EP0466762A1

EP0466762A1 - Thrust bearing

Info

Publication number: EP0466762A1
Application number: EP19900905590
Authority: EP
Inventors: Norman Kenneth 18 Semaphore Road Bowers
Original assignee: Vickers PLC
Current assignee: Vinters Ltd
Priority date: 1989-04-05
Filing date: 1990-04-05
Publication date: 1992-01-22
Also published as: GB2230305A; GB8907626D0; AU5419590A; WO1990012216A1

Abstract

Palier à butée à lubrification par film fluide, comprenant un élément rotatif (12), tel qu'une rondelle de butée sur un arbre soumis à une charge axiale (18), et des semelles (10) en un matériau élastomère (20) destinées à assurer une réaction vis-à-vis de la charge axiale. Le démarrage de la rotation, lorsque l'élément (12) est sollicité par la charge, est rendu possible par inclinaison des faces des semelles contre lesquelles l'élément tournant (12) se déplace, par exemple en interposant une support en forme de cale (22) entre la matériau élastomère (20) et un élément d'appui ou de renfort (14) pour aider à la formation de films fluides lorsque l'élément (12) est entraîné en rotation. L'introduction d'un fluide sous pression entre les éléments (12, 14) permet d'obtenir une réaction hydrostatique de la charge axiale (18) et de réduire en outre le couple de démarrage. Le fluide peut être constitué par de l'huile ou de l'eau.Fluid film lubrication thrust bearing comprising a rotary element (12), such as a thrust washer on a shaft subjected to an axial load (18), and flanges (10) made of an elastomeric material (20) intended to ensure a reaction with respect to the axial load. The start of rotation, when the element (12) is stressed by the load, is made possible by tilting the faces of the flanges against which the rotating element (12) moves, for example by interposing a wedge-shaped support. (22) between the elastomeric material (20) and a support or reinforcement element (14) to assist in the formation of fluid films when the element (12) is rotated. The introduction of a pressurized fluid between the elements (12, 14) makes it possible to obtain a hydrostatic reaction of the axial load (18) and to further reduce the starting torque. The fluid can consist of 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.

The invention also relates to a shoe for such a bearing.

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.

GB-A-1271774 mentions the use of curved bearing pads and plain pads for journal bearings, but for thrust bearings it proposes the use of flat pads parallel to the thrust face or collar (in the circumferential direction) with curved entries and exits. This will not be an effective arrangement, and will only allow the use of light loadings. GB-A-1197850 discloses the use of rubber lined bearings for journals and thrust bearings. However it uses very large diameter bearings to reduce the specific loading and to increase the surface velocity as rubber bearings are said to function best when the surface velocity is high and the load per unit area is low. Convex faces are used on the thrust faces to give maximum lubrication.

In accordance with one aspect of the present invention, a fluid film lubricated thrust bearing comprises 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 substantially planar and oriented so as to present an acute lead-in angle to the rotary member. The invention provides 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. The invention also provides a fluid film lubricated thrust bearing of simpler structure than a Kingsbury or Michell bearing that can nevertheless react high axial loads. The thrust bearing will carry a high specific load at a relatively low surface speed so that bearing size can be kept small and losses minimised.

The present invention provides a fluid film lubricated thrust bearing in which the fluid can be oil or grease but particularly water (including fresh and sea water) . in a bearing as 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) .

Thus, in accordance with a second aspect of the present invention, a method of operating a load bearing assembly comprising a thrust bearing according to the first aspect of the present invention comprises supplying lubricating fluid to the thrust bearing, the fluid being selected from, for example, oil, grease and water.

At the entry sides of the shoes with reference to an intended primary direction of shaft rotation the shoes converge towards the rotary member. Thus the faces of the shoes against which the rotary member runs are inclined at least at their entry sides at an acute, preferably small, angle. This angle may be in the range 0.75-4.5° when each shoe is in an unloaded condition and is preferably about 3°. Tests have shown surprisingly that the bearing can sustain very high loads, up to three times those expected.

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, e.g. 15° or 30°. Surprisingly it has been found that reverse running can take place under considerable load with these large angles on the side which is the exit side when running in the normal direction.

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. This should be contrasted with conventional bearings in which the radial dimensions of shoes in a single ring are increased as necessary.

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 attutude 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 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 shoe for a thrust bearing comprising an elastomeric pad and a rigid backing member on which the pad is mounted-, wherein opposed planar faces of the pad and backing member extend at an acute angle to one another.

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 shoe forming part of a thrust bearing? Figure 3 is a transverse section of a second form of 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 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 10 for a seawater lubricated thrust bearing is in compression between a rotary member or disc 12 and a stationary support 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 shoesin the inner ring and about 90shoes i_n the outer ring, but a smaller installation might have a single ring with 6, 8 or 12 ^~iioes 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 thesupport 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 3° 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 30° 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 10a attached to shoe carrier 46. As seen in Figure 4, the carrier 46 carries several rings of theshoes 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 theshoes; 10a 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 shoe 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 10b. 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 10a 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 byshoes 10b. 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

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 substantially planar and oriented so as to present an acute lead-in angle to the rotary member.

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 for use with a lubricating fluid of oil or grease.

4. A bearing according to any of claims 1 to 3, wherein the acute lead-in angle lies in the range 0.75-4.5° when each shoe is in an unloaded condition.

5. A bearing according to claim 4, wherein the faces of the shoes against which the rotary member runs are inclined at an angle of about 3° to the surface of the rotary member when in an unloaded condition.

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

7. A bearing according to claim 6, wherein the exit sides of the shoes diverge from the rotary member at an angle in the range 15-30°.

8. 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.

9. A bearing .according to any of claims 1 to 7, wherein the shoes are disposed in a multiplicity of concentric rings coaxial with the axis of rotation of the member.

10. A bearing accoring 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.

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

12. A bearing according to claim 13, wherein the rigid material is ebonite or another rigid plastics material.

13. A bearing according to claim 11 or 12, wherein the backings of rigid material are bolted to the support.

14. A bearing according to claim 13, wherein the support is formed in radial segments each carrying one or more shoes, each- segment being independently removable.

15. A bearing according to any preceding claim, wherein the shoes have an elongate dimension which is directed radially.

16. A bearing according to claim 15, wherein the shoes have lengths greater than their widths.

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

18. A bearing according to claim 17, 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.

19. 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.

20. 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.

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

22. A method of operating a load bearing assembly comprising a thrust bearing according to any of the preceding claims in which lubricating fluid is supplied to the thrust bearing.

23. A method according to claim 22, wherein the lubricating fluid is oil or grease.

24. A method according to claim 22, wherein the lubricating fluid is water.

25. A shoe for a thrust bearing, the shoe comprising an elastomeric pad and a rigid backing member on which the pad is mounted, wherein opposed planar faces of the pad and backing member extend at an acute angle to one another.

26. A shoe according to claim 25, wherein the pad has substantially parallel opposed faces,^" "One of the pad faces being mounted on a face of the backing member, wherein opposed faces of the backing member extend at the acute angle to one another.

27. A shoe according to claim 25 or claim 26, wherein the elastomeric pad is cut back at its edge facing away from the direction in which the planar faces of the pad and backing member extend at an acute angle to- define in use a relatively large exit angle with an applied rotary member.