JP3571849B2 - Manufacturing method of electric fusion joint - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for manufacturing an electric fusion joint in which a heating wire is embedded in a joint surface of a joint made of a thermoplastic resin.
[0002]
[Prior art]
Conventionally, for the connection of synthetic resin pipes such as gas pipes and water supply / hot water supply pipes, sockets are provided at both ends of the joint body made of synthetic resin, and electric heating wires are embedded on the inner peripheral surface of each socket. Is used. The method for manufacturing this conventional joint will be described below with reference to FIG.
[0003]
First, a continuous spiral groove 11a is engraved on the surface of a cylindrical body 1a made of a thermoplastic resin, a heating wire 3a is fitted along the spiral groove 11a, and a terminal pin 4a is inserted into the end thereof. Fix it. Next, the cylindrical body 1a on which the heating wire 3a and the terminal pins 4a are disposed is set in the mold 5a, and the molten resin is injected into a cavity formed between the mold 5a and the cylindrical body 1a. Thus, the molten resin is integrally fused to the outer peripheral surface of the cylindrical body 1a.
[0004]
[Problems to be solved by the invention]
However, in the case of this conventional manufacturing method, when the molten resin is injected into the cavity, the outer peripheral surface of the cylindrical body 1a melts and the heating wire 3a thermally expands. 3a sometimes came close to each other and short-circuited. Further, even if the heating wire 3a does not short-circuit during the injection molding, when the heating wire 3a is energized to generate heat at the time of piping construction at the site, the heating wire 3a moves or kinks, causing a short-circuit. However, sufficient fusion bonding may not be obtained.
[0005]
The present invention has solved the above problem, and it is possible to prevent the shortening of the heating wire when injecting the molten resin, and also when the heating wire is energized to generate heat when piping at the site is constructed. An object of the present invention is to provide a method for manufacturing an electro-fusion joint that can achieve a sufficient fusion bonding without causing a short circuit.
[0006]
[Means for Solving the Problems]
According to the present invention, in manufacturing an electrofusion joint in which a heating wire is buried in a joint surface of a joint made of a thermoplastic resin, first, a locking groove that is continuous in a spiral shape is formed on a surface of a cylindrical body made of a thermoplastic resin. Set up. Next, the surface of the cylindrical body is covered with an insulating sheet, and the heating wire is fitted into the locking groove via the insulating sheet while the heating wire is wound around the outer periphery of the cylindrical body. Then, the cylindrical body on which the heating wire is wound is set in a mold, and the molten resin is injected into a cavity formed between the mold and the cylindrical body.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a front view showing an embodiment of a cylindrical body used in the present invention, and FIG. 2 is a sectional view of a main part showing a state in which a cylindrical body wound with a heating wire is set in a mold. Reference numeral 1 denotes a cylindrical body made of a thermoplastic resin such as polyethylene or polybutene, 2 denotes an insulating sheet, 3 denotes a heating wire, and 4 denotes a terminal pin.
[0008]
In the present invention, first, a spirally continuous locking groove 11 is formed on the outer peripheral surface of the cylindrical body 1. A support ring 12 is provided on the outer periphery of both ends of the cylindrical body 1 approaching the end of the locking groove 11, and an insertion hole 121 is provided in the support ring 12 so that the terminal pin 4 can be vertically set up. When the cylindrical body 1 is manufactured by injection molding, the locking groove 11 and the support ring 12 are integrally formed at the same time as the cylindrical body 1 is formed, and the support ring 12 is provided with a fitting hole 121. Good.
[0009]
The core 6 is inserted into the cylindrical body 1, and the outer peripheral surface of the cylindrical body 1 is covered with the insulating sheet 2. As the insulating sheet 2, a sheet made of polyimide resin, polyester resin, or the like having a higher melting temperature than polyethylene, polybutene, or the like can be preferably used. The insulating sheet 2 wound or formed into a cylindrical shape is extrapolated to the cylindrical body 1. After covering the outer peripheral surface of the cylindrical body 1 with the insulating sheet 2 in this manner, the heating wire 3 is fitted into the locking groove 11 via the insulating sheet 2 while the heating wire 3 is wound around the outer periphery of the cylindrical body 1.
[0010]
The heating wire 3 may be a nichrome wire having a wire diameter of 0.2 mm to 3.0 mm or the like depending on the diameter of the joint, but the heating wire 3 is fitted into the locking groove 11 via the insulating sheet 2. At this time, it is important to form a locking groove 11 having a width and a depth so that the heating wire 3 does not move.
[0011]
Next, the terminal pins 4 are fitted into the fitting holes 121 of the support ring 12 provided on the outer periphery of both ends of the cylindrical body 1 to stand vertically, and the ends of the heating wires 3 are connected to the bases of the terminal pins 4, 4. . Then, the cylindrical body 1 around which the heating wire 3 is wound is set in the mold 5, and the molten resin is injected into a cavity formed between the mold 5 and the outer peripheral surface of the cylindrical body 1. Then, the molten resin filled in the cavity is fusion bonded to the front surface of the insulating sheet 2 and the heating wire 3, and the back surface of the insulating sheet 2 is fusion bonded to the cylindrical body 1. During the injection molding, the heating wire 3 wound around the outer periphery of the cylindrical body 1 is separated by the insulating sheet 2, so that the heating wire 3 does not move or kink and short-circuit between the heating wires 3.
[0012]
Finally, when the mold 6 is unfolded and the core 6 is pulled out, the heating wire 3 is spirally wound at a predetermined interval, and the adjacent heating wires 3 are separated by the insulating sheet 2. A joint is obtained. When performing on-site piping construction using this electric fusion joint, since the adjacent heating wires 3 are separated by the insulating sheet 2, even if the heating wire 3 generates heat and thermally expands, there is no short circuit. In addition, since the energizing time to the heating wire 3 is maintained at a predetermined time set in advance according to the size of the joint and the like, strong fusion bonding can be obtained.
[0013]
【The invention's effect】
As described above in detail, according to the present invention, the heating wire is inserted into the locking groove via the insulating sheet. Therefore, even when the cylindrical body on which the heating wire is wound is set in the mold and the molten resin is injected, the heating wire is inserted. There is no short circuit between the hot wires. In addition, when the electric fusion joint manufactured according to the present invention is used, since the heating wire does not move or kink when it generates heat and does not short-circuit, the current supply time to the heating wire is always kept constant, and a strong A fusion bond is obtained.
[Brief description of the drawings]
FIG. 1 is a front view showing an embodiment of a cylindrical body used in the present invention.
FIG. 2 is a sectional view of a main part showing a state where a cylindrical body around which a heating wire is wound is set in a mold.
FIG. 3 is a sectional view of a main part showing a conventional manufacturing process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylindrical body 2 Insulating sheet 3 Heating wire 4 Terminal pin 11 Locking groove

Claims (1)

Production of an electric fusion joint in which a heating wire is embedded in a joint surface of a joint made of a thermoplastic resin, comprising the following steps (1) to (3): production of an electric fusion joint Method.
{Circle around (1)} Engraving a spirally continuous locking groove (11) on the surface of a cylindrical body (1) made of a thermoplastic resin;
{Circle around (2)} The surface of the cylindrical body (1) is covered with an insulating sheet (2), and while the heating wire (3) is wound around the outer periphery of the cylindrical body (1), the locking groove ( 11) inserting a heating wire (3) into the heating wire;
{Circle around (3)} The cylindrical body (1) on which the heating wire (3) is wound is set in a mold (5), and is formed between the mold (5) and the outer peripheral surface of the cylindrical body (1). Injecting molten resin into the cavity

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