JPH03278919A - Manufacture of electro-fusion-joint - Google Patents

Abstract

PURPOSE:To obtain a normal electrofusion joint by dissolving electric short- circuit by contact between naked electric wires, by performing injection molding by providing a sheet on a core directly below a gate or on a mold. CONSTITUTION:A sheet 5 made of polyethylene whose thickness is a little thicker than the diameter of a covered electric heating wire 2 is stuck to a gate directly blow the same in a core 1 and the covered electric heating wire 2 is wound round both sides of the sheet in a coil-like state. Then after setting-up of the core 1 within a mold, molten polyethylene is pressed into the mold through the gate 3. With this construction, since the molten resin pressed into the mold through the gate collides with the sheet 5 and does not collides directly with the coated electric heating wire, the covered electric heating wire 2 is hard to become a naked wire and electric short-circuiting is hard to occur. Then the sheet 5 to be used has a thickness of 1-3mm and prossesses the thickness equal to the diameter of the covered electric heating wire or thicker. Furthermore, since the same material as that of a joint is used, the plastic is melted at the time of molding and homogenized with the joint.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing an electrofusion joint that is used to connect plastic pipes and has a coiled heating wire embedded inside.

Conventional technology Plastic pipes such as polyethylene have various advantages such as having appropriate rigidity and flexibility, being lighter than metal pipes, and not corroding. It has come to be widely used for pipes, etc. In piping work, when connecting branch pipes using pipe-to-pipe or saddle joints, the conventional method is to press the pipe end faces, circumferential sides, and saddle joints against a heater to heat and melt them, and then butt them together to melt and join them. However, in recent years, an electrofusion joint has been developed, which consists of a molded product with a coil embedded inside, and fuses the joint with the pipe by heating and melting the contact surface with the pipe by applying electricity.

This joint has conventionally been manufactured as follows.

In other words, taking a pipe joint as an example, as shown in FIG. 2, a coated heating wire 2 is wound around a core 1 in a coil shape as shown in the figure, and then the molten resin is poured into a mold through a gate 3. In many cases, a method has been adopted in which the material is press-fitted into the cavity 4 and molded.

Problem to be Solved by the Invention When molten resin is press-fitted into a cavity through a gate during injection molding, the covering of the coated heating wire near the gate wound around the core is melted by the molten resin, and the heating wire becomes a bare wire. It was difficult to form a normal electrofusion joint because it was carried away by the flow of molten resin and came into contact with an adjacent bare wire in a similar condition, causing an electrical short (see FIG. 3). These problems occur not only in pipe joints, but also in the molding of saddle joints and other electrofusion joints.

An object of the present invention is to provide a method for manufacturing an electrofusion joint that can solve the above problems.

Means for solving the problem and operation The present invention deals with injection molding, and a sheet is provided on the core or mold directly under the gate.In other words, the present invention provides a sheet on the core directly under the gate or on the mold. This method of manufacturing an electrofusion joint involves injecting molten resin into a cavity, and is characterized in that a sheet is provided on a core or mold directly below a gate during molding.

According to the present invention, the molten resin press-fitted through the gate collides with the sheet and does not directly collide with the coated heating wire, so that the coated heating wire is less likely to become a bare wire and electrical short-circuits are less likely to occur.

The electrofusion joint targeted by the present invention includes:
Examples include pipe joints, saddle joints, elbow joints, etc.

Further, the sheet used in the present invention has a thickness of, for example, 1 to 3
N, preferably has a thickness equal to or greater than the diameter of the coated heating wire, and more preferably a plastic made of the same material as the joint, and is melted and homogenized with the joint during molding.

The sheet may also be attached by pasting only on the core directly under the gate or on the required part of the mold, or in the case of a pipe joint, it may be attached by wrapping it around the core in a ring shape.

Embodiment Fig. 1 shows the case of a pipe joint, in which a polyethylene sheet 5, which is thicker than the diameter of the covered electric heating vA2, is attached to the core l directly below the gate, and covered heating wires 2 are coiled on both sides. wrapped in a shape. Next, the core 1 was placed in a mold, and then molten polyethylene resin was press-fitted through the gate 3.

When the joint formed as described above was inspected, no short circuit in the heating wire was observed.

Effects of the Invention According to the present invention, as described above, by injection molding the gate by providing a sheet on the core directly below it or on the mold, electrical shorts caused by contact between bare wires are eliminated, and normal operation is possible. Electrofusion fittings can be obtained.

Also, if the sheet is made of the same resin as the joint,
During molding, the sheet is melted and homogenized into the joint.

[Brief explanation of drawings]

Figure 1 is a sectional view of the main part of the mold when the method of the present invention is used, Figure 2 is a sectional view of the main part of the mold when the conventional method is used, and Figure 3 is a diagram showing the state when the bare wire is short-circuited. It is. 1. Core 2. Covered heating wire 3. Gate 4. Cavity 5. Sheet

Claims (5)

[Claims] (1) In the manufacturing method of electrofusion joints in which a coated heating wire is placed in a mold and then molten resin is injected into a cavity through a gate, a sheet is provided on the core or mold directly below the gate during molding. How to characterize it. (2) The method according to claim 1, wherein the sheet is made of the same material as the joint resin to be injected. (3) The method according to claim 1 or 2, wherein the sheet has a thickness that is the same as or larger than the diameter of the coated heating wire. (4) Claim 1 in which the sheet is pasted onto the core or mold.
Method described. 5. The method of claim 1, wherein the sheet is annular and wrapped around the core.