JP7530165B2 - Corrugated Pipe - Google Patents

Description

The present invention relates to a corrugated pipe .

Conventionally, resin corrugated pipes are molded by extrusion molding or injection molding.
An example of a molding method using extrusion molding is extrusion blow molding. In extrusion blow molding, molten resin is extruded into a mold, and then air is blown into the mold and vacuum is applied from the peaks of the corrugator block, so that the molten resin adheres to the inner surface of the corrugator mold, which has peaks and valleys. In extrusion blow molding, the space between the mold plug and the corrugated pipe is not completely sealed, so the pressure of the air blown cannot be increased, and a corrugated pipe with a large thickness cannot be molded. As a result, a corrugated pipe suitable for applications requiring pressure resistance could not be obtained.

An example of a molding method using injection molding is a method in which molten resin is poured into a mold having a predetermined shape, and the molded resin is then released from the mold. With injection molding, in order to release the undercuts (the uneven shapes corresponding to the peaks and valleys) inside the molded corrugated pipe from the mold, the diameter of the core of the mold had to be reduced. Therefore, if the undercuts were large, the mold strength required to mold the corrugated pipe could not be obtained. As a result, a corrugated pipe with a large undercut could not be obtained.

As a method for forming corrugated pipes, bulge forming is used using hollow polyurethane rubber with an abacus-shaped hollow section (see, for example, Patent Document 1). This bulge forming is a method for metal pipes that utilizes plastic deformation during cold working.

Patent No. 3769350

Plastic pipes (hereinafter referred to as "plastic pipes") cannot maintain their shape even if they are plastically deformed into a corrugated shape in the cold state as in the method described in Patent Document 1. Therefore, the plastic pipes must be heated and molded. However, when the plastic pipes are heated, the hollow urethane rubber melts or deforms significantly due to the heat, making it impossible to mold a corrugated pipe of the desired shape. Furthermore, in order to mold one uneven shape (peak or valley), a cycle consisting of a molding start process, a pre-molding process, and a main molding process is required. Therefore, in order to mold multiple uneven shapes, the above cycle must be repeated multiple times, which increases the molding time.

The present invention has been made in consideration of the above circumstances, and aims to provide a corrugated resin pipe that has excellent pressure resistance and flexibility. It also aims to provide a manufacturing method for a corrugated resin pipe that can mold multiple concave and convex shapes in a single cycle.

The present invention has the following aspects.
[1] A corrugated pipe made of a tubular member, in which annular peaks that are convex radially outward of the tubular member and annular valleys that are concave radially outward of the tubular member are alternately formed in the axial direction to form a bellows-like shape, wherein a ratio (D1/t1) of an outer diameter D1 of the tubular member at the apex of each peak to a radial thickness t1 of the tubular member at the apex of each peak is 17 or less.
[2] The corrugated pipe according to [1], wherein the ratio (D1/D2) of the outer diameter D1 of the tubular member at the apex of the ridge to the outer diameter D2 of the portion of the tubular member where the ridges and the valleys are not formed is 1.5 or more.
[3] A method for manufacturing a resin corrugated pipe made of a tubular member and having annular peaks and valleys that are convex radially outward of the tubular member and concave radially outward of the tubular member, alternately formed in the axial direction to form a bellows-like shape, the method comprising the steps of: inserting a core into a resin tubular member; heating an outer circumferential surface of the tubular member with the core inserted; placing the heated tubular member with the core inserted into a lower mold and an upper mold of a mold that is divided into a plurality of sections with gaps provided along the axial direction of the tubular member, and then clamping the lower mold and the upper mold; compressing the core from both ends of the tubular member toward the center of the axial direction of the tubular member, thereby expanding the tubular member into the gaps between the sections of the lower mold and the gaps between the sections of the upper mold; and bringing the sections of the lower mold and the sections of the upper mold closer to each other along the axial direction of the tubular member to form the peaks and the valleys in the tubular member.
[4] The method for manufacturing a corrugated pipe described in [3], wherein the core has an elastic tubular woven fiber fabric, a deformable solid filled within the tubular woven fiber fabric, and a jig arranged at both ends of the tubular woven fiber fabric for compressing the solid from both axial ends of the tubular woven fiber fabric toward the center of the axial direction of the tubular woven fiber fabric.
[5] The method for manufacturing a corrugated pipe according to [4], wherein the solid is oil clay or a particle group.

According to the present invention, it is possible to provide a resin corrugated pipe that has excellent pressure resistance and flexibility. In addition, according to the present invention, it is possible to provide a manufacturing method for a resin corrugated pipe that can mold multiple concave and convex shapes in a single cycle.

1 is a schematic cross-sectional view showing a corrugated pipe according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing a first step in a method for manufacturing a corrugated pipe according to an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a third step in a method for manufacturing a corrugated pipe according to one embodiment of the present invention. FIG. 11 is a schematic cross-sectional view showing a fourth step in a method for manufacturing a corrugated pipe according to one embodiment of the present invention. FIG. 11 is a schematic cross-sectional view showing a fifth step in a method for manufacturing a corrugated pipe according to one embodiment of the present invention. FIG. FIG. 4 is a schematic cross-sectional view showing a modified example of a corrugated pipe according to an embodiment of the present invention.

An embodiment of the corrugated pipe and the manufacturing method thereof of the present invention will be described.
It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Corrugated pipe]
The corrugated pipe of the present invention is a resin pipe consisting of a tubular member, in which annular peaks that are convex radially outward of the tubular member and annular valleys that are concave radially outward of the tubular member are alternately formed in the axial direction to form a bellows-like shape.
Hereinafter, an embodiment of a corrugated pipe according to the present invention will be described with reference to FIG.

FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a corrugated pipe according to the present embodiment.
As shown in Fig. 1, the corrugated pipe 1 of this embodiment is made of a tubular member 10. The corrugated pipe 1 of this embodiment is a resin pipe in which annular peaks 11 that are convex radially outward of the tubular member 10 and annular valleys 12 that are concave radially outward of the tubular member 10 are alternately formed in the axial direction to form a bellows-like shape. That is, the corrugated pipe 1 has peaks 11 and valleys 12 alternately in the axial direction.

The outer diameter D1 of the tubular member 10 at the apex of the peak 11 shown in FIG. 1, the outer diameter D2 of the portion of the tubular member 10 where the peak 11 and valley 12 are not formed, the radial thickness t1 of the tubular member 10 at the apex of the peak 11, and the thickness t2 of the portion of the tubular member 10 where the peak 11 and valley 12 are not formed are not particularly limited and are adjusted as appropriate depending on the application of the corrugated pipe 1 and the flexibility and pressure resistance required of the corrugated pipe 1.

In the corrugated pipe 1 of the present embodiment, the ratio (D1/t1) of the outer diameter D1 to the thickness t1 is 17 or less, and preferably 9 or more.
It should be noted that D1/t1 corresponds to SDR1 expressed by the following formula (1).
SDR1=2σ/(P/S)+1 (1)
In the above formula (1), σ represents the 50-year creep strength, which is 10 MPa for PE100. PE100 is a polyethylene material for water distribution polyethylene pipes and pipe joints, and is a polyethylene material that has been proven to have a constant stress value of 10.0 MPa or more at which the pipe will not break for 50 years at 20°C.
In the above formula (1), P represents the maximum design water pressure inside the pipe, which is 1.0 MPa for a water supply. In the above formula (1), S represents the safety factor, which is 1.25 in ISO 4427.

If PE100 is used as the material for the tubular member 10, SDR1 = 17 in order to withstand an internal pressure of 1.0 MPa, such as a water pipe, for more than 50 years. Therefore, if the above-mentioned D1/t1 is 17 or less, the corrugated pipe 1 can withstand an internal pressure of 1.0 MPa for more than 50 years.

The ratio (D1/D2) of the outer diameter D1 of the tubular member 10 at the apex of the ridge 11 to the outer diameter D2 of the portion of the tubular member 10 where the ridges 11 and valleys 12 are not formed is preferably 1.5 or more. When the ratio (D1/D2) is 1.5 or more, the corrugated pipe 1 has excellent flexibility.

The material of the tubular member 10 is not particularly limited as long as it is a material generally used for water distribution pipes, but olefin resins are preferable. For polyethylene, specific examples include PE100, PE80, and PE63.

According to the corrugated pipe 1 of this embodiment, the ratio (D1/t1) of the outer diameter D1 of the tubular member 10 at the apex of the peak 11 to the radial thickness t1 of the tubular member 10 at the apex of the peak 11 is 17 or less, so a corrugated pipe made of resin with excellent pressure resistance and flexibility can be provided. Note that pressure resistance in this embodiment refers to the ability to withstand an internal pressure of 1.0 MPa for 50 years or more without breaking.

[Method of manufacturing corrugated pipe]
A method for producing a corrugated pipe according to the present invention will now be described.
The method for manufacturing a corrugated pipe of the present invention is a method for manufacturing a resin corrugated pipe made of a tubular member, in which annular peaks that are convex radially outward of the tubular member and annular valleys that are concave radially outward of the tubular member are alternately formed in the axial direction to form a bellows-like shape, the method comprising the steps of: inserting a core into a resin tubular member (hereinafter referred to as a "first step"); heating the outer circumferential surface of the tubular member with the core inserted (hereinafter referred to as a "second step"); and heating the tubular member with the core inserted after heating by separating the tubular member with a metal core that is divided into a plurality of portions with gaps provided along the axial direction of the tubular member. The method includes the steps of placing the tubular member in a lower mold and an upper mold and then clamping the lower mold and the upper mold together (hereinafter referred to as the "third step"); compressing the core from both ends of the tubular member toward the axial center of the tubular member, causing the tubular member to expand into the gaps between the respective portions of the lower mold and into the gaps between the respective portions of the upper mold (hereinafter referred to as the "fourth step"); and bringing the respective portions of the lower mold and the respective portions of the upper mold closer together along the axial direction of the tubular member, thereby forming the peaks and valleys in the tubular member (hereinafter referred to as the "fifth step").
The method for manufacturing a corrugated pipe according to the present invention will be described below with reference to FIGS. 2 to 5 as appropriate.

Figure 2 is a schematic cross-sectional view showing a first step in the method for manufacturing a corrugated pipe of this embodiment. Figure 3 is a schematic cross-sectional view showing a third step in the method for manufacturing a corrugated pipe of this embodiment. Figure 4 is a schematic cross-sectional view showing a fourth step in the method for manufacturing a corrugated pipe of this embodiment. Figure 5 is a schematic cross-sectional view showing a fifth step in the method for manufacturing a corrugated pipe of this embodiment.

As shown in Figure 2, in the first step, a core 30 is inserted into a resin tubular member 20.

The tubular member 20 is a member that becomes the tubular member 10 of the corrugated pipe 1 described above.
The thickness of the tubular member 20 is not particularly limited, and is adjusted as appropriate depending on the application of the corrugated pipe 1 and the flexibility, pressure resistance, and other properties required of the corrugated pipe 1 .
The length of the tubular member 20 is adjusted appropriately depending on the length required for the corrugated pipe 1 .

The materials for the tubular member 20 can be the same as those for the tubular member 10 described above.

The core 30 has an elastic tubular woven fiber fabric 31, a deformable solid 32 filled in the tubular woven fiber fabric 31, and jigs 33 arranged on both ends of the axial direction (longitudinal direction) Q of the tubular woven fiber fabric 31.

The length of the tubular fiber woven fabric 31 is adjusted appropriately according to the number of peaks 11 and valleys 12 required for the corrugated pipe 1.

Examples of the tubular woven fiber fabric 31 include stretchable materials such as tights, stockings, rubber bags, etc.
Examples of the fiber material constituting the tubular fiber woven fabric 31 include nylon and cellulosic materials.

The deformable solid 32 is not particularly limited as long as it is easily deformed when compressed in the tubular woven fiber fabric 31, but is preferably, for example, oil clay or a particle group.
Oil clay is made by mixing mineral powders such as kaolin with walnut, castor oil, vegetable oil, and mineral oil. Oil clay does not harden when naturally dried, and has excellent plasticity because it is stiff and easy to stretch.
Examples of the particle group include sand and spherical alumina balls with a particle diameter of 1 mm to 2 mm.

The jig 33 has a tip 33A that contacts the solid 32 placed inside the tubular fiber woven fabric 31, and an axial core 33B that is connected to the tip 33A and is used to push the tip 33A into the tubular member 20. By pushing the axial core 33B into the tubular member 20, the tip 33A can compress the core 30 (solid 32 inside the tubular fiber woven fabric 31) from both ends of the tubular member 20 toward the center of the axial direction Q of the tubular member 20.

The outer diameter of the tip portion 33A is approximately equal to the inner diameter of the tubular member 20. This prevents the deformable solid 32 from protruding toward the axial core portion 33B when the core 30 is compressed from both ends of the tubular member 20 toward the center of the axial direction Q of the tubular member 20.

In the second step, the outer circumferential surface 20a of the tubular member 20 with the core 30 inserted therein is heated.
The method for heating the tubular member 20 is not particularly limited, but examples thereof include a method using an infrared heater and a method using an oil bath.

In the second step, the heating temperature of the outer peripheral surface 20a of the tubular member 20 is preferably set to a temperature equal to or lower than the melting point of the resin that constitutes the tubular member 20. The higher the heating temperature, the smaller the load that deforms the tubular member 20, making it easier to mold the tubular member 20. Therefore, it is more preferable that the heating temperature of the outer peripheral surface 20a of the tubular member 20 is set to a temperature equal to or higher than the glass transition point, which is the temperature at which the resin that constitutes the tubular member 20 softens, and equal to or lower than the melting point, which is the temperature at which the resin that constitutes the tubular member 20 does not melt.

As shown in FIG. 3, in the third step, a mold 100 having a lower mold 110 and an upper mold 120 is used. In the third step, the tubular member 20 containing the heated core 30 is placed in the lower mold 110 and the upper mold 120 of the mold 100, which is divided into multiple parts with gaps 100a along the axial direction of the tubular member 20, and then the lower mold 110 and the upper mold 120 are clamped together.

As shown in FIG. 3, in the third step, the lower mold 110 is divided into a plurality of parts 110A, 110B, 110C, 110D, and 110E with gaps 110a provided along the axial direction of the tubular member 20, and the parts are arranged at equal intervals. That is, the size (spacing) of the gaps 110a between the plurality of parts 110A, 110B, 110C, 110D, and 110E is all equal. Also, the upper mold 120 is divided into a plurality of parts 120A, 120B, 120C, 120D, and 120E with gaps 120a provided along the axial direction of the tubular member 20, and the parts are arranged at equal intervals. That is, the size (spacing) of the gaps 120a between the plurality of parts 120A, 120B, 120C, 120D, and 120E is all equal. Also, the size (spacing) of the gaps 110a and the gaps 120a facing each other is equal.

The inner peripheral surface 110b of the lower die 110 and the inner peripheral surface 120b of the upper die 120 have shapes corresponding to the peaks 11 and valleys 12 of the corrugated pipe 1.

The force for clamping the lower die 110 and the upper die 120 is not particularly limited, but it is preferable that the force is such that the tubular member 20 does not shift position when the lower die 110 and the upper die 120 are compressed along the axial direction Q of the tubular member 20 while holding the tubular member 20 with the core 30 inserted between them, and the respective parts 110A, 110B, 110C, 110D, and 110E of the lower die 110 and the respective parts 120A, 120B, 120C, 120D, and 120E of the upper die 120 are brought into close contact with each other. It is also preferable that the force is such that the movement of the core 30 within the tubular member 20 is not restricted.

As shown in FIG. 4, in the fourth step, the core 30 is compressed from both ends of the tubular member 20 toward the center of the axial direction Q of the tubular member 20, causing the tubular member 20 to expand into the gaps 110a between the portions 110A, 110B, 110C, 110D, and 110E of the lower mold 110 and into the gaps 120a between the portions 120A, 120B, 120C, 120D, and 120E of the upper mold 120.

In the fourth step, the axial core 33B of the jig 33 is pushed into the tubular member 20, and the tip 33A of the jig 33 compresses the core 30 (the solid 32 in the tubular fiber woven fabric 31) from both ends of the tubular member 20 toward the center of the axial direction Q of the tubular member 20. Then, since the core 30 located in the gaps 110a and 120a is not held by the mold 100, the solid 32 in the tubular fiber woven fabric 31 tries to move into the gaps 110a and 120a. This movement of the solid 32 causes the tubular member 20 to expand into the gaps 110a and 120a. That is, the tubular member 20 expands radially outward. In other words, the tubular member 20 expands toward the inner circumferential surface 110b of the lower mold 110 and toward the inner circumferential surface 120b of the upper mold 120.

As shown in FIG. 5, in the fifth step, adjacent portions of the lower mold 110 (110A, 110B, 110C, 110D, 110E) and adjacent portions of the upper mold 120 (120A, 120B, 120C, 120D, 120E) are brought closer together along the axial direction Q of the tubular member 20 to alternately form peaks 21 corresponding to the peaks 11 and valleys 22 corresponding to the valleys 12 on the tubular member 20.

As shown in FIG. 5 , in the fifth step, adjacent portions of the respective portions 110A, 110B, 110C, 110D, and 110E of the lower mold 110 and adjacent portions of the respective portions 120A, 120B, 120C, 120D, and 120E of the upper mold 120 are brought closer to each other, so that the tubular member 20, which has expanded radially outward, is brought into close contact with the inner surface 110b of the lower mold 110 and the inner surface 120b of the upper mold 120, and peaks 21 and valleys 22 are formed, thereby obtaining the above-mentioned corrugated pipe 1.
After the corrugated pipe 1 has cooled, the jig 33 and the core 30 are removed from inside the corrugated pipe in the axial direction of the corrugated pipe 1. When removing the core 30, the solid body 32 deforms along the inner surface of the corrugated pipe. The core 30 may be pushed out by the jig 33 or another jig, or may be pulled out.
The corrugated pipe 1 is then demolded by removing the surrounding mold 100.

The manufacturing method of the corrugated pipe of this embodiment includes the above-mentioned steps 1 to 5, and therefore can provide a manufacturing method of a resin corrugated pipe that can mold multiple uneven shapes (peaks 11 and valleys 12) in one cycle. In addition, it is possible to manufacture a resin corrugated pipe 1 in which the ratio (D1/t1) of the outer diameter D1 of the tubular member 10 at the apex of the peaks 11 to the radial thickness t1 of the tubular member 10 at the apex of the peaks 11 is 17 or less, and the ratio (D1/D2) of the outer diameter D1 of the tubular member 10 at the apex of the peaks 11 to the outer diameter D2 of the portion of the tubular member 10 where the peaks 11 and valleys 12 are not formed is 1.5 or more, which was difficult to achieve with conventional manufacturing methods.

In this embodiment, the jig 33 is pushed into the tubular member 20 to compress the core 30 (solid 32 in the tubular fiber fabric 31) from both ends of the tubular member 20 toward the center of the axial direction Q of the tubular member 20, but the method for manufacturing a corrugated pipe of the present invention is not limited to this. In the method for manufacturing a corrugated pipe of the present invention, the core may be compressed by air pressure from both ends of the tubular member toward the center of the axial direction of the tubular member.

[Modification]
FIG. 6 is a schematic cross-sectional view showing a modified example of the corrugated pipe of the present embodiment.
As shown in Fig. 6, two corrugated pipes 1 may be joined together by butt welding to form a long corrugated pipe 200. The corrugated pipe 200 has a butt fusion portion 210 at the joint between the two corrugated pipes 1. The long corrugated pipe 200 may be formed by cutting straight pipe portions on both sides of the bellows portion of the corrugated pipe 1 and joining only the bellows portion.

The present invention can provide a resin corrugated pipe that has excellent pressure resistance and flexibility. The present invention can also provide a method for manufacturing a resin corrugated pipe that can mold multiple concave and convex shapes in a single cycle.

Reference Signs List 1 Corrugated pipe 10 Tubular member 11 Peak portion 12 Valley portion 20 Tubular member 30 Core 31 Cylindrical fiber woven fabric 32 Solid 33 Jig 100 Mold 100a Gap 110 Lower mold 110a Gap 110A, 110B, 110C, 110D, 110E Part 120 Upper mold 120a Gap 120A, 120B, 120C, 120D, 120E Part

Claims (2)

A corrugated pipe made of resin is made of a tubular member, and has annular peaks that are convex radially outward of the tubular member and annular valleys that are concave radially outward of the tubular member, which are alternately formed in an axial direction to form a bellows-like shape,
a ratio (D1/t1) of an outer diameter D1 of the tubular member at the apex of the peak to a radial thickness t1 of the tubular member at the apex of the peak is 9 or more and 17 or less,
The D1/t1 corresponds to SDR1 represented by the following formula (1):
The material of the tubular member is a polyethylene corrugated pipe that is any one of PE100, PE80, and PE63 specified in ISO4427.
SDR1=2σ/(P/S)+1 (1)
(In formula (1), σ represents the 50-year creep strength, P represents the maximum design water pressure, and S represents the safety factor.) The corrugated pipe according to claim 1, wherein the ratio (D1/D2) of the outer diameter D1 of the tubular member at the apex of the crest to the outer diameter D2 of the portion of the tubular member where the crest and the valley are not formed is 1.5 or more.

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