In operation, air flows through compressor 12 and compressed air is supplied to combustor 20. Combustion gases 28 from combustor 20 propel turbine 14. Turbine 14 rotates rotor shaft 18, compressor 12, and electric generator 16 about a longitudinal axis 30.
Turbine bucket tip shroud 60 includes a platform 72 having seal rails 74 formed thereon. Seal rails 74 engage honeycomb seal insert 66 to cut or groove the honeycomb material 68 such that a desired clearance is defined between bucket tip shroud 60 and case shroud segment 64. Although turbine bucket tip shroud 60 shown in
In the exemplary embodiment of the invention, cutter teeth 80 are fabricated to be sacrificial cutter teeth. More specifically, cutter teeth 80 are temporary cutter teeth that are fabricated from a material designed to erode or corrode in the hot gas environment of turbine bucket 46. Optionally, cutter teeth 80 may be fabricated from a material that is designed to liberate after the initial hours of engine operation without causing damage to downstream gas path components. For example, in one embodiment, cutter teeth 80 may be fabricated from a corrosion susceptible ferrous material. Alternatively, cutter teeth 80 may be fabricated from a low chromium nickel alloy. Cutter teeth 80 may also be fabricated from a material such as a cold-rolled steel material that is susceptible to corrosion, but is strong enough to last long enough to groove honeycomb material 68. Cutter teeth 80 may be fabricated using a variety of known fabrication methods including laser cutting processes or water jet processes. Alternatively, cutter teeth 80 may be stamped using a progressive die process. After fabrication, cutter teeth 80 may be coated with an oil or other preservative to inhibit premature corrosion. In one embodiment, cutter teeth 80 may be coupled to seal rails 74 via spot welding. Alternatively, cutter teeth 80 may be attached to seal rails 74 by brazing or any other known coupling process. In another embodiment, the cutter teeth 80 are thermally sprayed to the seal rails 74. Because cutter teeth 80 are temporary, or become insignificant, cutter teeth 80 do not require machining to be removed from tip shroud 60.
In the exemplary embodiment, cutter teeth 80 are positioned proximate an outer end of seal rails 74. However, it is to be understood that cutter teeth 80 may be positioned at any point along seal rails 74. The temporary nature of cutter teeth 80 eliminates the need to strategically locate the cutter tooth mass. Moreover, with cutter teeth 80, tip shroud 60 is not exposed to a substantial increase in creep. Additionally, the temporary nature of cutter teeth 80 facilitates reducing turbulence in the gas flow path, as compared to cutter teeth that are prematurely mounted.
The above-described apparatus provides a cutter tooth that can be located anywhere along the seal rail without generating substantial creep issues. The cutter teeth form desired grooves in the honeycomb shroud during the initial hours of operation of the engine and are worn away or corrode away to become insignificant with continued engine operation. Optionally, the cutter tooth may be removed without extensive unit down time or excessive cost. The cutter tooth design facilitates improving maintainability of the turbine assembly and improving the operating efficiency of the gas turbine engine in a cost-effective and reliable manner.
Exemplary embodiments of cutter teeth for grooving a honeycomb shroud in a turbine engine are described above in detail. The apparatus is not limited to the specific embodiments described herein, but rather, the cutter teeth may be utilized independently and separately from other components described herein. For example, the cutter teeth may be applied to existing non-cutter tooth buckets without requiring casting tool changes. As such, honeycomb shrouds may be used in engines that do not currently use this technology. Moreover, cutter teeth may be scaled appropriately for different sized buckets.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.