WO1996006746A1 - Castor fork - Google Patents

Abstract

A castor fork (1) which supports a wheel (2) is formed from two discrete parts (9, 10). Each part (9, 10) has a leg portion (3) and a body portion (5). The two parts (9, 10) are clamped together by means of screws or bolts (12, 13) and receive a bearing race (11) to which is attached a support member (6) of an article to which the wheel (2) is to be attached. The castor fork (1) thus constructed is stronger than known assemblies and can be assembled and dismantled more quickly, easily and accurately. The arrangement allows recesses and spigots to be precast into the parts and tailored to the particular castor, for example to accurately locate multiple bearing races, wheel bosses and brakes.

Description

CASTOR FQRK DESCRIPTION

The present invention relates to a castor fork and particularly to a castor fork for containing a precision radial bearing or bearings for a swivel assembly.

Traditionally, castor forks are moulded from a thermoplastic material around a radial bearing race in the upper part and a wheel is fixed at the lower part between the two arms of the fork. This is an expensive process and the plastic material has limited strength.

Alternatively the castor fork is formed of pressed metal, the radial bearing race is pushed into a recess in the upper part of the fork and the edges of the recess are rolled over to hold it in place. The fork itself has more strength than a plastic fork but the rolled edges will only hold the bearing race in place up to certain loadings and this arrangement is too unreliable to use for heavy duty applications or those where safety is paramount. Sometimes tabs are added to a die casting and these are displaced to hold the bearing race in place but this is not always satisfactory since die cast materials are brittle and not always malleable enough for this sort of application.

The present invention aims to provide an improved castor fork assembly which can be easily assembled, made from strong material in a cost effective manner and retain the bearing race efficiently and reliably for relatively high loads.

According to the present invention there is provided a castor fork comprising two discrete parts, each part having a leg portion and a body portion with a recess for receiving a radial bearing race and the two parts being connectable together to retain the radial bearing race in the co-joined recesses.

Preferably the recess is shaped so that the bearing is securely retained by transverse walls of the body portion, e.g. between upper and lower walls of the recess.

The two parts are most cost effectively formed of die cast metal but a glass filled plastics material may be used.

A bearing assembly formed using a castor fork according to the present invention can be made stronger than known assemblies, and can be assembled quickly, accurately and easily, particularly compared to traditional methods which require rivetting and screwing operations. A particular advantage is the ease with which such a bearing assembly can be disassembled, for example if it is required to change the bearing. The two die cast parts of the fork may be clamped together or alternatively bolted or screwed or a retaining cap may be slotted over the body portions of the two parts, for example over the upper section.

By forming the fork in two discrete die cast parts, grooves or other indentations can be cast into the inner surfaces of the fork legs so as to hold items in place between the legs without the need to drill holes right through the legs: such drill holes are unsightly and in any case difficult to accurately position. In particular a spindle may be moulded into one or each leg part to support the castor wheel .

According to a particular preferred embodiment the leg portions of the two parts are connected to the castor wheel axis in such a way that the axle bolt is concealed. This can be achieved using a plug on one side of the wheel and an axle bolt passing through the plug and the axle into one fork leg portion. The plug is arranged to hold the head of the axle bolt and the other leg portion has an internal recess into which the plug fits snugly. The forces exerted by the wheel on the axle bolt tend to be born more by the first part of the fork into which the bolt is screwed and thus this first part may be made slightly stronger. However, the upper fastening of the body portions in combination with the rigidity of the fork provides sufficient support for the wheel and offers resistance to impacts and side loads .

For a better understanding of the present invention, reference will be made by way of example to the accompanying drawings, in which:

Figure 1 is a side elevation of a castor fork according to the invention in an assembled condition.

Figure 2 is a cross-section of the fork of Figure 1 on the line A-A.

Figure 3 is a cross-section of the fork of Figure 1 on the line B-B.

Figure 4 is a cross-section of one embodiment of a castor fork according to the invention.

Figure 5 is a part cross-section of a castor fork according to the invention illustrating an alternative form of assembly.

Figure 6 is a cross-section of an embodiment of the invention with two bearing races.

Figure 7 is a part cross-section of an alternative form of the embodiment of Figure 6.

Figure 8 is an enlarged view of part of the castor fork of the invention showing one way of attaching the wheel to the fork.

Figure 9 is an enlarged view showing an alternative way of attaching the wheel to the fork.

In Figure 1 a castor fork 1 supports a wheel 2 between legs 3 on boss 20, connected by bolt 4 or rivet and has an upper portion 5 in which a bearing and its race is retained and to which is attached a support member 6 of an article, e.g. a trolley or wheelchair to which the wheel 2 is to be attached in swivelable manner.

Figure 2 is a cross-section along line A-A of Figure 1 and shows the two leg parts 7 and 8 of the castor fork 1 supporting wheel 2 on boss 20. The two parts 9 and 10 of the head 5 of the fork are clamped around bearing race 11 by means of screws or bolts 12 and 13 in drilled cooperating holes in the two parts.

Figure 3 is a cross-section on line B-B of Figure 1 and again like parts are indicated by like reference numbers.

In Figure 4 a side elevation cross-section is shown illustrating the bearing race 11 which provides a swivel joint with the support member 6.

Figure 5 illustrates an alternative method of assembling the two castor fork parts wherein a sheath or cap 14 is slotted over the two head parts 9 and 10 to hold the bearing race 11 in place in the recess between the two parts.

Figure 6 is a side elevation cross-section view of a castor fork with two bearing races 11A and 11B clamped between the two head parts.

Figure 7 also illustrates an arrangement with two bearing races but shows the alternative method of assembly using a sheath or cap 14 fitted over the head of the castor fork.

In Figure 8 the two leg parts 7 and 8 are joined by axle bolt 4 through the axle of wheel 2. The bolt head 15 and nut 16 are housed in recesses 17 and 18 in the outer surfaces of the leg parts 7 and 8 respectively. They could be covered by a plastic or metal cap to improve the outward appearance of the castor. The wheel bearing race 19 is securely held by the appropriately shaped lateral internal extensions 20 and 21 of the leg parts providing a boss for the wheel and extra strength.

In Figure 9 an embodiment is shown in which the axle bolt 4 is concealed so that the external surfaces of the legs 7 and 8 can be made smooth. Here the bolt 4 is screwed into threading in the left hand leg 7 and a plug 22 is positioned on the right hand side of wheel 2 to hold the bolt head. The right hand castor for leg 8 has an internal recess 23 into which the plug 22 fits snugly, the lateral walls of the recess bearing on the outer walls of the plug. This interference fit connection together with the rigidity of the castor fork parts and the fastening at the top of the fork, provides adequate support and resists damage by impacts or side loads.

Of course many other alternatives are envisaged within the scope of the present invention. For example the two parts might be fastened by a clamping band. Preferably the fastening at the top of the fork is such that the clamping force is in line with or below the line of the bearing or bearings to resist the two parts separating. This is particularly advantageous in the embodiment of Figure 9 where the concealed axle bolt is used. Spindles to support the wheel might be moulded or cast integrally with the castor fork parts to obviate the need for bolt or rivet 4 and the attendant drilling. Any number of recesses or spigots can be moulded or cast into the parts as appropriate to accurately and firmly locate not only the bearing race or races and the wheel but also brake parts as appropriate.

Claims

1. A castor fork comprising two discrete parts, each part having a let portion and a body portion with a recess for receiving a radial bearing race and the two parts being connectable together to retain the radial bearing race in the co- joined recesses.

2. A castor fork as claimed in claim 1, wherein each of the two parts is formed from die cast material.

3. A castor fork as claimed in claim 1, wherein each of the two parts is formed from a plastics material.

4. A castor fork as claimed in claim 3, wherein each of the two parts is formed from a glass-filled plastics material.

5. A castor fork as claimed in any of the preceding claims, wherein the two parts of the fork are clamped together.

6. A castor fork as claimed in any of claims 1 to 4, wherein the two parts of the fork are bolted or screwed together.

7. A castor fork as claimed in any one of the preceding claims comprising a retaining cap located over the body portion of the two parts.

8. A castor fork as claimed in any of the preceding claimed wherein each body portion comprises a plurality of recess for receiving a plurality of radial bearing races.

9. A castor fork as claimed in any of the preceding claims, further comprising a spindle or spindle part integrally formed with one or both of the castor fork parts to support a castor wheel.

10. A castor fork as claimed in claim 9 comprising an axle bolt passing through the spindle and connecting the two parts.

11. A castor fork as claimed in claim 9 comprising an axle bolt which is secured to the spindle integral with one fork part and is at least partly covered by the other fork part, to provide a concealed axle bolt.