GB2198486A - Bearings - Google Patents

Abstract

A bearing for use in harsh environments eg cement conveying plants or rock drills comprises ceramic inserts disposed in a metallic substrate having ceramic inserts joined thereto. In a preferred embodiment the bearing is a journal bearing and the metallic substrate includes generally axially extending slots (18) having ceramic inserts (20) retained therein. The slots may have side walls (19) of re-entrant form to facilitate retention of the inserts. <IMAGE>

Description

BEARINGS The present invention relates to bearings and particularly to bearings which include ceramics.

Where bearings have to operate in harsh environments it is sometimes desirable to employ non-metallic materials for one or both of the mating bearing surfaces. Where the operating environment is abrasive such as in, for example, powder handling equipment for cement conveying plant and in rock drills the use of ceramics may be advantageous.

A simple closely-fitting ceramic tube applied to the outside of a shaft journal would burst as a result of a relatively small temperature rise due to both the difference in the coefficients of linear expansion between many metals and ceramics and the poor resistance of most ceramics to tensile stresses.

According to the present invention a bearing having a ceramic running surface comprises a metallic substrate having ceramic bearing inserts joined thereto.

One embodiment of the present invention comprises a journal bearing. The surface of the shaft journal comprises generally axially extending slots or recesses having therein ceramic inserts the running surface of which ceramic inserts extends above the surface level of a metallic shaft substrate.

The axially-extending slots may be either parallel to the journal axis or may be skewed in relation to the journal axis.

The ceramic inserts may be located and held within the journal slots by any suitable means.

The inserts may, for example, be held by screws or by adhesive bonding or may alternatively be located by means of the insert and slot having co-operating "dovetailed" cross-sections. Where the latter is the case added security may be achieved by making the insert a shrink fit or utilising additional locating means such as adhesive bonding.

After fitting of the inserts to the shaft journal the assembly may be machined by, for example, grinding to a desired dimension or profile.

In another embodiment of the present invention which comprises a substantially planar thrust bearing the ceramic insert may again be secured in a slot or recess in a metallic substrate.

The ceramic may comprise any known ceramic which is suitable for the environment in which it is to operate. Examples of such ceramics may include silicon nitride, silicon carbide etc.

In order that the present invention may be more fully understood an example will now be described by way of illustration only with reference to the accompanying drawings of which: Figure 1 shows an end view of a shaft journal constructed according to the present invention, and Figure 2 which shows the shaft journal of Figure 1 sectioned through the plane including the line AA 1 and the shaft axis incorporated into a bearing assembly.

Referring now to Figures 1 and 2 and where the same features have common reference numerals. A bearing assembly intended to accept radial loads and also thrust loads in the direction T is shown generally at 10. The assembly comprises a housing 11 having a silicon nitride bush 12 fitted therein and a thrust washer 13 in a recess 14. Supported in the bush 12 is the end 15 of. a shaft 16. The end 15 is made of steel and is of generally cylindrical form 17. Machined into the end 15 are axially-extending slots 18 having inwardly sloping sides 19.

Held within the slots 18 are silicon nitride inserts 20 of cross-sectional form which co-operate with the slots 18. The end 15 also has a recess 21 in which is held a second thrust washer 22. The shaft 16 and end 15 are provided with conduits 23 for the supply of lubricant to the bearing elements 12, 13, 20, 22. Dirt and debris is prevented or inhibited from entering the bearing per se by a seal 24 held in a housing ring 25 secured to the main housing 11 by screws 26.

The inserts 20 may be held by interference within the slots 18 by, for example, shrink fitting. The inserts may alternatively be held by adhesive means or mechanical means such as screws or locking plates, for example, affixed to the shaft end.

Any ceramic material suitable for the intended application may be used as may of course any metallic material for the shaft or housing appropriate to, for example, a corrosive environment in which the bearing may operate.

In the example given the shaft rotates within the housing, however, in some aplications the bushed housing 11 may rotate about the shaft. An example of the latter may include a cutter for mining or drilling applications.

The number of ceramic inserts used may largely depead upon the physical size of the shaft to which they are to be fitted. For high speed applications it may be advantageous to employ an odd number of inserts to minimise vibration.

In a modification of the above emobdiment the use of the second thrust washer 22 could be avoided by allowing the inserts 20 to protrude beyond the radial face of the shaft end 15. The insert ends may subsequently be ground flat. The thrust washer 13 and recess 14 would of course have to be of a larger diameter to accommodate such a modification.

Claims (13)

1. A bearing having a ceramic running surface comprising a metallic substrate and having ceramic inserts joined thereto.

2. A bearing according to Claim 1 wherein the bearing is a journal bearing.

3. A bearing according to Claim 2 wherein the metallic substrate comprises generally axially extending slots having the ceramic inserts therein.

4. A bearing according to Claim 3 wherein the slots are parallel to the substrate axis.

5. A bearing according to Claim 3 wherein the slots are skewed in relation to the substrate axis.

6. A bearing according to any one of Claims 3 to 5 wherein the slot side walls have re-entrant form for retaining the inserts.

7. A bearing according to Claim 6 wherein the ceramic inserts are retained by a mechanical interference fit.

8. A bearing according to any one of Claims 3 to 6 wherein the ceramic inserts are retained by adhesive means.

9. A bearing according to any one preceding claim wherein the ceramic inserts comprise silicon nitride.

10. A bearing according to any one claim from 1 to 8 wherein the ceramic inserts comprise silicon carbide.

11. A bearing according to any one preceding claim from 3 to 10 wherein the ceramic inserts protrude from the ends of the slots in which they are retained and the ends of the inserts form a thrust bearing.

12. A bearing according to any one preceding claim wherein there is an odd number of inserts.

13. A bearing substantially as hereinbefore described with reference to the accompanying specification and drawings.