FR2503020A1 - Heating coil inserts for fusing thermoplastic pipe socket joints - preformed so that the concealed wire is adjacent to the interface - Google Patents

Abstract

Conductive metal coil inserts for induction heating of interfaces of socket joints in thermoplastic pipe are made by winding resistance wire having thermoplastic sheathing and then dilating the mandrel radially until most of the sheathing matl. is forced beyond the circumferential interface between the mandrel and the wire. The resulting assymetrically insulated wire is then incorporated into a moulded socket like a conventional heater insert. Suitable for an in situ fusion of socket joints in high density polyethylene or PVC pipes by induction heating. The conductor wires are very close to the socket wall surface, minimising the thickness of wall to be heated to provide heat to the joint interface and opt. also to the spigot surface. Minimises risk of overheating the socket material whilst keeping the wires within the socket surface so they are not displaced by insertion of the spigot.

Description

 The present invention relates to a new type of electrofusion fitting, called R B S, in thermoplastic dobby; the term “thermoplastic” means in particular polyolefins, such as polyethylene, in particular high density (PEaD) and polyvinyl chloride (PVC); as well as the manufacture of said fittings.

 In the field of fluid distribution (under medium pressure, such as water and gas, plastics are increasingly tending to replace traditional metallic materials because of the economy they provide and their remarkable properties constituted by their chemical inertness, their absence of corrosion and the ease of implementation. Buried pipes are currently the preferred field of application for plastics.

Several official bodies from various European countries, including the Fringe and the Federal Republic of Ilemaane have adopted high density polyethylene as the material for their entire city gas distribution network.

 The watertight assembly of two or more pipes or tubes of thermoplastic material, with the reliability required for this type of operation is only obtained by the electro-welding technique. This technique consists in heating in situ and very locally by means of an electrical resistance the contact surfaces of the assembled parts, so as to reach the welding temperature of the two materials; the electrical resistance remaining inserted in the material.

 This type of assembly is done by means of an electrofusion fitting consisting of a cylindrical sleeve made of very thick thernoplastic material. This sleeve comprises, in its calibrated internal orifice, a winding of metal wire partially or completely resistant, embedded in the thermoplastic material. The ends of the wire are generally fixed to terminals or lugs to ensure good electrical contact with a generator.

The electrofusion fitting is usually integrated at each end, either of a straight fitting, or of a tee, or of a spider allowing to connect respectively, 2, 3 or 4 thermoplastic tubes together.

 The end of the tube to be connected is cut beforehand to facilitate the fitting of the electrofusion fitting; on the other hand, the external surface of the tube in contact with the HES is previously pickled to obtain better weldability. Said fitting is then presented in the axis of the pipe and engaged on this with an adjusted socket, then the RES is connected to a regulator adjusted on the heating program in relation to the diameter of the RES; the welding time is between ten seconds and a few minutes and the cooling time of the order of 20 minutes.

 The advantage of this type of fitting gives the installer the possibility of welding between the fitting and the pipe after the laying and assembly of the pipes has been completed.

 The electrofusion fitting must meet two essential characteristics, namely perfect sealing and mechanical resistance at least equal to that of the tube.

 Two types of electrofusion fittings have already been proposed. There are currently RES fittings with visible resistant wire and RETS with resistant wire embedded in the thermoplastic connection.

 According to the first type of electrofusion fitting, the resistant wires are clearly visible inside the sleeve, while being partially embedded in the thermoplastic material.

 In the second type of electrofusion fitting, the resistant wires are not visible, but embedded in the thermoplastic material.

 The manufacture of electrofusion fittings with visible resistant wire has been studied for more than twenty years. Thus, the American patent 3,062,940, under German priority of February 17, 1958 of South Veat Chemie origin, teaches a manufacturing technique according to which the resistant wire is wound on a PVC sleeve for example, which is then introduced into a fitting. in polyethylene, then a metallic, heating and extensible core is inserted into the PVC sleeve so as to melt the polyethylene and to thread the wire into the fitting, the still hot PVC sleeve being finally broken and extracted by hand.

 French patent 2,111,818, in the name of MANNESMAN, relates to the production of a thermoplastic sleeve obtained by winding an extruded plastic film on a core provided with the wound wound wire.

The extruded film is wound with a large stretch so as to give the thermoplastic high tensions which contribute to its shrinkage during welding. This type of electrofusion sleeve seems more particularly suitable for welding large diameter tubes.

 Numerous manufacturing processes have been studied in the field of electrofusion fittings with embedded resistant wire. This characteristic implies a technique different from that of BES with visible wires, and leads to winding a resistant wire on a thermoplastic sleeve, then to overmolding the sub-assembly thus formed by injection to obtain the finished product.

 Since 1955, the work of SUD WEST CHEMIE for the production of a cylindrical sleeve within which a winding of resistant wire is embedded has been the subject in particular of the American patent 3,094,452.

According to this process, the wire winding is immersed either in a bath of molten resin, or by spraying the molten resin, or by winding on the winding of resistant wire a film of thermoplastic resin then heated, until the resin melts. . Then we can incorporate in a fitting by overmolding - injection of a thermoplastic resin.

 A few years later, in 1962, the ROLLMAPLAST Company developed a process for manufacturing RES, described in French patent 1,372,303, according to which a resistant wire, previously sheathed with a thermoplastic material is wound around a cylindrical core, the assembly then being placed in an injection molding machine in order to coat the winding with a thermoplastic material and obtain an electrofusion fitting.

The technique resulting from the work carried out at SUSQUnELLSYA
CORPORATION and exposed in US Patent 3,378,672 leads to a type of sleeve widespread in the trade. These electrofusion fittings are manufactured from a resistant enamelled metal wire and coated with a rectangular sheath of thermoplastic material. The wire is wound on contiguous turns on a cylindrical mandrel and welded together by means of a hot point, then the sleeves thus obtained are housed between two male and female pipes to ensure their assembly by electrofusion.

 Ectemments PCT application WO 79/01018, in the name of STWY [, describes a method of manufacturing an electrofusion sleeve from a tube made of thermoplastic material previously extended, then placed on a mandrel provided with a winding bare or sheathed resistant wire.

The wire is heated at the same time as the tube which shrinks on the winding of resistant wire and drowns the wire in the thermoplastic material of the tube; the resistant wire is thus protected against accidental impact during the fitting of the tube into the electrofusion fitting.

 These two known types of electrofusion fittings have advantages and disadvantages respectively.

 The electroweldable connection with visible resistant wire has the advantage of bringing the resistant wire into direct contact with the tube to be welded and the connection; during heating by Joule effect, the material of the tube and that of the connector melt at the same time and this constitutes a favorable factor for obtaining a good weld.

 On the other hand, the main defect of this type of connection lies in the fact that the visible turns of the wire are vulnerable and can be moved when the tube fits into the electrofusion fitting. Such an accident leads to rejecting the fitting because generally, the resistant wire cannot be replaced.

 Electrofusion fittings with embedded wire do not have this drawback because the resistant wire is protected; however, they have another drawback which appears all the more when the resistive wire is distant from the wall of the tube to be welded, that is to say when the resistive wire is embedded deep in the electro-weldable connection.

 In this case during heating by Joule effect, it is necessary to melt the thermoplastic material located between the heating wire and the wall of the tube before this wall is hot and has reached the appropriate temperature to ensure a correct weld between the tube and the connection As the thermoplastic material is not very conductive of heat, there is a risk of overheating, which causes its thermal degradation and affects its weldability.

 A heating sleeve was sought which constituted the best compromise between the need to protect the resistant wire against mechanical shock during the interlocking of the tube to be welded and the need to position the resistant wire so that it was practically in contact with the wall of the tube to be welded.

 And a new type of electroweldable thermoplastic connection has been found which allows satisfactory welds to be produced with almost 100% success.

 According to the invention, the electrofusion fitting into which a cylindrical sleeve of thermoplastic material is inserted, comprising in its calibrated inner orifice a winding of resistant metallic wire, the ends of which are fixed to terminals or lugs ensuring good contact with a generator. characterized in that the resistant wire completely coated in the thermoplastic material is flush with the inside of the fitting, being covered with an extra-thin thermoplastic film, a generator of said resistant cylindrical wire tangent to the inner surface of the sleeve. , the resistant wire is therefore practically in contact with the wall of the tube to be welded while being protected during nesting. It has been discovered that the outcrop of the resistant wire inside proves to be a practically necessary condition for obtaining a good weld.

The resistant wire is a nickel-copper alloy wire whose resistivity is substantially constant whatever the temperature.
The wire diameter is between 0.2 and 2.1, preferably between 0.30 and 1 mm; the surface of the wire being oxidized so as to make it electrically insulating and thus avoiding electrical short circuits in the event that 2 or more wires come into contact.

The resistant wire is covered by a thermoplastic sheath whose thickness is between 0.1 and arma, preferably between 0.30 and 0.50mu,
The sheathed wire is wound with contiguous turns, the winding being either two-wire so as to obtain that the two ends of the resistant wire are on the same side of the winding, or single-wire so as to obtain each end of the resistant wire on each side of the winding.

 The electrofusion fitting, into which the sleeve is inserted, is designed in such a way that a safety space is provided inside said sleeve on each side of the winding of the resistant wire.

Each safety space has a length at least equal to 30% of the length of the winding. The spaces can be equal, their purpose is to avoid the possible leakage of the liquid thermoplastic material on each side of the space occupied by the winding of the resistant wire, during welding by Joule effect.

The sheathed resistant wire is wound in contiguous turns on an extensible mandrel made of electrically insulating and temperature resistant material
Then, the resistant wire wound on the mandrel is brought by the Joule effect, to the softening temperature of the thermoplastic sheath. At this time, the mandrel is put in extension until a wire generator is in contact with the external surface of the mandrel; without the need to put the resistance wire itself in extension.

 After extension, the assembly is allowed to cool to room temperature, then the sleeve obtained is removed from the mandrel.

 Then, this sleeve can be inserted into an eletro-weldable connector by the conventional overmolding-injection technique, while providing inside the sleeve, a safety space on either side of the winding of resistant wire.

 The manufacturing process is illustrated without limitation by Figures 1,2 and 3 of the accompanying drawing and by the following example.

 Figure 1. is a sectional view of the resistive wire wound on an extendable mandrel.

 Figure 2 is a sectional view of the resistive wire wound on the extendable mandrel after heating of the wire by an electric current and extension of the mandrel.

 FIG. 3 represents a finished electrofusion fitting with the tube to be assembled introduced into the electrofusion fitting ready to be welded by Joule effect.

Example g
The resistant wire (1) is a wire 0.8 mm in diameter made of an alloy of nickel and copper, the resistivity of which is practically constant whatever the temperature. The wire is coated with a sheath (2) made of high density polyethylene 0.35mm thick. The sheathed wire is wound, with contiguous turns, on the extendable mandrel (3) provided with a conical piece (4) for expansion, the diameter of the mandrel in PIFFE is approximately 4011.. The winding of the resistant wire is two-wire so as to obtain the two ends of the resistant wire of the same side of the winding. The not shown pot formed by the wires (8) and (9) is fixed to the mandrel (3) by the screw (5) and the washer (6) g the screw (5) is screwed into the tapped hole (7 ) of the mandrel (3). The ends (10) and (11) of the resistant wire are held on a part, not shown, other than the mandrel (3).

 When the winding is carried out, the ends of the resistant wire are connected to an electric generator adjusted in such a way that the temperature of the resistant wire as well as that of the sheath are brought to the softening zone of the high density polyethylene, that is to say about 200 ° C., this temperature is reached after ten seconds of heating.

 At this moment, the mandrel (3) is put in extension by pushing the conical core (4) into the mandrel (3) (figure 2) 1 the extension of the mandrel (3) is continued until the outer surface of the mandrel is practically in contact with a generator of the resistant wire (i) (FIG. 2).

 Then the conical core (4) is brought back to the position of figure (1) 3 one removes the screw (5), and the winding of the resistant wire of which all the turns are welded together, forms a sleeve which lton removes from the mandrel ( 3).

 This sleeve is then inserted into an electrosoadable connector using the conventional overmolding-injeotion technique. As shown in FIG. 3, the RES is made in such a way that safety spaces b and c are provided on each side of the space a where the winding of resistant wire is located.

Claims (8)

- CLAIMS  1 - Electrofusion fitting into which a cylindrical heating sleeve made of thermoplastic material is inserted, the said sleeve comprising in its calibrated interior orifice a winding of resistant metallic wire, the ends of which are fixed to terminals or lugs ensuring good contact with a generator , characterized in that the resistant wire, completely coated in the thermoplastic material is flush with the inside of the fitting, being covered with an extra-thin thermoplastic film, a generator of said resistant cylindrical wire tangent to the inner surface of the sleeve.  2 - Electrofusion fitting according to claim 1, characterized in that the resistant wire is a nickel-copper alloy whose resistivity is substantially constant whatever the temperature, the surface of the wire being oxidized so that it is electrically insulating, the wire diameter being between 0.2 and 2mm, preferably between 0.3 and Imm.  3 - Electrofusion fitting according to claim 1 or 2, charac tersed in that the sheath of thermoplastic material which covers the resistant wire has a thickness between 0.1 and imm, preferably between 0.30 and 0.50-.  4 - Electrofusion fitting according to any one of claims 1 to 3, characterized in that the sheathed wire is wound with contiguous turns, the winding being two-wire so that the two ends of the resistant wire is on the same side of the winding.  5 - Electrofusion fitting according to any one of claims 1 to 3, characterized in that the sheathed wire is wound with contiguous turns, the winding being single-wire so that each end of the resistant wire is on each side of the winding.  6 - Electrofusion fitting according to any one of the claims 1 to 5, characterized in that a safety space is provided inside the sleeve on each side of the winding of the resistant wire, said space being at least equal to 30 ffi of the length of the winding.  7- A method of manufacturing the cylindrical heating sleeve inserted in an electrofusion fitting according to any one of claims 1 to 6, characterized by the following stages: a) the resistive wire is sheathed in contiguous turns on an extensible mandrel made of electrically insulating and resistant material at temperature b) the resistive wire wound on the mandrel is brought to the softening temperature of the thermoplastic sheath by effect Joule and at this moment puts the mandrel in extension until a wire generator is in contact with the external surface of the mandrel - c) after extension, the assembly is allowed to cool to room temperature, then the chuck sleeve.  8- Method of frabrication of the electrofusion fitting according to claim 7, characterized in that the sleeve is inserted into an electrofusion fitting by overmolding-injection while providing inside the sleeve a safety space on either side of the winding of resistant wire.