Method of repairing seal fin of rotating body

Abstract

To provide a method of repairing a seal fin of a rotating body capable of shortening repairing time without applying heat treatment after build-up.SOLUTION: A method for repairing a seal fin of a rotating body according to an embodiment is a method for repairing a worn seal fin provided on a rotating body. In this repairing method, weld surfaces 41a and 51a are formed by machining tip portions of the worn seal fins 41 and 51, a build-up layer 156 is formed on the weld surface by build-up welding by TIG welding using a weld wire 155, and the build-up layer 156 formed on the weld surface is machined into an original seal fin shape.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for repairing a seal fin of a rotating body. [Background technology]

[0002] In order to improve the performance of a steam turbine, it is important to suppress steam leakage from the steam passage through which the steam that rotates the turbine flows. To suppress steam leakage, seal fins are provided at the tips of the turbine rotor and moving blades.

[0003] Seal fins installed on rotating bodies such as turbine rotors and blades prevent steam from leaking between the rotating body and the stationary body facing the rotating body. The seal fins wear out due to contact with the stationary body during operation of the steam turbine. Therefore, worn seal fins need to be repaired to restore their function as seal fins.

[0004] Conventionally, as a method for repairing a seal fin, a method of melting a powder welding material with a laser beam to perform build-up on the worn portion of the seal fin has been considered. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-29573 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional repair methods using laser beams and powder welding materials, the thickness of the bead layer (buildup layer) formed in one pass is thin. In other words, the thickness of each buildup layer is thin. Therefore, in order to restore the worn portion of the seal fin to its original state, many buildup layers must be layered. Here, one pass means one welding. A buildup layer formed in one pass means a buildup layer formed in one welding pass, without multiple welding operations such as going back and forth with the welding equipment.

[0007] As described above, conventional repair methods using laser beams and powder welding materials require the application of many build-up layers, which takes a long time to complete, and therefore increases the length of time that the steam turbine must be shut down for seal fin repairs.

[0008] Furthermore, in conventional repair methods, after building up multiple buildup layers, heat treatment is performed to remove residual stress. However, heat treatment of the blades and turbine rotors together with the built-up seal fins carries the risk of reducing the strength of the blades and turbine rotors and oxidizing their surfaces.

[0009] The problem to be solved by the present invention is to provide a method for repairing seal fins of a rotating body, which can shorten the repair time without requiring heat treatment after build-up welding. [Means for solving the problem]

[0010] In one embodiment, a method for repairing a worn seal fin on a rotating body includes machining a tip of the worn seal fin to form a welded surface, forming a buildup layer on the welded surface by TIG welding using a welding wire, and machining the buildup layer formed on the welded surface to return it to its original shape. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a meridian section of a steam turbine including a rotor having seal fins repaired by a repair method of an embodiment. [Figure 2] 1 is a front view showing a configuration of a repair device for carrying out a method for repairing a seal fin of a rotating body according to an embodiment of the present invention; [Figure 3] FIG. 3 is a cross-sectional view of FIG. 2 taken along line AA. [Figure 4] 2. FIG. 4 is a cross-sectional view corresponding to the cross-section AA in FIG. 2, showing another configuration of a repairing device for carrying out the method for repairing a seal fin of a rotating body according to the embodiment. [Figure 5] 1 is a cross-sectional view schematically showing an example of a build-up processing device used in a method for repairing a seal fin of a rotating body according to an embodiment. FIG. [Figure 6] 5A to 5C are diagrams for explaining steps of a method for repairing a seal fin of a rotating body according to an embodiment. [Figure 7] 1 is a cross-sectional view schematically showing a plurality of buildup layers formed by a method for repairing a seal fin of a rotating body according to an embodiment of the present invention; [Figure 8] 1 is a cross-sectional view schematically showing a seal fin on which a buildup portion has been processed by a method for repairing a seal fin of a rotating body according to an embodiment of the present invention; [Figure 9] 1 is a diagram showing a cross section of a buildup layer formed by a repair method according to an embodiment of the present invention; [Figure 10] FIG. 10 is a diagram showing a cross section of a buildup layer formed by a comparative repair method. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] The seal fins to be repaired by the repair method of the embodiment are provided to reduce the amount of leakage of working fluid between a rotating body and a stationary body. In this embodiment, a method for repairing seal fins provided on a rotating body will be described.

[0014] Examples of rotating bodies include turbine rotors and moving blades provided on turbine rotors in steam turbines and gas turbines. Seal fins are provided on the outer circumferential surface of the turbine rotor and the outer circumferential surface of the tip of the moving blade.

[0015] Fig. 1 is a diagram showing a meridian section of a steam turbine 1 including a rotor 2 having seal fins 41, 51 to be repaired by a repair method according to an embodiment. Fig. 1 shows an example of a meridian section of a steam turbine including a turbine rotor having blades as a rotor.

[0016] As shown in Fig. 1, the steam turbine 1 has a rotating body 2 including a cylindrical or columnar turbine rotor 10 and moving blades 20 implanted in a rotor disk 11 of the turbine rotor 10. The tips of the moving blades 20 are formed with shrouds 21. The steam turbine 1 also has a stationary body 3 including stator blades 30, a diaphragm outer ring 31 that supports the stator blades 30 from the outer diameter side, and a diaphragm inner ring 32 that supports the stator blades 30 from the inner diameter side.

[0017] A seal portion 40 is formed between the turbine rotor 10 and a diaphragm inner ring 32 disposed on the outer periphery of the turbine rotor 10 at a distance. In addition, a seal portion 50 is formed between the shroud 21 of the rotor blade 20 and a diaphragm outer ring 31 disposed on the outer periphery of the shroud 21 at a distance.

[0018] First, the configuration of the seal portion 40 will be described.

[0019] 1, seal fins 41 that protrude radially outward from the outer peripheral surface 10a are formed on the outer peripheral surface 10a of the turbine rotor 10. These seal fins 41 are formed continuously around the circumferential direction of the turbine rotor 10 and have an annular shape. The seal fins 41 may be configured integrally with the outer peripheral surface 10a of the turbine rotor 10, or may be formed by overlay welding using TIG welding, which is used in this embodiment.

[0020] The radial direction is a direction perpendicular to the central axis direction of the turbine rotor 10 (hereinafter referred to as the rotor axis direction). The radially outer side refers to the side in the radial direction that is farther away from the turbine rotor central axis O (hereinafter referred to as the rotor central axis O). The radially inner side refers to the side in the radial direction that is closer to the rotor central axis O.

[0021] Here, the seal portion 40 has a so-called high-low type structure in which adjacent seal fins 41 in the rotor axial direction have different radially outward protruding lengths, but the structure is not limited to this. For example, adjacent seal fins 41 may have the same radially outward protruding lengths.

[0022] There is a predetermined gap between the tip of the seal fin 41 and the inner peripheral surface 32a. Therefore, the inner peripheral surface 32a of the diaphragm inner ring 32 facing the seal fin 41 is formed with irregularities corresponding to the protruding length of the seal fin 41. Here, the protruding length is the radial height from the outer peripheral surface 10a of the turbine rotor 10 to the tip of the seal fin 41.

[0023] The seal fin 41 is made of a plate-like member having a width (thickness) T1 in the rotor axial direction of approximately 1 mm to 3.5 mm. As shown in Fig. 1, the seal fin 41 has a shape such that the thickness of the tip gradually decreases toward the tip. The seal fin 41 is made of, for example, the same material as the material that constitutes the turbine rotor 10. Specifically, the seal fin 41 is made of, for example, CrMo steel, CrMoV steel, 12Cr steel, or the like.

[0024] Next, the configuration of the seal portion 50 will be described.

[0025] As shown in Fig. 1, seal fins 51 are formed on the outer peripheral surface 21a of the shroud 21 of the rotor blade 20, protruding radially outward from the outer peripheral surface 21a. For example, multiple stages of seal fins 51 are provided in the rotor axial direction. The seal fins 51 are formed in the circumferential direction. The seal fins 51 may be integrally formed with the outer peripheral surface 21a of the shroud 21, or may be formed by overlay welding using TIG welding, which is used in this embodiment.

[0026] For example, each rotor blade 20 includes a shroud 21 with seal fins 51. By forming a rotor blade cascade by implanting a plurality of rotor blades 20 around the turbine rotor 10, the plurality of shrouds 21 come into contact with each other in the circumferential direction to form an annular shroud 21. Similarly, by forming a rotor blade cascade, the plurality of seal fins 51 come into contact with each other in the circumferential direction to form an annular seal fin 51.

[0027] Although an example has been shown in which the rotor blade cascade is configured by planting each separate rotor blade 20 in the circumferential direction, the configuration is not limited to this. The rotor blade cascade may be configured, for example, by planting a rotor blade group, in which a plurality of rotor blades 20 are integrally formed, in the circumferential direction. The shrouds 21 and seal fins 51 in one rotor blade group are integrally formed in the circumferential direction. The circumferential length of the shrouds 21 and seal fins 51 in one rotor blade group corresponds to the number of rotor blades 20.

[0028] Although the seal portion 50 has a high-low type structure similar to the seal portion 40, the structure is not limited to this. For example, the radially outward protruding lengths of the seal fins 51 adjacent to each other in the rotor axial direction may be the same.

[0029] There is a predetermined gap between the tip of the sealing fin 51 and the inner peripheral surface 31a. Therefore, the inner peripheral surface 31a of the diaphragm outer ring 31 facing the sealing fin 51 is formed with irregularities corresponding to the protruding length of the sealing fin 51. Here, the protruding length is the radial height from the outer peripheral surface 21a of the sealing fin 51 to the tip of the sealing fin 51.

[0030] The shape of the seal fin 51 is the same as that of the seal fin 41. The width (thickness) T2 of the seal fin 51 in the rotor axial direction is approximately 1 mm to 3.5 mm.

[0031] The seal fins 51 are made of the same material as the material that constitutes the rotor blades 20 and the shroud 21. That is, the seal fins 51 are made of the same material as the material that constitutes the seal fins 41, for example.

[0032] In the steam turbine 1 described above, the rotor 2 rotates due to the introduced steam. Note that the flow direction of the steam is indicated by an arrow in Fig. 1 . The rotation of the rotor 2 may cause the seal fins 41 to come into contact with the inner peripheral surface 32a of the diaphragm inner ring 32, or the seal fins 51 to come into contact with the inner peripheral surface 31a of the diaphragm outer ring 31. This causes wear at the tips of the seal fins 41, 51.

[0033] (Seal fin repair device) Fig. 2 is a front view showing the configuration of a repair device 60 for carrying out the method for repairing the seal fins 41, 51 of a rotating body according to the embodiment. Fig. 3 is a view showing a cross section taken along line AA in Fig. 2. Fig. 4 is a view showing another configuration of the repair device 60 for carrying out the method for repairing the seal fins 41, 51 of a rotating body according to the embodiment, in a cross section corresponding to the cross section taken along line AA in Fig. 2. Fig. 5 is a cross section showing a schematic example of an overlay processing device 150 used in the method for repairing the seal fins 41, 51 of a rotating body according to the embodiment.

[0034] 2 to 4 show a state in which a turbine rotor 10 equipped with the rotor blade 20 shown in FIG. 1 is supported by a repair device 60. FIGS. 2 and 3 show a case in which a build-up processing device 150 is provided as the repair processing device 90. FIG. 4 shows a case in which a weld surface processing device 140 or a shape processing device 160 is provided as the repair processing device 90. FIG. 5 is a diagram showing a cross section along the direction in which the build-up layer 156 is formed. In FIG. 5, a portion of the build-up processing device 150 is shown in cross section.

[0035] As shown in Figures 2 to 4, the repair device 60 includes a holding device 70 that rotatably holds the turbine rotor 10, support devices 80 and 85 that support the turbine rotor 10 from below, a repair processing device 90 that performs repair processing on the seal fins, and a position adjustment device 110 that adjusts the position of the repair processing device 90.

[0036] The holding device 70, the support devices 80 and 85, the repair treatment device 90, and the position adjustment device 110 are each configured to be portable, and therefore these devices are transported to the installation site of the turbine rotor 10 and installed in accordance with the turbine rotor 10.

[0037] The holding device 70 includes a chuck portion 71 that rotatably holds one end of the turbine rotor 10, a drive portion 72 that drives the chuck portion 71 to rotate, and a base portion 73. The chuck portion 71 is detachable from one end of the turbine rotor 10. The chuck portion 71 also holds the turbine rotor 10 rotatably around the rotor central axis O as the axis of rotation. The drive portion 72 includes a drive device such as a motor, and rotates the chuck portion 71 at a set speed. The drive portion 72 is fixed to the base portion 73. The base portion 73 supports the drive portion 72 from below.

[0038] The support devices 80, 85 include support portions 81, 86 that support the turbine rotor 10 from below, and base portions 82, 87 that support the support portions 81, 86 from below. The support portions 81, 86 are fixed to the base portions 82, 87. The support portion 81 supports one end of the turbine rotor 10, and the support portion 86 supports the other end of the turbine rotor 10. The support portions 81, 86 support the turbine rotor 10 rotatably.

[0039] The turbine rotor 10 is supported by the holding device 70 and the support devices 80, 85 so that the rotor central axis O is horizontal. As a result, the turbine rotor 10 is rotated by the drive unit 72 with the rotor central axis O as the rotation axis.

[0040] The repair processing device 90 includes a welding surface processing device 140, a build-up processing device 150, and a shape processing device 160. The position adjustment device 110 includes a height position adjustment device 120 and a horizontal position adjustment device .

[0041] First, the position adjustment device 110 will be described.

[0042] As shown in FIGS. 2 to 4, the height position adjustment device 120 adjusts the position of the repair processing device 90 in the height direction (vertical direction). The height position adjustment device 120 includes an arm portion 121, a pillar portion 122, and a base portion 123. The repair processing device 90 is fixed to one end of the arm portion 121. The other end of the arm portion 121 is supported horizontally by the pillar portion 122 so as to be movable in the height direction. The pillar portion 122 extends in the height direction (vertical direction), and its bottom is fixed to the base portion 123. The pillar portion 122 includes a moving device for moving the arm portion 121 in the height direction to position it at an arbitrary height. The moving device is configured, for example, by a motor drive or the like.

[0043] The horizontal position adjustment device 130 adjusts the horizontal position of the repair processing device 90. The horizontal position adjustment device 130 is disposed on the bottom surface of the base 123 and supports the base 123 from below. The horizontal position adjustment device 130 includes a moving device (not shown) such as a roller or a rail.

[0044] The height position of the repair processing device 90 is adjusted by displacing the height position of the arm part 121 relative to the base part 123. The horizontal position of the repair processing device 90 is adjusted by horizontally moving the base part 123 with the horizontal position adjustment device 130.

[0045] The configuration of the position adjustment device 110 is not limited to the above configuration, but may be any configuration that allows adjustment of the position of the repair processing device 90 in the vertical and horizontal directions.

[0046] Next, the repair treatment device 90 will be described.

[0047] The welding surface treatment device 140 machines the tip portions of the seal fins 41, 51 to be repaired to form a welding surface. The tip portions of the seal fins 41, 51 are cut by, for example, rotating the turbine rotor 10 with a cutting tool 141 such as a cutting tool. As shown in FIG. 4, the cutting tool 141 is fixed to, for example, one end of the arm portion 121. The welding surface treatment device 140 may be configured with a large lathe that allows the vertical and horizontal position of the cutting tool 141 to be adjusted.

[0048] During this cutting process, the tip of the seal fin 41, 51, which is configured in the circumferential direction, is cut to match the portion with the greatest amount of wear. The portion with the greatest amount of wear is the portion of the tip of the seal fin 41, 51 that is recessed most radially inward. This forms a welding surface made of a circumferential surface that is at the same radial distance (position) from the rotor central axis O. The welding surface is the surface on which the first stage of buildup welding is performed.

[0049] The build-up processing device 150 performs build-up welding by TIG welding using a welding wire 155 on the welding surfaces of the seal fins 41, 51 whose welding surfaces have been processed by the welding surface processing device 140. As shown in FIG. 5 , the build-up processing device 150 includes a tungsten electrode 151 and a guide 152. The tungsten electrode 151 is a rod-shaped electrode for generating an arc 153 between the tungsten electrode 151 and the welding surfaces 41 a, 51 a of the seal fins 41, 51, which are the base material. The guide 152 is a cylindrical body for guiding an inert gas 154, such as argon or helium, introduced around the tungsten electrode 151 so as to cover the outer periphery of the arc 153.

[0050] The welding wire 155 is a filler metal having a long, thin rod-like shape. A tip of the welding wire 155 is fed into the arc 153 generated between the tungsten electrode 151 and the welding surfaces 41 a, 51 a to perform build-up welding. The welding wire 155 may be fed, for example, by a wire feeder that feeds the tip of the welding wire 155 into the arc 153 at a predetermined feed rate.

[0051] Here, the welding wire 155 is made of a Ni-based alloy. Examples of the Ni-based alloy include a Ni-based alloy containing Ni as the main component and Cr, Mo, Nb, etc., and a Ni-based alloy containing Ni as the main component and Cr, Fe, etc. Specifically, examples of the Ni-based alloy that can be used include Alloy 625 and Alloy 600.

[0052] Here, if the welding wire 155 is made of the same material as the turbine rotor 10 or the rotor blade 20, the hardness of the weld metal portion will be too high, posing a risk of post-weld cracking, and therefore post-weld heat treatment will be necessary. On the other hand, if the welding wire 155 is made of a Ni-based alloy, the weld metal portion will not harden, and post-weld heat treatment will not be necessary.

[0053] When the welding wire 155 is cylindrical, it is preferable that the diameter of the welding wire 155 be 0.6 mm to 2.0 mm. If the diameter of the welding wire 155 is thinner than 0.6 mm, the bead will have an unstable, irregular shape. On the other hand, if the diameter of the welding wire 155 is thicker than 2.0 mm, the heat input will be insufficient within the range of the heat input of TIG welding described below. Furthermore, by setting the diameter of the welding wire 155 within the above range, it is possible to form the buildup layer 156 that covers the entire weld surfaces 41 a, 51 a in one pass. Furthermore, when the buildup layer 156 is formed, the welding wire 155 is effectively used for forming the buildup layer 156.

[0054] If the cross-sectional shape of welding wire 155 perpendicular to the length direction is not circular as described above, it is preferable that the diameter of a circle calculated from the cross-sectional area of ​​the cross-sectional shape falls within the above-mentioned range.

[0055] For TIG welding, it is preferable to use TIG pulse welding in order to reduce the average heat input. The pulse frequency in pulse current control is preferably 0.5 Hz to 15 Hz. By using TIG pulse welding, the heat-affected zone of the seal fins 41, 51 can be narrowed and the bead shape can be stabilized. The pulse frequency is set within this range in order to reduce the heat input to the base material. Furthermore, in order to form a stable bead shape, it is more preferable that the pulse frequency be 1 Hz to 5 Hz.

[0056] The heat input supplied to the welding wire 155 during TIG welding is preferably 1000 J / cm to 5000 J / cm. Here, if the heat input is less than 1000 J / cm, the base material at the welding wire 155 and the welding surfaces 41 a, 51 a will not melt sufficiently, resulting in an irregular bead with an unstable shape. On the other hand, if the heat input exceeds 5000 J / cm, although a good bead is formed, the base material will be diluted so much that the characteristics of low-heat-input TIG pulse welding cannot be fully utilized. Furthermore, if the heat input exceeds 5000 J / cm, weld cracks and the like are likely to occur. Furthermore, in particular, for the purpose of stabilizing the bead shape, it is more preferable to set the heat input to 1500 J / cm to 3000 J / cm.

[0057] Furthermore, by keeping the heat input within the above range, the heat-affected zone during TIG welding can be confined within the seal fins 41, 51. The heat-affected zone refers to a region of the base material where characteristics such as the microstructure and mechanical properties change due to heat from welding, buildup, etc. Therefore, the hardness of the heat-affected zone changes compared to the conventional base material, and there is a risk of a decrease in material strength. By confining this heat-affected zone within the seal fins 41, 51, the damage range of destruction can be confined within the seal fins 41, 51 even if an external force is applied. Furthermore, the thermal effects on the turbine rotor 10, shroud 21, and rotor blades 20 can be prevented.

[0058] When TIG welding is performed using welding wire 155 having the diameter within the above range and within the heat input range, the feed rate (feed amount) of welding wire 155 is preferably 1 g / min to 8 g / min. By setting the feed rate within this range, a stable bead shape can be achieved with an appropriate deposition amount. Furthermore, by setting the feed rate of welding wire 155 within the above range, it is possible to form buildup layer 156 having a predetermined thickness that covers the entire welding surfaces 41a, 51a in one pass. Furthermore, in order to form a stable bead shape, the feed rate of welding wire 155 is more preferably 1.5 g / min to 5 g / min.

[0059] The welding speed is preferably 50 mm / min to 250 mm / min. Here, the welding speed is the speed at which a bead is placed during TIG welding, and is expressed as the bead length per minute. For example, as shown in FIG. 2, when repairing while rotating the turbine rotor 10, the rotational speed of the turbine rotor 10 is set according to the welding speed. If the welding speed is slower than 50 mm / min, a convex bead will result. On the other hand, if the welding speed exceeds 250 mm / min, a humping bead will result. Furthermore, in order to form a bead shape suitable for multiple layers, the welding speed is more preferably 60 mm / min to 150 mm / min.

[0060] The shape processing device 160 machines the deposited portions of the seal fins 41, 51 to process them into the original shapes of the seal fins 41, 51. Here, the welding surface processing device 140 can be used as the shape processing device 160 (see FIG. 4). Therefore, redundant explanations will be omitted here.

[0061] The buildup portions of the seal fins 41, 51 are machined, for example, by rotating the turbine rotor 10 and using a cutting tool 141 such as a cutting tool. As a result, the buildup portions are machined into a shape in which the thickness gradually decreases toward the tip, like the seal fins 41, 51 shown in Fig. 1. The buildup portions are machined into this shape in the circumferential direction.

[0062] (How to repair seal fins) Next, a method for repairing the seal fin will be described.

[0063] 6 is a diagram illustrating the steps of the method for repairing a seal fin of a rotating body according to an embodiment. As shown in FIG. 6, the method for repairing a seal fin includes an installation step S10, a welding surface formation step S11, a build-up step S12, and a processing step S13. (Installation process S10) The turbine rotor with the seal fin to be repaired is rotatably supported in place by the holding device 70 and the support devices 80, 85.

[0064] In the installation step S10, one end of the turbine rotor 10 is held by the chuck portion 71. The turbine rotor 10 is also supported from below by the support devices 80 and 85. This allows the turbine rotor 10 to be held horizontally and rotatably.

[0065] (Welding surface formation process S11) Next, the welding surface treatment device 140 is placed in correspondence with the tip portions of the seal fins 41, 51 to be repaired (see FIG. 4). Specifically, the height position adjustment device 120 and the horizontal position adjustment device 130 are used to place the welding surface treatment device 140 in a predetermined position so that the cutting portion of the cutting tool 141 is positioned so that it can cut the tip portions of the seal fins 41, 51 to be repaired. As shown in FIG. 4, the cutting portion of the cutting tool 141 is placed at the same height as the rotor central axis O, that is, on the same horizontal plane as the rotor central axis O.

[0066] Then, the turbine rotor 10 is rotated, and the tip portions of the seal fins 41, 51 are cut by the cutting tool 141. This forms welding surfaces consisting of circumferential surfaces that are the same radial distance from the rotor central axis O. When repairing multiple seal fins 41, 51, the welding surfaces 41a, 51a are formed for each of the multiple seal fins 41, 51 to be repaired using the method described above.

[0067] After the welding surface forming step S11 is completed, the welding surface treatment device 140 is moved from its installed position.

[0068] (Overlay process S12) As described above, the rotor blade cascade is formed by implanting individually separated rotor blades 20 or rotor blade groups each formed by a plurality of rotor blades 20 in the circumferential direction. These rotor blades 20 and rotor blade groups each include a shroud 21 having seal fins 51. When the rotor blade cascade is formed, gaps are formed between circumferentially adjacent seal fins 51.

[0069] Therefore, to prevent the arc 153 from being interrupted between the seal fins 51 during TIG welding, bridge welding is performed before the build-up process to fill the gaps between adjacent seal fins 51 and integrate them. In this bridge welding, welding is performed to the extent that the gaps near the welding surfaces 41 a, 51 a are filled. In the bridge welding, TIG welding using a welding wire 155 is used.

[0070] The material of the welding wire 155 is more ductile than the material of the seal fin 51. Therefore, although a radial restraining force occurs in the seal fin 51 integrated by bridge welding, this force is relaxed in terms of stress.

[0071] After the bridge welding described above, the following processing is carried out.

[0072] The build-up processing device 150 is installed corresponding to the welding surfaces 41a, 51a of the seal fins 41, 51 (see FIGS. 2 and 3). Specifically, the build-up processing device 150 is installed at a predetermined position by the height position adjustment device 120 and the horizontal position adjustment device 130 so that the central axis of the tungsten electrode 151 is positioned at the center of the welding surfaces 41a, 51a in the rotor axial direction and vertically above the rotor central axis O. At this time, the tip of the tungsten electrode 151 is in a position on the welding surfaces 41a, 51a where welding is possible. The rotor axial center of the welding surfaces 41a, 51a is the center of the width of the welding surfaces 41a, 51a in the rotor axial direction.

[0073] In this way, the build-up processing device 150 is installed so as to perform build-up welding in a downward position from vertically above the rotor central axis O. By installing the build-up processing device 150 in such a stable position, a good bead can be formed.

[0074] Then, the turbine rotor 10 is rotated, and the buildup layer 156 is formed on the welding surfaces 41 a, 51 a by the buildup processing device 150 (see FIG. 5). In TIG welding using the buildup processing device 150, an arc 153 is generated between the tungsten electrode 151 and the welding surfaces 41 a, 51 a in an atmosphere of inert gas 154, and the welding wire 155 is melted using the arc heat. Then, the buildup layer 156 is formed on the welding surfaces 41 a, 51 a.

[0075] The ranges of conditions such as the amount of heat input, the feed rate of the welding wire 155, and the welding speed during the build-up process are as described above.

[0076] 7 is a cross-sectional view schematically showing a plurality of buildup layers 156 formed by the method for repairing a seal fin of a rotating body according to the embodiment. Note that FIG. 7 is a view showing a cross section perpendicular to the direction in which the buildup layers 156 are formed.

[0077] 7, one buildup layer 156 is formed by one bead. That is, one buildup layer 156 is formed by one welding, in other words, one pass. By forming one buildup layer 156 in one pass, incomplete fusion is prevented more effectively than when one buildup layer 156 is formed in multiple passes.

[0078] The width of one bead is set to be larger than the width W of the welding surfaces 41a, 51a in the rotor axial direction. That is, as shown in Fig. 7, the buildup layer 156 is formed so as to protrude from the welding surfaces 41a, 51a in the rotor axial direction.

[0079] Then, by rotating the turbine rotor 10, one continuous bead is formed in the circumferential direction, thereby forming one layer of buildup layer 156 that is continuous in the circumferential direction.

[0080] 7, when depositing the buildup layer 156 radially outward, first, a first buildup layer 156a that is continuous in the circumferential direction is formed on the welding surfaces 41a, 51a. Next, the buildup processing device 150 is moved radially outward by the height position adjustment device 120 in accordance with the thickness (radial height) of the formed first buildup layer 156a. In other words, the buildup processing device 150 is moved radially outward by the height position adjustment device 120 by the thickness of the formed first buildup layer 156a.

[0081] Next, a second buildup layer 156b is formed on the first buildup layer 156a, extending continuously in the circumferential direction. Using the same method as described above, a third buildup layer 156c is then formed on the second buildup layer 156b. This results in the buildup portion 157 consisting of three layers, as shown in FIG. 7.

[0082] Here, the thickness (radial height) of one buildup layer formed by the buildup processing device 150 is 0.5 mm or more. The thickness of one buildup layer is preferably 0.5 mm to 2.0 mm. Furthermore, the thickness of one buildup layer is more preferably 0.5 mm to 1.0 mm. If the thickness of one buildup layer is thicker than 2.0 mm, the bead shape will be too convex, making the shape of the next layer weld bead unstable. If the thickness of one buildup layer is less than 0.5 mm, it will be necessary to stack multiple buildup layers to obtain a buildup portion of the specified thickness, which is inefficient. The thickness of the buildup layer is measured using a laser sensor, dial gauge, etc.

[0083] After the build-up process, the build-up portion 157 is slowly cooled in the atmosphere. After the build-up process S12 is completed, the build-up processing device 150 is moved from its installation position.

[0084] (Processing process S13) Next, the shaping device 160 is installed corresponding to the buildup portions of the seal fins 41, 51 (see FIG. 4). Specifically, the shaping device 160 is installed at a predetermined position by the height position adjustment device 120 and the horizontal position adjustment device 130 so that the cutting portion of the cutting tool 141 is positioned so that it can cut the buildup portions of the seal fins 41, 51. As shown in FIG. 4, the cutting portion of the cutting tool 141 is installed at the same height as the rotor central axis O, that is, on the same horizontal plane as the rotor central axis O.

[0085] Then, the turbine rotor 10 is rotated, and the buildup portions of the seal fins 41, 51 are cut by the cutting tool 141. Fig. 8 is a cross-sectional view schematically showing the seal fins 41, 51 on which the buildup portion 157 has been machined by the method for repairing a seal fin of a rotor according to the embodiment. Fig. 8 shows the cross section after the buildup portion 157 shown in Fig. 7 has been machined. Fig. 8 shows a cross section perpendicular to the direction in which the buildup layer 156 is formed.

[0086] 8, the build-up portion 157 is processed into a shape in which the thickness gradually decreases toward the tip, thereby allowing the build-up-plated seal fins 41, 51 to obtain the original shape of the seal fins 41, 51.

[0087] After the seal fins 41 and 51 are processed into their original shapes, the welded portions formed by bridge welding before the overlay welding are cut off, thereby releasing the radial restraining force.

[0088] (Evaluation of the thickness of the build-up layer) Next, a comparison is made between the buildup layer formed by the repair method of this embodiment and the buildup layer formed by a conventional repair method using a laser beam and a powder welding material. Here, a comparison is made for a single buildup layer formed by each repair method. Note that hereinafter, the conventional repair method using a laser beam and a powder welding material will be referred to as the comparative repair method.

[0089] In the TIG welding of this embodiment, a welding wire 155 made of Alloy 600 and having a diameter of 1.2 mm was used. On the other hand, in the comparative repair method, a powder welding material made of Alloy 600 and having an average particle size of 30 μm was used.

[0090] The heat input supplied to the welding wire 155 and filler metal was 2000 J / cm, the supply rate (supply amount) of the welding wire 155 and filler metal was 2 g / min, and the welding speed was 80 mm / min.

[0091] CrMo steel was used as the base material 100 on which the buildup layer was formed. The welding surface 100a on which the buildup layer was formed was machined into a flat surface with a width of 2.5 mm and a length of 100 mm. The base material 100 was made of the same material as the seal fins 41 and 51. The width W1 of the base material 100 was approximately the same as the widths (thicknesses) T1 and T2 of the seal fins 41 and 51 in the rotor axial direction.

[0092] Under the above conditions, an overlay layer was formed to cover the entire welding surface 100a. The overlay method in this embodiment is as described in the overlay step S12. In the overlay method in the comparative repair method, a powder welding material was sprayed from the center of the nozzle along with gas toward the welding surface 100a, and laser beams were irradiated onto the welding surface 100a from two directions. The laser beams were irradiated so as to overlap on the welding surface 100a.

[0093] Fig. 9 is a diagram showing a cross section of a buildup layer 101 formed by the repair method of the embodiment. Fig. 10 is a diagram showing a cross section of a buildup layer 102 formed by a comparative repair method. Figs. 9 and 10 are diagrams showing cross sections perpendicular to the direction in which the buildup layers 101 and 102 are formed.

[0094] As shown in Figure 9, in the repair method of this embodiment, the entire weld surface 100a is covered with one bead. In the comparative repair method, the entire weld surface 100a is covered with two beads. In addition, the thickness (height) H1 of the buildup layer 101 in the repair method of this embodiment was 1.0 mm. In the comparative repair method, the thickness (height) H2 of the buildup layer 102 was 0.2 mm. The thickness of the buildup layer was measured using a laser sensor.

[0095] In this way, the repair method of this embodiment can cover the entire weld surface 100a with a single bead. Furthermore, the thickness H1 of the buildup layer 101 in the repair method of this embodiment is about five times thicker than the thickness H2 of the buildup layer 102 in the comparative repair method.

[0096] Although the heat input, supply rate, and welding speed are the same, the range of heat input energy supplied onto the welding surface 100a in the comparative repair method is narrower than the range of heat input energy supplied onto the welding surface 100a in the repair method of this embodiment. In other words, the range in which the filler material can be melted in the comparative repair method is narrower than the range in which the welding wire 155 can be melted in the repair method of this embodiment. Therefore, the bead width that constitutes the weld overlay 102 is narrower than the bead width that constitutes the weld overlay 101.

[0097] As a result, with the comparative repair method, two buildup layers 102, i.e., two beads, are required to cover the entire weld surface 100a. Furthermore, with the comparative repair method, the energy supply range is narrow, so some filler metal is scattered outside without being used to form the buildup layer 102. In other words, with the comparative repair method, it is difficult to effectively supply filler metal to the heat input energy supply range to form the buildup layer 102.

[0098] In contrast, the energy supply range in the repair method of this embodiment is wider than the energy supply range in the comparative repair method, and the supplied welding wire 155 is effectively used to form the buildup layer 102. Therefore, the repair method of this embodiment produces a wide and thick bead. As a result, the repair method of this embodiment can cover the entire welding surface 100a with a single buildup layer 101, and produce a thick buildup layer 101. In other words, the repair method of this embodiment can form the buildup layer 101 by effectively supplying the welding wire 155 to the heat input energy supply range.

[0099] (Evaluation of TIG welding conditions) Here, it will be explained that the conditions for TIG welding in this embodiment, that is, the amount of heat input supplied to welding wire 155 and the feed speed of welding wire 155, are suitable.

[0100] The specifications of the welding wire 155 used here and the base metal on which the buildup layer was formed were the same as those used in the evaluation of the buildup layer thickness. Here, a buildup layer consisting of a single bead was formed on the weld surface of the base metal under several conditions with different heat input and supply speeds. The welding speed was set to 80 mm / min to reduce heat input and optimize the bead shape. In addition, the buildup layer (bead) was formed by TIG pulse welding. The pulse frequency in TIG pulse welding was set to 2 Hz.

[0101] Then, the build-up layer (bead) formed under each condition was evaluated for thickness, width, and condition of the build-up layer.

[0102] The thickness and width of the build-up layer were measured using a laser sensor, and the condition of the build-up layer was evaluated visually.

[0103] Table 1 shows the measurement results of the thickness and width of the buildup layer formed under each condition and the results of the quality assessment of the buildup layer. In Table 1, ○ indicates a good buildup layer (bead), and × indicates an irregular buildup layer (irregular bead). Note that a good buildup layer means a buildup layer with a smooth bead surface, and an irregular buildup layer means a buildup layer with an uneven and discontinuous bead surface.

[0104] [Table 1]

[0105] As shown in Table 1, in Examples 1 to 6, where the heat input and supply rate were within the ranges of the present embodiment, good buildup layers were obtained. In Examples 1 to 6, the buildup layer thickness was 0.5 mm or more. In addition, in Examples 1 to 6, the width of one bead, i.e., the width of one buildup layer, was greater than the width of the base material (2.5 mm). Therefore, the buildup layers in Examples 1 to 6 have a cutting allowance that can be used to machine the buildup into the original seal fin shape, for example.

[0106] On the other hand, in Comparative Examples 1 to 4, where at least one of the heat input and the supply rate was outside the range of this embodiment, a good buildup was not obtained, and an irregular buildup was obtained. In Comparative Examples 1 and 4, where the supply rate was slower than the lower limit of the range of this embodiment, the buildup was 0.2 mm or less in thickness. In Comparative Examples 2 and 3, where the supply rate was faster than the upper limit of the range of this embodiment, the buildup was thick, but the buildup was irregular.

[0107] The results in Table 1 show that in Examples 1 to 6, where the TIG welding conditions such as heat input and supply rate are within the range of the present embodiment described above, a good buildup layer is obtained, and a buildup layer having a thickness of 0.5 mm or more and a width greater than the width of the base material (2.5 mm) is obtained.

[0108] As described above, according to the repair method of this embodiment, the seal fins 41 and 51 can be repaired without thermally affecting the turbine rotor 10 provided with the seal fins 41 or the shroud 21 and rotor blades 20 provided with the seal fins 51.

[0109] Furthermore, in the repair method of this embodiment, by setting the overlay welding conditions such as the welding method (TIG welding), heat input, supply speed, welding speed, and material of the welding wire 155, it is possible to form an overlay layer with a wider overlay width and a thicker overlay thickness (height) than in conventional repair methods using a laser beam and powder welding material, even on the welding surfaces of thin parts such as seal fins 41 and 51.

[0110] As described above, the repair method of this embodiment can form a wide and thick buildup layer, so that the entire welding surface 41a, 51a of the seal fins 41, 51 can be covered with a single buildup layer, and a thick buildup layer can be formed. Even when building up buildup layers to obtain a buildup portion of a predetermined thickness, this can be achieved with fewer passes. This shortens the repair period.

[0111] Furthermore, by using TIG welding for the overlay welding and using the welding wire 155 made of a Ni-based alloy, heat treatment after overlaying is not required. As a result, even when repairing while rotating the turbine rotor 10, heat treatment after overlaying is not required, and there is no risk of a decrease in strength of the turbine rotor 10, the rotor blades 20, etc., or oxidation of the surface.

[0112] The overlay welding of this embodiment can also be used, for example, when forming a new seal fin. In this case, the method of forming a new seal fin by overlay welding of this embodiment can reduce manufacturing costs compared to a conventional method of forming a seal fin by cutting it out of material.

[0113] According to the embodiment described above, it is possible to shorten the repair time without performing heat treatment after build-up welding.

[0114] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0115] 1... steam turbine, 2... rotating body, 3... stationary body, 10... turbine rotor, 10a, 21a... outer peripheral surface, 11... rotor disk, 20... moving blade, 21... shroud, 30... stationary blade, 31... diaphragm outer ring, 31a, 32a... inner peripheral surface, 32... diaphragm inner ring, 40, 50... seal portion, 41, 51... seal fin, 41a, 51a, 100a... welding surface, 60... repair device, 70... holding device, 71... chuck portion, 72... drive portion, 73, 82, 87, 123... base portion, 80, 85... support device, 81, 86... support portion , 90...repair processing device, 100...base material, 101, 102, 156...overlay layer, 110...position adjustment device, 120...height position adjustment device, 121...arm portion, 122...column portion, 130...horizontal position adjustment device, 140...welding surface processing device, 141...cutting tool, 150...overlay processing device, 151...tungsten electrode, 152...guide, 153...arc, 154...inert gas, 155...welding wire, 156a...first overlay layer, 156b...second overlay layer, 156c...third overlay layer, 157...overlay portion, 160...shape processing device.

Claims

1. A method for repairing worn seal fins provided on a rotating body, comprising: machining the worn tip of the seal fin to form a welding surface; forming a buildup layer on the weld surface by TIG welding using a welding wire; A method for repairing a seal fin of a rotating body, comprising machining the buildup layer formed on the welded surface to return it to its original shape.

2. In the seal fin repair method, the seal fins are installed on the rotating body in a circumferential direction of the rotating body, the rotating body is supported rotatably around a rotation center axis of the rotating body, 2. The method for repairing a seal fin of a rotating body according to claim 1, wherein the seal fin is repaired while the rotating body is being rotated.

3. the welding surface is formed to be a surface parallel to the rotation central axis, 3. The method for repairing a seal fin of a rotating body according to claim 2, wherein the TIG welding is performed in a vertically downward position.

4. 2. The method for repairing a seal fin of a rotating body according to claim 1, wherein the overlay layer covering the entire surface of the welded surface is formed in one pass.

5. 2. The method for repairing a seal fin of a rotating body according to claim 1, wherein when forming a plurality of layers of said buildup layers, each layer of said buildup layer is formed in one pass.

6. 2. The method for repairing a seal fin of a rotating body according to claim 1, wherein the welding wire is made of a Ni-based alloy.

7. 2. The method for repairing a seal fin of a rotating body according to claim 1, wherein the TIG welding is TIG pulse welding.

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