Patent Publication Number: US-2015069721-A1

Title: Metal gasket

Description:
TECHNICAL FIELD 
     The present invention relates to a metal gasket. In particular, the present invention relates to a metal gasket used in order to prevent leakage of a fluid in an ultrahigh vacuum device used in a semiconductor production device, a nuclear investment or the like. 
     BACKGROUND ART 
     Conventionally, in a semiconductor production device, various metal gaskets are used in order to obtain a high degree of air-tightness. 
     For example, a metal hollow O-ring gasket is produced by forming a metal pipe such as stainless steel or Inconel into a ring-like form by bending or the like, and the both ends of the pipe are welded with each other. In this metal hollow O-ring gasket, sealing is conducted by deforming the metal ring by applying a strong clamping pressure. 
     However, as mentioned above, the above-mentioned metal hollow O-ring gasket is produced by welding the both ends of a metal pipe that has been bent in the form of a ring. Therefore, normally, burrs generated at the time of welding remain in the inside and outside of the pipe. By removing the burrs in the outside of the pipe by cutting, polishing or the like, the wall thickness of the pipe is slightly decreased. As a result, when clamped, the compression strength of the welded part and other parts may become un-uniform. 
     Accordingly, when used in applications where ultrahigh vacuum is required, leakage may occur from the welded part having a reduced wall thickness. 
     Further, various metal gaskets have been used in a gas supply line in a semiconductor manufacturing device. In order to allow the gas supply line to be compact, there has been a move for standardizing it as an integrated gas system in an SEMI (Semiconductor Equipment and Materials International). As for the properties of the gasket used in this integrated gas system, the gasket is required to be capable of maintaining a ultrahigh vacuum degree of 1×10 −11  Pa·m 3 /sec He or less and is required to be capable of conducting sealing if it is changed 20 times or more in the same flange. 
     In this integrated gas system, a metal gasket is inserted into various components such as a flange, a valve, a filter or the like that constitute a gas supply channel and fixed by means of a bolt. Since the diameter of the bolt is small, a large force cannot be applied to the bolt. Therefore, for a metal gasket, a decrease in clamping force required for sealing is demanded. 
     In order to respond to the above-mentioned requirement or demand, various technologies have been proposed. 
     For example, in Patent Document 1, a technology of a metal seal is disclosed. In this technology, the metal seal is provided with a first annular beam part having a first non-sealing surface and a first protruded part with a first annular sealing surface facing in a first axial direction to contact a first member for creating a first annular sealing dam therebetween; a second annular beam part having a second non-sealing surface and a second protruded part with a second annular sealing surface facing in a second axial direction, which is opposite to the first axial direction, to contact a second member for creating a second annular sealing dam therebetween; an annular inner surface extending between the first and second sealing surfaces to form a central passageway; an annular outer surface extending between the first and second sealing surfaces and spaced from the annular inner surface to form an annular columnar part of a material extending substantially perpendicular to the first and second annular beam parts therebetween; and one of the annular inner and outer surfaces has an annular recessed part extending in a substantially radial direction to at least partly define an effective minimum width of the annular columnar part. 
     Patent Document 2 discloses a technology of a metal gasket in which, in an annular metal gasket having a lateral U-shaped cross-sectional shape (i.e. having an opening on the outer peripheral side), at least one annular protrusion having a trapezoidal cross-sectional shape is formed on the circumferential direction on the two flat sealing surfaces that contact the mating surface, and the center of the crest of the annular protrusion is positioned within a range of a thickness t 0  of the center of the gasket. 
     Further, in Patent Document 3, in an annular metal gasket having a lateral U-shaped or C-shaped cross section (i.e. having an opening on the outer peripheral side), an annular space having a width of 40% or more of the wall thickness t 0  of the center of the gasket and a height H of 5% or more of the gasket height is provided on the innermost part of the circumferential direction of the two flat sealing surfaces that contact the mating surface, and the cross-section of the space is formed in the shape of a tuning fork. 
     Patent Document 4 discloses a metal static sealing member formed of an annular body provided with a bead, and first and second wing parts extending orthogonally with respect to the seal member axis and laterally connected to the bead, the shape of a lateral cross section along the axis of the sealing member is “V”, and the tapered surfaces of the branches of the “V” to which they are attached are slightly inclined with respect to the planar surfaces of the bead being orthogonal to the steal member axis. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: JP-A-2001-355731 
     Patent Document 2: JP-A-2003-194225 
     Patent Document 3: JP-A-2004-301159 
     Patent Document 4: JP-A-S64-500137 
     SUMMARY OF THE INVENTION 
     However, in the technologies in the above-mentioned Patent Documents 1, 2 and 3, since only one sealing part is provided in correspondence with each sealing surface, an improvement in reliability in sealing or the like has been desired. 
     As for the technology of Patent Document 4, although two or more sealing parts are provided in correspondence with each sealing surface, as mentioned above, use of the sealing material in a gas-supply line in a semiconductor production device or satisfying the requirements as the property of the gasket used in this integrated gas system still has room for improvement. 
     Further, in the metal gasket, further improvement in sealing performance or reduction in clamping force required for sealing has been demanded. 
     The present invention has been made taking the above into consideration, and is aimed at providing a metal gasket that can improve entire sealing performance or reliability of sealing, and can reduce a clamping force required for sealing. 
     In order to attain the object, the metal gasket of the present invention comprises: a columnar part formed in a cylindrical shape; a beam part that extends in a radial direction over the entire outer peripheral surface of the columnar part; and a circumferential groove formed in the middle of a peripheral surface of the beam part; wherein 
     the columnar part and the beam part are formed deformably; 
     on a first surface that is formed by one end of the columnar part and the surface of a disk part on one end side of the beam part, a first sealing part and a second sealing part that respectively form a circular sealed part by contacting a first object are provided, and on a second surface that is formed by the other end of the columnar part and the surface of a disk part on the other end side of the beam part, a third sealing part and a fourth sealing part that respectively form a circular sealed part by contacting a second object are provided; 
     the first sealing part is formed as a protruded part, and the second sealing part is formed by deformation of the disk part on one end side of the beam part when the protruded first sealing part is pressed by the first object; and 
     the third sealing part is formed as a protruded part, and the fourth sealing part is formed by deformation of the disk part on the other end side of the beam part when the protruded third sealing part is pressed by the second object. 
     According to the metal gasket of the present invention, due to the provision of the first sealing part, the second sealing part, the third sealing part and the fourth sealing part, reliable and excellent sealing performance can be exhibited. Further, a clamping force required for sealing can be reduced, whereby entire sealing performance or reliability of sealing performance can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of the metal gasket according to a first embodiment of the present invention; 
         FIG. 2  is a schematic view of the metal gasket according to a first embodiment of the present invention, in which (a) is a side view, and (b) is a cross-sectional view taken along the line A-A in  FIG. 1 ; 
         FIG. 3  is a schematic enlarged cross-sectional view of the essential parts for explaining the metal gasket according to a first embodiment of the present invention in the state before compression; 
         FIG. 4  is a schematic enlarged cross-sectional view of the essential parts for explaining the metal gasket according to a first embodiment of the present invention in the state after compression; 
         FIG. 5  is a schematic view of the metal gasket according to a second embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line B-B; 
         FIG. 6  is a schematic view of the metal gasket according to a third embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line C-C; 
         FIG. 7  is a schematic view of the metal gasket according to a fourth embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line D-D; 
         FIG. 8  is a schematic view of the metal gasket according to a fifth embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line E-E; 
         FIG. 9  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 1 of the present invention, in which (a) is a cross-sectional view before compression, and (b) is a cross-sectional view after compression; 
         FIG. 10  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 2 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression; 
         FIG. 11  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 3 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression; 
         FIG. 12  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 4 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression; and 
         FIG. 13  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 5 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
       FIG. 1  is a schematic plan view of the metal gasket according to a first embodiment of the present invention. 
       FIG. 2  is a schematic view of the metal gasket according to a first embodiment of the present invention, in which (a) is a side view, and (b) is a cross-sectional view taken along the line A-A in  FIG. 1 . 
     In  FIGS. 1 and 2 , a metal gasket  10  of this embodiment is provided with a columnar part  11  that is formed almost in a cylindrical form, a beam  12  that extends in a radial direction over the entire outer peripheral surface VL of this columnar part  11 , and a circumferential groove  13  formed in the middle of the peripheral surface of the beam part  12 . 
     As will be explained later, the columnar part  11  and the beam part  12  mentioned above are formed deformably. 
     Due to the formation of the circumferential groove  13 , in the beam part  12 , a disk part  121  on one end side (hereinafter referred to as the “one-end-side disk part  121 ) and a disk part  123  on the other side (hereinafter referred to as the “other-end-side disk part  123 ”) are formed. That is, the one-end-side disk part  121  extends, from the one end side of the columnar part  11 , in a radial direction over the entire perimeter in a cantilever form. The other-end-side disk part  123  extends, from the other end side of the columnar part  11 , in a radial direction over the entire perimeter in a cantilever form. 
     The cross sectional shape of the circumferential groove  13  is substantially a shape that is formed by dividing an ellipsoid into equal parts. The circumferential groove  13  of this embodiment has a configuration that it does not reach the outer peripheral surface VL of the columnar part  11 . 
     The columnar part  11  and the beam part  12  are connected. In this state, as shown in  FIG. 2(   b ), the outer peripheral surface VL of the columnar part  11  is a virtual outer peripheral surface. The outer part of the outer peripheral surface VL is the beam part  12 , and the inner part of the outer peripheral surface VL is the columnar part  11 . 
     In the metal gasket  10 , on one end of the columnar part  11  and a first surface PL 1  formed by the surface of the one-end-side disk part  121  of the beam part  12 , a first sealing part  111  and a second sealing part  122  that respectively form a circular sealed part (that is, a first sealed part  21  and a second sealed part  22 ) by contacting a first object B 1  (see  FIGS. 3 and 4 ) are provided. 
     Further, in the metal gasket  10 , on the second surface PL 2  that is formed by the other end of the columnar part  11  and the surface of the other-end-side disk part  123  of the beam part  12 , a third sealing part  112  and a fourth sealing part  124  that respectively form a circular sealed part (that is, a third sealed part  23  and a fourth sealed part  24 ) by contacting a second object B 2  (see  FIGS. 3 and 4 ) are provided. 
     The first sealing part  111  is formed as a protruded part, and as will be mentioned later, the second sealing part  122  is formed by deformation of the one-end-side disk part  121  of the beam part  12  when the protruded first sealing part  111  is pressed by the first object B 1 . 
     The third sealing part  112  is formed as a protruded part, and as will be mentioned later, the fourth sealing part  124  is formed by deformation of the other-side-disk part  123  of the beam part  12  when the protruded third sealing part  112  is pressed by the second object B 2 . 
     Here, the “protruded” means a ring-like convex shape. 
     It is preferred that the protruded first sealing part  111  and the protruded third sealing part  112  be respectively formed on the end of the one end side and outside of the columnar part  11  and on the end of the other end side and outside of the columnar part  11  in a shape having a mountain-like cross section in a radial direction. It suffices that the width W (see  FIG. 2(   b )) of the apex of the mountain-like cross section be shorter than the height H of the mountain-like cross section. 
     Due to such a configuration, since the apex of the cross section of the mountain shape has a ring-like flat surface having a width W, when pressed by the first object B 1  and the second object B 2 , the objects contact on this flat surface. Accordingly, no abnormal concentrated load is generated, and an almost uniform surface pressure distribution is obtained, whereby excellent sealing performance can be exhibited. In addition, when pressed by the first object B 1  and the second object B 2 , the protruded first sealing part  111  and the protruded third sealing part  112  deform in the direction of compression. If the width W of the apex of the mountain-like cross section is shorter than the height H of the mountain shape, due to a small contact area, a clamping force required for sealing can be reduced. 
     Here, the height H of the mountain-like cross section shape means a height from the end surface of the columnar part  11 . The end surfaces of the columnar part  11  serve as the first surface PL 1  and the second surface PL 2 , respectively. 
     It is further preferred that the width W of the apex of the mountain-like cross-section be formed shorter than ⅔ of the height H of the mountain shape. 
     Due to such a configuration, when pressed by the first object B 1  and the second object B 2 , the contact area of the protruded first sealing part  111  and the protruded third sealing part  112  can be further reduced, whereby a clamping force required for sealing can be further reduced. 
     In the meantime, the width W of the apex of the mountain-like cross section is normally long enough to prohibit occurrence of leakage even when particles are caught. 
     In this embodiment, a first concave part  113  and a second concave part  114  are respectively formed on the end of the one end side and inside of the columnar part  11  and the end of the other end side and inside of the columnar part  11 . That is, the inner slope of the first sealing part  111  is extended, and the first concave part  113  is formed at a position nearer to the other end side than the first surface PL 1 . Further, the inner slope of the third sealing part  112  is extended, and the second concave part  114  is formed at a position nearer to the one end side than the second surface PL 2 . 
     Due to such a configuration, when pressed by the first object B 1  and the second object B 2 , the surfaces of the first concave part  113  and the second concave part  114  do not contact the first object B 1  and the second object B 2 . As a result, a clamping force required for sealing can be reduced. 
     It is preferred that the first sealing part  111  and the second sealing part  122  be formed almost concentrically, and is also preferred that the third sealing part  112  and the fourth sealing part  124  be formed almost concentrically. 
     Due to such a configuration, when the protruded first sealing part  111  is pressed by the first object B 1 , the amount of deformation of the one-end-side disk part  121  of the beam part  12  can be allowed to be almost the same in the circumferential direction, and the shape of the second sealing part  122  formed by deformation can be stabilized, whereby an almost uniform surface pressure distribution in a circumferential direction can be obtained in the second sealing part  122 , leading to excellent sealing performance. 
     Similarly, when the protruded third sealing part  112  is pressed by the second object B 2 , the amount of deformation of the other-end-side disk part  123  of the beam part  12  can be allowed to be almost the same in the circumferential direction, and the shape of the fourth sealing part  124  formed by deformation can be stabilized, whereby an almost uniform surface pressure distribution in a circumferential direction can be obtained in the fourth sealing part  124 , leading to excellent sealing performance. 
     In the meantime, the end of the one-end-side disk part  121  on the one end side and the end of the other-end-side disk part  123  on the other side are normally subjected to chamfering. 
     Further, it is preferred that the metal gasket  10  have a configuration that the air-tightness of a first sealed part  21  (see  FIG. 4 ) formed by the first sealing part  111  and the first object B 1  is higher than the air-tightness of a second sealed part  22  formed by the second sealing part  122  and the first object B 1 . 
     Further, it is preferred that the metal gasket  10  have a configuration that the air-tightness of a third sealed part  23  (see  FIG. 4 ) formed by the third sealing part  112  and the second object B 2  is higher than the air-tightness of a fourth sealed part  24  formed by the fourth sealing part  124  and the second object B 2 . 
     Due to such a configuration, by the first sealing part  111  and the third sealing part  112 , reliable and excellent sealing performance can be exhibited, whereby a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122  and the fourth sealing part  124 , entire sealing performance or reliability of sealing can be improved. In addition, by contact of the first sealing part  111  and the second sealing part  122  with the first object B 1 , and by contact of the third sealing part  112  and the fourth sealing part  124  with the second object B 2 , the metal gasket  10  in the sealed state is stabilized, and reliability of sealing relative to variations in pressure, vibration or the like can be improved. 
     Meanwhile, in this embodiment, the metal gasket is configured such that the air-tightness of the first sealed part  21  is higher than the air-tightness of the second sealed part  22 , and such that air-tightness of the third sealed part  23  is higher than the air-tightness of the fourth sealed part  24 . The configuration is, however, not limited thereto. 
     For example, the metal gasket may be configured such that the first sealed part  21  has air-tightness that is almost equal to or lower than the air-tightness of the second sealed part  22 , or the metal gasket may be configured such that the air-tightness of the third sealed part  23  is almost equal to or lower than the air-tightness of the fourth sealed part  24 . 
     That is, the metal gasket  10  of this embodiment is normally used in a clean room and has the first sealing part  111  and the second sealing part  122 , and the third sealing part  112  and the fourth sealing part  124 . Accordingly, although not shown, for example, as compared with a metal gasket that only has the first sealing part  111  and the third sealing part  112 , the risk of insufficient sealing due to caught-in of particles can be reduced by about ½. In this respect, reliability of sealing can be improved. 
     Further, it is preferred that the second sealing part  112  and the fourth sealing part  124  be overlapped with the circumferential groove  13  formed in the beam part  12  in the axial direction of the beam part  12 . That is, in the metal gasket  10 , the one-end-side disk part  121  has the second sealing part  122  that contacts the first object B 1  by deformation, and the other-end-side disk part  123  has the fourth sealing part  124  that contacts the second object B 2  by deformation. 
     Due to such a configuration, the second sealing part  122  and the fourth sealing part  124  may be formed without allowing the structure to be complicated. 
     In the metal gasket  10 , normally, a metal material such as a stainless steel and Inconel, or those obtained by plating or depositing a soft metal such as nickel on these surfaces, are used. 
     Further, if the metal gasket  10  is used in a semiconductor industry, a single material of an austenite-based stainless steel such as SUS316L having excellent corrosion resistance or a vacuum double-dissolved material thereof or a vacuum triple-dissolved material thereof (a material that is dissolved/refined in vacuum twice to three times in order to reduce the amount of various chemical components that cause contamination) is preferable. 
     The metal gasket  10  can be formed by subjecting a metal round bar or a metal tube to cutting or a known mechanical processing (processing for removing a material) such as plain turning, milling, grinding or knurling. Further, it can be formed also by a method such as die forging in which a material is not removed at all. 
     The metal gasket  10  having the configuration mentioned above is used after being compressed by disposing between a pair of objects. The state of the use or the like will be explained with reference to the drawings. 
       FIG. 3  is a schematic enlarged cross-sectional view of the essential parts for explaining the metal gasket according to a first embodiment of the present invention in the state before compression. 
       FIG. 4  is a schematic enlarged cross-sectional view of the essential parts for explaining the metal gasket according to a first embodiment of the present invention in the state after compression. 
     As shown in  FIG. 3 , the metal gasket  10  is disposed between the first object B 1  and the second object B 2 . 
     The first object B 1  has a first abutting surface B 11  having a recessed part for accommodating the metal gasket  10  and a second abutting surface B 12  that abuts the retainer LT. 
     The second object B 2  has a first abutting surface B 21  having a recessed part for accommodating the metal gasket  10  and a second abutting surface B 22  that abuts the retainer LT. 
     The retainer LT is disposed between the second abutting surface B 12  of the first object B 1  and the second abutting surface B 22  of the second object B 2 , and is inserted into a space between the one-end-side disk part  121  of the metal gasket  10  and the other-end-side disk part  123  of the metal gasket  10 , thereby to fix the metal gasket  10  temporarily. 
     As for the metal gasket  10  disposed between the first object B 1  and the second object B 2 , the first sealing part  111  abuts the first abutting surface B 11 , and the third, sealing part  112  abuts the first abutting surface B 21 . 
     Further, in the state shown in  FIG. 3 , by further bringing the first object B 1  and the second object B 2  closer, in the metal gasket  10 , the first sealing part  111  and the third sealing part  112  are started to be crushed by pressing. 
     Subsequently, as shown in  FIG. 4 , when the first object B 1  abuts the second object B 2  through the retainer LT, the first sealing part  111  and the third sealing part  112  are crushed and deformed. 
     In this state, by contact of the first sealing part  111  and the first object B 1 , the first sealed part  21  is formed. Due to pressing of the protruded first sealing part  111  by the first object B 1 , the outer peripheral part of the one-end-side disk part  121  of the beam part  12  is deformed in the direction of the first object B 1 , thereby forming the second sealing part  122  that contacts the first object B 1 . As a result, a part where the second sealing part  122  and the first object B 1  contacts becomes the second sealed part  22 . 
     Similarly, by contact of the third sealing part  112  and the second object B 2 , the third sealed part  23  is formed. Further, due to pressing of the protruded third sealing part  112  by the second object B 2 , the outer peripheral part of the other-end-side disk part  123  of the beam part  12  is deformed in the direction of the second object B 2 , thereby forming the fourth sealing part  124  that contacts the second object B 2 . As a result, a part where the fourth sealing part  124  contacts the second object B 2  becomes the fourth sealed part  24 . 
     That is, as mentioned above, in the metal gasket  10 , an almost uniform surface pressure distribution can be obtained in the first sealing part  111  and the third sealing part  112 , whereby excellent sealing performance can be exhibited. Further, due to a reduction in contact area, a clamping force required for sealing can be reduced. 
     Further, the metal gasket  10  is configured such that the air-tightness of the first sealed part  21  becomes higher than the air-tightness of the second sealed part  22 , and that the air-tightness of the third sealed part  23  becomes higher than the air-tightness of the fourth sealed part  24 . Accordingly, by the first sealing part  111  and the third sealing part  112 , reliable and excellent sealing performance can be exhibited, and a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122  and the fourth sealing part  124 , entire sealing performance and reliability of sealing can be improved. 
     As mentioned hereinabove, according to the metal gasket  10  of this embodiment, not only entire sealing performance or reliability of sealing can be improved, but also a clamping force required for sealing can be reduced. 
     Second Embodiment 
       FIG. 5  is a schematic view of the metal gasket according to a second embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line B-B. 
     In  FIG. 5 , a metal gasket  10   a  of this embodiment differs from the metal gasket  10  of the first embodiment mentioned above in that the deepest part of the circumferential groove  13   a  formed in the beam part  12  is almost positioned in the outer peripheral surface (VL) of a columnar part  11   a,  and a first recessed part  125  and a second recessed part  126  are formed in the one-end-side disk part  121   a  and the other-end-side disk part  123   a  of the beam part  12   a,  respectively. Meanwhile, other configurations of this embodiment are almost the same as those of the metal gasket  10 . 
     Therefore, in  FIG. 5 , the same constituting elements as those in  FIGS. 1 and 2  are indicated by the same referential numerals and a detailed explanation is omitted. 
     The columnar part  11   a  differs from the columnar part  11  of the first embodiment in that it does not have parts corresponding to the first recessed part  113  and the second recessed part  114  and hence has a thickness smaller by an amount that corresponds to the depths of the first recessed part  113  and the second recessed part  114 . In this columnar part  11   a,  a first sealing part  111   a  having an almost similar shape as that of the first sealing part  111  is formed on the one end side, and a third sealing part  112   a  having an almost similar shape as that of the third sealing part  112  is formed on the other end side. 
     Further, in the beam part  12   a,  on an inner edge part of the surface in the one end side of a one-end-side disk part  121   a,  a first recessed part  125  having an almost rectangular cross section is formed as a ring groove. Further, on an inner edge part of the surface in the other end side of the other-end-side disk part  123   a,  a second recessed part  126  having an almost rectangular cross section is formed as a ring groove. 
     In the metal gasket  10   a,  on the first surface PL 1 , a first sealing part  111   a  and a second sealing part  122   a  that respectively form a circular sealed part by contacting the first object B 1  are provided. 
     Further, in the metal gasket  10   a,  on the second surface PL 2 , a third sealing part  112   a  and a fourth sealing part  124   a  that respectively form a circular sealed part by contacting the second object B 2  are provided. 
     Here, the second sealing part  122   a  is formed in a part that is the surface in the one end side of the one-end-side disk part  121   a  and in the vicinity of the first recessed part  125 . The fourth sealing part  124   a  is formed in a part that is the surface in the other end side of the other-end-side disk part  123   a  and in the vicinity of the second recessed part  126 . 
     Further, the first sealing part  111   a  and the second sealing part  122   a  are formed almost concentrically, and the third sealing part  112   a  and the fourth sealing part  124   a  are formed almost concentrically. 
     As almost in the case of the first embodiment, in the metal gasket  10   a  having the above-mentioned configuration, an almost uniform surface pressure distribution can be obtained in the first sealing part  111   a  and the third sealing part  112   a,  and the metal gasket can exhibit excellent sealing performance. In addition, by reducing the contact area, a clamping force required for sealing can be reduced. 
     Further, the metal gasket  10   a  is configured to allow the air-tightness in the first sealed part  21  to be higher than the air-tightness in the second sealed part  22 , and is configured to allow the air-tightness in the third sealed part  23  to be higher than the air-tightness in the fourth sealed part  24 . Accordingly, by the first sealing part  111   a  and the third sealing part  112   a,  reliable and excellent sealing performance can be exhibited, and a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122   a  and the fourth sealing part  124   a,  and other features, entire sealing performance or reliability of sealing can be improved. 
     As explained hereinabove, according to the metal gasket  10   a  of this embodiment, in an almost same manner as in the first embodiment, entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     Third Embodiment 
       FIG. 6  is a schematic view of the metal gasket according to a third embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line C-C. 
     In  FIG. 6 , a metal gasket  10   b  of this embodiment differs from the metal gasket  10   a  of the second embodiment in that a first recessed part  125   b  and a second recessed part  126   b  each having an almost triangular cross section are formed instead of the first recessed part  125  and the second recessed part  126 . Here, other configurations of this embodiment are almost the same as those of the metal gasket  10   a.    
     Therefore, in  FIG. 6 , the same constituting elements as those in  FIG. 5  are indicated by the same referential numerals and a detailed explanation is omitted. 
     In the beam part  12   b,  on an inner edge part of the surface in the one end side of the one-end-side disk part  121   b,  a first recessed part  125   b  having an almost right-angled rectangular cross section is formed as a ring groove. Further, on an inner edge part of the surface in the other end side of the other-end-side disk part  123   b,  a second recessed part  126   b  having an almost right-angled rectangular cross section is formed as a ring groove. 
     In the metal gasket  10   b,  on the first surface PL 1 , a first sealing part  111   a  and a second sealing part  122   b  that respectively form a circular sealed part by contacting the first object B 1  are provided. 
     Further, in the metal gasket  10   b,  on the second surface PL 2 , a third sealing part  112   a  and a fourth sealing part  124   b  that respectively form a circular sealed part by contacting the second object B 2  are provided. 
     Meanwhile, the second sealing part  122   b  is formed in a part that is the surface of one end side of the one-end-side disk part  121   b  and in the vicinity of the inclined surface of the first recessed part  125   b.  The fourth sealing part  124   b  is formed in a part that is the surface of the other end side of the other-end-side disk part  123   b  and in the vicinity of the inclined surface of the second recessed part  126   b.    
     Further, the first sealing part  111   a  and the second sealing part  122   b  are formed almost concentrically, and the third sealing part  112   a  and the fourth sealing part  124   b  are formed almost concentrically. 
     As almost in the case of the second embodiment, in the metal gasket  10   b  having the above-mentioned configuration, an almost uniform surface pressure distribution can be obtained in the first sealing part  111   a  and the third sealing part  112   a,  and hence the metal gasket can exhibit excellent sealing performance. In addition, by reducing the contact area, a clamping force required for sealing can be reduced. 
     Further, the metal gasket  10   b  is configured to allow the air-tightness in the first sealed part  21  to be higher than the air-tightness in the second sealed part  22 , and is configured to allow the air-tightness in the third sealed part  23  to be higher than the air-tightness in the fourth sealed part  24 . Accordingly, by the first sealing part  111   a  and the third sealing part  112   a,  reliable and excellent sealing performance can be exhibited, and a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122   b  and the fourth sealing part  124   b,  and other features, entire sealing performance or reliability of sealing can be improved. 
     As explained hereinabove, according to the metal gasket  10   b  of this embodiment, in an almost same manner as in the second embodiment, entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     Fourth Embodiment 
       FIG. 7  is a schematic view of the metal gasket according to a fourth embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line D-D. 
     In  FIG. 7 , a metal gasket  10   c  of this embodiment differs from the metal gasket  10   a  of the second embodiment in that a first sealing part  111   c  and a third sealing part  112   c  each having a large protrusion are formed, and that the first recessed part  125  and the second recessed part  126  are not formed. Meanwhile, other configurations of this embodiment are almost the same as those of the metal gasket  10   a.    
     Therefore, in  FIG. 7 , the same constituting elements as those in  FIG. 5  are indicated by the same referential numerals and a detailed explanation is omitted. 
     In this embodiment, the first recessed part  125  and the second recessed part  126  are not formed, and the amounts of protrusion of the first sealing part  111   c  and the third sealing part  112   c  are adjusted. That is, as compared with the first sealing part  111   a  and the third sealing part  112   a,  the first sealing part  111   c  and the third sealing part  112   c  are respectively formed such that the protruded amount is almost twice as large. As a result, the angle of the slope is acute. 
     In the metal gasket  10   c,  on the first surface PL 1 , a first sealing part  111   c  and a second sealing part  122   c  that respectively form a circular sealed part by contacting the first object B 1  are provided. 
     Further, in the metal gasket  10   c,  on the second surface PL 2 , a third sealing part  112   c  and a fourth sealing part  124   c  that respectively form a circular sealed part by contacting the second object B 2  are provided. 
     Here, the second sealing part  122   c  is formed in a part that is the surface of one end side of the one-end-side disk part  121   c  and in the vicinity of the edge part on the outside (the edge part inside of the chamfered part), and the fourth sealing part  124   c  is formed in a part that is the surface of the other side of the other-end-side disk part  123   c  and in the vicinity of the edge part on the outside (the edge part inside of the chamfered part). 
     Further, the first sealing part  111   c  and the second sealing part  122   c  are formed almost concentrically, and the third sealing part  112   c  and the fourth sealing part  124   c  are formed almost concentrically. 
     As almost in the case of the second embodiment, in the metal gasket  10   c  having the above-mentioned configuration, an almost uniform surface pressure distribution can be obtained in the first sealing part  111   c  and the third sealing part  112   c,  and hence the metal gasket can exhibit excellent sealing performance. In addition, by reducing the contact area, a clamping force required for sealing can be reduced. 
     Further, the metal gasket  10   c  is configured to allow the air-tightness in the first sealed part  21  to be higher than the air-tightness in the second sealed part  22 , and is configured to allow the air-tightness in the third sealed part  23  to be higher than the air-tightness in the fourth sealed part  24 . Accordingly, by the first sealing part  111   c  and the third sealing part  112   c,  reliable and excellent sealing performance can be exhibited, and a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122   c  and the fourth sealing part  124   c,  and other features, entire sealing performance or reliability of sealing can be improved. 
     As explained hereinabove, according to the metal gasket  10   c  of this embodiment, in an almost same manner as in the second embodiment, entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     Meanwhile, the deepest part of the circumferential groove  13   a  formed in the beam part  12   c  can be remote from the outer peripheral surface (VL) of the columnar part  11   a  as in the case of the first embodiment, according to the material, or the like. 
     Fifth Embodiment 
       FIG. 8  is a schematic view of the metal gasket according to a fifth embodiment of the present invention, in which (a) is a plan view, and (b) is a cross-sectional view taken along the line E-E. 
     In  FIG. 8 , a metal gasket  10   d  of this embodiment differs from the metal gasket  10  of the first embodiment in that an inner circumferential groove  115  is formed on the inner peripheral surface of a columnar part  11   d.  Other configurations of this embodiment are almost the same as those of the metal gasket  10 . 
     Therefore, in  FIG. 8 , the same constituting elements as those in  FIGS. 1 and 2  are indicated by the same referential numerals and a detailed explanation is omitted. 
     In the columnar part  11   d,  in almost the middle of the inner peripheral surface (in almost the middle in the axial direction of the columnar part  11   d ), the inner circumferential groove  115  having a curved surface is formed. 
     In this inner circumferential groove  115 , the dimension in the axial direction of the columnar part  11   d  is L 1  and the depth is L 2 . In this embodiment, the dimension L 1  is almost the same as the dimension of the axial direction of an opening of the circumferential groove  13 . The dimension L 2  is a depth that almost reaches a virtual line (not shown) connecting the apexes of the cross sections of the mountain shapes of the first sealing part  111  and the third sealing part  112 . However, the dimensions L 1  and L 2  are not limited thereto, and can be appropriately set. 
     In the metal gasket  10   d  having the above-mentioned configuration, when used, if the first object B 1  and the second object B 2  abut through the retainer LT, the first sealing part  111  and the third sealing part  112  are crushed and deformed (see  FIG. 4 ). 
     In this state, in an almost same manner as in the first embodiment, by contact of the first sealing part  111  and the first object B 1 , the first sealed part  21  is formed. Further, by pressing of the protruded first sealing part  111  by the first object B 1 , the outer peripheral part of the one-end-side disk part  121  of the beam part  12  is deformed in the direction of the first object B 1  to form the second sealing part  122  that contacts the first object B 1 . As a result, a part where the second sealing part  122  contacts the first object B 1  forms a second sealed part  22 . 
     Further, by contact of the third sealing part  112  and the second object B 2 , the third sealed part  23  is formed. Further, by pressing of the protruded third sealing part  112  by the second object B 2 , the outer peripheral part of the other-end-side disk part  123  of the beam part  12  is deformed in the direction of the second object B 2  to form a fourth sealing part  124  that contacts the second object B 2 . As a result, a part where the fourth sealing part  124  contacts the second object B 2  becomes a fourth sealed part  24 . 
     Here, in the metal gasket  10   d,  since the inner circumferential groove  115  is formed on the inner peripheral surface of the columnar part  11   d,  when the protruded first sealing part  111  is pressed by the first object B 1 , the one-end-side disk part  121  of the beam part  12  is more largely deformed in the one end side than in the first embodiment, whereby sealing performance or the like of the second sealing part  122  can be improved. 
     Further, when the protruded third sealing part  112  is pressed by the second object B 2 , the other-end-side disk part  123  of the beam part  12  is more largely deformed in the other end side than in the first embodiment, whereby sealing performance or the like of the fourth sealing part  124  can be improved. 
     As almost in the case of the first embodiment, in the metal gasket  10   d  having the above-mentioned configuration, an almost uniform surface pressure distribution can be obtained in the first sealing part  111  and the third sealing part  112 , and the metal gasket can exhibit excellent sealing performance. In addition, by reducing the contact area, a clamping force required for sealing can be reduced. 
     Further, the metal gasket  10   d  is configured to allow the air-tightness in the first sealed part  21  to be higher than the air-tightness in the second sealed part  22 , and is configured to allow the air-tightness in the third sealed part  23  to be higher than the air-tightness in the fourth sealed part  24 . Accordingly, by the first sealing part  111  and the third sealing part  112 , reliable and excellent sealing performance can be exhibited, and a clamping force required for sealing can be reduced. Further, due to complementary sealing of the second sealing part  122  and the fourth sealing part  124 , and other features, entire sealing performance or reliability of sealing can be improved. 
     Further, since the one-end-side disk part  121  of the beam part  12  and the other-end-side disk part  123  of the beam part  12  are largely deformed as compared with the first embodiment, the sealing performance of the second sealing part  122  and the fourth sealing part  124 , or the like can be improved. 
     As explained hereinabove, according to the metal gasket  10   d  of this embodiment, in an almost same manner as in the first embodiment, entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     EXAMPLE 1 
     As Example 1, the metal gasket  10  of the above-mentioned first embodiment was subjected to a stress analysis by using the finite element method. Next, an explanation will be made on this Example 1 with reference to the drawings. 
       FIG. 9  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 1 of the present invention, in which (a) is a cross-sectional view before compression, and (b) is a cross-sectional view after compression. 
     The shape of the metal gasket  10  that was subjected to a stress analysis is almost similar to the shape shown in  FIG. 9(   a ). As the physical property value of the material of the metal gasket  10 , the physical property value of the SUS316L was used. 
     Further, as shown in  FIG. 4 , the metal gasket  10  is sealed in the state where it is sandwiched between a first abutment surface B 11  of the first object B 1  and a first abutment surface B 21  of the second object B 2 . 
     Regarding the results of the stress analysis, as shown in  FIG. 9(   b ), the metal gasket  10  was deformed. Parts protruding sharply from the first sealing part  111 , the second sealing part  122 , the third sealing part  112  and the fourth sealing part  124  each indicate a stress distribution, indicating that a larger amount of a protruded part means generation of a larger stress. 
     By this stress analysis, it has been revealed that, in the metal gasket  10 , the air-tightness of the first sealed part  21  formed by the first sealing part  111  and the first object B 1  is higher than the air-tightness of the second sealed part  22  formed by the second sealing part  122  and the first object B 1 . Further, it has been revealed that the air-tightness of the third sealed part  23  formed by the third sealing part  112  and the second object B 2  is higher than the air-tightness of the fourth sealed part  24  formed by the fourth sealing part  124  and the second object B 2 . 
     Further, it has been revealed that the maximum surface pressure, i.e. the maximum surface pressure at the first sealing part  111  and the third sealing part  112 , can be 2200 MPa, for example, and entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     EXAMPLE 2 
     As Example 2, the metal gasket  10   a  of the above-mentioned second embodiment was subjected to a stress analysis by using the finite element method. An explanation will be made on this Example 2 with reference to the drawings. 
       FIG. 10  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 2 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression. 
     The shape of the metal gasket  10   a  subjected to the stress analysis is almost the same as the shape shown in  FIG. 10(   a ). Other conditions are almost the same as those in Example 1. 
     Regarding the results of the stress analysis, as shown in  FIG. 10(   b ), the metal gasket  10   a  was deformed. Parts protruding sharply from the first sealing part  111   a,  the second sealing part  122   a,  the third sealing part  112   a  and the fourth sealing part  124   a  each indicate a stress distribution. A larger amount of a protruded part means generation of a larger stress. 
     By this stress analysis, it has been revealed that, in the metal gasket  10   a,  the air-tightness of the first sealed part  21  formed by the first sealing part  111   a  and the first object B 1  is higher than the air-tightness of the second sealed part  22  formed by the second sealing part  122   a  and the first object B 1 . Further, it has been revealed that the air-tightness of the third sealed part  23  formed by the third sealing part  112   a  and the second object B 2  is higher than the air-tightness of the fourth sealed part  24  formed by the fourth sealing part  124   a  and the second object B 2 . 
     Further, it has been revealed that the maximum surface pressure, i.e. the maximum surface pressure at the first sealing part  111   a  and the third sealing part  112   a  can be 1680 MPa, for example, and entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     EXAMPLE 3 
     As Example 3, the metal gasket  10   b  of the above-mentioned third embodiment was subjected to a stress analysis by using the finite element method. An explanation will be made on this Example 3 with reference to the drawings. 
       FIG. 11  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 3 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression. 
     The shape of the metal gasket  10   b  subjected to the stress analysis is almost the same as the shape shown in  FIG. 11(   a ). Other conditions are almost the same as those in Example 1. 
     Regarding the results of the stress analysis, as shown in  FIG. 11(   b ), the metal gasket  10   b  was deformed. Parts protruding sharply from the first sealing part  111   a,  the second sealing part  122   b,  the third sealing part  112   a  and the fourth sealing part  124   b  each indicate a stress distribution. A larger amount of a protruded part means generation of a larger stress. 
     By this stress analysis, it has been revealed that, in the metal gasket  10   b,  the air-tightness of the first sealed part  21  formed by the first sealing part  111   a  and the first object B 1  is higher than the air-tightness of the second sealed part  22  formed by the second sealing part  122   b  and the first object B 1 . Further, it has been revealed that the air-tightness of the third sealed part  23  formed by the third sealing part  112   a  and the second object B 2  is higher than the air-tightness of the fourth sealed part  24  formed by the fourth sealing part  124   b  and the second object B 2 . 
     Further, it has been revealed that the maximum surface pressure, i.e. the maximum surface pressure at the first sealing part  111   a  and the third sealing part  112   a  can be 1520 MPa, for example, and entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     EXAMPLE 4 
     As Example 4, the metal gasket  10   c  of the above-mentioned fourth embodiment was subjected to a stress analysis by using the finite element method. An explanation will be made on this Example 4 with reference to the drawings. 
       FIG. 12  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 4 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression. 
     The shape of the metal gasket  10   c  subjected to the stress analysis is almost the same as the shape shown in  FIG. 12(   a ). Other conditions are almost the same as those in Example 1. 
     Regarding the results of the stress analysis, as shown in  FIG. 12(   b ), the metal gasket  10   c  was deformed. Parts protruding sharply from the first sealing part  111   c,  the second sealing part  122   c,  the third sealing part  112   c  and the fourth sealing part  124   c  each indicate a stress distribution. A larger amount of a protruded part means generation of a larger stress. 
     By this stress analysis, it has been revealed that, in the metal gasket  10   c,  the air-tightness of the first sealed part  21  formed by the first sealing part  111   c  and the first object B 1  is higher than the air-tightness of the second sealed part  22  formed by the second sealing part  122   c  and the first object B 1 . Further, it has been revealed that the air-tightness of the third sealed part  23  formed by the third sealing part  112   c  and the second object B 2  is higher than the air-tightness of the fourth sealed part  24  formed by the fourth sealing part  124   c  and the second object B 2 . 
     Further, it has been revealed that the maximum surface pressure, i.e. the maximum surface pressure at the first sealing part  111   c  and the third sealing part  112   c  can be 920 MPa, for example, and entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     EXAMPLE 5 
     As Example 5, the metal gasket  10   d  of the above-mentioned fifth embodiment was subjected to a stress analysis by using the finite element method. An explanation will be made on this Example 5 with reference to the drawings. 
       FIG. 13  is a schematic enlarged view of the essential parts for explaining the metal gasket according to Example 5 of the present invention, in which (a) is a cross-sectional view in the state before compression and (b) is a cross-sectional view in the state after compression. 
     The shape of the metal gasket  10   d  subjected to the stress analysis is almost the same as the shape shown in  FIG. 13(   a ). Other conditions are almost the same as those in Example 1. 
     Regarding the results of the stress analysis, as shown in  FIG. 13(   b ), the metal gasket  10   d  was deformed. Parts protruding sharply from the first sealing part  111 , the second sealing part  122 , the third sealing part  112  and the fourth sealing part  124  each indicate a stress distribution. A larger amount of a protruded part means generation of a larger stress. 
     By this stress analysis, it has been revealed that, in the metal gasket  10   d,  the air-tightness of the first sealed part  21  formed by the first sealing part  111  and the first object B 1  is higher than the air-tightness of the second sealed part  22  formed by the second sealing part  122  and the first object B 1 . Further, it has been revealed that the air-tightness of the third sealed part  23  formed by the third sealing part  112  and the second object B 2  is higher than the air-tightness of the fourth sealed part  24  formed by the fourth sealing part  124  and the second object B 2 . 
     Further, it has been revealed that the maximum surface pressure, i.e. the maximum surface pressure at the first sealing part  111  and the third sealing part  112 , can be 1367 MPa, for example, and entire sealing performance or reliability of sealing can be improved, and a clamping force required for sealing can be reduced. 
     Hereinabove, the metal gasket of the present invention was explained with reference to preferred embodiments, or the like. The metal gasket according to the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the invention. 
     For example, in the above-mentioned embodiments, the cross-sectional shape of the circumferential groove  12  is substantially a shape formed by dividing an ellipse into equal parts. The shape is not limited thereto. For example, although not shown, the cross-sectional shape of the circumferential groove may be rectangular, triangle or substantially a shape formed by dividing an oval shape into equal parts. 
     Although only some exemplary embodiments and/or examples of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments and/or examples without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 
     The documents described in this specification and the Japanese application specification claiming priority under the Paris Convention are incorporated herein by reference in its entirety.