Abstract:
A method of improving an erosion resistance at the leading edge of a compressor blade includes: a) cleaning a leading edge portion of the compressor blade airfoil; and b) attaching one or more erosion or corrosion-resistant shims to the leading edge portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to turbine technology and, more specifically, to an article and a method for mitigating damage caused by compressor blade leading edge erosion and/or corrosion. 
         [0002]    Compressor blade leading edge erosion/corrosion is a common problem in turbine engines. Turbine blades, and particularly the leading edges of the turbine compressor blades or airfoils, are particularly susceptible to erosion and/or corrosion resulting from exposure to harsh environments. Repair and/or replacement of damaged turbine blades requires costly downtime that may not coincide with normal service intervals. 
         [0003]    It would be advantageous, therefore, to develop techniques or processes to mitigate the incidence or damage caused by erosion and/or corrosion of blade leading edges. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In accordance with one exemplary but nonlimiting embodiment, the invention relates to a compressor blade comprising an airfoil portion and a mounting portion; the airfoil portion having leading and trailing edges, the leading edge having an erosion or corrosion-resistant shim attached thereto. 
         [0005]    In another aspect, the invention relates to a method of improving erosion or corrosion resistance at the leading edge of a compressor blade airfoil comprising: a) cleaning a leading edge portion of the compressor blade airfoil; and b) attaching one or more erosion or corrosion-resistant shims to the leading edge portion. 
         [0006]    The invention will now be described in more detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a compressor blade in accordance with an exemplary embodiment of the invention; and 
           [0008]      FIG. 2  is a section taken along the line  2 - 2  in  FIG. 1 , but with the shim exaggerated in scale. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    With reference to  FIG. 1 , a vane or blade  10 , e.g., a turbine compressor blade, includes an airfoil portion  12  and a dovetail mounting portion  14 . The airfoil portion  12  has a leading edge  16 , a trailing edge  18 , a pressure side  20  and a suction side  22 . 
         [0010]    It is the leading edge  16  that is most susceptible to erosion and/or corrosion due to incoming air flow (containing, for example, dry particles, salt fog, etc.) at the compressor inlet. 
         [0011]    In accordance with a non-limiting exemplary embodiment of this invention, one or more shims  24  may be applied to the leading edge  16  of the airfoil portion. With further reference to  FIG. 2 , the shim  24  substantially encloses the leading edge  16 , extending into both the pressure and suction sides  20 ,  22  of the airfoil. Note that in  FIG. 2 , the shim is shown in greatly exaggerated scale simply to facilitate an understanding of the invention. One shim may extend along part or substantially the entire length of the leading edge, or alternatively, plural shim segments may be employed to reduce shear strain at the airfoil/shim interface. 
         [0012]    In a preferred configuration, the shim  24  has a thickness in a range of from 1 to 30 mils. The shim or shims may be composed of corrosion-resistant compositions including Cr-rich materials such as Ni-25Cr sheet; Al-rich or Ti-rich materials. Alternatively, hard, erosion resistant materials such as TiN, Ti/TiN, TiN/CrN, NiCrWC, etc. may be employed. The shim or shims could also be constructed of an erosion-resistant polymeric material such as polypropylene, or a corrosion-resistant tape, e.g., 3M Protective Polyurethane Tape, having a thickness of about 1-10 mils. It will be appreciated that the shim or shims may also be constructed of a suitable metal coated with an erosion or corrosion resistant material, i.e., using a powder form of the compositions mentioned above. 
         [0013]    The shim or shims  24  in metal form may be attached to the leading edge  16  by any of several known techniques such as, for example, welding, brazing, soldering and/or by an adhesive film. One suitable adhesive film is available under the name 3M Structural Adhesive Tape. Additional adhesive material shown at  26 ,  28 , may be applied along the edges  30 ,  32  of the metal shim in order to smooth out shim edges where they interface with the airfoil. 
         [0014]    In any event, thermal expansion characteristics of the airfoil and shim should be matched to the extent possible to reduce the amount of cyclic straining, noting that in the front end of the machine temperature swings are relatively mild, i.e., from about 70° F. to about 400° F. In this regard, low temperature adhesive for attaching the metal shims, or for use as the shims themselves, are advantageous in that no cutting is required, thus preserving the properties of the base metal. 
         [0015]    Prior to the attachment of one or more shims  24 , surface preparation at the leading edge  16  is required through milling, shot-peening, grit blasting, vibratory finishing or combinations of the above. For attachment of a shim by means of a high pressure adhesive tape such as the 3M structural adhesive tape mentioned above, additional preparation is required. For example, the facing surfaces of the shim and the airfoil leading edge may be rinsed, alkaline-degreased, etched, dried, primed and cured. After the shim is applied by means of the adhesive tape, the blade may be placed in an autoclave, for example, for curing the adhesive. 
         [0016]    When utilizing a low temperature adhesive such as the 3M Protective Polyurethane Tape as the shim, the facing surfaces simply need to be rinsed and degreased prior to application of the tape. 
         [0017]    It is contemplated that the shims described herein would be added to blades at the time of manufacture. On the other hand, they could be retrofitted to existing blades so long as the blades are in acceptable condition. 
         [0018]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.