Pipe Fittings

Abstract

To provide a pipe joint capable of ensuring necessary surface pressure between a bulging portion of an inner ring and a tube even if the fastening torque of a union nut is not increased.SOLUTION: A pipe joint 1 is equipped with an inner ring 4 that has a bulging portion 6 pressed in a tip end portion of a tube 8, a joint body 2 in which an end portion of an inner ring 4 is pressed in an inner periphery and which has a male screw portion 2b on an outer periphery, and a union nut 3 that has a female screw portion 3a fastened by the male screw portion 2b, and presses the tip end portion of the tube 8 by fastening the female screw portion 3a with the male screw portion 2b. The bulging portion 6 has a tapering portion 13 that is pressed by the union nut 3 to generate surface pressure between the tube 8 and the tapering portion 13. An outer peripheral surface 15 of the tapering portion 13 has a recessed curved surface portion 15a formed in a recessed curved surface in a cross-sectional view in an axial direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pipe joint. [Background technology]

[0002] In manufacturing processes in various technical fields such as semiconductor manufacturing, medical and pharmaceutical manufacturing, and food processing and chemical industries, pipe fittings made of synthetic resin, for example, are used as connection structures for connecting flow paths formed in tubes and fluid devices in piping paths through which fluids such as chemical liquids, high-purity liquids, ultrapure water, cleaning liquids, etc. One known pipe fitting of this kind includes an inner ring attached to the inner periphery of the tip of the tube, a cylindrical joint body attached to the outer periphery of the tip of the tube, and a union nut attached to the outer periphery of the joint body (see, for example, Patent Document 1).

[0003] The inner ring has a cylindrical main body, a bulge formed at one axial end of the main body so as to protrude radially outward, and a seal formed at the other axial end of the main body. A fluid flow path is formed inside the inner ring. The bulge of the inner ring is pressed into the tip of the tube to expand the diameter of the tip of the tube. The union nut presses the outer circumferential surface of the tube, the diameter of which is expanded by the bulge of the inner ring, due to the driving force generated when the union nut is attached to the joint body. This allows the seal of the inner ring to be pressed against the seal groove formed in the joint body, and prevents the tube from slipping out. Furthermore, a surface pressure is generated between the tube and the bulge, so that leakage of fluid from between the tube and the bulge can be suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-168947 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the tube is pressed by the thrust of the union nut, the inner peripheral surface of the tube comes into contact with the outer peripheral surface of the bulging portion of the inner ring over a wide range in the axial direction, so that the range in which surface pressure is generated between the tube and the bulging portion is wide in the axial direction. Therefore, in order to ensure the surface pressure required to suppress fluid leakage between the tube and the bulging portion, it is necessary to increase the tightening torque of the union nut, which causes a problem of poor workability.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a pipe fitting that can ensure the necessary surface pressure between the bulge portion of the inner ring and the tube without increasing the tightening torque of the union nut. [Means for solving the problem]

[0007] (1) A pipe fitting of the present invention comprises an inner ring having a bulge formed so as to protrude radially outward on one axial side and which is pressed into a tip of a tube; a fitting body into which an end of the inner ring on the other axial side is pressed into the inner circumference with the bulge pressed into the tip of the tube; and a union nut having a female threaded portion fastened to the male threaded portion and which presses the tip of the tube toward the other axial side when fastened to the male threaded portion, wherein the bulge is tapered from a midpoint in the axial direction toward one axial side and has a tapered portion that generates surface pressure between the bulge and the tube when pressed by the union nut, and the outer peripheral surface of the tapered portion has a concave curved portion formed into a concave curved shape when viewed in axial cross section.

[0008] According to the pipe joint of the present invention, a concave curved surface is formed on the outer peripheral surface of the tapered portion of the bulging portion of the inner ring, so that when the union nut presses the tube, the tube is less likely to come into contact with the bottom of the concave curved surface. As a result, the axial range in which surface pressure is generated between the tapered portion of the bulging portion and the tube is narrower than in the past, so that the surface pressure generated between the tapered portion of the bulging portion and the tube can be increased more than in the past. Therefore, the necessary surface pressure can be secured between the bulging portion of the inner ring and the tube without increasing the tightening torque of the union nut. As a result, it is possible to suppress leakage of fluid to the outside from between the bulging portion and the tube.

[0009] (2) It is preferable that the concave curved surface portion is formed over the entire axial length of the outer circumferential surface of the tapered portion. in this case, swelling Since the axial range in which surface pressure is generated between the tapered portion of the protruding portion and the tube can be further narrowed, the surface pressure generated between the tapered portion of the bulging portion and the tube can be further increased.

[0010] (3) It is preferable that the outer circumferential surface of the tapered portion has a convex curved surface portion formed in a convex curved shape on one axial side of the concave curved surface portion in an axial cross section. In this case, compared to the above case (2), the radial thickness of the end portion on one axial side of the tapered portion can be made thicker than the concave curved surface portion of the tapered portion. This increases the strength of the end portion of the tapered portion, so that even if the tapered portion is pressed by the union nut through the tube, the end portion of the tapered portion can be prevented from collapsing radially inward. As a result, the flow of fluid in the inner ring can be prevented from being obstructed by the tapered portion of the bulging portion.

[0011] (4) A pipe fitting from another viewpoint of the present invention comprises an inner ring having a bulge formed so as to protrude radially outward on one axial side and which is press-fitted into a tip of a tube, a fitting body into which an end of the inner ring on the other axial side is press-fitted into an inner circumference with the bulge pressed into the tip of the tube, and having a male threaded portion on an outer periphery, and a union nut having a female threaded portion tightened to the male threaded portion and which presses the tip of the tube toward the other axial side when the female threaded portion is tightened to the male threaded portion, wherein the bulge is tapered from a midpoint in the axial direction toward one axial side and has a tapered portion that generates a surface pressure between the bulge and the tube when pressed by the union nut, and a diameter D of one axial end of the outer axial surface of the tapered portion and an inner diameter d of a non-deformed portion of the tube that does not deform when the bulge is pressed into the tube satisfy the relationship 1.0d≦D≦1.4d.

[0012] According to the pipe joint of the present invention, the diameter D of one axial end of the outer peripheral surface of the tapered portion of the bulging portion of the inner ring and the inner diameter d of the non-deformed portion of the tube satisfy the relationship D≦1.4d, so the tightening torque of the union nut does not become high. Also, the diameter D of one axial end of the outer peripheral surface of the tapered portion and the inner diameter d of the non-deformed portion of the tube satisfy the relationship 1.0d≦D, so the necessary surface pressure can be secured between the bulging portion of the inner ring and the tube without increasing the tightening torque of the union nut. As a result, leakage of fluid to the outside from between the bulging portion and the tube can be suppressed. Effect of the Invention

[0013] According to the present invention, the necessary surface pressure can be ensured between the bulging portion of the inner ring and the tube without increasing the tightening torque of the union nut. [Brief description of the drawings]

[0014] [Figure 1] 1 is an axial cross-sectional view of a pipe joint according to a first embodiment of the present invention. [Diagram 2]FIG. 4 is an axial cross-sectional view showing an inner ring of the pipe joint. [Diagram 3] 3 is an enlarged cross-sectional view of a main part of FIG. 2, showing a bulging portion of the inner ring. FIG. [Figure 4] 5 is a cross-sectional view showing a contact state between the tapered portion of the bulging portion and a tube. FIG. [Diagram 5] 4 is a cross-sectional view showing a state in which a tapered portion of the bulging portion is tilted radially inward. FIG. [Figure 6] FIG. 6 is an enlarged axial cross-sectional view showing a bulging portion of an inner ring in a pipe fitting according to a second embodiment of the present invention. [Figure 7] 13 is a cross-sectional view showing a contact state between a tapered portion of a bulging portion and a tube in a second embodiment. FIG. [Figure 8] FIG. 11 is an enlarged axial cross-sectional view showing the vicinity of a bulging portion of an inner ring in a pipe fitting according to a third embodiment of the present invention. [Figure 9] 13 is an enlarged axial cross-sectional view showing a modified example of the bulging portion of the inner ring in the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. [First embodiment] Fig. 1 is an axial cross-sectional view showing a pipe fitting according to a first embodiment of the present invention. In Fig. 1, the pipe fitting 1 is used in a piping path through which a chemical liquid (fluid) used in, for example, semiconductor manufacturing equipment flows. The pipe fitting 1 includes a fitting body 2, a union nut 3, and an inner ring 4. Hereinafter, in this embodiment, for convenience, the left side of Fig. 1 will be referred to as one axial side, and the right side of Fig. 1 will be referred to as the other axial side (the same applies to Figs. 2 to 9).

[0016] The inner ring 4 is formed into a cylindrical shape from a synthetic resin material such as polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), or a fluororesin (perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.).

[0017] The inner ring 4 includes a cylindrical main body 5, a bulge 6 formed on one axial side of the main body 5, and a seal 7 formed on the other axial side of the main body 5. A fluid flow path 4a is formed on the radial inside of each of the main body 5, the bulge 6, and the seal 7 of the inner ring 4. The fluid flow path 4a communicates between a flow path 8a formed inside the tube 8 and a flow path 2c formed inside the joint body 2.

[0018] The bulge 6 is formed to protrude radially outward on one axial side of the main body 5. The bulge 6 is press-fitted into the tip of a synthetic resin (PFA, etc.) tube 8 to expand the diameter of the tip of the tube 8. Details of the bulge 6 will be described later. The seal portion 7 has an annular primary seal portion 7a and a cylindrical secondary seal portion 7b.

[0019] The primary seal portion 7a is formed protruding from the radially inner side of the other axial end of the main body 5 to the other axial side. The outer peripheral surface of the primary seal portion 7a is formed to gradually reduce in diameter from one axial end to the other axial end. The primary seal portion 7a is press-fitted into a primary seal groove 2d (described later) of the joint main body 2. The secondary seal portion 7b is formed protruding from the radially outer side of the other axial end of the main body 5 to the other axial side. The secondary seal portion 7b is press-fitted into a secondary seal groove 2e (described later) of the joint main body 2.

[0020] The joint body 2 is formed in a cylindrical shape from a synthetic resin material such as PVC, PP, PE, or fluororesin (PFA, PTFE, etc.). The inner diameter of the joint body 2 is set to be approximately the same as the inner diameter of the inner ring 4 so as not to impede the movement of the chemical solution. A socket portion 2a is formed at one axial end of the joint body 2. A seal portion 7 (the other axial end) of the inner ring 4, in which a bulge portion 6 is press-fitted into the tip of the tube 8, is press-fitted into the inner periphery of the socket portion 2a. As a result, the one axial end of the joint body 2 is attached to the outer periphery of the tip of the tube 8. A male thread portion 2b is formed on the outer periphery of the socket portion 2a.

[0021] The joint body 2 has an annular primary seal groove 2d and an annular secondary seal groove 2e formed radially inward of the socket portion 2a. The primary seal groove 2d is tapered so as to gradually reduce in diameter from one axial end to the other axial end on the radially inner side of the joint body 2. The secondary seal groove 2e is formed radially outward of the primary seal groove 2d in the joint body 2.

[0022] The union nut 3 is formed in a cylindrical shape from a synthetic resin material such as PVC, PP, PE, or fluororesin (PFA, PTFE, etc.). The union nut 3 has a female thread portion 3a formed on the inner circumference on the other axial side, and a pressing portion 3b formed on one axial side so as to protrude radially inward.

[0023] The female thread portion 3a of the union nut 3 is fastened to the male thread portion 2b of the joint body 2. By this fastening, the union nut 3 is attached to the joint body 2, and the corner portion 3c formed at the other axial end portion of the pressing portion 3b presses the enlarged diameter portion 8b of the tube 8, the diameter of which is enlarged by the bulging portion 6 of the inner ring 4, toward the other axial side. Note that in this embodiment, the portion of the pressing portion 3b that presses the tube 8 is not limited to the corner portion 3c. For example, a chamfered portion may be formed instead of the corner portion 3c at the other axial end portion of the pressing portion 3b, and the tube 8 may be pressed by the chamfered portion.

[0024] With the above configuration, when the female thread portion 3a of the union nut 3 is fastened to the male thread portion 2b of the joint body 2, the primary seal portion 7a and the secondary seal portion 7b of the inner ring 4 are press-fitted into the primary seal groove 2d and the secondary seal groove 2e of the joint body 2, respectively. This ensures the sealing performance of the connection portion between the inner ring 4 and the joint body 2. In addition, the corner portion 3c of the union nut 3 presses the enlarged diameter portion 8b of the tube 8 toward the other axial side, thereby preventing the tube 8 from slipping out.

[0025] Fig. 2 is an axial cross-sectional view showing the inner ring 4. In Fig. 1 and Fig. 2, the bulging portion 6 of the inner ring 4 has a maximum thickness portion 11 where the radial thickness is maximum, a base end portion 12 formed on the other axial side of the maximum thickness portion 11, and a tapered portion 13 formed on one axial side of the maximum thickness portion 11.

[0026] The maximum thickness portion 11 is formed over a predetermined length in the axial direction. The outer peripheral surface of the base end portion 12 is formed so as to gradually decrease in diameter from the other axial end of the maximum thickness portion 11 toward the other axial side. As a result, the base end portion 12 is formed so as to gradually decrease in radial thickness from the other axial end of the maximum thickness portion 11 toward the other axial side. The other axial end of the base end portion 12 is connected to the main body portion 5. In the cross-sectional view of FIG. 2, the outer peripheral surface of the base end portion 12 is inclined in a flat shape, but may be inclined in a curved shape.

[0027] The inner peripheral surface 14 of the tapered portion 13 is formed so as to gradually expand in diameter from the other axial side toward one axial end. The outer peripheral surface 15 of the tapered portion 13 is formed so as to gradually reduce in diameter from one axial end of the maximum thickness portion 11 toward one axial end. As a result, the tapered portion 13 is formed so as to gradually reduce in radial thickness from the axial midpoint of the bulging portion 6 toward one axial end, that is, to taper. Between the outer peripheral surface 15 of the tapered portion 13 and the inner peripheral surface of the enlarged diameter portion 8b of the tube 8, the enlarged diameter portion 8b is pressed by the corner portion 3c of the union nut 3, so that a surface pressure is generated.

[0028] Fig. 3 is an enlarged cross-sectional view of a main part of Fig. 2 showing the bulging portion 6 of the inner ring 4. The outer peripheral surface 15 of the tapered portion 13 of the bulging portion 6 has a concave curved surface portion 15a formed in a concave curved shape so as to be recessed radially inward. The concave curved surface portion 15a is formed in, for example, a concave arc shape. In this embodiment, the concave curved surface portion 15a is formed over the entire axial length of the outer peripheral surface 15 of the tapered portion 13.

[0029] As described above, the concave curved surface portion 15a is formed on the outer peripheral surface 15 of the tapered portion 13 of the bulging portion 6 of the inner ring 4, so that when the enlarged diameter portion 8b of the tube 8 is pressed toward the other axial side by the union nut 3 (not shown) as shown in FIG. 4, the inner peripheral surface of the tube 8 is less likely to come into contact with the bottom portion 15a1 of the concave curved surface portion 15a. As a result, the axial range in which surface pressure is generated between the tapered portion 13 of the bulging portion 6 and the tube 8 is narrower than in the past, so that the surface pressure generated between the tapered portion 13 of the bulging portion 6 and the tube 8 can be increased more than in the past. Therefore, the necessary surface pressure can be secured between the bulging portion 6 of the inner ring 4 and the tube 8 without increasing the tightening torque of the union nut 3. As a result, it is possible to suppress the leakage of the chemical liquid flowing through the fluid flow path 4a of the inner ring 4 from between the bulging portion 6 and the tube 8 to the outside.

[0030] In addition, since the concave curved surface portion 15a is formed over the entire axial length of the outer circumferential surface 15 of the tapered portion 13, the axial range in which surface pressure is generated between the tapered portion 13 of the bulging portion 6 and the tube 8 can be further narrowed compared to a case in which the concave curved surface portion 15a is formed over only a portion of the axial length of the outer circumferential surface 15 of the tapered portion 13. This makes it possible to further increase the surface pressure generated between the tapered portion 13 of the bulging portion 6 and the tube 8.

[0031] In this embodiment, the tapered portion 13 has a thin radial thickness at its tip (one axial end), so that when the tapered portion 13 is pressed by the union nut 3 through the tube 8, the tip of the tapered portion 13 tends to collapse radially inward (toward the fluid flow path 4a) as shown in Fig. 5, and the tube 8 and the inner circumferential surface 14 do not become flush with each other. If the tip of the tapered portion 13 collapses in this manner, the flow of the chemical solution in the fluid flow path 4a of the inner ring 4 may be obstructed by the tip of the tapered portion 13. Therefore, in a second embodiment described later, a configuration is provided that suppresses the collapse of the tip of the tapered portion 13.

[0032] [Second embodiment] 6 is an enlarged axial cross-sectional view showing the bulge 6 of the inner ring 4 in a pipe fitting 1 according to a second embodiment of the present invention. In the second embodiment, the shape of the outer circumferential surface 15 of the tapered portion 13 of the bulge 6 differs from that of the first embodiment. The differences will be described below.

[0033] The outer peripheral surface 15 of the tapered portion 13 of the bulging portion 6 has a concave curved surface portion 15a formed in a concave curved surface shape so as to be recessed radially inward, and a convex curved surface portion 15b formed in a convex curved surface shape so as to protrude radially outward on one axial side from the concave curved surface portion 15a. The concave curved surface portion 15a is formed in a concave arc shape, for example. The convex curved surface portion 15b is formed in a convex arc shape, for example.

[0034] The concave curved surface portion 15a is formed between the other axial end of the outer peripheral surface 15 and a midway portion on one axial side. The convex curved surface portion 15b is formed between the midway portion of the outer peripheral surface 15 and one axial end. As a result, the concave curved surface portion 15a and the convex curved surface portion 15b are formed continuously in the axial direction on the outer peripheral surface 15 of the tapered portion 13, and the convex curved surface portion 15b is formed at the tip portion of the tapered portion 13. Since the other configurations of the second embodiment are similar to those of the first embodiment, the same reference numerals are used and the description thereof is omitted.

[0035] As described above, in the pipe fitting 1 of the second embodiment, the concave curved surface portion 15a is formed on the outer peripheral surface 15 of the tapered portion 13 of the bulging portion 6 of the inner ring 4, so that when the enlarged diameter portion 8b of the tube 8 is pressed toward the other axial side by the union nut 3 (not shown) as shown in FIG. 7, the inner peripheral surface of the tube 8 is less likely to come into contact with the bottom portion 15a1 of the concave curved surface portion 15a. As a result, the axial range in which surface pressure is generated between the tapered portion 13 of the bulging portion 6 and the tube 8 is narrower than in the past, so that the surface pressure generated between the tapered portion 13 of the bulging portion 6 and the tube 8 can be increased more than in the past. Therefore, the necessary surface pressure can be secured between the bulging portion 6 of the inner ring 4 and the tube 8 without increasing the tightening torque of the union nut 3. As a result, it is possible to suppress leakage of the chemical liquid flowing through the fluid flow path 4a of the inner ring 4 from between the bulging portion 6 and the tube 8 to the outside.

[0036] In addition, since the outer peripheral surface 15 of the tapered portion 13 has a convex curved surface portion 15b formed on one axial side of the concave curved surface portion 15a, the radial thickness of the tip of the tapered portion 13 can be made thicker than in the first embodiment. This increases the strength of the tip of the tapered portion 13, so that even if the tapered portion 13 is pressed by the union nut 3 through the tube 8, the tip of the tapered portion 13 can be prevented from falling significantly radially inward as in the first embodiment (see FIG. 5). As a result, the flow of the chemical solution in the fluid flow path 4a of the inner ring 4 can be prevented from being obstructed by the tapered portion 13 of the bulging portion 6.

[0037] [Third embodiment] 8 is an enlarged axial cross-sectional view showing the vicinity of the bulging portion 6 of the inner ring 4 in a pipe fitting 1 according to a third embodiment of the present invention. In the third embodiment, the shape of the tapered portion 13 of the bulging portion 6 differs from that of the first embodiment. The differences will be described below.

[0038] The tapered portion 13 of the bulging portion 6 is formed shorter in the axial direction than the tapered portion 13 of the bulging portion 6 in the first embodiment. A flat surface 16 extending in the radial direction is formed at one axial end of the tapered portion 13. The flat surface 16 extends radially inward from one axial end 15c of the outer circumferential surface 15 of the tapered portion 13 and is connected to one axial end of the inner circumferential surface 14 of the tapered portion 13.

[0039] The outer peripheral surface 15 of the tapered portion 13 is formed into a convex curved shape (e.g., a convex arc shape) over its entire axial length. The diameter D of one axial end 15c of the outer peripheral surface 15 of the tapered portion 13 and the inner diameter d of the non-deformed portion 8c of the tube 8 are set to satisfy the relationship 1.0d≦D≦1.4d. The non-deformed portion 8c is a portion of the tube 8 that does not deform even when the bulging portion 6 of the inner ring 4 is press-fitted into the tip end of the tube 8.

[0040] The reason why D≦1.4d is that if the diameter D of the axial end 15c exceeds 1.4d, the pressing force generated in the axial direction by the corner 3c of the union nut 3 is generated on the entire flat surface 16, which increases the tightening torque of the union nut 3. The reason why 1.0d≦D is that if the diameter D of the axial end 15c is below 1.0d, the axial range in which the surface pressure is generated between the tapered portion 13 of the bulge 6 and the tube 8 becomes long, making it impossible to ensure the necessary surface pressure between the bulge 6 and the tube 8. The other configurations of the third embodiment are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted.

[0041] Although the flat surface 16 is formed at one axial end of the tapered portion 13, a shape other than a flat surface (for example, a tapered surface, etc.) may be formed. Furthermore, the shape of the outer circumferential surface 15 of the tapered portion 13 is not limited to a convex curved surface, but may be formed into a flat surface, for example, as shown in FIG.

[0042] As described above, according to the pipe joint 1 of the third embodiment, the diameter D of the axial end 15c of the outer circumferential surface 15 of the tapered portion 13 at the bulging portion 6 of the inner ring 4 and the inner diameter d of the non-deformed portion 8c of the tube 8 satisfy the relationship D≦1.4d, so the tightening torque of the union nut 3 does not become high. 15 Since the diameter D of the axial end 15c of the tube 8 and the inner diameter d of the non-deformed portion 8c of the tube 8 satisfy the relationship 1.0d≦D, the necessary surface pressure can be secured between the bulging portion 6 of the inner ring 4 and the tube 8 without increasing the tightening torque of the union nut 3. As a result, the liquid medicine flowing through the fluid flow path 4a of the inner ring 4 can be prevented from leaking to the outside from between the bulging portion 6 and the tube 8.

[0043] [others] The pipe joint of the present invention can be applied not only to semiconductor manufacturing equipment, but also to the liquid crystal / organic electroluminescence (EL) field, the medical / pharmaceutical field, and the automotive-related field.

[0044] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above meaning, and is intended to include all modifications within the scope of the claims and the meaning equivalent thereto. [Explanation of symbols]

[0045] 1 Pipe fittings 2. Joint body 2b Male thread 3 Union Nut 3a Female thread 3c Corner 4 Inner Ring 6 Bulge 8 Tubes 8c Non-deformed part 13 Tapered section 15 Outer surface 15a Concave curved part 15b Convex curved part 15c One axial end

Claims

[Claim 1] an inner ring having a bulge formed on one axial side thereof so as to protrude radially outward and which is press-fitted into a tip end portion of the tube; a joint body into which an end portion on the other axial side of the inner ring is press-fitted into an inner periphery with the bulge portion press-fitted into the tip portion of the tube, and which has a male thread portion on an outer periphery; a union nut having a female threaded portion that is fastened to the male threaded portion and that presses the tip end of the tube toward the other axial side by fastening the female threaded portion to the male threaded portion, The bulging portion is formed so as to taper from a middle portion in the axial direction toward one side in the axial direction, and has a tapered portion that generates a surface pressure between the tube and the bulging portion when the union nut is pressed against the tube, an outer circumferential surface of the tapered portion has a concave curved surface portion formed in a concave curved surface shape in an axial cross section, and a convex curved surface portion formed in a convex curved surface shape on one axial side of the concave curved surface portion, The convex curved surface portion is formed at a tip end portion of the tapered portion.

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