GB2187946A - Castor assemblies - Google Patents

Abstract

A castor assembly of the kind incorporating a castor wheel and a main brake for the castor wheel, in which an additional braking member (80; 100; 123, 124) is provided to retard rotation of the castor wheel and thus help to prevent uncontrollable movement of a structure supported by the castor assembly when the main brake is released. <IMAGE>

Description

SPECIFICATION Castor assemblies This invention relates to castor assemblies.

In certain applications of such assemblies, for example for use on structures such as movable scaffolding towers or trolleys which may be required to be moved manually from one position to another on a floor having a slight gradient it has been found that there is a tendency for the structure to run away when the normal brakes are released from the castor wheels. This can be dangerous since the operator may lose control of the situation.

The normal types of brake which may be provided on a castor assembly are designed to lock the wheel against rotation, and may also move the wheel, which may be rotatably supported by a housing such as a fork carried by a swivel mounting, into a position where its axis lies substantially centrally below the swivel mounting, thus immobilising the structure which it supports. Such brakes are not usually suitable for controlling a moving structure since they require the operator to locate their operating mechanism (which may be a small lever) with his foot, which may be difficult, and the- locking of one castor wheel adjacent his foot may not be effective to prevent the structure swinging about the locked wheel.

According to the invention, a castor assembly comprises a housing and a castor wheel rotatably mounted relative thereto, a braking member being provided on the housing and spring-loaded into engagement with the castor wheel or a member rotatable therewith so as to tend to retard rotation of the castor wheel without being capable of locking the wheel.

The braking torque produced by the braking member on the castor wheel is arranged to provide sufficient retardation to prevent the supported structure from accelerating uncontrollably when being moved on surfaces having the greatest gradient likely to be encountered in normal operation, whilst being insufficient seriously to impede such manual movement of the structure as may be required from time to time.

The braking member may be arranged to engage the outer peripheral surface of the castor wheel or a tyre mounted on the wheel, or it may engage one or both sides of the wheel or tyre. Examples of suitable braking members comprises a spring steel member fastened to the housing so as to tend to move a part of the spring steel member radially inwardly to engage a wheel outer surface or tyre tread, or a generally U-shaped spring steel member may be fixed to the housing so as to straddle the wheel and bear on the sides of the wheel or tyre. In the latter example, the free ends of the steel member may be bent back to engage the inner sides of the housing fork limbs, or side members of a wheel carrier mounted between the fork limbs, so as to intensify the pressure exerted on the wheel or tyre.

In a third example a frictional torque may be generated by the insertion of a spring washer, e.g. a "wavy" washer, between each of the inner sides of the housing fork limbs and the side of the wheel hub, or between the wheel hub and a side member of a wheel carrier mounted between the fork limbs. In this third example the spring washers are arranged to be subjected to an axial compression when assembled on to an axle to achieve the required torque.

Three embodiments of the invention will now be described, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a castor assembly in accordance with the invention, with the wheel in the running position: Figure 2 is an end view of the cast or assembly shown in Fig. 1; Figure 3 is a view corresponding to Fig. 1 showing an alternative embodiment of the invention; Figure 4 is an end view of the castor assembly shown in Fig. 3; Figure 5 is an end view of a castor assembly showing a further alternative embodiment of the invention; Figure 6 us a detail view of a spring washer, and Figure 7 is a side view of the washer shown in Fig. 6.

The castor assembly 10 illustrated in Figs. 1 and 2 comprises a housing 11 having a swivel mounting 12 by which it is rotatably secured to a cylindrical steel plug 13 of suitable diameter to enter and be fixed in the lower end of, for example, a scaffolding tube forming part of a movable tower. Alternatively, socket or top plate types of mounting could by employed to suit the operational requirement.

The swivel mounting 12, which is generally conventional in its construction, enables the housing 11 to rotate freely about a vertical axis. The housing 11, which is originally produced from a flat plate by a series of pressing operations, extends downwardly to provide side plates 16, 17, to which a wheel carrier 20 is secured by means of a horizontal pivot constituted by a pair of shouldered rivets 21, 22, fastened to the side plates 16, 17 respectively.

The wheel carrier 20 comprises a pair of side members 25, 26 which are sheet-metal pressings pivotally mounted in parallel relationship on the rivets 21, 22 to enable the wheel carrier to be tilted about a horizontai pivot axis defined by the rivets. The ends of the side members 25, 26 are secured together, respectively, by nut and bolt assemblies 30, 31 which incorporate spacer sleeves 33 (shown partly broken-away in Fig. 2) to unite the side members in a rigid structure having a pair of arms 35, 36 and providing aligned holes through which a bolt 40 is passed to provide an axle for a castor wheel 41. The axle and castor wheel are generally conventional, the bolt being secured by a nut 42 which, via washers 45, 46 compresses the side members 25, 26 against the ends of a spacer tube 48.Bearing bushes (not shown) of a low-friction plastics material are rotatable on the spacer tube 48 and support the castor wheel 41 which is of conventional cast metal incorporating a rubber tyre 50.

The side plates 16, 17 of the housing 11 are cranked inwardly, as seen in Fig. 2, so that their lower portions extend closely adjacent the wheel, and as shown in Fig. 1, the lower surfaces 55, 56 of the side plates are designed to abut the washers 45, 46, respectively to provide direct transmission of the load on the housing to the wheel axle in the running position of the wheel as shown in Fig.

1, thus relieving the wheel carrier from this load.

The side plates 16, 17 also incorporate cutaway portions 60 which enable the wheel carrier 20 to be moved from the running position shown in Figs. 1 and 2 to a locked position by depression of the arm 36, causing the wheel carrier to move about its pivot until the wheel axis lies vertically below the swivel, with the wheel axis intersecting the swivel axis. In this locked position, the upper region of the tyre comes into contact with an abutment (not shown) provided by a star-rivetted end of the plug 13.In this locked positon the wheel has no tendency to turn about the swivel axis when sideways forces are exerted on the supported structure and since the washers 55, 56 are clear of the side plates of the housing the full load of the structure is imposed directly on the upper region of the castor wheel by its direct engagement with the plug 13, thus braking the wheel and at the same time relieving the wheel axle of the vertical load which, particularly in its use on scaffolding towers, may be very substantially greater when the tower is in use with the castor in the locked position.

The arms 35 and 36 of the wheel carrier 20 are stiffened by forming them with pressed-in grooves 70, 71 and in order to provide additional stability to the carrier in the running or trailing position shown in Fig. 1, dimples 72 are formed in the metal of the side plates 16, 17 of the housing 11. The dimples 72 and corresponding grooves 71 are arranged to be sprung into interfitting relationship in the trail poisition of the wheel carrier, providing retention against inadvertent displacement of the carrier.

Second pairs of interengageable formations, to provide retention of the wheel carrier against inadvertent displacement from the locked postion, comprises second dimples 73, formed one in each side plate 16, 17 and engageable with the lower edges 74 of the adjacent side members 25, 26 forming the arm 35. The pairs of formations 73, 74 are arranged to be sprung into interengaging relationship as the arm 35 moves upwardly past the second dimples 73 into the locked position.

By the arrangement described above, in order to move the wheel carrier from a running position to a locked position, or vice versa the operator needs to apply downward foot pressure to the appropriate arm 36 or 35.

In accordance with the present invention, means is provided for applying a retarding torque to the castor wheel when in the running position as shown in Fig. 1. This comprises, in the arrangement shown in Figs. 1 and 2, a braking member 80 formed from spring steel bent to a suitable shape so as to provide a shoe portion 81 for engagement with the tyre 50 of the castor wheel, and a bracket portion 82 of complementary shape to that of the housing 11, the bracket portion 82 being secured to the housing 11 by a rivet 85. A flange 86 of the bracket portion 82 fits against the adjacent edge of the housing to prevent rotation of the braking member 80 and a rounded flange 87 is provided on the shoe portion 81 to ensure smooth engagement with the tyre of the castor wheel.

The braking member 80 is arranged to provide sufficient retardation to ensure stability of the supported structure on the usual gradients which may be encountered in service, but is designed so that the full braking torque which it exerts is insufficient to cause undue difficulty in moving the structure.

The castor wheel assembly shown in Figs.

3 and 4 is generally similar to that shown in Figs. 1 and 2, and will therefore not be described in detail. In the arrangement shown in Figs. 3 and 4, however, a braking member 100 replaces the member 80, and is of generally "U" shaped form in which the base 101 of the "U" shape is secured by rivets 102, 103 to the upper part of the housing 11 The "U" shaped spring steel member 100 comprises a pair of parallel chordally-extending shoe portions 105, 106 which straddle the castor wheel 41 and engage the sides of the wheel 41 and tyre 50 to provide a braking action. The free ends 108, 109 of the shoes 105, 106 are bent back to engage abutment faces 111, 112 forming part of the side members 25, 26 of the wheel carrier, the effect of this arrangement being to intensify pressure exerted on the wheel and tyre.

In an alternative arrangement as applied to a castor assembly which does not have a pivotted wheel carrier, the braking member shown in Figs. 3 and 4 may be arranged to abut the inner surfaces of the housing fork limbs to intensify the axial pressure exerted on the wheel assembly.

Fig. 5 shows a further alternative embodi ment of the invention in which frictional torque may be exerted on end faces 120, 121 of the hub 122 of the castor wheel 41 by the insertion of spring ("wavy") washers 123, 124.

The washers 123, 124, illustrated in plan and side elevations respectively in Figs. 6 and 7, are arranged to be clamped under axial compression between the side members 25, 26 and the hub portion of the wheel, the lengths of the. hub portion 122 and the spacer tube 48 being selected to provide the required compression.

In the arrangement shown in Figs. 1 to 4, the retarding torque offered by the braking members 80, 100 may be operative only in the running position, although by suitable design they could be effective also in the locked position. The arrangements shown in Figs. 5 to 7 provide a permanent retarding torque whatever the position of the castor wheel assembly.

Claims (8)

1. A castor assembly comprising a housing and a castor wheel rotatably mounted relative thereto, a braking member being provided on the housing and spring-loaded into engagement with the castor wheel or a member rotatable therewith so as to tend to retard rotation of the castor wheel without being capable of locking the wheel.

2. A castor assembly according to Claim 1 wherein the braking member comprises a spring member mounted on the housing and having a shoe portion engageable with the tyre or outer periphery of the castor wheel.

3. A castor assembly according to Claim 1 wherein the braking member comprises a generally "U" shaped spring member fixed to the housing so as to straddle the wheel and bear on the sides of the wheel or tyre.

4. A castor assembly according to Claim 3 wherein the free ends of the spring member are bent back to engage the inner sides of the housing fork limbs or side members of a wheel carrier mounted between the fork limbs so as to intensify the pressure exerted by the spring member on the wheel or tyre.

5. A castor assembly according to Claim 1 wherein at least one spring washer is inserted between the inner side of a housing fork limb and a side of a wheel hub or between a wheel hub and a side member of a wheel carrier, the spring washer being arranged to be subjected to an axial compression to provide a frictional torque.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claim 1 above has been textually amended.

New or textually amended claims have been filed as follows:

1. A castor assembly comprising a housing and a castor wheel rotatably mounted relative thereto, a main brake for the castor wheel, and an additional braking member being provided on the housing and spring-loaded into engagement with the castor wheel or a member rotatable therewith so as to tend to retard rotation of the castor wheel without being capable of locking the wheel.

6. A castor assembly constructed and arranged substantially as described in the Description and illustrated in Figs. 1 and 2 of the accompanying Drawings.

7. A castor assembly constructed and arranged substantially as described in the Description and illustrated in Figs. 3 and 4 of the accompanying Drawings.

8. A castor assembly constructed and arranged substantially as described in the Description and illustrated in Figs. 5-7 of the accompanying Drawings.