The present invention relates to paper and board machines. More specifically, the present invention relates to a method according to the preamble of claim 1 and to an arrangement according to the preamble of claim 7 for control of rolls, in particular for control of relieving, the deflection line of rolls, the linear load in a nip between rolls and/or quick-opening of a set of rolls in a calender, in particular in a soft calender, a multi-roll calender, such as a supercalender, and/or in an on-or off-line calender.

Calendering is a method by means of which the properties, in particular the thick- ness profile, smoothness, gloss, surface porosity and translucence of a web-like material, such as a paper web, are sought to be generally improved. In calendering the paper web is passed into a nip which is formed between rolls pressed against each other and in which the paper web is deformed by the action of temperature, moisture and nip pressure, in which connection the physical properties of the paper web can be affected by controlling the above-mentioned parameters and the time of action. The good physical properties attained by calendering lead to better print quality, thereby bringing a competitive advantage to the manufacturer of paper.

-In the papermaking art, grades of ever higher quality are required today. As the running speeds required of paper machines are continuously increasing, the direction in calendering technology is more and more towards on-line solutions, which include soft calendering and multi-roll on-line calendering.

When the aim is to make higher quality printing paper grades having a surface smoothness of PPS < 2 item, such as, for example, SC-A and LWC- roto grades and glossy coated paper grades, a substantial problem is that this kind of grades can be produced in practice only by using, after drying a fibrous web, intermediate winding and off-line supercalenders, several of said

supercalenders, usually two or three, being used side by side to meet produc- tion capacity.

-Soft calendering is calendering in a calender unit in which nips are formed between a smooth-surface press roll, such as a metal roll, and a roll covered with a resilient coating, such as a polymer roll. In a soft calender, the nips are formed between separate roll pairs. In order to treat both sides of the web in the soft calender, the order of the roll pairs forming successive nips is reverse with respect to the web in order that the resilient-surface roll may be caused to work on both surfaces of the web.

-Supercalendering is calendering in a calender unit in which nips are formed between a smooth-surface press roll, such as a metal roll, and a roll covered with a resilient coating, such as a polymer or paper roll. The resilient-surface roll adapts itself to the contours of the surface of paper and presses the opposite side of paper evenly against the smooth-surface press roll. Today, the supercalender typically comprises 10-12 nips and for the purpose of treating the sides of the web, the supercalender comprises a so-called revers- ing nip in which there are two resilient-surface rolls against each other.

-Multi-roll on-line, off-line calendering is calendering in a calender unit in which the number of rolls is higher than in a soft calender, most commonly 6-16. Multi-roll calenders are soft-nip calenders.

Linear load increases in multi-roll calenders from the top nip to the bottom nip because of the force of gravity. In order to eliminate this downwardly increasing linear load, to control the deflection line of the roll, as well as to quickly open the set of rolls, the multi-roll calenders of today employ the relieving of rolls which is accomplished by means of a cylinder and lever arm mechanism and which compen- sates for the force of gravity. One such relieving system for rolls is the linear load compensation and roll relieving system marketed by the applicant under the trade- mark OptiLoad'.

The primary aim of the present invention is to eliminate and to reduce the problems and the effects resulting from them in connection with the prior-art relieving of rolls

in a multi-roll calender, and to provide a new, inventive method and arrangement for controlling the relieving of rolls, the deflection line of rolls, the linear load in the nip between rolls and/or the quick-opening of a set of rolls, which method and arrangement function above all more reliably, more accurately and faster than prior- art systems.

This aim is achieved by means of a method and an arrangement of the kind men- tioned at the beginning. The principal characteristic features of the method are set forth in the characterizing part of independent claim 1. The principal characteristic features of the arrangement are set forth in the characterizing part of claim 7.

Thus, the invention is based on the new and inventive idea that the impact of the weight of the roll is relieved partly or totally, the deflection line of the roll is con- trolled and/or the linear load in the nip between rolls is controlled, advantageously by means of long-stroke slide bearing elements (i. e. slide shoes) by regulating the loading of the slide elements placed in different positions, i. e. vertically and/or obliquely in an upper and/or a lower position, whereby the force of gravity can be compensated for, when desired, fully or partly.

With respect to the benefits of the invention, it may be mentioned that because of the relieving arrangement of the roll integrated into a slide bearing, the impact of the weight of rolls can be relieved fully or partly and the set of rolls can be controlled in quick-opening, that the relieving of rolls can be controlled accurately by means of pressure measurements and slide bearing elements, and that the damping, loading and relieving capacity of the hydraulic system is improved.

The invention will described in the following in more detail by means of one of its embodiments regarded as advantageous with reference to the accompanying drawing, in which Figure 1 schematically shows a roll pair in a calender in which one of the rolls is provided with a roll relieving arrangement integrated into a slide bearing according to the invention, and

Figure 2 schematically shows the cross section of a roll relieving arrangement according to the invention and one advantageous hydraulic control system associated therewith.

With reference to Figs. 1 and 2, regarding the operational function and structure of a slide bearing arrangement 10, it is generally stated that in connection with multi- roll calenders 1 of paper machines, the main function of the slide bearing arrange- ment 10, which is not in itself any new and inventive element in connection with a paper machine, is to reduce the kinetic friction arising from the rotation of a roll 3 and to maintain the roll 3 in a correct position. In order to minimize the kinetic friction, the roll 3 rotates in the slide bearing 10 on thin pressurized medium films, advantageously hydraulic oil films 18 produced by pressurized mediums, advantage- ously hydraulic oils, passed through slide elements lls and 11v. The forces parallel to the nip between the two rolls 2 and 3, i. e. CD forces, and the forces parallel to the length of the paper machine, i. e. MD forces, are transmitted into the bearing housings 10 through a sliding sleeve (not shown in the figures) mounted on an axle 5 of the roll. Vertical and diagonal slide elements 11v mounted in the bearing housings 10 and serving as loading elements receive the forces parallel to the nip, i. e. the CD forces, and horizontal slide elements Ils mounted in the bearing housings and serving as lateral control elements receive the forces parallel to the length of the paper machine, i. e. the MD forces. From these elements the forces are transmitted further through the bearing housings 10 to the frame of the paper machine. Mechanical-hydraulic control valves 15 and 19 coupled to the slide bearing elements Ils and 11v control the loading of the slide bearing elements lls and 11v and cause the roll 3 to be maintained in a desired correct position. The pressurized hydraulic oil according to the invention is passed to the control valves 15,19 and from the control valves to the slide bearing elements l lus and lly by bores or tubes 12,16; 13 and 14, and the coupling to the hydraulic system of the paper machine is advantageously provided separately for each individual bearing housing, which enables the control of the load of the roll to be bearing-housing specific.

In accordance with the invention, the arrangement for relieving the roll has been integrated into the slide bearing, advantageously into the operational function of the slide bearing described above and into the structure of the bearing housing of the slide bearing. In that connection, the impact of the weight of the roll can be relieved partly or fully, and the deflection line of the roll and/or the linear load in the nip between the rolls can be controlled, advantageously by means of long-stroke vertical slide bearing elements lls (i. e. slide shoes or slide elements) loaded straight and/or diagonally against the axle 5 of the roll 3 by regulating the loading of the slide elements 11v placed in different positions at a distance from one another in the direction of the circumference of the axle 5 of the roll 3, i. e.

-in an upper and a lower position at a perpendicular vertical line at an angle of 180° to each other, -in an upper position obliquely upwards symmetrically with respect to the perpendicular vertical line, and/or -in a lower position obliquely downwards symmetrically with respect to the perpendicular vertical line, thereby enabling the force of gravity to be compensated for, when desired, fully or partly, and together with these loads it is possible -to relieve the impact of the weight of the rolls 2,3 partly or totally, -to control the deflection line of the roll 2,3, -the linear load of the nip between the rolls 2,3, and -to accomplish quick-opening of the calender 1.

The positioning of the rolls 2 and 3 of the calender 1 in the lateral direction and the control of them to maintain them in a desired correct position are accomplished by means of the horizontal slide bearing elements lls (i. e. slide shoes or slide elements) according to the invention, integrated into the operational function of the slide bearing and into the structure of the bearing housing 10 of the slide bearing, substantially in the same way as the relieving of the rolls 2,3. The slide bearing elements lls operate as lateral control elements in the relieving arrangement of the roll 2,3 according to the invention.

In the following, the invention will be described with reference to Fig. 2. In accord- ance with the invention, bearing-housing specific control of the relieving and the deflection line of the roll 3 is provided by hydraulic-mechanical loading of the slide elements lls and lly, which control can be used, for example, in multi-roll calen- ders instead of prior-known cylinder and lever arm mechanisms. The arrangement according to the invention includes a loading and supporting arrangement of the roll 3 axle 5 integrated into the bearing housing 10 of the slide bearing for relieving the impact of the weight of the roll, for controlling the deflection line of the roll 3 and the linear load in the nip, and for maintaining the roll 3 in a desired position. As shown in Fig. 2, in this embodiment of the invention, the loading and supporting arrangement includes: -slide elements which are loaded horizontally opposite each other against the axle 5 of the roll 3 from the opposite sides thereof and which serve as lateral control elements lls of the axle 5 of the roll 3 in the relieving arrangement of the roll 2,3 in accordance with the invention, -slide elements which are loaded vertically against the axle 5 of the roll 3 and which serve as loading elements lly in the relieving arrangement of the roll 3 in accordance with the invention, -feed means 12,15,16; 13; 14,19 for feeding a pressurized medium, advantage- ously hydraulic oil according to the invention, into a space 20 for receiving a pressurized medium, which space is defined by the inner wall of a station- ary cylinder 21, a slide element lls or 11v moving like a piston inside the cylinder 21, and an annular seal 22, e. g. an O-ring seal, sealing a circumfer- ential space between the cylinder 21 and the slide element, for loading the loading and lateral control elements lls and 11v, and from the receiving space 20 through the slide elements 11S or lly into a space between the outer circumferential surface of the axle 5 of the roll 3 and the slide element 1 ils or 11v for the purpose of forming a hydraulic oil film 18 in said intermediate space, -pressure measurement means 30 for monitoring the state of the nip in the set of rolls by measuring the pressure of the pressurized medium in the receiving space 20.

In this connection, it shall be noted that, in connection with rolls which are lighter in weight than the thermo roll of the calender described above, there is no need for the same number of slide shoes or slide elements 11 and 1 ls but in connection with lighter rolls, it is sufficient that there are four slide shoes or slide elements 1 lv and 1 ils mounted at an angle of 90° with respect to one another, and in that connection, by regulating only the loading of the opposite slide shoes 1 lv located in upper and lower positions, the relieving of the roll weight impact and the regulation of the linear load in the nip can be fully controlled, and the lateral control elements lls need to be adjusted only when needed.

In order that the impact of the weight of the rolls may be relieved totally or, when desired, only partly and in order that the set of rolls may be controlled fully in quick-opening, slide elements lly and lls with a sufficiently long stroke are used in the roll relieving arrangement according to the invention. In accordance with the invention, at least the vertical slide elements are this kind of long-stroke slide elements I lv* By means of the roll relieving arrangement according to the invention, a linear load distribution, which is uniform in the running direction of the web or has another kind of desired form, is produced in the nips of the set of rolls by loading the slide elements 11 and l ls, utilizing in that connection a computing unit of an automation system incorporated in the control system of the paper machine as well as, for example, pressure measurement values obtained from the pressure measurement unit 30 connected to the slide element 11v and lys.

As is further shown in Fig. 2, the hydraulic system controlling the roll relieving arrangement according to the invention comprises three inlet ducts for hydraulic oil.

A first inlet duct 12 is intended for control of the slide elements which are loaded horizontally against the axle 5 of the roll 3, i. e. for control of the lateral control elements 1 ls of the roll relieving arrangement according to the invention. Hydraulic oil is passed through the first inlet duct 12, which is a lateral positioning duct, through the first control valve 15, which comprises a distribution chamber for hydraulic oil and a piston member controlling the distribution of hydraulic oil, into two separate hydraulic oil distribution tubes 16 and 17, of which one hydraulic oil

distribution tube 17 leads to the hydraulic oil receiving space 20 in connection with the lateral control element 1 ls on the left-hand side, from which space 20 hydraulic oil is passed through the slide element 1 lys into a space between the slide element 11 ls and the axle 5 of the roll 3 in order to form a hydraulic oil film 18 in it, and of which the other hydraulic oil tube 16 passes hydraulic oil to the hydraulic oil receiving space 20 in connection with the lateral control element lls on the right- hand side, from which space 20 hydraulic oil is passed through the slide element lls into the space between the slide element lls and the axle 5 of the roll 3 in order to form the hydraulic oil film 18 in it. A second inlet duct 13, which is a supporting duct, and a third inlet duct 14, which is a loading duct, are intended for control of the slide elements 11 loaded both perpendicularly and diagonally against the axle 5 of the roll 3, i. e. for control of the loading elements 11v of the roll relieving arrangement according to the invention. Hydraulic oil is passed through the second hydraulic oil inlet duct 13 directly into a hydraulic oil receiving space 20 associated with the loading element 11 located perpendicularly vertically beneath the roll axle 5, and from the receiving space 20 hydraulic oil is passed through the slide element 1 lv into the space between the slide element 1 lez and the roll axle 5 in order to form the hydraulic oil film 18 in it. Hydraulic oil is passed through a third hydraulic oil inlet duct 14 first into the second control valve of the arrangement, which is a check valve 19, and after that hydraulic oil is passed or distributed into a hydraulic oil receiving space 20, which is associated with -the vertical loading element 11v placed perpendicularly vertically on top of the roll axle 5, and/or -each vertical loading element 1 lv placed above the horizontal line of the axle 5 of the roll 3.

From the receiving space 20, hydraulic oil is passed through the slide element 11v into the space between the slide element lly and the roll axle 5 in order to form the hydraulic oil film 18 in it.

In accordance with the invention, it is advantageous that pressure is measured from the hydraulic oil receiving space 20. In that connection, the measurement means 30 passed into the hydraulic oil receiving space 20 provides the necessary measurement

signal which can be used in controlling the feed of the hydraulic oil for the purpose of controlling the position and loading of the roll.

In order that the set of rolls may be fully controlled in accordance with the invention and moved a distance required for relieving rolls, for their deflection line and/or for the linear load between rolls and/or for quick-opening of the set of rolls, the roll control arrangement according to the invention employs slide elements 11v and lls with a sufficiently long stroke. In that connection, the smallest stroke length is needed for opening the nip between the topmost rolls, and the stroke length increases as multiples from one nip to the next towards the bottom nip of the set of rolls. In that connection, the stroke length of the slide shoe 11v and lls is in a range of 5-100 mm for moving the roll 2,3 according to the invention, and by loading the slide elements 11v and llg, the roll can be moved the distance required by the relieving of the rolls, the deflection line of the rolls and/or the linear load between the rolls and/or the quick-opening of the set of rolls. In accordance with one embodiment of the invention considered particularly advantageous, the quick-opening of the set of rolls is controlled by means of long-stroke vertical slide shoes lly intended for relieving of the set of rolls and by means of chambers (not shown in the figures) mounted on the sides of the bearing housings 10 and provided with quick- opening pistons (not shown in the figures), which slide shoes 11v and the quick- opening chambers (not shown in the figures) provided with pistons totally replace the prior-art cylinder and lever mechanisms intended for relieving of calender rolls.

Above, the invention has been described only by way of example by means of one of its embodiments relating to a calender and considered to be advantageous. This is of course not intended to limit the invention in any way and, as is clear to a person skilled in the art, various alternative arrangements and modifications are feasible within the inventive idea and the scope of protection thereof as defined in the accom- panying claims. Thus, it must be noted that the method and the arrangement according to the invention also cover slide bearing arrangements in which there are more bearing elements than one in the axial direction of bearings, whereby the elements or pairs of elements can be controlled together or separately.