Abstract:
A shaft seal mechanism ( 11 ) that blocks a fluid (G) flowing within a ring-shaped space ( 14 ) is equipped with: a ring-shaped seal housing ( 21 ) disposed on a fixed section ( 12 ); a plurality of thin-plate seal pieces ( 22 ) that are secured to the seal housing ( 21 ), are in sliding contact with a rotating shaft ( 13 ), and are layered in a ring shape; a ring-shaped high-pressure-side plate ( 25 ) that forms a high-pressure-side gap (δH) between itself and the seal housing ( 21 ); a ring-shaped low-pressure-side plate ( 26 ) that forms a low-pressure-side gap (δL) between the seal housing ( 21 ) and the thin-plate seal pieces ( 22 ); stepped sections ( 31, 32 ) that are formed on side edge sections ( 22   c,    22   d ) of the thin-plate seal pieces ( 22 ); and locking sections ( 25   b,    26   b ) that lock the stepped sections ( 31, 32 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a shaft seal mechanism that is disposed in the vicinity of a rotating shaft of a steam turbine or a gas turbine and reduces a leakage of a fluid from a high pressure side to a low pressure side. 
         [0002]    BACKGROUND ART 
         [0003]    Conventionally, a shaft seal mechanism for reducing a leakage of a fluid from a high pressure side to a low pressure side is disposed in the vicinity of a rotating shaft of a steam turbine or a gas turbine, in order to suppress a loss of driving force. Such a shaft seal mechanism has a ring-shaped seal structure in which thin-plate seal pieces having flat plate shapes with their width dimensions being in the rotating shaft direction are arranged into multiple layers in the circumferential direction of the rotating shaft. Outer-circumferential-side proximal end sections of the thin-plate seal pieces are fixed to a ring-shaped seal housing; on the other hand, inner-circumferential-side distal end sections of the thin-plate seal pieces are in sliding contact with the outer circumferential surface of the rotating shaft at a predetermined preload. In the shaft seal mechanism having this configuration, the surrounding space of the rotating shaft can be divided into a high-pressure-side region and a low-pressure-side region with the boundary formed by a large number of the thin-plate seal pieces arranged into a ring shape outward in the radial direction of the rotating shaft. 
         [0004]    While the rotation of the rotating shaft is stopping, the inner-circumferential-side distal end sections of the thin-plate seal pieces are into contact with the outer circumferential surface of the rotating shaft at the predetermined preload. On the other hand, while the rotating shaft is rotating, the thin-plate seal pieces are bent by pressure difference due to relative positional shift in pressure distribution between the top and bottom surfaces of the thin-plate seal pieces and by dynamic pressure effect of the fluid generated by the rotation of the rotating shaft, and accordingly, the inner-circumferential-side distal end sections of the thin-plate seal pieces are lifted up from the outer circumferential surface of the rotating shaft into a noncontact state. This configuration prevents abrasion of and heat generation in the thin-plate seal pieces and the rotating shaft. The bottom surfaces of the thin-plate seal pieces refer to surfaces facing the rotating shaft, and the top surfaces thereof refer to surfaces opposite to the bottom surfaces. 
         [0005]    Such a conventional shaft seal mechanism is disclosed, for example, in Patent Document 1 listed below. 
       CITATION LIST 
     Patent Document 
       [0006]    Patent Document 1: US Unexamined Patent Application Publication No. 2013/0154199A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In this shaft seal mechanism, gaps of predetermined sizes are provided on both low pressure and high pressure sides of the thin-plate seal pieces. The sizes of the low-pressure-side gap and the high-pressure-side gap are adjusted to generate the pressure difference in the thin-plate seal pieces and thus to provide lifting-up force to the thin-plate seal pieces. That is, control of the sizes of the low-pressure-side gap and the high-pressure-side gap is highly important to lift up the thin-plate seal pieces. 
         [0008]    Unfortunately, the gap sizes are minute and defined by the thin-plate seal pieces and multiple support members disposed in the vicinity thereof. As a result, even if the gap sizes are preset correctly, a machining error, an assembling error, or the like of the thin-plate seal pieces and the support members may cause the actual gap sizes in assembly not to be appropriate to provide stable lifting-up force, in some cases. 
         [0009]    At this time, the actual gap sizes smaller than appropriate gap sizes disturb the pressure distribution and pressure difference and may thus apply pressing force in a direction opposite to the applying direction of the lifting-up force to the thin-plate seal pieces in some cases. If the pressing force pressing the inner-circumferential-side distal end sections is applied to the thin-plate seal pieces, the inner-circumferential-side distal end sections come into contact with the rotating shaft and may have abrasion. 
         [0010]    To solve the above problem, an object of the present invention is to provide a shaft seal mechanism that, even if pressing force is applied to thin-plate seal pieces, can suppress deformation due to the pressing force and prevent abrasion due to contact with a rotating shaft in the thin-plate seal pieces. 
       Solution to Problem 
       [0011]    A shaft seal mechanism according to a first invention that solves the above problem, is disposed in a ring-shaped space defined between a fixed section and a rotating shaft to divide the ring-shaped space into a high-pressure-side region and a low-pressure-side region and to block a fluid flowing from the high-pressure-side region to the low-pressure-side region in a rotating shaft direction within the ring-shaped space, the shaft seal mechanism including: a ring-shaped seal housing being disposed on an inner circumferential section of the fixed section; multiple thin-plate seal pieces including outer-circumferential-side proximal end sections fixed to the seal housing and inner-circumferential-side distal end sections being free ends forming acute angles with an outer circumferential surface of the rotating shaft, the thin-plate seal pieces having width dimensions in the rotating shaft direction, and the thin-plate seal pieces being layered in a ring shape in a circumferential direction of the rotating shaft; a ring-shaped high-pressure-side plate being disposed adjacent to high-pressure-side side edge sections, facing the high-pressure-side region, of the thin-plate seal pieces so that a high-pressure-side gap is defined between the high-pressure-side plate and the seal housing in the rotating shaft direction; a ring-shaped low-pressure-side plate being held between low-pressure-side side edge sections, facing the low-pressure-side region, of the thin-plate seal pieces and the seal housing so that a low-pressure-side gap is defined between the low-pressure-side side edge sections and the seal housing in the rotating shaft direction; high-pressure-side stepped sections being formed on the high-pressure-side side edge sections; low-pressure-side stepped sections being formed on the low-pressure-side side edge sections; a high-pressure-side locking section being formed on the high-pressure-side plate and locking the high-pressure-side stepped sections from an inside in a radial direction of the rotating shaft; and a low-pressure-side locking section being formed on the low-pressure-side plate and locking the low-pressure-side stepped sections from the inside in the radial direction of the rotating shaft. 
         [0012]    In a shaft seal mechanism according to a second invention that solves the above problem, the high-pressure-side stepped sections each include an inclined end surface engaged with an inclined surface of the high-pressure-side locking section in the radial direction of the rotating shaft; and the low-pressure-side stepped sections each include an inclined end surface engaged with an inclined surface of the low-pressure-side locking section in the radial direction of the rotating shaft. 
         [0013]    A shaft seal mechanism according to a third invention that solves the above problem, is disposed in a ring-shaped space defined between a fixed section and a rotating shaft to divide the ring-shaped space into a high-pressure-side region and a low-pressure-side region and to block a fluid flowing from the high-pressure-side region to the low-pressure-side region in a rotating shaft direction within the ring-shaped space, the shaft seal mechanism including: a ring-shaped seal housing being disposed on an inner circumferential section of the fixed section; multiple thin-plate seal pieces including outer-circumferential-side proximal end sections fixed to the seal housing and inner-circumferential-side distal end sections being free ends forming acute angles with an outer circumferential surface of the rotating shaft, the thin-plate seal pieces having width dimensions in the rotating shaft direction, and the thin-plate seal pieces being layered in a ring shape in a circumferential direction of the rotating shaft so that a low-pressure-side gap is defined between low-pressure-side side edge sections facing the low-pressure-side region and the seal housing in the rotating shaft direction; low-pressure-side stepped sections being formed on the low-pressure-side side edge sections; and a low-pressure-side locking section being formed on the seal housing and locking the low-pressure-side stepped sections from the inside in a radial direction of the rotating shaft. 
         [0014]    In a shaft seal mechanism according to a fourth invention that solves the above problem, the shaft seal mechanism further includes a ring-shaped low-pressure-side plate being held between the low-pressure-side side edge sections and the seal housing so that the low-pressure-side gap is defined between the low-pressure-side side edge sections and the seal housing; and the low-pressure-side locking section locks the low-pressure-side stepped sections inward in the radial direction of the rotating shaft with respect to an inner-circumferential-side distal end section of the low-pressure-side plate. 
         [0015]    In a shaft seal mechanism according to fifth invention that solves the above problem, the low-pressure-side stepped sections each include an inclined end surface engaged with an inclined surface of the low-pressure-side locking section in the radial direction of the rotating shaft. 
       Advantageous Effects of Invention 
       [0016]    The shaft seal mechanism according to the present invention locks the thin-plate seal pieces from the inside in the radial direction of the rotating shaft and accordingly, even if pressing force is applied to the thin-plate seal pieces, can suppress deformation due to the pressing force and prevent abrasion due to contact with the rotating shaft in the thin-plate seal pieces. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a schematic configuration diagram of a shaft seal mechanism according to the present invention. 
           [0018]      FIG. 2  is an axial cross-sectional view of the shaft seal mechanism according to the present invention. 
           [0019]      FIG. 3  is an exploded view of a support structure of thin-plate seal pieces. 
           [0020]      FIG. 4  is a detailed view of a shaft seal mechanism according to Example 1 and is a front view of a thin-plate seal piece. 
           [0021]      FIG. 5  is a detailed view of a shaft seal mechanism according to Example 2 and is a front view of a thin-plate seal piece. 
           [0022]      FIG. 6  is a detailed view of a shaft seal mechanism according to Example 3 and is a front view of a thin-plate seal piece. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    A shaft seal mechanism according to the present invention will be described in detail with reference to the drawings. 
       EXAMPLES 
       [0024]    With reference to  FIG. 1 , a shaft seal mechanism  11  according to the present invention is applied to, for example, a steam turbine or a gas turbine and is disposed in a ring-shaped space  14  defined between a fixed section (stationary section)  12  and a rotating shaft  13  of a casing, a vane, or the like. 
         [0025]    Specifically, with reference to  FIGS. 1 and 2 , a seal housing  21  being an outer shell of the shaft seal mechanism  11  is disposed on an inner circumferential section of the fixed section  12  in the circumferential direction of the rotating shaft  13  and has a ring shape. A ring-shaped groove  21   a  is formed in an inner circumferential section of the seal housing  21 . In the ring-shaped groove  21   a , a large number of thin-plate seal pieces  22  are arranged in the circumferential direction of the rotating shaft  13 . 
         [0026]    Outer-circumferential-side proximal end sections  22   a  of the thin-plate seal pieces  22  are fixed to the ring-shaped groove  21   a ; on the other hand, inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  are in sliding contact with the outer circumferential surface of the rotating shaft  13  at a predetermined preload. Here, the thin-plate seal pieces  22  are arranged in such a manner that the inner-circumferential-side distal end sections  22   b  being free ends are inclined in the rotational direction with respect to the outer circumferential surface of the rotating shaft  13  and form acute angles with the outer circumferential surface. Bottom surfaces of the thin-plate seal pieces  22  supported in an inclined manner refer to surfaces facing the rotating shaft  13 , and top surfaces thereof refer to surfaces opposite to the bottom surfaces. 
         [0027]    A fluid G, such as steam and combustion gas, flows from a high pressure side to a low pressure side in the axial direction of the rotating time  13  in the ring-shaped space  14  defined between the fixed section  12  and the rotating shaft  13 . In response to this, the shaft seal mechanism  11  has a ring-shaped seal structure in which the thin-plate seal pieces  22  are arranged into multiple layers in the circumferential direction of the rotating shaft  13 . The ring-shaped space  14  is divided into a high-pressure-side region being an upstream side in the fluid flowing direction and a low-pressure-side region being an downstream side in the fluid flowing direction with the boundary formed by a large number of the thin-plate seal pieces  22  arranged into a ring shape. This configuration reduces a leakage of the fluid G from the high-pressure-side region to the low-pressure-side region. 
         [0028]    With reference to  FIGS. 2 and 3 , each of the thin-plate seal pieces  22  is made from a flexible material having flexibility and is formed into a flat plate shape with its width dimension being in the axial direction of the rotating shaft  13 . Specifically, the thin-plate seal piece  22  is formed into a T shape in which the plate width on the proximal end side (the outer-circumferential-side proximal end section  22   a ) is wider than the plate width on the distal end side (the inner-circumferential-side distal end section  22   b ) and is thinned so as to exhibit flexibility. The thin-plate seal pieces  22  are arranged into a ring shape while having minute gaps of a certain size therebetween in the circumferential direction of the rotating shaft  13 . 
         [0029]    The proximal end sides of the thin-plate seal pieces  22  are held between a pair of right and left retainers  23 ,  24  for maintaining the ring-shaped arrangement of the thin-plate seal pieces  22  so as to be enclosed from both sides in the plate width direction. The retainers  23 ,  24  are fitted into the ring-shaped groove  21   a  of the seal housing  21 . 
         [0030]    A high-pressure-side plate  25  and a low-pressure-side plate  26  are disposed respectively on the high pressure side and the low pressure side of the thin-plate seal pieces  22  and function as guide plates for the fluid G. 
         [0031]    Specifically, the high-pressure-side plate  25  having a ring shape is disposed on left side sections (side sections positioned at the left in  FIGS. 2 and 3  on paper), facing the high-pressure-side region, of the thin-plate seal pieces  22 . This high-pressure-side plate  25  is disposed adjacent to high-pressure-side side edge sections  22   c , facing the high-pressure-side region, of the thin-plate seal pieces  22  and is held between the high-pressure-side side edge sections  22   c  and the retainer  23 . 
         [0032]    Here, an inner-circumferential-side distal end section  25   a  of the high-pressure-side plate  25  extends to an opening edge section of the ring-shaped groove  21   a  but does not reach the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22 . Moreover, a high-pressure-side gap δH of a certain size is defined between a high-pressure-side side surface  21   b , facing the high-pressure-side region, of the ring-shaped groove  21   a  and the high-pressure-side plate  25  in the axial direction of the rotating shaft  13  (the fluid flowing direction, the plate width direction of the seal pieces). 
         [0033]    The high-pressure-side plate  25  provided in this way allows the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  to be positioned inward in the radial direction of the rotating shaft  13  with respect to the inner-circumferential-side distal end section  25   a  of the high-pressure-side plate  25 . Accordingly the fluid G flows in from the high-pressure-side region through the distal end side of the thin-plate seal pieces  22 . 
         [0034]    On the other hand, the low-pressure-side plate  26  having a ring shape is disposed on right side sections (side sections positioned at the right in  FIGS. 2 and 3  on paper), facing the low-pressure-side region, of the thin-plate seal pieces  22 . This low-pressure-side plate  26  is disposed adjacent to low-pressure-side side edge sections  22   d , facing the low-pressure-side region, of the thin-plate seal pieces  22  and is held between the low-pressure-side side edge sections  22   d , and the retainer  24  and a low-pressure-side side surface  21   c , facing the low-pressure-side region, of the ring-shaped groove  21   a.    
         [0035]    IIere, an inner-circumferential-side distal end section  26   a  of the low-pressure-side plate  26  does not reach an opening edge section of the ring-shaped groove  21   a  and the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  and is positioned outward in the radial direction of the rotating shaft  13  with respect to the inner-circumferential-side distal end section  25   a  of the high-pressure-side plate  25 . In other words, the low-pressure-side plate  26  is shorter than the high-pressure-side plate  25 . Moreover, a low-pressure-side gap δL of a certain size is defined between the low-pressure-side side surface  21   c  of the ring-shaped groove  21   a  and the low-pressure-side side edge sections  22   d  in the axial direction of the rotating shaft  13 . 
         [0036]    The low-pressure-side plate  26  provided in this way allows the low-pressure-side gap δL to be defined between the low-pressure-side side surface  21   c  and the low-pressure-side side edge sections  22   d . The low-pressure-side gap δL is defined by the thickness of the low-pressure-side plate  26 , and the size of the low-pressure-side gap δL can thus be set by adjusting the thickness of the low-pressure-side plate  26 . 
         [0037]    The pressure distribution of the fluid G generated in the top and bottom surfaces of the thin-plate seal pieces  22  can be set in accordance with the sizes of the high-pressure-side gap δH and the low-pressure-side gap δL. In addition, the magnitude of the pressure difference (lifting-up force) due to relative positional shift in the pressure distribution between the top and bottom surfaces of the thin-plate seal pieces  22  can be set in accordance with the quantitative relationship between the size of the high-pressure-side gap δH and the size of the low-pressure-side gap δL. 
         [0038]    In the shaft seal mechanism  11  according to the present invention, the radial gap size between the inner-circumferential-side distal end section  26   a  of the low-pressure-side plate  26  and the outer circumferential surface of the rotating shaft  13  is greater than the radial gap size between the inner-circumferential-side distal end section  25   a  of the high-pressure-side plate  25  and the outer circumferential surface of the rotating shaft  13 , in order to yield stable lifting-up force. 
         [0039]    With this configuration, while the rotation of the rotating shaft  13  is stopping, the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  are in contact with the outer circumferential surface of the rotating shaft  13  at the predetermined preload. On the other hand, while the rotating shaft  13  is rotating, lifting-up force is applied to the thin-plate seal pieces  22  by the pressure difference due to relative positional shift in the pressure distribution between the top and bottom surfaces of the thin-plate sheet pieces  22  and by dynamic pressure effect of the fluid G generated by the rotation of the rotating shaft  13 . This force bends the thin-plate seal pieces  22 , and accordingly, the inner-circumferential-side distal end sections  22   b  thereof are lifted up from the outer circumferential surface of the rotating shaft  13  into a noncontact state, resulting in prevention of abrasion of and heat generation in the rotating shaft  13  and the thin-plate seal pieces  22 . At the same time, the thin-plate seal pieces  22  in a noncontact state with the rotating shaft  13  reduce a leakage of the fluid G flowing from the high-pressure-side region to the low-pressure-side region. 
         [0040]    With reference to  FIG. 4 , a stepped section (high-pressure-side stepped section)  31  and a stepped section (low-pressure-side stepped section)  32  are respectively formed on the high-pressure-side side edge section  22   c  and the low-pressure-side side edge section  22   d  of each of the thin-plate seal pieces  22 . 
         [0041]    These stepped sections  31 ,  32  are disposed in radial intermediate sections (longitudinal intermediate sections) of the side edge sections  22   c ,  22   d  and are shaped into such steps that a section, inward from the stepped section  31  in the radial direction, of the thin-plate seal piece  22  has a uniform plate width and that the thin-plate seal piece  22  is tapered. The steps of the stepped sections  31 ,  32  are formed by inclined end surfaces. These inclined end surfaces face inward in the radial direction of the rotating shaft  13  and are inclined such that an inclined end section outward in the plate width direction of the seal piece is positioned inward in the radial direction of the rotating shaft  13  with respect to an inclined end section inward in the plate width direction of the seal piece. 
         [0042]    In response to this, a locking section (high-pressure-side locking section)  25   b  is formed on the inner-circumferential-side distal end section  25   a  of the high-pressure-side plate  25 . The locking section  25   b  is formed so as to protrude from the high-pressure-side plate  25  toward the high-pressure-side side edge section  22   c  in the plate width direction of the thin-plate seal piece  22 , and a ring-shaped inclined surface is formed on the distal end section of the protrusion. This inclined surface faces outward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section inward in the plate width direction of the seal piece is positioned outward in the radial direction of the rotating shaft  13  with respect to an inclined end section outward in the plate width direction of the seal piece. 
         [0043]    In addition, a locking section (low-pressure-side locking section)  26   b  is formed on the inner-circumferential-side distal end section  26   a  of the low-pressure-side plate  26 . The locking section  26   b  is formed so as to protrude from the low-pressure-side plate  26  toward the low-pressure-side side edge section  22   d  in the plate width direction of the thin-plate seal piece  22 , and a ring-shaped inclined surface is formed on the distal end section of the protrusion. This inclined surface faces outward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section inward in the plate width direction of the seal piece is positioned outward in the radial direction of the rotating shaft  13  with respect to an inclined end section outward in the plate width direction of the seal piece. 
         [0044]    That is, the inclined end surface of the stepped section  31  and the inclined surface of the locking section  25   b  can be engaged with each other in the radial direction of the rotating shaft  13 , and the inclined end surface of the stepped section  32  and the inclined surface of the locking section  26   b  can be engaged with each other in the radial direction of the rotating shaft  13 . This configuration prevents detachment in the radial direction of the rotating shaft  13 , between the inclined surfaces of the locking sections  25   b ,  26   b  and the inclined end surfaces of the stepped sections  31 ,  32  that are engaged with each other. 
         [0045]    For example, if the pressure of the fluid G flowing from the high-pressure-side region to the low-pressure-side region in turbine operation presses the thin-plate seal pieces  22  toward the low-pressure-side region, or if a mechanism assembling error occurs after assembly of the shaft seal mechanism  11 , the size of the low-pressure-side gap δL becomes smaller than the gap size for yielding stable lifting-up force (for example, δH&gt;δL), resulting in disturbance in the pressure distribution and pressure difference generated in the thin-plate seal pieces  22 . This disturbance applies pressing force in a direction opposite to the applying direction of the lifting-up force to the thin-plate seal pieces  22 . Accordingly, the inner-circumferential-side distal end sections  22   b  are deformed to be pressed against the rotating shaft  13  by pressure greater than the preload while the rotation of the rotating shaft  13  is stopping. 
         [0046]    However, in the shaft seal mechanism  11  according to the present invention, the locking sections  25   b ,  26   b  provided in the high-pressure-side plate  25  and the low-pressure-side plate  26  can be engaged with the stepped sections  31 ,  32  of the thin-plate seal pieces  22  from the inside toward the outside in the radial direction of the rotating shaft  13 . This engagement allows the stepped sections  31 ,  32  to be hooked on the locking sections  25   b ,  26   b  even if pressing force greater than the preload is applied to the thin-plate seal pieces  22  and thus suppresses deformation of the thin-plate seal pieces  22  against the rotating shaft  13 . This configuration can maintain the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  in a noncontact state without contact with the rotating shaft  13 , resulting in prevention of abrasion of the thin-plate seal pieces  22 . 
         [0047]    The inclined surfaces of the locking sections  25   b ,  26   b  and the inclined end surfaces of the stepped sections  31 ,  32  can be engaged with each other in the radial direction of the rotating shaft  13 . Consequently, even if the thin-plate seal pieces  22  are assembled while being inclined toward the high pressure side or the low pressure side, the locking sections  25   b ,  26   b  ensure locking of the stepped sections  31 ,  32 . 
         [0048]    Furthermore, in the shaft seal mechanism  11  according to the present invention, only the thin-plate seal pieces  22 , the high-pressure-side plate  25 , and the low-pressure-side plate  26  change in shapes among the components of existing seal mechanisms. A large component, such as the seal housing  21 , is not required to change in shape, so that abrasion of the thin-plate seal pieces  22  due to pressing force can be prevented without a significant design change. 
         [0049]    The thin-plate seal pieces  22  are locked by the high-pressure-side plate  25  and the low-pressure-side plate  26  in the aforementioned embodiment but may be locked by the seal housing  21  as illustrated in  FIGS. 5 and 6 . 
         [0050]    With reference to  FIG. 5 , a stepped section (low-pressure-side stepped section)  33  is formed on the low-pressure-side side edge section  22   d  of each of the thin-plate seal pieces  22 . This stepped section  33  is disposed inward in the radial direction of the rotating shaft  13  with respect to the inner-circumferential-side distal end section  26   a  of the low-pressure-side plate  26  and is shaped into a notch formed by cutting out a portion of the low-pressure-side side edge section  22   d . A step of the stepped section  33  is formed by an inclined end surface. This inclined end surface faces inward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section outward in the plate width direction of the seal piece is positioned inward in the radial direction of the rotating shaft  13  with respect to an inclined end section inward in the plate width direction of the seal piece. 
         [0051]    In response to this, a locking section (low-pressure-side locking section)  21   d  is formed on the low-pressure-side side surface  21   c  of the seal housing  21 . The locking section  21   d  is formed so as to protrude from the low-pressure-side side surface  21   c  toward the low-pressure-side side edge section  22   d  in the plate width direction of the thin-plate seal piece  22 , and a ring-shaped inclined surface is formed on the distal end section of the protrusion. This inclined surface faces outward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section inward in the plate width direction of the seal piece is positioned outward in the radial direction of the rotating shaft  13  with respect to an inclined end section outward in the plate width direction of the seal piece. 
         [0052]    That is, the locking section  21   d  is positioned inward in the radial direction of the rotating shaft  13  with respect to the inner-circumferential-side distal end section  26   a  of the low-pressure-side plate  26 , and the inclined surface of the locking section  21   d  and the inclined end surface of the stepped section  33  can be engaged with each other in the radial direction of the rotating shaft  13 . This configuration prevents detachment in the radial direction of the rotating shaft  13 , between the inclined surface of the locking section  21   d  and the inclined end surface of the stepped section  33  that are engaged with each other. 
         [0053]    The locking section  21   d  provided in the seal housing  21  can be engaged with the stepped sections  33  of the thin-plate seal pieces  22  from the inside toward the outside in the radial direction of the rotating shaft  13 . This engagement allows the stepped sections  33  to be hooked on the locking section  21   d  even if pressing force greater than the preload is applied to the thin-plate seal pieces  22  and thus suppresses deformation of the thin-plate seal pieces  22  against the rotating shaft  13 . This configuration can maintain the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  in a noncontact state without contact with the rotating shaft  13 , resulting in prevention of abrasion of the thin-plate seal pieces  22 . 
         [0054]    Moreover, the locking section  21   d  is provided in the seal housing  21  being a large component and can thus have enhanced rigidity, resulting in maintaining an engagement state between the locking section  21   d  and the stepped sections  33  over a long period. 
         [0055]    With reference to  FIG. 6 , a stepped section (low-pressure-side stepped section)  34  is formed on the low-pressure-side side edge section  22   d  of each of the thin-plate seal pieces  22 . This stepped section  34  is disposed in a radial intermediate section (longitudinal intermediate section) of the low-pressure-side side edge section  22   d  and is shaped into such a step that the thin-plate seal piece  22  is tapered by being recessed toward the center of the thin-plate seal piece  22  in the plate width direction. The step of the stepped section  34  is formed by an inclined end surface. This inclined end surface faces inward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section outward in the plate width direction of the seal piece is positioned inward in the radial direction of the rotating shaft  13  with respect to an inclined end section inward in the plate width direction of the seal piece. 
         [0056]    In response to this, a locking section (low-pressure-side locking section)  21   e  is formed on the low-pressure-side side surface  21   c  of the seal housing  21 . The locking section  21   e  is formed so as to protrude from the low-pressure-side side surface  21   c  toward the low-pressure-side side edge section  22   d  in the plate width direction of the thin-plate seal piece  22 , and a ring-shaped inclined surface is formed on the distal end section of the protrusion. This inclined surface faces outward in the radial direction of the rotating shaft  13  and is inclined such that an inclined end section inward in the plate width direction of the seal piece is positioned outward in the radial direction of the rotating shaft  13  with respect to an inclined end section outward in the plate width direction of the seal piece. 
         [0057]    That is, the inclined surface of the locking section  21   e  and the inclined end surface of the stepped section  34  can be engaged with each other in the radial direction of the rotating shaft  13 . This configuration prevents detachment in the radial direction of the rotating shaft  13 , between the inclined surface of the locking section  21   e  and the inclined end surface of the stepped section  34  that are engaged with each other. 
         [0058]    The locking section  21   e  provided in the seal housing  21  can be engaged with the stepped sections  34  of the thin-plate seal pieces  22  from the inside toward the outside in the radial direction of the rotating shaft  13 . This engagement allows the stepped sections  34  to be hooked on the locking section  21   e  even if pressing force greater than the preload is applied to the thin-plate seal pieces  22  and thus suppresses deformation of the thin-plate seal pieces  22  against the rotating shaft  13 . This configuration can maintain the inner-circumferential-side distal end sections  22   b  of the thin-plate seal pieces  22  in a noncontact state without contact with the rotating shaft  13 , resulting in prevention of abrasion of the thin-plate seal pieces  22 . 
         [0059]    Moreover, the locking section  21   e  is provided in the seal housing  21  being a large component and can thus have enhanced rigidity, resulting in maintaining an engagement state between the locking section  21   e  and the stepped sections  34  over a long period. In addition, the low-pressure-side plate  26  is not required to be provided, so that the shaft seal mechanism  11  can have a simple configuration and that the manufacturing cost of the shaft seal mechanism  11  can be reduced. 
       INDUSTRIAL APPLICABILITY 
       [0060]    The shaft seal mechanism according to the present invention can prevent damage of the thin-plate seal pieces due to pressing force and increase the life of the seal pieces, and can thus be applied significantly advantageously in continuous operation of a turbine. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           11  Shaft seal mechanism 
           12  Fixed section 
           13  Rotating shaft 
           14  Ring-shaped space 
           21  Seal housing 
           21   a  Ring-shaped groove 
           21   b  High-pressure-side side surface 
           21   c  Low-pressure-side side surface 
           21   d ,  21   e  Locking section 
           22  Thin-plate seal piece 
           22   a  Outer-circumferential-side proximal end section 
           22   b  Inner-circumferential-side proximal end section 
           22   c  High-pressure-side side edge section 
           22   d  Low-pressure-side side edge section 
           23 ,  24  Retainer 
           25  High-pressure-side plate 
           25   a  Inner-circumferential-side distal end section 
           25   b  Locking section 
           26  Low-pressure-side plate 
           26   a  Inner-circumferential-side distal end section 
           26   b  Locking section 
           31  to  34  Stepped section 
         G Fluid 
         δH High-pressure-side gap 
         δL Low-pressure-side gap