Inner ring and pipe joint

Abstract

An inner ring according to the present disclosure includes: a main body part that is inserted into a joint main body; a seal part that is integrally provided on the main body part on one side in an axial direction and is inserted into a seal groove formed in the joint main body; a bulging part which is integrally provided on the main body part on the other side in the axial direction and of which an outer peripheral face is formed protruding radially outward; and a tube part that is provided integrally on the other side in the axial direction of the bulging part and that is inserted into a pressing part of a union nut. An inner diameter of the tube part is the same as an inner diameter of the bulging part. An outer peripheral face of the bulging part has a first inclined peripheral face part which increases in diameter from the other side in the axial direction toward the one side in the axial direction, and to which the pressing part of the union nut abuts when a female thread of the union nut is tightened to a male thread of the joint main body.

Description

Inner Ring and Pipe Joint

[0001] The present disclosure relates to an inner ring and a pipe joint. This application claims priority based on Japanese Application No. 2025-068099 filed on April 17, 2025, the entire contents of which are incorporated herein by reference.

[0002] In manufacturing apparatuses in various technical fields such as semiconductor manufacturing, medical and pharmaceutical manufacturing, pipe joints are known as connection structures for connecting flow paths formed in respective fluid devices such as tubes (see, for example, Patent Document 1). Fig. 5 is a cross-sectional view showing a conventional pipe joint. A conventional pipe joint 90 includes an inner ring 91 mounted on the inner periphery of an end portion of a tube 98, a cylindrical joint body 92 mounted on the outer periphery of the end portion of the tube 98, and a union nut 93 mounted on the outer periphery of the joint body 92.

[0003] The inner ring 91 has a main body portion 91a, a bulging portion 91b formed to protrude radially outward at one axial end portion of the main body portion 91a, and a seal portion 91c formed at the other axial end portion of the main body portion 91a. The internal space of the inner ring 91 is defined as a flow path 91d through which a fluid flows. The bulging portion 91b of the inner ring 91 is press-fitted into the end portion of the tube 98 to expand the diameter of the end portion of the tube 98.

[0004] When the union nut 93 is attached to the joint body 92, the union nut 93 presses the outer peripheral surface of the tube 98 whose diameter has been expanded by the bulging portion 91b of the inner ring 91. As a result, the seal portion 91c of the inner ring 91 is press-fitted into the seal groove 92a formed in the joint body 92, so that the sealing performance between the joint body 92 and the inner ring 91 is ensured, and the tube 98 can be prevented from coming off from the inner ring 91. Furthermore, a surface pressure is generated between the inclined peripheral surface portion 91e on the distal end side of the outer peripheral surface of the bulging portion 91b and the inner peripheral surface 98a of the tube 98. This surface pressure seals the space between the inclined peripheral surface portion 91e of the bulging portion 91b and the inner peripheral surface 98a of the tube 98, so that leakage of the fluid flowing through the flow path 91d can be suppressed.

[0005] JP 2018-168947 A

[0006] In conventional pipe fittings 90, the bulge 91b of the inner ring 91 is press-fitted into the tube 98, creating a depression 95 between the tip of the bulge 91b and the inner circumferential surface of the tube 98. As a result, when fluid flows through the inner ring 91, the fluid tends to accumulate in the depression 95, reducing fluid displaceability. In particular, in semiconductor manufacturing equipment where a high degree of cleanliness is required, this reduction in displaceability is a factor that worsens the cleanliness, and countermeasures are desired.

[0007] This disclosure aims to improve the replaceability of the fluid flowing within the inner ring.

[0008] (1) The inner ring of the present disclosure is an inner ring in a pipe fitting comprising: a fitting body having male threads on its outer circumference; a union nut having female threads that are tightened onto the male threads and an annular pressing portion that protrudes radially inward from the female threads; and an inner ring provided on the fitting body through which fluid flows. The inner ring comprises: a body portion inserted into the fitting body; a seal portion integrally provided on one axial side of the body portion and inserted into a seal groove formed in the fitting body; a bulge portion integrally provided on the other axial side of the body portion and having an outer circumferential surface that protrudes radially outward; and a tube portion integrally provided on the other axial side of the bulge portion and inserted into the pressing portion of the union nut. The inner diameter of the tube portion is the same as the inner diameter of the bulge portion, the outer circumferential surface of the bulge portion expands in diameter from the other axial side to the one axial side, and has a first inclined circumferential surface portion that contacts the pressing portion of the union nut when the female threads of the union nut are tightened onto the male threads of the fitting body.

[0009] According to the inner ring of this disclosure, the tubular portion is integrally provided with the bulge portion, and since the inner diameter of the bulge portion and the inner diameter of the tubular portion are the same, the inner circumferential surface of the bulge portion and the inner circumferential surface of the tubular portion can be made flush. As a result, no recess is formed between the axial end of the bulge portion on the other side and the inner circumferential surface of the tubular portion, so that fluid flowing inside the inner ring does not stagnate. As a result, the fluid displaceability can be improved. In particular, in semiconductor manufacturing equipment where a high degree of cleanliness is required, the deterioration of cleanliness caused by a decrease in fluid displaceability can be effectively suppressed, making the inner ring with an integrated tubular portion of this disclosure even more effective.

[0010] Furthermore, when the female thread of the union nut is tightened onto the male thread of the joint body, the pressing portion of the union nut comes into contact with the first inclined circumferential surface of the outer surface of the bulge, allowing the tightening torque of the union nut to be gradually increased. Therefore, by tightening the union nut, the sealing portion of the inner ring can be easily inserted into the sealing groove of the joint body.

[0011] (2) In the inner ring of (1) above, the inner ring is preferably made of synthetic resin, and the outer peripheral surface of the bulging portion extends axially adjacent to one axial side of the first inclined peripheral surface portion, and further has an outermost peripheral surface portion which is the maximum outer diameter of the inner ring, and a gate mark is formed on the outermost peripheral surface portion.

[0012] In the conventional inner ring 91 shown in Figure 5, as described above, the space between the inclined circumferential surface 91e of the bulging portion 91b and the inner circumferential surface 98a of the tube 98 must be sealed by the surface pressure between these two surfaces 91e and 98a. Therefore, if a gate mark is formed on the outermost surface of the bulging portion 91b, the gate mark is likely to cause irregularities in a part of the circumferential direction of the outermost surface. When such irregularities occur, the surface pressure between the two surfaces 91e and 98a decreases, and there is a risk of fluid leakage. Consequently, in the conventional inner ring 91, a gate mark is inevitably formed on the outer circumferential surface of the main body portion 91a.

[0013] In contrast, in the inner ring of the present disclosure, since the tube is not press-fitted onto the outer circumferential surface of the bulge, the position of the gate mark formation is not limited as in the conventional method. The inventor of the present invention focused on this point and completed the invention described in (2) above. According to this invention, a gate mark is formed on the outermost circumferential surface of the bulge, which is the outer circumferential surface of the portion with the maximum radial thickness in the inner ring. In other words, when the inner ring is molded using a mold, the gate of the mold is positioned to mold the outermost circumferential surface, which is the portion with the maximum radial thickness in the inner ring. As a result, molten resin can be poured from the portion with the maximum radial thickness (outermost circumferential surface) of the inner ring toward the portions with thinner radial thickness (first inclined circumferential surface portion and main body portion, etc.), making it easy to fill the mold with molten resin.

[0014] (3) In the inner ring of (2) above, the outer peripheral surface of the bulging portion further has a second inclined circumferential surface portion adjacent to one axial side of the outermost circumferential surface portion, which decreases in diameter as it moves from the other axial side toward the one axial side, and preferably the axial length of the second inclined circumferential surface portion is set such that the entire axial length of the second inclined circumferential surface portion is inserted into the joint body when the female thread of the union nut is tightened onto the male thread of the joint body.

[0015] In this case, with the female thread of the union nut tightened onto the male thread of the joint body, the entire axial portion of the second inclined circumferential surface on the outer surface of the bulge is inserted into the joint body. This makes the second inclined circumferential surface shorter in the axial direction compared to the case where a portion of the second inclined circumferential surface is exposed on the other axial side of the joint body when tightened. As a result, the outermost circumferential surface can be made longer in the axial direction, which increases the degree of freedom in the position of the gate mark formation on the outermost circumferential surface of the bulge.

[0016] (4) The pipe fitting of the present disclosure comprises a fitting body having male threads on its outer circumference, a union nut having female threads that are tightened into the male threads and an annular pressing portion that protrudes radially inward from the female threads, and an inner ring as described in any of (1) to (3) above, provided in the fitting body through which fluid flows. The pipe fitting of the present disclosure provides the same effects as the inner ring.

[0017] According to this disclosure, the replaceability of the fluid flowing inside the inner ring can be improved.

[0018] This is a cross-sectional view showing a pipe fitting according to an embodiment of the present disclosure. This is a cross-sectional view showing the inner ring of the pipe fitting. This is a plan view of the inner ring viewed from the radially outward direction. This is a schematic cross-sectional view showing a mold for forming the inner ring. This is a cross-sectional view showing a conventional pipe fitting.

[0019] Next, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. [Pipe Fittings] Figure 1 is a cross-sectional view showing a pipe fitting according to an embodiment of the present disclosure. The pipe fitting 1 of this embodiment is used, for example, in a piping path through which a fluid (chemical solution) used in semiconductor manufacturing equipment flows. The pipe fitting 1 comprises a fitting body 2, a union nut 3, and an inner ring 4.

[0020] The joint body 2, union nut 3, and inner ring 4 are all made of synthetic resin. Examples of synthetic resin materials include polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), or fluororesin (perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF), etc.).

[0021] In this specification, "axial direction" refers to the direction along the axis C of the pipe fitting 1. For convenience, the right side of Figure 1 is referred to as one axial side, and the left side of Figure 1 is referred to as the other axial side. "Radial direction" refers to the direction perpendicular to the axis C of the pipe fitting 1. "Circumferential direction" refers to the direction around the axis C of the pipe fitting 1.

[0022] The joint body 2 is formed in a cylindrical shape. The joint body 2 has a joint portion 21 and a socket portion 22. The internal space of the joint portion 21 is a fluid passage 23. The socket portion 22 extends from the joint portion 21 to the other axial direction. A male screw 24 is formed on the outer circumference of the socket portion 22. The inner diameter of the socket portion 22 is larger than the inner diameter of the joint portion 21. An inclined circumferential surface portion 22a and a circular circumferential surface portion 22b are formed on the inner circumferential surface of the socket portion 22. The inclined circumferential surface portion 22a is formed at the end of the inner circumferential surface of the socket portion 22 on the other axial side. The inclined circumferential surface portion 22a decreases in diameter from the other axial side to the one axial side. The circular circumferential surface portion 22b is formed adjacent to the inclined circumferential surface portion 22a on the one axial side. The circumferential surface portion 22b is formed on the inner circumferential surface of the receiving portion 22, extending over the entire length on one axial side compared to the inclined circumferential surface portion 22a. The inner diameter of the circumferential surface portion 22b is constant throughout the entire axial direction.

[0023] The joint body 2 has a seal groove 25 formed radially inward from the socket portion 22. The seal groove 25 in this embodiment has a primary seal groove 25a and a secondary seal groove 25b. The primary seal groove 25a is a tapered groove formed radially inward of the joint body 2, with its diameter decreasing from the other axial side to the one axial side. The secondary seal groove 25b is formed in a cylindrical shape between the socket portion 22 and the primary seal groove 25a.

[0024] The union nut 3 has a nut portion 31 and a pressing portion 32. An internal thread 31a is formed on the inner circumference of the nut portion 31. The internal thread 31a of the nut portion 31 is tightened onto the external thread 24 of the joint body 2. The pressing portion 32 is integrally provided on the other axial side of the nut portion 31. The pressing portion 32 protrudes radially inward from the internal thread 31a of the nut portion 31. The pressing portion 32 is formed in an annular shape over the entire circumference of the union nut 3. When the internal thread 31a of the union nut 3 is tightened onto the external thread 24 of the joint body 2, the internal peripheral edge 32a on one axial side of the pressing portion 32 abuts against the external circumferential surface 72 of the bulge portion 7 of the inner ring 4, pressing the bulge portion 7 in one axial direction.

[0025] [Inner Ring] Figure 2 is a cross-sectional view showing the inner ring 4. In Figures 1 and 2, the inner ring 4 is provided in the joint body 2. The internal space of the inner ring 4 is a fluid passage 4a through which fluid flows. The fluid passage 4a of the inner ring 4 is in communication with the fluid passage 23 of the joint body 2. The inner ring 4 comprises a main body portion 5, a sealing portion 6, a bulging portion 7, and a tube portion 8.

[0026] The main body portion 5 is inserted into the socket portion 22 from the other axial side of the joint body 2. The inner diameter of the main body portion 5 is the same as the inner diameter of the joint portion 21. The outer diameter of the main body portion 5 is slightly smaller than the inner diameter of the circumferential surface portion 22b of the socket portion 22. The outer circumferential surface of the main body portion 5 is fitted into the circumferential surface portion 22b of the socket portion 22.

[0027] The seal portion 6 is integrally provided on one axial side of the main body portion 5. The seal portion 6 is inserted into the seal groove 25 of the joint body 2. The seal portion 6 of this embodiment has a primary seal portion 6a and a secondary seal portion 6b. The primary seal portion 6a protrudes from the radially inward side of the end of the main body portion 5 on one axial side to the other axial side. The primary seal portion 6a is formed in an annular shape. The outer circumferential surface of the primary seal portion 6a decreases in diameter from the other axial side toward the one axial side. The primary seal portion 6a is inserted into the primary seal groove 25a of the joint body 2.

[0028] The secondary seal portion 6b protrudes from the radially outward side of the primary seal portion 6a at one axial end of the main body portion 5 to the other axial side. The secondary seal portion 6b is formed in a cylindrical shape. The secondary seal portion 6b is inserted (press-fitted) into the secondary seal groove 25b of the joint body 2. Note that the seal portion 6 and the seal groove 25 may each have only the primary seal portion 6a and only the primary seal groove 25a, or only the secondary seal portion 6b and only the secondary seal groove 25b.

[0029] The bulge portion 7 of the inner ring 4 is integrally provided on the other axial side of the main body portion 5. The inner circumferential surface 71 of the bulge portion 7 has a constant inner diameter along its entire axial direction. The inner diameter of the bulge portion 7 is the same as the inner diameter of the main body portion 5. The outer circumferential surface 72 of the bulge portion 7 is formed to protrude radially outward. The outer circumferential surface 72 of the bulge portion 7 has a first inclined circumferential surface portion 73, an outermost circumferential surface portion 74, and a second inclined circumferential surface portion 75.

[0030] The first inclined circumferential surface portion 73 expands in diameter from the other axial side to the one axial side. The outermost circumferential surface portion 74 is formed adjacent to the first inclined circumferential surface portion 73 on the one axial side. The outermost circumferential surface portion 74 extends straight from the first inclined circumferential surface portion 73 to the other axial side. In other words, the outer diameter of the outermost circumferential surface portion 74 is constant throughout its entire axial direction. The outer diameter of the outermost circumferential surface portion 74 is the maximum outer diameter of the inner ring 4.

[0031] When the female thread 31a of the union nut 3 is tightened onto the male thread 24 of the joint body 2, and the main body 5 is inserted into the receiving portion 22, the first inclined circumferential surface portion 73 and the outermost circumferential surface portion 74 are located on the other axial side of the main body 5. In this state, when the female thread 31a of the union nut 3 is tightened onto the male thread 24 of the joint body 2, the inner circumferential edge portion 32a of the pressing portion 32 of the union nut 3 comes into contact with the first inclined circumferential surface portion 73 of the bulging portion 7 of the inner ring 4. Therefore, the tightening of the union nut 3 presses the inner ring 4 in one axial direction. As a result, the sealing portion 6 of the inner ring 4 (primary sealing portion 6a and secondary sealing portion 6b) is inserted into the sealing groove 25 (primary sealing groove 25a and secondary sealing groove 25b) of the joint body 2.

[0032] Figure 3 is a plan view of the inner ring 4 as seen from the radially outward direction. In Figures 2 and 3, gate marks 76 are formed at predetermined locations in the circumferential direction on the outermost outer surface 74 of the bulging portion 7. The gate marks 76 are shear marks formed when the gate 42 of the mold 40 is separated from the inner ring 4 after the inner ring 4 has been molded by the mold 40 (see Figure 4), which will be described later. The gate marks 76 are formed, for example, in a circular shape in plan view.

[0033] In Figures 1 and 2, the second inclined circumferential surface portion 75 of the bulging portion 7 is formed adjacent to one side of the outermost circumferential surface portion 74 in the axial direction. The second inclined circumferential surface portion 75 decreases in diameter as it moves from the other side in the axial direction toward the one side in the axial direction. The axial length L of the second inclined circumferential surface portion 75 is set so that, with the main body portion 5 inserted into the receiving portion 22 as described above, the entire axial length of the second inclined circumferential surface portion 75 is inserted into the receiving portion 22. The second inclined circumferential surface portion 75 is fitted into the inclined circumferential surface portion 22a within the receiving portion 22.

[0034] The tube portion 8 of the inner ring 4 is integrally provided on the other axial side of the bulge portion 7. The tube portion 8 is formed in a cylindrical shape and extends from the bulge portion 7 in the other axial direction. The inner diameter of the tube portion 8 is the same as the inner diameter of the bulge portion 7. The inner circumferential surface 8a of the tube portion 8 is flush with the outer circumferential surface 72 of the bulge portion 7. The outer diameter of the tube portion 8 is smaller than the inner diameter of the pressing portion 32 of the union nut 3.

[0035] As described above, with the main body 5 inserted into the receiving portion 22, one axial side of the tube portion 8 is inserted into the pressing portion 32, and the other axial side of the tube portion 8 protrudes axially beyond the pressing portion 32. The end face of the synthetic resin tube 80 is connected to the other axial end face of the tube portion 8 by welding or the like.

[0036] [Mold] The main body portion 5, seal portion 6, bulge portion 7, and tube portion 8 of the inner ring 4 are integrally molded by injection molding. Figure 4 is a schematic cross-sectional view showing the mold 40 for molding the inner ring 4 by injection molding. The mold 40 has a cavity surface 41 formed therein. The cavity surface 41 has a first cavity surface 41a, a second cavity surface 41b, a third cavity surface 41c, a fourth cavity surface 41d, and a fifth cavity surface 41e.

[0037] In Figures 2 and 4, the first cavity surface 41a is the surface that forms the outer circumferential surface of the tube portion 8. The second cavity surface 41b, the third cavity surface 41c, and the fourth cavity surface 41d are the surfaces that form the first inclined circumferential surface portion 73, the outermost circumferential surface portion 74, and the second inclined circumferential surface portion 75 of the outer circumferential surface 72 of the bulge portion 7. The fifth cavity surface 41e is the surface that forms the outer circumferential surface of the main body portion 5 and the outer circumferential surface of the secondary seal portion 6b.

[0038] The mold 40 has a gate 42 formed inside for supplying molten resin. In this embodiment, the gate 42 is formed in the mold 40 to open at the third cavity surface 41c that forms the outermost outer surface 74 of the bulge portion 7. The molten resin supplied into the mold 40 from the gate 42 flows in the order of the third cavity surface 41c, the fourth cavity surface 41d on one axial side, and the fifth cavity surface 41e. The molten resin supplied into the mold 40 also flows in the order of the third cavity surface 41c, the second cavity surface 41b on the other axial side, and the first cavity surface 41a.

[0039] Therefore, the molten resin supplied into the mold 40 flows from the portion of the inner ring 4 with the maximum radial thickness (outermost outer surface portion 74) toward the portion on one axial side where the radial thickness gradually decreases (second inclined circumferential surface portion 75, main body portion 5, and secondary seal portion 6b). Also, the molten resin supplied into the mold 40 flows from the portion of the inner ring 4 with the maximum radial thickness (outermost outer surface portion 74) toward the portion on the other axial side where the radial thickness gradually decreases (first inclined circumferential surface portion 73 and tube portion 8). As a result, the mold 40 is filled with molten resin and the inner ring 4 can be molded.

[0040] [Effects] According to the pipe joint 1 of this embodiment, the tube portion 8 is integrally provided on the bulge portion 7 of the inner ring 4, and since the inner diameter of the bulge portion 7 and the inner diameter of the tube portion 8 are the same, the inner circumferential surface 71 of the bulge portion 7 and the inner circumferential surface 8a of the tube portion 8 can be made flush. As a result, no recess is formed between the other axial end of the bulge portion 7 and the inner circumferential surface 8a of the tube portion 8, so that fluid flowing inside the inner ring 4 does not stagnate. As a result, the fluid replaceability can be improved. In particular, in semiconductor manufacturing equipment that requires a high degree of cleanliness as in this embodiment, the deterioration of cleanliness caused by a decrease in fluid replaceability can be effectively suppressed, making the inner ring 4 with the integrated tube portion 8 of this embodiment even more effective.

[0041] When the female thread 31a of the union nut 3 is tightened onto the male thread 24 of the joint body 2, the pressing portion 32 of the union nut 3 comes into contact with the first inclined circumferential surface portion 73 of the outer circumferential surface 72 of the bulging portion 7 of the inner ring 4. This allows the tightening torque of the union nut 3 to be gradually increased. Therefore, by tightening the union nut 3, the sealing portion 6 of the inner ring 4 can be easily inserted into the sealing groove 25 of the joint body 2.

[0042] A gate mark 76 is formed on the outermost outer surface 74 of the bulging portion 7 in the inner ring 4. In other words, when the inner ring 4 is injection molded using a mold 40, the gate 42 of the mold 40 is positioned to mold the outermost outer surface 74, which is the portion of the inner ring 4 with the maximum radial thickness. This allows molten resin to be poured from the portion of the inner ring 4 with the maximum radial thickness (outermost outer surface 74) towards the portions where the radial thickness gradually decreases (first inclined circumferential surface portion 73 and tube portion 8, etc.), making it easy to fill the mold 40 with molten resin.

[0043] With the female thread 31a of the union nut 3 tightened onto the male thread 24 of the joint body 2, and the main body portion 5 inserted into the socket portion 22, the entire axial length of the second inclined peripheral surface portion 75 on the outer peripheral surface 72 of the bulging portion 7 is inserted into the socket portion 22. As a result, compared with the case where part of the second inclined peripheral surface portion 75 is exposed on the other axial side relative to the joint body 2 while the main body portion 5 is inserted into the socket portion 22, the second inclined peripheral surface portion 75 can be made shorter in the axial direction. As the result, since the outermost peripheral surface portion 74 can be formed to be longer in the axial direction, the degree of freedom of the formation position of the gate mark 76 on the outermost peripheral surface portion 74 of the bulging portion 7 can be increased.

[0044] [Others] Each of the embodiments disclosed above is illustrative in all respects and not restrictive. For example, the pipe joint 1 of the above embodiment may be applied to fields such as liquid crystal and organic EL fields, medical and pharmaceutical fields, or automotive related fields, in addition to semiconductor manufacturing apparatuses. Further, the gate mark 76 may be formed at a position other than the outermost peripheral surface portion 74 of the bulging portion 7 on the outer peripheral surface of the inner ring 4. The outer peripheral surface 72 of the bulging portion 7 only needs to have at least the first inclined peripheral surface portion 73.

[0045] 1 Pipe Joint 2 Joint Body 3 Union Nut 4 Inner Ring 5 Main Body Portion 6 Seal Portion 7 Bulging Portion 8 Tube Portion 24 Male Thread 25 Seal Groove 31a Female Thread 32 Pressing Portion 72 Outer Peripheral Surface 73 First Inclined Peripheral Surface Portion 74 Outermost Peripheral Surface Portion 75 Second Inclined Peripheral Surface Portion 76 Gate Mark L Axial Length of Second Inclined Peripheral Surface Portion

Claims

1. An inner ring in a pipe fitting comprising: a fitting body having a male thread on its outer circumference; a union nut having a female thread that is tightened onto the male thread and an annular pressing portion that protrudes radially inward from the female thread; and an inner ring provided in the fitting body through which fluid flows, the inner ring comprising: a body portion inserted into the fitting body; a seal portion integrally provided on one axial side of the body portion and inserted into a seal groove formed in the fitting body; a bulge portion integrally provided on the other axial side of the body portion and having an outer circumferential surface that protrudes radially outward; and a tube portion integrally provided on the other axial side of the bulge portion and inserted into the pressing portion of the union nut, wherein the inner diameter of the tube portion is the same as the inner diameter of the bulge portion, the outer circumferential surface of the bulge portion expands in diameter from the other axial side to the one axial side, and has a first inclined circumferential surface portion that contacts the pressing portion of the union nut when the female thread of the union nut is tightened onto the male thread of the fitting body.

2. The inner ring according to claim 1, wherein the inner ring is made of synthetic resin, the outer peripheral surface of the bulging portion extends axially adjacent to one axial side of the first inclined peripheral surface portion and further has an outermost peripheral surface portion which is the maximum outer diameter of the inner ring, and a gate mark is formed on the outermost peripheral surface portion.

3. The inner ring according to claim 2, wherein the outer peripheral surface of the bulging portion further has a second inclined circumferential surface portion adjacent to one axial side of the outermost circumferential surface portion, and decreasing in diameter as it moves from the other axial side toward the one axial side, and the axial length of the second inclined circumferential surface portion is set such that the entire axial length of the second inclined circumferential surface portion is inserted into the joint body when the female thread of the union nut is tightened onto the male thread of the joint body.

4. A pipe fitting comprising: a fitting body having male threads on its outer circumference; a union nut having female threads that are tightened onto the male threads and an annular pressing portion that protrudes radially inward from the female threads; and an inner ring according to any one of claims 1 to 3, provided in the fitting body through which a fluid flows.

Images