GB2215355A

GB2215355A - Spacer wheel for steel cages

Info

Publication number: GB2215355A
Application number: GB8804414A
Authority: GB
Inventors: Michael Carmel Cachia
Original assignee: M C M
Current assignee: M C M
Priority date: 1988-02-25
Filing date: 1988-02-25
Publication date: 1989-09-20
Also published as: GB8804414D0; EP0330519A1

Description

A p SPACER WHEEL FOR STEEL CAGES n The present invention relates to spacer

wheels f or the steel reinforcement cages of concrete piles.

When making a steel reinforced concrete pile, a bore is excavated and f illed with concrete. A steel cage is lowered into the hole, usually after it has been filled with concrete, and it is important f or the cage to be spaced from the walls of the bore.

In order to maintain the spacing between the cage and the bore, it is known to use spacer wheels which can be slipped over the horizontal bars of the cage and act not only as spacers but also as guides for the cage as it is lowered into the bore. The spacer wheels must be capable of being fitted to an assembled cage and a known spacer wheel designed to achieve this aim is illustrated in Figure 1.

The wheel in Figure 1 is a one piece plastics moulding and has an interrupted rim 10 connected by spokes 12 to a discontinuous hub 14. This construction permits the wheel to be slipped onto a bar by pushing the bar into the gap 16 in the rim, the bar being guided into the hub where it is retained by two generally semi-circular prongs 18. The disadvantage of this construction is that though the wheel can easily be slipped onto a cage bar, it is also easily dislodged from the bar and on meeting an obstruction can twist and come away from the cage. If this should occur while the cage is being lowered into the wet concrete, then the problem will not be noticed and the cage can be incorrectly located in the pile thereby considerably reducing its strength.

With a view to mitigating the foregoing disadvantage, the present invention provides a spacer wheel for mounting on a bar of a concrete reinforcement cage, comprising an interrupted rim connected by spokes to a hub, the latter defining a central aperture for receiving a cage bar introduced therein through the gap in the rim of the wheel, wherein the aperture is shaped as a keyhole having a circular portion which, in use, receives the cage bar and serves as a bearing, and a passage leading from the circular portion to the gap in the rim, and wherein the passage is narrower that the diameter of the circular portion and is the only interruption in the circumferential wall of the circular portion.

The spacer wheel of the invention dif fers from that shown in Figure 1, in that the keyhole slot for receiving the cage bar is defined by the hub and not by resilient prongs disposed within the hub. Insertion and release of the cage bar requires deformation of the hub and as the hub is strengthened by the spokes and the rim, it cannot readily be distorted. By contrast, in the prior art illustrated in Figure 1, even though the prongs cannot splay apart without coming into contact with the hub, the can twist out of the plane of the drawing to permit the wheel to come away f rom the cage bar.

It is preferable that webs be formed in between the spokes as this further strengthens the wheel and the hub against deformation. The presence of webs also serves to prevent wet concrete from being trapped between the spokes when the cage is introduced into the bore and in this way reduces the drag on the wheel and the tendency for the wheel to come away from the cage bar. By contrast, the wheel of Figure 1 is hollow in the spaces between the spokes.

Advantageously, the gap in the rim of the wheel is also narrow requiring the cage bar to be forced past the rim. This minimises the f lat spot on the rim created by the 1 i gap, the presence of which flat spot can cause the wheel to slide over the surface of the bore instead of rolling. It will be noted that in the wheel shown in Figure 1, the gap 16 in the rim is greater than the diameter of the bar to be received between the prongs 18.

As the cage is lowered into wet concrete, drag is experienced by the surface of the rim which adds to the forces tending to dislodge the wheel from the cage bar. To reduce this problem, it is preferred than the axial length of the rim should be narrower that the axial length of the hub. In this way, the hub retains sufficient strength to withstand twisting but the rim creates less drag when it is inserted into wet concrete.

Conveniently, the hub is formed of two concentric and interconnected interrupted rings, the inner ring serving to retain the cage bar and the outer ring being connected to the spokes. The rings are preferably interconnected at three point on the circumference of the inner ring spaced from the passage for the introduction of the cage bar. In this way, the force required to position the wheel on a cage bar is significantly greater than the force required to dislodge the wheel.

In order to reduce frictional drag at the bearing surface the inner surface of the inner ring may be provided with radial teeth to contact the surface of the cage bar. Such a construction also accommodates minor variations in the diameter of the cage bar and permit the wheel to be re-sized to fit other diameters of cage bar.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows the construction of a known wheel as has been described previously, and Figure 2 is a similar view of a wheel of the invention.

The wheel shown in Figure 2 has an outer rim 2 0 with a gap 26 narrower that the diameter of a cage bar on which the wheel is to be mounted. The rim 20 is connected by spokes 22 to a two part hub 24 comprising an outer ring 24a and a inner ring 24b. The rim 20 is axially narrower than the hub 24 and the spokes 22 taper being wider near the hub 24 than near the rim 22.

The outer ring has a wide interruption which narrows down gradually into the gap 26 in the rim. The inner ring 24 has a single interruption 24c of narrower width than the cage bar on which the wheel is to be mounted which forms part of an insertion passage defined 20 between two guide lips 27.

The inner ring 24b is connected to the outer ring 24a at three points 24d spaced from the interruption 24c. Webs 30 fill the gaps between adjacent spokes 22.

To mount the wheel on a cage bar, the wheel is position with the gap 26 in line with the bar and it hammered so that the bar first passes through the gap 26, then through the passage 24c into the centre of the inner ring 24b of the hub 24. The inner ring 24b has inwardly extending teeth 32 which grip the cage bar and form a bearing surface allowing the wheel to rotate about the cage bar.

When inserted into the inner ring 24 of the hub 24 the bar is firmly captured and the construction of the wheel ensure that it cannot be dislodged with ease. The inner ring 24b and outer ring 24a are connected at several 2 t> points so that the inner ring cannot be twisted out of the plane of the outer ring 24a and the latter is made rigid by its own depth the spokes 22, the webs 30 and the rim 20. Introduction of the bar into the central bearing is facilitated by the long guide lips which act as levers tending to prise apart the passage 24c. Removal of the wheel through the same passage, on the other hand requires much greater force as there is no lever action assisting in spreading of the passage 24c and on the contrary any f orce tending to move the cage bar towards the passage 24c is opposed by the two teeth which are formed as extensions of the lips 27.

Claims

1. A spacer wheel for mounting on a bar of a concrete reinforcement cage, comprising an interrupted rim connected by spokes to a hub, the latter defining a central aperture for receiving a cage bar introduced therein through the gap in the rim of the wheel, wherein the aperture is shaped as a keyhole having a circular 0. - portion which, in use, receives the cage bar and serves as a bearing, and a passage leading from the circular portion to the gap in the rim, and wherein the passage is narrower that the diameter of the circular portion and is the only interruption in the circumferential wall of the circular portion.

2. A wheel as claimed in claim 1, wherein webs are formed to fill the spaces between the spokes.

3. A wheel as claimed in claim 1 or 2, wherein the gap in the rim of the wheel is narrower that the inner diameter of the circular portion of the aperture in the hub.

4. A wheel as claimed in any preceding claim, wherein the axial length of the rim is narrower than the axial length of the hub.

5. A wheel as claimed in any preceding claim, wherein the hub is formed of two concentric and interconnected interrupted rings, the inner ring serving to retain the cage bar and the outer ring being connected to the spokes.

6. A wheel as claimed in claim 5, wherein the rings are interconnected at three point on the circumference of the inner ring spaced from the passage for the introduction of the cage bar. 1 1 1

7. A wheel as claimed in claim 5 or 6, wherein the inner surface of the inner ring is provided with radial teeth to contact the surface of the cage bar.

8. A spacer wheel for mounting on a bar of a concrete reinforcement cage, constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in Figure 2 of the accompanying drawings.

Published 19B9 atThe Patent Office, State House, 68.11 High Holborn, London WClR 4TP. Further copies maybe obtainedfrom The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87