Abstract:
During the complete masking of film cooling holes when coating a component with film cooling holes, problems frequently arise when the cooling gas exits from the film cooling hole. The method is provided which proposes that the masking is only carried out sectionally such that part of the coating is present in the film cooling hole. Thus the flow may still form like a film on the component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/065542, filed Nov. 20, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09000151.2 EP filed Jan. 8, 2009. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to the partial masking of film-cooling holes and to components thus produced. 
       BACKGROUND OF INVENTION 
       [0003]    Components which are subject to high thermal stresses, such as turbine blades or vanes, often have film-cooling bores, out of which air or steam which forms a protective film of air or gas on the turbine blade or vane flows. Here, the film-cooling hole has a diffuser, i.e. a flattening region, such that no separation of the air flow also takes place. 
         [0004]    Problems arise during the coating of turbine blades or vanes with preexisting film-cooling holes, in the case of which the coating from the prior art leads to problems. 
       SUMMARY OF INVENTION 
       [0005]    It is therefore an object of the invention to solve this problem. The object is achieved by a method as claimed in the claims and by a component as claimed in the claims. 
         [0006]    The dependent claims list further advantageous configurations which can be combined with one another, as desired, in order to obtain further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIGS. 1 ,  4 ,  6 - 9  are various views showing exemplary embodiments of a film-cooling hole with masking, 
           [0008]      FIGS. 2 ,  3  show examples of diffusers, 
           [0009]      FIG. 5  shows a component with a coating in the diffuser, 
           [0010]      FIG. 10  shows a gas turbine, 
           [0011]      FIG. 11  shows a turbine blade or vane, and 
           [0012]      FIG. 12  shows a combustion chamber. 
       
    
    
       [0013]    The description and the figures represent only exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0014]      FIG. 1  shows a film-cooling hole  4  of a substrate of a component  1 ,  120 ,  130  ( FIG. 11 ),  155  ( FIG. 12 ). 
         [0015]    The component  1  is preferably a turbine blade or vane  120 ,  130  of a gas turbine  100  ( FIG. 10 ). 
         [0016]    The film-cooling hole  4  has an inner, preferably cylindrical portion  7 . The inner portion  7  begins in the cavity  30  and extends as far as the diffuser  10  (4=7+10). The inner portion  7  preferably has a constant cross section. 
         [0017]    The film-cooling hole  4  also has an outer diffuser  10 , which deviates from the geometry of the inner region  7 , i.e. the cross section thereof increases toward the outer surface  36 . The diffuser  10  is also characterized in particular by a widening of the cross-sectional opening transversely to a direction of flow  13  of a hot gas, which flows past the component  1  ( FIG. 3 ). The diffuser  10  represents the entire outward delimitation of the film-cooling hole  4 . 
         [0018]    Therefore, as seen in the direction of flow  13  (parallel to the surface  36  of the substrate), the diffuser  10  has an end  19 , the region of which extends in a more shallow manner with respect to the surface  36  than in the cylindrical portion  7  of the film-cooling hole  4 , i.e. the angle of inclination β in the diffuser  10  with respect to the surface  36  is smaller than the angle α in the cylindrical portion  7 . 
         [0019]    There is preferably only an inclination a in the cylindrical portion  7  and preferably only an inclination β in the diffuser  10 . In particular, there is no further step in the region with the inclination β. The inner surface  11  of the diffuser  10  extends rectilinearly, that is to say has no step or depression. 
         [0020]    If a component  1 ,  120 ,  130 ,  155  is to be coated, a masking material  22 , in particular a polymer, is introduced into the film-cooling hole  4  and thus into the diffuser  10 . The polymer may contain ceramics or reinforcing particles and/or be cured (by UV) before the coating. 
         [0021]    The polymer is preferably introduced only partially into the film-cooling hole  4 . Here, an upper part  33  of the inner portion  7  of the film-cooling hole  4  is preferably filled completely with the polymer, whereas the diffuser  10  is filled only partially. There is therefore preferably no masking material  22  (polymer) at the end  19  of the diffuser  10 . Where it is introduced, however, the masking material  22  preferably passes at least as far as the height of the outer surface  36  of the substrate  30  ( FIG. 1 ). 
         [0022]    The majority of the polymer (masking material  22 ) is arranged in the film-cooling hole  4 , and there is less or preferably no polymer at all in the inner cavity  30  of the component  1 ,  120 ,  130 ,  155  with the film-cooling holes  4  which issue into the cavity  30 . 
         [0023]    The masking material  22  is preferably present only in the film-cooling hole  4 . 
         [0024]    A free space  12  therefore remains in the film-cooling hole  4  at the end  19  underneath the imaginary continued plane of the outer surface  36 , in which there is no masking  22 . The masking  22  can also preferably protrude beyond the surface  36  above the cylindrical portion ( FIG. 6 ), and then preferably has a height h, which corresponds to or is preferably higher than the coating to be applied. 
         [0025]      FIG. 2  shows a plan view onto  FIG. 1 , in which the opening of the film-cooling hole  4  can be seen. 
         [0026]    The overall length of the film-cooling hole  4  as seen in the direction of flow  13  is a+b. 
         [0027]    A masking  22  is present over the length a, but no masking is present in the section b. The ratio of a:b is preferably 2:1. 
         [0028]      FIG. 3  shows a further exemplary embodiment of a diffuser  10 . 
         [0029]    The diffuser  10  also widens transversely to the direction of flow  13 . However, in this case, too, the polymer is present only partially, i.e. there is no polymer at the end  19  of the diffuser  10 . The width of the region within the diffuser  10  where there is no polymer is the length b. 
         [0030]    The polymer can likewise be applied only thinly over the length b, such that it is still present at the start of the coating process but is removed by erosion and/or the action of heat, and thus only then is a coating possible in the diffuser  10  ( FIG. 4 ). 
         [0031]    In this case, too, a free space  12  remains in the film-cooling hole  4  underneath the outer surface  36 . Here, the masking  22  in the diffuser  10  does not extend as far as the surface  36 . In this case, too, the masking material  22  can preferably protrude beyond the surface  36  of the substrate above the cylindrical portion  7  ( FIG. 7 ). 
         [0032]    If only a small amount of masking material  22  has been used in the diffuser ( FIGS. 4 ,  7 ), this is removed by erosion and/or the action of heat during the coating, and, during the process for coating the component  1 , the diffuser  10  is temporarily also coated, as a result of which the layer thickness is thinner in the diffuser  10  than on the surface  36 . 
         [0033]    It is likewise preferable that the diffuser  10  can also be filled completely with masking material  22  at least as far as the surface  36  ( FIGS. 8 ,  9 ). Since the diffuser  10  extends in a shallow manner at the end  19 , the masking material  22  erodes more quickly there during the coating as a result of thermal attack (molten material/vapor), and the diffuser  10  can be coated at the end  19 . If appropriate, the polymer is cured to a lesser extent at the end  19  in order to achieve a higher material removal rate there. 
         [0034]      FIG. 5  shows a film-cooling hole  4  after coating, which preferably had a polymer masking as shown in  FIG. 1 ,  2 ,  3 ,  4 ,  6 ,  7 ,  8  or  9 . 
         [0035]    Since no or little masking was present at the end  19  of the diffuser  10 , a part  28  of the coating  25  is deposited there during coating of the component  1 ,  120 ,  130 ,  155  with the film-cooling hole  4 . This creates a smooth transition for the ascending gas station within the film-cooling hole  4  in the diffuser  10 , and the air stream does not stop outside the film-cooling hole  4 . 
         [0036]    The coating  28  extends preferably only in the diffuser and very particularly only partially in the diffuser  10 , i.e. at a considerable distance from the transition of the inner part  7 . The layer thickness of the coating  28  preferably decreases in the direction of the inner portion  7 . 
         [0037]      FIG. 8  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0038]    In the interior, the gas turbine  100  has a rotor  103  with a shaft  101  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0039]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
         [0040]    The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  foam the turbine  108 . 
         [0041]    Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  faulted from rotor blades  120 . 
         [0042]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by means of a turbine disk  133 . 
         [0043]    A generator (not shown) is coupled to the rotor  103 . 
         [0044]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
         [0045]    While the gas turbine  100  is operating, the components which are exposed to the hot working medium  113  are subject to thermal stresses. The guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. 
         [0046]    To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant. 
         [0047]    Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0048]    By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . 
         [0049]    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. 
         [0050]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion (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, scandium (Sc) and/or at least one rare earth element, or hafnium). 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. 
         [0051]    It is also possible for a thermal barrier coating to be present on the MCrAlX, consisting 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. 
         [0052]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0053]    The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor  103  and is fixed to a securing ring  140  of the stator  143 . 
         [0054]      FIG. 9  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0055]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0056]    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 . 
         [0057]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0058]    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 . 
         [0059]    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. 
         [0060]    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 . 
         [0061]    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 . 
         [0062]    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. 
         [0063]    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. 
         [0064]    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. 
         [0065]    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. 
         [0066]    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. 
         [0067]    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). 
         [0068]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0069]    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. 
         [0070]    The density is preferably 95% of the theoretical density. 
         [0071]    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). 
         [0072]    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-11A1-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0073]    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. 
         [0074]    The thermal barrier coating covers the entire MCrAlX layer. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0075]    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. 
         [0076]    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. 
         [0077]    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). 
         [0078]      FIG. 10  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107 , which generate flames  156 , arranged circumferentially around an axis of rotation  102  open out into a common combustion chamber space  154 . For this purpose, the combustion chamber  110  overall is of annular configuration positioned around the axis of rotation  102 . 
         [0079]    To achieve a relatively high efficiency, the combustion chamber  110  is designed for a relatively high temperature of the working medium M of approximately 1000° C. to 1600° C. To allow a relatively long service life even with these operating parameters, which are unfavorable for the materials, the combustion chamber wall  153  is provided, on its side which faces the working medium M, with an inner lining formed from heat shield elements  155 . 
         [0080]    On the working medium side, each heat shield element  155  made from an alloy is equipped with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is made from material that is able to withstand high temperatures (solid ceramic bricks). 
         [0081]    These protective layers may be similar to the turbine blades or vanes, i.e. for example 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. 
         [0082]    It is also possible for a, for example, ceramic thermal barrier coating to be present on the MCrAlX, consisting 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. 
         [0083]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0084]    Other coating processes are possible, e.g. 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. 
         [0085]    Refurbishment means that after they have been used, protective layers may have to be removed from heat shield elements  155  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the heat shield element  155  are also repaired. This is followed by recoating of the heat shield elements  155 , after which the heat shield elements  155  can be reused. 
         [0086]    Moreover, a cooling system may be provided for the heat shield elements  155  and/or their holding elements, on account of the high temperatures in the interior of the combustion chamber  110 . The heat shield elements  155  are then, for example, hollow and may also have cooling holes (not shown) opening out into the combustion chamber space  154 .