US-12617137-B2 - Method and device for manufacturing bent resin pipe

Abstract

A production method and device for a curved resin pipe via resin injection molding that uses an assist material. An inner curve part and/or an outer curve part of a pre-selected curved section of a cavity which is formed in a mold is configured from a temperature-adjustable piece section. After molten resin is injected into the cavity from an injection molding device, the temperature of the piece section is controlled by a control unit such that the inner curve part has a lower temperature than the outer curve part, and an assist material is injected into the cavity from an assist material injection unit and is passed through the cavity so as to form a pipe path. The resin remaining in the cavity is cured to produce a curved resin pipe.

Inventors

• Nobuaki KURIBAYASHI

Assignees

• THE YOKOHAMA RUBBER CO., LTD.

Dates

Publication Date

20260505

Application Date

20220822

Priority Date

20220113

Claims (19)

1. 1 . A method for manufacturing a bent resin pipe, the method comprising: manufacturing a bent resin pipe by injecting molten resin into a cavity that extends while bending and is formed in a pair of molds assembled together, subsequently injecting an assist material into the cavity, and curing the resin injected, wherein at least one of a bent inner portion or a bent outer portion of a pre-selected bent portion of the cavity includes a pair of temperature adjustable piece portions respectively incorporated into the pair of molds, a surface of one of the piece portions defines only part of the entire length of the cavity in an extension direction of the cavity formed in one of the molds, a surface of the other one of the piece portions defines only part of the entire length of the cavity in the extension direction of the cavity formed in the other one of the molds, and in injecting the assist material into the cavity, the bent inner portion being caused to have a lower temperature than the bent outer portion by using a control unit for controlling a temperature of the pair of piece portions, wherein a heat insulating layer is interposed between the one piece portion and portions of the one mold other than the one piece portion, and another heat insulating layer is interposed between the other piece portion and portions of the other mold other than the other piece portion.
2. 2 . The method for manufacturing a bent resin pipe according to claim 1 , wherein a temperature difference between the bent inner portion and the bent outer portion is 20° C. or more and 40° C. or less.
3. 3 . The method for manufacturing a bent resin pipe according to claim 1 , wherein a temperature of the bent inner portion is 30° C. or more and 70° C. or less.
4. 4 . The method for manufacturing a bent resin pipe according to claim 1 , wherein the bent inner portion of the pre-selected bent portion has a bend angle of 90° or less and a radius of curvature of 20 mm or less.
5. 5 . A device for manufacturing a bent resin pipe, the device comprising: a pair of molds in which a cavity that extends while bending is formed; an injection molding machine configured to inject molten resin into the cavity; and an assist material injection unit configured to inject an assist material into the cavity into which the resin is injected; at least one of a bent inner portion or a bent outer portion of a pre-selected bent portion of the cavity is made up of a pair of temperature adjustable piece portions respectively incorporated into the pair of molds, a surface of one of the piece portions defines only part of the entire length of the cavity in the extension direction of the cavity formed in one of the molds, a surface of the other one of the piece portions defines only part of the entire length of the cavity in the extension direction of the cavity formed in the other one of the molds, a control unit configured to control the temperature of the pair of piece portions is included, and controlling, in injecting the assist material into the cavity, the temperature of the piece portions from the control unit causes the bent inner portion to have a lower temperature than the bent outer portion, wherein a heat insulating layer is interposed between the one piece portion and portions of the one mold other than the one piece portion, and another heat insulating layer is interposed between the other piece portion and portions of the other mold other than the other piece portion.
6. 6 . The device for manufacturing a bent resin pipe according to claim 5 , wherein the pair of piece portions is formed of a metal having a higher thermal conductivity than a metal forming portions of the pair of molds other than the pair of piece portions.
7. 7 . The method for manufacturing a bent resin pipe according to claim 2 , wherein a temperature of the bent inner portion is 30° C. or more and 70° C. or less.
8. 8 . The method for manufacturing a bent resin pipe according to claim 2 , wherein the bent inner portion of the pre-selected bent portion has a bend angle of 90° or less and a radius of curvature of 20 mm or less.
9. 9 . The method for manufacturing a bent resin pipe according to claim 3 , wherein the bent inner portion of the pre-selected bent portion has a bend angle of 90° or less and a radius of curvature of 20 mm or less.
10. 10 . The method for manufacturing a bent resin pipe according to claim 1 , wherein the pair of piece portions is formed of a metal having a higher thermal conductivity than a metal forming portions of the pair of molds other than the pair of piece portions.
11. 11 . The method for manufacturing a bent resin pipe according to claim 10 , wherein the pair of piece portions is formed of beryllium copper alloy.
12. 12 . The method for manufacturing a bent resin pipe according to claim 1 , wherein only one of the bent inner portion or the bent outer portion is made up of the pair of piece portions.
13. 13 . The method for manufacturing a bent resin pipe according to claim 1 , wherein each of the pair of piece portions constitutes a range of only 15 mm or more and 20 mm or less in the extension direction of the cavity of a bend apex of the bent inner portion or the bent outer portion of the cavity.
14. 14 . The method for manufacturing a bent resin pipe according to claim 1 , wherein only the bent inner portion out of the bent inner portion and the bent outer portion is made up of the pair of piece portions.
15. 15 . The device for manufacturing a bent resin pipe according to claim 5 , wherein only one of the bent inner portion or the bent outer portion is made up of the pair of piece portions.
16. 16 . The device for manufacturing a bent resin pipe according to claim 5 , wherein only the bent inner portion out of the bent inner portion and the bent outer portion is made up of the pair of piece portions.
17. 17 . The method for manufacturing a bent resin pipe according to claim 1 , wherein each of the pair of piece portions has a dedicated flow path therein and the temperature of each of the pair of piece portions is controlled to a desired temperature range by flowing a medium through the corresponding dedicated flow path and adjusting the temperature of the medium by a temperature controller of the control unit.
18. 18 . The device for manufacturing a bent resin pipe according to claim 5 , wherein each of the pair of piece portions has a dedicated flow path through which a medium flows therein and the control unit controls the temperature of each of the pair of piece portions to a desired temperature range by adjusting the temperature of the medium flowing in the dedicated flow path.
19. 19 . The method for manufacturing a bent resin pipe according to claim 1 , wherein the pair of piece portions are disposed only in a localized area of the pair of molds directly adjacent to the bent inner portion or the bent outer portion of the cavity.

Description

TECHNICAL FIELD The present invention relates to a method and a device for manufacturing a bent resin pipe and particularly relates to a method and a device for manufacturing a bent resin pipe that can more reliably correct uneven thickness of a bent portion in manufacturing the bent resin pipe by resin injection molding using an assist material, such as a gas assist molding method. BACKGROUND ART A known gas assist molding method includes, in molding a resin pipe by resin injection molding, injecting molten resin into a mold and subsequently injecting a high-pressure gas, such as nitrogen gas, into the mold (see, for example, Patent Document 1). Instead of the high-pressure gas, water, a metal ball, or a resin ball may be injected, as an assist material, into the mold at high pressure. When a bent resin pipe is manufactured by resin injection molding using an assist material, the assist material injected into a cavity of a mold tends to pass through a bent portion of the cavity along the shortest route. Thus, the injected assist material passes through the bent portion of the cavity while being unevenly distributed on the inner side of the bend, and the thickness of the resin at a bent inner portion becomes thinner than that at a bent outer portion, resulting in uneven thickness. Accordingly, it becomes difficult for the manufactured bent resin pipe to have pressure resistance to withstand a preset target internal pressure. In response to this, providing a rib formation portion at the bent inner portion of the cavity and forming a rib at the bent inner portion of the manufactured bent resin pipe to reinforce the inner portion to have pressure resistance is proposed (see Patent Document 2). Unfortunately, this proposed method causes the bent inner portion of the bent resin pipe to remain relatively thin and have a shape in which the rib that is essentially unnecessary protrudes. Thus, there is room for improvement in reliably correcting the uneven thickness of the bent portion. CITATION LIST Patent Literature Patent Document 1: JP 2003-181868 APatent Document 2: JP 2020-82621 A SUMMARY OF INVENTION Technical Problem An object of the present invention is to provide a method and a device for manufacturing a bent resin pipe that can more reliably correct uneven thickness of a bent portion in manufacturing the bent resin pipe by resin injection molding using an assist material, such as a gas assist molding method. Solution to Problem To achieve the above object, a method for manufacturing a bent resin pipe according to an embodiment of the present invention includes manufacturing a bent resin pipe by injecting molten resin into a cavity that extends while bending and is formed in a mold, subsequently injecting an assist material into the cavity, and curing the molten resin injected. In the method, in injecting the assist material into the cavity, a bent inner portion of a pre-selected bent portion of the cavity may be caused to have a lower temperature than a bent outer portion of the pre-selected bent portion. A device for manufacturing a bent resin pipe according to an embodiment of the present invention includes a mold in which a cavity that extends while bending is formed, an injection molding machine configured to inject molten resin into the cavity, and an assist material injection unit configured to inject an assist material into the cavity into which the resin is injected. In the device, at least one of a bent inner portion or a bent outer portion of a pre-selected bent portion of the cavity may be made up of a piece portion whose temperature is adjustable, a control unit configured to control a temperature of a piece portion may be included, and controlling, in injecting the assist material into the cavity, the temperature of the piece portion from the control unit may cause the bent inner portion to have a lower temperature than the bent outer portion. Advantageous Effects of Invention According to an embodiment of the present invention, in injecting an assist material into a cavity into which molten resin has been injected, a bent inner portion of a pre-selected bent portion of the cavity is caused to have a lower temperature than a bent outer portion. This causes, when the injected assist material passes through, the injected molten resin to be harder at the bent inner portion than at the bent outer portion. For this reason, even if the assist material tends to be unevenly distributed to the bent inner portion when passing through the bent portion, the molten resin filled in the bent inner portion is less likely to be removed (less likely to be scraped away) by the passing assist material. As a result, uneven thickness of the bent portion can be more reliably corrected. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram illustrating a manufacturing device for a bent resin pipe according to an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating, in a plan vi