Resin pipe, assembly of resin pipe and hose, and method for manufacturing resin pipe

Abstract

Provided are a resin pipe, an assembly of the resin pipe and a hose, and a method for manufacturing the resin pipe, with which it is possible to reduce weight and to improve durability and sealability of a nipple to which the hose is externally fitted and caulked. A metal core pipe 5 is internally fitted in a predetermined range X including the total length of a caulking range CA in which a hose 7 is caulked in the longitudinal direction of a resin nipple 4 at the tip part of a resin pipe 1, and a fitting recess 4a and a fitting projection 4b formed in the nipple 4, and a notch part 6a and a recessed part 6b formed in the core pipe 5 restrict the movement of the core pipe 5 in the axial direction and the circumferential direction in relation to the nipple 4 to integrate the nipple 4 and the core pipe 5. A hose fitting 8 is externally inserted in a state in which the hose 7 is externally fitted to the nipple 4, and the hose fitting 8 is caulked to fix the hose 7 to the nipple 4.

Description

Resin pipe, assembly of this resin pipe and hose, and manufacturing method of this resin pipe

[0001] The present invention relates to a plastic pipe, an assembly of this plastic pipe and a hose, and a method for manufacturing this plastic pipe. More specifically, the present invention relates to a plastic pipe that can be made lighter while suppressing deformation of the nipple onto which the hose is fitted and crimped, thereby improving durability and sealing performance, and a method for manufacturing this plastic pipe.

[0002] Various structures for fitting a pipe body onto a nipple and fixing it are known (see, for example, Patent Documents 1 and 2). Patent Document 1 discloses a structure in which a resin first low-pressure pipe is fitted onto a resin first cylindrical portion (corresponding to a nipple) and fixed thereto (paragraphs 0020 to 0023, Figure 2, etc.). Patent Document 2 discloses a structure in which a resin tube is fitted onto a press-fit mounting portion (corresponding to a nipple) of a quick connector and fixed thereto (paragraph 0013, Figure 1, etc.).

[0003] In recent years, various studies have been conducted to replace metal pipes with resin pipes for piping in vehicles such as automobiles in order to reduce weight. In resin pipes with nipples at their distal ends, a hose is fitted onto the nipple and crimped. Specifically, after fitting the hose onto the nipple, the hose fitting fitted onto the distal end of the hose is crimped to firmly secure the hose to the nipple. Compared to metal nipples on metal pipes, resin nipples on resin pipes have lower rigidity. Therefore, with simple resin pipes, resin nipples are easily deformed when the hose is crimped to secure it, resulting in problems such as reduced durability and reduced sealing performance between the hose and the nipple compared to nipples on metal pipes. Therefore, there is room for improvement in reducing weight while suppressing deformation of nipples fitted onto hoses and crimping them to improve durability and sealing performance.

[0004] Japanese Patent No. 6714784 Japanese Patent Application Laid-Open No. 2004-263729

[0005] The object of the present invention is to provide a resin pipe that can be made lighter while suppressing deformation of the nipple onto which the hose is fitted and crimped, thereby improving durability and sealing performance, as well as an assembly of this resin pipe and hose, and a method for manufacturing this resin pipe.

[0006] In order to achieve the above object, the plastic pipe of the present invention is a plastic pipe having a cylindrical nipple onto which a hose fitted thereon is crimped, and is characterized in that it has a metal core tube fitted into the nipple and positioned in a predetermined range in the longitudinal direction of the nipple that includes the entire length of the crimping range in which the hose is crimped, and the core tube and the nipple have regulating portions that regulate the axial and circumferential movement of the core tube relative to the nipple.

[0007] The assembly of a plastic pipe and a hose of the present invention is an assembly of the above-mentioned plastic pipe and a hose that is fitted onto the outside of the nipple of the plastic pipe and crimped, characterized in that the core tube has a notch at its tip, the notch is positioned outside the crimping range in the longitudinal direction of the nipple, a part of the resin forming the nipple penetrates into the notch, and the resin that has penetrated into the notch and the notch constitute the regulating portion.

[0008] The method for manufacturing a resin tube of the present invention is characterized in that, in the method for manufacturing a resin tube described above, the core tube is placed in a nipple molding section that forms the nipple of a cavity for forming the resin tube extending into a mold, and while the mold is clamped, molten resin is injected from one end of the cavity to the other end using an injector, and then an assist material is injected into the cavity to discharge excess molten resin from the cavity, thereby hardening the cylindrical molten resin remaining in the cavity to form the resin tube, and the core tube is fitted into the nipple while restricting its axial and circumferential movement relative to the nipple.

[0009] According to the resin pipe of the present invention, a metal core tube is fitted within a predetermined area of ​​the nipple in the longitudinal direction, including the entire length of the crimping area where the hose is crimped, thereby improving the rigidity of this crimping area. Therefore, even when the hose is crimped to the nipple, deformation of the nipple is suppressed, improving the durability of the nipple and the sealing performance between the hose and the nipple. The restricting portion restricts axial and circumferential movement of the core tube relative to the nipple, stably fixing the core tube to the nipple, further improving the durability and sealing performance of the nipple. Furthermore, because the core tube is integrated within the predetermined longitudinal area of ​​the resin nipple, the weight can be reduced compared to nipples made entirely of metal.

[0010] According to the assembly of the present invention, the durability of the resin pipe is improved, thereby ensuring a strong and stable connection between the nipple and the hose, which is advantageous for maintaining an excellent seal between them for a long period of time. Furthermore, the weight of the resin pipe is reduced, resulting in a lighter assembly. Furthermore, the resin pipe manufacturing method of the present invention can be used to manufacture the resin pipe in which the core pipe is fitted into the nipple and integrated with it.

[0011] FIG. 1 is an explanatory diagram illustrating an embodiment of a resin pipe in a longitudinal cross section. FIG. 2 is an explanatory diagram illustrating the resin pipe of FIG. 1 rotated 45° around its axis. FIG. 3 is an explanatory diagram illustrating the resin pipe of FIG. 1 as viewed from an arrow A. FIG. 4 is an explanatory diagram illustrating the resin pipe of FIG. 1 as viewed from a cross section B-B. FIG. 5 is a perspective view of the core tube of FIG. 1. FIG. 6 is an explanatory diagram illustrating the resin pipe of FIG. 1 separated from the core tube. FIG. 7 is a perspective view showing a modified core tube. FIG. 8 is a perspective view showing another modified core tube. FIG. 9 is an explanatory diagram illustrating an assembly of a resin pipe and a hose in a longitudinal cross section. FIG. 10 is an explanatory diagram illustrating the assembly of FIG. 9 as viewed from a cross section C-C. FIG. 11 is an explanatory diagram illustrating the process of crimping a hose to a nipple. FIG. 12 is an explanatory diagram illustrating a resin pipe manufacturing apparatus. FIG. 13 is an explanatory diagram illustrating a portion of one of the molds of FIG. 12, together with the core tube and support pipe, as viewed from the front. Fig. 14 is an explanatory diagram illustrating a state in which a core tube is placed in the nipple molding portion of Fig. 13. Fig. 15 is an explanatory diagram illustrating a schematic illustration of the interior of the cavity filled with injected molten resin after the mold of Fig. 14 is closed. Fig. 16 is an explanatory diagram illustrating a schematic illustration of a state in which an assist material is injected into the cavity of Fig. 15. Fig. 17 is an explanatory diagram illustrating a schematic illustration of a state in which the molten resin remaining in the cavity of Fig. 16 has hardened. Fig. 18 is an explanatory diagram illustrating a schematic illustration of a state in which the support pipe has been removed after the mold of Fig. 17 is opened.

[0012] Hereinafter, a resin pipe, an assembly of this resin pipe and a hose, and a method for manufacturing this resin pipe according to the present invention will be described based on the embodiments shown in the drawings.

[0013] The embodiment of the resin pipe 1 illustrated in Figures 1 to 4 has a resin nipple 4 at its longitudinal tip. A metal core tube 5 is fitted into this nipple 4, and the core tube 5 is integrated with the resin pipe 1. The resin pipe 1 is a cylinder having a pipe wall 2 formed from a cured resin R2, and a conduit 3 extending in the longitudinal direction. The dashed-dotted line CL in the figures indicates an axis passing through the center of the cross section of the conduit 3 of the resin pipe 1 and the core tube 5. The extension direction of this axis CL is the axial direction (longitudinal direction) of the resin pipe 1 and the core tube 5.

[0014] The inner diameter of the resin pipe 1 is, for example, 4 mm to 16 mm, and is set to a substantially constant value throughout the entire length of the pipe. The inner diameter of the resin pipe 1 and the inner diameter of the core tube 5 are substantially the same, and the inner circumferential surfaces of the resin pipe 1 and the core tube 5 are smoothly connected in the axial direction to form the conduit 3. The wall thickness of the resin pipe 1 is, for example, 1 mm to 3 mm. This resin pipe 1 is used as piping for various devices, such as piping for air conditioners installed in vehicles such as automobiles. The resin pipe 1 may be a straight pipe or a bent pipe depending on the application (place of use). As will be described in more detail below, a hose 7 fitted over the nipple 4 is crimped and connected to it, as shown in Figures 9 and 10.

[0015] The nipple 4 is a tapered cylindrical body that tapers slightly toward the longitudinal tip. That is, the outer peripheral surface of the nipple 4 is inclined so that it tapers slightly toward the longitudinal tip. The tapered outer peripheral surface of the nipple 4 has anti-slip projections formed at intervals in the axial direction.

[0016] A locking portion 2a is formed on the outer circumferential surface of the resin pipe 1. This locking portion 2a is an annular groove that is continuous around the entire circumference. The locking portion 2a is located axially rearward of the core pipe 5. In other words, the core pipe 5 located at the tip of the resin pipe 1 does not extend as far as the locking portion 2a.

[0017] The resin for forming the resin pipe 1 is selected from various known injectable thermoplastic resins, and an appropriate type is selected depending on the performance required of the resin pipe 1. For example, when manufacturing a resin pipe 1 for an air conditioner installed in an automobile, polyamide, polypropylene, ABS resin, etc. are used, and nylon resin (nylon 6, nylon 66, nylon 12, nylon 11), polyethylene, polycarbonate, polystyrene, polyoxymethylene, polymethyl methacrylate, polybutylene terephthalate, acrylic, polyether ether keto, thermoplastic polyurethane, polyethylene terephthalate, and polyvinyl chloride are preferred.

[0018] The resin pipe 1 can be made of only thermoplastic resin, but it can also be made to contain various types of fibers (such as glass fiber or carbon fiber, either short or long) mixed as reinforcing fibers f in a predetermined ratio (e.g., 30% to 40% by mass per 100 parts by mass of resin). When the reinforcing fibers f are short fibers, their size is, for example, an outer diameter of 0.001 mm to 1.0 mm, and a length of 0.01 mm to 10 mm. In this embodiment, the reinforcing fibers f are mixed into the cured resin R2.

[0019] The core tube 5 shown in Figure 5 is made of carbon steel, stainless steel, or the like. The inner and outer diameters of the core tube 5 are set to substantially constant values ​​over the entire length of the tube. The wall thickness of the core tube 5 is, for example, 0.3 mm to 1.0 mm, and is substantially constant over the entire length of the tube (excluding the recess 6b). The length of the core tube 5 is, for example, 10 mm to 80 mm. Since it is difficult to ensure sufficient rigidity with an aluminum core tube 5, it is preferable to form the core tube 5 from a material having a tensile strength equal to or greater than that of SS400.

[0020] The core tube 5 has notches 6a at its tip. In this embodiment, four rectangular notches 6a are arranged at equal intervals in the circumferential direction. Recesses 6b are formed on the outer circumferential surface of the core tube 5. In this embodiment, the recesses 6b are grooves with semicircular cross sections that extend around the entire circumferential direction. These recesses 6b, which are circumferential grooves, are formed in multiple locations (three locations) spaced apart in the axial direction. The depth of the recesses 6b is very small, for example, about 0.1 mm.

[0021] As shown in Figure 6, when the resin tube 1 and core tube 5 are separated, a mating recess 4a of the same shape as the outer surface of the core tube 5 is formed on the inner surface of the nipple 4. That is, the inner surface of the nipple 4 has a mating recess 4a whose shape is transferred by pressing the outer surface of the core tube 5 into it. More specifically, the inner surface of the nipple 4 has an engaging protrusion 4b that fits into the notch 6a of the core tube 5 at a position corresponding to the notch 6a, and an annular small protrusion that fits into the recess 6b at a position corresponding to the recess 6b. The depth of the mating recess 4a is substantially the same as the wall thickness of the core tube 5. The core tube 5 is fitted into this mating recess 4a and is integrated with the resin tube 1.

[0022] The core tube 5 is fitted into the fitting recess 4a, restricting axial movement relative to the nipple 4. Furthermore, the engagement protrusions 4b fit into the cutouts 6a, restricting axial and circumferential movement of the core tube 5 relative to the nipple 4. Furthermore, the small protrusions on the inner peripheral surface of the nipple 4 fit into the recesses 6b, restricting axial movement of the core tube 5 relative to the nipple 4. In this way, the fitting recess 4a, engagement protrusions 4b, and small protrusions on the inner peripheral surface of the nipple 4, as well as the cutouts 6a and recesses 6b of the core tube 5, function as restricting portions that restrict axial and circumferential movement of the core tube 5 relative to the nipple 4. This restricting portion prevents the core tube 5 from shifting relative to the nipple 4 and stably fixes it in a predetermined position on the nipple 4, preventing the core tube 5 from falling off the resin tube 1.

[0023] Furthermore, the formation of the recess 6b increases the contact area between the outer circumferential surface of the core tube 5 and the inner circumferential surface of the nipple 4. As a result, this is advantageous for stably fixing the core tube 5 at a predetermined position on the nipple 4.

[0024] The portion functioning as the restricting portion can have various specifications. The notch 6a formed in the core tube 5 is not limited to a rectangular shape, and various shapes such as a triangular shape, a semicircular shape, or a semi-elliptical shape can be used. A trapezoidal shape that narrows toward the tip of the core tube 5, such as the notch 6a shown in FIG. 7, or a trapezoidal shape that widens toward the tip of the core tube 5, such as the notch 6a shown in FIG. 8, can also be used. The number of notches 6a needs to be at least one, and any number of notches may be used. When multiple notches 6a are provided, they should be arranged at equal intervals in the circumferential direction. Multiple types of notches 6a with different shapes and sizes may also be used. The fitting protrusion 4b has a shape that corresponds to the shape of the notch 6a.

[0025] The recess 6b formed by a circumferential groove as illustrated in Fig. 5 may be formed in only one location, or in multiple locations spaced apart in the axial direction. As illustrated in Fig. 7, recess 6b formed by linear grooves extending parallel to the axial direction of the core tube 5 may also be employed. This linear groove recess 6b may be formed in only one location, or in multiple locations (four locations) spaced apart in the circumferential direction as in this embodiment. When multiple linear groove recesses 6b are formed, they should be arranged at equal intervals in the circumferential direction.

[0026] As shown in Fig. 8, a recess 6b consisting of a spiral groove extending spirally around the axis CL can also be used. The recess 6b shown in Figs. 7 and 8 may be formed over the entire longitudinal length of the core tube 5, or may be formed only within a specific range in the longitudinal direction. The minute protrusions on the inner peripheral surface of the nipple 4 that fit into the recess 6b have a shape that corresponds to the shape of the recess 6b.

[0027] The recesses 6b are not limited to extending grooves, but may be dot-like depressions, and the outer peripheral surface of the core tube 5 may be configured with scattered depressions as recesses 6b. Instead of or in addition to the recesses 6b, protrusions (extending projections or dot-like projections) may be used. That is, it is sufficient if the outer peripheral surface of the core tube 5 is formed unevenly by the recesses 6b or protrusions. The inner peripheral surface of the nipple 4 is shaped according to the unevenness of the outer peripheral surface of the core tube 5, so that the resin on the inner peripheral surface of the nipple 4 is embedded in the recesses 6b. Therefore, the recesses 6b on the outer peripheral surface of the core tube 5 and the resin embedded in these recesses 6b function as the restricting portion described above.

[0028] A plurality of types of recesses 6b and protrusions with different shapes and sizes may be mixed, and the recesses 6b and protrusions may be formed in combination with desired notches 6a. The recesses 6b and protrusions may be provided arbitrarily, and the outer peripheral surface of the core tube 5 may be made smooth without minute irregularities, with only the fitting protrusions 4b and the notches 6a functioning as the above-mentioned restricting portions.

[0029] The core tube 5 is disposed in a predetermined range X that includes the entire length of the crimping range CA in the longitudinal direction of the nipple 4, where the hose 7 is crimped. In other words, the core tube 5 is disposed so as to encompass at least the crimping range CA. The crimping range CA is the range in which the crimping force substantially acts when crimping the hose 7 to the nipple 4. By comparing the outer diameters of the nipple 4 before and after crimping the hose 7, the position (range) where there is a difference between the two can be determined to be the crimping range CA, and a position (range) where there is no difference between the two can be determined to be outside the crimping range CA. Generally, crimping force does not act in the range from the tip of the nipple 4 (plastic pipe 1) to approximately 5 mm or more and 20 mm or less in the axial direction, so this range is outside the crimping range CA.

[0030] In this embodiment, the tip position of the core tube 5 coincides with the tip position of the plastic tube 1, and the rear end position of the core tube 5 is located approximately 5 mm behind the rear end position of the crimping area CA. The tip position of the core tube 5 can be set slightly back from the tip position of the plastic tube 1, but by making the tip positions of both the core tube 5 and the plastic tube 1 coincident with each other, it becomes easier to manufacture the plastic tube 1. The rear end position of the core tube 5 can also be made substantially coincident with the rear end position of the crimping area CA to reduce weight.

[0031] The notch 6a is located outside the crimping range CA. In this embodiment, the leading end of the notch 6a coincides with the leading end of the plastic pipe 1, and the rear end of the notch 6a is located approximately 5 mm forward of the leading end of the crimping range CA. The rear end of the notch 6a can also be made to substantially coincide with the leading end of the crimping range CA to reduce weight.

[0032] 9 and 10 show an embodiment of an assembly 9 of a resin pipe 1 and a hose 7, in which the hose 7 is fitted onto the nipple 4 of the resin pipe 1 and crimped. The core tube 5 has a notch 6a at its tip, which is positioned outside the crimping range CA in the longitudinal direction of the nipple 4. The hose 7 may be a rubber hose or a resin hose in which a reinforcing layer 7c made of reinforcing wire material is coaxially laminated between an inner layer 7a and an outer layer 7b.

[0033] To explain the structure of the assembly 9 in detail, the hose 7 fitted onto the nipple 4 is covered by a cylindrical hose fitting 8. At one end of the hose fitting 8, an annular locking portion 8a protrudes inward, and this locking portion 8a is locked to a locking portion 2a formed on the outer surface of the resin pipe 1. When the outer surface (pressing portion 8b) of the hose fitting 8 is pressed firmly by a crimping jig, the hose 7 together with the hose fitting 8 deforms toward the nipple 4 (axial center CL), and the hose 7 is crimped to the nipple 4.

[0034] To manufacture the assembly 9, as shown in Fig. 11 , the locking portion 8a of the hose fitting 8 is locked onto the locking portion 2a of the resin pipe 1, and the hose fitting 8 is attached so as to cover the outer peripheral surface of the nipple 4 with a gap therebetween. The nipple 4 is then inserted into one end of the hose 7, and the one end of the hose 7 is forced into the gap between the nipple 4 and the hose fitting 8. Next, the outer peripheral surface of the hose fitting 8 is pressed strongly toward the axis CL using a crimping jig. This deforms the hose 7 together with the hose fitting 8 toward the nipple 4 (axis center CL), and the hose 7 is crimped and connected to the nipple 4. Various known types of hose fittings 8 and crimping jigs may be used.

[0035] The crimping force applied when the hose 7 is crimped to the nipple 4 acts on the crimping range CA. The core tube 5 is fitted into the nipple 4 within a predetermined range X that includes the entire length of the crimping range CA, improving the rigidity of the crimping range CA of the nipple 4. Therefore, deformation of the nipple 4 to which the hose 7 is crimped is suppressed compared to a resin nipple. This avoids damage to the nipple 4 when the hose 7 is crimped, which is advantageous in suppressing deformation and damage over time, improving the durability of the nipple 4. In other words, the hose 7 can be fixed to the nipple 4 with a stronger crimping force compared to a resin nipple, improving the sealing performance between the hose 7 and the nipple 4. As a result, the hose 7 is stably fixed to the nipple 4 over a long period of time, which is advantageous in maintaining a good sealing performance between the hose 7 and the nipple 4.

[0036] The restricting portion restricts the axial and circumferential movement of the core tube 5 relative to the nipple 4, so that the core tube 5 is stably fixed to the nipple 4. This is even more advantageous in improving the durability and sealing performance of the nipple 4. Furthermore, because the core tube 5 is integrated into the resin nipple 4 within a predetermined range X in the longitudinal direction, the weight of the nipple 4 can be reduced compared to when the entire nipple 4 is made of metal.

[0037] In this embodiment, the notch 6a is formed at the tip of the core tube 5 and is located outside the crimping range CA. In other words, the range where the notch 6a is formed is not a part necessary for suppressing deformation of the nipple 4 due to the crimping force, so the core tube 5 can be made lighter and prevented from falling off from the nipple 4 without impairing the effect of suppressing deformation of the nipple 4.

[0038] An example of a procedure for manufacturing the resin pipe 1 will be described below.

[0039] The resin pipe 1 is manufactured using a manufacturing apparatus 10 illustrated in Fig. 12. This manufacturing apparatus 10 includes an injector 11, an assist material injector 14, and a mold 16. In this embodiment, a pair of left and right molds 16 are used.

[0040] The injection machine 11 has a cylinder 12 and a screw 13 disposed within the cylinder 12. The injection machine 11 is not limited to the type shown in the figure, and various known resin injection molding machines, such as pre-plasticizers, can be used. An injection path 18a is connected to an injection port 12a at the tip of the cylinder 12. The injection path 18a is connected to a mold 16. The resin used is heated inside the cylinder 12 to become molten resin R1, and the rotating screw 13 injects the molten resin R1 from the injection port 12a through the injection path 18a into the interior of the mold 16.

[0041] The assisting material injector 14 has a storage section 15 that stores a gas used as the assisting material As. Various known injectors can be used as the assisting material injector 14. A gas (gaseous substance) such as nitrogen gas or air is used as the assisting material As.

[0042] An injection path 18b is connected to an injection port 15a at the tip of the accommodation portion 15. The injection path 18b is connected to the mold 16. The assist material As is injected at a predetermined pressure from the injection port 15a through the injection path 18b toward the inside of the mold 16. For example, a gas at room temperature (20°C ± 15°C) is injected as the assist material As.

[0043] The mold 16 is composed of one mold 16A and the other mold 16B that are assembled together. The molds 16A and 16B come into contact with and separate from each other at a parting line PL. In this embodiment, the mold 16 is not limited to a two-piece mold, and various other known types of molds 16 can be used.

[0044] A hollow cavity 17 is formed inside the mold 16. The cavity 17 extends linearly from one end 17a to the other end 17b and is non-annular. The outer shape of this cavity 17 is the same as the outer shape of the resin pipe 1 to be manufactured. In this embodiment, the cavity 17 extends vertically between the upper end 17a and the lower end 17b, and a pair of left and right molds 16A, 16B are used.

[0045] An injection port 12a is connected to one end 17a of the cavity 17 via an injection path 18a, and an injection port 15a is connected to the other end 17b of the cavity 17 via an injection path 18b. The injection port 12a may be connected indirectly or directly to the one end 17a of the cavity 17, and the injection port 15a may be connected indirectly or directly to the other end 17b of the cavity 17.

[0046] 13, the other end 17b of the cavity 17 is a nipple forming portion 19. A pipe fixing portion 19a is connected to this nipple forming portion 19. A support pipe 20 is used to position the core tube 5 in the nipple forming portion 19.

[0047] The support pipe 20 has a cylindrical body with an opening 20a at its tip and a larger-diameter base 20b connected to the lower end of the cylinder. The core tube 5 is inserted into this cylinder, and the outer diameter of the cylinder is set to be almost the same as the inner diameter of the core tube 5, but only slightly smaller, so that the core tube 5 is inserted around the cylinder with virtually no gap. A flow path that is continuous with the injection path 18b penetrates the support pipe 20, and the tip of this flow path becomes the opening 20a. Therefore, the opening 20a serves as the outlet for the injection path 18b. The pipe fixing portion 19a is formed as a recess of the same shape as the base 20b.

[0048] As shown in Figure 14, when manufacturing the resin pipe 1, the mold 16 is opened and the core tube 5 is placed in the nipple molding portion 19. That is, the base 20b of the support pipe 20, around which the core tube 5 is inserted, is fitted to the pipe fixing portion 19a, leaving a gap between the outer circumferential surface of the core tube 5 and the inner circumferential surface of the nipple molding portion 19. The core tube 5 is placed on the base 20b with its lower end, where the notch 6a is formed, abutting against the base 20b. In this embodiment, the opening 20a protrudes upward from the upper end of the core tube 5, but it can also be located at the same position as this upper end or slightly below this upper end.

[0049] Next, the molds 16A and 16B are assembled together and closed, and then, as illustrated in Fig. 15, the molten resin R1 is injected into the cavity 17 of the closed mold 16 by the injector 11. In this embodiment, the molten resin R1 mixed with the reinforcing fibers f is injected from the injector 11. The injected molten resin R1 is injected into the cavity 17 from the injection port 12a via the injection path 18a.

[0050] More specifically, molten resin R1 is injected from one end 17a to the other end 17b of the cavity 17, filling the cavity 17 with the molten resin R1. In the nipple molding portion 19, the molten resin R1 fills the cylindrical gap between the inner circumferential surface of the nipple molding portion 19 and the outer circumferential surface of the core tube 5. The molten resin R1 penetrates into the notched portion 6a and the recessed portion 6b and fills them. Note that the reinforcing fibers f mixed with the molten resin R1 are not shown in Figures 15 to 18.

[0051] 16, the assist material (gas) As is injected into the mold 16 by the assist material injector 14. That is, the assist material As is injected at a predetermined pressure from the opening 20a toward the other end 17b of the cavity 17 filled with the molten resin R1 toward the one end 17a. In this way, the assist material (gas) As is injected into the cavity 17 in the direction opposite to the injection direction of the molten resin R1. The injected assist material As passes through the interior of the cavity 17 along the extension direction of the cavity 17.

[0052] As the assist material As passes through the cavity 17, excess molten resin R1 is discharged from one end 17a of the cavity 17, leaving a cylindrical molten resin R1 in the cavity 17. In the nipple molding portion 19, the molten resin R1 that filled the gap (cylindrical gap) between the inner peripheral surface of the nipple molding portion 19 and the outer peripheral surface of the core tube 5 remains. The molten resin R1 that filled the cutout portion 6a and the recessed portion 6b also remains. A discharge path (not shown) separate from the injection path 18a is connected to one end 17a of the cavity 17, and excess molten resin R1 is discharged into this discharge path.

[0053] As shown in Figure 17, the remaining molten resin R1 in the cavity 17 hardens and becomes cured resin R2, forming the resin pipe 1. That is, the cured resin R2 becomes the pipe wall 2, and the hollow portion becomes the pipe line 3. The molten resin R1 filled in the gap (cylindrical gap) between the inner surface of the nipple-forming portion 19 and the outer surface of the core tube 5 becomes cured resin R2, forming the nipple 4 and the mating recess 4a. The molten resin R1 filled in the cutout portion 6a becomes cured resin R2, forming the mating protrusion 4b, and the molten resin R1 filled in the recess 6b becomes cured resin R2, forming the annular micro-protrusion. At this stage, the waste portion of the cured resin R2 (resin discharged from the cavity 17) extends and integrates with one end of the resin pipe 1.

[0054] Next, the molds 16A and 16B are separated at the parting line PL to open the mold 16, and the support pipe 20 is removed from the mold 16, as shown in Fig. 18. The molded resin pipe 1 is then removed together with the unnecessary portion of the cured resin R2. The unnecessary portion of the cured resin R2 is cut away from the removed resin pipe 1, thereby producing the resin pipe 1 in which the core tube 5 is integrated with the nipple 4, as shown in Figs. 1 to 4.

[0055] This assembly 9 ensures a strong and stable connection between the nipple 4 and the hose 7, along with the improved durability of the plastic pipe 1, which is advantageous for maintaining an excellent seal between them for a long period of time. In addition, as the plastic pipe 1 becomes lighter, the assembly 9 also becomes lighter.

[0056] The injection temperature of the molten resin R1 is generally set in the range of, for example, 150°C or higher and 350°C or lower. The temperature of the mold 16 (cavity 17) is generally set in the range of, for example, 30°C or higher and 120°C or lower. Therefore, the injection temperature of the molten resin R1 and the temperature of the mold 16 (cavity 17) are appropriately determined within these ranges to control the viscosity of the molten resin R1 in the cavity 17 to a desired range. In other words, to ensure that the molten resin R1 in the cavity 17 has an appropriate viscosity, the temperature of the molten resin R1 injected into the cavity 17 and the temperature of the mold 16 (cavity 17) are set within the desired range.

[0057] The appropriate injection pressure of the assist material (gas) As varies depending on the length and shape of the resin pipe 1 (cavity 17), the viscosity of the molten resin R1 in the cavity 17, and other factors, and therefore cannot be set uniformly and comprehensively. Therefore, to achieve a desired viscosity range for the molten resin R1 in the cavity 17, the temperature of the molten resin R1 injected into the cavity 17 and the temperature of the mold 16 (cavity 17) are set within the above-described ranges. Then, under these set temperature conditions, test molding is performed with multiple different injection pressures of the assist material As to produce samples of the resin pipe 1. The injection pressure at which the wall thickness of the pipe wall 2 of the sample resin pipe 1 produced by each test molding falls within a standard range (e.g., 1.5 mm or more and 1.75 mm or less) is determined, and this determined injection pressure is set as the appropriate injection pressure for the assist material As. In the actual production of the resin pipe 1, the temperature of the molten resin R1 is set to the conditions set in the test molding, and the assist material As is injected into the cavity 17 at this set appropriate injection pressure to manufacture the resin pipe 1.

[0058] In this embodiment, gas is used as the assist material As, but a liquid such as water or a solid such as metal or resin spheres can also be used as the assist material As. The assist gas injector 14 employs a known appropriate mechanism depending on the type of assist material As.

[0059] As the gaseous assist material As passes through the cavity 17 filled with the molten resin R1, the temperature of the molten resin R1 that comes into contact with the gas can be prevented from dropping rapidly compared to when a solid or liquid assist material As is used. Furthermore, the gaseous assist material As does not allow the molten resin R1 to adhere to the assist material As, as occurs with a solid assist material As. Therefore, molding the resin pipe 1 using a gas as the assist material As is advantageous in reducing the variation in the wall thickness of the pipe wall 2 over the entire length of the pipe, even if the pipe is long.

[0060] Various known molding methods that do not use the assist material As can also be used to mold this resin pipe 1. For example, the resin pipe 1 can be molded by injecting molten resin R1 into the cavity 17 with a core placed in the cavity 17, and then removing the core to form the pipe line 3.

[0061] Analytical models were created for four types of samples (Examples 1 to 4) of resin pipes with the same structure as the resin pipes shown in Figures 1 to 4, but differing only in the material of the core pipe and the thickness of the core pipe wall, as well as a simple resin pipe sample (Comparative Example) in which the core pipe portion of Examples 1 to 4 was replaced with resin. For these five types of samples, the same hose was crimped under the same conditions to produce the assembly shown in Figures 9 and 10, and the maximum stress generated in each nipple due to the crimping force was calculated. The results are shown in Table 1.

[0062] The resin tube was made of nylon 6 resin, the nipple had an inner diameter of 11.0 mm and an outer diameter of 15.0 mm, and the core tube was positioned within a range of 35 mm from the tip of the nipple near the engaging portion of the resin tube. In Examples 1 to 4, the thickness of the resin portion of the nipple's tube wall was calculated as "the difference between the outer and inner diameters of the nipple x 0.5 - the wall thickness of the core tube." The crimping force for each sample was set to a practically applicable value based on actual data. In Table 1, the maximum stress was evaluated using an index, with a standard of 100 representing a practically acceptable level. The smaller the index value, the smaller the maximum stress and the better the durability.

[0063]

[0064] The results in Table 1 show that the nipples of Examples 1 to 4 have sufficient durability. In addition, the nipple of the comparative example was unable to be evaluated because it underwent excessive deformation due to the crimping force compared to the nipples of Examples 1 to 4, and was found to have inferior durability compared to Examples 1 to 4.

[0065] REFERENCE SIGNS LIST 1 Resin pipe 2 Pipe wall 2a Locking portion 3 Pipe line 4 Nipple 4a Fitting recess (restricting portion) 4b Fitting protrusion (restricting portion) 5 Core pipe 6a Notched portion (restricting portion) 6b Recessed portion (restricting portion) 7 Hose 7a Inner surface layer 7b Outer surface layer 7c Reinforcing layer 8 Hose fitting 8a Locking portion 8b Pressing portion 9 Assembly 10 Resin pipe manufacturing device 11 Injection machine 12 Cylinder 12a Injection port 13 Screw 14 Assist material injection machine 15 Storage portion 15a Injection port 16 (16A, 16B) Mold 17 Cavity 17a One end 17b Other end 18a Injection path 18b Injection path 19 Nipple molding portion 19a Pipe fixing portion 20 Support pipe 20a Opening 20b Base PL Parting line R1 Molten resin R2 Hardened resin As Assist material f Reinforcement fiber

Claims

1. A plastic pipe having a cylindrical nipple onto which a hose is fitted and crimped, the plastic pipe having a metal core tube fitted into the nipple and positioned within a predetermined range in the longitudinal direction of the nipple that includes the entire length of the crimping range over which the hose is crimped, the core tube and the nipple having regulating portions that regulate the axial and circumferential movement of the core tube relative to the nipple.

2. A resin pipe as described in claim 1, wherein the core tube has a notch at its tip, the notch is positioned outside the crimping range in the longitudinal direction of the nipple, a portion of the resin forming the nipple penetrates into the notch, and the resin that has penetrated into the notch and the notch constitute the restricting portion.

3. A resin pipe as described in claim 1 or 2, wherein an unevenness is formed on the outer peripheral surface of the core tube, a part of the resin forming the nipple penetrates into a concave portion of the unevenness, and the resin that has penetrated into the concave portion and the concave portion constitute the restricting portion.

4. An assembly of a plastic pipe and a hose which is fitted around the nipple of the plastic pipe as described in claim 1 and crimped, wherein the core tube has a notch at its tip, the notch is positioned outside the crimping range in the longitudinal direction of the nipple, a part of the resin forming the nipple penetrates into the notch, and the resin that has penetrated into the notch and the notch constitute the regulating portion.

5. An assembly of a plastic pipe and a hose as described in claim 1, which is fitted onto the nipple of the plastic pipe and crimped, wherein the outer peripheral surface of the core tube is uneven, a part of the resin forming the nipple fits into a recess in the unevenness, and the resin that has fit into the recess and the recess constitute the restricting portion.

6. A plastic pipe and hose assembly as described in claim 4, wherein the outer peripheral surface of said core tube is formed with irregularities, a part of the resin forming said nipple fits into a concave part of said irregularities, and said resin fitting into said concave part and said concave part constitute said restricting part.

7. A method for manufacturing a plastic tube as defined in any one of claims 1 to 3, comprising the steps of: arranging the core tube in a nipple forming section which forms the nipple of a cavity for forming the plastic tube extending into a mold; injecting molten resin from one end of the cavity to the other end with the mold closed; injecting an assist material into the cavity and discharging excess molten resin from the cavity, thereby hardening the cylindrical molten resin remaining in the cavity to form the plastic tube; and fitting the core tube into the nipple while restricting axial and circumferential movement of the core tube relative to the nipple.

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