacuum. By means of the arrangement shown in Fig. 3B, it is possible to improve the lifetime of the bearing of the thermo roll and to improve the usability of the calender e.g. due to the decreased number of bearing replacements. Fig. 3B further shows an insulation tube 38 of the second heating-oil flow which is arranged at the end of the roll shell in the flow channel of heating oil. The insulation tube 38 is depicted in more detail in connection with Fig. 6 and its description.

Fig. 4 shows a structure of an advantageously composite-structured polymer roll C and a diagram of a system for the real-time balancing of the temperature of all polymer rolls of the on-line multi-roll calender 10. A shell part 40 of the polymer roll has a steel body 41 and around the body there is a polymer cover 42. The polymer cover 42 advantageously consists of several layers, such as a base layer, an intermediate layer and a top layer around the steel body. The total thickness of an advantageous embodiment of the polymer cover 42, the trade name of which is CalTiger 92, is about 25 mm, of which the thickness of the top layer is about 14 mm. The nominal usable thickness of the cover is 7-10 mm which can be ground due to maintenance or profile change. The hardness of the presented cover is 92 ShD +/- 1 ShD, the maximum surface temperature continuously 13O ⁰ C and the surface roughness less than 0.2 μm at process. The presented cover is repairable both locally and zone-specifically band-like. The steel body 41 and end pieces 43 of the roll enclose a water volume 44 in which the water of the temperature balancing system of the roll C flows inside one end of the roll C through the shaft of the end piece 43 and of which water volume 44 the water flows out from the other end of the roll C through the shaft of the end piece.

In addition to a tube system 45 joining each polymer roll C of the on-line multi- roll calender 10 to the system, the temperature balancing system of the polymer roll C of Fig. 4 comprises a circulation water pump 46 for circulating water in the tube system 45 and the water volumes 44 of the system, a heat exchanger 47 for increasing or decreasing the temperature of water i.e. for obtaining the water cir-

culating in the polymer rolls C to a suitable use temperature, an expansion tank 48 for accommodating the thermal expansion of water, a filling valve 49 and a strainer 50. The temperature of each polymer roll C is monitored by the temperature observation means and diagnosed in the upper-level control in order to con- trol the temperature balancing system of polymer-surfaced calendering rolls C real-time, whereby e.g. the speed of the circulation pump 46 can be changed and the heat exchanger 47 controlled to produce hotter or colder water in the tube system 45 or the flow in the water volume 44 of each polymer roll C can be limited with an adjustable valve or choker joined to a tube leading to this certain water volume.

The fly roll F shown in Fig. 5 has a shaft which consists of a cylindrical middle part 52 and shaft journals 51 at the ends of the middle part 52. The shaft is rotata- bly supported by its shaft journals to end bearings 53 which are located outside the web, minimising the leaking risk of the lubricant onto the web. On top of the middle part 52 of the shaft is arranged a cylindrical flexible composite shell 54 rotating along the shaft which shell is supported from the middle on the cylindrical middle part 52 of the shaft. On the outer surface of the shell 54, there is a cover 55 which has excellent wear resistance, heat resistance, chemical resistance, and the cover 55 can be antistatic. The hardness of an advantageous cover of the shell is 0+2 P&J, the maximum temperature 16O ⁰ C and the typical thickness 2 mm. The trade name of such a cover is Ultima.

The amount and direction of the bow of the fly roll F can be adjusted according to the requirements set by each fly roll position. The flexible end supports of the shell allow the composite shell to accommodate to the small changes of the tension profile during run, which enables the even tension of the web in varying operating conditions and minimises the time required for adjusting the fly rolls. In certain positions, the fly rolls F can be used as combined spreader and tension- measuring rolls. The flexible and continuously bowing composite shell 54 of the fly roll F keeps the web tight in both the cross-machine direction CD and the ma-

chine direction MD and the contact of the shell is also good in the edge areas of the web, the control of which by traditional three-piece fly rolls is many times awkward. The use of the fly roll F provided with the one-piece composite shell 54 is advantageous in improving runnability because of its lightness, its low residual imbalance due to accurate manufacturing, and its properties damping the vibrations of the materials and the structure. As advantages are obtained better control of web tension, equally high paper quality, little adjustment requirement during run, and effortless servicing. Also the outer diameter of the fly roll F can be dimensioned smaller than the one of conventional fly rolls, which is advantageous when the fly rolls F are used in the same on-line multi-roll calender 10 utilising polymer rolls C provided with a smaller diameter.

Fig. 6 shows the advantageous location of a taper 60 of the polymer roll C, a section of an extra wide web W to be cut and an insulation tube 38 of the thermo roll T in relation to each other when one wishes, in the on-line multi-roll calender 10, to decrease the load of the edge of the polymer cover 42 of the polymer roll C and to decrease the transfer of heat of the thermo roll T into the polymer roll C. The web W being calendered is arranged extra wide so that, during run, the web is wider than the end area of the shell 30 of the hot thermo roll T of which a consid- erable amount of heat can be conducted or emitted into the cover 42 of the polymer roll C. The web W is arranged in the on-line multi-roll calender 10 intentionally wider than the hot area of the thermo roll T considerably affecting the cover of the polymer roll C during run in order to protect by means of the extra wide web W and especially its section 63 to be cut out, which is not exactly properly in contact with the hard nor soft calendering surfaces, the edge area of the cover 42 of the polymer roll C from heat which could be conducted or emitted from the hot area of the thermo roll T.

The polymer roll C includes the body 41, the cover 42 and the end piece 43. In the cover, there is the taper area 60 which includes a rough taper 61 and a micro taper

62. The purpose of tapers is to decrease the load of the edge of the polymer cover

42. The thermo roll T includes the shell part 30, whereby the purpose of insulation tubes in the heating medium flow channels 64 in it at the end of the thermo roll is to decrease the thermal expansion of the thermo roll T in the radial direction. The transfer of heat from the thermo roll to the polymer roll can be decreased by the insulation tubes 38 and the extra wide web W. By means of the extra wide web W, it is possible to guarantee the cleanness of the edge of the soft roll cover 42. The section 63 of the web to be cut out is advantageously at least 15 mm wide measured from the inner edge of the insulation tube 38 of the thermo roll T outwards, i.e. in Fig. 6 from the right edge of the insulation tube 38 outwards. The micro taper 62 advantageously starts at a point 65 about 10 mm inwards from the inner edge of the insulation tube 38 of the thermo roll T and continues in the direction of the edge of the cover 42 advantageously about 20 mm, whereby the middle point of the micro taper 62 is at the inner edge of the insulation tube 38 of the thermo roll T.

Furthermore, the temperature of the edge of the soft cover 42 of the polymer roll C can be measured by using advantageously contact-free measuring, such as infrared temperature measuring. Then, the temperature monitoring of both edges of the roll cover can include a high temperature alarm and an automatic opening of the nip. For monitoring, two fixed measurement heads are arranged in each position of the polymer roll C at both roll ends.

Optionally, the temperature of the edge of the soft cover 42 can further be cooled in each polymer roll position by cooling shoes arranged at the edge areas of the soft cover 42 of the polymer rolls C at both roll ends in which shoes pressurised air is blown in the edge area of the roll cover 42 being cooled. The cooling effect can be adjusted in the axial direction by adjusting the number of segments arranged in the cooling shoe in the axial direction of the roll. The infrared temperature measurement heads are advantageously integrated into connection with the cooling shoes.

Fig. 7 shows an advantageous structure suitable for real-time roll offset by means of which the bearing cups of the roll to be offset are supported in the calender body. The shown structure is described e.g. in specification FI 20055407. The online multi-roll calender 10 comprises the polymer-surfaced calendering roll C, 13, first actuators 100 providing the offset RO and first mechanisms 101 for transferring the polymer-surfaced calendering roll C, 13 during run sideways RO in relation to the press plane of the roll stack.

The structure of Fig. 7 utilises a motor and a screw jack as the actuator 100 by means of which a transfer mechanism 101 is moved for implementing the offset RO. The transfer mechanism 101 comprises a lever mechanism 102 which includes an upper lever and a lower lever coupled together with a connecting lever. Both the upper lever and the lower lever are fastened to eccentric joints 103 which are rotatably and playlessly fastened in the upper and lower section of a fastening stand 104 of the bearing cup. When the actuators 100 of the offset devices at both ends of the roll to be offset transfer the levers of the lever mechanisms 102, they rotate the eccentric joints 103 arranged in the support and load arms 29b, causing the offset of the fastening stands 104 of the bearing cup in the offset direction RO. The transfer mechanism 101 is rotatably pivoted in the body R of the on-line multi-roll calender 10 in relation to a hole 29c of the support and load arm 29b and the relief cylinder 29a is pivoted in relation to a hole 29d at the end of the lever of the lever-like support and load arm 29b.

In the method, for improving the runnability of the on-line multi-roll calender 10 - the real-time state of the on-line multi-roll calender during run is monitored by measuring means and diagnostic means the measuring means measure at least the vibration of the calender body R or at least the vibration of one roll

- measurement data is analysed by first diagnostic means (e.g. Sensodec S6) - pre-processed data is conveyed (e.g. TCP/IP) into an upper level automation system (e.g. DNA = Dynamic Network of Applications) which as

second diagnostic means in real-time runnability diagnostics analyse pre- processed vibration measurement; and - after the vibration has increased to a preset reaction limit (barring), one of the following two steps or both following steps is/are implemented: - controlling the first actuators providing the offset RO of the polymer-surfaced calendering roll C, 13 during on-line calendering so that the polymer-surfaced calendering roll C, 13, which is advantageously third in the upper position of the roll stack (Fig. 1), is transferred sideways in relation to the press plane of the roll stack, - after the vibration has increased to a preset reaction limit (barring), controlling the second actuators providing a change of distance WS of the fly roll F with a composite shell from the adjacent thermo roll T during on-line calendering so that the distance of the fly roll F with a composite shell from the adjacent thermo roll increases or decreases, whereby the length of the web W in the roll stack changes accordingly.

Advantageously, the distance of the fly roll F with a composite shell adjacent the thermo roll T, 12 advantageously second in the upper position in the roll stack is changed WS in relation to said thermo roll (Fig. 1).

The real-time setting of the length of the web i.e. the web set WS by changing the distance of the fly roll F from the thermo roll T and the sideways roll offset RO of the polymer roll C cause a decrease in vibration during run onto a level in which the runnability of the web is better.

According to an embodiment of the method, the machine-direction MD and the cross-machine direction CD profile of the web W is monitored and diagnosed real-time for adjusting the profiles in the roll stack of the calender. For this, in the roll stack of the on-line multi-roll calender 10 are arranged suitable measuring devices (web touch).

Such a measuring device is a roll 70 suitable for e.g. tension measurement which is implemented by means of a technique based on deformation or pressure detection or an electro-magnetic foil (EMFi). An EMFi roll is known by the trade name iRoll, Metso Paper, Inc. Below the roll cover, advantageously comprising several layers, protecting the body of the tension-measuring roll 70 and functioning as a spring is arranged a foil-like sensor measuring the force caused by the web or the nip in the shape of an oblique spiral. One part of the sensor is under the effect of each measured force, whereby the sensor measures a cross (pressure) profile as the spiral twists. On the cover above the pressure sensor or the EMFi sensor, a deformation is created due to the force caused onto its surface, the deformation presses the sensor which reacts to the deformation by producing an electric signal. The sensor rotating, a tension profile is created of which the CD-directional tension can be calculated real-time based on the angle position of the roll. From the rotating tension-measuring roll is sent a measured signal utilising wireless data transmission, and the electric power for the measuring electronics in the tension- measuring roll is wirelessly transferred e.g. by means of induction. By one tension-measuring position, it is possible to provide the on-line multi-roll calender a feedforward profile measurement for the profile adjustments of the calender.

Thus e.g. preceding the first nip of the on-line multi-roll calender can be arranged one tension-measuring roll 70 (Fig.1) the measurement profile of which can be formed as a profile chart in the MD and CD direction. When running the web W on the calender, a feedforward is made of each momentary situation into the thickness etc. profile adjustments of the calender, whereby at each moment the real-time CD profile and the expected situation of the web going to the calender are known. The measurement data is utilised so that the profile adjustments of the calender are revised predictively or on-line, because the profile of the web W is known beforehand.

According to an embodiment of the method, the temperature of each thermo roll T and each polymer roll C is monitored and diagnosed real-time in the roll stack of the calender.

According to an embodiment of the method, all quality flaws (e.g. coating streaks, felt marks and water spots) of the web W are inspected real-time by means of a web inspection system (WIS) advantageously arranged in the roll stack of the calender at any speed. The analysis of the web inspection system WIS is based on optical detection (video shot), preclassification and flaw classification, whereby the documentation on time, type, size and location of flaws (e.g. hole) possibly causing a machine control signal or alarm is usable real-time in on-line reeling.

Above were described only some advantageous embodiments of the invention and it is evident to those skilled in the art that several modifications can be made to them within the scope of the enclosed claims.