Patent Application
20150008140
The subject matter disclosed herein relates to industrial machinery, such as turbomachinery, subject to high temperatures during operation. More specifically, but not by way of limitation, the subject matter relates to surface cooling passages and the formation of surface cooling passages in hot gas path components of turbine engines, particularly turbine rotor and stator blades.
It will be appreciated that in a turbine engine, a fuel is brought together with compressed air, which is typically supplied by an axial compressor and combusted within a combustor. The thermal energy released by the combustion creates a kinetically charged flow of hot gases, which is directed through multiple stages of airfoils or blades within a turbine section of the engine. The hot gases induce the rotor blades to rotate about a central shaft, thereby converting the chemical energy of the fuel into the kinetic energy of the rotating shaft, which then may be used to drive a generator for the production of electricity or some other purpose.
Because efficiency improves at higher operating temperatures, there is a constant push for increasing temperature through the hot gas path of gas turbine engines. As a result, there is a demand for technologies that improve the resiliency of hot gas path components through this area of the engine. However, the extreme thermal and mechanical loads through the region and the limitations of available materials mean the challenge of realizing further gains is a significant one.
One manner in which thermal loads are lessoned is circulating a coolant, which is typically compressed air bled from the compressor, through the component during operation. The effectiveness of this technique has limitations. First, because the supply of coolant is compressed air that is diverted from the main gas path, its usage reduces the efficiency of the engine. Accordingly there is a push to limit its usage as much as possible. Second, the casting processes used to form rotor blades and other hot gas components is limited in how close cooling circuits may be formed to hot outer surfaces. This reduces the cooling effectiveness of the channels.
One known manner for dealing with this issue is to enclose open channels that are machined into the surface of the component after its casting. For example, the open channel may be formed and then enclosed by a surface coating. In such cases, a filler may be used to fill the channel and support the coating while it hardens. Once hardened, the filler is leached from the channel such that a hollow, enclosed cooling channel is created that is positioned very close to the surface of the component. However, while this method has been used with a certain amount of success, it will be appreciated that the filler/leaching process is time-consuming and expensive, and, because the channel is enclosed by only a layer of coating, durability issues may arise.
In a similar known method, an open channel may be formed having a narrow neck at the surface of the component that supports the coating without the need for a filler. This approach avoids the time consuming process of filling/leaching, while the narrower neck at the component surface creates a more durable product because the span distance of the coating that encloses the channel is reduced. It will be appreciated, though, that this type of channel geometry is difficult to form, which greatly complicates and increases the cost of the machining process. As such, there is a need for improved processes for manufacturing robust cooling passages positioned close to the surface of hot gas path components.
The present application thus discloses a method for manufacturing a microchannel cooling passage in a surface of a machine component that includes: forming an elongated open channel in the surface of the machine component, the open channel comprising a cross-sectional profile having a mouth and a floor, and, defined therebetween, a middle region; inserting a corresponding elongated electrode having a directional bias into the channel; and using the electrode as a tooling piece in an electrochemical machining process, widening the middle region of the open channel.
The present application further discloses a method for manufacturing a microchannel cooling passage in a surface of a hot gas path component in a gas turbine engine that includes: forming an open channel having a non-overhanging cross-sectional profile; determining a removal area and a non-removal area within walls of the formed open channel that relate to a desired overhanging cross-sectional profile; configuring an electrode for insertion into the formed open channel such that a directional bias of the electrode aligns: a) an electrically exposed region opposite the removal area of the formed open channel; and b) an electrically insulated region opposite the non-removal area of the formed open channel; and using the electrode as a tooling device to electrochemically machine the formed open channel from the non-overhanging cross-sectional profile to the overhanging cross-sectional profile.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
In an aspect, the combustor 104 uses liquid and/or gas fuel, such as natural gas or a hydrogen rich synthetic gas, to run the engine. For example, fuel nozzles 110 are in fluid communication with an air supply and a fuel supply 112. The fuel nozzles 110 create an air-fuel mixture, and discharge the air-fuel mixture into the combustor 104, thereby causing a combustion that creates a hot pressurized exhaust gas. The combustor 100 directs the hot pressurized gas through a transition piece into a turbine nozzle (or “stage one nozzle”), and other stages of buckets and nozzles causing turbine 106 rotation. The rotation of turbine 106 causes the shaft 108 to rotate, thereby compressing the air as it flows into the compressor 102. In an embodiment, hot gas path components, including, but not limited to, shrouds, diaphragms, nozzles, buckets and transition pieces are located in the turbine 106, where hot gas flow across the components causes creep, oxidation, wear and thermal fatigue of turbine parts. Controlling the temperature of the hot gas path components can reduce distress modes in the components. The efficiency of the gas turbine increases with an increase in firing temperature in the turbine system 100. As the firing temperature increases, the hot gas path components need to be properly cooled to meet service life. Components with improved arrangements for cooling of regions proximate to the hot gas path and methods for making such components are discussed in detail below with reference to
Each rotor blade 115 generally includes a root or dovetail 122 which may have any conventional form, such as an axial dovetail configured for being mounted in a corresponding dovetail slot in the perimeter of the rotor disk 117. A hollow airfoil 124 is integrally joined to dovetail 122 and extends radially or longitudinally outwardly therefrom. The rotor blade 115 also includes an integral platform 126 disposed at the junction of the airfoil 124 and the dovetail 122 for defining a portion of the radially inner flow path for combustion gases 116. It will be appreciated that the rotor blade 115 may be formed in any conventional manner, and is typically a one-piece casting. It will be seen that the airfoil 124 preferably includes a generally concave pressure sidewall 128 and a circumferentially or laterally opposite, generally convex suction sidewall 130 extending axially between opposite leading and trailing edges 132 and 134, respectively. The sidewalls 128 and 130 also extend in the radial direction from the platform 126 to a radially outer tip or blade tip 137. A number of surface outlets 121 may be positioned on the airfoil and provide an outlet for coolant being circulated through the rotor blade.
Further, the pressure and suction sidewalls 128 and 130 are spaced apart in the circumferential direction over the entire radial span of airfoil 124 to define at least one internal flow chamber or channel for channeling cooling air through the airfoil 124 for the cooling thereof. Cooling air is typically bled from the compressor in any conventional manner. The inside of the airfoil 124 may have any configuration including, for example, serpentine flow channels with various turbulators therein for enhancing cooling air effectiveness, with cooling air being discharged through various holes through airfoil 124 such as conventional film cooling holes and/or trailing edge discharge holes. It will be appreciated that such inner cooling passages may be configured or used in conjunction with the surface cooling channels of the present invention via machining an passage that connects the inner cooling passage to the formed surface channel. This may be done in any conventional manner. In addition, as discussed in more detail below, surface channels according to the present invention may be formed to intersect existing coolant outlets such that, once the surface channel is enclosed, the pressurized coolant forces the flow of coolant through the surface channel. The rotor blade assembly of
As discussed above, microchannel cooling has the potential to significantly reduce cooling requirements by placing the cooling as close as possible to the surface heat zone, thus reducing the temperature difference between the hot side and cold side for a given heat transfer rate. However, current techniques for forming microchannels typically require the use of a sacrificial filler to keep the coating from being deposited within the microchannels, to support the coating during deposition, as well as the removal of the sacrificial filler after deposition of the coating system. However, both the filling of the channels with a filler material, and the later removal of that material present potential problems for current microchannel processing techniques. For example, the filler must be compatible with the substrate and coatings, yet have minimal shrinkage, but also have sufficient strength. Removal of the sacrificial filler involves potentially damaging processes of leaching, etching, or vaporization, and typically requires long times. Residual filler material is also a concern.
As mentioned, an overhanging profile that creates a narrowed-mouth may be used to avoid the need for filler during the coating process, as the narrowed-mouth of the overhanging profile creates a narrowed mouth that the coating can bridge without further support. As such, this approach avoids the time consuming process of filling/leaching, while the narrower neck at the component surface creates a more durable product by shortening the span distance of the coating that encloses the channel. It will be appreciated, though, that this type of channel geometry is difficult to form in the casting process because of necessary tolerances between the core and the surface of the component. Further, conventional post-cast machining processes are unable to form such geometries without greatly complicating and increasing the cost of the necessary machining. As discussed below in relation to
Methods according to the present invention include an electrochemical machining process (“ECM”). Unless otherwise stated, any type of ECM may be used that is able to meet the functionality described below. As will be appreciated, an ECM system typically includes a power supply, a cathode or tooling piece (depicted as wall 140 below), an anode or workpiece (depicted as tooling piece or electrode 150), an electrolyte pump, and an electrolyte tank. In operation, as one of ordinary skill in the art will appreciate, the tooling piece and the workpiece are positioned (and repositioned as the machining process continues) such that a relatively narrow inter-electrode gap is defined by the space between them. The power supply is then used to apply a voltage across the workpiece and tooling piece, i.e., the anode and cathode, respectively, of the electrolytic cell that is formed. The ECM system may include an electrolyte system, which, as shown, operates to pump a continuous stream of pressurized electrolyte into the inter-electrode gap. A suitable electrolyte, for example, aqueous sodium chloride (table salt) solution, is chosen so that the shape of the tooling piece remains substantially unchanged during the machining process. The electrolyte is pumped from an electrolyte tank and delivered to the tooling piece at a relatively high rate and pressure. The tooling piece must be positioned such that the necessary inter-electrode gap is maintained between it and the workpiece as the machining process continues. This generally includes a control system that gradually moves the tooling piece toward the workpiece as it is being machined. This may include movement along a single axis or two axes. It will be appreciated that the present invention includes using a tooling piece electrode having a specific configuration. Unless otherwise stated, the other components of the ECM system of the present application may include any conventional form that adheres to the functionality described herein.
In operation, metal removal is achieved by electrochemical dissolution of the anodically polarized workpiece, which, as stated, is one part of an electrolytic cell in ECM. Hard metals can be shaped electrolytically by using ECM and the rate of machining generally does not depend on their hardness. The tooling piece, i.e., the other electrode in the electrolytic cell in ECM, used in the process does not wear, and therefore, soft metals may be used as tools to form shapes on harder workpieces, unlike conventional machining methods. As one of ordinary skill in the art will appreciate, ECM may be used to smooth surfaces, drill holes, form complex shapes, and remove fatigue cracks in steel structures. The rate at which metal is removed from the anode (i.e., the workpiece) is approximately in inverse proportion to the distance between the electrodes. As machining proceeds, and with the simultaneous movement of the cathode at a typical rate toward the anode, the width of the inter-electrode gap along the electrode length will gradually tend to a steady-state value. A typical gap width may be about 0.0004 meters.
Turning now to
In one preferred embodiment, as shown in
As illustrated, the cross-sectional profile of the directionally biased electrode 150 includes at least one exposed region 151 and one insulated region 152. It will be appreciated that the exposed region 151 is one in which an electrical conducting surface of the electrode 150 is not covered by an electrically insulating material. The insulated region 152 is one in which an electrically insulating material covers the electrical conducting surface of the electrode 150. Any appropriate conventional electrically insulating material may be used. In one embodiment, as illustrated in
In another embodiment, as illustrated in
The step of forming the elongated open channel 155 may include any conventional machining or casting process. For example, the open channel 155, because of its simple profile, may be mechanically machined in a cost-effective manner. In other cases, as discussed below, the open channel 155 may be formed via an electrochemical machining process. The open channels 155 may also be cast into the component when the component is formed.
As part of one preferred embodiment, the step of forming the elongated open channel 155 includes forming a plurality of parallel elongated open channels 155. In this case, the step of inserting the corresponding elongated electrode 150 having a directional bias may include inserting a corresponding plurality of elongated electrodes 150 having a directional bias into the plurality of parallel elongated open channels 155. As illustrated in
Pursuant to the present invention, another step of the fabrication process may include applying a coating 144 to enclose the machined channel 155. Additionally, at one end of the channel 155, a supply feed 145 may be formed per any conventional method. Opposite the supply feed 145 at the other end of the channel 155, a surface outlet 121 may be formed through the coating 144 that allows cooling fluid to exit the channel 155 once it passes therethrough.
Pursuant to another preferred embodiment, a method of the present invention includes the steps of: forming an open channel 155 having a non-overhanging cross-sectional profile; determining a removal area and a non-removal area within a wall of the formed open channel 155 that relate to a desired overhanging cross-sectional profile for a post-machining open channel 155; configuring an electrode 150 for insertion into the formed open channel 155 so that a directional bias of the electrode 150 aligns such that: a) an electrically exposed region 151 is opposite the removal area of the formed open channel 155, and b) an electrically insulated region 152 is opposite the non-removal area of the formed open channel 155; and then using the electrode 150 as a tooling device to electrochemically machine the formed open channel 155 from the non-overhanging cross-sectional profile to the desired overhanging cross-sectional profile. As stated, the non-overhanging cross-sectional profile of the formed open channel 155 is a configuration in which the mouth of the channel 155 has a width that is at least as wide as a greatest width within an interior of the formed open channel 155. Consistent with this, an overhanging cross-sectional profile includes a narrowed-mouth that has a width that is less than the widest section within the interior of the channel 155. Pursuant to one preferred embodiment, the overhanging profile includes a mouth having a width that is less than 50% of the greatest width within the interior of the channel 155. Accordingly, the non-removal area typically includes the area defined about the mouth of the formed open channel 155, whereas the removal area includes one or both of the sidewalls within an interior of the formed open channel 155.
The electrically biased electrode 150 may be as described above. In one preferred embodiment, as shown in
As portrayed in
Once the widening of the channel 155 is complete, the open channel 155 then may be enclosed via a coating 144, as shown in
It will be appreciated that the above described invention enables the cost-effective fabrication of microchannels that are very close to the surface of the component, which enhances cooling capabilities, while also having the narrowed-mouth profiles that enhances the robustness of a coating enclosure. That is, by enabling the efficient construction of channels having very narrow surface openings, the channel may be covered with the least amount of difficulty, thereby lowering manufacturing costs. Additionally, overall cooling effectiveness is improved by minimizing the thickness of the cover layer of coating.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
