JPH05285980A - Manufacture of corrosion proof pipe coupling - Google Patents

Abstract

PURPOSE:To reduce difference in thickness of injection resin and cool melted resin faster so as to mold easily by injecting thermoplastic resin into an inner face of a recess of a metal pipe coupling for a plurality of times. CONSTITUTION:First injection molding dies 21-23 are inserted into each end part of a malleable cast iron pipe coupling tee body 1. Melted resin is injected into a cavity 55 from a runner 3 in the die 21 through a gate 4, cooled and solidified so as to set a thickness of a resin-coated layer 55 to 1/2 of a final thickness. As the coated layer 55 is in contact with the metal face of the body 1, cooling speed becomes faster. Next, the dies 21-23 are removed and dies 61-63 for final shape are inserted into the coupling body 1 having the resin layer 55, and injected into a cavity 85 from a runner 7 through a gate 8 so as to be solidified. Then, the dies 61-63 are removed. The resin layers 55 and 85 are fixed at an uneven part 10 formed in the corner of the resin layer 55. Accordingly, the resin layer can be cooled faster and working will be easy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an inner resin-coated anticorrosion pipe joint for connecting an inner resin-coated steel pipe used for piping for water supply, hot water supply, etc., and particularly to injection on the inner surface of a metal pipe joint. The present invention relates to a resin coating molding method for coating a resin by molding.

[0002]

2. Description of the Related Art In order to prevent red water generated by rusting of an iron substrate, an inner surface of a steel pipe coated with a resin is used for a pipe for supplying water, hot water, or the like. As a pipe joint for connecting the inner surface resin-coated steel pipe, an anticorrosion pipe joint having an inner surface coated with resins 12 and 13 as shown in FIG. 4 is used. This anticorrosion pipe joint has a joint body 1 made of malleable cast iron and has a JI
Using the screw-in type pipe joint specified in S, the inner surface of the central part excluding the female thread on the inner surface of the end is covered with the synthetic resin layer 12, and the tubular portion 13 is extended from the synthetic resin layer 12 toward the end. It was done.

When the inner surface resin-coated steel pipe 20 connected to this corrosion-resistant pipe joint is screwed in and connected, the outer periphery of the tubular portion 13 comes into contact with the inner surface 21 of the resin-coated layer of the inner surface resin-coated steel pipe 20 to be cut off. For this reason, the end surface of the steel pipe 20 is protected from the internal fluid, and the inner surface of the joint body 1 is protected, so that good corrosion resistance is exhibited. In this manufacturing method of the anticorrosion pipe joint, a molten resin is injected into the inner surface of the joint body 1 by an injection molding machine, and the synthetic resin layer 12 at the central portion and the tubular portion 13 at the end portion are injection molded at once. ..

[0004]

According to the shape of the joint body 1 and the shape of the mold for injection molding, the anticorrosion pipe joint has a thick synthetic resin layer 12 at the center as shown in FIG.
The thickness of 3 becomes thinner. The thick part and the thin part have a large wall thickness of 4: 1. However, from the viewpoint of injection molding, it is desirable that the wall thickness of the molding resin be as uniform as possible. Especially with crystalline resins that undergo a large volume shrinkage during melting and solidification of the resin, molding defects such as sink marks and distortion are likely to occur. As a result, there are drawbacks such as difficulty in manufacturing control in injection molding and poor yield. For example, polyethylene and polypropylene resin may reach about 20% when volume contraction from melting to solidification is included, and even after the resin of the gate is solidified by the molding method of the mold, the unsolidified portion remains in the cavity part. If there is a thick thick portion that remains, a large sink mark will occur in that portion.

Therefore, in order to prevent the occurrence of sink marks,
It is sufficient to increase the injection pressure by increasing the injection pressure and replenish the resin until the thick wall portion is solidified. In such a case, a large injection pressure is applied to the joint body 1 and the joint body 1 swells. There is a problem that the main body 1 is cracked. The present invention solves the above-mentioned problems, and provides a manufacturing method capable of efficiently manufacturing a corrosion-resistant pipe joint having excellent quality without sink marks or distortion when injection-molding a resin.

[0006]

DISCLOSURE OF THE INVENTION The gist of the present invention is to connect a pipe for injection-molding a thermoplastic resin to the inner surface of the recess of a metal pipe joint having an internal thread at the end and a recess at the center. In a method for obtaining an anticorrosion pipe joint that protects the end face of the metal pipe joint and the inner surface of the metal pipe joint from the internal fluid, the thermoplastic resin is injection-molded in a plurality of times on the inner surface of the recess of the metal pipe joint, and the desired anticorrosion pipe A method for manufacturing a corrosion-resistant pipe joint, which is characterized in that a joint is obtained.

In the above, the resins used in the first and second or subsequent injection moldings are basically resins of the same material, and they are heat-sealed in the respective molding resin layers. Resins having different compositions or types may be used as long as they are shaped to engage with. For example, the first injection-molded resin may be molded with hard vinyl chloride having a low shrinkage ratio, the second may be molded with soft vinyl chloride having a high shrinkage ratio, and the heat-resistant engineering resin may be used for the second time. Molding work becomes easier by molding polybutene-1 having excellent flexibility and heat resistance and a large shrinkage ratio. In addition, the most stable shape is that of splitting in the radial direction and injection molding, but depending on the shape of the joint body and the shape of the molding resin, splitting may be performed in the axial direction for injection molding. Furthermore, by making the wall thickness at the time of the first injection molding larger than the wall thickness at the time of the final injection molding, it is possible to obtain a stable quality without sink marks in the final injection molding.

[0008]

Since the present invention has the above-mentioned structure, the thick wall portion of the inner surface resin layer is injection-molded in plural times. Therefore, the difference in thickness between the thick-walled portion and the thin-walled portion of the resin is significantly reduced as compared with the case where injection molding is performed once, and the thickness can be equalized. In addition, the resin capacity at the time of one injection molding is significantly reduced as compared with the conventional one, and the cooling rate of the resin after molding is increased. For this reason, after the resin is injected, the molded resin parts are cooled uniformly, and the conventional sink mark due to the uneven thickness does not occur. Therefore, it is not necessary to apply a large injection molding pressure in order to prevent sink marks, and injection molding can be performed with a low molding pressure that can sufficiently withstand the strength of the joint body. In addition, if the volume of injection resin is large, the molding conditions such as the resin temperature during molding and the temperature of the mold greatly affect the quality after molding, but as mentioned above, the resin capacity is small, the cooling speed is fast, and uniform cooling is possible. In this case, the injection molding conditions are not so affected and the resin molding operation can be easily performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are sectional views showing an embodiment of the present invention, and FIG. 1 shows the first injection molding for the first time. Reference numeral 1 denotes a malleable cast iron pipe joint chase body, into which injection molding dies 21, 22, 23 are inserted on the inner surface of each end of the body 1. Mold 2
1, 22 and 23 are the first molding dies for molding in two times, and the thickness of the resin coating layer 55 is 1/2 of the final thickness.
To 2/3 (the ratio of A and B shown in FIG. 2). This is because the first resin coating layer 55 is in contact with the metal surface of the joint body 1, so that the cooling rate is faster than that of the second and subsequent molding resins, and the first resin coating layer 55 is also used. Even if shrinkage occurs, the thickness of the final injection molding is thin and the resin capacity is small, so the first coating layer 5
This is because it is possible to form an accurate coating layer 85 having a dimension that is not shrinkable on the surface of 5. The molten resin of the injection molding machine is injected into the cavity 55 from the runner-3 provided inside the mold 21 through the gate 4 and filled. After the injected molten resin is sufficiently cooled and solidified, the molds 21, 22 and 23 are pulled out to the end side of the joint body 1 and removed, and the first injection molding operation is completed.

Next, FIG. 2 shows the second injection molding. After the first molding is completed, the final-shape molds 61, 62, 63 are inserted into the joint body 1 having the first-stage resin layer 55. Then
Molten resin is injected into the cavity 85 through the gate 8 from the runner 7 provided inside the die 61. After the injection resin is sufficiently cooled and solidified as in the first time, the molds 61, 62,
63 is removed from the joint body 1 to finish the second injection molding. The first resin layer 55 and the second resin layer 85 are
It is heat-sealed by the molten resin injected for the second time and integrally bonded to the resin layer 55 for the first time. Further, even when the first and second resin are different, the first resin layer 55 provided on the corner
It is firmly fixed by the uneven portion 10.

FIG. 3 shows another example of the fixing structure for the first and second molding resins, in which four concavo-convex portions 11 are arranged in the circumferential direction.
May be provided with a length in the axial direction to fix the resin layers 55 and 85 to each other. In this case as well, the mold can be removed on the end side of the joint body after injection molding. Further, in the above-described embodiment, the method of performing injection molding a plurality of times by dividing it in the radial direction has been shown, but it is also possible to perform injection molding a plurality of times by sequentially dividing it in the axial direction from the center of the joint body.

In addition, the first resin is fixed to the joint body 1 by using hard vinyl chloride having a small shrinkage ratio or engineering resin such as PFE, PSF, PES, PEEK having high heat resistance, and the second resin is water. From the viewpoint of hygiene, soft vinyl chloride, polyethylene, polybutene-1 and the like can be used to facilitate injection molding, and in consideration of economy, a resin that best suits the intended function can be selected.

[0013]

According to the present invention, the difference in the thickness of the resin injected into the joint body can be made sufficiently small and the volume of resin injected at one time becomes small, so that the cooling rate of the injected molten resin is high, Each part is cooled uniformly. Therefore, the molding process of the resin is facilitated, and a corrosion-resistant pipe joint with stable quality can be easily obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first resin molding process showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a final second resin molding showing an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a fixed shape of resin layers according to an embodiment of the present invention.

FIG. 4 is a connection cross-sectional view of an anticorrosion pipe joint and a pipe for explaining a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Joint main body 3,7 Runner-4,8 Gate 9 Cylindrical part 10 Corner uneven part 21,22,23 1st molding die 61,62,63 2nd molding die 55 1st time Molded resin layer 85 Second molded resin layer

Claims (1)

[Claims] 1. A thermoplastic resin is injection-molded on the inner surface of the recess of a metal pipe joint having an internal thread at the end and a recess at the center, and the end face of the pipe to be connected and the inner face of the metal pipe joint are In a method for obtaining an anticorrosion pipe joint that protects from an internal fluid, the thermoplastic resin is injection-molded into the recess inner surface of the metal pipe joint in a plurality of times in order to obtain a target anticorrosion pipe joint. Method for manufacturing food pipe joint.