JPH10166386A - Manufacture of electric fusion joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a shortcircuiting from being formed under a state wherein at the time of injection-molding, heating wires are pressed by a strong resin pressure, and bent. SOLUTION: For this method, in a stage wherein a resin is injection-molded in a die 1 comprising an external die and a core 12, a heating wire 3 is embedded in the wall. In this case, a process to prepare a state wherein the resin coated heating wire 3 is wound around the core 12, and a process wherein after forcibly cooling the core part which is confronted with a resin gate of the external mold, or while cooling the core part, the resin is injection-molded in the mold 1, are provided.

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 such as a socket joint, an elbow joint, a cheese joint, etc., for joining a resin gas pipe or a pipe for water supply and sewage by electric fusion.

[0002]

2. Description of the Related Art An electro-fusion joint manufactured by a method of injection molding a resin around a core around which a heating wire that generates heat by energization is wound, the heating wire is swept away due to resin flow during injection molding. There is a problem that bending, short-circuiting or disconnection may occur.

In view of this problem, for example, Japanese Patent Application Laid-Open
No. 44896 proposes a method in which a resin-coated heating wire is wound around a core and a synthetic resin is injected around the core to form a cylindrical resin layer in which the heating wire is embedded.

[0004]

However, according to this method, even if the side portions of the wound resin-coated heating wires are in contact with each other, the resin-coated layer functions as an insulating layer. Although the effect of preventing short-circuiting of the heating wire can be seen in the molded product obtained, there is a problem that as the number of molding shots increases, the molded product in which the heating wire is bent and the adjacent heating wire is short-circuited occurs.

[0007] After a close examination of the cause, it has been found that the bending of the heating wire is greatly related to the injection molding conditions, and that the higher the temperature of the core and the higher the holding pressure, the larger the bending of the heating wire. did. That is, when the state of deformation of the heating wire during the injection molding was observed in detail, as shown in FIG. 5, the temperature of the core c increased as the number of molding shots increased, and from the initial stage of filling as shown in FIG.
When the process proceeds to the pressure-holding stage shown in (c) after the injection end stage shown in (b), the heat causes the resin-coated layer b of the resin-coated heating wire a to be in a softened state. It has been clarified that the resin coating layer b eventually peels off and the heating wire c is exposed and bent, resulting in a short circuit due to the strong resin pressure acting from the side surface of.

The present invention solves the above-mentioned conventional problems and provides a method of manufacturing an electro-fusion joint in which a heating wire is not pressed by strong resin pressure and short-circuited in a bent state during injection molding. It was done for the purpose of doing.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing an electro-fusion joint in which a heating wire is embedded in a wall in a step of injecting a resin into a mold comprising an outer mold and a core, A step of forming a resin-coated heating wire around the core;
After forcibly cooling the core portion facing the resin gate of the outer mold, or while cooling, and injecting a resin into a mold.

In the present invention, for example, a stainless steel wire, a copper nickel wire, an iron chrome wire, etc. are used as the heating wire constituting the resin-coated heating wire. As the resin constituting the resin coating layer of the resin-coated heating wire, the same resin as that constituting the resin ring is used.

In the present invention, as the resin for injection molding, for example, polyolefins such as hard polyvinyl chloride, polyethylene and polypropylene are used.

In the present invention, as a method of winding the resin-coated heating wire around the core, the resin-coated heating wire may be wound around the core, or the resin-coated heating wire may be coiled in advance. May be attached.

The present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory view showing a part of an example of a mold used in the method for manufacturing an electrofusion joint of the present invention.

Reference numeral 1 denotes a mold, which comprises an outer mold 11 and a core 12. The outer mold 11 is composed of mold pieces 111 and 112 which are divided into two and can be opened and closed freely.
11, a resin gate 111a is provided at a substantially central portion, and a through hole 111 for leading out an end portion of the resin-coated heating wire is provided on an inner peripheral surface at both ends.
b, 111b.

The core 12 includes a pair of cylindrical mold pieces 121, 1
22. Each cylindrical mold piece 121, 122
The enlarged diameter portion 121 is slightly wider along the circumferential direction at the base end portion.
a, 122a are formed, and flange portions 123, 12
4 are provided.

At the time of injection molding, the core 12 has a pair of cylindrical mold pieces 121 and 122 whose tip end faces abut each other and is closed with the outer mold to form a pair of cylindrical mold pieces 121. , 122, the inner surfaces of the flanges 123, 124, and the inner surface of the outer mold, the cavity 13 for forming the electrofusion joint is formed.

When the mold is opened, the cylindrical mold pieces 121, 1
The gap between the tips of the 22 is open so that the molded product can be released from the mold.

Next, an example of a method for manufacturing an electrofusion joint of the present invention using the mold 1 shown in FIG. 1 will be described with reference to FIG. As shown in FIG. 2, the tip surfaces of a pair of cylindrical mold pieces 121 and 122 are in contact with each other.

The resin-coated heating wires 3 are formed on the outer peripheral surfaces of the pair of cylindrical mold pieces 121 and 122, except for the outer peripheral surfaces of the opposed ends and the outer diameter portions 121a and 122a formed on the base end. Are wound spirally so that there is no gap between them, and cylindrical mold pieces 12 are
In this state, only the resin-coated heating wires 3 ′ connecting the resin-coated heating wires 3 spirally wound around the outer peripheral surfaces of the first and second 122 are wound.

Next, the outer mold 1 is moved by the spot cooler 4.
By spraying the cooling medium 41 onto the core portion facing the one resin gate 111a, the portion is forcibly cooled.

Thereafter, the mold 1 is closed, and molten resin from an injection molding machine (not shown) is fed from the resin gate to the mold 1.
Injection molding is performed and the pressure is maintained for a predetermined time. At this time, the molten resin injected into the mold 1 collides with the core portion facing the resin gate 111a, and is cooled in place to solidify the side surface portion of the resin-coated heating wire 3, and then the top surface is heated next. Since the supplied molten resin is filled around the resin-coated heating wire 3 wound spirally, the resin-coated heating wire 3 is filled.
Strong resin pressure does not act on the side surface of.

Thereafter, the mold is opened and the cylindrical mold pieces 121 and 12 are opened.
Then, the gap between the tips is opened and the mold is removed to obtain an electrofusion joint in which the heating wire is buried in the wall without short circuit.

Next, another example of the method for manufacturing the electro-fusion joint of the present invention using the mold 1 shown in FIG. 1 will be described with reference to FIGS. As shown in FIG. 3, a pair of cylindrical mold pieces 121,
122 are in contact with each other.

The resin-coated heating wires 3 are formed on the outer peripheral surfaces of the pair of cylindrical mold pieces 121 and 122 except for the outer peripheral surfaces of the opposed ends and the outer peripheral surfaces of the enlarged diameter portions 121a and 122a formed at the base end. Are wound spirally so that there is no gap between them, and cylindrical mold pieces 12 are
In this state, only the resin-coated heating wires 3 ′ connecting the resin-coated heating wires 3 spirally wound around the outer peripheral surfaces of the first and second 122 are wound.

Next, as shown in FIG. 4, the coolant 5 is caused to flow down in the core 12 so that the resin gate 1 of the outer mold 11 is formed.
The core portion facing 11a is forcibly cooled.

Thereafter, the mold 1 is closed, and molten resin from an injection molding machine (not shown) is fed from the resin gate to the mold 1.
Injection molding is performed and the pressure is maintained for a predetermined time. At this time, the molten resin injected into the mold 1 collides with the core portion facing the resin gate 111a, and is cooled in place to solidify the side surface portion of the resin-coated heating wire 3, and then the top surface is heated next. Since the supplied molten resin is filled around the resin-coated heating wire 3 wound spirally, the resin-coated heating wire 3 is filled.
Strong resin pressure does not act on the side surface of.

[0025]

The method for manufacturing an electro-fusion joint according to the present invention comprises a step of winding a resin-coated heating wire around a core and a step of forcibly cooling a core portion facing an outer resin gate. The step of injecting the resin into the mold while cooling, the molten resin injected into the mold is cooled in place when it hits the core part facing the resin gate, and the resin coating is applied. The side surface of the heating wire is solidified and the molten resin to be supplied next is filled around the spirally wound resin-coated heating wire, so strong resin pressure acts on the side surface of the resin-coated heating wire. In this case, even if the number of molding shots increases and the temperature of the core increases, and the heat causes the resin coating layer of the resin coating heating wire to soften, the resin coating layer peels off and the heating wire is exposed and bent. Short circuit There is no thing Migihitsuji.

[0026]

The present invention will be described below with reference to examples. Example 1

As shown in FIG. 2, the resin-coated heating wire 3 was wound around the core 12. As the resin-coated heat generating wire 3, a wire having a diameter of 1.2 mm in which a nichrome wire having a diameter of 0.6 mm was coated with a polyethylene resin (trade name “HIZEX 6300M” manufactured by Mitsui Petrochemical Co., Ltd.) was used.

The spot cooler 4 applies a temperature of 15 ° C. to the core portion of the outer mold 11 facing the resin gate 111a.
Forcibly cool by blowing cold air at a flow rate of 20 l / min.
Cooled to 18 ° C.

Injection molding machine (Meiki Seisakusho, Model "M-35
0II) through a process of injection-molding a polyethylene resin (trade name “HIZEX 6300M” manufactured by Mitsui Petrochemical Co., Ltd.), and a socket having an inner diameter of 90 mm and a wall thickness of 14 mm, in which a heating wire is embedded in a cylindrical wall. A mold-type electrofusion joint was obtained. As the molding conditions, the injection temperature was set to 200 ° C.
Each piece was molded.

An X-ray image apparatus (trade name “13ST-1505” manufactured by Soflon Co., Ltd.) was obtained for the obtained electrofusion joint.
Was used to observe the X-ray image to judge the quality. The results are shown in Table 1. In addition, the pass / fail judgment was made when the heating wire was 0.5
Those deviated by not less than mm were regarded as defective.

Embodiment 2 As shown in FIG. 4 and FIG.
The core wall facing the resin gate 111a of the outer mold 11 was forcibly cooled by flowing water at a flow rate of 20 liter / min, and the cylindrical wall was cooled in the same manner as in Example 1 except that it was cooled to 20 ° C. A socket-type electro-fusion joint having a heating wire embedded therein was obtained. About the obtained electric fusion joint,
The same pass / fail judgment as in Example 1 was performed. The results are shown in Table 1.

Comparative Example A socket-type electrofusion joint similar to that of Example 1 was obtained in the same manner as in Example 1 except that forced cooling was not performed. With respect to the obtained electro-fusion joint, the same quality judgment as in Example 1 was performed. The results are shown in Table 1.

[0033]

[Table 1]

[0034]

According to the method for manufacturing an electro-fusion joint of the present invention having the above-described structure, an electric wire in which a heating wire in a resin-coated heating wire is not bent and short-circuited by being pressed by a resin pressure. A fusion joint can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a mold used in the method for manufacturing an electro-fusion joint of the present invention.

FIG. 2 is a front view illustrating an example of a method for manufacturing an electrofusion joint of the present invention using the mold shown in FIG.

FIG. 3 is a front view for explaining another example of the method for manufacturing an electro-fusion joint of the present invention using the mold shown in FIG. 1;

FIG. 4 is an enlarged cross-sectional view showing a portion indicated by a circle in FIG. 3;

FIGS. 5A and 5B are explanatory views of a conventional method, in which FIG. 5A is a main part sectional view showing an initial stage of filling, FIG. 5B is a stage of ending injection, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 3,3 'Resin-coated heating wire 11 Outer mold 12 Core 111a Resin gate

Claims (1)

[Claims] 1. A method of manufacturing an electro-fusion joint in which a heating wire is buried in a wall in a step of injection molding a resin in a mold comprising an outer mold and a core, wherein the resin-coated heating wire is provided around the core. And a step of injecting a resin into a mold after forcibly cooling the core portion facing the resin gate of the outer mold or while cooling. Manufacturing method of the joint.