Abstract:
A mask for performing high speed media finishing on airfoils includes a thicker portion and a thinner portion. The thicker portion is spaced further from an edge that will become a leading edge in the final airfoil than the thinner portion. The media is redirected by the thicker portion toward the edge where the finishing is to occur.

Description:
RELATED APPLICATIONS 
     This application claims priority to Singapore Application No. 200800203.2, filed Jan. 9, 2008. 
     BACKGROUND OF THE INVENTION 
     This application relates to a mask for a trailing edge of an airfoil. 
     Airfoils, such as used as compressor blades for gas turbine engines, are in part formed with a shearing operation. The leading edge of the airfoil is initially an unprofiled blunt edge after the shearing operation. 
     Typically, the airfoil and the rest of the blade are placed in a high speed media finishing centrifuge. Media is directed at high speed toward the leading edge such that the initial blunt edge is formed into a smoother rounded edge in a final desired shape that helps facilitate airflow. Essentially, small stones are moved at a high speed toward the leading edge to create the rounded surface. 
     In the prior art, the remainder of the airfoil which does not need rounding is masked by tape. Although the tape does protect the airfoil, the tape does not serve to direct the media toward the leading edge. Instead, the thin vinyl tape only serves to protect the non-repaired area from erosion by preventing contact from media. 
     SUMMARY OF THE INVENTION 
     In the disclosed embodiment of this invention, a mask for a trailing edge of an airfoil is formed to have a slot extending from an open end inwardly to an inner end. A thicker portion of the mask is spaced further away from the open end and thinner portions are spaced toward the open end. The thicker portion of the mask serves to redirect media stones toward the leading edge, thus creating a more efficient media finishing operation. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a blade and mask. 
         FIG. 2  is a schematic view of the mask and blade within a centrifuge. 
         FIG. 3  shows the removal of the mask from the blade. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary blade and mask system  20  is illustrated in  FIG. 1 . The blade  22  has a platform and root section  24 , and an airfoil  26 . In a final form, the airfoil  26  has a leading edge  28  and a trailing edge  27 . Initially, the airfoil  26  is formed from an initial metal medium using a shearing operation such that a blunt shearing edge  30  remains after the shearing operation. Subsequently, a media finishing operation is performed to round the shearing edge of the intermediate part to the final leading edge  28 . A mask  32  is mounted on the trailing edge  27  during this tumbling operation. As shown in the figure, the blade  22  is slipped into the pre-fabricated masking “fixture” by being moved into slot  38 . 
     As shown in  FIG. 2 , a centrifuge tumbling system  50  is used for a media finishing the airfoil  26 . The mask  32  has thicker portions  36  more removed from the leading edge  28  than thinner portions  34 , which are spaced toward the leading edge  28 . Stated another way, the mask is thicker at areas adjacent to the trailing edge, and thinner at locations spaced toward the leading edge. As shown, an outer periphery surface of the mask  32  is substantially curved at the thicker portions  36  and tapers inwardly towards the thinner portions  34 . The media is now directed more toward the leading edge  28  and the shearing edge  30  to be removed. As shown schematically, one media stone  99  has struck the outer periphery surface of the mask  32  adjacent to thicker portion  36 . A trajectory of the stone  99  will now be changed toward the leading edge  28 . 
     As can be appreciated from  FIGS. 2 and 3 , the slot  38  has an open end  39  extending inwardly to an inner end  41 . The trailing edge  27  of the airfoil extends into the inner end  41 . The thinner portions  34  can be seen to be spaced toward the open end  39  relative to the thicker portions  36 . As shown in the figures, the outer profile of the mask  32  from the thicker portions  36  leading to the thinner portions  34  is curved to guide the media  99  toward the blunt edge  30  to facilitate formation of the leading edge  28 . Shapes other than curves may be utilized. Further, the terms “thicker” and “thinner” are defined by the distance from the trailing edge  27  to an outer profile of the mask at the locations when the mask is received on an airfoil. While the thicker portion  36  may not redirect all of the media toward the blunt edge  30 , it will serve to redirect a good deal of the media towards the edge  30 . 
     The prior art tape, which was of a thin, uniform width, would not direct any more media toward the edge than what may have been directed in some other direction. 
     While a centrifuge tumbling system is disclosed, the mask can be utilized with other tumbling machines for media and stock removal and for rounding operations. As an example, vibratory tumbling machines could benefit from the disclosed mask. 
     As compared to typical media finishing operations, the media finishing utilizing such a mask is done much more efficiently, in that the media is concentrated on the area to be finished. 
     As shown in  FIG. 3 , once the media finishing operation is complete, the mask  32  can be easily removed from the airfoil  22 . The mask  32  is preferably formed of a suitable material, such as rubber or plastic. Generally, the mask can be made of a material that is flexible enough to mount the blade, but rigid enough not to deform under the media impact. In one embodiment, a rubber material that temporarily deforms to allow mounting and returns to original shape, and maintains its shape during the process was used. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.