JPH0681999B2 - Manufacturing method of union socket for plastic pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of a union socket used in a joint of a plastic pipe such as a polyethylene pipe for water supply to be joined to a water meter, a water faucet or other metal members.

[0002]

2. Description of the Related Art Recently, since plastic pipes are lightweight and have high corrosion resistance, they have been widely used in various fields such as water supply and industrial use. On the other hand, the union socket is made of metal such as gun metal. For example, as shown in FIG. 4, a cap nut 102 and a ring 103 are passed through a plastic pipe 100, and a tapered in-core 101 is tapped from the pipe end to the inner surface of the pipe to fix the pipe end, and in this state, the pipe end is fitted into the fitting portion of the union socket 1a. Insert into the cap nut 102 and union socket 1a
Tighten the screw part on the outer surface to join the plastic pipe 100 and the union socket 1a. On the other hand, a cap nut 2a is externally fitted to the metal member, for example, the meter side, through the union socket 1a and the retaining ring 104, and the joint portion is assembled so as not to separate. Similar to pipes, the use of plastics as pipe joints is also increasing, and in accordance with this, so-called electrofusion (electrofusion welding) in which a heating wire is embedded in the joining surface as a plastic molded body on the plastic side of the union socket ) Type is also being developed. That is, after the plastic tube is inserted into the plastic molded body, the contact surface of the molded body and the outer peripheral surface of the plastic tube which is in contact with this surface are welded by the heat generation of the heating wire.
In addition, bonding with adhesives and mechanical joints have been conventionally applied.

[0003]

Among the union sockets of the prior art, those made of metal have high material strength and high reliability, but their corrosion resistance cannot be said to be perfect when they are buried in the ground, so they can be used for a long period of time. During use, it may be corroded by moisture in the ground or chemical atmosphere. In addition, as shown in FIG. 4, there are many types of members for joining, and there are many joining procedures, so that the direction of the ring 103 may be wrong and
There is also a risk of making a mistake such as forgetting to enter 01.
Further, the union socket 1a, which is a cast product, has a problem that the weight is large and the unit price including the processing cost is high. Even when the cap nut on the water meter side is attached, the snap ring 104 must be fitted from the union socket side, which has a drawback that the work becomes complicated. On the other hand, the plastic union socket solves the problem that remains in the gun metal fittings in terms of corrosion resistance and weight, but it is much weaker than the metal cap nut on the water meter side, so when combining both, There is a concern that the plastic end may be deformed or damaged. Further, when an external force is applied during construction or after mounting, stress concentrates on the joint portion between the cap nut and the plastic molded body, and there is a strong possibility that the molded body having low strength cannot be withstood and damaged. Also in this case, the joint with the plastic pipe can be easily performed by electrofusion welding, but the joint with the metal cap nut must be fitted in the middle from the molded body side as in the previous example. As a result, the assembly work is complicated.

In order to solve the above-mentioned problems, it is an object of the present invention to provide a method for efficiently manufacturing a union socket in which the difference in strength between a plastic molding and a metal cap nut is reduced.

[0005]

In the method of manufacturing a union socket for a plastic pipe according to the present invention, a slide pin is fitted between an upper die and a lower die of a molding die to form a gap corresponding to a plastic molding. Then, a metal cap nut is supported by an upper die, a lower die, and a slide pin on a gap corresponding to one joining surface via a metal annular support metal fitting, and then combined,
The above-mentioned problems were solved by injecting and filling molten plastic into the gap and sandwiching a support metal member to integrally manufacture a metal cap nut and a plastic molded body.

[0006]

1 is a sectional view showing an embodiment of the present invention.
The operation of the present invention will be described based on the drawings. A slide pin 7 is inserted from the left side of the figure between the upper die 5 and the lower die 6 of the injection molding die to form a gap 1M corresponding to a plastic molded body, and the upper die, the lower die and the slide pin 3 The person supports the metal cap nut 2 at a position above the end of the gap 1M. Inner surface 21 and flange 22 on which internal thread of cap nut 2 is engraved
Then, the support metal fitting 3 is attached so as to cover the mold surface and block the end of the gap of 1M. By interposing the support metal fitting between the gap 1M and the cap nut 2 in this way, even if the molten plastic is injected from the right side of the figure to completely fill the gap 1M, the internal thread of the cap nut is transmitted. No plastic can penetrate.

For reference, FIG. 2 shows the operation when it is assumed that the cap nut and the plastic molded body are integrally molded at the same time without interposing this support fitting. The plastic filled in the gap 1M is plastic molded. While the body 1 is being formed, the plastic 4 that has leaked to the entire inner surface along the screw bottom of the cap nut 2 is left.

[0008]

EXAMPLE FIG. 3 is an example showing a polyethylene molded body for a water pipe polyethylene pipe manufactured by the above-mentioned manufacturing method. The heating wire 8 is spirally wound around the polyethylene pipe joining side of the polyethylene molded body 1, and the support metal fitting 3 is externally fitted on one of the cap nut joining sides. The portion 11 is reinforced over the entire circumference and has an effect of effectively protecting a portion where stress is most likely to concentrate.

The polyethylene pipe for water supply is a linear low density polyethylene (LLDPE) having a density of 0.91.
It is in the range of 5 to 0.940 g / cm ³ , and its tensile strength is about 9.8 to 14.7 N / mm ² . On the other hand, the polyethylene molded body has a density of 0.930 to 0.940 g / cm ³ of medium density polyethylene (hereinafter referred to as “MDPE”) or a density of 0.950 to 0.965 g / cm ³ of high density polyethylene (hereinafter “ If it is made of "HDPE"), it has a tensile strength of at least 17.7 N / mm ² or more (MDPE), or at least 19.6 N / mm ² or more (HDPE), so external force is applied to the pipeline. Even if the stress is concentrated on the molded body, it can sufficiently withstand the stress and maintain the function of the pipeline normally. In addition, if 2 to 3% of carbon black is blended in the molded product, the weather resistance will be improved in all parts, and the outer peripheral surface exposed to direct sunlight will be no exception and the quality will deteriorate compared to the conventional one. No trouble occurs. In addition, since the density of the molded body of the union socket is higher than that of the conventional polyethylene pipe, the high density provides the property of strongly resisting the intrusion of chlorine contained in tap water. Therefore, the troubles that cause the deterioration of the quality from the inner peripheral surface do not occur, and the weather resistance and the chlorine water resistance are lined up at the same time. Further, in order to improve the chlorine resistance, HDPE containing no carbon is used only in the water contact portion of the joint. So-called 2
Color molding is also conceivable.

Further, when the water pipe and the union socket are electro-welded to each other, a core metal fitting is closely attached to the inner surface of the pipe and fitted inside, and if an excessive electric load is applied, the inner surface of the pipe is subjected to thermal expansion. It tries to bulge out and is blocked, but it is converted into a reaction force that presses strongly on the contact surface. In this embodiment, since the material strength of the polyethylene molded body is large, the outer peripheral surface of the free molded body cannot be swollen, so that extremely strong pressing force acts on the molten resin while being restrained from both sides, and compact welding To form a part. The support metal fitting is a ring-shaped metal and its shape and wall thickness may be appropriately set. In this example, stainless steel corrosion-resistant alloy steel was used. However, a corrosion-resistant copper alloy may be used. In addition, since the cap nut joint side of the polyethylene molded body is generally provided with a step and the flange 12 is projected,
It is desirable to use a support fitting that is bent twice at a right angle so as to cover the entire circumference from the upper surface of the flange to the body portion. Although a polyethylene union socket is shown here, the material of the joint body can be applied to all synthetic resins such as polybutene and polyvinyl chloride in addition to polyethylene. In addition to the electrofusion method, the connection between the pipe and the joint body can be applied to, for example, adhesion or mechanical.

[0011]

As described above, according to the present invention, the side where the cap nut made of metal is joined reinforces the low strength of the plastic and intentionally strengthens the portion where external force tends to concentrate. Eliminates the possibility that the joint surface of the will be deformed or damaged. Further, since the plastic molded body and the cap nut can be molded integrally in a joined state, the complicated assembly work of both members is eliminated, and the production process can be reduced. On the other hand, the effect peculiar to the embodiment is that the union socket joining the polyethylene pipe for water supply can be easily carried out by electrofusion welding, and the strength, weather resistance, and chlorine resistance especially required for the union socket of water supply polyethylene are obtained. It has the advantages that it is easy to perform the fusion welding work and promises a perfect joint.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the requirements of the present invention are lacking.

FIG. 3 is a cross-sectional view showing an example of a product manufactured according to an example.

FIG. 4 is a sectional view showing an example of a conventional technique.

[Explanation of symbols]

 1 Plastic molded body 1M Gap formed in mold 2 Cap nut 3 Support metal fitting 5 Upper mold 6 Lower mold 7 Slide pin 8 Heating wire

Claims (1)

[Claims] 1. A method of manufacturing a union socket for a plastic pipe by plastic injection molding, comprising:
A slide pin is fitted between the upper mold and the lower mold of the molding die to form a gap corresponding to the plastic molding, and a metal annular support metal fitting is placed on the gap corresponding to one joint surface. A metal cap nut is supported and combined with an upper die, a lower die and a slide pin, molten plastic is injected and filled into the gap, and a support metal fitting is sandwiched between the metal cap nut and a plastic molded body to be manufactured simultaneously at the same time. And a method for manufacturing a union socket for plastic pipes.