Abstract:
A deflection compensated roll has a stationary support structure and a shell rotatably arranged around it by means of slide bearings. The shell is additionally supported on the support structure with hydraulic loading devices by which the axial profile of the shell can be controlled. In the procedure, at least the pressure acting in the main bearing elements of the slide bearings effective in oppsite directions in the nip plane is measured by conducting pressure data from a pressure space between a control valve associated with the main bearing elements and each main bearing element by means of measurement ducts outside the roll where the pressure data is passed to a pressure sensor.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority on Finnish Application No. 20000873, Filed Apr. 12, 2000, the disclosure of which is incorporated by reference herein. 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for measuring slide bearing pressure in a deflection-compensated roll with a fixed shell. 
     In paper and board machines, deflection-compensated rolls (TK) are in general used which are formed from a stationary support structure and a tubular shell arranged to rotate therearound, said shell being bearably carried on the ends to a support structure by end bearings. Between the shell and the support structure, hydraulically loaded loading elements are moreover provided, being supported to the support structure and acting on the inner face of the shell in a radial direction, wherewith the profile of the shell can be adjusted in the axial direction. A row of loading elements to be used for adjusting the profile of the shell is positioned in the nip plane and with said loading elements, the bending of the shell of the TK roll and the backing roll is compensated so that the force acting on the web in the nip plane is equal across the entire axial direction of the shell. To intensify the profiling, so-called loading elements forming a counterzone can in addition be used on the opposite side of the support structure in relation to the nip in the TK roll. The loading elements of the counterzone can be positioned in one row, whereby a row is in the nip plane, or in two rows, whereby the rows are located symmetrically on both sides of the nip plane. By means of the loading members of the counterzone the shell can also be loaded with a desired force, whereby the configuration of the shell is profiled to be as desired. 
     The TK rolls can be divided into rolls with a mobile shell and rolls with a fixed shell. In the present context the TK rolls with a mobile shell refer to rolls in which the end bearings can be moved in radial direction, that is, normally in the nip plane relative to the support structure, whereby also the shell moves together with the end bearings in the nip plane. Transferring of end bearings is normally carried out so that pressure spaces acting in the nip plane are arranged between the end bearings and the support structure. By conducting a pressure medium into said pressure spaces, the end bearings can be transferred in the nip plane. By means of said transfer of the end bearings relative to the support structure, the opening and closing of the nip can be carried out, as well as partial loading and relief of the TK roll against the backing roll. 
     The TK rolls with a fixed shell refer to rolls in which the shell is not, at least to a significant extent, moved in a radial direction relative to the support structure. On fixed-shell TK rolls, the opening and closing of the nip and the loading and relief of the TK roll against the backing roll are performed with hydraulically operating loading arms supported to the support structure of the TK roll. In fixed-shell rolls, mechanical rolling bearings or hydraulic slide bearings can be used as end bearings. In a fixed-shell roll provided with rolling bearings, the end bearings are locked in radial direction to the support structure and the shell is locked in radial direction to the end bearings. In a fixed-shell roll provided with hydraulic slide bearings, the shell is able to move slightly in a radial direction owing to the nature of the bearing. 
     In rolls with a mobile shell and a fixed shell, rolling bearings or slide bearings can be used for end bearings between the shell and the support structure. 
     The present invention can be embodied in fixed-shell TK rolls provided with hydraulic slide bearings, in which the slide bearing operation is carried out essentially without strokes. 
     In FI patent No. 76870 (Kleinewefers GmbH), a TK roll with a fixed shell is disclosed, in which the shell is bearably carried on the ends of a support structure with rolling bearings. Indicators are arranged in the area of the rolling bearings, the measurement values of which indicate loading of the end bearings in the nip plane. By means of a control device, pressures to be supplied to the loading shoes of the loading zone and the loading shoes of the backing zone are controlled, being dependent on parameters measured in operation and/or determined in advance, and depending on the measurements of the indicators so that the loading of the end bearings is approximately zero in the nip plane. 
     Instead of measuring the direct bearing force with the aid of indicators arranged in the area of the rolling bearings, the forces acting on the rolling bearings can be defined also indirectly. This can be carried out by measuring the forces acting on the support spots of the support structure of the backing roll, the forces acting on the support spots of the support structure of the TK roll and the forces caused by the loading devices on the shell of the TK roll. On the basis of said forces, the forces acting on the rolling bearings of the TK roll are calculated. In the loading spots in which the forces are generated with the hydraulic loading devices, the pressures of the hydraulic loading devices are measured and on the basis thereof and of the surface areas of the pressure chambers of the pistons of the hydraulic loading devices, the forces acting on the hydraulic loading devices are calculated. In the calculations, the masses acting in the support spots and the friction factors acting in different locations are moreover paid attention to. The bearing force calculated with this kind of method is naturally inaccurate. 
     FI patent No. 79177 discloses a deflection-compensated roll with a mobile shell provided with rolling bearings. Therein, the shell is bearably carried on both ends to the support structure with rolling bearings arranged on top of the annular parts. Between the annular parts and the support structure, hydraulic loading members are disposed. With the loading members, the shell can be transferred relative to the support structure for opening and closing the nip. By the loading members, the shell can also be loaded against the backing roll. 
     In the mobile-shell TK rolls, in which a transfer of the end bearings based on the rolling bearings is carried out with a hydraulics medium brought into the pressure spaces between the bearings and the support structure, the pressure of the pressure medium conducted into said pressure spaces can be measured. A certain nip profile requires the use of a bearing force of a given magnitude, whereby the pressure equivalent thereto is tried to be kept under the bearing. The bearing force is determined on the basis of the surface areas of the pressure spaces influencing the bearings. 
     SUMMARY OF THE INVENTION 
     With the method according to the invention, sufficiently precise information is achieved each time of the pressures acting on the slide bearings of the fixed-shell TK roll being carried with slide bearings, on the basis whereof the forces acting on the slide bearings can be calculated. 
     The slide bearing of a TK roll comprises main bearing elements acting in opposite directions in the nip plane and side bearing elements acting in a transverse direction relative to the nip plane. Immediately below the first main bearing element focussed on the nip, that is, the guiding main bearing element, a first control valve is positioned, which on the basis of the loading acting on the main bearing elements distributes the pressure medium between the main bearing elements. To that main bearing element on which a greater load is at each moment acting, a greater flow and pressure is fed and respectively, to an opposite main bearing element, a lesser flow and pressure is fed. The control of the side bearing elements is carried out in an equivalent manner with the aid of a second control valve. The control valves should be located right below the guiding bearing element so that their response to an external loading can be made as brief as possible. 
     The invention is described below in detail, referring to the example embodiments of the invention presented in the figures of the accompanying drawings, whereto the invention is not intended to be solely restricted. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 presents a schematic longitudinal section of one end of a fixed-shell, deflection-compensated roll provided with slide bearings, shown above the central axis. 
     FIG. 2 presents a schematic cross-section of the end of the roll of FIG. 1 at the hydraulic slide bearing. 
     FIG. 3 presents a schematic cross-section of an arrangement of measurement tubes used in measuring pressures of the slide bearings. 
     FIG. 4 presents a schematic longitudinal section of an arrangement of measurement tubes used in measuring pressures of the slide bearings. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 presents a schematic longitudinal section of one end of a fixed-shell, deflection-compensated roll  10  provided with slide bearings  13  shown above the central axis X—X. The roll  10  comprises a stationary support structure  11  and a shell  12  rotating therearound. The shell  12  is supported on the ends to the support structure  11  by means of hydraulic slide bearings  13 . Between the hydraulic slide bearings  13 , the shell  12  is moreover supported in the nip plane to the support structure  11  by means of hydraulic loading devices  14 . The end of the roll is closed with an end piece  15  supported in axial direction to the support structure  11  with a support member  16 . The support in axial direction may also be implemented in the other end of the roll only, whereby support members  16  are provided in axial direction on both sides of the end piece  15  of the roll. An individual supply duct  20  for pressure medium leads here to each loading device  14 , whereby each loading device  14  can be adjusted individually. The loading devices  14  may also be divided into groups so that one pressure medium supply duct  20  is inside the roll divided for a number of loading devices  14  so that each group forms one adjustment zone. In an extreme case, a group may extend onto the length of the entire nip, whereby the roll is provided with one zone and one supply duct  20  only. The control valves of the pressure medium ducts  20  leading to the loading devices  14  can be located in a separate control valve unit outside the roll (not shown in the figures) or they may be attached to the end part of the roll axle. On the other hand, the control valve  22  positioned in the pressure medium supply duct  21  leading to the slide bearings  13  may be located in the immediate adjacency to the slide bearings  13 . 
     The hydraulic end bearing shown in FIG. 2 is comprised of end bearing elements  13   a,    13   b  acting in opposite directions in the main loading direction, that is, in the direction of the nip plane A—A, and of side bearing elements  13   c,    13   d  acting transversely in opposite directions to the nip plane A—A. With the main bearing elements  13   a,    13   b,  the position of the shell  12  is adjusted relative to the nip plane A—A. With the side bearing elements  13   c,    13   d,  the shell  12  is kept in right position transversely to the nip plane A—A. With the main bearing elements  13   a,    13   b  and the side bearing elements  13   c,    13   d,  also the oscillations are attenuated in the direction of the nip plane A—A and respectively, in the transverse direction. A first main bearing element  13   a  acting in the nip direction in the nip plane A—A is a so-called guiding bearing element and a second main bearing element  13   b  acting in the opposite direction is a so-called slave bearing element. Respectively, a first side bearing element  13   c  acting in transverse direction is a guiding bearing element and a second side bearing element  13   d  acting in opposite direction is a slave bearing element. 
     The supply of pressure medium to the bearing elements  13   a,    13   b,    13   c,    13   d  is carried out so that in a first supply line  21   a  the pressure medium is supplied to a first control valve  22   a  located immediately under the first main bearing element  13   a.  Said first control valve  22   a  distributes in turn the pressure medium to the first main bearing element  13   a  and to the opposite second main bearing element  13   b.  In addition, the pressure medium is supplied in a second supply line  21   b  to a second control valve  22   b  immediately under the first side bearing element  13   c,  said valve distributing the pressure medium to the first side bearing element  13   c  and the opposite second side bearing element  13   d.  The control valves  22   a,    22   b  distribute the pressure medium so that, irrespective of the external loading directed at the roll, a power balance is created between the bearing elements  13   a,    13   b;    13   c,    13   d  being in opposite directions so that the shell  12  is kept in desired position relative to the bearing housing. 
     When loading is directed at the roll, e.g. in the direction of the nip at the first main bearing element  13   a,  the first control valve  22   a  increases the pressure and flow of the pressure medium supplied to the first main bearing element  13   a,  and, respectively, decreases the pressure and flow of the pressure medium to the second main bearing element  13   b,  whereby the shell  12  is kept stationary relative to the bearing housing. 
     In the arrangement shown in FIGS. 3 and 4 a measurement duct system  30  is shown, being conducted in a duct  31  formed in the support structure  11  into the roll at one end of the roll. Here, the measurement duct system comprises nine measurement ducts  30 , each being inside the roll connected to the object to be measured. The slide bearing on each roll end contains four bearing pressures, of which measurement data is desired and in addition, one measurement duct is used e.g. for measuring the pressure prevailing inside the roll. Each of the measurement ducts is connected inside the roll to a pressure space between a bearing element  13   a,    13   b,    13   c,    13   d  and a control valve  22   a,    22   b  in association with the bearing element, whereby the pressure acting on the pressure chamber under the piston of the bearing element can at all times be measured. FIG. 2 shows a measurement point M 1  in association with a first bearing element  13   a,  a measurement point M 2  in association with a second main bearing element  13   b,  a measurement point M 3  in association with a first side bearing element  13   c  and a measurement point M 4  in association with a second side bearing element  13   d.    
     The measurement duct system is taken out of the roll through a flange structure  40  attached to an end of the roll. The measurement ducts are sealedly attached to the flange structure  40  and the flange structure is attached sealedly to the support structure of the roll in order not to release pressure medium and any overpressure possibly prevailing inside the roll. Outside the roll, the measurement ducts  30  can be connected to measurement connectors  50  attached to an appropriate base. On the other end of the measurement connector  50 , ducts  51  leading to measurement sensors  60  may in turn be connected [(not shown in the figures)]. 
     The measurement duct system  30  can be comprised of individual measurement ducts arranged to pass in a space between the support structure  11  and the shell  12 . The measurement ducts or some portions thereof may also be implemented as borings made in the support structure  11 . 
     By means of the measurement arrangement of the invention, the pressure of each slide bearing element of the slide bearings on each end of the roll can be measured, on the basis whereof the force acting on said bearing element can be calculated. Bearing forces can be used for adjusting to a desired level the forces acting on the nip. In this manner, the rightfulness and controllability of the nip profile is brought to the same level as in slide-bearably carried rolls with a mobile shell. 
     The measured bearing forces may also be utilized in error diagnostics. When the forces acting on the slide bearings are moreover calculated in conventional fashion indirectly from other forces acting on the nip, a directly measured bearing force and an indirectly calculated bearing force are available. Hereby, calibration of parameters used in the calculation can be carried out so that the indirectly calculated bearing forces correspond to the directly measured bearing forces. 
     If the directly measured and the indirectly calculated calibrated bearing forces change thereafter as a function of time relative to each other, such conclusions may be drawn thereon that a valve or a sensor acting on the nip is faulty or requires calibration. 
     If, on the other hand, the thickness profile of a calendered web is deteriorating rapidly without any changes in the bearing force, the fault lies obviously in the thickness profile of the entering web, that is, before the calender. 
     On the basis of a measurement of the bearing force, also the condition of the rolls can be estimated. Variations in the bearing pressure synchronized with the speed of rotation of the TK roll are an obvious indication of a fault in the TK roll or in the banking roll  61 , of non-roundedness, of resemblance to a banana, of a coating being damaged or of dirt accumulated e.g. on the surface of the roll. Pressure measurement and pressure oscillation can be used, in addition to other measurement data, e.g to prevent a more serious roll damage or e.g. disengaging of the coating. In a situation in which a measurement of bearing force indicates damage, the nip can be opened in order to prevent more serious damage. 
     In the embodiments of the figures, one main bearing element  13   a,    13   b  is provided in the nip plane A—A in both directions, though each main bearing element  13   a,    13   b  may, in fact, be comprised e.g. of two partial bearing elements. The partial bearing elements are in such instance located symmetrically on both sides of the nip level A—A. 
     The claims are presented below, within the scope of the inventive idea determined by which various details of the invention may vary and deviate from what is described above only in exemplary fashion.