Methods and apparatus for fabricating turbine engines

A method for fabricating a turbine bucket and an apparatus facilitate reducing tip shroud creep. The method includes providing a turbine bucket that includes a tip shroud including at least one seal rail. The method also includes coupling at least one cutter tooth to the tip shroud, wherein the at least one cutter tooth is fabricated from an abradable material that enables the at least one cutter tooth to be removed from the tip shroud during operation of the turbine engine.

BACKGROUND OF THE INVENTION

This invention relates generally to turbine engines and, more particularly, to methods and apparatus for constructing turbine bucket cutter teeth.

At least some known turbine engines include at least one stator assembly and at least one rotor assembly that includes at least one row of circumferentially-spaced turbine blades or buckets. The blades extend radially outward from a platform to a tip. A plurality of static shrouds coupled within the stator assembly abut together to define a flow path that extends substantially circumferentially around the rotor assembly. A seal may be provided at the tip of the buckets to facilitate enhancing turbine efficiency and performance.

At least some known rotor assemblies include a tip shroud formed on the outboard end of each bucket. Known tip shrouds each include a shelf and a sealing rail. A honeycomb structure may surround the tip shroud, and in such embodiments, the sealing rail may include one or more cutter teeth that cut through some of the honeycomb material to establish a tip clearance. Minimizing tip clearances facilitates improving turbine performance, but the tip clearance must still be sized large enough to facilitate rub-free engine operation through the range of available engine operating conditions.

Known tip shroud areas, may be vulnerable to creep damage arising when the cutter tooth mass is exposed to high operating temperatures and rotational stresses that may be present during engine operation. To facilitate reducing creep issues, at least some turbine assemblies, centrally locate cutter teeth relative to each bucket. However, because the cutter teeth serve no purpose after the honeycomb structures have been cut through and the tip clearances established, it would be advantageous if the cutter teeth could be removed after the initial hours of operation of the engine. However, with known rotor assemblies, to remove the cutter teeth, the engine would have to be shut down and the rotor assembly removed to enable a user to remove the cutter teeth from the engines.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for fabricating in a turbine bucket to facilitate reducing tip shroud creep is provided. The method includes providing a turbine bucket that includes a tip shroud including at least one seal rail. The method also includes coupling at least one cutter tooth to the tip shroud, wherein the at least one cutter tooth is fabricated from a consumable material that enables the at least one cutter tooth to be removed from the tip shroud during operation of the turbine engine.

In another aspect, an airfoil bucket for a gas turbine engine is provided. The bucket includes a tip shroud extruding from the airfoil and at least one cutter tooth extending from the tip shroud. The cutter tooth is fabricated from a material that is configured to wear away during operation of the gas turbine engine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration of an exemplary gas turbine engine10coupled to an electric generator16. In the exemplary embodiment, gas turbine system10includes a compressor12, a turbine14, and generator16arranged in a single rotor or shaft18. In an alternative embodiment, shaft18is segmented into a plurality of shaft segments, wherein each shaft segment is coupled to an adjacent shaft segment to form rotor shaft18. Compressor12supplies compressed air to a combustor20wherein the air is mixed with fuel supplied via a stream22.

In operation, air flows through compressor12and compressed air is supplied to combustor20. Combustion gases28from combustor20propel turbine14. Turbine14rotates rotor shaft18, compressor12, and electric generator16about a longitudinal axis30.

FIG. 2is a schematic illustration of a portion of a high pressure turbine, such as turbine14, that may be used with turbine engine10. Turbine14includes a plurality of stages40which each include a rotating row of turbine blades or buckets46and a stationary row of stator vanes48. Turbine buckets46are supported by rotor disks50coupled to a rotor shaft, such as rotor shaft18. A turbine casing52extends circumferentially around turbine buckets46and stator vanes48, such that stator vanes48are supported by casing52.

FIG. 3is an enlarged portion of turbine14shown inFIG. 2and taken along area3. Specifically,FIG. 3illustrates an exemplary tip shroud60positioned radially outward from a turbine bucket46. A plurality of case shroud segments64are coupled to casing52such that each segment64is radially outward from a row of turbine blades46within a respective turbine stage40. In the exemplary embodiment, each shroud segment64includes a honeycomb seal insert66including a honeycomb seal material68. Honeycomb seal insert66facilitates reducing gas leakage between bucket tip shroud60and case shroud segment64. Moreover, honeycomb seal insert66facilitates enhancing the rub tolerance between bucket tip shroud60and case shroud segment64. In the exemplary embodiment, shroud case segment64also includes seal rails70that also facilitate reducing gas leakage between case shroud segment64and bucket tip shroud60.

Turbine bucket tip shroud60includes a platform72having seal rails74formed thereon. Seal rails74engage honeycomb seal insert66to cut or groove the honeycomb material68such that a desired clearance is defined between bucket tip shroud60and case shroud segment64. Although turbine bucket tip shroud60shown inFIG. 3including only two seal rails74, it should be understood turbine tip shroud60may be fabricated with more or less than two seal rails74. Similarly, case shroud segment64may be fabricated with any number of radially seal rails70. For example, in one embodiment, case shroud segment64does not include any seal rails70.

FIG. 4is a schematic top plan view of turbine bucket tip shroud60. Turbine bucket46includes an airfoil78(shown in phantom outline). Turbine bucket tip shroud60is formed at a tip of airfoil78. To facilitate cutting or grooving honeycomb material68(shown inFIG. 3), seal rails74are provided with cutter teeth80. In an exemplary embodiment, at least one cutter tooth80is provided on each side of seal rail74. Cutter teeth80create grooves within honeycomb material68during operation of engine10. Cutter teeth80may be provided on one or more stages40of turbine14(shown inFIG. 2). In the exemplary embodiment, cutter teeth80are provided on at least one of the last stages40of turbine14.

In the exemplary embodiment of the invention, cutter teeth80are fabricated to be sacrificial cutter teeth. More specifically, cutter teeth80are temporary cutter teeth that are fabricated from a material designed to erode or corrode in the hot gas environment of turbine bucket46. Optionally, cutter teeth80may 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 teeth80may be fabricated from a corrosion susceptible ferrous material. Alternatively, cutter teeth80may be fabricated from a low chromium nickel alloy. Cutter teeth80may 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 material68. Cutter teeth80may be fabricated using a variety of known fabrication methods including laser cutting processes or water jet processes. Alternatively, cutter teeth80may be stamped using a progressive die process. After fabrication, cutter teeth80may be coated with an oil or other preservative to inhibit premature corrosion. In one embodiment, cutter teeth80may be coupled to seal rails74via spot welding. Alternatively, cutter teeth80may be attached to seal rails74by brazing or any other known coupling process. In another embodiment, the cutter teeth80are thermally sprayed to the seal rails74. Because cutter teeth80are temporary, or become insignificant, cutter teeth80do not require machining to be removed from tip shroud60.

In the exemplary embodiment, cutter teeth80are positioned proximate an outer end of seal rails74. However, it is to be understood that cutter teeth80may be positioned at any point along seal rails74. The temporary nature of cutter teeth80eliminates the need to strategically locate the cutter tooth mass. Moreover, with cutter teeth80, tip shroud60is not exposed to a substantial increase in creep. Additionally, the temporary nature of cutter teeth80facilitates 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.