JPH0642690A - Manufacture of electrofusion joint - Google Patents

Abstract

PURPOSE:To enhance the cooling efficiency of a molded article withdrawn from dies, and to uniformly cool the same in the axial direction, and to prevent a coil from being applied thereto with stress during cooling so as to prevent an electric heater wire from shortcircuiting upon fusing to a plastic pipe. CONSTITUTION:After winding a heating wire onto each of halves of a metal sleeve 14 split at the center part thereof, a slide core 12 is fitted before injection molding. Then, a molded article 17 attached thereto with the sleeve 14 is taken out from dies, and is cooled by a spot cooler, or by a rod through which cooling water flows. After cooling, the sleeve is pulled out from the article 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in piping work using plastic pipes such as socket joints, elbow joints, cheese joints or cap joints for connecting pipes,
The present invention relates to a method for manufacturing an electrofusion joint in which a heating wire is embedded in a coil shape.

[0002]

2. Description of the Related Art An electrofusion joint has been recently developed as a joint for plastic pipes used in plumbing works such as water and sewerage and gas pipes. There are various types of fittings, among them are socket fittings used to connect pipes, elbow fittings, cheese fittings, cap fittings attached to the ends of the pipes, and the like.

[0003] Such a joint is generally a molded product in which a heating wire is embedded in a coil shape on the inside, and the fusion with the pipe is performed by inserting the pipe from three sides, both sides or one side of the joint. It is carried out by energizing afterwards and heating and melting the contact surface. Taking a socket joint as an example, as a conventional manufacturing method of such a joint, as shown in FIG. 2, a covered wire 2 is formed on the outer periphery of a solid rod 1 in which one half 1a is combined with the other half 1b and connected. There is known a method of separately winding on the right side, setting it in the mold 3, and then performing injection molding.

In the above method, when the size of the joint becomes large, the weight of the core also becomes large, which makes it difficult to handle, and there is a danger in the work. When mass-producing joints,
After molding, after cooling the molded product taken out of the mold, the core is removed, and the heating wire is wound around the extracted core, so the time until the next molding will be longer and the production Sex decreases. If you prepare a large number of cores and wind the heating wire in advance and replace the core with the heating wire each time you finish molding, productivity will increase and automation will be possible, but you will have many cores Causes high cost.

In order to solve the above-mentioned problems, Japanese Patent Laid-Open No. 3-150118 discloses a bolt-shaped half 12a in the mold 11.
And the other half 12b are combined with each other, and each of them is provided with a slide core 12 that can slide independently in the axial direction, and the slide core 12 is divided into two parts.
There is disclosed a method in which a sleeve 14 having a step 16 wound around is fitted and mounted, and then injection molded into a cavity 15.

[0006]

In the conventional method described above as shown in FIG. 1, the molded article after injection molding is cooled from the mold and then the sleeve is mounted for 30 minutes to 30 minutes.
It is performed by leaving it in the atmosphere for about 1 hour, but with such cooling, it takes longer to cool the larger size, and it cannot be sufficiently cooled even if left in the atmosphere for about 1 hour. If the sleeve is pulled out in a state where the coil is not sufficiently cooled, the molded product is held by the coil until the resin is cooled and solidified, so that the coil is in a stressed state. When a molded product solidified in such a state is used to energize for fusion with a plastic tube, when the resin around the coil softens, the stressed coil moves due to contraction, and adjacent heating wires contact each other. It is easy to cause a short circuit.

Japanese Unexamined Patent Publication (Kokai) No. 3-150118 discloses steps up to molding, but does not disclose anything about cooling after molding. The present invention focuses on a sleeve as disclosed in Japanese Unexamined Patent Publication No. 3-150118, and attempts to solve the above-mentioned problems by cooling after mounting the sleeve after mounting.

[0008]

According to the method of manufacturing an electrofusion joint of the present invention, therefore, a step of winding a coated wire or a heating wire around a metal sleeve and an axial direction using a core provided in a mold as a slide core are set. Using a mold configured to be able to move forward and backward, the slide core is mounted on the slide core with the sleeve wound with the covered wire or heating wire by moving the slide core forward and backward, and then injection molding is performed. Back, the molded product is taken out, and the sleeve is inserted into the molded product and cooled until it is cooled.

[0009]

The sleeve is made of metal, has air flowability, and the molded product is cooled from the inside and outside, so that the cooling efficiency is good and it is uniformly cooled over the entire length. Also, the molded product is kept in shape by the sleeve until it is cooled, so there is no stress on the coil. The joint according to the present invention is a socket joint, an elbow joint, a cheese joint, a cap joint, etc., the sleeve used for the elbow joint is divided at the central portion, and the sleeve used for the socket joint and the cheese joint is also preferably divided into two. Alternatively, it is divided into three parts so that the sleeve can be extracted from two or three directions, and the sleeve can be easily extracted from the molded product.

There are various methods for cooling the molded product used in the present invention, but the following method is particularly effective. (1) Cooling in a thermostatic chamber, (2) Spray cooling with a spot cooler, (3) Cooling water circulation system rod insertion cooling by inserting a rod through which cooling water is passed.

[0011]

EXAMPLE A mold 11 provided with a slide core 12 as shown in FIG. 2 was used. First, each side of a sleeve 14 with a step 16 was wrapped around a heating wire 13 and assembled in series, and then the slide core 12 was formed. The core is mounted by advancing and retracting it, and injection molded into the cavity 15.

After molding, the slide core 12 is retracted and the molded product 17 is taken out from the mold 11 with the sleeve 14 attached, and cooled in a thermostatic chamber, or by spray cooling with a spot cooler, or by passing cooling water. The rod is inserted and cooled (see FIG. 3). After cooling, molded product 17
Remove the sleeve 14 from both sides.

[0013]

The present invention is constructed as described above and has the following effects. According to the manufacturing method of claim 1, since the molded product has a hollow central portion, the molded product is cooled from the inside as well, and the cooling efficiency is good in all cooling methods.
In addition to cooling in a relatively short time, the molded product is cooled uniformly in the axial direction, so the quality is stable, and since it is held by the sleeve during cooling and no stress is applied to the coil, it does not adhere to the plastic tube during fusion The heating wire will not short circuit.

When the sleeve is divided into two or three parts like the sleeve according to claims 2 to 4, the sleeve can be removed from each side of the molded product, and the sleeve can be easily removed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mold used in a conventional method.

FIG. 2 is a sectional view of a mold used in another method.

FIG. 3 is a sectional view showing a state during cooling by the method of the present invention.

[Explanation of symbols]

11 ... Mold 12 ... Slide core 13 ... Heating wire 14 ... Sleeve 15 ... Cavity 16 ... Step 17 ... Molded product 18 ... Cavity

Claims (5)

[Claims] 1. A step of winding a covered wire or a heating wire around a metal sleeve, and a slide core which is configured to be able to advance and retreat in the axial direction using a core provided in the die as a slide core. By mounting the above-mentioned sleeve around which the covered wire or heating wire is wound on the slide core and then injection molding, and after injection molding, retract the slide core to take out the molded product, and insert the sleeve into the molded product. A method for manufacturing an electrofusion joint, comprising the steps of: 2. The method of making an electrofusion joint of claim 1, wherein the joint is a socket and the sleeve is split at a central portion. 3. The method of manufacturing an electrofusion joint according to claim 1, wherein the joint is an elbow joint, and the sleeve and the core are divided into two parts, and each core is movable back and forth along two intersecting directions. 4. The method of manufacturing an electrofusion joint according to claim 1, wherein the joint is a cheese joint, and the sleeve and the core are divided into three parts, and each core can be moved back and forth along three directions of the T shape. . 5. The method of manufacturing an electrofusion joint according to claim 1, wherein the joint is a cap joint and the sleeve is composed of a single body.