GB2351257A

GB2351257A - A multi-layered electrofusion coupler

Info

Publication number: GB2351257A
Application number: GB0019501A
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: 2000-12-27
Anticipated expiration: 2016-11-25
Also published as: GB2319496B; GB2351257B; GB2319496A; GB9624524D0; GB0019501D0

Abstract

An electrofusion coupler comprises a multilayered construction including an innermost layer 16a of relatively permeable fusible plastics and a barrier layer 20 of relatively impermeable plastics. Tie layers between said plastics layers or an outermost layer 18 may be provided. Preferably the coupler may be made by winding electrical resistance wire upon a cylindrical core, forming a layer of fusible plastics over the wound core then forming a barrier layer of plastics over the fusible layer. Optionally the layers may be formed by spraying the molten plastics or injection moulding. A preform of fusible plastics may be formed around which the wire may be wound before the subsequent layers are added. The coupler can be formed by extruding a pipe containing said layers and cutting a helical slot in the inner fusible layer into which the heating wire is pressed.

Description

i-- 2351257 1

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 brief ly 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 'IT" fittings (adapted to connect three pipe 2 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.

3 According to one aspect of the invention there is provided an electrofusion coupler having a multi-layered construction, including an innermost layer of relatively permeable fusible plastics, an outermost layer, and an intermediate, barrier layer of relatively impermeable plastics.

According to another aspect of the invention, there is provided 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, forming a barrier layer of relatively impermeable plastics over said layer of fusible plastics, and forming a further layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

According to a still ftirther 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 barTier layer over the wound preform or over a tie layer formed over the wound preform, and forming a further layer of plastics over said barrier layer or over a fie layer formed over said barrier layer.

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, ill said inner layer and said heating wire pressed into said helical slot.

4 Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which:- FIGURES 1 to 4 are partial views, in axial section, of embodiments of the invention.

In Figures I to 4, for convenience, there is shown, in each case, only one of two sectioned regions, in an axial section, corresponding to the cross-hatched areas, lying in symmetrical mirror-image relationship on opposite sides of the longitudinal axis of the electrofusion coupler.

Referring to Figure 1, 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 20 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 I is to wind the resistance heating wire around a two-part mould core, place the wound core in a first injection mould and inject a thin layer 16 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 a 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 third injection mould in which an outer layer 18, which forms the remainder of the body of the electrofusion coupler, is moulded around the barrier layer 20.

Referring to Figure 2, this shows a variant electrofusion coupler having, like that of Figure 1, an inner layer, referenced 16a of plastics material, an intermediate layer 20 comprising a barrier polymer and formed, for example, of Nylon (polyamide), with again an outer layer 18 of plastics 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 1 and 2 have improved barrier properties, i.e. are less permeable, than couplers made by conventional techniques. Furthermore, couplers made by the method described with reference to Figures 1 and 2 may have improved pressure performance due to the presence of the higher modulus barrier.

Figure 3 illustrates an electrofusion coupler similar to that of Figure 2 but differing from that of Figure 2 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 2 and the outer layer 18 of die 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 6 affmity for the material of the preform l6b 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 3 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 4 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 2 and 3. A first tie layer 26 is applied, e.g. by injection moulding, over the outer surface of the preform 16c 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 16c 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 he method described with reference to Figure 4 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.

An electrofusion coupler of the form illustrated in Figure 2 may be formed alternatively by a manufacturing technique which differs fi-om that described above for the coupler of Figure 2 in that the barrier polymer layer 20 is applied 7 not by injection moulding but by spraying, or applying by some other coating technique, the barrier polymer onto the wound preform.

In a further alternative technique for the manufacture of an electrofusion coupler of the form shown in Figure 2, 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 4 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 4, 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 8 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 forin illustrated in Figures 2 and 4, 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 2, 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 electrofasion coupler of the form illustrated in Figure 4 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 frorn the respective multi-layer pipe and the workpiece thus fortned 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 lastnoted technique is particularly suitable for low volume production or where only a single electrofusion coupler of a particular size and construction is required.

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Claims

1. An electrofasion coupler having a multi-layered construction, including an innermost layer of relatively permeable fusible plastics, an outermost layer, and an intermediate, barrier layer of relatively impermeable plastics.

2. An electroftision coupler according to claim 1, including a tie layer between said relatively impermeable layer and one of the adjoining plastics layers.

3. An electroftision coupler according to claim I including a respective fie layer between said impermeable layer and each of the adjoining plastics layers.

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

5. A method according to claim 4 wherein said fW-ther layer is formed by placing the wound core, with said layer of fusible plastics and said barrier layer thereon, in an injection mould and iqjecting said further layer therearound.

6. A method according to claim 5 wherein the imiermost layer of fusible plastics is formed by injection moulding around the wound core.

7. A method according to claim 5 or claim 6, wherein said barrier layer is formed by injection moulding around the innermost layer of fusible plastics.

8. A method according to claim 4 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.

9. 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, forming a barrier layer over the wound preform or over a tie layer formed over the wound preform, and fon-ning a further layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

10. A method according to claim 9 wherein said bai-rier layer is formed by injection moulding around the iimermost layer of fusible plastics.

11. A method according to claim 10 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.

12. A method of manufacturing an electrofasion 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.

11

13. An electrofusion coupler having a multi-layered construction, including an innermost layer of relatively permeable plastics, an outermost layer of an impermeable, barrier polymer, and an intermediate tie layer.

14. A method of manufacturing an electrofusion coupler comprising forming a preform of fusible plastics, winding electrical resistance wire over the preform, forming a fie layer over the wound preform and forming over the tie layer an outer layer of an impermeable barrier polymer.

15. An electrofusion coupler substantially as herembefore described with reference to and as shown m any of Figures 1 to 4 of the accompanying drawings.

16. A method of manufacturing an electroffision coupler, substantially as hereinbefore described with reference to any one of Figures 1 to 4 of the accompanying drawings.

16. A method of manufacturing an electrofusion coupler, substantially as hereinbefore described with reference to any one of Figures 1 to 4 of the accompanying drawings.

)z Amendments to the claims have been filed as follows 1. An electrofusion coupler having a multi-layered construction, including an innermost layer of relatively permeable fusible plastics, an outermost plastics layer, and an intermediate, barrier layer of relatively impermeable plastics.

2. An electrofusion coupler according to claim 1, including a tie layer between said relatively impermeable layer and one of the adjoining plastics layers.

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

4. 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, forming a barrier layer of relatively impermeable plastics over said layer of fusible plastics, and forming a further layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

5. A method according to claim 4 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.

6. A method according to claim 5 wherein the innermost layer of fusible plastics is formed by injection moulding around the wound core.

13 7. A method according to claim 5 or claim 6, wherein said barrier layer is formed by injection moulding around the innermost layer of fusible plastics.

8. A method according to claim 4 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.

9. 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, forming an impermeable plastics barrier layer over the wound preform or over a tie layer formed over the wound preform, and forming a fin-ther layer of plastics over said barrier layer or over a tie layer formed over said barrier layer.

10. A method according to claim 9 wherein said barrier layer is formed by injection moulding around the innermost layer of fusible plastics.

12. A method of manufacturing an electrofusion coupler comprising a plurality of layers of plastics including an inner fusible layer and an impen-neable 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 1 technique in which a helical slot is cut in said inner layer and said heating wire pressed into said helical slot.

13. An electrofusion coupler having a multi-layered construction, including an innermost layer of relatively permeable plastics, an outermost layer of an impermeable, barrier polymer, and an intermediate fie layer.

14. A method of manufacturing an electrofusion coupler comprising forming a preform of fusible plastics, winding electrical resistance wire over the preform, forming a fie layer over the wound preform and forming over the fie layer an outer layer of an impermeable barrier polymer.

15. An electrofusion coupler substantially as hereinbefore described with reference to and as shown in any of Figures 1 to 4 of the accompanying drawings.