Abstract:
A rotor for an axial flow turbomachine is provided, having a number of a plurality of disc-shaped or drum-shaped rotor components and at least one pin-shaped tie-rod extending through the rotor components, wherein a counter-bearing is screwed onto each of the projecting ends of the tie-rod for axially bracing the rotor components arranged therebetween. The tie-rod has at least two axially adjacent tie-rod elements which are each connected to one another in a detachable manner by connector. Elastic stretching characteristics of the two tie-rod elements are matched to each other such that, with the rotor components being clamped between the two counter-bearings, a clamping of the counter-bearing and the connection element and the rotor components arranged therebetween is at least partially released.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2013/068505 filed Sep. 6, 2013, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102012215886.3 filed Sep. 7, 2012. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a rotor for an axial flow turbomachine, comprising a number of multiple disk-shaped or drum-shaped rotor components and at least one tie-rod extending through the rotor components, with a counter-bearing being screwed onto each of the projecting ends of this tie-rod in order to axially clamp the rotor components arranged therebetween. 
       BACKGROUND OF INVENTION 
       [0003]    Such rotors are very well known from the comprehensive available prior art relating to static gas turbines. For example, a rotor of the type mentioned in the introduction is shown in the book “Stationare Gasturbinen” [“Static Gas Turbines”] (Eds Christoph Lechner and Jorg Seume), on page  629 . The rotor is designed as what is termed a disk construction, wherein the rotor disks bear blades, either for the compressor or for the turbine unit of the gas turbine, on their outer circumference. A central hollow shaft as a drum-shaped component is arranged between the compressor disks and the turbine disks. A central tie-rod extends through all the rotor components and, with the aid of two counter-bearings, the forward hollow shaft and the rear hollow shaft, clamps together the rotor components arranged between these two hollow shafts. In that context, the tie-rod is stretched elastically up to its yield point, thus clamping together the individual rotor components. 
         [0004]    A similar construction is also possible with decentralized tie-rods, wherein for example twelve tie-rods are arranged evenly distributed at the same radius. 
         [0005]    It is further known, from EP 2 415 967 A1, to divide the rotor—embodied with a disk construction—of a gas turbine into a compressor section and a turbine section, whose respective central tie-rod is screwed into a central shaft connecting the former two to one another. In that context, the compressor disks are clamped between a first pre-clamping screw nut—screwed onto the end—and the central shaft, and the turbine disks are also clamped between the central shaft and a second pre-clamping screw nut—also screwed onto the end, wherein the pre-clampings of the compressor section and turbine section are independent of one another. 
         [0006]    A further disk clamping of a compressor rotor is also known from DE 10 2005 052 819 A1. According to this teaching, the multi-part tie-rod comprises two tension sleeves and a compression sleeve. 
         [0007]    Furthermore, a double nut is known from U.S. Pat. No. 5,454,662. 
         [0008]    It is also known to weld together the disk-shaped or drum-shaped rotor components. Even combinations of the aforementioned embodiments, in which for example the compressor rotor is welded and the rotor components of the turbine unit are clamped by means of a screwed connection with bolts at the circumference, are also known. 
       SUMMARY OF INVENTION 
       [0009]    The invention has an object of proposing an alternative construction of rotors for an axial flow turbomachine. The invention has a further object of providing the components necessary therefor. 
         [0010]    The object relating to the rotor may be achieved with a rotor according to the features of the claims. The object relating to the components may be achieved with a double nut according to the features of the claims. Advantageous configurations and refinements are indicated in the dependent claims. 
         [0011]    The invention differs from the current embodiment of tie-rods in that the latter are of one-piece design. According to aspects of the invention, it is now provided that the tie-rod or tie-rods is or are divided axially into at least two tie-rod elements, wherein the directly adjacent tie-rod elements are in each case releasably connected to one another by a connector. 
         [0012]    Advantageously, the rotor comprises, along its longitudinal extent, a first rotor end section, at least a further rotor section and a second rotor end section, wherein the connector, as seen axially, is arranged in one of the further rotor sections. Particular advantages are realized in the configuration in which the connector and one of the rotor components are configured such that, after the counter-bearing arranged on the second rotor end section has been released, the connector adjacent to the second rotor end section, with the counter-bearing arranged on the first rotor end section, clamps together the rotor components arranged therebetween. A particular advantage of this configuration is that, in a first assembly step, those rotor components which are threaded onto the first tie-rod element can already be clamped by one of the two counter-bearings and the connector, although the rotor is not yet completely stocked with rotor components. Only once the second or further tie-rod element has been attached are the further disk-shaped or drum-shaped rotor components to be threaded thereon, after which the second counter-bearing can then be screwed onto the end of the second or further tie-rod element, whereby all the disk-shaped or drum-shaped rotor components of the rotor can finally be clamped together. According to aspects of the invention, it is provided in that context that the clamping which acts in the interim from one of the two counter-bearings and the connector on a part of the disk-shaped or drum-shaped rotor components is then released again. In this respect, the elastic stretching characteristics of the two tie-rod elements are matched to each other such that, with the rotor components being clamped between the two counter-bearings, the initial clamping of the counter-bearing and the connector is at least partially—or entirely—released. This is of particular interest for gas turbine installations in which, instead of a welded compressor rotor, a modular rotor having a disk construction should be used, which modular rotor should further also be clamped to the turbine rotor and with the aid of tie-rods. This improves the handling of the rotor during maintenance work of an operationally stressed gas turbine and reduces the time necessary for carrying out the maintenance work, since it is not necessary to unstack the entire rotor but only the turbine-side rotor section. Particularly, the connector is designed as a screw nut into which are screwed the mutually opposing ends of axially adjacent tie-rod elements. Instead, it is of course also conceivable for the connector to be connected in one piece with one of the tie-rod elements. In other words, a tie-rod element can also have, at one end, an internal thread as the connection for screwing onto another tie-rod element. 
         [0013]    According to a first advantageous refinement, the connector has multiple openings for guiding a fluid from one of the rotor (end) sections through to another of the rotor (end) sections. Particular advantages are realized in the configuration in which the respective connector has a circumferential shaft collar which is arranged on the circumference and in which are arranged the openings as throughflow openings for cooling fluid. When the rotor is used in a gas turbine, it is then for example possible to feed compressor air—bled from the compressor—into the interior of the rotor and to guide this air through the connector into a turbine rotor, where the cooling air can be used for cooling purposes. By using a shaft collar at the circumference of the connector, it is possible to arrange the throughflow openings, which are necessary for feeding through the fluid, on a larger radius. It is thus possible to create larger throughflow cross sections and accordingly to feed through a greater cooling air mass flow rate with low pressure losses. 
         [0014]    Further, the connector can also be used to create a support for the tie-rod in order to reduce vibrations when the turbomachine is in operation. To that end, only a radial support for at least one of the rotor components at the relevant connector is necessary. 
         [0015]    Particular advantages are realized in the configuration in which the rotor is designed as a gas turbine rotor, the first rotor end section is designed as a compressor rotor, the further rotor section is designed as a central rotor section and the second rotor end section is designed as a turbine rotor. In that context, the central rotor section can be formed solely from a hollow shaft or from multiple bladeless rotor disks and the rotor end sections from rotor disks. It is further provided that the double nut for connecting two tie-rod elements has, centrally between the two screw openings, an inward-oriented ring or a separating web which prevents the tie-rod elements from being screwed too far into the double nut. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be explained in more detail with reference to exemplary embodiments in the figures. In that context, further features and advantages are indicated in the description of the figures, in which: 
           [0017]      FIG. 1  shows a partial longitudinal section through a rotor according to the invention for a static axial flow turbomachine; 
           [0018]      FIG. 2  shows a detail from the longitudinal section of  FIG. 1 , in the region of two mutually connected tie-rod elements; 
           [0019]      FIG. 3  shows the same detail of  FIG. 2 , according to an alternative exemplary embodiment; 
           [0020]      FIG. 4  shows a connection element for connecting two tie-rod elements with a shaft collar arranged at the circumference; 
           [0021]      FIG. 5  shows, in a perspective representation, the connection element of  FIG. 4  and 
           [0022]      FIG. 6  shows a connection element bearing radially against the rotor component, in the longitudinal section of  FIG. 2 . 
       
    
    
       [0023]    In all figures, identical features are provided with identical reference signs. 
       DETAILED DESCRIPTION OF INVENTION 
       [0024]      FIG. 1  shows a partial longitudinal section through the rotor  10  of an axial flow turbomachine. In the exemplary embodiment shown, the rotor  10  is configured as a gas turbine rotor, wherein the remaining constituents of the gas turbine are not represented in more detail here. The construction of the rotor  10  is fundamentally modular and is to be termed disk construction. 
         [0025]    Consequently, the rotor  10  comprises a number of rotor disks  12 , which in this case are also termed disk-shaped rotor components  14 . In addition, the rotor  10  further comprises a drum-shaped rotor component  16  which in the exemplary embodiment is termed central hollow shaft  18 . In addition to the central hollow shaft  18 , there is also a forward hollow shaft  22 , screwed onto the end of a tie-rod  20 , and a rear hollow shaft  24 , screwed on at the opposite end. In this case, the forward hollow shaft  22  is also termed first counter-bearing  26  and the rear hollow shaft  24  is termed second counter-bearing  28 . The two counter-bearings  26 ,  28 , with the aid of the tie-rod  20 , clamp the rotor components  14 ,  16  together and press them securely against one another. In order to achieve this, the entire tie-rod  20  is stretched elastically by the two counter-bearings  26 ,  28 . 
         [0026]    According to the invention, it is provided that the tie-rod  20  comprises two separately manufactured tie-rod elements  30 ,  32 . In the exemplary embodiment shown in  FIG. 1 , the tie-rod  20  also comprises a connector  34  which releasably connects the two one-piece tie-rod elements  30 ,  32  to one another. The connector  34  is designed as a screw nut or as a double nut which has, centrally between its two screw openings  37  ( FIG. 5 ), an inward-oriented ring  36 . 
         [0027]    The rotor  10  can theoretically be split axially into a first rotor end section  38 , a further rotor section  40  and a second rotor end section  42 , wherein the connector  34 , seen axially, is arranged in the further rotor section  40 . In the shown gas turbine rotor  10 , the first rotor end section  38  is designed as a compressor rotor  44 , and the second rotor end section  42  is designed as a turbine rotor  48 . In the region of the further rotor section  40 , a combustion chamber of the gas turbine is arranged radially outside the rotor  10 . In order, when servicing the gas turbine, to release where relevant only the rotor disks  12  of the turbine rotor  48 , without at the same time the central hollow shaft  18  and the rotor disks  12  arranged in the compressor rotor  44  releasing, it is provided that, after the counter-bearing  28  arranged on the second rotor end section  42  has been released, the connector  34  adjacent to the second rotor end section  42 , with the counter-bearing  26  arranged on the first rotor end section  38 , clamps together the rotor components  14 ,  16  arranged therebetween. In order to achieve this, multiple exemplary embodiments are conceivable. To that end,  FIGS. 2 ,  3  and  4  show various exemplary embodiments.  FIGS. 2 to 4  show, in longitudinal section, a detail from the transition region between the further rotor section  40  and the second rotor end section  42 . Represented are the two tie-rod elements  30  and  32  and, as connector  34 , a double nut  35  connecting the two ends of the former to one another. The central hollow shaft  18  is arranged radially adjacent to the double nut  35 . The double nut  35  has a conical face  50  whose gradient matches an inward-oriented face  52  of the central hollow shaft  18 . In addition, a smaller shaft collar  54  is provided centrally between the two screw openings  37  of the double nut  35 , the side face  56  of which collar bears against a side face  58 —parallel thereto—of the central hollow shaft  18 . During assembly of the rotor  10 , the first counter-bearing  26  is first screwed onto the end of the tie-rod element  30 . This subassembly is then set upright such that the individual disk-shaped or drum-shaped rotor components  14 ,  16  can be placed onto the first counter-bearing  26  from above. Then, the double nut  35  is screwed onto that end of the tie-rod element  30  which has been left free, wherein in the process the rotor components  14 ,  16  located between the double nut  35  and the first counter-bearing  26  are clamped together. The second tie-rod element  32  is then screwed into the double nut  35 , after which the rotor disks  12  provided for the turbine rotor  48  can be threaded on and placed onto the second tie-rod element  32  from above. Finally, the second counter-bearing  28  is screwed onto that end of the tie-rod element  32  which has been left free. In so doing, the entire tie-rod  20  is stretched elastically such that the clamping of the double nut  35  or, as the case may be, of the connector  34  and the first counter-bearing  26  is released. 
         [0028]    According to the exemplary embodiment of  FIG. 2 , axial bores  60  can be provided both in the central hollow shaft  18  and in the double nut  35 , by means of which bores a cooling device can be guided from one rotor (end) section to another rotor (end) section. 
         [0029]      FIG. 3  shows the same detail as  FIG. 2 , but in which the construction for axially clamping in the region of the double nut  35  and of the central hollow shaft  18  is slightly modified in comparison with the construction of  FIG. 2 . The radial overlap between the double nut and the central hollow shaft  18 , required in order to establish the axial clamping, is achieved here with the use of a sleeve  62  which is arranged therebetween and is provided with a flange. 
         [0030]      FIG. 4  shows a further exemplary embodiment for clamping the rotor components  14 ,  16  between a first counter-bearing (not shown in  FIG. 4 ) and the connector  34 . The connector  34  is again configured as a double nut  35  with two mutually opposite screw openings  37 . A larger shaft collar  54  is provided on the outer circumference, centrally between the screw openings  37 , in which collar are provided, distributed evenly about the circumference, openings  64  for guiding through a cooling fluid. The two parallel side faces  56  of the shaft collar  54  transition, via a radius, into curved, tapered flanks  57  which end at the screw openings  37 .  FIG. 5  shows this double nut  35  with the screw opening  37  and four evenly distributed throughflow openings  64  in a perspective representation. 
         [0031]    In order to avoid radial vibrations of the tie-rod  20  in operation, it is possible to provide, on the casing-side face of the shaft collar  54 , a circumferential groove  66  with a support wire  68  therein, with the aid of which the tie-rod  20  is supported radially on one of the rotor components, according to  FIG. 6  on the central hollow shaft  18 . 
         [0032]    The exemplary embodiments of  FIGS. 2 to 6  all show gas turbine rotors  10  in which the second counter-bearing  28  is not yet screwed onto the second tie-rod element  32 , such that only those rotor components  14 ,  16  depicted to the left of the double nut  35  in  FIGS. 2 to 6  are clamped with the first counter-bearing  26  and those rotor components  14 ,  16  depicted to the right thereof are not. 
         [0033]    Overall, the invention thus relates to a rotor  10  for an axial flow turbomachine, comprising a number of multiple disk-shaped or drum-shaped rotor components  14 ,  16  and at least one pin-shaped tie-rod  20  extending through the rotor components  14 ,  16 , with a counter-bearing  26 ,  28  being screwed onto each of the projecting ends of this tie-rod in order to axially clamp the rotor components  14 ,  16  arranged therebetween. 
         [0034]    In order to provide a rotor  10  by means of which shorter service interval times can be achieved, it is provided that the tie-rod  20  comprises at least two axially adjacent tie-rod elements  30 ,  32  which are in each case releasably connected to one another by a connector  34 .