GB2230305A

GB2230305A - Thrust bearing.

Info

Publication number: GB2230305A
Application number: GB8907626A
Authority: GB
Inventors: Norman Kenneth Bowers
Original assignee: Vickers PLC
Current assignee: Vinters Ltd
Priority date: 1989-04-05
Filing date: 1989-04-05
Publication date: 1990-10-17
Also published as: WO1990012216A1; EP0466762A1; GB8907626D0; AU5419590A

Abstract

A fluid film lubricated thrust bearing comprises a rotatory member (12) such as a thrust collar on a shaft subject to axial load (18) and shoes (10) of elastomeric material (20) for reacting the axial load. Starting of rotation when the member (12) is subject to load is enabled by tilting the faces of the shoes against which the rotatory member (12) runs e.g. by interposing a wedge-shaped backing (22) between the elastomeric material (20) and a support or backing member (14) to assist formation of fluid films as the member (12) rotates. Introduction of pressure fluid between the members (12, 14) can provide hydrostatic reaction of the axial load (18) and further reduce starting torque. The fluid may be oil or water.

Description

THRUST BEARING The present invention relates to a thrust bearing for use particularly, though not exclusively, on a rotary shaft which may be a horizontal or vertical shaft of e.g. a pump or generator or may be a marine propeller shaft.

Pivoted segmental thrust bearings in which a load on a shaft shoulder or collar is reacted by tiltable shoes or pads in a bearing housing with an oil-film between the shaft shoulder or collar and the pads (so-called Kingsbury or Michell bearings) are known.

It is a first object of the invention to provide a fluid film lubricated thrust bearing that does not require pivoted shoes, has a lower power consumption, and can be stopped and restarted repeatedly without seizing. It is a second object of the invention to provide a fluid film lubricated thrust bearing of simpler structure than a Kingsbury or Michell bearing that can nevertheless react high axial loads.

The present invention provides a fluid film lubricated thrust bearing in which the fluid can be water (including fresh water and seawater). Such a bearing may comprise a rotary member subject to axial load and shoes of resilient or elastomeric material for reacting the axial load, wherein the faces of the shoes against which the rotary member runs are directed to assist formation of fluid films as the member rotates. Water lubricated thrust bearings in which a rotary member runs against pads of resilient material are believed to be new.

In a bearing ds aforesaid the faces of the shoes against which the rotary member runs are preferably of natural or synthetic rubber. If the rubber is an oil-resistant rubber the lubricating fluid may be an oil or grease. But the use of water as the fluid is preferred for many applications (e.g. marine propulsion shafts).

In a preferred structure, at the entry sides of the shoes with reference to an intended direction of shaft rotation the shoes converge towards the rotary member.

Thus the faces of the shoes against which the rotary member runs may be inclined at least at their entry sides at a small angle (typically at about 30 in an unloaded condition) towards the rotary member. To reduce the likelihood of break-away of material at the trailing edges of the pads or shoes under high applied loads, the exit sides of the shoes preferably diverge from the rotary member at a relatively large angle.

The shoes may be disposed in a single ring coaxial with the axis of rotation of the member, or they may be disposed in a multiplicity of concentric rings coaxial with the axis of rotation of the member. The shoes do not need to be pivoted as in a Michell bearing, and thus the bearing may comprise a support and means attaching the shoes to the support so that the shoes maintain a fixed attitude to the rotary member.

Each shoe may comprise a pad of elastomeric material attached to a backing of rigid material which may be a metallic or a non metallic material such as ebonite and the backing of each pad may be mechanically connected to a support by bolts or studs or other suitable means. The pads may be generally rectangular when viewed in plan (i.e. when viewed in the direction of the shaft axis of rotation) or may be segments of a ring, are preferably radially directed and may have lengths greater than their widths. To enable a damaged pad to be removed without dismantling the whole of the bearing, it is preferred that the backing is formed in radial segments each carrying one or more pads, each segment being independently removable.

The rotary member may be a shaft shoulder or collar, and first and second sets of shoes may be provided that can run against opposed end faces of the shaft shoulder or collar if it is desired to react load in either axial direction.

Particularly from the standpoint of ease of starting rotation it is in some applications desirable to provide means for applying fluid pressure to the rotary member to react at least part of the axial load and reduce the thrust on the pads or shoes. Thus the bearing preferably has a housing, the rotary member fits within the housing and has a cylindrical side surface, a seal in the housing acts on the side surface of the rotary member to provide a fluid chamber containing a set of bearing pads, and means is provided for feeding pressure fluid into the fluid chamber to react axial load.

In a further aspect, the invention provides a fluid film lubricated thrust bearing comprising a rotary member, shoes for reacting load on the rotary member and means for applying fluid pressure to the rotary member to react at least a part of the axial load.

A bearing as aforesaid may have a housing that is also provided with a journal bearing or the like to maintain trueness of the bearing housing relative to the shaft or other rotary member during rotation thereof.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures 1 and 2 are a transverse section and a plan of a first form of pad or shoe forming part of a thrust bearing; Figure 3 is a transverse section of a second form of pad or shoe forming part of a thrust bearing; Figure 4 is a diagrammatic exploded view of a thrust bearing in which load is reacted using the pads or shoes of Figure 1 or Figure 3; and Figure 5 is a diagrammatic longitudinal section of the thrust bearing.

In Figures 1 and 3 a shoe or pad 10 for a seawater lubricated thrust bearing is in compression between a rotary member or disc 12 and a stationary support or backing member 14, the direction of rotation of member 12 being indicated by arrow 16 and the axial load on the member 12 being indicated by the arrow 18. The shoe 10 comprises a constant thickness rubber pad 20 typically of Shore A hardness 70 to 80, attached onto a rigid backing member 22 of ebonite or other suitable material and may be laminated with carbon fibre, kevlar or polyester fibres to resist tensile loads and minimise stress cracking (see below).

The pad 20 may be generally rectangular as shown or may be keystone-shaped, conveniently has a radial length greater than its circumferential width with a typical aspect ratio of about 2:1 or more, is radially directed and occupies only a small angular sector of rotary member 12, there being at least one ring of pads. It may have two or more rings of concentric pads with a multiplicity of pads in each ring thereby maximising the number of working pads and hence the load that can be carried. Thus for a thrust bearing for a large marine propeller shaft there might be four rings with about 50 pads in the inner ring and about 90 pads in the outer ring, but a smaller installation might have a single ring of pads with 6, 8 or 12 pads in the ring. The backing member 22 is formed with fixing holes 24 that receive bolts or studs for attachment of the pad 10 to the backing member 14. It is of wedge profile as shown in Figure 1, so as to cause the face of the pad 20 to present an angle of about 30 to the adjoining face of rotary member 12 when there is no substantial axial load 18 on the member 12. It will be appreciated that as the axial load 18 increases to several tonnes or tens of tonnes as may happen in normal running, the rubber pad 20 will distort so that its surface approaches parallelism with the adjoining face of the rotary member 12.

It has been found that a water-lubricated thrust bearing using shoes as shown can run under high applied loads, and further that it can be brought to rest and restarted under load with a reduced tendency to seize and a comparatively low starting torque. The convergent taper of the face of rubber pad 20 relative to the member 12 (as viewed in the direction of rotation 16 of the member 12) is believed to promote formation of a lubricating film of water between the members 12 and 20, and its ability to do so has been observed to persist under axial load. In contrast, it has been found that an initially parallel pad does not generate a lubricating film so easily and can only sustain comparatively small axial loads. If need be, hydrostatic pressure is applied to the bearing to react at least part of the shaft load as described below.An advantage of non-brittle pad materials such as rubber is that they are resistant to shock loads which could lead to catastrophic failure of pads of brittle material, Consequently a bearing using an elastomeric pad material is likely to be reliable in service under a range of adverse conditions.

It has been shown that the mode of failure of elastomeric (rubber) faced fixed taper thrust pads is by the breaking off of small portions (see the dotted line in Figure 1) of the elastomeric (rubber) pad at the trailing edge. This breaking off is caused by the high peak pressure on the face of the pad together with the tension T in the pad (Figure 1) caused by the drag of the disc on the pad surface. The load at which portions break off can be significantly increased by re-inforcing the rubber in the direction of motion of the thrust disc e.g. transversely across the pad.

Such reinforcement may be in the form of fibres such as polyester or kevlar or carbon embedded in the rubber. Such re-inforcement will stiffen the pad surface and resist fracture due to tension. It will also help to resist penetration of the rubber by the high peak pressure that occurs towards the trailing edge of the pad. To minimise the risk of break-away, a modified pad structure (Figure 3) has a tapered trailing edge 24 which typically makes an angle of 15 to 300 with the member 12. The pad profile may be modified if the shaft rotates in both directions by providing tapers on a pair of opposite edges. The pad profile may be curved as well as angular.

In Figures 4 and 5, a thrust bearing 30 for reacting axial load 31 on a shaft 32 comprises a housing through which the shaft 30 passes and defined by cover 34, stationary support 36 and sets of side plates 38, 40 (only one group shown) that together make up a cylindrical side surface of the housing. The shaft 30 has an integral collar 42 attached to which is a thrust collar or disc 44 that rotates with the shaft 32. Under the normal load direction in shaft 32 which is indicated by arrow 31, the thrust at collar 42 is reacted by shoes lOa attached to shoe carrier 46. As seen in Figure 4, the carrier 46 carries several rings of the pads 10a and is divided into quadrants or sectors 46a, 46b etc, that are attached to and individually removable from the support 36.This arrangement permits inspection of the pads l0a and replacement of any damaged ones by pulling the quadrants or sectors out radially without dismantling of the bearing assembly in the axial direction, and cover plates 40 are divided into matching quadrants or sectors to permit inspection and pad removal to be carried out. For occasions when load direction 31 is reversed, the cover 34 has a second carrier 48 in sectors 48a-48b etc, and carrying a second set of shoes lOb. The support 36 also carries a journal bearing 50 (which is advantageously also water-lubricated) to maintain the housing closely concentric with the shaft 30 as the latter rotates.

To further facilitate shaft rotation, especially when starting from rest under axial load, it is preferable to react at least part of the shaft load 31 hydrostatically. For this purpose an annular seal 52 supported in a groove 54 of side plates 38 and energised by pressure fluid at line 56 runs on the cylindrical surface of collar 44. A fluid-tight internal chamber 58 of the housing containing the set of shoes lOa is thereby defined. Supply of pressure fluid from line 60 by pump 62 or other suitable means into the chamber 58 reacts the pressure at collar 44.

By selection of the pressure provided by pump 62, the axial load 31 may be partly relieved, may be balanced out so that the shaft 30 "floats" hydrostatically in the bearing, or may be over-compensated so that a reverse thrust is reacted by pads lOb. If the pressure provided by pump 62 almost cancels out the axial thrust 31, the frictional resistance to shaft rotation is reduced, and the starting torque necessary for shaft rotation is reduced. If desired the bearing can be run in normal operation for extended periods with hydrostatic reaction of the load as aforesaid.

Claims

CLAIMS:

1. A fluid film lubricated thrust bearing comprising a rotary member subject to axial load and shoes of elastomeric material for reacting the axial load, wherein the faces of the shoes against which the rotary member runs are directed to assist formation of fluid films as the member rotates.

2. A bearing according to Claim 1, wherein the faces of the shoes against which the rotary member runs are of natural or synthetic rubber.

3. A bearing according to Claim 2, wherein the rubber is an oil-resistant rubber and the lubricating fluid is an oil or grease.

4. A bearing according to Claim 2, wherein the lubricating fluid is water.

5. A bearing according to any preceding claim, wherein at the entry sides of the shoes with reference to an intended direction of shaft rotation the shoes converge towards the rotary member.

6. A bearing according to Claim 5, wherein the faces of the shoes against which the rotary member runs are inclined at least at their entry sides at a small angle towards the rotary member.

7. A bearing according to Claim 6, wherein the faces of the shoes against which the rotary member runs are inclined at an angle of about 30 to the surface of the rotary member when in an unloaded condition.

8. A bearing according to any preceding claim, wherein the exit sides of the shoes diverge from the rotary member.

9. A bearing according to Claim 8, wherein the exit sides of the shoes diverge from the rotary member at a relatively large angle.

10. A bearing according to any preceding claim, wherein the shoes are disposed in a single ring coaxial with the axis of rotation of the member.

11. A bearing according to any of Claims 1-9, wherein the shoes are disposed in a multiplicity of concentric rings coaxial with the axis of rotation of the member.

12. A bearing according to any preceding claim, further comprising a support and means attaching the shoes to the support so that the shoes maintain a fixed attitude to the rotary member.

13. A bearing according to any preceding claim, wherein each shoe comprises a pad of elastomeric material attached to a backing of rigid material.

14. A bearing according to Claim 14, wherein the rigid material is ebonite or another rigid plastics material.

15. A bearing according to Claim 13 or 14, wherein the backings of rigid material are bolted to the support.

16. A bearing according to any preceding claim, wherein the shoes are directed radially.

17. A bearing according to Claim 16, wherein the shoes have lengths greater than their widths.

18. A bearing according to any of Claims 13-17, wherein the backing is formed in radial segments each carrying one or more pads, each segment being independently removable.

19. A bearing according to any preceding claim, wherein the rotary member is a shaft shoulder or collar.

20. A bearing according to Claim 19, wherein first and second sets of shoes are provided that can run against opposed end faces of the shaft shoulder or collar for reacting load in either axial direction.

21. A bearing according to any preceding claim, further comprising means for applying fluid pressure to the rotary member to react at least part of the axial load.

22. A bearing according to any preceding claim, further comprising a housing, wherein the rotary member has a cylindrical side surface, a seal in the housing acts on the side surface of the rotary member to provide a fluid chamber containing a set of bearing pads, and means is provided for feeding pressure fluid into the fluid chamber to react axial load.

23. A bearing according to any preceding claim, further comprising journal bearing means maintaining the bearing closely concentric with the rotary member.

24. A fluid film lubricated thrust bearing comprising a rotary member, shoes for reacting load on the rotary member and means for applying fluid pressure to the rotary member to react at least part of the axial load.

25. A bearing according to Claim 24, wherein the fluid is oil or grease.

26. A bearing according to Claim 24, wherein the fluid is water.

27. A bearing according to any of Claims 24, 25 or 26, comprising a housing, wherein the rotary member has a cylindrical side surface, a seal in the housing acts on the side surface of the rotary member to provide a fluid chamber containing a set of bearing pads, and means is provided for feeding pressure fluid into the fluid chamber to react axial load.

28. A bearing according to any of Claims 25-27, wherein the rotary member is a shaft shoulder or collar.

29. A bearing according to Claim 28, wherein first and second sets of shoes are provided that can run against opposed end faces of the shaft shoulder or collar for reacting load in either axial direction.

30. A thrust bearing substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or Figure 3 or Figures 4 and 5 of the accompanying drawings.