Abstract:
A disk made of a first material has a groove in which a blade made of a second material is retained. A strip is placed between the blade and the disk to minimize rubbing damage to the blade and the disk and an insulating material is place between the rub strip and the blade for minimizing damaging responses of the blade to galvanic forces created by rubbing of the first material and the second material.

Description:
BACKGROUND 
     Components of gas turbine engines are subject to wear and damage. Even moderate wear and damage in certain components may interfere with optimal operation of the engine. Particular areas of concern involve the airfoils of various blades and vanes. Wear and damage may interfere with their aerodynamic efficiency, produce damaging dynamic force and imbalances, and even, in more extreme cases, structurally compromise or damage parts. 
     Because blades tend to be forced outwardly within a rotor due to centrifugal forces during operation, wear between interlocking portions of a blade and the rotor in which the blade is disposed is an area of interest. 
     SUMMARY 
     According to an exemplar disclosed herein, a disk made of a first material has a groove in which a blade made of a second material is retained. A strip is placed between the blade and the disk to minimize rubbing damage to the blade and the disk and an insulating material is place between the rub strip and the blade for minimizing damaging responses of the blade to galvanic forces created by rubbing of the first material and the second material. 
     According to a further exemplar disclosed herein, a blade made of a first material for retention within a disk made of a second material has a strip placed thereon for minimizing rubbing damage to the blade from the disk, and an insulating material is disposed between the rub strip and the blade for minimizing response of the blade to galvanic forces. 
     According to a still further exemplar disclosed herein, a die has an electroforming body having a shape conforming to a portion of a shape of a root of a blade. The portion conforms to areas of the root in which rubbing between the blade and a disk occurs. The body has a non-conductive strip to create a gap in a part electroformed on the die so that the part may be easily removed from the die. 
     According to a still further exemplar disclosed herein, rub strip for use with a disk made of a first material and having a groove that holds a blade root made of a second material, has a strip having a contour closely mimicking a contour of the blade root and the groove for placement between the blade root within the groove, the strip minimizing rubbing damage to the blade, and an insulating material disposed on a inner surface of said strip between the rub strip and the blade for minimizing damaging responses of the blade to galvanic forces between the first material and the second material. 
     These and other features of the disclosed examples 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 rotor having a blade seated therein. 
         FIG. 2  is a cross-sectional view taken along the lines  2 - 2  of  FIG. 1  partially cutaway. 
         FIG. 3  is a cutaway view of the blade and rotor taken along the lines  2 - 2  of  FIG. 2 . 
         FIG. 4  shows a view of the root structure of the blade of  FIG. 3 . 
         FIG. 5  shows a perspective view of the blade of  FIG. 3 . 
         FIG. 6  is a view of an example die. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a disk  201  for use in a gas turbine engine, not shown, having an annular shape, a front face  205 , a rear face  207  and an outer surface  209  is shown. Grooves  211 , which may follow a rectilinear path through the outer surface  209  of the disk  201  from the front face  205  to the rear face  207 , extend at an angle to an axial centerline A. Though grooves  211  form a dovetail (see  FIG. 3 ) shape  213 , other shapes that secure a blade  203  to the disk  201  are contemplated herein. The disk may be made of titanium or an alloy thereof. 
     As seen in  FIGS. 2 and 3 , a blade  203  has a root portion  214  placed within the grooves  211  of the disk  201 . The root portion  214  has a contour  216  that closely mimics the dove tail shape  213  of the grooves  211  for retention of the blade  203  therein. Though the fit between the contour  216  and the shape  213  is close to an interference fit, space between the root portion  214  and the groove  211  exists due to imperfection in manufacturing techniques and to enable the blade  203  to be inserted and removed efficiently. The root portion  214  has a tab  219  depending therefrom towards the axial center line A that abuts a shoulder  212  in the disk  201  to position properly and limit the travel of the blade  203  during insertion of the blade  203  into the groove  211 . A split lock ring  222  is placed behind the blades and the disk  201  to minimize forward movement of the blades  203 . The tabs  219  also minimize rearward movement of the blades. The blade  203  may be constructed of aluminum or other alloys. 
     Referring now to  FIGS. 3 ,  4  and  5 , the blade  203  includes a platform  221  between the root portion  214  and an airfoil  215 . After installing the blades  203  into the grooves  211  of the disks  201 , the platform  221  serves the fill in gaps  223 ,  224  and  225  which are exaggerated for ease of viewing. The platform  221  defines a small portion of the inner boundary of the core engine flow path (not shown). As seen in  FIG. 3 , the platforms  221  are flush with the outer surface  209  of the disk  201 . Though the gap  225  may be small, during operation, as the disk spins, centrifugal forces move the blades  203  radially outwardly away from centerline A so that gap  225  is eliminated and potentially damaging rubbing between the root portion  214  and the disk  201  may occur. 
     Referring now to  FIGS. 4 ,  5  and  6 , a rub strip  230 , which may be electroformed, as will be discussed hereinbelow, is disposed on the contour  216 , a bottom portion  235 , and the tab  219  of the root portion  214 . The rub strip  230  closely mimics the shape of the contour  216 , a bottom portion  235 , and the tab  219  of the root portion  214  so that the gap  225  is minimized. During operation, the rub strip contacts the disk  201  and minimizes damage to the root portion  214  of the blade  203 . 
     A bonding agent  300 , such as an epoxy glue as is known in the art, is used to electrically isolate the rub strip  230  from the blade  203  and its root portion  214 . The bonding agent  300  minimizes galvanic reaction caused by moisture and rubbing of dissimilar metals between the rub strip  230  and the root portion  214  that might tend to degrade the root portion  214 . The bonding agent  300  also minimizes rub strip  230  slippage. 
     Referring to  FIG. 6 , a die  250  shaped like the contour  216  of the blade  203  is plated by using electric current to reduce cations of a desired material to coat the die  250 . The die  250  may be made of a conductive nickel titanium and the layer of material deposited thereon forms a rub strip  230 . A nano-nickel/cobalt or a conventional nickel material, or the like could be a suitable material for electroplating on the die  250 . The rub strips  230  provide wear resistance and corrosion protection. The rub strips have complementary halves  231 ,  232  formed on the die  250  so that the halves  231  and  232  are easily removed from the die  250 . The halves are created by positioning a non-conductive strip  255  on the bottom of the die to create a gap  260  between the halves. Because the die  250  mimics that contour  216 , the halves  231  and  232  are easily glued to the root portion  214 . 
     If a blade  203  is placed within groove  211  as the disk  201  spins, the blade is moved radially outwardly from centerline A and the rub strip halves  231 ,  232  are brought into contact with the grooves  211 . The rub strip halves  231 ,  232  absorb rubbing to minimize fatigue and wear within the blade root. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.