WO2011102558A1

WO2011102558A1 - Pad-type thrust bearing and submerged motor and submerged motor pump

Info

Publication number: WO2011102558A1
Application number: PCT/JP2011/054411
Authority: WO
Inventors: Hiroyuki Kato
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2010-02-19
Filing date: 2011-02-21
Publication date: 2011-08-25
Anticipated expiration: 2012-08-19
Also published as: JP2011169424A; JP5470085B2

Abstract

A pad-type thrust bearing is used to support axial thrust load acting on a rotating shaft by a plurality of bearing pads disposed on a stationary surface through a disk-shaped thrust disk. The pad-type thrust bearing includes a plurality of bearing pads (11), a bearing housing (10) configured to house the bearing pads (11), and a lift pump (12) for pressurizing and supplying a lubricating liquid to surfaces of the bearing pads (11). The impeller (12a) of the lift pump (12) is provided in the bearing housing (10).

Description

DESCRIPTION

Title of Invention

PAD-TYPE THRUST BEARING AND SUBMERGED MOTOR AND SUBMERGED MOTOR PUMP

Technical Field

[0001] The present invention relates to a pad-type thrust bearing for use in a rotating machine, and more particularly to a pad-type thrust bearing which can reduce starting torque and a submerged motor and a vertical submerged motor pump having such pad-type thrust bearing.

Background Art

[0002] A pad-type thrust bearing is configured to support axial thrust load acting on a rotating shaft by a plurality of bearing pads disposed on a stationary surface through a disk-shaped thrust disk. The bearing pads are supported from a stationary side by a tiltable structure in order to increase load carrying capacity, as typified by Kingsburry bearing (tilting pad bearing) .

[0003] Fig. 1 is a cross-sectional view showing a conventional pad-type bearing. Generally, a bearing pad 4 comprises an upper bearing pad 2 provided above a bearing disk 5 and a lower bearing pad 3 provided below the bearing disk 5 so as to support thrust load in both of upper and lower directions. The bearing load is supported by hydrodynamic pressure action generated between the upper bearing pad 2 and the bearing disk 5 and between the lower bearing pad 3 and the bearing disk 5 by rotation of the bearing disk 5 fixed to a rotating shaft (main shaft) 6. The upper bearing pad 2 and the lower bearing pad 3 comprise a plurality of bearing pads, respectively, and these bearing pads 2,3 and the bearing disk 5 are housed in a bearing cover Ί comprising an upper bearing cover la and a lower bearing cover lb, thus constructing an integrated unit. Reference numeral 10 represents a bearing housing.

[0004] When the rotating shaft 6 is rotated to rotate the bearing disk 5, the tiltable upper bearing pad 2 and the tiltable lower bearing pad 3 are slightly tilted, and a lubricating liquid film is formed between the upper bearing pad 2 and the bearing disk 5 and between the lower bearing pad 3 and the bearing disk 5 by hydrodynamic pressure effect. Thus, the bearing disk 5, the upper bearing pad 2 and the lower bearing pad 3 can support large load in a fluid lubrication state without solid contact.

[0005] When the rotating shaft 6 is not rotated in a stationary state of the rotating machine, the hydrodynamic pressure effect is not generated and the lubricating liquid film is not formed between the bearing disk 5 and the bearing pad 4. In the case where the lubricating liquid comprises an oil having a relatively high viscosity, the oil remains on small irregularities of the surfaces of the bearing disk 5, the upper bearing pad 2 and the lower bearing pad 3. At this time, if load acting on the surfaces of the upper bearing pad 2 and the lower bearing pad 3 in a stationary state is small, in some cases, the bearing can be started in a boundary friction lubrication state without galling . However, if the load acting on the surfaces of the upper bearing pad 2 and the lower bearing pad 3 is not small, the bearing becomes in a solid friction lubrication state and galling is liable to occur. Particularly, in the case where the lubricating liquid having very low boundary lubrication effect such as water having a low viscosity is used, the bearing is liable to be in a solid friction lubrication state at the time of startup, thus causing galling easily.

[0006] Because a rotating body's own weight acts on a thrust bearing ina vertical rotating machine, the thrust bearing becomes in a boundary friction lubrication state or a solid friction lubrication state having large coefficient of friction at the time of startup . Therefore, the torque of this vertical rotating machine is required to be 10 to 100 times that of the rotating machine which becomes in a fluid lubrication state at steady operation.

[0007] In order to reduce starting torque acting on the thrust bearing in such vertical rotating machine, in some cases, a lift pump 8 for pressurizing and supplying a lubricating liquid to the bearing pad 4 from the outside is provided, as shown in FIG. 2. In the example shown in FIG. 2, the lift pump 8 is configured to pressurize a lubricating liquid in a reservoir tank 9 and to supply the lubricating liquid to small holes formed in the lower bearing pad 3. Further, in thrust bearing apparatuses disclosed in Japanese Laid-open Patent Publication 60-065908 and Japanese Laid-open Patent Publication 07-027140, a lubricating liquid is introduced from a bearing housing through piping to a lift pump suction part and the lubricating liquid pressurized by the lift pump is introduced through flexible tubes or the like to the upper and lower bearing pad parts, and then the lubricating liquid is supplied under pressure through small holes provided at central parts of the bearing pads to bearing clearances (clearance between a disk and a bearing pad) .

[0008] The pressure of the lubricating liquid is adjusted so as to allow the bearing disk 5 to be floated from the lower bearing pad 3. Suppose that a flow rate of the lubricating liquid Q, a pressure Δ P (inlet pressure Pi-outlet pressure P₂ of the bearing pad) , a bearing clearance h, a coefficient of viscosity of the lubricating liquid μ, , a radius r₂ in the case where the pad is approximately-circular, and a radius of central small hole ri, the relationship is approximately defined as follows (mechanical Engineer's Handbook) :

<2=π · η³· ΔΡ/ {6 · μ 1 ο_§Θ ( r ₂/ r ₁) }

From the above equation, a pressure reaction force p acting on the bearing pad is defined as follows: Wp=J^r2 _rl {Px-Q/ (π h³/6 /z 1 o g_e (r/r )} - 2 π r · d r When the load Wg acting on the rotating body becomes equal to the pressure reaction force Wp, the rotating body is floated, thus facilitating the startup . After the rotating body is started to develop hydrodynamic pressure in the bearing part, fluid lubrication is realized, and thus injection of the lubricating liquid from the lift pump becomes unnecessary.

[0009] In the case where the pressure Ph in the bearing housing 10 at the time of startup is high, when the lift pump 8 installed outside as shown in FIG. 2 is used, discharge pressure becomes P_P = AP + Ph. In the case where Ph is larger than ΔΡ, the discharge pressure of the lift pump 8 is mostly consumed to resist the pressure in the bearing housing 10, and thus only limited discharge pressure is used for flotation of the bearing. In this case, because the discharge pressure of the lift pump 8 becomes larger than the pressure ΔΡ for flotation of the bearing, the bearing disk 5 is pressed against the upper bearing pad 2 by slight excess of the discharge pressure. Therefore, pressure control of the lift pump 8 should be strictly performed.

[0010] Further, in the case where the pressure Ph in the bearing housing 10 at the time of startup is high, the pressure piping connecting the lift pump 8 and the bearing housing 10 is required to withstand high pressure, and the possibility of leakage of the internal liquid from pipe joints due to vibration of the rotating machine itself, pressure change, temperature change or the like increases. Particularly, in the case where the rotating machine comprises a vertical seal-less motor pump having non-leakage quality, the lift pump 8 and the pressure piping also need to secure non-leakage quality.

Summary of Invention

Technical Problem

[0011] However, the conventional technology cannot sufficiently deal with the requirement that pressure control of the lift pump 8 should be strictly performed in the case where the pressure Ph in the bearing housing 10 is high at the time of startup and the requirement that the pressure piping connecting the lift pump 8 and the bearing housing 10 has high pressure resistance and non-leakage quality, particularly the lift pump 8 and the pressure piping have non-leakage quality in the case where the rotating machine comprises a vertical seal-less motor pump having non-leakage quality.

[0012] The present invention has been made in view of the above circumstances . It is therefore an obj ect of the present invention to provide a pad-type thrust bearing which has a lift pump for reducing starting torque and has a structure to prevent leakage of a lubricating liquid, and a submerged motor and a vertical submerged motor pump having the above pad-type thrust bearing.

Solution to Problem

[0013] In order to achieve the above object, according to a first aspect of the present invention, there is provided a pad-type thrust bearing comprising : a plurality of bearing pads ; a bearing housing configured to house the bearing pads; and a lift pump for pressurizing and supplying a lubricating liquid to surfaces of the bearing pads; wherein an impeller of the lift pump is provided in the bearing housing.

[0014] In a preferred aspect of the present invention, the lift pump has a motor for rotating the impeller, and a motor housing of the motor is coupled to the bearing housing such that at least a part of the motor housing is inserted into the bearing housing.

[0015] In a preferred aspect of the present invention, the lift pump comprises a seal-less motor pump.

[0016] In a preferred aspect of the present invention, the seal-less lift pump is integrally removable from the bearing housing from the outside of the bearing housing. [0017] According to a second aspect of the present invention, there is provided a pad-type thrust bearing comprising: a plurality of bearing pads; a bearing housing configured to house the bearing pads; and a lift pump for pressurizing and supplying a lubricating liquid to surfaces of the bearing pads; wherein the lift pump comprises a seal-less motor pump, and a motor housing of the seal-less motor pump is coupled to the bearing housing such that the motor housing forms a seal surface to seal the bearing housing from the lubricating liquid.

[0018] In a preferred aspect of the present invention, the lubricating liquid is water or water solution.

[0019] According to another aspect of the present invention, there is provided a vertical submerged motor comprising: a motor casing; a stator housed in the motor casing; a rotor disposed at a central part of the stator and fixed to a rotating shaft; and the pad-type thrust bearing for supporting the rotating shaft.

[0020] According to another aspect of the present invention, there is provided a vertical submerged motor pump comprising: a motor casing; a stator housed in the motor casing; a rotor disposed at a central part of the stator and fixed to a rotating shaft; an impeller fixed to the rotating shaft; and the pad-type thrust bearing for supporting the rotating shaft. Advantageous Effects of Invention

[0021] According to the present invention, because the impeller of the lift pump is provided in the bearing housing of the thrust bearing, even if the lubricating liquid becomes high pressure, the lubricating liquid can be prevented from leaking.

Brief Description of Drawings

[0022]

[FIG. 1] FIG. 1 is a schematic cross-sectional view showing a conventional tilting pad bearing. [FIG. 2] FIG. 2 is a schematic cross-sectional view showing the conventional tilting pad bearing having an external lift pump.

[FIG. 3] FIG. 3 is a top plan view showing a bearing pad having pressure liquid discharge holes according to the present invention.

[FIG. 4] FIG. 4 is a schematic cross-sectional view showing a tilting pad-type thrust bearing having a built-in lift pump according to an embodiment of the present invention.

[FIG. 5] FIG. 5 is a schematic cross-sectional view showing a vertical submerged motor pump which uses the tilting pad-type thrust bearing having the built-in lift pump according to another embodiment of the present invention.

[FIG. 6] FIG. 6 is a schematic cross-sectional view showing a universal joint according to the present invention.

Description of Embodiments

[0023] Apad—type thrust bearing, a submergedmotor and a submerged motor pump according to embodiments of the present invention will be described below with reference to drawings. Like or corresponding parts are denoted by like or corresponding numerals throughout drawings and will not be described below repetitively.

FIG. 4 is a cross-sectional view showing a pad-type thrust bearing according to an embodiment of present invention. The pad-type thrust bearing is provided with a built-in seal-less motor-type lift pump, and the lift pump is integrated with a bearing housing 10. The seal-less motor comprises a canned motor comprising a stator core and a stator winding which are enclosed by a can.

[0024] As shown in FIG. 4, an upper bearing pad 2 and a lower bearing pad 3 are provided in a bearing cover 1 comprising an upper bearing cover la and a lower bearing cover lb such that a bearing disk 5 fixed to a rotating shaft (main shaft) 6 of a rotating machine is located between the upper bearing pad 2 and the lower bearing pad 3. The upper bearing pad 2 comprises a plurality of bearing pads, and each of the bearing pads is supported by the upper bearing cover la through a tiltingmechanism 7. Likewise, the lower bearing pad 3 comprises a plurality of bearing pads, and each of the bearing pads is supported by the lower bearing cover lb through a tilting mechanism 7.

[0025] FIG. 3 is a top plan view showing the lower bearing pad 3. As shown in FIG .3, the lower bearingpad 3 comprises a plurality of bearing pads 11 (eight in FIG. 3) which are arranged along the circumference of the lower bearing cover lb. Each of the bearing pads 11. has a pressure liquid discharge hole 11a for discharging a lubricating liquid for bearing lift at the central part of the bearing pad 11. Further, each of the bearing pads 11 has a pressure liquid inlet hole lib for introducing the lubricating liquid for bearing lift at the lower surface of the bearing pad 11.

[0026] As shown in FIG. 4, the upper bearing cover la is substantially cylindrical in shape, and has an upper wall lc having a through-hole le at the central part of the upper wall lc for allowing themain shaft 6 to pass therethrough. The tilting mechanism 7 is provided at the lower surface of the upper wall lc to support each bearing pad 11. A side wall Id extends downward from an outer circumferential edge of the upper wall lc, and the side wall Id is connected to the lower bearing cover lb. The side wall Id has a plurality of holes If.

[0027] Further, a plurality of through-holes lg passing through the lower bearing cover lb are provided at positions corresponding to the pressure liquid inlet holes lib of the bearing pads 11 of the lower bearing pad 3. A cover 17 for forming a lubricating liquid passage is attached to the lower surface of the lower bearing cover lb. The cover 17 has a hole 17a at the central portion of the cover 17 for allowing the lift pump 12 to be inserted therethrough, and a disk-shaped lubricating liquid passage 18 is formed between the cover 17 and the lower surface of the lower bearing cover lb . The cover 17 is connected to the bearing housing 10 through legs 19. Because the load acting on the thrust bearing is supported by the bearing housing 10 through the legs 19, other legs for connecting the bearing cover 1 and the bearing housing

10 may be separately provided as a reinforcement structure.

[0028] The lift pump 12 comprises a motor unit M and a pump unit P. The motor unit M has a canned motor 12c, and the lift pump 12 is constructed as a seal-less motor pump. The lift pump 12 has a rotating shaft 20, and a centrifugal impeller 12a is fixed to the upper end of the rotating shaft 20 such that a suction side of the impeller 12a is directed to downward. A pump casing 21 comprising an upper pump casing member 21a and a lower pump casingmember 21b for forming a lubricating liquid suction passage is provided between the impeller 12a and the canned motor 12c, and the pump casing 21 is fixed to a motor housing 22. The pump casing 21 is inserted into the hole 17a at the central portion of the cover 17, and the upper pump casing member 21a for plugging up the hole 17a and the lower pump casing member 21b fixed to the motor housing 22 are joined together by a joint portion 24. A discharge-side guide vane 23 may be provided on an upper surface, of the pump casing 21. Further, the j oint portion 24 may be formed as a suction-side guide vane in the lubricating liquid suction passage 18.

[0029] The rotating shaft 20 of the lift pump 12 is supported by radial bearing 25,26 and a thrust bearing 27 in the canned motor 12c. The motor housing 22 has an annular attachment flange 22a for the lift pump, and the lift pump 12 is fastened and fixed through the attachment flange 22a to the bearing housing 10 in such a state that the lift pump 12 is inserted into a hole 10a formed at the lower part of the bearing housing 10.

[0030] The pressure liquid inlet hole lib of each bearing pad lg of the lower bearing cover lb corresponding to the pressure liquid inlet hole lib through a universal joint 16. As shown in FIG. 6, the universal joint 16 is in the form of cylindrical tube and has substantially spherical heads at both ends of the universal joint 16. The universal joint 16 is inserted into the pressure liquid inlet hole lib of each bearing pad 11 of the lower bearing pad 3 and the through-hole lg formed in the lower bearing cover lb, and 0 rings 28 are mounted on the respective spherical heads of the universal joint 16 to seal the pressurized lubricating liquid. Therefore, each bearing pad 11 of the lower bearing pad 3 and the lower bearing cover lb are allowed to be displaced in an axial direction and a direction perpendicular to the axial direction of the universal joint 16 with respect to the universal joint 16. Thus, the lubricating liquid can be sealed reliably, and a complicated movement of the bearing disk 5 during rotation of the main shaft 6 is not inhibited.

[0031] The connection between the pressure liquid inlet hole lib of each bearing pad 11 of the lower bearing pad 3 and the through-hole lg of the lower bearing cover lb is not limited to the universal joint 16, but may be performed by a flexible tube or the like.

[ 0032 ] With the above arrangement , when the lift pump 12 is rotated, the lubricating liquid is sucked from the inside of the bearing housing 10 into the impeller 12a, and the lubricating liquid is pressurized by the impeller 12a and introduced into the pressure liquid inlet hole lib of each bearing pad 11 of the lower bearing pad 3. Then, the lubricating liquid floats the bearing disk 5, and is then discharged into the bearing housing 10.

[0033] Because the impeller 12a of the lift pump 12 is disposed in the bearing housing 10 and the suction passage and the discharge passage are disposed in the bearing housing 10, the lubricating liquid piping to be provided outside the bearing housing 10 can be eliminated, and the possibility of leakage of the liquid due to vibration of the rotating machine itself, pressure change, temperature change or the like can be eliminated.

[0034] In the lift pump 12, the outer diameter of the impeller 12a, the outer diameter of the pump casing 21 (comprising the upper pump casing member 21a and the lower pump casing member 21b) and the outer diameter of part of the motor housing 22 which is inserted into the bearing housing 10 are smaller than the inner diameter of the hole formed in the bottom of the bearing housing 10. Therefore, the lift pump 12 can be integrally inserted into the position adjacent to the lower bearing cover lb through the bottom of the bearing housing 10 and can be integrally removed from the bottom of the bearing housing 10. Therefore, the pressure-resistant connection part can be limited only to the seal surface between the flange 22a provided on the motor casing 22 of the lift pump 12 and the bearing housing 10, and the lift pump 12 itself comprises a seal-less pump, thus reducing the chance of leakage of the lubricating liquid even if the lubricating liquid becomes high pressure.

[0035] The lift pump 12 may comprise not a canned motor pump, but a so-called Poly Winding motor pump having motor coil wires coated with water-resistant material.

[0036] FIG. 5 is a cross-sectional view showing a seal-less vertical submerged motor pump which uses the pad-type thrust bearing shown in FIG .4. As shown in FIG.5, the vertical submerged motor pump comprises a pump unit P and a motor unit M, and is configured such that the bearing housing 10 of the pad-type thrust bearing 30 shown in FIG.4 is fixed to a bottom of a motor casing 41 of the motor unit M. The motor unit M of the vertical submerged motor pump comprises a cannedmotbr in which a stator 44 comprising a stator core 42 and a stator winding 43 mounted on the stator core 42 is fitted into and fixed to the motor casing 41 and the stator 44 is enclosed by a can 45.

[0037] A rotor 48 fixed to a rotating shaft 40 is disposed at the central part of the stator 44, and the bearing disk 5 of the pad-type thrust bearing 30 is fixed to the lower end portion of the rotating shaft 40. The rotating shaft 40 is supported in a thrust direction by the pad-type thrust bearing 30 and in a radial direction by radial bearings 46, 47 disposed in the motor casing 41. Further, the pump unit P is configured such that a pump impeller 52 fixed to the upper end of the rotating shaft 40 is disposed in a pump casing 51.

[0038] According to the vertical submerged motor pump having the above structure, because weight of the rotor 48 of the submerged motor, the pump impeller 52 and the rotating shaft 40 acts on the pad-type thrust bearing 30, in some cases, solid friction occurs at the bearing part to cause galling of the bearing at the time of startup when a lubricating liquid film is not formed yet. However, if the motor pump is started after the bearing disk 5 is floated by the lift pump 12, the possibility of galling of the bearing can be eliminated.

[0039] The submerged motor pump having the above structure can be used for a large-scale seal-less motor pump such as a cooling water circulating pump in a nuclear reactor in which an internal pressure is high enough to be in the range of 70 to 160 bar and leakage of the internal liquid is not allowable. For example, in the case where a large-scale seal-less pump having output power of 5500kw class is used for a primary coolant pump of a pressurized water reactor, static weight of a rotating body of about 12 tons acts on a thrust bearing of such seal-less pump. If the submerged bearing comprises a pad-type thrust bearing having an outer diameter of about 900mm, when the bearing disk is floated by the external pressurization-type lift pump 8 (see FIG. 2) , the required head of the lift pump 8 necessitates about 164 bar including a pressure for resisting the internal pressure.

[0040] In this case, the pressure required for controlling flotation of the rotating body can be estimated to be 4 bar. Only by 10 percent higher than this estimation, i.e. 0.4 bar higher than this estimation, the rotating body is moved to the upper bearing pad side and adheres to the upper bearing pad 2. Specifically, in the case of the external lift pump 8, unless setting allowable value of discharge pressure of the lift pump 8 is controlled with 0.25 percent accuracy with respect to 164 bar, the rotating body cannot be maintained in a stable flotation state. On the other hand, as in the present embodiment, in the case where the lift pump 12 is installed in the bearing housing 10 , the head needs 4 bar required only for flotation of the rotating body. Thus, the power of the lift pump 12 becomes about 1/41 that of the external lift pump 8, and the rotating body can be maintained in a sufficiently stable flotation state with setting accuracy of 0.4 bar, i.e. about 10 percent accuracy.

[0041] Further, according to the present embodiment, because pressure-resistant sealing part which forms the boundary between the surrounding environment and the internal space is limited to the mounting portion where the motor housing of the lift pump 12 is mounted on the bearing housing 10 when coupling the lift pump 12 and the bearing housing 10, prevention of leakage of the internal liquid can be more reliable than the case where piping is provided outside the bearing housing 10. Further, at the time of maintenance, the lift pump 12 can be integrally removed from the bearing housing 10, and thus maintenance work can be performed in a short time. By using a small seal-less motor pump which is the same type as the main pump for the lift pump 12, the lift pump 12 can ensure high reliability equivalent to the main pump.

[0042] Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. Industrial Applicability

[0043] According to the present invention, the impeller of the lift pump is provided in the bearing housing of the thrust bearing . Therefore, the present invention can be utilized for providing a pad-type thrust bearing which can prevent a lubricating liquid from leaking even if the lubricating liquid becomes high pressure . Further, the present invention can be utilized for providing a submerged motor having such pad-type thrust bearing and a vertical submerged motor pump hiving such pad-type thrust bearing.

Claims

[Claim 1]

A pad-type thrust bearing comprising:

a plurality of bearing pads;

a bearing housing configured to house said bearing pads; and

a lift pump for pressurizing and supplying a lubricating liquid to surfaces of said bearing pads;

wherein an impeller of said lift pump is provided in said bearing housing.

[Claim 2]

A pad-type thrust bearing according to claim 1, wherein said lift pump has a motor for rotating said impeller, and a motor housing of said motor is coupled to said bearing housing, such that at least a part of said motor housing is inserted into said bearing housing.

[Claim 3]

A pad-type thrust bearing according to claim 1 or 2, wherein said lift pump comprises a seal-less motor pump.

[Claim 4]

A pad-type thrust bearing according to claim 3, wherein said seal-less lift pump is integrally removable from saidbearing housing from the outside of said bearing housing.

[Claim 5]

A pad-type thrust bearing comprising:

a plurality of bearing pads;

a bearing housing configured to house said bearing pads; and

wherein said lift pump comprises a seal-less motor pump, and a motor housing of said seal-less motor pump is coupled to said bearing housing such that said motor housing forms a seal surface to seal said bearing housing from said lubricating liquid.

[Claim 6]

A pad-type thrust bearing according to any one of claims 1 to 5, wherein said lubricating liquid is water or water solution.

[Claim 7]

A vertical submerged motor comprising:

a motor casing;

a stator housed in said motor casing;

a rotor disposed at a central part of said stator and fixed to a rotating shaft; and

said pad-type thrust bearing according to any one of claims 1 to 6 for supporting said rotating shaft.

[Claim 8]

A vertical submerged motor pump comprising:

a motor casing;

. a stator housed in said motor casing;

a rotor disposed at a central part of said stator and fixed o a rotating shaft;

an impeller fixed to said rotating shaft; and

said pad-type thrust bearing according to any one of claims to 6 for supporting said rotating shaft.