Abstract:
A method for coating a shroud assembly is provided that includes inserting the shroud segment into a clamping fixture such that at least two edges of the shroud are masked by the clamping fixture, mounting the clamping fixture into a spraying fixture such that the shroud segment is oriented in approximately the same orientation as a sprayer, and moving the sprayer and the spraying fixture relative to each other at predetermined rates apply a layer of coating to the shroud segment.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines, and more specifically to turbine shroud assemblies used in gas turbine engines. 
   Gas turbine engines generally include, in serial flow arrangement, a high pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a high pressure turbine. The high pressure compressor, combustor and high pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low pressure compressor, or booster, for supplying compressed air to the high pressure compressor. 
   Generally, gas turbine engines operate more efficiently as combustion and exhaust temperatures increase. However, the operating temperature of the combustion gases is normally limited by the materials used to fabricate the hot-section components of the engine, such as the combustor and the turbine. To facilitate operating the engine at a higher operating temperature, at least some known turbine assemblies are coated with a thermal barrier coating (TBC). The TBC facilitates thermally, insulating the components from the combustible gases. 
   To facilitate maintaining turbine tip clearance, known shroud assemblies are masked prior to applying the TBC. However, masking of shroud segments is a time consuming process that is typically done by hand. Furthermore, during the TBC application process, the tape may blister and deform when exposed to the heat generated during the TBC application process. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method for coating a shroud assembly for a gas turbine engine is provided. The method comprises inserting the shroud segment into a clamping fixture such that at least two edges of the shroud are masked by the clamping fixture, mounting the clamping fixture into a spraying fixture such that the shroud segment is oriented in approximately the same orientation as a sprayer, and moving the sprayer and the spraying fixture relative to each other at predetermined rates to apply a layer of coating to the shroud segment. 
   In another aspect, an apparatus for clamping and locating shroud segments during a spraying operation is provided. The apparatus includes a base and a pair of elongated arms, each having a first end and a second end. The first ends of the arms are coupled to the base. A clamping element is coupled to the second end of each arm. The clamping elements secure a shroud segment to the base such that at least one edge of the shroud segment is masked by the clamping elements. A locating member is coupled to the base between the pair of arms for positioning the shroud segment with respect to said base. The locating member is configured to engage a shroud segment surface for positioning the shroud segment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an exemplary shroud segment for a gas turbine engine; 
       FIG. 2  is a perspective view of a shroud clamp and location fixture with a shroud segment inserted therein; 
       FIG. 3  is an alternative perspective view of the shroud clamp and locating fixture shown in  FIG. 2 ; 
       FIG. 4  is an exploded view of the shroud clamp and locating fixture shown in  FIG. 3 ; and 
       FIG. 5  is a perspective view of an exemplary spraying fixture for use with the shroud clamp and locating fixture shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a perspective view of an exemplary shroud segment  10 . Shroud segment  10  is used in a turbine section of a gas turbine engine (not shown). Shroud segment  10  includes a radially inner side  11  and an opposite radially outer side  19 . Outer side  19  includes a center rib  16 , and a pair of end ribs  17  that are each positioned at opposite circumferential outer edges  15  of shroud segment  10 . Shroud segment  10  also includes a leading edge side  12  and an opposite trailing edge side  14 . Leading and trailing edge sides  12  and  14 , respectively, include mounting channels  18  formed therein. 
   Prior to the application of a thermal barrier coating (TBC) material, shroud  10  is masked to facilitate ensuring that TBC material is only applied to desired locations. Specifically, masking is applied to leading and trailing edge sides  12  and  14  respectively, and also to and mounting channels  18  during the coating process. More specifically, the masking facilitates preventing the coating materials, which include a base coat and a ceramic upper layer, from contacting the mounting channels  18  of shrouds  10 . 
     FIG. 2  is a perspective view of a shroud clamp and location fixture  20  with a shroud segment  10  inserted therein.  FIG. 3  is an alternative perspective view of shroud clamp and locating fixture  20 .  FIG. 4  is an exploded view of shroud clamp and locating fixture  20 . 
   Shroud clamp and locating fixture  20 , as described in more detail below, receives a shroud segment  10  between clamping elements  24 , to facilitate preventing coating material from contacting leading and trailing edge sides  12  and  14 , respectively during a coating process. In one embodiment, the coating applied is a thermal barrier coating, TBC. 
   Fixture  20  includes a base  22 , a pair of shroud clamping elements  24 , a pair of arms  26 , and a locating member  28 . Base  22  includes an upper body portion  30  and a lower body portion  32 . Lower body portion  32  includes a slot  34  defined therein that extends between a pair of mounting arms  31  and  33 . Slot  34  facilitates coupling fixture  20  to a spraying fixture (not shown in  FIGS. 2–4 ) with a fastener  39 . Upper body portion  30  includes a slot  36  defined therein that is sized to receive at least a portion of locating member  28  therein. 
   Each arm  26  includes a first end  35  used to couple each arm  26  to base  22 , and a second end  37 . Clamping elements  24  are coupled to each arm second end  37  using fasteners  38 . Spacers (not shown in  FIGS. 2–4 ) may be inserted between clamping elements  24  and arm second end  37  to facilitate accommodating shroud segments of varying widths. At least one of arms  26  is deflectable from a first position wherein shroud segment  10  is held between clamping elements  24 , to a second position wherein shroud segment  10  is released from clamping elements  24 . More specifically, the deflectable arm  26  is biased towards the first-position such that shroud segment  10  is retained by clamping elements  24 . In one embodiment, at least one of arms  26  is a leaf spring. 
   Clamping elements  24  each include a shroud mating face  40  that is contoured substantially complementary to shroud leading and trailing edge sides  12  and  14  respectively. In one embodiment, mating face  40  is machined to form the contour. More specifically, thus, clamping elements  24  contact shroud leading and trailing edge sides  12  and  14  in sealing contact to facilitate prohibiting the application of coating materials against sides  12  and  14 , as described in more detail below. 
   Locating member  28  includes a mounting end  44  that is used to couple locating member  28  to base  22 , and a shroud engagement end  46 . Shroud engagement end  46  includes a slot  48  defined therein that receives at least a portion of shroud center rib  16  to facilitate aligning shroud  10  within fixture  20 . In one embodiment, locating member  28  is yoke-shaped. Locating member  28  also includes a cam  52  that is positioned within slot  48 . A cam adjuster  54  extends through an opening  56  formed in locating member  28  and is coupled to cam  52 . In one embodiment, cam adjuster  54  is keyed to cam  52 . Cam  52  spreads arms  26  apart to permit the insertion and removal of shroud segment  10 . More specifically, cam adjuster  54  moves arms  26  from a first position, wherein shroud segment  10  is retained by clamping elements  24 , to a second position wherein shroud segment  10  is removable from clamping elements  24 . 
   In operation, deflectable arm  26  is initially biased towards the first position such that shroud segment  10  is retained with in fixture  20  by clamping elements  24 . In order to insert shroud segment  10 , cam adjuster  54  is rotated, causing cam  52  to spread arms  26  apart. Shroud segment  10  is then inserted between clamping elements  24  such that center rib  16  is positioned within slot  48  on locating member  28 . Accordingly, shroud segment  10  is facilitated to be aligned with respect to fixture  20 . Shroud  10  leading and trailing edge sides  12  and  14  are then aligned using mating faces  40  of clamping elements  24 , and cam adjuster  54  is operated to enable arms  26  to return to their original biased position such that shroud  10  is retained between clamping elements  24 . More specifically, cam adjuster  54  is rotated causing cam  52  to spread arms  26  apart. Shroud segment  10  is inserted between clamping elements  24  such that mating faces  40  seal sides  12  and  14  to facilitate prohibiting the application of coating materials against sides  12  and  14 . 
   As shroud segment  10  is being held in clamp and locating fixture  20 , thermal barrier coatings can be applied without entry of the coating material into leading and trailing edge sides  12  and  14 . Shroud clamp and locating fixture  20  facilitates the application of a uniform coating to shroud segment  10 . In order to facilitate maintaining turbine blade to shroud clearances in the gas turbine engine, all of the shroud segments in a shroud assembly are coated at the same time with each shroud segment  10  held in one shroud clam and locating fixture  20 . 
     FIG. 5  illustrates an exemplary spraying fixture  60  that may be used to apply ceramic coatings. Spraying fixture  60  includes supports  62  and an annular ring  64  that includes a plurality of shroud mounting stations  66  that extend circumferentially around an inner perimeter of Ring  64 . One or more mounting stations may be used as a test station  68  on ring  64 . Spraying fixture  60  is mounted on a rotating table (not shown). During a spraying process, spraying fixture  60  is rotated around a sprayer (not shown) that is positioned in a geometric center  70  of ring  64  when the spraying process is performed. 
   In operation, shroud segments  10  are individually placed in a clamp and locating fixture  20 . With the fixture  20 , masking, with tape, of shroud  10  is not necessary. The holding face  40  of clamping elements  24  seals leading and trailing edge sides  12  and  14  of shroud  10  so that sides  12  and  14  are masked by the clamping elements  24 . It is to be noted, however, that when installed in fixture  20 , shroud ends  15  are exposed to overspray. This is if little consequence because a final machining operation is performed on shroud ends  15  after the coating process. Locating member  28  facilitates the uniform positioning of shroud segments  10  in their respective fixture  20 . When the shroud segments  10  are mounted in fixture  20 , fixtures  20  are then mounted in spraying fixture  60  by placing each fixture  20  in a shroud mounting station  66  of spray fixture ring  64 . In one embodiment,  42  shroud segments are mounted in spray fixture ring  64 . When shrouds  10  and shroud fixtures  20  are mounted in spray fixture ring  64 , final adjustments are made to shroud fixtures  20  so that each shroud segment  10  is the same distance from the sprayer and the same height relative to the sprayer. The sprayer, which is positioned at geometric center  70  of spray fixture ring  64  oscillates up and down while spraying fixture  60  is rotated around the sprayer. In this manner, a thin even coating of material is applied to each shroud segment  10 . The coating is applied in thin layers over several revolutions of spraying fixture  60 . In one embodiment, 128 revolutions of the spraying fixture is made to achieve the desired coating thickness. Test stations  68  are provided on ring  64  to verify the results of the coating process. 
   The above described shroud segment clamping and locating fixture provides a cost effective and highly reliable apparatus for the masking and coating of shroud segments. The fixture facilitates eliminating failures due to blistering and deformation of the masking tape due to the heat of the spraying process and eliminates the cost of rework and repair. The cost of the masking tape is also eliminated. 
   Exemplary embodiments of a shroud clamp and locating apparatus are described above in detail. The shroud clamp and locating assemblies are not limited to the specific embodiments described herein, but rather each component may be utilized independently and separately from other components described herein. Each component can also be used in combination with other shroud clamp and locating components. 
   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.