Abstract:
A safety device for a turbine blade is provided. The safety device includes a shear pin, a clamping piece and a securing element, wherein the shear pin is arranged in a corresponding bore in the turbine blade foot and the clamping piece is designed having an upper limb and a lower limb, wherein the clamping piece exerts a radial force on the turbine blade foot for radial safeguarding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2010/063701, filed Sep. 17, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09011885.2 EP filed Sep. 17, 2009. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention relates to a rotor comprising at least one turbine blade and a locking device for the axial and radial locking of the turbine blade, wherein the rotor comprises a blade groove and the turbine blade comprises a turbine blade root, wherein the blade groove and the turbine blade root are designed in such a way that the turbine blade root is fitted in the blade groove. 
     BACKGROUND OF INVENTION 
     Blade fastenings are usually used for the fastening of rotor blades on a rotor of a turbomachine, especially a steam turbine. As a result of the comparatively fast rotation of the rotor, the rotor blades which are arranged on the rotor are exposed to high centrifugal forces. The turbine blade root of the turbine blades must therefore withstand high forces and is pushed radially outward in the blade groove. In addition to the centrifugal forces, severe vibrational loads present a further problem which can result in mechanical damage, material fatigue, corrosion and a migratory movement of the blade root inside the blade groove. For fixing the turbine blade root inside the blade groove, various solutions, such as metal wedges, spring rings or sealing pieces, are known. Metal wedges certainly create a locking of the associated blade root inside a blade groove both axially and radially, but in the case of large rotor blades it is difficult to create sufficient retaining forces with such metal wedges during rotation in the radial direction. Disk springs create only radial retaining forces and necessitate additional expenditure for locking in the axial direction of the associated blade groove. Furthermore, complex measurements are necessary for disk springs during installation. As sealing pieces, provision must always be made for two parts, the installation of which, moreover, partially necessitates the machining of the parts by hand. 
     SUMMARY OF INVENTION 
     The invention is based on the object of providing a blade fastening for a turbomachine in which a precise and fixed retention of blades in associated blade holders is ensured over a long operating period. 
     This object is achieved by means of a rotor comprising at least one turbine blade according to the claims. 
     The locking device has a clamping piece which exerts a radial force from the rotor onto the turbine blade root. The clamping piece is arranged in this case in a groove which is located in the rotor, wherein the groove itself can be like the groove in which the shear pin is arranged. The size of the clamping piece is selected in such a way that a force is created, acting in the radial direction. This means that the turbine blade is pressed against the bearing flanks of the blade groove. Up to a certain rotational frequency, a movement of the blades in the groove is therefore effectively prevented. Beyond a certain rotational frequency, the centrifugal forces are of such magnitude that a movement is prevented as a result of the abutment against the bearing flanks. However, it is almost unavoidable that the turbine blade vibrates despite root fastening. The fastening according to the invention, moreover, prevents a relative movement between the turbine blade root and the blade groove, as a result of which surface damage is reduced. 
     Up to this rotational frequency, an axial displacement of the turbine blade is possible. Above the certain rotational frequency, the centrifugal forces are of such magnitude that an axial displacement is avoided, since the friction forces, which act as a consequence of the centrifugal force, effectively prevent a displacement of the turbine blade in the blade groove. 
     The clamping piece has an upper leg and a lower leg, wherein the upper leg butts against the turbine blade root and exerts a force against the turbine blade root in the radial direction. The lower leg butts against the rotor. 
     The invention is distinguished by the fact that the upper leg and the lower leg basically form a V-shape and by skilful material selection a spring force is exerted, acting from the rotor upon the turbine blade root in the radial direction. 
     In one advantageous development the shear pin butts against the lower leg. 
     Advantageous developments are disclosed in the dependent claims. 
     The invention is based on the idea that in a blade groove both radial and axial locking can be arranged. The shear pin is arranged in a corresponding hole in the turbine blade root and advantageously butts against an edge on the rotor. As a result, an axial movement of the turbine blade root is not possible. If a shear pin is arranged both on the leading edge and on the trailing edge of the turbine blade root in each case, then an axial displacement of the turbine blade root is effectively prevented both in the one direction and in the other direction. 
     The shear pin in this case is installed in a groove which is arranged in the rotor. The installation of the shear pin is carried out after the turbine blade has been installed in the rotor in the corresponding blade groove. 
     In order to avoid an unwanted loosening of the clamping piece, use is made of a locking element which is designed for locking the clamping piece. To this end, the clamping piece is designed as a locking plate and is arranged between the clamping piece and the rotor. By bending over the locking plate on the edge of the clamping piece, a displacement of the clamping piece is avoided, wherein at the same time the locking plate has to be arranged in a corresponding groove in the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the solution according to the invention is subsequently explained in more detail with reference to the attached schematic drawings. 
       In the drawings: 
         FIG. 1  shows a side view of a rotor with a turbine blade in the installed state; 
         FIG. 2  shows a cross-sectional view of a part of a rotor with installed turbine blade; 
         FIG. 3  shows an enlarged view of a detail from  FIG. 2 ; 
         FIG. 4  shows an enlarged view of a clamping piece; 
         FIG. 5  shows a perspective view of the clamping piece; 
         FIG. 6  shows a perspective view of a shear pin; 
         FIG. 7  shows a perspective view of a locking element. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows a side view of a part of a rotor  1  with an installed turbine blade  2 . The turbine blade  2  has a turbine blade root  3  which is fitted into a corresponding blade groove  4 . The turbine blade  2  is inserted into the blade groove  4  in the axial direction  5 . The blade groove  4  is designed as a fir-tree blade groove and comprises a plurality of bearing flanks  6 . 
     The turbine blade  2  is locked in the blade groove  4  both in the axial direction  5  and in the radial direction  29 . The radial direction  29  basically corresponds to the longitudinal orientation of the turbine blade  2  and the axial direction  5  basically corresponds to the rotational axis, which is not shown in more detail in  FIG. 1 . 
     For locking the turbine blade  2 , a locking device  7 , which is arranged beneath the turbine blade root  3 , is implemented. The turbine blade root  3  is designed in this case in such a way that this is fitted into the blade groove  4 , i.e. can basically move in the axial direction  5 . 
     In  FIG. 2 , a sectional view through a part of the rotor  1  is shown. The locking device  7  in essence comprises three components. These would be, on the one hand, a shear pin  8 , a clamping piece  9  and a locking element  10 . The locking device  7  is arranged in a corresponding groove  11  in the rotor  1 . This groove  11  is formed both on the steam inlet side  12  and on the steam exit side  13 . The installation of at least two locking devices  7 , i.e. both on the steam inlet side  12  and on the steam exit side  13 , offers the advantage that the turbine blade  2  can no longer move in the axial direction  5 . The principle of operation and also the installation of the locking device  7  are explained in more detail with reference to  FIG. 3 . 
     The shear pin  8  is of a cylindrical design and has a length L which is less than the height  14  of the groove  11 . As a result, a problem-free insertion of the shear pin  8  into the groove  11  is possible. The shear pin  8  is introduced into a hole  15  which is located in the blade root  3 . The hole  15  and the groove  11  in this case are designed in such a way that in the installed state the shear pin  8  butts against an edge  16  in the rotor  1 . A displacement of the turbine blade root  3  in the axial direction  5  is therefore no longer possible. 
     A further element of the locking device  7  forms the clamping piece  9 . In  FIGS. 4 and 5 , a perspective and enlarged view of the clamping piece  9  is to be seen. In essence, the clamping piece  9  is constructed with a basic body  17 , which is of a cubic design, and with an upper leg  18  and a lower leg  19 . Between the upper leg  18  and the lower leg  19  a gap  20  is formed. The dimensions of the clamping piece  9  are selected in such a way that the height  21  of the clamping piece  9  is less than the height  14  of the groove. Inserting the clamping piece  9  into the blade groove  4  is therefore possible without any problem. The dimensions are also selected in such a way that in the installed state the upper leg  18  presses a force, which is similar to a spring force, against the turbine blade root  3 . The upper leg  18  has a projection  22  for this, which is about a third of the length of the clamping piece  9 . Both the upper leg  18  and the lower leg  19  are of a wedge-like construction, i.e. the upper leg  18  and the lower leg  19  taper from the basic body  17  in the direction of the legs  18 ,  19 . 
       FIG. 6  shows a perspective view of the shear pin  8 . A third element of the locking device  7  is the locking element  10  which is constructed as a locking plate. The locking element  10  is explained in more detail with reference to  FIG. 7 . In essence, the locking element  10  is designed as a sheet metal piece of an elongated form which is completely folded over once at its tip  23 , as a result of which a projection  28  is created. In the installed state, this projection  28  lies in a corresponding locking groove  24 . As shown in  FIG. 3 , an axial displacement  5  of the locking element  10  is effectively avoided as a result. Furthermore, the locking element  10  has an end piece  26  which, in relation to a main piece  25 , is bent perpendicularly at the bending point  27 . 
     The locking device  7  is now installed as follows: First of all, the turbine blade  2  is introduced into the corresponding blade groove  4 . Next, the shear pin  8  is fitted into the corresponding hole  15 . The locking element  10  is inserted in the unbent state and at the tip  23  has a projection  28  which is arranged in a corresponding locking groove  24 . The clamping piece  9  is pushed onto the locking element  10  into the groove  11  in such a way that the shear pin  8  butts against the lower leg  19 . The possibility of the shear pin  8  falling out of the hole  15  is consequently avoided. The locking element  10  is inserted in the unbent state and at the tip  23  has a projection  28  which is arranged in a corresponding locking groove  24 . The locking element  10  is finally bent at the bending point  27 , as a result of which the possibility of the clamping piece  9  falling out of the groove  11  is effectively avoided.