A circumferentially symmetrical tapering mechanical seal device for a nuclear power plant primary pump

Abstract

The present application relates to the field of main pump, especially to a circumferential symmetry taper mechanical seal device for nuclear power plant main pump, which comprises a dynamic ring and a static ring of mechanical seal, the sealing end face of the static ring and the dynamic ring is an annular end face, the inner side of the annular end face is a dam area, the dam area is inclined to the outside to form a converging wedge, a plurality of U-shaped grooves with nanometer depth are arranged on the inclined surface, the U-shaped grooves have the characteristic of symmetry taper, the top of the U-shaped grooves is connected with the dam area, and the opening is towards the outside of the annular end face, the dam face ratio is 0.1-0.6, and the groove weir ratio is 0.2-0.8. The present application is suitable for the harsh environmental requirements of long-period stable operation of the nuclear power plant main pump shaft seal under the conditions of start-stop, high pressure, variable load and high temperature by using the dynamic and static pressure mixing effect.

Description

Technical Field

[0001] This invention relates to the field of main pumps, and more particularly to a mechanical seal device for a nuclear power plant main pump with a circumferentially symmetrical taper. Background Technology

[0002] Mechanical seals are installed at the dynamic and static joints of the main pump in a nuclear power plant to prevent fluid leakage. The main pump mechanical seal, such as... Figure 1 The device shown consists of a rotating ring, a stationary ring, an O-ring, and a spring. The end face of the rotating ring assembly contacts the end face of the stationary ring assembly, forming a sealing pair. The relative movement of the sealing pair generates friction.

[0003] The friction state of a sealing pair can be divided into three states: boundary friction, mixed friction, and fluid friction.

[0004] At the liquid boundary between the two end faces, the thickness is at the molecular level. The friction of the sealing pair at this thickness is called boundary friction. Since the roughness of the sealing surface is much larger than the boundary membrane, severe wear of the solid surface will occur during sliding, resulting in a very short sealing life.

[0005] When the liquid boundary film thickness on both end faces is sufficiently thick, exceeding the sum of the roughness of the sealing surfaces of the sealing pair, the sliding surfaces are no longer in direct contact. At this point, friction is generated only by the shear force of the viscous liquid, and there is no wear of solids. This state is called fluid friction, and the sealing pair can operate for a long time without damage.

[0006] Between the two boundary membrane thicknesses mentioned above, there is mixed friction, and the lifespan of the sealing pair is uncontrollable.

[0007] For the main pump mechanical seal under harsh operating conditions such as high pressure, variable load, and high temperature, the concept of fluid friction, i.e. non-contact sealing, is adopted. In a controlled leakage manner, the microstructure design of the sealing pair end face generates a fluid dynamic pressure effect, allowing the sealing pair to operate in a fluid friction state. The end face is non-contact, forming a certain liquid film thickness, thereby achieving long-term stable operation of the seal.

[0008] There are two technical means to achieve non-contact sealing face. One is hydrodynamic technology, which uses three elements to form hydrodynamic pressure: velocity, groove shape, and viscous medium. By setting a structural groove shape on the sealing face, pressure is generated between the sealing face using the rotational speed, and a liquid film is formed, thus opening the face and ensuring that the sealing face operates in a fluid friction state. The other is hydrostatic technology, which designs a wedge-shaped converging taper structure on the sealing face. Hydrostatic pressure is used to form a pressure gradient distribution between the wedge-shaped face, thus opening the sealing face, regardless of the sealing rotation speed.

[0009] However, existing hydrodynamic technology produces a film with high stiffness, a thin liquid film, low leakage, and high heat generation. The medium in the sealing pair is prone to vaporization, especially during start-up and shutdown, when the hydrodynamic effect is not formed and the sealing pair end faces come into contact, which can easily cause end face wear. Hydrostatic technology produces a film with low stiffness and a thick liquid film, but it has a large leakage. Under high pressure and variable load, the seal is unstable and the leakage varies greatly, resulting in unacceptable leakage in critical applications. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a mechanical seal device for a nuclear power plant main pump with a circumferentially symmetrical taper, which utilizes the dynamic and static pressure mixing effect to meet the harsh environmental requirements of long-term stable operation under conditions such as start-up and shutdown of the main pump shaft seal of the nuclear power plant, high pressure, variable load, and high temperature.

[0011] The present invention provides a mechanical seal device for a nuclear power plant main pump with circumferential symmetrical taper, including a dynamic ring and a stationary ring of the mechanical seal, wherein the sealing end faces of the stationary ring and the dynamic ring are annular end faces;

[0012] The inner side of the annular end face is a dam area, and the dam area slopes outward to form a converging wedge;

[0013] Several U-shaped grooves with nanometer-level depths are provided on the inclined surface, and the U-shaped grooves have the characteristic of symmetrical taper;

[0014] The top of the U-shaped trough connects to the dam area, and the opening faces outward from the annular end face;

[0015] The dam surface ratio is 0.1~0.6;

[0016] The channel-to-weir ratio is 0.2 to 0.8.

[0017] In one specific embodiment of the present invention, the U-shaped grooves are evenly distributed on the inclined surface.

[0018] In one specific embodiment of the present invention, the number of U-shaped grooves is 4 to 16.

[0019] In one specific embodiment of the present invention, the depth h of the U-shaped groove is 2.0~16.0μm.

[0020] In one specific embodiment of the present invention, the width δ1 of the dam area is 2.0~7.0 mm.

[0021] In one specific embodiment of the present invention, the convergence wedge depth δ2 is 0.5~2.0μm.

[0022] In one specific embodiment of the present invention, the dam surface ratio is 0.1 to 0.4.

[0023] In one specific embodiment of the present invention, the channel-to-weir ratio is 0.5 to 0.7.

[0024] Compared with the prior art, the circumferentially symmetrical tapered mechanical seal device for nuclear power plant main pumps of the present invention has the following advantages:

[0025] (1) The sealing end face is designed with a groove with a circumferentially symmetrical tapered U-shaped curve. By utilizing the dynamic pressure effect, the opening capacity and liquid film stability of the sealing end face are improved, thus solving the sealing problem of preventing the medium from vaporizing under high temperature conditions.

[0026] (2) By controlling parameters such as dam face ratio and channel-weir ratio, leakage can be controlled by varying the width of different dam areas;

[0027] (3) The converging wedge structure of the sealing end face utilizes the static pressure effect to improve the opening capability of the seal under variable load and low pressure, and solves the problem of seal performance stability under high load.

[0028] (4) This invention realizes the addition of hydrostatic pressure effect on the basis of hydrodynamic pressure, and combines the advantages of hydrodynamic pressure and hydrostatic pressure to meet the harsh environmental requirements of the start-up and shutdown of the main pump shaft seal of the nuclear power plant, high pressure, variable load and high temperature, and long-term stable operation. Attached Figure Description

[0029] Figure 1 This diagram shows a mechanical seal.

[0030] Figure 2 A schematic diagram showing the annular end face structure of the present invention;

[0031] Figure 3 This is a schematic diagram of a single U-shaped groove according to the present invention;

[0032] Figure 4 This is a side view of the U-shaped groove of the present invention;

[0033] Figure 5 This is a top view of the U-shaped groove of the present invention;

[0034] In the figure, 1-moving ring, 2-stationary ring, 3-O-ring, 4-spring, 5-converging wedge, 6-U-groove, 7-U-shaped curve feature, 8-taper feature, 9-dam area, A-single U-groove, h-depth of U-groove, δ1-width of dam area, δ2-depth of convergent wedge, α-single-sided angle of U-groove, β-half-angle within one cycle, θ-angle within one cycle. Detailed Implementation

[0035] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0036] An embodiment of the present invention discloses a circumferentially symmetrical tapered mechanical seal device for a nuclear power plant main pump, such as... Figures 2-5 As shown, the mechanical seal includes a dynamic ring 1 and a stationary ring 2. The sealing end face of the stationary ring 2 is a tungsten carbide hard alloy with circumferential symmetrical tapered features, and the sealing end face of the dynamic ring 1 is a planar graphite ring.

[0037] The inner side of the converging wedge 5 is the dam area 9, and the converging wedge 5 is formed by the dam area 9 tilting outward.

[0038] The dam area 9 is used to control sealing leakage, and the converging wedge 5 helps to form a static pressure effect;

[0039] Several U-shaped grooves 6 with a depth of micrometers are provided on the sealing end face of the stationary ring 2. The U-shaped grooves 6 have a U-shaped curve feature 7 and a symmetrical taper feature 8 in depth, as well as a dam area 9 to control sealing leakage and a converging wedge 5 to form a static pressure effect, such as Figure 4 As shown; specifically, a symmetrical taper is formed with the radius of the stationary ring 2 as the axis of symmetry;

[0040] The U-shaped grooves 6 are preferably evenly distributed on the inclined surface;

[0041] The number of U-shaped grooves is preferably 4 to 16, and more preferably 8 to 12;

[0042] The top of the U-shaped groove 6 is connected to the dam area 9, and the opening faces the outside of the converging wedge 5;

[0043] The depth h of the U-shaped groove is 2.0~16.0μm;

[0044] The dam surface ratio Dm = (rg-ri) / (ro-ri) has a value range of 0.1 to 0.6, preferably 0.1 to 0.4;

[0045] ri is the inner diameter of the sealing ring, ro is the outer diameter of the sealing ring, and rg is the outer diameter of the dam area;

[0046] Channel-to-weir ratio G m =α / β, with a numerical range of 0.2~0.8, preferably 0.5~0.7;

[0047] One groove region and one convergence wedge (also known as weir region) constitute one cycle. Each annular end face is set with 8 to 12 cycles. α is the angle of one side of the U-shaped groove, β=θ / 2 is half the angle within one cycle, and θ is the angle of one cycle.

[0048] The width δ1 of the dam area 9 is 2.0~7.0 mm;

[0049] The depth δ2 of the convergence wedge 5 is 0.5~2.0μm.

[0050] When the main nuclear pump is operating, the fluid in the tapered area of ​​the U-shaped groove 6 on the contact surface experiences a dynamic pressure effect due to the continuous depth convergence of the sealing pair formed by the rotating ring 1 and the stationary ring 2 in the circumferential direction. This dynamic pressure pushes the sealing end face open, achieving a non-contact sealing effect. Simultaneously, the fluid passing through the converging wedge 5 and the U-shaped groove 6 acts on the sealing end face due to the hydrostatic pressure, causing the sealing end face to open, thus achieving the purpose of hydrostatic opening effect. The dam area 9 on the sealing end face is used to control leakage. The fluid enters the sealing end face through the action of dynamic and hydrostatic pressure, forming a micron-level fluid lubrication film between the sealing end faces. This film serves to lubricate and reduce wear, thereby meeting the harsh environmental requirements of the main pump shaft seal in nuclear power plants, such as start-up and shutdown, high pressure, variable load, and high temperature conditions, and long-term stable operation.

[0051] Traditional hydrodynamic seals have insufficient opening force during start-up and shutdown, resulting in the sealing pair being in a pressurized closed state. This causes the dynamic ring 1 and the stationary ring 2 to rub against each other, leading to wear.

[0052] In this invention, a hydrostatic effect is added to the hydrodynamic pressure.

[0053] 1. During operation, the pressure difference between the inside and outside of the seal is P1 to P2, and the pressure when the main pump starts is P3.

[0054] Before startup, the rotating ring 1 and stationary ring 2 are relatively stationary, and the rotating ring 1 and stationary ring 2 are closed by the external liquid pressure and the force of the spring 4. High-pressure liquid enters the annular end face along the U-shaped groove 6 and the converging wedge 5 between the rotating ring 1 and stationary ring 2, generating an opening force. When the pressure is less than P3, the opening force is less than the closing force, and the rotating ring 1 and stationary ring 2 are in a closed state. When the pressure reaches P3, the opening force is greater than the closing force, forming a hydrostatic effect, and the rotating ring 1 and stationary ring 2 separate, ensuring that the rotating ring 1 and stationary ring 2 will not collide or rub when the main pump starts at pressure P3.

[0055] 2. After the main pump starts running, the rotating ring 1 rotates, and there is relative movement between the rotating ring 1 and the stationary ring 2. The liquid flows between the rotating ring 1 and the stationary ring 2. The medium in the U-shaped groove 6 on the sealing end face of the stationary ring forms a hydrodynamic pressure effect with the end face of the rotating ring. When the end faces of the rotating and stationary rings are small, the hydrodynamic pressure effect increases, increasing the opening force and ensuring that the sealing surfaces do not contact. When the end faces of the rotating and stationary rings are large, the hydrodynamic pressure effect decreases, and the closing force increases. The sealing surface closing force, such as the main pump pressure and the spring force, will reach a balance point with the hydrodynamic pressure generated by the U-shaped groove 6, controlling the sealing gap between the rotating and stationary rings to maintain within a stable range, thereby forming a controllable sealing leakage.

[0056] 3. By varying the width of the dam area 9, leakage can be controlled. Fluid, relying on dynamic and static pressure, enters the converging wedge 5, forming a micron-level fluid lubrication film between the sealing end faces. This provides lubrication and prevents wear, thus meeting the stringent environmental requirements of the nuclear power plant's main pump shaft seal, including start-up and shutdown, high pressure, variable load, and high temperature conditions, and long-term stable operation.

[0057]

[0058] Comparative Explanation: For hydrodynamic mechanical seals, the characteristics are a thin liquid film and high rigidity, resulting in low leakage. However, due to the thin liquid film, surface wear is common, leading to a relatively short service life. For hydrostatic mechanical seals, the characteristics are a thick liquid film and low rigidity, resulting in less surface wear. However, leakage is greater, and due to electrophoresis, a layer of rust forms on the surface, affecting liquid film stability over time, resulting in a moderate service life. The hydrodynamic-hydrostatic mechanical seal developed in this study combines the advantages of both hydrodynamic and hydrostatic pressure. Its characteristics include a moderate liquid film thickness and good rigidity. While leakage is slightly higher than that of the hydrodynamic type, it is more conducive to heat dissipation, benefiting long-term operation. Simultaneously, leakage is significantly lower than that of the hydrostatic type. Overall, it features a stable liquid film, good rigidity, minimal surface wear, and a service life far exceeding that of both hydrodynamic and hydrostatic mechanical seals, demonstrating superior overall performance.

[0059] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0060] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A circumferentially symmetrically tapered mechanical seal assembly for a nuclear power plant primary pump, comprising a mechanical seal rotating ring and a stationary ring, characterized in that, The sealing end faces of the stationary ring and the rotating ring are annular end faces; The inner side of the annular end face is a dam area, and the dam area slopes outward to form a converging wedge; Several U-shaped grooves with nanometer-level depths are provided on the inclined surface, and the U-shaped grooves have the characteristic of symmetrical taper; The top of the U-shaped trough connects to the dam area, and the opening faces outward from the annular end face; The dam surface ratio is 0.1~0.6; The channel-to-weir ratio is 0.2 to 0.8; The depth h of the U-shaped groove is 2.0~16.0μm; the width δ1 of the dam area is 2.0~7.0 mm; and the depth δ2 of the converging wedge is 0.5~2.0μm.

2. The circumferentially symmetrical tapered mechanical seal device for a nuclear power plant main pump according to claim 1, characterized in that, The U-shaped grooves are evenly distributed on the inclined surface.

3. The circumferentially symmetrical tapered mechanical seal device for a nuclear power plant main pump according to claim 2, characterized in that, The number of U-shaped grooves is 4 to 16.

4. The circumferentially symmetrical tapered mechanical seal device for a nuclear power plant main pump according to claim 1, characterized in that, The dam surface ratio is 0.1 to 0.

4.

5. The circumferentially symmetrical tapered mechanical seal device for a nuclear power plant main pump according to claim 1, characterized in that, The channel-to-weir ratio is 0.5 to 0.7.

Images