Abstract:
A multi-functional rotary turning and positioning apparatus and method for performing multiple service operations on a turbomachinery rotor while the rotor remains continuously supported with the apparatus. The apparatus includes a platform, a rotary headstock mounted to the platform, a spindle coupled to and rotatably supported by the headstock and adapted for coupling to a turbomachinery rotor, bearing pedestals mounted to the platform and adapted for rotatably supporting the rotor, at least one motor for turning the spindle at at least two different rotational speed ranges, equipment mountable to the platform for performing multiple service operations on the rotor, and equipment for controlling the rotational speed and position of the spindle for the purpose of performing the service operation with the operating equipment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to turbomachinery rotors, and more particularly to an apparatus configured to enable multiple service operations to be performed on a turbine rotor while the rotor remains continuously supported with the apparatus. 
         [0002]    Depending on design considerations and their operating conditions, turbomachinery rotors used in steam turbines, gas turbines, and jet engines may have assembled or monolithic constructions. For example, large steam turbines typically have a bolted construction made up of separate rotors, each having a shaft with an integrally-formed wheel. Rotors for gas turbines and jet engines are often constructed by bolting a series of disks and shafts together. Another rotor construction involves welding together rotor segments formed of dissimilar materials, forming what may be termed a multiple alloy rotor (MAR). Monolithic multiple alloy rotors have also been proposed. In each case, the rim of the wheel (disk) is configured for mounting buckets (blades). A conventional mounting technique is to form slots having dovetail cross-sections configured to interlock with complementary dovetail features on the root portions of the buckets. 
         [0003]    Turbine rotors operate at high rotational speeds in a thermally-hostile environment. Though significant advancements have been made in alloys to achieve long service lives, wear, erosion, corrosion, shock, fatigue and/or overstress inevitably occur, necessitating periodic inspection and, if necessary, repair or replacement of a rotor or its components. The dovetail region of a wheel is particularly susceptible to cracking as a result of the rim being subjected to higher stresses. Inspection and servicing of large steam turbine rotors and their components typically entail removing the rotor from the steam turbine and transporting the rotor to a service center, incurring cost and cycle time. At the service center, the rotor is mounted on a lathe or a similar lathe-type apparatus adapted to rotate the rotor about its axis. The rotor is typically supported along its length with pedestals that help support the weight of the rotor without interfering with its ability to rotate. The rotor then undergoes the desired service operation, which may include cleaning, dimensional inspection, nondestructive examination (NDE), disassembly/assembly, machining, welding, stress relief, or balancing. These operations typically involve incrementally rotating the rotor to remove the buckets, incrementally or slowly rotating the rotor to remove damaged dovetail regions, perform a welding operation to build up material on the machined surfaces, stress relieve the weld buildup, and machine the weld buildup to reform the dovetail regions, and finally rotating the rotor at a speed sufficiently high to determine rotor alignment, from which balance weights can be added to the rotor to ensure that the rotor is balanced for rotation about its axis. 
         [0004]    Because of the different capabilities required for a given service operation, separate workstations are typically used to perform the various operations, for example, a lathe, mill, weld positioner, low-speed balance pit, etc., to perform the necessary operations. Each transfer between workstations requires breaking the previous setup, performing a new setup, and transporting the rotor between workstations by crane, train, tractor trailer, crawler, etc. It is not uncommon for a rotor to sit in a queue waiting for a nondedicated tool or workstation to be available to perform the next operation on the rotor. 
         [0005]    From the above, it can be appreciated that the use of dedicated rotor workstations incurs considerable cycle time and cost. Drawbacks of the conventional service approach have been addressed in part by establishing workstations dedicated to multiple operations, such as machining and welding, to reduce setup times, establish a more continuous flow through the process, and eliminate some queues in the system. However, such workstations have not been adapted to perform operations at which widely different rotational speeds are required, for example, when performing a dynamic balancing operation. Such workstations have also not typically lent themselves to installations outside of a service shop, and the service process still requires movement of a rotor through multiple process steps. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    The present invention provides a multi-functional rotary turning and positioning apparatus suitable for enabling multiple service operations to be performed on a turbomachinery rotor while the rotor remains continuously supported with the apparatus. 
         [0007]    According to a first aspect of the invention, the apparatus includes a platform, a rotary headstock mounted to the platform, a spindle coupled to and rotatably supported by the headstock and adapted for coupling to a turbomachinery rotor, bearing pedestals mounted to the platform and adapted for rotatably supporting the rotor, at least one motor means for turning the spindle at at least two different rotational speed ranges, operating means mountable to the platform for performing multiple service operations on the rotor, and means for controlling the rotational speed and position of the spindle for the purpose of performing the service operation with the operating means. 
         [0008]    According to a second aspect of the invention, a method of performing multiple service operations on a turbomachinery rotor includes providing a platform on which are mounted a rotary headstock and bearing pedestals, rotatably supporting a turbomachinery rotor on the bearing pedestals and coupling the rotor to a spindle coupled to and rotatably supported by the headstock, turning the spindle at a first rotational speed, and performing a first service operation on the rotor with a first operating means while controlling the rotational speed and position of the rotor. Then, and without uncoupling the rotor from the spindle and without removing the rotor from the bearing pedestals, the spindle is turned at a second rotational speed different from the first rotational speed, and a second service operation is performed on the rotor with a second operating means while controlling the rotational speed and position of the rotor. The rotor can then be uncoupled from the spindle and removed from the bearing pedestals. 
         [0009]    In view of the above, it can be seen that a significant advantage of this invention is a portable apparatus that enables a single setup for performing multiple service operations, such as machining, welding, and dynamic balancing of a turbomachinery rotor, as well as potentially other operations, such as cleaning, dimensional inspection, nondestructive examination (NDE), disassembly/assembly, etc. The apparatus is preferably portable and capable of eliminating the need to remove a rotor from its installation site, transport, lift or otherwise handle the rotor for movement between multiple workstations, and change the rotor fixturing setup. As a result, total cycle, labor input and cost can be significantly reduced and the risk of concentricity issues is reduced by performing a single setup. Particular operations performed on the rotor, including machining, welding, stress-relieving and dynamic balancing, can be numerically controlled. 
         [0010]    Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a portable multi-functional rotary turning and positioning apparatus in accordance with an embodiment of this invention. 
           [0012]      FIG. 2  represents a cross-sectional view of a headstock enclosure of the apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  illustrates a portable rotary turning and positioning apparatus  10  capable of positioning and rotating a turbomachinery rotor  12  at variable speeds for the purpose of performing multiple service operations, including but not limited to lathe turning, milling, welding, and low-speed dynamic balancing. The rotor  12  is represented as a steam turbine rotor, though it should be understood that the invention is not limited to any particular type of rotor or rotor construction. The shaft  16  of the rotor  12  is shown in  FIG. 1  as coupled to a spindle  20  extending from a headstock enclosure  14 . The apparatus  10  further includes bearing pedestals  22  for supporting the rotor  12  along its axial length. The apparatus  10  preferably has a load capacity sufficient for very large rotors, for example, up to about 140 tons (about 127 metric tons). 
         [0014]    The headstock enclosure  14  is shown in  FIG. 2  as including a headstock  24  that supports the spindle  20 , and a motor  26  and gearbox  27  for rotating the rotor  12  at relative high speeds. In part, the motor  26  is chosen based on the desired capability to both continuously and intermittently rotate the rotor  12  at speeds for performing operations such as machining, stress relief, dynamic balancing, etc., necessitating a high torque capability. The output speed capability of the motor  26  may be, for example, a motor armature speed of up to about 1750 rpm, and a suitable power output for the motor  26  is about 200 horsepower (about 150 kW), though it is foreseeable that motors with speed and power outputs outside of these ranges could also be use. A preferred motor  26  also has a stall torque capability of about 500 ft-lbf (about 680 J). Motors with these operating capabilities include electric motors currently used in the industry for this purpose, and therefore will not be discussed in further detail. 
         [0015]    To cover a lower range of speeds required to perform, for example, nondestructive examination, welding, etc., on the rotor  12 , a second motor  28  and gearbox  29  are shown mounted on the enclosure  14  and, with the first motor  26 , are adapted to be selectively engaged with the headstock  24  through a drive system  30 . Similar to the motor  26 , the motor armature speed of the motor  28  may be, for example, up to about 1750 rpm. A suitable power output for the motor  28  is about 30 horsepower (about 20 kW), though it is foreseeable that motors with speeds and power outside of these ranges could also be use. The motor  28  also preferably has a stall torque capability of about 100 ft-lbf (about 140 J). Motors with these operating capabilities include electric motors currently used in the industry for this purpose, and therefore will not be discussed in further detail. 
         [0016]      FIG. 2  represents the drive system  30  as including a toothed drive belt  32 , a pulley  34  mounted on the spindle  20  opposite the rotor  12 , and pulleys  36  and  38  mounted on the motors  26  and  28 , respectively. Tensioning of the belt  32  is preferably achieved by mounting the motors  26  and  28  on hinged platforms  44  and  46  that allow changing the center-to-center distances on the pulleys  36  and  38  individually, and set the correct belt tension. The platforms  44  and  46  may be actuated with, for example, hydraulics to raise the motors  26  and  28 , and then held in position with, for example, screw jacks. Other means for transferring power between the motors  26  and  28  to the spindle  20  are also within the scope of the invention. 
         [0017]    Taking into account the armature speeds of the motors  26  and  28 , the gearboxes  27  and  29  and drive system  30  are chosen to achieve a lower range of rotor speeds of about 0.01 to about 2.0 rpm with the motor  28 , and a higher range of rotor speeds of about 2.0 rpm or more with the motor  26 . For example, the gearbox  27  coupled to the motor  26  may have a gear ratio of, for example, about 13:1, to achieve relatively high speed outputs to the spindle  20  of up to about 140 rpm, and the gearbox  29  coupled to the motor  28  may have a much higher gear ratio of, for example, about 900:1, to achieve lower speed outputs to the spindle  20  of up to about 2 rpm. Those skilled in the art will appreciate that, instead of two separate motors  26  and  28 , the two-speed-range capability desired by this invention could be achieved with a single motor/gearbox drive line, and such embodiments are within the scope of this invention. 
         [0018]    In order to provide both precise speed and position control of the rotor  12 , the apparatus  10  preferably includes a computer numeric control (CNC) unit (not shown) coupled to velocity and position transducers (not shown) on the motors  26  and  28 , spindle  20  and/or rotor  12 , and the equipment performing the particular operation on the rotor  12 . According to standard practice, encoder feedback of motor speeds can be handled by the individual motors  26  and  28 , as supplied by the motor manufacturer. 
         [0019]      FIG. 1  represents robotic welding units  42  positioned alongside the rotor  12 , by which a welding operation can be performed on the rotor  12 , for example, on a wheel  18  of the rotor  12 . In addition to the welding units  42 , the apparatus  10  is adapted to accommodate a variety of other equipment capable of performing desired operations on the rotor  12 , particularly tool holders for performing machining operations (e.g., turning), a balance computer, spindle speed pickup, and accelerometers placed on the pedestals  22  for performing dynamic balancing operations, as well as equipment for performing cleaning, dimensional inspection, nondestructive examination (NDE), disassembly/assembly, and/or stress relief. Such equipment can be of conventional types known in the art or otherwise within the capabilities of those skilled in the art. However, in each case the equipment preferably utilize speed and/or position transducers by which the speed and angular position of the rotor  12  can be controlled with the motors  26  and  28 . 
         [0020]    The bearing pedestals  22  and their low-friction bearings that contact the rotor  12  must be capable of supporting the rotor  12  during relative low-speed machining and welding operations, as well as higher speeds required for dynamic rotor balancing operations. For this purpose, the bearing pedestals  22  may utilize hydrostatic bearings, though other types of bearing could be used, including rollers and hydrodynamic bearings disclosed in co-pending U.S. patent application Ser. No. 12/345,797. Otherwise, design aspects for the bearing pedestals  22  are generally known in the art or otherwise within the capabilities of those skilled in the art. 
         [0021]    The enclosure  14 , bearing pedestals  22 , and welding units  42  are shown in  FIG. 1  as being supported on a platform  40 . The platform  40  is preferably configured to provide the capability of transporting the apparatus  10  as a unit between installation, service facilities, and other locations where there may be a need to inspect and/or repair a turbomachinery rotor. The platform  40  preferably has the capacity to support the remaining components as a lifting beam, as well as provides points to tie down the apparatus  10  to a trailer for transport. 
         [0022]    In use, once the rotor  12  is set into place on the apparatus  10 , an operator simply arranges the drive system  30  to select the appropriate motor  26  or  28  to achieve a speed range appropriate for the particular operation to be performed. For example, typical NDE, turning, welding, and post-weld heat treatment operations can be performed at continuous rotational speeds of, respectively, about 0.25 to about 2 rpm, about 5 to about 20 rpm, about 0.01 to about 0.1 rpm, and about 4 to about 10 rpm. Without removing the rotor  12  from the apparatus  10 , a dynamic balancing operation can be subsequently performed at rotational speeds of about 100 to about 150 rpm. A precise rotational speed for the rotor  12  (and therefore a precise surface speed on any surface of the rotor  12 ) can be set, monitored and computer controlled through the speed transducers. The angular position of the rotor  12  can also be monitored and controlled through the same CNC unit using position transducers, thus enabling a fully-integrated numerically-controlled apparatus  10  capable of performing lathe (e.g., turning), milling, welding, and balancing operations with a single setup. This capability facilitates the portability of the apparatus  10  and significantly reduces setup and total cycle time. 
         [0023]    While the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the apparatus  10  could differ from that shown. Therefore, the scope of the invention is to be limited only by the following claims.