JPH102479A - Manufacturing method of electric fusion joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an electric fusion joint which can easily produce a joint having stable quality and obtain a strong fusion joint. SOLUTION: Engagement projections 11 are provided on the outer periphery of both ends of a mandrel 1.
And the resin-coated heating wire 2 is spirally wound on the outer peripheral surface of the mandrel 1 in close contact therewith, and the resin-coated heating wire 2 at the beginning and end of the winding is connected to each of the locking projections 11.
Hold with. Next, the mandrel 1 around which the resin-coated heating wire 2 is wound is set in a mold, and the molten resin is injected into the cavity. [Effect] A joint of stable quality can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric fusion joint in which a resin-coated heating wire is wound around the inner peripheral surface of the joint.

[0002]

2. Description of the Related Art Conventionally, an electric fusion joint as shown in a sectional view in FIG. 6 has been used for connecting a synthetic resin gas pipe, a water supply / hot water supply pipe and the like. To manufacture this electric fusion joint, a 1/4 circular groove 1 is formed on the outer peripheral surface as shown in FIGS.
A mandrel 1a having a spiral shape 1a is used. After the resin-coated heating wire 2a is engaged with the concave groove 11a and wound, the mandrel 1a is set in a mold and injection-molded. .

[0003]

However, in the case of this conventional method, there is a problem that the mandrel cannot be easily extracted from the injection-molded joint. In addition, a spiral groove is formed between the wound resin-coated heating wires on the inner peripheral surface of the obtained electric fusion joint, so that when the heating wires are heated and the synthetic resin pipe is fusion-bonded. In some cases, strong fusion bonding could not be obtained in portions where grooves exist. Also, the molten resin flows into the groove, so that the heating wire moves,
There was a risk of short-circuiting between the heating wires.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing an electro-fused joint capable of easily producing a joint having stable quality and obtaining a strong fusion-bonded joint.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a locking projection is provided on the outer periphery of both ends of a mandrel, and a resin-coated heating wire is tightly wound on the outer peripheral surface of the mandrel and spirally wound. It is characterized in that the resin-coated heating wire at the end of winding is held by each locking projection, then the mandrel on which the resin-coated heating wire is wound is set in a mold, and then the molten resin is injected into the cavity.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a partial front view of a mandrel used in the present invention, FIG. 2 is a partial cross-sectional view showing a state where the mandrel is set in a mold, and FIG. 3 is an enlarged cross-sectional view showing a main part of the mandrel. Denotes a mandrel, and 2 denotes a resin-coated heating wire. The resin-coated heating wire 2 is obtained by coating the outer surface of a heating wire such as a nichrome wire with an insulating resin such as polyethylene or polybutene.

On the other hand, the mandrel 1 used in the present invention can be divided at the center, and locking projections 11 are provided on the outer periphery of both ends. The locking projection 11 is provided around the outer periphery of the mandrel 1, and one surface of the mandrel 1, which is in contact with the resin-coated heating wire 2, is inclined by a desired angle θ with respect to a line perpendicular to the axis. Further, a step is provided at an intermediate position of the locking projection 11 that makes one round, and the step is shifted by a pitch p substantially equal to the diameter of the resin-coated heating wire 2. It can be held without rattling. At this time, as shown in FIG. 3, one side of the locking projection 11 is
And the height of the locking projection 11 may be set to be equal to or slightly lower than the diameter of the resin-coated heating wire 2.

According to the present invention, the resin-coated heating wire 2 is closely wound on the outer peripheral surface of the mandrel 1 and spirally wound, and the resin-coated heating wire 2 at the beginning and end of the winding is connected to each of the locking projections 11. Hold with. Next, the terminal pins 3 are connected to both ends of the resin-coated heating wire 2 and then set in the mold 4, and the molten resin is injected into the cavity. At this time,
Since both ends of the resin-coated heating wire 2 wound around the mandrel 1 are held by the locking projections 11, they do not move or shift. Finally, when the mold 4 is developed and the mandrel 1 is forcibly removed from both sides of the molded product, an electric fusion joint having a heating wire embedded in the inner peripheral surface of the joint as shown in FIG. 6 is obtained.

Although FIGS. 1 and 2 show an example in which the locking projection 11 is partially provided, the present invention is not limited to this embodiment. As shown by the chain line in FIG.
Can be the same height up to the end of the mandrel 1,
This has the advantage that the mandrel 1 can be easily extracted from the molded product.

[0010]

As described in detail above, according to the present invention, locking projections are provided on the outer periphery of both ends of the mandrel, and a resin-coated heating wire is tightly wound on the outer peripheral surface of the mandrel and spirally wound.
Since the resin-coated heating wire at the beginning and end of the winding is held by each locking projection, then the mandrel around which the resin-coated heating wire is wound is set in a mold, and then the molten resin is injected into the cavity. A joint of stable quality can be easily manufactured. Also, when the electric fusion joint according to the present invention is used, a strong fusion bonding can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial front view of a mandrel used in the present invention.

FIG. 2 is a partial sectional view showing a state where a mandrel is set in a mold.

FIG. 3 is an enlarged sectional view showing a main part of a mandrel.

FIG. 4 is a front view of a conventional example showing a winding step of a resin-coated heating wire.

FIG. 5 is an enlarged sectional view of a main part showing a state in which a resin-coated heating wire is wound around a mandrel.

FIG. 6 is a sectional view of the electric fusion joint.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mandrel 2 Resin-coated heating wire 3 Terminal pin 11 Locking projection

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29L 31:00

Claims (2)

[Claims] A mandrel (1) is provided with locking projections (11) on the outer periphery of both ends thereof, and a resin-coated heating wire (2) is brought into close contact with the outer peripheral surface of the mandrel (1) and spirally wound.
The resin-coated heating wire (2) at the beginning and end of the winding is held by the respective locking projections (11), and then the mandrel (1) around which the resin-coated heating wire (2) is wound is set in a mold. And then injecting the molten resin into the cavity. 2. The locking projection (11) has an inclined surface (111) and a vertical surface (11) on a surface where the resin-coated heating wire (2) abuts.
2. The method for producing an electro-fusion joint according to claim 1, wherein 2) is provided.