Method of manufacturing an electrofusion coupler

Abstract: In the manufacture of an electrofusion coupler, a winding (2) of an electrical resistance heating wire is wound directly around a mandrel (10) which comprises two parts providing respective ends of the mandrel. The mandrel supports electrically conducting terminal elements (5,6) by means of supporting locations (11) on the mandrel parts which form an integral part of the mandrel. The resistance wire (2) wound around the mandrel is connected to the electrically conducting terminal elements (5,6). Subsequently a body of thermoplastics (1) is moulded around the mandrel to form the electrofusion coupler, and thereafter the mandrel parts are extracted axially from the electrofusion coupler from opposite ends, leaving the winding (2) and terminal elements (5,6) in place in the electrofusion coupler. In a variant, a thermoplastic preform (3) is manufactured having electrically conducting terminal plates (5) secured thereto, the preform having an electrical resistance heating wire (2) wound therearound and secured to said terminal plates. An outer thermoplastics jacket (1) is then moulded around the wound preform (3) and said terminal plates (5), with bores being formed in said outer jacket extending to holes in the terminal plates. Subsequently electrical terminals having screw-threaded shanks (9) are screwed into said bores and into electrical contact with said terminal plates (5).

Description: THIS INVENTION relates to a method of manufacturing an electrofusion coupler for use in the construction of thermoplastics pipe systems wherein a welded joint between adjoining ends of adjoining sections of plastics pipe, or of such a pipe section and a tubular member forming part of the pipe fitting, valve or the like, is obtained by forcing such adjoining ends into such an electrofusion coupler and energising the same. Such an electrofusion coupler takes the form of a sleeve of thermoplastics material having an electrical resistance heater embedded therein and extended around the sleeve. When adjoining pipe ends or the like are forced into the sleeve from opposite ends and the resistance heating wire, and thus the sleeve, is subsequently heated by passing an electric current through the wire, both the material of the sleeve and the material of the inserted pipe ends or the like are locally softened and fused, whereby an intimate connection is obtained, in the form of a welded joint which, when the assembly has cooled, is leak-tight to fluids. The coupler remains in situ forming a permanent part of the joint. Typically, the electrical resistance wire takes the form of coil embedded in the thermoplastics sleeve and coaxial therewith, the wire lying close to the inner surface of the sleeve, the ends of the wire being connected to terminal points, exposed on the exterior of the sleeve for connection to a source of electrical current. British Gas Corporation British Patent No. 2090588 discloses a method of manufacturing an electrofusion coupler of the above-noted character in which a tubular thermoplastics preform, destined to form the radially inner part of the electrofusion coupler, is first formed by injection moulding and is subsequently mounted on a rotatable winding mandrel by means of which the preform is rotated about its axis to wind on its outer surface a helical winding of electrical resistance heating wire fed thereto by a guide. The guide incorporates a heater by means of which the wire is heated electrically as it is wound on the preform so that as it is wound on it melts the outer surface of the preform when it touches the same and thus becomes at least partially embedded in the preform. The wire guide incorporates an electrical heater which heats the wire as it passes therethrough onto the preform. The preform is provided with terminal pegs at either end, the free end of the wire being attached to the terminal peg at one end before winding commences and the wire being attached at its other end to the other terminal peg after winding. The wound preform is then inserted within a mould in which an outer encapsulating jacket of thermoplastics material is injection moulded therearound, becoming united with the preform, the now integral preform and encapsulating jacket forming the finished electrofusion coupler. FR-A-221679 discloses a method of manufacturing an electrofusion coupler, comprising providing a thermoplastic preform having peripheral grooves to receive resistance heating wire, and having apertures adjacent its ends for receiving terminal plates around which ends of the wire can be wrapped and having electrical contacts upstanding therefrom, the method including winding such heating wire around the preform, to lie in said grooves, winding the wire ends around the terminal plates, fitting the terminal plates in their apertures, and injection moulding an outer thermoplastics jacket around the wound preform and the terminal plates, the jacket having sockets into which the upstanding electrical contacts project. EP-A-0260014 discloses a method of manufacturing an electrofusion coupler in which a mandrel is provided comprising two cylindrical parts disposed end to end, each having a radially extending pin over which a respective hollow terminal can be placed. Electrical resistance heating wire is wound directly around the mandrel and its ends secured to respective ones of the hollow terminals, after which the assembly is placed in an injection mould, side cores are extended into the mould cavity over free end parts of the terminals, and thermoplastics injected into the mould cavity to form the electrofusion coupler. The side cores are then extracted, the mould opened and the mandrel parts extracted axially from the electrofusion coupler after inward radial withdrawal of the terminal-supporting pins into the mandrel parts. In a variant, the hollow terminals are secured to the mandrel parts by screws which are extracted before the mandrel parts are withdrawn. In a further variant, solid terminals are used having shearable stem portions which are extended into radial bores in the mandrel parts and are sheared by withdrawal of the mandrel parts from the electrofusion coupler. The invention relates to methods of manufacturing electrofusion couplers in which no plastics preform is utilised, the electrical heating wire being wound directly around a mandrel which subsequently forms the core of a mould in which the plastics body of the electrofusion coupler is moulded around the core and said winding. Thus, in accordance with the invention, there is provided a method of manufacturing an electrofusion coupler comprising providing a mandrel having integral supporting formations, supporting electrically conducting terminal elements on the mandrel by means of said supporting formations, winding an electrical resistance heating wire around the mandrel, connecting the resistance wire to the electrically conducting terminal elements, placing said mandrel, with the terminal elements and said winding, within an outer mould, so that a mould space is defined between the outer mould and the mandrel, extending side cores through said space to engage said terminal elements, subsequently injecting molten thermoplastics material into the space between the mandrel and the outer mould to form the electrofusion coupler, the side cores thus defining generally radially extending sockets in the moulded coupler which terminate at their inner ends in said terminal elements, retracting the side cores, opening the mould and extracting the mandrel from the electrofusion coupler leaving the winding and terminal elements in place in the electrofusion coupler, and wherein said mandrel comprises two parts, each having a cylindrical or frusto-conical surface, characterised in that each said part has a respective collar portion defining a respective end of the electrofusion coupler, each said supporting formation stands proud of the cylindrical or frusto-conical surface of the mandrel part and extends from the respective said collar in a direction parallel with the mandrel axis, each said formation and its supported terminal element being of such shapes as to allow the terminal element to be slid axially from its supporting formation, to allow the respective said part of the mandrel to be extracted axially from the moulded electrofusion coupler. Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which:- FIGURE 1A is a partial view in axial section of a mandrel or core, the thermoplastics body of an electrofusion coupler moulded around the core, a side core, a terminal plate and part of an electrical resistance heating winding of the electrofusion coupler, all in accordance with an embodiment of the invention, FIGURE 1 B is a partial view of the mandrel and a terminal plate in partial cross-section along the axis of the side core in Figure 1A, FIGURE 1C is a partial axial section view of the finished electrofusion coupler of Figure 1A, along the axis of an electrical terminal thereof, FIGURE 1D shows in end view in the upper part of the figure and in plan view (in the lower part of the figure) an insert segment used in the electrofusion coupler of Figure 1A, FIGURE 2A is a partial axial section view similar to Figure 1A but illustrating the manufacture of a third form of electrofusion coupler embodying the invention, FIGURE 2B is a partial axial section view of the third embodiment illustrating assembly of a terminal arrangement, FIGURE 2C illustrates an alternative terminal arrangement for the electrofusion coupler of Figures 2A and 2B, FIGURE 3A is a view similar to Figures 1A and 2A but showing the manufacture of a still further form of electrofusion coupler embodying the invention, FIGURE 3B is a partial view in cross section through the axis of the side core in Figure 3A, FIGURE 3C is a plan view of a terminal plate and attached heating wire, and FIGURE 3D is a partial axial section view corresponding to Figure 3A, but showing the finished electrofusion coupler with the mandrel or core removed. Referring to Figures 1A, 1B, 1C and 1D, there is illustrated schematically a method of manufacturing an electrofusion coupler. In this method, resistance heating wire 2 is wound directly around a mandrel 10 with said resistance heating wire being under longitudinal tension. The wire 2 is connected to electrically conducting elements or terminal plates 5. The mandrel 10 is in two parts which are removed axially, in opposite directions, from opposite ends of the moulded electrofusion coupler (see below). A respective terminal plate 5 is located adjacent each end of the finished electrofusion coupler. Accordingly a respective terminal plate 5 is carried by each mandrel part by a respective projection 11 which stands proud of the cylindrical or frusto-conical surface of the mandrel part in the region which adjoins the respective end of the electrofusion coupler subsequently moulded around the mandrel. The projection 11 includes a pair of parallel arms which are cantilevered from a root part of projection 11 in a direction towards the middle of the mandrel, parallel with the mandrel axis, whereby a space, into which the plastics material moulded around the mandrel can flow, is defined between these parallel arms and the curved mandrel surface. The parallel arms are spaced apart circumferentially of the mandrel and each has, along its side facing the other, a longitudinal groove to receive a respective lateral edge portion of terminal plate 5 when the plate is slid into the space between these parallel arms. The terminal plate 5 has tags 6 which are mechanically crimped around the heating wire at the appropriate stage in winding the wire around the mandrel. Thus the terminal plate 5 may be fitted between its parallel arms before the wire is engaged with said tags or the terminal plate tags may be crimped around the wire before the terminal plate is slid into place between the respective parallel arms. In either case, the aforementioned connections of the wire to the electrically conducting elements 5 serve to maintain the longitudinal tension in the resistance heating wire. The wire is then cut, as before, between the wire source and the mandrel and the wound mandrel is then encapsulated in thermoplastics in a moulding operation thus forming the electrofusion coupler 1. Just prior to moulding, a side core 12 of the mould is extended radially through a central aperture in the terminal plate 5 as shown in Figure 1A. This side core 12 has a relatively thin end portion which fits the aperture in terminal plate 5 and forms the hole into which the shank 9 (Figure 1C) of an outwardly projecting terminal 7 screws and a portion of greater diameter which defines, in the moulded product, the inner surface of a moulded socket surrounding terminal 7 and adapted to receive an electrical connector. After the thermoplastics material has been injection moulded around the mandrel, the side cores 12 are withdrawn radially and the mandrel core parts are extracted axially from the moulded product. On extraction of the mandrel 10 from the encapsulated electrofusion coupler 1, recesses are left in the end faces of the electrofusion coupler by the projections 11. These recesses are subsequently filled by inserting into each an insert segment 13 (shown in Figure 1D) having incorporated on them gripping quadrants or barbs 14 which prevent the insert segments from becoming dislodged. The insert segments, for example of plastics, isolate electrically the parts of terminal plates 5 exposed within said recesses. Finally, or if preferred prior to insertion of segments 13, a terminal 16, in the form of screw having an elongate plain enlarged head forming a terminal prong, and having a self-tapping screw shank, is screwed into the respective bore left by each side core until it passes into the hole in the respective terminal plate 5 to make good electrical contact with plate 5 and thus with wire 2. Referring to Figures 2A, 2B and 2C, there is illustrated schematically a variant of the method described with reference to Figures 1A to 1D. In this variant the terminal arrangement at each end of the electrofusion coupler comprises a generally cylindrical metal body 25, for example of brass, which has an annular groove therearound adjacent one end (the inner or lower end as viewed in Figures 2A to 2C). The cantilevered arms of projection 11 are in this case so dimensioned and spaced apart as to fit snugly in the groove 27, on either side of the body 25, when the latter is located between said arms, whereby the body 25 is supported in a position in which it extends radially outwardly with respect to the central axis of the mandrel as illustrated in Figure 2A. The body 25 has a diametral through bore through which the heating wire 2 can be threaded and has an axial, screw threaded bore extending from its end further from groove 27 to receive a clamping screw by means of which the wire 2 can be clamped within body 25. In the arrangement illustrated in Figures 2A and 2B, prior to and during the moulding step, the resistance heating wire 2 is held in bodies 25, and thus in tension around the mandrel, by a grub-screw 18, which is removed after the encapsulation moulding process and replaced by a screw-in terminal prong, referenced 26. As shown in Figure 2A, a respective side core 12 of the mould, which defines the recess in the finished product within which the respective terminal prong is located, engages the outer end of the respective body 25 and assists in holding the latter in place during moulding. It will be appreciated, of course, that the side core could be formed with an elongate bore to receive the head of prong screw 26 so that the screw 26 could be used from the start for clamping wire 2, dispensing with the need for a separate grub screw. In another possible arrangement, illustrated in Figure 2C, the clamping of the heating wire in the body 25 is effected by a side-action clamping screw 29 screwed into a screw threaded bore extending radially, perpendicular to the diametral bore through which wire 2 passes. In such an arrangement, the contact prong may, if desired, be integral with body 25. Referring to Figures 3A, 3B and 3C, there is illustrated schematically a further variant of the method of Figure 1. In this variant a contact plate 5, having again a central aperture, is so supported during moulding of the electrofusion coupler that, after moulding, the central portion of the plate 5, including the central aperture and the region surrounding it, is exposed on the radially inner side of the contact plate within a radially extending recess opening onto the wall of the main bore in the electrofusion coupler, and a terminal pin is screwed through the central aperture in plate 5 and through an aligned radial side bore from within the main bore, to project, as a contact prong, on the outside of the electrofusion coupler. Thus, in this variant, the projection 11 from the mandrel has the cross-sectional form shown in Figure 3B, i.e. has the form of a longitudinally extending rib which flares slightly towards its radially outer surface to have a dovetail shape. The terminal plate 5 has, in cross-section (Figure 3B) the form of an inverted channel with side walls which converge towards the channel mouth so that the channel has a cross section complementary with that of the outer part of rib 11 whereby the plate 5 can be slid longitudinally over the outer end of rib 11 to be retained reliably thereon during moulding. The rib 11 has a radial bore which aligns with the central aperture in plate 5 and receives the radially inner end of a minor diameter portion of a side core 12 of the mould which is extended radially through the central aperture in the plate 5 and into the bore in rib 11 prior to moulding the electrofusion coupler, in the injection mould, around the mandrel. The mandrel again has an outer portion of larger diameter, to define a contact prong recess in the finished coupler. As best shown in Figures 3A and 3C, the plate 5 again has a tag which is crimped around the wire 2 to secure the tag to the wire. With the wire 2 wound around the mandrel and crimped in the tags of the plates 5 fitted to the ribs 11 and with the wound mandrel located within the injection mould and the side cores extended through the plates 5 and into the bores in ribs 11, the thermoplastics body of the electrofusion coupler is moulded around the wound mandrel. The side cores are then withdrawn radially and the mandrel parts withdrawn axially whereby the ribs 11 are slid out of their plates 5, leaving the latter held captive by the moulded plastics. However, a radially extending recess, corresponding to the respective rib 11 and extending as far as the radially inner surface of each plate 5 is left extending from the wall of the main bore of the electrofusion coupler. There is now screwed through the central aperture in each plate 5 and into the respective aligned radial bore left by the side core in the plastics material, from the main bore, a respective terminal screw having a slotted head, which engages the radially inner surface of plate 5, a self-tapping screw-threaded shank portion adjoining the slotted head, and which self-tapping shank portion forms a complementary screw thread in the respective radial bore in the plastics body, and a plain shank portion, of reduced diameter relative to the self-tapping shank portion, and which projects into the recess in the plastics body defined by the larger diameter part of the respective side core and which plain shank portion forms a respective contact prong.

Claims: A method of manufacturing an electrofusion coupler comprising providing a mandrel (10) having integral supporting formations (11), supporting electrically conducting terminal elements (5, 25) on the mandrel by means of said supporting formations, winding an electrical resistance heating wire (2) around the mandrel, connecting the resistance wire to the electrically conducting terminal elements (5, 25), placing said mandrel (10), with the terminal elements and said winding, within an outer mould, so that a mould space is defined between the outer mould and the mandrel, extending side cores (12) through said space to engage said terminal elements (5, 25), subsequently injecting molten thermoplastics material into the space between the mandrel and the outer mould to form the electrofusion coupler, the side cores thus defining generally radially extending sockets in the moulded coupler which terminate at their inner ends in said terminal elements, retracting the side cores (12), opening the mould and extracting the mandrel (10) from the electrofusion coupler (1) leaving the winding and terminal elements in place in the electrofusion coupler, and wherein said mandrel comprises two parts, each having a cylindrical or frusto-conical surface, characterised in that each said part has a respective collar portion defining a respective end of the electrofusion coupler, each said supporting formation (11) stands proud of the cylindrical or frusto-conical surface of the mandrel part and extends from the respective said collar in a direction parallel with the mandrel axis, each said formation and its supported terminal element being of such shapes as to allow the terminal element (5, 25) to be slid axially from its supporting formation (11), to allow the respective said part of the mandrel to be extracted axially from the moulded electrofusion coupler. A method according to claim 1, wherein each said side core (12) has a larger diameter portion to define a terminal socket, extending into the electrofusion coupler from its outside and a smaller diameter end portion to define, in the moulded electrofusion coupler, a narrower bore extending inwardly from said terminal socket, and each said terminal element (5) has a hole therethrough which extends generally radially with respect to the mandrel when the terminal element is mounted on its supporting formation (11) on the mandrel, said side cores (12) being so positioned that the inner ends of said smaller diameter end portions thereof are aligned with, and engage in, the respective holes in the respective terminal elements (5) at the end of said step of extending said side cores (12) into said space, the method including providing electrical terminal pins (7) having screw-threaded shanks (9), and including the step, following opening of the mould and extraction of the mandrel parts from the electrofusion coupler, of inserting respective said terminal pins (7) into respective said sockets, and said screwthreaded shanks (9) through respective said narrower bores in the moulded electrofusion coupler, and screwing said shanks into respective said holes in the respective said terminal elements (5). A method according to claim 2 wherein said side cores (12) are extended into said holes in said terminal elements (5) mounted on their supporting formations (11) before the outer mould is closed above said terminal elements and said side cores. A method according to claim 1, wherein each said terminal element (25) is in the form of a body having a bore therethrough to receive said wire (2) and a transverse intersecting screw-threaded bore to receive a clamping screw (16, 26) for clamping said wire (2) in the first-mentioned bore. A method according to claim 4 including the step of locating contact pins (16, 26) in said sockets by screwing screw-threaded portions of the contact pins into said screw-threaded bores. A method according to any preceding claim wherein each said supporting formation (11) includes a root part adjoining said collar of the respective mandrel portion, and a pair of parallel arms which are cantilevered from said root part in a direction towards the middle of the mandrel (10), parallel with the mandrel axis, whereby a space into which molten plastics material can flow is defined between these parallel arms and the mandrel surface, the parallel arms being spaced apart circumferentially of the mandrel. A method according to claim 6 wherein each of the parallel arms of each said supporting formation (11) each has, on its side facing the other arm of that formation, a respective longitudinal groove and wherein said terminal elements (5) comprise terminal plates, the longitudinal grooves of the arms of each supporting formation receiving a respective lateral edge portion of the respective terminal plate when the terminal plate is supported by the supporting formation (11), each terminal plate having a central aperture to receive an end portion of the respective side core (12). A method according to claim 6 wherein each said terminal element (25) comprises a generally cylindrical metal body which has an annular groove (22) therearound adjacent one end, the cantilevered arms of the supporting formation (11) being so dimensioned and spaced apart as to fit snugly in the groove (27), on either side of the metal body, when the latter is located between said arms to be supported thereby.

Inventors: BARFIELD MALCOLM RAYMOND, BARFIELD, MALCOLM RAYMOND
Applicants: GLYNWED PIPE SYSTEMS LTD, GLYNWED PIPE SYSTEMS LIMITED
Application year: 1995
Main classification: B29D23
IPC codes: B29L23, B29C65, B29D23, F16L47, B29L31