This invention relates to the joining of hollow elongate members, and more particularly to a novel coupling element and method for joining of hollow elongate members by heat fusion.

Hollow elongate members such as plastic pipes and conduits frequently require to be joined to other components in a system, for example to extend the length of a pipe, to form a branch connection, or to connect to a fitting such as a tee, a bend or a diameter reducer. A popular method of connection is by electrofusion in which the pipe or conduit is fused or "welded" to another component by the action of an electrical heating element which may be a resistance or an induction heating element. Plastic pipes and conduits can, for example, be joined to another component using an electrofusion fitting in which the fusion or "welding" is accomplished by means of an electrical heating element which is located at or adjacent to the boundary between the inner wall of the fitting and the outer wall of the pipe or like member.

One type of electrofusion pipe fitting comprises a hollow thermoplastic sleeve member, having an electrical heating element located about the inner wall thereof, so that when in use the fitting is placed in mating contact

about a thermoplastic pipe or like member, and current is passed through the electrical heating element, the adjacent mating surfaces of the fitting and the pipe or like member melt, and fusion or "welding" of the surfaces takes place. Examples of electrofusion pipe fittings are described in US Patent Nos. 4313053 and 4906313, the entire disclosures of which are incorporated herein by reference.

The vast majority of available electrofusion pipe fittings are in-line couplers, as exemplified in the abovementioned US patents, due to the present difficulty of manufacturing more complicated shapes such as reducers, tees and bends. This substantially limits the field of use of electrofusion pipe fittings.

In another electrofusion method, a welding element, comprising a wire coil for electrical resistance heating embedded in a fusible plastics material, is positioned between the abutting components to be joined and the coil energised to fuse or weld the plastics material and the adjacent surfaces of the abutting components. Examples of welding elements of this type are described in US Patents Nos. 3378672, 4266997 and EPA 0160536, the entire disclosures of which are also incorporated herein by reference.

Difficulties have been experienced in connectorising the welding elements in the abovementioned patents in that in order to attach leads to the ends of the wire coil it is usually necessary to have wires crossing within the welding element, with the attendant risk of shorting. Attempts to eliminate this problem by using enamelled wires or bifilar windings have met with limited success.

In US Patent No. 4851647, the entire disclosure of which is also incorporated herein by reference, there is described a welding device for welding butt-welded plastic tubes which comprises a weldable plastic annular disc, having an external diameter equal to the external diameter of the tubes and an internal diameter equal to the internal diameter of the tubes, and a heating wire coil which spirals around the geometric centre of the disc on both surfaces that come into contact with the tube ends.

The welding device of US Patent No. 4851647 is of very limited application and can only be used to butt weld plastic tubes of substantial diameter and thickness. It cannot be used to join, for example, relatively thin- wall tubes, or tubes of different diameter.

European Patent No. 0184658 describes a saddle fitting having a disc-shaped heating element, in which

the core of the element is made from a fusible material, and a resistance wire, following in each case a spiral- shaped channel, is embedded into both surfaces of the disc. Again this device is of very limited application.

Finally, DE3226575 describes a device for jointing a pipe and mating pipe fitting which comprises a fusion ring, arranged between the pipe and the fitting, and having two coaxial heating coils embedded in the inner and outer surfaces of the ring, the inner heating coil having a smaller number of turns and/or a smaller heating power than the outer coil, the ring being axially pre- stressed prior to fusion jointing, or having an internal hollow space to accommodate means for generating a radial contact pressure.

The device of DE3226575 is complicated and expensive to manufacture, and involves an increased risk of shorting of the wires where they exit the fusion ring. There is also a possibility of leak paths being formed by movement of the wires where they exit the fusion ring during installation. Additionally there is a risk of overheating since the ring is slid completely into the space between the pipe and the fitting so that there are no identifiable features visible or accessible to the operator.

US4958857 describes a welding seal assembly comprising a thermoplastic welding sleeve with an embedded electric heating coil for fitting between a pipe and a socket, a mounting collar including a ring-like body that is fitted over the pipe and against the end of the socket with a thin-walled, compressible flange extending from the body over the outer side of the socket and overlying the overlapped elements of the joint, an electrical connector in a radially projecting tab on the ring, including electrical contacts connected to the heating coil, and a clamp ring surrounding the compressible flange and which compresses the flange around the joint. This construction of seal assembly is complicated to produce and can only be used with thin- wall sockets of defined thickness. The application of clamping pressure is essential to the operation of the seal assembly, which clamping pressure would be ineffective with large diameter pipes.

There is accordingly a need for a heat fusion system that is more versatile, in that it can join pipes of different sizes and in different situations, that can avoid the necessity for the manufacture of special pipe fittings, and that overcomes the difficulties of the prior art set out above.

According to the present invention the above objects can be achieved and the difficulties obviated by the use

of a heat fusion coupling element having electrical heating means on its inner and outer surfaces and electrical terminals on its outer surface.

In one aspect, the present invention provides a heat fusion coupling element comprising:

a hollow sleeve member formed from a fusible polymeric material,

the sleeve member having at least one electrical heating element disposed about its inner and outer surfaces, and

having electrical terminals mounted on its outer surface, the terminals being connected to the or each electrical heating element and disposed at or adjacent an end of the sleeve member.

In another aspect, the invention provides a method of coupling hollow elongate members formed from polymeric material, the hollow elongate members having end regions such that an end region of one hollow elongate member can be positioned within an end region of the other, which comprises:

interposing between the respective end regions a heat fusion coupling element comprising a hollow sleeve member formed from a fusible polymeric material having at least one electrical heating element disposed about its inner and outer surfaces, and having electrical terminals mounted on its outer surface, the terminals being connected to the or each electrical heating element and disposed at or adjacent an end of the sleeve member, and

connecting a source of electric power to the terminals in order to energise the electrical heating element or elements and thereby fuse the sleeve member to the hollow elongate members.

In a further aspect, the invention provides a method of manufacturing a heat fusion coupling element which comprises:

moulding a hollow sleeve member formed from a fusible polymeric material over a first electrical heating element so that the heating element is disposed about the inner surface of the sleeve member,

disposing a second electrical heating element about the outer surface of the sleeve member, and

electrically connecting the first and second electrical heating elements.

The coupling element of the present invention can, for example, have a simple hollow cylindrical shape, with a circular cross-section and constant diameter and wall thickness. In this form it can be inserted into the annular space between the overlapping ends of the two hollow elongate members to be joined. In other embodiments it can have a more complicated shape, for example, the coupling element can be provided with terminals for the electrical heating elements and upstanding protective boss members for the terminals. The coupling element can also form part of a heat fusion pipe fitting, simplifying the construction thereof by separating the manufacture of the electrical heating element component from the moulding of the rest of the body of the fitting. Thus, for example, the coupling element can form part of a junction, a tee, a bend, a diameter reducer, a bell and spigot joint, an end cap, a valve or similar construction which would present problems for, or be expensive to produce by, injection moulding as an integral structure.

The hollow sleeve member may be formed from any suitable fusible polymeric material, and can for example comprise a thermoplastic polymeric material, for example an olefinically unsaturated polymeric material such as

polyethylene, polypropylene, polybutylene, and higher olefinic polymers; copolymers of ethylene, propylene and butylene with each other and with other olefinically unsaturated monomers; olefinically unsaturated aromatic polymers such as polystyrene and styrene copolymers; and polymers and copolymers of vinyl monomers such as ethylenevinyl acetate copolymers, polycarbonates, and such like materials. Polyethylene is the preferred fusible polymeric material, particularly where polyethylene pipes or components are to be joined.

The hollow sleeve member may be of constant diameter and cross-section throughout its length, but this is not essential and other shapes having "step" regions and/or conical sections are not excluded.

The dimensions of the sleeve member will in general depend on the dimensions of the hollow members to be joined, but for example a typical length is from 5 to 20 cms, nominal diameter from 2 to 50 cms and wall thickness from 0.3 to 2.0 cms.

The or each electrical heating element preferably comprises a resistance heating element, although induction heating elements are not excluded. The or each electrical heating element preferably comprises a coil of resistance wire, and where a single electrical heating element is used this can, for example, be disposed about

the inner surface of the hollow sleeve member, pass around or through the wall of the hollow sleeve member, and then be disposed about the outer surface thereof. Where first and second electrical heating elements are used, these can be disposed respectively about the inner and outer surfaces of the hollow sleeve member, and electrically connected by a connector or connection passing around or through the wall of the hollow sleeve member. It is not usually necessary to use more than two electrical heating elements although in more complicated constructions three or more may be required.

Usually the electrical heating element or elements will be disposed in a substantially uniform manner about the whole of part of the respective inner and outer surfaces, although a departure from uniformity may be required in certain circumstances to obtain a desired pattern of heating.

A substantial advantage of the coupling element of the present invention is that the connections or terminals for the coupling element can be situated at or adjacent one end of the coupling element without requiring the crossing or overlapping of the wires of the heating element or elements, and without the use of bifilar windings. This greatly reduces the possibility of short circuits and also improves the ease of

manufacture by injection moulding where upstanding boss members for the terminals are present.

The advantage can be obtained, for example, by arranging the winding of the inner heating element to proceed from a first terminal at a first end of the coupling element to the other end thereof, where the inner heating element is connected to the outer heating element which is then wound back along the outer surface of the coupling element to a second terminal also situated at the first end. Such an arrangement involves no overlapping or crossing of wires as in the prior art.

The electrical heating element or elements is/are disposed about both the inner and outer surfaces of the t hollow sleeve member, and preferably such that a substantial portion of each surface is covered by, or affected by the heat from, its heating element or part thereof. The heating element or elements may be positioned adjacent to, on, or in the surfaces.

In a preferred construction, the or one of the electrical heating elements comprises a coil of resistance wire which is disposed about the inner surface of the hollow sleeve member, such that the electrical heating element is wholly or partly embedded in the wall of the hollow sleeve member adjacent the said inner surface. In another preferred construction, the or one

of the electrical heating elements comprises a coil of resistance wire disposed in a helical groove moulded or machined on the outer surface of the hollow sleeve member. The resistance or impedance of the electrical heating element or elements is such that, when powered by a direct or alternating current, the elements will heat up causing local fusion of the inner and outer surfaces of the hollow member, and in some cases local fusion of the adjacent surfaces of the hollow members, so as to fuse the sleeve member to the hollow members.

The electrical heating element is usually provided with two electrical terminals for connection to a suitable source of electric power such as for example a generator. Where two or more electrical heating elements are used, two electrical terminals will still usually be sufficient. More than two such terminals may of course be provided if necessary. The terminals may be of any suitable type for the attachment of power cables or the like, and may have screw-on or push-on fittings as appropriate. The terminals are disposed on an outer surface of the hollow sleeve member, adjacent one end thereof, and the connection to the inner electrical heating element can be made through the thickness of the sleeve member.

Each of the terminals are preferably surrounded by a protective boss member, which may cooperate with the

connector from the electric power source to form a coupling which firmly connects a lead from the power source to the terminal.

Preferably the two terminals, and associated boss members if present, are arranged at one end of the hollow sleeve member at an angular distance apart of about 90°.

This provides substantial advantages in simplifying the injection moulding of the sleeve.

The terminals may incorporate an auto recognition system whereby the power source is automatically set to the correct output, thereby avoiding over- or under- heating of the fusion region.

The coupling method of the invention can be used, for example, for coupling together hollow members having different diameters, thereby dispensing with the use of diameter reducing fittings and fusion couplers. The hollow members are such that an end region of one can be positioned within an end region of the other, and the coupling element can be positioned in the annular space between the overlapping ends. Preferably the coupling element fits firmly against the inner surface of the outer hollow member and the outer surface of the inner hollow member, with its electric terminals protruding from the overlap region. The hollow elongate members are

formed from a polymeric material, which is preferably the same as or similar to the polymeric material of the sleeve member.

The heat fusion coupling element of the invention can be manufactured by any suitable moulding method but is preferably formed by injection moulding. In a preferred method according to the invention, a first (inner) electrical heating element is wound on a moulding core and the hollow sleeve member injection moulded thereover. The sleeve member is preferably provided with moulded-in terminals for the first and second heating elements, and this may by accomplished using the methods of either of European Patents Nos 0260014 and 0243062 the entire disclosures of which are incorporated herein by reference.

Preferably the first heating element is connected to its terminal prior to the moulding step. After moulding the first electrical heating element is preferably wholly embedded in the inner surface of the sleeve member.

The moulded sleeve member preferably has a helical groove in its outer surface within which the second electrical heating element can be wound. Preferably the first and second heating elements are connected by means of a metal pin which is moulded into the wall of the sleeve member at the end thereof remote from the

terminals, and which extends through the wall from the inner to the outer surface thereof. The connection may be made by welding or crimping or any other convenient method.

Finally the second heating element is connected to its terminal by welding or crimping, or otherwise.

An embodiment of a coupling element, a heat fusion fitting and a coupling and manufacturing method according to the invention will now be described with reference to the accompanying Drawings in which:

Figure 1 shows an embodiment of a coupling element according to the invention in sectional side elevation;

Figure 2 shows the coupling element of Figure 1 in end elevation;

Figure 3 shows a top view of the coupling element of Figure 1;

Figures 4A and 4B show scrap views, in plan and in section, of the connection between the heating coils in the coupling element of Figure 1;

Figure 5 shows a scrap plan view of the terminal for the outer heating coil in the coupling element of Figure 1;

Figures 6A and 6B show respectively end elevational and sectional side elevational views of a diameter reducing pipe fitting body suitable for use with the coupling element of Figure 1;

Figures 7A and 7B show respectively end elevational and sectional side elevational views of a diameter reducing pipe fitting comprising the body of Figures 6A and 6B and the coupling element of Figure 1; and

Figure 8 shows in sectional side elevation a butt- welded coupling comprising two of the fittings of Figures 7A and 7B.

Referring to the Drawings, Figure 1 shows a coupling element illustrated generally at 1 which comprises a sleeve member 2, formed from fusible polymeric material, an inner resistance heating coil 3, and an outer resistance heating coil 4. The inner heating coil 3 is embedded within the inner surface 5 of the sleeve member 2 and the outer heating coil 4 is laid in a helical groove 6 on the outer surface 7 of the sleeve member 2. The coupling element 1 has a flange member 8 at one end 9 upon which are positioned terminals 10 and 11. The

terminals 10, 11 are surrounded respectively by protective boss members 12 and 13. At their ends remote from the terminals 10, 11, the heating coils 3 and 4 are joined by a metal pin 14 passing through the wall of the sleeve member 2.

The terminal 11 is provided, adjacent its boss member 13, with a longitudinally directed slot 15 which passes through the flange member 8 and has a width sufficient to allow the wire of heating coil 4 to be accommodated therein.

The coupling element 1 is manufactured by winding the inner heating coil 3 on to a former (not shown) and injection moulding sleeve member 2, flange 8 and boss members 12 and 13 thereover. Prior to injection moulding terminals 10 and 11 are supported in the mould, as described in European Patent No. 0260014, and one end 16 of heating coil 3 is welded to the base of terminal 10. The metal pin connector 14 is also moulded in to the wall of the sleeve member 2 adjacent the end 17 thereof.

The moulded coupling element is then removed from the mould, and the connector 14 is welded to the end 18 of the inner heating coil 3 which is situated in a run- out groove 19 (see Figure 4A).

The sleeve member 2 is moulded with a helical groove 6 in its outer surface, and within this groove there is

wound an outer heating coil 4. An end portion 20 of the outer heating coil 4 is passed through the slot 15 and welded to the base of the terminal 11 using the welding recess 21 (see Figure 2 and Figure 5). As can be seen from Figure 5, the end 20 of the outer heating coil 4 is accommodated in an internal groove 23 on the internal surface 5 of the sleeve member 2.

The coupling element 1 of the invention can be used to join together pipes of different diameters, specifically a pipe having an internal diameter corresponding to the external diameter of the sleeve member 2, and a pipe having an external diameter corresponding to the internal diameter of the sleeve member 2. In carrying out the coupling method of the invention, the coupling element may be fitted over an end of the smaller diameter pipe, and that end, together with the coupling element, can then be inserted in an end of the larger diameter pipe. Leads are connected to the terminals 10 and 11 and the coils 3 and 4 energised in order to cause localised fusion of the adjacent surfaces of the pipes and the coupling element, and form a fusion bond or weld.

The coupling element of the invention can form part of a heat fusion pipe fitting, and an example of the body of such a fitting is shown in Figures 6A and 6B. Illustrated in these Figures is a body portion of a heat

fusion diameter reducing fitting, indicated generally at 30, having a narrow diameter end portion 31 and a larger diameter end portion 32. The narrow diameter portion 31 has an end surface 33 which can be butt-welded to a pipe end, a pipe fitting, or another component. At the larger diameter end portion 32 the interior of the body portion is recessed and has a step at 34. The interior diameter of end portion 32 is just large enough to receive sleeve member 2 of the coupling element 1, and the coupling element can be pushed into the body portion until the edge 35 of the flange member 8 abuts against the end 36 of the body portion 30 as shown in Figures 7A and 7B. An end of a pipe, or another component, can then be inserted into the coupling element and fused to the coupling element and the reducer body portion as previously described. It will be apparent, that by using a variety of coupling elements of different internal diameter, a variety of pipe diameters can be accommodated in the diameter reducing fitting.

In Figure 8 there is shown a coupling that has been produced from two reducing fittings according to Figures 7A and 7B. The reducing fittings, designated 37 and 38 are butt welded together at their end surfaces 39 and 40 to produce an in-line pipe coupling. In use the pipe ends to be joined are located in the respective ends of the coupling and the heating elements energised to fuse the components together.

The reader's attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps or any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.