JPH09277313A - Mold for tubular molded article and molding method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold an electrofusion joint having a cylindrical inner surface. SOLUTION: Injection molding is conducted by using a mold 13 of which a core 11 is formed, in the shape of an ellipse of which the minor axis is made to coincide with the direction of injection of resin from a gate, in view of such a change in the shape after molding that the diameter comes to be long in the direction of injection of the resin from the gate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, an electrofusion joint, that is, a tubular molding such as an electrofusion joint in which a heating wire is embedded in a coil shape in a joint surface with a plastic pipe. The present invention relates to a mold used for molding an article and a molding method using the mold.

[0002]

2. Description of the Related Art Taking an electrofusion joint as an example, various joints such as socket joints, elbow joints, cheese joints, reducer joints, cap joints attached to pipe ends are used for connecting pipes. There is also a type of, and generally consists of a molded product in which the heating wire is embedded in a coil shape on the joint surface with the pipe. For fusion with the pipe, after fitting the plastic pipe from three sides, both sides or one side of the joint, or after pressing the joint against the outer peripheral surface of the plastic pipe, heat and melt the joint surface with the plastic pipe by energizing. Done by.

FIG. 1 shows a mold used for molding a socket joint among the above-mentioned joints. One side 2a and the other side 2b are combined and separably connected in the mold 1 which is divided into upper and lower parts. The cores 2a and 2 are arranged at the time of molding.
A heating wire (usually the coated heating wire 3 is used) is wound around each of b, set in the mold 1, and then injection-molded into the cavity 5 through the gate 4.

[0004]

Not only the above-mentioned insertion joint for inserting a pipe, but many cylindrical molded products are required to have a perfect circle on the inner surface or the outer surface. In the mold shown in Fig. 1, the core is formed in a perfect circle in order to obtain a joint with a perfect inner diameter. However, even if the molded product is cooled sufficiently after molding, the product taken out of the core will deform into an elliptical shape. Tend to be.

The present invention has been made for the purpose of solving this problem, and provides a mold capable of molding a molded product having an inner diameter of a perfect circle, and a molding method using this mold. It is something to try.

[0006]

Means for Solving the Problems The inventors of the present invention have investigated the direction of the ellipse of a molded product in order to elucidate the cause of the molded product becoming an ellipse. The direction of the major axis after molding is the injection direction of the resin injected from the gate. Found to match. The present invention has been made based on this finding, and as shown in FIG. 2, the core 11 has an elliptical shape, and the direction of the minor axis 2 is made to match the injection direction of the resin injected from the gate 12. It is set in the mold.

That is, according to the first aspect of the invention, in a mold having a core disposed inside and forming a cylindrical kibiti around the core, and a core having a short diameter is injected from the gate. The second invention is characterized by being injection-molded using the mold of the first invention.

According to the present invention, since the core has an elliptical shape and the minor axis direction thereof coincides with the injection direction of the resin injected from the gate, the molded product swells in the minor axis direction of the core and the inner diameter becomes a perfect circle. To do. As shown in FIG. 5, the cavities in the mold become thicker on the gate 12 and the opposite side because the minor axis direction L of the core 11 coincides with the injection direction of the resin injected from the gate 12. The thickness of the core 11 is also as shown in FIG.
Although it becomes thicker in the minor axis direction and thinner in the major axis direction, not only the inner surface but also the outer surface becomes a perfect circle, and in order to make the wall thickness uniform, the inner surface of the die forming the kievity 14 should also have the core 11 as shown in FIG. It is preferable to form an elliptical shape similar to the above so that the minor axis direction matches the injection direction of the resin injected from the gate.

The core used in each of the above inventions is a core 1 as shown in FIG. 1, that is, divided cores 2 on the left and right sides.
Although a and 2b are solid and a core is used for winding the coated heating wire 3, a core is divided into left and right as shown in FIG. It comprises slide cores 16a, 16b made possible and a sleeve core 18 which is fitted into each slide core 16a, 16b and wound with a coated heating wire 17 (may be a bare heating wire). A thing can also be used. According to the latter core, even if the core is large and heavy, the sleeve core is thin and lightweight, so it is easy to carry and handle when winding or mounting the mold. Since many sleeves are available, you can change the sleeve each time you finish molding, which improves productivity and allows automation. Only the slide core can be cooled to cool the core. Since such a structure may be adopted, there are effects such as cost reduction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The mold 13 shown in FIG. 5 is the same as the mold shown in FIG. 1, except that the core 11 is formed into an elliptical shape and the minor axis direction is the resin injection direction from the gate 12 (see FIG. 6, the mold 20 shown in FIG. 6 is the mold of the type shown in FIG. 5 in which the outer surface of the sleeve core 18 is elliptical and the minor axis direction is the gate 19. It is made to match the injection direction of the resin injected more.

Although the mold for molding the socket joint of the electrofusion joint has been illustrated above, in the molds for molding other insertion joints as well, the core is constructed as described above so that the inner surface is a perfect circle. It is possible to obtain an optimized joint. The same applies to molds for molding other tubular molded products.

[0012]

The present invention is configured as described above and has the following effects. According to the mold of claim 1 and the molding method of claim 5, a tubular molded product having an inner surface of a perfect circle or a substantially perfect circle can be obtained by making the core an elliptical shape in consideration of deformation after molding. According to the mold of the second aspect, it is possible to obtain an electrofusion joint having an inner surface of a perfect circle or a substantially perfect circle in the same manner.

According to the mold of the third aspect, it is possible to obtain a cylindrical molded product having a uniform circular thickness inside and outside and a uniform wall thickness. When the slide core and the sleeve core are formed as in the core according to claim 4, the sleeve core can be made thin and lightweight, so that even a molded product having a large diameter can be handled when the winding or the mold is mounted. It's easy and easy to work, and many wound sleeve cores can be prepared and replaced in a timely manner, improving productivity and only the slide core needs to be cooled. Has the effect of being able to reduce

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a mold.

FIG. 2 is a sectional view of a molded product obtained by the method of the present invention.

FIG. 3 is a sectional view of a mold according to the present invention.

FIG. 4 is a sectional view showing another example of a mold.

FIG. 5 is a sectional view of a mold according to the present invention.

FIG. 6 is a sectional view of another mold according to the present invention.

[Explanation of symbols]

1, 13, 20 ·· Mold 2, 11 · · Core 3, 17 · · Coated heating wire 4, 12, 19 ·
・ Gates 16a, 16b ・ ・ Slide core 18 ・ ・ Sleeve core

Continued Front Page (72) Inventor Fukuhiro Yoshimura 6-1-2 Waki, Waki-machi, Kuga-gun, Yamaguchi Mitsui Petrochemical Industry Co., Ltd.

Claims (5)

[Claims] 1. A mold in which a core is arranged inside, a cylindrical cavity is formed around the core, and a gate is provided to the cavities, in which a minor diameter of the core is injected from the gate. A mold for a cylindrical molded product, which is configured to have an elliptical shape that matches with. 2. The mold for a tubular molded article according to claim 1, wherein the tubular molded article is an electrofusion joint in which a heating wire is embedded in a joint surface with a plastic tube. 3. The tubular molded article according to claim 1, wherein the inner surface of the mold forming the cavity is also an elliptical shape similar to the core, and the minor axis direction coincides with the injection direction of the resin injected from the gate. Mold. 4. The core comprises a slide core which can advance and retreat in the axial direction, and a sleeve core which is fitted and mounted on the slide core and around which a heating wire or a coated heating wire is wound.
The described cylindrical molded product mold. 5. A method for molding a tubular molded article, which comprises performing injection molding using the mold according to claim 1.