Patent Publication Number: US-8535012-B2

Title: Arrangement for axially securing blades in a rotor of a gas turbine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2009/050363, filed Jan. 14, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08002388.0 EP filed Feb. 8, 2008. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention refers to an arrangement for axially securing rotor blades in a rotor of a gas turbine according to the features of the claims. 
     BACKGROUND OF INVENTION 
     An arrangement of this type is known for example from WO 2007/028703 A1 and is illustrated here in  FIGS. 1 and 2 . The arrangement  10  comprises a shaft collar  21  which is formed by a rotor disk  19 , which shaft collar  21  is part of the rotor  23  of a gas turbine. On the outer periphery  52  of the rotor  23 , provision is made in the rotor disk  19  for grooves  12  which extend in the axial direction. Inserted in the grooves  12  are the roots  54  of the respective rotor blades  14  which are secured against displacement along the groove  12 . For the securing, provision is made for so-called sealing elements  16  which at least partially cover the end-face opening of the respective groove  12  and which when assembled form an end-face sealing ring. On the end face  56  of the shaft collar  21 , provision is made for an annular groove  20  in which the essentially rectangular sealing element  16  is seated. Radially on the outside, the sealing elements  16  lie in grooves  24  which are provided on the undersides  26  of the platforms  28  of the rotor blades  14 . In order to secure the sealing elements  16  against displacement in the circumferential direction, at least one of the sealing elements  16  comprises a metal strip  30 , which is fastened to this, with a leg  64 , which leg  64  butts in a form-fitting manner either against the rotor blades  14  or their platforms  28  ( FIG. 1 ), or against the rotor disk  19  itself ( FIG. 2 ). In addition to securing the rotor blades  14 , the sealing elements  16  also have the task of guiding a cooling air flow along the end face of the rotor disk  19 . 
     During installation of the sealing elements and also during bending-in of the metal strip, these, however, can be incorrectly plastically deformed so that the sealing strip can sit in the annular groove with an excessively large clearance. As a result of this, cooling air losses can occur. Also, as a result of the plastic deformation which is not provided, the integrity of the sealing element and of the metal strip can be negatively influenced. Moreover, the slight spring-back of the metal strip after the bending-in process on account of its elasticity is disadvantageous. 
     SUMMARY OF INVENTION 
     The object of the invention is therefore the provision of an arrangement for axially securing rotor blades in a rotor of a gas turbine, in which the sealing elements can be installed and removed in a particularly reliable manner. 
     The solution provides that the material of the metal strip is a shape-memory alloy. By using the shape-memory alloy as the material for the metal strip, both the installation and the functional reliability of the metal strip can be enhanced. Moreover, it is provided that the metal strip butts against the sealing element in a clearance-free manner or under a pretension. As a result of this, an undesirable creeping of the sealing element in the circumferential direction can be reliably avoided. The reliable avoidance is attributed to the fact that a gap now no longer exists between sealing element and metal strip and therefore the metal strip is reliably locked by the machine component which butts against it, i.e. by the platform of the rotor blade or by the cam of the rotor disk. With the presence of a gap between sealing element and metal strip, in the worst case, depending upon its size, a relative movement between sealing element and machine component could occur, during which the machine component would slide into the gap. The last-mentioned, however, is prevented with the invention so that a particularly reliable securing of the sealing element against circumferential displacement can be achieved. 
     Components which are produced from shape-memory alloys are characterized in that as a result of temperature influence these can permanently alter their external shape, maintaining great rigidity. These components can therefore have a first geometry, i.e. shape and contour, and a second geometry. These components can be re-deformed from the second geometry into the first geometry by heat treatment alone. That geometry which the metal strip assumes after heat treatment has been carried out is subsequently also called the functional geometry. The second geometry can be almost any geometry and can be specified when producing the component. 
     The content which is described in publication WO 2007/028703 A1 is completely incorporated into this application by this reference. Particularly the arrangement according to  FIG. 1  and  FIG. 2  which is described in the prior art of WO 2007/028703 A1, and particularly the arrangements with reference to  FIG. 3  and  FIG. 4  according to the invention according to WO 2007/028703 A1, can be further improved by means of the invention which is described in this application. 
     The metal strip is produced in such a shape that in the installed state it shall later lock the position of the sealing elements. This preliminary shape corresponds to the first geometry. Before installation, the metal strip is then deformed in a suitable manner into the second geometry so that it can be fastened on the sealing element. The sealing element is then installed on the shaft collar. After installation, a temperature treatment is carried out, as a result of which the metal strip strives to re-deform itself into its first geometry. The temperature treatment can be carried out either by means of heating with the aid of an external source of heat just before putting the gas turbine into operation, or the initial operation of the gas turbine, during which high temperatures occur, can trigger the deformation of the metal strip. It is also possible for both temperature treatments to be applied in order to achieve a final deformation of the metal strip. 
     After the temperature treatment, the metal strip has assumed its functional geometry and secures the sealing element both against loss and against displacement in the circumferential direction. As long as functional geometry and first geometry differ from each other, a pretensioned fastening of sealing element or metal strip can be achieved. 
     In all, as a result of this an especially simple and secure installation of the metal strip or of the sealing element on the shaft collar of the rotor is made possible, as a result of which the disadvantages which occur in the prior art can be avoided. A manual bending-in of the metal strip therefore only needs to be carried out to a limited extent, or, in the best case, not at all. Consequently, faulty manual installation can be excluded, which increases the reliability of the gas turbine which is equipped therewith. 
     In particular, if the leg butts against the rotor blades or against the shaft collar under a pretension, an especially reliable connection and fastening of the sealing element on the shaft collar or on the rotor can be made possible. The developments which are known from the prior art can preferably be further developed in this way. The pretension which is created by the metal strip according to the invention then acts specifically between rotor blade and sealing element so that the outer end of the sealing element which is seated in the groove, on account of the pretension, can be pressed flat against a sidewall of the groove which is arranged in the underside of the platform of the rotor blade. The flat pressing-on leads to a particularly tight abutment of the sealing element in the outer groove. Leakage of cooling air, which is directed by the sealing element, which could occur between the outer end of the sealing element and the groove, can consequently be reduced and in the best case avoided. The same applies to the inner end of the sealing element which is arranged in the annular groove radially on the inside if the metal strip is supported on the shaft collar in a pretensioned manner and in the process presses the inner end of the sealing element in a tight and flat manner against a sidewall of the annular groove. 
     Advantageous developments are disclosed in the dependent claims. 
     The material preferably has a one-way effect. This means that during heating up of the metal strip, which is pseudoplastically deformed in the martensitic state beforehand, a single change of shape takes place. The cooling down after heating has been carried out no longer brings about a change of shape. The metal strip remains in its first geometry or functional geometry. 
     It is also conceivable for a further component consisting of a non-shape-memory alloy to be attached on the metal strip in order to achieve an improved form fit for securing the sealing element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained based on an exemplary embodiment which is represented in a drawing, wherein identical components are provided with the same designations. Further advantages and features result from the explanation. 
         FIGS. 1 ,  2  show two arrangements of axial securing of rotor blades 
         FIGS. 3-7  show different further constructions of the fastening of the sealing element which is known from the prior art with a metal strip according to the invention consisting of a shape-memory alloy, in a purely schematic representation. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     With reference to the description of  FIG. 1  and  FIG. 2  in the prior art, the metal strip  30 , which is shown there, may be produced from a shape-memory alloy according to the invention. The geometry of the metal strip  30  which is shown in  FIG. 1  and  FIG. 2  represents the first geometry. For installing the metal strip  30 , this is to be deformed into the second geometry beforehand so that the sealing element  16  can be inserted into an annular groove  20 . After installation of the sealing element  16 , the metal strip  30  can then be re-deformed into the functional geometry by means of heat treatment and can create the form fit between it and the platforms  28  ( FIG. 1 ) or the rotor disk  19  ( FIG. 2 ). As long as the functional geometry corresponds to the first geometry, the metal strip  30 , and therefore the sealing element  16 , is seated on the rotor  23  without tensioning or with clearance. 
     On the other hand, that configuration of the metal strip  30  which is formed according to the invention, which has a functional geometry which differs at least slightly from the first geometry in order to therefore create a pretension between rotor blade  14  or shaft collar  21  on one side and sealing element  16  on the other side, is especially preferable. A pretension is achieved if the first geometry of the metal strip  30  is selected so that despite the heat treatment this cannot be achieved on account of a mechanical blocking by other machine components. In this case, the metal strip  30  remains in the functional geometry after heat treatment has been carried out and in this case butts against the blocking machine component with pretension. The blocking machine component can be formed by the groove  24 , the annular groove  20 , the platform  28  of the rotor blade  14  or even by the shaft collar  21 . As long as the functional geometry is selected so that a pretension which is directed perpendicularly to the plane of the drawing is created, the sealing element  16 , radially on the outside, can be pressed flat with sealing effect onto the sidewall of the groove  24  which is arranged in the underside  26  of the platform  28 , and/or, radially on the inside, pressed flat with sealing effect onto a sidewall of the annular groove  20 , as a result of which a leakage of cooling air which is guided by the sealing element can be reduced and if necessary even avoided. 
     Instead of the configurations which are shown in  FIG. 1  and  FIG. 2 , the invention can also be applied according to the invention with alternative configurations. For this purpose, different configurations with different metal strips  30  are shown in  FIGS. 3 to 7 . Common to all the metal strips  30  which are shown therein is that they are fastened in a suitable manner on a sealing element  16 . 
     Each of  FIGS. 3-7  includes three sub-figures which have either the suffix a, b or c. The sub-figures according to suffix a show the metal strip  30  according to the invention in its original geometry, i.e. first geometry, wherein the metal strip  30  is fastened on the sealing element  16  by suitable means, which are not additionally shown. The metal strips  30  are transferred into the second geometry by means of a pseudoplastic deformation. The sub-figures according to suffix b show the respective metal strip  30  which has the second geometry in the insertion or installation situation. In the sub-figures according to suffix c, the metal strips  30  are shown in each case in their functional geometry which they achieve after a single heating has been carried out and which they then permanently maintain with high rigidity. In the sub-figures according to suffixes b and c, a closure element  40  is additionally also shown in each case, with which the metal strip  30  can be brought into a form fit. For this purpose, the metal strip  30  is only to be subjected to heat treatment so that this strives to reach the first geometry from the second geometry. The closure element  40  can be optionally configured and in  FIGS. 3-7  representatively is shown in an abstract manner either the pocket which is arranged on the shaft collar  21  or the tapering recess which is arranged between the platforms  26  of adjacent rotor blades  14 . 
     With regard to  FIGS. 3   a ,  3   b ,  3   c , the metal strip  30  according to the invention, which consists of a shape-memory alloy for securing the sealing element  16  against displacement in the circumferential direction and which is fastened thereupon, has a first geometry which is L-shaped in cross section. Therefore, the metal strip comprises two legs  62 ,  64 . One of the two legs of the metal strip, for example the leg  62 , is fastened by suitable means on the sealing element  16 . For example, the leg  62  of the metal strip  30  can be soldered to the sealing element  16 . The other leg  64  then serves for the form-fit fastening of the sealing element  16  or of the metal strip  30  in a recess  38 . The recess  38 , as shown in  FIG. 1 , can also alternatively be arranged in a tapering manner between the platforms  28  of two directly adjacent rotor blades  14 , or the recess  38  can be formed in this case by two teeth  68  which are arranged on the rotor disk  19  ( FIG. 2 ). 
       FIG. 4  shows a configuration of the metal strip  30  which is an alternative to  FIG. 3 . Instead of a second leg  64 , the metal strip  30  in the first geometry according to  FIGS. 4   a ,  4   c  comprises a bead-like end  65  which can be transferred into a second geometry by means of pseudoplastic deformation. In the second geometry according to  FIG. 4   b , the end  65  is of a plate-like design, which facilitates the installation of the sealing element in the arrangement. 
     Common to the configurations according to  FIG. 3  and  FIG. 4  is that the functional geometry and the second geometry coincide and consequently the sealing element  16  can be fastened in the recess  38  with clearance. 
       FIG. 5  and  FIG. 6  show configurations of a closure element  40  and of a metal strip  30 , in which the geometry of the closure element  40  and the first geometry of the metal strip are selected so that a pretensioning force by the metal strip  30  can act upon the closure element.  40 . By means of the pretensioning force, a clearance-free fastening of metal strip  30  or sealing element  16  on the closure element  40  is achieved. In order to achieve this, the functional geometry differs from the first geometry. The achieving of the first geometry of the metal strip  30 , consisting of the shape-memory alloy, during subsequent heat treatment is prevented on account of the selected shape of the closure element  40  by the complete re-deformation of the metal strip  30  being blocked at least to a small extent by means of the closure element  40 . As a result of this, a clearance-free and pretensioned fastening of sealing element  16  and closure element  40  can be achieved. As a result, the configuration according to  FIG. 5  differs from  FIG. 3  only in shape and contour of the closure element. 
       FIG. 7  shows a further developed construction according to  FIG. 3 . On the “movable” second leg  64 , a further element  60  consisting of a non-shape-memory alloy is fastened. The element  60  in this case can be designed in the form of a spigot. After heat treatment has been carried out, the element  60  is located in a recess  70 , as a result of which the metal strip  30  or the sealing element  16  is locked in a form-fitting manner against a movement in relation to the closure element  40 . 
     Common to all the exemplary embodiments is that as a result of using a shape-memory alloy as the material of the metal strip, a particularly reliable installation of the sealing element can be achieved without undesirable damage of the sealing element being able to occur on account of manual bending processes. Furthermore, as a result of components which are cleverly matched to each other a pretensioned fastening of the sealing element on the rotor can be achieved, which reduces leakage of cooling air as a result of the otherwise existing clearance-flawed seating of the sealing element in the groove. 
     In all, with the invention an arrangement for axially securing rotor blades of a rotor of a gas turbine is disclosed, which comprises a sealing element which is arranged on the end face of the rotor and which by means of a metal strip consisting of a shape-memory alloy can be fastened in a particularly reliable manner.