Method for producing resin tube

Abstract

Provided is a method for producing a resin tube, the method making it possible to improve the durability and sealability of a nipple to which a hose is externally fitted and crimped, and also acheive a weight reduction. One end part 17a of a cavity 17 and one end part-side discharge cavity 17d are blocked, and the cavity 17 is filled with a molten resin R1 injected from the one end part 17a, and then a communication path between the one end part 17a and an injection machine 11 is blocked, the one end part 17a and the one end part-side discharge cavity 17d are communicated, an assist material As is injected from another end part 17b, excess molten resin R1 is discharged from the cavity 17 to the one end part-side discharge cavity 17d, tubular-shaped molten resin R1 remaining in the cavity 17 is hardened to form a resin tube 1, and a fitting projection 4b to be fitted into a notch part 6a of a core tube 5 is formed on the nipple 4, and the axial- and circumferential-direction movement of the core tube 5 fitted into the nipple 4 is regulated.

Description

Resin pipe manufacturing method

[0001] The present invention relates to a method for manufacturing a resin pipe, and more specifically to a method for manufacturing a resin pipe that can reduce weight while suppressing deformation of a nipple onto which a hose is fitted and crimped, thereby improving durability and sealing performance.

[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] An object of the present invention is to provide a method for manufacturing a resin pipe that can suppress deformation of the nipple onto which the hose is fitted and crimped, thereby improving durability and sealing performance while also reducing weight.

[0006] In order to achieve the above object, the present invention provides a method for manufacturing a resin pipe, which includes a cylindrical nipple onto which a hose fitted thereon is crimped, and a metal core tube fitted into the nipple, the core tube and the nipple having restricting portions for restricting axial and circumferential movement of the core tube relative to the nipple, and the integrated nipple and core tube are disposed at a distal end in the longitudinal direction, the method comprising the steps of: a mold having a cavity for forming the resin pipe, the cavity having one end and the other end, extending between the one end and the other end; a nipple forming portion set at the other end; and a one-end side discharge cavity extending outside the cavity and capable of communicating with the one end; and and in a state where the communication between the one end and the one-end side discharge cavity is blocked and the mold is clamped, molten resin is injected from the one end toward the other end by an injector to fill the cavity with the molten resin, and then the communication path between the one end and the injector is blocked to connect the one end to the one-end side discharge cavity, and an assist material is injected from the other end toward the one end to discharge excess molten resin from the cavity into the one-end side discharge cavity, thereby hardening the cylindrical molten resin remaining in the cavity to form the resin tube with the hardened resin, and the restricting portion of the nipple is formed to restrict axial and circumferential movement of the core tube relative to the nipple, thereby fitting the core tube into the nipple.

[0007] According to the present invention, it is possible to manufacture a resin pipe in which a metal core tube is fitted and integrated into the nipple. The core tube is fitted into a predetermined longitudinal range of the nipple, including the entire length of the crimping range where the hose is crimped, improving the rigidity of this crimping range. 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 into the predetermined longitudinal range of the resin nipple, the weight of the resin pipe can be reduced compared to when the entire nipple is made of metal.

[0008] FIG. 1 is an explanatory diagram illustrating a resin pipe manufactured according to the present invention 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 a resin pipe manufacturing apparatus. FIG. 12 is an explanatory diagram illustrating a portion of one of the molds of FIG. 11, together with the core tube and support pipe, as viewed from the front. FIG. 13 is an explanatory diagram illustrating the state in which the core tube is placed in the nipple molding section of FIG. 12. Fig. 14 is an explanatory diagram illustrating the interior of the cavity filled with injected molten resin after the mold of Fig. 13 has been clamped. Fig. 15 is an explanatory diagram illustrating the state in which an assist material has been injected into the cavity of Fig. 14. Fig. 16 is an explanatory diagram illustrating the state in which the molten resin remaining in the cavity of Fig. 15 has hardened. Fig. 17 is an explanatory diagram illustrating the state in which the support pipe has been removed after the mold of Fig. 16 has been opened.

[0009] Hereinafter, a method for manufacturing a resin pipe according to the present invention will be described based on an embodiment shown in the drawings.

[0010] The resin pipe 1 shown in Figures 1 to 4 is manufactured according to the present invention. This resin pipe 1 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 cylindrical body having a pipe wall 2 formed from a cured resin R2, and a pipe line 3 extending in the longitudinal direction.

[0011] The pipe wall 2 of this resin pipe 1 has a two-layer structure in which a cylindrical inner pipe portion 2N and a cylindrical outer pipe portion 2T are stacked coaxially. The inner pipe portion 2N and the outer pipe portion 2T are formed from cured resins R2 of different specifications. Cured resins R2 of different specifications refer to different types of resin or different materials mixed into the resin. The dashed-dotted line CL in the figure indicates the axis passing through the center of the cross section of the pipe passage 3 of the resin pipe 1 and the core pipe 5. The extending direction of this axis CL is the axial direction (longitudinal direction) of the resin pipe 1 and the core pipe 5.

[0012] 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 peripheral surfaces of the resin pipe 1 and the core tube 5 are smoothly connected in the axial direction to form the pipe line 3. The thickness of the pipe wall 2 of the resin pipe 1 is, for example, 1 mm to 3 mm. The thickness of the outer pipe portion 2T is smaller than the thickness of the inner pipe portion 2N, for example, 0.5 mm to 2.0 mm.

[0013] This plastic pipe 1 is used as piping for various devices, for example, as piping for an air conditioner mounted on a vehicle such as an automobile. The plastic pipe 1 may be a straight pipe or a bent pipe depending on the application (place of use). As will be described in detail later, a hose 7 fitted onto the nipple 4 is crimped to connect and fix it, as shown in Figures 9 and 10.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The resin pipe 1 can be formed solely from thermoplastic resin, or it can be configured to contain various types of fibers (e.g., glass fibers or carbon fibers, either short or long) mixed as reinforcing fibers f in a predetermined proportion (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, 0.001 mm to 1.0 mm in outer diameter and 0.01 mm to 10 mm in length. In this embodiment, the inner pipe portion 2N and the outer pipe portion 2T are formed from the same cured resin R2. However, the cured resin R2 forming the outer pipe portion 2T contains reinforcing fibers f, while the cured resin R2 forming the inner pipe portion 2N does not contain reinforcing fibers f.

[0018] 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.

[0019] The core tube 5 has a notch 6a at its tip. In this resin tube 1, 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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. When multiple linear groove recesses 6b are formed, they should be arranged at equal intervals in the circumferential direction.

[0025] 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.

[0026] 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 can be 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 fills the recesses 6b. Therefore, the recesses 6b and the resin filling the recesses 6b function as the aforementioned restricting portion.

[0027] 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.

[0028] 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.

[0029] In this plastic pipe 1, the tip position of the core tube 5 coincides with the tip position of the plastic pipe 1, and the rear end position of the core tube 5 is located approximately 5 mm behind the rear end position of the crimping range CA. The tip position of the core tube 5 can be set slightly back from the tip position of the plastic pipe 1, but by making the tip positions of both pipes coincident, it becomes easier to manufacture the plastic pipe 1. The rear end position of the core tube 5 can also be made substantially coincident with the rear end position of the crimping range CA to reduce weight.

[0030] The notch 6a is located outside the crimping area CA. In this plastic pipe 1, 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 area CA. The rear end of the notch 6a can also be made to substantially coincide with the leading end of the crimping area CA to reduce weight.

[0031] 9 and 10 show 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.

[0032] 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.

[0033] To manufacture the assembly 9, 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.

[0034] 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.

[0035] 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.

[0036] In the above-described resin tube 1, 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.

[0037] Furthermore, because the pipe wall 2 of this resin pipe 1 has a two-layer structure consisting of an inner pipe portion 2N and an outer pipe portion 2T, the inner pipe portion 2N can be made to specifications that are more suitable for the fluid flowing through the pipe line 3, while the outer pipe portion 2T can be made to specifications that further improve weather resistance, impact resistance, etc. In this embodiment, impact resistance is improved by mixing reinforcing fibers f only into the outer pipe portion 2T. Also, because reinforcing fibers f are not mixed into the inner pipe portion 2N, it is possible to prevent the reinforcing fibers f from falling off for some reason and becoming mixed into the fluid flowing through the pipe line 3.

[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. 11. 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 indirectly connected to one end 17a of the cavity 17, and the injection port 15a may be indirectly connected to the other end 17b of the cavity 17.

[0046] Furthermore, the mold 16 is formed with a one-end discharge cavity 17d that extends outside the cavity 17 and can communicate with one end 17a of the cavity 17, and an other-end discharge cavity 17e that extends outside the cavity 17 and communicates with the other end 17b of the cavity 17. A switching unit 17c is provided in the communication path (injection path 18a) between the one end 17a and the injector 11. The one-end discharge cavity 17d is connected to this switching unit 17c. By operating the switching unit 17c, it is possible to switch between a mode in which one end 17a is connected to the injection path 18a and the communication between one end 17a and the one end side discharge cavity 17d is blocked, and a mode in which the communication between one end 17a and the injection path 18a is blocked and the one end 17a is connected to the one end side discharge cavity 17d.

[0047] 12, a nipple forming portion 19 is provided at the other end 17b of the cavity 17. 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.

[0048] 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 fitted onto the cylinder with virtually no gap. A flow path that is continuous with the injection channel 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 channel 18b. The pipe fixing portion 19a is formed as a recess shaped to fit the base 20b.

[0049] As shown in Figure 13, 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.

[0050] Next, the molds 16A and 16B are assembled and closed, and then, as illustrated in Fig. 14, molten resin R1 is injected by the injector 11 into the cavity 17 of the closed mold 16. In this embodiment, the molten resin R1 mixed with the reinforcing fibers f (the outer pipe molten resin R1 forming the outer pipe portion 2T) and the molten resin R1 not mixed with the reinforcing fibers f (the inner pipe molten resin R1 forming the inner pipe portion 2N) are injected from the injector 11. Each of the injected molten resins R1 is injected into the cavity 17 from the injection port 12a via the injection path 18a.

[0051] Specifically, by operating the switching element 17c, the first end 17a is connected to the injection path 18a, while the first end 17a is disconnected from the first end discharge cavity 17d. In this state, the outer-tube molten resin R1 is injected from the first end 17a toward the second end 17b to fill the cavity 17 in a cylindrical shape, and the inner-tube molten resin R1 is injected from the first end 17a toward the second end 17b to fill the inner periphery of the cylindrical outer-tube molten resin in a cylindrical shape. In the nipple molding portion 19, the outer-tube molten resin R1 and the inner-tube molten resin R1 are stacked and filled in the cylindrical gap between the inner periphery of the nipple molding portion 19 and the outer periphery of the core tube 5. The inner-tube molten resin R1 penetrates into the notch 6a and recess 6b to fill the gap. Excess molten resin R1 is discharged into the second end discharge cavity 17e. 14 to 17, the reinforcing fibers f mixed in the outer tube molten resin R1 are omitted.

[0052] Next, as illustrated in FIG. 15 , assist material (gas) As is injected into the mold 16 by the assist material injector 14. Specifically, the switching unit 17c is operated to block communication between the one end 17a and the injection path 18a, while connecting the one end 17a to the one-end discharge cavity 17d. In this state, assist material As is injected at a predetermined pressure from the opening 20a toward the other end 17b of the cavity 17, which is filled with the molten resin R1, toward the one end 17a. In this manner, 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.

[0053] As the assist material As passes through the cavity 17, excess molten resin R1 (mainly inner pipe molten resin R1) is discharged from one end 17a of the cavity 17 into the one-end discharge cavity 17d, and the inner pipe molten resin R1 remains in a cylindrical shape in the cavity 17. The outer pipe molten resin R1 remains in its cylindrical shape in the cavity 17. In the nipple molding portion 19, the outer pipe molten resin R1 and the inner pipe molten resin R1 that filled the gap (cylindrical gap) between the inner circumferential surface of the nipple molding portion 19 and the outer circumferential surface of the core tube 5 remain in a stacked state. The inner pipe molten resin R1 that filled the cutout portion 6a and recessed portion 6b also remains.

[0054] As shown in Figure 16, the remaining molten resin R1 inside the cavity 17 hardens to become hardened resin R2, thereby forming the resin pipe 1. That is, the inner pipe molten resin R1 hardens to form the inner pipe section 2N, and the outer pipe molten resin R1 hardens to form the outer pipe section 2T, which becomes the pipe wall 2, and the hollow section becomes the pipe line 3. The molten resin R1 filled in the gap (cylindrical gap) between the inner surface of the nipple forming section 19 and the outer surface of the core tube 5 becomes hardened resin R2, forming the nipple 4 and the mating recess 4a. The molten resin R1 filled in the cutout section 6a becomes hardened resin R2, forming the mating protrusion 4b, and the molten resin R1 filled in the recess 6b becomes hardened resin R2, forming the annular micro-protrusion. At this stage, the waste portions of the hardened resin R2 (the resin discharged into the one end side discharge cavity 17d and the other end side discharge cavity 17e) extend and are integrated at both ends of the resin pipe 1.

[0055] 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.

[0056] In this embodiment, excess molten resin R1 is discharged into one end discharge cavity 17d and the other end discharge cavity 17e, which are connected to the cavity 17. This allows the molten resin R1 (inner pipe molten resin R1 and outer pipe molten resin R1) to be stably layered without shortage at one end 17a and the other end 17b of the cavity 17, which is advantageous for manufacturing a resin pipe 1 in which the wall thicknesses of the inner pipe portion 2N and the outer pipe portion 2T are within a standard range.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] In the above-described embodiment, the pipe wall 2 has been described as having a two-layer structure consisting of an inner pipe portion 2N and an outer pipe portion 2T. However, the present invention can also be applied to the manufacture of a resin pipe 1 having a single-layer pipe wall 2. When manufacturing such a resin pipe 1, the above-described procedure can be applied assuming that the inner pipe portion 2N and the outer pipe portion 2T are made of the same resin. Note that when the pipe wall 2 has a single-layer structure, the other-end discharge cavity 17e can be omitted.

[0063] REFERENCE SIGNS LIST 1 Resin pipe 2 Pipe wall 2N Inner pipe portion 2T Outer pipe portion 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 injector 15 Storage portion 15a Injection port 16 (16A, 16B) Mold 17 Cavity 17a One end portion 17b Other end portion 17c Switching portion 17d One end side discharge cavity 17e Discharge cavity on other end side 18a Injection path 18b Injection path 19 Nipple molding portion 19a Pipe fixing portion 20 Support pipe 20a Opening 20b Base portion PL Parting line R1 Molten resin R2 Hardened resin As Assist material f Reinforcing fiber

Claims

1. A method for manufacturing a plastic pipe having a cylindrical nipple onto which a fitted hose is crimped, and a metal core tube fitted into the nipple and disposed within 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, the core tube and the nipple having a regulating portion that regulates axial and circumferential movement of the core tube relative to the nipple, and the integrated nipple and core tube are disposed at a longitudinal tip end, wherein a mold is provided with a cavity having one end and the other end and extending between the one end and the other end to form the plastic pipe, a nipple forming portion set at the other end, and a one-end side discharge cavity that extends outside the cavity and is capable of communicating with the one end, a regulating portion of the nipple that regulates axial and circumferential movement of the core tube relative to the nipple, and the core tube is fitted into the nipple. A method for manufacturing a resin tube, comprising the steps of: placing the core tube in the nipple molding portion; blocking communication between the one end and the one end cavity and clamping the mold; injecting molten resin from the one end toward the other end with an injector to fill the cavity with the molten resin; blocking the communication path between the one end and the injector to establish communication between the one end and the one end cavity; injecting an assist material from the other end toward the one end to discharge excess molten resin from the cavity into the one end cavity, thereby hardening the cylindrical molten resin remaining in the cavity, and forming the resin tube with the hardened resin; and forming the regulating portion of the nipple to regulate axial and circumferential movement of the core tube relative to the nipple, the method comprising the steps of:

2. A method for manufacturing a resin tube 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, and the regulating portion is formed by filling a portion of the molten resin into the notch and hardening the resin together with the notch.

3. A method for manufacturing a resin tube as described in claim 1 or 2, in which unevenness is formed on the outer peripheral surface of the core tube, and a portion of the molten resin is caused to enter into a recess in the unevenness, and the regulating portion is formed by the hardened resin that has entered the recess and hardened and the recess.

4. A method for manufacturing a resin tube as set forth in any one of claims 1 to 3, wherein the resin tube has a two-layer structure in which an inner tube portion and an outer tube portion formed of cured resins of different specifications are laminated coaxially, the mold is provided with an other-end discharge cavity extending outside the cavity and communicating with the other end, the molten resin is an outer tube molten resin forming the outer tube portion and an inner tube molten resin forming the inner tube portion, the outer tube molten resin is injected into the cavity as the molten resin, the outer tube molten resin is filled in a cylindrical shape in the cavity, and the inner tube molten resin is filled in a cylindrical shape on the inner periphery of the cylindrical outer tube molten resin, and excess molten resin is discharged into the other-end discharge cavity, and the resin tube is formed by hardening the cylindrical molten resin remaining in the cavity by injecting an assist material from the other end toward the one end and discharging the excess molten resin from the cavity into the one-end discharge cavity.

5. The method for manufacturing a resin pipe according to claim 4, wherein only the outer tube molten resin contains short reinforcing fibers among the molten resins.

6. The method for manufacturing a resin pipe according to any one of claims 1 to 5, wherein a gas is used as the assist material.

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