Micromixer tube repair EDM electrode, system and method

Abstract

To provide a micromixer tube repair EDM electrode, system and method.SOLUTION: The present invention provides a tool electrode for an EDM system for repairing a micromixer tube of a combustor, the EDM system, and a related method. The tool electrode includes: an elongated member; and a disk having a first side, a second side, an opening in a center of the disk, and a slot extending from the first side to the second side and from the opening to an outer periphery of the disk. The elongated member is coupled to the disk, and extends through the opening from the first side of the disk and beyond the second side of the disk. The disk is used to remove a damaged end portion of a micromixer tube from within the tube, and without debris damaging the tube or without a cutting tool damaging other tubes in a set of micromixer tubes.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present disclosure relates generally to the repair of combustors, and more particularly to electrical discharge machining (EDM) tool electrodes, systems, and methods for repairing micro-mixer tubes within a set of micro-mixer tubes of a combustor. [Background technology]

[0002] Gas turbine (GT) systems combust fuel to form a combustion gas stream that is converted to kinetic energy. The combustor in certain GT systems uses a micromixer, which includes multiple micromixer tubes, to mix fuel and air. The micromixer tubes are arranged in segments within the combustor's circular head-end assembly. Each segment contains multiple closely spaced micromixer tubes, many of which are positioned inside other micromixer tubes. During use, the tips of certain micromixer tubes can suffer damage, such as excessive burning or oxidation. Repair of these damaged micromixer tubes involves removing and replacing the end portion or tip of the micromixer tube. If the damaged micromixer tube is along the periphery of the segment, the removal and replacement process is relatively simple and can be performed using conventional machining techniques, such as cutting tools and welding systems. However, in some cases, when damaged micro-mixer tube(s) are inside other, possibly undamaged, outer micro-mixer tubes, they cannot be easily repaired without removing or damaging the end portions of the other, possibly undamaged, outer micro-mixer tubes. Vibrations from the repair tool can damage brazed joints on other parts of the micro-mixer. Additionally, physically cutting off the end portions can generate debris, such as chips or shavings, that can clog or obstruct various flow paths within the micro-mixer tubes or otherwise damage the micro-mixer tubes. Current approaches require the removal and replacement of all of the other micro-mixer tubes, regardless of damage to the other micro-mixer tubes, making repairs time-consuming and expensive. Summary of the Invention

[0003] All aspects, examples, and features described below can be combined in any technically possible manner.

[0004] One aspect of the present disclosure provides a tool electrode for an electrical discharge mechanical (EDM) system for repairing a micro-mixer tube of a combustor, the tool electrode comprising an elongated member and a disk having a first side, a second side, an opening in a center of the disk, and a slot extending from the first side to the second side and from the opening to an outer periphery of the disk, the elongated member being coupled to the disk and extending from the first side of the disk, past the second side of the disk, and through the opening.

[0005] Another aspect of the present disclosure includes any of the above aspects, wherein the outer periphery of the disc is serrated.

[0006] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the outer periphery of the disk includes a concave surface extending radially inward.

[0007] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein at least one of the first side and the second side of the disk is thicker at a radially outer portion thereof adjacent the concave surface than at a radially inner portion thereof.

[0008] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein at least one of the first side and the second side of the disk is thicker at its radially outer portion than at its radially inner portion.

[0009] Another aspect of the present disclosure includes any of the preceding aspects, wherein the disk includes a dielectric liquid flow path defined therein.

[0010] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the disk has an outer diameter within a range of 90% to 95% of the inner diameter of the micromixer tube.

[0011] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the elongated member is configured to couple to a power source of an EDM system.

[0012] Another aspect of the present disclosure includes an electrical discharge mechanical (EDM) system for removing an end portion of a micro-mixer tube of a combustor, the EDM system comprising: a tool electrode including an elongated member and a disk having a first side, a second side, an opening in a center of the disk, and a slot extending from the first side to the second side and from the opening to an outer periphery of the disk, the elongated member coupled to the disk and extending from the first side of the disk over the second side of the disk and through the opening; a power source operably coupled to deliver a repetitive voltage to the elongated member of the tool electrode and to the micro-mixer tube; a dielectric liquid delivery system configured to deliver a dielectric liquid between the tool electrode and an inner surface of the micro-mixer tube; and an actuator configured to rotate the tool electrode and move the disk in a trepanning path while maintaining an operating distance of the disk from the inner surface of the micro-mixer tube to gradually remove the end portion of the micro-mixer tube.

[0013] Another aspect of the present disclosure includes any of the above aspects, wherein the outer periphery of the disc is serrated.

[0014] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the outer periphery of the disk includes a concave surface extending radially inward.

[0015] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein at least one of the first side and the second side of the disk is thicker at a radially outer portion thereof adjacent the concave surface than at a radially inner portion thereof.

[0016] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein at least one of the first side and the second side of the disk is thicker at its radially outer portion than at its radially inner portion.

[0017] Another aspect of the present disclosure includes any of the preceding aspects, wherein the disk includes a dielectric liquid flow path defined therein.

[0018] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the disk has an outer diameter within a range of 90% to 95% of the inner diameter of the micromixer tube.

[0019] Another aspect of the present disclosure includes a method for removing an end portion of a combustor micro-mixer tube, the method including: positioning a tool electrode within the end portion of the micro-mixer tube, the tool electrode including an elongated member and a disk having a first side, a second side, an opening in a center of the disk, and a slot extending from the first side to the second side and from the opening to an outer periphery of the disk, the elongated member being coupled to the disk and extending from the first side of the disk, past the second side of the disk, and through the opening; rotating the tool electrode while moving the disk in a trepanning path while maintaining an operating distance of the disk from an inner surface of the micro-mixer tube; applying a dielectric liquid between the tool electrode and the inner surface of the micro-mixer tube; and repeatedly applying a voltage to the tool electrode and the micro-mixer tube to gradually remove the end portion of the micro-mixer tube.

[0020] Another aspect of the present disclosure includes any of the above aspects, and further includes, prior to the rotating while moving, adding the dielectric liquid, and repeatedly applying the voltage, moving an end portion of an elongated member extending beyond the second side of the disk within the end portion of the micro-mixer tube to identify a center of the micro-mixer tube.

[0021] Another aspect of the present disclosure includes any of the above aspects, wherein the rotating while moving is controlled by a computer numerically controlled (CNC) system.

[0022] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein applying the dielectric liquid includes passing the dielectric liquid through a dielectric liquid flow path defined in the disk.

[0023] Another aspect of the present disclosure includes any of the aspects described above, further including flattening an end face of the micro-mixer tube from which the end portion was removed, and bonding a new end portion onto the end face of the micro-mixer tube from which the end portion was removed.

[0024] Two or more aspects described in this disclosure, including those described in this Summary section, may be combined to form an embodiment not specifically described herein, i.e., all embodiments described herein can be combined with each other.

[0025] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description and drawings, and from the claims.

[0026] These and other features of the present disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure, taken in conjunction with the accompanying drawings which illustrate various embodiments of the present disclosure. [Brief explanation of the drawings]

[0027] [Figure 1] 1 shows a schematic diagram of a gas turbine system having a compressor, a combustor, and a turbine. [Figure 2] 1 shows a perspective view of a prior art micromixer for a combustor that can be repaired using the teachings of the present disclosure. [Figure 3] 1 shows a perspective view of a segment of a prior art micromixer of a combustor that can be repaired using the teachings of the present disclosure. [Figure 4] 1 illustrates a simplified top view of multiple micro-mixer tubes in a segment of a micro-mixer of a combustor that can be repaired according to an embodiment of the present disclosure. [Figure 5]FIG. 1 illustrates a simplified perspective view of multiple micro-mixer tubes in a segment of a micro-mixer of a combustor that can be repaired, according to an embodiment of the present disclosure. [Figure 6] 1 illustrates a side perspective view of a tool electrode for an electrical discharge mechanical (EDM) system for repairing micro-mixer tubes of a combustor, according to an embodiment of the present disclosure. [Figure 7] 1 illustrates a side perspective view of a disk of a tool electrode for an EDM system for repairing a micro-mixer tube of a combustor, according to an embodiment of the present disclosure. [Figure 8] 1 illustrates a top view of a disk of a tool electrode for an EDM system for repairing a micro-mixer tube of a combustor according to an embodiment of the present disclosure. [Figure 9] 1 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing a micro-mixer tube of a combustor according to an embodiment of the present disclosure. [Figure 10] 10 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing micro-mixer tubes of a combustor according to another embodiment of the present disclosure. [Figure 11] 10 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing micro-mixer tubes of a combustor according to an additional embodiment of the present disclosure. [Figure 12] 1 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing a micro-mixer tube of a combustor according to an embodiment of the present disclosure. [Figure 13] 10 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing micro-mixer tubes of a combustor according to another embodiment of the present disclosure. [Figure 14] 10 illustrates a cross-sectional view of a disk of a tool electrode for an EDM system for repairing micro-mixer tubes of a combustor according to an additional embodiment of the present disclosure. [Figure 15] FIG. 10 illustrates a top view of a disk of a tool electrode for an EDM system for repairing micro-mixer tubes of a combustor according to another embodiment of the present disclosure. [Figure 16]FIG. 1 illustrates a schematic side view of an EDM system including a tool electrode cutting an end portion from a micro-mixer tube of a combustor, according to an embodiment of the present disclosure. [Figure 17] FIG. 1 illustrates a top view of an EDM system including a tool electrode cutting an end portion from a micro-mixer tube of a combustor according to an embodiment of the present disclosure. [Figure 18] 10 illustrates a schematic side view of a tool electrode of an EDM system during an optional centering step of a micro-mixer tube of a combustor, according to an embodiment of the present disclosure. [Figure 19] 1 shows a side view of a micro-mixer tube with a damaged end region removed, according to an embodiment of the present disclosure. [Figure 20] 1 illustrates a side view of a repaired micro-mixer tube of a combustor according to an embodiment of the present disclosure.

[0028] It should be noted that the drawings of the present disclosure are not necessarily to scale. The drawings are intended to illustrate only typical aspects of the present disclosure and therefore should not be considered limiting of the scope of the present disclosure. In the drawings, like reference numerals represent like elements between the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0029] As an initial matter, a clear explanation of the subject matter of the present technology requires the selection of certain terminology when referring to and describing relevant mechanical components in an exemplary application of a gas turbine system, particularly its combustor. In doing so, common industry terminology will be used and adopted, whenever possible, in a manner consistent with its accepted meaning. Unless otherwise noted, such terminology should be given a broad interpretation consistent with the context of this application and the scope of the appended claims. Those skilled in the art will understand that in many cases, a particular component may be referred to using several different or overlapping terms. What may be described herein as a single component may include and be referred to in other contexts as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single component.

[0030] Additionally, several descriptive terms may be used conventionally herein, and it will prove useful to define these terms at the beginning of this section. These terms and their definitions are as follows, unless otherwise stated: As used herein, "downstream" and "upstream" are terms that indicate a direction relative to the flow of a fluid, such as a working fluid through a turbomachine, or the flow of a dielectric liquid, for example, through a micromixer tube. The term "downstream" corresponds to the direction of fluid flow, and the term "upstream" refers to the opposite direction to the flow.

[0031] It is often necessary to describe components at different radial positions relative to a central axis. The term "axial" refers to movement or position parallel to an axis, such as the axis of an elongated member of a tool electrode. The term "radial" refers to movement or position perpendicular to an axis, such as the axis of a disk of an electrical discharge machining tool electrode. In such cases, if a first component is closer to the axis than a second component, the first component will be described herein as being "radially inward" or "inside" the second component. Conversely, if a first component is farther from the axis than the second component, the first component may be described herein as being "radially outward" or "outside" the second component. Finally, the term "circumferential" refers to movement or position about an axis. As noted above, it will be understood that such terms may be applied with respect to the axis of the tool electrode.

[0032] Additionally, as described below, certain descriptive terms may be used conventionally herein: the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another, and are not intended to denote the location or importance of the individual components.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It will be further understood that the terms "comprise" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. "Optional" or "optionally" means that the subsequently-described event may or may not occur, or the subsequently-described feature may or may not be present, and that this statement includes instances in which the event occurs or the feature is present as well as instances in which the event does not occur or the feature is absent.

[0034] When an element or layer is referred to as "on," "engaged," "connected," or "coupled" to another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. Conversely, when an element is referred to as "directly on," "directly engaged," "directly connected," or "directly coupled" to another element or layer, there are no intervening elements or layers. Other terms used to describe relationships between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent to" versus "directly adjacent to," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The verb forms of "couple" and "mount" may be used interchangeably herein.

[0035] Embodiments of the present disclosure include a tool electrode for an electrical discharge machining (EDM) system for repairing combustor micro-mixer tubes, an EDM system, and an associated method. The tool electrode includes an elongated member and a disk coupled to the elongated member. The disk has a first side, a second side, an opening in the center of the disk, and a slot extending from the first side to the second side and from the opening to the outer periphery of the disk. The elongated member is coupled to the disk and extends from the first side of the disk, past the second side of the disk, and through the opening. The tool electrode is used to cut damaged end regions from individual micro-mixer tubes from the inside of the tubes using EDM. The system described herein significantly reduces the physical forces and vibrations applied to various micro-mixer tubes from conventional machining systems, reducing or eliminating damage to the micro-mixers or brazed joints within the tubes. The system also reduces or eliminates machining debris, such as chips or shavings, that can damage the micro-mixer tubes by, for example, clogging or otherwise obstructing various flow paths within the micro-mixer tubes. The system also allows for individual repair of micro-mixer tubes, thereby minimizing repair time and costs. The tool electrode disk is easily interchangeable, allowing for easy variability in geometry and size for any variety of micro-mixer tubes, enhancing speed and debris cleaning capabilities.

[0036] FIG. 1 shows a schematic diagram of a gas turbine (GT) system 10 that may use a combustor that occasionally requires micro-mixer tube repair. The GT system 10 may include a compressor 15 that compresses an incoming airflow 20. The compressor 15 delivers the compressed airflow 20 to a combustor 25, which mixes the compressed airflow 20 with a pressurized fuel flow 30 and ignites the mixture to generate a combustion gas flow 35. While only a single combustor 25 is shown, the GT system 10 may include any number of combustors 25. The combustion gas flow 35 is then delivered to a turbine 40. The combustion gas flow 35 drives the turbine 40 to produce mechanical work. The mechanical work produced by the turbine 40 drives the compressor 15 via a shaft 45 and an external load 50, such as a generator. The GT system 10 may use natural gas, various types of syngas, and / or other types of fuel. The GT system 10 may be any one of several different GT systems offered by GE Vernova of Cambridge, Massachusetts, USA, including, but not limited to, a 7 or 9 Series heavy-duty GT system. The GT system 10 may have different configurations and may use other types of components. Other types of GT systems may also use micromixers in their combustor(s).

[0037] 2 and 3 illustrate a micromixer 100, or a portion thereof, for use in the combustor 25 (FIG. 1). The micromixer 100 may include a base nozzle structure 102 in communication with a fuel plenum 104, an air inlet 106, and multiple micromixer tubes 108 forming one or more segmented micromixer tube sets or bundles. The base nozzle structure 102 supplies fuel to the fuel plenum 104, where the fuel exits the micromixer tubes 108. Air is directed through the air inlet 106 into the micromixer tubes 108 and mixes with the fuel to create an air / fuel mixture that exits the micromixer tubes 108 and enters the downstream combustion chamber. The micromixer tubes 108 are sometimes referred to as mixing tubes because they function to mix fuel and air.

[0038] 2 and 3 , the micromixer 100 may be segmented, meaning that the micromixer 100 may include several base nozzle structures 102. In a segmented micromixer 100, each base nozzle structure 102 is associated with a set or bundle of micromixer tubes 108 that are at least partially supported by the base nozzle structure 102. The base nozzle structures 102 may be attached to a combustor end plate 109. During operation of the GT system 10 ( FIG. 1 ), and more specifically, the combustor 25 ( FIG. 1 ), the micromixer tubes 108 may be subject to damage such as, but not limited to, overheating and / or oxidation.

[0039] FIG. 4 shows a top view, and FIG. 5 shows a perspective view of a simplified segment of a micro-mixer tube 108. (Note that the number of micro-mixer tubes 108 is not the same in FIGS. 4 and 5.) FIGS. 4 and 5 show damaged micro-mixer tube(s) 108X inside other outer micro-mixer tubes 108. The damaged micro-mixer tube(s) 108X cannot be easily repaired without removing or damaging the end portions of the other outer micro-mixer tubes 108. The micro-mixer tubes 108 are tubular members having diameters of 12.5 to 25.5 millimeters (mm), in non-limiting examples, and may have wall thicknesses in the range of approximately 2.5 mm, in non-limiting examples. The micro-mixer tubes 108 are relatively closely spaced. In non-limiting examples, the spacing between the micro-mixer tubes 108 may be in the range of 5 to 7.5 mm apart. In either case, it is not possible to position a cutting tool, such as a cutting saw or torch, to remove the end region of the micro-mixer tube 108X without damaging the nearby micro-mixer tubes 108.

[0040] FIG. 6 illustrates a perspective view of a tool electrode 200 for an electrical discharge machining (EDM) system 300 ( FIG. 16 ) for repairing micro-mixer tubes 108X ( FIGS. 4-5 ) of a combustor 25 ( FIG. 1 ) according to an embodiment of the present disclosure. Electrical discharge machining (EDM) is a metalworking technique that uses electrical discharges, i.e., sparks, to create a desired shape. EDM may also be recognized as spark erosion or spark machining. In EDM, metal is removed from a workpiece by a series of rapidly recurring electrical discharges between the tool electrode and the workpiece (second electrode), separated by a dielectric liquid. The tool electrode and the workpiece do not contact each other. As described below, the tool electrode 200 is used to cut end regions 302 ( FIG. 16 ) from individual damaged micro-mixer tubes 108X within the tube without damaging the remainder of the tube 108X or nearby tubes 108.

[0041] As shown in FIG. 6 , the tool electrode 200 has an elongated member 210 and a disk 220. FIG. 7 illustrates a perspective view of the disk 220 with the elongated member 210 removed, and FIG. 8 illustrates a top view of the disk 220 with the elongated member 210 removed, according to an embodiment of the present disclosure. Referring briefly to FIG. 16 , as further described herein, the tool electrode 200 is used in an EDM process to remove an end portion or tip 302 of a micro-mixer tube 108X from its inner surface 312. More specifically, the tool electrode 200 is placed within the micro-mixer tube 108X and used to remove the end portion 302 using EDM. In this manner, individual micro-mixer tubes 108 can be repaired without damaging other micro-mixer tubes.

[0042] 6-8 , the elongated member 210 of the tool electrode 200 may comprise any now known or later developed EDM rod or stick electrode and is configured to couple to a power supply 310 ( FIG. 16 ) of the EDM system 300 ( FIG. 16 ) in a known manner, for example, with a wire connection to the end 212 of the elongated member 210. The elongated member 210 is made of a conductive metal or metal alloy, such as, but not limited to, copper, brass, or carbide. The elongated member 210 may optionally include a channel 214 therein to allow a dielectric liquid 216 for EDM to pass therethrough in a known manner. The dielectric liquid 216 may include any now known or later developed EDM dielectric fluid, such as, but not limited to, a hydrocarbon oil, such as transformer oil, paraffin oil, or kerosene, a lubricating oil, or deionized water or other aqueous solution.

[0043] 6-8 , the disk 220 is part of the tool electrode 200 that provides EDM cutting of the end region 302 ( FIG. 16 ) of the micro-mixer tube 108X. As described below, the disk 220 is easily replaceable, allowing for easy adaptability of geometry and size to any variety of micro-mixer tubes to enhance speed and debris cleaning capabilities. The disk 220 has a first side 222 and a second side 224. The disk 220 also includes a periphery 230 connecting the sides 222, 224. Each side 222, 224 may have a generally circular cross-section. The disk 220 also includes an opening 226 in its center. As further described, the opening 226 is shaped and / or sized to connect the disk 220 to the elongated member 210 such that the disk 220 extends perpendicularly therefrom. The disk 220 also includes a slot 228 that extends from the first side 222 to the second side 224 and from the opening 226 to the outer periphery 230 of the disk 220. The slot 228 may extend substantially radially from the opening 226, but in some cases may be non-radial and / or curved. The disk 220 is made of a conductive metal or metal alloy, such as, but not limited to, brass, copper, or carbide.

[0044] Slot 228 may be used to allow disk 220 to slide onto torsion elongate member 210 and then release so that opening 226 grips or couples disk 220 to elongate member 210, thereby securing disk 220 to elongate member 210. Slot 228 also allows disk 220 to be easily replaced. Opening 226 may have any cross-sectional shape and / or size to accommodate this type of coupling with elongate member 210. In either case, elongate member 210 may be coupled to disk 220.

[0045] As shown, in certain embodiments, the elongated member 210 may extend from the first side 222 of the disk 220, past the second side 224 of the disk 220, through the opening 226. That is, at least an (end) portion 232 of the elongated member 210 extends past the second side 224 of the disk 220. In this case, the elongated member 210 and the disk 220 have an overall inverted T-shape in a side view or cross-section (see, for example, FIG. 16 ). In other embodiments not shown, the portion 232 may be flush with the second side 224 of the disk 220. As shown in FIG. 7 , the thickness T of the disk 220 is defined, at least in part, by the outer periphery 230, which may be configured to create a cut of a desired thickness in the inner surface 312 ( FIG. 16 ) of the micromixer tube 108X ( FIG. 16 ). In certain embodiments, disc 220 has a thickness T (FIG. 7) in the range of 0.8 to 1.2 mm, and in other embodiments, disc 220 has a thickness T of about 1.0 mm.

[0046] The disk 220 can take on a variety of geometric shapes and sizes to produce the desired EDM cut on the inner surface 312 (FIG. 16) of the micro-mixer tube 108X (FIGS. 4-5, 16) at the desired rate or speed. In FIGS. 6-7, the disk 220 has a rectangular cross-section in which the outer periphery 230 is perpendicular to the sides 222, 224 of the disk 220. FIGS. 9-15 show cross-sectional or top views of alternative embodiments of the disk 220 (with the elongated member 210 removed). The disk 220 can also have various configurations to enhance debris cleaning by the dielectric liquid 216. In FIGS. 9 and 10, the disk 220 includes one or more dielectric liquid channels 240 defined therein. The dielectric liquid flow channels 240(s) (hereinafter "flow channels 240(s)") may take any path through the disk 220 to deliver the dielectric liquid 216 to a desired location, typically the space between the outer periphery 230 and the inner surface 312 (FIG. 16) of the micromixer tube 108X (FIGS. 4-5, 16). In FIGS. 9 and 10, the flow channels 240 extend from the first side 222 of the disk 220 to the outer periphery 230. In FIG. 9, the flow channels 240 have turns 242 therein. However, as shown in FIG. 10, the flow channels 240 may be straight. Any number of flow channels 240 may be provided in the disk 220, and they may have any desired diameter depending on the type of dielectric liquid 216 used (FIGS. 1 and 16) and the desired flow rate.

[0047] 10, the outer periphery 230 of the disk 220 includes a concave surface 246 that extends radially inward, i.e., has an inwardly rounded surface, in the direction of the disk 220. In FIG. 11, the outer periphery 230 of the disk 220 includes a convex surface 248 that extends radially outward, i.e., has an outwardly rounded surface, in the direction of the disk 220. The radius of curvature of the concave surface 246 or the convex surface 248 in FIGS. 10 and 11, respectively, can be defined by a user to obtain a desired EDM cut of the inner surface 312 (FIG. 16) of the micro-mixer tube 108X (FIGS. 4-5, 16).

[0048] 12-14 show an embodiment similar to that of FIGS. 9-11 , except that at least one of the first side 222 and second side 224 of the disk 220 is thicker at its radially outer portion 250 than at its radially inner portion 252, e.g., closer to the opening 226. In FIG. 12 , at least one of the first side 222 and second side 224 of the disk 220 is thicker at its radially outer portion 250 adjacent the concave surface 246 than at its radially inner portion 252 adjacent the opening 226. While both side surfaces 222, 224 are shown thicker at the radially outer portion 250 in FIGS. 12-14 , this is not necessary in all cases; i.e., only one side surface can be thicker. The thicker areas of the radially outer portion 250, if present on both sides, can be, for example, 10% thicker than the radially inner portion 252, individually or collectively.

[0049] FIG. 15 illustrates an embodiment in which the outer periphery 230 of the disk 220 is sawtoothed, i.e., includes sawtooth 256. The type of sawtooth can be any form, such as, for example, sawtooth, concave, triangular spike (as shown), etc. The sawtooth 256 can be provided as an additional form of dielectric liquid flow channel 240 for directing the dielectric liquid 216 between the disk 220 and the inner surface of the tube 108X. The sawtooth 256 does not necessarily participate in any EDM function other than the dielectric liquid flow. The sawtooth 256 may be used alone or in combination with the flow channel(s) 240 within the disk 220. FIG. 15 illustrates, for example, both forms of flow channel 240.

[0050] Regardless of shape or form, the disk 220 is diametrically sized to fit closely within the micro-mixer tube 108X (FIGS. 4-5, 16). In certain embodiments, as shown in FIGS. 8, 15, and 16, the disk 220 has an outer diameter (OD) within 90% to 95% of the inner diameter (ID) (FIG. 16) of the micro-mixer tube 108X (FIGS. 4-5, 16). If sawtooth 256 is used, as in FIG. 15, the outer diameter OD may be based on the maximum outer diameter of the disk 220.

[0051] FIG. 16 shows a schematic cross-sectional view, and FIG. 17 shows a schematic top view, of an EDM system 300 for removing an end portion 302 of a micro-mixer tube 108X of a combustor 25 (FIG. 1). The end portion 302 may include any form of damage 304 for which repair is desired, such as a thinned area, an oxidized area, or an otherwise damaged area. The EDM system 300 includes, among other things, a tool electrode 200 as described herein. As previously described, the tool electrode 200 includes an elongated member 210 and a disk 220. The disk 220 has a first side 222, a second side 224, a central opening 226 therein, and a slot 228 extending from the first side 222 to the second side 224 and from the opening 226 to the outer periphery 230 of the disk 220. Elongated member 210 is coupled to disk 220 and extends from a first side 222 of disk 220 across a second side 224 of disk 220 through an opening 226 .

[0052] The EDM system 300 also includes a power supply 310 operably coupled to deliver a repetitive voltage to the tool electrode 200 and the micro-mixer tube 108X (second work electrode). The power supply 310 may include any now known or later developed EDM power supply capable of providing repeated or cyclic current discharges between the tool electrode 200 and the inner surface 312 of the micro-mixer tube 108X. Any form of electrical connection, such as, for example, electrical wires and associated connectors, may operably couple the power supply 310 to a portion of the tool electrode 200, such as the elongated member 210 or other portion, and the micro-mixer tube 108X.

[0053] The EDM system 300 may also include a dielectric liquid delivery system 320 configured to deliver the dielectric liquid 216 between the tool electrode 200 and the inner surface 312 of the micro-mixer tube 108X. The delivery system 320 may include any form of gravity-fed and / or force-fed system, for example, with a pump (not shown). The delivery system 320 may also include a dielectric liquid supply (not shown), such as a reservoir or catch basin, as well as any necessary conduits, such as pipes, hoses, and / or nozzles, to deliver the dielectric liquid 216 at a desired volume and / or flow rate within the micro-mixer tube 108X. Due to the narrow area within the micro-mixer tube 108X, the delivery system 320 may have a relatively small diameter hose positioned within the micro-mixer tube 108X so as not to interfere with the movement of the tool electrode 200. Although some of the dielectric liquid 216 may flow through the tool electrode 200, the delivery system 320 delivers a sufficient volume of the dielectric liquid 216 onto and / or around the disk 220 to ensure the desired EDM functionality. If flow channels 240 (FIGS. 9, 10, 15) are provided, the dielectric liquid 216 may flow through those channels for delivery to the desired location.

[0054] The EDM system 300 also includes an actuator 330 configured to provide two types of motion to the tool electrode 200. First, the actuator 330 rotates the tool electrode 200. That is, the actuator 330 rotates the tool electrode 200, including the elongated member 210 and the disk 220, about the axis of the elongated member 210 (see the circular arrows in FIGS. 16 and 17 ). The actuator 330 may include any form of rotational actuator, such as a motor, an engine, or the like. Additionally, the actuator 330 moves the disk 220 in a trepanning path (see the arrows in FIG. 16 and the different circular dashed paths in FIG. 17 ). As used herein, a trepanning path refers to a circular path of the tool electrode 200, and in particular, the outer periphery 230 of the disk 220 moves with a gradually increasing diameter so that the disk 220 gradually cuts through the micro-mixer tube 108X from its inner surface 312. FIG. 17 shows three dashed circles indicating three sequential paths (inside to outside) that can be used to achieve the trepanning path. The actuator 330 moves the disk 220 along the trepanning path to gradually remove the end portion 302 of the micro-mixer tube 108X while maintaining an operating distance D1 of the disk 220 with the inner surface 312 of the micro-mixer tube 108X. As shown in FIG. 16, the disk 220 has an outer diameter (OD) within 90% to 95% of the inner diameter (ID) of the micro-mixer tube 108X to help maintain the operating distance D1 with minimal radial movement of the tool electrode 200 to form the trepanning path and address any wear on the disk 220. The operating distance D1 may depend, among other factors, on the material(s) and geometry of the disk 220, the thickness and material(s) of the micro-mixer tube 108X, the desired rate of material removal from the micro-mixer tube 108X, and / or the level of power delivered from the power source 310. In either case, the operating distance D1 may be a range of distances that allows for EDM removal of at least a portion of the inner surface 312 of the micro-mixer tube 108X. While a manual actuator 330 is possible, the actuator 330 typically includes any now known or later developed automated system for moving tool elements in an automated and controlled manner.In one example, actuator 330 may include any of a variety of computer numerically controlled (CNC) actuators. The functionality of CNC actuators is well known in the art, and therefore further details are not necessary for one of ordinary skill in the art to understand how to implement such a system without undue experimentation.

[0055] Next, an embodiment of a method for removing the end portion 302 of a micro-mixer tube 108X of the combustor 25 (FIG. 1) will be described. As shown in FIGS. 16 and 17 , a tool electrode 200 is positioned within the end portion 302 of the micro-mixer tube 108X. The micro-mixer tube 108X can be any individual tube of the multiple micro-mixer tubes 108 (FIGS. 4-5). For clarity, the micro-mixer tube 108X is not shown in FIGS. 16-17 with adjacent micro-mixer tubes 108 (as in FIGS. 4-5), but it is emphasized that the micro-mixer tube 108X is still in place on its respective segment of the micro-mixer 100 (FIG. 2). That is, the micro-mixer tube 108X is on a segment of the fuel plenum 104 and / or air intake 106, as shown in FIGS. 4-5. The tool electrode 200, and in particular the disk 220 thereof, can be inserted to any desired depth to remove any desired length of the end portion 302.

[0056] 16 and 17, the actuator 330 rotates the tool electrode 200 while moving the disk 220 in the trepanning path while maintaining the disk 220 at an operating distance D1 from the inner surface 312 of the micro-mixer tube 108X. As described above, the actuator 330 may include a CNC actuator, and thus the rotation during movement may be controlled by the CNC actuator.

[0057] The method may also include adding a dielectric liquid 216 between the tool electrode 200 and the inner surface 312 of the micro-mixer tube 108X. The adding may be by flowing the dielectric liquid 216 into the end portion 302 of the micro-mixer tube 108X, for example, allowing gravity to cause the dielectric liquid 216 to flow between the disk 220 and the inner surface 312. Adding the dielectric liquid 216 may also include passing the dielectric liquid 216 through a dielectric liquid flow channel(s) 240 defined in (or by) the disk 220. That is, the dielectric liquid 216 may flow through the flow channel(s) 240 defined in the disk 220 and / or over any sawtooth 256 defined by the outer periphery 230 of the disk 220. During operation, the dielectric liquid 216 assists EDM and significantly reduces, if not eliminates, the formation of debris. In any case, the debris is significantly smaller than that experienced from the physical cutting of the micro-mixer tube and is easily removed during the EDM process.

[0058] 16 and 17 , the method also includes repeatedly applying a voltage to the tool electrode 200 and the micro-mixer tube 108X, for example, using a power supply 310, to gradually remove the end portion 302 of the micro-mixer tube 108X. More specifically, as the tool electrode 200 rotates, different portions of the outer periphery 230 of the disk 220 spark with the inner surface 312 of the micro-mixer tube 108X, removing portions of the inner surface 312. The rotation of the disk 220 evenly distributes the wear experienced by the disk 220 around its outer periphery 230. The trepanning paths generated by the actuator 330 gradually move the tool electrode 200 outward, cutting a small amount of the inner surface 312 with each path around the inner surface 312 until, ultimately, the end portion 302 is no longer coupled to the remaining portion 340 of the micro-mixer tube 108X. The number of EDM passes of the disk 220 around the inner surface 312 to remove the end portion 302 may depend, among other things, on the thickness of the micro-mixer tube 108X, the power used, the rotational speed of the disk 220, and / or the speed of the trepanning path. In one non-limiting example, two to three passes are required. In either case, the tool electrode 200 and EDM system 300 significantly reduce the physical forces and vibrations applied from conventional machining systems, reducing or eliminating damage to the brazed joints of the micro-mixer 100 ( FIG. 2 ). The tool electrode 200 and EDM system 300 also reduce or eliminate machining debris, such as chips or swarf, that can damage or clog the small cooling passages in the micro-mixer tube 108.

[0059] In an optional step, as shown in FIG. 18 , prior to the EDM process (i.e., rotating while moving, adding dielectric liquid, and repeatedly applying voltage), the end portion 232 of the elongated member 210 extending beyond the second side 224 of the disk 220 may be inserted and moved (see arrow) into the end portion 302 of the micro-mixer tube 108X to identify the center of the micro-mixer tube 108X. This step may include moving the end portion 302 in different directions to identify the inner surface 312 of the micro-mixer tube 108X and then identifying its center, i.e., the center of the micro-mixer tube 108X. That is, this step may be part of determining the X and Y location of the center of the micro-mixer tube 108X by an actuator 330 in the form of a CNC actuator. The center location may be used to appropriately move the tool electrode 200 during the EDM process.

[0060] FIG. 19 illustrates an end portion 302 removed from a remaining portion 340 of a micro-mixer tube 108X. After the end portion 302 is removed, the end surface 342 of the remaining portion 340 may not be in a condition for bonding a new end portion thereto; for example, it may be rough, non-planar, or otherwise imperfect for bonding a replacement tip. In this case, the end surface 342 of the micro-mixer tube 108X from which the end portion 302 was removed may be planarized, e.g., made flat and smooth, or otherwise prepared for bonding a replacement tip. Planarization may include, among other things, performing EDM using the second side 224 of the disk 220 to smooth it (touch EDM) and / or using an abrasive tool on the end surface 342. Planarization is generally indicated by the planarization tool 344 and arrow in some versions of FIG. 19.

[0061] 20 illustrates coupling a new end piece or replacement tip 350 onto the end face 342 of the micro-mixer tube 108X from which the end portion 302 (FIG. 19) was removed. The new end piece 350 can take any form, for example, a manufactured or repaired end piece that can be coupled to the remaining portion 340 and operable as part of the repaired micro-mixer tube 352. The new end piece 350 can be adhered to the end face 342 using any joining method(s) appropriate for the material(s) of the micro-mixer tube 352, such as, but not limited to, welding or brazing.

[0062] The above method may be repeated for any number of multiple micro-mixer tubes 108 (FIGS. 4-5) for which repair of end portions 302 is desired.

[0063] Embodiments of the present disclosure provide various technical and commercial advantages, examples of which are described herein. The system described herein significantly reduces the physical forces and vibrations applied from conventional machining systems, reducing or eliminating damage to the brazed joints of the micromixer. The system also reduces or eliminates machining debris, such as chips or swarf, that can damage or clog the small cooling passages in the micromixer tubes. The system also allows for individual repair of micromixer tubes, thereby minimizing repair time and costs. The tool electrode disk is easily replaceable, allowing for easy variability in geometry and size to enhance speed and debris cleaning capabilities.

[0064] As used herein throughout the present specification and claims, approximation language may be applied to modify any quantitative expression that can reasonably vary without resulting in a change in the relevant basic function. Thus, values ​​modified by one or more terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some cases, approximation language may correspond to the precision of the instrument used to measure the value. Here, and throughout the present specification and claims, range limitations may be combined and / or substituted, and such ranges are identified and include all subranges encompassed therein, unless the context or language dictates otherwise. "Approximately" or "about," as applied to a particular value in a range, applies to both endpoints and may indicate + / - 10% of the stated value(s), unless specifically dependent on the precision of the instrument used to measure the value.

[0065] The corresponding structure, material, acts, and equivalents of all means-plus-function or step-plus-function elements in the following claims are intended to include any structure, material, or acts for performing that function in combination with other specifically claimed elements. The description of the present disclosure has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The embodiments have been chosen and described in order to best explain the principles of the present disclosure and practical applications of the present technology, and to enable those skilled in the art to understand the embodiments and to consider various modifications of the embodiments that may be suitable for the particular use contemplated. [Explanation of symbols]

[0066] 10 Gas Turbine (GT) System 15 Compressor 20 Airflow 25 Combustor 30 Fuel flow 35 Combustion gas flow 40 Turbine 45 shaft 50 External Load 100 Micro Mixer 102 base nozzle structure 104 Fuel Plenum 106 Air intake 108 Multiple micromixer tubes, nearby tubes, outer micromixer tubes 108X Damaged micromixer tube 109 Combustor end plate 200 Tool electrode 210 Long and thin members 212 End 214 Channel 216 Dielectric Liquid 220 disc 222 First Aspect 224 Second Aspect 226 Opening 228 Slots 230 perimeter 232 End section 240 Dielectric Liquid Channel 242 turns 246 Concave 248 Convex 250 Radial outer part 252 Radial inner part 256 sawtooth 300 Electrical Discharge Machine (EDM) System 302 End region, end portion or tip 304 Damage 310 Power supply 312 Interior 320 Dielectric Liquid Delivery System 330 Actuator 340 Rest 342 End face 344 Flattening tool 350 New end piece or replacement tip 352 Repaired Micromixer Tube D1 Operating distance ID Inner Diameter OD outer diameter T Thickness

Claims

1. 1. A tool electrode (200) for an electrical discharge mechanical (EDM) system (300) for repairing a micro-mixer tube (108X) of a combustor (25), the tool electrode (200) comprising: an elongated member (210); a disk (220) having a first side (222), a second side (224), an opening (226) in the center of said disk (220), and a slot (228) extending from said first side (222) to said second side (224) and from said opening (226) to an outer periphery (230) of said disk (220); Equipped with the elongated member (210) is coupled to the disk (220) and extends from the first side (222) of the disk (220) past the second side (224) of the disk (220) through the opening (226); Tool electrode (200).

2. 2. The tool electrode (200) of claim 1, wherein the outer periphery (230) of the disk (220) is serrated or the outer periphery (230) of the disk (220) includes a concave surface (246) extending radially inward.

3. 3. The tool electrode (200) of claim 2, wherein at least one of the first side surface (222) and the second side surface (224) of the disk (220) is thicker at the at least one radially outer portion (250) adjacent the concave surface (246) than at the at least one radially inner portion (252), or at least one of the first side surface (222) and the second side surface (224) of the disk (220) is thicker at the at least one radially outer portion (250) than at the at least one radially inner portion (252).

4. The tool electrode (200) of claim 1, wherein the disk (220) includes a dielectric liquid flow channel (240) defined therein.

5. The tool electrode (200) of claim 1, wherein the disk (220) has an outer diameter (OD) in the range of 90% to 95% of an inner diameter (ID) of the micro-mixer tube (108X).

6. The tool electrode (200) of claim 1, wherein the elongated member (210) is configured to couple to a power source (310) of an EDM system (300).

7. 1. An electrical discharge mechanical (EDM) system (300) for removing an end portion (302) of a micro-mixer tube (108X) of a combustor (25), the EDM system (300) comprising: an elongated member (210); a disk (220) having a first side (222), a second side (224), an opening (226) in the center of the disk (220), and a slot (228) extending from the first side (222) to the second side (224) and from the opening (226) to an outer periphery (230) of the disk (220), wherein the elongated member (210) is coupled to the disk (220) and extends from the first side (222) of the disk (220) past the second side (224) of the disk (220) and through the opening (226); A tool electrode (200); a power source (310) operably coupled to deliver a repetitive voltage to the elongated member (210) of the tool electrode (200) and to the micro-mixer tube (108X); a dielectric liquid delivery system (320) configured to deliver a dielectric liquid (216) between the tool electrode (200) and an inner surface (312) of the micromixer tube (108X); an actuator (330) configured to rotate the tool electrode (200) and move the disk (220) in a trepanning path while maintaining an operating distance of the disk (220) from the inner surface (312) of the micro-mixer tube (108X) to gradually remove the end portion (302) of the micro-mixer tube (108X); An electrical discharge machine (EDM) system (300) comprising:

8. 8. The EDM system of claim 7, wherein the outer periphery of the disk is serrated or the outer periphery of the disk includes a radially inwardly extending concave surface.

9. 9. The EDM system of claim 8, wherein at least one of the first side surface and the second side surface of the disk is thicker at the at least one radially outer portion adjacent the concave surface than at the at least one radially inner portion, or at least one of the first side surface and the second side surface of the disk is thicker at the at least one radially outer portion than at the at least one radially inner portion.

10. The EDM system (300) of claim 7, wherein the disk (220) includes a dielectric liquid flow passage (240) defined therein.

11. The EDM system (300) of claim 7, wherein the disk (220) has an outer diameter (OD) in the range of 90% to 95% of an inner diameter (ID) of the micro-mixer tube (108X).

12. 1. A method for removing an end portion (302) of a micro-mixer tube (108X) of a combustor (25), the method comprising: positioning a tool electrode (200) within the end portion (302) of the micromixer tube (108X), the tool electrode (200) including an elongated member (210) and a disk (220) having a first side (222), a second side (224), an opening (226) in the center of the disk (220), and a slot (228) extending from the first side (222) to the second side (224) and from the opening (226) to an outer periphery (230) of the disk (220), the elongated member (210) being coupled to the disk (220) and extending from the first side (222) of the disk (220) past the second side (224) of the disk (220) through the opening (226); rotating the tool electrode (200) while moving the disk (220) through a trepanning path while maintaining an operating distance of the disk (220) from an inner surface (312) of the micromixer tube (108X); adding a dielectric liquid (216) between the tool electrode (200) and the inner surface (312) of the micromixer tube (108X); Repeatedly applying a voltage to the tool electrode (200) and the micromixer tube (108X) to gradually remove the end portion (302) of the micromixer tube (108X); A method comprising:

13. 13. The method of claim 12, further comprising, prior to the rotating while moving, the applying the dielectric liquid, and the repeatedly applying the voltage, moving an end portion (232) of the elongated member (210) that extends beyond the second side (224) of the disk (220) within the end portion (302) of the micromixer tube (108X) to identify a center of the micromixer tube (108X).

14. The method of claim 12 , wherein the rotating while moving is controlled by a computer numerically controlled (CNC) system.

15. The method of claim 12, wherein the applying the dielectric liquid (216) comprises passing the dielectric liquid (216) through a dielectric liquid flow path (240) defined in the disk (220).

16. flattening the end surface (342) of the micromixer tube (108X) from which the end portion (302) has been removed; coupling a new end portion (350) onto the end face (342) of the micromixer tube (108X) from which the end portion (302) was removed; The method of claim 12 further comprising:

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