CN105803385A - Valve used for steam environment and surface treatment method of valve - Google Patents

Abstract

The invention provides a method for surface treatment of a valve used in a steam environment, the valve comprising: a first chamber (10), a second chamber (20) and a valve stem (22), wherein the second chamber (20) is provided with a locking part (23) for locking the valve stem (22) and a hole (25) for accommodating the locking part (23), and the locking part (23) can move in the hole (25) to Two positions, engaging with the valve stem (22) at the first position to realize locking of the valve stem (22); at the second position with a certain gap from the valve stem (22) to realize loosening of the valve stem (22), the method includes : Carrying out carbonitriding treatment and chromizing treatment successively to the surface of valve stem (22) and locking part (23). The valve obtained by adopting the surface treatment method of the present invention can significantly improve corrosion resistance and wear resistance, thereby avoiding failures caused by problems such as rusting and the like, and can save costs.

Description

Valve used in steam environment and its surface treatment method

technical field

The invention belongs to the field of surface treatment of valves, in particular to the formation of corrosion-resistant and wear-resistant surface layers of valves.

Background technique

The rust prevention of valves used in steam environments is an important issue in their design and use. When components in a valve are exposed to high operating temperature water vapor and even corrosive environments, they can become severely rusted. On the one hand, rusting of components will affect the working life due to the surface defects it causes. More seriously, rust can also interfere with the normal movement of components, causing valves and even the system in which they are installed to fail. A typical example is a moving component in a steam turbine quick-closing valve system. In order to avoid over-speed rotation or other abnormal operation of the steam turbine system, as a key safety protection component, the quick-closing valve will quickly close to quickly close the steam flow into the turbine, thereby avoiding destructive damage to the steam turbine system or even personnel Injuried.

For quick-closing or throttling valves, smooth rotation of the locking member and free movement of the stem must be guaranteed for successful quick-closing. However, if a failure of the steam seal occurs, the locking component or adjacent components will be exposed to a high temperature water vapor and oxygen mixture and will be severely rusted within a very short period of time. Considering that there is only a small space as small as 0.01mm between the locking part and the bore, the rusting of the components is likely to prevent the normal rotation of the locking part and thus cause the failure of the quick-closing valve. Serious accidents due to damage to steam turbines with quick closing valve failures have been reported.

In the prior art, corrosion resistance can be improved by high concentration of chromium (such as stainless steel). However, high concentrations of chromium result in high material costs and are therefore not cost effective. Furthermore, high chromizing temperatures can lead to deformation of components. While maintaining the desired ductility, corrosion resistance, and wear resistance, advanced surface treatments for both the locking component and adjacent components need to be developed. But long-term mobility under high-temperature mixtures of water vapor and oxygen remains challenging and also involves increased component costs.

In addition, for the cavity in the valve cavity housing adjacent to the locking part (the component with the concave surface matching the locking part), it is usually made of cast iron (such as HT-200), its complex shape and the small space for 0.01mm High demand makes it more difficult for surface preparation including thermal spraying of ceramic coating, electroplating, PTFE coating, etc. And working conditions with temperatures over 250°C also make PTFE unsuitable for this application.

Contents of the invention

In order to avoid the failure of metal parts due to rust, the present invention provides a surface treatment method for valves used in steam environments, said valves comprising: a first chamber 10 with a valve disc 11 and a steam Channel 12; second chamber 20, and valve stem 22, including: first end 221, located in second chamber 20; and second end 222, located in first chamber 10, connected with valve disc 11, and The valve disc 11 can be driven to open or close the steam passage 12; wherein the second chamber 20 is provided with a locking part 23 for locking the valve stem 22 and a hole 25 for accommodating the locking part 23, and the locking part 23 can be placed in the hole 25 Move to two positions in the first position, and engage with the valve stem 22 at the first position to realize locking the valve stem 22; at the second position, there is a certain gap from the valve stem 22 to realize releasing the valve stem 22. The method includes: And the surface of the locking member 23 is subjected to carbonitriding and chromizing in this order.

Chromizing after carbonitriding can obtain corrosion resistance and wear resistance similar to that of Cr-rich steel, but does not need to be replaced by expensive Cr-rich steel materials, thereby greatly reducing the cost of the component. In addition, the chromizing treatment can be carried out after the carbonitriding pretreatment, so that the chromizing can reach a sufficient treatment depth (for example, 100 to 300 microns). Still further, after carbonitriding pretreatment, chromizing treatment can be carried out at a lower temperature, for example, higher than or equal to 500°C to lower than 800°C, preferably 500 to 750°C, without carbonitriding pretreatment , to get a deeper chromization depth, need at least 800 ℃. The reduced processing temperature can further avoid deformation of the metal parts that may be caused by high temperature processing. In a preferred embodiment, the chromizing treatment temperature is 550-700°C. The reduced processing temperature not only avoids possible deformation of the components, but also further reduces costs.

In a preferred embodiment, the nitriding treatment is further performed after the chromizing treatment. The nitriding treatment after the chromizing treatment can further improve the hardness, stability, corrosion resistance and wear resistance of the coating, and since the chromizing layer is directly in contact with the nitrided layer, there will be no damage caused by the nitriding treatment. Oxidation and rusting due to grain boundary channels formed during this process.

In a preferred embodiment, a bushing 29 is further provided outside the valve stem 22, and the locking member 23 realizes the locking of the valve stem 22 through the locking bush 29, and the surface of the bushing is further subjected to carbonitriding treatment in sequence. And chromizing treatment, more preferably further nitriding treatment. Specifically, the bushing 29 and the valve stem 22 are fixed to each other, and a groove cooperating with the locking part 23 can be formed on the bushing 29, so that the locking part can lock the valve stem, thus avoiding the direct formation of a groove on the valve stem and reduce its mechanical strength. However, in the absence of a bushing, it is necessary to form a groove on the valve stem to cooperate with the locking part 23 to form the locking of the locking part to the valve stem.

In a preferred embodiment, the method further includes: forming a Ni-P alloy coating on the inner surface of the cavity 25 that cooperates with the locking component 23 by electroless plating. In a preferred embodiment, the inner surface of the second chamber 20 matched with the valve stem 22 is also subjected to electroless plating to form a Ni-P alloy coating. For components with concave surfaces or complex shapes, such as cavity 25, spring 282, inner surface of housing 21, gear 30, etc., the chromizing treatment described above may be difficult to implement. And for the anti-rust of valve, because the clearance (as little as 0.01mm) between the components (such as locking part 23 and cavity 25) that cooperates with each other is very little, so any party gets rusty all may cause the fault of valve. Therefore, in a preferred solution of the present invention, electroless plating is used to carry out Ni-P alloy coating to the inner surface that the hole 25 cooperates with the locking part 23 to carry out surface treatment to it, so that it contacts with the locking part 23 Avoid rust on the surface. The Ni-P alloy coating can improve the corrosion resistance and wear resistance of components such as the inner surface of the cavity and the inner surface of the shell. And, the electroless plating process that the present invention adopts can prepare the coating that has uniform quality and uniform thickness, even the component (such as bore inner surface, the surface that second chamber cooperates with valve stem, etc.) with complicated structure gears, etc.), the coating thickness and quality of the surface can still be very uniform. Studies have shown that under dry and lubricated conditions, the electroless Ni-P alloy coating can achieve the wear resistance of hard chrome. And the Ni-P alloy coating is sufficient to resist the corrosion caused by the water vapor environment, thereby bringing sufficient corrosion resistance to the above-mentioned surface.

In a preferred embodiment, solid lubricant particles are added to the electroless plating solution for forming the Ni-P alloy coating. Solid lubricants can further improve the corrosion resistance and wear resistance of metal parts. In view of the use environment, that is, the high-temperature water vapor working condition, the preferred solid lubricant of the present invention is CaF ₂ or graphite fluoride. Compared with conventional MoS lubricants, CaF ₂ or graphite _fluoride have smaller friction coefficients under the wet environment caused by water vapor.

In a preferred embodiment, the particle size of the solid lubricant particles (such as CaF ₂ ) is less than 8 microns, and the content is 3-6 wt% based on the weight of the Ni-P alloy coating. The role of the solid lubricant is to form a self-lubricating composite coating in the alloy coating. If the particle size is too large, the friction coefficient of the self-lubricating composite coating may be larger. The self-lubricating composite coating obtained with lubricant particles smaller than 8 microns has a lower coefficient of friction. In addition, if the amount of solid lubricant is too large, the stability of the Ni-P alloy coating may be affected, and if it is too small, the technical effect of the lubricating layer may not be achieved. In the present invention, preferably, the content of the solid lubricant particles is 3-6 wt% based on the weight of the Ni-P alloy coating, so as to obtain a more stable Ni-P alloy coating with better wear resistance.

In a preferred embodiment, the valve is a quick-closing valve. The working environment of the quick-closing valve is in high-temperature water vapor, and it is precisely because of this working environment that it is easy to rust. However, rusting of the quick-closing valve will cause serious safety problems for the entire system. Therefore, the method of the present invention is particularly suitable for the quick-closing valve system.

The present invention also provides a valve used in a steam environment, comprising:

In the first, the electroless plating solution further includes a solid lubricant, preferably CaF ₂ or graphite fluoride. This kind of solid lubricant can form a self-lubricating composite coating after being added. It has the advantages of wide temperature range, high load resistance, and stable lubrication performance. It can be used in high vacuum, organic solvents, steam, strong alkali, and acidic media. middle. And, relative to conventional _MoS lubricants, _CaF2 or fluorinated graphite have smaller friction coefficients under the wet environment caused by water vapor.

In a further preferred embodiment, the particle size of the solid lubricant particles is less than 8 microns, and the content is 3-6 wt% based on the weight of the Ni-P alloy coating. Solid lubricant particles smaller than 8 microns can obtain a self-lubricating composite coating with a lower coefficient of friction. In addition, if the amount of solid lubricant is too large, the stability of the Ni-P alloy coating may be affected, and if it is too small, the technical effect of the lubricating layer may not be achieved. In the present invention, preferably, the solid lubricant particle content is 3-6 wt% based on the weight of the Ni-P alloy coating, so as to obtain a more stable Ni-P alloy coating with better wear resistance.

Description of drawings

Fig. 1 is a schematic structural view of a valve according to an embodiment of the present invention;

Fig. 2 is a schematic structural view of a valve according to a preferred embodiment of the present invention;

Fig. 3 is a schematic diagram of the surface treatment process of the locking member and the valve stem 22 according to an embodiment of the present invention, wherein Fig. 3A is a schematic cross-sectional view of the valve stem 22 before treatment, and Fig. 3B is a cross-sectional view of the valve stem 22 after carbonitriding Schematic diagram, FIG. 3C is a schematic diagram of a cross-section of the valve stem 22 after further chromization, and FIG. 3D is a schematic diagram of a cross-section of the valve stem 22 after further nitriding;

Fig. 4 is the comparison diagram of the corrosion rate with Ni-P alloy coating and the carbon steel without this coating;

5 is a schematic diagram of forming a Ni-P _- CaF protective layer on the inner surface of the cavity 25 by electroless plating according to an embodiment of the present invention, wherein FIG. 5A is a schematic cross-sectional view of the cavity 25 before processing, and FIG. 5B It is a schematic cross-sectional view of the cavity 25 after forming the Ni-P-CaF ₂ protective layer.

List of names and numbers of the various parts in the figure:

First chamber 10, valve disc 11, steam channel 12, second chamber 20, housing 21, bore 25, seal 27, valve stem 22, first end 221 of the valve stem, second end of the valve stem 222 , locking part 23 , bushing 29 , spring assembly 28 , spring seat 281 , spring 282 , gear 30 , and hand wheel 50 .

Wherein Fig. 1 and Fig. 2, 25 is the cross-sectional schematic view of the bore, and the bore 25 accommodates the locking member 23, so that the locking member 23 can rotate freely in the bore 25, and the locking member 23 can protrude a part from the bore and The groove on the valve stem 22 or the bushing 29 engages, thereby realizing locking of the valve stem 22 .

detailed description

For valves, rust prevention is always one of the important conditions that must be met. Especially for valves used in steam environments (see Figure 1 and Figure 2), such as quick-closing valves, the gap between its moving components is even as small as 0.01mm, once rusted, it will cause its movement to be blocked, causing the entire System failure. In addition, due to the high-temperature water vapor environment in which it works, quick-closing valves have higher requirements for rust prevention.

Compared with directly forming the nitride layer on the moving components, the anti-rust layer obtained by the surface treatment of the present invention has better corrosion resistance and is more stable. _The Fe2-3N phase is very brittle and therefore less controllable by low content, or easily removed by surface polishing. Also, the nitrided metal has reduced corrosion resistance compared to the same metal without the nitriding process, due to the fact that the channels along the grain boundaries formed during the nitriding process can be replaced by oxygen for nitrogen. And accelerate oxidation and rust.

In the disclosure of the present invention, different surface treatment methods are designed for different components of the valve: for components capable of carbonitriding and chromizing, such as the valve stem 22 and the locking part 23, carbonitriding and chromizing are carried out in sequence. Chromizing surface treatment; and for components that cannot be carbonitrided and chromized due to structural requirements, such as cavity 25, gear 30 and second chamber 20, electroless plating is used to form a Ni-P alloy coating, so that the valve The moving components in can improve corrosion resistance while maintaining high wear resistance. Especially for quick-closing or throttle valves, the present invention provides a simple and inexpensive solution to avoid rusting of critical components, avoiding high material replacement costs.

For locking parts, stems and bushings on stems, optional surface chroming is available to improve corrosion resistance. However, unlike the conventional chromizing process with high processing temperature, these components in the present invention are first treated with carbonitriding process to promote the subsequent chromizing process, and the carbonitriding process can accelerate the chromizing process to obtain Sufficient chromizing depth, so as to ensure its corrosion resistance and stability, and at the same time reduce the chromizing treatment temperature. Further short-time plasma nitriding treatment can further improve the stability and uniformity of the chromized layer, and further improve the corrosion resistance and wear resistance, see FIG. 3A to FIG. 3D .

Considering the complex shape of parts adjacent to the locking part or valve stem, such as the bore 25, the gear 30 or the mating part of the second chamber housing 21, different surface treatments of electroless plating can be used. A Ni-P alloy can be selected that has even higher corrosion resistance and wear resistance than the electroplated Cr layer. The strong corrosion resistance of the Ni-P alloy protective layer is shown in Figure 4. In oxygen-saturated water, the Ni-P alloy exhibits an extremely reduced corrosion rate. Electroless coatings exhibit uniform thickness and quality even with very complex structures. The nickel utilization rate of electroless nickel plating is high, and it has the characteristics of "permeable". No matter how complicated the structure is, as long as the plating solution can be touched, it will be covered by the plating layer. There is no deep plating ability and The problem of poor dispersion. Even the inner surfaces of blind holes, pipes and crevices of plated parts can be uniformly plated. Through the stable and controllable coating speed, the overall thickness of the coating can also be well controlled in the range of 20 to 300 μm, so as to meet the height requirement of a small gap of 0.01mm. In order to reduce the brittleness of the coating while maintaining sufficiently high corrosion resistance and wear resistance, a Ni-P alloy with 5–10 wt% P can be selected for electroless plating, followed by heat treatment at a temperature below 300 °C.

Additional solid lubricants can be used to further improve corrosion and wear resistance. Conventional _MoS2 lubricants exhibit enhanced friction coefficients in wet environments, especially when exposed to water vapor. Taking this into consideration, a combination of Ni _- P alloy and CaF solid lubricant particles is adopted in the preferred embodiment of the present invention, the particle size of the lubricant particles is less than 8 microns, and the content is 3-6wt%. The lubricant is added to the plating solution, and the combination is formed on the HT-200 component. The as-prepared Ni-P- _CaF2 coating is able to exhibit excellent corrosion resistance and also has good lubricating properties even at temperatures higher than 550 °C. See Figure 5 for a schematic diagram of the coating.

The surface treatment method designed in the present invention can not only be used to avoid the failure of the quick-closing valve, but also can be used to avoid the rusting of other components under high-temperature water vapor working conditions, especially moving components, such as tooth keys and the like.

The implementation of the present invention will be described exemplarily below in conjunction with specific examples, but these examples do not mean to limit the present invention to any extent.

Example 1

Select the locking parts, valve stem and bushing of the quick-closing valve, and perform the following treatments in sequence:

1. Carbonitridation. The locking part, stem and bushing are surface carbonitrided using an ion carbonitriding process, which allows the desired depth of carbonitriding to be achieved at lower temperatures. The equipment adopts a vacuum furnace with a glow discharge device, ammonia gas is used as the nitriding atmosphere, and acetone or propane can be used as the carburizing medium. Specific treatment parameters range: voltage 600-900V, air pressure 50-200Pa, temperature 500-600°C, treatment time 5-20 hours.

2. Chromizing. Chromizing adopts chloride salt bath chromizing process, the main components are CaCl ₂ , NaCl, CrCl ₃ , iron powder and chromium powder. The temperature of the salt bath is 500-750°C, and the treatment time is 5-20 hours.

3. Nitriding. A vacuum furnace with a glow discharge device is used for ion nitriding, and the nitriding atmosphere is ammonia gas. Specific treatment parameters range: voltage 400-800V, air pressure 300-600Pa, temperature 450-650°C, treatment time 1-3 hours. )

Example 2

For the inner surface of the cavity corresponding to the locking part formed by cast iron at one time, Ni-P electroless plating coating treatment is carried out. The composition of electroless plating solution is: NiSO ₄ .6H ₂ O (10～30g/L), NaH ₂ PO ₂ .2H ₂ O (15～30g/L), HBO ₃ (10～20g/L), lactic acid (10～ 30ml/L), KIO ₃ (2～3mg/L), and CaF ₂ powder. The pH range of the plating solution can be selected as 4.5-5.5, the temperature is 80-90° C., and the content of CaF ₂ is 3-6 wt%. Wherein the CaF ₂ powder requires an average particle size of less than 8 microns, preferably less than 2 microns. The processing time is determined according to the required coating thickness and plating speed, and the plating speed is about 10-30 microns/hour.

Comparative example 1

The valve stem and locking parts are selected and directly chromized at a temperature of 850°C.

Comparative example 2

The valve stem and locking parts are selected for direct nitriding treatment.

Anti-rust result detection

Under the high-temperature steam of 500-550°C in the simulated working environment, for 150-500 hours, the anti-rust effect is tested. The results are shown in Table 1.

Table 1

Comparative example 1 is owing to carry out chromization directly, not only chromization temperature is higher, its chromization depth is lower than 20 to 50 microns in the same time, far below the chromization depth (100 to 300 microns) of the present invention, also insufficient simultaneously To resist the corrosion of high temperature water vapor, which will cause the parts to rust.

Comparative Example 2 exhibited poorer corrosion and wear resistance due to greater brittleness and accelerated oxidation and rusting through the substitution of oxygen for nitrogen along the passage of grain boundaries formed during the nitriding process.

However, Examples 1 and 2 of the present invention not only have lower cost, but also exhibit higher corrosion resistance and wear resistance.

The valve stem, the locking part and the cavity obtained in Examples 1 and 2 are assembled together with other components of the valve to form a valve. The valve includes: a first chamber 10 with a valve disc 11 and a steam passage 12 inside The second chamber 20 includes a housing 21 and a seal 27 fixed on the housing 21, the seal 27 is used to isolate the first chamber 10 and the second chamber 20, and the valve stem 22 includes: a first end 221, located in the second chamber 20; and the second end 222, located in the first chamber 10, connected with the valve disc 11, and can drive the valve disc 11 to open or close the steam passage 12; wherein in the second chamber 20 A locking part 23 for locking the valve stem 22 and a cavity 25 for accommodating the locking component 23 are provided. The locking component 23 can move to two positions in the cavity 25, and engage with the valve stem 22 at the first position to realize locking Valve stem 22; at the second position, there is a certain gap from the valve stem 22 to realize the release of the valve stem 22, wherein the surfaces of the valve stem 22 and the locking member 23 are treated by carbonitriding, chromizing and nitriding in sequence, The inner surface of the cavity 25 is the inner surface of the Ni-P-CaF ₂ alloy coating formed by electroless plating.

In this valve, the locking parts and the cavity with a gap as small as 0.01mm are surface-treated corrosion-resistant and wear-resistant surfaces, so they can work in a steam environment for a long time without rust and will not cause valve failure . In addition, the anti-rust treatment of the valve stem also avoids accidental locking caused by its rust, and avoids the failure of the valve. The valve processed by the present invention avoids the most prone failure caused by rust in the prior art.

It can be known from the above results that the technical solution of the present invention not only saves the cost, but also further improves the corrosion resistance and wear resistance of the metal parts, especially the moving components. Advantages of the present invention can be summarized as follows:

1. The solution involved in the present invention can significantly improve valves, especially the corrosion resistance and wear resistance of valve components, thereby avoiding possible valve (such as quick-closing valve) failures;

2. The solution of the present invention does not involve replacing materials with expensive Cr-rich steel;

3. The present invention carries out surface treatment on the locking part and the valve stem part through surface chromization with pre-carbonitriding treatment, so that sufficient treatment depth can be obtained;

4. The surface chromization of the present invention can also reduce the processing temperature to avoid possible component deformation;

5. The surface chromization with subsequent post-nitridation of the present invention can further improve stability and performance;

6. The electroless Ni-P alloy plating of the present invention can improve the corrosion resistance and wear resistance of cast iron components;

7. The electroless plating process of the present invention can be used to prepare protective coatings with uniform quality and uniform thickness, even in complex structures, uniform coatings can be obtained;

8. The composite coating formed by the present invention using _CaF2 lubricating particles can simultaneously exhibit excellent corrosion resistance and good lubricating performance;

9. The surface treatment method of the present invention can not only be used to avoid failure of valves (such as quick-closing valves), but also can be used to prevent other components, especially mobile components, from rusting under high-temperature water vapor working conditions.

The present invention has been shown and described in detail through the drawings and preferred embodiments above, but the present invention is not limited to these disclosed embodiments, and other schemes deduced therefrom by those skilled in the art are also within the protection scope of the present invention.

Claims (17)

1. a surface treatment method for the valve used in steam ambient, described valve includes:

First chamber (10), is inside provided with valve disc (11) and steam channel (12)；

Second chamber (20), and

Valve rod (22), including: the first end (221), it is positioned at the second chamber (20)；With the second end (222), be positioned at the first chamber (10), be connected with valve disc (11), and actuatable valve dish (11) is turned on and off steam channel (12)；

Second chamber (20) is wherein provided with the locking parts (23) for locking valve rod (22) and is used for holding the vestibule (25) of locking parts (23), locking parts (23) can move to two positions in vestibule (25), engage with valve rod (22) in primary importance, it is achieved locking valve rod (22)；At second position distance valve rod (22) certain interval, it is achieved unclamping valve rod (22), described method includes:

The surface of valve rod (22) and locking parts (23) is sequentially carried out reductive carbo-nitridation and chromate treating.

2. surface treatment method as claimed in claim 1, carries out nitrogen treatment further after wherein said chromate treating.

3. surface treatment method as claimed in claim 1, lining (29) it is additionally provided with outside wherein said valve rod (22), locking parts (23) realizes the locking to valve rod (22) by locking bushing (29), and described method farther includes the surface of lining (29) is sequentially carried out reductive carbo-nitridation and chromate treating.

4. surface treatment method as claimed in claim 1, wherein said chromate treating temperature range is to lower than 800 DEG C be more than or equal to 500 DEG C.

5. surface treatment method as claimed in claim 1, described method farther includes: the inner surface that vestibule (25) is coordinated with locking parts (23) forms Ni-P alloy coat by chemical plating.

6. surface treatment method as claimed in claim 5, the inner surface farther including the second chamber (20) is coordinated with valve rod (22) forms Ni-P alloy coat by chemical plating.

7. surface treatment method as claimed in claim 5, wherein adds solid lubricant particle in the plating solution of described chemical plating.

8. surface treatment method as claimed in claim 7, the particle diameter of wherein said solid lubricant particle is less than 8 microns, and content is the 3-6wt% based on Ni-P alloy coat weight.

9. surface treatment method as claimed in claim 7 or 8, wherein said kollag is CaF₂Or fluorographite.

10. the valve used in steam ambient, including:

First chamber (10), is inside provided with valve disc (11) and steam channel (12)；

Second chamber (20), including housing (21) and the sealing member (27) that is fixed on housing (21), sealing member (27) is used for isolating the first chamber (10) and the second chamber (20)

Valve rod (22), including: the first end (221), it is positioned at the second chamber (20)；With the second end (222), be positioned at the first chamber (10), be connected with valve disc (11), and actuatable valve dish (11) is turned on and off steam channel (12)；

Second chamber (20) is wherein provided with the locking parts (23) for locking valve rod (22) and is used for holding the vestibule (25) of locking parts (23), locking parts (23) can move to two positions in vestibule (25), engage with valve rod (22) in primary importance, it is achieved locking valve rod (22)；At second position distance valve rod (22) certain interval, it is achieved unclamp valve rod (22),

Wherein, the surface of valve rod (22) and locking parts (23) is nitrogenize the surface after processing successively with chromaking through carbon.

11. valve as claimed in claim 10, wherein the surface of valve rod (22) and locking parts (23) is the surface after being nitridized process further.

12. valve as claimed in claim 10, wherein it is additionally provided with lining (29) outside valve rod (22), locking parts (23) realizes the locking to valve rod (22) by locking bushing (29), and lining (29) surface is nitrogenize the surface after processing successively with chromaking through carbon.

13. valve as claimed in claim 10, wherein, vestibule (25) inner surface coordinated with locking parts (23) has Ni-P alloy coat.

14. valve as claimed in claim 13, the inner surface of the second chamber (20) wherein coordinated with valve rod (22) has Ni-P alloy coat.

15. the valve as described in claim 13 or 14, wherein said Ni-P alloy coat comprises kollag.

16. the valve as described in claim 13 or 14, wherein said kollag is CaF₂Or fluorographite.

17. valve as claimed in claim 15, the particle diameter of wherein said solid lubricant particle is less than 8 microns, and content is the 3-6wt% based on described Ni-P alloy coat weight.