Metal working – Method of mechanical manufacture – Impeller making
Reexamination Certificate
1999-08-12
2001-01-16
Cuda, I (Department: 3726)
Metal working
Method of mechanical manufacture
Impeller making
Reexamination Certificate
active
06173491
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for replacing airfoils on turbine vanes, and more particularly, to a method of replacing airfoils such that they can be upgraded and/or repositioned within a turbine vane platform.
Components of gas turbine engines, especially those positioned within the hot section of the engine, are exposed to a harsh operating environment. Extreme operating temperatures, accompanied by repeated temperature cycling during engine warm-up, operation and cool-down can quickly deteriorate engine components. These components include HPT (high-pressure turbine) vane segments which can become damaged or worn such that they require repair or replacement.
A turbine engine vane segment is typically comprised of an outer and inner platform, between which one or more airfoils are positioned. The airfoils are either cast as a single unit with one or both of the platforms or are separately welded or brazed to the platforms in the form of a component assembly. Some turbine vanes are complex castings, comprising two, three or more airfoils integrally cast to the inner and outer platforms. Another form of turbine vanes is paired assemblies. A paired assembly is a vane in which a single airfoil is integrally cast between two platforms. Two of these castings are brazed or welded along mateface joints to create a doublet vane assembly.
It would be desirable to be able to modify these vanes from a single casting or welded or brazed pair to a multi-piece assembly consisting of individual airfoil segments attached to inner and outer platforms to facilitate subsequent vane repairs and airfoil replacement.
Advances in material science often provide improved materials for use as airfoil members, and may provide airfoils having sizes which differ from those used in existing vanes. In addition, airfoil positioning within the vane, i.e. location on the vane segment platform, might require adjustment. For example, an adjustment to the nozzle opening area between adjacent vanes (hereinafter the “class area”) may be required or desirable.
Components in gas turbine engines are air cooled and are fabricated from expensive materials. These components are also costly to assemble. As a result, it is desired to be able to efficiently repair the damage, while providing for upgraded components and materials within each vane, such that as much of the original materials as possible can be reused.
Conventional airfoil replacement repair procedures involve separating the platforms by cutting the airfoils therefrom. This procedure retains a stub on each platform where the airfoils are cut out. The replacement airfoils are then typically welded to the stubs using electron beam welding techniques. Because the new airfoils must be positioned on the existing stubs, the positioning of the new airfoils is restricted. Also, because airfoil stubs are retained, complete refurbishment of the platform gaspath surfaces by an automated process is not possible. The irregularly contoured stub protruding from each platform requires that brazing and contouring of the platforms be done by hand. It is desirable, however, to automate as many refurbishment operations as possible in order to minimize repair prices and time.
Another airfoil replacement procedure has been applied to HPT turbine vanes that were originally created as component assemblies as described above, in which the airfoil castings are brazed into pockets in the separately cast platforms. When repairing a component assembly vane, the entire assembly can be heated to a temperature sufficient to melt the brazed joint, allowing the components to be pulled apart. This procedure has been described in U.S. Pat. No. 5,444,911 to Goodwater et al. Alternatively, the airfoil can be cut from the platforms, followed by subsequent machining operations to restore the platform pocket. This alternative procedure has been described in U.S. Pat. No. 5,813,832 issued to Rasch et al. However, using either procedure, the replacement airfoil is limited to placement within the existing socket in the platform, thereby preventing the relocation of airfoils, i.e. class size alteration, or the use of airfoils which are of a different size from the original.
SUMMARY OF THE INVENTION
The present invention provides a method for refurbishing turbine engine vanes in which the airfoils are removed and replaced. The original configuration of the vanes is modified from a single casting or welded pair to a multi-piece component assembly comprising individual airfoil segments attached to the inner and outer platforms. The component assembly allows replacement of airfoils and/or platforms with improved castings. The improvements can be in the form of improved alloys, improved physical geometry, or both. The method of the present invention also allows modifications to be made in the vane class area without the need to modify the airfoil contour by brazing or other contour alteration processes.
For example, directionally solidified or single crystal replacement castings can be easily incorporated into the new vane assembly using the method of the present invention. Also, removing the airfoil stubs present after separating the vane platforms and sealing cooling holes and other passages in the platforms facilitates the automation of gaspath surface contouring operations. The present invention also makes subsequent repairs on the vane component assembly easier because performing airfoil replacement on a component assembly vane is simpler than performing this repair on a cast assembly. The method of the present invention therefore reduces repair, time and costs, and allows for component upgrade and vane performance optimization.
According to the present invention a method of repairing a turbine vane having at least one platform and at least one airfoil, the at least one platform having at least one opening, is provided in which the at least one platform is separated from the at least one airfoil, the openings in the at least one platform are sealed, at least one airfoil socket is cut into the at least one platform, and the vane is reassembled from the at least one platform and at least one replacement airfoil.
The present invention also provides a method of repairing a turbine vane having at least one platform and at least one airfoil, each of the platforms having at least one opening, in which the at least one platform is separated from the at least one airfoil, the openings in the at least one platform are plugged, a gaspath surface to the at least one platform is automatically restored, at least one airfoil socket is cut into the at least one platform, and the vane is reassembled from the at least one platform and at least one replacement airfoil.
In addition, the present invention provides a method of repairing a turbine vane having at least one platform and a plurality of airfoils, the distance between two of the plurality of airfoils defining a first class area, each of the platforms having at least one opening, in which the at least one platform is separated from the plurality of airfoils, at least one of the openings in the at least one platform is sealed, the openings including a plurality of airfoil openings corresponding to the plurality of airfoils. At least one airfoil socket is cut into the at least one platform, at least one of the airfoil sockets being cut at a location different from a corresponding airfoil opening. The vane is then reassembled from the at least one platform and at least one replacement airfoil.
Other features and advantages of the present invention will become apparent from the following description of the embodiments of the invention which refer to the accompanying drawings.
REFERENCES:
patent: 4883216 (1989-11-01), Patsfull
patent: 5197190 (1993-03-01), Coolidge
patent: 5269057 (1993-12-01), Mendham
patent: 5444911 (1995-08-01), Goodwater et al.
patent: 5522134 (1996-06-01), Rowe et al.
patent: 5554837 (1996-09-01), Goodwater et al.
patent: 5690469 (1997-11-01), Deel et al.
patent: 5732468 (1998-03-01), Galley et al.
patent:
Goodwater Frank
Kang David
Bittman Mitchell D.
Chromalloy Gas Turbine Corporation
Cuda I
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