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1. WO2006100345 - CALENDER AND A METHOD IN CALENDERING FIBRE WEB, ESPECIALLY PAPER OR BOARD WEB

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

Calender and a method in calendering fibre web, especially paper or board web

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

The invention relates also to a method in calendering a fibre web according to the preamble of claim 17.

As known from prior art, calendering means a process in which paper is pressed between two or more rolls, whereby paper, due to mechanical work and heat, changes its form in the direction of both plane and thickness. The calendering of coated papers may often be divided in two stages, pre-calendering and end-calendering.

Calendering mechanisms may be divided to four modes of impact: compression, replication, orienting and transferring. From the viewpoint of the development of smoothness, compression is the most important, factors affecting compression are perpendicular press force and total paper plasticity. Instead, the importance of transferring in smoothness is somewhat less important, transferring is mostly affected by planar forces and surface plasticity. Factors affecting gloss are replication, which is affected by perpendicular forces and surface plasticity, and orienting, i.e., oblong and laminar parts being positioned to the direction of plane, which, again, is affected by perpendicular forces and surface plasticity.

Machine-calendering is the oldest calendering method. Therein, paper is pressed between two or more hard rolls. A double-roll machine calender used in pre-calendering consists of a heatable thermo roll and a deflection-compensated roll with a chilled cast iron shell, which both have doctor blades. Before the nip, there is a spreader roll. The temperature of the thermo roll is 80-12O0C, and linear pressure 80-100 kN/m when running newsprint quality.

The difference of a soft calender compared to a machine calender is that at least one of the rolls forming the nip is soft-surfaced. The principal impact mechanism is compression and replication. Most soft calenders are on-line in paper or coating machines. The thermo roll is doctored, and before the nip there is a spreader roll. The temperature of the thermo roll is 100-250°C, and linear pressure varies between 50-350 kN/m.

Multi-roll calenders are soft-nip calenders in which the number of rolls is greater than in soft calenders, most usually 6-12. The principal impact mechanism in super-calendering is compression and replication, additionally fraying has a small effect. A conventional super calender is a calender which has 9-17, normally 12 rolls. The uppermost and the lowermost roll are deflection-compensated rolls with chilled cast iron surfaces. Intermediate rolls are alternately water-heated thermo rolls with chilled cast iron surfaces and paper rolls. For treating both sides, the multi-roll calender has a so-called reversing nip which has two paper rolls opposite each other. Cross-directional linear pressures vary from one nip to another due to different deflections of rolls, and differences to the distribution are caused by so-called spindle loads, forces affecting roll ends, for example, bearing cups and steam boxes. Thus, spindle-load relieving devices were developed to the super calenders, with which one was somewhat able to affect the line-load distribution from the upper nip to the lower nip, i.e., to lighten the weight of the set of rolls.

Super-calendering was the only multi-roll calendering method for a long time. The development of soft calendering was strongly related to the development of polymer covers and, gradually, the use of polymer-covered rolls became common also in super calenders. A change did not occur until in mid-1990s; the first methods purely based on polymer rolls; so-called polymer supering (super-calendering with polymer-covered rolls), when also on-line applications were created. In calendering based on polymer rolls, the calendering mechanism may be considered to be replication and compression. Due to the thinness of cover, planar forces have no effect on the calendering result.

Known from prior art is the so-called Janus calender concept which is totally based on polymer rolls. New characteristics compared to polymer super calenders are higher than previous temperatures, greater linear pressures and usually reversed roll order, i.e., the upper and the lower rolls are polymer-covered deflection-compensated rolls. The concept includes also double-framed alternatives. The set of rolls no longer has stems because the thickness of the polymer-roll cover does not vary like the one of the paper rolls of super calenders. The rolls are fastened by their bearing houses in which is also linked the relieving of spindle loads. In roll dimensioning, one has especially considered the minimising of roll weight in order to keep the line-pressure difference between the upper and the lower nip as small as possible. For the same purpose, one has divided the rolls in two frames, whereby an easier control of unequal sidedness and a lower structure are achieved, but with greater investment and operating costs, hi a divided stack, the free draw between the sets of rolls causes also extra drying of the web. The temperature of the thermo roll is 1500C.

Also known from prior art is the so-called OptiLoad calender which includes all afore-mentioned characteristics and additionally a special load system. All the intermediate rolls of the OptiLoad calender have the same specific deflection which allows their full relieving without the profile of cross-directional line pressure suffering because of it. The OptiLoad deflection-compensated rolls guarantee an equal line-pressure profile and a possibility to compensate the whole weight of the roll. The perfect compensation of the weight of the rolls means that the same linear pressure may be used in all nips. With the amount of relieving, one may also affect the line-pressure difference between the upper and the lower nip and, thus, for example, unequal sidedness. The load system entails most clearly the largest calendering window compared to all other calendering methods.

In calendering based on a long nip, the calendering mechanism may be considered to be replication and orienting. Because of the tensile stiffness of the cover, compression is extremely little. A long nip concept known from prior art is the calendering concept marketed with the applicant's trademark OptiDwell. It consists of two different long-nip calenders: of OptiDwell Shoe™ calender which is based on the shoe-press technique, and of OptiDwell Belt™ calender which is based on the roll/belt technique. The shoe calender concept utilises the shoe-press technique known on the part of compression. The shoe roll is the so-called SYMBELT™ roll. The shoe roll consists of a shoe, load elements, a lubricant system and a belt. In the shoe roll, belt exchange has been developed to be simple; there is no need to take the roll out of the machine. The thermo roll is a technique known from soft calenders. It may be a water-, steam-, oil- or induction-heatable roll.

The width of the nip is defined by the width of the shoe. The length of the shoe may be even 275 mm. The shoe nip enables the standardisation of nip width irrespective of load, roll diameters and belt characteristics. This enables the optimisation of important calendering factors of dwell time and nip pressure totally irrespective of each other.

The belt calender consists of a normal thermo roll of a soft calender, a belt loop and a counter roll which may be either a hard or a soft roll. The belt circulates via the counter roll and control/pull rolls. The simple structure of belt loop also enables the modernisation of old machine and soft calenders as belt calenders. Without the belt, one may use the calender as a usual machine or soft calender depending on the counter roll.

In belt calendering, nip time (nip length) and nip pressure are dependent on line load and the tensile stiffness (hardness) of the belt as also in soft calendering. In the belt calender, the nip length varies around 10-40 mm and the nip pressure 5- 20 MPa. In the soft calender, the corresponding values are around 5-15 mm and 5-50 MPa depending on its cover and line load.

In the metal-belt calender, the nip is formed between a metal belt and a roll. The calender includes control and/or belt-pull rolls, around which a metal belt is arranged for circulating. The nip length is defined by the placement of guide rolls and/or the design of a counter roll, simultaneously, contact pressure is directed at the nip which may be controlled from 0 Mpa to around 70 Mpa. The nip length may be from 10 mm to 3,000 mm and the temperature in the nip around 50-4000C and the thickness of the metal belt 0.1-3 mm.

In fibre webs, the limit 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/m2 and boards which are manufactured by multi-layer technique with a basis weight of 150-600 g/m2. As one notices, the limit between 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 fibre-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 40-48.8 g/m2, ash content 0-20%, PPS SlO roughness 3.0-4.5 μm, Brendtsen roughness 100-200 ml/min, density 600-750 kg/m3, 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/m2, ash content 0-35%, Hunter gloss < 20-50%, PPS S 10 roughness 1.0-2.5 μm, density 700-1 ,250 kg/m3, 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/m2, 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/m3, 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/m2, Hunter gloss 25-70%, PPS SlO roughness 2.2-2.8 μm, density 900-950 kg/m3, 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/m2, Hunter gloss 45-55%, PPS SlO roughness 1.5-2.0 μm, density 1,000-1,050 kg/m3, 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/m2, Hunter gloss 65-75%, PPS SlO roughness 0.6-1.0 μm, density 1,150-1,250 kg/m3, brightness 70-75% and opacity 89-94%.

The basis weight of HWC (heavy weight coated) paper is 100-135 g/m2 and it may even be 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/m2 (even 240 g/m2), Bendtsen roughness 250-400 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: once-coated: basis weight 90 g/m2, Hunter gloss 65-80%, PPS SlO roughness 0.75-2.2 jum, brightness 80-88% and opacity 91-94%; and twice-coated: basis weight 130 g/m2, 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/m2.

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

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 according to their intended use. Corrugated board which has a liner layer and a fluting board; box board of which one manufactures boxes, cartons, inter alia, liquid packaging board (FBB, WLC, SBS); graphic boards, inter alia, cards, files, screens, covers; wallpaper bases.

From prior art are known zone-controlled rolls which comprise a fixed centre shaft and a shell rotating around it which is supported by hydraulic load elements which are embedded in holes drilled to the centre shaft. In zone-controlled rolls used in calendering applications, the shell is usually either of cast iron or polymer-covered cast iron. The shell rotates supported by bearings which may fasten the position of the shell and the shaft to each other, or the shell may be self-loading in which case the shell may move freely in the nip direction. Such a zone-controlled roll known from prior art is the zone-controlled roll marketed by the applicant with trademark SymZ, in which roll mainly hydrostatic bearings provided with a piston are used, and which has a oil-pressure switching element. In this embodiment, load pressure also performs the lubrication of hydrostatic bearing. In some embodiments, self-loading rolls are used in connection with zone-controlled rolls, in which case external load cylinders are omitted and the construction is thus simpler. In such rolls, the bearing is installed with a load ring which may move freely in the nip direction, and the load elements are located between the transferable ring and the stationary shaft. Know from prior art are also corresponding zone-controlled rolls which are arranged so that their loading is profiling in the cross-direction in relation to the run direction of the web, i.e., so-called deflection-compensated rolls, the difference of which compared to conventional zone-controlled rolls is that each load element is individually controllable, whereby they are provided with their own oil supply system.

As prior art, we also refer to EP patent specification 698684 which describes a shoe-loaded deflection-compensated roll which comprises a stationary roll shaft on which is rotatably arranged a tubular roll shell which is bearing-mounted from its end on the roll shaft by means of end bearings. The roll shell of the deflection-compensated roll described in this publication is composed of fibre-reinforced composite material, whereby the frame-directional dimensional stability of the roll shell is good and the shaft-directional rigidity is small, and between the roll shell and the shaft are arranged hydraulic load shoes, loaded with a hydraulic pressure medium, in the nip level affecting the inner surface of the roll shell and supported on the roll shaft, by controlling the pressure of the pressure medium directed to them, the nip pressure may be profilable in the direction of the roll shaft.

Known from prior art, the variation of thickness of paper is usually controlled in connection with calendering by slow actuators, in which case the only possibility to affect the elimination of the machine-directional variation of the paper is to manufacture the rolls as sturdy as possible. In solutions known from prior art, this has led to the fact that, depending on the quality of rolls, the variation of thickness in the web has altered depending on how well one has succeeded in manufacturing the rolls and how the rolls have been treated during their use.

In so-called modern calenders known from prior art, in which the cross-machine directional control is implemented by a deflection-compensated roll, control speed is such that it enables the active control of roll pressures, even at the rotating frequency of the roll or at a higher frequency. A disadvantage of these known solutions has been that the great mass of the shell used causes a considerable dynamic delay and the actuator requires a lot of power.

A problem of multi-roll calenders known from prior art, i.e., calenders in which the set or sets of rolls of the calender consist of several rolls most commonly arranged to stacks, whereby the calender has several overlapping calendering nips at least in one roll stack, has related to the fact that in certain situations one requires a calendering run mode in which only the uppermost and the lowermost calendering nip are closed. This run method is called a so-called matte run mode. However, this run mode does not apply to all kinds of multi-roll calenders, because the used nips have to be at least mutually separately run and the deflection of a counter roll compared to the deflection of a deflection-compensated roll has been too great.

A problem of multi-roll calenders known from prior art might also have been the fact that, in loading the set of rolls in applications in which the nip load is implemented with lower lift cylinders, great frictions are created to the guides of the lower roll and to the pivots of the intermediate rolls, whereby the line load distributions of the nips have been difficult to control, and thus the profiles of the web have not always reached the desired level.

On the other hand, a problem of calendering have been the weaknesses of the profiling ability of a deflection-compensated roll, especially on the edge areas of the web. The weak cross-directional profile of the web causes waste and runnability problems in actuators after the calender, such as a roller and a slitter-winder. A problem in controlling the edge areas of the web has been the fact that the web is not usually uniform in the cross direction when coming from the paper converting stage preceding the calender, but the edge areas have been thicker or dryer.

A problem in connection with calendering has been that, in calendering webs of different widths, one has had to, for example with soft calenders, cool down the soft-roll surface of the soft calender in order not to damage it when the web has been narrower than the roll width, because in this kind of situation, the hot thermo roll heats up the surface of the soft roll too much on those areas in which the web does not reach.

A problem of multi-roll calenders known from prior art has also been their high price, because when the multi-roll calender has been provided, for example, with 6-12 rolls, and three different roll types have been usually used in the set of rolls of the calender: deflection-compensated rolls as the upper and the lower rolls, thermo rolls and polymer rolls as intermediate rolls, and thus one has required several different rolls and thus several different spare rolls for them.

In the calender, the uneven load caused by the variation of thickness of the web might have broken the surface of the roll. For example, a difference of one micrometre in the web thickness causes a load of 5 kN (0.5 MPa). If the paper remains rotating around the roll, even a 50 μm difference to the thickness profile is created, which has led to the roll having been damaged, whereby one has had to replace the roll or to repair the cover. Costs resulting from this may have been great, as, for example, a shutdown of an on-line calender causes the shutdown of the whole line, the costs of which easily rise to €200,000 per day.

A problem in connection with super calenders known from prior art has been that, as the run speeds of paper machines are increasing, the super calender has frequently become the bottleneck of the process, which either has slowed down the speed or has not reached the desired quality with too great a speed. Because of this, one has striven to increase the speed of the paper machine by modernising the calender and making process improvements to it and, simultaneously, one has striven to improve the quality of the end-product. On the other hand, the great speed of paper machines may also have caused the fact that the calender vibrates and thus damages the surfaces of soft calenders used in the super calender, whereby the replacements of rolls have increased, which has decreased the capacity of the calender and naturally increased the maintenance costs of the rolls.

A problem in connection with calendering is nip vibration, i.e., the so-called barring phenomenon which causes wear of the roll surfaces in calenders and sometimes limits the run speed of the calender and causes noise nuisances. A solution in solving this problem has been to change the relational position of the contact between rolls. That is, one has moved, for example, the intermediate roll of the calender in horizontal direction so that the mutual contact point of the rolls changes considerably to a different location in relation to the wavelength of vibration. This is, however, awkward as, in connection with deflection-compensated rolls, the roll-moving mechanism becomes heavy and expensive and, additionally, it may weaken the rigidity of the roll support and thus cause additional vibration.

The object of the invention is to provide a calender and a method for calendering a fibre web by utilising which the afore-described defects and disadvantages known from prior art have been eliminated or at least minimised.

To achieve the afore-mentioned objects and those that come out later, a calender according to the invention is mainly characterised in what is presented in the characterising part of claim 1.

A method according to the invention is mainly characterised in what is presented in the characterising part of claim 17.

The invention is applicable for several different types of calenders, such as soft calenders, multi-roll calenders and multi-roll calenders including one or two sets of rolls which usually have at least two calendering nips per a set of rolls. In addition, the invention is applicable in connection with metal-belt calenders. The invention is applicable for all kinds of paper and board grades. The invention is especially applicable for the speed range of 400-3,500 m/min. The invention may generally be applied in both philosophies known in calendering, i.e., in implementing a uniform treatment by calendering, in which case the profiling of the web is achieved with a headbox. On the other hand, the invention may also be applied for the profiling of the web with a calender, which however requires a more complex control but, by calendering according to the invention, the profiling is enabled even headbox-specifically.

According to the invention, a composite-shelled roll is able to follow with its outer surface the shape of the counter roll, whereby the relation of allowable deflection to the length of the roll in the composite-shelled roll is greater than 0,20 mm/m. According to the invention, the weight of the shell of the composite roll varies according to diameter and length; the weight of the shell of the composite roll is around 200-1,000 kg and the weight of the roll frame of the roll is around 2,000-40,000 kg, whereby the relation of the shell weight to the roll frame weight varies between around 1/10-1/40 (0.1-0.025).

According to the invention, one may use a deflected roll in the calender, whereby the roll shell of the roll is flexible, whereby one may deflect the roll on the profiling side with a lower pressure of corresponding shoes, and if the width of the web to be manufactured is standard, the load shoe spacing may be chosen accordingly. Then, there are at least one means for implementing deflecting in the ends of the roll at a certain distance. The means are advantageously placed on the opposite side of profiling members. There may be several deflecting means at a certain angle in relation to each other, for example at an angle of 30°. The invention thus enables the protecting of the edge area of the roll when manufacturing a narrower web than the length of the roll, because a clearance of desired size may be made between the roll and the counter roll, whereby the rolls of the calendering nip never touch each other on the edge areas nor does the hot thermo roll thus damage the cover of the soft roll, whereby one is able to run variable web widths by adjusting the clearance to the edges of the longitudinal area of the roll required by the web width run.

An advantage achieved with the invention is also that the problems occurring on the edge areas of the web have been solved, because load pressure may be conveyed in the shoes so that one achieves a desired loading, whereby for example, the problems caused by the support of roll bearings may be solved by loading the shoes of the edge areas so that the load differences caused by the bearing support may be compensated.

The invention enables the profiling of calendering in the cross direction of the web or completely same load in the cross direction of the whole web. When using a zone roll with a composite shell as the roll in the calender, the composite shell may be loaded in the longitudinal direction of the roll with each load shoe by a desired pressure so that a desired load profile is achieved. Then, one is able to achieve a better thickness profile of the web as the cross-directional thickness variation decreases. Then, waste is decreased even by 30-50% when the quality of the rolls is more uniform as the quality variation of the web is balanced.

In the invention, with calendering load profilable in the cross direction of the web, one also improves the durability of the soft cover of an oncoming nip roll, because via profiling, one is able to eliminate both calender errors and errors possibly occurred in the web.

According to an advantageous embodiment of the invention, the elimination of the machine-directional variation of thickness of the web is achieved by actively controlling the load pressures of the calender roll based on the thickness profile measurements of the web. The thickness profile of the web is measured, for example, with a moving sensor, in which case also a machine-direction component is included in the measurement, and this machine-direction component is separated from the measurement data by synchronisation and by processing the signal. Thus on the basis of machine-direction thickness-variation data, one may modulate for controlling the load of the zone roll according to the invention with a suitable amplitude and in a suitable stage, for example, a sine wave which is in contrasting stage with the variation of thickness. This modulation may be implemented either valve-specifically in the load shoes of the roll or by running the same wave to all valves.

An advantageous embodiment of the invention involves a roll which is provided with two different operation modes, both fixed and moving, whereby the roll shell is either fixed or moving. Then, lighter rolls may be used, whereby friction forces are smaller. In addition, the profiling result and simultaneously quality will improve and cost-savings will be achieved. Then, the calender may be run with the whole set of rolls closed when the zone roll positioned in the lower position according to the invention is in a fixed mode, i.e., its shell does not move, and the zone roll in the upper position is in a moving mode. In the fixed mode, bearing forces may be measured from the pressures of sleeve bearings. In this embodiment, the calendering nips are closed by lifting the lower lift cylinder upwards so long as each nip closes from down to up. The movement of the lower lift cylinders is stopped against a mechanical stopper, whereby the shell of the upper zone roll has risen somewhat upwards and, when the nips are so closed, the nips are loaded by pressurising the zones of the upper and the lower zone rolls to pressures corresponding desired line load. The correct level of the line load of the lower nip is controllable by means of the measurement of the bearing pressures of the lower roll, whereby by controlling the zone pressures of the zone roll, one modifies the measured bearing pressure to correspond calculatory values. This embodiment also enables partial nip run, for example the matte run mode, whereby the loading of the upper and the lower nip is performed in the same manner as may be implemented known from prior art as such, that is, one uses a zone roll provided with a moving shell against a fixed counter roll.

Certain advantages achieved by means of the invention will now be described by way of a summary. In connection with the invention, the use of zone roll with a composite shell as the roll of the calender reduces waste, because, when calendering with a zone roll with a composite shell, the thickness profile of the paper becomes better than with conventional rolls, especially the control of the edge area is better, whereby there is no need to cut a trimming from the web after the calender or at least the cutting width may be decreased. At their best, the edge rolls are produced as paper ready for sale. The better thickness profile of the web achieved with the invention additionally eliminates/decreases waste caused by the streakiness of paper and puckers formed in rolling.

Because of the flexibility of the composite shell of the zone roll with a composite shell used in connection with the invention, after breaks and shutdowns, one is able to return to production more quickly, because there are no dimensional errors caused by temperature and the temperature profile of the roll stabilises more quickly. Because of the better profiling ability of the roll, the grinding interval of the roll may be increased, whereby the efficiency of the calender increases as the time used in roll replacements decreases. In the invention, the duration of the local overload of the calendering nip provided with a zone roll with a composite shell is better than of conventional rolls, because the shell is flexible on the thicker local point maintaining local standard nip pressure, whereby the cover is not damaged or worn, and thus an increased grinding interval and better reliability for the roll are achieved. The better profiling enabled by means of the invention may better correct the errors of the counter roll and also increase the grinding intervals of the counter roll. In addition, the vibration damping qualities of a composite shell are better than the ones of a cast-iron shell, whereby the development of peripherical vibrations is smaller, whereby the occurrence risk of barring is decreased. The vibrations and damping between the shell and the cover are in the roll according to the invention better than with a cast roll and a cover.

With afore-described advantages, one is able to gain advantage in production either by improving the time-efficiency of the machine (fewer shutdowns) or by improving production-efficiency (more paper for sale). In addition, with the improved thickness profile achieved by means of the invention, also other web characteristics, inter alia, gloss etc., are improved. Furthermore, accelerating the smaller mass of the roll shell used in connection with the invention to the run speed requires less maximum output from the drives. After use, the composite shell may be utilised by recycling it to other uses, for example, as a machine felt leading roll.

When implementing different calendering concepts according to the invention, many different types of advantages are gained. In soft calenders, even with one nip, the thickness profile is corrected and a better profiling ability is achieved by using a zone roll according to the invention as the second roll of the nip. In hard calenders, the composite shell may be hard-covered, whereby, already with one nip provided with a roll according to the invention, the thickness profile is corrected and better profiling ability is achieved. In metal-belt calenders, a better profiling ability is achieved. In multi-roll calenders when using a zone roll with a composite shell as the upper roll of the calender, the profiling is corrected in the first nip, after which in other calendering nips, one is able to concentrate on other calendering characteristics, for example, increasing gloss. In super calender applications when using a zone roll with a composite shell as the upper roll, the profilings are corrected in the first nip, after which one is able to concentrate on other calendering characteristics, for example, increasing gloss. The invention may also be utilised in calenders so that the zone roll with a composite shell is placed between two thermo rolls, whereby a better profiling is achieved and thus cost-savings are gained, because one is able to use cheaper rolls compared to arrangements known from prior art when two zone rolls are replaced by one.

The invention will now be described in more detail with reference to the figures of the accompanying drawing, to the details of which the invention is, however, by no means intended to be narrowly confined. The figures schematically show certain advantageous embodiments of the invention.

Figures 1-6 schematically show certain embodiments of the invention for a set of rolls of the calender.

Figure 7 schematically shows an embodiment of the invention which uses a flexible roll.

Figure 8 schematically shows a bearing arrangement to be used in connection with the invention.

Figures 1-6 schematically show certain embodiments for a set of rolls of the calender, in which the roll stack 10 of the set of rolls comprises at least one zone roll 15 with a composite shell. In Figures 1-6, the thermo rolls of the set of rolls have been referred to with reference number 13, possible polymer rolls with reference number 12 and zone rolls with chilled cast iron shells with reference number 17. Even though the figures only show one roll stack 10 in each embodiment, the calender may naturally comprise several roll stacks, and the number of the nips may differ from the embodiments shown in the figures. In the figures, the calendering nip is referred to with reference N and the web with reference W. The reversing nip is referred to with reference NK. The zone roll 15 with a composite shell comprises a shaft 11, load shoes 14 and a composite shell 16 which is of carbon-fibre-reinforced epoxy and provided with a metallic cover. The zone roll 15 with a composite shell is advantageously structured as the type described in EP patent specification 698684.

Figure 1 schematically shows an embodiment in which a modernisation from a super calender with twelve rolls to a one with eleven or ten rolls has been performed. The figure shows either the first or the last nip N of the set of rolls 10 of which nips one or both are modernised so that into connection with a thermo roll 13 is arranged a composite-shelled polymer-covered zone roll 15 whereby, compared to the former construction, one may abandon a deflection-compensated roll with a cast iron shell and a paper roll which in the representation according to the figure are thus replaced by a zone roll 15 with a composite shell. Thus, the first and/or last calendering nips N of the set of rolls 10 of the calender are formed as profiling nips via the zone roll 15 with a composite shell, whereby a better profiling compared to prior art is achieved, and additionally the nip N is considerably better by its calendering efficiency compared to a solution according to prior art.

In the roll stack 10 shown in Figure 2, two different roll types are used: thermo rolls 13 and zone rolls 15 with composite shells. With this embodiment, a good calendering profiling ability and a cost-effective calender are achieved because of the smaller number of rolls. The embodiment employs zone rolls with composite shells or deflection-compensated rolls 15 in which the shell is of carbon-fibre composite, which enables excellent profiling abilities. It is also possible to run partial nip run with the calender according to the figure either in the upper or lower nip or the second and the third nip. Both shoe rows 14 of the roll 15 may be separately profiled so all nips N are profiling if required. The shoes 14 of one roll may also be interleaved in relation to the second row (not shown in the figures).

Figures 3 and 4 show a calender roll stack 10 of six rolls in which, in the reversing nip NK, one may also use instead of the second zone roll 15 (Figure 3) a polymer roll, or the reversing nip NK may be implemented by making the third and the fourth roll as thermo rolls, such as shown in Figure 4. Thus, one achieves a cost-effective calender with an excellent profiling ability, and with which one may run versatile different partial nip runs. Profiling is at its best in the first nip so, cost-effectively, in the second nip, one may use a roll which is not profiling in the cross machine direction but which has for example 1-8 zones. If desired, also the other composite roll may be manufactured totally with 1-8 zones, because the flexible shell itself enables an even line load for the second, the third and the fourth nip. Thus, one gains additional cost savings because of the smaller number of required valves and controls related to them.

Figure 5 shows a calender arrangement in which one has achieved a good profiling ability for the calender. As the upper roll of the calender roll stack 10, one has placed a hard-surfaced zone roll 17. Good profiling is achieved already in the first nip, as it has a zone roll 15 with a composite shell. In the second nip, the thickness profile is corrected so that the other nip increases web gloss with an even line load. The flexible shell of the zone roll 15 with a composite shell enables the even line load of the second nip, because the flexible shell follows the shapes of the thermo roll 13 being the counter roll and thus the force in each show is conveyed to the nip N. A special advantage gained is that one also is able to implement a good profiling ability for a calender of a conventional super-calender roll arrangement. In the calender roll stack 10 according to Figure 5, after the first thermo roll 13 follow two polymer rolls 12 on the both sides of the reversing nip NK, after which follows a thermo roll 13 below which is placed a polymer roll 12, and as the lowermost roll in the roll stack, a zone roll 17 with a chilled cast iron shell.

In the embodiment shown in Figure 6, in the roll stack 10, above and below the zone roll 15 with a composite shell are placed thermo rolls 13 and a corresponding roll arrangement is implemented after the reversing nip NK.

The presentation according to Figure 7 shows a longitudinal cross-section of an embodiment of the zone roll 15 with a composite shell, from which Figure 7, the simplified structure of the roll 15 becomes evident in this embodiment. The shell 16 of the roll 15 is of composite so it is flexible, and above it is placed a deflecting side T and below a profiling side P. At a certain range in the ends of the roll 15, there are at least one means (not shown in the figures) implementing deflecting, advantageously the means implementing deflecting are placed on the opposite side of the profiling member. There may be several members implementing deflecting placed at a certain angle in relation to each other, for example placed at the angle of 30°. Then, one is able to run webs of different widths by deflecting the edge areas via the deflecting side T separate from the calendering nip N so that the roll 15 does not get into a nip contact in the area of the clearance by choosing the pressure of the load shoes 14 so that when deflecting with the profiling side P, the pressure of corresponding shoes is smaller.

Figure 8 schematically shows a bearing arrangement of the roll in which to a sleeve bearing 21 is added an abutment bearing in order to eliminate the barring phenomenon. Into connection with the roll is arranged an actuator 22 for transferring the shell 16 horizontally. In the figure, the shell 16 has been transferred to an extreme position, whereby in the nip N occurs a displacement Z of the nip-contact position. Via the nip-contact position displacement Z occurring in the nip N, nip vibration may be eliminated. In this context, the abutment bearing of the bearing may be implemented, for example, with a 50 mm stroke, and the arrangement may be implemented in new devices and in connection with calender modernisation. In the embodiment of the figure, into connection with the sleeve bearing of the self-loading deflection-compensated roll is formed a bearing so that the order of vertical and horizontal bearings have been reversed. As a vertical bearing is a sleeve bearing of a normal strokeless roll, and as a horizontal bearing is a sleeve bearing of around 50 mm stroke which is provided with position control. By means of the horizontal bearing, the roll shell is transferred during run or reeling-drum exchange with the length of its stroke. Thus, the relational nip-contact point of the rolls is transferred, for example, around 20 mm, which is enough for eliminating or at least considerable decreasing of nip vibration. In the embodiment of the figure, to the bearing is added a horizontal stroke, whereby the stroke of the vertical bearing of the roll has been decreased and thus, however, the strength of the roll shaft has been retained. For the horizontal stroke, only two pieces per end are required. The positioning margin of nip-direction bearing shoes in relation to the roll shell is controlled suitable so that it is enough for the horizontal stroke set.

The invention was described above only referring to some of its advantageous embodiments, to the details of which the invention is, however, by no means intended to be narrowly confined.