Abstract:
Stacked wheels of the rotor of a rotary machine are axially coupled to one another by tie bolt assemblies. Each tie bolt assembly includes a stud having forward and aft ends. The aft end of the stud includes a self-locking nut to thereby lock the stud/nut assembly against rotation relative to the rotor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rotary machine and more particularly to a tie bolt and stacked wheel assembly for the rotors of such machines, wherein the tie bolts retain the stacked wheels in assembled relation without relative rotation between the tie bolts and the stacked wheels. Exemplary rotary machines to which this invention relates include turbines and/or compressors. 
     The rotors of rotary machines, such as turbines and compressors, are typically formed of axially stacked wheels, which hold individual blades about their periphery. For example, compressor rotors include a series of individual compressor wheels stacked together with a set of tie bolts extending generally axially through the stack. The wheels mount the blades which, together with stator blades, form the compressor stages. The tie bolts are typically elongated studs threaded at both ends for receiving nuts to maintain the wheels in stacked, assembled relation relative to one another. It will be appreciated, however, that tie bolts can have a headed end. In many such rotors formed of stacked wheels, the stacked wheels have ridge and groove arrangements along their interfaces so that the rotor torque can be carried through the stack. In a preferred form, however, sufficient clamp load is applied to the tie bolts to ensure that the rotor torque is carried through the stack by friction between the faces of the wheels and the nut faces. 
     It will be appreciated that any loosening of the nuts on the tie bolts would clearly reduce the tension on the bolts and, thus, lower the torque carrying capability of the rotor, eventually to unacceptable levels. Recognizing this problem, current design practice requires that the rotation of the nut relative to the bolt be prevented by redundant methods. One such method relies on the nut face friction against the threads and the stack. A second method of preventing rotation of the nut relative to the bolt is to run a jam nut against the primary nut to prevent its rotation relative to the stud. 
     It is also desirable to prevent rotation of the tie bolt assembly relative to the stacked wheels to facilitate assembly and ensure sufficient clamp load can be applied for rotor torque to be carried through the stack. A need remains for a reliable bolt and nut assembly mechanism that remains rotationally locked and assembled at all times to keep, e.g., the compressor wheels fully engaged during all operating conditions and in a manner which will not damage the tie bolt assembly or rotor. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention provides a simple and reliable bolt and nut mechanism for holding e.g., the aft nut of a compressor during assembly operations and also that remains assembled at all times to keep the compressor wheels fully engaged during all operating conditions. 
     In an embodiment of the invention, a tie bolt and stacked wheel assembly for the rotor of the rotary machine is provided wherein the stacked wheels are joined one to the other in an axial array by tie bolts, more specifically studs, provided at opposite ends with nuts to define bolt assemblies. To prevent rotation of the stud and nut combination within the rotor, a self-locking nut is provided at the aft end of the stud. 
     Thus, the invention may be embodied in a self locking nut comprising: a main body; a forward radial flange defined at a first longitudinal end of said main body; an aft radial flange defined at a second longitudinal end of said main body; and a tab component projecting radially from a radially outer peripheral surface of said aft radial flange. 
     The invention is also embodied a stacked wheel assembly for the rotor of a rotary machine comprising: a plurality of stacked wheels for rotation about a common axis and forming part of the rotor; and a plurality of elongated tie bolts passing through aligned bolt holes of said stacked wheels for retaining the wheels in axially stacked relation, said plurality of tie bolts being spaced from one another circumferentially of the rotor; at least one of said tie bolts comprising a stud having a locking nut at least one of mounted to and defined at one longitudinal end thereof, said locking nut comprising at least one tab component projecting radially therefrom, wherein an end face of said plurality of stacked wheels includes a receptacle for receiving said locking nut and said at least one tab component. 
     The invention is further embodied in a method for retaining stacked wheels for the rotor of a rotary machine in an assembled relation comprising: stacking a plurality of wheels so as to align bolt holes respectively defined therethrough, to thereby define a plurality of tie bolt passages axially of said stacked wheels; providing at least one tie bolt comprising a stud having a locking nut at least one of mounted to and defined at one longitudinal end thereof, said locking nut comprising at least one tab component projecting radially therefrom; inserting said stud through a said tie bolt passage defined by aligned bolt holes of said stacked wheels; disposing said locking nut and said at least one tab component in a receptacle defined in an end face of said plurality of stacked wheels; and axially fixing said at least one tie bolt to said stacked wheels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a rotor incorporating a self-locking nut embodying the invention; 
     FIG. 2 is a schematic, broken away view of an aft wheel shaft for accommodating a self-locking nut embodying the invention; 
     FIG. 3 is a view similar to FIG. 2 showing the self-locking nuts in position; 
     FIG. 4 is a perspective view of a self-locking nut embodying the invention; and 
     FIG. 5 is a side elevational view of the self-locking nut of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     By way of example, a compressor comprising a stacked wheel assembly and tie bolt embodying the invention is illustrated in FIG.  1 . The compressor, generally designated  10 , includes a plurality of wheels  12  axially stacked, each wheel mounting a plurality of circumferentially spaced compressor blades (not shown). The wheels are maintained in their axially stacked relation by a plurality of circumferentially spaced tie bolt assemblies. In the illustrated embodiment, each tie bolt assembly extends axially the length of the compressor. It is to be understood, however, that the invention may also be applied to compressor assembly wherein first and second tie bolt assemblies are provided coupling respective axial sets of stages to one another and overlap to maintain the compressor in axially stacked relation and keep the preload applied during the assembly process. 
     Each of the tie bolt assemblies includes a tie bolt, which may also be characterized as an elongated stud  14  having first and second longitudinal ends. In an exemplary embodiment, at the forward end of each stud (not shown), a locking nut assembly is provided. In this embodiment, a regular 12-point nut and a locking nut that prevents the former from disengagement are provided, although other locking nuts assemblies may be provided. 
     To rotationally lock the stud with respect to the stacked wheels, in an embodiment of the invention a self-locking nut  18  is provided at the aft end of the stud  14 . The self-locking nut  18  may be formed at the aft end of the shaft but is more preferably separately formed and secured to the shaft. In an exemplary embodiment, the nut  18  is threaded to threads defined on the aft end of the stud  14 , but the nut  18  may instead by secured to the stud by brazing or welding. 
     Referring more particularly to FIGS. 4 and 5, in the illustrated embodiment, where the nut is secured to the stud  14 , stud  14  is received in a bore  16  defined in self-locking nut  18 . The nut has a generally circular base portion or flange  20  at the forward end thereof, a reduced diameter portion  22  which may carry or define facets for securing the self locking nut to the stud  14 , and a circular head portion or flange  24  at the aft end thereof. At least one tab  28  is defined to project from the radially outer periphery  26  of the generally circular head portion  24 . 
     Referring to FIGS. 2 and 3, a receptacle or counter bore  30  is defined in the aft wheel shaft  40  for receiving self-locking nut  18 . Furthermore, the tab  28  of the self-locking nut  18  engages a correspondingly sized and shaped cutout or notch  32 , thus counteracting any slight rotational movement such as may be induced during compressor stud tensioning. In the illustrated embodiment, furthermore, the tab comprises inclined side surfaces  34 , 36  and an outer peripheral surface  38  generally parallel to the outer peripheral surface  26  of the aft flange  24  of the nut  18 . It is to be understood, however, that tab configurations other than that illustrated may be adopted without departing from the invention. Thus, the tab may be more rounded than illustrated, or may have straighter sides than those shown. The particular size and shape of the tab may thus be determined as necessary or desirable for ease of manufacture and assembly. It is also to be appreciated that while a single tab is provided on the locking nut  18  of the illustrated embodiment, if deemed necessary or desirable, two or three tabs may be, e.g., symmetrically, provided about the circumference of the nut  18  and receptacle  30  for further resisting rotation of the assembly. As presently proposed, however, a single tab and receptacle should be sufficient to resist forces to which the nut is likely to be exposed and will reduce manufacturing costs. 
     As will be appreciated, the self-locking nut minimizes the weight of the nut/stud locking assembly. In addition, the locking mechanism is simple, thereby reducing manufacturing costs. Also, assembly is easily accomplished as there is only a single feasible position of the locking nut. 
     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.