Rotor repairing method

Abstract

The rotor repair method is a rotor repair method provided with a rotor main body extending in an axial direction about an axis and a plurality of impellers arranged in the axial direction and fixed to the rotor main body, the rotor repair method comprising the steps of: welding a repair region of the rotor main body; filling the damaged part by using the welding part; after the welding is carried out, heat treatment is carried out only on the repair area in the rotor; and after the heat treatment, cutting a part of the welded part to form a machined surface smoothly connected to the outer surface.

Description

Technical Field

[0001] The invention relates to a method for repairing a rotor.

[0002] This application claims priority to Tokugan 2023-121995 filed in Japan on July 26, 2023, the contents of which are incorporated herein by reference. Background Art

[0003] Generally, a centrifugal compressor includes: a rotor having a plurality of impellers; and a casing that covers the impellers from the outside to form a flow path between the casing and the impellers. In the centrifugal compressor, a fluid supplied from the outside through the flow path formed in the casing is compressed by the rotation of the impellers. When the rotor of such a compressor is damaged, it is sometimes repaired without remaking the rotor.

[0004] For example, Patent Document 1 describes a repair method for repairing a damaged portion by forming a spray coating on the damaged portion to be repaired. Specifically, in the repair method described in Patent Document 1, first, the damaged portion of the rotor generated at the position supported by the bearing is removed and shaped by machining or the like. Then, the surface after removal and shaping is roughened by sandblasting, and a coating is formed by high-speed flame spraying. The formed coating is processed and finished, and then inspected, thereby obtaining a repaired rotor.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2004-256903

[0008] However, in the above-mentioned rotor repair, if the welded portion is not heat treated, the welded portion may have insufficient strength or excessive hardness compared to other unwelded portions. As a result, there is a case where the rotor after repair is in a state that does not meet the required performance. On the other hand, since a relatively large component such as a rotor is heat treated, the size of the rotor may change before and after the repair, making it difficult to obtain a rotor with the same shape as before the repair. Thus, when repairing a rotor, it is required to maintain the shape and performance of the rotor before and after the repair. Summary of the invention

[0009] The present invention provides a rotor repair method capable of stably maintaining the shape and performance of the repaired rotor.

[0010] Solutions to Solve Problems

[0011] The rotor repair method of the present invention is a rotor repair method having a rotor main body extending axially with an axis as the center, and a plurality of impellers arranged along the axial direction and fixed to the rotor main body, the rotor repair method comprising the following steps: welding the repair area of ​​the rotor main body, and filling the damaged part formed in a manner of being recessed from the outer surface of the rotor main body with the welded part; after performing the welding, performing heat treatment only on the repaired area in the rotor; and after performing the heat treatment, cutting a portion of the welded part to form a processed surface smoothly connected to the outer surface.

[0012] Effects of the Invention

[0013] According to the rotor repairing method of the present invention, the shape and performance of the repaired rotor can be stably maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram showing a rotor to be repaired according to the present embodiment.

[0015] Figure 2 1 is a flowchart showing a method for repairing a rotor according to the present embodiment.

[0016] Figure 3 This is an enlarged view of a main part of the rotor body for explaining the step of confirming a damaged portion in the present embodiment.

[0017] Figure 4 This is an enlarged view of a main part of the rotor body for explaining the steps of machining a damaged portion according to the present embodiment.

[0018] Figure 5 This is an enlarged view of a main part of the rotor body for explaining the step of welding the repair region according to the present embodiment.

[0019] Figure 6 This is an enlarged view of a main part of the rotor body for explaining how a heater is mounted in the step of performing partial heat treatment in the present embodiment.

[0020] Figure 7 This is an enlarged view of a main part of the rotor body for explaining how a heat insulating material is attached in the step of partially performing heat treatment in the present embodiment.

[0021] Figure 8 This is an enlarged view of a main part of the rotor body for explaining the step of forming a processed surface according to the present embodiment.

[0022] Description of reference numerals:

[0023] 1…Rotor

[0024] O…axis

[0025] 20…Impeller

[0026] 10…Rotor body

[0027] 11…First End

[0028] 12…Second end

[0029] 100…Area of ​​shaft end

[0030] 110…First shaft end area

[0031] 120…Second shaft end area

[0032] 130…Bearing area

[0033] 140…Thrust supported area

[0034] 150…Shaft journal supported area

[0035] 151…First journal supported area

[0036] 152…Second journal supported area

[0037] 160…Coupling fixed area

[0038] F…External surface

[0039] 8…Bearings

[0040] 81…Thrust bearing

[0041] 82…Journal bearings

[0042] 9…Coupling components

[0043] D…Injury site

[0044] Da…Axial

[0045] Dal…First end side

[0046] Da2…Second end side

[0047] Dr… Radial

[0048] S1…Rotor Repair Method

[0049] S2…Damage site confirmation step

[0050] S3…Damage Part Processing Steps

[0051] S4…Repair area welding steps

[0052] S5…local heat treatment step

[0053] S6...Processing surface forming step

[0054] A…Repair Area

[0055] C...concave

[0056] M…Welding Department

[0057] H…Heater

[0058] T…Insulation material

[0059] GF…Processing surface. DETAILED DESCRIPTION

[0060] Hereinafter, a method S1 for repairing a rotor according to the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

[0061] The rotor repair method S1 is a method for repairing the shaft end region 100 including the end of the rotor 1. The rotor 1 to be repaired is a rotating part of a rotary machine such as a compressor or a steam turbine. The rotor 1 of this embodiment is a rotor 1 of a multi-stage centrifugal compressor.

[0062] (Rotor Structure)

[0063] like Figure 1 As shown, the rotor 1 is a member rotatable about an axis O in a housing (not shown). The rotor 1 includes a rotor body 10 and an impeller 20. The rotor body 10 extends in an axial direction Da about the axis O as a center.

[0064] It should be noted that, hereinafter, the direction in which the axis O extends is referred to as the axial direction Da. When the rotor 1 is installed in the rotary machine, the axis O extends horizontally. The direction orthogonal to the axial direction Da is referred to as the radial direction Dr. That is, the radial direction Dr of the rotor 1 based on the axis O is referred to as the radial direction Dr.

[0065] A plurality of impellers 20 are arranged at intervals in the axial direction Da. Each impeller 20 is fixed to the rotor body 10. Each impeller 20 can rotate integrally with the rotor body 10 around the axis O. In the present embodiment, for example, a total of six impellers 20 are provided. These impellers 20 are arranged in the axial direction Da at the central part of the rotor body 10 between the side of the rotor body 10 close to the first end 11 (the first end side Da1, one side) and the side of the rotor body 10 close to the second end 12 (the second end side Da2, the other side) in the axial direction Da.

[0066] The rotor body 10 has an axial end region 100 including an end in the axial direction Da of the rotor body 10. The axial end region 100 is a region of a certain range from the end in the axial direction Da. The rotor body 10 of the present embodiment has a first axial end region 110 including an end on one side of the axial direction Da, i.e., a first end 11, and a second axial end region 120 including an end on the other side of the axial direction Da, i.e., a second end 12. The first axial end region 110 and the second axial end region 120 are formed separately from each other in the axial direction Da via a central portion. The first axial end region 110 and the second axial end region 120 are formed in a position that does not overlap with the impeller 20 in the axial direction Da.

[0067] In addition, the rotor body 10 is rotatably supported by the housing through the bearing 8. The rotor body 10 has a bearing area 130 supported by the bearing 8. The bearing 8 supporting the rotor body 10 has a thrust bearing 81 that restricts displacement of the rotor body 10 in the thrust direction and a pair of journal bearings 82 that rotatably support the rotor body 10. In other words, the rotor body 10 has a thrust supported area 140 supported by the thrust bearing 81 and a journal supported area 150 supported by the journal bearing 82.

[0068] The thrust supported region 140 is formed as a part of the second shaft end region 120. The thrust supported region 140 is formed at a position separated from the second end 12 in the axial direction Da. The journal supported region 150 has a first journal supported region 151 and a second journal supported region 152 separately in the axial direction Da. The first journal supported region 151 is formed as a part of the first shaft end region 110. The first journal supported region 151 is formed at a position separated from the first end 11 in the axial direction Da. The second journal supported region 152 is formed as a part of the second shaft end region 120. The second journal supported region 152 is formed at a position separated from the second end 12 and the thrust supported region 140 in the axial direction Da.

[0069] In addition, the coupling member 9 can be assembled at the first end 11 of the rotor body 10. The coupling member 9 can be loaded and unloaded not only relative to the first end 11 of the rotor body 10, but also relative to other rotating machines (not shown) arranged outside the housing. The rotor body 10 has a coupling fixed area 160 that can fix the coupling member 9. The coupling fixed area 160 is formed as a part of the first shaft end area 110. The coupling fixed area 160 is formed at a position separated from the first end 11 in the axial direction Da. The coupling fixed area 160 is formed at a position between the first journal supported area 151 and the first end 11 in the axial direction Da.

[0070] (Rotor repair method)

[0071] Reference Figure 2, the rotor repair method S1 is described. The rotor repair method S1 of this embodiment is implemented on the rotor 1 after it is removed from the housing. The rotor repair method S1 repairs the damaged part D including the scratches formed on the outer surface F of the rotor 1 in the shaft end area 100. The rotor repair method S1 includes a damaged part confirmation step S2, a damaged part processing step S3, a repair area welding step S4, a local heat treatment step S5 and a processed surface forming step S6.

[0072] (Injury site confirmation step)

[0073] In the damaged portion confirmation step S2, the damaged portion D formed in the shaft end region 100 of the rotor 1 is confirmed. For example, the operator visually checks the rotor 1 to confirm whether the damaged portion D is formed in the shaft end region 100. In this embodiment, Figure 3 As shown, the case where the damaged portion D exists in the coupling fixed region 160 of the first axial end region 110 is described as an example. Since the coupling member 9 is fixed to the rotor body 10 by hydraulic fitting, shrink fitting, etc., the damaged region in the coupling fixed region 160 is formed by loading and unloading the coupling member 9 relative to the rotor body 10. The damaged portion D is formed in a manner recessed from the outer surface F of the rotor body 10. In addition, the repaired repair region A is formed in the axial end region 100. The repaired repair region A is an area in the rotor body 10 that includes the damaged portion D. That is, in the present embodiment, in the coupling fixed region 160, a prescribed range including the area where the damaged portion D exists is set as the repair region A.

[0074] (Damage Part Processing Steps)

[0075] like Figure 2 As shown, the damaged part processing step S3 is performed after the damaged part confirmation step S2. Figure 4 As shown, in the damaged portion processing step S3, the damaged portion D is cut, and the repair area A is formed as a recessed portion C recessed from the outer surface F. The recessed portion C is formed over the entire circumference of the rotor body 10. The recessed portion C is formed in a manner that completely eliminates the damaged portion D from the rotor body 10. The recessed portion C is formed in a larger range than the position where the damaged portion D is formed. That is, in the state where the recessed portion C is formed, the damaged portion D is not present in the rotor body 10. In the present embodiment, the recessed portion C is formed in the coupling fixed region 160.

[0076] (Repair area welding steps)

[0077] In the repair area welding step S4, welding is performed on the repair area A. Figure 2As shown, the repair area welding step S4 of this embodiment is implemented after the damaged part processing step S3. In the repair area welding step S4, as shown in FIG. Figure 5 As shown, welding is performed on the shaft end region 100 in the repair region A, and the damaged portion D is filled with the weld portion M. In the present embodiment, welding is performed in a manner that the recessed portion C formed in the coupling fixed region 160 is filled with the weld portion M. That is, the weld portion M is formed over the entire circumference of the rotor body 10. The weld portion M is formed by surfacing the entire circumference of the recessed portion C using laser welding. The weld portion M is formed with a thickness that protrudes from the outer surface F in the radial direction Dr.

[0078] (Local heat treatment step)

[0079] like Figure 2 As shown, the local heat treatment step S5 is performed after the repair area welding step S4. In the local heat treatment step S5, after welding, only the shaft end area 100 in the rotor 1 is heat treated. Specifically, Figure 6 As shown, only the first axial end region 110 is heat treated. More specifically, in the present embodiment, only the coupling fixed region 160, which is the repair region A, is treated. The heat treatment is performed by annealing. That is, the coupling fixed region 160 is gradually heated to a specified temperature at a certain speed, kept at that temperature for a specified time, and then gradually cooled at a certain speed. In the present embodiment, a heater H composed of a nickel-chromium alloy wire or the like is wound seamlessly only in the region to be heat treated, i.e., the coupling fixed region 160. Then, as shown in FIG. Figure 7 As shown, the heat insulating material T is wound so as to cover the coupling fixed region 160 together with the heater H. In this way, in a state where the heater H and the heat insulating material T are mounted on the coupling fixed region 160 including the welded portion M, only the coupling fixed region 160 is annealed over the entire circumference of the rotor 1. At this time, the annealing conditions during the heat treatment are preferably implemented under the conditions that the coupling fixed region 160 after the heat treatment satisfies the Charpy value required for the low-temperature material.

[0080] It should be noted that the local heat treatment step S5 is preferably performed after the influence of heat generated by welding is completely removed from the rotor 1. The local heat treatment step S5 is preferably performed by standing the rotor 1 so that the axis O extends in the vertical direction.

[0081] (Processing surface forming step)

[0082] like Figure 2 As shown, the processing surface forming step S6 is implemented after the local heat treatment step S5. In the processing surface forming step S6, as shown in FIG. Figure 8As shown, after the heat treatment, a part of the welded portion M is cut to form a processed surface GF. The processed surface GF is formed by grinding the welded portion M. The processed surface forming step S6 is not performed before the local heat treatment step S5.

[0083] The machined surface GF is a surface smoothly connected to the outer surface F. The machined surface GF is formed in the axial direction Da at a position overlapping with the position where the welded portion M is formed. The machined surface GF is a smooth surface connected to the outer surface F at a position where the recessed portion C is not formed in the axial direction Da. The machined surface GF is formed over the entire circumference of the rotor body 10 so as to be a constant distance from the axis O in the radial direction Dr.

[0084] (Effect)

[0085] In the repair method S1 of the rotor having the above structure, welding is performed on the damaged part D to form the welded part M. Thus, the damaged part D is filled with the welded part M and repaired. However, if only welding is performed, the strength of the welded part M and its surroundings, i.e., the heat-affected part, may be insufficient compared to the required strength, or the hardness of the heat-affected part may exceed the required hardness. In contrast, by performing heat treatment, the strength of the heat-affected part can be increased to meet the required value, and the hardness can be reduced. At this time, the heat treatment is not performed on the entire rotor 1 and the entire rotor body 10, but only the first axial end area 110 including the repaired area A formed with the welded part M is heat treated. By not heating the entire rotor 1 and the entire rotor body 10, the influence of thermal elongation, thermal contraction, and strain caused by the heat treatment can be limited to the vicinity of the repaired area A. In other words, the range of changes in size and surface roughness caused by the influence of the heat treatment can be suppressed only to the vicinity of the repaired area A. Furthermore, after only the first axial end area 110 including the repaired area A is partially heat treated, a part of the welded part M is cut to form a processed surface GF. Therefore, the changes in the size and surface roughness that are limitedly generated in the first axial end region 110 can be cut off and corrected. In addition, by not performing heat treatment after forming the machined surface GF, the changes in the size and surface roughness of the machined surface GF that has already been formed can be suppressed. As a result, the rotor 1 with the same quality and shape as before the repair can be stably obtained. Therefore, the shape and performance of the repaired rotor 1 can be stably maintained.

[0086] In particular, in the present embodiment, heat treatment is applied only to the first axial end region 110. Thus, the influence of thermal expansion, thermal contraction, and strain caused by the heat treatment can be limited to the first axial end region 110. In other words, the range of changes in size and surface roughness caused by the heat treatment can be limited to the first axial end region 110.

[0087] In addition, the machined surface GF is formed at a constant distance from the axis O in the radial direction Dr over the entire circumference of the rotor body 10. Therefore, the repaired region A (region where the damaged portion D originally existed) where the welded portion M is formed can be machined with high precision over the entire circumference to match the original shape. Therefore, the rotor 1 having the same shape as before the repair can be obtained more stably.

[0088] In addition, the welded portion M is formed by laser welding. In particular, laser welding is performed on the entire circumference of the rotor body 10. Therefore, compared with the case where a portion of the rotor body 10 is welded, the thermal impact of welding becomes larger. Moreover, in a welding method with a large heat input such as TIG welding, the thermal impact generated on the rotor body 10 becomes even larger. However, by adopting laser welding, the heat input can be suppressed during welding, and the thermal impact generated on the rotor body 10 can be suppressed. As a result, the deformation of the rotor body 10 caused by welding can be suppressed.

[0089] In addition, when only the coupling fixed region 160 is locally heat treated, annealing is performed. Therefore, the residual stress generated in the coupling fixed region 160 due to the formation of the welded portion M can be removed. As a result, the repaired region A with the welded portion M formed can have a uniform and soft crystal structure, and the processability and toughness can be improved.

[0090] In addition, annealing is performed by winding a heater H and a heat insulating material T around the coupling fixed region 160. After being heated by the heater H, the coupling fixed region 160 is kept warm by the heat insulating material T. Therefore, heat is not easily transferred to regions other than the coupling fixed region 160 where the heat insulating material T is not wound, and the influence of the heat treatment is not easily generated in regions other than the coupling fixed region 160. Therefore, the influence on the entire rotor body 10 can be suppressed and the coupling fixed region 160 can be effectively annealed.

[0091] The repair region A is a region including a damaged portion D formed so as to be recessed from the outer surface F of the rotor body 10. Therefore, the repair can be performed after the damaged portion D such as a damage formed on the rotor body 10 is completely removed.

[0092] Furthermore, the damaged portion D is cut to form the recessed portion C. In addition, the welded portion M is formed in such a manner as to fill the recessed portion C. Therefore, no matter what shape the damaged portion D is formed in, the damaged portion D can be reliably removed and repaired. Furthermore, by cutting the recessed portion C from the outer surface F, the welded portion M is more likely to be in close contact with the repaired region A than when the welded portion M is directly formed on the damaged portion D, and the welded portion M can be stably formed.

[0093] (Other embodiments)

[0094] As mentioned above, although the embodiment of the present invention is described in detail with reference to the drawings, the specific structure is not limited to this embodiment, and design changes and the like are also included within the scope that does not depart from the gist of the present invention.

[0095] For example, the rotor 1 to be repaired is not limited to the rotor 1 of the above structure. The rotor 1 may be of a different shape as long as it is a rotor 1 of a rotary machine. Therefore, the number of impellers 20 provided on the rotor body 10 and the orientation of the impellers 20 are not limited to the above examples and can be changed as appropriate.

[0096] The rotor repair method S1 is not limited to the case where the damaged portion D is formed only in the coupling fixed region 160. The damaged portion D only needs to be formed in the shaft end region 100, and may be formed in the bearing region 130 or the second shaft end region 120.

[0097] In addition, in the rotor repair method S1, the damaged part processing step S3 is not necessarily performed. For example, the damaged part processing step S3 may not be performed. In this case, in the repair area welding step S4, the damaged part D is directly welded, and the welded part M is formed to directly cover the damaged part D.

[0098] In the rotor repair method S1, the local heat treatment step S5 is not limited to being performed only once as in the present embodiment. The local heat treatment step S5 may be performed multiple times as long as it is performed before the processed surface forming step S6.

[0099] <Notes>

[0100] The rotor repair method S1 described in the embodiment can be understood, for example, as follows.

[0101] (1) A rotor repair method S1 of a first embodiment is a rotor repair method S1 having a rotor body 10 extending along an axial direction Da with an axis O as a center, and a plurality of impellers 20 arranged along the axial direction Da and fixed to the rotor body 10, the rotor repair method S1 comprising the following steps: welding a repair area A of the rotor body 10 to fill the damaged area D formed in a recessed manner from the outer surface F of the rotor body 10 with a welded portion M; after the welding, heat treatment is performed only on the repaired area A of the rotor 1; and after the heat treatment, a portion of the welded portion M is cut to form a processed surface GF smoothly connected to the outer surface F.

[0102] In such a rotor repair method S1, welding is performed on the damaged part D to form a welded part M. Thus, the damaged part D is filled with the welded part M and repaired. However, if only welding is performed, the strength of the welded part M and its surroundings, that is, the heat-affected part, may be insufficient compared to the required strength, or the hardness of the heat-affected part may exceed the required hardness. In contrast, by performing heat treatment, the strength of the heat-affected part can be increased to meet the required value, and the hardness can be reduced. At this time, heat treatment is not performed on the entire rotor 1 and the entire rotor body 10, but only on the repair area A where the welded part M is formed. By not heating the entire rotor 1 and the entire rotor body 10, the influence of thermal elongation, thermal contraction, and strain caused by the heat treatment can be limited to the repair area A. In other words, the range of changes in size and surface roughness caused by the influence of the heat treatment can be suppressed only in the repair area A. In addition, after heat treatment is performed only partially on the repair area A, a part of the welded part M is cut to form a processed surface GF. Therefore, the changes in size and surface roughness that are limited to the repair area A can be cut off and corrected. In addition, by not performing heat treatment after forming the machined surface GF, it is possible to suppress changes in the size and surface roughness of the machined surface GF that has already been formed. As a result, it is possible to stably obtain a rotor 1 having the same quality and shape as before repair. Therefore, it is possible to stably maintain the shape and performance of the repaired rotor 1.

[0103] (2) A second rotor repair method S1 is the rotor repair method S1 of (1), wherein the repair region A is formed in an axial end region 100 of the rotor body 10 including the end in the axial direction Da.

[0104] Thus, the influence of thermal expansion, thermal contraction, and strain caused by heat treatment can be limited to the shaft end region 100. That is, the range of changes in dimensions and surface roughness caused by heat treatment can be limited to the shaft end region 100.

[0105] (3) A third rotor repair method S1 is the rotor repair method S1 of (1) or (2), wherein the processed surface GF is formed at a constant distance from the axis O over the entire circumference of the rotor body 10 .

[0106] Thus, the repaired region A having the welded portion M formed therein can be processed with high precision over the entire circumference to conform to the original shape. Therefore, the rotor 1 having the same shape as that before the repair can be obtained more stably.

[0107] (4) A rotor repair method S1 according to a fourth aspect is the rotor repair method S1 according to any one of (1) to (3), wherein the welded portion M is formed by laser welding.

[0108] By adopting laser welding in this way, the amount of heat input during welding can be suppressed, and the influence of heat on the rotor body 10 can be suppressed. Thus, deformation of the rotor body 10 caused by welding can be suppressed.

[0109] (5) A rotor repair method S1 according to a fifth aspect is the rotor repair method S1 according to any one of (1) to (4), wherein the heat treatment is annealing.

[0110] This can remove residual stress or the like generated in the repair region A due to the formation of the weld portion M. As a result, the crystal structure of the repair region A where the weld portion M is formed can be made uniform and soft, thereby improving workability and toughness.

[0111] (6) The rotor repair method S1 of the sixth scheme is based on any rotor repair method S1 in (1) to (5), and also includes the following steps: cutting the damaged part D to form the repair area A into a recessed portion C recessed from the outer surface F, and performing the welding in a manner of filling the recessed portion C with the welding portion M.

[0112] Thus, no matter what shape the damaged portion D is formed in, the damaged portion D can be reliably removed and repaired. Moreover, by cutting from the outer surface F to form the recessed portion C, the welded portion M is more likely to be in close contact with the repaired area A than when the welded portion M is directly formed on the damaged portion D, and the welded portion M can be stably formed.

[0113] Industrial Applicability

[0114] According to the rotor repairing method of the present invention, the shape and performance of the repaired rotor can be stably maintained.

Claims

1. A method for repairing a rotor, the rotor comprising: a rotor body extending axially with an axis as the center; and a plurality of impellers arranged along the axial direction and fixed to the rotor body, wherein: The rotor repair method comprises the following steps: Welding the repaired area of ​​the rotor body to fill the damaged area formed in a recessed manner from the outer surface of the rotor body with the welded portion; After performing the welding, heat treating only the repaired area in the rotor; and After the heat treatment, a portion of the welded portion is cut to form a processed surface smoothly connected to the outer surface.

2. The rotor repair method according to claim 1, wherein: The repair region is formed in an axial end region of the rotor body including the axial end portion.

3. The rotor repair method according to claim 1 or 2, wherein: The processed surface is formed at a constant distance from the axis over the entire circumference of the rotor body.

4. The rotor repair method according to claim 1 or 2, wherein: The welded portion is formed by laser welding.

5. The rotor repair method according to claim 1 or 2, wherein: The heat treatment is annealing.

6. The rotor repair method according to claim 1 or 2, wherein: The rotor repair method further comprises the following steps: cutting the damaged portion to form the repair region into a recessed portion recessed from the outer surface, The welding is performed so that the recessed portion is filled with the welded portion.

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