CA1242554A

CA1242554A - Castors

Info

Publication number: CA1242554A
Application number: CA000465814A
Authority: CA
Inventors: Michael J. James
Original assignee: Global Castors Ltd
Current assignee: Global Castors Ltd
Priority date: 1983-10-26
Filing date: 1984-10-18
Publication date: 1988-10-04
Also published as: IT1179778B; GB8328644D0; FR2554055A1; DE3436422A1; SE8405341L; SE8405341D0; FR2554055B1; DK160752B; GB2148704B; SE459242B; IT8468036A0; AU556478B2; AU3414284A; DE3436422C2; DK488184A; NZ209822A; DK488184D0; IT8468036A1; ZA847990B; GB2148704A

Abstract

A B S T R A C T O F T H E I N V E N T I O N

"CASTORS"

A twin-wheel castor comprises a moulded plastics body 1 and a pair of inset moulded plastics wheels 2. The body 1 has an upwardly open bore 3 to receive a mounting spindle. The wheels 2 are respectively mounted on the ends of a steel spindle 4 which is a tight interference fit in a through bore 5 in the body moulding 1, with an end chamfer 4a on the spindle providing a lead on assembly. A snap-on fixing of the wheels 2 on the ends of the spindle 4, with the wheels 2 free to rotate on the spindle 4, employs interengaging formations moulded in mounting bores 13 of the wheels 2 and formed by a rolling process on the metal spindle 4. Each such formation, both in the wheels 2 and on the spindle 4, comprises a peripheral projection in the form of an annular lip and an adjoining peripheral groove.

Description

2~2554 "CASTORS"

The invention relates to castors, and is in partieular concerned with twin-wheel castors the wheels of which are respectively mounted on the ends of a metal spindle whieh project from the body of the castor.
In some prior constructions of sueh castors the wheels have been secured on the spindle by means of a moulded internal fixing lip in each wheel which engayes a groove in the spindle, but moulding considerations set a limit to the radial dimension of sueh a lip and thus such means of securing are not favoured for heavy duty applieations. Beeause of this limitation high quality eastors have employed additional wheel fixing elements, sueh as spring rings and the like, or seeured the wheels by a riveting operation and in sueh eases the fixing accounts for a material portion of the costs of production. The object of the invention is to provide a castor having eomparable seeurity of wheel fixing without the use of fixing elements or a riveting operation, and thus to simplify the assembly of a heavy-duty twin-wheel eastor with materially redueed produetion eosts.
Aecording to the invention a twin-wheel eastor has plastics wheels moulded with eentral mounting bores and which are a snap-on fit on the respective ends of a metal spindle projeeting from a body of the eastor, eaeh wheel ,~
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mounting bore and the corresponding end of the spindle having two spaced sections of plain cylindrical form providing wheel bearing surfaces and also having interengaging formations disposed between said spaced sections with each such formation, both in said mounting bores and on said spindle, comprising a peripheral projection formed outwardly (or inwardly) of the diameter of said spaced sections and an adjoining peripheral groove formed radially inwardly (or outwardly) of said diameter, with said bearing surfaces in each mounting bore together spanning a ~ajor portion of the length of that bore.
Considering one wheel and the corresponding end of the spindle, the projection is in each case preferably an annular lip, with the spindle lip disposed inwardly with respect to the corresponding end of the spindle. The ends of the wheel bores and the ends of the spindle are preferably chamfered and the leading sides of the lips are preferably inclined to provide a lead as a wheel is pressed on to the spindle, an angle of about 45 on the lips being suitable for this purpose.
The wheels are moulded from a material having an appropriate flexibility and resilience to allow the snap-on fitting, and the interengaging formations of the invention enable a secure fixing equivalent to that at present obtained by the use of separate fixing elements or riveting to be achieved without the need for such elements or a separate fixing operation such as riveting. Furthermorer the formation of the spindle can be produced by a rolling - 2a -operation, with the metal which is displaced from each groove being upset to provide the adjoining projecting lip so that there is no waste of material and the spindle blanks can be of the finished diameter.
During the rolling operation the spindle can be symmetrically formed with two additional and similar groove/projection formations disposed between the wheel-. .~ *

~24X5~4 retaining formations, the projecting lips so formed engaging the castor body to provide axial location of the spindle therein. The spindle is preferably an interference fit in the body, with each wheel being freely rotatable on the spindle.
The invention will now be further described with reference to the accompanying drawings which illustrate, by way of example, a preferred embodiment of the invention.
In the drawings:
Figure 1 is plan view of a twin-wheel castor in accordance with the invention;
Figure 2 is a cross-sectional view on the line II-II
of Figure l;
Figures 3 and 4 are views of details of Figure 2 to a larger scale.
The castor illustrated in the drawings has a plastics moulded body 1 and a pair of inset moulded plastics wheels 2. The body 1 has an upwardly open bore 3 adapted to receive, in conventional manner, a mounting spindle (not shown) by which the castor can be pivotally mounted below a body to be supported, for example an item of furniture.
The wheels 2 are respectively mounted on the ends of a steel spindle or axle 4 which is a tight interference fit in a through bore 5 in a tubular portion 6 of the body moulding 1, with an end chamfer 4a on the spindle providing a lead on assembly. The invention relates to the fixing of the wheels 2 on the ends of the spindle 4, to ~2~Z5~4 this end the two wheels and the spindle being formed with interengaging formations illustrated in detail in Figures 3 and 4. In these two figures the formations concerned are illustrated in respect of the right-hand wheel 2 in Figure 2 and the corresponding end of the spindle 4. The embodiment will be further described with reference to this wheel and spindle end, the fixing of the other wheel being identical.
For retention of the wheel 2 the spindle 4 is rolled to provide an annular peripheral recess 7 with a rectangular section profile towards the end of the spindle.
The metal upset during the rolling operation produces a peripheral projecting annular lip 8 adjoining the groove 7.
This lip 8 has a side face 9 inclined at an angle of 45 to the axis 10 of the spindle 4, which face extends from the cylindrical base 7a of the annular groove 7 to the outer cylindrical face 11 of the annular lip 8.
The wheel 2 has a central boss 12 with a blind cylindrical bore 13 which is a running fit on the spindle diameter and which is open on the inner side of the wheel for mounting on the spindle 4. The wheel 2 is a dished moulding with radial strengthening webs 2a which extend between the boss 12 and a rim 2b. The bore 13 is moulded with a projecting annular lip 14 and an adjoining internal circumferential annular groove 15 which, respectively, engage with the groove 7 and lip 8 on the spindle 4. Such interengagement of the groove/lip formations in the wheel 2 and on the spindle 4 provides snap-on mounting of the wheel 12~Z554 and reliable axial retention thereof, leaving each wheel 2 freely rotatable on the spindle 4. The bore 13 has an end chamfer 16 of 60 which cooperates with the complementary chamfer 4a on the corresponding end of the spindle 4 to provide a lead on assembly, and for the same purpose the internal lip 14 of the wheel has a 45 inclined leading face 17 which matches the inclined leading face 9 on the external lip 8 of the spindle 4.
Spaced some distance in from the described groove/lip formation 7,8 each end of the spindle 4 has an identical groove/lip formation 18,l9. This is produced in the same rolling operation and its primary function is to provide a step 20 at the inner side of the lip 19 which engages the corresponding end of the tubular body portion 6 for axial location of the spindle 4. When the spindle is pressed through the body portion 6 the two lips 8 and 19 pass through with the inclined face 9, and a corresponding face 21 of the lip 19, provi.ding a lead. Once the lip 19 has passed through the body the spindle is retained in both directions by the two lips 19, thus providing snap-in fitting of the spindle 4 with sufficient axial retention to avoid relative spindle/body displacement as the wheels 2 are snap-fitted on to the ends of the spindle 2. This considerably facilitates assembly of the castor, during which the spindle 4 bottoms against central convex projections 22 at the blind ends of the wheel bores 13 to define the assembled position.
Although the annular lips 19 engage the body 1 ~2~255~
~ 6 --for axial location of the spindle 4 during the assembly operation, as has been described, in the assembled castor the wheels 2 engage the body 1 for this purpose. Thus the relative dimensions of the parts are such that the p]anar ends of the wheel bosses 12 normally run against the adjacent planar ends of the hollow body portion 6. The central portion of the spindle 4 between the lips 19 is lightly knurled to assist driving of the spindle 4 during rolling thereof, and this knurling also increases the frictional grip of the spindle 4 within the body bore 5.
The interengagement of adjoining lip and groove formations on the spindle and in the wheels not only ensures positive and reliable fixing of the wheels on the spindle, providing a double lip/groove retention for each wheel, with easy snap-on assembly and prior separate fixing elements or a fixing operation such as riveting not being required, but the components are easily manufactured. The spindle, as already mentioned, is formed in a single rolling operation without any metal waste, and the groove/lip formation in each wheel is produced in a simple moulding operation with only a single "jumping" operation in which the wheel is "jumped" off the moulding core. That is, the core simultaneously jumps the lip 14 and the groove 15 and as will be appreciated by those skilled in the moulding art this enables greater radial jumps to be employed than would be the case if separate sequential jumping was involved.
Furthermore, the basic castor construction _ 7 _ lZ4Z55~

comprises only four components - a body, a spindle and two identical wheels. This is a marked advantage as compared with conventional twin-wheel castors with comparable security of wheel fixing.
As can clearly be seen from the drawings, the wheel-retaining groove/lip formations 7,8 on the spindle 4 and 14,15 in the wheel bores 13 are, in each case, disposed between two spaced sections of the spindle and bore, respectively, of plain cylindrical form. These sections provide the wheel bearing surfaces and, for each wheel 2, span a major portion of the length of the corresponding wheel bore 13.

., ~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A twin-wheel castor having plastics wheels moulded with central mounting bores and which are a snap-on fit on the respective ends of a metal spindle projecting from a body of the castor, each wheel mounting bore and the corresponding end of the spindle having two spaced sections of plain cylindrical form providing wheel bearing surfaces and also having interengaging formations disposed between said spaced sections with each such formation, both in said mounting bores and on said spindle, comprising a peripheral projection formed outwardly, or inwardly, of the diameter of said spaced sections and an adjoining peripheral groove formed radially inwardly, or outwardly, of said diameter, with said bearing surfaces in each mounting bore together spanning a major portion of the length of that bore.

2. A twin-wheel castor according to claim 1, wherein the peripheral projection, considering one of said wheels and the corresponding end of the spindle, is in each case an annular lip, with the lip on the spindle disposed on the inner side of the adjoining groove with respect to the corresponding end of the spindle.

3. A twin-wheel castor according to claim 1, wherein the ends of the wheel mounting bores facing the castor body and the ends of the spindle are chamfered to provide a lead as each wheel is pressed on to the spindle.

4. A twin-wheel castor according to claim 1, 2 or 3, wherein the leading sides of the peripheral projections are inclined to provide a lead as each wheel is pressed on to the spindle.

5. A twin-wheel castor according to claim 2, wherein each said annular lip has a leading side inclined at an angle of about 45° to the longitudinal axis of the spindle and mounting bores, to provide a lead as each wheel is fitted on to the spindle.

6. A twin-wheel castor according to claim 1, 2 or 3, wherein said interengaging formations of the spindle are the result of a rolling operation performed on a spindle blank of the finished diameter of said spaced sections of the spindle, with the metal displaced from each groove of said formations during the rolling operation having been upset to provide the adjoining peripheral projection without any wastage of material.

7. A twin-wheel castor according to claim 1, 2 or 3, wherein said interengaging formations of the spindle are the result of a rolling operation performed on a spindle blank of the finished diameter, with the metal displaced from each groove of said formations during the rolling operation having been upset to provide the adjoining peripheral projection without any wastage of material, and the spindle is symmetrically formed by said rolling operation with two additional and generally similar groove/projection formations disposed between said wheel-retaining formations of the spindle, the additional projections so formed engaging the castor body to provide axial location of the spindle therein.

8. A twin-wheel castor according to claim 1, 2 or 3, wherein said spindle is an interference fit in a bore in the body of the castor, with each said wheel being freely rotatable on the spindle.

9. A twin-wheel castor according to claim 1, 2 or 3, wherein said spindle is an interference fit in a bore in the body of the castor, with each said wheel being freely rotatable on the spindle, and the spindle has a knurled central section to facilitate handling of the spindle and to increase the frictional grip of the latter within said bore in the body of the castor.

10. A twin-wheel castor according to claim 1, 2 or 3, wherein the ends of the wheel mounting bores facing the castor body and the ends of the spindle are chamfered to provide a lead as each wheel is fitted on to the spindle, said interengaging formations of the spindle being the result of a rolling operation performed on a spindle blank of the finished diameter, with the metal displaced from each groove of said formations during the rolling operation having been upset to provide the adjoining peripheral projection without any wastage of material, and the spindle being symmetrically formed by said rolling operation with two additional and generally similar groove/projection formations disposed between said wheel-retaining formations of the spindle, with the additional projections so formed engaging the castor body to provide axial location of the spindle therein and each of said additional projections being accommodated within the end chamfer of the mounting bore of the adjacent wheel.

11. A twin-wheel castor according to claim 2, wherein the ends of the wheel mounting bores facing the castor body and the ends of the spindle are chamfered to provide a lead as each wheel is pressed on to the spindle.