This invention relates to gas turbine engine vane assemblies and, more particularly, to an improved method and apparatus for repairing a brazed vane assembly.
In a gas turbine engine of the type to which the present invention is directly applicable, working medium gases are burned in a combustion section and are expanded through a turbine section. Disposed within the turbine section are one or more rows of stator vanes which are adapted to direct the working medium gases in vane assemblies to a preferred angle of approach into a downstream row of rotor blades.
The vanes of the turbine have a limited life and are among the most susceptible of gas turbine engine components to damage. The medium gases directed across the vanes are extremely hot and contain corrosive constituents. For example, the initial row of stator vanes in a modern turbine is exposed to gases having temperatures well in excess of two thousand degrees Fahrenheit (2000.degree. F.). Corrosive constituents contained within the medium gases include unreacted oxygen and oxides of sulfur. Violent energy reactions upstream of the stator vanes make it nearly impossible to control the homogeneity of the medium gases approaching the vanes. Accordingly, the vanes do not wear evenly and individual vanes are likely to need repair or replacement before the entire set.
For ease of installation of the vanes and for aerodynamic performance considerations, it is conventional practice to form a row of stator vanes from vane assemblies comprising a plurality of individual airfoils each attached to an inner and outer platform. The vane assemblies are disposed in end-to-end relationship circumferentially around the working medium flow path. Paired airfoils such as those illustrated in FIG. 3 are commonly employed although each assembly may also comprise three or more airfoils.
Such vane assemblies are complex in design and are relatively costly to manufacture. Therefore, it is desirable to repair, rather than to replace such vane assemblies which may have been worn or damaged during gas turbine engine operation. It has been recognized that a substantial portion of such wear or damage occurs to the airfoils of the vane assembly, e.g. to the leading or trailing edge of the airfoil. However, the repair of the airfoils and/or platforms is complicated due to its configuration as these components remain attached to each other in the assembly. Therefore, accessibility to areas requiring repair is restricted.