Abstract:
A process for coating an edge within a hole in a coated component is provided. The hole is a cooling-air hole operable conduct a coolant therethrough. According to the processes, an outer coating is provided on the outer surface of the component. An inner coating is provided on an inner surface within the hole, wherein the inner coating within the hole takes place using a coating nozzle at a different angle to the coating of the outer surface around the hole, if the spray angles for the outer coating and inner coating relate to the outer surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 10188083.9 EP filed Oct. 19, 2010, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to cooled and coated turbine blades or vanes in which the flow rate of the coolant is set. 
       BACKGROUND OF INVENTION 
       [0003]    In various cases, cooled turbine blades or vanes (guide vanes and/or rotor blades) with cooling-air holes have incorrect, in particular excessive, flow rates of the stream of cooling air. This has a negative effect on the efficiency of the gas turbine. The air compressed in the compressor is used as little as possible for cooling, but instead should be fed to the combustion process. Cooling-air openings are understood to mean the following: a cast or bored outlet edge, stem bores (longitudinal bores), EDM or laser shapes (diffusers), cylindrical EDM or laser bores. 
         [0004]    The fault pattern or the flow rate to be optimized is often determined relatively late in the process chain. 
         [0005]    The declaration of the components as rejects is therefore very costly. 
         [0006]    Examples for excessive flow rates are: 
         [0000]    faults in the casting; in the boring process; faults in the boring process during upgrades; additional ceramic coating or an increase in the layer thickness or a reduction in conductivity during refurbishment; the base material can also be attacked by the acid during stripping or reworking, such that the size of the cooling-air openings is increased. 
       SUMMARY OF INVENTION 
       [0007]    This problem relating to the excessive flow rates needs to be solved inexpensively. 
         [0008]    It is therefore an object of the invention to solve the aforementioned problem. 
         [0009]    The object is achieved by the features of the independent claim. 
         [0010]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to obtain further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIGS. 1-5  show various views of cooling holes with or without overspray, 
           [0012]      FIG. 6  shows a turbine blade or vane, and 
           [0013]      FIG. 7  shows a list of superalloys. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0014]    The figures and the exemplary embodiments are purely exemplary for the invention. 
         [0015]      FIG. 1  shows a component  1  with a hole  7 , here a cooling-air hole  7  for example. 
         [0016]    Purely by way of example, and in particular, the component  1  is a turbine blade or vane  120 ,  130  of a turbine, in particular a gas turbine  100 , and comprises a superalloy as shown in  FIG. 7 . 
         [0017]    A coolant (air, steam) can escape from the outer surface  4  through the cooling-air hole  7 . 
         [0018]    With preference, the cooling-air hole  7  can have a constant cross section in the outflow direction  8 , or can increase in size starting from a certain distance below the surface  4  to form a diffuser ( FIG. 2 ). 
         [0019]    This increase in size can occur continuously in the outflow direction  8 , or can be foamed by a diffuser  10  ( FIG. 2 ) in the region of the surface  4 , which represents a spreading of the hole starting from a certain depth below the surface  4 . 
         [0020]    By virtue of a constriction of the cross section in the hole  7 , it is possible, in particular, to set the throughput of coolant, if nothing changes in relation to the other conditions, such as the pressure of the escaping cooling medium. 
         [0021]    An outer coating  22  comprising a metallic and/or ceramic coating is applied to such components  120 ,  130  with cooling-air holes. 
         [0022]    If the cooling-air holes are not protected, a “coat down” takes place, but this would take place in an uncontrolled manner and is generally avoided. 
         [0023]    Here, the coat down is permitted and takes place in a controlled manner. 
         [0024]    The outer surface  4  is coated in the position  13  of the coating nozzle at an angle α of between 80° and 100°, preferably 90°. 
         [0025]    The position of the nozzle  13  for coating the surface  4  is shown by dashed lines in  FIG. 3 . 
         [0026]    In all the figures, reference signs  13 ,  13 ′,  13 ″ merely represent various angular positions of the same coating nozzle. 
         [0027]    The respective spray angle α always relates to the surface  25 ,  25 ′,  4  to be coated in each case. 
         [0028]    Therefore, as shown in  FIG. 3 , a constriction is set in a controlled manner by a coating  19 ′,  19 ″ in the hole  7  by setting a coating nozzle  13 ′, as far as possible, at a steep spray angle α of 50°-100°, preferably 80° to 100°, very preferably 90°, to the coated surface  25  in the cooling-air hole  7 . 
         [0029]    The spray angle α for the inner coating  19 ′,  19 ″ is between 50° and 100°, in particular 80° and 100°, very particularly 90°. 
         [0030]    Particularly in the position  13 ″ of the coating nozzle for coating the hole  7  in the region of the undercut, i.e. at an obtuse angle to the outer surface  4 , it is not possible to adhere to the spray angle of 90°. Thus, the preferred spray angle α is set, however, at least in some places, in particular for at least 20%, of the inner surface  25 ,  25 ′. 
         [0031]    The spray angle α between the nozzle  13 ″ and the inner surface  25 ′ should as far as possible be 90°, however. 
         [0032]    A constriction  19 ′,  19 ″ is thus produced all around in the hole  7 , as shown in  FIG. 4 , but does not extend completely into the depth of the hole  7  and also does not close the latter. 
         [0033]    In particular, the coating  19 ′,  19 ″ runs completely around the entire circumferential line of the cooling-air hole  7 , as shown in  FIG. 5 , an overhead view of a diffuser  10 . 
         [0034]    It is preferable to use finer powder grains for the coating  19 ′,  19 ″ in the hole  7  than for the coating  22  on the outer surface  4 , i.e. the mean size of the grains is preferably at least 10% smaller, very particularly 20% smaller. 
         [0035]    Thus, or preferably by virtue of varied production parameters (power of the nozzle), the powder particles for the coating  19 ′,  19 ″ undergo greater fusion, i.e. fusion which is greater preferably by at least 20%, very particularly by 30%, in particular by virtue of a higher temperature of the smaller powder particles. Thus, for the coating  22 , the melting temperature of the coarser powder particles is not exceeded, or only the outer shell of the powder particles is incipiently melted (at most 50%, in particular at most 35%), or is melted homogeneously thixotropically between solidus and liquidus. Metallic material, in particular an MCrAl alloy, is used with preference for the coating  19 ′,  19 ″ in the hole  7 . 
         [0036]    The outer coating comprises a metallic coating, preferably MCrAl, and a ceramic coating, preferably on the basis of ZrO 2 . 
         [0037]      FIG. 6  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0038]    Possible coating processes are APS, HVOF, VPS, SPS (Shrouded Plasma Spray, cold gas, . . . ). A metallic metal alloy layer (MCrAlY) is preferably sprayed on. 
         [0039]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0040]    The blade or vane  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade or vane platform  403  and a main blade or vane part  406  and a blade or vane tip  415 . 
         [0041]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0042]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
         [0043]    The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0044]    The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
         [0045]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
         [0046]    Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0047]    The blade or vane  120 ,  130  may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0048]    Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. 
         [0049]    Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. 
         [0050]    In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component. 
         [0051]    Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). 
         [0052]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0053]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0054]    The density is preferably 95% of the theoretical density. 
         [0055]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0056]    The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0057]    It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0058]    The thermal barrier coating covers the entire MCrAlX layer. 
         [0059]    Columnar grains are produced in the their Jai barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0060]    Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0061]    Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
         [0062]    The blade or vane  120 ,  130  may be hollow or solid in form. If the blade or vane  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines).