Abstract:
A method and apparatus for restoring displaced features on a turbine vane segment for a gas turbine engine, such as a vane segment in a low pressure turbine, and more specifically, the inner shroud thereof relative to the outer shroud thereof to meet the original design position and dimensions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       TECHNICAL FIELD 
       [0003]    This invention disclosure provides a method and apparatus to restore the displaced features on a turbine vane segment for a gas turbine engine, such as a low pressure turbine vane, and more specifically, the inner shroud relative to the outer shroud of a vane segment. 
       BACKGROUND OF THE INVENTION 
       [0004]    In advanced turbine engines, gas turbine parts in the hot gas path such as blades, vanes and outer air seals in the high pressure turbine and the low pressure turbine, are subjected to temperatures and loads that, over time, can distort the dimensions of these parts to the point that they deviate so substantially from the original equipment manufacturer&#39;s drawings and specifications that the parts are typically scrapped when the gas turbine engine is overhauled or repaired. In some cases, scrapping of the component and replacement with a new part may be driven by flight safety issues, but in other cases, the part is scrapped simply because there is no viable repair available. 
         [0005]    An example of one such part is the stator vane segment  11  in the third stage of the low pressure turbine on the Pratt &amp; Whitney PW4000 gas turbine engine, as shown in  FIG. 1 . Typically, a plurality of vanes  10  are clustered together to form a vane segment  11 , of which there are a plurality in the set of third stage, low pressure turbine vanes for this particular engine. These particular vanes  10  are cast from a nickel-base alloy, such as Mar-M 247, an alloy well known in the art. They are installed in the engine by engaging by the forward outer shroud rail  12  and the aft ward outer shroud rail  14 , as shown in  FIG. 1 , on the internal case rails of the low pressure turbine (not shown) of the engine. The inner shroud  16  includes an inner flange  18  which contains a bolt hole  20  that is used to bolt the vane segment  11  to an inner support (not shown) in the low pressure turbine. Due to thermal and aerodynamic loads, the inner shroud  16  may experience distortion such as displacement, or shifting, of the inner shroud  16 , relative to the outer shroud  24 , in the distortion direction  17 , and elongation of the bolt hole  20  and a displacement of the center  22  of the bolt hole  20  in a distortion direction  17  relative to the outer vane shroud  24 , which for the PW4000 would be clockwise from its original design location as viewed from a forward-looking-aft position, as shown in  FIG. 1 . This displacement of the center  22  of the bolt hole  20  is not isolated to one particular vane segment  11 , in any engine set, as all vane segments  11  in a set may experience this type of displacement. The degree, or dimensional amount, of displacement is not constant from one vane segment  11  to another vane segment  11 . 
         [0006]    What is needed is a method and apparatus for restoring displaced features on a turbine vane segment for a gas turbine engine, such as a vane segment in a low pressure turbine, and more specifically, the inner shroud thereof relative to the outer shroud thereof to meet the original design position and dimensions. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a method for restoring the inner shroud of a vane segment to its original design position and dimensions relative to the outer shroud of such vane segment. 
         [0008]    The present invention further provides an apparatus for practicing the method for restoring the inner shroud of a vane segment to its original design position and dimensions relative to the outer shroud of such vane segment. 
         [0009]    The present invention further provides a method for restoring the bolt hole in the inner shroud flange of a vane segment to its original design position and dimensions. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0010]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0011]      FIG. 1  is a forward-looking-aft view of a vane segment of the type which can be restored using the method and apparatus of the present invention, as viewed from the front of the gas turbine in which it is designed to operate. 
           [0012]      FIG. 2  is an elevation view of the apparatus of the present invention which is used to practice the method of the present invention. 
           [0013]      FIG. 3  is a side view of the apparatus of the present invention taken along line  3 - 3  of  FIG. 2 , with the piston block in a lowered position and the locking pin removed from the pinhole. 
           [0014]      FIG. 4  is the view of  FIG. 3 , with the piston in a raised position and the locking pin extending through the pin hole and the bolt hole. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The apparatus  50  used to practice the method of the present invention is shown in  FIGS. 2 ,  3  and  4 . The apparatus  50  includes an outer shroud holding fixture  52  and an inner shroud holding fixture  54 . The outer shroud holding fixture  52  is designed to receive and removably secure the forward rail  12  and aft ward rail  14  of the outer shroud  24  of the vane segment  11 , while the inner shroud holding fixture  54  is designed to slideably receive the inner shroud  24  of the vane segment  11 . The outer shroud holding fixture  52  and the inner shroud holding fixture  54  are secured to a base  56 . A means for applying a force to the inner shroud of the vane segment  11 , such as a mechanical or hydraulic press  58 , is likewise secured to the base  56  directly below the inner shroud holding fixture  54 . The press  58  has a piston  60  that can move along a first direction  61  relative to the outer shroud holding fixture  54 . 
         [0016]    The outer shroud holding fixture  52  is designed so as to (i) locate the inner shroud  16  directly in the path of the piston  60 , and (ii) orient the inner shroud  16  so that when the piston  60  is driven into contact with the inner shroud  16 , the inner shroud  16  is driven in a first direction  61  that is directly opposite the distortion direction  17 . As shown in  FIG. 2 , the outer shroud holding fixture  52  includes a clamping plate  62  that slides on guide pins  64 ,  66  towards a base plate  68  into which the guide pins are secured, and a bottom plate  70  located immediately below the clamping plate  62  for supporting the outer vane shroud  24  of the vane segment  11  when a the method of the present invention is being practiced. A vise bolt  72 , which extends through a hole  74  in the clamping plate  62 , is threaded into a hole in the base plate  68  which receives the threaded vise bolt  72 . The vise bolt  72  preferably has a vise handle  76  permanently attached to one end, to allow the vise bolt  72  to be rotated without the need for a separate tool. The threads of the vise bolt  72  and the threaded hole in the base plate  68  in which the vise bolt  72  is received are such that rotation of the vise handle  76  in a clockwise direction drives the clamping plate  62  towards the base plate  68 . Preferably, the surface of the clamping plate  62  which faces the base plate  68 , and the surface of the base plate  68  that faces the clamping plate  62 , each includes contours which conform to either the forward rail  12  of the outer shroud  24 , the aft ward rail  14  of the outer shroud  24 , or both, so that when one or both rails  12 ,  14  are clamped into the outer shroud holding fixture  52 , as described below, the force applied by the clamping plate  62  and the base plate  68  to the rails  12 ,  14  is distributed so as to avoid permanently distorting either of the rails  12 ,  14 . When the contoured surface of the clamping plate  62  is close to, but in spaced relation to, the contoured surface of the base plate  68 , the contoured surfaces cooperate to form grooves into which the forward rail  12 , the aft ward rail  14 , or both can easily slide so as to be positioned between the base plate  68  and the clamping plate  62 . Once so positioned, the vise handle  76  can be rotated in a clockwise position, sliding the clamping plate  62  towards the base plate  68 , until the forward rail  12 , aft ward rail  14 , or both, are clamped rigidly therebetween. In this manner, the outer shroud  24  of the vane segment  11  can be removably secured to the base  56  without damaging the vane segment  11 . As shown in  FIGS. 2-4 , the inner shroud holding fixture  54  has a face plate  80  and a backing plate  82 , which are connected by a spacing plate  84 . The spacing plate  84  holds the facing plate  80  in spaced relation to the backing plate  82 , providing a gap  83  therebetween which is sufficiently wide to slideably receive the inner shroud  16  of the vane segment  11  when the outer shroud  24  is removably secured to the base  56  as described above. A press block  86  is secured to the upper end  88  of the piston  60  immediately below the gap  83 , and the upper surface  90  of the press block  86  is preferably contoured to be substantially flush with the lower surface  92  of the inner shroud  16  when the press block  86  is driven into contact with the inner shroud  16  by the piston  60 , as described below. The face plate  80  includes a pin hole  94  extending therethrough at a predetermined location, that location being such that the pin hole  94  would be coaxial with the bolt hole  20  of the inner shroud flange  18  if the outer shroud  24  of a new vane segment  11  (which had not been run in an engine) were to be removably secured to the base  56  by the outer shroud holding fixture  52 , as described above. A locking pin  96 , long enough to be inserted into the pin hole  94  and extend through the bolt hole  20  when the pin hole  94  and bolt hole  20  are aligned, is included to be used as described below. 
         [0017]    With respect to a vane segment  11  that has been run in an engine and for which it is desired to restore the inner shroud  16  thereof to its original design position and dimensions relative to the outer shroud  24  of such vane segment  11 , the method of the present invention is practiced on the vane segment  11  as follows. The locking pin  96  is removed from the pin hole  94  and set aside, and the clamping plate  62  is positioned in spaced relation to the base plate  68  by rotating the vise handle  76  counterclockwise until the spaces between the contours of the clamping plate  62  and the base plate  68  are just wide enough to easily slide the forward rail  12 , the aft ward rail  14 , or both between the clamping plate  62  and the base plate  68 , and rest the outer shroud  24  of the vane segment  11  on the bottom plate  70 . The piston  60  is lowered so that the press block  86  is far enough below the inner shroud holding fixture  54  that it will not interfere with the effort to slide the forward rail  12 , the aft rail, or both between the clamping plate  62  and the base plate  68 , and rest the outer shroud  24  of the vane segment  11  on the bottom plate  70  during positioning of the vane segment  11  in the outer shroud holding fixture  52 . The vane segment  11  is then heated by placing it in a furnace (preferably a gas furnace) and heating it to a temperature within the range of 1600° F. to 2050° F., and preferably within in the range of 1925° F. to 1975° F., so that the vane segment  11  is “red hot”. The vane segment  11  is then taken out of the furnace, while red hot, and immediately the forward rail  12  and aft ward rail  14  of the outer shroud  24  are slid into the spaces between the contours of the clamping plate  62  and the base plate  68 , and lowered until the outer shroud  24  of the vane segment  11  comes to rest on the bottom plate  70 , and the inner shroud  16  is slideably received within the inner shroud holding fixture  54 . Some wiggling of the vane segment  11  may be required while lowering the vane segment  11  to insure that it comes to rest on the bottom plate  70  rather than becoming hung up on the clamping plate  62  or the base plate  68 . At this point, the vane segment  11  should still be red hot. The vane segment  11  is then secured to the base  56  by rotating the vise handle  76  clockwise until the forward rail  12 , the aft ward rail  14 , or both are rigidly clamped between the clamping plate  62  and the base plate  68  of the outer shroud holding fixture  52 . 
         [0018]    The press  58  is then operated to drive the piston  60  upward, until the contoured surface  90  of the piston block  86  comes into contact with the lower surface  92  of the inner shroud  16 , and then the press  58  continues to be operated, driving the inner shroud  16  upward, until the bolt hole  20  in the inner shroud flange  18  is aligned with the pin hole  94 . At this point, the locking pin  96  is inserted into the pin hole  94  and pushed through the bolt hole  20 , fixing the position of the inner shroud  16  relative to the base  56 . The vane segment  11  is then allowed to cool, preferably aided by fans, to ambient temperature, or at least until the vane segment  11  is cool enough that it can be handled by hand (i.e. cool enough to touch). The press  58  is then operated to lower the piston block  86  away from the inner shroud  16  of the vane segment  11 . The vane segment  11  is then released from the outer shroud holding fixture  52  by rotating the vise handle  76  counterclockwise and sliding the clamping plate  62  away from the base plate  68  until the forward rail  12  and aft ward rail  14  are sitting loosely between the clamping plate  62  and the base plate  68 . The locking pin  96  is then withdrawn from the bolt hole  20  and pin hole  94 , and set aside. At this point, the vane segment  11  can be lifted by hand and slid upward and out of the outer shroud holding fixture  52  and the inner shroud holding fixture  54  altogether. As those skilled in the art will readily appreciate, this method needs to be performed while the vane segment  11  is subject to plastic deformation to prevent cracking of the vane segment  11 , and so preferably, the time from when the vane segment  11  is removed from the furnace, until the time when the locking pin  96  is inserted into the pin hole  94  and the bolt hole  20 , is not more than  20  seconds. 
         [0019]    At this point, the bolt hole  20  is examined to determine whether the center  22  thereof has been displaced relative to the original equipment manufacturer&#39;s location (and the limits for that location). If the location of the bolt hole  20  has been displaced beyond those limits, the bolt hole  20  is drilled out to a pre-determined larger diameter hole, and then a cylindrical plug, having a diameter slightly smaller than that larger diameter, is brazed into the larger diameter hole. Preferably the plug is made of the same alloy as the inner shroud flange  18 , but it may be made of other suitable alloys. The bolt hole  20  is then re-drilled through the brazed-in plug, such that the diameter of the bolt hole  20 , and its center  22 , fall within the respective limits of the original equipment manufacturer. If the plug is thicker than the inner shroud flange  18 , the plug is machined down to match the original equipment manufacturer&#39;s dimensions for the inner shroud flange  18 . 
         [0020]    The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. Substitutions may be made and equivalents employed herein without departing from the scope of the invention as recited in the claims. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated and within the scope of the claims. 
         [0021]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. 
         [0022]    It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
         [0023]    Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.