WO2008068381A1

WO2008068381A1 - Loading element for a fibre-web machine

Info

Publication number: WO2008068381A1
Application number: PCT/FI2007/050654
Authority: WO
Inventors: Kari Holopainen; Pekka Korpelainen; Jorma Snellman
Original assignee: Metso Paper, Inc.
Priority date: 2006-12-04
Filing date: 2007-12-03
Publication date: 2008-06-12
Also published as: AT506500A3; AT506500A2; AT506500B1; FI20065771A0; DE112007002778T5

Abstract

The invention relates to a loading element of a fibre-web machine, comprising at least one lubricating medium chamber, or a pocket (22), which pocket (22) can be supplied with a pressurized medium through the loading element (20) along a capillary duct (15) to form and maintain a lubricant film between the surface of a slide element (5) of the loading element (20) and a surface coming to lie against the surface of the slide element in a loading situation. The loading element (20) further comprises an additional pocket (25) placed in the area of the highest pressure of a pressure formed between the surface of the slide element (5) and the surface coming to lie against the surface of the slide element in a loading situation to ensure the formation and maintenance of the lubricant film.

Description

Loading element for a fibre-web machine

The present invention relates to loading elements, or shoes, of fibre-web machines, such as paper or board machines. More specifically, the present invention relates to a loading element of a fibre-web machine according to the preamble of claim 1.

In fibre- web machines, one roll type that uses loading elements, i.e. shoes, is a deflection-compensated roll that includes: a stationary roll shaft provided with a loading cavity for a pressurized medium and for a loading arrangement, such as a loading shoe or a loading element, and a roll shell arranged to rotate around the roll shaft and loaded by the internal loading arrangement, which is loaded in the loading cavity radially against the inner surface of the roll shell; said loading arrangement comprising recesses, i.e. pockets, which are open towards the inner surface of the roll shell and define, with the inner surface of the roll shell, chambers which are supplied with a pressurized medium, for example, oil. hi the state- of-the-art rolls, the feed of the pressurized medium into the recesses on the surface of the loading element is accomplished through the loading element using the same size and the same number of capillaries, each pocket of the loading element being thus supplied with the same amount of flow of the pressurized medium. However, this arrangement has proved problematic in particular in connection with deflection-compensated rolls of the kind in which the roll shell is made of a composite, i.e. in connection with so-called composite rolls, because the composite shell, when in use, may undergo even large deformations, with the result that the medium film between the roll shell and the surface of the loading element disappears.

Deflection-compensated rolls are generally used as nip rolls. The so-called shoe rolls known in the prior art are usually hydraulically deflection-compensated zone-controlled rolls, in which the shell is supported and loaded from a non- rotating centre axle 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, allowing loading pressure to be adjusted in a cross-direction, i.e. in a direction transverse to the running direction of the web, i.e. the machine direction, according to the need for profiling. The division of zones in this kind of zone- controlled shoe roll can extend to individual elements of the loading arrangement, in which case the number of zones in the loading arrangement of the roll may exceed 60 - the shoe rolls marketed by the applicant under the trademarks SymCD™ and SymCDS™ may be mentioned as examples, or to a number of elements of the loading arrangement, in which case the roll and the loading arrangement normally include eight zones - the shoe rolls marketed by the applicant under the trademarks SymZ™ and SymZS™ may be mentioned as examples.

With respect to the state of the art, reference can be made to FI patent application 20002739 describing a deflection-compensated roll, in which in order to improve the profilability of the roll shell in the axial direction of the roll shell, i.e. in the cross direction of the machine, each loading element comprises a row of profiling chambers placed substantially at the nip and comprising at least two recesses, or profiling chambers, for one loading piston, which chambers are separated from one another by projecting intermediate parts extending in the circumferential direction, i.e. in the machine direction, and which chambers can be pressurized separately. However, the inclusion of the possibility of profiling in the loading element complicates the structure of the loading element and of the roll, thus in- creasing manufacturing costs.

In fibre-web machines, another roll type that employs a loading element, i.e. a shoe, is an extended-nip roll, i.e. a shoe roll that comprises an axle part supporting a stationary loading element, i.e. a press shoe, and two end flanges mounted in bearings to rotate on support of the axle part, and a flexible shell surrounding the axle part and comprising edge parts attached to the end flanges by means of at- tachment elements such that the shell rotates with the end flanges, the shell sliding over the surface of the press shoe. As known in the state of the art, the loading element in these comprises, in the machine direction, one hydrostatic lubrication pocket (which can be divided into separate pockets in the cross direction with respect to the machine direction), which lubrication pocket ensures lubrication between the loading element and the flexible shell. This arrangement has, however, proved problematic at high running speeds of the machine and when using high linear loads, when the temperature of the loading element tends to rise too high. Attempts have been made to solve the problems by using an additional flow, but that does not enable an increase in a lubricant film, for example, in an oil film, in the area of high pressure because the pressure is too high to let the lubricant film enter said high pressure area. Thus, in the area of hydrodynamic lubrication, the formation of the lubricant film has deteriorated and, in addition, the stability of the lubricant deteriorates and, further, the durability of the flexible shell, i.e. a belt, is reduced.

Extended-nip rolls are used, among other things, in the press section of the paper machine and in calendering. In the pressing zone of the extended-nip press or calender, the flexible shell of the extended-nip roll is forced by means of a counter roll into sliding contact with a press shoe. In the extended-nip press there are one or two press felts, in addition to a paper web, between the flexible shell and the counter roll.

An object of the present invention is to provide a roll for a fibre-web machine, in which roll it would be possible to eliminate or at least substantially reduce the above-mentioned problems.

With a view to achieving the objectives described above as well as those coming out later, the loading element according to the invention is mainly characterized by what is stated in the characterizing part of claim 1. The invention thus makes it possible to provide a loading element of a fibre-web machine, which is provided with an additional pocket in a high pressure area, which additional pocket is supplied with a medium through the loading element along a capillary feed duct such that the pressure in the area of the additional pocket is higher than in the area of other pockets and/or the amount of flow of the medium passed to said pocket is greater than that passed to the other pockets. By this means, the invention makes it possible to ensure a lubricating film during the operation of the loading element.

By the additional pocket in this description is meant a medium chamber or a medium feed which is arranged in the loading element in addition to conventional lubricating medium chambers and which is placed in that shoe area in which the pressure is highest to ensure the formation and maintenance of a lubricating medium film. The additional pocket is dimensioned such that the thickness of the oil film in the area of the shoe can be made uniform / linearly changing.

In accordance with one advantageous embodiment of the invention, the loading element/elements in the deflection-compensated roll is/are provided with an extra pocket, i.e. an additional pocket, in the area of the nip, and the capillaries leading to this pocket are dimensioned to be larger (or the number of the capillaries is increased) than the capillaries leading to the pockets located at the circumferential edges of the loading element. As a result of this, the pressure distribution between the loading element and the roll shell changes such that the highest pressure will be under the nip and the thickness of the medium film will remain sufficient in spite of deformations of the roll shell.

In accordance with another advantageous embodiment of the invention, the embodiment described above is applied in connection with thin-shell rolls when a thin-shell roll is used as a loading roll or as its counter roll, the pressure of the medium passed into the additional pocket being determined, when the loading element, i.e. the shoe, deflects, by the dimensioning of the capillaries according to pressure ratios. In applications having the same pressure in all chambers, a greater amount of flow is typically arranged in the high-pressure area located in the middle.

In accordance with a third advantageous embodiment of the invention, an additional pocket is added to the loading element of an extended-nip roll, i.e. a shoe roll, to the area of the highest pressure, which pocket and the lubricating medium passed into it ensure a sufficient lubricant film in the area of the highest pressure, whereby the temperatures of both the lubricant and the loading element will re- main in a desired, sufficiently low temperature range. In addition, in accordance with advantageous further features of the invention, the edges of the additional pocket are shaped to prevent the shell from striking against the edges of the additional pocket in case a paper clod gets between the shoe and a press felt. Furthermore, a sufficient pressure is arranged in the feed duct of the loading element in order to achieve a desired lubrication flow both into the basic pocket and into the additional pocket. Both the basic pocket and the additional pocket can be divided by projecting intermediate parts into separate pockets in a direction transverse to the machine direction. The lubrication flow between the basic pocket and the additional pocket is divided by means of the capillary dimensioning of the feed ducts, and the tilt selected for the shoe determines the pressures used in the chambers; when changing the tilt, the capillaries are changed correspondingly to achieve desired lubrication flows.

hi the following, the invention will be described in more detail with the help of some of its embodiments considered to be advantageous with reference to the appended patent drawings, to the details of which the invention is, however, by no means meant to be narrowly limited.

Figure 1 schematically shows a thickness distribution of an oil film.

Figure 2 schematically shows a pressure distribution on a shell surface. Figures 3 A and 3B are schematic views of one embodiment of the invention.

Figure 4 is a schematic view of another embodiment of the invention.

Figure 5 schematically shows an example of a roll in which the invention is applied, in a longitudinal sectional view of the roll.

In the figures, the same reference signs are used of parts corresponding to one another, unless otherwise mentioned.

Fig. 1 schematically shows a comparison of the thickness distribution of an oil film calculated by a flow-structure interaction analysis and comparing a state-of- the-art example case T with an example case K in accordance with the invention. In the comparison, in the example K of the invention the number of capillaries in the area of the middle chamber is double that of the state-of-the-art example T. As is clear from the calculation analysis results shown in the figure, in the example in accordance with the invention a thicker oil film is obtained for the entire shoe area from the leading edge to the trailing edge.

Fig. 2 schematically shows a comparison of the distribution of oil pressure on the surface of a shell calculated by a flow-structure interaction analysis and comparing a state-of-the-art example case T with an example case K in accordance with the invention. In the comparison, in the example K of the invention the number of capillaries in the area of the middle chamber is double that of the state-of-the-art example T. As is clear from the calculation analysis results shown in the figure, the pressure in the areas on the side of the leading and trailing edges of the shoe can be made higher in the example K according to the invention than in the state- of-the-art example T. In the middle area of the shoe, the pressure in the example K in accordance with the invention is lower than in the state-of-the-art example T, and thus the pressure distribution on the surface of the shell in the example K of the invention is more uniform in the entire shoe area than in the state-of-the-art example T.

Figs. 3 A-3B are schematic views of an embodiment of the loading element in ac- cordance with the invention for a deflection-compensated roll. Deflection- compensated rolls typically comprise a cross-direction row of hydraulically operated loading elements, and a roll can comprise several tens of loading elements, to compensate for the deflection of the roll and to load the roll shell against a counter roll. The loading element 20 is formed of a loading piston 4 and of one or more slide elements 5 substantially integrally connected to the loading piston. The loading element 20 can be loaded towards the inner surface of the shell 10 by means of a pressure produced with a hydraulic medium to bring the slide surface of the slide element 5 against said inner surface of the shell 10. A lubricant film is produced between the slide surface and the inner surface of the shell 10 by passing a pressure medium through the loading element 20 along capillaries 15 into recesses 22 provided on the slide surface of the slide element, which recesses are separated by projecting intermediate parts, and there can be several recesses one after another in the cross-direction. In accordance with the invention, a recess 22 provided with an additional pocket 25 is arranged in the loading element 20 in the area of high pressure, which additional pocket 25 is supplied with a medium through the loading element 20 along the capillary duct 14 such that in the area of the additional pocket 25 the pressure is higher than in the area of other recesses, i.e. the pockets 22, and/or the amount of flow of the medium passed to said additional pocket 25 is greater than that passed to the other pockets. The capillaries 14 lead- ing to the area of the additional pocket 25 are dimensioned to be larger (or the number of the capillaries 14 is increased) than the capillaries 15 leading to the pockets 22 located at the edges of the loading element 20. As a result of this, the pressure distribution between the loading element 20 and the roll shell 10 changes such that the highest pressure will be under the nip and the thickness of the me- dium film will remain sufficient in spite of deformations of the roll shell. By this means, the invention makes it possible to ensure a lubricating film during the op- eration of the loading element 20. The length of the additional pocket 25 is, on the one hand, 25-35 % of the length of the shoe, on the other hand, 1.5-4 times the length L of the nip.

Fig. 4 shows an embodiment of the invention in connection with an extended-nip roll. A shoe, i.e. a loading element 20, of the extended-nip roll is pressed against a counter roll 2 to produce a desired nip pressure on the inner side of a flexible shell 10, i.e. a belt 10. In calender applications, a web W is typically passed into a nip without a carrying fabric, as shown in the figure, and in press applications (not shown) typically between two carrying fabrics, such as felts. The shoe, or the loading element 20, of the extended-nip roll, or the shoe roll, extends over a substantial length of the entire roll as a continuous structure. A lubricating medium is passed to a recess 22 arranged on the surface of the shoe 5 along a capillary duct 15 arranged in the shoe, i.e. in the loading element 20, for the purpose of lubricat- ing the nip. A pocket 25 is added to the loading element 20 of the shoe roll in the area of the highest pressure, which pocket 25 and the lubricating medium passed to it along a capillary duct 14 ensure a sufficient lubricant film in the area of the highest pressure, whereby the temperatures of both the lubricant and the loading element 20 remain in a desired temperature range. A sufficient pressure is ar- ranged in a medium feed duct 16 of the loading element 20 in order to achieve a desired lubrication flow both in the pocket 20 and in the additional pocket 25. Both the pocket 20 and the additional pocket 25 can be divided into separate pockets by means of projecting intermediate parts in the cross-direction. The lubrication flow between the basic pocket and the additional pocket is divided by the dimensioning of the capillary ducts 14, 15. The medium feed duct 16 can be common to both ducts 14, 15 or, as shown in the figure, the feed duct 16 can be divided into two ducts, so that both capillary ducts have their own feed ducts, which may have different pressures pi, p2. The edges of the additional pocket 25 are advantageously shaped to prevent the shell from striking against the edges of the additional pocket 25 in case a paper clod should get between a press felt and the counter roll 2. The additional pocket 25 is dimensioned such that its length is 10-20 % of the length L of the nip, and the distance from the trailing edge JR of the pocket 25 to the end NL of the nip is 5-15 % of the length L of the nip.

Fig. 5 is a longitudinal sectional view of one example of a deflection-compensated roll 30 provided loading elements 20 in accordance with one embodiment of the invention. The roll 30 comprises a stationary roll axle 32, a roll shell 10 being revolvingly disposed on the axle and supported, in the main direction producing loading in the direction of the nip, on the roll axle 32 by means of the loading elements 20 in accordance with one embodiment of the invention. The loading elements 20 are effective in the main direction of the nip plane, and by means of them it is possible to adjust the shape of the roll shell 10 and to control the axial nip profile of the roll. In positions located in other directions, the structure and the operation of loading elements 33 supporting the roll shell 10 on the roll axle 32 are in accordance with choices per se known by a person skilled in the art from the state of the art. The structure and the operation of loading elements 35 supporting end flanges 34 of the roll are also in accordance with choices per se known by a person skilled in the art from the state of the art.

Above, the invention has been described only with reference to some of its advan- tageous embodiments, to the details of which the invention is, however, by no means meant to be narrowly limited.

Claims

1. A loading element, or a shoe (20), of a fibre-web machine, comprising at least one lubricating medium chamber, or a pocket (22), which pocket (22) can be sup- plied with a pressurized medium through the loading element (20) along a capillary duct (15) to form and maintain a lubricant film between the surface of a slide element (5) of the loading element (20) and a surface coming to lie against the surface of the slide element in a loading situation, characterized in that the loading element (20) further comprises an additional pocket (25) which is placed in the area of the highest pressure of a pressure formed between the surface of the slide element (5) and the surface coming to lie against it in the loading situation to ensure the formation and maintenance of the lubricant film.

2. A loading element of a fibre- web machine as claimed in claim 1, characterized in that the additional pocket (25) is a medium chamber or a medium feed arranged in the loading element in addition to conventional lubricating medium chambers (22).

3. A loading element of a fibre-web machine as claimed in claim 1 or 2, charac- terized in that a pressurized medium can be passed to the additional pocket (25) of the loading element (20) through the loading element (20) along at least one capillary duct (14) of the additional pocket (25).

4. A loading element of a fibre-web machine as claimed in any one of claims 1 to 3, characterized in that the additional pocket (25) of the loading element (20) is placed such that the distance from a trailing edge of the pocket to the end of a nip is 5-15 % of the length of the nip.

5. A loading element of a fibre-web machine as claimed in any one of claims 1 to 4, characterized in that the pressure in the capillary duct (14) of the additional pocket (25) of the loading element (20) is adjustable.

6. A loading element of a fibre-web machine as claimed in claim 5, characterized in that the pressure in the capillary duct (14) of the additional pocket (25) of the loading element (20) is higher than the pressure in the capillary duct (15) of the pocket (22) of the loading element (20).

7. A loading element of a fibre-web machine as claimed in any one of claims 1 to 4, characterized in that the amount of flow in the capillary duct (14) of the additional pocket (25) of the loading element (20) is adjustable.

8. A loading element of a fibre- web machine as claimed in claim 7, characterized in that the amount of flow in the capillary duct (14) of the additional pocket (25) of the loading element (20) is greater than the amount of flow in the capillary duct (15) of the pocket (22) of the loading element (20).

9. A loading element of a fibre-web machine as claimed in any one of claims 1 to 8, characterized in that the loading element (20) is placed in connection with an extended-nip roll, or a shoe roll, of the fibre- web machine.

10. A loading element of a fibre-web machine as claimed in any one of claims 1 to 8, characterized in that the loading element (20) is placed in connection with a deflection-compensated roll of the fibre-web machine.

11. A loading element of a fibre-web machine as claimed in claim 10, character- ized in that the loading element (20) is placed in connection with a thin-shell roll of the fibre-web machine.