GB2272366A

GB2272366A - Castor

Info

Publication number: GB2272366A
Application number: GB9223882A
Authority: GB
Inventors: Raymond Robert James Daniels
Original assignee: Guy Raymond Engineering Co Ltd
Current assignee: Guy Raymond Engineering Co Ltd
Priority date: 1992-11-13
Filing date: 1992-11-13
Publication date: 1994-05-18
Anticipated expiration: 2012-11-13
Also published as: GB9223882D0; GB2272366B

Abstract

A castor comprises a body 12 and two wheels 14. Each wheel is rotatably mounted to the body by two bearing arrangements a radially inner one of which comprises bearing surfaces 20, 22 provided by the body and wheel respectively and a radially outer one of which comprises bearing surfaces 24, 26 provided by the body and wheel respectively. In one aspect of the invention, the radially inner bearing is not essential. <IMAGE>

Description

CASTORS This invention relates to castors, and particularly although not exclusively, to castors which are required to be relatively small and yet have a high load carrying capacity. Such castors have many applications, for example, for desk drawer units which are used with desk tables, upholstered furniture such as settees and easy chairs, and beds.

The invention includes a castor comprising a body and a wheel rotatably mounted thereto, the body carrying (i) cylindrical bearing surface means cooperable with first cylindrical bearing surface means of the wheel and (ii) circumferentially extending bearing surface means disposed radially outwardly of said cylindrical bearing surface means of the body and cooperable with second cylindrical bearing surface means of the wheel.

The wheel may be axially retained on the body by respective cooperable snap fit engagement means on said second bearing surface means of the wheel and said circumferentially extending bearing surface means of the body. This avoids the need for extra components to be employed for axially retaining the wheel.

The snap-fit engagement means may comprise a circumferentially extending groove and a circumferentially extending rib. In a preferred embodiment the second bearing surface means of the wheel is provided with the rib and the circumferentially extending bearing surface means of the body is provided with the groove.

Preferably, the radial clearance between said second cylindrical bearing surface means and said circumferentially extending bearing surface means is greater than the radial clearance between said first cylindrical bearing surface means and said cylindrical bearing surface means carried by said body.

The bearing surface means carried by the body may be provided by parts of the body integrally moulded therewith and the first and second bearing surface means of the wheel may be provided by parts of the wheel integrally moulded therewith. In this case the body and the wheel may be respective plastics mouldings. It has been found that if the body is moulded in a plastics material which is different from the plastics material in which the wheel is moulded, the coefficient of friction between these components may be reduced. This has been found to be the situation, for example, if the plastics material in which the body is moulded comprises a polyamide and the plastics material in which the wheel is moulded comprises a polyacetal.

In the preferred embodiment, the wheel has a rim comprising a radially outwardly facing cylindrical ground engaging surface, and said second cylindrical bearing surface means of the wheel comprises a radially inwardly facing cylindrical surface of said rim. Furthermore, in the preferred embodiment, the circumferentially extending bearing surface means is provided by an annular member and the cylindrical bearing surface means carried by said body comprises a radially outwardly facing cylindrical surface of a spindle.

The invention also includes a castor comprising a body and a wheel rotatably mounted to the body; the wheel having a radially outwardly facing cylindrical ground engaging surface and a cylindrical bearing surface disposed closer to the ground engaging surface than the axis thereof, and the body carrying a circumferentially extending surface cooperably with said bearing surface.

Although reference has been made above to the provision of a wheel, it is to be understood that the invention is particularly applicable to castors, such as the castor of the preferred embodiment, provided with two wheels, a respective wheel being rotatably mounted to each of two opposite sides of the body.

In order that the invention may be well understood, the above-mentioned, preferred embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawings, in which: Figure 1 is an axial cross-section of a castor; Figure 2 is a view of a body of the castor of Figure 1 taken in the direction of arrow II in that figure; Figure 3, is a view of the body taken in the direction of arrow .111 in Figure 2; and Figure 4 is a cross section of the body taken along the line IV - IV in Figure 3.

Referring now to the drawings, there is shown a castor 10, comprising a body 12 and two wheels 14 rotatably mounted to the body, one to each of two opposite sides of the body.

The body 12 comprises a central portion 16 having a bore 18 for receiving a metal stem (not shown) which extends from the bore for mounting the castor on a piece of furniture.

The diameter of the wheels 14 is 40mm, which is also the overall height of the castor without the metal stem.

Each side of the central portion 16 is provided with respective means cooperable with a wheel for rotatably mounting the wheel to the body. These means are identical on each side of the body and accordingly will be described in connection with only one side.

Briefly, the body carries (i) cylindrical bearing surface means 20 cooperable with cylindrical bearing surface means 22 of the wheel and (ii) circumferentially extending bearing surface means 24 disposed radially outwardly of the bearing surface means 20 and cooperable with cylindrical bearing surface means 26 of the wheel. In the illustrated embodiment the bearing surface means 20 and 24 carried by the body 12 are provided by parts of the body integrally moulded therewith. More specifically, the cylindrical bearing surface means 20 comprises a radially outwardly facing cylindrical surface of a spindle 28 extending from the central portion 16 of the body and the circumferentially extending bearing surface means 24 is provided by an annular member 30 co-axial with the spindle and also extending outwardly from the side of the body central portion 16.

Additionally, the cylindrical bearing surface means 22 and 26 of the wheel are provided by parts of the wheel integrally moulded therewith. The cylindrical bearing surface means 20 which cooperate with the outwardly facing cylindrical surface of the spindle 28 is provided by a socket portion 32 of the wheel located at the hub thereof and the cylindrical bearing surface means 26 is provided by a radially inwardly facing cylindrical surface of a rim 34 of the wheel, the radially outwardly facing surface 36 of which is the ground engaging surface of the wheel.

The bearing surface means 26 is closer to the ground engaging surface 36 of the wheel than the axis thereof. The ground engaging surface may be textured to prevent skidding on carpets.

The radial clearance between the bearing surface means 24, 26 is greater than the radial clearance between the bearing surface means 20, 22. For example, typically the radial clearance between the former is O.lmm and the radial clearance between the latter is 0.025mm. It is the cooperation between the bearing surface means 20, 22 which primarily provides the rotatable mounting of the wheel to the body as will be appreciated from the above-mentioned radial clearance figures. However, when the castor is required to carry a load above a predetermined amount, the portion of the rim 34 of the wheel which engages the ground will deflect into engagement with the adjacent portion of the member 30 of the body and the circumferentially extending bearing surface means 24 provided by that member 30 will cooperate with the cylindrical bearing surface means 26 provided by the rim 34. The portions of the members 30 to each side of the body which will be engaged when the wheel rims deflect are strengthened by the provision of the channel section formation 35 in the body.

The body 12 and the wheels 14 are plastics injection mouldings. The wheels may be moulded in the same plastics material, for example a polyamide, as the body, but in the embodiment they are moulded form a different plastics material - specifically the body is moulded in a plastics material comprising a polyamide and the wheels are moulded in a plastics material comprising a polyacetal. This particular combination results in a coefficient of friction between the wheels and body which is less than the coefficient of friction when the wheels are moulded in the same polyamide material as the body.

It will be appreciated that the bearing surface means provided by the member 30 does not have to extend completely around the member and in this regard it will be noted that the radially outwardly facing surface of the member 30 is provided with opposed flats 42 which extend substantially parallel to the bore 18. These flats are provided across the parting line of the mould so that any flash which has been indicated in Figure 2 at 44 will be located radially inwardly of the circumferentially extending outer surface portions of the member 30 and will not interfere with the running of the wheel.

The wheel is axially retained on the body by respective cooperable snap-fit engagement means on the bearing surfaces 24, 26 on the member 30 of the body and the rim 34 of the wheel respectively. As illustrated the snap-fit engagement means comprise a circumferentially extending groove 38 on the member 30 and a circumferentially extending rib 40 on the rim 34. The rib 40 is annular, but the groove which would otherwise be annular is discontinuous at the flats 42.

Whilst the provision of the two bearing arrangements formed by surfaces 20, 22 and 24, 26 respectively is preferred for heavy load carrying applications, it is envisaged that the radially inner arrangement may be omitted for other applications and that the radially outer surface of body member 30 and the radially inner surface 26 of the wheel rim (or a cylindrical flange inwardly of the rim) may be used to provide the only means for rotatably mounting the wheel to the body.

Claims

CLAIMS:

1. A castor comprising a body and a wheel rotatably mounted thereto, the body carrying (i) cylindrical bearing surface means cooperable with first cylindrical bearing surface means of the wheel and (ii) circumferentially extending bearing surface means disposed radially outwardly of said cylindrical bearing surface means of the body and cooperable with second cylindrical bearing surface means of the wheel.

2. A castor as claimed in claim 1, wherein said wheel is axially retained on the body by respective cooperable snap fit engagement means on said second bearing surface means of the wheel and said circumferentially extending bearing surface means of the body.

3. A castor as claimed in claim 2, wherein said snap-fit engagement means comprises a circumferentially extending groove and a circumferentially extending rib.

4. A castor as claimed in any one of claims 1 to 3 wherein the radial clearance between said second cylindrical bearing surface means and said circumferentially extending bearing surface means is greater than the radial clearance between said first cylindrical bearing surface means and said cylindrical bearing surface means carried by said body.

5. A castor as claimed in any one of claims 1 to 4, wherein said bearing surface means carried by the body are provided by parts of the body integrally moulded therewith.

6. A castor as claimed in any one of claims 1 to 5, wherein said first and second bearing surface means of the wheel and provided by parts of the wheel integrally moulded therewith.

7. A castor as claimed in claim 6 when appended to claim 5, wherein the body and the wheel are respective plastics mouldings.

8. A castor as claimed in claim 7 wherein the body is moulded in a plastics material which is different from the plastics material in which the wheel is moulded.

9. A castor as claimed in claim 8, wherein the plastics material in which the body is moulded comprises a polyamide and the plastics material in which the wheel is moulded comprises a polyacetal.

10. A castor as claimed in any one of claims 1 to 9, wherein said wheel has a rim comprising a radially outwardly facing cylindrical ground engaging surface, and said second cylindrical bearing surface means of the wheel comprises a radially inwardly facing cylindrical surface of said rim.

11. A castor as claimed in any one of claims 1 to 10 wherein said circumferentially extending bearing surface means is provided by an annular member.

12. A castor as claimed in any one of claims 1 to 11, wherein said cylindrical bearing surface means carried by said body comprises a radially outwardly facing cylindrical surface of a spindle.

13. A castor comprising a body and a wheel rotatably mounted to the body; the wheel having a radially outwardly facing cylindrical ground engaging surface and a cylindrical bearing surface disposed closer to the ground engaging surface than the axis thereof, and the body carrying a circumferentially extending surface cooperably with said bearing surface.

14. A castor as claimed in any one of claims 1 to 13, wherein said body has a respective said wheel rotatably mounted to each of two opposite sides thereof.

15. A castor substantially as herein described with reference to the accompanying drawings.