JPH05164249A - Non-contact mechanical seal - Google Patents

Abstract

PURPOSE:To reduce fluid leakage from a mechanical seal by applying the constitution where a part of sealed fluid leaking outside due to the pressure of a main spiral groove on one of both seal faces of a mating ring and a primary ring, is returned to a processing side (sealing side) after the reversal of a flow with a sub-spiral groove formed on the other seal face. CONSTITUTION:A mating ring 3 and a primary ring 4 have seal faces 5 and 6 in contact with each other, and a main spiral groove 8 is formed on one of the faces 5 and 6 in such a way as extended from the internal or external edge thereof as a starting end and closed at the terminal end. Also, a sub-spiral groove 9 is formed on other seal face in such a way as extended from a position inside the internal or external edge as a staring end and closed at the terminal end approximately in agreement to the position of the terminal end of the main spiral groove 8. Furthermore, the grooves 8 and 9 are directionally so set as to have an approximate mirror image relationship.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a non-contact mechanical seal, and more particularly to a non-contact mechanical seal used as a shaft sealing device for fluid equipment such as a gas turbine and a compressor under high peripheral speed conditions.

[0002]

2. Description of the Related Art Conventionally, a non-contact mechanical seal for sealing between a rotary shaft and a casing in a compressor or the like has already been provided. For example, in Japanese Examined Patent Publication No. 1-22509, any one of the sealing surfaces facing a mating ring hermetically fixed to a rotary shaft and a primary ring hermetically mounted on a casing and axially biased by a pressing means. A non-contact mechanical seal in which one sealing surface is provided with a large number of spiral grooves of the same length having an advancing angle with respect to the relative rotation direction at regular intervals in the circumferential direction, and a sealed fluid is pumped between the sealing surfaces. Is provided.

However, in the conventional non-contact mechanical seal, a dynamic pressure toward the center is generated between the seal surfaces of the primary ring and the mating ring, and this dynamic pressure causes a gap of a micron unit between the seal surfaces. Since it is possible to rotate at a high peripheral speed while maintaining the non-contact state, the enclosed fluid (gas or liquid) is exposed to the outside through the gap controlled by this dynamic pressure and the sealing pressure (static pressure) of the enclosed fluid in principle. Leakage is inevitable.

Conventionally, a small amount of leakage through the gap formed between the seal surfaces has been ignored in principle as unavoidable, but it is necessary to further reduce this small amount of leakage for food equipment, pharmaceutical products. This is desired in non-contact mechanical seals used in equipment or precision equipment.

[0005]

In the non-contact mechanical seal, conventionally, all the enclosed fluid pressurized in the outward direction between the sealing surfaces of the mating ring and the primary ring leaks to the outside. In view of the above situation, the present invention is to solve the problem that a part of the enclosed fluid that is pressurized by the main spiral groove formed in one of the sealing surfaces of the mating ring and the primary ring and leaks to the outside is The point is to provide a non-contact mechanical seal with less leakage by allowing the auxiliary spiral groove formed on the sealing surface to reversely flow back to the process side (encapsulation side).

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is axially movable in a mating ring and a casing, which are hermetically fixed to a rotating shaft, and is hermetically mounted by a pressing means in the axial direction. The two sealing surfaces that are in contact with the urged primary ring, one main sealing surface extends from the outer peripheral edge or the inner peripheral edge as the starting end, and the main spiral groove that closes the end is provided, and the other sealing surface has the main spiral groove. A sub spiral groove extending from the outer peripheral edge or the inner peripheral edge with an inner position as a starting end and having its end substantially aligned with the end of the main spiral groove is provided,
The spiral grooves formed on both seal surfaces are oriented so as to have a substantially mirror image relationship with each other, and a dynamic pressure toward the end is generated in the main spiral groove on one of the seal surfaces with rotation of the rotary shaft in a specific direction, and A non-contact mechanical seal is created by generating dynamic pressure that causes the leaking fluid to flow backward with the auxiliary spiral groove on the sealing surface.

The dam width ratio of the main spiral groove is about 0.
It was set to 2 to 0.8 and the dam width ratio of the auxiliary spiral groove was set to about 0.3 to 0.7.

[0008]

In the non-contact mechanical seal of the present invention having the above-mentioned contents, the main spiral groove formed on one of the sealing surfaces of the mating ring and the primary ring allows the enclosed fluid to reach the end of the groove. A dynamic pressure to be pumped is generated, and by this fluid transport action, the pressure of the enclosed fluid pumped between the seal faces forms a gap between the two seal faces, and the auxiliary spiral groove formed on the other seal face causes the main spiral groove A part of the enclosed fluid pressure-fed to the outside is back-flowed to the process side (enclosed side) to minimize the leakage amount of the enclosed fluid.

[0009]

The present invention will be further described in detail with reference to the embodiments shown in the accompanying drawings. In this embodiment, the non-contact mechanical seal used for gas sealing will be mainly described, but the same applies to fluid sealing.

FIG. 1 shows the entire structure of a non-contact mechanical seal M according to the present invention, which is provided between a casing 1 and a rotary shaft 2 penetrating an open end of the casing 1. Here, in the figure, A indicates the atmospheric pressure (low pressure) side, and B indicates the high pressure (seal pressure) side. The atmospheric pressure side and the high pressure side may be reversed.

The non-contact mechanical seal M of this embodiment is
A mating ring 3 hermetically fixed to the rotary shaft 2;
Primary ring 4 hermetically mounted on the casing 1
The mating ring 3 and the primary ring 4 have their sealing surfaces 5 and 6 in contact with each other, and the primary ring 4 is axially movable in a sealed state, and
A pressing means 7 associated with the casing 1 urges the sealing surfaces 5 and 6 in the axial direction toward each other.

Then, as shown in FIG. 2, on the sealing surface 5 of the mating ring 3, a main spiral groove 8 extending inward from the outer peripheral edge thereof and having an advancing angle with respect to the rotational direction R is circumferentially formed. Many are provided at regular intervals in the direction. On the other hand, as shown in FIG. 3, the sealing surface 6 of the primary ring 4 extends inward from the outer peripheral edge of the primary ring 4 with the inward position as the starting end.
A large number of sub spiral grooves 9 having a receding angle with respect to the relative rotation direction R _r (direction opposite to the rotation direction R) are provided at regular intervals in the circumferential direction. That is, the main spiral groove 8 and the sub spiral groove 9 are
When the two sealing surfaces 5 and 6 are in contact with each other, they are formed in such a direction that they are in a substantially mirror image relationship with each other. Here, the inner ends of the main spiral groove 8 and the sub spiral groove 9 are closed at substantially coincident radial positions, that is, they are flush with the other flat surface portions of the seal surfaces 5 and 6. Here, it is preferable that the end of the auxiliary spiral groove 9 is located slightly inward in the radial direction from the end of the main spiral groove 8.

The mating ring 3 is coaxially externally fitted to a fixed sleeve 10 coaxially externally fitted to the rotary shaft 2, and a flange portion 11 extending from one end of the fixed sleeve 10 is provided with a side surface opposite to the sealing surface 5. And the flange portion 11 is fixed to the step portion 12 formed on the rotary shaft 2, and the fastening sleeve 13 externally fitted to the fixed sleeve 10 and the end portion of the fixed sleeve 10 are screwed onto the rotary shaft 2. It is fixed to the rotating shaft 2 together with the fixed sleeve 10 by tightening the combined holding nut 14, and the rotating shaft 2 and the flange portion 1
1, between the mating ring 3 and the fixed sleeve 10 and between the mating ring 3 and the flange portion 11, respectively.
The rings 15, 16 and 17 are interposed and sealed.

The primary ring 4 is axially movable to a predetermined position by an annular holding device 18 which is hermetically fixed to the casing 1 so as to hermetically hold it, and a pressing means 7 seals the sealing surface 5 of the mating ring 3. When,
The sealing surface 6 of the primary ring 4 is urged in the approaching direction. Here, the holding device 18 has one outer peripheral end abutting against the stepped portion 19 of the casing 1 and the other end abutting against the fixed sleeve 20 to restrict axial movement.
Further, an O-ring 21 is provided between the casing 1 and the outer circumference of the holding device 18, and an O-ring 23 is provided between the outer circumference of an annular sliding portion 22 extending axially from the inner circumference and the inner circumference of the primary ring 4. The primary ring 4 is axially movable in a hermetically sealed state by interposing. Then, the other end of the pressing means 7 made of an elastic member such as a plurality of coil springs and the like, one end of which is engaged with the holding device 18, is provided on the opposite side of the seal surface 6 of the primary ring 4 via the annular disc 24. Correspondingly, the primary ring 4 is elastically biased toward the mating ring 3 so that the pressing force always acts in the direction in which the two sealing surfaces 5 and 6 approach each other.

The primary ring 4 does not come into complete contact with the mating ring 3 at the time of rotation, but the mating ring 3 is caused by contact resistance at an initial stage when the rotating shaft 2 starts rotating from a stationary state. When the rotating shaft 2 is rotated over a certain number of revolutions, the dynamic pressure due to the main spiral groove 8 increases and a gap is formed between the sealing surfaces 5 and 6, so that the primary ring 4 slides. Stops sliding. The rotation speed at which the sliding substantially stops depends on the viscosity of the fluid interposed between the seal surfaces 5 and 6.

Further, in this embodiment, an example of the non-contact mechanical seal M provided with a pair of the mating ring 3 and the primary ring 4 has been shown, but a tandem in which a plurality of these are used and arranged in axial relation to each other is used. It can also be used for molds.

2 and 3 show examples of patterns of the main spiral groove 8 and the sub spiral groove 9 formed on the sealing surfaces 5 and 6 of the mating ring 3 and the primary ring 4 of the present invention, respectively. Main spiral groove 8 and sub spiral groove 9
Are formed in a substantially mirror image relationship with each other.

Next, the dam width ratio of the mating ring 3 is defined by the following equation. Dam width ratio = (GD-ID) / (OD-ID) (1) Dam width ratio = (OD-GD) / (OD-ID) (2) Here, OD is the common part of the sealing surfaces 5 and 6. Outline, ID
Is the inner diameter, and GD is the diameter of the contour circle formed at the boundary between the groove area and the flat area of the main spiral groove 8.

The dam width ratio of the primary ring 4 is defined by the following equation. Dam width ratio = (OD-GDO + GDI-ID) / (OD-ID) (3) Here, similarly to the above, OD is the outer shape of the common portion of the sealing surfaces 5 and 6, ID is the inner diameter, and GDO is the auxiliary spiral groove 9. The diameter of the outer contour circle formed at the boundary between the groove area and the flat area, GDI is the diameter of the inner contour circle formed at the boundary between the groove area and the flat area of the auxiliary spiral groove 9.

Expression (1) is an expression applied when the main spiral groove 8 is formed with the outer peripheral edge of the sealing surface 5 as the starting end,
(2) is a formula applied when the inner peripheral edge is formed as the starting end, and in the present invention, the dam width ratio of the main spiral groove 8 is set to about 0.2 to 0.8. The optimum value of this dam width ratio depends on other parameters such as the type and pressure of the enclosed fluid,
The dam width ratio of the main spiral groove 8 is about 0.3 to 0.6 as a more preferable value, although it varies depending on the rotation speed and the like. Further, the expression (3) is an expression applicable to both the auxiliary spiral groove 9 formed with the inner end of the seal surface 6 as the inner end or the outer end of the inner peripheral edge as the starting end, and in the present invention, the dam of the auxiliary spiral groove 9 is formed. The width ratio is set to about 0.3 to 0.7, and a more preferable value is about 0.4 to 0.5. Here, when the main spiral groove 8 and the sub spiral groove 9 are formed on the outer peripheral side, the GD of the formula (3) is calculated.
I substantially matches the GD of the expression (1), and when formed on the inner peripheral side, the GDO of the expression (3) substantially matches the GD of the expression (2).

Here, the main spiral groove 8 and the sub spiral groove 9 in the present invention have a depth of about 2 to 15 μm, and the width and the advance angle are determined by the sealing pressure of the enclosed fluid, the number of revolutions and the like. To be done. Here, the depth of the groove is set shallow for gas sealing and deeper for liquid sealing. Further, the pattern of the spiral groove is not limited to that shown in FIGS. 2 and 3, and various patterns can be adopted.

Then, the spiral groove is formed on the surface of the sealing surface by forming the mating ring 3 and the primary ring 4 into a predetermined shape with a material such as tungsten carbide, silicon carbide, silicon nitride, alumina ceramics, and a metal material. After that, a spiral groove is formed on the surface to be the sealing surface by using a chemical, physical or electrochemical method. For example, it can be formed by etching, powder blasting, and various plating treatments. It is also possible to form the mating ring 3 from the above-mentioned material having high hardness and the primary ring 4 from carbon having low hardness.

Next, in the non-contact mechanical seal M of this embodiment, since the primary ring 4 receives pressure on its inner circumference, its pressure balance is: balance = (BD ² -ID ²⁾ is represented by ^{/ (OD 2 -ID 2) (} 4), its value is set to 0.5 to 1.5.

Thus, the rotary shaft 2 is rotated in the specific rotation direction R.
The operation in the case of being rotated to will be described. As shown in FIGS. 4 and 5, when the mating ring 3 rotates in the R direction as the rotating shaft 2 rotates at a high speed, a predetermined spiral is formed by the main spiral groove 8 formed with an advancing angle on the sealing surface 5. A sealed fluid having a pressure is pumped between the sealing surfaces 5 and 6, so that a dynamic pressure higher than the sealing pressure P _{S in} the radial inside of the sealing surfaces (near the end of the main spiral groove 8) as shown in FIG. P _MM occurs. Note that P _A is the atmospheric pressure and F _M
Indicates the direction of fluid flow by the main spiral groove 8 of the mating ring 3.

On the other hand, the sealing surface 6 of the primary ring 4
Since the auxiliary spiral groove 9 formed at 5 has a receding angle with respect to the relative rotation direction R _{r of the} primary ring 4, the auxiliary spiral groove 9 causes the end portion of the main spiral groove 8 between the seal surfaces 5 and 6 to end. A part of the existing fluid is caused to flow back to the high pressure side B which is the outer circumference in the radial direction, and as shown in FIG. 7, the pressure P _N at the end portion is decreased and the pressure P _PM at the start portion is increased. Here, FIG.
F _{P in the} inside indicates the flow direction of the fluid by the auxiliary spiral groove 9 of the primary ring 4.

FIG. 8 shows an outline of the pressure distribution in the gap between the seal surfaces 5 and 6 which combines the actions of the main spiral groove 8 of the mating ring 3 and the sub spiral groove 9 of the primary ring 4. In FIG. 8, P _TM1 indicates the pressure at the end of the main spiral groove 8 and the auxiliary spiral groove 9, and P _TM2 indicates the pressure at the start of the auxiliary spiral groove 9. As described above, in the conventional single spiral groove formed, as shown in FIG. 6, a pressure distribution having a maximum pressure is generated at one place between the seal surfaces 5 and 6, but In the invention, as shown in FIG. 8, the pressure distribution is such that a high-pressure region is formed widely inward between the sealing surfaces 5 and 6, and the flow F _T of the sealed fluid into this gap is reduced, so that the outside (atmospheric pressure side) Leakage to A) is reduced.

As described above, the mating ring 3 and the primary ring 4 have the seal pressure P _S , the dynamic pressure P _MM due to the main spiral groove 8, the dynamic pressure (P _N , P _PM ) due to the auxiliary spiral groove 9 and the pressing force. The state is balanced with the pressing force of the means 7, that is, the non-contact state in which a parallel gap is formed between the sealing surfaces 5 and 6.

[0028]

According to the non-contact mechanical seal of the present invention as described above, the mating ring hermetically fixed to the rotary shaft and the casing are axially movable and hermetically mounted and attached in the axial direction by the pressing means. A main spiral groove that is a pair of sealing surfaces that are in contact with the urged primary ring and that extends from the outer peripheral edge or the inner peripheral edge as a starting end and closes the end is provided on one sealing surface, and the other sealing surface has an outer peripheral edge. A secondary spiral groove that extends from the inner edge of the peripheral edge or the inner peripheral edge as the starting end and is closed at the end of the main spiral groove is provided so that the spiral grooves formed on both sealing surfaces have a substantially mirror image relationship with each other. The main spiral groove on one of the seal surfaces generates a dynamic pressure toward the end with the rotation of the rotary shaft in a specific direction, and the sub spiral groove on the other seal surface generates a dynamic pressure to reverse the leak fluid. Occurrence Therefore, the main spiral groove formed on one of the sealing surfaces of the mating ring and the primary ring creates a dynamic pressure that pumps the enclosed fluid to the end of the groove, and this fluid transport action A pressure is applied between the sealing surfaces to form a gap between the two sealing surfaces, and the auxiliary spiral groove formed on the other sealing surface allows a part of the enclosed fluid to be sent to the outside by the main spiral groove. Can be back-flowed to the process side (filling side),
Thereby, the leakage amount of the enclosed fluid can be suppressed to the minimum.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts in a state where a non-contact mechanical seal of the present invention is mounted between a rotary shaft and a casing.

FIG. 2 is an end view showing an example of a pattern of main spiral grooves formed on a sealing surface of a mating ring.

FIG. 3 is an end view showing an example of a pattern of a sub spiral groove formed on a sealing surface of a primary ring.

FIG. 4 is an end view showing the state where the mating ring and the sealing surface of the primary ring are in contact with each other, as seen through the primary ring.

FIG. 5 is a simplified explanatory diagram showing the positional relationship between the mating ring and the primary ring.

FIG. 6 is a pressure distribution diagram by the main spiral groove of the mating ring.

FIG. 7 is a pressure distribution diagram by the auxiliary spiral groove of the primary ring.

FIG. 8 is a pressure distribution diagram in an actual state in which both actions of the main spiral groove of the mating ring and the sub spiral groove of the primary ring are combined.

[Explanation of symbols]

M non-contact mechanical seal 1 casing 2: rotating shaft 3 mating ring 4 primary ring 5 seal surface 6 seal surface 7 pressing means 8 main spiral groove 9 auxiliary spiral groove 10 fixed sleeve 11 flange portion 12 step portion 13 tightening sleeve 14 retention Nut 15 O-ring 16 O-ring 17 O-ring 18 Holding device 19 Step 20 Fixed sleeve 21 O-ring 22 Sliding part 23 O-ring 24 Disc

Claims (3)

[Claims] 1. A seal surface which is in contact with a mating ring which is hermetically fixed to a rotary shaft and a primary ring which is axially movable and hermetically mounted in a casing and is axially biased by a pressing means, A main spiral groove is formed on one of the sealing surfaces, with the outer or inner peripheral edge as the starting end, and the end is closed, and the other sealing surface extends from the inner or outer peripheral edge as the starting end to the end. Is provided with a closed sub-helical groove that is substantially aligned with the end of the main helical groove, and the spiral grooves formed on both sealing surfaces are oriented so as to have a substantially mirror image relationship with each other. The non-contact mechanical seal is characterized in that the main spiral groove on the seal surface of the second seal generates a dynamic pressure toward the end, and the sub spiral groove of the other seal surface generates a dynamic pressure that causes a leak fluid to flow backward. 2. The dam width ratio of the main spiral groove is about 0.2 to.
The non-contact mechanical seal according to claim 1, which is set to 0.8. 3. The dam width ratio of the sub spiral groove is about 0.3 to.
The non-contact mechanical seal according to claim 1, which is set to 0.7.