Patent Abstract:
A method of repairing a seal wire groove is disclosed, the groove forming an annular structure having an outer surface and an inner surface and defining an original profile when new, comprising the steps of: removing a less-than-annular portion of the original profile of the groove to remove damaged portions of at least one of the inner and outer surfaces thereby forming a void; adding new material to the void; and shaping the new material to form a new profile of the groove.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/524376, filed Aug. 17, 2011, the disclosure of which is hereby incorporated in its entirety by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The technology described herein relates generally restoration of grooves used in conjunction with seal wire, particularly to methods of restoring the profile of such grooves, and more particularly, to thermal spray techniques for such restorations. 
         [0003]    Many gas turbine engine assemblies include a seal between adjacent surfaces of moving and non-moving parts, such as a rotating disk and a stationary structure, or between parts which have clearances between their mating surfaces. One common construction for such seals utilizes a seal wire formed of one or more segments which is inserted into a groove in one part and biased against the opposing part in sealing engagement. 
         [0004]    During operation, the constant contact between the seal wire and the mating surface results in wear of the seal wire and/or movement of the seal wire within its groove. Since the seal wires are typically fashioned from one or more segments, with abutting ends located at one or more locations around their circumference. movement of the seal wire within the groove may result in fretting and/or other wear of the groove resulting from the motion of the seal wire ends. Over time this fretting or wear of the groove enlarges the groove and reduces the effectiveness of the seal wire arrangement, 
         [0005]    During repair and overhaul operations it is desirable to restore the seal wire and groove assembly to original or other suitable dimensions and tolerances. However, due to limitations of current repair methods it is frequently necessary to scrap and replace the rotor assembly with a new one having the proper groove dimensions. There remains a need for a repair method which will restore the groove geometry in a durable and economical fashion. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In one aspect, a method of repairing a seal wire groove, the groove forming an annular structure having an outer surface and an inner surface and defining an original profile when new, comprising the steps of: removing a less-than-annular portion of the original profile of the groove to remove damaged portions of at least one of the inner and outer surfaces thereby forming a void; adding new material to the void; and shaping the new material to form a new profile of the groove. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional illustration of an exemplary gas turbine engine assembly; and 
           [0008]      FIG. 2  is a cross-sectional elevational illustration of an exemplary compressor spool depicting a representative location for remaining illustrations; 
           [0009]      FIG. 3  is an enlarged partial elevational sectional illustration of a compressor blade mounted on a compressor spool; 
           [0010]      FIG. 4  is a more enlarged partial elevational sectional illustration depicting and defining relevant dimensions; 
           [0011]      FIG. 5  is a cross-sectional illustration of a complete revolution of the compressor spool including seal wire sections installed; 
           [0012]      FIG. 6  is a view similar to  FIG. 4  depicting fretting wear due to motion of the seal wire in service; 
           [0013]      FIG. 7  is a view similar to  FIG. 6  depicting a portion of the compressor spool after material removal of the damaged portion; 
           [0014]      FIG. 8  is a perspective view of the portion of the compressor spool of  FIG. 7  taken through an intermediate station of the material removal to illustrate the end of the removal; 
           [0015]      FIG. 9  is a view similar to  FIG. 7  after new repair material has been added; and 
           [0016]      FIG. 10  is a view similar to  FIG. 9  after the new repair material of  FIG. 9  has been machined to the correct profile. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  is a cross-sectional schematic illustration of an exemplary gas turbine engine assembly  10  having a longitudinal axis  11 . Gas turbine engine assembly  10  includes a fan assembly  12  and a core gas turbine engine  13 . Core gas turbine engine  13  includes a high pressure compressor  14 , a combustor  16 , and a high pressure turbine  18 . In the exemplary embodiment, gas turbine engine assembly  10  also includes a low pressure turbine  20 , and a multi-stage booster compressor  32 , and a splitter  34  that substantially circumscribes booster  32 . 
         [0018]    Fan assembly  12  includes an array of fan blades  24  extending radially outward from a rotor disk  26 , the forward portion of which is enclosed by a streamlined spinner  25 . Gas turbine engine assembly  10  has an intake side  28  and an exhaust side  30 . Fan assembly  12 , booster  22 , and turbine  20  are coupled together by a first rotor shaft  11 , and compressor  14  and turbine  18  are coupled together by a second rotor shaft  22 . 
         [0019]    In operation, air flows through fan assembly  12  and a first portion  50  of the airflow is channeled through booster  32 . The compressed air that is discharged from booster  32  is channeled through compressor  14  wherein the airflow is further compressed and delivered to combustor  16 . Hot products of combustion (not shown in  FIG. 1 ) from combustor  16  are utilized to drive turbines  18  and  20 , and turbine  20  is utilized to drive fan assembly  12  and booster  32  by way of shaft  21 . Gas turbine engine assembly  10  is operable at a range of operating conditions between design operating conditions and off-design operating conditions. 
         [0020]    A second portion  52  of the airflow discharged from fan assembly  12  is channeled through a bypass duct  40  to bypass a portion of the airflow from fan assembly  12  around core gas turbine engine  13 . More specifically, bypass duct  40  extends between a fan casing or shroud  36  and splitter  34 . Accordingly, a first portion  50  of the airflow from fan assembly  12  is channeled through booster  32  and then into compressor  14  as described above, and a second portion  52  of the airflow from fan assembly  12  is channeled through bypass duct  40  to provide thrust for an aircraft, for example. Splitter  34  divides the incoming airflow into first and second portions  50  and  52 , respectively. Gas turbine engine assembly  10  also includes a fan frame assembly  60  to provide structural support for fan assembly  12  and is also utilized to couple fan assembly  12  to core gas turbine engine  13 . 
         [0021]    Fan frame assembly  60  includes a plurality of outlet guide vanes  70  that extend substantially radially between a radially outer mounting flange and a radially inner mounting flange and are circumferentially-spaced within bypass duct  40 . Fan frame assembly  60  may also include a plurality of struts that are coupled between a radially outer mounting flange and a radially inner mounting flange. In one embodiment, fan frame assembly  60  is fabricated in arcuate segments in which flanges are coupled to outlet guide vanes  70  and struts. In one embodiment, outlet guide vanes and struts are coupled coaxially within bypass duct  40 . Optionally, outlet guide vanes  70  may be coupled downstream from struts within bypass duct  40 . 
         [0022]    Fan frame assembly  60  is one of various frame and support assemblies of gas turbine engine assembly  10  that are used to facilitate maintaining an orientation of various components within gas turbine engine assembly  10 . More specifically, such frame and support assemblies interconnect stationary components and provide rotor bearing supports. Fan frame assembly  60  is coupled downstream from fan assembly  12  within bypass duct  40  such that outlet guide vanes  70  and struts are circumferentially-spaced around the outlet of fan assembly  12  and extend across the airflow path discharged from fan assembly  12 . 
         [0023]      FIG. 2  is a cross-sectional elevational illustration of an exemplary compressor spool  90  forming a part of the compressor  14  of  FIG. 1 , depicting a representative location identified with the circle and numeral  3  for the more detailed illustrations which follow. 
         [0024]      FIG. 3  is an enlarged partial elevational sectional illustration of a compressor blade  91  mounted on a compressor spool  90 . As shown in  FIG. 3 , the compressor blade  91  includes several elements such as an airfoil  92 , a dovetail  93 , and a platform  95  between the airfoil  92  and the dovetail  93 . The dovetail  93  is sized and shaped to fit in dovetail slot  97  of compressor spool  90  to secure the blade  91  to the spool  90 . The spool  90  and dovetail slot  97  are annular structures and a plurality of blades  91  are secured to the spool  90  around their circumference, though only a single blade  91  is illustrated for clarity. Also shown in  FIG. 3  is a seal wire groove  94  for containing a seal wire  96  to form a seal between the platform  95  and the spool  90  to enhance efficiency of the compressor  14  in operation and thereby improve fuel consumption of the gas turbine engine assembly  10 . 
         [0025]      FIG. 4  is a more enlarged partial elevational sectional illustration of the elements of  FIG. 3 . As shown in  FIG. 4 , the seal wire groove  94  is spaced inwardly from the edge of the disk portion  98  of the compressor spool  90  by a dimension A which forms a shoulder  99  and a dimension B which forms a horizontal surface on the outer side of the groove  94 . These shapes and dimensions are sized, shaped, and configured for the specific gas turbine engine assembly  10  for which they are intended, so the illustrations herein are intended to be illustrative and not limiting in terms of geometry. The platform  94  typically has a complementary shape to the radially-outer surfaces of the disk portion  98 . As shown in  FIG. 4 , the seal wire  96  is located in the seal wire groove  94  and typically biased radially outwardly against the underside of the platform  94 . The disk portion  98  may be formed from a metallic material, in which case the inner and outer surfaces of the groove  94  are formed of a metallic material. The seal wire  96  may also be formed of a metallic material and may be generally rectangular in cross section. 
         [0026]      FIG. 5  is a cross-sectional illustration of a complete revolution of the compressor spool  90  including sections of seal wire  96  installed in groove  94 . The seal wire  96  will typically comprise multiple (more than one) pieces of material and thus have at least two ends  100 , In the exemplary embodiment shown in  FIG. 5 , the seal wire  96  is formed in three (3) sections having six (6) ends labeled  100 . Each of the ends  100  is a potential source for wear of the seal wire groove  94 . 
         [0027]    In service, the vibrations, pressures, and thermal effects experienced by the seal wire  96  often result in “fretting” wear to the surfaces of the groove  94  in the vicinity of the ends  100  due to their movement in various directions. This wear results in removal of material from the surfaces of the groove  94  such as depicted in wear zones  101  in  FIG. 5 , such that the grove  94  is enlarged in cross section and deviates from the original profile of the groove  94  When in a new condition. Wear may occur to the outer surface (proximal to the shoulder  99 ), to the opposing inner surface, or both. This results in a reduced sealing capability of the seal wire  96  and may also accelerate wear as the ends  100  of the seal wire have more freedom of movement as the degree of wear increases. 
         [0028]      FIG. 6  is a view similar to  FIG. 4  depicting fretting wear  101  due to motion of the ends  100  of the seal wire  96  in service. In contrast to the condition of the surfaces and elements depicted in  FIG. 4 , as shown in  FIG. 6  portions of the groove  94  are worn away and enlarged such that the surfaces of the groove  94  are no longer consistent with the original profile of the groove  94  when it was in a like-new, as-manufactured condition. Surfaces of the seal wire  96  in this illustration are also shown as irregular and worn. Typically the condition of the seal wire  96  is of less concern than the condition of the groove  94  as the seal wire  96  is typically replaced with a new seal wire during repair while for economic reasons it is desirable to repair and restore the profile of the groove  94  and retain the disk portion  98  of the spool  90  for continued service. 
         [0029]      FIG. 7  is a view similar to  FIG. 6  depicting a portion of the compressor spool  90  after material removal of the damaged portion in the wear zone  101 . Material removal of the worn, irregular, soiled, or otherwise deteriorated portion of the surfaces groove  94  is the first step in the method of repairing the groove  94 . This removal results in a void having a new profile  102  which differs from the original profile  103  (shown in dotted line in  FIG. 7 ), and has surfaces which are relatively solid, smooth, and of uniform character. In the exemplary embodiment shown, the repair method is being accomplished on the outer surface (proximal to shoulder  99 ) of the groove  94 , although it could be equally applied to the opposing inner surface, or to both surfaces. Material removal to generate the new profile  102  may be accomplished by mechanical means, such as machining by rotary tools such as a saw blade or abrasive disk, or other means such as chemical or electrical machining processes, and may be done in one pass or in multiple steps or stages. A tool with an appropriate profile may be used, or a tool with a generic profile which is controlled in such a manner as to generate the proper profile may be used. 
         [0030]      FIG. 8  is a perspective view of the portion of the disk portion  98  of the compressor spool  90  of  FIG. 7  taken through an intermediate station of the material removal section (new profile  102 ) to illustrate the end  104  of the removal. Because the material removal occurs over a less-than-annular portion or segment of the annular disk  98 , it by definition forms a void having at least two ends  104  for each material removal and defines a localized repair area. It is believed that these ends  104 , being defined by remaining portions of original material of the disk  98 , provide stability and support for the new material to be added to restore the original profile  103  of the groove  94 . The lead in angle and radius characteristics of the ends  104 , such as an exit radius, may be determined with both the tooling and techniques used for the material removal, as well as the adhesion and minimum thickness requirements for the new material to be added. Repairs made with new material which is too thin in cross section or comparatively lower adhesion characteristics may tend to spall during engine operation. 
         [0031]      FIG. 9  is a view similar to  FIG. 7  after new repair material  104  has been added to build back material equal to or greater than the original profile  103  of the groove  94 . Said differently, new material is added in excess of the volume of the void. The addition of new material can be accomplished by any suitable method or apparatus depending upon the quantity and type of material to be added and upon the size, shape, and material from which the disk  98  is constructed. 
         [0032]    Metal Thermal Spray is one category of suitable material addition processes. In an exemplary embodiment, the material addition may be Inco 718 material being sprayed using the Hyper-Velocity Oxy-Fuel (HVOF) process, Various metals can be applied using this method, not just Inco  718 . Other metal spray processes such as Plasma spray may also be utilized. Representative processes involve spraying molten metal through a nozzle at the target area of the part being repaired and building up the material in the seal wire groove  94  to achieve a condition such as shown in  FIG. 9 . The HVOF process has been found to exhibit a lesser amount of voiding and is easier to machine to the desired finished profile than some other potential processes. It has also been found to do a minimal amount of parent material damage (i.e., to the disk material at or below the removal profile  102 ) because it maintains the repair area parent material temperatures below solution or melting. With certain other processes such as a typical weld process, it could heat the area to a point that could alter the metal grain structure or cause micro cracking. 
         [0033]      FIG. 10  is a view similar to  FIG. 9  of the disk  98  after the new repair material  104  of  FIG. 9  has been shaped, such as by machining, to the proper finished profile  105 . The new finished profile  105  will typically be the same as or substantially similar to the original as-manufactured profile  103  shown in  FIGS. 7 and 8 . However, under certain circumstances the new profile  105  could differ particularly if a replacement seal wire  96  having a different geometry were to be used. In such a scenario, the remaining portions of the circumference of the seal wire groove  94  may or may not be machined to match the new profile  105 . 
         [0034]    Material removal or shaping of the newly-added repair material to generate the finished profile  105  may be accomplished by mechanical means, such as machining by rotary tools such as a saw blade or abrasive disk, or other means such as chemical or electrical machining processes, and may be done in one pass or in multiple steps or stages. A tool with an appropriate profile may be used, or a tool with a generic profile which is controlled in such a manner as to generate the proper profile may be used. 
         [0035]    The steps described above may be repeated multiple times at different annular stations around the groove, and performed either simultaneously or sequentially. 
         [0036]    While much of the discussion has focused on an aviation gas turbine engine as the context for this repair, it is foreseeable that such methods may be suitable for use in other environments wherein a wire-type seal is used with a complementary groove and rejuvenation is required, such as steam turbines or other turbomachinery. 
         [0037]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Technology Classification (CPC): 8