JP2000104883A - Electro fusion coupling and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a fused resin in which a fusion interface is expanded to be pushed out outside a coupling, and prevent generation of vacuum bubbles after fusion is completed by arranging a closed circuit of a heating wire having a degree such that resin whose heating value is smaller or equal than/to that of the heating wire which is insulated from an outer layer part of the heating wire and which is buried in a joining surface is not fused. SOLUTION: A socket coupling 4 is formed in such a constitution that a first heating wire 2 is buried in a joining surface 1 in a coil shape, and a second heating wire 3 insulated from the first heating wire is buried in an outer layer part of the first heating wire 2 as a closed circuit of a coil shape. Since rigidity is reduced by heating the outer peripheral part of the coupling at the time of fusion, the resin of the fusion interface is pushed out to a coupling side so as to prevent overflow, or a pushing out rate is reduced, even if the resin of a fusion interface is fused and expanded. When the coupling is contracted at the time of cooling and leaving after fusion is completed, a fusion part is easily contracted since an outer peripheral part is also contracted. It is thus possible to prevent generation of bubbles on the fusion part, or it is possible to almost prevent it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrofusion system for connecting plastic pipes in a piping system using plastic pipes, wherein a heating wire is preferably embedded in a coil or spiral shape at a joint surface with the plastic pipe. The present invention relates to a joint and a manufacturing method thereof.

[0002]

2. Description of the Related Art Electrofusion joints include socket joints used for connecting pipes, elbow joints, cheese joints, reducer joints, saddle joints used for connecting branch pipes, service tee joints, and pipe ends. There are various types such as cap joints to be attached, and in each case, a heating wire is generally embedded in a coil or spiral shape at the joint surface with the pipe, and the heating wire is connected to the pipe by energization. This is performed by causing heat to melt the resin at the fusion interface.

[0003]

In the electrofusion joint, the fusion resin often protrudes from between the joint and the pipe during fusion, or bubbles are generated near the heating wire after fusion. . The present inventors have conducted various studies on the cause of the above problem, and found that the cause of the molten resin protruding is that the resin around the heating wire has the highest temperature and the largest thermal expansion, while the outer layer Since the temperature decreases and the stiffness increases as going to the part, the expanded molten resin at the fusion interface is extruded out of the joint in search of an escape area. In addition, the cause of the generation of bubbles near the heating wire is that the molten resin tends to shrink when left to cool after the end of fusion, but the resin having a low temperature in the outer layer cannot shrink due to high rigidity, It has been found that the molten resin is pulled by the high rigidity portion of the outer layer portion to generate a vacuum bubble.

[0004] It is an object of the present invention to provide an electrofusion joint that can solve the above-mentioned problems, and a method of manufacturing the same.

[0005]

The invention according to claim 1 is used for connecting a plastic pipe, and in an electrofusion joint in which a heating wire is embedded in a joining surface with the plastic pipe, preferably in a coil shape or a spiral shape. An induction current is generated by a magnetic field generated in a current flowing through the first heating wire, which is insulated from the first heating wire in an outer layer portion of the heating wire (hereinafter, referred to as “first heating wire”) embedded in the surface. Second
That the second heating wire has a smaller or equal heating value than that of the heating wire buried in the joint surface, and more preferably a second heating wire that heats the resin so as not to melt the resin. Features.

According to the present invention, the outer layer portion of the joint is heated by the second heating wire to reduce rigidity, so that expansion of the molten resin at the fusion interface is easily absorbed. Further, after cooling, the resin whose outer layer portion has low rigidity also contracts when cooled, so that the molten resin easily contracts. The second heating wire of the present invention forms a loop-shaped closed circuit while being insulated from the first heating wire, and both heating wires may be made of the same material, However, the first heating wire may be a nichrome wire, and the second heating wire may be a copper wire. When the first heating wire and the second heating wire are made of the same material, the resistance value can be arbitrarily set by changing the diameter and / or length of the heating wire.

The ratio of the resistance value R of the first heating wire to the resistance value r of the second heating wire is arbitrary, but preferably R: r
= 100: 1 to 1: 1, more preferably 100: 1 to 1
At 2: 1, the calorific value of the second heating wire is preferably 1 to 100% of the calorific value of the first heating wire, more preferably 10 to 100%.
50%.

[0008] The invention according to claim 2 relates to a method for manufacturing an electrofusion joint according to the invention according to claim 1, and preferably comprises a resin and a phase used for molding on a coil-shaped or spiral-shaped first heating wire. Attach a tubular body or sheet made of a soluble resin, and more preferably,
A heating wire forming a second closed circuit, which is insulated from the first heating wire in a coil shape or a spiral shape, is attached and insert-molded. Each of the above inventions is a socket joint, an elbow joint, a cheese joint, used for connecting pipes,
The present invention can be applied to all joints that are subjected to electrofusion such as reducer joints, saddle joints used for connecting branch pipes, service tee joints, and cap joints attached to pipe ends.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first heating wire 2 buried in a coil shape on a joint surface 1 and a second heating wire 3 in an outer layer portion insulated from the first heating wire. 1 shows a socket joint 4 embedded as a coil-shaped closed circuit.
2a to 2c show a method of manufacturing the socket joint 4, in which the first coated heating wire 2 is wound on both sides of the core 6 at a constant pitch, and then a cylindrical body 7 made of polyethylene is inserted. And a second coated heating wire 3 is further wound thereon at a constant pitch, mounted in a mold, and injection-molded with a polyethylene resin.

FIG. 3 shows that a first heating wire 13 is spirally buried in a joint surface 12 of a saddle portion 11a, and a second heating wire 14 insulated from the first heating wire is formed in an outer layer portion thereof. Also shows a saddle joint 11 embedded as a spiral closed circuit. 4A to 4C illustrate the saddle joint 11.
The first coated heating wire 13 is spirally wound, and as shown by a dotted line in FIG. A plate-like sheet 17 made of polyethylene is placed on which a second coated heating wire 14 is spirally wound, and as described above, a donut plate-like sheet 17 is heat-sealed at a plurality of locations in a radial manner. And mounting it in a mold to injection mold polyethylene resin. In the above embodiments, the socket joint and the saddle joint are illustrated, but other joints such as an elbow joint, a cheese joint, a reducer joint, a service tee joint, and a cap joint are similarly configured.

[0011]

According to the electrofusion joint of the first aspect of the present invention, the outer layer portion of the joint is also heated at the time of fusion and its rigidity is reduced. It is extruded to the side and does not protrude, or the extrusion amount is smaller, and after the fusion is completed, when the joint shrinks when left to cool, the outer layer part also shrinks, so the molten part also shrinks. And no or little air bubbles are formed in the molten portion.

According to the manufacturing method of the invention according to claim 2,
The electrofusion joint according to the first aspect of the present invention can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a socket joint.

FIG. 2 is a view showing a method of manufacturing the joint shown in FIG. 1;

FIG. 3 is a sectional view of a saddle joint.

FIG. 4 is a view showing a method of manufacturing the joint shown in FIG. 3;

[Explanation of symbols]

 1, 12 joining surface 2, 13 first heating wire 3, 14 second heating wire 4, socket joint 6, core 7, tubular body 11, saddle joint 15, 16 , 17-sheet

Continued on the front page (72) Inventor Hiroaki Tanaka 1-2-1, Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term in Mitsui Chemicals, Inc. 3H019 GA03 GA12

Claims (2)

[Claims] 1. Used to connect plastic tubes,
In an electrofusion joint in which a first heating wire is embedded in a joint surface with a plastic pipe, a first heating wire is embedded in an outer layer portion of the joint.
An electrofusion joint in which a heating wire forming a second closed path, which is insulated from the heating wire and generates an induced current by a current flowing through the first heating wire, is embedded. 2. A resin tubular body or sheet compatible with a resin used for molding is mounted on the first heating wire, and a second closed wire insulated from the first heating wire is further mounted thereon. 2. The method for manufacturing an electrofusion joint according to claim 1, wherein a heating wire forming a circuit is attached and insert molding is performed.