Patent Publication Number: US-2023151911-A1

Title: Inner ring and pipe joint

Description:
TECHNICAL FIELD 
     The present invention relates to an inner ring and a pipe joint. 
     BACKGROUND ART 
     In manufacturing processes in various technical fields such as semiconductor manufacturing, medical/pharmaceutical manufacturing, and food processing/chemical industries, in a pipe path through which fluids such as chemical solutions, high-purity liquids, ultrapure water, or cleaning solutions flow, for example, a pipe joint made of a synthetic resin is used as a connection structure that connects flow passages formed in tubes or fluid devices. As such a pipe joint, a pipe joint that includes an inner ring mounted on the inner circumferential side of an end portion of a tube, a cylindrical joint body mounted on the outer circumferential side of the end portion of the tube, and a union nut mounted on the outer circumferential side of the joint body, is known (see, for example, PATENT LITERATURE 1). 
     As shown in  FIG.  5   , an inner ring  110  in a conventional pipe joint  100  has a cylindrical body portion  111 , a bulge portion  112  formed at one axial end portion of the body portion  111 , and a press-fitting portion  113  formed at another axial end portion of the body portion  111 . A fluid flow passage  114  is formed inside the inner ring  110 . The bulge portion  112  is formed so as to project to the radially outer side with respect to the body portion  111 , and is press-fitted into an end portion of a tube  120 . The press-fitting portion  113  is formed so as to project in the axial direction from the body portion  111 , and the press-fitting portion  113  is press-fitted into an end portion of a joint body  140  when a union nut  130  is tightened. 
     When the bulge portion  112  and the press-fitting portion  113  of the inner ring  110  are press-fitted into the end portion of the tube  120  and the end portion of the joint body  140 , respectively, both end portions in the axial direction of the inner ring  110  are pressed toward the radially inner side, whereby both end portions in the axial direction of the inner circumferential surface of the inner ring  110  are deformed so as to fall down toward the radially inner side. At this time, when both end portions in the axial direction of the inner circumferential surface of the inner ring  110  protrude into the fluid flow passage  114 , the replacement characteristics of a fluid flowing in the pipe joint  100  are reduced, causing adverse effects such as taking time for flushing the inside of the pipe joint  100 . 
     Therefore, as shown in  FIG.  6   , tapered surfaces  115  and  116  are respectively formed at both end portions in the axial direction of the inner circumferential surface of the inner ring  110  such that the diameters thereof gradually increase from the axially inner side toward the axially outer ends thereof. Accordingly, even when both end portions in the axial direction of the inner ring  110  are pressed toward the radially inner side, both end portions in the axial direction of the inner circumferential surface of the inner ring  110  are inhibited from protruding into the fluid flow passage  114 . 
     CITATION LIST 
     Patent Literature 
     PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No. 2018-168947 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     As shown in  FIG.  7   , at the one axial end portion of the inner ring  110 , when a length L′ in the axial direction of the tapered surface  115  is short, the deformation margin of the one axial end portion of the inner circumferential surface of the inner ring  110  to the radially inner side is insufficient. Therefore, as shown in  FIG.  8   , when the bulge portion  112  of the inner ring  110  is press-fitted into the end portion of the tube  120 , the one axial end portion of the inner circumferential surface of the inner ring  110  cannot be inhibited from protruding into the fluid flow passage  114  side. In addition, although not shown, at the other axial end portion of the inner ring  110  as well, the same problem arises when the length in the axial direction of the tapered surface  116  is short. 
     As shown in  FIG.  9   , at the one axial end portion of the inner ring  110 , when the length L′ in the axial direction of the tapered surface  115  is long, the thickness (cross-sectional area) in the radial direction of the one axial end portion of the inner ring  110  is excessively small. Therefore, as shown in  FIG.  10   , when the bulge portion  112  of the inner ring  110  is press-fitted into the end portion of the tube  120 , the one axial end portion of the inner circumferential surface of the inner ring  110  easily falls down toward the radially inner side and thus cannot be inhibited from protruding into the fluid flow passage  114 . In addition, although not shown, at the other axial end portion of the inner ring  110  as well, the same problem arises when the length in the axial direction of the tapered surface  116  is long. 
     The present invention has been made in view of such circumstances, and an object of the present invention is to allow an end portion in the axial direction of the inner circumferential surface of an inner ring to be effectively inhibited from protruding into a fluid flow passage. 
     Solution to Problem 
     (1) An inner ring of the present invention is an inner ring including: a bulge portion formed at one axial end portion such that an outer circumferential surface thereof projects toward a radially outer side, and to be press-fitted into an end portion of a tube; a press-fitting portion formed at another axial end portion and to be press-fitted into an end portion of a joint body; and a cylindrical body portion formed between the bulge portion and the press-fitting portion and having a constant outer diameter over an entirety in an axial direction, the outer diameter being smaller than a maximum outer diameter of the bulge portion, wherein a fluid flow passage is formed inside an inner circumferential surface of the inner ring, the inner ring includes a tapered surface formed at one axial end portion of the inner circumferential surface such that a diameter thereof gradually increases from another axial side toward one axial end thereof in a state before the bulge portion is press-fitted into the end portion of the tube, and a diameter increase starting point of the tapered surface is located in a range from a deformation starting point, which serves as a starting point from which the inner circumferential surface is deformed due to the bulge portion receiving external force from the tube when the bulge portion is press-fitted into the end portion of the tube, to a position, on the inner circumferential surface, corresponding to one axial end of an outer circumferential surface of the body portion. 
     In the inner ring of the present invention, the diameter increase starting point of the tapered surface formed at the one axial end portion of the inner circumferential surface of the inner ring is not located on the one axial side with respect to the deformation starting point which serves as a starting point from which the inner circumferential surface is deformed due to the bulge portion receiving the external force from the tube. Accordingly, the diameter increase starting point of the tapered surface can be inhibited from being deformed toward the radially inner side due to the external force, so that a deformation margin of the one axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be ensured. 
     Moreover, the diameter increase starting point of the tapered surface is not located on the other axial side with respect to the position, on the inner circumferential surface, corresponding to the one axial end of the outer circumferential surface of the body portion. That is, the diameter increase starting point of the tapered surface is not located at a portion, of the inner ring, at which the thickness in the radial direction thereof is small. Accordingly, even though the tapered surface is formed, the thickness (cross-sectional area) in the radial direction of the one axial end portion of the inner ring can be inhibited from being excessively small, so that the degree of deformation of the one axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be reduced. 
     Owing to the above, the one axial end portion of the inner circumferential surface of the inner ring can be effectively inhibited from protruding into the fluid flow passage. 
     (2) Preferably, a maximum outer diameter portion having a maximum outer diameter is formed at the outer circumferential surface of the bulge portion over a predetermined length in the axial direction, and the diameter increase starting point of the tapered surface is located in a range, in the inner circumferential surface, corresponding to a range of the predetermined length of the maximum outer diameter portion. 
     In this case, since the diameter increase starting point of the tapered surface is located at a portion, of the bulge portion, at which the thickness in the radial direction thereof is the largest, even though the tapered surface is formed, the degree of decrease in the thickness in the radial direction of the one axial end portion of the inner ring can be reduced. Accordingly, the degree of deformation of the one axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be further reduced. 
     (3) Preferably, the deformation starting point is located at a position, on the inner circumferential surface, corresponding to one axial end of the maximum outer diameter portion, and the diameter increase starting point of the tapered surface is located on the deformation starting point. 
     In this case, the diameter increase starting point of the tapered surface can be inhibited from being deformed toward the radially inner side due to the external force, and the degree of decrease in the thickness in the radial direction of the one axial end portion of the inner ring can also be reduced as much as possible. Accordingly, the degree of deformation of the one axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be further reduced. 
     (4) According to another aspect, an inner ring of the present invention is an inner ring including: a bulge portion formed at one axial end portion such that an outer circumferential surface thereof projects toward a radially outer side, and to be press-fitted into an end portion of a tube; a press-fitting portion formed at another axial end portion and to be press-fitted into an end portion of a joint body; and a cylindrical body portion formed between the bulge portion and the press-fitting portion and having a constant outer diameter over an entirety in an axial direction, the outer diameter being smaller than an outer diameter of the press-fitting portion, wherein a fluid flow passage is formed inside an inner circumferential surface of the inner ring, the inner ring includes a tapered surface formed at another axial end portion of the inner circumferential surface such that a diameter thereof gradually increases from one axial side toward another axial end thereof in a state before the press-fitting portion is press-fitted into the end portion of the joint body, and a diameter increase starting point of the tapered surface is located in a range from a deformation starting point, which serves as a starting point from which the inner circumferential surface is deformed due to the press-fitting portion receiving external force from the joint body when the press-fitting portion is press-fitted into the end portion of the joint body, to a position, on the inner circumferential surface, corresponding to another axial end of an outer circumferential surface of the body portion. 
     In the inner ring of the present invention, the diameter increase starting point of the tapered surface formed at the other axial end portion of the inner circumferential surface of the inner ring is not located on the other axial side with respect to the deformation starting point which serves as a starting point from which the inner circumferential surface is deformed due to the press-fitting portion receiving the external force from the joint body. Accordingly, the diameter increase starting point of the tapered surface can be inhibited from being deformed toward the radially inner side due to the external force, so that a deformation margin of the other axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be ensured. 
     Moreover, the diameter increase starting point of the tapered surface is not located on the one axial side with respect to the position, on the inner circumferential surface, corresponding to the other axial end of the outer circumferential surface of the body portion. That is, the diameter increase starting point of the tapered surface is not located at a portion, of the inner ring, at which the thickness in the radial direction thereof is small. Accordingly, even though the tapered surface is formed, the thickness (cross-sectional area) in the radial direction of the other axial end portion of the inner ring can be inhibited from being excessively small, so that the degree of deformation of the other axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be reduced. 
     Owing to the above, the other axial end portion of the inner circumferential surface of the inner ring can be effectively inhibited from protruding into the fluid flow passage. 
     (5) Preferably, the diameter increase starting point of the tapered surface is located on the deformation starting point. 
     In this case, the diameter increase starting point of the tapered surface can be inhibited from being deformed toward the radially inner side due to the external force, and the degree of decrease in the thickness in the radial direction of the other axial end portion of the inner ring can also be reduced as much as possible. Accordingly, the degree of deformation of the other axial end portion of the inner circumferential surface of the inner ring to the radially inner side can be further reduced. 
     (6) According to another aspect, a pipe joint of the present invention includes: a joint body having an external thread portion formed on an outer circumference thereof; a union nut having an internal thread portion formed on an inner circumference thereof and to be tightened to the external thread portion; and the inner ring according to any one of the above (1) to (5). 
     With the pipe joint of the present invention, the same advantageous effects as those of the inner ring are achieved. 
     ADVANTAGEOUS EFFECTS OF THE INVENTION 
     According to the present invention, the end portion in the axial direction of the inner circumferential surface of the inner ring can be effectively inhibited from protruding into the fluid flow passage. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an axial cross-sectional view showing a pipe joint according to an embodiment of the present invention. 
         FIG.  2    is an axial cross-sectional view showing an inner ring of the pipe joint. 
         FIG.  3    an enlarged cross-sectional view of a main part of  FIG.  2    showing a first tapered surface at an inner circumferential surface of the inner ring. 
         FIG.  4    is an enlarged cross-sectional view of a main part of  FIG.  2    showing a second tapered surface at the inner circumferential surface of the inner ring. 
         FIG.  5    is an axial cross-sectional view showing a conventional pipe joint. 
         FIG.  6    is an axial cross-sectional view showing a conventional inner ring. 
         FIG.  7    is an enlarged cross-sectional view showing the case where a tapered surface formed at the inner circumferential surface of the conventional inner ring is short in the axial direction. 
         FIG.  8    is an enlarged cross-sectional view showing a state where the tapered surface of the inner ring in  FIG.  7    is deformed. 
         FIG.  9    is an enlarged cross-sectional view showing the case where the tapered surface formed at the inner circumferential surface of the conventional inner ring is long in the axial direction. 
         FIG.  10    is an enlarged cross-sectional view showing a state where the tapered surface of the inner ring in  FIG.  9    is deformed. 
     
    
    
     DETAILED DESCRIPTION 
     Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     Entire Configuration of Pipe Joint 
       FIG.  1    is an axial cross-sectional view showing a pipe joint according to an embodiment of the present invention. In  FIG.  1   , a pipe joint  1  is used, for example, in a pipe path through which a chemical solution (fluid) used in a semiconductor manufacturing apparatus flows. The pipe joint  1  includes a joint body  2 , a union nut  3 , and an inner ring  4 . Hereinafter, in the present embodiment, for convenience, the left side of  FIG.  1    is referred to as one axial side, and the right side of  FIG.  1    is referred to as another axial side (the same applies to  FIG.  2    to  FIG.  4   ). 
     The inner ring  4  is formed in a cylindrical shape, for example, from a synthetic resin material such as polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), or a fluorine resin (perfluoroalkoxy alkane (PFA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like). 
     A fluid flow passage  4   b  is formed inside an inner circumferential surface  4   a  of the inner ring  4 . The fluid flow passage  4   b  provides communication between a flow passage  8   a  formed inside a tube  8  and a flow passage  2   c  formed inside the joint body  2 . The inner ring  4  includes a bulge portion  5  formed at one axial end portion thereof, a press-fitting portion  6  formed at another axial end portion thereof, and a cylindrical body portion  7  formed between the bulge portion  5  and the press-fitting portion  6 . 
     The bulge portion  5  is press-fitted into an end portion of the tube  8 , which is made of a synthetic resin material (PFA or the like), to increase the diameter of the end portion of the tube  8 . The bulge portion  5  has an outer circumferential surface  5   a  which is formed in a mountain shape so as to project toward the radially outer side. The outer circumferential surface  5   a  of the bulge portion  5  has a maximum outer diameter portion  5   b  having a maximum outer diameter, a first reduced-diameter portion  5   c,  and a second reduced-diameter portion  5   d.    
     The maximum outer diameter portion  5   b  is formed over a predetermined length L in the axial direction (see  FIG.  2   ). The first reduced-diameter portion  5   c  is formed such that the diameter thereof gradually decreases from one axial end of the maximum outer diameter portion  5   b  toward the one axial side. The second reduced-diameter portion  5   d  is formed such that the diameter thereof gradually decreases from the other axial end of the maximum outer diameter portion  5   b  toward the other axial side. Another axial end of the second reduced-diameter portion  5   d  is connected to an outer circumferential surface  7   a  of the body portion  7 . 
     The press-fitting portion  6  is press-fitted into an end portion (one axial end portion) of the joint body  2 . The press-fitting portion  6  includes a cylindrical press-fitting body  6   a,  an annular primary sealing portion  6   b,  and a cylindrical secondary sealing portion  6   c.    
     The press-fitting body  6   a  is press-fitted into a receiving portion  2   a  (described later) of the joint body  2 . 
     The primary sealing portion  6   b  is formed so as to project from the radially inner side of another axial end of the press-fitting body  6   a  toward the other axial side. An outer circumferential surface  6   b   1  of the primary sealing portion  6   b  is formed such that the diameter thereof gradually decreases from one axial end thereof to the other axial end thereof. The primary sealing portion  6   b  is press-fitted into a primary sealing groove  2   d  (described later) of the joint body  2 . 
     The secondary sealing portion  6   c  is formed so as to project from the radially outer side of the other axial end of the press-fitting body  6   a  toward the other axial side. The secondary sealing portion  6   c  is press-fitted into a secondary sealing groove  2   e  (described later) of the joint body  2 . An annular groove  6   d  is formed between the primary sealing portion  6   b  and the secondary sealing portion  6   c  so as to have an arc cross-sectional shape. The outer diameter of the secondary sealing portion  6   c  is equal to the outer diameter of the press-fitting body  6   a.  Accordingly, the press-fitting portion  6  (the press-fitting body  6   a  and the secondary sealing portion  6   c ) has a constant outer diameter D 3  (see  FIG.  2   ) over the entirety in the axial direction. 
     The body portion  7  of the inner ring  4  has a constant outer diameter D 1  over the entirety in the axial direction, and the outer diameter D 1  is smaller than a maximum outer diameter D 2  of the bulge portion  5  and smaller than the outer diameter D 3  of the press-fitting portion  6  (see  FIG.  2   ). The outer circumferential surface  7   a  of the body portion  7  is connected to an outer circumferential surface  6   f  of the press-fitting portion  6  via a step surface  6   e  formed at one axial end of the press-fitting portion  6 . 
     The joint body  2  is formed in a cylindrical shape, for example, from a synthetic resin material such as PVC, PP, PE, or a fluorine resin (PFA, PTFE, or the like). The inner diameter of the joint body  2  is set to substantially the same dimension as the inner diameter of the inner ring  4  such that the movement of the chemical solution is not hindered. The cylindrical receiving portion  2   a  is formed at one axial end portion of the joint body  2 . The press-fitting portion  6  of the inner ring  4  in which the bulge portion  5  is press-fitted into the end portion of the tube  8  is press-fitted to the inner circumference of the receiving portion  2   a . Accordingly, the one axial end portion of the joint body  2  is mounted on the outer circumference of the end portion of the tube  8 . An external thread portion  2   b  is formed on the outer circumference of the receiving portion  2   a.    
     The joint body  2  has the annular primary sealing groove  2   d  and the cylindrical secondary sealing groove  2   e  which are formed on the other axial side with respect to the receiving portion  2   a.  The primary sealing groove  2   d  is formed on the radially inner side of the joint body  2  in a tapered shape that is cut such that the diameter thereof gradually decreases from one axial end thereof toward the other axial end thereof. The secondary sealing groove  2   e  is formed on the radially outer side with respect to the primary sealing groove  2   d  in the joint body  2 . 
     The union nut  3  is formed in a cylindrical shape, for example, from a synthetic resin material such as PVC, PP, PE, or a fluorine resin (PFA, PTFE, or the like). The union nut  3  has a pressing portion  3   a  formed at the one axial end portion thereof so as to project toward the radially inner side, and an internal thread portion  3   b  formed on the inner circumference of the other axial end portion thereof. The internal thread portion  3   b  is tightened to the external thread portion  2   b  of the joint body  2 . By the tightening, the union nut  3  is attached to the joint body  2 , and another axial end portion of the pressing portion  3   a  also presses the outer circumferential surface of the tube  8  which bulges on the radially outer side by the bulge portion  5  of the inner ring  4 . 
     With the above configuration, when the internal thread portion  3   b  of the union nut  3  is tightened to the external thread portion  2   b  of the joint body  2 , the primary sealing portion  6   b  and the secondary sealing portion  6   c  of the inner ring  4  are press-fitted into the primary sealing groove  2   d  and the secondary sealing groove  2   e  of the joint body  2 , respectively, so that sealing performance at the connection portion between the inner ring  4  and the joint body  2  can be ensured. In addition, the pressing portion  3   a  of the union nut  3  can prevent the tube  8  from being removed. 
     Inner Circumferential Surface of Inner Ring 
       FIG.  2    is an axial cross-sectional view showing the inner ring  4 , and shows a state before the bulge portion  5  and the press-fitting portion  6  are press-fitted into the end portion of the tube  8  and the end portion of the joint body  2 , respectively. As shown in  FIG.  2   , the inner ring  4  includes a first tapered surface  11  formed at one axial end portion of the inner circumferential surface  4   a,  and a second tapered surface  12  formed at another axial end portion of the inner circumferential surface  4   a.    
     The first tapered surface  11  is formed at the one axial end portion of the inner circumferential surface  4   a  such that the diameter thereof gradually increases from the other axial side toward one axial end thereof. The first tapered surface  11  of the present embodiment is formed, for example, in a curved surface shape. The first tapered surface  11  may be formed in a flat surface shape. 
     The second tapered surface  12  is formed at the other axial end portion of the inner circumferential surface  4   a  such that the diameter thereof gradually increases from the one axial side thereof toward another axial end thereof. The second tapered surface  12  of the present embodiment is formed, for example, in a flat surface shape. The second tapered surface  12  may be formed in a curved surface shape. 
       FIG.  3    is an enlarged cross-sectional view of a main part of  FIG.  2    showing the first tapered surface  11  at the inner circumferential surface  4   a  of the inner ring  4 . In  FIG.  3   , a diameter increase starting point P 11  of the first tapered surface  11  is preferably located in a range R 11  from a deformation starting point P 12  of the inner circumferential surface  4   a  to a position P 13 , on the inner circumferential surface  4   a,  corresponding to one axial end of the outer circumferential surface  7   a  of the body portion  7 . Here, the “in a range R 11  from a deformation starting point P 12  . . . to a position P 13 ” means to also include the position on the deformation starting point P 12  and the position on the position P 13 . 
     The deformation starting point P 12  is a position serving as a starting point from which the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  is deformed so as to fall down toward the radially inner side due to the bulge portion  5  receiving external force from the tube  8  and the union nut  3  when the bulge portion  5  is press-fitted into the end portion of the tube  8  and when the union nut  3  (internal thread portion  3   b ) is tightened to the joint body  2  (external thread portion  2   b ). Therefore, at the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4 , a portion on the one axial side with respect to the deformation starting point P 12  is deformed so as to fall down toward the radially inner side. The deformation starting point P 12  in the present embodiment is a position, on the inner circumferential surface  4   a,  corresponding to the one axial end of the maximum outer diameter portion  5   b  in the outer circumferential surface  5   a  of the bulge portion  5 . 
     When the diameter increase starting point P 11  of the first tapered surface  11  is located in the range R 11 , the following advantageous effects are achieved. 
     The diameter increase starting point P 11  of the first tapered surface  11  is not located on the one axial side with respect to the deformation starting point P 12 . Accordingly, the diameter increase starting point P 11  of the first tapered surface  11  can be inhibited from being deformed toward the radially inner side due to the external force from the tube  8  and the union nut  3 , so that a deformation margin of the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be ensured. 
     Moreover, the diameter increase starting point P 11  of the first tapered surface  11  is not located on the other axial side with respect to the position P 13 . That is, the diameter increase starting point P 11  of the first tapered surface  11  is not located at a portion, of the inner ring  4 , at which the thickness in the radial direction thereof is small. Accordingly, even though the first tapered surface  11  is formed, the thickness (cross-sectional area) in the radial direction of the one axial end portion of the inner ring  4  can be inhibited from being excessively small, so that the degree of deformation of the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be reduced. 
     Therefore, when the diameter increase starting point P 11  of the first tapered surface  11  is located in the range R 11 , the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  can be effectively inhibited from protruding into the fluid flow passage  4   b.    
     The diameter increase starting point P 11  of the first tapered surface  11  is further preferably located in a range R 12 , in the inner circumferential surface  4   a,  corresponding to the range of a length L of the maximum outer diameter portion  5   b  in the outer circumferential surface  5   a  of the bulge portion  5 . In this case, since the diameter increase starting point P 11  of the first tapered surface  11  is located at a portion, of the bulge portion  5 , at which the thickness in the radial direction thereof is the largest, even though the first tapered surface  11  is formed, the degree of decrease in the thickness in the radial direction of the one axial end portion of the inner ring  4  can be reduced. Accordingly, the degree of deformation of the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be further reduced. 
     The diameter increase starting point P 11  of the first tapered surface  11  in the present embodiment is located on the deformation starting point P 12  in the range R 12 . In this case, the diameter increase starting point P 11  of the first tapered surface  11  can be inhibited from being deformed toward the radially inner side due to the external force, and the degree of decrease in the thickness in the radial direction of the one axial end portion of the inner ring  4  can also be reduced as much as possible. Accordingly, the degree of deformation of the one axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be further reduced. 
     As shown in  FIG.  1   , when the bulge portion  5  is press-fitted into the end portion of the tube  8  or when external force is generated by tightening the union nut  3 , the entire first tapered surface  11  is deformed so as to fall down toward the radially inner side, whereby the first tapered surface  11  in the present embodiment extends straight in the axial direction along the inner circumferential surface  4   a.  Therefore, when the bulge portion  5  is press-fitted into the end portion of the tube  8 , even if an axial part of the inner circumferential surface  4   a  of the inner ring  4  is deformed so as to fall down toward the radially inner side, the axial part of the inner circumferential surface  4   a  does not protrude into the fluid flow passage  4   b.    
       FIG.  4    is an enlarged cross-sectional view of a main part of  FIG.  2    showing the second tapered surface  12  at the inner circumferential surface  4   a  of the inner ring  4 . In  FIG.  4   , a diameter increase starting point P 21  of the second tapered surface  12  is preferably located in a range R 21  from a deformation starting point P 22  of the inner circumferential surface  4   a  to a position P 23 , on the inner circumferential surface  4   a,  corresponding to the other axial end of the outer circumferential surface  7   a  of the body portion  7 . Here, the “in a range R 21  from a deformation starting point P 22  . . . to a position P 23 ” means to also include the position on the deformation starting point P 22  and the position on the position P 23 . 
     The deformation starting point P 22  is a position serving as a starting point from which the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  is deformed so as to fall down toward the radially inner side due to the primary sealing portion  6   b  of the press-fitting portion  6  receiving external force from the joint body  2  when the press-fitting portion  6  is press-fitted into the end portion of the joint body  2 , in particular, when the primary sealing portion  6   b  is press-fitted into the primary sealing groove  2   d.  Therefore, at the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4 , a portion on the other axial side with respect to the deformation starting point P 22  is deformed so as to fall down toward the radially inner side. 
     When the diameter increase starting point P 21  of the second tapered surface  12  is located in the range R 21 , the following advantageous effects are achieved. 
     The diameter increase starting point P 21  of the second tapered surface  12  is not located on the other axial side with respect to the deformation starting point P 22 . Accordingly, the diameter increase starting point P 21  of the second tapered surface  12  can be inhibited from being deformed toward the radially inner side due to the external force from the joint body  2 , so that a deformation margin of the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be ensured. 
     Moreover, the diameter increase starting point P 21  of the second tapered surface  12  is not located on the one axial side with respect to the position P 23 , on the inner circumferential surface  4   a,  corresponding to the other axial end of the outer circumferential surface  7   a  of the body portion  7 . That is, the diameter increase starting point P 21  of the second tapered surface  12  is not located at a portion, of the inner ring  4 , at which the thickness in the radial direction thereof is small. Accordingly, even though the second tapered surface  12  is formed, the thickness (cross-sectional area) in the radial direction of the other axial end portion of the inner ring  4  can be inhibited from being excessively small, so that the degree of deformation of the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be reduced. 
     Therefore, when the diameter increase starting point P 21  of the second tapered surface  12  is located in the range R 21 , the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  can be effectively inhibited from protruding into the fluid flow passage  4   b.    
     In the present embodiment, the deformation starting point P 22  is located at the point of intersection of the inner circumferential surface  4   a  and a virtual tangent line K which is tangent to the annular groove  6   d  and extends in the radial direction. The diameter increase starting point P 21  of the second tapered surface  12  in the present embodiment is located on the deformation starting point P 22  in the range R 21 . In this case, the diameter increase starting point P 21  of the second tapered surface  12  can be inhibited from being deformed toward the radially inner side due to the external force, and the degree of decrease in the thickness in the radial direction of the other axial end portion of the inner ring  4  can also be reduced as much as possible. Accordingly, the degree of deformation of the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  to the radially inner side can be further reduced. 
     As shown in  FIG.  1   , when the press-fitting portion  6  is press-fitted into the end portion of the joint body  2 , the entire second tapered surface  12  is deformed so as to fall down toward the radially inner side, whereby the second tapered surface  12  in the present embodiment extends straight in the axial direction along the inner circumferential surface  4   a.  Therefore, when the press-fitting portion  6  is press-fitted into the end portion of the joint body  2 , even if the other axial end portion of the inner circumferential surface  4   a  of the inner ring  4  is deformed so as to fall down toward the radially inner side, the other axial end portion does not protrude into the fluid flow passage  4   b.    
     Others 
     The maximum outer diameter portion  5   b  in the outer circumferential surface  5   a  of the bulge portion  5  of the above embodiment is formed over the predetermined length L in the axial direction, but may be formed only at a point in the axial direction. In addition, the press-fitting portion  6  of the above embodiment includes the press-fitting body  6   a,  the primary sealing portion  6   b,  and the secondary sealing portion  6   c,  but it is sufficient that the press-fitting portion  6  includes at least the primary sealing portion  6   b.  In addition, the pipe joint  1  and the inner ring  4  of the present invention can also be applied to the liquid crystal/organic EL field, the medical/pharmaceutical field, automotive-related fields, etc., in addition to a semiconductor manufacturing apparatus. Moreover, only either the first tapered surface  11  on the bulge portion  5  side or the second tapered surface  12  on the press-fitting portion  6  side may be applied to the inner ring  4 . 
     The embodiments disclosed herein are merely illustrative in all aspects and should not be recognized as being restrictive. The scope of the present invention is defined by the scope of the claims rather than the meaning described above, and is intended to include meaning equivalent to the scope of the claims and all modifications within the scope. 
     REFERENCE SIGNS LIST 
       1  pipe joint 
       2  joint body 
       2   d  primary sealing groove 
       2   e  secondary sealing groove 
       3  union nut 
       4  inner ring 
       4   a  inner circumferential surface 
       4   b  fluid flow passage 
       5  bulge portion 
       5   a  outer circumferential surface 
       5   b  maximum outer diameter portion 
       6  press-fitting portion 
       7  body portion 
       7   a  outer circumferential surface 
       8  tube 
       11  first tapered surface (tapered surface) 
       12  second tapered surface (tapered surface) 
     P 11 , P 21  diameter increase starting point 
     P 12 , P 22  deformation starting point 
     P 13 , P 23  position on inner circumferential surface