Electrofusion joint and hot water supply header using the same

Abstract: The improved electrofusion joint and header for supplying hot water that perform satisfactorily at elevated temperatures as evidenced by high heat resistance, that exhibit good sealing property and that can be handled efficiently in mounting and various other operations have a crosslinked thermoplastic resin layer and at least one joining portion which comprises a non-crosslinked thermoplastic resin layer that is formed as an integral part of said crosslinked thermoplastic resin layer in the area where it contacts a tubular member to be joined, and a heating electric wire provided either within or on the outer or inner surface of said non-crosslinked thermoplastic resin layer. Such electrofusion joint and header are applicable to any part of a piping system for supplying hot water and they will withstand use for a prolonged period.

Description: The present invention relates to an electrofusion joint with which members such as polyolefin pipes, in particular, conduits for supplying hot water are joined or connected either to themselves or to the lateral side of other conduits. The present invention also relates to an electrofusion joint fitted with a connecting member for establishing connection to terminals such as nozzles on a conduit header. The present invention further relates to a header for distributing hot water from a heat source providing apparatus such as a hot water supplier to more than one site of use. Pipes made of crosslinked polyolefins such as silane-crosslinked polyethylene are used as conduits for supplying hot water. Crosslinked polyolefins perform satisfactorily at elevated temperatures as evidenced by high heat resistance and good high-temperature creep characteristic and have a shape-retaining capability. However, unlike non-crosslinked polyolefins, crosslinked polyolefins cannot be fused to members to be joined. Hence, electrofusion joins used to connect non-crosslinked polyolefin pipes are not applicable to crosslinked polyolefin pipes. It is also impossible to form electrofusion joints using crosslinked polyolefins. Therefore, crosslinked polyolefin pipes are currently joined by means of mechanical couplings, or joints that rely upon mechanical couplings are produced from crosslinked polyolefins. However, mechanical joints used in connecting hot water pipes which require high strength to withstand high operating pressures involve a complicated structure and cannot be handled efficiently in piping work. Further, compressive sealing performed with these mechanical joints causes the disadvantage that their performance will decrease with time as exemplified by deterioration in the reliability of sealing due to creeping in pipes or stress relaxation of pipes and sealants. Further, if thin-walled resin pipes are connected by conventional electrofusion joints, the joined portions will thermally deform and bulge inwwardly to restrict the fluid passage. An electrofusion joint formed of a thermoplastic resin is known that is provided with a fine orifice in the body of the joint, through which the resin that has become molten when a member of interest is joined by fusion will come out to provide a measure for checking whether said member has completely fused to the joint (see, for example, Unexamined Published Japanese Patent Application No. 61-62696). However, being formed of a kind of thermoplastic resin, this prior art electrofusion joint has the disadvantage that the molten resin coming out of the orifice has the same color as the surrounding resin of which the joint is formed and that extrusion of this resin is difficult to identify. Thus, the time at which fusion has been completed cannot be detected precisely. Further, connecting terminals such as nozzles on a conduit header are usually metallic and it is difficult to connect them to crosslinked thermoplastic resin pipes. Fig. 23 is a diagram showing a piping system for supplying hot water. Shown by 81 in the diagram is a header by which hot water from a heat source providing apparatus 82 such as a hot water supplier is distributed to a faucet 83 in the kitchen, a faucet 84 in the lavatory, a faucet 85 in the bathroom, and other outlets. The heat source providing apparatus 2 receives water from a supply pipe 86, heats it by burning the gas supplied through a gas pipe 87, and supplies the heated water through a hot water main 88 to the header 81. Header 81 is shaped of a metal in hollow form and has a single receptacle 91 on the inlet side and a plurality of receptacles of same diameter 92a, 92b, 92c, 92d, ... on the outlet side. The receptacle 91 on the inlet side is connected to the hot water main 88 by fastening means such as screws, whereas the receptacles 92a, 92b, 92c, 92d, ... on the outlet side are connected to branch pipes 93a, 93b, 93c, 93d, ... by fastening means such as screws. The branch pipes 93a, ... have such bore diameters that faucets 83, 84, 85, ... are supplied with hot water in the necessary flow rates that correspond to the capacities of the respective faucets. The conventional header 81 has had several problems on account of the fact that it is formed of metal. First, it is liable to corrosion and is heavy. Second, it is difficult to connect to plastic pipes and is not suitable for large-scale production. Further, the header 81 fitted with a plurality of receptacles of same diameter 92a, ... on the outlet side has to be connected to branch pipes 93a, ... of smaller diameter by means of reducers and this has been another factor that makes the header unsuitable for large-scale production. FR-A-2,606,487 discloses an electrofusion joint in which a meltable layer is provided around the entire internal surface of the joint. EP-A-0,333,379 discloses an electrofusion joint made entirely of non-crosslinked polyolefin or in which the layer of non-crosslinked polyolefin covers the entire internal surface of the joint. Therefore, a first aim of the present invention is to provide an electrofusion joint that uses a crosslinked thermoplastic resin such as a crosslinked polyolefin to provide enhanced heat resistance, that yet allows for fusion to insure enhanced sealing property and that can be handled with efficiency. A second aim of the present invention is to provide an electrofusion joint that has not only the features described above but also a capability for fusion without causing thermal deformation of the member to be joined. A third aim of the present invention is to provide an electrofusion joint that uses a crosslinked thermoplastic resin to provide enhanced heat resistance, that enables the operator to easily check the completion of joint fusion, thereby insuring that member to be joined is completely fused to the joint to provide enhanced sealing performance, and that can be handled with efficiency. A fourth aim of the present invention is to provide an electrofusion joint fitted with a connecting member that uses a crosslinked thermoplastic resin to provide enhanced heat resistance, that yet allows for fusion to insure enhanced sealing performance, that enables crosslinked thermoplastic resin pipes to be easily joined to connecting terminals such as nozzles on a conduit header, and that can be handled with efficiency. A fifth aim of the present invention is to provide an electrofusion joint fitted with a connecting member that has not only the features described above but also a capability for fusion without causing thermal deformation of the member to be joined. A sixth aim of the present invention is to provide an electrofusion joint that uses a crosslinked thermoplastic resin to provide enhanced heat resistance, that yet allows for fusion to insure enhanced sealing performance, that can be connected to the lateral side of a conduit at will, and that can be handled with efficiency. A seventh aim of the present invention is to provide a header for supplying hot water that is lightweight and corrosion-resistant, that can be easily connected to plastic pipes, and that is suitable for large-scale production. An eighth aim of the present invention is to provide a header for supplying hot water that is lightweight and corrosion-resistant, that can be easily connected to plastic pipes having different bore diameters, and that is suitable for large-scale production. According to the present invention there is provided an electrofusion joint comprising a main body portion comprised of a crosslinked thermoplastic resin layer and integrally moulded therewith at least one joining portion which is adapted to be heat-welded to a tubular member, wherein said joining portion comprises a non-crosslinkable thermoplastic resin, and has an electrical heating wire disposed thereon or embedded therein and is embedded in at least one major surface of said main body; characterised by: a supporting portion, a groove into which a tubular member is to be inserted being defined between the supporting portion and the surface of said main body wherein the joining portion is embedded, and in that said joining portion does not extend to the extreme end of the electrofusion joint. Optionally according to the present invention, said crosslinked thermoplastic resin layer and the non-crosslinked thermoplastic resin layer on the inner surface thereof have different colours, which crosslinked thermoplastic resin layer has a fine orifice that extends from its outer surface to a point close to the boundary between said crosslinked thermoplastic resin layer and said non-crosslinked thermoplastic resin layer. According to the present invention, said electrofusion joint may further include a connecting portion comprising a tubular crosslinked thermoplastic resin layer and a connecting member that is secured to said crosslinked thermoplastic resin layer by being inserted inwardly or outwardly of the same. The present invention also provides a header for distributing hot water from a heat source, comprising a header body comprising a crosslinked thermoplastic resin, said header body being provided with at least one inlet and at least one outlet; wherein at least one of said at least one inlet and at least one outlet of said header body has a joining portion which is to be heat-welded to a tubular member; said joining portion comprises a non-crosslinkable thermoplastic resin, has an electrically conductive heating wire disposed thereon or embedded therein, and does not extend to an extreme end of the inlet or outlet; said joining portion is integrally moulded with said header body; said joining portion is embedded in the interior surface of said at least one inlet or outlet; and said header body has a supporting portion defining a groove, into which the tubular member is to be inserted, with the interior surface of said main body in which the joining portion is embedded. The present invention further provides a method of manufacturing an electrofusion joint comprising a main body portion having a supporting portion and comprising a crosslinked thermoplastic resin and at least one joining portion comprising a non-crosslinkable thermoplastic resin which is to be heat-welded to a pipe, said joining portion being embedded in an interior surface of said main body, a groove into which a tubular member is to be inserted being defined between the supporting portion and the surface of said main body wherein the joining portion is embedded; the method comprising the steps of disposing in an injection mould said at least one joining portion having an electrically heating wire disposed thereon or embedded therein and not extending to an extreme end of said electrofusion joint; and injecting into said mould an uncrosslinked crosslinkable thermoplastic resin and crosslinking said uncrosslinked crosslinkable thermoplastic resin to form said main body portion comprising said crosslinked thermoplastic resin. The present invention will be further explained hereinafter with reference to the following description of exemplary embodiments and the accompanying schematic drawings, in which: Figs. 1, 2 and 3 are partial fragmentary views of three examples of an electrofusion joint described for reference purposes; Figs. 4 and 5 are of two examples of an electrofusion joint according to an embodiment of the present invention; Figs. 6, 7 and 8 are cross sections of three examples of an electrofusion joint equipped with a connecting member according to another embodiment of the present invention; Figs. 9 and 10 are partial fragmentary front views of two examples of a header for supplying hot water; Figs. 11 and 12 are partial fragmentary front views of two examples of a header for supplying hot water; Fig. 13 is a diagram showing an illustrative piping system for supplying hot water. The present invention is described in detail below. In the electrofusion joint and the header for supplying hot water of the present invention, the crosslinked thermoplastic resin layer is adjacent to and integral with the non-crosslinked thermoplastic resin layer. Crosslinked thermoplastic resins such as crosslinked polyolefins do not fuse, so even if a crosslinked thermoplastic resin and non-crosslinked thermoplastic resin such as a non-crosslinked polyolefin are shaped by extrusion molding, injection molding or some other methods, the layers of the respective resins will not fuse together but separate from each other. Instead, if a crosslinkable thermoplastic resin yet to be crosslinked and a non-crosslinked thermoplastic resin are thermoformed into an integral unit and with the crosslinkeble thermoplastic resin being subsequently crosslinked, a laminate which is an integral unit of the crosslinked thermoplastic resin and the non-crosslinked thermoplastic resin will be obtained. The electrofusion joint of the present invention uses this laminate in which the crosslinked thermoplastic resin layer unit. The crosslinked thermoplastic resin has a steric structure created by crosslinking between the molecules of a thermoplastic resin. Crosslinking may be achieved with the aid of a crosslinking agent as in the case of silane-crosslinked thermoplastic resins and divinylbenzene-crosslinked thermoplastic resins. Alternatively, direct crosslinking may be effected by such means as organic peroxides and radiation. The crosslinkable thermoplastic resins yet to be crosslinked according to the present invention comprises polyolefins which have a crosslinking ability created by reacting polyolefins with the crosslinking agent, such as a silane compound, but are not yet crosslinked. The electrofusion joint and the header for distributing hot water from a heat source providing apparatus are fabricated by thermoforming such the crosslinkable thermoplastic resin layer yet to be crosslinked and the non-crosslinked thermoplastic resin layer into an integral unit. Thereafter, the crosslinkable thermoplastic resin layer yet to be crosslinked is crosslinked by including crosslinking reaction by means of a hot water treatment and the like. The non-crosslinked thermoplastic resin is selected from among non-crosslinkable thermoplastic resins such as polyolefins which generally are used as thermoplastic resins. Polyolefins are preferably used as thermoplastic resins of the crosslinkable thermoplastic resin yet to be crosslinked and the non-crosslinked thermoplastic resin in the present invention and illustrative polyolefins include homo- and copolymers of α-olefins having 2-20, preferably 2-12, carbon atoms. Preferred α-olefins include ethylene, propylene, butene-1 and 4-methylpentene-1. The electrofusion joint of the present invention is such that at least one its joining portion is fabricated by the following procedure: the non-crosslinked thermoplastic resin layer having a heating electric wire either within or on its outer or inner surface or having said wire wound onto its surface is inserted into an injection mold cavity; a crosslinkable thermoplastic resin is injected and laminated on said non-crosslinked thermoplastic resin layer; thereafter, the crosslinkable thermoplastic resin layer is crosslinked to form the crosslinked thermoplastic resin layer. The thus fabricated electrofusion joint is mounted on the joining parts of members to be joined such as thermoplastic resin (e.g. polyolefin) tubes in such a way that the non-crosslinked thermoplastic resin layer will contact said members. When an electric current is applied to the electric wire, the non-crosslinked thermoplastic resin layer will melt and fuses to the member to become an integral part of the latter. Members to be joined by the electrofusion joint of the present invention are preferably such that the surface layer or the entire portion is made of a thermoplastic resin, in particular, a miscible thermoplastic resin. Members made of non-crosslinked thermoplastic resins such as polyolefins will exhibit particularly good fusing ability. Figs. 1, 2 and 3 are front views of electrofusion joints, described for reference purposes, with their right half shown in cross section. In each of these drawing, the electrofusion joint 10 has a tubular crosslinked polyolefin layer 12 forming the main body of the joint, and two joining portions that comprise a non-crosslinked polyolefin layer 13 formed as an integral part of said crosslinked polyolefin layer 12 on the inner side thereof at each of the positions where it contacts two members to be joined 15 and 16, and a heating electric wire 14 provided either within or on the outer or inner surface of said non-crosslinked polyolefin layer 13. The members 15 and 16 are pipes having a layer of a thermoplastic resin such as polyethylene. While they may be totally made of fusible thermoplastic resin, pipes formed of a heat-resistant material such as a crosslinked polyolefin should be coated with a fusible thermoplastic resin on the outer surface. The crosslinked polyolefin layer 12 has a tubular structure that surrounds the entire circumference of the members 15 and 16 in their mating portion 17 and nearby areas. The non-crosslinked polyolefin layer 13 is superposed on the inner surface of the crosslinked polyolefin layer 12 in areas at opposite ends thereof in its longitudinal direction that correspond to the members 15 and 16. The heating electric wire 14 is provided either within the non-crosslinked polyolefin layer 13 as shown in Fig. 1, or in its outer surface as shown in Fig. 2, or in its inner surface as shown in Fig. 3. The electric wire 14 is fitted with leads (not shown) so that it can be connected to an external power source also not shown. The electrofusion joint 10 having the construction described above is fabricated by the following procedure: with the heating electric wire 14 buried in or wound around the non-crosslinked polyolefin layer 13, a crosslinkable polyolefin layer containing a crosslinking agent, a crosslinking aid, a catalyst, etc. in a polyolefin is laminated over said non-crosslinked polyolefin layer 13 to form an integral unit, and thereafter, said crosslinkable polyolefin layer is crosslinked to form the crosslinked polyolefin layer 12. The thus fabricated electrofusion joint 10 is mounted in the mating portion 17 of members 15 and 16 and nearby areas in such a way that the non-crosslinked polyolefin layer 13 will contact said members 15 and 16. When an electric current is applied to the electric wire 14 from an external power source connected by leads (not shown), the non-crosslinked polyolefin layer 13 will melt and fuses to the members 15 and 16 to become an integral part of the latter. In the electrofusion joint 10, the tubular crosslinked polyolefin layer 12 forming the main body of the joint is responsible for imparting heat resistance to the joint. Hence, the joint is capable of retaining its own shape in an effective way even if it is used to join hot water supply pipes. Further, the non-crosslinked polyolefin layer 13 which is an integral part of the crosslinked polyolefin layer 12 fuses to the members 15 and 16 to become an integral part thereof. Hence, the joint 10 has good sealing property which is maintained for a prolonged period even if it is used to join hot water pipes. The shapes and structures of the crosslinked polyolefin layer 12 and the non-crosslinked polyolefin layer 13 are not limited to those shown in Figs. 1-3 and various modifications are possible. In the examples shown in these drawings, members 15 and 16 meet directly each other in the mating portion 17 inside the electrofusion joint 10. If desired, the members 15 and 16 may be caused to meet a projection provided on the crosslinked polyolefin layer 12. In the examples shown in Figs. 1-3, the non-crosslinked polyolefin layer 13 having the heating electric wire 14 is provided independently on either side of the mating portion 17 in the areas of contact with the members 15 and 16. Alternatively, a continuous single layer of non-crosslinked polyolefin may be provided to cover the areas of contact with the members 15 and 16 if the electric wire 14 is to be provided on either the outer or inner surface of the non-crosslinked polyolefin layer 13, it may be wound around said non-crosslinked polyolefin layer 13 or the members 15 and 16. In the examples shown in Figs. 1-3, the electrofusion joint 10 connects two members 15 and 16 in a straight line with their ends meeting each other. An embodiment of the present invention is described below with reference to Figs. 4 and 5. The electrofusion joint according to the present invention has not only the constituent elements described above but also a support of the member to be joined which is provided in the joining portion to form a groove into which the end of said member to be joined is to be inserted. The support is preferably provided on the side that faces the non-crosslinked thermoplastic layer. The groove into which the member to be joined is to be inserted is formed in such a way that it opens at the connecting end of the electrofusion joint. The Support of the member to be joined is desirably formed as an integral part of the crosslinked thermoplastic resin layer by being made of a crosslinked or non-crosslinked thermoplastic resin. If desired, the support may be made of other materials. As above, the electrofusion joint according to the second embodiment is fabricated by crosslinking a cross-linkable thermoplastic resin that has been shaped as a laminated integral part of a non-crosslinked thermoplastic resin having a heating electric wire buried in or wound on it. In this embodiment, the support of the member to be joined may be formed as an integral part of either the crosslinkable thermoplastic resin which is to form the crosslinked thermoplastic resin layer or the non-crosslinked thermoplastic resin. The thus fabricated electrofusion joint is used in the following manner: a member to be joined such as a thermoplastic resin tube is inserted at one end into the groove which is open at the connecting end of the joint; the member is mounted in such a way that it contacts the non-crosslinked thermoplastic resin layer and is supported by said support; when an electric current is applied to the electric wire, the non-crosslinked thermoplastic resin layer will melt and fuses to the member of interest to become an integral part of the latter. As the non-crosslinked thermoplastic resin layer melts, the member to be joined such as a thermoplastic resin tube will soften but will not deform since its inner surface is supported by its support. Examples of the embodiment of the present invention are described below in a specific way with reference to drawings. Figs. 4 and 5 are cross sections of two different examples of an electrofusion joint according to the present invention. Except for the groove into which the member to be joined is to be inserted and the support of said member, the electrofusion joints shown in Figs. 4 and 5 have the same construction as the electrofusion joint 10 shown in Fig. 1 and hence, the same components are identified by like numerals and will not be described in detail. Each of the electrofusion joints 20 and 21 shown in Figs. 4 and 5, respectively, has a crosslinked polyolefin layer 12 forming the main body of the joint, non-crosslinked polyolefin layers 13 and heating electric wires 14. Further, these joints have supports 23 of members 15 and 16 to be joined which are provided in such a way as to form grooves 22 inwardly of the non-crosslinked polyolefin layers 13 into which the members 15 and 16 can be inserted at their ends. In the examples shown, the joining portion cosisting of non-crosslinked polyolefin layer 13, heating electric wire 14, groove 22 and support 23 is provided on each side of the electrofusion joint 20 or 21. In the electrofusion joint 20 shown in Fig. 4, the supports 23 are made of a crosslinked polyolefin and extend from the center of the crosslinked polyolefin layer 12 as an integral part thereof in such a way as to form grooves 22 between those supports and the non-crosslinked polyolefin layers 13. The electrofusion joint 20 may be fabricated by the process described in connection with the electrofusion joint 10, except that the injection mold cavity used must be so designed as to permit the shaping of grooves 22 and supports 23. After fabricating the electrofusion joint 20 as described above, the members to be joined 15 and 16 such as polyolefin tubes are inserted at one end into grooves 22 on opposite sides of the joint 20 and mounted in such a way that they contact the non-crosslinked polyolefin layers 13 and are supported by the supports 23. Thereafter, an electric current is applied to the electric wires 14, whereupon the non-crosslinked polyolefin layers 13 are melted and fuse to become an integral part of the members 15 and 16. As the non-crosslinked polyolefin layers 3 melt, the members 15 and 16 which are made of thermoplastic resin will soften but will not deform since their inner surfaces are supported by the supports 23. Thus, the fluid passage of each of the members 15 and 16 will not become narrower but maintains a cross-sectional area substantially the same as before these members were joined. As in the case of the electrofusion joint 21 shown in Fig. 5, the embodiment of the present invention may be such that the supports 23 are formed as integral parts of the non-crosslinked polyolefin layers 13 by being made of a non-crosslinked polyolefin. The shapes and structures of the crosslinked polyolefin layer 12, non-crosslinked polyolefin layers 13, heating electric wires 14, supports 23, etc. are not limited to those shown in Figs. 4 and 5 and various modifications are possible. It should be particularly noted that in an embodiment of the present invention, the portions to be joined by the non-crosslinked polyolefin layers 13 having heating electric wires 14 are not limited to the circumferences of the members 15 and 16 and they may be the inner and outer circumferences of these members including their ends or the inner circumferences of such members. It should also be noted that the electrofusion joint according to the invention need only have at least one joining portion containing the supports 23 which are provided in such a way as to form grooves 22 into which the members 15 and 16 are to be inserted. The number of such joining portions and their shape and structure, as well as the shape of the main body of the joint, and even the structure of other joining portions are not limited in any particular way. Further, the joint may or may not have a connecting member. As described above in detail, the electrofusion joint of the present invention has a joining portion that comprises heating electric wires provided either within or on the outer or inner surface of non-crosslinked thermoplastic resin layers which are integral parts of a crosslinked thermoplastic resin layer, and a support of a member to be joined that is provided in such a way as to form a groove into which said member is to be inserted. Because of this construction, the joint performs satisfactorily at elevated temperatures as evidenced by high heat resistance and exhibits good sealing property. In addition, this joint is capable of connecting members without causing their deformation and it can be handled efficiently in mounting and various other operations. In an electrofusion joint according to the present invention the outer crosslinked thermoplastic resin layer and the inner non-crosslinked thermoplastic resin layer have different colors, while crosslinked thermoplastic resin layer has a fine orifice that extends from its outer surface to a point close to the boundary between said crosslinked thermoplastic resin layer and the inner non-crosslinked thermoplastic resin layer. When the non-crosslinked termoplastic resin layer fuses to a member to be joined, the interior of said resin layer is melted to expand by the heat supplied from the current carrying electric wire and the pressure in the molten resin layer will increase. When satisfactory conditions of fusion are reached, the melt of non-crosslinked thermoplastic resin will come out of the fine orifice to indicate the point of time at which the fusion was completed. The extruding non-crosslinked thermoplastic resin has a different color than the surrounding crosslinked thermoplastic resin layer and hence can be readily indentified. The crosslinked thermoplastic resin will not become fluid but remains as a gel even if it is melted, and only the non-crosslinked thermoplastic resin will become fluid and come out of the orifice. The orifice is formed simultaneously with the time when the non-crosslinked polyolefin layer 13 is laminated as an integral part of a yet to be cross-linked polyolefin layer. The second polyolefin layer is then crosslinked to form the crosslinked polyolefin layer 12. When fusion occurs, the non-crosslinked polyolefin layers 13 will be melted to expand by the heat supplied from the electric wires 14 and the pressure in the melt of non-crosslinked polyolefin layers 13 will increase. When satisfactory conditions of fusion are reached, the melt of non-crosslinked polyolefin will come out of the fine orifice to indicate the time at which the fusion was completed. The extruding non-crosslinked polyolefin has a different color than the crosslinked polyolefin layer 12 and hence can be readily identified. The crosslinked polyolefin layer 12 will not become fluid but remains as a gel even if it is melted and only the non-crosslinked thermoplastic resin will become fluid. Hence, the point of time at which fusion was completed can be correctly indicated, allowing the operator to stop of the application of current to the electric wires 14 at the right time. A joint according to the invention may have one connecting portion having a tubular crosslinked thermoplastic resin layer and a connecting member that is inserted inwardly or outwardly of said crosslinked thermoplastic resin layer and secured thereto either mechanically by a screw or some other means or chemically by means of an adhesive material such as a modified thermoplastic resin. Illustrative connecting members that can be used in the present invention include metal tubes and non-metallic tubes such as ceramic tubes and resin tubes having at one end a screw or some other mechanical means which allow for connection to connecting terminals. Such connecting members are preferably secured to the crosslinked thermoplastic resin layer by means of an adhesive material such as a modified thermoplastic resin. The adhesive material is preferably provided between the connecting member and the crosslinked thermoplastic resin layer. If desired, the adhesive material may be dispersed in the crosslinked thermoplastic resin layer. Illustrative modified thermoplastic resins that can be used in the present invention are polyolefins that have been modified by graft copolymerization with modifying monomers including unsaturated carboxylic acids such as acrylic acid and maleic acid, unsaturated carboxylic acid anhydrides such as maleic anhydride, amides of unsaturated carboxylic acids, and unsaturated epoxides such as glycidyl methacrylate. The content of a modifying monomer in the modified thermoplastic resin is desirably within the range of from 0.001 to 5 wt% of the modified thermoplastic resin. The electrofusion joint fitted with a connecting member according to the present invention may be fabricated by the following procedure: at least two components, i.e., the non-crosslinked thermoplastic resin layer having a heating electric wire provided either within or on its outer or inner surface and a connecting member having a coating of an adhesive material such as a modified thermoplastic resin, are inserted into an injection mold cavity; a crosslinkable thermoplastic resin is injected and laminated on said non-crosslinked thermoplastic resin layer and said connecting member to form an integral assembly; thereafter, the crosslinkable thermoplastic resin layer is crosslinked to form the crosslinked thermoplastic resin layer. If desired, the adhesive material need not be coated on the connecting member but may be dispersed in the crosslinkable thermoplastic resin which is to be injected into the mold cavity. The thus fabricated electrofusion joint is used in the following manner: the connecting member in the connecting portion is joined to a connecting terminal such as a nozzle on a conduit header; at the same time, a member to be joined such as a thermoplastic resin tube is mounted in such a way that it contacts the non-crosslinked thermoplastic resin layer in the joining portion; when an electric current is applied to the electric wire from an external power source connected by a lead, the non-crosslinked thermoplastic resin layer will melt and fuses to the member of interest to become an integral part of the latter. By following this procedure, the metallic connecting terminal can be connected to the resin tube in a leak-free and reliable manner. Another embodiment of the present invention is described below with reference to Figs. 6 to 8. The electrofusion joint according to the invention has at least one electrofusion joining portion provided with a support of the member to be joined as in the previous embodiment and at least one connecting portion having a connecting portion. As in the electrofusion joint according to the first embodiment, the support of the member to be joined may be formed as an integral part of the crosslinked thermoplastic resin layer or the non-crosslinked thermoplastic resin layer. Alternatively, the support may be formed as an integral part of the connecting member, or it may be formed of other materials. The groove into which the member to be joined is to be inserted may be formed in such a way that it opens at one end of the electrofusion joint. The electrofusion joint equipped with a connecting member according to this embodiment of the present invention can be fabricated by the same procedure as adopted in the fourth embodiment. The adhesive material for adhering the connecting member to the joint need not be coated on the connecting member but may be dispersed in the crosslinkable thermoplastic resin which is to be injected into the mold cavity. The support of the member to be joined may be preliminarily formed as an integral part of the connecting member. Alternatively, it may be formed as an integral part of the crosslinkable thermoplastic resin layer which is to form the crosslinked thermoplastic resin layer. This embodiment of the present invention is described below with reference to the preferred examples shown in Figs. 6 to 8, which are cross sections showing three different examples of the electrofusion joint equipped with a connecting member according to this embodiment. The electrofusion joints with a connecting member that are indicated by 40 and 41 in Figs. 6 and 7 are the same as the electrofusion joints shown in Figs. 4 and 5 except that one end thereof (the left open end as viewed in these drawings) is formed as a connecting portion fitted with a connecting member. The electrofusion joint 40 shown in Fig. 6 has the following essential components: a tubular crosslinked polyolefin layer 12 forming the main body of the joint; an electrofusion joining portion that comprises a non-crosslinked polyolefin layer 13 formed as an integral part of the crosslinked polyolefin layer 12 on the inner surface at one end (on the right side as viewed in Fig. 6 ) in the area where it contacts the member to be joined 15, a heating electric wire 14 provided either within or on the outer or inner surface of said non-crosslinked polyolefin layer 13, and a support 23 of the member 15 provided in such a way as to form a groove 22 inwardly of the non-crosslinked polyolefin layer 13 into which the member 15 is to be inserted; and a connecting portion that comprises a connecting member 33 secured to the other end (on the left side as viewed in Fig. 6 ) of the crosslinked polyolefin layer 12 by being inserted inwardly of the same, and a modified polyolefin layer 34 serving as an adhesive material which is provided between the inserted portion 33a of the connecting member 33 and the crosslinked polyolefin layer 12. According to this embodiment, the support 23 is formed as an integral part of the crosslinked polyolefin layer 12 in the example shown in Fig. 6 by being made of a crosslinked polyolefin, and it is formed as an integral part of the non-crosslinked polyolefin layer 13 in the example shown in Fig. 7 by being made of a non-crosslinked polyolefin. In the electrofusion joint 42 fitted with connecting member and which is shown in Fig. 7, the support 23 extends as an integral part of the inserted portion 33a of the connecting member 33 in such a way as to form the groove 22 between said support and the non-crosslinked polyolefin layer 13, into which groove the member to be joined is to be inserted. The electrofusion joint 42 having the construction described above may be fabricated by the following procedure: the non-crosslinked polyolefin layer 13 having the heating electric wire 14 either buried within or in its outer or inner surface or wound around its surface, as well as the inserted portion 33a of the connecting member 33 coated with the modified polyolefin layer 34 on the outer surface and the support 23 are inserted into an injection mold cavity; subsequently, a crosslinkable polyolefin containing a crosslinking agent, a crosslinking aid, etc. in a polyolefin is injected and laminated on the non-crosslinked polyolefin layer 13, the connecting member 33 and the support 23 to form an integral assembly; and thereafter said crosslinkable polyolefin layer is crosslinked to form the crosslinked polyolefin layer 12. Each of the electrofusion joints 40, 41 and 42 according to the fifth embodiment can be connected to a connecting terminal such as a nozzle on a conduit header by threading the screw 36 in the projection 33b of the connecting member 33 into said terminal. Subsequently, the member to be joined 15 such as a polyolefin tube is inserted into the groove 22 and the non-crosslinked polyolefin layer 13 integral with the crosslinked polyolefin layer 12 will thermally melt to fuse to become an integral part of the member 15. Thus, the joints 40, 41 and 42 according to the fifth embodiment not only have high ability to retain their own shape but also exhibit good sealing performance which will be maintained for a prolonged period even if they are used to joint hot water supply pipes. As the non-crosslinked polyolefin layer 13 melts, the member 15 which is made of a thermoplastic resin will soften but will not deform since its inner surface is supported by the support 23. Thus, the fluid channel of the member 5 will not become narrow but maintains a cross-sectional area substantially the same as before the member 15 was joined. As described above, the electrofusion joint fitted with a connecting member according to the fifth embodiment of the present invention has both the joining portion used in the second embodiment and the connecting portion fitted with a connecting member as in the fourth embodiment. Thus, the joint can be designed according to the various examples of these previous embodiments to exhibit the advantages they attain. As described in detail on the foregoing pages, the electrofusion joint equipped with a connecting member according to this embodiment of the present invention has both a connecting portion to which a connecting member is secured and a joining portion having a non-crosslinked thermoplastic resin layer furnished with heating electric wire and a support of a member to be joined. This joint can be easily connected to a connecting terminal such as a nozzle on a conduit header for supplying hot water. Further, the joint will perform satisfactorily at elevated temperatures as evidenced by high heat resitance and exhibits good sealing property. In addition, this joint is capable of joining various members without causing their deformation and it can be handled efficiently in mounting and various other operations. The present invention is not limited to these examples alone and may embrace joints having more than one portion for connecting members to be joined such as an elbow joint, a T-joint and a cross joint. A blind joint closed at one end is also included within the present invention. If joints having two or more connecting portions are used, at least one of the connecting portions must be an electrofusion joining portion that comprises the crosslinked polyolefin layer 12 and the non-crosslinked polyolefin layer 13 that is integral with said crosslinked polyolefin layer 12 and which has the heating electric wire 14. Thus, the other connecting portions may have a connecting member such as a screw secured thereto. The main body of the joint need not be totally formed of the crosslinked polyolefin layer 12 but from the viewpoint of molding, it is preferred that the main body of the joint is totally formed of the crosslinked polyolefin layer 12. In the examples described above, the non-crosslinked polyolefin layer having the heating electric wire in the joining portion is formed on the inner surface of the crosslinked polyolefin layer so that it will contact the circumference of the members to be joined. However, the present invention is not limited to this case alone and the non-crosslinked polyolefin layer may be formed on the outer surface of the cross-linked polyolefin layer in such a way that it will join the inside surfaces or ends of the members to be joined. A header for distributing hot water from a heat source providing apparatus is described below with reference to Figs. 9 and 10. The header comprises a header body shaped of a crosslinked thermoplastic resin in a hollow form, a receptacle provided on the inlet side of said header body and at least one receptacle on the outlet side, at least part of which receptacles is an electrofusion joining portion of the same type as used in the first embodiment which comprises a crosslinked thermoplastic resin and a non-crosslinked thermoplastic resin having a heating electric wire provided either within or on its outer or inner surface. When the non-crosslinked thermoplastic resin layer and the heating electric wire are to be formed at one or more receptacles, the other receptacles may be fitted with connecting member commonly used to establish connection to pipes. An illustrative connecting member is a metal tube having at one end a screw or some other means for establishing coupling to connecting terminals. The connecting member is preferably secured to the crosslinked thermoplastic resin layer by means of bonding with an adhesive material such as a modified thermoplastic resin. The adhesive material is preferably interposed between the connecting member and the crosslinked thermoplastic resin layer but if desired, it may be dispersed in the crosslinked thermoplastic resin layer. The header is fabricated by the following procedure: a tubular non-crosslinked thermoplastic resin layer having a heating electric wire provided either within or on its outer or inner surface is inserted into an injection mold cavity; a crosslinkable thermoplastic resin is injected and laminated on the non-crosslinked thermoplastic resin layer to form an integral unit; thereafter, the crosslinkable thermoplastic resin layer is crosslinked to form the crosslinked thermoplastic resin layer. If a connecting member is necessary, it may be attached to the completed header. Alternatively, it may be injection molded together with the other components, with it being inserted into the mold cavity after it was coated with an adhesive material such as a modified thermoplastic resin. In this latter case, the adhesive material need not be coated on the non-crosslinked thermoplastic resin layer but may be dispersed in the crosslinkable thermoplastic resin to be injected. The so fabricated header is used with the water supply main from the heat source providing apparatus being connected to the receptacle on the inlet side and branch pipes to the necessary faucets being connected to the receptacles on the outlet side. In the case where a connecting member is used, the header is installed in such a way that the connecting member is connected to the connecting terminal of a member to be joined (i.e., a pipe) whereas a plastic pipe such as a thermoplastic tube is brought into contact with the non-crosslinked thermoplastic layer. When an electric current is applied to the heating electric wire, the non-crosslinked thermoplastic resin will melt and fuse to become an integral part of the plastic pipe. This enables the header to be connected to all pipes in a leak-free and reliable manner. As in the case of members to be joined by the electrofusion joints described on the foregoing pages, pipes to be connected to the header are preferable such that the surface layer or the entire portion is made of a thermoplastic resin, in particular, a miscible thermoplastic resin. Pipes made of non-crosslinked thermoplastic resins such as polyolefins will exhibit particularly good fusing ability. The header for supplying hot water is described below in a specific way by reference to the examples shown in Figs. 9 and 10, which are partial fragmentary front views of two different examples of the header. The header generally indicated by 60 is composed of a hollow header body 61 and a crosslinked polyolefin layer 62 forming a tubular receptacle 91 on the inlet side and a plurality of tubular receptacles 92a, 92b, 92c and 92d on the outlet side. The header body and the receptacles are shaped of a crosslinked polyolefin into an integral unit. The receptacle 91 on the inlet side is open at one end of the header 60 whereas the receptacles 92a, ... on the outlet side which are arranged in a row are open in a direction perpendicular to the receptacle 91. All receptacles 91, 92a, 92b, 92c and 92d (in the example shown in Fig. 9) or receptacles on the outlet side 92a-92d (in the example shown in Fig. 10) have the following construction: on the inner surface of the tubular crosslinked polyolefin layer 62 shaped as an integral part of the header body 61, a tubular non-crosslinked polyolefin layer 63 is laminated to become an integral part of the crosslinked polyolefin layer 62, and a coil of heating electric wire 64 is buried within the non-crosslinked polyolefin layer 63 and connected to terminals 65 and 66 to form an electrofusion joining portion of the same type as described in connection with the first embodiment. A connecting member 33 is attached to the receptacle 91 on the inlet side of the header shown in Fig.10. The connecting member 33 is a metal tube which has a screw 36 formed on the projection 33b on the side opposite to the inserted portion 33a to serve as connecting means. A hexagonal flange 37 which is to be gripped with a spanner is formed midway between 33a and 33b. A modified polyolefin layer 34 is disposed along the entire circumference of the space between the inserted portion 33a of the connecting member 33 and the crosslinked polyolefin layer 62 to adhere them together. The header 60 having the construction described above is fabricated by the following procedure: the non-crosslinked polyolefin layer 63 having the heating electric wire 64 either buried within or on its outer or inner surface or wound around its surface is inserted into an injection mold cavity; a crosslinkable polyolefin containing a crosslinking agent, a crosslinking aid, etc. in a polyolefin is injected and laminated over the non-crosslinked polyolefin layer 63 to form an integral unit; thereafter, the crosslinkable polyolefin layer is crosslinked to form the crosslinked polyolefin layer 62. The connecting member 33 may be ether attached to the completed header or injection molded together with the other components, with the inserted portion 33a of the connecting member 33 being inserted into the mold cavity after it was coated with the modified polyolefin layer 34 on the outer surface. The thus fabricated header 60 is used in such a way that the water main 88 from the heat source providing apparatus 82 (see Fig. 23) is connected to the receptacle 91 on the inlet side whereas branch pipes 93a, 93b, 93c and 93d to faucets 83, 84, 85, etc. are connected to the receptacles 92a, 92b, 92c and 92d, respectively, on the outlet side. If the header is fitted with the connecting member 33 as shown in Fig. 10, said member is connected to the connecting terminal of the water main 88 whereas branch pipes 93a, 93b, 93c and 93d which are made of plastics such as polyolefins are mounted in such a way that they contact the non-crosslinked polyolefin layer 63 in receptacles 92a, 92b, 92c and 92d as shown in Fig. 13. In the example shown in Fig. 9, both the water main 88 and branch pipes 93a, 93b, 93c and 93d are connected to the receptacles 91, 92a, 92b, 92c and 92d in such a way they contact the non-crosslinked polyolefin layer 63 in these receptacles as shown in Fig. 13. Thereafter, an electric current is applied to the electric wire 64 via terminals 65 and 66, whereupon the non-crosslinked polyolefin layer 63 will melt and fuse to become an integral part of each pipe to be connected. This insures that the header 60 is positively connected to the necessary pipes in a leak-free way. The connecting member 33 is suitable for establishing connection to metal pipes whereas the electrofusion joint is suitable when a plastic pipe is to be connected. Thus, the layout of these devices can be determined in accordance with the specific pipe to be joined. The header 60 has the crosslinked polyolefin layer 62 as a member responsible for imparting heat resistance, so it is capable of retaining its own shape effectively even if it is used to join hot water pipes. Further, the non-crosslinked polyolefin layer 63 has fused to become an integral part of the crosslinked polyolefin layer 62 together with the connecting member 33, so the header will exhibit good sealing property which is maintained for a prolonged period even if it is used to join hot water pipes. In the example shown in Fig. 10, the connecting member 33 is fitted to the receptacle 91 on the inlet side but it may be attached to one or more of the receptacles on the outlet side. The connecting member 33 may have connecting means other than screws. As described on the foregoing pages, the header has an electrofusion joining portion that comprises a non-crosslinked thermoplastic resin layer and a heating electric wire and that is fitted to at least one of the receptacles on the header body made of a crosslinked thermoplastic resin. Because of this arrangement, the header has high heat resistance, exhibits good sealing performance, is lightweight and resistant to corrosion, can be easily connected to plastic pipes, and is suitable for large-scale production. A header for supplying hot water is described below with reference to Figs. 11 and 12. and comprises a header body shaped of a crosslinked thermoplastic resin in hollow form and a plurality of receptacles on the outlet side of the header body which are formed of a crosslinked thermoplastic resin as an integral part of said header body in such a way that said tubular resin layer has a bore diameter sufficient to admit the flow rate of hot water distributed to each receptacle. Preferably, the receptacle on the inlet side and the plurality of receptacles on the outlet side are each made of a laminate of the tubular crosslinked thermoplastic resin layer and a tubular non-crosslinked thermoplastic resin layer that is capable of joining by fusion. More preferably, each of these receptacles is an electrofusion joining portion that has a heating electric wire provided either within or on its outer or inner surface as in the first embodiment. In fabricating the header, an injection mold must be employed whose cavity configuration is such that a plurality of receptacles having different bore diameters can be molded on the outlet side. Lamination of a non-crosslinked thermoplastic resin layer on a receptacle, placement of a heating electric wire and fixation of a connecting member can be performed in entirely the same manner as above and will not be described in detail. The so fabricated header is used with the water supply main from the heat source providing apparatus being connected to the receptacle on the inlet side and branch pipes to the necessary faucets being connected to the receptacles on the outlet side. The receptacles on the outlet side having different bore diameters are connected to branches having the corresponding bore diameters. In the case where a connecting member is attached to a receptacle, it is coupled to the connecting terminal of the pipe to which said receptacle is to be connected. In the case where a non-crosslinked thermoplastic resin layer is laminated on a receptacle, a plastic pipe such as a thermoplastic resin tube is mounted in such a way that it contacts the non-crosslinked thermoplastic resin layer and thereafter connected by some other means such as an electrofusion joint. If both a non-crosslinked thermoplastic resin layer and a heating electric wire are to be provided on a receptacle, the pipe to be connected is mounted in the same way and a current is applied to the electric wire, whereupon the non-crosslinked thermoplastic resin layer will melt and fuse as an integral part of the pipe. Thus, either method insures that the header is positively connected to the necessary pipe in a leak-free way. Two different examples of the header are shown in Figs. 11 and 12. The headers shown in these drawings are identical to those shown in Figs. 9 and 10, respectively, except that the receptacles on the outlet side of the header body have different bore diameters, so the same components are identified by like numerals and will not be described in detail. In the header generally indicated by 70 in Figs. 11 and 12, the receptacle 91 on the inlet side open at one end of the header whereas the receptacles 92a, 92b, 92c and 92d on the outlet side which are arranged in a row are open in a direction perpendicular to the receptacle 91 and have different bore diameters Da, Db, Dc and Dd that are sufficient to admit the flow rate of hot water distributed to each receptacle. The header 70 having the construction described above is used with the water main 88 from the heat source providing apparatus 82 being connected to the receptacle 91 on the inlet side and with differently sized branch pipes 93a, 93b, 93c and 93d to faucets 83, 84, 85, etc. being connected to receptacles 92a, 92b, 92c and 92d on the outlet side which have bore diameters corresponding to those of the associated branch pipes. If the header is fitted with the connecting member 33 as shown in Fig. 12, said member is connected to the connecting terminal of the water main 88 whereas branch pipes 93a, 93b, 93c and 93d which are made of plastics such as polyolefins are mounted in such a way that they contact the non-crosslinked polyolefin layer 63 in receptacles 92a, 92b, 92c and 92d as shown in Fig. 13. In the example shown in Fig. 11, both the water main 88 and branch pipes 93a, 93b, 93c and 93d are connected to the receptacles 91, 92a, 92b, 92c and 92d in such a way that they contact the non-crosslinked polyolefin layer 63 in these receptacles as shown in Fig. 13. Thereafter, an electric current is applied to the electric wire 64 via terminals 65 and 66, whereupon the non-crosslinked polyolefin layer 63 will melt and fuse to become an integral part of each pipe to be connected. This insures that the header 70 is positively connected to the necessary pipes in a leak-free way. The header 70 has the crosslinked polyolefin layer 62 as a member responsible for imparting heat resistance, so it is capable of retaining its own shape effectively even if it is used to join hot water pipes. Further, the receptacles 92a, ... one the outlet side of the header body have different bore diameters that are sufficient to admit the flow rate of hot water distributed to each receptacle, so they can be directly connected to branch pipes of different bore diameters without using reducers. Thus, the header insures effective sealing and high operational efficiency. In addition, the non-crosslinked polyolefin layer 63 has fused to become an integral part of the crosslinked polyolefin layer 62 together with the connecting member 33, so the header will exhibit good sealing property which is maintained for a prolonged period even if it is used to join hot water pipes. The header body and receptacles on its outlet side having different bore diameters are shaped as an integral unit by molding of a crosslinked thermoplastic resin. Thus, the resulting header has high heat resistance, is lightweight and resistant to corrosion, can be easily connected to plastic pipes having different bore diameters, and is suitable for large-scale production. If a non-crosslinked thermoplastic resin layer and even a heating electric wire are provided at the receptacle on the inlet side or the plurality of receptacles on the outlet side, a header can be obtained that exhibits high sealing performance, particularly for a prolonged period, and that allows for easy connection to pipes. Although not illustrated the electrofusion joints of the headers described above are provided with supporting portions according to the invention. EXAMPLES The present invention is hereunder described in greater detail with reference to the following examples. (Example 1) A medium density polyethylene colored by using a coloring agent was used as the non-crosslinked thermoplastic resin 13 of the present invention. The colored medium density polyethylene crosslinked by using 1.5% by weight of a crosslinked agent (vinyl trimethoxysilane) was used as the crosslinked thermoplastic resin 12 of the present invention. A Ni-Cr alloy wire (0.3 mm ) was used as the material of the heating electric wire 14. The electrofusion joint 20 having a structure as shown in Fig. 4, to which the tubes 15 and 16 to be connected having an adaptable caliber of 8 to 21.5 mm can be joined, was fabricated in accordance with the above-described methods. The tubes 15 and 16 to be connected, which were made of the same materials and have an adaptable caliber, were inserted at one end into grooves on opposite sides of the electrofusion joint 20. Thereafter, an electric current was applied to the above-described heating electric wires 14 which have been connected to an external electric power for about 20 seconds by controlling the voltage in order to give an appropriate energy density. For example, conditions for the application of electric current in the case of an adaptable caliber (outer diameter) of the tubes being 13 mm were as follows: resistance of the heating electric wire 14, 14.5 Ω; voltage, 40 V; and the application time, 20 seconds. When sealing properties of the joining portion were checked after completion of the connection, no leakage was found for at least 100 hours under a pressure of 10 kg/cm² at 90°C, which confirmed similar sealing properties of the joint to those of the pipes to be connected. It was confirmed also that the joint can be handled more efficiently in mounting and other various operations than in the case of joining using wrenches and the like. (Example 2) A modified polyethylene 34 was prepared as the adhesive material for use in the connecting member 33 made of brass, by performing graft copolymerization of a medium density polyethylene and maleic acid by means of a melt kneading. Using the modified polyethylene thus prepared and the same resin materials and electric heating wire materials as described in Example 1, the electrofusion joint 40 equipped with the connecting member having the structure as shown in Fig. 6 wherein the adaptable caliber of the pipe 15 to be connected is 8 to 21.5 mm was fabricated in accordance with the above-described methods. The pipe 15 to be connected made of the same material having an adaptable caliber was inserted into the joint, and the joining portion was connected by applying electric current to the above-described electric heating wires 14 in the same manner as described in Example 1. When sealing properties of the joining portion were checked after completion of the connection, it was confirmed that the joint had similar sealing properties to those of the pipes to be connected as the results described in Example 1. It was also confirmed that the joint can be handled more efficiently in mounting and other various operations than in the case of joining using wrenches and the like as described in Example 1.

Claims: An electrofusion joint (10) comprising a main body portion (12) comprised of a crosslinked thermoplastic resin layer and integrally moulded therewith at least one joining portion (13) which is adapted to be heat-welded to a tubular member, wherein said joining portion comprises a non-crosslinkable thermoplastic resin, and has an electrical heating wire (14) disposed thereon or embedded therein and is embedded in at least one major surface of said main body; characterised by: a supporting portion (23), a groove (22) into which a tubular member is to be inserted being defined between the supporting portion and the surface of said main body wherein the joining portion is embedded; and in that said joining portion does not extend to the extreme end of the electrofusion joint. An electrofusion joint of claim 1, wherein said crosslinked thermoplastic resin comprises a crosslinked polyolefin; and said non-crosslinkable thermoplastic resin comprises a non-crosslinkable polyolefin resin. An electrofusion joint of claim 1 or 2, wherein said joining portion is embedded in said main body portion of the joint on its interior major surface so that the joining portion may be heat-welded to the outer surface of the tubular member. An electrofusion joint of claim 1 or 2, wherein said joining portion is embedded to said main body of the joint on its exterior major surface so that the joining portion may be heat-welded to the pipe on its inner surface. An electrofusion joint of claim 1, 2, 3 or 4, wherein one end of said main body has a tubular configuration; and said joining portion is provided on said tubular end, and embedded in one major surface of said main body. An electrofusion joint according to any one of the preceding claims, wherein said supporting portion is moulded in one piece with said main body of the joint comprising the crosslinked thermoplastic resin. An electrofusion joint according to any one of claims 1 to 5, wherein said supporting portion is moulded in one piece with said joining portion comprising the non-crosslinkable thermoplastic resin. An electrofusion joint according to claim 3 or any claim dependent thereon, wherein said crosslinked thermoplastic resin constituting said main body (12) has a colour different from that of said non-crosslinkable thermoplastic resin constituting said joining portion (13) embedded in the interior surface of said main body; and said main body has an orifice (26) extending from the exterior surface of said main body to a point in the vicinity of the boundary between the main body and the joining portion, such that, upon heating of the joining portion, a portion of the softened non-crosslinkable thermoplastic resin of the joining portion is urged by the pressure produced by the heating to rise within said orifice to enable the state of the joining portion to be estimated by visual inspection from the exterior of the main body. An electrofusion joint according to any one of the preceding claims, wherein said main body portion has a tubular configuration at the end opposite to said end provided with said joining portion; and said electrofusion joint further comprises a connecting member (33) fitted onto and fixedly secured inside or outside of said tubular end of the main body, said connecting member being provided with a mechanically connecting means (36). The electrofusion joint according to claim 9, wherein said connecting member is firmly secured to said tubular end of the main body portion, by an intervening layer (34) comprising a modified thermoplastic resin. An electrofusion joint according to claim 9 or 10, wherein said supporting portion is moulded in one piece with said connecting member. A method of manufacturing an electrofusion joint comprising a main body portion (12) having a supporting portion and comprising a crosslinked thermoplastic resin and at least one joining portion (13) comprising a non-crosslinkable thermoplastic resin which is to be heat-welded to a pipe, said joining portion being embedded in an interior surface of said main body, a groove into which a tubular member is to be inserted being defined between the supporting portion and the surface of said main body wherein the joining portion is embedded; the method comprising the steps of disposing in an injection mould said at least one joining portion having an electrically heating wire (14) disposed thereon or embedded therein and not extending to an extreme end of said electrofusion joint; and injecting into said mould an uncrosslinked crosslinkable thermoplastic resin and crosslinking said uncrosslinked crosslinkable thermoplastic resin to form said main body portion comprising said crosslinked thermoplastic resin. A header for distributing hot water from a heat source, comprising a header body (61) comprising a crosslinked thermoplastic resin, said header body being provided with at least one inlet (91) and at least one outlet (92a...d); wherein at least one of said at least one inlet and at least one outlet of said header body has a joining portion (63) which is to be heat-welded to a tubular member (93a); said joining portion comprises a non-crosslinkable thermoplastic resin, has an electrically conductive heating wire (64) disposed thereon or embedded therein, and does not extend to an extreme end of the inlet or outlet; said joining portion is integrally moulded with said header body; said joining portion is embedded in the interior surface of said at least one inlet or outlet; and said header body has a supporting portion defining a groove, into which the tubular member is to be inserted, with the interior surface of said main body in which the joining portion is embedded. A header according to claim 13 wherein the or each said outlet of said header body has an inner diameter determined in accordance with the amount of the hot water to be distributed therethrough.

Inventors: MITO KAZUNORI MITSUI PETROCHEM, NAGATANI FUMIO MITSUI PETROCHE, NAKAOKA MIKIO SHINWA SANGYO CO, NAKASHIBA AKIO OSAKA GAS CO LT, NISHIMURA HIROYUKI OSAKA GAS C, SHIBABUCHI TOSHIO SHINWA SANGY, MITO, KAZUNORI, MITSUI PETROCHEMICAL IND., LTD., NAGATANI, FUMIO, MITSUI PETROCHEMICAL IND., LTD., NAKAOKA, MIKIO, SHINWA SANGYO CO., LTD., NAKASHIBA, AKIO, OSAKA GAS CO., LTD., NISHIMURA, HIROYUKI, OSAKA GAS CO., LTD., SHIBABUCHI, TOSHIO, SHINWA SANGYO CO., LTD.
Applicants: MITSUI PETROCHEMICAL IND, OSAKA GAS CO LTD, SHINWA SANGYO KK, MITSUI PETROCHEMICAL INDUSTRIES, LTD., OSAKA GAS COMPANY, LIMITED, SHINWA SANGYO CO., LTD.
Application year: 1990
Main classification: F16L47
IPC codes: F16L47, B29C65