GB2293418A

GB2293418A - Bearing assembly for a castor

Info

Publication number: GB2293418A
Application number: GB9419272A
Authority: GB
Inventors: Stafford Thomas Screen
Original assignee: Colson Castors Ltd
Current assignee: Colson Castors Ltd
Priority date: 1994-09-23
Filing date: 1994-09-23
Publication date: 1996-03-27
Also published as: GB9419272D0

Abstract

A bearing assembly, which is particularly useful in a castor, has a bearing race (4), and a shroud (11) for the race. The shroud has a circumferential, radially extending flange (12) which extends into a housing which may, for example, form the upper part (3) of a castor fork (1). The pressures exerted on the housing by a turning moment (7, 8) of the bearing race are spread over a larger area (9, 10) of the housing and are thus less likely to result in wear or displacement, thereby holding the bearing more securely in place. The shroud may comprise a single piece of stamped metal. <IMAGE>

Description

CASTORS DESCRIPTION The present invention relates to castors and particularly to bearing retainment in castors.

Traditionally to hold a standard precision single row ball bearing in place in a castor at the required position to provide a swivel joint, the bearing race is encased in a housing, for example fixed into a shaped recess in a moulded part. Usually the moulded part is of plastics material for versatility and cost effectiveness. However problems are encountered with heavy duty castor applications since the precision bearing race required is of metal which wears the plastic since it can only be held at the outer member, resulting in weaknesses in the castor and unacceptable movement of the bearing race within the housing.

According to the present invention there is provided an arrangement comprising a bearing race, a shroud for the race having a circumferential flange extending radially of the race, and a housing for the race abutting an area in the region of the circumference of the shrouded bearing race so as to hold the race substantially against a turning movement thereof.

A suitable shroud is preferably made from two pieces of metal of a generally circular shape with opposing stepped peripheral cross-sections so as to cooperate to enclose the circumference of the bearing race and to provide an outwardly radially extending flange beyond the normal outer periphery of the bearing race. The shroud could alternatively be made of a single piece of stamped metal.For example it may be made with a first and a second part of a flat circular shape each for abutting respectively the top and bottom of the bearing race, a third part extending generally perpendicular to and joining the first and second parts and arranged for abutting the perimeter edge of the outer bearing race, and a fourth part extending generally perpendicular to the third part and joined thereto and extending radially outward of the bearing race so as to penetrate the housing encasing the shroud and race. The shroud may comprise the bearing cover rather than be a separate additional element or elements.

With a shroud of this shape, the pressures exerted on the plastic housing by a turning moment of the bearing race in use are no longer concentrated on points adjacent to the edges of the race but are spread along the flange. Thus less concentrated wear on the housing occurs than with traditional arrangements and the invention thus prolongs the life of castor arrangements and improves the safety of them. It also allows a wider choice of plastic materials.

The invention is particularly applicable to deep groove ball bearing arrangements.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example, to the accompanying drawings in which: Figure 1 is a part cutaway cross sectional view of a known bearing arrangement, according to the prior art.

Figure 2 is a part cutaway cross sectional view of a bearing arrangement according to the present invention.

In both figures the features are identified by like reference numbers.

The castor of the figures comprises a body portion 1 in the form of a castor fork with means 2 for attachment to a wheel (not shown). The upper part 3 of the body portion 1 forms a housing for a bearing having inner and outer races 4 and deep groove ball bearings 5. The castor fork 1 is preferably moulded of plastics material. The outer race 4 of the bearing is secured in a groove 13 in the wall of a vertical bore 14 in the upper part 3 of the castor fork. In fact the outer ball race may be integrally moulded into the upper part of the castor fork.

The axis 6 is the upright swivel axis of the castor about which the castor fork 1 can swivel relative to the article to which it is swivellingly connected (e.g. a wheelchair).

In use, when a weight is supported by the castor, then the bearing is subjected to a turning moment about axis 6, generally in the direction of arrows 7 and 8. This turning moment causes stress, and eventually wear, by the edges of the outer bearing race 4 on the housing material, tending in the worst case to remove the areas of material indicated by dark shading and denoted 9 and 10.

In Figure 2 the bearing has a peripheral shroud 11 with a radially extending flange 12 extending more deeply into the housing material. In this arrangement when a similar turning moment is generated for the bearing then stresses will result as the outer bearing race 4 tries to displace the housing material. However in this case the stresses are spread over a larger area and thus are less likely to result in actual wear or displacement, thus the bearing is more securely held in place. This is illustrated clearly from a comparison of Figures 1 and 2 in which is indicated by shaded areas 9 and 10 the potential areas which the outer bearing race 4 needs to displace in order to move in response to the turning moment. This area is much larger in the arrangement of the invention than in the prior art castor and would thus require equivalently larger forces to cause displacement. Thus it will be clear that the arrangement of the invention provides a stronger more reliable castor than was hitherto available.

Claims

CLAIMS:

1. A bearing assembly comprising a bearing race, a shroud for the race having a projection extending radially of the race and a housing for the race abutting an area in the region of the circumference of the shrouded bearing race so as to hold the race substantially against a turning movement thereof.

2. A bearing assembly as claimed in claim 1, wherein the projection comprises a circumferential flange.

3. A bearing assembly as claimed in claim 1 or claim 2, wherein the shroud is formed from two pieces of metal of a generally annular shape with opposing stepped peripheral cross-sections so as to cooperate to enclose the circumference of the bearing race and to provide an outwardly radially extending flange beyond the normal outer periphery of the bearing race.

4. A bearing assembly as claimed in claim 1 or claim 2, wherein the shroud comprises a single piece of stamped metal.

5. A bearing assembly as claimed in claim 4, wherein the shroud comprises first and second parts of flat annular shape each for abutting respectively the top and bottom of the bearing race, a third part extending generally perpendicular to and joining the first and second parts and arranged for abutting the perimeter edge of the outer bearing race, and a fourth part extending generally perpendicular to the third part and joined thereto and extending radially outward of the bearing so as to penetrate the housing encasing the shroud and race.

6. A bearing assembly as claimed in any of the preceding claims, wherein the shroud comprises the bearing cover.

7. A bearing assembly substantially as herein described, with reference to, and as illustrated in, Fig. 2 of the accompanying drawings.

8. A castor comprising a bearing assembly as claimed in any of the preceding claims.