Abstract:
A method of repairing a turbomachine rotor wheel including a first outer circumferential edge extending to a second outer circumferential edge through a circumferential surface, a dovetail interface extending across the outer circumferential surface between the first and second outer circumferential edges, and a bucket mounted to the dovetail interface includes identifying a defect on one of the first and second outer circumferential edges of the rotor wheel adjacent the bucket, securing the bucket in the dovetail interface to substantially constrain axial movement, and removing a portion of the one of the first and second outer circumferential edges to remove the defect.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to a method and apparatus for repairing a gas turbine rotor wheel. 
         [0002]    In general, turbomachines include a number of stages each having an associated rotor wheel. The rotor wheel includes an outer circumferential surface that supports a plurality of buckets or blades. The blades are secured to the rotor wheel through a dove tail interface provided on the outer circumferential surface. The dovetail interface includes a plurality of acute corners that define a dove tail slot that extends axially along the circumferential surface. Each bucket includes a base portion having a mating dovetail member. During operation, the rotor wheel rotates at very high speeds and is subjected to high thermal gradients. The high speeds and thermal gradients create stresses at the acute corners of the dovetail interface. Over time, cracks develop near the acute corners as a result of the stresses. 
         [0003]    Conventional methods for repairing a rotor disk require removal of the blades and allow repair of cracks having a length of less than 0.25 inches (6.35 mm) In cases where the crack is greater than 0.25 inches, no repair option is presently available. As such, in the event a crack of greater than 0.25 inches is found, the rotor wheel must be scrapped. Scrapping a rotor wheel leads to a direct increase in operational cost of the turbomachine due to down time and service time required to dissemble the associated turbine stage, remove the rotor wheel, dissemble the blades, install the blades on a new rotor wheel and subsequently install the new rotor wheel in the turbomachine. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the exemplary embodiment, a method of repairing a turbomachine rotor wheel including a first outer circumferential edge extending to a second outer circumferential edge through a circumferential surface, a dovetail interface extending across the outer circumferential surface between the first and second outer circumferential edges, and a bucket mounted to the dovetail interface, includes identifying a defect on one of the first and second outer circumferential edges of the rotor wheel adjacent the bucket, securing the bucket in the dovetail interface to substantially constrain axial movement, and removing a portion of the one of the first and second outer circumferential edges to remove the defect. 
         [0005]    According to another aspect of the exemplary embodiment, a rotor wheel repair apparatus includes a first rotor wheel ring having a first outer surface and a first annular recess configured and disposed to receive a first outer circumferential edge of a rotor wheel, a second rotor wheel ring having a second outer surface and a second annular recess configured and disposed to receive a second outer circumferential edge of the rotor wheel, and a linking bar having a first mounting element and a second mounting element. The first mounting element is configured and disposed to be joined to the first outer surface of the first rotor wheel ring and the second mounting element is configured and disposed to be joined with the second outer surface of the second rotor wheel ring. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a perspective view of a turbomachine rotor wheel including a rotor wheel repair apparatus in accordance with an exemplary embodiment; 
           [0009]      FIG. 2  is an exploded perspective view of the turbomachine rotor wheel of  FIG. 1 ; 
           [0010]      FIG. 3  is a partial cross-sectional side view of the turbomachine rotor wheel of  FIG. 1 ; 
           [0011]      FIG. 4  is an exploded, partial cross-sectional view of the turbomachine rotor wheel of  FIG. 3 ; 
           [0012]      FIG. 5  is a partial top plan view of the turbomachine rotor wheel of 
           [0013]      FIG. 1 ; 
           [0014]      FIG. 6  is a partial perspective view of the turbomachine rotor wheel of  FIG. 1  after a repair operation illustrating first and second spacers arranged to position a turbine bucket, at least one of the spacers being repaired in accordance with the exemplary embodiment; 
           [0015]      FIG. 7  is a perspective view of the turbomachine rotor wheel of  FIG. 5  shown with one of the first and second spacers removed; 
           [0016]      FIG. 8  is a lower right perspective view of one of the first and second spacers in accordance with one aspect of the exemplary embodiment; 
           [0017]      FIG. 9  is a lower right perspective view of one of the first and second spacers in accordance with another aspect of the exemplary embodiment; and 
           [0018]      FIG. 10  is a partial lower right perspective view of a bucket repaired in accordance with the exemplary embodiment. 
       
    
    
       [0019]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referencing  FIGS. 1-5 , a turbomachine rotor wheel is indicated generally at  2 . Rotor wheel  2  includes a body  4  having a central hub  6  and an outer rim  8 . Outer rim  8  includes a first outer circumferential edge  10  and a second outer circumferential edge  11  that are separated by an outer surface  14 . Outer surface  14  includes a plurality of dovetail grooves, one of which is indicated at  20 , that are configured to receive a corresponding plurality of turbomachine buckets such as shown at  25 . Buckets  25  are held in place by a first spacer  30  and a second or balance spacer  31 . Of course, buckets  25  can be held in place by other means as will be discussed more fully below. During turbomachine operation, stresses induced by various forces result in crack formation in first and second outer circumferential edges  10  and  11 . Over time, any defects such as cracks, pits, and the like will propagate and may lead to failure of a rotor wheel. Accordingly, it is desirable to repair any cracks before failure can occur. Thus, often times, rotor wheels are inspected both visually and with various testing equipment to locate and identify any cracks that may be present on the outer circumferential edges  10  and  11 . Depending on crack size, the rotor wheel will be repaired as will be detailed more fully below. 
         [0021]    In accordance with the exemplary embodiment, cracks having a length of from about 0.1 inches (2.54 mm) up to about 0.5 inches (12.7 mm) can be removed by machining turning grooves in the outer circumferential edges  10  and  11 . Prior to any machining, buckets  25  must be fixed in dovetail grooves  20 . In accordance with an exemplary embodiment, buckets  25  are retained to rotor wheel  2  with a first rotor wheel ring  40  positioned about first outer circumferential edge  10  and a second rotor wheel ring  43  positioned about second outer circumferential edge  11 . A plurality of linking bars, one of which is indicated at  46 , join first rotor wheel ring  40  to second rotor wheel ring  43 . In this manner, buckets  25  are constrained to outer rim  8  when a turning groove is formed in first and second outer circumferential edges  10  and  11  as will be discussed more fully below. 
         [0022]    In further accordance with the exemplary embodiment, first rotor wheel ring  40  includes an outer surface  55  and an annular recess  57  that is configured to receive first outer circumferential edge  10 . First rotor wheel ring  40  also includes a plurality of mounting members, one of which is indicated at  60  that are arrayed about outer surface  55 . Mounting members  60  take the form of threaded openings, such as indicated at  62  that extend from outer surface  55  toward annular recess  57 . Similarly, second rotor wheel ring  43  includes an outer surface  65  and an annular recess  67 . A plurality of mounting members, one of which is indicated at  70 , are arrayed about outer surface  65 . Mounting members  70  take the form of threaded openings  72  that extend from outer surface  65  toward annular recess  67 . 
         [0023]    Linking bar  46  includes a body member  80  having a first end  82  that extends to a second end  83  through an intermediate portion  84 . First end  82  includes a first mounting element  87  that takes the form of an opening  88 . Similarly, second end  83  includes a second mounting element  91  that takes the form of an opening  92 . With this arrangement, linking bar  46  is positioned across outer surface  14  between adjacent buckets  25 . First mounting element  87  is aligned or placed in registration with first mounting member  60  and second mounting element  91  is aligned or placed in registration with second mounting member  70 . Once aligned, a first fastener  95  is passed through first mounting element  87  and engaged with threaded opening  62  and a second fastener  96  is passed through second mounting element  91  and engaged with threaded opening  72 . At this point, additional linking bars (not separately labeled) are mounted between first and second rotor wheel rings  40  and  43  to constrain buckets  25  within dovetail grooves  20 . 
         [0024]    After securing first and second rotor wheel rings  40  and  43  to rotor wheel  2 , a first portion of material  106  is removed from first outer circumferential edge  10  forming a first turning groove  107 . ( FIGS. 6  &amp; &amp; 7 ) The removal of first portion of material  106  removes defects that may have formed at first outer circumferential edge  10 . Similarly, a second portion of material  108  is removed from second outer circumferential edge  11  forming a second turning groove  109 . The removal of second portion of material  108  removes defects from second outer circumferential edge  11 . In the event that defects are only found on one of first and second outer circumferential edges  10  and  11 , material may be removed from the other of the first and second outer circumferential edges  10  and  11  to provide any desired balance for rotor wheel  2 . 
         [0025]    As shown in  FIGS. 8-9 , removing first and second portions of material  106  and  108  to form corresponding first and second turning grooves  107  and  109  also results in material loss from spacers  30  and  31 . More specifically, the formation of turning groove  107  results in a groove  111  ( FIG. 8 ) formed in spacer  30  while turning groove  109  results in a groove  114  ( FIG. 9 ) formed in spacer  31 . The lost material that creates grooves  111  and  114  includes connecting portions that serve to secure spacers  30  and  31  to rotor wheel  2  in dovetail groove  20 . Accordingly, after forming turning grooves  107  and  109 , spacers  30  and  31  are removed from dovetail groove  20 . A chamfer region  116  is formed on spacer  30 , and first and second chamfer regions  119  and  120  are formed on spacer  31 . Chamfer regions  116 ,  119 , and  120  provide wedgeable surfaces that facilitate securing or staking spacers  30  and  31  to rotor wheel  2  in dovetail groove  20 . 
         [0026]    In certain arrangements spacers are not utilized. In such cases, a bucket, such as shown at  125  in  FIG. 10 , includes a base portion  127  having first and second end portions  128  and  129  that extend between first and second outer circumferential edges  10  and  11 . The formation of turning grooves to take out defects leads to the creation of first and second grooves  132  and  133  in first and second end portions  128  and  129 . In this arrangement, a chamfer region  137  is formed at one of the first and second end portions  128  and  129 . Chamfer region  137  provide a wedgeable surface that facilitate securing or staking bucket  125  to rotor wheel  2  in dovetail groove  20 . 
         [0027]    At this point it should be understood that the exemplary embodiments describe a method and apparatus for repairing a turbomachine rotor wheel. The apparatus secures buckets to the rotor wheel during a repair operation. Securing the buckets allows for material to be removed from outer edge portions of the wheel to facilitate the removal of defects that may have formed. If left unsecured, the removal of the material would allow the buckets to slide out from the rotor wheel. Maintaining rotor wheel integrity allows turning grooves to be formed that can remove defects, such as cracks up to about 0.5 inches (12.7 mm) Previously, cracks over 0.25 inches (6.35 mm) required that the rotor wheel be taken out of service. Accordingly, the exemplary embodiments enable repair of rotor wheels that would otherwise been discarded. It should be understood that the term “defect” includes actual cracks, pits, cuts or other imperfections that may form or develop in the rotor wheel or buckets. Leaving the buckets on the wheel during repair leads to a desired final geometry of the wheel and spacer after any necessary repairs. That is, leaving the buckets on the wheel results in initial geometry of the assembly (pre-repair) being as close to a final geometry (post repair) as possible. In this manner, the cut face on the wheel and the cut face on the spacer are in alignment thereby eliminating potential windage heating. 
         [0028]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.