Resin pipe manufacturing method

Abstract

To improve sealing performance with use of an O-ring by preventing short shots from occurring at a flange part when molding a resin pipe by sending gas with pressure into a molten resin.SOLUTION: A mold 11 has: an annular O-ring groove molding part 41a for molding an O-ring groove on a flange part 3; and a thin-wall part molding part 41b for forming an annular thin wall part between the O-ring groove on the flange part 3 and a pipe body part 2. Inflow of a molten resin fluidized by a gas, to a portion corresponding to the flange part 3 is restricted by the thin-wall part molding part 41b.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a resin pipe by using a molten resin material. [Background technology]

[0002] Resin pipes have been widely used as various piping components in automobiles, for example, and come in straight shapes, complexly curved shapes, etc. When connecting this type of resin pipe to another piping component, a structure is widely used in which a flange is provided at the end of the resin pipe and this flange is fixed to the flange of the piping component.

[0003] As a method for manufacturing the above-mentioned resin pipe, for example, a method is known in which molten resin is poured into a portion of the mold corresponding to one end of the resin pipe while pressure-feeding gas, and the molten resin is molded while flowing toward a portion of the mold corresponding to the other end of the resin pipe, as disclosed in Patent Documents 1 and 2. This manufacturing method also makes it possible to integrally mold the flange portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-187131 [Patent Document 2] Patent Publication No. 2021-53954 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, since an O-ring must be disposed in the flange portion as a sealing material, an O-ring groove for fitting the O-ring is formed in the molding die. However, in the manufacturing methods of causing molten resin to flow by pressurizing gas as in Patent Documents 1 and 2, the gas also flows into the portion of the molding die corresponding to the flange portion, which can cause a so-called short shot, in which the resin solidifies without filling the portion that should have been filled.

[0006] If a short shot occurs in the flange, unintended irregularities may occur on the inner surface of the O-ring groove, or a cavity leading to the O-ring groove may form in the flange, and these molding defects will lead to a deterioration of sealing performance.

[0007] The present disclosure has been made in consideration of these points, and its purpose is to prevent short shots from occurring in the flange portion and improve the sealing performance of the O-ring when a resin pipe is formed by pressurizing gas into molten resin. [Means for solving the problem]

[0008] To achieve the above object, a first aspect of the present disclosure can be premised on a method for manufacturing a resin pipe having a flange portion with an O-ring groove molded at one end of the pipe main body. The method includes a first step of filling a portion of a cavity of a molding die used to mold the resin pipe with molten resin, and causing the molten resin to flow into a portion of the cavity of the molding die that corresponds to the flange portion and that communicates with the portion corresponding to the flange portion, a second step of causing the molten resin to flow toward the portion corresponding to the flange portion while simultaneously pumping a gas into the cavity of the molding die, and a third step of causing the molten resin that flowed from the portion corresponding to the flange portion to the portion corresponding to the pipe main body in the first step and the molten resin that was caused to flow by the gas in the second step to merge in the molding die cavity, and molding the portion of the molten resin corresponding to the pipe main body into a hollow shape while flowing the gas toward the portion corresponding to the one end of the pipe main body, and solidifying the molten resin to integrally mold the flange portion with the pipe main body. The molding die has an annular O-ring groove molding portion for molding the O-ring groove in the flange portion, and a thin-walled portion molding portion for molding an annular thin-walled portion between the O-ring groove in the flange portion and the pipe main body. In the third step, the thin-walled portion molding portion can restrict the molten resin caused to flow by the gas in the second step from flowing into the portion corresponding to the flange portion.

[0009] According to this configuration, the molten resin filled in the portion corresponding to the flange portion in the first step merges with the molten resin flowed by the gas from the portion corresponding to the other end of the pipe main body, and the flange portion is integrally molded into the pipe main body. Before the molten resin solidifies, the gas pumped in the second step flows toward the portion corresponding to one end of the pipe main body, and since the flange portion is formed at this end of the pipe main body, the gas attempts to flow toward the portion of the cavity corresponding to the flange portion. At this time, the thin-wall portion molding portion of the molding die is positioned to protrude toward the portion corresponding to the flange portion, since it is the portion that molds the thin-wall portion. This restricts the flow of gas into the portion corresponding to the flange portion, preventing short shots from occurring in the flange portion.

[0010] In a second aspect of the present disclosure, an annular groove is formed between the O-ring groove in the flange and the pipe body, and the thin-walled portion can be obtained by the annular groove. In this case, a rib connected to the pipe body can be formed inside the annular groove. With this configuration, the rib can compensate for the loss of strength caused by the formation of the thin-walled portion.

[0011] In a third aspect of the present disclosure, the annular groove may be formed deeper than the O-ring groove. With this configuration, the thickness of the thin-walled portion of the flange is thinner than the portion of the flange where the O-ring groove is formed. This makes it even more difficult for gas to flow into the portion corresponding to the flange, further suppressing the occurrence of short shots.

[0012] In a fourth aspect of the present disclosure, the O-ring groove molding portion and the thin-walled portion molding portion can be provided in a common slide mold. In this case, the slide mold is advanced in the first step and held there until the third step, and then retracted after the third step, thereby molding the O-ring groove and the thin-walled portion in the same step. [Effects of the Invention]

[0013] As explained above, the thin-walled molding portion can prevent the molten resin, which has been fluidized by gas, from flowing into the portion corresponding to the flange portion. Therefore, when gas is pumped into the molten resin to form a resin pipe, short shots can be prevented from occurring in the flange portion, and the sealing performance of the O-ring can be improved. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a side view of a resin pipe manufactured by a method for manufacturing a resin pipe according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of the resin pipe as seen from the flange portion side. [Figure 3] FIG. 10 is a view corresponding to FIG. 2 according to a modified example. [Figure 4] 1 is a cross-sectional view of a molding die used in a method for manufacturing a resin pipe according to an embodiment of the present invention. [Figure 5] 5 is a view equivalent to FIG. 4 showing a state in which molten resin has flowed into the cavity. FIG. [Figure 6] 5 is a view equivalent to FIG. 4, illustrating a state in which gas is pumped to cause the molten resin to flow. [Figure 7] 4 and shows the state after molding of the pipe body and flange portions is completed. FIG. [Figure 8] FIG. 2 is a perspective view of a resin pipe seen from the flange portion side immediately after molding and before unnecessary resin portions are removed. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

[0016] (Configuration of resin pipe 1) Before describing the method for manufacturing a resin pipe, the configuration of the resin pipe manufactured by this manufacturing method will be described. Fig. 1 shows a resin pipe 1 manufactured by the method for manufacturing a resin pipe according to an embodiment of the present invention. The resin pipe 1 has a pipe body 2 and a flange 3 integrally molded with the pipe body 2. The flange 3 is a portion for connecting to other piping members, devices, etc., and is fastened in a state where it overlaps with a flange (not shown) of the other piping member, device, etc.

[0017] The resin pipe 1 can be used, for example, as a piping component for an automobile's intake system or blow-by gas introduction system, or as a piping component for hot water, cooling water, etc. The resin pipe 1 can also be used as a piping component for homes and factory facilities, in addition to automobiles. The flow direction of the fluid flowing through the resin pipe 1 is not particularly limited, and the fluid may flow from top to bottom in FIG. 1, or from bottom to top. The resin material constituting the resin pipe 1 is not particularly limited, and may be a resin material mixed with reinforcing glass fibers.

[0018] One end of the pipe body 2 is defined as the lower end in Fig. 1, and the other end of the pipe body 2 is defined as the upper end in Fig. 1, but this definition is for convenience of explanation only and does not limit the posture of the resin pipe 1 during use or the direction during manufacturing. Since the flange portion 3 is provided at the lower end in Fig. 1, the resin pipe 1 has a structure having the flange portion 3 at one end of the pipe body 2. Although not shown, the flange portion may also be provided at the other end of the pipe body 2.

[0019] The flange portion 3 is a plate-like portion extending in a direction intersecting the axis of one end of the pipe body 2 (the axis extending vertically in FIG. 1 ), and is molded simultaneously with the molding of the pipe body 2, as described below. Therefore, providing the flange portion 3 does not increase the number of parts of the resin pipe 1, which reduces the number of assembly steps into, for example, an automobile, and also ensures high airtightness and liquidtightness because there is no seam between the flange portion 3 and one end of the pipe body 2. The extension direction of the flange portion 3 and the axis of one end of the pipe body 2 are generally perpendicular to each other, but they do not have to be generally perpendicular to each other.

[0020] Fig. 2 is a perspective view of the flange portion 3 side of the resin pipe 1 of Fig. 1, viewed from below. As shown in Fig. 2, one end of the pipe main body 2 faces the center of the connection surface 30 of the flange portion 3, which is used for connecting with other piping components, and an opening 2a is formed where the one end of the pipe main body 2 opens. An annular O-ring groove 31 is molded in the connection surface 30 of the flange portion 3, surrounding the opening 2a of the pipe main body 2. An O-ring (not shown) made of rubber, elastomer, or the like is fitted into this O-ring groove 31. The O-ring fitted into the O-ring groove 31 abuts against the flange portion of the other piping component, etc., to provide a tight seal.

[0021] The flange portion 3 has spaced-apart insertion holes 32, 32 through which fastening members (not shown) are inserted to fasten the flange portion 3 to a flange portion of another piping member or the like. The insertion holes 32, 32 are located outside the O-ring groove 31 of the flange portion 3 and penetrate the flange portion 3 in its thickness direction. Metal bushings, collars, or the like are inserted into the insertion holes 32, 32. The fastening members are, for example, bolts or screws. The flange portion 3 can be fastened to a flange portion of another piping member or the like by inserting the fastening members into the bushings or collars of the insertion holes 32, 32 and threading them onto nuts, or the like (not shown), of the flange portion of the other piping member or the like. The flange portion 3 can also be connected to members other than other piping members (such as various containers or pumps). In this case, an O-ring fitted in the O-ring groove 31 abuts against a member other than the other piping member, and the flange portion 3 is fastened to a member other than the other piping member.

[0022] An annular thin-walled portion 33 is formed in the flange portion 3 between the O-ring groove 31 and one end of the pipe body 2. That is, an annular groove 34 is formed in the flange portion 3 between the O-ring groove 31 and one end of the pipe body 2, and this annular groove 34 provides the thin-walled portion 33. The annular groove 34 is formed deeper than the O-ring groove 31. For example, the depth of the O-ring groove 31 can be at least half the thickness of the flange portion 3, and in this case, the depth of the annular groove 34 can be at least two-thirds or three-quarters the thickness of the flange portion 3. Specifically, when the thickness of the flange portion 3 is 10 mm, the depth of the O-ring groove 31 can be set in the range of 2.0 mm to 5.0 mm, and the depth of the annular groove 34 can be set in the range of 6.0 mm to 8.5 mm. The deeper the annular groove 34, the thinner the thickness of the thin-walled portion 33, and the thickness of the thin-walled portion 33 can be set to, for example, 2.5 mm or less or 2.0 mm or less. The effect of forming the thin-walled portion 33 will be described later.

[0023] FIG. 3 shows a resin pipe 1 according to a modified example. In this modified example, a rib 35 is molded inside the annular groove 34, continuing onto the outer peripheral surface of one end of the pipe body 2. That is, if a thin-walled portion 33 is formed in the flange portion 3 due to the annular groove 34, the strength of the flange portion 3 will be reduced, and depending on the usage conditions, the flange portion 3 may not satisfy the standards. In such a case, molding the rib 35 can compensate for the reduction in strength due to molding the annular groove 34. The number of ribs 35 is not particularly limited, and may be one or more. When multiple ribs 35 are molded, they are preferably arranged at equal intervals around the circumference of the annular groove 34.

[0024] As shown in FIG. 1, a curved section 2c and a straight section 2b are provided between one end and the other end of the pipe body 2. The curved section 2c is provided in a portion of the pipe body 2 closer to the other end, but may also be provided in a portion closer to the one end or in the middle. The straight section 2b is provided in a portion of the pipe body 2 closer to the one end, but may also be provided in a portion closer to the other end or in the middle. Either or both of the curved section 2c and the straight section 2b may be omitted. The shape and diameter of the pipe body 2 can be set as desired.

[0025] That is, the shape of the pipe body 2 is not limited to the above-mentioned shape, but may be a straight pipe, or may consist of multiple curved sections and straight pipe sections. The length of the straight pipe section and the radius of curvature of the curved sections can also be freely set. Furthermore, the cross-sectional shape of the pipe body 2 can be, for example, circular or elliptical, and can be freely shaped.

[0026] Although not shown, a branch pipe section may be provided in the middle of the pipe body 2. The branch pipe section may also be molded integrally with the pipe body 2.

[0027] (Configuration of molding device 10) Next, a molding apparatus 10 used in a manufacturing method of a resin pipe 1 according to an embodiment will be described with reference to FIG. 4. The molding apparatus 10 includes an injection machine (not shown) that injects molten resin at a predetermined pressure, a molding die 11, a gas supply machine (not shown) that supplies gas at a predetermined pressure during molding, and a control device (not shown). The injection machine mixes and heats the resin to melt it and includes an injection cylinder that injects a constant amount at a predetermined speed. The gas supply machine is a device that pumps and delivers high-pressure gas (e.g., air) that can flow through the molten resin. The injection machine and the gas supply machine are connected to a control device. The injection machine is controlled by the control device, which controls the start and end of injection of the molten resin, the flow rate during injection, etc. The gas supply machine is also controlled by the control device, which controls the start and end of gas pressure delivery, the flow rate during pressure delivery, etc.

[0028] The molding die 11 includes, for example, a fixed die and a movable die, and a die drive device that drives the movable die in a direction toward and away from the fixed die. The die drive device is connected to the control device and operates at a predetermined timing to open and close the molding die 11. By driving the movable die with the die drive device, the molding die 11 can be switched between a clamped state and an open state. To prevent gas or molten resin from leaking from the joint between the fixed die and the movable die, there is almost no gap between the fixed die and the movable die when the die is clamped.

[0029] Inside the mold 11 are provided a molding surface 12 for molding the outer surface of the resin pipe 1, and a first gate 21 and a second gate 22 into which molten resin flows from the nozzle of the molding machine through a spool and runner. For example, by providing a hot runner inside the mold 11 and using valve gates as the first and second gates 21 and 22, it becomes possible to precisely control the injection amount of molten resin and reduce the amount of runner waste.

[0030] A cavity R for molding the resin pipe 1 is defined inside the molding die 11 by a molding surface 12. The cavity R has a first space R1 for molding the pipe body 2 and a second space R2 for molding the flange portion 3. The first space R1 is the portion of the cavity R that corresponds to the pipe body 2, and the second space R2 is the portion of the cavity R that corresponds to the flange portion 3, and the first space R1 and the second space R2 are mutually connected. The volume of the second space R2 is smaller than the volume of the first space R1. Furthermore, the molding die 11 is provided with a slide die 41 and a drive device 42 that drives the slide die 41.

[0031] The surface of the slide die 41 facing the second space R2 is a surface for molding the flange portion 3. That is, the surface of the slide die 41 facing the second space R2 is configured to form the connecting surface 30, O-ring groove 31, insertion hole 32, and annular groove 34 of the flange portion 3, and the thin-walled portion 33 is obtained by forming the annular groove 34. More specifically, the surface of the slide die 41 facing the second space R2 has an annular O-ring groove molding portion 41a for molding the O-ring groove 31, a thin-walled portion molding portion 41b for molding the annular thin-walled portion 33 between the O-ring groove 31 in the flange portion 3 and the pipe main body 2, and insertion hole molding portions 41c, 41c for molding the two insertion holes 32. The O-ring groove molding portion 41a is configured as a ridge portion that protrudes toward the second space R2 and extends continuously in the circumferential direction. The thin-walled portion molding portion 41b also protrudes toward the second space R2 and is composed of a ridge portion that extends continuously in the circumferential direction, but the amount of protrusion of the thin-walled portion molding portion 41b is greater than the amount of protrusion of the O-ring groove molding portion 41a, thereby obtaining the thin-walled portion 33. The insertion hole molding portions 41c, 41c are pin-shaped and protrude toward the second space R2.

[0032] The drive unit 42 is connected to the control device and controlled by the control device to switch the slide mold 41 from the advanced state shown in Fig. 4 etc. to a retracted state (not shown) at a predetermined timing, and also switch from the retracted state to the advanced state. The advancing and retracting direction of the slide mold 41 coincides with the thickness direction of the flange portion 3, i.e., the depth direction of the O-ring groove 31 and the annular groove 34 and the penetration direction of the insertion holes 32, 32.

[0033] A cavity 41d is formed inside the slide mold 41, and communicates with a portion of the first space R1 that corresponds to one end of the pipe main body 2. The cavity 41d extends along the extension direction of the pipe axis of the one end of the pipe main body 2.

[0034] Further, the forming die 11 is provided with a gas supply pipe 40 for supplying the above-mentioned gas to the cavity R. The downstream end of the gas supply pipe 40 is connected to a portion of the first space R1 corresponding to the other end of the pipe main body 2. The upstream end of the gas supply pipe 40 is connected to the above-mentioned gas supplier.

[0035] (Manufacturing method of resin pipe 1) Next, a manufacturing method for manufacturing a resin pipe 1 using the molding apparatus 10 of the embodiment will be described. First, the molding die 11 is closed, and the slide die 41 is advanced by the drive device 42 as shown in FIG. 4. The advanced state of the slide die 41 is maintained until the third step, which will be described later. The timing at which the molding die 11 is closed and the timing at which the slide die 41 is advanced may be the same or different.

[0036] Thereafter, the molten resin is injected from the injection cylinder of the injection machine. The injected molten resin flows from the nozzle of the molding machine through a spool and a runner, and reaches the first gate 21 and the second gate 22.

[0037] As shown in Figure 5, the molten resin A that reaches the second gate 22 is filled into the second space R2, which is the portion corresponding to the flange portion 3. The molten resin filled into the second space R2 also flows into the portion of the first space R1 that corresponds to one end of the pipe main body 2. In other words, the amount of molten resin flowing out from the second gate 22 is set to be greater than the volume of the second space R2. This is the first step. Before proceeding to the second step, the outflow of molten resin from the second gate 22 is stopped.

[0038] Meanwhile, the molten resin B that has reached the first gate 21 flows into the portion of the first space R1 that corresponds to the other end of the pipe main body 2. Also, as shown in FIG. 6, gas is pumped from the gas supply pipe 40 to the portion of the first space R1 that corresponds to the other end of the pipe main body 2. The pumped gas causes the molten resin to flow toward the second space R2. This is the second step. In the second step, after the injection of the molten resin from the first gate 21 is stopped, gas is supplied from the gas supplier to the gas supply pipe 40.

[0039] In the first step, molten resin A flows from the second space R2 into the first space R1, and in the second step, molten resin B flows toward the second space R2 using gas, and these two flows meet in the cavity R of the mold 11. As shown in FIG. 7, the portion of the molten resin filling the first space R1 that is in contact with the molding surface 12 has begun to solidify, so the gas flows, forming a hollow portion near the radial center. In this way, while the gas is flowing toward the portion of the first space R1 that corresponds to one end of the pipe main body 2, the molten resin in the portion corresponding to the pipe main body 2 is molded into a hollow shape, and the molten resin is solidified to integrally form the flange portion 3 with the pipe main body 2. This is the third step.

[0040] In the third step, the slide mold 41 is in an advanced state, so the thin-walled portion molding portion 41b protrudes toward the second space R2 on the side closer to the first space R1 than the O-ring groove molding portion 41a. Because the thin-walled portion molding portion 41b protrudes toward the second space R2, the distance between the tip of the thin-walled portion molding portion 41b and the molding surface 12 is shortened. In short, the vicinity of the entrance from the first space R1 to the second space R2 is narrowed by the thin-walled portion molding portion 41b.

[0041] Therefore, the thin-walled portion forming portion 41b can restrict the molten resin, which has been fluidized by the gas in the second step, from flowing into the second space R2. In other words, when the molten resin is filled into the second space R2, the thin-walled portion forming portion 41b can prevent the resin from flowing into the first space R1, thereby preventing short shots in the flange portion 3 (in the second space R2).

[0042] The timing of flowing the molten resin through the first gate 21 and the timing of flowing the molten resin through the second gate 22 may be the same or different. The timing of flowing the molten resin through the first gate 21 and the second gate 22 may be set so that the molten resin flowing through the second gate 22 fills the second space R2 and a portion of it flows into the first space R1 before the molten resin flowing through the first gate 21 reaches the vicinity of the second space R2.

[0043] Furthermore, the internal pressure of the first space R1 and the second space R2, which has increased due to the pressurized gas supply, can be released through a gap formed between the outer surface of the slide die 41 and the molding die 11. The shape and size of this gap are set so that the molten resin does not leak out from it. Furthermore, a valve (not shown) for releasing the internal pressure of the first space R1 and the second space R2 may be provided in the slide die 41. It is also possible to provide both the gap and the valve. In either case, care must be taken to prevent the supplied gas from damaging the pipe main body 2 and the flange portion 3. This allows the pipe main body 2 with the flange portion 3 to be molded continuously from one end to the other.

[0044] After the third step, i.e., after the molten resin has solidified, the slide mold 41 is retracted. When the slide mold 41 is retracted, the O-ring groove 31 is formed in the space left by the O-ring groove molding portion 41a, the annular groove 34 (i.e., the thin-walled portion 33) is formed in the space left by the thin-walled portion molding portion 41b, and the insertion hole 32 is formed in the space left by the insertion hole molding portion 41c. The rib 35 shown in FIG. 3 can also be formed by the slide mold 41.

[0045] Furthermore, since the molten resin flows into the hollow portion 41d of the slide mold 41 and solidifies, when the slide mold 41 is retracted, the unwanted resin portion 101 is integrally molded into one end of the pipe main body 2. As shown in FIG. 8, the unwanted resin portion 101 is cylindrical, and its tip is blocked with resin material. After demolding, the unwanted resin portion 101 is cut off from one end of the pipe main body 2 along the cutting line shown by the dashed line in FIG. 8. Furthermore, as shown in FIG. 7, an unwanted resin portion 102 is also integrally molded at the other end of the pipe main body 2, and this unwanted resin portion 102 is also cut off after demolding. By going through the above steps, the resin pipe 1 is obtained.

[0046] The second step may be performed at the same time as the injection of molten resin in the first step, or after the completion of the injection of molten resin in the first step. Furthermore, the injection of molten resin in the second step may be started a predetermined time after the start of the injection of molten resin in the first step. The amount of molten resin injected in each step can be set arbitrarily depending on the shape and length of the pipe body 2. The same applies to the amount of molten resin injected in the second step. Gas supply may be performed after all injections of molten resin have stopped.

[0047] (Effects of the embodiment) As described above, in this embodiment, the molten resin filled in the second space R2 for forming the flange portion 3 flows into the first space R1 and merges with the molten resin flowing toward the second space R2 due to the gas. The molten resin in the first space R1 and the second space R2 solidifies, forming the flange portion 3 integrally with the pipe main body 2. Before the molten resin solidifies, the pressurized gas flows toward the portion corresponding to the flange portion 3. However, the thin-walled portion molding portion 41b of the slide mold 41 is positioned to protrude into the second space R2, preventing the gas from flowing toward the portion corresponding to the flange portion 3. This prevents short shots from occurring in the flange portion 3, allows the inner surface of the O-ring groove 31 to be molded as intended, and prevents the formation of cavities in the flange portion 3. This improves the sealing performance of the O-ring.

[0048] The above-described embodiments are merely examples in all respects and should not be construed as limiting. Furthermore, all modifications and variations within the scope of the claims are within the scope of the present invention. [Industrial Applicability]

[0049] As described above, the method for manufacturing a resin pipe according to the present invention can be used, for example, when manufacturing piping components for automobiles. [Explanation of symbols]

[0050] 1. Resin pipe 2 Pipe body 3 Flange 11 Molding mold 31 O-ring groove 33 Thin-walled section 34 Annular groove 35 Ribs 41 Slide type 41a O-ring groove forming part 41b Thin wall molding part R cavity R1 First space (corresponding to the pipe body of the cavity) R2 Second space (corresponding to the flange of the cavity)

Claims

1. A method for manufacturing a resin pipe (1) having a flange (3) with an O-ring groove (31) formed at one end of a pipe body (2), comprising: a first step of filling a portion (R2) of a cavity (R) of a mold (11) for molding the resin pipe (1) corresponding to the flange portion (3) with molten resin and allowing the molten resin to flow into a portion (R1) corresponding to the pipe main body portion (2) that communicates with the portion (R2) corresponding to the flange portion (3); a second step of flowing molten resin into a portion (R1) of the cavity (R) of the mold (11) corresponding to the other end of the pipe body (2) while supplying gas under pressure, thereby causing the molten resin to flow toward a portion (R2) corresponding to the flange portion (3); and a third step of joining the molten resin flowed from the portion (R2) corresponding to the flange portion (3) into the portion (R1) corresponding to the pipe main body (2) in the first step with the molten resin flowed by the gas in the second step in the cavity (R) of the mold (11), and molding the molten resin in the portion (R1) corresponding to the pipe main body (2) into a hollow shape while flowing the gas toward the portion (R1) corresponding to one end of the pipe main body (2), and solidifying the molten resin to integrally mold the flange portion (3) with the pipe main body (2). The molding die (11) has an annular O-ring groove molding portion (41a) for molding the O-ring groove (31) in the flange portion (3), and a thin-walled portion molding portion (41b) for molding an annular thin-walled portion (33) between the O-ring groove (31) in the flange portion (3) and the pipe main body (2), and in the third step, the molten resin caused to flow by the gas in the second step is restricted by the thin-walled portion molding portion (41b) from flowing into the portion (R2) corresponding to the flange portion (3).

2. The method for manufacturing a resin pipe according to claim 1, A method for manufacturing a resin pipe, comprising: forming an annular groove (34) between the O-ring groove (31) in the flange portion (3) and the pipe body portion (2); obtaining the thin-walled portion (33) by the annular groove (34); and forming a rib (35) connected to the pipe body portion (2) inside the annular groove (34).

3. The method for manufacturing a resin pipe according to claim 2, The method for manufacturing a resin pipe is characterized in that the annular groove (34) is formed deeper than the O-ring groove (31).

4. In the method for manufacturing a resin pipe according to any one of claims 1 to 3, The O-ring groove forming portion (41a) and the thin-walled portion forming portion (41b) are provided in a common slide mold (41), In the first step, the slide mold (41) is advanced and held until the third step, A method for manufacturing a resin pipe, characterized in that after the third step, the slide mold (41) is retracted.

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