JP4049024B2 - Overlaying method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for reducing voids in a built-up portion in a method for building up a workpiece surface using pulse discharge.
[0002]
[Prior art]
There is a need to maintain the original characteristics by building up damaged parts such as cracks and thinning of the workpiece surface caused by aging and wear. A typical example of the overlaying method is a plasma overlaying method. In this method, a wire-shaped cladding material is put into a heat source such as a plasma arc, and the tip of the material is melted in the heat source and adhered to the surface of the workpiece. According to this method, a thick build-up portion can be obtained, but there is a problem that the workpiece is thermally deformed because the temperature of the build-up portion rises.
[0003]
For this reason, overlaying techniques that can be constructed with low heat input are required. As a build-up technique that can be applied with low heat input, there is a pulse discharge build-up method (for example, see Non-Patent Document 1). The pulse discharge build-up method is a liquid generated by melting an electrode by discharging a voltage by applying a voltage between the electrode and a workpiece, melting the tip of the electrode by Joule heat and arc heat generated at the time of discharge. This is a method of depositing droplets by depositing them on damaged parts of the workpiece.
[0004]
[Non-Patent Document 1]
Principles and Applications of Electro-Spark Deposition, Roger N. Johnson, Surface Modification Technologies TS Sudarshan and DG Bhat The Metallurgical Society, 1988
[0005]
[Problems to be solved by the invention]
In the pulse discharge build-up method, build-up is performed by depositing a large number of droplets at a damaged portion of a workpiece. Therefore, unlike the plasma overlay method, a molten pool is not formed on the workpiece surface. For this reason, there is a concern about the poor deposition between the droplets and the remaining voids due to gas mixture in the built-up portion. If voids are present on the surface of the built-up portion, corrosion or cracks may develop from the location, which may cause a decrease in corrosion resistance and mechanical strength.
[0006]
An object of the present invention is to provide a method and an apparatus for reducing a gap in a built-up portion when building up a damaged portion on a workpiece surface using a pulse discharge build-up method.
[0007]
[Means for Solving the Problems]
In a pulse discharge overlaying method in which an electrode material is melted by pulse discharge to form a build-up portion on a workpiece, the workpiece is heated and then pulse discharge overlay is applied to the workpiece.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As a result of the inventor's examination of the pulse discharge overlaying method, it has been obtained as a new finding that the porosity of the overlaying portion is reduced by heating the workpiece to an ambient temperature or higher before the pulse discharge overlaying operation. . Hereinafter, the experimental method and results will be described.
[0009]
FIG. 1 shows the relationship between the build-up portion porosity and the work piece temperature when pulse discharge build-up is performed after the work piece has been heated in advance. Fig.1 (a) has shown the construction conditions of this experiment, and FIG.1 (b) has shown the workpiece temperature dependence of the built-up part porosity. The porosity in this experiment was evaluated as an area ratio of voids in the entire visual field by observing the cross-sectional structure of the built-up portion at a magnification of 1000 times. The workpiece was SUS304 stainless steel, the electrode material was SUS316L stainless steel and Inconel 600, and the shielding gas was pure argon and pure nitrogen. From Fig. 1 (b), in any combination condition of electrode material and shield gas, when the workpiece is heated in advance to the ambient temperature (27 ° C) or higher before the pulse discharge cladding is applied, it is not heated. It was found that the porosity can be reduced compared to.
[0010]
Here, the relationship between the porosity and the penetrant testing will be described. FIG. 2A shows an outline of the penetration test, and FIG. 2B shows the result of measuring the relationship between the detection sensitivity of the opening defect on the surface of the built-up part and the porosity of the build-up part by the penetration test. As shown in FIG. 2 (a), the penetrant flaw detection test consists of (1) applying a penetrating liquid to the surface of the workpiece, (2) washing the excess penetrating liquid, and (3) a developer on the surface of the workpiece. Is performed by coating. In (3), when the penetrant at the flaw detection site is leached, an opening defect is detected. From the measurement result of FIG. 2 (b), it was found that if the porosity of the built-up portion was 0.5% or less, the opening defect by the penetration flaw detection test was below the detection limit. Here, if the opening defect by the penetration flaw detection test is below the detection limit, the quality standard of the built-up portion is satisfied. Further, when the porosity is larger than 0.5%, an opening defect is detected. Even in this case, if the distance between the opening defects is equal to or larger than a reference value, the overlay portion Will meet the quality standards. Therefore, at the time of build-up construction, first, in the penetration flaw detection test, it is desirable that the build-up part is below the opening defect detection limit, that is, the porosity is 0.5% or less. Here, from FIG. 1B, the workpiece heating temperature (hereinafter referred to as “optimum workpiece heating temperature”) for the porosity to be 0.5% or less is (1) Inconel as the electrode material. 600, 100 to 130 ° C. when argon is used as the shielding gas, (2) SUS316L as the electrode material, 40 to 80 ° C. when argon is used as the shielding gas, (3) SUS316L as the electrode material, nitrogen as the shielding gas When it is used, it becomes 50-80 degreeC. The optimum workpiece heating temperature depends on the electrode material and the shielding gas. When heating the workpiece, it is necessary to select an appropriate heating temperature for the selection of the electrode material and the shielding gas. Here, the optimum workpiece heating temperature is a heating temperature at which the porosity is 0.5% or less, and has a certain range.
[0011]
As described above, from FIG. 1 and FIG. 2, the porosity can be reduced by heating the workpiece in advance before the pulse discharge overlay construction. Further, by setting the heating temperature of the workpiece to the optimum workpiece heating temperature, the porosity can be reduced to 0.5% or less, that is, the detection sensitivity of the opening defect or less.
[0012]
The inventor also examined the upper limit values of the input heat amount W and the workpiece heating temperature T. FIG. 3 is a conceptual diagram showing the relationship between the input heat amount W and the workpiece temperature T. W _max and T _max indicate the upper limit values of the input heat amount W and the workpiece temperature T, respectively, which do not cause He cracking. Yes. The amount of heat input W from the electrode to the workpiece can be estimated by multiplying the pulse voltage value V, the current value A, the pulse frequency f, the pulse width t, and the electrode scanning speed S. Since the quality of the built-up part depends on the cooling rate during construction (approximately proportional to the temperature difference between the droplet and the workpiece), a constant cooling rate (temperature difference) is required to maintain the quality of the built-up part. Need to hold. Therefore, when the input heat amount W (droplet temperature) is increased, the workpiece temperature T must also be increased. However, when heat is applied to a member having a high neutron irradiation amount such as a shroud, a He crack may occur. Therefore, even if the workpiece is a member having a high neutron irradiation amount by setting the input heat amount W and the workpiece temperature T to the upper limit values (W _max , T _max ) that do not cause He cracking, He cracking is possible. Can be prevented.
[0013]
Furthermore, the inventors examined the dependence of the gas flow rate on the workpiece temperature. FIG. 4A shows an outline of the measurement method, and FIG. 4B shows an experimental result of the dependence of the workpiece temperature on the gas flow rate. As shown in FIG. 4 (a), SUS304L is used as a base material and SUS316L is used as an electrode material, and overlaying is performed by a pulse discharge overlay method, and the workpiece is attached to the back surface (the surface opposite to the overlay surface). The temperature of the workpiece was measured with a thermocouple. The construction conditions were the same as in FIG. 1 (a), and 60 ° C. was set as the workpiece temperature before enforcement. After the temperature of the workpiece reached 60 ° C., only the gas flow rate was changed, and overlaying was performed for 60 seconds. As a result, when building up while injecting a gas flow rate of 40 L / min, the temperature of the workpiece was about 100 ° C. at the maximum. On the other hand, when the gas flow rate is 0 L / min, that is, when building up without injecting the gas, the temperature of the workpiece reaches 350 ° C. at the maximum, and the construction point is estimated to rise to a higher temperature. In this experiment, the build-up was performed for 60 seconds. However, when the construction is continued for a longer time, the workpiece temperature may reach a temperature range causing He cracking. Therefore, when building up a workpiece with a high neutron irradiation amount, it is necessary to adjust the workpiece temperature and the construction conditions so as not to exceed the temperature causing He cracking even if the temperature rises with construction. Become.
[0014]
Example 1
The first embodiment of the present invention will be described below. A 1st Example is an Example in the case of constructing the pulse discharge cladding method of this invention with respect to the workpiece in a nuclear reactor vessel.
[0015]
FIG. 5 shows an outline of an apparatus for applying the pulse discharge cladding method of the present invention to a BWR (boiling water nuclear power plant) reactor. The electrode 1 is attached to the scanning arm 5 and discharged while moving on the surface of the workpiece 2 in the pressure vessel, and the damaged portion of the surface of the workpiece 2 is built up by pulse discharge. A pulse is applied to the electrode 1 from the pulse power source 3 installed outside the pressure vessel through the power cable 8. During discharge, shield gas is supplied from a gas cylinder 6 installed outside the pressure vessel, and is injected from the periphery of the electrode tip through the gas pipe 12. This shielding gas suppresses water exclusion and oxidation.
[0016]
FIG. 6 is a flowchart showing the work procedure of the present embodiment. First, a periodic inspection start command is given, and the reactor operation is stopped, fuel is taken out, and the pressure vessel is opened (S1 to S4). Then, the inspection equipment is carried in, the inside of the furnace is inspected, and the damage location and the damage state data confirmed by the inspection are stored in a database (inspection database) (S5 to S7). After the inspection is completed, the inspection equipment is removed (S8). When damage is confirmed by inspection, repair equipment is carried in, and the damaged portion is repaired by the pulse discharge overlay method of the present invention according to the construction conditions determined based on the inspection data obtained in S7 ( S9 to S12). After the repair is completed, the repair equipment is removed (S13). Thereafter, the pressure vessel is closed, the fuel is restored, the periodic inspection is finished, and the operation of the reactor is resumed (S14 to S17). If damage is not confirmed by inspection or damage that cannot be repaired, the periodic inspection is completed by closing the pressure vessel and restoring the fuel without performing repairs (S10 to S13). Then, the operation of the reactor is resumed (S14 to S17).
[0017]
FIG. 7 is a flowchart showing the detailed procedure of the repair (S12) in FIG. When a repair start command is issued, the damaged state of the damaged portion is grasped based on the inspection data obtained in S7 (S12-1, S12-2). Next, based on the grasped damage status and workpiece material, the construction database prepared in advance controls the amount of heat input to the workpiece, heat input to the workpiece, shield gas, etc. The conditions and the heating temperature of the workpiece are selected, and each is attached or set (S12-3 to S12-5). If necessary, the heating temperature is set to T _max or less in order to prevent He cracking. Here, the construction database creation procedure will be described with reference to FIG. The enforcement database is a database in which the optimum electrode material, construction conditions, and workpiece heating temperature for the workpiece material and the built-up part quality are investigated in advance. First, construction specifications such as a damaged part and a damaged state of the test workpiece and a built-up part quality are input (a). Next, an electrode material for satisfying the construction specifications is selected (b). The amount of heat input to the workpiece is determined by the construction conditions and the workpiece heating temperature, but is mainly governed by the former. Therefore, prior to selecting the workpiece heating temperature, first the construction conditions are optimized. The procedure for optimizing the construction conditions is shown below. Voltage value, pulse shape, pulse frequency, electrode diameter, standoff (standoff is the distance between the electrode and the workpiece, and it must be kept within the distance that causes dielectric breakdown in order to build up. 0, that is, when the electrode and the workpiece come into contact with each other, there is a possibility that the workpiece will be short-circuited and the workpiece may be ground.) After adjusting the construction conditions, which is a combination of factors composed of shielding gas (c), Implement surfacing under the enforcement conditions. After the build-up is performed, the build-up part quality is investigated (d), and the correlation between the construction conditions and the build-up part quality is made into a database (database 1). After repeating the overlaying under the predetermined construction conditions, the buildup part quality survey and the creation of a database, the optimum construction condition for the overlay part quality is selected based on the database 1 (e). Next, the procedure for selecting the workpiece heating temperature is shown. In order to select the workpiece heating temperature, the temperature of the workpiece is adjusted (f), and overlaying is performed at the temperature. After the build-up is conducted, the build-up part quality is investigated (g), and the correlation between the workpiece heating temperature and the build-up part quality is made into a database (database 2). After repeating the build-up under predetermined construction conditions, the build-up portion quality survey and the creation of a database, the optimum workpiece heating temperature for the build-up portion quality is selected based on the database 2 (h). With the above procedure, data such as workpiece material, build-up part quality, selected electrode material, optimum construction conditions, workpiece heating temperature, etc. are made into a database (construction database).
[0018]
Thereafter, actual repair work (building up) is started (S12-6). A build-up range is set based on the enforcement data (S12-7). Next, the temperature adjusting device 4 is attached to the workpiece 2, and the surface of the workpiece 2 is heated and held constant until a predetermined temperature is reached (S12-8, S12-9). Thereafter, construction is started (S12-10). Start the build-up on the damaged part of the surface of the workpiece 2 under the selected construction conditions, until the predetermined condition is satisfied (until the area sufficiently covers the damaged part and the thickness that can withstand stress and corrosion) The filling is performed (S12-11, S12-12). After the predetermined area and thickness are built up, the build-up is finished (S12-13). After the build-up operation is completed, the presence or absence of opening defects (holes caused by uneven deposition) on the surface of the built-up part is checked by UT (ultrasonic flaw detection test), VT (visual test), etc., and the soundness of the built-up part is confirmed. (S12-14). When the soundness can be confirmed, the build-up is finished and the repair is finished (S12-15 to S12-17). If the soundness cannot be confirmed, overlay is performed again.
[0019]
According to this embodiment, the porosity can be reduced by heating the workpiece in advance before the pulse discharge overlaying. Furthermore, if the workpiece temperature is set to be equal to or lower than T _max , He cracking can be prevented.
[0020]
(Example 2)
The second embodiment of the present invention will be described below. A 2nd Example is an Example in the case of constructing the pulse discharge overlay of this invention with respect to the workpiece 2 which does not need on-site construction, such as a small component.
[0021]
FIG. 9 shows an overlay apparatus applied in this embodiment. The electrode 1 is attached to the tip of the scanning arm 5 and scanned according to a scanning pattern transmitted from the electrode position control device 10 through the communication cable 11. The electrode position information such as the scanning pattern and the XYZ coordinates of the electrode 1 is displayed on the screen in the electrode position control device 10. A pulse is applied to the electrode 1 from the pulse power source 3 through the power cable 8. The shield gas supplied from the gas cylinder 6 is injected from the vicinity of the tip of the electrode 1 through the gas pipe 12. Pulse information such as voltage value, pulse shape, pulse period, electrode diameter, standoff, etc. is displayed on the screen of the pulse information display device 7. A temperature measuring device 9 is attached to the surface of the workpiece 2, and the actually measured temperature data is transmitted to the temperature adjusting device 4. Control is performed by the temperature adjusting device 4 so that the temperature of the workpiece 2 is kept constant at a predetermined workpiece heating temperature.
[0022]
The details of the selection of the execution conditions and the workpiece heating temperature, and the overlaying method are the same as in Example 1 and will be omitted.
[0023]
According to this embodiment, the porosity can be reduced by heating the workpiece in advance before the pulse discharge overlaying. Furthermore, if the workpiece temperature is set to be equal to or lower than T _max , He cracking can be prevented.
[0024]
In addition, according to the present embodiment, the pulse discharge build-up of the present invention is performed on the work piece 2 that does not need to be constructed in the field, such as small parts, so that the temperature adjustment device 4 can be easily mounted and temperature-controlled. .
[0025]
In each of the above embodiments, the optimum workpiece heating temperature can be selected as the workpiece heating temperature. By selecting the optimum workpiece heating temperature as the heating temperature of the workpiece, the void ratio of the built-up portion can be made 0.5% or less, that is, the detection sensitivity of the opening defect or less.
[0026]
In each of the above embodiments, the electrode used in the pulse discharge overlay construction can be an electrode to which a rotational motion is applied. FIG. 10 shows a build-up device provided with electrodes subjected to rotational movement. The electrode 1 is subjected to rotational movement in the axial direction or radial direction during construction. Thereby, the welding at the time of the electrode 1 contacting with the workpiece 2 can be prevented.
[0027]
In each of the above embodiments, the temperature adjusting device 4 can be formed according to the shape of the workpiece 2. FIG. 11 shows a temperature adjusting device formed according to the shape of the workpiece 2. In the case of a workpiece 2 having a complicated shape, when a temperature adjusting device having a flat temperature adjusting unit is used, the distance between the temperature adjusting device 4 and the workpiece 2 cannot be made constant. Therefore, the heat transfer property becomes non-uniform and the temperature of the workpiece 2 tends to be non-uniform. On the other hand, by using the temperature adjusting device 4 formed according to the shape of the workpiece 2, the interval between the temperature adjusting device 4 and the workpiece 2 can be made constant, and has a complicated shape. Even for the workpiece 2, the temperature can be adjusted uniformly.
[0028]
In each of the above embodiments, gas can be applied as the temperature adjusting means. FIG. 12 shows a case where gas is applied as the temperature heating means of the workpiece 2. After adjusting the temperature of the gas by the gas temperature adjusting device 14, the gas is injected from the periphery of the tip of the electrode 1, and the surface of the workpiece 2 is heated to a predetermined temperature using the gas as a medium. Taking the heat transfer into consideration, the gas temperature is set to be higher than a desired workpiece heating temperature and adjusted so that the surface of the workpiece 2 reaches a predetermined temperature. Since the temperature of the entire surface in contact with the gas can be adjusted, the workpiece 2 having a complicated shape can be easily heated. Further, since the temperature of the workpiece 2 is not directly adjusted, the gas temperature adjusting device 4 can be remotely installed, and the application to a narrow environment becomes easy.
[0029]
In each of the above embodiments, water 13 can be applied as the temperature adjusting means. FIG. 13 shows a case where water 13 is applied as the temperature heating means of the workpiece 2. The workpiece 2 is placed in the water 13, the water 13 is heated to a predetermined temperature by the temperature adjusting device 15, and the workpiece 2 is heated using water as a medium. In this case, the water temperature needs to be set higher than the desired workpiece heating temperature in consideration of heat transfer. As a result, the workpiece having a complicated shape can be easily heated, and the temperature of the workpiece 2 can be kept uniform. The medium used for heating in this embodiment is not limited to water, but may be any liquid that is suitable for heating the workpiece.
[0030]
【The invention's effect】
In the pulse discharge overlay method in which the electrode material is melted by pulse discharge to form a build-up portion on the workpiece, the build-up portion is formed by applying the pulse discharge build-up to the workpiece after heating the workpiece. Voids can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a void ratio of a built-up portion and a workpiece temperature.
FIG. 2 is a diagram showing a relationship between an opening defect detection limit and a porosity.
FIG. 3 is a conceptual diagram showing the relationship between the workpiece temperature and the input heat quantity.
FIG. 4 is a diagram showing the gas flow rate dependency of the workpiece temperature.
FIG. 5 is a view showing a pulse discharge cladding apparatus according to the present invention.
FIG. 6 is a flowchart showing the procedure of the first embodiment.
FIG. 7 is a flowchart showing a repair procedure.
FIG. 8 is a flowchart showing a procedure for creating an enforcement database.
FIG. 9 is a view showing a pulse discharge cladding apparatus according to the present invention.
FIG. 10 is a view showing a build-up device including an electrode to which a rotational motion is applied.
FIG. 11 is a view showing a temperature adjustment device molded into a shape similar to a workpiece.
FIG. 12 is a diagram showing temperature adjusting means when gas is applied as heating means.
FIG. 13 is a diagram showing a temperature adjusting means when water is applied as a heating means.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electrode, 2 ... Workpiece, 3 ... Pulse power supply, 4,15 ... Temperature adjusting device, 5 ... Scanning arm, 9 ... Temperature measuring device, 10 ... Electrode position control device, 13 ... Water, 14 ... Gas temperature adjustment apparatus.

Claims (6)

In the pulse discharge build-up method in which the electrode material is melted by pulse discharge to form a build-up part on the workpiece,
A pulse discharge build-up method, comprising: applying a pulse discharge build-up to the workpiece after heating the workpiece to a temperature at which the porosity of the build-up portion is 0.5% or less. Based on the material of the workpiece and the electrode material and shield gas used in the pulse discharge overlay, the heating temperature of the workpiece is selected,
After heating the workpiece to the selected temperature,
The pulse discharge build-up method according to claim 1 , wherein pulse discharge build-up is applied to the workpiece using the electrode material and the shield gas. The workpiece is SUS304 stainless steel, the electrode material is Inconel (registered trademark) 600, the shielding gas is argon, and the heating temperature of the workpiece is 100 ° C. or more and less than 130 ° C. The pulse discharge build-up method according to claim 1 or 2 . The workpiece is SUS304 stainless steel, the electrode material is SUS316L stainless steel, claim shielding gas is argon, the heating temperature of the workpiece is characterized in that less than 80 ° C. 40 ° C. or higher The pulse discharge overlaying method according to claim 1 or 2 . The workpiece is SUS304 stainless steel, the electrode material is SUS316L stainless steel, claim shield gas is nitrogen, the heating temperature of the workpiece is characterized in that less than 80 ° C. or higher 50 ° C. The pulse discharge overlaying method according to claim 1 or 2 . Pulse power supply,
An electrode to which a pulse is applied;
A gas supply device for supplying a shielding gas between the electrode and the workpiece surface;
A scanning device for scanning the electrode on the surface of the workpiece;
And a temperature regulating device pulse discharge cladding overlaid portion porosity of which is formed by the adjusting the temperature of 0.5% the workpiece so as to become less,
The said temperature adjustment apparatus adjusts the temperature of the said workpiece before pulse discharge build-up enforcement, The pulse discharge build-up apparatus characterized by the above-mentioned .

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