GB2300682A

GB2300682A - A gripping device

Info

Publication number: GB2300682A
Application number: GB9604823A
Authority: GB
Inventors: Michael Taylor
Original assignee: Polypipe PLC
Current assignee: Polypipe PLC
Priority date: 1995-03-10
Filing date: 1996-03-07
Publication date: 1996-11-13
Anticipated expiration: 2016-03-07
Also published as: GB9504884D0; GB2300682B; GB9604823D0

Abstract

The gripping device 1, for use in a pipe coupling, comprises a plurality of teeth 2 disposed to grip a member, in use, at least one tooth 2 being provided with strengthening means 4 to prevent deformation of the tooth 2 under pressure. The strengthening means 4 comprises flanges 8 on either side of each tooth which is otherwise of planar form.

Description

A GRIPPING DEVICE The present invention relates to a gripping device, a pipe coupling including such a gripping device, and a plumbing system also including such a gripping device.

In particular, the invention relates to, but is not limited to, gripping devices used in retaining pipes in place in joints and couplings.

Toothed retaining rings also referred to as grab rings, are widely used as a means of fastening a rod or rivet in a hole or a wheel on a shaft. The rod or rivet can be of a variety of materials. Similar types of retaining rings are used in a number of pipe joints to retain a pipe against the internal pressure.

The general construction of such a fastener includes a ring of inwardly projecting inclined teeth flexibly and resiliently hinged to the supporting skirt. When deflected, the teeth have a tendency to return to their former positions.

The diameter of the circle formed by the free ends of the teeth is less than the diameter of the rod which it is designed to fit. When the rod or pipe is inserted through the ring, the teeth are deflected at their free ends and forced to hinge at the fixed end by bending the material at the tooth root. The free ends of the teeth maintain a contact force on the rod or pipe which is a function of rod diameter, ring diameter, tooth length and ring material.

If an attempt is made to withdraw the rod or pipe, the teeth tend to dig into the rod and resist the force tending to pull it out.

Under these conditions the rod/pipe end load is transferred to the retaining ring skirt via the retaining ring teeth, which behave as struts in axial compression.

If the end load is increased sufficiently, one or more of these struts may fail by buckling, though this is not the only possible failure mode. Furthermore, the toothed ring is commonly manufactured from thin sheet material and the resulting teeth have a low resistance to failure by buckling in compression.

A further problem with existing retaining rings is seen when a grab ring of this kind is used on a pipe or rod made of a complaint material (such as a plastic pipe) to that seen when the pipe is of a rigid material such as copper.

On a rigid pipe the grab ring raises a burr when a force is applied to withdraw the pipe. The pipe material is sufficiently hard to resist penetration of the pipe wall by the wall by the teeth of the ring. This burr is sufficiently strong to resist the sliding action of the teeth along the pipe surface as the force is increased to the point where the grab ring fails by one of a number of failure modes, as described above.

On a plastic pipe with properties similar to those of polybutylene and at ambient temperature (i.e. 20 degrees centigrade) the teeth raise a burr on the pipe and as the pullout force is increased the teeth begin to penetrate the pipe wall. As the force is increased further the teeth are forced to hinge at the tooth root and the subsequent rotation causes the teeth to penetrate the pipe wall even further.

This eventually weakens the pipe wall and the end of the pipe is effectively cut off by the action of the grab ring.

The best performance for a toothed grab ring is effected when the ring can be made to embed at a moderate load to gain a good hold on the pipe but, as the load is increased further, the tendency to cut into the pipe is reduced. Hence the failure by cutting off of the pipe end is delayed or averted. This is particularly important when using plastic pipe at elevated temperatures when the physical properties of the plastic material are much reduced and the pipe end can be much more easily severed.

It is an object of the invention to seek to mitigate disadvantages such as this.

Thus according to the present invention there is provided a gripping device, comprising a plurality of teeth disposed to grip a member, in use, at least one tooth being provided with strengthening means to prevent deformation of the tooth under pressure.

It is preferred that the strengthening means is adapted to strengthen a substantially central portion of the tooth, and it is further preferred that the strengthening means comprises an integral part or parts of the tooth.

The strengthening means may comprise a flange extending from an edge of the tooth, and the flange preferably extends from a longitudinal edge of the tooth.

It is further preferred that the flange extends substantially the entire length of a longitudinal edge of the tooth. The tooth may comprise at least two flanges, whereby the tooth is of substantially channel configuration.

When a pipe is first inserted into the device the tooth ends have a very small contact area. The contact pressure is therefore high and the tooth immediately raises a burr and begins to embed. As the tooth is pushed further into the pipe wall by the increasing load, the area in contact is increased as the channel section flanges are progressively pushed into the pipe wall. Since the area of the tooth end in contact has been increased, the effort required to cause further penetration is also increased and this continues until the whole of the tooth end is embedded.

It is preferred that the tooth comprises a substantially planar part, and that the strengthening means projects out of the plane of the planar part. Preferably, the strengthening means projects at substantially 90" to the planar part.

According to a second aspect of the invention there is provided a pipe coupling including a gripping device as defined hereinabove.

According to a third aspect of the invention there is provided a plumbing system including a gripping device as described hereinabove.

The invention will further be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a plan view of a gripping device embodying the invention; Figure 2 is a sectional view through the gripping device of Figure 1; Figure 3is an enlarged view of a tooth of the gripping device of Figures 1 and 2; and Figures 4a to 4d are a series of schematic views of a gripping device embodying the invention, in use.

Referring to the drawings, there is illustrated a gripping device 1 comprising a plurality of teeth 2 disposed to grip a member 3, in use, at least one tooth 2 being provided with strengthening means 4 to prevent deformation of the tooth 2 under pressure.

Referring in particular to Figures 1 and 2, the gripping device 1 consists of a ring, or washer, the inner circumference of which is provided with a series of teeth 2 projecting inwardly from it. In the illustrated embodiment, the teeth 2 are formed as an integral part of the ring by any suitable means. The root 5 of each tooth is broader than the tip 6 which is a strengthening feature. Although the gripping device 1 illustrated has eleven teeth, the number of teeth 2 can be varied as required.

Referring particularly to Figure 3, each tooth has a substantially planar body part 7 from which two flanges 8 project at substantially 90". These flanges 8 are preferably folded from the material of the tooth to form a channel section. Each tooth 2 may be provided with strengthening means or alternatively, one or more tooth 2 may be so provided. In the illustrated embodirnent, the flanges 8 are shown extending along each longitudinal edge 9 of each tooth 2. It will be appreciated that the dimensions of the flanges 8 may be varied, although flanges 8 extending substantially the length of the longitudinal edges 9 provide the greatest strengthening effect.

In use, a gripping device 1 as illustrated is employed in, for example, a pipe coupling, in which it is inserted prior to assembly of the coupling. The inner diameter of the ring is selected to be less than the diameter of the pipe 3 (Fig.

4a) so that upon insertion of the pipe 3, the teeth are bent away from the direction of insertion by the pipe surface, but remain in contact with it (Fig. 4b).

The teeth 2 bend at, or about their roots 5. If the pipe 3 is pulled in the opposite direction under moderate force, the teeth 2 bite into the surface of the pipe 3 (Fig. lc). As will be appreciated, in this situation, the teeth 2 are subjected to a considerable pressure, and in the current invention the resistance of the teeth 2 to buckling is increased by the folded longitudinal edges. This essentially forms a channel section and increases the bending stiffness at least at the mid point of the tooth where it is most needed.

As can be seen from Fig. 4d, under a high force in the outward direction the tooth 2 is pushed further into the pipe wall, the area in contact is increased as the flanges 8 are progressively pushed into the pipe wall. Since the area of the tooth end in contact has been increased, the effort required to cause further penetration is also increased, substantially preventing the severing of the pipe end.

Thus, it can be seen that the teeth 2 of the device illustrated and described hereinabove have an increased resistance to failure by buckling in compression, due to the provision of the strengthening means, which is effective and relatively simple to manufacture.

Claims

1. A gripping device, comprising a plurality of teeth disposed to grip a member, in use, at least one tooth being provided with strengthening means to prevent deformation of the tooth under pressure.

2. A gripping device according to claim 1, wherein the strengthening means is adapted to strengthen a substantially central portion of the tooth.

3. A gripping device according to claim 1 or claim 2, the strengthening means comprising a flange extending from an edge of the tooth.

4. A gripping device according to claim 3, the flange extending from a longitudinal edge of the tooth.

5. A gripping device according to claim 4, the flange extending substantially the entire length of a longitudinal edge of the tooth.

6. A gripping device according to any of claims 3 to 6, comprising at least two flanges whereby the tooth is of substantially channel configuration.

A A gripping device according to any preceding claim, the strengthening means comprising an integral part or parts of the tooth.

8. A gripping device according to any preceding claim, the tooth comprising a substantially planar part.

9. A gripping device according to claim 8, the strengthening means projecting out of the plane of the planar part.

10. A gripping device according to claim 9, the strengthening means projecting at substantially 90C to the planar part.

11. A gripping device substantially as hereinbefore described with reference to the accompanying drawings.

12. A pipe coupling including a gripping device as claimed in any of claims 1 to 11.

13. A plumbing system including a gripping device as claimed in any of clairns 1 to 11.