Abstract:
The invention relates to a component for a thermal machine, in particular a gas turbine, which includes a corner and/or edge subjected to a thermally high load. The cooling of the component is improved in a manner such that at least one cooling channel is countersunk into the surface of the component in the immediate vicinity of the corner and/or edge in order to cool the corner and/or edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT/EP2013/053116 filed Feb. 15, 2013, which claims priority to Swiss application 00210/12 filed Feb. 17, 2012, both of which are hereby incorporated in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of thermal machines. It concerns a component for a thermal machine, in particular for a gas turbine, according to the preamble of claim  1 . 
       BACKGROUND 
       [0003]    In the case of thermal machines, in particular gas turbines, there are various components that on the one hand have corners and edges as a result of their structural design and on the other hand are exposed to high thermal loading at these places during operation. An example of such a component is a moving blade of a gas turbine, made up of multiple parts, such as that disclosed for example in the document EP 2 189 626 A1. FIGS. 1 and 2 of this document are reproduced as  FIG. 1  in the present application. 
         [0004]    The parts shown in  FIG. 1 , a platform element  10  and a blade airfoil element  20 , are assembled and connected to one another to form a moving blade. The platform element  10  has in the upper side  11  a through-opening  12 , through which the blade airfoil element  20  can be fitted with the blade airfoil  17 , ending in a blade tip  18 . Serving for securing the assembled blade are legs  13 ,  14  with formed-on hooks  15 ,  16  on the underside of the platform element  10  and a blade root  21  on the blade airfoil element  20 , which is connected to the blade airfoil  17  by way of a shaft  19 . 
         [0005]    In the assembled state, there is a transition between the blade airfoil  17  and the upper side  11  of the platform element  10 , which is shown enlarged and in section in  FIG. 2 . A gap  23 , which is formed between the parts  17  and  11  and is subjected to the hot gas flowing around the blade airfoil  17 , produces an edge  22  with a corner region  24 , which is subjected to high thermal loading. 
         [0006]    Until now, this edge  22  (running perpendicularly to the plane of the drawing in  FIG. 2 ) has been cooled by a cast cooling channel being provided parallel to the edge  22 . However, such a cooling channel is not very efficient, because
       a) with a cast channel, the distance from the surface is comparatively great, which leads to higher temperatures in the corner region  24 ; and   b) with a cast channel, the inside diameter is comparatively great, which leads to a higher consumption of cooling air.       
 
         [0009]    For this reason, oxidation and crack formation occur to a not inconsiderable extent at the edge  22  because of inadequate cooling. 
         [0010]    To solve this problem, it has already been proposed (see the document JP 2010144656 or U.S. Pat. No. 7,597,536 B1) to reduce the extent to which the edge is subjected to hot gas by for example providing flushing with cooling air. The disadvantage of this is that a considerable amount of flushing air is required to keep down the temperature of the mixed hot gas. In particular in the case of relatively large gaps, the required amount of flushing air increases significantly. If the gap width changes during operation in a way that does not correspond to the desired amount of flushing air, this type of cooling becomes ineffective. In the worst case, the flushing air may flow directly into the main stream, if the flow conditions change during operation. For these reasons, the gap is left largely without cooling, because both solution proposals presuppose a balanced mixture of hot gas penetrating into the gap and flushing air supplied through bores. 
       SUMMARY 
       [0011]    An object of the invention is to provide a component of the type mentioned at the beginning that avoids the disadvantages of known components and is always sufficiently cooled in the region of corners or edges that are subjected to high thermal loading, while expending a small amount of coolant. 
         [0012]    The object is achieved by the features of claim  1  as a whole. The component according to the invention, which is intended for a thermal machine, in particular a gas turbine, and has a corner or edge that is subjected to high thermal loading, is characterized in that, for cooling the corner or edge, at least one cooling channel recessed into the component from the surface is arranged in the direct vicinity of the corner or edge. 
         [0013]    An embodiment of the component according to the invention is characterized in that the corner or edge extends along a predetermined line, and in that the at least one cooling channel runs substantially parallel to the corner or edge over a predetermined distance. 
         [0014]    Another embodiment is distinguished by the fact that several parallel-running, recessed cooling channels are arranged in the direct vicinity of the corner or edge. 
         [0015]    A further embodiment is characterized in that the cooling channels respectively comprise a cooling tube introduced into a groove. 
         [0016]    In particular, the cooling tube is respectively embedded in a filling material filling the groove and is thereby thermally coupled to the surrounding material of the component. 
         [0017]    Another embodiment is distinguished by the fact that the groove with the introduced cooling tube is closed with respect to the surface to be cooled. 
         [0018]    In particular, a welded-on covering layer is provided for closing the groove. 
         [0019]    A further embodiment of the invention is characterized in that the cooling channel has a distance of its central axis from the surface to be cooled in the region of 1 mm. 
         [0020]    According to another embodiment, the cooling channel has an inside diameter in the region of approximately 1 mm. 
         [0021]    Yet another embodiment of the invention is characterized in that the cooling channel has an outlet on the side of the surface to be cooled and an inlet on the opposite side. 
         [0022]    According to a further embodiment, the component is provided with a thermal barrier coating. This comes into consideration in particular for components that are subjected to high thermal loading, for example those in a gas turbine. 
         [0023]    According to another embodiment, the component is formed as a blade of a gas turbine. 
         [0024]    In particular, the blade is assembled from separate components, the corner or edge to be cooled being formed at a transition between the separate components. 
         [0025]    The corner or edge may in this case be bounded on one side by a gap that is flooded by the hot gas 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention is to be explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing, in which: 
           [0027]      FIG. 1  shows an assembled moving blade of a gas turbine known from the document EP 2 189 626 A1, to which the invention can be applied; 
           [0028]      FIG. 2  shows in section a corner or edge of the blade from  FIG. 1  that is subjected to high thermal loading; 
           [0029]      FIGS. 3-5  show various exemplary embodiments of a cooling of the corner or edge from  FIG. 2  according to the invention; 
           [0030]      FIG. 6  shows in longitudinal section (A) and cross section (B) a cooling channel configuration given by way of example for the corner cooling according to the invention; 
           [0031]      FIG. 7  shows in plan view from above a platform with a constructed blade with a peripheral cooling channel according to the invention; and 
           [0032]      FIG. 8  shows corner cooling channels according to the invention at the outer corners or edges of the platform element from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    According to the invention, a technology of cooling channels recessed near the surface is used for the cooling of corners or edges of gas turbine components that are subjected to high thermal loading, such as for example moving blades, stationary blades or heat shields. In the case of a configuration according to  FIG. 2 , there is the problem that the edge  22  is exposed to hot gas from two surface areas butting one against the other, and is consequently subjected to particularly high thermal loading in the corner region  24 . 
         [0034]    According to  FIG. 3 , a cooling channel  25  running parallel to the edge  22  and having a small inside diameter is then provided in the edge region directly beneath the surface, in order to cool the corner region  24  effectively and with reduced use of coolant, generally cooling air. The inlet  30  and the outlet  29  of the cooling channel  25  are indicated in  FIG. 3  by dashed lines. 
         [0035]    The cooling channel  25  starts (with the inlet  30 ) from a plenum filled with cooling air, then runs parallel to the edge  22  to be cooled and then emits the heated air via the outlet  29  into the gap  23 . The outlet  29  may, however, also lead to the surface, in order to let out the heated air directly into the stream of hot gas and produce on the surface a film of cooling air constituting film cooling. 
         [0036]    Should a single cooling channel  25  according to  FIG. 3  not be sufficient to cool the edge  22 , two parallel-running cooling channels  25   a  and  25   b , which are correspondingly connected to the plenum and the hot gas channel, may be provided according to  FIG. 4 . Should this also be insufficient, more than two cooling channels  25   a ,  25   c  and  25   d  may run parallel to the edge  22  according to  FIG. 5 . 
         [0037]    The basic method by means of which thin cooling channels can be subsequently introduced from the surface into a preformed component very close to the surface to be cooled is illustrated on the basis of  FIG. 6 ,  FIG. 6  (A) showing the longitudinal section through an arrangement given by way of example, and  FIG. 6  (B) showing the cross section in the plane B-B: a groove  41  is introduced into a component  26  from the upper side by a suitable method (for example die sinking) with a suitably formed tool, the groove being introduced into the wall of the component that at one end runs out obliquely upward with a bend  31   a  (outlet  29 ) and at the other end has after a bend  31   b  a passage to the underside (inlet  30 ). A correspondingly dimensioned and shaped cooling tube  31  is introduced into the groove formed in this way and is thermally closely coupled to the surrounding material of the component  26  by means of a filling material  32  (for example brazing alloy or the like). The arrangement thus formed can then be closed, in that a covering layer  33  is applied by welding. It forms a cooling channel  27  near the surface, through which the cooling medium  28 , for example cooling air, flows during operation. 
         [0038]    The cooling channel  27  produced in this way has for example a distance from the central axis to the surface in the region of 1 mm, with an inside diameter in the region of approximately 1 mm. Its length generally lies in a range from 10 mm to 100 mm, preferably 20 mm to 40 mm. In the case of channel lengths beyond that, a plurality of cooling channels  27  are arranged in series, as is shown by way of example in  FIGS. 7 and 8 . Successive cooling channels  27  may differ from one another in their length, in order for example to make allowance for different thermal stresses or design constraints. In the interests of an optimum cooling effect, they may be flowed through by the cooling medium in the same direction or in opposite directions. The same also applies to cooling channels arranged in parallel. 
         [0039]    In the case of a platform element  34  according to  FIG. 7 , which has on the upper side  35  a through-opening  36 , which is bordered by an arcuate curve that resembles a blade profile, the at least one cooling channel  37  according to the invention must be made to replicate this arcuate curve. A number of cooling channels  37  arranged one behind the other, which may also be formed in an arcuate manner, follow the contour of the curve. The actual length of the individual channels  37  depends in particular on the thermal loading of the platform element  34 . It will generally be between 20 mm and 40 mm. 
         [0040]    In the case of a platform element according to  FIG. 1 , however, cooling air channels according to the invention may also be used at the outer edges, as is indicated in  FIG. 8  for the cooling channels  38  and  39 . 
         [0041]    The advantages of the invention can be summarized as follows:
       a) the efficiency of the machine is improved by reduced cooling air consumption;   b) the cooling takes place as close as possible to the location to be cooled;   c) the corners or edges that are subjected to high thermal loading, which are formed at annular surfaces butting against one another and as a result are subjected to particularly high loading, are cooled effectively; and   d) the service life of the component that is cooled in this way is extended significantly.