Patent Application
20100054932
The invention relates to components in the hot working gas path of a gas turbine, and particularly to turbine shroud surfaces on platforms of turbine vanes, including metal and ceramic matrix composite (CMC) surfaces.
Gas turbines have a compressor assembly, a combustor assembly, and a turbine assembly. The compressor compresses ambient air, which is then channeled into the combustor, where it is mixed with a fuel. The fuel and compressed air mixture is ignited, creating a working gas that may reach temperatures of 2500 to 2900° F. (1371 to 1593° C.). This gas then passes through the turbine assembly. The turbine assembly has a rotating shaft holding a plurality of circular arrays or “rows” of rotating blades. The turbine assembly also has a plurality of circular arrays of stationary vanes attached to a casing of the turbine. Each row of blades is preceded by a row of vanes to direct the working gas at an optimum angle against the blades. Expansion of the working gas through the turbine assembly results in a transfer of energy from the working gas to the rotating blades, causing rotation of the shaft.
Each vane may have an outer platform connected to a radially outer end of the vane airfoil for attachment to the turbine casing, and an inner platform connected to the inner end of the vane airfoil. The outer platforms for a given row of vanes are mounted adjacent to each other as segments in a circular array, defining an outer shroud ring. The inner platforms are likewise mounted adjacent to each other in a circular array, defining an inner shroud ring. These outer and inner shroud rings define a flow channel between them that channels the working gas over the stationary airfoils.
The vane assemblies may include passages for a cooling fluid such as air. However, the surfaces of the vane assemblies exposed to the working gas are subjected to high operational temperatures and thermal stresses. This can cause cracks in the vane platforms. Typically, each vane airfoil and its two platforms are formed together as a unitary structure, so damage to a platform may require replacement of an entire vane assembly, even when the airfoil is still in a serviceable condition.
The invention is explained in the following description in view of the drawings that show:
A retainer 66 is attached to the cooled face 48 of the vane platform 26. For example, the retainer 66 may be attached by bolts 68 through holes 70, 71 in the retainer to a vane carrier attachment flange 72, or by another attachment mechanism. The retainer 66 contacts each insert 54, 56 to prevent sliding of the insert in its cage 58, 60. The retainer 66 may be formed of a steel or superalloy plate with a protruding lock mechanism 74, 76 (
Each cage 58, 60 has a working face frame portion 59 and keyways 78 that guide the inserts 54, 56 into and out of the cage. Each insert 54, 56 may have corresponding keys 80 that contact the keyways 78. The keys 80 may be depressed on the working gas side of the inserts as shown, so that the working gas faces 55, 57 of the inserts 54, 56 are flush with the working gas face 44 of the vane platform 26.
The insert plates 54, 56 may be made of a ceramic matrix composite (CMC) material, such as a silicone-carbide CMC. In one embodiment, the inserts can be made of an oxide-based hybrid CMC system, such as disclosed in U.S. Pat. Nos. 6,676,783, 6,641,907, 6,287,511, and 6,013,592. Alternately, the inserts may be made of metal, such as a single crystal advanced alloy. For example, the inserts may be made of the same material as the platform cages 58-60 in which they are received, such as IN939 alloy and ECY768 alloy. The inserts may be made of a material that may or may not have a greater resistance to heat compared to the material of the cages. For example, the inserts 34 may be made from an inexpensive material, so that the cost of a replacement insert would be minimized.
The insert plates 54, 56 are only illustrated on the outer platform 26, but they may also be installed on the inner platform 24. An inner boss or flange such as the illustrated inner flange 51 may be used for attachment of an inner retainer for locking such insert plates on the inner platform. The inserts can be used in selected areas of the inner and/or outer shroud rings 25, 27 where failures or damage has been known to occur, especially in the first row of vanes after the combustor, among other locations. If an insert becomes damaged during engine operation, the insert can be easily replaced, and the platforms 24, 26 and the airfoil 22 can be reused. As a result, the life of the vane/platform assembly is extended. The inserts may be made of refractory materials such as CMC that have a lower thermal conductivity than metal, thus reducing cooling requirements compared to all-metal platforms.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
