Abstract:
A turbine rotor including an elongated shaft having at least an HP region, the HP region having a first section supporting a stage 1 rotor wheel and a second section supporting a stage 2 rotor wheel, the first section formed of a relatively higher-temperature-capability material and the second section formed of a relatively lower-temperature-capability material. Various mechanical couplings and described for securing the first and second sections.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to rotors for turbomachines and, more specifically, to the construction of rotors in axial sections of different materials. 
         [0002]    In a recent steam turbine rotor, and following a tendency to high temperatures for steam, a 12% chromium steel is used, as it is excellent in high temperature strength and toughness. In such a rotor, both for a high temperature portion exposed to a high temperature steam and a low temperature portion exposed to a low temperature steam, the same 12% chromium steel is used. But as rotors have become larger in recent years, it is becoming difficult and expensive to manufacture the rotor so as to satisfy characteristics both of the high temperature portion and the low temperature portion with one material. 
         [0003]    While the expensive 12% chromium steel satisfies the required heat resistance, creep characteristics, etc. of the portion exposed to the high temperature steam, it is not necessary to use such an expensive material for the low temperature portion, so long as the requisite toughness is retained. In order to meet these problems it has attempted to join rotor portions of different materials together by welding to make a single rotor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    In a first exemplary but non-limiting embodiment, this invention relates to a turbine rotor comprising an elongated shaft including at least an HP region, the HP region having a first axial section supporting a stage 1 rotor wheel and a second axial section supporting a stage 2 rotor wheel, the first axial section formed of a relatively higher-temperature-capability material and the second axial section formed of a relatively lower-temperature-capability material; and means for mechanically coupling the first axial section and the second axial section. 
         [0005]    In another aspect, the invention relates to the turbine rotor comprising an elongated shaft including at least HP and IP regions, a combined HP/IP region having at least a first section supporting a stage 1 rotor wheel and a second section supporting a stage 2 rotor wheel, the first section formed of a relatively higher-temperature-capability material and the second section formed of a relatively lower-temperature-capability material; and wherein said first and second sections are joined by a mechanical coupling 
         [0006]    The invention will now be described in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic diagram of a turbine rotor region with mechanically-coupled sections in accordance with a first exemplary but nonlimiting embodiment; 
           [0008]      FIG. 2  is a schematic diagram similar to  FIG. 1  but with an alternative mechanical coupling between the turbine sections in accordance with an exemplary but nonlimiting embodiment; 
           [0009]      FIG. 3  is a schematic diagram similar to  FIG. 2  but with an alternative mechanical coupling between the turbine sections in accordance with an exemplary but nonlimiting embodiment; 
           [0010]      FIG. 4  is a schematic diagram similar to  FIG. 3  but with an alternative mechanical coupling between the turbine sections in accordance with an exemplary but nonlimiting embodiment; 
           [0011]      FIG. 5  is a schematic diagram similar to  FIG. 4  but with an alternative mechanical coupling between the turbine sections in accordance with an exemplary but nonlimiting embodiment; and 
           [0012]      FIG. 6  is a schematic diagram similar to  FIG. 5  but with an alternative mechanical coupling between the turbine sections in accordance with an exemplary but nonlimiting embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    With reference initially to  FIG. 1 , a steam turbine rotor  10  is shown in schematic from and includes at least a high pressure (HP) region (or combined HP and intermediate pressure (IP) region)  12  that is formed to include at least first and second stage rotor wheels  14 ,  16 , each of which supports a row of buckets  18 ,  20 , respectively. Within the HP or combined HP/IP region  12 , the rotor  10  is formed in two axially-oriented and aligned sections  22 ,  24 . Section  22  includes the first stage rotor wheel  14  while section  24  includes the second stage rotor wheel  16 . It will be appreciated that section  22  is in a high temperature region, exposed to steam at temperatures of about and above 1050° F. Section  24 , on the other hand, is in a lower temperature region, exposed to steam at a temperature of about and less than 1050° F. 
         [0014]    The inventors have recognized that significant cost savings can be realized by using different materials for the rotor sections  22 ,  24  within the HP or combined HP/IP region  12 . 
         [0015]    For the rotor section  22 , a more expensive 12% Cr material (e.g., ASTM A982, Grade B) is suitable while for section  24 , a less expensive, lower % Cr material such as a Cr-MO-V material (e.g. ASTM A470, Grade D, Class 8) is suitable. 
         [0016]    The rotor sections  22  and  24  are preferably joined together by any of several suitable mechanical coupling arrangements. In  FIG. 1 , for example, the rotor sections  22  and  24  are provided with (or formed with) facing radial flanges  26 ,  28 , respectively, located between the first and second stage rotor wheels  14 ,  16  and joined by a circumferential array of axially-extending fasteners such as bolts  30  passing through the flanges and secured by nuts  32 . 
         [0017]      FIG. 2  illustrates an alternative coupling arrangement where the radial flange  28  is eliminated and flange  26  is bolted directly to a hub portion  15  of the rotor wheel  16  using similar fasteners  30 ,  32 . 
         [0018]      FIG. 3  illustrates another mechanical coupling arrangement between the rotor sections  22 ,  24 . In this example embodiment, a reduced diameter end portion  34  of the section  24  is received within a blind bore  36  formed in section  22  axially between the rotor wheels  14 ,  16 . The coupled sections are secured by two or three fasteners (e.g. bolts)  38  oriented radially with respect to the longitudinal axis of the rotor. 
         [0019]      FIG. 4  illustrates another example embodiment wherein a partially-threaded stud  40  extends between the rotor sections  22 ,  24 . Specifically, a threaded, blind bore  42  is formed in the end of rotor section  24 , aligned with a smooth through-bore  44  formed in rotor section  22 . The stud  40  is inserted through the smooth through-bore  44  and the threaded end  46  of the stud is threaded into the blind bore  42 . A threaded opposite end  48  of the stud  40  projects from the rotor section  22  and a nut  50  is applied there to lock the stud  40  in place, with sections  22 ,  24  joined together axially between the rotor wheels  14 ,  16 . Alternatively, the smooth portion of the stud  40  could terminate short of the flange  51  and a separate bolt could be threaded into the end of the bore  44  to lock the stud in place. 
         [0020]      FIG. 5  illustrates yet another exemplary mechanical coupling utilizing a spline arrangement. Specifically, a reduced-diameter male spline  52  is formed at one end of the rotor section  24 . A female spline  54  is formed in the rotor section  22 , with elongated slots (i.e., complimentary spline slots)  56  aligned to receive the elongated ribs  58  of the male spline  52 . As in the previously described embodiments, the coupling occurs between the rotor wheels  14 ,  16 . 
         [0021]      FIG. 6  illustrates a variation of the spline coupling of  FIG. 5 . Here, the male spline  60  of the rotor section is in a cross-shape, with four equally-spaced ribs  62 . Similarly, the female spline  64  in rotor section  22  is formed with four aligned slots  66  that receive the ribs  62 . 
         [0022]    For the embodiments illustrated in  FIGS. 5 and 6 , it will be appreciated that the spline arrangements may be reversed, with the male spline in rotor section  22  and the female spline on rotor section  24 . 
         [0023]    Other mechanical coupling arrangements are within the scope of the invention. In all cases, secure axial coupling that prevents relative rotation of the rotor sections is required. 
         [0024]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.