Patent Publication Number: US-2022213960-A1

Title: Mechanical seal

Description:
TECHNICAL FIELD 
     The present invention relates to a mechanical seal that seals a rotating shaft. 
     BACKGROUND ART 
     A mechanical seal in the related art is configured such that a stationary seal ring which is fixed to a housing and a rotating seal ring which is fixed to a rotating shaft to rotate together with the rotating shaft rotate relative to each other to seal a gap between the housing and the rotating shaft. 
     For example, in the mechanical seal in the related art, the rotating seal ring is fixed to the rotating shaft via a retainer. The holding of the rotating seal ring by the retainer is performed by so-called shrink fitting in which after the rotating seal ring is inserted in a state where the retainer is heated and thermally expanded, the retainer is cooled and shrunk to cause a holding portion, which has an annular shape and protrudes from an inner periphery of the retainer toward an inner diameter side, to be fitted to an outer periphery of the rotating seal ring. Since an inner periphery of the holding portion is crimped to the outer periphery of the rotating seal ring, the sealing performance between the rotating seal ring and the retainer is secured without use of a secondary seal such as an O-ring. 
     In addition, in a case where the rotating seal ring is made of a plastic material such as ceramic, when a large contact pressure of the holding portion which comes into contact with the outer periphery of the rotating seal ring during shrink fitting is locally applied, damage to the rotating seal ring or distortion of a sliding surface is generated, which is a problem. Therefore, in a mechanical seal of Patent Citation 1, a holding portion is in wide contact with an outer periphery of a rotating seal ring in an axial direction, so that the contact pressure is substantially uniformly applied over a contact range. 
     CITATION LIST 
     Patent Literature 
     Patent Citation 1: US 2007/0210526 A (page 3, FIG. 1, and FIG. 5) 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the mechanical seal of Patent Citation 1 has a structure where the holding portion of a retainer is connected to a base end member, to which a bellows is welded and fixed, by an annular connection portion extending from an outer diameter side of the holding portion in the axial direction. The fitting force of the holding portion with respect to the outer periphery of the rotating seal ring is designed by the difference between an inner diameter of the holding portion and an outer diameter of the rotating seal ring before shrink fitting. When the annular connection portion is deformed by the pressure of a sealed fluid during use of the mechanical seal, the holding portion is further displaced from a shrink fitted state to cause the fitting force to become too large. Therefore, not only a sliding surface of the rotating seal ring is deformed, but also the retainer is damaged, which is a problem. 
     The present invention has been made in view of such problems, and an object of the present invention is to provide a mechanical seal in which a sliding surface of a seal ring is not deformed, and a retainer is unlikely to be damaged. 
     Solution to Problem 
     In order to solve the foregoing problems, a mechanical seal according to the present invention is a mechanical seal including: a pair of seal rings that rotate relative to each other; and a retainer that holds one of the seal rings, wherein the retainer includes an annular base portion, an annular holding portion that is externally fitted to an outer periphery of the seal ring, and an annular connection portion that connects the annular base portion and the annular holding portion in an axial direction, wherein an annular space partially surrounded by the annular base portion, the annular connection portion, and the annular holding portion is formed between the outer periphery of the seal ring and an inner periphery of the retainer, and wherein the retainer is provided with a plurality of beams which are disposed in the annular space to connect the annular base portion and the annular holding portion. According to the aforesaid feature of the present invention, since the beams which connect the annular base portion of the retainer and the annular holding portion are formed in the annular space on an inner diameter side of the annular connection portion to increase the structural strength of the annular connection portion, the displacement of the annular holding portion caused by the bending action of the annular connection portion can be restricted. Therefore, during use of the mechanical seal, the influence of the pressure of a sealed fluid on the fitting force of the annular holding portion is suppressed, so that a sliding surface of the seal ring is not deformed and damage to the retainer can be prevented. 
     It may be preferable that the beams are equiangularly arranged in a circumferential direction. According to this preferable configuration, the structural strength of the annular connection portion is uniformly increased in the circumferential direction by the beams that are equiangularly arranged in the circumferential direction. Therefore, the displacement of the annular holding portion can be reliably restricted. 
     It may be preferable that the beams are formed to divide the annular space into a radially inner space and a radially outer space. According to this preferable configuration, the displacement of the annular holding portion can be restricted while the annular connection portion located on a radially outer space of the annular space divided by the beams. Therefore, the fitting force of the annular holding portion can be properly maintained to suppress deformation of the sliding surface of the seal ring. 
     It may be preferable that the beams are made of a material which makes the annular base portion and are integrally formed with the annular base portion. According to this preferable configuration, during shrink fitting, the thermal expansion and shrinkage of the beams can be made equal to the thermal expansion and shrinkage of the annular base portion. Therefore, the fitting force of the annular holding portion can be stabilized. 
     It may be preferable that the annular holding portion extends from the annular connection portion in an inward radial direction, and further extend toward the annular base portion in the axial direction. According to this preferable configuration, a tip of the annular holding portion wraps around a radially inner side of the annular space and is close to the annular base portion, so that the annular space on the radially outer side is disposed close to an annular holding portion side in the axial direction. Therefore, the bending action of the annular connection portion can be sufficiently exerted. 
     It may be preferable that the mechanical seal may further include a bellows that is welded and fixed to the annular base portion. According to this preferable configuration, a base end member to which the bellows is welded and fixed and the retainer can be integrated in structure. Therefore, the structural strength can be increased without forming a joint portion in the retainer. 
     It may be preferable that the retainer may be integrally formed by a three-dimensional fabricating apparatus. According to this preferable configuration, the annular space or the beams formed in the retainer can be simply formed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view illustrating one example of a mechanical seal in an embodiment of the present invention. 
         FIG. 2  is an enlarged cross-sectional view illustrating a retainer and a stationary seal ring in the embodiment. 
         FIG. 3A  is a cross-sectional view taken along line A-A extending along a radial direction in  FIG. 2 , and  FIG. 3B  is a cross-sectional view taken along line B-B extending along a circumferential direction in  FIG. 2 . 
         FIG. 4  is a cross-sectional view illustrating a modification example of the retainer in the embodiment. 
         FIG. 5  is a cross-sectional view illustrating a modification example of the retainer in the embodiment. 
         FIG. 6  is a cross-sectional view illustrating a modification example of the retainer and the stationary seal ring in the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Modes for implementing a mechanical seal according to the present invention will be described below based on an embodiment. 
     Embodiment 
     A mechanical seal according to the embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . Incidentally, a description will be given based on the premise that an inner diameter side of a rotating seal ring and a stationary seal ring forming the mechanical seal is an atmosphere side as a leakage side (i.e., low-pressure side) and an outer diameter side is a sealed fluid side (i.e., high-pressure side).  
     A mechanical seal  1  for a general industrial machine illustrated in  FIG. 1  is an inside mechanical seal that seals a sealed liquid tending to leak from the outer diameter side toward the inner diameter side of a sliding surface, and mainly includes a rotating seal ring  20  having an annular shape as a seal ring that is provided so as to be rotatable together with a rotating shaft  2  and a sleeve  3  fixed to the rotating shaft  2 , and a stationary seal ring  10  having an annular shape as a seal ring that is provided on a seal cover  5  fixed to a housing  4  of a mounted apparatus so as to not be rotatable but be movable in an axial direction. The stationary seal ring  10  is biased in the axial direction by a bellows  6 , so that a sliding surface  10   a  of the stationary seal ring  10  and a sliding surface  20   a  of the rotating seal ring  20  slide in close contact with each other. Incidentally, one end in the axial direction of the bellows  6  is welded and fixed to a retainer  11  made of metal and holding the stationary seal ring  10 , and the other end in the axial direction is welded and fixed to a collar  12  made of metal and integrally fixed to the seal cover  5  with a bolt  50 . 
     The stationary seal ring  10  and the rotating seal ring  20  are made of, representatively, SiC (as an example of hard material) or a combination of SiC and carbon (as an example of soft material), but are not limited thereto, and a sliding material can be applied as long as the sliding material is used as a sliding material for a mechanical seal. 
     Incidentally, materials consisting of different components and compositions of two or more phases, for example, SiC in which graphite particles are dispersed, reaction-sintered SiC consisting of SiC and Si, SiC—TiC, SiC—TiN, and the like including a sintered body in which boron, aluminum, carbon, or the like is used as a sintering additive can be used as the SiC. Resin molded carbon, sintered carbon, and the like including carbon in which a carbonaceous material and a graphite material are mixed as the carbon. In addition, in addition to the above sliding materials, metallic materials, resin materials, surface modifying materials (coating materials), composite materials, or the like can also be applied. Further incidentally, when a highly corrosive fluid is used as the sealed fluid, a highly corrosion-resistant material such as a nickel-based superalloy can also be applied. 
     As illustrated in  FIG. 1 , the rotating seal ring  20  is formed in a substantially L shape in a cross-sectional view, and is inserted into an inner periphery of a retainer  21  with an O-ring  22  interposed therebetween, the retainer  21  having a substantially cylindrical shape and being integrally fixed to the sleeve  3  with a bolt  30 , so that the rotating seal ring  20  is held. Incidentally, the O-ring  22  functions as a secondary seal to secure the sealing performance between the rotating seal ring  20  and the retainer  21 . In addition, a locking pin  23  extending from the retainer  21  in the axial direction is inserted into a recessed portion  20   b  formed on an opposite side in the axial direction of the rotating seal ring  20  from the sliding surface  20   a , so that the rotating seal ring  20  can rotate together with the rotating shaft  2 . 
     As illustrated in  FIG. 2 , the stationary seal ring  10  is formed in a substantially rectangular shape in a cross-sectional view, and an annular holding portion  11   c  of the retainer  11  is fitted to a substantially central portion in the axial direction of an outer peripheral surface  10   c  in a state where the outer diameter side of a back surface  10   b  on an opposite side in the axial direction of the stationary seal ring  10  from the sliding surface  10   a  is in contact with an inner surface  11   d  of the retainer  11  having a substantially cylindrical shape in the axial direction, so that the stationary seal ring  10  is held. The holding of the stationary seal ring  10  by the retainer  11  is performed, for example, by so-called shrink fitting in which the stationary seal ring  10  is inserted into the retainer  11  that is heated and thermally expanded, and in a state where the back surface  10   b  is in contact with the inner surface  11   d  of the retainer  11  in the axial direction, the retainer  11  is cooled and shrunk to cause the annular holding portion  11   c  to be fitted to the outer peripheral surface  10   c  of the stationary seal ring  10 . Accordingly, an inner peripheral surface  11   e  of the annular holding portion  11   c  is crimped to the outer peripheral surface  10   c  of the stationary seal ring  10 , so that the sealing performance between the stationary seal ring  10  and the retainer  11  is secured without use of a secondary seal such as an O-ring. In addition, since the back surface  10   b  of the stationary seal ring  10  and the inner surface  11   d  of the retainer  11  are in contact with each other in the axial direction, the position in the axial direction of the stationary seal ring  10  with respect to the retainer  11  is stable during shrink fitting or use. Incidentally, in  FIG. 2 , for convenience of description, the illustration of the bellows  6  which is welded and fixed to the retainer  11  is omitted. 
     Next, the structure of the retainer  11  will be described in detail. As illustrated in  FIGS. 2 and 3 , the retainer  11  has a substantially L shape in a cross-sectional view, which includes a base portion  11   a  having an annular shape, an annular connection portion  11   b , and the annular holding portion  11   c . An annular space S surrounded by the base portion  11   a , the annular connection portion  11   b , and the annular holding portion  11   c  is formed on an inner periphery of the retainer  11 . A plurality of beams  110  which connect the base portion  11   a  and the annular holding portion  11   c  in the axial direction are evenly disposed in the annular space S in a circumferential direction (particularly, refer to  FIG. 3 ). Incidentally, the retainer  11  is integrally made of the same material by a three-dimensional fabricating apparatus, for example, a 3D printer. Further incidentally, the annular space S is a space that is substantially closed in a state where the stationary seal ring  10  is held by the retainer  11 . 
     The base portion  11   a  includes the inner surface  11   d , with which the back surface  10   b  of the stationary seal ring  10  is in contact, on one end side in the axial direction, an annular extending portion  11   f , which extends in the axial direction, on the outer diameter side of the inner surface  11   d , and a fixed portion  11   g , to which one end in the axial direction of the bellows  6  is welded and fixed, on the other end side in the axial direction. Incidentally, a tapered surface  11   h  which is inclined toward an outer diameter direction is formed on one end side in the axial direction of an inner periphery of the annular extending portion  11   f , so that the annular extending portion  11   f  has a pentagonal shape in a cross-sectional view. 
     The annular connection portion  11   b  extends from one end in the axial direction of the annular extending portion  11   f  of the base portion  11   a  in the axial direction. Incidentally, the annular connection portion  11   b  has a smaller plate thickness than the annular extending portion  11   f , and easily exerts a bending action during shrink fitting or a bending action by the pressure of the sealed fluid during use of the mechanical seal.  
     The annular holding portion  11   c  extends to the inner diameter side from a free end portion that is one end portion in the axial direction of the annular connection portion  11   b , and then bends to a base portion  11   a  side to extend in the axial direction, so that the annular holding portion  11   c  has a substantially L shape in a cross-sectional view. Incidentally, a tapered surface  11   k , which is inclined toward an inner diameter direction to be substantially parallel to the tapered surface  11   h  of the annular extending portion  11   f , is formed at a tip on the base portion  11   a  side of the annular holding portion  11   c . In addition, an inner surface  11   m , which extends from an inner diameter end of the tapered surface ilk toward the inner diameter direction and is orthogonal to the inner peripheral surface lie of the annular holding portion  11   c , is formed at the tip on the base portion  11   a  side of the annular holding portion  11   c.    
     The beam  110  extends in the axial direction to connect a virtual tapered surface, which is obtained by extending the tapered surface ilk at the tip of the annular holding portion  11   c  in the circumferential direction, and a virtual tapered surface obtained by extending the tapered surface  11   h  of the annular extending portion  11   f  of the base portion  11   a  in the circumferential direction. Specifically, as illustrated in  FIG. 3A , the beam  110  is formed as a columnar body having a substantially rectangular shape in a cross-sectional view, which is formed by a surface  110   a  on an inner peripheral side, a surface  110   d  on an outer peripheral side, and two side surfaces  110   b  and  110   c  extending in a radial direction. Incidentally, the surface  110   a  on the inner peripheral side of the beam  110  is formed as a flat surface extending to the base portion  11   a  side in the axial direction from an inner diameter end of the virtual tapered surface, which is obtained by extending the tapered surface  11   k  in the circumferential direction, toward an inner diameter end of the virtual tapered surface obtained by extending the tapered surface  11   h  in the circumferential direction. In addition, the surface  110   d  on the outer peripheral side of the beam  110  is formed as an L-shaped bent surface that extends to the base portion  11   a  side in the axial direction from an outer diameter end of the virtual tapered surface, which is obtained by extending the tapered surface  11   k  in the circumferential direction, and then bends to the outer diameter side to extend toward an outer diameter end of the virtual tapered surface obtained by extending the tapered surface  11   h  in the circumferential direction. In addition, the surfaces  110   a  and  110   d  of the beam  110  on inner and outer sides in the radial direction may be curved in the circumferential direction. 
     In addition, a first annular space S 1  surrounded by the annular connection portion  11   b , the annular holding portion  11   c , and the surface  110   d  on the outer peripheral side of the beam  110  is formed on the outer diameter side of the beam  110 , namely, inside the retainer  11 . In addition, a second annular space S 2  surrounded by the base portion  11   a , the inner surface  11   m  of the annular holding portion  11   c , and the surface  110   a  on the inner peripheral side of the beam  110  is formed on the inner diameter side of the beam  110 , namely, between the beam  110  and the outer peripheral surface  10   c  of the stationary seal ring  10  held on the inner diameter side of the retainer  11 . In addition, the first annular space S 1  and the second annular space S 2  communicate with each other through communication holes  111  formed between the beams  110  that are evenly disposed in the circumferential direction. In other words, the annular space S is separated into the first annular space S 1  and the second annular space S 2  on the inner and outer sides in the radial direction by the plurality of beams  110 . Incidentally, the first annular space S 1  and the second annular space S 2  are formed to have substantially the same length in the axial direction (particularly, refer to  FIG. 2 ). Further incidentally, the ratio of the lengths of the beam  110  and the communication hole  111  in the circumferential direction is in the range of 2:1 to 1:2, preferably 1:1, and the lengths are substantially the same in the present embodiment (particularly, refer to  FIG. 3 ). 
     Accordingly, since the beams  110  which connect the annular extending portion  11   f  of the base portion  11   a  of the retainer  11  and the annular holding portion  11   c  are formed in the annular space S on the inner diameter side of the annular connection portion  11   b  to increase the structural strength of the annular connection portion  11   b , the displacement of the annular holding portion  11   c  caused by the bending action of the annular connection portion  11   b  can be restricted. Therefore, during use of the mechanical seal  1 , the influence of the pressure of the sealed fluid on the fitting force of the annular holding portion  11   c  is suppressed, so that the sliding surface  10   a  of the stationary seal ring  10  is not deformed and damage to the retainer  11  can be prevented. In addition, since the beams  110  can restrict the displacement of the annular holding portion  11   c  without increasing the plate thickness of the annular connection portion  11   b , the fitting force of the annular holding portion  11   c  with respect to the outer peripheral surface  10   c  of the stationary seal ring  10  is properly, easily maintained, and crack of the stationary seal ring  10 , distortion of the sliding surface  10   a , or the like can be prevented. 
     In addition, since the structural strength of the annular connection portion  11   b  is substantially uniformly increased in the circumferential direction by the beams  110  that are evenly disposed in the circumferential direction, the displacement of the annular holding portion  11   c  can be reliably restricted. 
     In addition, since the annular space S formed on the inner periphery of the retainer  11  is separated into the first annular space S 1  and the second annular space S 2  on the inner and outer sides in the radial direction by the beams  110 , the annular connection portion  11   b  which is located on the outer diameter side of the first annular space S 1  separated on the outer diameter side by the beams  110  is easily deformed particularly during shrink fitting, and the displacement of the annular holding portion  11   c  can be restricted by the beams  110  while the fitting force of the annular holding portion  11   c  generated by the bending action of the annular connection portion  11   b  is properly maintained. Therefore, during use of the mechanical seal  1 , the fitting force of the annular holding portion  11   c  for the pressure of the sealed fluid can be properly maintained to suppress deformation of the sliding surface  10   a  of the stationary seal ring  10 . 
     In addition, since the beam  110  is integrally made of the same material as that of the base portion  11   a , the annular connection portion  11   b , and the annular holding portion  11   c , during shrink fitting, the thermal expansion and shrinkage of the beam  110  can be made equal to the thermal expansion and shrinkage of the retainer  11 . Therefore, the fitting force of the annular holding portion  11   c  with respect to the outer peripheral surface  10   c  of the stationary seal ring  10  can be stabilized. 
     In addition, the annular holding portion  11   c  extends inward from the annular connection portion  11   b  in the radial direction, and further extends toward the base portion  11   a  in the axial direction to wrap around the annular space S, particularly, an inner side in the radial direction of the first annular space S 1 , so that the tapered surface  11   k  at the tip of the annular holding portion  11   c  is close to the tapered surface  11   h  of the annular extending portion  11   f  in the axial direction. Accordingly, the beams  110  and the annular connection portion  11   b  can be separated from each other in the radial direction with the first annular space S 1  interposed therebetween, and the first annular space S 1  can be disposed close to an annular holding portion  11   c  side in the axial direction, namely, a free end portion side of the annular connection portion  11   b . Therefore, the bending action of the annular connection portion  11   b  can be sufficiently exerted. Namely, since the beams  110  are formed to be separated from the free end portion of the annular connection portion  11   b  in the radial direction and the axial direction, the beams  110  do not disturb the bending action of the annular connection portion  11   b , which contributes to the fitting force of the annular holding portion  11   c  during shrink fitting, and during use of the mechanical seal  1 , the influence of the pressure of the sealed fluid on the fitting force of the annular holding portion  11   c  can be suppressed. 
     In addition, since both ends in the axial direction of the beam  110  connect the virtual tapered surface, which is obtained by extending the tapered surface  11   h  of the annular extending portion  11   f  of the base portion  11   a  in the circumferential direction, and the virtual tapered surface obtained by extending the tapered surface  11   k  at the tip of the annular holding portion  11   c  in the circumferential direction, the cross-sectional areas of both ends in the axial direction of the beam  110  can be formed to be large, thus to increase the strength of the beam  110 . 
     In addition, since the beam  110  has an inclined structure as described above, a part of a radial stress component caused by the pressure of the sealed fluid during shrink fitting or use of the mechanical seal  1  is dispersed in the axial direction. Therefore, the fitting force of the annular holding portion  11   c  is unlikely to become too large, and damage to the stationary seal ring  10  or the retainer  11  can be effectively prevented. 
     In addition, since the base portion  11   a  of the retainer  11  has an integral structure to also serve as a base end member to which the bellows  6  is welded and fixed, the structural strength can be increased without forming a joint portion in the retainer  11 . 
     In addition, since the retainer  11  is integrally formed by a three-dimensional fabricating apparatus such as a 3D printer, the first annular space S 1  or the beams  110  formed inside the retainer  11  can be simply formed.  
     In addition, since the retainer  11  can properly maintain the fitting force of the annular holding portion  11   c  with respect to the outer peripheral surface  10   c  of the stationary seal ring  10 , a highly corrosion-resistant material such as a nickel-based superalloy can be applied to the stationary seal ring  10  of the mechanical seal  1 . 
     The embodiment of the present invention has been described above with reference to the drawings; however, the specific configuration is not limited to the embodiment, and the present invention also includes changes or additions that are made without departing from the concept of the present invention. 
     For example, in the embodiment, the configuration where the beams  110  are formed in the retainer  11  holding the stationary seal ring  10  has been described; however, the present invention is not limited thereto, the beams may be formed in the retainer  21  holding the rotating seal ring  20 , or the beams may be formed in both the retainers  11  and  21  holding the stationary seal ring  10  and the rotating seal ring  20 . 
     In addition, the beam and the communication hole are not limited to being formed to have substantially the same length in the circumferential direction, and for example, as illustrated in a modification example of  FIG. 4 , a communication hole  211  may be formed as an elongated hole which is longer than a beam  210  in the circumferential direction. In addition, the present invention is not limited to the configuration where the plural of beams are provided, and one beam which has a C shape is long in the circumferential direction may be provided. 
     In addition, in the embodiment, the configuration where the beam  110  extends in the axial direction to connect the virtual tapered surface, which is obtained by extending the tapered surface  11   k  at the tip of the annular holding portion  11   c  in the circumferential direction, and the virtual tapered surface obtained by extending the tapered surface  11   h  of the annular extending portion  11   f  of the base portion  11   a  in the circumferential direction has been described; however, the present invention is not limited thereto, and for example, as illustrated in a modification example of  FIG. 5 , a beam  310  may be formed to connect the base portion and the inner surface of the annular holding portion, the inner surface being orthogonal to the axial direction. Incidentally, the annular extending portion  11   f  may not be formed in the base portion  11   a.    
     In addition, the shape of the beam may be freely configured as long as the beam connects the base portion  11   a  and the annular holding portion  11   c . In addition, the beam may be formed in a circular shape in a cross-sectional view or in a polygonal shape in a cross-sectional view. 
     In addition, in the embodiment, the configuration where the annular space S formed on the inner periphery of the retainer  11  is separated into the first annular space S 1  and the second annular space S 2  on the inner and outer sides in the radial direction by the beams  110 , and the annular connection portion  11   b  is located on the outer diameter side of the first annular space S 1  has been described; however, the present invention is not limited thereto, and the first annular space S 1  may not be formed on the outer diameter side of the beams, and the beams may be integrally formed along a surface on the inner diameter side of the annular connection portion  11   b . In addition, a part of the beams, for example, a part on the base portion  11   a  side may be integrally and partially formed on the surface on the inner diameter side of the annular connection portion  11   b.    
     In addition, the beam may be made of a material different from that of the base portion  11   a , the annular connection portion  11   b , and the annular holding portion  11   c  of the retainer  11 , and both ends of the beam may be welded and fixed to the base portion  11   a  and the annular holding portion  11   c , respectively.  
     In addition, the annular holding portion  11   c  may not be formed to wrap around the inner side in the radial direction of the first annular space S 1 . 
     In addition, as illustrated in a modification example of  FIG. 6 , a recessed portion  410   a  provided in an outer peripheral surface of a stationary seal ring  410  may form the second annular space S 2  between the stationary seal ring  410  and an inner periphery of a retainer  411 . 
     In addition, the back surface  10   b  of the stationary seal ring  10  may not be in contact with the inner surface  11   d  of the base portion  11   a  of the retainer  11 . In this case, the annular holding portion  11   c  of the retainer  11  may be fitted to a recessed groove having an annular shape and formed in the outer peripheral surface  10   c  of the stationary seal ring  10  such that the positional offset of the stationary seal ring  10  with respect to the retainer  11  in the axial direction can be prevented. 
     In addition, the base portion of the retainer  11  and a base end member to which the bellows  6  is welded and fixed may be formed separately. 
     In addition, in the embodiment, the configuration where the stationary seal ring  10  is biased in the axial direction by the biasing force of the bellows  6  has been described; however, the present invention is not limited thereto, and biasing force may be applied by a spring that is disposed separately. 
     REFERENCE SIGNS LIST 
       1  Mechanical seal 
       2  Rotating shaft 
       3  Sleeve 
       4  Housing 
       5  Seal cover 
       6  Bellows 
       10  Stationary seal ring (seal ring) 
       10   a  Sliding surface 
       11  Retainer 
       11   a  Annular base portion 
       11   b  Annular connection portion 
       11   c  Annular holding portion 
       11   f  Annular extending portion 
       11   h ,  11   k  Tapered surface 
       12  Collar 
       20  Rotating seal ring (seal ring) 
       20   a  Sliding surface 
       21  Retainer 
       110  Beam 
       111  Communication hole 
       210  Beam 
       211  Communication hole 
       310  Beam 
       410  Stationary seal ring 
       410   a  Recessed portion 
       411  Retainer 
     S Annular space 
     S 1  First annular space (radially outer space) 
     S 2  Second annular space (radially inner space)