Patent Publication Number: US-2017370238-A1

Title: Thickened radially outer annular portion of a sealing fin

Description:
This claims the benefit of German Patent Application DE 102016211337.2, filed Jun. 24, 2016 and hereby incorporated by reference herein. 
     The present invention relates to a blisk for a gas turbine, and further to a compressor and a turbine having such a blisk, and to a method for manufacturing a blisk. 
     BACKGROUND 
     Compressors are used in gas turbines, such as, for example, in aircraft engines, to compress the air passing therethrough and thereby bring it to a higher energy state. A mixture of the air and a fuel is then ignited in a combustor and subsequently expanded in actual turbines (expanders) respectively associated therewith. Generally, one part of the energy produced in this manner is used to further drive the compressor, and the other part is used, as useful energy, for driving the respective unit or for generating thrust. 
     Compressors, just as turbines, generally include a rotor having a plurality of rows of rotor blades which are connected to a rotor shaft and externally surrounded by a casing, so that a flow duct is formed between the rotor shaft and the casing. Stator vanes attached to the casing are adapted to suitably direct gas flowing through the flow duct onto the rotor blades. The rotor blades may be manufactured separately and inserted into receiving grooves of the rotor shaft. Alternatively, it is possible to use one-piece blisks (blades disks) which each include a disk or a ring having a plurality of rotor blades integrally formed therewith or joined (e.g., welded) thereto. Such blisks have the advantage over the rotor blade rows composed of separate blades that they have greater mechanical strength and lower weight. 
     In order to avoid losses, it is in particular required that passages formed between moving and stationary components be kept as small as possible. For instance, in order to seal such passages between the rotor shaft and the radially inner tips of the stator vanes, it is known to use so-called “sealing fins.” These are generally configured as an annular radial projection and adapted to engage, with a radially outer section (herein also called “rub-in portion” of the respective sealing fin), in abradable liners provided on the tips of the stator vanes. As used herein and unless otherwise stated, the terms “radial” and “axial” always relate to an (intended) axis of rotation of the rotor shaft. 
     In order for the sealing fins to resist the mechanical and thermal stresses occurring during engagement in the abradable liners, the correspondingly stressed surfaces there are generally coated. However, selective application of a coating in the desired regions requires that the intended regions be accessible for the respective coating tool. In the case of the advantageous one-piece blisks, due to a rotor blade row disposed at a short distance or because another, proximate sealing fin, it may be impossible or at least very difficult to apply a coating in an axial direction because coating may be feasible in a radial direction only (from the outside inwards). Thus, flanks of a sealing fin which extend substantially radially (perpendicularly to the axis of rotation) are not adequately reached and are therefore insufficiently protected from friction resulting from deep penetration and simultaneous axial movements of the rotor and the casing relative to each other. As a result, metal-to-metal contact may occur at these flanks. This may cause damage to the sealing fins, which may result in premature failure of the rotor and severe damage to the engine. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a technology which will overcome the above-mentioned disadvantages. 
     The present invention provides a blisk, a compressor, a turbine, and a method for manufacturing a blisk. 
     A blisk according to the present invention is intended for installation in a gas turbine (e.g., an aircraft engine) or already installed in a gas turbine, in particular in a compressor or in a turbine (an expander). The blisk has a rotor blade row extending around an (abstract) central axis and, axially spaced therefrom, at least one annular sealing fin extending coaxially with the rotor blade row, the central axis being the (intended) axis of rotation of the gas turbine. 
     The at least one sealing fin has a radially outer annular portion (i.e., a ring-like portion) that is thickened (in the axial direction) as compared to a radially more inward annular portion of the sealing fin; i.e., has a greater axial thickness than the radially more inward annular portion. As used herein, the terms “axial thickness” or simply “thickness” of an annular portion refer to its maximum extent (extension) in the axial direction. 
     The exact boundaries of the aforementioned annular portions are not necessarily defined physically. Rather, they may be defined on the sealing fin as respective annular portions having the required properties. 
     Due to the greater thickness of the radially outer annular portion, this portion axially overhangs radially more inward annular portion in at least one section. Thus, the radially more inward annular portion forms an undercut with respect to this section. In particular, the thickened annular portion may have at least one surface facing the central axis. Therefore, when an axial movement of the rotor relative to the stator or stator vanes occurs during operation, contact may occur only at the overhang of the respective flank of the sealing fin; i.e., at the overhanging section of the thickened annular portion. Therefore, coating of the thickened annular portion alone may already avoid the above-mentioned disadvantages resulting from contact. Since this thickened radially outer annular portion is relatively well accessible from radially outside, a blisk according to the present invention advantageously facilitates and improves the application of a coating, thus providing an efficient way of improving a seal. 
     An inventive compressor and an inventive turbine for a gas turbine each include a rotor and a casing having at least one row of stator vanes. The stator vanes extend radially inwards, and their (radially inner) tips are provided with an abradable liner, which may in particular include honeycomb seal cells. The abradable liner may be a single piece or include a plurality of (connected or separate) components. 
     In particular, different components of the abradable liner may be disposed at different tips and may be connected to one another (thus forming, for example, a ring). 
     The rotor of an inventive compressor or an inventive turbine includes at least one blisk according to any of the embodiments disclosed herein, whose at least one sealing fin at least partly engages in the abradable liner. 
     In an advantageous embodiment of a blisk according to the present invention, the thickened annular portion of the at least one sealing fin is provided with a protective coating on a radially outer surface. Preferably, the coating extends to an axial overhang of the thickened annular portion over the radially more inward annular portion. As mentioned, contact may occur at this overhang during axial movement of the rotor and the stator relative to each other, and the coating in this region can avoid or at least reduce the resulting disadvantages, in particular wear or damage to the material (e.g., due to metal-to-metal contact). 
     It should be noted that the coating may itself be composed of a plurality of separate layers and therefore does not necessarily have to exhibit the same material properties across the entire cross-sectional area. Thus, the coating (in the case of a blisk according to the present invention or a blisk produced using a method according to the present invention) may, for example, include an adhesion layer of a nickel-based alloy, preferably NiAl, and an overlayer of ceramic, preferably Al 2 O 3 —TiO 2 . The coating is preferably applied by plasma spraying. 
     A method according to the present invention is used for manufacturing a blisk, in particular an inventive blisk according to any of the embodiments disclosed herein. The method includes producing a (one-piece) blisk having a rotor blade row extending around a central axis and at least one annular sealing fin which is axially spaced from the rotor blade row and extends coaxially therewith and which has a radially outer annular portion that is thickened (in the axial direction) as compared to a radially more inward annular portion of the sealing fin. The production of the blisk may include, for example, milling, friction welding, precise electrochemical machining and/or additive manufacturing (e.g., selective laser melting, electron beam melting). 
     The method further includes applying a coating at least to a radially outer surface of the thickened annular portion. The application may be performed in particular solely or partially radially from the outside. This facilitates coating. 
     In accordance with a preferred embodiment, the application process includes providing the coating over at least part of a surface of an axial overhang of the thickened annular portion over the radially more inward annular portion. As mentioned, this makes it possible to protect a potential contact region between the sealing fin and the abradable liner during use of the blisk. 
     Preferably, the thickened annular portion (or even the entire sealing fin) of a blisk according to the present invention or a blisk produced using a method according to the present invention is composed of a uniform or homogeneous material. Thus, any coating that may be present on the thickened annular portion will be considered as not forming part thereof inasmuch as the thickness of the annular portions is determined without considering such a coating, and the thickened annular portion is thicker than the radially more inward portion even without the coating. 
     In an advantageous embodiment of the present invention, the thickened annular portion is provided, on a side facing the rotor blade row and/or on a side facing away therefrom, with an edge that runs along a circular path around the central axis and along which the thickened annular portion has its greatest axial thickness. Thus, during coating of the thickened annular portion radially from the outside, a protective layer can be built up on the edge, which may extend beyond the edge in the axial direction (due to the viscosity of coating material). This makes it possible to prevent contact of the thickened annular portion with the abradable liner during use of the blisk. 
     Preferably, the thickened annular portion includes a radially outermost section in which the thickened annular portion tapers (continuously and strictly monotonically) radially outwardly (i.e., becomes increasingly thinner with increasing distance from the central axis). An embodiment that is particularly advantageous is one in which the axial thickness of the thickened annular portion is assumed to be in such a radially outermost section. Thus, in this case, the thickened annular portion becomes increasingly thinner radially outwardly from its thickest region. If, as mentioned above, the thickened annular portion has edges on its side facing the rotor blade row and on its side facing away from the rotor blade row, the radially outermost section may, for example, be radially inwardly bounded by an abstract plane connecting the edges and taper radially outwardly. 
     Such a taper allows the thickened annular portion to have a particularly large surface that is accessible radially from the outside, thus allowing a coating to be applied over a particularly large area in this direction. 
     Preferably, the entire surface of the radially outermost section is provided with a (or the) coating. In particular, the surface that is coated using a method according to the present invention may include a surface of a radially outermost section in which the thickened annular portion has its maximum thickness and which tapers radially outwardly. 
     In an advantageous embodiment, the thickened annular portion (i.e., the radially outer section thereof) is chamfered or curved on its side facing the rotor blade row and/or on its side facing away therefrom, so that it preferably has a radially outermost surface (facing away from the central axis) which spans the thickened annular portion also laterally, at least partially, but nevertheless faces away from the central axis. 
     This allows a suitable coating to be applied radially from the outside also over parts of the lateral surfaces of the thickened annular portion. As mentioned, contact may occur at these lateral surfaces during axial oscillations of the rotor and the casing relative to each other. 
     On a side facing the rotor blade row and/or on a side facing away therefrom, the thickened annular portion may, for example, extend substantially along the lateral surface of an (abstract; i.e., imaginary, and preferably straight) circular cone about the central axis (which thus coincides with the axis of the cone). In an advantageous embodiment, the cone angle of such a circular cone is no more than 120°, more preferably no more than 100° and/or at least 60°, more preferably at least 80°. 
     Such opening angles advantageously enable the respective lateral surfaces of the thickened annular portions to be reached when applying a coating (substantially) radially from the outside; i.e., they enable an advantageously large extent of the thus reached inclined surfaces in the radial direction. 
     In an advantageous variant, the radially more inward annular portion has an extent in the radial direction that is at least twice the extent of the thickened annular portion in the radial direction. Thus, even when the thickened portion penetrates deeply into the abradable liner, the sealing fin can be protected from axial contact with the abradable liner, namely along the full radial extent of the radially more inward, less thick annular portion. 
     Preferably, the radially more inward annular portion and/or the thickened annular portion are/is configured substantially symmetrically to a plane extending perpendicular to the axis of rotation. Such an embodiment advantageously provides substantially the same protection on both axial sides of the sealing fin. 
     In an advantageous embodiment, the radially more inward annular portion and the thickened annular portion are sections of an intended rub-in portion of the sealing fin, which is thus adapted to engage in an abradable liner (possibly after a rub-in process during initial use of the blisk). Preferably, the rub-in portion is disposed on a sealing fin base, whose thickness in the axial direction is greater than the thickness of the thickened annular portion. This increases the stability of the sealing fin in a radially innermost portion that is not intended for engagement in an abradable liner, i.e., which remains spaced from the abradable liner during operation. 
     In the present patent application, the term “abradable liner” includes also honeycomb structures. 
     Analogously, the radially more inward annular portion may advantageously thicken radially inwardly, which improves the stability of the sealing fin, in particular of the rub-in portion thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the present invention will be described in greater detail below with reference to the drawings. It is understood that individual elements and components may be combined in other ways than those described. Corresponding elements are identified by the same reference characters throughout the figures and may not be described again for each figure. 
       In the schematic drawings, 
         FIG. 1  shows a perspective view of the configuration of an exemplary blisk according to the present invention; 
         FIG. 2  shows part of a meridional section through an exemplary compressor according to the present invention; and 
         FIG. 3  shows a meridional cross-sectional detail view of a sealing fin according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary blisk  10  having a ring section  13 , a rotor blade row  12  (having rotor blades  12   a ), and a plurality of annular sealing fins  11  which, although not discernible in this figure, preferably have a radially outer annular portion and a radially more inward annular portion, as described herein. Rotor blade row  12  and sealing fins  11  extend coaxially about a common central axis X which forms the axis of rotation during use of the blisk. Sealing fins  11  are spaced apart (i.e., offset) from rotor blade row  12  in the axial direction. 
       FIG. 2  shows part of a schematic meridional section through a compressor  1  according to the present invention. This partial view shows a portion of a blisk  10  with a central axis X, as well as a casing  30  of the compressor, to which are attached stator vane rows having stator vanes  20   a . A flow duct  40  is formed between casing  30  and a ring section  13  of the blisk which, together with other components, forms a rotor shaft. During normal operational use, air is passed through flow duct  40  in the direction indicated by the arrow. 
     The radially inner tips of stator vanes  20   a  are provided with abradable liners  21  which engage sealing fins  11 , thereby minimizing the passage of air between abradable liners  21  and sealing fins  11 . 
       FIG. 3  presents a detail view of a sealing fin according to an embodiment of the present invention. This figure, too, shows part of a schematic meridional section taken along central axis X. 
     Sealing fin  11  (in particular its thickened annular portion  111  and its radially more inward annular portion  113 ) is configured symmetrically to a plane E which is perpendicular to the plane of the drawing of  FIG. 3  and pierced orthogonally by central axis X. Sealing fin  11  includes a radially outer annular portion  111  and a radially more inward annular portion  113 . Radially outer annular portion  111  is thickened as compared to radially more inward annular portion  113 , because its axial thickness d 1  is greater than the axial thickness d 2  of radially more inward annular portion  113 . The axial thicknesses of the annular portions are their respective greatest extent in the axial direction. In the meridional cross-sectional view shown in the figure, such a maximum thickness is thus a maximum width of the representation of the respective annular portion (parallel to the central axis). 
     In the example shown, radially outer annular portion  111  and radially more inward annular portion  113  adjoin each other and form part of a rub-in portion  117  of the sealing fin which may engage in an abradable liner  21  (such as is shown in  FIG. 2 ) during normal operational use. Radially more inward annular portion  113  thickens toward central axis X, which improves the stability thereof. 
     In radial direction R, radially more inward annular portion  113  has an extent a 2  which, in the example shown, is more than twice the radial extent a 1  of radially outer annular portion  111  in the radial direction. Thus, detrimental lateral contact of the sealing fin with an abradable liner may occur only in a relatively small section of rub-in portion  117 , and this small section is protected by the coating. 
     Rub-in portion  117  of the illustrated sealing fin  11  is disposed on a sealing fin base  118 , which is intended to remain spaced from abradable liner  21 , in particular not to engage therein. 
     Sealing fin base  118  has a greater axial thickness than rub-in portion  117  of the sealing fin, in particular than the thickened radially outer annular portion  111  thereof, which serves to advantageously stabilize the sealing fin. 
     In the example shown, thickened radially outer annular portion  111  has a surface  119  on both sides (i.e., on the side facing the rotor blade row not shown in  FIG. 3  and on the side facing away therefrom), which surface  119  faces the central axis and radially inwardly bounds an overhang of thickened annular portion  111  over radially more inward annular portion  113 . 
     Thickened radially outer annular portion  111  is provided with a coating  116  on a radially outer surface  115 . The coating spans thickened radially outer annular portion  111  over the entire thickness thereof and thus acts as a protective layer also for the thinner, radially more inward annular portion during axial movement of the sealing fin (and, respectively, of the blisk of which it forms part) relative to an abradable liner. 
     Thickened radially outer annular portion  111  assumes its maximum axial thickness d 1  along edges  114   a ,  114   b . The applied coating  116  extends slightly beyond the edges in the axial direction (due to the viscosity of coating material and/or a minimal inclination of a coating direction), thereby forming a possible contact surface at which sealing fin  11  may contact an abradable liner, and thus protecting the sealing fin laterally. 
     A radially outermost section  112  of thickened annular portion  111  tapers strictly monotonically radially outwardly. In the example shown, the base of radially outermost section  112  lies in an imaginary plane connecting the edges  114   a ,  114   b , so that the full axial thickness of the thickened annular portion, which is from where the radially outermost section tapers strictly monotonically radially outwardly, is reached in this section  112 . 
     In particular, thickened annular portion  111  is chamfered on both of its sides (which each may face or face away from a rotor blade row not shown). Hence, radially outer surface  115  of the thickened annular portion spans the thickened annular portion partially also laterally and faces away from the central axis at these sides as well. This made it possible to reach also the sloped lateral surfaces during the application of the coating radially from the outside. 
     The sloped sides of the thickened annular portion each extend substantially along the lateral surface of an (abstract; i.e., imaginary, and preferably straight) circular cone about central axis X. In the figure, for the sake of clarity, this is only shown for one of the sloped sides. The associated cone has a cone angle α of preferably no more than 120°, more preferably no more than 100° and/or at least 60°, more preferably at least 80°. 
     An inventive blisk  10  for a gas turbine includes a rotor blade row  12  extending around a central axis X and, axially spaced therefrom and extending coaxially therewith, at least one annular sealing fin  11 . The sealing fin has a radially outer annular portion  111  that is thickened as compared to a radially more inward annular portion  113 . 
     A turbine according to the present invention includes a rotor and a casing. The casing includes at least one stator vane row having at least one abradable liner  21 . The rotor includes at least one blisk according to an embodiment of the invention disclosed herein, whose at least one sealing fin  11  at least partly engages in the abradable liner. 
     Analogously, a compressor  1  according to the present invention includes a rotor and a casing  30 . The casing includes at least one stator vane row having at least one abradable liner. The rotor includes at least one blisk  10  according to an embodiment of the invention disclosed herein, whose at least one sealing fin  11  at least partly engages in the abradable liner. 
     A method according to the present invention for manufacturing a blisk  10  for a gas turbine includes producing a blisk  10  having least one annular sealing fin  11 , as well as applying a coating  116  to a radially outer surface  115  of a thickened annular portion  111  of sealing fin  11 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  compressor 
           10  blisk 
           11  sealing fin 
           12  rotor blade row 
           12   a  rotor blade 
           13  ring 
           20   a  stator vane 
           21  abradable liner 
           30  casing 
           40  flow duct 
           111  thickened annular portion 
           112  radially outermost section of the thickened annular portion 
           113  radially more inward annular portion 
           111   a ,  114   b  edge along which thickened annular portion  111  has its greatest axial thickness 
           115  radially outer surface 
           116  coating 
           117  rub-in portion 
           118  sealing fin base 
           119  surface facing the central axis 
         a 1  extent of the thickened annular portion in the radial direction 
         a 2  extent of the radially more inward annular portion in the radial direction 
         d 1  thickness of the thickened annular portion 
         d 2  thickness of the radially more inward annular portion 
         E plane 
         R radial direction 
         X central axis 
         α cone angle