JP5748632B2 - Flexible ball joint unit, assembling method of the unit, and piping method using the unit - Google Patents

Description

  The present invention relates to a flexible ball joint called a so-called flexible pipe joint.

  As a flexible ball joint for water and gas, a flexible pipe joint having a spherical sliding bearing structure like a universal joint and capable of bending in any direction within a predetermined solid angle range is well known.

JP5-240394A (summary) JP2004-225837A (summary) JP2008-303901A (Summary)

Patent Documents 1 and 2 disclose a structure in which a straight pipe part is welded to a flexible part in the field.
However, since the work of welding the straight pipe part to the flexible part is not a standard work, the work will be difficult.

  Patent Document 3 discloses a technique for inserting and fixing an insertion portion of a polyethylene pipe into a receiving portion of a straight pipe. However, there is no disclosure about inserting and fixing a polyethylene tube to the flexible part.

  Accordingly, an object of the present invention is to provide a flexible ball joint unit that can be easily applied to a polyethylene pipe line.

In order to achieve the above object, a flexible ball joint unit of the present invention is a flexible ball joint unit for polyethylene pipes, and is composed of a metal first fluid pipe having a spherical convex surface, and the first fluid pipe includes: A first receiving portion having an inner surface covered with the convex surface and curved and recessed is provided on the opposite side of the convex surface, and the convex surface is fitted and rotated relative to the convex surface relative to the predetermined rotational center. The second fluid pipe made of metal having a spherical concave surface and the first receiving section of the first fluid pipe having the first insertion section A and the first insertion section being expanded in diameter. And a first polyethylene pipe having a first outer end surface exposed from the first receiving portion, and the first insertion portion of the first polyethylene pipe in order to maintain the expanded state. A first inner core fitted in the inner peripheral surface of the first insertion portion; Unit with.

By providing the unit of the flexible ball joint of the present invention in a hard polyethylene pipe line, the pipe line exhibits flexibility.
In particular, a new polyethylene straight pipe can be welded to the metal first fluid pipe via the first polyethylene pipe and connected with a non-bolt, that is, piping work is performed by standard welding work. be able to. Therefore, it is easy to use and the cost can be reduced.

In a preferred embodiment of the present invention, the second fluid pipe is integrally formed with a second receiving part having an inner surface that is curved and recessed, and is connected to the flexible part having the concave surface. A second outer end surface fitted into the second receiving portion of the second fluid pipe in a state where the second insertion portion has an enlarged diameter and exposed from the second receiving portion; A second polyethylene pipe having a second inner core fitted into an inner peripheral surface of the second insertion portion in order to maintain a state where the diameter of the second insertion portion of the second polyethylene pipe is expanded. In addition.

In this case, the unit can be placed between the polyethylene tube and the polyethylene tube.

In the present invention, the piping method using the unit includes a step of assembling the unit in a factory in advance, and one of the first and second outer end surfaces of the assembled unit is already piped. A first welding step of welding to an end surface of a polyethylene pipe, and a second welding step of welding an end surface of another polyethylene pipe to be subsequently piped to the other outer end surface of the unit after the first welding step. Prepare.

In this case, the piping work can be performed by welding the polyethylene pipe to be piped and the first or second polyethylene pipe of the unit at the piping site according to a conventional method. Therefore, piping work at the piping site is easy.

In the present invention, the method of assembling the unit in a factory includes a first insertion step of inserting the first inner core into the first polyethylene pipe, and the first fluid pipe and the second fluid pipe separated from each other. In a state, after the first insertion step of inserting the first insertion portion of the first polyethylene pipe into the first reception portion of the first fluid pipe, and after the first and second insertion steps, In a state where the first fluid pipe and the second fluid pipe are separated from each other, a force is applied to the first inner core from the inside of the first inner core toward the outer side in the radial direction of the first inner core. The first inner core is expanded to expand in the outward direction, thereby exhibiting a work hardening phenomenon in which the first inner core is plastically deformed and does not return to its original shape. By expanding the core diameter, The inner surface of the first insertion portion is pushed outward by the first inner core, and the first insertion portion is expanded and expanded in diameter toward the outside. A first diameter expanding step for fitting the inner surface of the first receiving portion so that the portion does not separate from the first receiving portion, and a third inserting step for inserting the second inner core into the second polyethylene pipe And inserting the second insertion part of the second polyethylene pipe into the second reception part of the second fluid pipe in a state where the first fluid pipe and the second fluid pipe are separated from each other. After the fourth insertion step and after the third and fourth insertion steps, the second inner core from the inside of the second inner core in a state where the first fluid pipe and the second fluid pipe are separated from each other. The second inner core is applied with a force directed outward in the radial direction of the second inner core. The diameter of the second inner core is expanded so that the second inner core is plastically deformed and does not return to its original shape, thereby expanding the second inner core. Due to the diameter, the inner surface of the second insertion portion is pushed outward by the second inner core, and the second insertion portion swells and expands outward to increase the diameter. After the second diameter-enlarging step that fits into the inner surface of the second receiving portion so that the two insertion portions do not separate from the second receiving portion, and after the first and second diameter-expanding steps, the first Connecting the fluid pipe and the second fluid pipe to each other.

In this case, the first and second polyethylene pipes can be easily connected to the first and second fluid pipes, respectively, by known bulge processing.

1A and 1B show an embodiment of the flexible ball joint of the present invention, and FIGS. 1A and 1B are longitudinal sectional views showing states before and after bending, respectively. FIG. 2 is a longitudinal sectional view showing a main part of the unit. FIG. 3A is a front view showing the opening of the flexible portion of the first fluid pipe, and FIG. 3B is a front view showing the retaining ring. 4A and 4B are longitudinal sectional views showing a method of connecting the first polyethylene pipe to the first fluid pipe, respectively. 5A and 5B are longitudinal sectional views showing a method of connecting the second polyethylene pipe to the second fluid pipe, respectively. 6A, 6B and 6C are longitudinal sectional views showing a method of connecting the first fluid pipe and the second fluid pipe, respectively. 7A and 7B are side views, partly in section, illustrating the piping method.

In a preferred embodiment of the unit, a distance from the predetermined rotation center to a virtual plane including a first inner end surface opposite to the first outer end surface in the first polyethylene pipe is the first polyethylene. It is characterized in that the length is 1/4 or less of the inner diameter of the tube.

  In the present invention, when the first fluid pipe and the second fluid pipe are bent, a part of the first inner end face of the first polyethylene pipe rotates around the rotation center O and approaches the axis of the second polyethylene pipe. Therefore, the fluid flow resistance tends to increase. In this example, since the distance is small, the flow resistance is difficult to increase.

  In another preferred example of the unit, the unit is integrally formed with the first receiving portion of the first fluid pipe, and the first fluid pipe and the second fluid pipe are bent with respect to each other. The first polyethylene pipe is further provided with a protruding pipe portion that covers the first polyethylene pipe and protrudes from the second fluid pipe so that the outer peripheral surface of the first polyethylene pipe does not contact the inner peripheral surface of the second fluid pipe.

In this case, the outer peripheral surface of the first polyethylene pipe does not come into contact with the inner peripheral surface of the second fluid pipe, and therefore, stress concentration hardly occurs in the bent first polyethylene pipe.

In a more preferable example of this unit, the first inner core 4A extends from the end surface of the protruding tube portion toward the first outer end surface, and extends from the end surface of the protruding tube portion to the first outer core. A length of 1/3 or more of the inner diameter of the first polyethylene pipe protrudes toward the end surface.

  In this case, the part of the first polyethylene pipe further protruding from the protruding pipe part is reinforced from the inside by the first inner core. Therefore, the stress concentration will be less likely to occur.

The invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the examples and drawings are merely illustrative and the scope of the invention is defined by the claims. In the accompanying drawings, the same part numbers in a plurality of drawings indicate the same or corresponding parts.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1A and 1B, this unit U includes cast iron first and second fluid pipes 1A and 1B, first and second polyethylene pipes 2A and 2B, and first and second inner cores 4A, 4B.

The first fluid pipe 1 </ b> A and the second fluid pipe 1 </ b> B are flexibly connected to each other with a known structure such as a spherical sliding bearing in the flexible portion 15. Accordingly, when the ground sinks after the main unit U shown in FIG. 1A is buried, the main unit U bends at the flexible portion 15 as shown in FIG. Let's go.

That is, each of the first and second fluid pipes 1A and 1B in FIG. 2 has a spherical convex surface 13 and a concave surface 14 that are fitted to each other. The convex surface 13 fits into the concave surface 14, the convex surface 13 and the concave surface 14 are in sliding contact with each other about the rotation center O, and the first fluid pipe 1A and the second fluid pipe 1B rotate with each other. The flexible portion 15 having the concave surface 14 can be bent.

A spherical seal ring 16 is interposed between the first fluid pipe 1A and the second fluid pipe 1B for sealing between the two. A retaining ring 17 is inserted into the open end 15e of the flexible portion 15 of the second fluid pipe 1B.

The retaining ring 17 has a spherical concave surface 17f having the same curvature as the concave surface 14 formed in the second fluid pipe 1B. 3B is inserted into the opening 150 of the opening end 15e of FIG. 3A and then accommodated in the flexible portion 15 of FIG. The first fluid pipe 1A is prevented from being detached from the second fluid pipe 1B by engaging with the second fluid pipes 1A and 1B.

The first fluid pipe 1A has a concave first receiving portion 10A. The first receiving portion 10 </ b> A has an inner surface 101 covered with the convex surface 13 on the opposite side of the convex surface 13. The inner surface 101 is curved and recessed in a barrel shape. On the other hand, the second receiving portion 10B is integrally connected to the flexible portion 15 of the second fluid pipe 1B.

The first polyethylene pipe 2A has a first insertion part 12A and is fitted into the first receiving part 10A of the first fluid pipe 1A in a state where the diameter of the first insertion part 12A is expanded, and As shown in FIG. 1A, the first outer end face 210 is exposed from the first receiving portion 10A. The first inner core 4A in FIG. 2 is fitted in the inner peripheral surface of the first insertion portion 12A in order to maintain the state where the first insertion portion 12A of the first polyethylene pipe 2A has an enlarged diameter. .

The distance from the predetermined rotation center O to a virtual plane including the first inner end surface 211 opposite to the first outer end surface 210 in the first polyethylene pipe 2A is 1 / of the inner diameter of the first polyethylene pipe 2A. The length is set to 4 or less. With this setting, in the bent state of FIG. 1B, the portion 212 of the first polyethylene pipe 2A on the first inner end surface 211 does not approach the second axis L2 of the second polyethylene pipe 2B. Smooth fluid flow can be expected.

In FIG. 2, the first inner end surface 211 is formed integrally with the first fluid pipe 1A, and abuts against an annular first stopper 19A extending toward the first axis L1 of the first polyethylene pipe 2A. In the case of this embodiment, the first stopper 19A is orthogonal to the first axis L1 and extends along an imaginary plane including the rotation center O.

The first fluid pipe 1 </ b> A includes a protruding pipe portion 18. The protruding pipe portion 18 is formed integrally with the first receiving portion 10A of the first fluid pipe 1A, and in a state where the first fluid pipe 1A and the second fluid pipe 1B of FIG. 1B are bent with respect to each other. The first polyethylene pipe 2A covers the first polyethylene pipe 2A so that the outer peripheral surface of the first polyethylene pipe 2A does not come into contact with the inner peripheral surface of the second fluid pipe 1B, and the first polyethylene pipe 2A extends from the flexible portion 15 of the second fluid pipe 1B. It protrudes in the direction along the one axis L1.

The first inner core 4A extends in a direction from the end surface 18f of the protruding tube portion 18 toward the first outer end surface 210, and from the end surface 18f of the protruding tube portion 18 toward the first outer end surface 210. The length protrudes more than 1/3 of the inner diameter.

The second polyethylene pipe 2B has a second insertion part 12B and is fitted into the second reception part 10B of the second fluid pipe 1B in a state where the diameter of the second insertion part 12B is expanded, and 1B, it has the 2nd outer end surface 220 exposed from the said 2nd receiving part 10B. The second inner core 4B of FIG. 2 is fitted into the inner peripheral surface of the second receiving portion 10B in order to maintain the state in which the diameter of the second insertion portion 12B of the second polyethylene pipe 2B is expanded. Yes.

For example, first and second seal rings 3A and 3B made of rubber or the like are inserted between the receiving portions 10A and 10B and the insertion portions 12A and 12B, respectively. The space between the receiving portion and the insertion portion is sealed by 3B.

The inner cores 4A and 4B made of tubular metal are fitted into inner peripheries of the insertion portions 12A and 12B of the polyethylene pipes 2A and 2B. Each of the inner cores 4A and 4B is plastically deformed by a jig described later, for example. Thereby, the bulging part 40 whose longitudinal cross-sectional shape curved so that it may bulge outward of the radial direction of fluid pipe | tube 1A, 1B is formed in said inner core 4A, 4B.
The bulging part 20 deformed so that the insertion parts 12A, 12B of the polyethylene pipes 2A, 2B bulge outward in the radial direction of the fluid pipes 1A, 1B is along the bulging part 40 of the inner core 4. Is formed. That is, the outer peripheral surface of the bulging portion 20 is formed in a curved convex shape.

On the other hand, the polyethylene pipes 2A and 2B are engaged with the outer peripheral surfaces of the polyethylene pipes 2A and 2B on the inner circumferences of the receiving portions 10A and 10B of the fluid pipes 1A and 1B, respectively. First and second engaging means 11A and 11B are formed for preventing the outlet portions 10A and 10B from being detached. Each engaging means 11A, 11B is formed integrally with each fluid pipe 1A, 1B, and is composed of, for example, an annular ridge or a number of stab-like protrusions.

The structures of the engaging means 11A and 11B, the polyethylene pipes 2A and 2B, and the inner cores 4A and 4B and the manufacturing method thereof are disclosed in WO2008 / 149590A1 and US2008 / 030277A1, which are described here. Incorporated into.

For example, the jig 5 shown in FIGS. 4A and 5A is used to plastically deform the inner cores 4A and 4B to form the bulging portion 40. FIG. Note that the jig 5 in FIG. 4A and the jig 5 in FIG. 5A are functionally the same, and will be described below using the jig 5 in FIG. 4A as an example.
As shown in FIG. 4A, the jig 5 includes a pressing part 50, a cylinder part 51, and a slider 52. The cylindrical portion 51 is formed in a cylindrical shape extending along the tube axis direction X of the first fluid pipe 1A and the first polyethylene pipe 2A, and a first flange portion is provided at an end of the cylindrical portion 51. 53 is formed.

The slider 52 is formed so as to be slidable in the tube axis direction X in the cylindrical portion 51, and a second flange portion 54 is formed at the end of the slider 52.
Between the first flange portion 53 of the cylindrical portion 51 and the second flange portion 54 of the slider 52, the ring-shaped pressing portion 50 made of, for example, urethane rubber is provided. The length of the pressing portion 50 in the axial direction is preferably provided over most of the region in which the inner core 4 is plastically deformed.

How to form this unit:
First insertion step;
First, the outer diameter is uniform on the inner peripheral side of the insertion portion 12A of the first polyethylene pipe 2A before deformation shown in FIG. 4A in a state where the first fluid pipe 1A and the second fluid pipe 1B are separated from each other. The first inner core 4A before deformation is inserted.

First insertion step;
Thereafter, in a state where the first fluid pipe 1A and the second fluid pipe 1B are separated from each other, the first polyethylene pipe 2A before deformation into which the first inner core 4A is inserted is the receiving port of the first fluid pipe 1A. It is inserted into the part 10A.

First diameter expansion step;
After the second insertion step, as shown in FIG. 4A, the jig 5 is inserted into the inner core 4A. When the slider 52 is pulled in the detaching direction X2 in a state where the cylindrical portion 51 is set at a predetermined position with respect to the polyethylene pipe 2A, the second flange portion 54 moves in the detaching direction X2 as shown in FIG. 4B. By such movement, the pressing portion 50 is pressed between the second flange portion 54 and the first flange portion 53 and pushed toward the inner core 4A. When the pressing portion 50 comes into contact with and pushes out the inner peripheral surface of the inner core 4A, a force directed outward in the radial direction R from the inner peripheral surface of the inner core 4A is applied to the inner core 4A.

As a result, the inner peripheral surface of the polyethylene pipe 2A is pushed outward in the radial direction R by the inner core 4A, the inner core 4A is expanded, and the inner core 4A is plastically deformed to return to its original shape. Presents no phenomenon of work hardening. At the same time, the diameter of the polyethylene pipe 2A is increased by the expansion of the inner core 4A, and a bulging portion 20 is formed in the polyethylene pipe 2A. The bulge portion 20 increases in diameter until it comes into contact with the plurality of protrusions 11A of the receiving portion 10A. By forming the bulging portion 20, the protrusion 11 </ b> A engages with the polyethylene pipe 2 </ b> A to exhibit the function of preventing the separation of the polyethylene pipe 2 </ b> A, and the seal ring 3 is compressed and deformed, so that the outer circumference of the polyethylene pipe 2 </ b> A is Adhere to the surface.

Sampling step of the jig 5;
After the diameter expansion, the slider 52 is returned to the direction X1 to release the deformation of the pressing portion 50, and then the jig 5 is pulled out from the inner core 4A and the polyethylene pipe 2A. Note that the plastically deformed inner core 4A retains the deformed shape by work hardening by the plastic deformation even after the pressing portion 50 is extracted. Thereby, the shape of the polyethylene pipe 2A is also maintained.

Next, a method for processing the second inner core 4B and the second polyethylene pipe 2B shown in FIGS. 5A and 5B will be described. This processing method is the same as the processing method of the first inner core 4A and the second polyethylene pipe 2B shown in FIGS. 4A and 4B, and will be described briefly.

In FIG. 5A, first, a third insertion step of inserting the second inner core 4B into the second polyethylene pipe 2B is performed. Subsequently, in a state where the first fluid pipe 1A and the second fluid pipe 1B are separated from each other, the second insertion portion 12B of the second polyethylene pipe 2B is connected to the second inlet of the second fluid pipe 1B. The 4th insertion process inserted in receiving part 10B is performed.

After the third and fourth insertion steps, a second diameter expansion step described below is performed.
That is, a direction toward the outside in the radial direction of the second inner core 4B from the inside of the second inner core 4B is applied to the second inner core 4B so that the second inner core 4B moves outward. The diameter is expanded and the second inner core 4B is plastically deformed.
As a result, the second inner core 4B is plastically deformed and exhibits a work hardening phenomenon that does not return to its original shape, and the inner circumference of the second insertion portion 12B is directed outwardly by the second inner core 4B. The second receiving portion 10B is pressed so that the second inserting portion 12B does not detach from the second receiving portion 10B so that the second inserting portion 12B expands outward and expands in diameter. Fit into.

The first fluid pipe 1A of FIG. 6A sub-assembled by the first diameter expansion step is inserted into the second fluid pipe 1B of FIG. 6B sub-assembled by the second diameter expansion step, and then the retaining ring 17 is inserted. By fitting into the opening end 15e, the first fluid pipe 1A and the second fluid pipe 1B are connected to each other as shown in FIG. 1A. Thereby, the unit U is produced | generated in a factory.

Next, a piping method using the unit U will be described.
A first welding step is performed in which one outer end surface 220 of the first or second outer end surfaces 210 and 220 of the assembled unit U is welded to the end surface 230 of the already piped polyethylene pipe 2C. After the first welding step, a second welding step is performed in which the end surface 240 of the polyethylene pipe 2D to be piped next is welded to the other outer end surface 210 of the unit U.
In these first and second welding steps, the polyethylene pipe itself is commonly used, and therefore piping work on site is easy.

As described above, the preferred embodiments have been described with reference to the drawings. However, those skilled in the art will readily understand various changes and modifications within the obvious scope by looking at the present specification.
For example, the second polyethylene pipe 2B may be connected to a valve, a cast iron pipe or the like by a flange joint or a mechanical joint instead of the second receiving portion 10B.
Further, the inner diameters of the first inner core and the first polyethylene pipe may be increased in a tapered shape in the vicinity of the first inner end face of the first polyethylene pipe.
The flexible part of the second fluid pipe may be divided into two in the pipe axis direction to form a retaining ring. Further, the material of the inner core may be any metal that is more excellent in extensibility than the material of the fluid pipe, and generally a copper-based metal such as brass, stainless steel, or the like can be employed.
Accordingly, such changes and modifications are to be construed as within the scope of the present invention as defined by the claims.

  The present invention can be applied to water and gas pipelines that require earthquake resistance.

1A: 1st fluid pipe, 1B: 2nd fluid pipe 10A: 1st receiving part, 10B: 2nd receiving part 101: Inner surface, 102: Inner surface 11A: 1st engaging means, 11B: 2nd engaging means 12A: 1st insertion part, 12B: 2nd insertion part 13: Convex surface, 14: Concave surface 15: Flexible part, 15e: Opening end part, 150: Opening 16: Spherical seal ring 17: Stop ring 18: Projection tube portion, 18f: end surface 19A: first stopper, 19B: second stopper 2A: first polyethylene tube, 2B: second polyethylene tube, 2C: polyethylene tube 2D: polyethylene tube, 20: bulge portion 210: first outer End surface, 220: second outer end surface 211: first inner end surface 3A: first seal ring, 3B: second seal ring 4A: first inner core, 4B: second inner core, 40: bulge portion 5: jig, 50: Pressing part, 51: Tube part, 2: slider, 53: first flange 54: second flange L1: first axis, L2: second axis O: rotation center R: radial direction U: unit X: tube axis direction, X1: direction, X2: Exit direction

Claims (7)

A flexible ball joint unit U for polyethylene pipes,
A metal first fluid pipe 1A having a spherical convex surface 13 and a first receiving port having an inner surface 101 covered with the convex surface 13 and curved and recessed on the opposite side of the convex surface 13. Part 10A,
A second fluid pipe 1B made of metal having a spherical concave surface 14 in which the convex surface 13 is fitted and rotates relative to the convex surface 13 with a predetermined rotational center O in sliding contact with each other;
The first insertion port 12A is fitted into the first receiving port 10A of the first fluid pipe 1A in a state where the first insertion port 12A has an enlarged diameter, and the first receiving port 10A. A first polyethylene pipe 2A having a first outer end surface 210 exposed from
A unit U comprising a first inner core 4A fitted into the inner peripheral surface of the first insertion portion 12A in order to maintain the state where the first insertion portion 12A of the first polyethylene pipe 2A is expanded in diameter. . In unit U of claim 1,
In the second fluid pipe 1B, a second receiving portion 10B having an inner surface 102 that is curved and recessed is formed integrally with the flexible portion 15 having the concave surface 14.
The second insertion port 12B is fitted into the second receiving port 10B of the second fluid pipe 1B in a state where the second insertion port 12B has an enlarged diameter, and the second receiving port 10B. A second polyethylene pipe 2B having a second outer end surface 220 exposed from
In order to maintain the state where the diameter of the second insertion portion 12B of the second polyethylene pipe 2B is expanded, a second inner core 4B fitted to the inner peripheral surface of the second insertion portion 10B is further provided. In unit U of claim 1,
A distance from the predetermined rotation center O to a virtual plane including the first inner end surface 211 on the opposite side of the first outer end surface 210 in the first polyethylene tube 2A is 1 / of the inner diameter of the first polyethylene tube 2A. The length is 4 or less. In unit U of claim 1,
An outer peripheral surface of the first polyethylene pipe 2A formed integrally with the first receiving portion 10A of the first fluid pipe 1A, and the first fluid pipe 1A and the second fluid pipe 1B are bent with respect to each other. Further includes a protruding pipe portion 18 that covers the first polyethylene pipe 2A so as not to contact the inner peripheral surface of the second fluid pipe 1B and protrudes from the second fluid pipe 1B. In unit U of claim 4,
The first inner core 4A extends in the direction X2 from the end surface 18f of the protruding tube portion 18 toward the first outer end surface 210, and from the end surface 18f of the protruding tube portion 18 toward the first outer end surface 210. The first polyethylene pipe 2A protrudes by a length of 1/3 or more of the inner diameter. A piping method using the unit U of claim 2,
Assembling the unit U in a factory in advance;
A first welding step of welding one outer end surface of the first or second outer end surfaces 210 and 220 of the assembled unit U to the end surface 230 of the already piped polyethylene pipe 2C;
After the first welding step, a second welding step of welding an end surface 240 of another polyethylene pipe 2D to be piped next to the other outer end surface of the unit U is provided. A method of assembling the unit U of claim 2 in a factory,
A first insertion step of inserting the first inner core 4A into the first polyethylene pipe 2A;
In a state where the first fluid pipe 1A and the second fluid pipe 1B are separated from each other, the first insertion part 12A of the first polyethylene pipe 2A is used as the first receiving part of the first fluid pipe 1A. A second insertion step of inserting into 10A;
After the first and second insertion steps, the diameter of the first inner core 4A from the inside of the first inner core 4A with the first fluid pipe 1A and the second fluid pipe 1B separated from each other. A direction of outward R in the direction is applied to the first inner core 4A to expand the diameter of the first inner core 4A in the outward direction, whereby the first inner core 4A It exhibits a phenomenon of work hardening that does not return to its original shape due to plastic deformation,
Due to the diameter expansion of the first inner core 4A, the inner surface of the first insertion portion 12A is pushed outward by the first inner core 4A, and the first insertion portion 12A is moved outward. A first diameter expanding step of fitting into the inner surface 101 of the first receiving port portion 10A so that the first insertion port portion 12A does not detach from the first receiving port portion 10A.
A third insertion step of inserting the second inner core 4B into the second polyethylene pipe 2B;
In a state where the first fluid pipe 1A and the second fluid pipe 1B are separated from each other, the second insertion part 12B of the second polyethylene pipe 2B is used as the second receiving part of the second fluid pipe 1B. A fourth insertion step of inserting into 10B;
After the third and fourth insertion steps, the diameter of the second inner core 4B from the inside of the second inner core 4B with the first fluid pipe 1A and the second fluid pipe 1B separated from each other. A direction of outward R in the direction is applied to the second inner core 4B to expand the second inner core 4B in the outward direction, whereby the second inner core 4B It exhibits a phenomenon of work hardening that does not return to its original shape due to plastic deformation,
Due to the diameter expansion of the second inner core 4B, the inner surface of the second insertion portion 12B is pushed outward by the second inner core 4B, so that the second insertion portion 12B is moved outward. A second diameter expanding step of fitting into the inner surface 102 of the second receiving port portion 10B so that the second insertion port portion 12B does not detach from the second receiving port portion 10B.
A step of connecting the first fluid pipe 1A and the second fluid pipe 1B to each other after the first and second diameter increasing steps;

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