JP3170417B2 - Manufacturing method of electrofusion joint and core for its winding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a socket joint, an elbow joint, a cap joint, and the like, which are used in piping work of a plastic pipe and have a heating wire embedded in a coil inside.
The present invention relates to a method for manufacturing an electrofusion joint such as a cheese joint, and a metal winding core used in the method.

[0002]

2. Description of the Related Art Of the various electrofusion joints described above, taking a socket joint as an example, as a conventional method of manufacturing this kind of joint, as shown in FIG. After setting the solid core 2 in which the right half core 2a and the left half core 2b around which the heating wire is wound (hereinafter simply referred to as a heating wire) are set in a mold, a thermoplastic resin is placed in the cavity 4. Has been adopted.

According to this method, as the size of the joint increases, the weight of the core also increases, which makes handling difficult and involves a risk of work. Remove the core from the left and right of
Since it is necessary to wind a heating wire around each of the cores that have been pulled out, the time until the next molding is performed becomes longer, reducing productivity.Preparing a large number of cores and winding the heating wire in advance If you set the core around which the heating wire is wound one after another in the mold each time molding is completed, productivity will increase and automation will be possible. In addition, it is difficult to cool each core internally for cooling the molded product, which is disadvantageous in that the cost is high. Therefore, recently, as shown in FIG. 2, the left and right cores 6a and 6b around which the heating wire 1 is wound are hollowed, and slide cores 8a and 8b which can be advanced and retracted are inserted into the mold 7 from the right and left, and then set in the cavity. Injection molding of a thermoplastic resin into the resin 9 has been frequently used. According to this method, since the core is hollow and lightweight, handling is easy,
Even if the internal cooling is performed, only the slide core needs to be cooled, and the cost is reduced. Therefore, it is possible to increase the productivity by preparing a large number of cores.

FIG. 3 shows an electrofusion joint 11 obtained by the method described above. An elbow joint can also be obtained by a similar method. That is, as shown in FIG. 4, the above-described core 6 around which the heating wire 1 is wound
a and 6b are passed through the slide cores 13a and 13b, set in the mold 14, and then injection molded with a thermoplastic resin in the cavity 15.
FIG. 5 shows the elbow joint 16 thus obtained.

[0006] Similarly, as shown in FIG. 6, the above-mentioned core 6 a or 6 b around which the heating wire 1 is wound also has a cap joint.
And then set in the mold 19 through the slide core 18 and then injection molding a thermoplastic resin into the cavity 20. FIG. 7 shows the cap joint 21 thus obtained.

[0006]

When a core is extracted from a molded product taken out of a mold, the molded product shrinks due to the subsequent cooling, and the inner diameter tends to be reduced. The reduction in the inner diameter dimension is small at the place where the heating wire is buried, and becomes large at the opening where the heating wire is not buried and at the back of the joint. In particular, the elbow joint 16 as shown in FIG. 5 and the cap joint as shown in FIG. In No. 21, the shrinkage at the center of the joint and the thick part at the back is remarkable, and the shrinkage of the inner diameter at the cold zone at the back of the joint is large. In addition, the reason for providing a cold zone in the joint is
This is to prevent the molten resin from flowing out of the joint or flowing into the joint at the time of fusion.

The plastic pipe inserted into the joint at the time of fusion is, for example, the socket joint 11 shown in FIG. 3, a projection 12 projecting inward at the center of the joint, an elbow joint 16 shown in FIG. The cap joint 21 shown in FIG. 7 is positioned by the steps 17 and 22 and is inserted until it comes into contact with the protrusions or steps. It may not be possible to insert it to the position.

As measures to solve such problems and prevent shrinkage of the inner diameter of the joint, the cooling time during molding or the time until the core is pulled out from the molded product is extended to sufficiently form the molded product. Cooling is effective, but there is a limit to measures to reduce the shrinkage of the inner diameter in the cold zone by this method, and there is also a problem that the molding cycle is lengthened and the productivity is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem, and the inner diameter of the obtained joint is not changed at the place where the heating wire is buried or at the back cold zone. It is an object of the present invention to provide a method for manufacturing an electrofusion joint which does not hinder the insertion of a coil, and a winding core used in the manufacturing method.

[0010]

The method of manufacturing an electrofusion joint according to the present invention is directed to a method of manufacturing an electrofusion joint in which a core around which a heating wire is wound is set in a mold, and then a thermoplastic resin is injection-molded. The dimension of the cold zone part deeper than the place where the heating wire is buried when viewed from the joint opening is made larger than the dimension of the place where the heating wire is buried, and the difference is based on the difference in the shrinkage allowance due to shrinkage, It is characterized in that it is molded within a range with a slight width, and in the case of elbow joints and cap joints, the inner diameter dimension in the cold zone at the back of the joint is further enlarged and molded to the maximum dimension And

According to this method, when the core is pulled out after molding, even if the dimension of the cold zone portion is reduced due to shrinkage of the molded product, the difference from the dimension of the portion where the heating wire is embedded is eliminated or reduced. can do. Even if the shrinkage in the cold zone at the center or back of the joint is large, such as an elbow joint or a cap joint, the difference between the heating wire and the place where the heating wire is buried can be eliminated or reduced by forming the dimensions at this place large. can do.

The thermoplastic resin used in the present invention is not particularly limited, as long as it can show a soft state for several hours after molding. Specifically, polyolefins such as polyethylene and polybutene can be exemplified. Among them, those having a density of 0.915 to 0.968 g / cm ³ are preferable, and medium density polyethylene is particularly preferable. The winding core used in the above manufacturing method has an outer diameter at a tip portion of the core where the heating wire is not wound is larger than an outer diameter at a location where the heating wire is wound, and the difference in shrinkage of the formed joint is reduced. , With the difference between the shrinkage allowances at the two places being a reference, and within a range having a certain width above and below it.

The core may be formed integrally with the entire core, including the large-diameter portion at the distal end, or a ring may be fitted to the distal end of the straight core and screwed to increase the diameter at the distal end. May be fixed. If the tip and the core body form a step, when removing the core from the molded product, the part where the heating wire is embedded will be caught by the step and it will be difficult to remove the core, or if you forcibly pull it out, the molded product May be undercut. In order to solve this problem, it is advisable to incline or bend without steps. That is, it is preferable to incline or bend toward the core tip having a larger diameter than the core body around which the heating wire is wound. This prevents the core from getting caught,
You will come out smoothly.

[0014] Figure 8 shows an example of a core 23 of elbow joint or cap fitting, the outer diameter d ₁ and frontage part of the core body 23b having an outer diameter d ₂ and the heating wire 24 of the distal end portion 23a is wound the outer diameter d ₀ of 23c formed as _{d 2> d 0> d 1} , it is between the core body 23b and the tip portion 23a and the inclined portion 23d. A pin 25 that fits into a fitting hole (not shown) of the mold is screwed into the flange 23e serving as a mounting portion to the mold so as to be stably and firmly mounted in the mold. It is supposed to be.

In the example shown, the heating wire 24 is provided in the core body 2.
Although it is wound around only 3b, it may be wound up to the inclined portion 23d. As the heating wire 24, either a covered wire or a bare wire can be used, but among them, it is easy to keep the pitch of the heating wire constant, and when the core is pulled out, damage to the metal wire due to rubbing with the core is avoided. Fewer coated wires are preferred.

The core according to the present invention is generally used as hollow cores 6a and 6b combined with a slide core as shown in FIG. 2, but the solid cores 2a and 2b as shown in FIG.
b can also be used. The core according to the present invention can also be used in any of the manufacturing methods of a socket joint as shown in FIG. 3, an elbow joint as shown in FIG. 5, a cap joint as shown in FIG. .

[0017]

【Example】

 Example 1 Outside diameter d of frontage portion 23c₀Is 115.30mm and the heating wire is
Outer diameter d of core body 23d to be wound₁Is 115.03
mm, outer diameter d of tip 23a_TwoIs 115.93mm in Figure 8.
The elbow joint core 23 shown in FIG.
After setting in mold 14, medium density of resin temperature 220 ℃
Polyethylene was injection molded. A certain time has passed after molding
After that, the molded product is removed from the mold 14 and the core 23 is extracted.
Then, an elbow joint with a nominal diameter of 100 mm shown in Fig. 5 was manufactured.
Was. After cooling the obtained molded product to room temperature,
When the inside diameter of the part was measured,
Diameter d ₀Is 115.01 mm, the inner diameter d of the place where the heating wire is buried.₁Is
115.12 mm, inner diameter d of the cold zone on the back side_TwoIs 1
It was 14.56 mm.

[0018] Example 2 d ₀ is 115.30mm, d ₁ is 114.90Mm, except that d ₂ is used the core 23 of 115.85Mm, were fabricated elbow joint to nominal diameter 100mm in the same manner as in Example 1 . Then, after cooling to room temperature, the inner diameter d _{0 of} each part of the joint,
When d ₁ and d ₂ were measured, each was 114.94 m
m, 114.76 mm and 114.56 mm.

[0019] Comparative Example 1 d ₀ is 115.30mm, d ₁ is 115.15Mm, nominal diameter and except that d ₂ is used the core of a conventional straight type shown in Figure 2 of 115.15Mm is in the same manner as in Example 1 100
mm elbow joint was manufactured. After cooling to room temperature, the inner diameters d ₀ , d _1, and d ₂ of each part of the joint were measured to be 114.67 mm, 115.00 mm, and 11 respectively.
3.78 mm.

[0020] Example 3 frontage part 23c of the outer diameter d ₀ is 61.00Mm, the outer diameter d ₁ is 60.55mm coil body 23b, the outer diameter d ₂ core elbow joint of 61.23mm tip portion 23a An elbow joint having a nominal diameter of 50 mm was manufactured under the same conditions as in Example 1.
Then after cooling to room temperature, it was measured inner diameter of the joint each section, the inner diameter d ₀ of the cold zone of the frontage, 60.
57 mm, the inner diameter d ₁ of the location where the heating wire is buried is 60.96 mm,
The inner diameter d ₂ of the cold zone on the far side was 60.33 mm.

Example 4 d ₀ is 61.00 mm, d ₁ is 60.30 mm, and d ₂ is 6
An elbow joint having a nominal diameter of 50 mm was manufactured in the same manner as in Example 3 except that a core of 1.00 mm was used. After cooling to room temperature, the inner diameters d ₀ , d _1, and d ₂ of each part of the joint were measured, and found to be 60.62 mm, 60.59 mm,
60.25 mm.

Comparative Example 2 d ₀ was 61.30 mm, d ₁ was 60.55 mm, and d ₂ was 6
Except for using a 0.55mm straight type core,
An elbow joint having a nominal diameter of 50 mm was manufactured in the same manner as in Example 3. After cooling to room temperature, the inner diameter d of each part of the joint
_{When 0} , d ₁ and d ₂ were measured, 60.88 respectively
mm, 60.38 mm and 59.46 mm.

Table 1 shows the above results.

[0024]

[Table 1] As described above, the inner diameter of each of the embodiments is smaller than that of the comparative example using a conventional straight type core. The dimensional difference was reduced, and there was no problem in inserting the plastic tube to the predetermined position.

[0025]

The present invention is configured as described above and has the following effects. The manufacturing method according to claim 1 and claim 4.
According to the electrofusion joint manufactured by using the described winding core, the difference between the location where the heating wire is buried and the dimension in the cold zone is eliminated or reduced, and the plastic pipe is formed into protrusions or steps. It can be inserted without hindrance to a predetermined position where it abuts and is positioned.

According to the manufacturing method of the second aspect, even for an elbow joint or a cap joint that has a large shrinkage in the cold zone at the back, the difference between the inner diameter at the cold zone at the back of the joint and the inner diameter at the other part is different. Is reduced or reduced, and the insertion of the plastic tube can be performed without any trouble. If a covered wire is used as the heating wire as in the manufacturing method of the third aspect, the heating wire can be wound on the core at a constant pitch.

If the whole is integrally formed as in the core according to the fifth aspect, it can be manufactured in one step using a mold or the like. According to the core of the sixth aspect, by combining a straight core and a ring that are easy to manufacture, the core can be easily manufactured without using a machining process or a mold having a complicated shape.

In the core according to the present invention, it is possible to cope with the manufacture of joints of various sizes by replacing the ring with a ring having a different thickness. By using the core described in claim 8, the core can be relatively smoothly extracted from the molded product without damaging the covered wire. According to the core of the ninth aspect, the core is reduced in weight, so that it is easy to handle. Further, by cooling the slide core, cooling of the core can be omitted, and the cost can be reduced. Can be prepared to increase the productivity.

The core according to the tenth aspect has a simple structure and can be manufactured at low cost. In the core according to the eleventh aspect, the core can be stably and firmly mounted in the mold.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold used for manufacturing a socket joint according to a conventional method.

FIG. 2 is a sectional view showing another embodiment of the mold.

FIG. 3 is a sectional view of the obtained socket joint.

FIG. 4 is a sectional view of a mold used for manufacturing an elbow joint.

FIG. 5 is a sectional view of the obtained elbow joint.

FIG. 6 is a sectional view of a mold used for manufacturing a cap joint.

FIG. 7 is a sectional view of the obtained cap joint.

FIG. 8 is a view showing a winding core according to the present invention.

[Explanation of symbols]

1, 24 ... heating wire 2, 6a, 6b,
23: Core 3, 7, 14, 19 ... Mold 4, 9, 15, 2
0 ... cavity 8a, 8b, 13a, 13b, 18 ... slide core 11 ... socket joint 12 ... projection 16 ... elbow joint 17, 22 ...
Step 21: Cap joint

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84 B29C 33/00-33/76 B29C 65/00-65/82 F16L 47 / 02

Claims (11)

(57) [Claims] In a method of manufacturing an electrofusion joint, wherein a core around which a heating wire is wound is set in a mold, a thermoplastic resin is injection-molded. The size of the cold zone part shall be larger than that of the part where the heating wire is buried, and the difference shall be within the range with a slight width up and down based on the difference in shrinkage allowance due to shrinkage. A method for producing an electrofusion joint, comprising: 2. The method for manufacturing an electrofusion joint according to claim 1, wherein the joint is an elbow joint or a cap joint. 3. The method for producing an electrofusion joint according to claim 1, wherein a covered wire is used as the heating wire. 4. An outer diameter of a core tip portion on which a heating wire is not wound is made larger than an outer diameter of a portion where a heating wire is wound,
2. The electrofusion according to claim 1, wherein the difference is set within a range having a certain width above and below the difference in shrinkage allowance at the two places due to shrinkage of the molded joint. Metal winding core used in the manufacturing method of joints. 5. The core as a whole is integrally formed.
The metal core for winding described. 6. The metal winding core according to claim 4, wherein the core is fixed by fitting a ring having a required thickness to a tip portion. 7. The metal winding core according to claim 6, wherein the ring is detachably fastened by a screw. 8. The metal winding core according to claim 4, wherein the core has an inclined portion or a curved portion which is inclined or curved toward a tip end portion from a position where the heating wire is wound. 9. The metal winding core according to claim 4, wherein the core is a hollow core, and is fitted into a slide core supported to be able to advance and retreat in a mold. 10. The metal wound core according to claim 4, wherein the core is a solid core and is detachably attached to a mold. 11. The metal winding core according to claim 4, wherein the core is formed by radially projecting a pin fitted to the mold on a flange serving as an attachment portion to the mold.