Abstract:
The invention relates to a turbine blade, including a blade having a front edge and a rear edge, which blade transitions by means of a shaft into a blade root designed for fastening the turbine blade, and including a platform, which is arranged at the lower end of the blade in order to bound a flow channel. The platform is designed as a separate component and can be connected to the blade in a form-fit manner. Flexible application is achieved in that the platform is composed of several individual platform elements, which enclose the blade in the assembled state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT/EP2013/056610 filed Mar. 27, 2013, which claims priority to European application 12162372.2 filed Mar. 30, 2012, both of which are hereby incorporated in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention concerns the field of turbomachines. It relates to a turbine blade or vane as per the preamble of claim  1 , as is used as a guide vane or rotor blade in particular in gas turbines. 
       BACKGROUND 
       [0003]    Blades or vanes for gas turbines, which are used in the compressor part or turbine part as guide vanes or rotor blades, are usually produced as one part by forging or investment casting. This also applies in particular to blades or vanes which have a platform and/or a shroud segment. 
         [0004]    The loading of guide vanes and rotor blades in the gas turbine is increased by the continuously encouraged increase in the hot gas temperature and the reduction of the cooling air consumption. It is therefore desirable to reduce stresses which arise on the blades or vanes by design measures. Components which experience reduced levels of stress can withstand higher temperatures with the same service life. In this way, it is possible to accommodate for the demand for a higher hot gas temperature and a lower cooling air consumption. 
         [0005]    EP 2 189 626 A1 discloses a rotor blade arrangement for a gas turbine, which rotor blade arrangement can be fastened to a blade carrier and comprises in each case a main blade part element and a platform element, wherein the platform elements of a blade row form a continuous inner shroud. A reduced level of stress is achieved therein by virtue of the fact that the blade airfoil element and the platform element are formed as separate elements and can each be fastened to the blade carrier separately. A disadvantage of this solution is that it is not suitable for retrofit tasks, because the nature of the fastening to the rotor changes by virtue of the platform element, and therefore the rotor itself has to be adapted. 
         [0006]    U.S. Pat. No. 7,762,781 B1 discloses an arrangement made up of a turbine blade or vane and a platform, in which the platform is formed as a separate element which is fastened to the blade or vane by special pins. This solution has the disadvantage that the individual elements are very expensive to produce. 
       SUMMARY 
       [0007]    It is an object of the invention to specify a turbine blade or vane which avoids the disadvantages of known turbine blades or vanes and is distinguished by the fact that use is made of a separate platform which can be attached to the rotor without any change on the fastening side. 
         [0008]    This and other objects are achieved by the entirety of the features of claim  1 . 
         [0009]    The turbine blade or vane according to the invention comprises a blade or vane airfoil with a leading edge and a trailing edge, which merges via a shaft into a blade or vane root formed for the fastening of the turbine blade or vane, and also a platform, which is arranged at the lower end of the blade or vane airfoil to delimit a flow channel, wherein the platform is formed as a separate component and can be connected to the blade or vane airfoil with a positive fit. The turbine blade or vane according to the invention is distinguished by the fact that the platform is composed of a plurality of individual platform elements, which, when assembled, enclose the blade or vane airfoil. The composite design of the platform makes it possible to fasten the latter directly to a blade or vane, such that adjustments in the region in which the blade or vane is fastened can be avoided. 
         [0010]    According to one embodiment of the invention, the platform is composed of two platform elements. 
         [0011]    Another embodiment of the invention is characterized in that the two platform elements, when assembled, butt against one another with joint surfaces in a separating plane which extends from the leading edge or, respectively, the trailing edge of the main blade or vane part in an axial direction with respect to the associated edge of the platform. 
         [0012]    In particular, the platform elements are each provided with recesses which proceed from the separating plane and, when assembled, form an opening adapted to the profile of the blade or vane airfoil for the blade or vane airfoil passing through the platform. 
         [0013]    It is preferred that the platform is sealed off with respect to the main blade or vane part. 
         [0014]    In particular, a circumferential sealing groove, which receives an appropriate seal, is made in the platform elements for sealing off with respect to the blade or vane airfoil along the opening. 
         [0015]    According to another embodiment of the invention, the two platform elements are sealed off with respect to one another in the separating plane. 
         [0016]    In particular, a sealing groove, which receives a matching seal, is provided for sealing off in the separating plane. 
         [0017]    A further embodiment of the invention is characterized in that the two platform elements are releasably connected to one another. 
         [0018]    In particular, the two platform elements can be screwed or riveted to one another. 
         [0019]    It is preferred that flange sections which are oriented parallel to the separating plane, butt against one another in the separating plane and through which the two platform elements are screwed or riveted to one another are formed on the two platform elements. 
         [0020]    According to a further embodiment of the invention, the two platform elements are locked to one another by locking means. 
         [0021]    In particular, the platform elements, when assembled, overlap one another with overlapping sections, wherein a locking channel is formed in the overlapping region between the overlapping sections, and the locking channel is filled with a filling. 
         [0022]    According to a further embodiment of the invention, the platform is fastened to the turbine blade or vane. 
         [0023]    In particular, the platform is hooked to the turbine blade or vane. 
         [0024]    It is preferred that the platform or the platform elements is (are) equipped with hooks, by way of which it (they) is (are) hooked into a groove in the region of the shaft of the turbine blade or vane. 
         [0025]    Alternatively, the platform or the platform elements can be integrally connected to the turbine blade or vane. 
         [0026]    According to a particularly preferred variant, the platform or the platform elements is (are) connected to the turbine blade or vane by means of a filling poured into a locking channel, in such a manner that the joint surfaces of a section of the turbine blade or vane and of the platform or of the platform elements are equipped with opposing recesses, which together form a cavity that is suitable for being filled with a solidifying filler, for example a molten metal. 
     
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         [0027]    The invention will be explained in more detail hereinbelow on the basis of exemplary embodiments in conjunction with the drawing, in which: 
           [0028]      FIG. 1  shows, in a perspective view, a platform which can be assembled from two individual elements, according to one exemplary embodiment of the invention; 
           [0029]      FIG. 2  shows, in a perspective view, a turbine blade or vane having a platform as shown in  FIG. 1 ; 
           [0030]      FIG. 3  shows, in a sectional view, the way in which a platform element is sealed off with respect to the blade or vane airfoil in the arrangement as shown in  FIG. 2 ; 
           [0031]      FIG. 4  shows, in the side view ( a ) and the plan view from above ( b ), an exemplary embodiment of a screwed platform according to the invention; 
           [0032]      FIG. 5  shows, in the side view ( a ) and the plan view from above ( b ), an exemplary embodiment of a locked platform according to the invention, and 
           [0033]      FIG. 6  shows an alternative embodiment of the way in which a platform element is fastened and sealed off with respect to the blade or vane airfoil in the arrangement as shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 2  shows, in a perspective view, a turbine blade or vane having a platform according to one exemplary embodiment of the invention. The turbine blade or vane  10 , which for example can be a rotor blade or a guide vane of a gas turbine, comprises a blade or vane airfoil  11 , which ends at the top in a blade or vane tip  12  and has a leading edge  13  and a trailing edge  14 . The blade or vane airfoil  11  merges downward into a shaft  15 , this being adjoined by a blade or vane root  16 , which is formed like a fir tree in a manner known per se in order to be inserted into a corresponding receptacle on the rotor. 
         [0035]    At its lower end, the blade or vane airfoil  11  is surrounded by a platform  17 , which, as shown in  FIG. 1 , is composed of two separate platform elements  17   a  and  17   b  in a separating plane  19 , the two platform elements  17   a, b  butting against one another with corresponding joint surfaces  19   a  and  19   b  ( FIG. 1 ). Proceeding from the joint surfaces  19   a  and  19   b,  recesses  18   a  and  18   b  are made in the two platform elements  17   a, b,  said recesses forming an opening  18 , when the platform  17  is assembled, through which the blade or vane airfoil  11  can extend ( FIG. 2 ). As can be gathered from  FIGS. 1 and 2 , the separating plane  19  extends on both sides of the blade or vane airfoil  11  in an axial direction from the leading edge  13  to the front edge of the platform  17  and, respectively, from the trailing edge  14  to the rear edge of the platform  17 . 
         [0036]      FIG. 3  shows, by way of example, the way in which the platform elements  17   a, b  are fastened to the blade or vane airfoil  11  and also the corresponding seal between the platform elements  17   a, b  and the blade or vane airfoil  11 . For fastening purposes, that side of the platform elements  17   a, b  which faces toward the blade or vane airfoil  11  is provided with hooks  23 , by way of which the platform elements  17   a, b  engage into a corresponding groove  22  on the shaft  15  of the blade or vane. In this way, the blade or vane root  16  remains free of any interference by the platform  17 . To provide a seal, a circumferential sealing groove  20 , which receives a matching seal  21 , is provided in the platform elements  17   a, b  at the edge which faces toward the opening  18 . 
         [0037]    The two platform elements  17   a  and  17   b  can be connected in different ways.  FIG. 4  shows, by way of example, a screwed connection of the two elements. To this end, flange sections  27   a, b  which are oriented parallel to the separating plane  19 , butt against one another in the separating plane  19  and through which the two platform elements  17   a, b  are connected to one another by means of a connecting element  26 , in particular in the form of a stud, are formed on the two platform elements  17   a,  b. Instead of the stud, it is also possible to use a rivet. As is shown in  FIG. 4(   a ), a seal can also be provided between the platform elements  17   a, b  in the separating plane  19 . For this purpose, a sealing groove  24 , which receives a matching seal  25 , is formed in the separating plane  19 . 
         [0038]    Instead of the detachable screwed connection, the platform elements  17   a, b  can also be connected integrally by means of welding or soldering, however. 
         [0039]    As a further possibility for connecting the platform elements  17   a,  b,  FIG. 5  shows a special type of locking, which is known under the keyword “bi-cast” and is described, for example, in U.S. Pat. No. 5,797,725. In this case, the two platform elements  17   a, b  overlap with corresponding overlapping sections  28   a  and  28   b,  a locking channel  29  being formed in the overlapping region and being filled with a metallic filling  30 , after the platform elements  17   a, b  have been joined together, which then reliably prevents a relative movement between the overlapping sections  28   a,  b. As the section along the plane A-A from  FIG. 5(   b ), as is shown in  FIG. 5(   a ), makes clear, laterally protruding lugs of the filling  30  can be provided in the locking channel  29 , in order to prevent the filling  30  from slipping out in the longitudinal direction of the connecting channel  29 . 
         [0040]      FIG. 6  shows, as an alternative to that shown in  FIG. 3 , a further embodiment of the fastening of the platform elements  17   a, b  to the main blade or vane part  11  which combines the functions of the mechanical fastening and the sealing with one another. Instead of a non-positively and positively fitting connection by means of the fastening elements groove  22  and hook  23  and also the sealing elements groove  20  and seal  21 , as shown by way of example in  FIG. 3 , an integral connection of these components arises by means of a solidifying filling  30 , which can be poured into a locking channel  29  formed between said turbine blade or vane components to be connected. In order to achieve this, the facing joint surfaces of the recess  18  of the platform elements  17   a, b  and also of the blade or vane airfoil  11  or of the shaft  15  of the turbine blade or vane  10  are provided with opposing grooves for the introduction of a pourable filling  30 , in particular a molten metal. After the filling material introduced has solidified, for example after it has hardened or cured, the blade or vane components are fixedly connected to one another. In this respect, it is self-evident to select a filling material which remains in the solid state and does not experience any thermal damage under the conditions of the intended use of the turbine blade or vane  10 . If the locking channel  29  is continuously formed in such a way that it forms a closed ring around the airfoil  11  or the shaft  15  of the turbine blade or vane  10 , this connection performs the dual function of fastening and sealing, since a connection of this type is by nature sufficiently fluid-tight. The requirement for an additional seal between the main blade or vane part  11  or shaft  15  and the platform  17  therefore no longer applies. 
         [0041]    The invention achieves mechanical decoupling between the platform and the blade or vane, which avoids undesirable stresses and at the same time is flexible in use and can also be retrofitted without a change to the way in which the blade or vane is fastened.