Abstract:
The coupling between discrete axially aligned first and second turbine shafts includes a flange on one end of one shaft and a rotor wheel on the other shaft. Holes in axial alignment with one another through the flange and rotor wheel receive fastening elements securing the rotor wheel and flange to one another, thereby securing the shaft sections to one another. The fastening elements engage segments on the side of the rotor wheel remote from the flange to facilitate clamping of the flange and rotor wheel to one another. The segments also include outer arcuate surfaces which form sealing surfaces with radially opposed labyrinth teeth of packing ring segments forming part of the turbine diaphragms.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus and methods for joining adjacent ends of turbine rotor shafts and particularly relates to couplings between axially aligned steam turbine rotor shafts in a manner to reduce bearing-to-bearing span, increase rotor stiffness and enable additional rotor staging or rotor length reduction. 
     In turbines, particularly steam turbine rotor trains, it is frequently necessary to couple rotor shafts in axial alignment with one another within a given steam path due to material property limitations in the rotor shafts. The coupling requires axial space which adds span to the bearing-to-bearing length. In typical axial couplings for aligned rotor shafts, the axially adjoining rotor shaft ends have flanges with aligned bolt holes enabling the flanges to be bolted directly to one another. It will be appreciated therefore that the shaft end portions mounting the flanges require considerable additional axial extent to accommodate their coupling. This in turn leads to increases in overall span length between bearings with undesirably reduced rotor stiffness. Consequently, it has been found desirable to couple adjoining rotor shaft end portions to one another in a manner with reduced bearing-to-bearing span, thus stiffening the rotor, and enabling tighter clearances and additional turbine staging or rotor length reduction. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with a preferred embodiment of the present invention, there is provided apparatus and methods for coupling the adjacent axially aligned end portions of turbine rotor shafts substantially without increase in axial span of the rotor. To accomplish the foregoing, one of the rotor end portions includes a conventional flange having a circumferential array of holes for receiving fastening elements, e.g., bolts. The opposing end portion, however, includes an adjacent rotor wheel having a circumferential array of openings, i.e., holes, therethrough in alignment with the holes through the flange of the adjoining shaft. Thus, the rotor wheel and flange of the adjoining rotor shaft end portions are secured directly to one another, the fastening elements being received through the aligned holes. 
     Additionally, a plurality of segments on the side of the rotor wheel remote from the flange, serve in conjunction with the fastening elements, to clamp the flange and rotor wheel to one another. The segments also form seals with the radial opposing diaphragms. The segments have one or more holes therethrough for receiving the fastening elements which join the shaft end portions to one another. The segments also include radially facing arcuate sealing surfaces in radial opposition to the diaphragm seals at an axial location between the rotor wheel and an adjacent rotor wheel on the same shaft. Thus, the segments have seal surfaces which cooperate with the radially opposed labyrinth teeth of the diaphragm seals. As a consequence of this arrangement, additional axial space is gained for additional staging, reduced axial bearing-to-bearing span and increased stiffness, resulting in significant enhanced performance of the turbine. 
     In a preferred embodiment according to the present invention, there is provided a turbine comprising a rotor having an axis and including discrete first and second axially aligned shafts, a coupling between axially adjacent ends of the shafts including a flange on one of the shafts and a rotor wheel on another of the shafts, the flange and the rotor wheel having circumferentially spaced holes axially aligned with one another and fastening elements received through the aligned holes to secure the flange and the rotor wheel to one another, thereby securing the first and second axially aligned shafts to one another. 
     In a further preferred embodiment according to the present invention, there is provided a turbine having a flowpath, comprising a rotor having an axis and including first and second axially aligned rotor shafts, the first shaft having an end flange including a plurality of circumferentially spaced holes through the flange, the second shaft including a rotor wheel having a plurality of circumferentially spaced holes aligned with the holes of the flange, threaded nuts in alignment with the holes and located on a side of the wheel remote from the flange and threaded fastening elements extending through the aligned holes and in threaded engagement with the nuts for coupling the flange and rotor wheel to one another. 
     In a further preferred embodiment according to the present invention, there is provided a method of coupling axially aligned shafts of a turbine rotor to one another, comprising the steps of extending fastening elements through axially aligned holes in an end flange of one of the shafts and a rotor wheel of another of the shafts and securing the fastening elements to the flange and the rotor wheel to secure the shafts to one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary cross-sectional view of a portion of a turbine illustrating discrete turbine shafts joined one to the other according to the prior art; 
         FIG. 2  is a fragmentary cross-sectional view illustrating a coupling between adjoining discrete turbine shafts according to a preferred embodiment of the present invention; 
         FIG. 3  is a view similar to  FIG. 2  illustrating a further embodiment of the present invention; and 
         FIG. 4  is a perspective view of segments which form part of the coupling between adjoining rotor shafts. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing figures, particularly to  FIG. 1 , there is illustrated a turbine, generally designated  10 , and including a rotor  12  formed by axially aligned and joined discrete rotor shafts  14  and  16 , respectively. Rotor shaft  14  forms part of an upstream turbine section and includes a plurality of buckets  18  and nozzles  20  forming multiple stages of the turbine  10  and disposed in a hot gas path  22 . The buckets  18  are mounted on rotor shaft wheels  24 , while the nozzles  20  extend radially inwardly from a fixed casing  26 . Similarly, rotor shaft  16  includes a plurality of buckets  28  and nozzles  30  in a downstream turbine section, the nozzles  30  being fixed to the stationary casing  32 . Buckets  28  are disposed on turbine wheels  34 . 
     As conventional, the two turbine rotor shafts  14  and  16  are joined together in axial alignment with one another by clamping a pair of flanges  36  and  38  to one another at their junction. The flanges  36  and  38  each have holes  40  aligned with one another for receiving fastening elements  42 , for example, studs or bolts. The illustrated studs have nuts  44  at opposite threaded ends and it will be appreciated that bolts with threads at one end and a bolt head at an opposite end may be utilized. As illustrated, the two flanges axially joined to one another require considerable axial spacing of the turbine sections from one another, leading to inefficiencies and degraded performance. Particularly, the bearing-to-bearing span of the rotor is increased, thus rendering the rotor more flexible and inhibiting turbine staging. 
     In accordance with the present invention as illustrated in  FIGS. 2 and 3 , there is provided unique apparatus and methods for joining adjacent ends of rotor shafts to one another in a manner to reduce bearing-to-bearing span, increase rotor stiffness and enable additional rotor staging or rotor length reduction. To accomplish the foregoing and referring to  FIG. 2 , there is illustrated, similarly as in  FIG. 1 , a rotor  50  comprised of upstream and downstream turbine sections  51  and  53 , respectively, having rotor shafts  52  and  54  joined axially one to the other. Shafts  52  and  54  mount buckets  56  and  58  on rotor wheels  60  and  62 , respectively. Turbine section  51  includes nozzles  64  fixed to the stationary casing  66  while turbine section  53  mounts nozzles  68  fixed to the stationary component  70 . In the embodiment illustrated in  FIG. 2 , the upstream end of the rotor shaft  54  is provided with a conventional flange  72  for joining with the opposing end portion of rotor shaft  52 . The flange  72  is provided with circumferentially spaced, axially extending openings  74 . 
     In contrast to the prior art illustrated in  FIG. 1 , rotor shaft  52  does not include an adjoining flange. Rather, the end portion of the rotor shaft  52  terminates in the last-stage wheel  60  of that turbine section. Wheel  60  includes a plurality of circumferentially spaced, axially extending holes  76  aligned with the holes  74  through the flange  72  of shaft  54 . To secure the shafts  52  and  54  to one another, fastening elements  78  are passed through the aligned openings  74  and  76 . Each fastening element  78  may comprise a bolt or stud with at least one end  80  having threads for threaded engagement with female threads on a nut or segment  82  disposed between the last-stage wheel  60  adjacent the end of turbine shaft  52  and the next upstream wheel  84  of turbine section  52 . It will be appreciated that the nuts or segments  82  are circumferentially spaced one from the other, located between the adjacent wheels  60  and  84  of turbine section  52  and, when the ends of the fastening elements  78  are threadedly received, facilitate clamping of the flange  72  and wheel  60  to one another. The opposite end of the fastening element may comprise a nut  86  or the head of a bolt. Consequently, with this arrangement, the shafts  52  and  54  are coupled to one another by the engagement of fastening elements through flanges on one shaft and a rotor wheel on the adjoining shaft. 
     Referring to  FIG. 4 , each segment  82 , in addition to a hub  90  carrying the female threads  92 , has a radially outer sealing surface  94  and a flange  96  which projects axially from the hub  90 . It will be appreciated that when the segments  82  are secured to the wheel  60 , the segments are circumferentially aligned with one another. The sealing surfaces  94  of the segments  82  form a circular seal surface  95  extending 360° about the rotor shaft  52 . The sealing surfaces  94  lie in radial opposition to packing ring segments  98  carried by the diaphragms  100  of the stationary component. The packing ring segments  98  mount labyrinth seal teeth  102  ( FIG. 4 ) which provide inter-stage seals. Consequently, the segments  82  facilitate the clamping of the adjoining shafts  52  and  54  to one another, as well as afford part of the inter-stage seals between adjacent wheels. Further, the axially extending flange  96  on the segments  82  overlies a shoulder or rim  106  formed on the next-adjacent upstream wheel  84 . The flanges  96  and the shoulder  106  cooperate with one another in conjunction with the fastening elements  78  to prevent the segments  82  from rotating about the axis of the fastening elements  78 . The shoulder  106  is preferably, but need not be, necessarily circular about the axis of the turbine rotor. Thus, the cooperating surfaces of the flanges  96  and shoulder  106  provide an anti-rotation feature for each segment  82 . 
     In the embodiment of  FIG. 2 , the segments are located on the upstream turbine section  51  and shaft  52 . In the embodiment illustrated in  FIG. 3 , the segments  82  are located on the downstream turbine section shaft. In  FIG. 3 , like reference numerals are applied to like parts as in the preceding embodiment, advanced by “100.” In the embodiment of  FIG. 3 , the upstream turbine section  151  and shaft  152  mount a conventional radially extending flange  172  with holes  174  circumferentially spaced one from the other. The downstream turbine section  153  and shaft  154  mount a first stage wheel  162  which has holes  120  circumferentially spaced one from the other and in alignment with the holes  174  through flange  172 . Consequently, to secure the shafts  152  and  154  to one another, fastening elements  178  are passed through the aligned holes  174  and  120 . The threaded end of each fastening element  178  is threaded into the female threaded hub  90  of segment  82 , clamping the rotor wheel  162  and flange  172  to one another and, hence, clamping the shaft sections  152  and  154  to one another. The opposite end of the fastening element  178  may, as in the preceding embodiment, comprise a bolt head or a nut  186 . In this form, the segments  82  are reversed in axial configuration such that the flanges  196  overlie the rim  206  about the next stage rotor wheel  208  of turbine section  210  in a downstream direction. Thus, the arrangement in  FIG. 3  is the opposite of the arrangement in  FIG. 2 . Note also that the surfaces  94  of the segments  82  lie in radial opposition to packing ring segments  198  on the diaphragms of the downstream turbine section  153  whereby the packing ring segment and segment  82  form inter-stage seals. 
     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.