JP2014238142A - Valve device and valve device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a valve device capable of exhibiting oxidation resistance in a high temperature environment and a valve device manufacturing method.SOLUTION: According to an embodiment, the valve device includes: a valve rod serving as a movable member operating as a valve is opened/closed; and a bush serving as a stationary member slidably contacting this valve rod. A slide contact surface of at least either the valve rod or the bush is provided integrally with a padding portion 157. The padding portion 157 includes: a first coating film 102 formed by generating a pulsed discharge between an electrode formed of a compact mainly containing a first metal and a treatment target portion 100 of either the valve rod or the bush, and welding and depositing a material of the electrode on a surface of the treatment target portion 100; and a second coating film formed on a surface of the first coating film by spraying plasmas raw material powder mainly containing a second metal using a plasma spray gun.

Description

  Embodiments described herein relate generally to a valve device and a method for manufacturing the valve device.

  Steam turbines such as thermal power plants are equipped with various valve devices such as a main steam stop valve, a steam control valve, a reheat steam stop valve, an intermediate stop valve, and a turbine bypass valve in order to control the inflow of steam. ing.

  In the valve device, as a combination of a movable member and a stationary member that is in sliding contact with the movable member, for example, a valve stem and a bush, the bush material is made of, for example, 12% chromium for the purpose of increasing wear resistance and extending the service life. It is widely known that the material of steel and valve stem is nickel 30-50% austenitic heat-resistant alloy, and nitriding is performed as a surface treatment method for these members.

  In addition, the seat part where the valve seat and valve body abut has thermal shock resistance and oxidation resistance to prevent damage due to thermal shock, erosion, corrosion, etc. due to inflow and outflow of high-temperature and high-pressure superheated steam. It is known to build-up a cobalt-based hard alloy having a hardness higher than that of a valve base material.

  However, since oxidation resistance cannot be obtained by nitriding treatment, when the valve device is oxidized by high-temperature steam, a sliding member composed of a movable member and a stationary member that is in sliding contact with the oxidized scale generated with the passage of operating time. The gap between them is reduced. As a result, if the oxidized scale is not removed at every periodic inspection of a power plant or the like, the sliding member will be fixed.

JP-A-6-101769 JP 2008-275035 A JP 2005-272855 A JP 2007-270701 A JP 2007-307565 A

  In recent years, higher efficiency of thermal power plants and the like has been pushed forward, and the steam temperature has increased to 593 ° C., 600 ° C., 610 ° C., and the like. In the future, it is conceivable that the steam temperature will be 700 ° C. or higher.

  On the other hand, in the nitriding treatment applied to the contact surface between the valve stem and the bush, the metal surface is activated at high temperatures, and easily reacts with high-temperature water vapor in the atmosphere to generate an oxide film. The generated oxide film peels off each time the valve is repeatedly opened and closed, and the peeled pieces are deposited locally in the recesses on the surface by sliding the valve stem, filling the gap with the bush and generating the stick on the valve stem. Let In addition, the nitride layer formed on the contact surface between the valve stem and the bush has a property of decomposing and softening at about 500 ° C. or more depending on the nitriding temperature, and the oxidation resistance of the sliding member of the valve device is not sufficient. .

  The problem to be solved by the invention is to provide a valve device that exhibits oxidation resistance in a high temperature environment and a method for manufacturing the valve device.

  According to the embodiment, the valve device includes a valve stem as a movable member that operates in association with opening and closing of the valve and a bush of a stationary member that is in sliding contact with the valve stem, and is in sliding contact with at least one of the valve stem and the bush. A built-up portion is integrally provided on the surface, and the built-up portion generates a pulsed discharge between an electrode constituted by a molded body mainly composed of the first metal and a portion to be processed of the valve stem or bush. Then, the first coating formed by welding and depositing the electrode material on the surface of the treated portion and the raw material powder mainly composed of the second metal are subjected to plasma spraying using a plasma spray gun. A valve device having a built-up portion including a second coating formed on the surface of one coating is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the valve apparatus which exhibits the oxidation resistance in a high temperature environment can be provided.

Sectional drawing which shows an example of a structure of the valve apparatus in 1st Embodiment. The conceptual diagram which shows the principle of the overlaying method of the 1st film | membrane by 1st Embodiment. The conceptual diagram which shows the principle of the plasma spraying method which overlays the 2nd film | membrane by 1st Embodiment. The flowchart which shows an example of the procedure for formation of the 1st membrane | film | coat and 2nd membrane | film | coat in 1st Embodiment. The figure which shows the state which formed the build-up part in the to-be-processed part in 1st Embodiment. The figure which shows the state which performed the surface treatment of the build-up part of a 2nd film | membrane in the build-up part after building up the 1st film | membrane in 1st Embodiment. The figure which shows the state which formed the build-up part of the 2nd film | membrane on the surface of the build-up part after building up the 1st film | membrane in 1st Embodiment. The figure which shows the state which gave the finishing process to the surface of the buildup part in the to-be-processed part after building up the 2nd film | membrane in 1st Embodiment. The flowchart which shows an example of the procedure for formation of the 1st membrane | film | coat and 2nd membrane | film | coat in 3rd Embodiment. The figure which shows the state which gave the machining to the 2nd membrane | film | coat in 3rd Embodiment. Sectional drawing which shows an example of a structure of the valve apparatus in 4th Embodiment.

(First embodiment)
Hereinafter, a first embodiment will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the configuration of the valve device according to the first embodiment. Here, a steam control valve that is installed in a preceding stage of a high-pressure turbine (not shown) and is used to control the rotation speed of the high-pressure turbine by controlling the amount of inflow steam will be described as an example.
The steam control valve in the first embodiment is, for example, a steam control valve for a steam turbine installed in a thermal power plant. The steam control valve has a steam valve main body 200, a bush 201, an upper lid 202, a valve seat 203 provided at a steam outlet, a valve body 204, a valve rod 205, an opening 207, an opening 208, and an opening 209. The opening 207 is a steam inlet. The opening 208 is a steam outlet. The opening 209 is an insertion port for the valve rod 205 and the valve body 204.

In the steam valve main body 200, the valve body 204 opens and closes the opening 208 of the valve seat 203 by the axial movement of the valve rod 205 inserted into the steam chamber 210 through the opening 209.
The upper lid 202 is fixed to the upper part of the opening 209 of the steam valve main body 200 and closes the upper surface of the steam valve main body 200. A hydraulic drive mechanism 206 is installed above the upper lid 202. A valve rod 205 is connected to the hydraulic drive mechanism 206 downward (vertical direction).

The valve rod 205 is reciprocated up and down by a hydraulic drive mechanism 206. In the steam control valve, the through hole of the upper lid 202 is a sliding surface with the valve rod 205. For this reason, a cylindrical bush 201 made of a metal resistant to friction is inserted into this portion, and the outer peripheral surface of the valve rod 205 is attached to the bush 201 so that the valve rod 205 moving in the axial direction does not move sideways. Guide by sliding.
The valve body 204 has a cylindrical shape and is provided so as to contact the valve seat 203 and open and close the opening of the valve seat 203. The central portion of the valve body 204 is provided so as to be connected to the distal end portion of the valve rod 205.

  In order to exhibit oxidation resistance that can be used for a long time under oxidizing conditions of high-temperature steam in the sliding portion constituted by the inner peripheral surface of the bush 201 and the outer peripheral surface of the valve stem 205, the surface of the member is used in the initial stage. It is necessary that the oxide film formed in the above has a protective property and prevents the generation of a new oxide thereafter.

  In order for an oxide film to exhibit protective properties, the film needs to be dense, although depending on the type of oxide forming the film. Such a dense oxide film can prevent excess oxygen in the atmosphere from passing therethrough. Moreover, such an oxide film can suppress the generation of oxides by the metal forming the sliding member. Moreover, it is preferable that an oxide film (film | membrane) has a characteristic which can also suppress that a metal component elutes through an oxide film and produces | generates an oxide scale.

  As a means for forming such a preferable film (build-up part), a vapor deposition method in which the raw material to be the film (build-up part) is evaporated at a high temperature and adsorbed on the surface of the base material of the part to be processed, or a film (meat) There is a thermal spraying method or the like in which a raw material to be a prime portion) is melted and projected onto the surface of the base material of the treated portion. However, the film (build-up part) obtained from these manufacturing methods is formed by attaching raw material particles to the surface of the base material of the part to be processed. Therefore, such a film (building-up part) is inferior in adhesiveness with a base material, and has the fault of peeling in a short time when applied to a valve device.

  Therefore, in the first embodiment, instead of performing the conventional nitriding treatment, first, a stellite (registered trademark) of a cobalt base hard alloy having excellent wear resistance is built up on the sliding contact surface as the first film.

FIG. 2 is a conceptual diagram showing the principle of the electric discharge machining method for overlaying the first film in the first embodiment.
As shown in FIG. 2, the electrode 101 is connected to the cathode of the DC power supply 103 in an electrically insulating liquid L or air in an electric discharge machine (mostly not shown).

  Further, in the first embodiment, the voltage of the DC power supply 103 is applied to the electrode 101, the processing target 100, and the processing target 100 connected to the anode of the DC power supply 103 while maintaining a minute gap. Apply between or stop applying. This generates a pulsed discharge. Then, the material of the electrode 101 is deposited and deposited on the surface of the processing target 100 by the discharge energy.

  Here, the to-be-processed part 100 means the sliding contact surface which contact | connects while either the valve rod 205 in FIG. 1, or the bush 201 slides between the other. In the first embodiment, the build-up portion 102 of the first film is integrally provided on at least one sliding contact surface of the valve rod 205 and the bush 201 as the processing target portion 100.

  In the first embodiment, a pulsed discharge is generated between an electrode formed of a molded body containing a metal as a main component and a processing target 100 including a valve rod 205 or a bush 201. Then, the first film (building-up portion) 102 is formed by welding and depositing the electrode material on the surface of the processing target portion 100.

  Note that the role of the liquid L shown in FIG. 2 is to prevent the processing waste of the electrode 101 from being scattered by pulsed discharge and preventing it from being welded to the electrode 101 again. Since most of the tip portion is covered with bubbles, the effect obtained by discharging in the gas from the beginning does not change.

  As the electrode material, cobalt-based hard alloy stellite can be used. Stellite is an alloy containing cobalt as a main component and containing about 30% chromium and 4 to 15% tungsten, and is widely known as a material excellent in wear resistance. Stellite has a high oxidation resistance because it contains a large amount of cobalt.

In the electric discharge machining method, a base material is melted in units of electrode particles to form a built-up portion. For this reason, there is little heat input to the base material of the to-be-processed part 100. FIG. For this reason, it is possible to perform the overlaying with almost no deformation of the processing target portion 100.
Furthermore, in the electric discharge machining method, the electrode component is melted and bonded to the portion to be processed. Therefore, the adhesiveness between the film (build-up part) and the base material of the part to be processed is high, and the film (build-up part) does not peel off.

  However, the film (covered part) formed in this way has high hardness, and electrode particles are deposited on the surface of the film (covered part). For this reason, it becomes a porous structure | tissue which the void | hole opened between the uneven | corrugated unevenness | corrugation and the particle | grains of an electrode. For this reason, the sliding member provided with these films (building-up portions) attacks the mating member during sliding, and wears the mating member or causes galling. For this reason, it is impossible to directly use the electric discharge machining film (the built-up portion) as the sliding contact surface of the sliding member.

For this reason, in the first embodiment, a second film is newly formed on the first film and used as a sliding surface of the sliding member.
The second coating is formed using a plasma spraying method using a high-temperature, high-speed plasma jet as a heat source. The procedure for forming the second film is that the molten particles are accelerated by a plasma jet, filled from the surface of the first film (build-up part) having a porous structure as described above, and filled and deposited. Let Then, the electrode film deposited by electric discharge machining and the melted particle of plasma spraying are mechanically coupled to perform overlaying as a second film.

FIG. 3 is a conceptual diagram showing the principle of the plasma spraying method for overlaying the second film.
As shown in FIG. 3, the powder feed type plasma spray gun 150 has a nozzle 152. The nozzle 152 ejects a thermal spray powder 151 to be melted by a plasma flame.
The thermal spray gun 150 adds argon gas (Ar gas) or hydrogen gas (H ₂ gas) as an auxiliary gas, argon gas (Ar gas) or helium gas (He gas) as a working gas, and adds auxiliary gas to the working gas. The mixed supply gas 159 is supplied into the nozzle 152.

  By adding and mixing the auxiliary gas to the working gas, the amount of generated heat and the speed of the plasma jet can be increased. Specifically, by adding an auxiliary gas to the working gas, the dissociation voltage is increased, the arc voltage is increased, the amount of generated heat is increased at the same current, and the plasma jet flow rate is increased.

  The thermal spray gun 150 uses a nozzle 152 as an anode, applies a direct current from a direct current power source 154 to a cathode 153 provided in the nozzle 152 to generate a direct current arc 155, and the working gas is converted into plasma by the arc. The plasma flame 156 of about 12,000 to 18,000 ° C. is generated by the auxiliary gas.

The thermal spray gun 150 supplies the thermal spray powder 151 in front of the DC arc 155 and instantaneously melts the thermal spray powder 151. The thermal spray gun 150 ejects the molten thermal spray powder 151 at a higher speed than the tip of the nozzle 152.
When the thermal spray powder 151 in a molten state is sprayed (collises) on the surface of the processing target portion 100 by the plasma flame 156, a build-up portion 157 of the second film is formed (coupled).

  A cooling water introduction hole 158 for cooling the tip portion is formed in the vicinity of the tip portion of the nozzle 152. By introducing the cooling water into the cooling water introduction hole 158, the nozzle tip is prevented from being heated by the plasma flame 156.

  Here, in particular, in the plasma spraying method, since the amount of heat retained by the spray particles is small, the temperature rise of the portion to be processed remains at about 100 to 150 ° C., and the thermal influence on the base material due to heat input can be suppressed. For this reason, a 2nd membrane | film | coat (building-up part) can be formed, deform | transforming a to-be-processed part hardly and there is almost no distortion.

If chromium (Cr) is used as a thermal spray material to be a plasma spray coating (covered part), the plasma flame 156 may cause the particles of the thermal spray material to become high temperature during the thermal spraying process, forcibly oxidizing the coating. it can. For this reason, it becomes a dense oxide film of chromium oxide (Cr ₂ O ₃ ) derived from chromium (Cr) and having high protective properties. This suppresses generation of new oxide (next to the oxide film) during operation of the valve device. As a result, the aforementioned preferable oxide film is formed on the surface of the build-up portion 157 of the second film.

Next, an example of a specific manufacturing method for forming the built-up portion 102 provided integrally with the processing target portion 100 will be described.
FIG. 4 is a flowchart illustrating an example of a procedure for forming the first film and the second film in the first embodiment.
First, the build-up part 102 of the 1st film | membrane is formed in the surface of a to-be-processed part (step S1). Next, in the build-up part 102 after building up the first film, the base process of the build-up part 157 of the second film as step S2 is performed (step S2).
Next, the build-up part 157 of the second film is formed on the surface of the build-up part 102 after the first film is built up (step S3).
Next, in the to-be-processed part 100 after building up the second film, the surface of the film (building up part) 157 as step S4 is finished.
Next, details of each procedure will be described.
First, the process of forming the build-up part 102 of the 1st film | membrane on the surface of a to-be-processed part as step S1 is demonstrated.
FIG. 5 shows a state in which the build-up portion 102 is formed on the processing target (material) 100 using the electric discharge machine shown in FIG.
The build-up portion 102 formed by the electric discharge machining method has a diffusion / penetration layer 102a in which particles of the material of the electrode 101 are diffused and penetrated from the surface of the treated portion 100, and particles of the material of the electrode 101 with respect to the diffusion / penetration layer 102a. And a deposited layer 102b deposited by welding.

  The diffusion / penetration layer 102a is formed by depositing a cobalt base hard alloy on the processing target part 100 by electric discharge machining. For this reason, the fusion | melting part which has a gradient composition from which a composition ratio changes in the thickness direction is produced | generated.

  Here, in order to prevent the strength of the base material from being reduced by limiting the amount of heat input to the base material by selecting an appropriate discharge condition when forming the build-up portion 102, the diffusion and penetration that becomes the molten portion The thickness of the layer 102a is, for example, 20 μm or less, and it is preferably 1 μm or more, desirably 5 μm or more. Thereby, the adhesion strength of the build-up portion 102 can be increased while suppressing deformation of the base material.

  The build-up portion 102 having the melted portion becomes a functionally gradient material having a gradient composition, and the linear expansion coefficients near the boundary in contact with the base material of the processing target portion 100 are substantially equal, and there is almost no difference in the linear expansion coefficients. For this reason, the residual stress of the build-up part 102 can be eliminated. As a result, it is possible to prevent the occurrence of cracks in the built-up portion 102 applied to the surface of the processing target portion 100.

  There is no limitation on the thickness of the deposited layer 102b resulting from the use of electric discharge machining. However, the thickness of the deposited layer 102b is 50 μm in order to effectively exhibit the wear resistance and oxidation resistance of the cobalt-based hard alloy and to mechanically entangle and bond the second film in the subsequent manufacturing process. About 300 μm is desirable.

  Here, the electrode 101 is a molded electrode formed of a molded body obtained by compressing or heat-treating a powder containing metal as a main component with a press. However, it may be molded by other known manufacturing methods. Furthermore, the particle diameter of the raw material powder of the electrode 101 may be fine powder of about 10 μm.

  Further, as the material of the electrode 101, a cobalt base hard alloy or a nickel base hard alloy having thermal shock resistance and oxidation resistance and having a hardness higher than that of the base material of the processing target 100 is suitable. In addition to these, examples of the material of the electrode 101 include a fine ceramic material having a high oxidation start temperature of, for example, 800 ° C. or higher and exhibiting excellent oxidation resistance at high temperatures. Examples of the fine ceramic material include chromium nitride (CrN), titanium aluminum nitride (TiAlN), titanium tungsten nitride (Ti-W) N, titanium molybdenum (Ti-Mo) C, chromium silicon nitride (CrSiN), and titanium silicon nitride. (TiSiN) or the like.

  An electrode 101 formed from a powder of these fine ceramics or a powder obtained by mixing the powder and the hard alloy is also conceivable. Further, even if a new material is developed with further increase in steam conditions in the future, according to the manufacturing method by electric discharge machining of the present embodiment, the build-up portion can be a functionally gradient material, so that it can be applied. Needless to say.

Next, the ground treatment of the overlaying portion 157 of the second coating as step S2 in the overlaying portion 102 after overlaying the first coating will be described.
FIG. 6 shows a state in which the base treatment of the build-up part 157 of the second film is performed in the build-up part 102 after the first film is built up. This ground treatment is a process for accurately controlling the thickness of the second film. In this treatment, the distorted unevenness generated by the deposition of electrode particles on the surface of the coating (building-up part) is machined.

  This machining is a process in which the surface roughness (maximum height roughness) Rz is made finer than 12.5 so as to have a predetermined shape, size and geometric tolerance by, for example, a grinding machine or a polishing machine. is there.

  In addition, in order to improve the adhesion of the second coating, the predetermined shape, dimensions, and geometric tolerances change with respect to the overlaying portion 102 after overlaying the first coating as a pretreatment before spraying or a ground treatment. Blasting or chemical corrosion may be performed to such an extent that it does not occur.

Next, the process for forming the overlaying portion 157 of the second coating as step S3 on the surface of the overlaying portion 102 after overlaying the first coating will be described.
FIG. 7 shows that the second coating overlay 157 is formed on the surface of the build-up portion 102 after depositing the first coating using chromium (Cr) as the thermal spray material by the plasma spraying method shown in FIG. Shows the state.

This build-up portion 157 is an oxide film of chromium oxide (Cr ₂ O ₃ ). This oxide film is forcibly oxidized by the plasma flame 156 during the thermal spraying process, and is a dense and highly protective film.

  In order not to affect the temperature rise of the portion 100 to be processed, there should be no variation (bias) in the thickness of the build-up portion 157 due to the spraying operation. However, since the finishing process of the surface is scheduled in the subsequent manufacturing process, the thickness of the built-up portion 157 is desirably about 100 μm.

  The particle size of the raw material powder for plasma spraying is smaller than the particle size of the electrode material used for electric discharge machining, and the particle size is preferably 10 μm or less, and preferably a fine powder having a particle size of 0.05 to 1 μm. When the value of the particle diameter is set as described above, the raw material powder in the plasma flame can be easily melted. Further, the plasma sprayed molten particles can be mechanically entangled with the first coating formed by electric discharge machining. Thereby, the bonding force between the films can be further strengthened.

  Further, for the purpose of further strengthening the bonding force between the coatings, the build-up portion 102 of the first coating is preheated to about 100 to 150 ° C. before plasma spraying, so that the gap between the molten particles and the processing target portion 100 is increased. A temperature difference may not be generated.

  In addition to the chromium (Cr) described above, the thermal spray material of the plasma spraying method includes molybdenum (Mo), cobalt (Co), silicon (Si), nickel (Ni), aluminum (Al), titanium (Ti), copper ( One or more metals selected from Cu) and iron (Fe). During the thermal spraying process, the thermal spray material is forcibly oxidized by the plasma flame 156 when the thermal spray particles become high temperature.

Therefore, an oxide film such as molybdenum oxide (MoO ₃ ) derived from each material is formed, and generation of a new oxide, that is, an oxide next to the oxide film is suppressed during operation of the valve device. Note that other gas such as nitrogen may be used as an auxiliary gas for the supply gas 159 in order to promote oxidation during the thermal spraying process.

Further, in the formation of the overlay of the second film shown in FIG. 7, as shown in FIG. 3, the supply amount of the auxiliary gas of the supply gas 159 supplied to the nozzle 152 is controlled, so that the amount of argon (Ar) or the like is not increased. Plasma spraying can be performed while supplying a large amount of active gas. Then, even if the plasma flame 156 is at a high temperature, the thermal spray material itself is hardly oxidized or altered, so that chromium oxide (Cr ₂ O ₃ ) itself can be used as the thermal spray material. Therefore, a dense and highly protective oxide film can be formed.
Note that if a large amount of auxiliary gas for the supply gas 159 is supplied, minute pores formed in the oxide film can be reduced, so that a denser oxide film can be formed.

As a thermal spray material for performing plasma spraying in such an inert gas, in addition to chromium oxide (Cr ₂ O ₃ ), zirconia (ZrO ₂ ), titanium oxide (TiO ₂ ), chromium carbide (Cr ₃ C ₂ ), Alumina (Al ₂ O ₃ ), silicon carbide (SiC), titanium carbide (TiC), nichrome (Ni—Cr), silicon oxide (SiO ₂ ), cobalt-based hard alloy, nickel-based hard alloy, and the like can be given. Even if these are used to form the build-up portion 157 of the second film, the same effects can be obtained. Further, the overlaying part 157 of the second coating by plasma spraying may have a multi-layered structure of two or more layers by changing the type of thermal spray material.

  Needless to say, even if a new material is developed as a thermal spray material for the plasma spraying method, the developed material can be applied as long as the characteristics and effects of the obtained coating are the same. .

  In addition, even if new thermal spraying methods are developed in the future, such as plasma spraying under reduced pressure conditions to form a dense film, or applying thermal spraying methods other than plasma, such as arc spraying and flame spraying, this Thermal spraying method is applicable if the amount of heat kept by the thermal spray particles is small, the temperature rise of the treated part is low, the heat effect on the base material due to heat input can be suppressed, and the resulting effect is the same Needless to say.

Next, the process of finishing the surface of the coating (building-up portion) 157 as step S4 in the processing target 100 after building up the second coating will be described.
FIG. 8 illustrates a process of finishing the distorted unevenness generated on the surface of the coating (building-up portion) 157 in the processing target 100 after the second coating is overlaid, for example, a predetermined shape by a grinding machine or a polishing machine, The finished state is shown to have dimensions.

Here, the finishing surface of the film (building-up portion) 157 is chromium oxide (Cr ₂ O ₃ ), which becomes the surface (sliding surface) of the sliding member. Therefore, it is desirable that the surface roughness is fine. The specific surface roughness (maximum height roughness) Rz is preferably finer than 6.3.

  In order that the second film 157 remaining after the finishing process is not peeled off and the oxidation resistance characteristic of the second film 157 is sufficiently exhibited, the thickness of the remaining second film 157 should be 50 μm or less. preferable.

  Therefore, the sliding member provided with the second film 157 is formed of a smooth surface with a fine surface roughness. Therefore, when the sliding member slides, the sliding contact surface does not attack or wear the mating member, and does not cause galling.

(Second Embodiment)
Next, a second embodiment will be described.
As described above, FIG. 5 shows a state in which the built-up portion 102 is formed on the portion to be processed (material) using an electric discharge machine.
In the electric discharge machining method for forming the build-up portion 102, a pulsed discharge is generated between the electrode and the portion to be processed, and the material of the electrode is welded to the surface of the portion to be processed by the discharge energy. It is a method of depositing.

  For this reason, the processing time required to form the build-up portion 102 is naturally long. From the viewpoint of productivity, it is desired to reduce the processing time required for forming the built-up portion 102.

  The time required for machining in such an electric discharge machining method, that is, the build-up speed (lamination speed), as a result of the test, has been found to be closely related to the density (coarse density) of the metal structure of the build-up part. .

  The fineness (coarse density) of this structure is mainly determined by the discharge current, discharge voltage application time (time when pulsed discharge is generated) set by the electric discharge machine, and application stop time (discharge is paused). Time). In addition, when the discharge current value is large, the application time is long, and the application stop time is short, the metal structure of the built-up portion increases in density (becomes dense).

For example, by changing the way of view, the discharge current, the application time, and the application stop time are set to be constant with an electric discharge machine, and the processing is performed by regarding the feed speed of the parts to be processed as the build-up speed (stacking speed). In the execution of this processing, there is a difference in the denseness (coarse density) of the structure of the built-up portion between the case where the feed speed of the parts is high and the case where the parts are slow.
That is, when the feed rate is high, the coarse density of the structure of the built-up portion is coarse, and when the feed rate is low, the coarse density of the structure of the build-up portion is dense.

  Next, in a test in which a plurality of conditions are set so that there is a three-fold speed difference in the part feed speed, that is, the build-up speed (stacking speed), the pores of the deposited layer 102b of the build-up portion 102 under each condition The result of measuring the rate and determining the denseness (coarse density) of the structure of the built-up portion will be described.

  As a result, the average porosity of the deposited layer 102b when the feed rate is high is 45 to 55%. When the feed rate is low, the average porosity of the deposited layer 102b is 31 to 35%. Thus, a difference of 1.5 times or more was clearly recognized in the average porosity of the deposited layer 102b between the case where the feed rate was high and the case where the feed rate was slow.

  The porosity is obtained by observing the metal structure by magnifying the deposited layer of the built-up portion that is a porous structure with a metal microscope, and measuring the area ratio of the pores per unit area. When the porosity of the deposited layer 102b is large, the ratio of the area of the voids to the area of the entire surface increases, so that the denseness (coarse density) of the structure becomes rough. On the contrary, if the porosity of the deposited layer 102b is small, the ratio of the area of the vacancies to the area of the entire surface is small, so that the denseness (coarse density) of the structure becomes dense.

  An object of the present embodiment is to provide a valve device that can exhibit oxidation resistance even in a high temperature environment, and a method for manufacturing the valve device. As a basic technique for achieving this purpose, It is required that the film exhibiting the chemical conversion does not peel from the sliding surface.

  That is, it is a necessary condition that the adhesion between the film exhibiting oxidation resistance (second film in the first embodiment) and the base material (first film in the first embodiment) is strong. In order for the adhesiveness to be strong, it is preferable that the base material and the film are mechanically entangled and bonded. For this purpose, it is preferable that the porosity of the matrix on the base material side is large to some extent.

  In the second embodiment, a porous structure having a large porosity can be obtained by increasing the build-up speed (stacking speed) on the base material by the electric discharge machining method. The porosity in the second embodiment is preferably 40% or more from the result of the test described above.

Thus, in the second embodiment, the metal structure of the first film is preferably a porous structure having a higher porosity. For this reason, the material of the electrode is not limited to the type already described in the first embodiment, as long as it has heat resistance, oxidation resistance and high temperature strength, and can form a porous structure having a large porosity. good.
In the second embodiment, since the processing time can be shortened by increasing the build-up speed (stacking speed), the merit of improving productivity can be obtained.

(Third embodiment)
Hereinafter, a third embodiment will be described.
FIG. 9 is a flowchart illustrating an example of a procedure for forming the first film and the second film in the third embodiment.
First, as steps S1 to S4 described in the first embodiment, the formation of the build-up part of the first film, the ground treatment of the build-up part 157 of the second film, the formation of the build-up part 157 of the second film, The surface of the built-up part is finished.
Then, the second film is removed up to the surface of the built-up portion 102 after the first film is built up, and finish processing is performed (step S31).

Next, details of step S31 will be described.
FIG. 10 shows the surface of the built-up portion 102 after the second coating (building-up portion) 157 is further machined from the state shown in FIG. The state in which the second film is removed and finishing is shown.

  Here, since the finished surface after removing the second film is the surface (sliding surface) of the sliding member, it is desirable that the surface roughness be fine. The specific surface roughness (maximum height roughness) Rz is preferably finer than 6.3.

  The build-up portion 102 is in a state where the second film is left in the porous pores on the exposed surface of the first film, and an oxide film of a metal material is formed on the remaining second film. One film and the second film appear distributed on the same sliding contact surface.

Therefore, the surface of these built-up portions 102 is completely free of the unique porous structure seen in the electric discharge machining as shown in FIG. These coatings (build-up parts) do not attack, wear, or cause galling of the mating member when sliding. Therefore, the surface of these built-up portions 102 can be used as a sliding contact surface of the sliding member.
Furthermore, the surface property has the advantage that the wear resistance by the first film and the oxidation resistance by the second film are synergistically effective.

(Fourth embodiment)
Hereinafter, a fourth embodiment will be described.
FIG. 11 is a partial cross-sectional view showing the structure of the steam control valve in the fourth embodiment, particularly the structure around the valve body. In addition, the basic part of the valve apparatus in 4th Embodiment is the same as that of the steam control valve in 1st Embodiment shown in FIG. For this reason, detailed description of components having the same function is omitted. Therefore, the following description will focus on the parts that are different from the first embodiment.
As shown in FIG. 11, the steam control valve in the fourth embodiment operates the valve rod 205 and the valve body 312 linked to the valve rod 205 in the axial direction to change the opening of the valve. It has a function of adjusting the steam flow rate. In a series of operations, the valve stem 205 operates with the bush 201 installed inside the upper lid 310 as a guide. Similarly, the valve body 312 operates using the sleeve 311 as a guide.

  The sleeve 311 is fixed to the upper lid 310 inside the steam valve main body (not shown). The valve body 312 is provided so as to come into contact with a valve seat (not shown), and is assembled at the tip of the valve stem 205.

  In the first embodiment shown in FIG. 1, the valve device includes a valve rod 205 as a movable member that operates as the valve opens and closes, and a bush 201 as a stationary member that slides on the valve rod 205.

  On the other hand, in the fourth embodiment, the valve device uses the valve body 312 as a movable member and the sleeve 311 as a stationary member. That is, the outer surface of the valve body 312 and the inner surface of the sleeve 311 constitute a sliding contact surface.

  In order to sufficiently exhibit the oxidation resistance that can be used for a long time under oxidation conditions of high-temperature steam in the sliding portion composed of the valve body 312 and the sleeve 311, as described in the first embodiment, the initial stage It is necessary that the oxide film formed on the surface of the member in the stage has a protective property and prevents the subsequent generation of a new oxide. In order to sufficiently exhibit the oxide film protecting property, the film needs to be dense although it depends on the type of oxide forming the film.

  As described in the first embodiment, such a dense oxide film can prevent excess oxygen in the atmosphere from permeating. Moreover, such an oxide film can suppress the generation of oxides by the metal forming the sliding member. Moreover, it is preferable that an oxide film (film | membrane) has a characteristic which can also suppress that a metal component elutes through an oxide film and produces | generates an oxide scale. For this reason, an oxide film is formed by the method described in the first to third embodiments.

  As described above, the valve device in each embodiment applies a coating formed by combining an electric discharge machining method and a plasma spraying method, and a bush (or sleeve) of a sliding member that comes into contact with high-temperature steam sent from a boiler, A preferable oxide film can be formed on at least one sliding contact surface of the valve stem (or valve body).

  For this reason, since the oxide film (film) can suppress the generation of new oxide (the oxide next to the oxide film) during operation of the valve device, the generation of oxide scale reduces the gap between the sliding portions. There is no end. For this reason, it becomes possible to use the valve device at a higher temperature or for a longer time without lowering the slidability.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 100 ... To-be-processed part, 101 ... Electrode, 102 ... Overlaying part of 1st film | membrane, 102a ... Diffusion osmosis | permeation layer, 102b ... Deposition layer, 103 ... DC power supply, 150 ... Powder feeding type plasma spray gun, 151 ... Spraying powder , 152 ... Nozzle, 153 ... Cathode, 154 ... DC power supply, 155 ... DC arc, 156 ... Plasma flame, 157 ... Overlaying part of second coating, 158 ... Cooling water introduction hole, 159 ... Supply gas, 200 ... Steam valve Main body, 201 ... bush, 202, 310 ... upper lid, 203 ... valve seat, 204, 312 ... valve body, 205 ... valve rod, 206 ... hydraulic drive mechanism, 311 ... sleeve.

Claims (10)

A valve device including a valve stem as a movable member that operates in association with opening and closing of the valve, and a bush as a stationary member that is in sliding contact with the valve stem,
A built-up portion is integrally provided on at least one sliding contact surface of the valve stem and the bush,
The build-up part is
A pulsed discharge is generated between an electrode constituted by a molded body containing a first metal as a main component and a portion to be treated of the valve stem or the bush, and the material of the electrode is transferred to the surface of the portion to be treated. A first film formed by depositing and depositing on,
A valve having a built-up portion including a second coating formed on the surface of the first coating by plasma spraying a raw material powder mainly composed of a second metal using a plasma spray gun. apparatus. A valve device including a valve body as a movable member that operates in association with opening and closing of the valve, and a sleeve as a stationary member that is in sliding contact with the valve body,
A built-up portion is integrally provided on at least one sliding contact surface of the valve body and the sleeve,
The build-up part is
A pulsed discharge is generated between an electrode formed of a molded body containing a first metal as a main component and a portion to be processed of the valve body or the sleeve, and the material of the electrode is transferred to the surface of the portion to be processed. A first film formed by depositing and depositing on,
A valve having a built-up portion including a second coating formed on the surface of the first coating by plasma spraying a raw material powder mainly composed of a second metal using a plasma spray gun. apparatus. The first coating of the build-up part is
A diffusion permeation layer in which particles of the material of the electrode as the first metal are diffused and permeated from the surface of the treated portion;
A deposited layer in which particles of the electrode material are deposited on the diffusion layer,
The valve device according to claim 1 or 2, wherein the porosity of the deposited layer is 40% or more. The second coating of the build-up part is
The first metal film is formed by plasma spraying after finishing the surface of the first film using a raw material powder smaller than the particles of the electrode material as the first metal, preferably having a particle diameter of 10 μm or less. The valve device according to claim 1 or 2. The first coating and the second coating of the build-up part are:
Formed by filling and depositing the molten particles of the second metal by the plasma spraying inside the pores opened on the surface of the deposition layer of the first coating,
The first film and the second film are:
The valve device according to any one of claims 1 to 4, wherein the valve device is mechanically entangled and bonded inside the deposition layer of the first film. The first coating of the build-up part is
The said 1st metal is formed with the material containing at least any one of a cobalt base hard alloy, a nickel base hard alloy, and a ceramic material, The any one of Claim 1 thru | or 5 characterized by the above-mentioned. Valve device. The material of the second metal is chromium (Cr), molybdenum (Mo), cobalt (Co), silicon (Si), nickel (Ni), aluminum (Al), titanium (Ti), copper (Cu) and iron One or more selected from (Fe),
The second coating of the build-up part is
An oxide film containing at least chromium oxide (Cr ₂ O ₃ ) derived from the second metal is formed by oxidizing the second metal with a plasma flame during the plasma spraying process. The valve device according to any one of claims 1 to 6. The second coating of the build-up part is
Increasing the supply amount of the auxiliary gas added to and mixed with the working gas during the plasma spraying process to an amount that can prevent oxidation of the material of the second metal itself by the plasma flame,
The material of the second metal is chromium oxide (Cr ₂ O ₃ ), zirconia (ZrO ₂ ), titanium oxide (TiO ₂ ), chromium carbide (Cr ₃ C ₂ ), alumina (Al ₂ O ₃ ), silicon A material selected from carbide (SiC), titanium carbide (TiC), nichrome (Ni-Cr), silicon oxide (SiO ₂ ), cobalt base hard alloy and nickel base hard alloy,
The valve device according to any one of claims 1 to 6, wherein the second metal material itself is formed as the second film. In the first film and the second film of the build-up part,
In the state where the second film is removed and the surface of the first film is exposed, the residual film is left in a state where the second film is left in the porous pores on the surface of the exposed first film. The second film is formed by forming an oxide film containing the second metal material,
The valve device according to any one of claims 1 to 8, wherein the first coating and the second coating are distributed on the same sliding contact surface. A method of manufacturing a valve device including a movable member that operates in accordance with opening and closing of the valve and a stationary member that is in sliding contact with the movable member,
In electrically insulating liquid or air
A pulsed discharge is generated between an electrode constituted by a molded body mainly composed of a first metal material and a portion to be treated of the movable member or the stationary member, and the material of the electrode is treated. A first film formed by welding and depositing on the surface of the part;
A build-up portion including a second coating formed on the surface of the first coating of the portion to be processed by plasma spraying a raw material powder mainly containing a second metal material as the movable member or the stationary member A method for manufacturing a valve device, wherein the valve device is formed on at least one sliding contact surface.

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