The present invention relates to rolls, in particular rolls of a paper machine or equivalent. More specifically, the present invention relates to a deflection- compensated roll, in particular a roll with a composite shell, according to the preamble of claim 1.

Such a deflection-compensated roll, in particular a roll with a composite shell, includes: a stationary roll shaft provided with a loading cavity for a pressurized medium and for a loading arrangement, such as a loading shoe, and a roll shell arranged to rotate around the roll shaft, which roll shell is loaded by the internal loading arrangement loaded in the loading cavity radially against the inner surface of the roll shell; said loading arrangement comprising recesses which are open towards the inner surface of the roll shell and which define with the inner surface of the roll shell chambers into which a pressurized medium is passed.

In a deflection-compensated roll loaded by means of shoes, and in particular of the shell of such a roll, different properties are required in the direction of the circumference of the shell and in the direction of the roll shaft. Deflection- compensated rolls are commonly used as nip rolls, and in that case the shape of the shell must remain unchanged even at high nip loads. However, when the nip pressures are to be profiled in the axial direction of the roll, the rigidity of the roll shell in the axial direction must be low. The shells of deflection-compensated rolls are typically rather thick cast iron shells, in which case the profiling of the nip pressures requires that very high forces be applied to the roll shell. For this reason, in certain cases, it would be advantageous if the roll shell could be made thinner.

The technique of manufacture that is currently used, however, restricts any reduction of the thickness of the cast iron shells. A second problem associated

with today's deflection-compensated rolls is the high weight of the thick roll shell and the drawbacks resulting from this weight. It is a significant drawback arising from the weight of the roll shell that the vibration properties of the roll shell are poor. The so-called shoe rolls of the prior art are usually hydraulically deflection- compensated zone-controlled rolls in which the shell is supported and loaded from a non-rotating central shaft of the roll by means of a hydrostatic loading arrangement, such as a row of loading shoes. The row of loading shoes is generally also divided into zones, in which connection the loading pressure can be regulated in a direction transverse to the running direction of the web, or to the machine direction, that is, in the cross direction according to the need of profiling.

The zone division in this kind of zone-controlled shoe roll may comprise individual elements of the loading arrangement, in which connection the number of zones in the loading arrangement may exceed 60-as examples may be mentioned the shoe rolls marketed by the applicant under the trademarks SymCD and SymCDSTM, or the zone division may comprise a group of elements of the loading arrangement, in which connection the roll and the loading arrangement normally comprise eight zones-as examples may be mentioned the shoe rolls marketed by the applicant under the trademarks SymZTM, SymZSTM, SymZLTM, SymZLCTM.

A problem in such deflection-compensated thin-shell rolls, in particular rolls having a composite shell is the stability of the lubricating film in the circumferential direction of the shell and the reduction of its thickness in the nip area between the shell and the loading arrangement loading it. The problem is caused by the nip load between the deflection-compensated roll and its counter roll, which nip load deflects the shell of the thin-shell roll and bends the loading arrangement, with the result that the roll shell and the lubricating film between the loading arrangement and the shell of the thin-shell roll become wave-shaped while, in the edge areas of the loading arrangement, the edge gap between the shell of the thin-shell roll and the loading arrangement becomes so large that all hydraulic fluid, advantageously hydraulic oil, fed through the loading

arrangement is able to escape through said edge gaps without forming a lubricating film between the loading arrangement and the shell of the thin-shell roll. This will have problematic consequences in the form of contact between the shell of the thin-shell roll and the loading arrangement as well as in the form of problems with the profiling of the web.

Published patent applications CA 2,227,790 and WO 98/04844 disclose loading shoes for a thin-shell deflection-compensated roll, in which shoes both frontal faces of the shoes lying against the shell comprise a central lubricating fluid and loading pocket and, on both sides thereof, stabilizing pockets which are substantially smaller in dimensions and which stabilize the motion of the loading shoe.

The primary object of the present invention is to provide an improved deflection- compensated roll in which the above-mentioned problems in the axial and/or circumferential direction of the roll could be eliminated or at least substantially reduced.

This object is achieved by a deflection-compensated roll of the kind mentioned at the beginning, the special features characteristic of the roll being set forth in the appended set of claims.

The invention is thus based on a new and inventive idea that, in order to improve the profiling of a roll shell in the axial direction of the roll shell, i. e. in the cross direction, a pressurized medium is passed to a loading arrangement situated between the roll shell and the shaft, which loading arrangement includes several loading pistons placed one after the other in the cross direction, the pressure in a pressure space situated under said loading pistons being adjustable individually for each piston or by zones for groups of a few pistons or which all can be at the same pressure, as well as one or more slide elements co-operating with the loading piston. Each slide element comprises, in the axial direction of the roll, i. e.

in the cross direction, substantially at the nip, at least two pressure pockets, i. e. profiling chambers, for one loading piston, and each of these profiling chambers can be pressurized separately to produce profiling pressure. To ensure that the lubricating film is maintained between the roll shell and the loading arrangement, each slide element comprises, in the machine direction, i. e. in the circumferential direction, on the inlet and outlet sides of the nip area, edge or lubricant chambers/chamber rows which are formed of one or more recesses and into which a pressurized medium is passed.

In accordance with an advantageous embodiment of the invention, a profiling medium is passed into the profiling chambers and a lubricating medium is passed into the edge or lubricating chambers. In that connection, it is advantageous that a higher pressure is arranged in the profiling chambers, so that the pressures in the edge chambers are clearly lower than in the profiling chambers. By this means, the loading of the shell outside the nip is reduced and, thus, the deflection of the shell is reduced and the thickness of the lubricating film becomes even.

In accordance with the invention, it is advantageous that the hydraulic loading and lubricating medium, preferably oil, is fed to the loading arrangement along a separate loading and lubricating medium line. It is also advantageous that the profiling medium, preferably oil, is fed to the loading arrangement along a separate profiling medium line. In that connection, it is further advantageous that the feed of both the loading and lubricating medium and the profiling medium is accomplished as a capillary feed through the loading arrangement. hi accordance with the invention, the loading element advantageously comprises: - one loading piston and one slide element, - several loading pistons and one slide element, - several loading pistons and several slide elements, in which case there may be as many loading elements as there are slide elements or there may be fewer loading elements than there are slide elements, or

a loading piston and a slide element are formed of an integral structure.

In the following, the invention will be described in greater detail by means of one of its embodiments regarded as advantageous with reference to the appended drawings in which FIG. 1 is a sectional view of a loading arrangement placed inside a deflection- compensated roll provided with a composite shell in accordance with a first embodiment of the invention considered advantageous, FIG. 2 is an axial sectional view of the loading arrangement shown in Fig. 1 viewed from the side, FIG. 3 shows the loading arrangement of Figs. 1 and 2 viewed from the top, FIG. 4 shows a second embodiment of the loading arrangement in accordance with the invention viewed from the top, FIG. 5 is an axial sectional view of a loading arrangement in accordance with a third embodiment of the invention viewed from the side.

The deflection-compensated roll shown in the figures includes a thin-wall shell 2, preferably made of a composite material, which rotates around a stationary shaft 1 and forms together with the outer surface of a counter roll 3 a nip N in which the nip load tends to produce a deformation in the shell 2. A loading arrangement is arranged between the stationary shaft 1 and the roll shell 2, which loading arrangement comprises a row of hydraulically operating loading pistons 20 placed in a cross direction, and which roll may comprise several tens of loading pistons, to compensate for the deflection of the roll and to load the roll shell against the counter roll. A hydraulic loading cavity 4,4', 4"is formed in the stationary shaft 1 for each loading piston 20, and a pressurized medium, advantageously hydraulic oil, is fed into the loading cavity through a feed duct 5. Each loading piston 20 may have a separate pressure feed line 17n and it can be introduced into the roll through the stationary shaft 1. A pressurized medium is passed through the feed duct 5 into the loading cavities 4,4'and 4"for moving a loading element 10

radially with respect to the shaft 1. The loading element 10 comprises a loading piston 20 and one or more slide elements 22 which are integral parts thereof. By means of the pressure produced with the hydraulic medium in the loading cavities 4,4'and 4", the loading element 10 can be loaded against the timer surface of the shell 2 to bring a slide face 10a of the slide element 22 against said inner surface of the shell 2. A lubricant film is formed between the slide face 1 Oa and the inner surface 2 of the shell 2 by passing a pressure medium through the loading element 10 into recesses provided in its slide face 10a. To form and to maintain a lubricating film between the loading element and the shell 2, the recesses in the slide face 10a of the slide element 22 form, together with the inner surface of the roll shell 2, lubricating chambers 12 and 12', into which a pressurized medium flows from capillary ducts 13. The lubricating chambers 12,12'are located, as separated by projecting parts 16, on both sides of a central row of profiling chambers of the slide element 22 of the invention placed in the axial direction, i. e. in the cross direction. There may be several lubricating chambers one after the other in the cross direction.

Fig. 2 is a sectional view of the loading arrangement of the deflection- compensated roll shown in Fig. 1, seen in the axial direction of the roll at the nip, i. e. at the central profiling chambers 11, which loading arrangement is formed of a number of loading elements 10 placed one after the other, each of the loading elements comprising one loading piston 20 and one slide element 22. A pressure medium is passed into the loading cavity 4"of each element 10 from the pressure line 17, the pressure of which can be regulated independently of the pressure of the other loading pistons. In the slide face 10a of the loading element 10 there are two or more recesses, i. e. profiling chambers 11, 11', 11"at the nip, a pressurized profiling medium, advantageously hydraulic oil, being passed into each profiling chamber along respective profiling pressure lines 18, 18'and 18"through capillary ducts 14,14', 14". The capillary ducts 14,14', 14"are separated from the pressure of the loading cavity 4"by members 6,6', 6", which are tube ducts allowing the flow of a medium and the radial movement of the element 10,

advantageously flexible hoses, thereby providing a profiling medium feed which is independent of the loading pressure prevailing in the loading cavity 4". The pressure in each pressure line 18,18'18"can be regulated separately by means of a control valve, which can be placed outside the roll in a valve manifold or in the roll itself, for example, in a valve section integrated into the roll head. There are at least two profiling chambers 11,11',... for one loading element 10. This makes it possible to achieve more accurate profile control in the area of one loading element 10 than allowed by the state-of-the-art arrangements because the number of controllable profiling chambers is higher than the number of loading elements.

For example, in a roll with a length of the order of 10 metres, in which the number of loading elements is about 60 and the CD width of the slide face 10a of the loading element 10 is typically of the order of about 145 mm, by the profiling element in accordance with the invention a profiling accuracy is achieved which is at least half of the width of the element or even still more accurate. Alternatively, if there is no need to increase profiling accuracy, the length of the element can be increased and their number in the roll can be reduced without the profilability suffering.

Fig. 3 shows the slide face 10a of the loading element 10 shown in Figs. 2 and 3 as viewed from the top. Generally, the slide face 10a of the loading element comprises a projecting edge part 15, projecting intermediate parts 16 extending in the circumferential direction and projecting intermediate parts 19 extending in the axial direction as well as recesses 11,12 remaining between these projecting parts. At the projecting parts, the loading element is in contact with the roll shell through a thin oil film. In the slide element structure shown in Fig. 3, the slide face 10a is formed of three rows of recesses 11,12 12'extending in the circumferential direction, of which rows the middle row of the profiling chambers 11,11', 11"is positioned substantially at the nip and the rows of the lubricating chambers 12,12'are positioned on both sides of this row.

Advantageously, in the slide face structure in accordance with the invention, the slide face 10a is fonned of several rows of recesses separated by projecting parts 16 from one another, said recesses opening to the slide face 1 Oa and forming with the roll shell 2 a row of central profiling chambers 11 and rows of lubricating chambers 12,12'on both sides of the profiling chambers such that in each parallel row of chambers 11,12,12', the projecting parts 19 separating the chambers 11, 12,12'from one another in the axial direction are facing the chambers 11,12,12' of the adjacent row in the direction of the circumference of the roll shell 2, i. e. the chambers 11,12,12'advantageously form a brick-wall-like structure in which the individual chambers in the parallel rows of chambers 11,12,12'are displaced in the axial direction, for example, by half of the length of the chamber 11,12,12' with respect to the chambers 11,12,12'in another row. In that connection, a continuous lubricating effect without discontinuities is provided in the cross direction in the entire area of the loading element 10 by means of at least one lubricating chamber 12,12'owing to the lubricating chambers placed in overlapping relationship to one another.

In accordance with the invention, by means of the chamber rows which are situated in the loading element 10 in the area of the nip N and which are parallel in the machine direction and composed of separate chambers 11,12,12'it is possible to - profile the roll shell 2 in the axial direction, i. e. in the cross direction, and equalize the deformations of the roll shell and make them lower in the machine direction, and - ensure the stability of the lubricating slide film in the machine direction in the area of the loading element 10.

In the embodiment of the invention shown in Fig. 3 there are chambers 11, 12,12' advantageously in three rows in the direction of the circumference of the roll shell, i. e. in the machine direction, and there are at least two chambers in the row

of profiling chambers in the area of each loading element 10, the profiling pressure produced by means of a medium in the profiling chambers being independently controllable. For the purpose of achieving the object of the invention, it is, of course, also possible to use a higher number of parallel chamber rows in the machine direction, for example, five, seven or even nine chamber rows. It shall be noted, however, that the achievement of the object of the invention is not substantially promoted by a number of rows exceeding one central row of profiling chambers and four rows of lubricating chambers arranged on both sides of the row of profiling chambers.

In the arrangements described above, each loading element 10 comprises one loading piston 20 and a slide element part 22 integral therewith. Within the scope of the invention, an arrangement is also feasible in which one slide element 22 extends over the area of several loading pistons 20, for example, over the length of an area where 2 to 10 loading pistons are effective or, in the extreme case, over the entire axial length of the roll shell. Fig. 4 illustrates the case in which the slide element 22 extends over the length of three loading pistons. The positions of the loading pistons 20,20a, 20b are shown in Fig. 4 with dashed lines. The slide face 10a of the slide element 22 is provided with profiling chambers 11 in accordance with the invention, the number of said chambers being at least two for each loading piston 20. In the case of the figure, in the area where one loading piston 20 is effective there are three profiling chambers (11 la, 1 la', 1 la", l lb, l lb', l lb", etc). The pressure introduced into each profiling chamber lli can be controlled separately independently of the pressures in the other profiling chambers. Thus, the profiling width can be selected to be narrower than the spacing of the loading pistons 20 in the loading arrangement.

Advantageously, the number of the profiling chambers 11 is higher than the number of the lubricating chambers 12 in one lubricating chamber row. In that connection, for example, a brick-wall-like pattern of the projecting parts is achieved which is advantageous with a view to ensuring the stability of the

lubricating film. When the number of the profiling chambers 11 in the slide element is three for one loading piston, it is advantageous that the number of lubricating chambers in one lubricating chamber row is one or two. If there were two profiling chambers 11 for one loading piston, the corresponding advantageous number of lubricating chambers would be one.

Fig. 5 illustrates a third advantageous embodiment of the inventive idea. As appears in the sectional view of this embodiment shown in the figure, the problems with the bending of the loading arrangement and with the stability of the lubricating film can be solved by arranging the loading element 10 belonging to the loading arrangement to extend in the cross direction as a continuous and rigid element across the entire width of the roll. In that connection, for loading the roll shell, in the loading arrangement 11 in accordance with the inventive idea, loading cavities 4 of the loading pistons have separate feeds 17 for a pressurized medium and the lubrication and the profiling of the roll shell 2 have separate feeds 18 for a pressurized medium, of which feeds at least the medium feed 18 associated with profiling is advantageously provided with flow and pressure control. In such an arrangement, it is an advantage that the profiling width and the spacing of the loading pistons can be separated from each other, and the spacing of the profiling chambers can be selected to be even 10 mm, but, in practice, on long rolls a sufficient spacing is of the order of 50 to 100 mm, while the spacing of the pistons is typically 140 to 200 mm. When the chambers are arranged with a narrower spacing than the loading pistons 20, there is the advantage that the profiling width can be selected to be narrower than the spacing of the piston-like loading pistons of the loading arrangement. An adequate lubricating film is achieved between the loading element 10 and the roll shell 2 in the entire area of the loading arrangement when in the slide face 1 Oa of the loading element 10 there are at least three rows of chambers 11,12 and 12'in the machine direction, of which chambers the middle chamber 11 is provided with the highest pressure of the medium, i. e. profiling pressure, in the area of the nip. In that connection, the pressures in the outermost chambers 12 and 12'are clearly smaller, with the result

that the loading applied to the roll shell 2 outside the nip is reduced and, thus, the deflection of the roll shell 2 is reduced and the thickness of the lubricating film becomes even.

By changing the flow of the pressurized profiling medium in the capillary ducts 14 of the profiling chambers 11 and the flow of the lubricating medium in the capillary ducts 13 of the lubricating chambers 12,12', the deformations caused by the nip load in the shell 2 can be substantially reduced, i. e. the roll shell can be profiled in the cross direction, and the deformation of the shell 2, which is shaped at the nip so as to be wavelike symmetrically with respect to the counter roll 3 in the machine direction, can be equalized or made lower, that is, the peaks of the waves of the shell 2 can be made lower, whereby it is possible to substantially reduce or even prevent escape of the lubricating fluid in the machine direction between the slide face of the loading element 10 and the inner surface of the shell 2, thus ensuring that the lubricating slide film is maintained.

For profiling the roll shell in the cross direction, it is advantageous that the highest pressure of the pressurized medium is arranged in the machine direction in the middle row of profiling chambers 11, in which connection it is advantageous to keep the pressures of the edge chambers 12,12'situated on the sides of the profiling chamber row substantially lower. Thus, on the one hand, the loading of the shell 2 on the outside of the nip N is reduced and, on the other hand, the deformation tendency of the loading element 10 to bending is diminished and, thus, the deflection of the shell 2 and the bending of the loading element 10 are reduced, and the thickness of the lubricating film between the shell 2 and the loading element 10 is made even, which things together ensure that the oil film is maintained between the shell 2 and the loading element 10.

Above, the invention has been described only by means of some of its embodiments considered advantageous. This is, of course, not intended to limit the invention to this kind of single embodiments and, as is clear to a person skilled

in the art, various alternatives and modifications are feasible within the inventive idea and within the scope of protection defined in the claims thereof.

Thus, it may be stated - that the capillary tubes 13,14 of the lubricating and/or profiling chambers can be provided with throttling, - that the loading cavities can be connected to form one cavity common to all medium chambers, the pressurized loading medium fed into said cavity producing a radial movement of the loading shoe in said cavity, - that the pressure introduced into the lubricating ducts 12,12'of the outlet and the inlet side may be the same or separately controllable.