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EP-4464499-B1 - PRODUCTION METHOD AND DEVICE FOR CURVED RESIN PIPE

EP4464499B1EP 4464499 B1EP4464499 B1EP 4464499B1EP-4464499-B1

Inventors

  • KURIBAYASHI, Nobuaki

Dates

Publication Date
20260506
Application Date
20220822

Claims (6)

  1. A method for manufacturing a bent resin pipe (1), the method comprising: manufacturing a bent resin pipe (1) by injecting molten resin (R) into a cavity (11) that extends while bending and is formed in a mold (10), subsequently injecting an assist material (S) into the cavity (11), and curing the resin (R) injected, wherein at least one of a bent inner portion (14a) or a bent outer portion (14b) of a pre-selected bent portion (12) of the cavity (11) is made up of a piece portion (15) whose temperature is adjustable, and wherein a control unit (17) controls the temperature of the piece portion (15); and controlling, in injecting the assist material (S) into the cavity (11), the temperature of the piece portion (15) from the control unit (17) to cause the bent inner portion (14a) to have a lower temperature than the bent outer portion (14b), characterized by interposing a heat insulating layer (16) between the piece portion (15) and the portion of the mold (10) other than the piece portion (15), and incorporating the piece portion (15) as a part of the mold (10).
  2. The method for manufacturing a bent resin pipe (1) according to claim 1, wherein a temperature difference between the bent inner portion (14a) and the bent outer portion (14b) is 20°C or more and 40°C or less.
  3. The method for manufacturing a bent resin pipe (1) according to claim 1 or 2, wherein a temperature of the bent inner portion (14a) is 30°C or more and 70°C or less.
  4. The method for manufacturing a bent resin pipe (1) according to any one of claims 1 to 3, wherein the bent inner portion (14a) of the pre-selected bent portion (12) has a bend angle of 90° or less and a radius of curvature of 20 mm or less.
  5. A device (7) for manufacturing a bent resin pipe (1), the device (7) comprising: a mold (10) in which a cavity (11) that extends while bending is formed; an injection molding machine (8) configured to inject molten resin (R) into the cavity (11); an assist material injection unit (9) configured to inject an assist material (S) into the cavity (11) into which the resin (R) is injected; and a control unit (17) configured to control the temperature of the piece portion (15), wherein at least one of a bent inner portion (14a) or a bent outer portion (14b) of a pre-selected bent portion (12) of the cavity (11) is made up of a piece portion (15) whose temperature is adjustable, and, in injecting the assist material (S) into the cavity (11), the control unit (17) is configured to control the temperature of the piece portion (15) to cause the bent inner portion (14a) to have a lower temperature than the bent outer portion (14b), characterized in that a heat insulating layer (16) is interposed between the piece portion (15) and the portion of the mold (10) other than the piece portion (15), and the piece portion (15) is incorporated as a part of the mold (10).
  6. The device (7) for manufacturing a bent resin pipe (1) according to claim 5, wherein the piece portion (15) is formed of a metal having a higher thermal conductivity than a metal forming a portion of the mold (10) other than the piece portion (15).

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, JP 2003 181868 A). 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 JP 2020 082621 A). 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. Lin, K.-Y., et al., "Using differential mold temperatures to improve the residual wall thickness uniformity around curved sections of fluid-assisted injection-molded tubes", International Communications in Heat and Mass Transfer, 36(5), 2009, pp. 491-497 (DOI: 10.1016/j.icheatmasstransfer. 2009.02.009) investigates fluid-assisted injection molding of curved plastic tubes and how differential mold temperatures affect residual wall-thickness uniformity. Using a spiral tube mold with eight curved water channels around two bends, inner channels (U2, L2) were held at 40°C while outer channels (U1, L1) were set to 40-70°C to create ΔT of 0/10/20/30°C. Water-assisted molding yielded more uniform walls than gas-assisted. The optimum uniformity occurred at ΔT ≈ 20°C. Numerical simulations of melt temperature corroborated the mechanism and guided channel/parameter optimization and settings. JP H08 25397 A discloses gas-assisted injection molding of hollow articles where mold regions intended to form gas channels - e.g., ribs, thick sections, curved portions - use metals of high thermal conductivity (≥ 85 W/m·K), such as Be-Cu or comparable inserts. The conductive material accelerates cooling of adjacent thin areas, raising resin viscosity so the injected gas preferentially flows into the target region, suppressing cavity irregularities. Examples report reduced "void turbulence" and stable hollow formation relative to molds using conventional carbon-steel inserts. 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 The object is achieved, in accordance with the present invention, by the provision of a method for manufacturing a bent resin pipe as defined in independent claim 1 and by the provision of a device for manufacturing a bent resin pipe as defined in independent claim 5. Further preferred embodiments and advantageous refinements are specified in dependent claims 2 to 4 and 6. Advantageous Effects of Invention According to 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 be