WO1993014871A1

WO1993014871A1 - Bearing system in a refiner

Info

Publication number: WO1993014871A1
Application number: PCT/SE1992/000841
Authority: WO
Inventors: Rolf B. Reinhall; Olof Kjellqvist
Original assignee: Sunds Defibrator Industries Aktiebolag
Priority date: 1992-01-28
Filing date: 1992-12-07
Publication date: 1993-08-05
Also published as: SE469782B; SE9200222L; SE9200222D0; AU3411693A; NO942794L; NO942794D0; CA2122142A1; SE469782C

Abstract

A bearing system in a refiner for manufacturing pulp, where the raw material is refined in a refining gap between at least one pair of refining members (22, 24) rotating relative to one another, and where at least one of said refining members (24) is supported by an axially movable and rotary axle (26). The bearing system comprises a combined hydrostatic/hydrodynamic axial bearing arrangement and consists of a housing (32) with at least one rotary piston (30), which is attached on the rotary axle (26) for rotation with the same. A stationary holder (29, 33) is located in the housing (32) on at least one side of the rotary piston (30). An outer and an inner ring cylinder (200, 210 and, respectively, 202, 212) are arranged axially movable in an outer and an inner chamber, respectively (40, 41 and, respectively, 42, 43) in the holder (29, 33). The ring cylinders thereby are arranged to be pressed against one end surface of the piston (30) so that sealing gaps (211) are formed therebetween. Between the ring cylinders (200, 210, and, respectively, 202, 212), the piston (30) and the holder (29, 33) a cavity (213, 214) is defined, and a channel (246, 248) is provided for the supply of a hydraulic pressure medium to said cavity (213, 214) for determining the axial position of the piston.

Description

Bearing system in a refiner

This invention relates to a bearing system in refiners or beaters comprising a pair of opposed, axially adjustable refining members, which rotate relative to each other and between themselves define a refining gap, through which the raw material is passed. During the passage, considerable axial forces are generated which act against the means arranged to maintain the desired refining gap between the refining members.

The invention, more precisely, relates to a refiner of rotating disc type for refining papermaking pulp and the like, where the raw material for refining or other treatment is passed through a refining gap defined between a pair of refining discs, which are axially adjustable relative to each other. These refining discs rotate relative to each other in a plane perpendicular to their axles. At least one of the discs is axially movable and attached on a rotary axle, which is axially movable with the movable refining disc in response to the pressure acting on the discs. The raw material, which can be wood chips, bagasse, fiber suspensions or like material, is fed to the central portion of the refining gap, through which it is accelerated radially by action of the centrifugal force generated by the rotation of the discs. After the refining operation, the treated material passes out of the refining gap through a peripheral opening between the discs and enters a surrounding housing.

The axial movement of the rotary axle is controlled for maintaining the predetermined refining gap between the discs. The gap has different sizes, depending on the use of the refiner. In conventional refiners, for example, the refining gap usually is between 0.1 and 1 mm, while in refiners for waste paper the gap can be as large as 2.5 mm. At other applications, the refining gap can be as small as 0.05 mm. Pulp refiners of the type described are shown in the patent specifications USA 4082 233, 4 253 613, 4 283 016, 4378 092 and A 801 099.

The rapid acceleration of the material through the narrow refining gap generates axial compressive forces, which tend to separate the discs from each other and thereby widen the refining gap, resulting in a serious deterioration of the refiner efficiency.

When the refiners or beaters are part of a closed and pressurized system, for example for the treatment of a liquid slurry, additional power must be supplied to the drive means in addition to the axial compressive forces acting on the discs. This additional power is required not only for driving the discs for obtaining desired refining or beating, but also for driving the discs against the liquid friction or hydraulic braking forces acting on the discs, whereby additional axial load variations on the rotary axle are obtained.

If the effect of these forces on the axial position of the rotating axle is not controlled effectively, the refiner will break down. A further fact is, that the resistance against these compressive forces increases substantially with increasing disc diameter.

Due to the increasing demand for refining systems with high capacity, which require refining discs with a large diameter, for example of the magnitude 150 cm or larger, the absorption of these axial compressive forces has become an ever more expressed problem. Newly developed refiners have disc diameters of 165-170 cm, with a rate of rotation of 1500-3600 rpm and an effective output of 15 000-50 000 kW.

In order to better understand the enormous axial loads or compressive forces acting on the rotation axle, one must imagine that a disc with a diameter of 150 cm rotating at 1800 rpm generates a centrifugal force corresponding to about 2800 g which accelerates the material to be refined through the refining disc. This centrifugal force can apply on the axle an axial load of more than 100 ton, which has to be taken up by the bearing structure. Such abnormally high axial loads, at present structural designs, are distributed on a complicated bearing system, which requires a plurality of bearings and servo-motors with resulting increased dimensions and manufacturing costs for the refiner

One example of a bearing structure of the aforesaid type is shown in patent specification USA 3 717 308. This patent shows a bearing system with combined axial and radial bearings supporting the rotation axle. Each bearing is coupled to a servo-motor for taking up the axial compressive forces acting on the rotation axle. Other examples of bearing structures used heretofore are shown in patent specifications USA 4 1 1 8 800 , 3 21 2 721 , 4 073 442 and

3 276 701 .

Patent specification USA 4 402 463 suggests a different solution of the above problem.

The aforesaid patents have in common, as their state of art, the fact that the hydraulic pistons in the servo-motors for the thrust bearings are non-rotary.

Patent specification USA 4 801 099, however, suggests the use of one or several hydraulic rotary pistons , which are rigidly connected to the rotating axle and fully replace the present systems with expensive and complicated axial, roller and/or block bearing systems. This bearing system with rotating pistons comprises one or several cylinder pistons mounted on the rotary axle so . as to rotate together with the axle in a pressure chamber, which is formed in a stationary cylindric housing, where the piston or pistons can be moved axially, acting by a pressure medium supplied to at least one of

the ends of the rotating piston(s) in a controlled manner, in order to constantly counteract varying axial compressive forces acting on the movable rotary axle and maintain a predetermined size of the refining gap.

This system, however, depends for its function on a plurality of sealing devices, both at the inlets of the rotating axle in the stationary cylindric pressure housing and between the circumference of the rotating piston and the cylinder housing. These circumferential sealings are exposed to vibrations of the rotating axle which are caused by the bias of the refining elements and/or the non-uniform distribution over the refining elements of the material to be refined. In order to prevent breakdowns, it is therefore necessary to maintain relatively large radial gaps at the sealing surfaces. These gaps, thus, must exceed the maximum radial vibration deflections. This implies, that great amounts of pressure medium supplied to the piston housing are lost as leakage through the radial sealing gaps and at necessary, relatively high hydraulic pressures of

100-4-00 bar require much energy and large expensive pump installations.

The present invention has the object to eliminate the greater part of this leakage which is not required for the axial balancing and control of the axle. According to the invention, this can be achieved by transferring all necessary sealing surfaces from the circumference of the axle and the circumference of the piston to one or several radial planes on the end surfaces of the rotating piston. These end surfaces are not affected significantly by the radial vibrations of the rotating axle caused by rotation bias etc. and thereby can operate with minimum sealing gaps, without risk of breakdowns. This results in considerably less leakage of supplied pressure medium.

The characterizing features of the invention are apparent from the attached claims.

The invention is described in greater detail in the following, with reference to the accompanying Figures.

Fig. 1 is a partially cut-open lateral view of a refiner according to the invention.

Fig. 2 is a longitudinal section of the hydraulic axial bearing system of the refiner according to the invention, in combination with conventional radial bearings movably supporting the rotation axle.

The embodiment shown in the Figures comprises a stand 10, in which an axially movable axle 26 is supported in two bearing elements 34 and 36. These bearing elements can be slide bearings, roller bearings, axially movable radial roller bearings etc. One end 27 of the axle 26 is driven by a motor (not shown). The other end of the axle 26 supports a rotary adjustable disc 24, which together with a stationary disc 22 define between themselves a refining gap. Both discs are provided with conventional refining segments 23. The refining discs are enclosed in a refiner housing 20, in which the stationary disc 22 is mounted by

means of screw joints 25. The raw material is fed

through an opening 11 by a conventional feed worm

12 and introduced into the refining gap through a

central opening in the stationary disc 22. The bearing elements 34,36 are supported by a bearing housing 32, which between the two bearing elements is formed with a preferably cylindric space 31 and with two stationary axial holders 29,33 directed toward each other. In these holders outer ring cylinders 200,210 and inner ring cylinders 202, 212 are located. The ring cylinders are axially movable in an outer and, respectively, inner chamber 40,41 and, respectively, 42,43 in the holders 29,33. The ring cylinders are sealingly fitted into the corresponding chamber and are preferably

non-rotary. Between the holders 29,33, a rotary piston 30 is located. This piston preferably is cylindric and attached on the axle 26 to rotate together with the same. The ring cylinders abut the end surfaces of the rotary piston so that sealing gaps 211 are formed between the ring cylinders and said end surfaces. The ring cylinders, thus, are formed with a sealing surface joining the radial end surfaces of the piston 30.

Between the outer and inner ring cylinder 200,202

and, respectively, 210,212 a cavity 213,214 is formed, which on one side is defined by a holder 29,33 and on the other side by the rotary piston 30. Passageways

246,248 are provided for the supply of a hydraulic pressure medium to the cavities 213,214. Furthermore, outer and, respectively, inner channels 70,72 and, respectively, 74,76 are provided for the supply of hydraulic pressure medium to the outer and, respectively, inner chambers 40,41 and, respectively, 42,43. The pressure in these chambers is adjusted so that the pressing contact of the ring cylinders with the rotary piston 30 balances the hydraulic pressure profile in the sealing gaps 211. The space 31 outside the piston 30 preferably is atmospheric.

The axial position of the rotary piston 30 is controlled and adjusted by axial movement of the two non-rotary, but axially movable ring cylinders 200,210. The movement of the ring cylinders 200,202 and, respectively, 210,212 and the force, by which the hydraulic pressure maintained in the cavities 213,214 acts on the rotating piston 30, are determined by means of a sensor 220, which senses the axial position of the axle. A hydraulic control valve 240 is affected via a return mechanism, which can comprise an electric link 231 and a stepping motor 230 for changing the nominal value.

This control valve receives supply of the hydraulic pressure medium from an oil container 243 provided with a pump 241. The control valve 240 distributes and controls the pressure of the hydraulic medium via channels 242,244,246,248 to respective cavities 213 , 214 so that the set axial position of the rotating axle is maintained constantly irrespective of varying axial axle loads. These load variations originate from the refining disc 24 and from sub- or excess atmospheric pressure maintained or varying in the refiner housing 20.

The pressure in the outer and, respectively, inner chambers 40,41 and, respectively, 42,43 preferably is maintained at the same level and related in a suitable manner to the pressure in the cavities 213,214- The contact pressure of the ring cylinders 200,210 and, respectively, 202,212 against the rotary piston 30 can thereby be adjusted so that the size of the sealing gaps 211 is increased or reduced with corresponding variation in the gap leakage. A normal leakage at a refiner designed according to the invention is less than 5 1/min compared to previous hydraulic piston or block bearings, which normally require 50-200 l/min for a corresponding area of application. The present invention, thus, eliminates these disadvantages of expensive pump and control equipment and saves pump energy corresponding to the reduced demand of hydraulic medium.

The relation between pressure-. in the cavities and, respectively, chambers, thus, is such that, when the pressure in the cavities 213,214 is P, the pressure in the outer and, respectively, inner chambers 40,41 and, respectively, 42,43 is α · P, where α is a number lying in the interval 1.0-0.5- The pressure α · P can be achieved, for example, in a known manner by means of hydraulic valves. The value of α can be predetermined constant or be controlled by P in such a way, that α is reduced in steps with increasing P beginning, for example, at α = 1-0. It is also possible to make α dependant on different process parameters, such as number of revolutions, temperature etc. α can, for example, advantageously be controlled by the f-low in the channel 242,246 and, respectively, 244,248 in such a way, that at increasing flow in the channel 242,246 α increases and thereby increases the pressure in the channels 70 and 74, so that the oil flow again decreases to the desired level.

One or several of the ring cylinders 200,202,210,212 can be provided with one or several passages 215, which extend from the cavity 213,214 to the sealing gap 211 between the ring cylinder and the rotary piston 30.

The passage preferably opens into a groove 216 extending all around in the surface of the ring cylinder abutting the rotary piston. This groove is intended to bring about uniform distribution of the pressure medium. The passage is formed with flow resistance or restriction, for example in the form of a sharp bend. By

this arrangement, a suitable pressure drop can be obtained in operation, whereby the size of the sealing gap 211 can be determined and ensured, that metallic contact between the sealing surfaces is prevented.

The sealing surfaces forming the sealing gap 211 preferably are plane, but can also be wedge-shaped in the direction of the radius, curved etc.

At the embodiment shown, the bearing system is formed with a holder and associated ring cylinders on both sides of the rotary piston 30. It is possible, however, to arrange ring cylinders only on one side, viz. the side of the rotary piston remote from the associated refining disc.

Various combinations of the bearing system according to the invention with radial bearings of different types can also be imagined. Instead of placing a radial bearing on each side of the bearing housing 32, two radial bearings can be placed outside or inside the bearing housing, counted in axial direction. Instead of conventional radial bearings, other types of bearings can be used, for example slide bearings, combined axial-radial bearings etc.

The invention is not restricted to the embodiments set forth above, but can be varied within the scope of the invention idea.

Claims

1. A bearing system in a refiner for the manufacture of pulp, where the raw material is refined in a refining gap between at least one pair of refining members (22, 24) rotating relative to one another, and where at least one of these refining members (24) is supported by an axially movable and rotary axle (26), comprising a

combined hydrostatic/hydrodynamic axial bearing arrangement for this axle, and where a housing (32) comprises at least one rotary piston (30) with two opposed end surfaces, which piston is attached on the rotary axle

(26) for rotation therewith, c h a r a c t e r i z e d i n that a stationary holder (29,33) is located in the housing (32) on at least one side of the rotary piston (30), that an outer and an inner ring cylinder (200,210 and, respectively, 202,212) are arranged axially movable in an

outer and, respectively, inner chamber (40,41 and respectively, 42,43) in the holder (29,33), that the ring cylinders are arranged to be pressed against one end surface of the piston (30), so that sealing gaps (211) are formed therebetween, that a cavity (213,214) is

defined between the ring cylinders (200,210 and, respectively, 202,212), the piston (30) and the holder

(29,33), and that a channel (246,248) is provided for the supply of a hydraulic pressure medium to said cavity (213,214) for determining the axial position of the

piston.

2. A bearing system as defined in claim 1, c h a r a c t e r i z e d i n that an outer and an inner channel (70,72 and, respectively, 74,76) are arranged for the supply of hydraulic pressure medium to the

outer and, respectively, inner chamber (40,41 and, respectively, 42,43) in the holder (29,33) for pressing the ring cylinders (200,210 and, respectively, 202,

212) against the rotary piston (30).

3. A bearing system as defined in claim 2, c h a r a c t e r i z e d i n that the outer and the inner' ring cylinder (200,210 and, respectively, 202,212) are arranged to be pressed with the same pressure againstthe piston (30).

4. A bearing system as defined in claim 2 or 3, c h a ra c t e r i z e d i n that the pressure in the outer and inner chamber (40,41 and, respectively, 42, 43) corresponds to the pressure in the cavity (213,214) multiplied by a factor α , where α is a number in the

interval 1.0-0.5.

5. A bearing system as defined in claim 4, c h a r a c t e r i z e d i n that α is a predetermined constant.

6. A bearing system as defined in claim 4, c h a r a c t e r i z e d i n that the factor α is arranged to decrease in steps with increasing pressure in the cavity (213,214).

7. A bearing system as defined in claim 4, c h a r a c t e r i z e d i n that the factor α depends on different process parameters, such as number of revolutions, temperature etc.

8. A bearing system as defined in claim 7, c h a r a c t e r i z e d i n that the factor α depends on the flow in the channel (246,248) for the supply of hydraulic pressure medium to the cavity (213,214).

9. A bearing system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that a holder (29,33) is located on each side of the rotary piston (30).

10. A bearing system as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the ring cylinders (200,210 and, respectively,

202,212) are provided with a passage (215) extending from the cavity (213,214) to the corresponding refining gap.

11. A bearing system as defined in claim 10. c h a ra c t e r i z e d i n that the passage (215) opens into a groove (216) extending all around in the surface of the ring cylinder abutting the rotary piston (30).