Patent Application
20120295061
The invention relates generally to gas turbine engines, and, more specifically, to micro-channel cooling therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT), which powers the compressor, and in a low pressure turbine (LPT), which powers a fan in a turbofan aircraft engine application, or powers an external shaft for marine and industrial applications.
Engine efficiency increases with temperature of combustion gases. However, the combustion gases heat the various components along their flowpath, which in turn requires cooling thereof to achieve a long engine lifetime. Typically, the hot gas path components are cooled by bleeding air from the compressor. This cooling process reduces engine efficiency, as the bled air is not used in the combustion process.
Gas turbine engine cooling art is mature and includes numerous patents for various aspects of cooling circuits and features in the various hot gas path components. For example, the combustor includes radially outer and inner liners, which require cooling during operation. Turbine nozzles include hollow vanes supported between outer and inner bands, which also require cooling. Turbine rotor blades are hollow and typically include cooling circuits therein, with the blades being surrounded by turbine shrouds, which also require cooling. The hot combustion gases are discharged through an exhaust which may also be lined, and suitably cooled.
In all of these exemplary gas turbine engine components, thin metal walls of high strength superalloy metals are typically used for enhanced durability while minimizing the need for cooling thereof. Various cooling circuits and features are tailored for these individual components in their corresponding environments in the engine. For example, a series of internal cooling passages, or serpentines, may be formed in a hot gas path component. A cooling fluid may be provided to the serpentines from a plenum, and the cooling fluid may flow through the passages, cooling the hot gas path component substrate and coatings. However, this cooling strategy typically results in comparatively low heat transfer rates and non-uniform component temperature profiles.
Micro-channel cooling has the potential to significantly reduce cooling requirements by placing the cooling as close as possible to the heated region, thus reducing the temperature difference between the hot side and cold side of the main load bearing substrate material for a given heat transfer rate. However, to achieve micro-channel cooling, the channels should have sharp edges to facilitate a flaw free deposition of a first metallic (structural) coating, and to reduce or eliminate interface voids that could initiate cracking.
It would therefore be desirable to provide a method for forming micro-channels with sharp edges to facilitate a flaw free deposition of a first structural coating, and to reduce or eliminate interface voids that could initiate cracking. It would further be desirable to provide a method for forming micro-channels with reduced processing time and reduced channel-to-channel variation.
One aspect of the present invention resides in a method of forming one or more grooves in a component. The method includes using a first machining technique to form one or more preliminary grooves in an outer surface of a substrate. Each preliminary groove has a base and extends at least partially along the outer surface of the substrate, and the substrate has an inner surface that defines at least one hollow, interior space. The method further includes using a second machining technique to further machine the preliminary groove(s) to form the respective groove(s). In addition, the method includes forming one or more access holes through the base of a respective groove to connect the respective groove in fluid communication with the respective hollow interior space.
Another aspect of the present invention resides in a method of forming one or more grooves in a component. The method includes depositing a structural coating on an outer surface of a substrate, where the substrate has at least one hollow interior space. The method further includes using a first machining technique to form one or more preliminary grooves in the structural coating. Each preliminary groove has a base and extends at least partially along the substrate. The method further includes using a second machining technique to further machine the preliminary groove(s) to form the respective one or more grooves in the structural coating. In addition, the method includes forming one or more access holes through the base of a respective groove to connect the respective groove in fluid communication with the respective hollow interior space.
Yet another aspect of the present invention resides in a component that includes a substrate comprising an outer surface and an inner surface, where the inner surface defines at least one hollow, interior space. The outer surface defines one or more grooves, and each groove extends at least partially along the outer surface of the substrate and has a base. Each groove is characterized by a sidewall radius R in a range of 0≦R≦0.127 mm. One or more access holes extend through the base of a respective groove to place the groove in fluid communication with the respective hollow interior space. The component further includes a coating disposed over at least a portion of the outer surface of the substrate and extending over the groove(s), such that the groove(s) and the coating together define one or more channels for cooling the component.
Another aspect of the present invention resides in a component that includes a substrate comprising an outer surface and an inner surface, where the inner surface defines at least one hollow, interior space. The component further includes a structural coating disposed over at least a portion of the outer surface of the substrate. The structural coating defines one or more grooves, where each groove extends at least partially along the substrate and has a base. One or more access holes extend through the base of a respective groove to place the groove in fluid communication with the respective hollow interior space. Each groove is characterized by a sidewall radius R in a range of 0≦R≦0.127 mm. The component further includes at least one additional coating disposed over the structural coating and over the groove(s), such that the groove(s) and the additional coating together define one or more channels for cooling the component. At least one exit hole extends through the additional coating for each of the respective channels, to receive and discharge a coolant fluid from the respective channel.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The modifier “about” used in connection with a quantity is inclusive of the stated value, and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). In addition, the term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.
Moreover, in this specification, the suffix “(s)” is usually intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., “the passage hole” may include one or more passage holes, unless otherwise specified). Reference throughout the specification to “one embodiment,” “another embodiment,” “an embodiment,” and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described inventive features may be combined in any suitable manner in the various embodiments.
The gas turbine system 10 may include a number of hot gas path components 100. A hot gas path component is any component of the system 10 that is at least partially exposed to a high temperature flow of gas through the system 10. For example, bucket assemblies (also known as blades or blade assemblies), nozzle assemblies (also known as vanes or vane assemblies), shroud assemblies, transition pieces, retaining rings, and compressor exhaust components are all hot gas path components. However, it should be understood that the hot gas path component 100 of the present invention is not limited to the above examples, but may be any component that is at least partially exposed to a high temperature flow of gas. Further, it should be understood that the hot gas path component 100 of the present disclosure is not limited to components in gas turbine systems 10, but may be any piece of machinery or component thereof that may be exposed to high temperature flows.
When a hot gas path component 100 is exposed to a hot gas flow 80, the hot gas path component 100 is heated by the hot gas flow 80 and may reach a temperature at which the hot gas path component 100 fails. Thus, in order to allow system 10 to operate with hot gas flow 80 at a high temperature, increasing the efficiency and performance of the system 10, a cooling system for the hot gas path component 100 is required.
In general, the cooling system of the present disclosure includes a series of small channels, or micro-channels, formed in the surface of the hot gas path component 100. For industrial sized power generating turbine components, “small” or “micro” channel dimensions would encompass approximate depths and widths in the range of 0.25 mm to 1.5 mm, while for aviation sized turbine components channel dimensions would encompass approximate depths and widths in the range of 0.15 mm to 0.5 mm. The hot gas path component may be provided with a cover layer. A cooling fluid may be provided to the channels from a plenum, and the cooling fluid may flow through the channels, cooling the cover layer.
A method of forming one or more grooves 132 in a component 100 is described with reference to
The substrate 110 is typically cast prior to forming the preliminary grooves 131 in the surface 112 of the substrate 110. As discussed in U.S. Pat. No. 5,626,462, substrate 110 may be formed from any suitable material. Depending on the intended application for component 100, this could include Ni-base, Co-base and Fe-base superalloys. The Ni-base superalloys may be those containing both γ and γ′ phases, particularly those Ni-base superalloys containing both γ and γ′ phases wherein the γ′ phase occupies at least 40% by volume of the superalloy. Such alloys are known to be advantageous because of a combination of desirable properties including high temperature strength and high temperature creep resistance. The substrate material may also comprise a NiAl intermetallic alloy, as these alloys are also known to possess a combination of superior properties including high temperature strength and high temperature creep resistance that are advantageous for use in turbine engine applications used for aircraft. In the case of Nb-base alloys, coated Nb-base alloys having superior oxidation resistance will be preferred, particularly those alloys comprising Nb-(27-40)Ti-(4.5-10.5)Al-(4.5-7.9)Cr-(1.5-5.5)Hf-(0-6)V, where the composition ranges are in atom percent. The substrate material may also comprise a Nb-base alloy that contains at least one secondary phase, such as a Nb-containing intermetallic compound comprising a silicide, carbide or boride. Such alloys are composites of a ductile phase (i.e., the Nb-base alloy) and a strengthening phase (i.e., a Nb-containing intermetallic compound). For other arrangements, the substrate material comprises a molybdenum based alloy, such as alloys based on molybdenum (solid solution) with Mo5SiB2 and Mo3Si second phases. For other configurations, the substrate material comprises a ceramic matrix composite, such as a silicon carbide (SiC) matrix reinforced with SiC fibers. For other configurations the substrate material comprises a TiAl-based intermetallic compound.
As indicated, for example, in
For the example process shown in
As noted above, for the example process shown in
In addition, and as explained in U.S. patent application Ser. No. 12/790,675, the water jet system can include a multi-axis computer numerically controlled (CNC) unit. The CNC systems themselves are known in the art, and described, for example, in U.S. Patent Publication 2005/0013926 (S. Rutkowski et al), which is incorporated herein by reference. CNC systems allow movement of the cutting tool along a number of X, Y, and Z axes, as well as rotational axes. Beneficially, the preliminary grooves 131 can be formed using an abrasive liquid jet at a linear rate of up to 2.5 cm per second for channels that are roughly 0.75 mm by 0.75 mm in cross section. However, because the preliminary grooves 131 formed using abrasive liquid jets may not possess highly precise and uniform widths and may lack the desired sharp edges at the groove-coating interface, the second machining technique is used to finish the grooves 132.
The second machining technique may be formed using a variety of machining processes. For example, the second machining technique may be selected from the group consisting of electrochemical machining (ECM), EDM, milling EDM (EDM with a spinning electrode 165), and laser machining (laser drilling). More particularly, if ECM is selected, either etching through an electrically insulating mask or plunge ECM may be employed. U.S. Pat. No. 6,644,921, Bunker et al., “Cooling passages and methods of fabrication,” which is incorporated by reference herein in its entirety, describes a pulsed ECM process. Briefly, pulsed ECM uses the ECM process with an electrode having a patterned mask to block the machining in regions where material removal is not desired. For plunge ECM, no mask is employed. If a mask is used, the method may further include depositing an electrically insulating mask (not shown) on the substrate prior to performing the first machining operation, using an abrasive liquid jet to form the preliminary grooves, and then etching through the mask to form the grooves. As noted above, U.S. Pat. No. 6,644,921 describes performing ECM by etching through a mask.
For the example process shown in
As noted above, the abrasive liquid jet system may include a multi-axis CNC unit (not shown). For certain arrangements, the spinning electrode 165 may be mounted on a machining platform or device similar to that used for the liquid jet 160. For these configurations, the spinning electrode 165 may be controlled by application of machining programming similar to that used for the liquid jet, in order to run the spinning electrode along the channels and “clean up” the side walls to make them vertical, and to remove any edge radiusing from the liquid jet process. This milling EDM process could proceed as a single step for each channel in which the milling EDM tool diameter is large enough to just fit inside the channel. However, because the liquid jet channels may not possess highly precise and uniform widths, the milling EDM may be performed in two passes, once on each channel side wall 135. In this latter case, the milling EDM tool diameter may be much smaller, and thus not affect the formation of recast as much. This will also allow a much greater degree of freedom in channel width variation, divorcing the milling EDM process from tight tolerances. The milling EDM tool need not extend to the bottom of the channels, and for particular embodiments will not. The primary objective of the milling EDM operation is to form sharp edges at the top of the channels. Thus, the CNC may be programmed to simply “kiss off” those edges and leave the remainder of the side walls 135 somewhat non-vertical, as indicated in
Beneficially, this hybrid machining process provides the speed (and hence reduced manufacturing cost) of abrasive liquid jet, with the precision machining of milling EDM. In this way, the inventive method provides the desired sharp edges to facilitate a flaw free deposition of the first metallic coating. In addition, similar component datum and programming can be used for both operations, or the programming for one of the machining techniques may be based on the programming for the other machining technique.
Re-entrant grooves 132 are discussed in commonly assigned, U.S. patent application Ser. No. 12/943,624, Bunker et al., “Components with re-entrant shaped cooling channels and methods of manufacture,” which is incorporated by reference herein in its entirety. Beneficially, the use of re-entrant shaped grooves makes it easier to deposit a coating across the top of the groove, while also permitting the formation of sufficiently large channels 130 to meet the cooling requirements for the component 100. For particular configurations, the base 134 of a respective one of the re-entrant shaped grooves 132 is at least 2 times wider than the top 136 of the respective groove 132. For example, if the base 134 of the groove 132 is 0.75 millimeters, the top 136 would be less than 0.375 millimeters in width, for this configuration. For more particular configurations, the base 134 of the respective re-entrant shaped groove 132 is at least 3 times wider than the top 136 of the respective groove 132, and still more particularly, the base 134 of the respective re-entrant shaped groove 132 is in a range of about 3-4 times wider than the top 136 of the respective groove 132. Beneficially, a large base to top ratio increases the overall cooling volume for the micro-channel 130, while making it easier to deposit a coating across the top of the groove.
Additionally, the component fabrication method may optionally further include drying, curing or sintering the fugitive coating 30 prior to performing the machining operations. For particular process configurations, the thickness of the fugitive coating 30 deposited on the substrate 110 is in a range of about 0.5-2.0 millimeters. In one non-limiting example, the fugitive coating 30 comprises a one millimeter thick polymer based coating. The fugitive coating 30 may be deposited using a variety of deposition techniques, including powder coating, electrostatic coating, dip-coating, spin coating, chemical vapor deposition and application of a prepared tape. More particularly, the fugitive coating is essentially uniform and is able to adhere, but does not harm the substrate 110 during processing or subsequent removal.
For particular process configurations, the fugitive coating 30 is deposited using powder coating or electrostatic coating. For example process configurations, the fugitive coating 30 comprises a polymer. For example, the fugitive coating 30 may comprise a polymer based coating, such as pyridine, which may be deposited using chemical vapor deposition. Other example polymer based coating materials include resins, such as polyester or epoxies. Example resins include photo-curable resins, such as a light curable or UV curable resin, non-limiting examples of which include a UV/Visible light curable masking resin, marketed under the trademark Speedmask 729® by DYMAX, having a place of business in Torrington, Conn., in which case, the method further includes curing the photo-curable resin 30, prior to performing the machining operations. For other process configurations, the fugitive coating 30 may comprise a carbonaceous material. For example, the fugitive coating 30 may comprise graphite paint. Polyethylene is yet another example coating material. For other process configurations, the fugitive coating 30 may be enameled onto the substrate 110.
The fugitive coating 30 is removed after performing the second machining technique, and it should be noted that the fugitive coating may be removed before or after the access holes 140 (
The structural coating may be deposited using a variety of techniques. For particular processes, the structural coating is deposited by performing an ion plasma deposition (cathodic arc). Example ion plasma deposition apparatus and method are provided in commonly assigned, US Published Patent Application No. 20080138529, Weaver et al, “Method and apparatus for cathodic arc ion plasma deposition,” which is incorporated by reference herein in its entirety. Briefly, ion plasma deposition comprises placing a cathode formed of a coating material into a vacuum environment within a vacuum chamber, providing a substrate 110 within the vacuum environment, supplying a current to the cathode to form a cathodic arc upon a cathode surface resulting in arc-induced erosion of coating material from the cathode surface, and depositing the coating material from the cathode upon the substrate surface 112.
For certain hot gas path components 100, the structural coating comprises a nickel-based or cobalt-based alloy, and more particularly comprises a superalloy or a (NiCo)CrAlY alloy. For example, where the substrate material is a Ni-base superalloy containing both γ and γ′ phases, structural coating may comprise similar compositions of materials, as discussed in greater detail below with reference to U.S. Pat. No. 5,626,462.
For particular process configurations, a structural coating is deposited by performing at least one of a thermal spray process and a cold spray process. For example, the thermal spray process may comprise combustion spraying or plasma spraying, the combustion spraying may comprise high velocity oxygen fuel spraying (HVOF) or high velocity air fuel spraying (HVAF), and the plasma spraying may comprise atmospheric (such as air or inert gas) plasma spray, or low pressure plasma spray (LPPS, which is also know as vacuum plasma spray or VPS). In one non-limiting example, a NiCrAlY coating is deposited by HVOF or HVAF. Other example techniques for depositing the structural coating include, without limitation, sputtering, electron beam physical vapor deposition, electroless plating, and electroplating. In addition, the method may further optionally include performing a heat treatment after depositing the structural coating 54 and prior to performing the machining operations.
As indicated in
Although not expressly shown, the process described above with reference to
Another method of forming one or more grooves 132 in a component 100 is described with reference to FIGS. 12 and 16-18. As indicated, for example, in
As indicated in
As indicated in
Example first and second machining techniques are described above. For the illustrated process, the first machining technique comprises abrasive liquid jet, and the preliminary grooves 131 are formed by directing an abrasive liquid jet 160 at the structural coating 54. As discussed above, examples for the second machining technique include ECM, EDM, milling EDM, and laser machining. More particularly, if ECM is selected, plunge ECM may be employed. For particular processes, the first machining technique comprises abrasive liquid jet, and the second machining technique comprises milling EDM.
Although not expressly shown, re-entrant shaped grooves may be formed in the structural coating 54 using this method. For example, re-entrant shaped (see
Although not expressly shown, a fugitive coating 30 may be used as a mask when forming grooves in the structural coating. For this process, the method further includes depositing a fugitive coating 30 on the structural coating 54 prior to performing the first machining technique. For this process, the structural coating 54 is machined through the fugitive coating 30, and the machining forms one or more openings 34 (
A component 100 embodiment of the invention is described with reference to
One or more access holes 140 extend through the base 134 of a respective groove 132 to place the groove 132 in fluid communication with the interior space(s) 114, as shown for example in
As indicated in
For the example configuration shown in
For the particular configuration shown in
Another component 100 embodiment of the invention is described with reference to
One or more access holes 140 extend through the base 134 of a respective groove 132 to place the groove 132 in fluid communication with the interior space(s) 114, as shown for example in
As indicated in
The coatings 54, 56 are described above. For particular configurations, the additional coating 56 comprises a second structural coating 56. As noted above, for particular configurations, the structural coatings 54, 56 comprise the same coating material. For other configurations, the two structural coatings 54, 56 may comprise different coating materials. The structural coatings 54, 56 may be deposited using the same or different deposition techniques.) For example configurations, the structural coating 54 has a thickness of less than about 1.0 mm and, more particularly, less than about 0.5 mm. For example, structural coatings 54 formed using an ion plasma deposition may have thicknesses of less than about 0.5 mm, but for a thermal plasma spray (such as high velocity oxygen fuel spraying) coating, the thickness of the structural coating 54 may be less than about 1 mm.
As noted above the above-described hybrid machining processes provide the speed (and hence reduced manufacturing cost) of abrasive liquid jet, with the precision machining of milling EDM. In this way, the inventive methods can be used to produce cooled components with the desired sharp edges at the channel/coating interface, to facilitate a flaw free deposition of the first metallic (structural) coating.
Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
