Slide bearing system for a multi-roll calender

The present invention relates to a slide bearing system for a multi-roll calender. The invention relates to slide bearing systems of rolls used in calenders of paper, board or tissue machines.

Rolls of paper machines and paper finishing devices, exclusive of rolls in which the shell of the roll is able to move with respect to the shaft of the roll, have typically been mounted by means of roller bearings on frame structures of the machine. In particular, in connection with rolls forming a nip, such as calender rolls and soft calender rolls, such roller bearings have caused certain problems, whose solution has required special arrangements.

In some cases, it would be desirable to operate soft calenders in particular at linear loads that produce a very small load, even the so-called zero load, on roller bearings. This is very problematic in the case of roller bearings because in the zero load situation the rolling members of the roller bearing may slide with respect to bearing races, thus causing the bearing to break rather quickly.

Successful lubrication of bearings is particularly critical in the case of heatable rolls, heatable calender rolls in particular. In connection with roller bearings, special arrangements have often become necessary. Roller bearings additionally involve a vibration problem because the roller bearing in itself does not have any structure to damp vibration. The rolling accuracy of the roller bearing is also limited.

It is known to provide a calender roll with a hydrostatic bearing system, in which case the roll is mounted by its shaft on a bearing housing or an equivalent frame member by means of several hydraulically loaded hydrostatic bearing elements, of which at least one bearing element, a so-called main bearing element, acts in a

principal loading direction and one bearing element, a so-called abutment bearing element acts in a direction opposite to the principal loading direction. Said bearing elements are often provided with bearing shoes positioned around the neck of the roll shaft to support said shaft and roll rotatably with respect to the frame member, such as a bearing block.

EP 1 209 287 A3 describes an earlier invention of the applicant in which a slide bearing package replaceable as one unit is disposed at the end of a roll in a paper or board machine. The bearing system disclosed in the publication is also well suited for calenders even though in that case a separate mechanism moving the roll through the bearing block is needed to open nips in order that the nips over the entire length of the calender may be opened with a sufficient movement.

WO 01/21889 Al describes an earlier invention of the applicant in which the relieving and quick-opening of calender rolls is accomplished by means of a hydraulic system integrated into a slide bearing. According to the publication, rolls are moved against one another by slide elements 1 Iv movable in a piston- like manner using the hydraulic system. For quick-relieving the rolls, the sides of the bearing housings of the slide bearing are fitted with special quick-opening pistons, by which the nip can be opened, when needed, in an emergency. EP 0 897 484 Al also describes an earlier invention of the applicant in which bearing shoes of a slide bearing are hydraulically movable against the shaft of the roll such that the roll nips can be controlled by a hydraulic system.

It is an object of the present invention to provide a slide bearing arrangement of a roll for a multi-roll calender, by means of which control of the nips in a multi-roll calender is improved and/or manufacture of a multi-roll calender is facilitated and/or maintenance of a multi-roll calender is facilitated and/or the costs of manufacture and/or operation of a multi-roll calender are reduced.

In accordance with a first aspect of the invention, a slide bearing according to claim 1 is provided for mounting and rotating a calender roll by means of the bearing.

By the slide bearing system of a roll is meant a slide bearing system that is supported on the roll outside a surface intended for treatment of a fibrous web. Advantageously, the slide bearing system is supported against the neck of the roll shaft. By means of the slide bearings in accordance with the first aspect, rolls can be supported and/or loaded at both ends of the rolls without needing to use loading arms movably attaching the rolls to the frame of the calender, thus allowing the rolls to be attached to the frame of the calender more firmly than before. Stroking actuating members of the slide bearing in accordance with the first aspect enable the nip of the roll coupled with the bearing to be opened and closed sufficiently to separate the roll from the fibrous web and, advantageously, also enable the roll to be removed from the calender for maintenance.

In accordance with a second aspect of the invention, a multi-roll calender according to claim 7 is provided.

In accordance with a third aspect of the invention, a method for operating a multi- roll calender according to claim 12 is provided.

The invention provides a significant advantage over prior art arrangements, and of these advantages, among other things, the following may be mentioned. The structure of the bearing body containing the slide bearing system is simple and compact, so that it can be easily designed. The bearing body structures are advantageously replaceable, which means that servicing is easy to perform, for example, by replacement. Standard components can be used as bearing elements for the slide bearing system, wherefore in view of maintenance the delivery times of spare parts are short as compared with the availability of special components and, in addition, their price is lower. In the slide bearing system of a multi-roll

calender in accordance with the invention, control of forces in each individual nip is easy.

With respect to the other characteristic features and advantages of the invention, reference is made to the dependent claims of the set of claims and to the following special part of the description, in which preferred embodiments of the invention and how they can be accomplished are described in detail, but only by way of example.

In the following, the invention will be described by way of example with reference to the appended drawings, in which

Figure 1 shows a multi-roll calender comprising two roll stacks, Figure 2 illustrates details of the multi-roll calender of Fig. 1, Figure 3 shows a slide bearing system of an intermediate roll, which bearing system is fixedly attached to a frame of the multi-roll calender, Figure 4 shows pressure connections of the slide bearing system shown in

Fig. 3 in connection with a vertical bearing element 23 above a shaft

22, Figure 5 shows pressure connections of the slide bearing system shown in

Fig. 3 in connection with a vertical bearing element 23 under the shaft 22, Figure 6 shows a nip-open situation in connection with an intermediate roll

11 of a roll stack Ia shown in Fig. 1, Figure 7 shows the intermediate roll of Fig. 1 in a situation where the nip above the intermediate roll is open and the nip under it is closed, Figure 8 shows the intermediate roll of Fig. 1 in a situation where the nips of the intermediate roll are closed.

The hydrostatic slide bearing arrangement of the multi-roll calender 1 shown in Fig. 1 is based on check- valve control when load is received and on constant

pressures when load is relieved. The forces in each individual nip are controlled using controlled constant pressures. The bearing systems of each intermediate roll mounted by means of slide bearings can be loaded both upwards and downwards because each bearing body in the slide bearing system placed outside the intermediate roll is provided, in both loading directions, with a check valve and with a controlled constant pressure. The invention employs seat valves, which are cartridge type check valves and which allow large flow volumes and pressure control of loading. These check valves are advantageously controlled mechanically. The stroke length of the valves is advantageously sufficient to allow the opening and closing of nips even considering changes in roll diameter caused by the maintenance of rolls. The check valves are used for assuring loads that may come from both directions. The multi-roll calender 1 is arranged to be self-loading by means of deflection compensated rolls placed as top and bottom rolls. Stroking capability for controlling different running modes is provided in connection with the slide bearing system. The stroking capability of the slide bearing system accomplished by means of check valves enables control of disturbance situations, when needed, without external actuators, for example, in a situation where a disturbance occurs in the loading or lubrication system of the slide bearing system. Pressure control in the slide bearing system accomplished in accordance with the invention is stepless, which means that, on the one hand, relief of load is stepless and, on the other hand, the closing and loading of the nips can be performed steplessly.

In the multi-roll calender in accordance with the invention, a number of rolls are arranged in one or more calendering groups, the rolls being loadable against one another to calender a fibrous web in respective roll nips. Fig. 1 shows a multi-roll calender 1 comprising two roll stacks Ia and Ib. The left-hand roll stack Ia in Fig.

1 comprises three rolls, of which the uppermost roll, i.e. top roll 10, is a deflection compensated roll and the lowermost roll, i.e. bottom roll 15, is a deflection compensated roll. The roll mounted by means of slide bearings and serving as an intermediate roll 11 is, for example, a thermo roll having a nip Nl above it and a

nip N2 below it. The right-hand roll stack Ia is typically formed by a bottom roll 15', a lower thermo roll 14, a polymer roll 13, an upper thermo roll 12, and a top roll 10'. The right-hand roll stack Ib forms nips N3 ... N6 in a corresponding manner.

The right-hand roll stack Ib in Fig. 1 comprises five rolls, of which the top roll 10' and the bottom roll 15' are deflection compensated rolls and the three intermediate rolls 12, 13, 14 between the top and bottom rolls are rolls mounted by means of slide bearings. Advantageously, all five rolls are provided at both of their shaft ends with compact and replaceable bearing bodies in accordance with the invention. The intermediate rolls 12, 13, 14 are fixedly attached by means of bearing bodies 21 of their external slide bearing systems 16 to a frame F of the multi-roll calender 1. Fig. 2 illustrates details of the ends of two rolls externally mounted by means of slide bearings in the multi-roll calender of Fig. 1.

The movements of the rolls in each roll stack Ia, Ib, such as opening and closing of nips, can be arranged to take place by means of the deflection compensated rolls serving as top and bottom rolls, when it is desirable to operate with all the nips of the roll stack closed, advantageously from below upwards. Each intermediate roll is capable of moving within the limits determined by the movement distance of the slide bearings 16 at its roll ends. The roll stacks Ia, Ib of the multi-roll calender 1 are closed and opened, and they are thus loaded on support of the bearings of the rolls, so that the loads of different directions in the nips can be controlled by means of control valves of the slide bearings. Known loading arms are therefore not needed to produce movements of the rolls.

In the multi-roll calender it is possible to shift the intermediate rolls 11, 12, 13 of the roll stack laterally using a suitable shifting member to eliminate a vibration problem, i.e. barring, sometimes occurring in the roll stacks Ia, Ib. A known mechanical, pneumatic or hydraulic shifting member, such as, for example, a screw jack, is suitable for use as a shifting member.

Fig. 3 is a more detailed schematic view of the structure of the external slide bearing system 16 in accordance with the invention. The slide bearing system 16 includes a bearing body 21 fixedly attached to the frame F of the multi-roll calender 1. The bearing body 21 can also be attached by means of adjustment pieces to the frame F of the multi-roll calender 1. The bearing body 21 is provided with hydrostatic vertical bearing elements 23 placed around a shaft 22 of the intermediate roll 11, 12, 13, 14. The vertical bearing elements 23 are provided with slide elements 24, which have a slide surface 24a directed towards the shaft. The slide surface 24a is arranged directly or indirectly against an outer surface 22a of the shaft 22 to support said shaft 22 and thereby the intermediate roll 11 , 12, 13, 14 rotatably with respect to the bearing body 21. The slide elements are arranged to conduct a lubricant between the slide surface and the shaft, for example, along capillary ducts, such that during operation the shaft rotates while hydrostatically supported by a lubricant film. At one end of the intermediate roll the slide bearing system comprises an axial bearing arrangement 25 that retains the roll in the axial direction, at the other end the roll can move on support of the slide bearing system 16 in the axial direction to allow thermal expansion. The slide bearing system 16 additionally comprises two side bearing arrangements 26 on the opposite sides of the shaft 22, of which bearing arrangements only one is shown here although both are advantageously situated on the opposite sides of the shaft. A slide element 27 of the side bearing arrangement 26 is provided with a slide surface 27a. At the axial ends of the bearing body 21 there are end covers with their sealing members to seal the bearing body 21 in a lubricant-tight manner around the shaft 22. The side bearing arrangement 26 is accomplished such that it allows a transverse movement for the shaft 22. In that connection, the slide surface 27a can follow the roll in the vertical direction and the seal follows the resulting position error. This ability of the side bearing to follow the shaft 22 must be dimensioned suitably and taken into account when dimensioning the motion range of the vertical bearing arrangement 23. The side bearing arrangement is advantageously accomplished using pressure distribution valves such that the

bearing arrangement attempts by itself to centre the roll 11, 12, 13, 14 shell with respect to the shaft 22.

The side bearing arrangement 26 can also be mounted so as to be in synchronicity with the vertical bearing elements, for example, in the bearing body 21 such that the side bearing arrangement 26 moves along with the shaft in such a way that the position of the slide surface 27a with respect to the side bearing arrangement 26 and the shaft 22 does not change. The side bearing arrangement damps vibration reasonably well and positions the shaft accurately enough.

A check valve combined with a slide element 24 is used as vertical slide bearing elements. The slide element 24 is advantageously provided with capillaries or tubes and lubrication pockets, from which a hydraulic fluid serving as a pressure medium is distributed under constant pressure to the area of the slide bearing between the slide surface 24a and the shaft 22.

The axial bearing arrangement shown in Fig. 3 is based on a ring disposed on the shaft 22 or on a bearing arrangement disposed directly on a shaft journal, on support of which bearing arrangement the shaft is mounted in the longitudinal direction by means of the axial bearing 25. Alternatively, the shaft 22 can be mounted by means of bearings at both ends in a manner similar to that of the axial bearing system of press rolls by disposing, at one end of the shaft 22, a first axial bearing loaded by a constant pressure and, at the opposite end of the shaft, a second axial bearing loaded by controllable axial control pressure. The first and second axial bearings are arranged to mount the roll in the longitudinal direction and allow the roll to be positioned in the longitudinal direction by control of a controlling check valve. In that case, the side and vertical bearing arrangement of the roll can be connected to the body firmly and in a vibration-reducing manner without a possibility of axial play. It is also possible to arrange axial controllability for the axial bearing arrangement 25 shown in Fig. 3, for example,

in connection with maintenance of the roll so that the longitudinal position of the roll can be changed.

Pressure connections of the slide bearing system 16 are shown, in principle, in Fig. 4 with respect to the vertical bearing element 23 above the axle 22 and in Fig. 5 with respect to the vertical bearing element 23 under the shaft 22. The figures illustrate the interchangeability of the slide bearings and the interchangeability of the bearing elements. The system pressure of the check valves serving as a hydrostatic pressure component of the slide bearing system 16 loadable in two directions is denoted with PJ in Figs. 4 and 5. In Fig. 4, the constant pressure of the stroke side is designated by Pl. The outward-directed stroke pressure of the stroke-side check valve is designated with PiI and, correspondingly, the inward- directed stroke pressure of the stroke-side check valve is designated with PiO. The check valves are advantageously controlled mechanically by means of a backing member 28 provided in the vertical bearing element 23, which backing member is, for example, a pin or a rod that complies with the movement of the shaft 22 or follows with the slide element 24. When the backing member 28 is operating the check valve in the direction of the constant pressure Pl; P2, the backing member 28 accomplishes pressure control of loading mechanically. The supply pressure of the side bearing 26 is designated with PS and the supply pressure of the axial bearing 25 is designated with PA (Fig. 6). Forces in each nip can be controlled by regulating constant pressures: Pl on the stroke side and P2 on the opposite side of the stroke. Constant-pressure hydraulic fluids are advantageously used for forming a hydrostatic support between the slide surface 24a of the slide element 24 and the shaft 22. The opposite ends of the rolls are advantageously connected to common pressure connections so that both ends of the rolls move in the same manner. If the weight distribution of the rolls is not naturally symmetric, difference can be corrected hydraulically or mechanically.

The hydrostatic actuating member operating the check valve, shown in Figs. 3, 4 and 5, advantageously allows quick positioning of the roll with hydraulic

feedback such that the roll can be moved between calendering and servicing stations by means of the hydraulic system using members inside the bearing system. To control the load of the rolls, the hydraulic actuating member has a separate constant pressure circuit from the circuit provided for quick movement of the rolls. The hydraulic actuating members can thus be contemplated to comprise two parts operated independently of each other.

The method of the invention for operating a multi-roll calender can be illustrated by means of a series of figures which are described in more detail below and in which Fig. 6 shows a nip open situation in connection with the intermediate roll 11 , in Fig. 7 the nip above the intermediate roll 11 is open and the nip under it is closed, and Fig. 8 shows the intermediate roll 11 in a situation where the nips of the intermediate roll are closed. By means of the method, the nips of the multi-roll calender can be closed, opened or loaded in a versatile manner, also in different directions. The method makes it possible to separately close, open or load the roll nips in a calendering group formed by the rolls of the calender without control devices placed outside the bearing systems of the rolls, such as loading arms of the rolls known in the art.

Fig. 6 shows a nip open situation in connection with the intermediate roll 11 of the left-hand roll stack Ia of Fig. 1. In the slide bearing system 16 in accordance with the invention, similar components are used as hydrostatic pressure components in both upward and downward loading directions. The lower check valve 30 of the slide bearing system 16 is in a strike position, i.e. pushed out. Consequently, the nip N2 below the intermediate roll 11 is open. The top roll 10 of the left-hand roll stack has also been raised up using the hydrostatic pressure component below the shaft so that the nip Nl above the intermediate roll 11 is open. In that connection, the check valve 30 of the stroke side carries the mass of the roll 11. On the side of the upper bearing component 40 of the slide bearing system 16, i.e. on the opposite side of the lower component, there is a constant pressure P2 that secures lubrication flow. The constant pressure P2 is, for example, about 1 MPa. The

operation of the upper check valve 40 starts when the roll 11 has risen a little, for example, 0.1 mm - 1 mm, which is above the range of operation of the lower check valve 30. In other words, the operation of the upper check valve starts only after the operation range of the lower check valve has ended and the lower check valve has closed, so that only a controlled constant pressure remains for the lower bearing arrangement. In that case, a situation cannot arise in which the bearing system of the roll is controlled by the check valve in both directions. In Fig. 6, the roll 11 rests on the lower check valve 30, which adjusts a suitable supporting pressure. If the intermediate roll 11 moves upwards or downwards when both valves 30, 40 are pressurized and the hydrostatic pressure components on both sides of the shaft operate ideally, the check valves limit the movement to a distance by which the check valve is adjusted to its full position, for example, to 0.05 millimetres. The operation range of the check valves of the slide bearing system can be controlled by controlling the length of the mechanical backing member 28 of the upper and lower bearing element 30; 40, which backing member is described in connection with Figs. 4 and 5.

Fig. 7 shows the position of the intermediate roll of Fig. 1 in a situation where the roll under the depicted roll has been raised by means of its vertical bearing below the shaft into contact with the depicted roll. When the movement of said roll under the depicted roll continues, the depicted roll closes the nip gap above it and reaches the situation of Fig. 8.

Fig. 8 shows the position of the intermediate roll 11 of Fig. 1 in a situation where the upper nip Nl and the lower nip N2 are closed, for example, in a matte operation situation. In that case, the lower hydrostatic actuating member, i.e. the lower check valve 30, is in a stroke position. The upper hydrostatic actuating member 40 loads the shaft downward only with a pressure Pl required by lubrication flow. The constant pressure P2 of the lower hydrostatic actuating member now carries the mass of the roll 11 and the load caused by lubrication above the shaft less the load required for the matte operation. The lower check

valve 30 is also supplied with the necessary constant pressure to ensure lubrication flow.

The nips of the right-hand roll stack in Fig. 1 can be controlled in at least two different ways. To reduce the rolls' tendency to wander, it is advantageous to mount the upper thermo roll fixedly. In that case, the upper deflection compensated roll 10' is raised out of contact with the upper thermo roll and again lowered into contact with this, as needed. The centre roll 13 (typically a polymer roll), the lower thermo roll 14 and the bottom roll 15' are separated from the upper thermo roll by lowering the rolls on support of the bottom roll 15' until they stop to their own limiters in succession, beginning from above, and leave a nip gap of, for example, about 10 mm above them. In a corresponding manner, when it is desirable to close the rolls from the bottom roll 15' to the centre roll 13, the bottom roll is started to be raised by driving its lower hydrostatic actuating member to its pushed-out position, so that the bottom roll lifts the lower thermo roll against the polymer roll and the thus formed group of three rolls further against the upper thermo roll when the movement is continued. As a second alternative, the upper thermo roll can be released allowing it to move down out of contact with the top roll when the bottom roll and the rolls resting on it are started to be lowered such that the nips open one by one from above downward. Similarly, the nips can be closed and loaded by driving the bottom roll from below upward up to the topmost nip N3. The invention also allows the roll nips to be opened, for example, from below upward or in a direction away from the middle. The nips can be closed in the same order as or in a different order from that in which they were opened. Some of the nips can also be left open or unloaded, for example, for matte operation. In all movements, the nip loads must be monitored so that none of the nips is overloaded considering the properties of the rolls and the fibrous web. This can be accomplished simply by monitoring and, when needed, limiting the constant pressures Pl and P2.

Above, the invention has been described by way of example with reference to the figures in the accompanying drawings. However, the invention is not limited exclusively to the disclosure in the description and in the figures, but the different embodiments of the invention may vary within the inventive idea defined in the appended claims.