JP2001047464A - Production of electrofusion joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of irregularity in dimensional shrinkage caused by the atmospheric temp. at a time of cooling and to set the inner diameter of a receiving port so as to satisfy a specification value. SOLUTION: An electrofusion joint formed into a cylindrical shape and enabling the end part of a resin pipe to be fitted to the inner peripheral surface thereof and having a resistor wire 12 generating heat by the passage of current embedded therein in a coil form is produced by injection molding. After injection molding is performed by using a mold consisting of a fixed template 11 provided with a cavity 11a and the diameter contractible core attached to a movable template 1, a cooling core is inserted in the receiving port of the electrofusion joint to cool the joint.

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 for fusion-bonding a gas pipe or a water pipe made of synthetic resin.

[0002]

2. Description of the Related Art Conventionally, when a synthetic resin pipe, for example, a polyethylene pipe is connected, a method of electrically connecting the pipes by heat fusion has been widely used. In the electric fusion joint used for such connection, a resistance wire is buried in a coil shape on the inner peripheral surface of the receiving port, and when the polyethylene tube is inserted into the receiving port, electricity is supplied and the resistance wire generates heat. Thereby, the outer surface of the polyethylene pipe and the socket of the electric fusion joint are fusion-bonded.

When the nominal diameter of the above-mentioned electrofusion joint is 150 or more, it is manufactured by injection molding using a mold having a mold core capable of contracting and expanding. More specifically, after a resistance wire covered with a polyethylene resin is wound into a coil shape and inserted into a mold core in a reduced diameter state, the mold core is expanded and filled with resin. Then, after holding and cooling for a certain period of time, the mold core is reduced in diameter to form a compact (electro-fusion joint).
The method of taking out has been done.

[0004] The electrofusion joint obtained by the above injection molding is thick and not cooled to room temperature at the stage of being taken out of the mold. The temperature may indicate 120 ° C. Therefore, when the molded product is taken out of the mold and cooled at room temperature, the molded product undergoes cooling shrinkage. The shrinkage at this time depends on the ambient temperature at the time of cooling, and the higher the ambient temperature, the higher the degree of crystallinity, and the higher the shrinkage. Therefore, for example, a molded body molded at a low temperature shrinks at a high temperature, so that dimensional shrinkage occurs in the inner diameter of the receiving port of the electrofusion joint, and the standard value is deviated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing an electro-fusion joint having a dimensional shrinkage that does not vary depending on the ambient temperature during cooling and an inner diameter of a receiving port satisfying a standard value. .

[0006]

According to a method of manufacturing an electrofusion joint of the present invention, the joint is formed in a cylindrical shape, and the inner peripheral surface of the joint is formed in a cylindrical shape at the end of a resin tube. A method for manufacturing an electric fusion joint in which an end portion of a resin tube is fitted with a resistance wire that generates heat by energization in a coil shape by injection molding, wherein a fixed side provided with a cavity is provided. When performing injection molding using a molding die having a core that can be reduced in diameter and attached to a mold plate and a movable mold plate, a) resistance to a drum having an outer diameter substantially equal to the core outer diameter of the molding die; A bobbin making step of winding a wire to form a bobbin; b) a bobbin attaching step of fitting the bobbin to a core in a reduced diameter state; c) a thermoplastic resin melted by closing a molding die after expanding the core. A molding process in which the resin is injected into the cavity of the molding die; d) a step of reducing the diameter of the core after cooling the thermoplastic resin injected into the cavity, and taking out the drawn molded body out of the molding die; and e) cooling the receiving port of the molded body taken out of the molding die. And cooling the core.

[0007]

According to the present invention, there is provided an electric welding method comprising forming a cylindrical shape into which an end of a resin tube can be fitted, and a resistance wire which generates heat when energized is buried in a coil shape. A method for manufacturing a joint by injection molding, when performing injection molding using a molding die composed of a core that can be reduced in diameter and attached to a fixed-side mold plate provided with a cavity and a movable-side mold plate, After fixing the coil-shaped resistance wire on the outer peripheral surface of the core in the reduced diameter state, the core is expanded, and a resin is filled between the core and the mold to perform injection molding. Next, by taking out from the molding die to the outside of the mold and inserting a cooling core into the receiving port of the molded body and cooling, there is no variation in dimensional shrinkage due to the ambient temperature at the time of cooling, and the receiving port dimensions satisfy the standard value. An electric fusion joint can be obtained.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. 1 to 4 show an embodiment of the present invention. FIG. 1 is a schematic sectional view showing a molding die and a bobbin mounted on a core of the molding die. FIG. 2 is a partially cutaway schematic sectional view showing a drum and a bobbin produced by winding a resistance wire. FIG. 3 is a schematic sectional view of the clamped molding die. FIG. 4 is a schematic cross-sectional view showing a state in which a cooling core is inserted into a molded body to be cooled.

First, a molding die used in the present invention will be described. The molding die shown in FIG. 1 includes a movable mold plate 1 to which a core 4 is attached and which can be freely opened and closed, a stripper plate 2, a mold plate 3, and a fixed mold plate 11 provided with a cavity 11a. The core 4 can be reduced in diameter and provided with a protrusion 6 having a height of about 0.5 mm on the outer peripheral surface thereof. The bobbin 5 is fitted on the core 4 of the molding die, and the end of the bobbin 5 is in contact with the projection 6.

Next, a method of manufacturing the electrofusion joint will be described in accordance with the procedure of the process. a) A bobbin manufacturing process is shown in FIG. In FIG. 2, 1
Reference numeral 3 denotes a drum, and the outer diameter of the drum 13 is substantially the same as the outer diameter of the core 4 of the molding die. The bobbin 5 is manufactured by winding the coated resistance wire 12 made of polyethylene resin while rotating the drum 13. An iron is applied to the outer periphery of the bobbin 5 to heat and melt the coating of the coating resistance wire 12 to form a iron stopper 14, and the coating resistance wire 12 is fixed by fusing each other.

B) A bobbin mounting step is shown in FIG. The core 4 of the molding die is reduced in diameter, and the core 4 is
The bobbin 5 removed from the core 3 is fitted, and the end of the bobbin 5 is brought into contact with the projection 6, thereby disposing the bobbin 5 at a predetermined position on the core 4.

C) The injection molding process is shown in FIG. Bobbin 5
After expanding the diameter of the core 4 fitted with the mold, the movable mold plate 1 that can be opened and closed is moved in the direction of the mold plate 11 provided with the cavity 11a, and the molding die is closed as shown in FIG. The obtained polyethylene resin (not shown) is injected into the cavity 11a of the molding die through the sprue 11b to perform injection molding.

D) Step of taking out the molded body from the molding die At the stage where the injected resin is cooled down to a temperature at which the pressure is maintained, the movable mold plate 1 is retracted in the direction opposite to the mold plate 11 and molded. After opening the mold, the injection-molded molded body is
Withdraw from Next, the core 4 is reduced in diameter, the stripper plate 2 is advanced, and a polyethylene resin molded article (electro-fusion joint) in which the bobbin 5 is embedded is drawn out of the core 4 and taken out of the mold.

The surface temperature of the molded body when the molded body is taken out of the mold is preferably 40 to 120 ° C. When the temperature is lower than 40 ° C., the molded body is easily damaged when a cooling core described later is inserted, and when the temperature exceeds 120 ° C., the molded body may be deformed during cooling by the cooling core.

FIG. 4 shows the step of cooling the molded body outside the mold. The cooling core 18 is inserted into the receiving port 17a of the molded body 17 taken out of the mold and cooled while correcting the inner diameter of the receiving port 17a. It is preferable that the cooling core 18 is pulled out of the molded body 17 when the surface temperature of the molded body 17 becomes 40 ° C. or less. The outer diameter of the cooling core 18 is preferably set to be slightly smaller than the inner diameter of the receiving port 17a so that the cooling core 18 can be smoothly inserted into or removed from the receiving port 17a of the molded body 17.

In order to promote the cooling of the molded body 17, the molded body 17 may be cooled with air or water from the inside or the outside, or may be cooled by circulating the air or water inside the cooling core 18. May be promoted. The material of the cooling core 18 is preferably a metal having good thermal conductivity, such as copper and its alloy, sunless, aluminum and its alloy.

The method for reducing and expanding the diameter of the core 4 is as follows.
The method is not particularly limited, and for example, a method described in Japanese Patent Application Laid-Open No. 5-261557 is preferably used.

Through the above-described manufacturing process, it is possible to obtain the electrofusion joint 17 in which the coated resistance wire 12 is embedded in a coil shape on the inner peripheral surface of the receiving port 17a. Terminal pins (not shown) for supplying current to the resistance wire are separately attached to both ends of the coated resistance wire 12 of the electric fusion joint 17.

Example 1 A high-density polyethylene resin-made electric fusion joint (one-sided socket having a nominal diameter of 200) was manufactured by the above-described manufacturing method at a resin temperature of 230 ° C. and a mold temperature of 25.
After injection molding at 600 ° C and a molding cycle of 600 seconds, a cooling core was inserted into the socket of the electrofusion joint and allowed to cool at ambient temperatures of 20 ° C and 40 ° C for 30 minutes, respectively. Was 0.4%.

(Comparative Example 1) After injection-molding an electro-fusion joint in the same manner as in Example 1, a cooling core was not inserted into the socket of the electro-fusion joint, and at an ambient temperature of 20 ° C and 40 ° C, respectively.
After cooling for two minutes, the difference in dimensional shrinkage between the two was 1.2%
Met.

[0021]

The method for manufacturing an electro-fusion joint of the present invention has the above-described structure, and a cooling core is inserted into a receiving port of an injection-molded electro-fusion joint to cool the joint. Provided is an electric fusion joint having excellent dimensional accuracy without being affected by temperature.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a molding die and a bobbin mounted on a core of the molding die.

FIG. 2 is a partially cutaway schematic sectional view showing a drum and a bobbin produced by winding a resistance wire.

FIG. 3 is a schematic cross-sectional view of a clamped molding die.

FIG. 4 is a schematic cross-sectional view showing a state in which a cooling core is inserted into a molded body to perform cooling.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Movable mold plate 2 Stripper plate 3 Mold plate 4 Core 5 Bobbin 6 Protrusion 11 Fixed mold plate 11a Cavity 12 Covering resistance wire 13 Drum 14 Iron stop 17 Molded body (electric fusion joint) 17a Molded body receiving port 18 Cooling core

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F202 AA05 AD15 AD18 AD35 AG08 AH11 CA11 CB01 CB12 CB20 CK25 CK54 CK82 CL09 CM29 CQ05 CQ07 4F206 AA05 AD15 AD18 AD35 AG08 AH11 JA07 JB12 JB20 JF05 JLJ JM02 JM01 JQ81 JT06 JW15 4F211 AA05 AD15 AD18 AD35 AG08 AH11 TA08 TC11 TH02 TJ09

Claims (1)

[Claims] 1. An electric fusion joint having a cylindrical shape, an end portion of a resin tube being fitted to an inner peripheral surface thereof, and a resistance wire which generates heat by energization being buried in a coil shape. A method of manufacturing by injection molding, wherein when injection molding is performed using a molding die composed of a core that can be reduced in diameter and attached to a fixed mold plate and a movable mold plate each having a cavity, a) A bobbin producing step of producing a bobbin by winding a resistance wire around a drum having an outer diameter substantially the same as the core outer diameter of the molding die; b) a bobbin attaching step of fitting the bobbin to a core in a reduced diameter state; A) a molding step of closing the molding die after expanding the core and injecting the molten thermoplastic resin into the cavity of the molding die; and d) reducing the core diameter after cooling the thermoplastic resin injected into the cavity. Out of the molding die Step and, e) step and, the method of manufacturing an electro-fusion fitting which is characterized in that it consists of cooling by inserting a cooling core into the socket of the molded article was taken out into the molding die outside retrieve.