It is well known to fusion join polymers from the same chemical family using methods such as hot gas welding, butt fusion welding and resistive or inductive electrofusion. These methods are suitable for joining two pipes, for example, of identical materials (e. g. high density polyethylene) or for joining physically dissimilar (but chemically substantially identical) materials such as random polypropylene and homopolymer polypropylene.

It is desirable to be able to join chemically dissimilar materials to provide a number of advantages. To date, this can only be done with the use of"compatibilisers" which are polymeric structures which act as an intermediate layer in the joining of the chemically dissimilar materials. The use of compatibilisers entails extra expense and the long-term performance of the joint is not clear.

The Applicant is not, however, aware of any known method by which chemically dissimilar materials may be effectively joined, without the use of compatibilisers, to withstand long-term loading as is required in underground thermoplastic pressure pipes.

It is thus an object of the present invention to provide apparatus and a method for joining chemically dissimilar

materials which seeks to overcome the above-mentioned disadvantages.

According to a first aspect of the invention there is provided a fitting for use in the joining of two or more chemically dissimilar materials comprising: * a body which, in use, substantially encloses the region to be joined; and * one or more fusion zones located, in use, adjacent the region to be joined, the fusion zone (s) comprising alternating sections of each of said chemically dissimilar materials.

Preferably, each of said alternating sections comprises a helically-wound wire coated in one of said chemically dissimilar materials. Alternatively, the or each fusion zone may comprise an induction heater cage over which said alternating sections are moulded.

Each of said alternating sections can be of substantially square, rectangular or circular cross-section.

Said fitting may be integrally-formed in the end of a pipe comprising one of said chemically dissimilar materials to be joined.

Also, the or each fusion zone may comprise alternating sections of three chemically dissimilar materials.

Preferably, said body comprises one of said chemically dissimilar materials.

In a preferred form, one of said chemically dissimilar

materials comprises a blend of two chemically dissimilar materials.

It will be appreciated that the invention includes within its scope a fitting for use in the joining of two or more chemically dissimilar materials substantially as described herein with reference to and as illustrated by Figure 1.

According to a second aspect of the invention there is provided a method for joining two or more chemically dissimilar materials comprising the steps of: *providing a fitting having a heating element and one or more fusion zones comprising alternating sections of each of said chemically dissimilar materials; * substantially enclosing the region to be joined with the fitting; and * effecting electrofusion of the fitting with the materials to be joined.

Preferably, the method further comprises the steps of: providing the same number of wires as there are dissimilar materials to join; * coating each wire with one of said dissimilar materials; * helically winding said wires around a mandrel; and * overmoulding the wires with another one of said dissimilar materials to provide said fitting.

Alternatively, the method further comprises the steps of: *providing the same number of wires as there are dissimilar materials to join;

* helically winding said wires around a mandrel; * moulding a first set of sections of one of said dissimilar materials around one of said wires; and overmoulding the wires with another one of said dissimilar materials to provide the alternating sections around another one of said wires and the body of said fitting.

Alternatively, the method further comprises the steps of: * moulding a first set of sections of one of said dissimilar materials; * overmoulding the fitting with another one of said dissimilar materials to provide alternating sections around the body of said fitting; * providing the same number of helically-wound wires as there are dissimilar materials to join; and * ploughing in the helically-wound wires into the alternating sections.

In a further preferred form, the method further comprises the steps of: * providing a number of metal rings or a metal cage ("the inductive element"); * coating alternate sections of said inductive element with one of said dissimilar materials; * slipping said inductive element around a mandrel ; and * overmoulding said inductive element with another one of said dissimilar materials to provide said fitting.

Alternatively, the method further comprises the steps of:

* providing a number of metal rings or a metal cage ("the inductive element"); * slipping said inductive element around a mandrel; * moulding a first set of sections of one of said dissimilar materials around said inductive element; and overmoulding said inductive element with another one of said dissimilar materials to provide the alternating sections and the body of said fitting.

Alternatively, the method further comprises the steps of: moulding a first set of sections of one of said dissimilar materials; * overmoulding the fitting with another one of said dissimilar materials to provide alternating sections around the body of said fitting; * providing a number of metal rings or a metal cage ("the inductive element"); * ploughing in the inductive element into the alternating sections.

It will be appreciated that the invention includes within its scope a method for joining two or more chemically dissimilar materials substantially as described herein with reference to and as illustrated by Figure 1.

Preferred embodiments of the invention will now be more particularly described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a schematic cross-sectional view of two chemically dissimilar pipes which are to be joined by the apparatus and method of the present invention.

Referring to Figure 1, an example will now be described in which it is intended to join a PP pipe 1 to a PE pipe 2.

A fitting 3 is located as shown in Figure 1 so as to enclose the region of the pipes 1,2 which are to be joined. The fitting 3 comprises a PE body 4 of substantially circular outer wall cross-section, for example, which has fusion zones 5,6 located adjacent the outermost surfaces of the pipes 1,2.

The fusion zones comprise alternating sections 7,8 which are each made up of a helically-wound wire 9 coated in either PE or PP, arranged so that the different material sections alternate as shown. It is of note that the materials selected for the alternating sections are the same as those of the chemically dissimilar pipes which are to be joined. The body 4 also comprises one of these materials (in this example, PE).

It is envisaged that one of the for the materials alternating sections 7,8 could actually be formed from a blend of two thermoplastics polymers, for example polyethylene blended with polypropylene. In this instance, one of the helically-wound wires 9 could be coated in the blend of thermoplastics polymers to improve the fusion of the wires to the body, when fusion takes place.

In a further alternative embodiment, one of the materials for the alternating sections 7,8 could comprise a thermoplastics polymer (for example) blended with nylon.

This would have the advantage of the nylon acting as a barrier to the ingress of fluids into the joined pipes.

Furthermore, if the material of a helically-wound wire 9 also includes nylon, the wire itself can bond to the nylon in the nylon/thermoplastics polymer blend.

At either end of each fusion zone 5,6 are provided cold zones 10 where there are no alternating sections. These zones are necessary to contain the expanding fusible material, in use, so as to maintain radial pressure on the pipes to be joined.

The fitting 3 can be produced by, firstly, coating one wire with PP and another with PE (i. e. coating the same number of wires as there are dissimilar materials to join -in this case two). Then, the wires are helically wound together around a mandrel.

The two wires are then overmoulded with PE to provide a substantially PE fitting having fusion zones 5,6 comprising alternating sections of PE and PP.

Alternatively, the fitting can be produced by using the "two-colour"moulding process to form the alternating sections of PP and PE around a single wire coil or indeed an induction heater cage. In this method, the wire is wound in its bare state around, or the cage is slipped over, the mandrel and a first mould enables moulding of the first sections of, for example, PP. Then a second mould is employed to overmould the second sections, as well as the body of the fitting, in the other material for example PE.

In a further alternative method, the fitting can be produced using the so-called"ploughing-in"technique.

In this method, the two-colour moulding process is employed to form the alternating sections of PP and PE in the absence of a wire coil or induction heater cage. The wire coil or induction heater cage is then pushed or "ploughed"into the alternating sections of plastics material.

When the fitting 3 is located as shown in Figure 1 so as to enclose the region to be joined of each pipe 1,2, the electrofusion process can begin. During this process, the fusion zones 5,6 are heated by passing an electric current down the wires or by inductively energising the cage, causing the materials to melt and expand. Fusion occurs between the PP pipe 1 and the PP sections 7 of the fitting and also between the PE pipe 2 and the PE sections 8 of the fitting. The wires or cage are also bonded to the body of the fitting. Weak bonds may also occur between the PP pipe 1 and the PE sections 8 (and vice versa). In any event, a castellated interference joint is formed between the fitting and the dissimilar material pipe which is axially very strong.

An O-ring seal could additionally be provided in one or both more cold zones 10 if there was any doubt as to the integrity of the fluid seal between the dissimilar components.

The above-described apparatus and method is suitable for the joining of numerous different polymeric materials, for example PP, PE, polybutylene, polyoxymethylene

(acetyl), ABS, polyketones and nylons.

It is envisaged that a fitting having fusion zones comprising more than two alternating materials may be provided. A fitting having alternating sections of three chemically dissimilar materials may be used to join sections of pipe comprising any of the three materials.

Such a fitting will also reduce the number of fittings containing different materials which need to be manufactured to enable joining of commonly-desired combinations of pipes.

A further application of the present invention is the possibility of joining pipes of chemically similar material with a fitting of a chemically dissimilar material. This enables the joining of, for example, two pipes with a fitting of material having different properties (e. g. higher strength). For example two cross-linked PE pipes could be joined with a fitting made from polysulphone (a material having higher temperature resistance and better strength than the ordinary pipe material (PE)).

It will thus be appreciated that the present invention is not limited to the joining of chemically-dissimilar pipes: it may be applied more generally for the joining of chemically-dissimilar materials, for example as described above.

The joining of chemically dissimilar materials using the above-described invention has numerous advantages, for example:

1. Underground pipes need not be of the same material throughout their length, i. e. sections of different material may be inserted where it is desired to have certain properties such as high impact resistance, high stiffness or high temperature resistance. In this way sections of the pipeline can be tailored to the particular environment in which they are located. For example, as PP is inherently stronger than PE, it would be possible to insert a PP section in a PE pipe over an unsupported area such as a bridge. Alternatively, a plastic flange, which is required to have good stiffness, strength and toughness (but is made of more costly material) can be joined to pipe made from lower cost material.

2. The apparatus and method of the invention could be used to join sheets (rather than pipes) of chemically dissimilar material so that the technology could be applied to the car industry, for example. A vehicle bumper could be moulded in two halves of dissimilar material and then fusion welded together to provide a bumper with an aesthetically-pleasing top half and an impact resistant lower half, for example.

3. The apparatus and method of the invention could be used to provide power tools, for example, with an easily grippable handle material which does not peel off (as is the tendency with known rubber coated handles).

4. The technology is of particular use to enable the insertion of sections of pipe having particular desired characteristics. For example, where a pipe leads from a compressor exit (where the gas temperature is very low),

conventionally a section of metal pipe is used closest to the compressor, until the gas warms up. Using the present invention, the metal section could be replaced by a relatively much cheaper polymeric section having resistance to low temperature.