Abstract:
A bellows type mechanical seal is provided that is capable of reducing adverse effects on the bellows. The bellows type mechanical seal includes a first annular member fixed on a rotary shaft, a second annular member resiliently supported by the bellows in a housing axially to the outside of the first annular member, a seal ring having a first end seal face contacting the first annular member and a second end seal face contacting the second annular member, both seal faces being perpendicular to the shaft. A centering member is arranged contacting the inner surface of the seal ring and the inner surface of the second annular member within an annular space formed between both of the inner surfaces and the shaft to keep the sealing ring and the second annular member in alignment with each other.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bellows type mechanical seal. 
     BACKGROUND OF THE INVENTION 
     A mechanical seal with bellows is known as a shaft seal device of a pump that handles fluid of high temperature over 200° C. and containing great amount of solid content such as asphalt, tar, pitch, and the like in petroleum refinery, petrochemical plant, iron making chemical plant, and the like (see non-patent document 1). 
     The bellows type mechanical seal will be described with reference to  FIG. 6  to  FIG. 8 .  FIG. 6  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal according to the conventional example.  FIG. 7  is a view seen from X of  FIG. 6 .  FIG. 8  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal according to another conventional example. 
     A mechanical seal  100  shown in  FIG. 6  has a configuration in which a seal ring  102 , which is resiliently supported by a housing  200  through a retainer  104 , a bellows  101 , a collar  105 , a seal cover  202 , and the like, and a mating ring  103  fixed to a rotating shaft  300  contact in a freely slidable manner with each other to seal an annular space between the housing  200  and the rotating shaft  300 . 
     The seal ring  102  is burn fitted or press fitted to the retainer  104  welded to one end of the bellows  101 . The collar  105  is welded to the other end of the bellows  101 . The collar  105  is fixed to the seal cover  202  attached to an opening of a shaft hole  201  of the housing  200 . The mating ring  103  is fixed to a sleeve  301  fixed to an outer circumferential surface of the rotating shaft  300 . 
     The seal ring  102  and the mating ring  103  are arranged axially lined so that the end faces of the seal ring and the mating ring perpendicular to the shaft contact with each other, and are configured to slidably move in the circumferential direction to each other where when the rotating shaft  300  rotates with respect to the housing  200 . The seal ring  102  has higher follow-up property with respect to the mating ring  103  as the bellows  101  resiliently receive the slidable movement torque generated by the slidable movement with the mating ring  103 . 
     A baffle sleeve  203  for guiding the quench fluid such as steam to the end sealing face, cleaning the oozed and leaked solution from the end sealing face, and cooling and lubrication of the end sealing face is also arranged. The baffle sleeve  203  is attached to the seal cover  202 , and includes a cylindrical portion  203   a  extending axially on the inner diameter side of the seal ring  102  and the mating ring  103 . 
     As shown in  FIG. 7 , a damper  109   a  configured by a plurality of projections projecting out in the inner diameter direction is arranged on the inner peripheral surface of the retainer  104 . The damper  104   a  is projected out so as to partially narrow the space between the inner peripheral surface of the retainer  104  and the outer peripheral surface of the cylindrical portion  203   a  of the baffle sleeve  203  in a range the axial movement of the retainer  104  is not inhibited. The movement in the direction perpendicular to the shaft in the retainer  104  is thereby regulated, the occurrence of circumferential microscopic vibration (stick slip) of high cycle at the end sealing face due to lack of lubricant at the end sealing face and the like is suppressed, and the breakage of the welded portion of the bellows  101  by the vibration is prevented. 
     However, in the configuration in which the seal ring  102  is burn fitted or press fitted to the retainer  104  so as to be integrated, lowering of sealability, damage due to local contact at the end sealing face etc. occur from the influence of the difference in coefficients of thermal expansion of the bellows  101 , the seal ring  102 , and the retainer  104  at the time of high temperature use. 
     In the mechanical seal  100 ′ shown in  FIG. 8 , the seal ring  102 ′ is not fixed to the retainer  104 ′, and they are contacted at the lapped (surface polished) surfaces. Thus, the influence of the difference in coefficients of thermal expansion can be reduced, the sealability can be maintained even at the time of high temperature use, and damages due to the influence of heat deformation and the like can be suppressed. Furthermore, special steps such as burn fitting and press fitting, and the subsequent heat processing and the like are unnecessary, so that the manufacturing cost can be reduced. 
     In such mechanical seal  100 ′, a projection  203   b  arranged at the distal end of the cylindrical portion  203   a  of the baffle sleeve  203 ′ is loosely engaged to the cutout  102   a  formed on the inner peripheral surface of the seal ring  102 ′, so that the baffle sleeve  203 ′ clutches the seal ring  102 ′. The slidable movement torque thus is prevented from being transmitted to the bellows  101 . 
     A damper  104   a ′ or a plurality of projections projecting in the inner diameter direction is arranged on the inner peripheral surface of the retainer  104 ′. The damper  104   a ′ is projected out in the inner diameter direction so as to partially narrow the space between the retainer  104 ′ and the cylindrical portion  203   a  of the baffle sleeve  203 ′ in a plurality of areas on the inner peripheral surface of the retainer  104 ′ to regulate the movement of the retainer  104 ′ in the direction perpendicular to the shaft and suppress the oscillation of the bellows  11 , similar to the damper  104   a  of the mechanical seal  100  shown in  FIG. 6 . 
     Furthermore, an annular recess is formed by a step difference portion  102   b  and a stepped portion  104   b  for partially reducing the outer diameter is formed at the outer peripheral surface of the seal ring  102 ′ and the outer peripheral surface of the retainer  104 ′, and a centering case  106  for centering the seal ring  102 ′ and the retainer  104 ′ is attached to the recess. 
     However, since the centering case  106  is fitted with a very small gap in view of the change in dimension by thermal expansion, the vibration is transmitted to the bellows  101  when fluid such as tar and pitch enters the space and is fixed thereat, thereby damaging the bellows  101 . 
     PRIOR ART DOCUMENT 
     Non-Patent Document 
     Non-patent document 1: Hidekazu Takahashi, “High temperature bellows seal with breakage prevention mechanism”, “Industrial machinery No. 682 July 2007”, The Japan Society of Industrial Machinery Manufacturers, Jul. 20, 2007, p. 38-40. 
     SUMMARY OF THE INVENTION 
     In view of solving the problems of the prior art, it is an object of the present invention to provide a bellows type mechanical seal capable of reducing the influence of vibration on the bellows. 
     Means for Solving the Problems 
     In order to achieve the above object, according to the present invention, there is provided a bellows type mechanical seal for sealing an annular space between a shaft hole formed in a housing and a rotating shaft inserted to the shaft hole, including a first annular member fixed to the rotating shaft, a second annular member resiliently supported with respect to the housing through a bellows at a position on an opening side of the shaft hole closer than the first annular member, and a seal ring having a first end sealing face contacting the first annular member in a freely slidable manner and a second end sealing face contacting the second annular member, both sealing faces being perpendicular to the axis line, wherein a centering member is arranged contacting an inner peripheral surface of the seal ring and an inner peripheral surface of the second annular member facing a non-sealed region in the annular space to keep shaft centers of the seal ring and the second annular member in alignment with each other. 
     According to the present invention, the propagation of vibration to the bellows due to the fixation of the sealed fluid such as in the prior art is suppressed since the centering member for keeping the axis lines of the seal ring and the second annular member in alignment with each other is arranged in the non-sealed region. In other words, according to the present invention, the sealed fluid, which is a liquid body that has fluidity at high temperature but solidifies when the temperature lowers, such as tar and pitch does not enter the space between the centering member, and the seal ring and the second annular member and fix thereat. Therefore, the vibration due to the slidable movement of the first annular member and the seal ring is suppressed from being transmitted to the bellows, and the bellows is suppressed from being damaged. 
     The bellows type mechanical seal may include a baffle sleeve including a cylindrical portion, axially extending between an outer peripheral surface of the rotating shaft and the inner peripheral surfaces of the second annular member and the seal ring, for guiding a quench fluid to the inner peripheral side of the seal surface between the second annular member and the seal ring, the baffle sleeve being fixed to the housing. 
     Therefore, the space between the centering member, and the seal ring and the second annular member is cleaned with the quench fluid, so that the contacting state of the seal surfaces between the seal ring and the second annular member is maintained satisfactory. 
     The bellows type mechanical seal may include an elastic member for acting an elastic force on the second annular member in a radially outwardly direction. 
     Therefore, the vibration generated at the second annular member due to the slidable movement of the first annular member fixed to the rotating shaft and the seal ring is buffered by the elastic member, so that the vibration can be suppressed from being propagated to the bellows. 
     The bellows type mechanical seal may include the elastic member which is attached between an outer peripheral surface of the cylindrical portion of the baffle sleeve and an inner peripheral surface of the centering member, or between an outer peripheral surface of the cylindrical portion of the baffle sleeve and an inner peripheral surface of the second annular member. 
     The bellows type mechanical seal may include the elastic member which is a plate spring formed in an annular shape. 
     Thus, the configuration for suppressing the vibration of the bellows can be easily formed. 
     According to the present invention, the influence of vibration on the bellows can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view describing the configuration of a bellows type mechanical seal according to a first example of the present invention. 
         FIG. 2  is a schematic cross-sectional view describing the configuration of a bellows type mechanical seal according to a second example of the present invention. 
         FIG. 3A  is a schematic cross-sectional view of an elastic member. 
         FIG. 3B  is a cross-sectional view seen from arrow A of  FIG. 3A . 
         FIG. 4  is a schematic cross-sectional view describing the configuration of a bellows type mechanical seal according to a third example of the present invention. 
         FIG. 5  is a schematic perspective view describing other configurations of the elastic member. 
         FIG. 6  is a schematic cross-sectional view describing the configuration of a bellows type mechanical seal according to a conventional example. 
         FIG. 7  is a view seen from X of  FIG. 6 . 
         FIG. 8  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal according to another conventional example. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The best modes for carrying out the invention will be hereinafter illustratively described in detail based on the examples with reference to the drawings. It should be recognized that the dimension, material, shape, relative arrangement and the like of the components described in the example are not intended to limit the scope of the invention unless specifically stated in particular. 
     FIRST EXAMPLE 
     A bellows type mechanical seal according to a first example of the present invention will be described with reference to  FIG. 1 .  FIG. 1  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal according to the first example of the present invention. 
     The bellows type mechanical seal  1  according to the present example is used as shaft seal device of a pump that handles fluid of high temperature over 200° C. and containing great amount of solid content such as asphalt, tar, pitch, and the like in petroleum refinery, petrochemical plant, iron making chemical plant, and the like. 
     In outline, the bellows type mechanical seal  1  is configured such that a seal ring  12  sealably contacts a mat ing ring  13  fixed to a rotating shaft  30  and a retainer  14  resiliently supported by a housing  20  through a bellows  11 , a collar  15 , a seal cover  22  and the like to seal an annular space between a shaft hole  21  of the housing  20  and the rotating shaft  30 . Thus, the sealed fluid such as tar and pitch is prevented from leaking from a sealed region (O), which is the inside of the device, to a non-sealed region (A), which is the atmosphere side. 
     The bellows type mechanical seal  1  also includes a baffle sleeve  23  for guiding a quench fluid such as steam for cleaning a seal surface of the seal ring  12  and the retainer  14 . The baffle sleeve  23  includes a cylindrical portion  23   a  axially extending between the inner peripheral surface of the seal ring  12 , the retainer  14 , or the like and the outer peripheral surface of the rotating shaft  30 . The baffle sleeve  23  is made from a metal material such as SUS 630. 
     The mating ring  13  serving as a first annular member is fixed to the sleeve  31  fixed on the outer peripheral surface of the rotating shaft  30  by a retainer  32  made of a metal material having low coefficient of thermal expansion of around 5×10 −6  1° C. such as 42% Ni—Fe. The mating ring  13  has an end face  13   a  perpendicular to the shaft at the end on the opening side of the shaft hole  21 . 
     The retainer  14  serving as a second annular member is an annular member made from a different type of material having a coefficient of thermal expansion substantially approximate to the metal such as inconel 625 and the material of the bellows  11 , where one end of the bellows  11  is welded to the end on the opening side of the shaft hole  21 . 
     The bellows  11  is an accordion-like member made of metal such as inconel 625. As shown in  FIG. 1 , the bellows  11  is configured by coupling the inner peripheral parts or the outer peripheral parts of a plurality of metal discs (metal diaphragm plates) formed to have a wave-like cross section to each other by welding and the like so as to become an accordion-like tube shape as a whole. 
     The bellows  11  shown in  FIG. 1  merely shows one example of a specific configuration of the welded bellows, and the configuration of the bellows used in each example of the present invention is not limited to the configuration shown in  FIG. 1 . The illustration of a specific shape of the bellows  11  is omitted in  FIG. 2 ,  FIG. 5 ,  FIG. 6 , and  FIG. 8 . 
     The collar  15  is welded to the other end of the bellows  11 . The collar  15  is an annular member made of metal such as SUS 304, and is fixed to the seal cover  22  attached to the opening of the shaft hole  21  of the housing  20 . 
     The three members, the retainer  14 , the bellows  11 , and the collar  15  that are welded to each other can be assembled to the housing  20  (seal cover  22 ) as one unit (bellows assembly). 
     The retainer  14  has an end face  14   a  perpendicular to the axis at the end on the side opposite to the opening of the shaft hole  21 . The retainer  14  includes a damper  14   b  configured by a projection that projects out in the radially inwardly direction at plural areas on the inner peripheral surface to partially narrow the space between the inner peripheral surface of the retainer  19  and the outer peripheral surface of the cylindrical portion  23   a  of the baffle sleeve  23 . The specific configuration of the damper  14   b  is similar to the damper  104   a  of the mechanical seal  100  shown in  FIG. 6  (see  FIG. 7 ) and the damper  104   a  of the mechanical seal  100 ′ shown in  FIG. 8 , and thus the detailed description will be omitted. The space between the retainer  14  and the cylindrical portion  23   a  of the baffle sleeve  23  forms an enlarged flow path in which the region enlarged between the adjacent projections easily guides the quench fluid supplied from a quench hole  22   a  of the seal cover  22  to the end sealing face side along the outer periphery of the cylindrical portion  23   a  of the baffle sleeve  23 . 
     The seal ring  12  includes end sealing faces  12   a   1 ,  12   a   2  perpendicular to the axis on both sides in the axial direction. The end sealing face  12   a   1  (first end sealing face) on the side opposite to the opening (Device side) of the shaft hole  21  contacts the end face  13   a  of the mating ring  13 , and the end sealing face  12   a   2  (second end sealing face) on the opening side of the shaft hole  21  contacts the end face  14   a  of the retainer  14 . The face width of the end sealing face  12   a   2  that contacts the retainer  14  is set to be substantially the same or slightly narrower than the face width of the end sealing face  12   a   1  that contacts the mating ring  13 . 
     The end face  13   a  of the mating ring  13  and the end face  14   a  of the retainer  14  are both lapping finished (surface polished), and have the surface roughness and the planarity same as the end sealing faces  12   a   1 ,  12   a   2  of the seal ring. The lapping surfaces sealably contact each other by the spring load of the bellows  11  and the pushing force by the fluid pressure. 
     One or a plurality of cutouts  12   b  is formed on the inner peripheral surface of the seal ring  12 , so that the protrusion  23   b  arranged at the distal end of the cylindrical portion  23   a  of the baffle sleeve  23  interlocks (loosely engage) with the cutout  12   b  with a very small gap (see circled broken line part at the central part of  FIG. 1 ). The seal ring  12  is configured to be freely movable in the axial direction but regulated in the movement in the peripheral direction, that is, the rotating movement by the clutch mechanism. 
     Therefore, the end sealing face  12   a   1  that contacts the end face  13   a  of the mating ring  13  contacts in a freely slidable manner by the rotation of the rotating shaft  30 , but the end sealing face  12   a   2  that contacts the end face  14   a  of the retainer  14  becomes a substantially stationary sealed surface that does not generate slidable movement by rotation since the rotation of the seal ring  12  with respect to the retainer  14  is regulated. 
     A step  12   c  for enlarging the inner diameter on the retainer  14  side of the seal ring  12  is provided on the inner peripheral surface of the seal ring  12 . A step  14   c  for enlarging the inner diameter on the seal ring  12  side of the retainer  14  is also provided on the inner peripheral surface of the retainer  14 . The steps  12   c ,  14   c  have the inner diameter dimension set to be substantially the same, and an annular recess is formed at the boundary of the seal ring  12  and the retainer  14 . A centering case  16  serving as a centering member for aligning the seal ring  12  and the retainer  14  is attached to the recess. The centering case  16  is an annular member manufactured with the material same as the seal ring  12  or the material (e.g., SiC) having a coefficient of thermal expansion same as or smaller than the seal ring  12 , and is fitted with a very small gap in the radial direction with respect to the recess. 
     As described above, in the present example, the seal ring  12  is not fixed to the retainer  14  as in the conventional example, and is configured to be freely slidable in a direction perpendicular to the axis between the mating ring  13  and the retainer  14 . Therefore, the dimensional change in the axial direction due to influence of thermal expansion and the like is absorbed by the expansion and contraction of the bellows  11 , and the dimensional change in the direction (radial direction) perpendicular to the axis is absorbed when the end sealing faces perpendicular to the axis slidably move (shift) with respect to each other. The planarity of the end sealing face of the seal ring  12  that slidably contacts the mating ring  13  is thus not subjected to the influence of thermal expansion even in high temperature atmosphere, and sealability can be maintained. The planarity is also not influenced by pressure deformation and thermal deformation of the retainer  14  itself. 
     Furthermore, since the seal ring  12  is not fixed to the retainer  14 , special steps such as burn fitting and press fitting, and the subsequent heat processing and the like as in the prior art are unnecessary, and the jigs involved therewith are also unnecessary. The cost thus can be reduced and the number of steps can be reduced. The seal ring replacement task is also facilitated. 
     In the present example, the centering case  16  for aligning the seal ring  12  and the retainer  14  is attached to the stepped portion provided on each inner peripheral surface that becomes the non-sealed region side in the seal ring  12  and the retainer  14 . In other words, the centering case  16  fitted with a very small gap in view of the difference in the coefficient of thermal expansion has a configuration of not being in the sealed fluid, and hence the sealed fluid does not fix to the space between the centering case  16  and the seal ring  12  and the retainer  14  even if the sealed fluid is the fluid having the property of easily solidifying and fixing at low temperature or the fluid having great amount of solid content. Furthermore, the gap is cleaned with the quench fluid on a constant basis since the centering case  16  is arranged on the quench fluid side, and hence the lapped end faces of the seal portion may smoothly slip with each other on a constant basis. 
     SECOND EXAMPLE 
     A bellows type mechanical seal  1 ′ according to a second example of the present invention will be described with reference to  FIG. 2  to  FIG. 3B .  FIG. 2  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal  1 ′ according to the second example of the present invention.  FIG. 3A  and  FIG. 3B  are schematic views describing the configuration of the elastic member, where  FIG. 3A  is a schematic cross-sectional view of an elastic member and  FIG. 3B  is a cross-sectional view seen from arrow A of  FIG. 3A . The same reference numerals are attached to the configurations similar to the first example to omit the detailed description thereof, and only the portions different from the first example will be described. The configurations that are not described are the configurations similar to the first example. 
     The present example includes an elastic member  17  for acting an elastic force in a radially outwardly direction with respect to the retainer  14 . The elastic member  17  is attached to an annular groove  16   a  provided on the inner peripheral side of the centering case  16 ′, and is configured to elastically contact the cylindrical portion  23   a  of the baffle sleeve  23 . The elastic member  17  is a very thin band member (annular plate spring member) having elasticity, where a great number of R-shaped projections  17   a  is arranged at equal interval on one surface. The elastic member  17  is annularly attached between the cylindrical portion  23   a  of the baffle sleeve  23  and the centering case  16 ′, and the projection  17   a  is accommodated in the annular groove  16   a  on the inner periphery of the centering case  16 ′ so that the axial movement is regulated. 
     The elastic member  17  has the plane portion (inner peripheral side)  17   b  contacting the outer periphery of the cylindrical portion  23   a  of the baffle sleeve  23  at a very low surface pressure by the elastic biasing force obtained when the projection  17   a  deforms in the radial direction, and buffers the vibration of the seal ring  12  and the retainer  14  through the centering case  16 ′. The plane portion (inner peripheral side)  17   b  of the elastic member  17  and the outer periphery of the cylindrical portion  23   a  of the baffle sleeve  23  can freely slidably move in the axial direction. 
     The dimension and configuration of each portion of the elastic member  17 , the magnitude of the area pressure (elastic force) to act on the inner peripheral surface of the centering case  16 ′ and the outer peripheral surface of the cylindrical portion  23   a  of the baffle sleeve  23 , and the like are appropriately set so that the vibration generated by the slidable movement of the sealing  12  and the mating ring  13  can be sufficiently buffered by the deformation of the projection  17   a  and the plane portion  17   b  contacts at a low surface pressure of an extent of not inhibiting the free displacement (expansion and contraction of the bellows  11 ) in the axial direction of the seal ring  12  and retainer  14 . 
     According to the present example, in the unlikely event that the joint portion of the lapped end sealing faces is fixed, the stick slip of the end sealing face may be propagated to the retainer  14  and vibrate, but the propagation of the vibration to the bellows  11  is suppressed since the vibration is buffered by the elastic member  17  and hence the breakage etc. of the welded portion of the bellows  11  is prevented. 
     The elastic member  17  is accommodated in the inner periphery of the centering case  16 ′ and the centering case  16 ′ is independent, and thus it can be easily fitted to the cylindrical portion  23   a  of the baffle sleeve  23  and the assembly is facilitated. 
     THIRD EXAMPLE 
     A bellows type mechanical seal  1 ′ according to a third example of the present invention will now be described with reference to  FIG. 4 .  FIG. 4  is a schematic cross-sectional view describing the configuration of the bellows type mechanical seal  1 ″ according to the third example of the present invention. The same reference numerals are attached to the configurations similar to the each example above to omit the detailed description thereof, and only the portions different from each example will be described. The configurations that are not described are the configurations similar to each example. 
     In the present example, an annular groove  14   d  is provided on the inner peripheral side of the retainer and the elastic member  17  is attached to the annular groove  14   d . In other words, the vibration of the seal ring  12  and the retainer  14  is buffered through the centering case  16 ′ in the second example, whereas the vibration of the retainer  14 ′ is directly buffered by the elastic member  17  in the present example. 
     With the configuration of directly buffering the vibration of the retainer  14 ′ without interposing another member, the change in buffering property caused by the dimensional change from thermal expansion and the like can be suppressed to a minimum. 
     The configuration of the elastic member  17  according to the second example and the third example is not limited to the above described configuration, and any configuration may be appropriately adopted as long as the elastic force can be exerted in the radial direction. For instance, the elastic member  17 ′ shown in  FIG. 5  may be adopted.  FIG. 5  is a schematic perspective view describing another configuration of the elastic member. 
     The elastic member  17 ′ shown in  FIG. 5  is configured by forming a plurality of projections  17   a ′ through press molding on a thin band-shaped plate material made of stainless steel and the like, and curved to an annular shape. The elastic member  17  has a wave-like cross-sectional shape in the peripheral direction (cross-sectional shape seen from axial direction) by the plurality of projections  17   a ′, where the vibration of the retainer and the like is buffered to suppress the propagation of the vibration to the bellows  11  when the plurality of projections  17   a ′ elastically contacts the centering case  16 ′ and the retainer  14 ′. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  bellows type mechanical seal 
           11  bellows 
           12  seal ring 
           13  mating ring 
           14  retainer 
           15  collar 
           20  housing 
           21  shaft hole 
           22  seal cover 
           23  baffle sleeve 
           30  rotating shaft