JP7066433B2 - mechanical seal - Google Patents

Description

The present invention relates to a mechanical seal.

Conventionally, as a device for sealing the sealed fluid inside the rotating device, a static sealing ring fixed to the casing side and a rotating sealing ring rotatably attached to the rotating shaft side are arranged side by side in the axial direction. , A mechanical seal in which the sealing surfaces of the static sealing ring and the rotary sealing ring that face each other are in sliding contact with each other is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2017-078460

In the rotating device, the rotation axis may be tilted with respect to the casing due to poor accuracy or the like. In such a case, there is a problem that the mechanical seal cannot be assembled to the rotating device in a state of being aligned with the inclination of the rotating shaft.

The present invention has been made in view of such circumstances, and an object of the present invention is to enable a mechanical seal to be assembled even in a rotating device having a tilted rotating shaft.

(1) The mechanical seal of the present invention is provided on a rotating shaft so as to be integrally rotatable, and is provided on a rotating side unit having a rotating sealing ring and a casing surrounding the rotating shaft, and the rotating sealing ring is in sliding contact with the rotating shaft. A stationary side unit having a static sealing ring, wherein the stationary unit has an outer ring attached to the casing and an inner ring arranged on the inner peripheral side of the outer ring and provided with the static sealing ring. It has a sealing member that seals between the inner circumference of the outer ring and the outer circumference of the inner ring, and a detent mechanism that restricts the inner ring from rotating about its axis with respect to the outer ring. A concave curved surface is formed on the inner circumference of the outer ring so that the inclination of the inner ring with respect to the outer ring can be adjusted according to the inclination of the rotation axis with respect to the casing on the outer periphery of the inner ring. A convex curved surface is formed so as to face the concave curved surface.

According to this mechanical seal, the convex curved surface formed on the outer periphery of the inner ring is arranged facing the concave curved surface formed on the inner circumference of the outer ring on the casing side, so that the stationary side unit of the mechanical seal is rotated. When assembling to the casing of the device, the inclination of the inner ring with respect to the outer ring can be adjusted according to the inclination of the rotation axis with respect to the casing. As a result, the mechanical seal can be attached even to a rotating device whose rotation axis is tilted with respect to the casing.

(2) It is preferable that the outer ring is attached to the casing so as to be adjustable in position in a direction perpendicular to the axis of the outer ring.
If the center of tilt of the axis of rotation is located away from the casing, the axis of rotation may tilt in a direction perpendicular to the axis of the outer ring. In such a case, according to the mechanical seal of (2) above, the position of the outer ring can be adjusted so as to be biased in the direction perpendicular to the axis of the casing in accordance with the bias of the rotation axis. Further, the inclination of the inner ring with respect to the outer ring can be adjusted according to the inclination of the rotation axis. As a result, the mechanical seal can be attached even to a rotating device in which the rotating shaft is inclined in a direction perpendicular to the axis of the outer ring with respect to the casing.

(3) It is preferable that the stationary side unit further includes a regulating member that regulates the inner ring from tilting beyond a predetermined range with respect to the outer ring.
In this case, the restricting member can suppress the deterioration of the sealing performance of the sealing member due to the inner ring tilting beyond a predetermined range with respect to the outer ring.

(4) The seal member is an O-ring, and it is preferable that an annular groove to which the O-ring is mounted is formed on the inner circumference of the outer ring.
In this case, since the O-ring is attached to the outer ring on the fixed side, it is possible to prevent the O-ring from coming off as compared with the case where the O-ring is attached to the inner ring on the movable side.

According to the present invention, the mechanical seal can be attached even to a rotating device whose rotating shaft is tilted.

It is sectional drawing which shows the mechanical seal which concerns on one Embodiment of this invention. It is a front view of the outer ring. It is an enlarged sectional view of the main part of FIG.

Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.
[overall structure]
FIG. 1 is a cross-sectional view showing a mechanical seal according to an embodiment of the present invention. In FIG. 1, the mechanical seal 1 of the present embodiment is used for a rotating device such as a pump and a stirrer, and is arranged between the rotating shaft S of the rotating device and the casing C surrounding the rotating shaft S. Has been done.

The mechanical seal 1 seals the fluid to be sealed inside the rotating device, and has a rotating side unit 2 rotatably provided on the rotating shaft S rotating at a low speed and a stationary side provided on the casing C. It is equipped with a unit 3. In the present specification, the left side of FIG. 1 is referred to as the outside A of the aircraft, and the right side of FIG. 1 is referred to as the inside B of the aircraft (the same applies to FIG. 3).

[Rotating side unit]
The rotation side unit 2 of the mechanical seal 1 has a sleeve 11 fitted on the rotation shaft S, a drive ring 12 fitted on the outer circumference of the machine inside B of the sleeve 11, and an inner circumference of the machine outside A of the drive ring 12. It is provided with an annular rotary sealing ring 13 fitted to the above.

A plurality of stopper rings 14 (only one is shown in FIG. 1) are fitted to the outer periphery of the outer circumference A of the sleeve 11 at predetermined intervals in the circumferential direction, and a plurality of stopper rings 14 are screwed into the stopper rings 14. The sleeve 11 is fixed to the rotating shaft S by tightening the set screw 15. A rubber O-ring 16 is provided on the inner circumference of the machine inner side B of the sleeve 11 to seal (secondary seal) between the sleeve 11 and the outer peripheral surface of the rotating shaft S.

A rubber O-ring 17 is provided on the outer periphery of the machine inner side B of the sleeve 11 to seal (secondary seal) between the sleeve 11 and the inner peripheral surface of the drive ring 12. Further, an engaging pin 18 projects and is fixed to the outer periphery of the machine inner side B of the sleeve 11 in the radial direction.

An engaging hole 12a is formed at the end of the machine inner side B of the drive ring 12, and an engaging pin 18 fixed to the sleeve 11 is engaged with the engaging hole 12a. As a result, the drive ring 12 is restricted from rotating relative to the sleeve 11. On the inner peripheral side of the drive ring 12, an engaging pin 19 projects and is fixed to the outside A of the machine.

An engaging hole 13b is formed at the end of the machine inner side B of the rotary sealing ring 13, and an engaging pin 19 fixed to the drive ring 12 is engaged with the engaging hole 13b. As a result, the rotation sealing ring 13 is restricted from rotating relative to the sleeve 11 via the drive ring 12.

The rotary sealing ring 13 is made of, for example, a sintered body of silicon carbide (SiC) having excellent wear resistance and sealing performance. The end surface of the machine outside A of the rotary sealing ring 13 is a sealing surface 13a. A rubber O-ring 20 is provided on the outer periphery of the rotary sealing ring 13 to seal (secondary seal) between the drive ring 12 and the drive ring 12.

[Static side unit]
The stationary side unit 3 of the mechanical seal 1 has an outer ring 31 attached to the casing C, an inner ring 32 arranged on the inner peripheral side of the outer ring 31, and an annular number attached to the inner circumference of the inner ring 32. It includes one retainer 33, an annular second retainer 34 attached to the inside B of the first retainer 33, and an annular static sealing ring 35 attached to the inside B of the second retainer 34. The attachment structure of the outer ring 31 to the casing C and the attachment structure of the inner ring 32 to the outer ring 31 will be described later.

The first retainer 33 is fixed to the inner peripheral side of the machine outside A of the inner ring 32 by a screw 36. A bush 37 for forming a clearance seal with the outer peripheral surface of the sleeve 11 is fitted and fixed to the inner circumference of the first retainer 33. An end portion of the machine outside A of the second retainer 34 is connected to the inner circumference of the machine inside B of the first retainer 33 via a connecting pin 38.

A plate 39 made of an annular plate protrudes outward in the radial direction and is fixed to the outer periphery of the second retainer 34. Further, on the outer periphery of the second retainer 34, a rubber O-ring 40 is provided on the inner side B of the machine rather than the plate 39 to seal (secondary seal) between the inner ring 32 and the inner ring 32.

A static sealing ring 35 made of carbon, for example, is fitted and fixed to the inner circumference of the machine inside B of the second retainer 34. At the end of the machine inside B of the static sealing ring 35, a sealing surface 35a to which the sealing surface 13a of the rotary sealing ring 13 is in sliding contact is formed.

A plurality of springs 41 are provided between the first retainer 33 and the plate 39 at predetermined intervals in the circumferential direction as pressing members for pressing the plate 39 toward the inside B of the machine (only one is shown in FIG. 1). .. In addition to the spring 41, another pressing member such as a bellows may be used.

From the above, the sealing surface 35a of the static sealing ring 35 is in sliding contact with the sealing surface 13a of the rotary sealing ring 13 while being pressed by the pressing force of the spring 41 to seal between the machine outside A and the machine inside B. There is. Therefore, the mechanical seal 1 can prevent the fluid to be sealed on the inside B of the machine from leaking to the outside A of the machine.

[Attachment structure of outer ring to casing]
FIG. 2 is a front view of the outer ring 31. In FIGS. 1 and 2, the outer ring 31 has an outer peripheral surface 31d formed of a circumferential surface centered on the axis X. The position of the outer ring 31 can be adjusted in the direction perpendicular to the axis X (vertical direction in FIG. 1) with respect to the casing C in a state where the end surface of the machine inside B is in contact with the end face of the machine outside A of the casing C. It is attached.

Specifically, a plurality of (4 in FIG. 2) notched grooves 31a are formed on the outer periphery of the outer ring 31 in the circumferential direction. Each notch groove 31a is formed by notching long in a direction perpendicular to the axis X (vertical direction in FIG. 2). Of these notch grooves 31a, a part (upper two in FIG. 2) of the notch grooves 31a1 opens on one side (upper side in FIG. 2) in the vertical direction, and the rest (lower side in FIG. 2). The two) notch grooves 31a2 are open on the other side (lower side of FIG. 2) in the vertical direction.

A stud bolt 42A is inserted through each notch groove 31a1, and a stud bolt 42B is inserted through each notch groove 31a2. One end of the stud bolts 42A and 42B is screwed into a bolt hole C1 formed on the end surface of the machine outside A of the casing C. A nut 43 is screwed into the other end of the stud bolts 42A and 42B protruding from the notch groove 31a to the outside A of the machine via a washer 44.

From the above, by loosening the nut 43 tightened to the stud bolts 42A and 42B, the outer ring 31 is attached to the casing C with respect to the casing C until the bottom of the upper notch groove 31a1 in FIG. 2 abuts on the stud bolt 42A. It can be moved upward. Further, by loosening the nut 43, the outer ring 31 can be moved downward in FIG. 1 with respect to the casing C until the bottom portion of the notch groove 31a2 on the lower side of FIG. 2 abuts on the stud bolt 42B. As a result, the position of the outer ring 31 can be adjusted in the vertical direction of FIG. 1 with respect to the casing C.

In FIG. 1, a gasket 45 for sealing (secondary sealing) between the end surface of the machine inside B of the outer ring 31 and the end face of the machine outside A of the casing C is provided. The gasket 45 is made of, for example, polytetrafluoroethylene (PTFE).

[Mounting structure of inner ring to outer ring]
FIG. 3 is an enlarged cross-sectional view of a main part of FIG. In FIG. 3, on the inner circumference of the outer ring 31, a concave curved surface 31b is formed from the end of the outer side A of the machine to the middle position in the axial direction, and the circumferential surface 31c is formed from the middle position to the end of the inner side B of the machine. Is formed. The concave curved surface 31b of the present embodiment is made of a concave spherical surface.

A convex curved surface 32b is formed on the entire outer circumference of the inner ring 32. In the present embodiment, the convex curved surface 32b is formed of a convex spherical surface and has a curvature slightly shorter than that of the concave curved surface 31b. The center of curvature P (see FIG. 1) of the concave curved surface 31b and the convex curved surface 32b coincides with the axis X of the outer peripheral surface 31d of the outer ring 31. Either one or both of the concave curved surface 31b and the convex curved surface 32b may be toroidal surfaces.

From the above, the convex curved surface 32b of the inner ring 32 is arranged so as to be movable in the left-right direction in FIG. 3 so as to face the concave curved surface 31b of the outer ring 31. Therefore, by moving the convex curved surface 32b with respect to the concave curved surface 31b, the inner ring 32 can be tilted with respect to the outer ring 31.
Further, since the circumferential surface 31c is formed on the inner peripheral B of the inner circumference of the outer ring 31, the inner ring 32 is inserted from the inner B of the outer ring 31 to the inner peripheral side of the outer ring 31. The inner ring 32 can be easily assembled.

The inner circumference of the outer ring 31 may have a concave curved surface on the inner side B of the machine and a circumferential surface on the outer side A of the machine. In this case, the inner ring 32 may be inserted from the machine outer side A of the outer ring 31.
Further, the entire inner circumference of the outer ring 31 may be a concave curved surface. In this case, the outer ring 31 may be divided in the circumferential direction and configured, and the divided body of the outer ring 31 may be assembled on the outer peripheral side of the inner ring 32.

In FIG. 1, in a state where the inner ring 32 is tilted with respect to the outer ring 31, the mechanical seal 1 aligns and fixes the stationary side unit 3 other than the outer ring 31 with respect to the rotating side unit 2, and is statically sealed. A fixing jig 80 for setting the mounting length of the ring 35 (pressing pressure of the spring 41) to a normal value is provided. The fixing jig 80 of the present embodiment includes a plurality of set claws 81 (only one is shown in FIG. 1) arranged across the stopper ring 14 of the rotating side unit 2 and the first retainer 33 of the stationary side unit 3. , Each set claw 81 is composed of a plurality of bolts 82 for fixing to the stopper ring 14. The set claw 81 is formed, for example, in a substantially rectangular parallelepiped shape. The machine outside A of the set claw 81 is fixed to the stopper ring 14 by a bolt 82, and the machine inside B of the set claw 81 is locked to the outer periphery of the first retainer 33.

Returning to FIG. 3, the stationary side unit 3 further includes a sealing member 50 that seals between the inner circumference of the outer ring 31 and the outer circumference of the inner ring 32. The seal member 50 of the present embodiment is composed of, for example, a first O-ring 51 and a second O-ring 52. The sealing member 50 may use one or three or more O-rings or other sealing means.

The first O-ring 51 is attached to the concave first annular groove 31e formed on the concave curved surface 31b of the outer ring 31, and is in contact with the machine outside A of the convex curved surface 32b of the inner ring 32. The second O-ring 52 is attached to the concave second annular groove 31f formed on the circumferential surface 31c of the outer ring 31, and is in contact with the machine inner B of the convex curved surface 32b of the inner ring 32. Further, the second O-ring 52 has a wire diameter larger than that of the first O-ring 51. Correspondingly, the second annular groove 31f is formed larger than the first annular groove 31e.

The stationary side unit 3 further includes a detent mechanism 60 that restricts the inner ring 32 from rotating about its axis with respect to the outer ring 31. The detent mechanism 60 of the present embodiment is composed of a pin 61 fixed to the inner circumference of the outer ring 31 and a groove portion 62 formed on the outer periphery of the inner ring 32.

Specifically, on the inner circumference of the outer ring 31, a pin 61 projects radially inward and is fixed at a predetermined position in the circumferential direction between the first annular groove 31e and the second annular groove 31f. The pin 61 of the present embodiment is formed in a columnar shape, for example, and is fixed so as to straddle the boundary between the concave curved surface 31b and the circumferential surface 31c on the inner circumference of the outer ring 31.

A groove 62 into which the pin 61 is inserted is formed on the outer periphery of the inner ring 32 in the middle of the axial direction (left-right direction in FIG. 3). The groove portion 62 is formed of, for example, a cylindrical groove and has an inner diameter larger than the outer diameter of the pin 61. As a result, the pin 61 is inserted into the groove 62 with play.

From the above, while allowing the inner ring 32 to tilt with respect to the outer ring 31 within the range of the play, the pin 61 comes into contact with the inner peripheral surface of the groove portion 62, whereby the inner ring 32 with respect to the outer ring 31 Can be restricted from rotating around its axis.
The detent mechanism 60 may be composed of anything other than the pin 61 and the groove 62 as long as it restricts the inner ring 32 from rotating around its axis with respect to the outer ring 31.

The stationary side unit 3 further includes a regulating member 70 that regulates the inner ring 32 from tilting beyond a predetermined range with respect to the outer ring 31. The regulating member 70 projects and is fixed to the circumferential surface 31c of the inner circumference of the outer ring 31 at the machine inner side B rather than the inner ring 32. The regulating member 70 of the present embodiment is made of, for example, an annular plate, and its outer peripheral end is fixed to the circumferential surface 31c.

The regulating member 70 is arranged at a position where the outer peripheral end portion of the machine inner side B of the inner ring 32 comes into contact with the outer ring 31 when the inner ring 32 is tilted to a predetermined inclination angle. As a result, the regulating member 70 regulates that the inner ring 32 is tilted with respect to the outer ring 31 beyond a predetermined range.

The predetermined range is set within the play range, and specifically, when the inner ring 32 is tilted with respect to the outer ring 31, each of the first and second O-rings 51 and 52 is set. It is set within a range not separated from the convex curved surface 32b.

[Inclination of rotating shaft with respect to casing]
In FIG. 1, the rotary shaft S of the present embodiment is rotatably supported by a bearing (not shown) at a position separated from the casing C to the machine outside A by a predetermined distance. Therefore, when an accuracy defect occurs in the rotating device, the axis Y of the rotating axis S becomes the axis X of the outer ring 31 on the casing C side with the support portion of the bearing as the center, as shown by the broken line in FIG. On the other hand, it may be inclined in a direction perpendicular to the axis X (downward in FIG. 1).

As described above, the stationary side unit 3 of the mechanical seal 1 is assembled to the rotating device in which the axis Y of the rotating axis S is inclined in a direction perpendicular to the axis X.
That is, with respect to the bias of the rotation axis S in the vertical direction, the position of the outer ring 31 is adjusted so as to be biased in the vertical direction with respect to the casing C in accordance with the bias. In this position adjustment, the nut 43 tightened to the stud bolts 42A and 42B is loosened, and the outer ring 31 is vertically aligned so that the relative position between the notch groove 31a of the outer ring 31 and the stud bolt 42A (42B) is displaced. This can be done by moving in any direction (see also FIG. 2).

Further, with respect to the inclination of the rotation axis S, the inclination of the inner ring 32 with respect to the outer ring 31 is adjusted according to the inclination. This inclination can be adjusted by moving the convex curved surface 32b of the inner ring 32 with respect to the concave curved surface 31b of the outer ring 31 (see FIG. 3).

As described above, by adjusting the position of the outer ring 31 in the direction perpendicular to the casing C and adjusting the inclination of the inner ring 32 with respect to the outer ring 31, the stationary side unit 3 of the mechanical seal 1 is placed in the casing C. Can be assembled in.

[Example of deformation of the inclination of the rotating shaft with respect to the casing]
Regarding the mechanical seal 1 of the present embodiment, as shown by the two-dot chain line of FIG. 1, the axis Y of the rotation axis S is also tilted about the center of curvature P of the concave curved surface 31b of the outer ring 31. The stationary side unit 3 can be assembled. In this case, the stationary side unit 3 is assembled as follows.

That is, the inclination of the inner ring 32 with respect to the outer ring 31 is adjusted according to the inclination of the rotation axis S with respect to the center of curvature P. This inclination can be adjusted by moving the convex curved surface 32b of the inner ring 32 with respect to the concave curved surface 31b of the outer ring 31 (see FIG. 3).

[Action effect]
According to the mechanical seal 1 of the present embodiment, the convex curved surface 32b formed on the outer periphery of the inner ring 32 is arranged so as to face the concave curved surface 31b formed on the inner circumference of the outer ring 31 on the casing C side. Therefore, in a rotating device in which the axis Y of the rotating shaft S is tilted about the center of curvature P of the concave curved surface 31b of the outer ring 31, as shown by the two-dot chain line in FIG. 1, the stationary side unit 3 is casing C. The inclination of the inner ring 32 with respect to the outer ring 31 can be adjusted according to the inclination of the rotation axis S with respect to the casing C. As a result, the mechanical seal 1 can be attached to the casing C even in a rotating device in which the rotation axis S is tilted about the center of curvature P of the concave curved surface 31b of the outer ring 31.

Further, in a rotating device in which the axis Y of the rotating axis S is inclined in a direction perpendicular to the axis X of the outer ring 31, as shown by the broken line in FIG. 1, when the stationary side unit 3 is assembled to the casing C. Can adjust the position of the outer ring 31 so as to be biased in the direction perpendicular to the casing C in accordance with the deviation of the rotation axis S. Further, the inclination of the inner ring 32 with respect to the outer ring 31 can be adjusted according to the inclination of the rotation axis S. As a result, the mechanical seal 1 can be assembled even in a rotating device in which the rotating shaft S is inclined in a direction perpendicular to the axis X of the outer ring 31 with respect to the casing C.

Further, the stationary side unit 3 includes a regulating member 70 that regulates the inner ring 32 from tilting beyond a predetermined range with respect to the outer ring 31. This prevents the first and second O-rings 51 and 52 of the sealing member 50 from being separated from the convex curved surface 32b due to the inner ring 32 being tilted with respect to the outer ring 31 beyond the predetermined range. can do. As a result, the deterioration of the sealing performance of the sealing member 50 can be suppressed by the regulating member 70.

Further, since the first and second O-rings 51 and 52 are mounted on the first and second annular grooves 31e and 31f of the outer ring 31 on the fixed side, they are mounted on the inner ring 32 on the movable side. It is possible to prevent the first and second O-rings 51 and 52 from coming off as compared with the case where the first and second O-rings 51 and 52 are disengaged.

[others]
The notch groove 31a of the outer ring 31 in the present embodiment is notched long in a direction perpendicular to the axis X and in a direction in which the rotation axis S is biased, such as the left-right direction in FIG. 2, in addition to the vertical direction in FIG. It suffices if it is formed. Further, a long hole may be formed instead of the notch groove 31a.

The mechanical seal of the present invention is not limited to the configuration of the above embodiment, and can be applied to mechanical seals of other configurations.
For example, the mechanical seal 1 of the present embodiment is provided with a pressing member (spring 41, bellows, etc.) for sliding contact while pressing the rotary sealing ring 13 and the static sealing ring 35 on the stationary side unit 3. Although it is a so-called stationary mechanical seal, it can also be applied to a so-called rotary mechanical seal in which the pressing member is provided on the rotation side unit 2 side.

Further, the mechanical seal 1 of the present embodiment is a so-called inside type mechanical seal in which the radial inside of the rotary sealing ring 13 and the static sealing ring 35 is the region of the machine outer side A, but the rotary sealing ring 13 and the static sealing are provided. It can also be applied to a so-called outside type mechanical seal in which the radial outer side of the ring 35 is the region of the machine outer side A.

The embodiments disclosed this time should be considered to be exemplary and not restrictive in all respects. The scope of the present invention is indicated by the scope of claims, not the above-mentioned meaning, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

1 Mechanical seal 2 Rotating side unit 3 Resting side unit 13 Rotating sealing ring 31 Outer ring 31b Concave curved surface 31e First annular groove 31f Second annular groove 32 Inner ring 32b Convex curved surface 35 Static sealing ring 50 Sealing member 51 First O-ring 52 Second O-ring 60 Anti-rotation mechanism 70 Regulatory member C Casing S Rotating axis X Outer ring axis

Claims (3)

A rotating unit that is integrally rotatable on the rotating shaft and has a rotating sealing ring,
A stationary side unit provided in a casing surrounding the rotating shaft and having a stationary sealing ring to which the rotating sealing ring is slidably contacted.
The stationary side unit is
The outer ring attached to the casing and
An inner ring arranged on the inner peripheral side of the outer ring and provided with the static sealing ring, and an inner ring.
A sealing member that seals between the inner circumference of the outer ring and the outer circumference of the inner ring,
With respect to the outer ring, it has a detent mechanism that regulates the inner ring from rotating about its axis.
A concave curved surface is formed on the inner circumference of the outer ring.
On the outer periphery of the inner ring, a convex curved surface arranged to face the concave curved surface is formed so that the inclination of the inner ring with respect to the outer ring can be adjusted according to the inclination of the rotation axis with respect to the casing. ,
The detent mechanism has a pin that protrudes and is fixed radially inward on the inner circumference of the outer ring, and a groove portion that is formed on the outer periphery of the inner ring and the pin is inserted radially with play.
The stationary side unit is a mechanical seal further comprising a regulating member that regulates the inner ring from tilting with respect to the outer ring beyond a predetermined range set within the range of play . The mechanical seal according to claim 1, wherein the outer ring is attached to the casing so as to be adjustable in position in a direction perpendicular to the axis of the outer ring. The sealing member is an O-ring and is an O-ring.
The mechanical seal according to claim 1 or 2 , wherein an annular groove in which the O-ring is mounted is formed on the inner circumference of the outer ring.

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