A turbine shroud and a method for manufacturing the turbine shroud

FIELD OF THE INVENTION

0001The present invention generally involves a turbine shroud that may be located in a hot gas path of the turbine. Particular embodiments of the present invention may include a method for manufacturing the turbine shroud.

BACKGROUND OF THE INVENTION

0002Turbines are widely used in a variety of aviation, industrial, and power generation applications to perform work. Each turbine generally includes alternating stages of peripherally mounted stator vanes and rotating blades. The stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and the rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as steam, combustion gases, or air, flows along a gas path through the turbine to produce work. The stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work. Compressed working fluid that leaks around or bypasses the stator vanes or rotating blades reduces the efficiency of the turbine. As a result, the casing surrounding the turbine often includes an inner shell of shrouds or shroud segments that surround and define the outer perimeter of the gas path to reduce the amount of compressed working fluid that bypasses the stator vanes or rotating blades.

0003Continuous exposure of the turbine shroud to the gas path may result in excessive heating and/or failure of the outer surface of the turbine shroud, particularly in the case of turbines that operate with high temperature compressed working fluids, such as gas and steam turbines. Although several systems and methods have been developed to cool the turbine shroud, the ability to efficiently and cost-effectively cool the outer surface of the turbine shroud remains difficult. For example, <patcit id="pcit0001" dnum="US5957657A"><text>U.S. Patent 5,957,657</text></patcit> describes a method for forming a cooling passage in a turbine shroud that includes forming a groove in the outer surface of the turbine shroud and covering the groove with a plug to form the cooling passage along the outer surface. Although the outward facing cooling passage may be easily machined into existing shrouds, continuous exposure of the plug to the gas path and associated temperature changes in the gas path may weaken and/or damage the plug, possibly introducing damaging debris into the gas path. <patcit id="pcit0002" dnum="US7284954B"><text>U.S. Patent 7,284,954</text></patcit> describes a turbine shroud that includes a plurality of fluid passages machined into the turbine shroud, and a cooling fluid, such as compressed air, may be supplied through the various fluid passages to cool the outer surface of the turbine shroud. Although <patcit id="pcit0003" dnum="US7284954B"><text>U.S. Patent 7,284,954</text></patcit> overcomes the previous disadvantages of exposing a plug to the gas path, the machining required to form the fluid passages may be relatively difficult, time-consuming, and expensive to accomplish. In addition, although the fluid passages communicate the cooling fluid to the outer surface of the turbine shroud, the relatively high flow rate of the cooling fluid through the fluid passages under-utilizes the heat capacity of the cooling fluid. As a result, continued improvements in systems to cool turbine shrouds and methods of manufacturing turbine shrouds would be useful.

0004<patcit id="pcit0004" dnum="US7704039B1"><text>US 7,704,039 B1</text></patcit> discloses a blade outer air seal for use in a gas turbine engine. The blade outer air seal includes a plurality of first diffusion and impingement cooling air cavities separated by stiffener ribs. Each diffusion and impingement cavity is connected to a cooling air supply cavity through a first metering and impingement hole.

BRIEF DESCRIPTION OF THE INVENTION

0005The invention is defined by the appended claims. In the following, any method and/or apparatus referred to as embodiments but nevertheless do not fall within the scope of the appended claims are to be understood as examples helpful in understanding the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

0006A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: <ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref> is a simplified cross-section view of a turbine according to one embodiment of the present invention;</li><li><figref idref="f0002">Figure 2</figref> is an enlarged side cross-section view of the shroud shown in <figref idref="f0001">Figure 1</figref> according to one embodiment of the present invention;</li><li><figref idref="f0003">Figure 3</figref> is an axial cross-section view of the shroud shown in <figref idref="f0002">Figure 2</figref> taken along line A-A; and</li><li><figref idref="f0004">Figure 4</figref> is a top plan view of the shroud shown in <figref idref="f0002">Figure 2</figref>.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0007Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.

0008Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims.

0009<figref idref="f0001">Figure 1</figref> provides a simplified cross-section view of a portion of a turbine 10 according to one embodiment of the present invention. As shown in <figref idref="f0001">Figure 1</figref>, the turbine 10 may include stationary and rotating components surrounded by a casing 12. The stationary components may include, for example, stationary nozzles or stator vanes 14 attached to the casing 12. The rotating components may include, for example, rotating blades 16 attached to a rotor 18. A compressed working fluid 20, such as steam, combustion gases, or air, flows along a hot gas path through the turbine 10 from left to right as shown in <figref idref="f0001">Figure 1</figref>. The first stage of stator vanes 14 accelerates and directs the compressed working fluid 20 onto the first stage of rotating blades 16, causing the first stage of rotating blades 16 and rotor 18 to rotate. The compressed working fluid 20 then flows across the second stage of stator vanes 14 which accelerates and redirects the compressed working fluid 20 to the next stage of rotating blades (not shown), and the process repeats for each subsequent stage.

0010As shown in <figref idref="f0001">Figure 1</figref>, the radially inward portion of the casing 12 comprises a series of segmented shrouds 22 connected to the casing 12 that circumferentially surround and define the hot gas path to reduce the amount of compressed working fluid 20 that bypasses the stator vanes 14 or rotating blades 16. As used herein, the term "shroud" may encompass and include virtually any static or stationary hardware in the hot gas path exposed to the temperatures and pressures associated with the compressed working fluid 20. For example, in the particular embodiment shown in <figref idref="f0001">Figure 1</figref>, the shroud 22 is located radially outward of the rotating blades 16, while in other particular embodiments the shroud 22 may also be located radially inward of the rotating blades 16 or radially inward or outward of the stator vanes 14.

0011<figref idref="f0002">Figure 2</figref> provides an enlarged side cross-section view of the shroud 22 shown in <figref idref="f0001">Figure 1</figref> according to one embodiment of the present invention. <figref idref="f0003">Figure 3</figref> provides an axial cross-section view of the shroud 22 shown in <figref idref="f0002">Figure 2</figref> taken along line A-A, and <figref idref="f0004">Figure 4</figref> provides a top plan view of the shroud 22 shown in <figref idref="f0002">Figure 2</figref>. As shown in <figref idref="f0002 f0003 f0004">Figures 2-4</figref>, the shroud 22 generally comprises a body 24 having a plurality of sides. Specifically, front and rear sides 26, 28 and lateral sides 30 may be configured to connect to or mate with adjacent shrouds (not shown). For example, as shown most clearly in <figref idref="f0002">Figures 2</figref> and <figref idref="f0003">3</figref>, the front 26, rear 28, and/or lateral sides 30 may include a notch or indent 32 to accommodate a pin or segment (not shown). The pin or segment may fit in the notches or indents 32 between adjacent shrouds or casing 12 to flexibly hold the shroud 22 in place while still minimizing or preventing compressed working fluid 20 from escaping from the hot gas path between the adjacent shrouds. In addition, the body 24 may comprise an inner surface 34 and an outer surface 36 opposed to the inner surface 34. As used herein, the inner surface 34 refers to the surface of the body 24 facing away from the hot gas path, and the outer surface 36 refers to the surface of the body 24 facing toward the hot gas path and configured for exposure to the hot gas path. For example, as shown most clearly in <figref idref="f0002">Figures 2</figref> and <figref idref="f0003">3</figref>, the outer surface 36 of the body 24 may include a thermal barrier coating 38 or other heat resistant surface to protect the outer surface 36 from excessive temperatures present in the hot gas path.

0012The shroud 22 further includes one or more inward facing grooves or slots formed in or defined by the sides 26, 28, 30 and/or inner surface 34. As used herein, the terms "grooves" and "slots" are meant to be interchangeable and encompass or include any channel, crevice, notch, or indent defined by the sides 26, 28, 30 and/or inner surface 34. Specifically, the inward facing groove(s) or slot(s) may extend laterally across a width of the front and/or rear sides 26, 28 and/or axially along a length of one or both of the lateral sides 30. For example, as shown in <figref idref="f0002">Figures 2</figref> and <figref idref="f0003">3</figref>, first and second inward facing grooves or slots 40, 42 may be defined by the lateral sides 30 and/or inner surface 34 so that the inward facing grooves or slots 40, 42 extend axially along a length of the body 24. The inward facing grooves or slots 40, 42 may be formed in the sides 26, 28, 30 and/or inner surface 34 by conventional machining, such as by grinding the groove or slot 40, 42 into the sides 26, 28, 30 and/or inner surface 34. Alternately, the body 24 may be forged or cast around a suitable mold, thereby defining the inward facing grooves or slots 40, 42 at the desired location in the sides 26, 28, 30 and/or inner surface 34.

0013As seen most clearly in <figref idref="f0003">Figures 3</figref> and <figref idref="f0004">4</figref>, the shroud 22 further includes a seal connected, for example by welding or brazing, to the side 26, 28, 30 and/or inner surface 34 proximate to an opening 44 created by each inward facing groove or slot 40, 42. For example, a first seal 46 may cover the opening 44 in the first inward facing groove or slot 40, and a second seal 48 may cover the opening 44 in the second groove or slot 42. In this manner, each seal 46, 48 covers, spans, or extends across the opening 44 created by the inward facing grooves or slots 40, 42 to define fluid passages 50 in the respective grooves or slots 40, 42. Each seal 46, 48 may include one or more inlet ports 52 through the seal 46, 48 that provide fluid communication through the seal 46, 48 and into the proximate or associated fluid passage 50. In addition, the shroud 22 or body 24 may further include one or more outlet ports 54 through the sides 26, 28, 30 and/or outer surface 36 of the body 24. The outlet ports 54 may be located along the side 26, 28, 30 proximate to or associated with each fluid passage 50 to provide fluid communication from the fluid passage 50 through the proximate or associated side 26, 28, 30 and/or outer surface 36. In this manner, the combination of inlet ports 52 and outlet ports 54 may provide a continuous fluid pathway through each seal 46, 48, into the proximate or associated fluid passage 50, and out of the proximate or associated side 26, 28, 30 or outer surface 36.

0014As shown most clearly in <figref idref="f0004">Figure 4</figref>, a fluid may be provided to each shroud 22 to remove heat from or cool the shroud 22. The fluid may comprise, for example, compressed air, an inert gas, or steam, and the present invention is not limited to any particular fluid used to cool the shroud 22. The fluid may first impact the center portion of the body 24 to provide impingement cooling to the bulk of the body 24. The fluid may then flow through one or more inlet ports 52 to pass through the seals 46, 48 and into the fluid passages 50 to remove heat from the sides 26, 28, 30 of the body 24. For example, as shown at the bottom of <figref idref="f0004">Figure 4</figref>, inlet ports 52 arranged along the second seal 48 may direct the fluid through the second seal 48 and against the side 30 of the body 24 to provide additional impingement cooling to the side 30 of the body 24. The fluid may then flow through the fluid passage 50 to remove additional heat from the side 30 and bottom surface 36 of the body 24 through convective cooling before exiting the fluid passage 50 through the outlet ports 54. Alternately, or in addition, as shown at the top of <figref idref="f0004">Figure 4</figref>, the inlet port 52 located at one end of the first seal 46 may direct the fluid through the first seal 46 into the fluid passage 50, and the fluid may then flow through the fluid passage 50 to remove heat from the side 30 of the body 24 through convective cooling before exiting the fluid passage 50 through the outlet ports 54.

0015It is anticipated that the various embodiments of the shroud 22 shown in <figref idref="f0002 f0003 f0004">Figures 2-4</figref> may be manufactured at lower costs than previous cast designs. Specifically, the body 24 of the shroud 22 may be cast or forged to form the front side 26, rear side 28, lateral sides 30, inner surface 34, and the outer surface 36, as previously described. Concurrently or separately, the inward facing grooves or slots 40, 42 may be defined in the sides 26, 28, 30 and/or inner surface 34 by machining, casting, or forging, and the seals 46, 48 may be welded or brazed to the sides 26, 28, 30 and/or inner surface 34 so that the seals 46, 48 extend across each groove or slot 40, 42 to define the proximate or associated fluid passage 50 therein. The inlet and or outlet ports 52, 54 may be readily machined into the respective seals 46, 48 and/or sides 26, 28, 30 and/or outer surface 36, for example by drilling. In this manner, the shroud 22 may be readily manufactured to include the desired fluid passages 50 that provide cooling to the sides 26, 28, 30 and outer surface 36, and the seals 46, 48 forming the fluid passages 50 will not be exposed to the hot gas path.

0016This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims.