GB2319496A

GB2319496A - Electrofusion coupler for plastic pipes

Info

Publication number: GB2319496A
Application number: GB9624524A
Authority: GB
Inventors: Richard Statham; Michael Bull
Original assignee: Glynwed Pipe Systems Ltd
Current assignee: Glynwed Pipe Systems Ltd
Priority date: 1996-11-25
Filing date: 1996-11-25
Publication date: 1998-05-27
Anticipated expiration: 2016-11-25
Also published as: GB2351257B; GB2351257A; GB9624524D0; GB2319496B; GB0019501D0

Abstract

Two electrofusion couplers for connecting plastic pipes are disclosed along with methods for their construction. In one form, the body of the coupler (10, Fig. 1) is made from a blend of thermoplastic polymers, preferably including polyethylene and possibly also polyamide or polyvinylidenefluoride (PVDF). Such a coupler is formed by moulding the polymer blend around a wound wire core (12, Fig. 1). In another form, the body of the coupler has a multi-layered construction including a layer of relatively permeable plastic 18 and a barrier layer 28 which is relatively impermeable e.g. nylon or metal foil. It preferably includes an innermost layer 16c of fusible plastic, the barrier layer 28 and an outermost layer 18. Tie layers 26, 30 may also be included to improve bonding between adjacent layers. A multi-layered coupler can be formed by forming an inner layer around a wound wire core (Fig. 2) and then sequentially forming the respective outer layers. Alternatively, the inner layer may be moulded without a wire core, the wire core being wound around the core once it has been removed from the mould and the outer layers then moulded sequentially over this core. As another alternative, the body may be extruded as a pipe comprising the required layers and then the wire is pressed into a helical slot cut in the pipe.

Description

DESCRIPTION OF INVENTION Title: "Improvements in or relating to electrofusion couplers" THIS INVENTION relates to electrofusion couplers or welding muffs, that is to say to fitments adapted to be secured to thermoplastics pipes by fusion of plastics material of such pipes and of the fitments induced by passing electrical current through electrical resistance wire embedded in such couplers close to an internal surface thereof.

Typically, an electrofusion coupler comprises a plastics sleeve or muff open at both ends to receive respective ends of two lengths of plastics pipe to be joined in a pipe line.

In use of electrofusion couplers of this type, the respective thermoplastics pipe ends are inserted into the bores, of complementary diameter, provided at opposite ends of the coupler and electrical current is passed briefly through the electrical resistance wire embedded in the electrofusion coupler to fuse the plastics material of the coupler close to or at the respective internal surface of each said bore and likewise to fuse the thermoplastics material of the peripheral surface of the inserted pipe end adjacent that internal surface, whereby the pipes and the electrofusion coupler are caused to fuse together forming a strong and fluid-tight connection between the inserted pipe ends and the coupler and hence between the two lengths of pipe connected by the coupler.

Other forms of electrofusion coupler are, however, known, such as "T" fittings (adapted to connect three pipe ends), elbows or bends (to facilitate changes in direction of the pipe system) saddle fittings (adapted to connect a smaller, branch pipe to a larger plastics pipe at the region of an aperture formed in the larger pipe) and the present invention is also applicable to these, and other kinds of electrofusion fittings.

Thermoplastics pipelines incorporating such electrofusion couplers may be required, in some instances, to convey hydrocarbon fluids and alcohol based fuels.

In addition some pipework systems may be required to transport fluids, for example, potable (drinking) water, through contaminated ground. However, the material normally used for such pipelines, polyethylene, is subject to attack and permeation by certain aggressive chemicals and it is for this reason that composite and multi-layer pipes have been developed. However, at present adjoining sections of such pipes are still in the main connected by conventional electrofusion couplers (normally also made of polyethylene) so that the electrofusion couplers form sites in such pipelines at which chemical attack and subsequent permeation may occur, with possible deterioration of the respective joints, which may eventually lead to leakage.

It is an object of the present invention to provide an electrofusion coupler suitable for use in plastics pipe lines designed for the conveyance of aggressive fluids which have a tendency to attack or permeate through conventional plastics pipes.

According to one aspect of the invention there is provided an electrofusion coupler having a body made of a blend of thermoplastics polymers.

According to another aspect of the invention, there is provided an electrofusion coupler having a multi-layered construction, including a layer of a relatively inexpensive commodity plastic material and a barrier layer which is relatively impermeable.

According to a further aspect of the invention, there is provided a method of manufacturing an electrofusion coupler1 comprising winching electrical resistance wire upon a cylindrical mould core, placing the wound core in an injection mould, injecting into the mould, around the wound core, in a molten state, a blend of thermoplastics polymers, allowing the blend to cool and solidify, de-moulding the product and extracting the wound core longitudinally from the product.

According to a still further aspect of the invention, there is provided a method of manufacturing an electrofusion coupler, comprising winching electrical resistance wire upon a cylindrical mould core, forming a layer of fusible thermoplastics over the wound core, and forming a barrier layer over said layer of fusible thermoplastics, or over a tie layer formed over said layer of fusible plastics.

According to a still further aspect of the invention, there is provided a method of manufacturing an electrofusion coupler, comprising forming a hollow preform of fusible plastics by injection moulding the preform around a mould core in an injection mould, removing the core and preform from the mould, winding electrical resistance wire upon the preform, and forming a barrier layer over the wound preform or over a tie layer formed over the wound preform.

According to a yet further aspect of the invention there is provided a method of manufacturing an electrofusion coupler comprising a plurality of layers including an inner fusible layer and a barrier layer, comprising extruding a pipe comprising said layers, cutting a section off said pipe and inserting an electrical heating wire in said inner fusible layer, without penetrating said barrier layer by a ploughing technique in which a helical slot is cut, in said inner layer and said heating wire pressed into said helical slot.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a view in axial section of a first embodiment of the invention, FIGURES 2 to 7 are partial views, also in axial section of further embodiments of the invention Referring to Figure 1, this shows, in axial section, an electrofusion coupler which is conventional in construction, comprising a unitary cylindrical plastics sleeve 10 having, embedded therein, adjacent the internal surface of the bore therethrough, single layer windings 12 of electrical resistance heater wire the ends of which are connected with terminal pins (not shown) shrouded by integral plastics sleeves 14 extending from the outer periphery of the electrofusion coupler.

The electrofusion coupler of Figure 1 is preferably made by a process, known per se, in which the resistance wire is first wound around a cylindrical mandrel or mould core (not shown - but comprising two cylindrical parts which meet in the middle of the finished coupler). The ends of the winding are secured to the terminal pins temporarily in manner also known per se, the wound core then being disposed within an injection mould and the plastics body of the electrofusion coupler being moulded around the wound core, after which the two halves of the core are extracted longitudinally from opposite ends of the electrofusion coupler thus formed. The electrofusion coupler of Figure 1 differs from conventional electrofusion couplers in that the plastics material used for the body of the electrofusion coupler comprises a blend of fusible polymers, for example a blend of "Nylon" (polyamide) and polyethylene. Alternatively, the material of the body of the electrofusion coupler may comprise PVDF (polyvinylidenefluoride) and polyethylene.

Other blends incorporating a polyethylene phase may also be useful.

The embodiment described above with reference to Figure 1 has improved barrier properties particularly with respect to hydrocarbon gases and liquids, as compared with conventional polyethylene electrofusion couplers.

Furthermore, manufacturing facilities normally used for the manufacture of conventional electrofusion couplers can readily be converted for the manufacture of, for example, Nylon/polyethylene blend electrofusion couplers with little or no capital investment.

In a variant, (not illustrated), the resistance wire wound around the mould core during manufacture is resistance wire having a coating of polyethylene. This variant has been found to have improved adhesion characteristics as compared with the product made using uncoated wire.

In Figures 2 to 7, for convenience, there is shown, in each case, only one of the two sectioned regions corresponding to the cross-hatched areas lying in symmetrical mirror-image relationship on opposite sides of the longitudinal axis of the coupler in Figure 1.

Furthermore, for clarity, the sectioned regions are not shown cross-hatched in Figures 2 to 7.

Referring to Figure 2, the electrofusion coupler shown comprises an inner layer 16 and an outer layer 18 of relatively inexpensive thermoplastics such as polyethylene, functionalised polyethylene or a polyethylene/functionalised polyethylene blend, with a barrier polymer layer between the inner and outer layers, the barrier polymer layer being of a less permeable plastics material for the proposed application, for example Nylon (polyamide). The preferred method of manufacturing the electrofusion coupler of Figure 2 is to wind the resistance heating wire around a two-part mould core in the same way as described with reference to Figure 1, place the wound core in a first injection mould and inject a thin layer of plastic material onto the wound core and incorporating the resistance wire winding. The core, with the resistance wire winding and said thin layer of plastic material, is then placed in a second injection mould, in which the barrier layer 20 is formed around the inner layer 16 by injection moulding. After the barrier layer has solidified, the core, with the inner and barrier layers and the resistance winding is demoulded and placed in a third injection mould in which the outer layer 18 which forms the remainder of the body of the electrofusion coupler, is moulded around the barrier layer 20.

Referring to Figure 3, this shows a variant electrofusion coupler having, like that of Figure 2, an inner layer, referenced 16a of plastic material, an intermediate layer 20 comprising a barrier polymer and formed, for example, of Nylon (polyamide), with again an outer layer 18 of plastic material. This coupler is, however, formed by the technique, known per se, of first moulding a thin-walled preform, forming the inner layer 16a of the finished electrofusion coupler around a mould core, the electrical resistance wire being thereafter wound around the preform supported on the core. Thereafter, the wound preform and core are placed within a first injection mould in which the barrier layer 20 is injected around the preform. After the barrier layer has solidified, the product, still on the mould core, is de-moulded and placed with the mould core in a further injection mould in which the outer layer 18 of plastic material is moulded.

Electrofusion couplers made by the methods described with reference to Figures 2 and 3 have improved barrier properties, i.e. are less permeable, than couplers made by either of the techniques described above with reference to Figure 1. Furthermore, couplers made by the method described with reference to Figures 2 and 3 may have improved pressure performance due to the presence of the higher modulus barrier layer.

Figure 4 illustrates an electrofusion coupler similar to that of Figure 3 but differing from that of Figure 3 in that a so-called "tie layer" 24 is applied, e.g. by injection moulding, over the wound preform, referenced 16b, in place of the barrier layer 20 of Figure 3 and the outer layer 18 of the electrofusion coupler is formed of an appropriate barrier polymer which is impermeable to the fluid to be carried by the associated pipe line. Such polymer may, for example, be Nylon (polyamide) or a polymeric blend or alloy incorporating such a barrier polymer. The tie layer 24 comprises a plastic material which has a good affinity for the material of the preform 16k and that of the outer layer 18 and thus effectively forms a bond between the outer layer and the preform.

Electrofusion couplers made by the method described with reference to Figure 4 have very good barrier properties, due to the thickness of the barrier polymer layer, and have increased mechanical integrity compared to couplers without tie layers.

The electrofusion coupler of Figure 5 comprises five successive layers, comprising an injection moulded preform 16c providing the innermost layer and upon which the winding of electrical resistance wire is wound as in Figures 3 and 4. A first tie layer 26 is applied, e.g. by injection moulding, over the outer surface of the preform 16 and the winding, a barrier layer 28, e.g. of Nylon, is applied over the first tie layer and a second tie layer 30 is applied over the barrier layer 28. An outer layer 18 of relatively low cost plastics such as polyethylene is then applied, by injection moulding, over the outer tie layer 30. Thus, the first tie layer 26 serves to form a bond between the barrier layer 28 and the preform 16e whilst the second tie layer 30 serves to form a bond between the barrier layer 28 and the outer layer 18.

Electrofusion couplers made by the method described with reference to Figure 5 have again very good barrier properties, i.e. low permeability, and the higher modulus barrier layer 28 may provide improved pressure performance.

Such couplers also have good mechanical integrity, with resistance to separation of the layers by virtue of the tie layers.

Referring to Figure 6, the electrofusion coupler shown comprises a preform 16d forming the innermost layer, the electrical resistance heating winding being wound on the preform 16d and an outer plastics layer 18 being injection moulded around the preform and winding. The structure of the electrofusion coupler is thus conventional, but its composition is not. Thus, the coupler of Figure 6 differs from the conventional couplers in that the preform 16d is formed from a polyethylene based material whilst the outer plastics layer 18 is formed from a plastic material impermeable to the fluid to be conveyed, and may thus, for example, be formed of a barrier polymer or barrier polymer blend or alloy. Such an electrofusion coupler again has very good barrier properties, with improved pressure performance due to the substantial thickness of the higher modulus barrier layer. Like couplers made by the methods described with reference to Figure 1, electrofusion couplers can easily be made by the method described with reference to Figure 6, using conventional techniques and equipment.

The electrofusion coupler of Figure 7 comprises an inner layer 16 of polyethylene, incorporating the winding of resistance wire, a layer of metallic foil 34 around the innermost layer, (the polyethylene of the innermost layer insulating the winding from the metallic foil), and an outer layer 18 of low cost plastics such as polyethylene.

The preferred mode of manufacture of the electrofusion coupler of Figure 7 is to wind the resistance wire upon a two-part core of the kind referred in relation to the couplers of Figures 1 and 2, after which the wound core is placed in a first injection mould in the same way as described in relation to Figure 2, in which polyethylene is injected into the mould around the wound core to form the preform 16e incorporating the winding. The preform is then wrapped in metallic foil 34 which is secured in place on the preform and thereafter the outer layer or encapsulation 18 of plastic material is formed by placing the wrapped preform, with the core, in a further injection mould and injection moulding the polymeric outer layer 18 around the wrapped preform. An electrofusion coupler made by this technique has excellent barrier properties, being substantially impermeable. The metallic barrier layer provides improved burst strength and, indeed, may allow the overall wall thickness of such an electrofusion coupler to be reduced for a given burst strength, as compared with a coupler made of polyethylene throughout. Furthermore, electrofusion couplers can be made by this technique with only minimal adaption of existing conventional equipment.

An electrofusion coupler of the form illustrated in Figure 3 may be formed alternatively by a manufacturing technique which differs from that described above for the coupler of Figure 3 in that the barrier polymer layer 20 is applied not by injection moulding but by spraying, or applying by some other coating technique, the barrier polymer on to the wound preform.

In a further alternative technique for the manufacture of an electrofusion coupler of the form shown in Figure 3, the barrier polymer layer 20 is applied by wrapping a thin film of the barrier polymer around the wound preform 16a before placing the preform, still on its core, within an injection mould and applying the outer layer by injection moulding. Similarly, an electrofusion coupler of the same form as that illustrated in Figure 5 may be made by a technique in which, instead of the tie layers 26, 30 and barrier polymer layer 28 being formed by injection moulding, the wound preform 16c is wrapped in a plastics film comprising a film of barrier polymer to which has been applied, on each surface thereof, a respective tie layer. After this composite film has been wrapped around the wound preform, it is secured in position and the wound and wrapped preform is placed in an injection mould in which the outer layer 18, for example a polyethylene encapsulation, is formed by injection moulding.

In another variant method for manufacture of an electrofusion coupler of the form illustrated in Figure 5, the inner tie layer 26 is applied to the wound preform by a spraying technique. The barrier layer 28 may likewise be applied to the inner tie layer by the same spraying technique and the outer tie layer 30 may similarly be applied, by the same spray technique to the barrier polymer layer 28. Thereafter, the wound preform, with the tie layers 26, 30 and barrier layer 28 is placed, still around its core, within an injection mould and the outer encapsulation 18 of polyethylene formed by injection moulding. It will be appreciated that various combinations of these techniques may be used, for example, any of the tie layers 26, 30 or the barrier polymer layer 28 may be applied by injection moulding, or applied in the form of a film, or applied by spraying the respective molten plastics provided that the technique used allows the tie layers to be fused with the layers above and below.

Electrofusion couplers of the form illustrated in Figures 3 and 5, for example, may also be formed by a still further different technique. Thus, electrofusion couplers of this form may be formed as sections cut from continuously extruded pipe material comprising a plurality of continuous layers. Thus, for an electrofusion coupler of the form shown in Figure 3, the extruded pipe is used which comprises a polyethylene based inner layer, an intermediate layer of a barrier polymer and a polyethylene based outer layer. An electrofusion coupler of the form illustrated in Figure 5 may likewise be formed from a section cut from an extruded pipe comprising an inner polyethylene layer, a tie layer adjacent the polyethylene layer, a barrier polymer layer adjacent the first tie layer, a second tie layer around the barrier polymer layer and an outer polyethylene layer. Techniques for extruding plastics pipes comprising a plurality of concentric layers are well known and will not be described in detail here.

In manufacture of electrofusion couplers by the last noted techniques, the appropriate length is cut from the respective multi-layer pipe and the workpiece thus formed is subjected, if necessary, to machining operations to ensure that the required dimensional tolerances are met.

The resistance windings in this variant technique are then fitted using a technique known per se in which a helically extending slit is cut around the interior of the workpiece and the wire inserted into this slit, by a "ploughing-in" technique. The radial depth of the slit is, of course, so controlled as not to penetrate the barrier layer. The last noted technique is particularly suitable for low volume production or where only a single electrofusion coupler of a particular size and construction is required.

Claims

1. An electrofusion coupler having a body made of an alloy or blend of thermoplastics polymers.

2. An electrofusion coupler according to claim 1 wherein said blend includes polyethylene.

3. An electrofusion coupler according to claim 2 wherein said blend also comprises other polymeric materials such as Nylon (polyamide) or PVDF (polyvinylidenefluoride).

4. An electrofusion coupler having a multi-layered construction, including a layer of relatively permeable plastics and a barrier layer which is relatively impermeable.

5. An electrofusion coupler according to claim 4 including an innermost layer of fusible plastics, an outermost layer, and an intermediate layer of relatively impermeable plastics.

6. An electrofusion coupler according to claim 5 including a tie layer between said relatively impermeable layer and one of the adjoining plastics layers.

7. An electrofusion coupler according to claim 5 including a respective tie layer between said impermeable layer and each of the adjoining plastics layers.

8. An electrofusion coupler according to claim 4 wherein said barrier layer is of metal foil.

9. A method of manufacturing an electrofusion coupler, comprising winching electrical resistance wire upon a cylindrical mould core, placing the wound core in an injection mould, injecting into the mould, around the wound core, in a molten state, a blend of thermoplastics polymers, allowing the blend to cool and solidify, demoulding the product and extracting the wound core longitudinally from the product.

10. A method according to claim 9 wherein the electrical resistance wire wound onto said core is plastics-coated wire coated with a thermoplastics compatible with said blend of polymers.

11. A method of manufacturing an electrofusion coupler, comprising winding electrical resistance wire upon a cylindrical mould core, forming a layer of fusible thermoplastics over the wound core, and forming a barrier layer over said layer of fusible thermoplastics, or over a tie layer formed over said layer of fusible plastics.

12. A method as claimed in claim 11 further including forming a further layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

13. A method according to claim 12 wherein said further layer is formed by placing the wound core, with said layer of fusible plastics and said barrier layer thereon, in an injection mould and injecting said further layer therearound.

14. A method according to claim 13 wherein the innermost layer of fusible plastics is formed by injection moulding around the wound core.

15. A method according to claim 13 or claim 14, wherein said barrier layer is formed by injection moulding around the innermost layer of fusible plastics.

16. A method according to claim 11 wherein at least one of said layers is formed by spraying molten plastics, to form the layer onto the core or onto the preceding layer.

17. A method of manufacturing an electrofusion coupler, comprising forming a preform of fusible plastics by injection moulding the preform around a mould core in an injection mould, removing the core and preform from the mould, winding electrical resistance wire upon the preform, and forming a barrier layer over the wound preform or over a tie layer formed over the wound preform.

18. A method according to claim 17 further including forming a further layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

19. A method according to claim 18 wherein said barrier layer is formed by injection moulding around the innermost layer of fusible plastics.

20. A method according to claim 19 wherein said barrier layer and/or said further layer and/or said tie layer comprises a respective plastics layer formed by a suitable spraying technique.

21. A method according to claim 17 wherein said barrier layer is formed of metal foil.

22. A method of manufacturing an electrofusion coupler comprising a plurality of layers including an inner fusible layer and a barrier layer, comprising extruding a pipe comprising said layers, cutting a section off said pipe and inserting an electrical heating wire in said inner fusible layer, without penetrating said barrier layer by a ploughing technique in which a helical slot is cut, in said inner layer and said heating wire pressed into said helical slot.

23. An electrofusion coupler substantially as hereinbefore described with reference to and as shown in any of the accompanying drawings.

24. A method of manufacturing an electrofusion coupler, substantially as hereinbefore described with reference to any one of the accompanying drawings.

25. Any novel feature or combination of features disclosed herein.