JPH09303663A - Electrofusion joint and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrofusion joint which does not shortcircuit due to the bending of a heating wire by the thermal contraction of the joint and thermal expansion of the heating wire when fused. SOLUTION: A heating wire is wound around a metal core in a regular pitch and a U-shaped bent part 3 is formed at the end of the coil toward a terminal 4 and is then insert-molded to obtain an electrofusion joint. The bent part absorbs and relaxes the buckling stress caused by the thermal contraction of the joint and thermal expansion of the heating wire when fused to prevent the shortcircuit by bending in another part of the heating wire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrofusion joint used in piping work using a plastic pipe, in which a heating wire is embedded in a coiled or spiral shape on a joint surface with the plastic pipe, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Electrofusion joints have recently been developed as joints for plastic pipes used in plumbing works such as water and sewage pipes and gas pipes. There are various types of fittings, such as socket fittings used to connect pipes, elbow fittings, cheese fittings, reducer fittings, saddle fittings used to connect branch pipes, cap fittings attached to pipe ends, etc. There is a type, which is generally formed of a molded product in which a heating wire is embedded in a coil shape or a spiral shape on a joint surface with a tube. Then, fusion with the pipe is performed by inserting a plastic pipe from three sides, both sides, or one side of the joint, or pressing the joint against the outer peripheral surface of the plastic pipe, and then heating and melting the joint surface with the plastic pipe by energization. Is going.

[0003]

In the electrofusion joint, heat shrinks during fusion, whereas the heating wire thermally expands, so that the heating wire buckles and bends, making contact with the adjacent heating wire to cause a short circuit. Sometimes. It is an object of the present invention to provide an electrofusion joint that can solve the above problems and a method for manufacturing the same.

[0004]

Therefore, the electrofusion joint of the first invention is characterized in that a bent portion which functions as a buffer for absorbing the buckling stress of the heating wire is provided at an appropriate position of the heating wire buried in a coil shape. And The above-mentioned bent portion may be provided at an appropriate position of the coil, but it is desirable to provide it at the coil end because molding can be performed easily.

Therefore, a second invention is characterized in that the bent portion of the first invention is provided at the coil end. In a preferred embodiment, the bent portion is formed in a hook shape, and in a more preferred embodiment, the bent portion is bent into a U shape having a constant length. Therefore, the bent portion in the first and second inventions is formed by bending it into a hook shape in the third invention and a U shape with a constant length in the fourth invention.

The present invention is particularly effective for socket joints, elbow joints, cheese joints, and other insertion joints into which plastic pipes are inserted, particularly large diameter pipes having a diameter of 150 mm or more, but can also be applied to saddle joints. A fifth aspect of the present invention relates to a method for manufacturing a plug-in joint in which a plastic tube is inserted among the electrofusion joints of the above-described inventions. Preferably, it is characterized in that a bent portion bent into a U shape is formed and wound, and then insert molding is performed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example in which a hook-shaped bent portion 2 is provided in a portion extending to a terminal 4 at an end of a coil 1.
The angle θ formed by the bent portion 2 refracted from the coil 1 and the extension of the coil 1 is preferably within 20 to 30 ° so that buckling does not occur at the bending point a where buckling stress is likely to concentrate during fusion bonding. In order to achieve the above, it is desirable to make θ as small as possible.

FIG. 3 shows an example in which the above-mentioned θ is set to 0, and the bent portion 3 is formed by bending it into a U shape, and the heating wire slightly returned from the bent portion does not come into contact with the coil portion. It is provided above the coil portion. This bend is
If the length l ₂ becomes long, the electric resistance value of the heating wire also becomes large, and conversely if it becomes too short, it becomes difficult to fulfill the role of a buffer, so about 20 to 30 mm is desirable. Bend 3 of this example
Then, since the two heating wires are close to each other, the temperature rise at the time of fusion is faster than other portions, and the resin around them is softened more quickly. Therefore, when the heating wire is thermally expanded by the bent portion 3, It can play a role of a buffer, and as a result, stress concentration can be relaxed and short-circuit with an adjacent heating wire due to bending of the heating wire in other portions can be prevented.

[0009]

【Example】

Example 1 A coated heating wire or a bare heating wire is wound around a metal core (not shown) at a pitch of 3.0 mm, and a hook-shaped bent portion 2 (l ₁ = 15 mm) is provided at a coil end portion reaching the terminal 4. After forming, insert molding was performed to obtain an electrofusion socket joint having a diameter of 150 mm. 1 and 2 show the coil shape of this joint. Next, a plastic tube was inserted into this joint from both sides, and a heating current was passed from a heating power source connected to the coil to fuse the plastic tube and the joint. For the fusion, the fusion interface temperature was measured, and the energization was continued until the temperature reached 230 ° C, and when the temperature reached 230 ° C, the energization was stopped. After fusing, the heating wire was bent by X-ray observation and examined for the presence of a short circuit in the heating wire.
One of them was a short circuit between the heating wires on both sides due to the bending of the heating wire.

Embodiment 2 As shown in FIGS. 3 and 4, U is attached to the coil end portion of the coil.
An electrofusion socket joint having a caliber of a bent portion 3 and a diameter of 150 mm was obtained in the same manner as in Example 1.
Then, fusion with a plastic pipe was performed under the same conditions as in Example 1, and after the fusion, bending of the heating wire and short circuit of the heating wire were examined, and it was found that no short circuit due to bending of the heating wire occurred in any of the 10 joints I was not able to admit.

COMPARATIVE EXAMPLE A heating wire having a conventional coil shape shown in FIG.
A mm electrofusion socket joint was obtained in the same manner as in Example 1 and fused with a plastic tube. After fusion, bending of the heating wire and short circuit of the heating wire were examined. As a result, a short circuit with the heating wire on both sides due to bending of the heating wire was observed in all of the five joints.

[0012]

According to the electrofusion joint obtained by the present invention and the method of the present invention, the buckling stress of the heating wire due to the thermal contraction of the joint during fusion and the thermal expansion of the heating wire is absorbed and relaxed at the bent portion. Therefore, it is possible to prevent bending of the heating wire and a short circuit due to the bending. Especially, if the bent portion is bent into a U shape, it is particularly effective in preventing bending and a short circuit of the heating wire.

If the bent portion is provided at the coil end, the bent portion can be easily formed and the molding can be facilitated.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of a coil.

FIG. 2 is a perspective view of the coil shown in FIG.

FIG. 3 is a plan view of a main part showing another example of a coil.

FIG. 4 is a perspective view of the coil shown in FIG.

FIG. 5 is a perspective view of a conventional coil.

[Explanation of symbols]

 1 ... Coil 2, 3 ... Bent section 4 ... Terminal

Front Page Continuation (72) Inventor Tetsuo Ishikawa 5-11-61 Toroshima, Konohana-ku, Osaka City Osaka Gas Co., Ltd. In-house (72) Inventor Noboru Kato 6-1-2 Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture Mitsui Petrochemical Co., Ltd. (72) In-house Kazuto Sugiyama 6-1, Waki, Waki-cho, Yamaguchi Prefecture No. 2 Mitsui Petrochemical Industry Co., Ltd. (72) Inventor Sumio Matsuno 2480, Santo, Hiratsuka-shi, Kanagawa Mitsubishi Plastics Corporation Hiratsuka Plant (72) Inventor Yuichi Shiohama 3-15-1, Negishidai, Asaka, Saitama Prefecture Sekisui Chemical Co., Ltd.

Claims (8)

[Claims] 1. An electrofusion joint in which a heating wire is embedded in a coil shape or a spiral shape on a joint surface with a plastic pipe, and the resin on the joint surface is heated and melted by energizing the heating wire to fuse with the plastic pipe. 2. An electrofusion joint according to claim 1, wherein a bent portion that functions as a buffer that absorbs the buckling stress of the heating wire is provided at an appropriate position of the heating wire that is embedded in a coil shape or a spiral shape. 2. The electrofusion joint according to claim 1, wherein the bent portion is provided at a coil end. 3. The electrofusion joint according to claim 1, wherein the bent portion is formed in a hook shape. 4. The electrofusion joint according to claim 1, wherein the bent portion is formed by bending into a U shape. 5. The method of manufacturing an electrofusion joint for insertion according to claim 1, wherein the heating wire is formed on the core at a constant pitch by forming bent portions at appropriate places and wound, and then insert-molded. 6. The method for manufacturing an electrofusion joint according to claim 5, wherein the bent portion is formed at the coil end. 7. The method for manufacturing an electrofusion joint according to claim 5, wherein the bent portion is formed in a hook shape. 8. The bent portion is formed in a U shape.
A method for producing the electrofusion joint described.