GB2388635A

GB2388635A - A composite electrofusion fitting

Info

Publication number: GB2388635A
Application number: GB0210999A
Authority: GB
Inventors: Jeremy Bowman
Original assignee: Uponor Innovation AB
Current assignee: Uponor Innovation AB
Priority date: 2002-05-14
Filing date: 2002-05-14
Publication date: 2003-11-19
Anticipated expiration: 2022-05-14
Also published as: GB0210999D0; GB2388635B

Abstract

A composite electrofusion fitting comprising a hollow thermoplastic body having an electrical heating element located about an inner wall thereof, the body comprising a plurality of hollow thermoplastic sleeve members butt-fused together, and wherein the electrical heating element is located so as to extend across a butt-fused region of the body.

Description

it, COMPOSITE ELECTROFUSION FITTING

This invention relates to electrofusion fittings, and more particularly to composite electrofusion fittings 5 anti methods for manufacturing such fittings.

Electrofusion fittings generally comprise a hollow thermoplastic body member for connection to thermoplastic pipes or like members in which a portion of an inner 10 peripheral wall of the fitting is arranged to be joined by fusion to a portion of an outer peripheral wall of a pipe or like member. In electrofuslon fittings, the fusion is accomplished by means of an electrical heating element, which is located at or adjacent to the boundary 15 between the inner wall of the fluting and the outer wall of the pipe or like member. In use, when 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 20 fitting and the pipe or like member melt, and fusion of the surfaces takes place.

Conventionally, electrofusion fittings are usually manufactured by injection moulding the body member over 25 the electrical heating element. This method is acceptable for small fittings, but large fittings require a high shot volume and therefore involve high manufacturing and tooling costs. Intrusion moulding IS also a problem when injection moulding large shot weight 30 fittings.

It is known to manufacture a composite electrofusion fittings by butt fusing together two or more hollow thermoplastic sleeve members, for example, as described 35 in EP0717824 and EP0535247. The butt-fused region(s) of ., , .. . ,

the body, however, represent a potential source of weakness, and the bead left by butt fusion can create a potential obstacle to material in the fluid passing through the pipe which can lead to build-up and eventual 5 blocking of the pipe.

A further problem in the manufacture of conventional injection moulded electrofusion fittings is that the central section of the body, which takes the majority of 10 the stress in the fitting, may need to be made thicker than the end sections in order to provide the assembled joint with adequate mechanical strength.

The present invention provides, in one aspect, a composite electrofusion fitting in which a butt-fused region of the body is reinforced by the electrical heating element.

In a first aspect, the present invention provides a 20 composite electrofusion fitting comprising a hollow thermoplastic body having an electrical heating element located about an inner wall thereof, the body comprising a plurality of hollow thermoplastic sleeve members butt-

fused together, and wherein the electrical heating 25 element is located so as to extend across a butt-fused region of the body.

In a further aspect, the invention provides a method of manufacturing an electrofusion fitting, the fitting 30 comprising a hollow thermoplastic body having an electrical heating element located about an inner wall thereof, which comprises butt-fusing a plurality of hollow thermoplastic sleeve members together to form a body, and disposing an electrical heating element about 35 an inner wall thereof, such that the electrical heating . . ,. I.

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r 3 element extends across a butt-fused region of the body.

The invention also provides, in another aspect, a composite electrofusion fitting comprising butt-fused 5 sections having different physical properties, for example, mechanical strength.

In a further aspect, therefore, the invention provides a composite electrofusion fitting comprising a hollow 10 thermoplastic body having an electrical heating element located about an inner wall thereof, the body having a diameter of 150 mm or greater, and comprising a plurality of hollow thermoplastic sleeve members of dissimilar polymeric materials butt-fused together, at least one of 15 the sleeve members having a higher mechanical strength than the other or others, and being positioned where such strength is required to give the desired mechanical strength to a pipe joint made using the fitting.

20 The composite electrofusion fitting can comprise, for example, a large in-line coupler, a junction, a tee, a bend, a reducer, or any other similar construction which would present problems for, or be expensive to produce by, a single injection moulding. The invention is 25 particularly suitable for the manufacture of composite electrofusion pipe fittings having a diameter of greater than 250 mm, and especially greater than 400 mmO Preferably each of the hollow thermoplastic sleeve members has an end region which can be joined to another 30 sleeve member by butt-fusion, to form a more complex structure. Two or more, and preferably three hollow thermoplastic sleeve members may be used.

In a preferred aspect, a composite electrofusion fitting 35 according to the invention comprises a body having a mid ... . ..,,,...

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section and two end sections, comprising three hollow, thermoplastic sleeve members butt-fused in-line. The hollow thermoplastic sleeve member comprising the mid-

section of the body preferably has physical properties, 5 and especially mechanical strength, higher than the physical properties of the hollow thermoplastic sleeve members comprising the end sections of the body. This provides the mid-section, which in an electrofusion coupler is usually the section under greatest stress, 10 with improved resistance to internal pressures and other stresses. The plurality of thermoplastic hollow sleeve members may each be formed from any suitable thermoplastic polymeric 15 material or materials. Suitable materials include, 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 20 olefinlcally unsaturated monomers, olefinically unsaturated aromatic polymers, such as polystyrene and styrene copolymers; and polymers and copolymers of vinyl monomers such as ethylene vinyl acetate copolymers, -

polycarbonates, and such like materials.

25 - The sleeve members can be formed from the same or different grades of the same polymer. Suitable grades of -

polyethylene include, for example, P80 and P100. As an example of the use of different grades, an excellent -

30 electrofusion fitting may be formed having end sections formed from P80 polyethylene and a central section formed -

from P100 polyethylene.

The or each hollow sleeve member may be of constant 35 diameter throughout its length, but the invention also -

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r 5 includes the possibility that one or more of the sleeve members may comprise at least two regions of different diameter separated by a "step" region. The hollow sleeve members can be formed by any suitable method, including, 5 for example, extrusion and injection moulding.

The electrical heating element or elements may be disposed about the inner wall of the body of the fitting by any suitable means, but preferably it or they is/are 10 inserted by the technique of "wire ploughing". In this technique a cutting tool makes a helical groove around the internal surface of a hollow member and a heating wire is then inserted into the groove so formed. Various techniques for wire ploughing are known and are 15 described, for example, in GB2135747, GB2148158, and GB2298466. The entire disclosures of all these patents

are incorporated herein by reference for all purposes.

In GB2135747, for example, a weldable pipe fitting is 20 formed from a thermoplastic sleeve by incising around the internal wall of the sleeve a helical cut inclined to the surface of the wall along the line of the cut, the cutting tool and its angular relationship to the bore of the sleeve being chosen such that during incision an 25 internally extending flap of thermoplastic material produced by the incision is caused to open out and deform transversely to the direction of incision whereby a helical cavity is formed within the sleeve wall. An electrically conducting wire is fed into the cavity and 30 the ends anchored.

Preferably the inner wall of the body of the composite electrofusion fitting is skimmed or machined before or after the insertion of the electrical heating element, or 35 both. Machining or skimming after insertion is useful in . . .,,,.,, 4,.

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order to remove any excess material from the edges of the surface grooves and to ensure full coverage of the buried lead-in portion of the electrical heating element.

Machining or skimming has the additional advantages that 5 it can at the same time remove any weld bead formed on the internal wall by the butt fusion process, any other excess polymeric material or distortions of the fusion wall of the fitting, and any dirt that may have lodged on the internal wall of the fitting after moulding but prior 10 to insertion of the heating element.

In the first aspect of the invention, the electrical heating element extends across a butt-fused region of the body. In effect, this means that the butt-fused region 15 generally lies within the heated region of the electrofusion fitting. The butt-fused region is thereby supported and reinforced by the electrical heating element and by the underlying pipe in the assembled pipe joint. Moreover, the heating of the fitting to fuse the 20 inner surface adjacent to the electrical heating element can also help to heal any weakness and improve the butt fusion joint. In a preferred arrangement, the axial length of the electrical heating element exceeds the axial length of the butt-fused region, so that the 25 electrical heating element straddles the butt-fused region and extends for a distance on either side of the butt-fused region. Preferably the axial length of the electrical heating element is at least 5 times, and more preferably at least 20 times, the axial length of the 30 butt-fused region. The butt-fused region may be centrally disposed with respect to the electrical heating element, but this is not essential, provided that there is a sufficient degree of overlap.

35 The electrical heating element preferably comprises a ...,,,.. ..

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1 1 coil of resistance wire, which is disposed about the inner wall of the body of the fitting. For example, in a preferred construction, the coil of resistance wire is embedded in the wall of the body so as to extend across a 5 butt-fused region of the body. The resistance, or impedance, of the electrical heating element is such that, when powered by a direct or alternating current, the element will heat up, causing local fusion of the inner surface of the hollow body to the outer surface of 10 the pipe, so as to fuse the sleeve member to the pipe.

The electrical element is normally provided with two electrical terminals for connection to a suitable power source, such as a generator. More than two such 15 terminals may of course be provided if necessary. The terminal 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 body and the 20 connections to the electrical heating element are made through the thickness of the body.

A specific embodiment of an electrofusion pipe fitting according to the invention will now be described, by way 25 of example only, with reference to and as illustrated in Figure 1 of the accompany Drawings, which shows the fitting in sectional side elevation.

The electrofusion pipe fitting, illustrated generally at 30 1, is an inline electrofusion coupler having a body 2 and electrical heating elements 3, 3', comprising coils of resistance wire 4, 4'. The composite body comprises end sections 5, 5' and a mid-section 6. End sections 5, 5' are injection moulded from P80 polyethylene and 35 central section 6 is injection moulded from P100 . . i,. .,,, i,...

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l polyethylene. The designations "P80" and "P100" refer to pressure retention characteristics, and the invention provides the possibility of manufacturing an electrofusion fitting with a mid-section having higher 5 pressure retention characteristics without increasing the wall thickness above that of the end sections.

The coils 4, 4' of the electrical heating elements 3, 3' are connected to terminals 7, 7' positioned within 10 upstanding turrets 8, 8'. A stop means 9 is moulded into the internal wall of the mid-section 6, serving to limit the travel of the pipe ends inserted into the fitting.

End sections 5, 5' and mid-section 6 are butt-fused 15 together, the butt fusion regions being indicated at 10, 10'. External beads 11, 11' are shown in the figure, although it will be appreciated that these could be removed by machining or skimming if desired.

20 In the method of the invention, end sections 5, 5' and mid-section 6 are independently injection moulded and then butt-fused together by conventional means. Butt fusion results in the formation of external beads 11, 11', and corresponding internal beads (not shown). The 25 internal beads are preferably removed by machining or skimming before insertion of the electrical heating elements. The electrical heating elements 3, 3' are then inserted by wire ploughing, and connected to external terminals 7, 7'. In the embodiment as shown, the coils 30 4, 4' are electrically connected together by connecting wire 12. It can be seen that the wire ploughing technique disposes the coils 4, 4' about the internal periphery of the body 2 and beneath the surface thereof.

A final skimming or machining operation can remove any 35 excess plastics material created by the wire ploughing .. , .,., i, /, , Hi,,,.I,

g process. As shown, the butt fusion regions 10, 10' are axially positioned about two thirds of the way along their 5 respective electrical heating elements 3, 3'. It will be appreciated that other arrangements are also possible, depending upon the relative dimensions of the components of the electrofusion fitting.

10 In the jointing step, polyethylene pipes, which may be cross-linked or uncross-linked, are inserted into the ends of hollow sections 5, 5' until they abut against the stop member 9. The terminals 7, 7' are then connected to a generator and electrofusion effected in the usual way.

15 It is found that the wire coils 4, 4' provide a substantial reinforcement for the butt-fused regions 10, 10' and after electrofusion the butt-fused regions 10, 10' become fused directly to the underlying pipes, thus providing further reinforcement.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application

and which are open to public inspection with this 25 specification, and the contents of all such papers and

documents are incorporated herein by reference.

All of the features disclosed in this specification

(including any accompanying claims, abstract and 30 drawings), and/or all of the steps of 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.

35 Each feature disclosed in this specification (including

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i 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 5 feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any 10 novel one, or any novel combination, of the features disclosed in this specification (including any

accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

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Claims

1. A composite electrofusion fitting comprising a hollow thermoplastic body having an electrical 5 heating element located about an inner wall thereof, the body comprising a plurality of hollow thermoplastic sleeve members butt-fused together, and wherein the electrical heating element is located so as to extend across a butt-fused region 10 of the body.

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2. A fitting according to claim 1, having a diameter of -treater than 250 mm...CLME: 15

3. A fitting according to claim 1 or 2, which comprises three hollow thermoplastic sleeve members butt-fused together to form an in-line coupler.

4. A fitting according to claim 3, in which the hollow 20 thermoplastic sleeve member comprising a mid-section of the body has a mechanical strength higher than that of the end sections of the body.

5. An electrofusion fitting according to any one of the 25 preceding claims, formed from different grades of polyethylene.

6. A fitting according to any one of the preceding claims, wherein the electrical heating element 30 comprises a coil of resistance wire which is disposed about the inner wall of the body of the fitting.

7. A fitting according to claim 6, wherein the wire is 35 embedded in the wall of the body.

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8. A fitting according to any one of the preceding claims, wherein the electrical heating element is disposed about the inner wall of the body of the 5 fitting by wire Sloughing.

9. A fitting according to any one of the preceding claims, wherein the electrical heating element is connected to a terminal disposed on an outer surface 10 of the hollow body.

10. A fitting according to any one of the preceding claims, wherein the electrical heating element straddles the butt-fused region of the body, such 15 that the butt-fused region lies wholly within the heated region of the electrofusion fitting.

11. An electrofusion fitting according to any one of the preceding claims, wherein the axial length of the 20 electrical heating element is at least five times the axial length of the overlying butt-fused region of the body.

12. A fitting substantially as described with reference 25 to and as illustrated in the accompanying Drawing.

13. A composite electrofusion fitting substantially as hereinbefore described.

30

14. A method of manufacturing an electrofusion fitting, the fitting comprising a hollow thermoplastic body having an electrical heating element located about an inner wall thereof, which comprises butt-fusing a plurality of hollow thermoplastic sleeve members 35 together to form a body, and disposing an electrical ... I,,,.,, ..

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heating element about an inner wall thereof, such that the electrical heating element extends across a butt-fused region of the body.

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15. A method according to claim 14 r wherein the electrical heating element is disposed about the inner wall of the body of the fitting by wire ploughing. 10

16. A method according to claim 14 or 15, wherein the inner wall of the body of the composite electrofusion fitting is skimmed or machined before or after the insertion of the electrical heating element, or both.

17. A method according to any one of claim 14 to 16, substantially as hereinbefore described.

18. A fitting according to any one of claims 1 to 13 20 manufactured by a method according to any one of claims 14 to 17.

19. A composite electrofusion fitting comprising a hollow thermoplastic body having an electrical 25 heating element located about an inner wall thereof, the body having a diameter of 150 mm or greater, and comprising a plurality of hollow thermoplastic sleeve members of dissimilar polymeric materials butt-fused together, at least one of the sleeve 30 members having a higher mechanical strength than the other or others, and being positioned where such strength is required to give the desired mechanical strength to a pipe joint made using the fitting.

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20. A fitting according to claim 19, comprising three . A\,,,,

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hollow thermoplastic sleeve members butt-fused in line.

21. A fitting according to claim 19 or 20, wherein the 5 mid-section of the body has a higher mechanical strength than the end sections of the body.

22. A fitting according to any one of claims 19 to 21, which is formed from different grades of the same 10 polymer. ,,..:.

23. A fitting according to claim 22, wherein the polymer is polyethylene.

15

24. A fitting according to any one of claims 19 to 23, which has been formed by a method according to any of claim 14 to 17.

25. A fitting according to any one of claims 19 to 24 20 substantially as hereinbefore described with reference to and as illustrated in the accompanying Drawing.

26. A composite electrofusion fitting according to claim 25 19 substantially as hereinbefore described.

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