JPH10648A - Manufacture of electric fusion bonding joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the manufacture of an electric fusion bonding joint which does not generate a jetting phenomenon during injection molding and is free from the deviation of a heating wire and in which molding strain is reduced and a socket is hardly made elliptic. SOLUTION: A molten resin injected from an injection port 15 is packed in a cavity 1a passing through a runner 14 and a gate port 13. The gate port 13 is formed in the end part on the side not corresponding to a socket 8 in a joint member 7. Simultaneously with the packing of the molten resin in the cavity 1a, the resin is packed in another cavity to mold an outer 2 at the same time. Accordingly, the molten resin injected from the gate port 13, after getting a cushion effect by colliding with the outer surface of an inner 4, flows in the axial direction from the end side toward the socket side and disperses also in the circumferential direction. An injection pressure is not applied directly to a heating wire 2 vertically.

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 used for gas or water distribution piping, and more particularly to a method suitable for producing a large diameter electric fusion joint by injection molding.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an electric fusion joint has a heating wire 2 spirally embedded in an inner peripheral surface of a joint member 7 made of a thermoplastic resin (such as polyethylene).
Both ends are connected to connector pins 3 and 3. Therefore, when the heating wire 2 is energized through the connector pins 3 and 3 to heat the heating wire 2, the receiving portion 8 is heated.
A pipe (not shown) made of a thermoplastic resin inserted into the above is electrically fused and connected.

[0003] In the electric fusion joint shown in the figure, the same joint member 7 as the joint member 7 is separately formed, and then the end surfaces thereof are heat-fused, that is, so-called butt-fused, to form the joint body 1.
Is what you get. Although the figure shows a socket type, there is also a case of an elbow or a chi, in which case, an intermediate member corresponding to each joint shape is interposed between the joint members 7,
Similarly, butt fusion is performed to obtain a joint body. These electrofusion joints are light and have excellent workability and are resistant to earthquakes, so they have been rapidly spreading in recent years, mainly for buried pipes for gas.Currently, they have been extended to large-diameter pipes with a nominal diameter of 200 mm or more. It is.

[0004] The electrofusion joint has conventionally been manufactured by an injection molding method. For example, a core is inserted into an inner cylindrical member called an inner member (reference numeral 4 in FIG. 2), and is formed on an outer surface of the inner member in advance. A method in which a heating wire is wound around the helical groove, the inner is set together with the core in a molding die, and an outer portion (reference numerals 5 and 6 in FIG. 2) is injection-molded thereon to obtain a joint body. Has been taken.

As an example of the injection molding method, a molten resin supply gate port (hereinafter simply referred to as a gate port) is provided at one or a plurality of locations in a substantially central portion of the joint body so that the resin is evenly rotated in the cavity. There has been a method of providing a portion and injecting the light in a direction perpendicular to the axis of the inner member.

Further, as disclosed in Japanese Patent Application Laid-Open No. Hei 7-217786, there is an injection molding method of injecting a resin in parallel with an axis of an inner set in a mold. Were provided on the end side surface of the joint body.

[0007]

[Problems to be solved by the invention] However, the nominal diameter 10
When forming a large-diameter electrofusion joint of 0 mm or more (hereinafter simply referred to as a joint), the joint body becomes considerably thick,
Its volume is quite large. Moreover, the thermal conductivity of the thermoplastic resin is poor, and the volume shrinkage from melting to solidification is large.
For this reason, internal defects are likely to occur, and in general, molding distortion tends to occur in large-diameter joints, especially when the inner diameter of the receiving portion is large and elliptical, the fusion strength varies, and during fusion, There is also a problem that the molten resin protrudes from the gap with the pipe.

In addition, in the former method, since the gate opening is located above the heating wire, the heating wire may receive a strong injection pressure and may be displaced or floated. As a result, there is a problem that the heating wire is liable to cause a short-circuit at the time of energization welding. In addition, since the gate opening is in the vertical direction and only on one side, the injection pressure tends to be biased only on one side, and it is considered that the ovalization is liable to be further worsened because the gate is molded as it is.

On the other hand, in the latter method, the gate port is provided at the end face and is injected at a high speed in parallel, so that the molten resin first jumps out at a stretch in the axial direction and expands, and then gradually from the near side close to the gate port. It shows the behavior of expanding in the radial direction. This is what is called a jetting phenomenon, and there is a problem that a difference occurs in the solidification time of the resin in the axial direction due to the jetting, and internal defects are easily generated. In addition, the jetting phenomenon usually occurs more easily as the injection speed increases, but in this case, since the gate port is provided on a relatively narrow end face, even if the injection speed is relatively low depending on the thickness and the dimensional balance of the gate port, the jetting phenomenon occurs. There is also a problem that setting of molding conditions is difficult.

The present invention solves the above-mentioned problems, and does not cause a jetting phenomenon or a displacement of a heating wire at the time of injection molding, has a small molding distortion, and has a small oval shape of a receiving portion. An object of the present invention is to provide a method for manufacturing an electric fusion joint.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a helically wound heating wire, an inner member made of a thermoplastic resin, mounted in a mold, and a cavity formed in the mold. A method for producing an electro-fusion joint by injection-molding a thermoplastic molten resin from a direction perpendicular to the axis of the inner to obtain a joint body, wherein a supply gate port of the molten resin is a part excluding the heating wire part. And a desirably a method for manufacturing an electro-fusion joint provided at an end of the joint body.

Further, the present invention comprises a heating wire wound in a spiral shape, wherein an inner member made of a thermoplastic resin is mounted in a mold,
An intermediate member formed by injection molding a thermoplastic molten resin into a cavity portion formed in the mold from a direction perpendicular to the axis of the inner member to form a joint member, and separately molding the joint members or the joint member. In the method for producing an electric fusion joint obtained by heat fusion to obtain a joint main body, a supply gate port of the molten resin in the injection molding is provided at a portion excluding a receiving portion side for receiving a connected pipe and the heating wire portion. Preferably, a method for manufacturing an electro-fusion joint provided at an end of a joint member.

In the above-mentioned manufacturing method, it is preferable that a plurality of molten resin supply gate ports are provided on the outer side and / or the inner side of the joint main body at equal circumferential intervals.

As described above, since the gate port is provided at a portion of the joint body where no heating wire is provided, particularly at the end thereof, a strong injection pressure is not applied to the heating wire, and the heating wire may shift or float during molding. Never do. In addition, the molten resin is injected from the direction perpendicular to the axis of the inner, but since the gate port corresponds to the end position of the cavity, the molten resin in this case once hits the outer surface of the inner. After the cushion effect is obtained, the fluid flows in the axial direction from one end to the other end. In other words, the flow becomes smooth with unidirectionality without causing the jetting phenomenon, and the radial pressure applied to the inner acts equally to avoid extreme ellipticalization.

On the other hand, in the method of obtaining the joint body by butt fusion later, when forming the joint member, the end side corresponding to the socket and the other side are clear. Therefore, in this case, a gate port is provided at an end on the side not corresponding to the socket of the joint body (the side corresponding to the center of the joint body). As a result, the jetting phenomenon does not occur as in the above case, and at the same time, the radial pressure acts evenly. In addition, since the injection pressure does not affect the receiving port side, the problem of ellipticity can be ignored. The side where the gate port is provided is usually designed to be thick, and naturally flows from the thick side to the thin side, and the flow and solidification of the molten resin are smooth.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a mold portion showing a method of manufacturing the joint member 7 shown in FIG. 2, and the same components as those in FIG. In addition, in this electric fusion joint, a joint body 1 is obtained by butt-welding the ends of the joint member 7 later, and the process is the same as that of the conventional art, so that the description thereof will be omitted. The mold 10 is divided into two parts, and the cores 11 and 12 divided in the upper and lower parts in the drawing are received at a substantially central part in the mold. The inner 4 is mounted on the cores 11 and 12 and set in a mold, and the mold and the core form a joint-shaped cavity 1a.
Next, the molten resin injected from the injection port 15 is filled into the cavity 1 a through the gate port 13 via the runner 14. Here, the gate port 13 is a side of the joint member 7 that does not correspond to the receiving portion 8 (a side corresponding to the center of the joint body).
At the extreme end. In this example, the gate port 13 is 1
Although only a plurality of gate openings are provided, a plurality of gate openings such as two or four at equal intervals in the circumferential direction may be provided.

At the same time as filling the cavity 1a with the molten resin, the cavity (not shown) on the left side of the drawing is used.
And the outer 2 is formed at the same time. For example, this is the same as the multilayer molding method disclosed in Japanese Patent Application Laid-Open No. 8-85154, in which a single mold has an inner mold, an outer mold (reference numeral 5 in FIG. 2), and an outer mold 2 (FIG. 2).
6) and that the cavity chambers are respectively formed so that synchronous molding can be performed.

As described above, the molten resin injected from the gate port 13 once hits the outer surface of the inner 4 to obtain a cushioning effect, and then flows in the axial direction from the end to the receiving side, and in the circumferential direction. Also spread. Here, if there are a plurality of gate openings in the circumferential direction, the resin spreads more evenly. At this time, the injection pressure does not directly act on the heating wire from the vertical direction, and the heating wire has little influence.

Next, a diameter of 200 mm
Manufactured socket joints. When the joint was observed by X-rays, the heating wire was at a predetermined position, and no displacement or lifting was observed. In addition, no internal defects such as voids occurred, and the ellipticity of the receiving portion, that is, the difference between the maximum diameter and the minimum diameter was 0.5 mm or less at the maximum, which was almost halved compared to the conventional case. Although the above-described embodiment is an electric fusion joint in which the joint bodies 7 are butt-fused to each other, a joint body obtained by integrally injection-molding the joint body from the beginning may also be used.
Almost the same results were obtained, and it was found that the ellipticity could be reduced.

As another embodiment of the present invention, a method is adopted in which a runner and a gate port are provided on the core side and a molten resin is injection-molded from the inside into the cavity. Also in this case, the gate openings are provided on the end side of the joint body avoiding the portion where the heating wire is located, and a plurality of gate openings can be provided at equal intervals in the circumferential direction, preferably at four places. Alternatively, in this case, even if it is not necessarily at the end, if injection molding is performed radially from the central part of the joint body, the effect of reducing damage to the heating wire can be obtained, and the gate port can be connected to a pipe. There is also an advantage that it can be used as a stopper or the like. Also,
An example in which the above-described embodiments are combined, that is, injection-molded from both the outer side and the inner side, and manufactured.

[0021]

The present invention is an injection molding method in which the jetting phenomenon does not occur, and the arrangement of the gate port is selected so that the resin flows in the axial direction and the injection pressure is not directly applied to the heating wire. As a result, internal defects are less likely to occur and the heating wire does not shift during injection molding. In addition, since the molten resin flows smoothly in one direction, there is little molding distortion due to uneven pressure in the inner diameter direction. A good electrofusion joint having a low rate can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold part showing one embodiment of a manufacturing method of the present invention.

FIG. 2 is a sectional view showing an example of a large-diameter electrofusion joint.

[Explanation of symbols]

1: Joint body 2: Heating wire
3 ... Connector pin 4 ... Inner 5 ... Outer 1
6 ... Outer 2 7 ... Coupling member 8 ... Receptacle
1a: Cavity section 10: Mold 11, 12: Core
13 ... Gate port 14 ... Runner 15 ... Resin injection port

Claims (4)

[Claims] A heating wire wound in a spiral shape, an inner member made of a thermoplastic resin is mounted in a mold, and a cavity formed in the mold is inserted into a cavity portion in a direction perpendicular to an axis of the inner member. In the method for producing an electric fusion joint obtained by injection molding a thermoplastic molten resin to obtain a joint main body, a supply gate port of the molten resin is provided at a portion other than the heating wire portion, Production method. 2. A heating wire wound spirally, an inner member made of a thermoplastic resin is mounted in a mold, and a cavity portion formed in the mold is inserted into a cavity portion in a direction perpendicular to an axis of the inner member. In a method for manufacturing an electro-fusion joint, a joint body is formed by injection-molding a thermoplastic molten resin to form a joint member, and each joint member or an intermediate member separately formed from the joint member is heated and fused to obtain a joint body. A method for manufacturing an electric fusion joint, wherein a supply gate port of a molten resin in molding is provided on a side of a receiving portion for receiving a pipe to be connected and a portion excluding the heating wire portion. 3. The method according to claim 1, wherein the supply port of the molten resin is provided at an end of the joint body or the joint member. 4. The electric power supply according to claim 1, wherein a plurality of the molten resin supply gate ports are provided on the outer side and / or the inner side of the joint body at equal intervals in a circumferential direction. Manufacturing method of fusion joint.