Abstract:
A method for adjusting the size of cooling holes ( 4 ) of a gas turbine component ( 1 ) is disclosed in which the component ( 1 ) is shielded with an easy removable and non conduction shielding material ( 7 ) without shielding the cooling holes ( 4 ) itself. The cooling holes ( 4 ) are then coated by means of a galvanic process and thereby a manufacturing tolerance of the size of the cooling holes ( 4 ) is reached. The shielding material ( 7 ) is removed and, subsequently, a heat treatment for securing a bonding of the metallic coating is applied.

Description:
FIELD OF INVENTION  
         [0001]    The invention relates to a method of adjusting sizes of cooling holes of a gas turbine component according to the preamble of the claim  1 .  
         STATE OF THE ART  
         [0002]    Components such as gas turbine blades, vanes and other cooled parts often contain cavities that distribute cooling air to a plurality of holes in the wall of the part that lead to the outer surface. Most turbine components are coated for protection from oxidation and/or corrosion with, for example, a MCrAlY coating (base coat) and some are also coated with a thermal barrier coating (TBC) for thermal insulation.  
           [0003]    Cooling holes are sometimes manufactured larger than the intended size limit. This could possible happen with a new component during the production of the holes. The problem is that enlarged cooling holes lead to an increased flow of cooling air and an altered film cooling air distribution and with that a changed cooling efficiency of the components at different locations. Thus, it can affect as well the overall efficiency in an unintended and negative manner using an excessive amount of cooling air. It can also lead to an increased degradation of the base component at locations where there is a reduced cooling effect. Thus, it is the aim to provide an easy method to restore the size of the cooling holes in new components to the originally intended limits and avoid a high rate of scrapping during production of the new parts, particularly during production start-up when errors occur often.  
           [0004]    Furthermore, the same problem occurs with components in which the size of cooling holes has been changed during service. This can happen due to oxidation, spallation and degradation of the base material exposed on the cooling hole surfaces. Again, it is the aim to find a method to repair these components rather than to use new parts by restoring the size of the cooling holes to a certain limit. For this case there are several methods known in the state of the art for repair the protective coating itself, trying to avoid the coating of the cooling holes. This is disclosed e.g. in U.S. Pat. No. 4,743,462 or in U.S. Pat. No. 5,800,695. But up to now there are no methods known for adjusting the size of cooling holes to bring them back to a given tolerance.  
         SUMMARY OF THE INVENTION  
         [0005]    It is object of the present invention to find a method of adjusting the size of cooling holes of a gas turbine component to a size within manufacturing tolerances. The method should be applicable to cooling holes which are manufactured with a greater size in the first place (before service) or by cooling holes which have an increased diameter due to oxidation and spallation during service.  
           [0006]    In the present invention a method according to the preamble of claim  1  is found characterised in that the component is shielded on least at the inside with a coating of wax or plastic or other easily removable and non conducting material; the component is subjected to a coating process, such as galvanic coating or a vapour phase coating process, in which a metallic coating is applied to the inside of the cooling holes to a thickness that restores the cooling holes to intended design manufacturing tolerances, after which the shielding material is removed. A heat treatment may be applied to the component to ensure the quality of the bonding of the new applied metallic coating to the component.  
           [0007]    With the method according to the present invention it is with advantage possible to bring the size of the cooling holes in an easy way to a desired tolerance. This applies for both cooling holes manufactured with a size greater than intended originally or for cooling holes which have a greater size due to oxidation or spallation during service. In the last case it might be necessary to remove remaining oxidised material before applying the process by any suitable means such as acid cleaning, grit blasting or Fluor Ion Cleaning.  
           [0008]    Where the component has two protective coatings, a metallic and a ceramic at the outside, the component is shielded during the method according to the invention with the shielding material only at the inside. On the other hand, where the component has only one protective coating, which is no ceramic coating, the component is shielded with the shielding material at both the inside and the outside.  
           [0009]    In an example the metallic coating could have a following composition (wt-%): 25% Cr, 5.5% Al, 2.7% Si, 1.0% Ta, 0.45-0.8% Y, max. 0.03% C, balance Ni and unavoidable impurities. Also possible is a metallic coating such as Pt or Ni-based and containing at least one of the following components Cr, Al, Y. When the metallic coating is Pt, the Pt is applied by means of a galvanic process, and this could be followed by an aluminising process using pack aluminising, above-the-pack aluminising or any other means for depositing on top of the already deposited Pt. In another possible embodiment the metallic coating is applied by means of a high temperature chemical vapour deposition or any other gas phases means, and the portions of the component not desired to be coated are protected with a high temperature resistant masking material.  
           [0010]    In an preferred embodiment the base component could have one of the following compositions:  
           [0011]    A. max. 400 ppm C, 65 ppm B, (wt.-%) 0.2% Hf, 6.4% Cr, 9.6% Co, 0.6% Mo, 6.4% W, 6.5% Ta, 2.9% Re, 5.6% Al, 1.0% Ti,  
           [0012]    B. 700 ppm C, 150 ppm B, (wt.-%) 1.4% Hf, 8.0% Cr, 9.0% Co, 0.5% Mo, 10.0% W, 3.2% Ta, 5.6% Al, 0.7% Ti,  
           [0013]    C. max. 1600 ppm C, 150 ppm B, (wt.-%) 1.4% Hf, 8.4% Cr, 10.0% Co, 0.7%Mo, 10.0% W, 3.0% Ta, 5.5% Al, 1.0% Ti 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention is illustrated by the accompanying drawings, in which  
         [0015]    [0015]FIG. 1 shows a gas turbine blade with cooling configuration,  
         [0016]    [0016]FIG. 2 shows a section through the turbine blade shown in FIG. 1 according to line II-II, comprising a cavity and a plurality cooling holes and  
         [0017]    FIGS.  3 - 6  show the steps of the method according to the invention. 
     
    
       [0018]    The drawings show only the parts important for the invention. Same elements will be numbered in the same ways in different drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 shows a component  1  such as blades or vanes of gas turbine engines comprising a cavity  2 , not visible in FIG. 1, and cooling holes  4 , which are on the external surface  6  of the component  1  as well as on the platform  3  of the component  1 . The present invention relates to a process of adjusting the size of the cooling holes  4  to a desired tolerance by means of applying a coating within the cooling holes  4 .  
         [0020]    According to line II-II in the FIG. 1 FIG. 2 shows a section through the component  1 . The component  1  comprising a cavity  2  and three cooling holes  4 . The number of the cooling holes  4  is given only as an example and may vary on the purpose the component  1  is used for. The component  1  has an external surface  6  and an internal surface  6   a.    
         [0021]    It is possible to apply the process for the adjusting the size of the cooling holes  4  of a new component  1  as well as to a component  1  which has to be repaired after use. For a new component  1  the size of the cooling holes  4  might be out of a margin of tolerance which can already occur during the production of the cooling holes  4  by means of laser drilling, a spark erosion process or any similar process. In that case of an used component  1  the size of the cooling holes  4  changed by oxidation or spallation during service. Both cases lead to an undesired decreased cooling efficiency which affect on the efficiency of the whole gas turbine.  
         [0022]    The steps of the process of the invention are given in FIGS.  3  to  6 , which show a cooling holes  4  from the component  1  in detail as given as an example in the circle III in the FIG. 2.  
         [0023]    The FIG. 3 shows the basic component  1  at the beginning for the method according to the invention. The external surface  6  is masked with a protective coating  5  such as MCrAlY, which is prevalent in the state of the art. It is a family of high temperature coatings, wherein M is selected from one or a combination of iron, nickel and cobalt. As an example U.S. Pat. No. 3,528,861 or U.S. Pat. No. 4,585,418 are disclosing such kind of oxidation resistant coatings. U.S. Pat. No. 4,152,223 as well discloses such method of coating and the coating itself. As seen from FIG. 3 the cooling holes  4  have greater size then desired. The margins of a tolerance within an intended limit are given by a dotted line. The aim of the method is to reach this intended limit.  
         [0024]    [0024]FIGS. 4 and 4 a  illustrate the first steps of the method according to the present invention. The component  1  is shielded at least on side of the surface  6 , 6 , a , which is in the FIGS. 4,4 a  the inner surface  6   a , with a shielding coating  7  of wax or plastic or other easily removable and non conducting material. In case, if there is a ceramic coating  5   a  at the outer surface this shielding coating  7  has only to be applied at the inner surface  6   a , as seen in FIG. 4 a . In contrary, FIG. 4 shows that both surfaces  6 , 6   a  are shielded due to a lack of this ceramic coating  5   a . In general, there might be no shielding necessary at all e.g. when there is a ceramic coating at the outside and a vapour phase aluminising is used for the new coating. Before that step, in case that the diameter of the cooling holes  4  has changed due to spallation or oxidation during service of the component  1 , there might be a step of cleaning the inside of the cooling holes  4  from remaining oxidised material by any suitable process such as acid cleaning, grit blasting, Fluor Ion Cleaning.  
         [0025]    After that and as seen in FIG. 5, the component  1  is subjected to a coating process, such as galvanic coating or a vapour phase coating process, in which a metallic coating  8  is applied to the inside of the cooling holes  4  to a thickness that brings back the cooling holes  4  to within manufacturing tolerances. There are different possible materials which could be used for the metallic coating  8 .  
         [0026]    The metallic coating  8  could have the following composition (wt-%): 25% Cr, 5.5% Al, 2.7% Si, 1.0% Ta, 0.45-0.8% Y, max. 0.03% C, balance Ni and unavoidable impurities. The metallic coating  8  could be as well be Pt or Ni-based and containing at least one of the following components Cr, Al, Y. When the metallic coating  8  is Pt, the Pt may be applied by means of a galvanic process, and this is followed by an aluminising process using pack aluminising, above-the-pack aluminising or any other means for depositing on top of the already deposited Pt. The method of aluminising is described in e.g. Metals Handbook, Desk Edition (2. Edition 1998), p.1166-1170, issued by the American Society of Metals (ASM). Possible ways of deposition is known in the state of the art as chemical or physical vapour deposition (CVD, PVD). Furthermore, the metallic coating  8  could be applied by means of a high temperature chemical vapour deposition or other gas phases means, and the portions of the component not desired to coated are protected with a high temperature resistant masking material  7 . This could be e.g. a paste comprising mainly metal oxides.  
         [0027]    At the last step of the invention the shielding material  7  is removed and the dimensions of the cooling holes  4  are within desired tolerances again. This could be done e.g. by a suitable heat treatment, which melts out the wax or plastic. This is seen from FIG. 6. In addition a heat treatment is applied to the component  1  to ensure the quality of the bonding of the new applied metallic coating  8 .  
         [0028]    The base component  1  could have one of the following compositions:  
         [0029]    A. max. 400 ppm C, 65 ppm B, (wt-%) 0.2% Hf, 6.4% Cr, 9.6% Co, 0.6% Mo, 6.4% W, 6.5% Ta, 2.9% Re, 5.6% Al, 1.0% Ti, balance Ni and unavoidable impurities.  
         [0030]    B. 700 ppm C, 150 ppm B, (wt-%) 1.4% Hf, 8.0% Cr, 9.0% Co, 0.5% Mo, 10.0% W, 3.2% Ta, 5.6% Al, 0.7% Ti, balance Ni and unavoidable impurities or  
         [0031]    C. max. 1600 ppm C, 150 ppm B, (wt-%) 1.4% Hf, 8.4% Cr, 10.0% Co, 0.7%Mo, 10.0% W, 3.0% Ta, 5.5% Al, 1.0% Ti balance Ni and unavoidable impurities.  
         [0032]    The invention is not limited to the embodiment according to the given description but has to be seen in the scope of the enclosed claims to any component with cooling holes therein which is used in an high temperature environment such as blade or vanes, or parts of a gas turbine burner.  
       Numbering  
       [0033]    [0033] 1  Turbine blade  
         [0034]    [0034] 2  Cavity  
         [0035]    [0035] 3  Plafform  
         [0036]    [0036] 4  Cooling holes  
         [0037]    [0037] 5  Protective coating (metallic coating)  
         [0038]    [0038] 5   a  Second protective coating (ceramic coating)  
         [0039]    [0039] 6  Outer surface  
         [0040]    [0040] 6   a  Inner surface  
         [0041]    [0041] 7  Shielding coating/shield material  
         [0042]    [0042] 8  Metallic coating within cooling holes  4