METHOD FOR REGULATION OF THE TEMPERATURE IN THE END AREAS OF THE ROLL MANTLE OF A VARIABLE-CROWN ROLL PROVIDED WITH GLIDE BEARINGS

Abstract: The invention concerns a method for regulation of the temperature in the end areas of the roll mantle of a variable-crown roll provided with glide bearings and/or for compensating for an error in the diameter of the roll arising from thermal expansion. The roll mantle (12) of the roll (10) is supported adjustably on the roll axle (11) by means of hydraulic loading elements (17, 17a) loaded by means of a pressure medium and acting upon the inner face of the roll mantle (12) at least in the direction of the nip plane. Further, the roll mantle (12) is supported on the roll axle (11) by means of hydraulic glide-bearing elements (14, 14a, 15, 16) loaded by means of a pressure medium and fitted in the areas of the ends of the roll mantle. In the method, into the end areas of the roll (10), a pressure medium is supplied, whose temperature and/or flow is/are regulated so as to keep the temperature in the end areas of the roll mantle (12) at the desired level, substantially at the same level as the temperature in the middle area of the roll (10).

Description: Method for regulation of the temperature in the end areas of the roll mantle of a variable-crown roll provided with glide bearings The invention concerns a method for regulation of the temperature in the end areas of the roll mantle of a variable-crown roll provided with glide bearings and/or for compensating for an error in the diameter of the roll arising from thermal expansion in a roll, whose roll mantle is supported adjustably on the roll axle by means of hydraulic loading elements loaded by means of a pressure medium and acting upon the inner face of the roll mantle at least in the direction of the nip plane, and which roll mantle is supported on the roll axle by means of hydraulic glide-bearing elements loaded by means of a pressure medium and fitted in the areas of the ends of the roll mantle. Variable-crown rolls are needed and used in paper machines, for example, in presses and in calenders, and, further, such rolls are used in paper finishing devices, such as supercalenders. Thus, it is an essential feature of such variable-crown rolls that said roll forms a nip with a backup roll, the paper web being passed through said nip. The roll is provided with necessary crown variation means, by whose means the roll mantle is loaded in the direction of the nip plane and by whose means the nip profile is controlled. Earlier, it was the commonest solution in variable-crown rolls that the tubular roll mantle of the roll was mounted from its ends on the roll axle by means of roller bearings. Such a conventional mode of journalling also had its advantages, for example, the journalling can be accomplished in a rather simple way, and, so far, the cost of this solution has been considered to be relatively reasonable. Such a conventional mode of journalling, in which the roll mantle is mounted from its ends stationarily on the axle, is, however, not suitable for even nearly all applications in paper machines. From variable-crown rolls which are in nip contact with a backup roll, quite often such a property is required that the roll mantle must be able to move in the radial direction in relation to the roll axle. In view of regulating the profile of linear load across the entire axial length of the roll, the roll ends must also be able to move in the radial direction in relation to the axle. This is why rolls have been developed in which this property has been accomplished so that the end bearings of the roll mantle have been mounted on separate annular parts, which can move radially in relation to the roll axle. One such roll is described, for example, in the EP Patent No. 0,332,594. Mounting of a roll by means of roller bearings has, however, caused a number of drawbacks and problems for the manufacture and operation of the roll. These drawbacks include the numerous machinings required by the roller bearings, the problems arising from wear of the bearings, limitations imposed by the roller bearings in respect of the oil used in the roll, limitations of running speeds with roller bearings, and accuracy of rolling of the bearings. This is why there has been a desire to abandon the roller bearings, and in recent years variable-crown rolls have been developed in which the journalling of the roll mantle has been accomplished by means of glide bearings. Such rolls with glide bearings have been described, for example, in the US Patents Nos. 5,060,357 and 5, 111,563 and in the Finnish Patent Applications Nos. 941107, 941991, 944272, and 950814. It is a problem in rolls with glide bearings that the end areas of the roll may be heated excessively, which has a highly detrimental effect on the nip profile. Heating of the end areas is, of course, a problem also in variable-crown rolls of other types which form a nip with a backup roll. One important factor in the excessive heating of the end areas is, among other things, the fact that in the middle area of the roll the heat can be conducted away from the roll through the paper web, whereas the ends are heated, because the web is substantially narrower than the roll mantle. In a roll with glide bearings, the risk of heating of the end areas can be even higher, because the generation of heat in a glide bearing is higher than in a roller bearing. The gener- ation of heat in the ends in a roll with glide bearings is a particular problem also because several glide bearing elements are effective at the same location on the inner circumference of the roll mantle. Part of the h at that is generated is, of course, carried away from the areas of the ends along with the oil flowing through the glide bearing, but in normal cases the quantity of oil is not sufficiently large to carry away the heat. The object of the present invention is to provide a novel method, by whose means an excessive generation of heat in the end areas of a roll provided with glide bearings and the problems arising from said generation of heat are avoided. In view of achieving this objective, the invention is mainly characterized in that, in the method, into the end areas of the roll, a pressure medium is supplied, whose temperature and/or flow is/are regulated so as to keep the temperature in the end areas of the roll mantle at the desired level, substantially at the same level as the temperature in the middle area of the roll. The advantages provided by means of the present invention over the prior-art solutions are based on the very fact that the heating of the end areas of the roll mantle are brought under control. As a result of this, the axial temperature profile of the roll does not distort the nip profile. The further advantages and characteristic features of the invention will come out from the following detailed description of the invention. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic sectional side view of a roll provided with glide bearings, to which roll the method of the present invention can be applied. Figure 2 is a schematic sectional view taken along the line II-II in Fig. 1. Figure 3 is a schematic longitudinal sectional view of one end area of a roll with glide bearings and of a first embodiment carrying out the method of the invention. Figure 4 is an illustration similar to Fig. 3 of a second embodiment of the method in accordance with the invention. Figure 5 is an illustration similar to Figs. 3 and 4 of a third embodiment of the invention. Figure 6 shows a fourth embodiment of the invention by means of a cross-sectional view of the roll. Thus, Figs. 1 and 2 are fully schematic sectional views of a tubular roll provided with glide bearings so that Fig. 1 is a sectional view of the roll taken in the axial vertical plane, and Fig. 2 is a sectional view of the roll of Fig. 1 taken along the line II-II. In Figs. 1 and 2 the roll is denoted generally with the reference numeral 10. The roll 10 is a variable-crown roll, which comprises a stationary roll axle 11 , on which a tubular roll mantle 12 is fitted revolving, which mantle 12 is supported on the roll axle by means of hydraulic loading elements 17 and by means of a second set of hydraulic loading elements 17a acting in the opposite direction. In the exemplifying embodiment shown in Fig. 1, the hydraulic loading elements 17, 17a act in the direction of the nip plane, and by their means it is possible to regulate the shape of the roll mantle 12 and to control the axial nip profile of the roll. As is shown in Figs. 1 and 2, the roll 10 is a roll mounted exclusively by means of glide bearings, so that the roll 10 has no conventional roller bearings fitted at the roll ends at all. The journalling of the roll 10 has been accomplished by means of glide bearing elements, of which the glide bearing elements acting in the loading direction, i.e. in the direction of the nip plane in the case of the roll as shown in Figs. 1 and 2, are denoted with the reference numerals 14 and 14a. The first glide bearing elements 14 act in the direction of the nip, i.e. against the load, and the second glide bearing elements 14a in the opposite direction. In the exemplifying embodiment shown in Figs. 1 and 2, it is shown further that the roll 10 is also provided with glide bearing elements 15,15a acting in opposite directions transverse to the loading direction. As was stated above, the roll 10 is a roll exclusively provided with glide bearings, so that it is also provided with glide bearing elements 16, 16a acting in opposite directions in the axial direction, which elements 16,16a are supported against the roll ends 13,13a by the intermediate of oil films. As is shown in Figs. 1 and 2, the glide bearing elements 14, 15, 14a, 15a are supported in the radial direction against the inner face of the roll mantle 12 by means of oil films. In the solution shown in Fig. 1, the glide bearing elements 14, 14a, 15, 15a that act in the radial direction have been arranged in pairs, so that there are two of each of said glide bearing elements, arranged side by side in the axial direction. The operation of the roll 10 does, however, not necessarily require such an arrangement, for the journalling can also be accomplished by means of single glide bearing elements alone. Such solutions are described in more detail in relation to Figs. 3...5. Fig. 2 concerns an embodiment in which the glide bearing elements 14, 14a, 15, 15a have been arranged to act in the direction of the primary loading plane and in the direction transverse to said plane. However, glide bearing elements can also be arranged radially in positions different from Fig. 2, in which case their number can also be different from that shown in Fig. 2. Regarding the glide bearing elements 16,16a acting in the axial direction, it can be stated that, differing from Fig. 1, the axial movements of the roll mantle 12 can be controlled by means of just one set of glide bearing elements 16, 16a acting in the same plane in opposite directions. On the other hand, there may be a greater number of these axial glide bearing elements 16,16a, which can be fitted, for example, as uniformly spaced in relation to one another, to act upon the inner faces of the roll ends 13,13a. The description given above in relation to Figs. 1 and 2 is expressly concerned with the general construc- tion of a roll with glide bearings. Fig. 3 illustrates a first embodiment of the method in accordance with the invention. With respect to the general construction of the roll 10, reference is made to the description related to Fig. 1 , and in this respect, in Fig. 3, reference denotations corresponding to Fig. 1 have been used. However, Fig. 3 differs from the illustra¬ tion of Fig. 1 in the respect that while in the roll 10 of Fig. 1 glide bearing elements arranged in pairs were employed, in the embodiment shown in Fig. 3 said elements have been substituted for by glide bearing elements 14, 14a, 15 arranged in one row. The solution as shown in Fig. 3 can, of course, also be applied in connection with a roll as shown in Fig. 1. In Fig. 3, the regulation of the temperatures in the end areas of the roll mantle 12 has been arranged so that, to the glide bearing elements 14, 14a, 15, 16 acting radially and/or axially at the roll ends, a supply 20,21 of pressure fluid of their own, separate from the hydraulic elements 17,17a of the roll 10, has been provided, so that the feed duct 20a has been provided with a regulation device 22 in order to control the supply of the pressure fluid. Said regulation device 22 can be a device that regulates the temperature (a heat exchanger or a device connected with a heat exchanger), in which case said regulation device 22 regulates the temperature of the pressure fluid supplied to the glide bearing elements 14,14a, 15, 16 to the desired level. Normally this desired level means that the temperature of the pressure fluid fed to the glide bearing elements 14, 14a, 15, 16 is lower than the temperamre of the pressure fluid passed to the hydraulic loading elements 17,17a. The temperature of the pressure fluid passed to the hydraulic glide bearing elements 14, 14a, 15, 16 is defined in accordance with the running speed and the loading situation. Sufficient accuracy can be achieved if the temperature is defined as variable with certain steps of running speed. On the other hand, the arrangement in accordance with Fig. 3 can be arranged so that the regulation device 22 is a flow regulator, by whose means the volumetric flow of the pressure fluid fed to the glide bearing elements 14, 14a, 15, 16 is regu¬ lated. In practice this means that the volumetric flow is adjusted to a higher level ("additional fluid" is fed to the glide bearing elements 14, 14a, 15, 16), in which case this larger flow equalizes the temperamre of the roll. In such a case, the temperamre of the pressure fluid fed to the glide bearing elements can be the same as the temperamre of the pressure fluid passed to the hydraulic loading elements 17, 17a. The supply of additional fluid can be arranged through the separate line shown in Fig. 3, or the supply of additional fluid can be arranged, for example, so that, as the glide bearing elements 14, 14a, 15, 16, shoes with invariable fluid flow of the sort described in the FI Patent Application 935165 are used. By means of such a shoe with invariable fluid flow, the volumetric flow of the pressure fluid passing through the shoe can be regulated in the desired way. Further, in the case of Fig. 3, it is possible to use a combination in which the temperamre of the pressure fluid is regulated by means of a regulation device 22, and the volumetric flow of the pressure fluid is regulated by means of the shoes with invariable fluid flow employed as the glide bearing elements 14, 14a, 15, 16. Fig. 4 shows an embodiment of the invention in which additional fluid is fed to the end areas of the roll into the space between the roll mantle 12 and the roll axle 11 through a separate duct. The feed duct for additional fluid is connected with a regulation device 23, which operates either as a device that regulates the temperamre or as a device that regulates the volumetric flow. If the regulation device 23 regu¬ lates the temperamre, the fluid feed devices 20,21 feed the fluid as of invariable volumetric flow. On the other hand, if the regulation device 23 regulates the volumetric flow, the temperamre of the additional fluid can be kept invariable. Thus, in the embodiment of Fig. 4, the regulation of the temperamre of the end areas of the roll is carried out by to the end ares supplying additional fluid and by regulating the temperamre or the volumetric flow of said additional fluid. The embodiment shown in Fig. 5 is in the other respects similar to the solution shown in Fig. 4, however, with the exception that the duct for the supply of additional fluid is provided with two regulation devices 24,25. One of the regulators can operate, for example, as a device that regulates the temperamre, whereas, by means of the other regulation device 25, the volumetric flow of the additional fluid is regulated. Thus, in the embodiment of Fig. 5, in view of regulation of the temperamre in the end areas of the roll 10, both the temperamre and the volumetric flow of the additional fluid are regulated. Fig. 6 shows a further embodiment of the invention. In the embodiment of Fig. 6, as a matter of fact, the temperamre of the end of the roll mantle is not regulated, but in this solution the error arising from thermal expansion in the shape of the roll mantle is regulated, which error again causes a fault in the nip profile. As was explained above, the ends of the roll 10 become hotter than the rest of the roll, whereby, owing to thermal expansion, the diameter of the roll mantle 12 becomes larger and produces a fault in the nip profile. In the embodiment shown in Fig. 6, this fault arising from thermal expansion has been compensated for and eliminated so that the roll mantle 12 is spread by means of the glide bearing elements 15, 15a acting in the direction transverse to the nip plane. This spreading of the roll mantle is illustrated in Fig. 6 schematically and with abundant exaggeration by means of dashed lines. As is seen from Fig. 6, when the roll mantle 12 is spread in the transverse direction, its diameter is, of course, reduced in the direction of the nip plane, in which case, by means of a suitable spreading force, the diameter of the roll mantle in the nip plane can be kept equal across the entire axial length of the roll mantle. In other words, the error arising from thermal expansion can be compen¬ sated for. In the regulation of the temperatures in the end areas of the roll 10 mantle and in compensating for the error arising from thermal expansion, it is, of course, possible to use various combinations of the embodiments described above. In different embodiments of the invention, the quantities, i.e. the volumetric flows and/or the temperatures of the fluid fed to the end areas of the roll 10 and/or to the glide bearing elements 14, 14a, 15, 16 and so also the force necessary in order to spread the roll mantle 12 can be calculated in advance from case to case. By means of the embodiments described above or by means of combinations of these embodiments, the problems arising from the temperatures in the end areas of the mantle of the roll provided with glide bearings can be brought under control, and these temperatures and the problems arising from them can be controlled smoothly in most varying situations of operation. Above, the invention has been described by way of example with reference to the exemplifying embodiments of the invention illustrated in the figures in the accom¬ panying drawing. The invention is, however, not confined to the exemplifying embodiments shown in the figures alone, but different embodiments of the invention can show variation within the scope of the inventive idea defined in the accompany¬ ing patent claims.

Claims: Claims 1. A method for regulation of the temperamre in the end areas of the roll mantle of a variable-crown roll provided with glide bearings and/or for compensating for an error in the diameter of the roll arising from thermal expansion in a roll (10), whose roll mantle (12) is supported adjustably on the roll axle (11) by means of hydraulic loading elements (17,17a) loaded by means of a pressure medium and acting upon the inner face of the roll mantle (12) at least in the direction of the nip plane, and which roll mantle (12) is supported on the roll axle (11) by means of hydraulic glide- bearing elements (14, 14a, 15, 15a, 16) loaded by means of a pressure medium and fitted in the areas of the ends of the roll mantle, characterized in that, in the method, into the end areas of the roll (10), a pressure medium is supplied, whose temperamre and/or flow is/are regulated so as to keep the temperamre in the end areas of the roll mantle (12) at the desired level, substantially at the same level as the temperamre in the middle area of the roll (10). 2. A method as claimed in claim 1, characterized in that a pressure medium whose temperamre and/or flow rate can be regulated is fed to the end areas of the roll through the glide bearing elements (14,14a,15,15a,16) of the roll so that said pressure medium, at the same time, operates as the pressure medium that produces the loading of the glide bearing elements (14,14a,15,15a,16). 3. A method as claimed in claim 1 or 2, characterized in that a pressure medium is fed to the end areas of the roll (10) to act directly upon the inner face of the roll mantle (12) so as to equalize the temperamre of the roll mantle (12). 4. A method as claimed in any of the preceding claims, characterized in that the temperamre of the pressure medium fed to the end areas of the roll (10) is deter¬ mined in accordance with the running speed and loading simation of the roll (10). 5. A method as claimed in claim 4, characterized in that the temperamre of the pressure medium fed to the end areas is regulated as stepwise variable based on the running speed. 6. A method as claimed in any of the preceding claims, characterized in that the pressure medium fed to the end areas is passed through a heat exchanger (22) or through an equivalent device for regulation of temperamre. 7. A method as claimed in any of the preceding claims, characterized in that the flow of the pressure medium fed to the end areas is regulated by means of a separate device for regulation of the flow. 8. A method as claimed in any of the claims 1 to 6, characterized in that, as the glide bearing elements (14, 14a, 15, 15a, 16), hydraulic loading shoes are used, by whose means the volumetric flow of the pressure medium passing through said shoes is regulated to be invariable at the desired level. 9. A method as claimed in any of the preceding claims, characterized in that, in order to correct an error, arising from the temperamre, in the diameter of the roll (10), the pressure medium fed to the end areas of the roll (10) is passed to the glide bearing elements (15,15a) of the roll so that said glide bearing elements (15,15a) spread the roll mantle (12) in the direction transverse to the nip plane and reduce the diameter measure of the roll mantle (12) in the direction of the nip plane.

Inventors: KIVIOJA PEKKA, LENSU ESA, KIVIOJA, PEKKA, LENSU, ESA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1996
Main classification: D21G1
IPC codes: D21F3, D21G1, F16C13