Abstract:
A brush seal assembly and method for a turbine machine having a rotary member and a stationary member circumscribing the rotary member. The seal assembly is comprised of a sealing member disposed at a radially inward region of the stationary member and a portion of the sealing member is in rubbing contact with the contact region. The sealing member is detachable from the stationary member for selective replacement and incorporates at least one integrally formed seal element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to dynamic seals of the type used in turbo machinery.  
         [0002]     Labyrinth-type packings and brush seals are widely used in steam turbines and in aircraft and industrial gas turbines to provide dynamic seals between the rotating and static turbine components, such as the rotor and diaphragm inner web of a steam turbine. Traditional labyrinth packing comprises a series of (hard) teeth that project radially inward from the circumference of a static component and toward but out of contact with the rotary component, thereby defining a series of partial barriers that create a tortuous axial flow path immediately adjacent the surface of the rotary component.  
         [0003]     Brush seals typically comprise metal bristles that, similar to the teeth of a labyrinth packing, project radially inward from the circumference of a static component toward a rotary component. In contrast to labyrinth packings, brush seals are normally intended to be in rubbing contact with the adjacent circumferential surface of the rotary component, creating a substantially continuous barrier to flow around the circumference of the rotary component. In this regard, brush seals provide a more effective barrier to secondary flow losses, i.e., provide better sealing performance, as compared to labyrinth packings, and therefore have the potential for significantly improving performance.  
         [0004]     The rotors of aircraft and industrial gas turbines are relatively stiff, and as a result their dynamic behavior is not generally affected by rubbing contact with a brush seal. In contrast, the rotor of a steam turbine typically includes a continuous solid shaft to which buckets are attached. Impulse-type steam turbines typically operate above the rotor&#39;s first bending critical frequency, and often near the second bending critical frequency. It has been shown that the rubbing contact between a brush seal and the rotor of a steam turbine can magnify rotor vibration through the first and second critical speeds of a rotor, resulting in unacceptable radial rotor movement. It is believed that this effect is particularly likely to occur if the rotor is bowed as a result of thermal, dynamic or manufacturing circumstances. More particularly, the friction resulting from the rubbing contact locally increases the surface temperature of the rotor, leading to nonuniform surface temperatures along its circumference. Because high (proud) spots of a bowed rotor are particularly prone to heating in this manner from more intense rubbing contact, the localized heating caused by brush seals can further increase bowing in a rotor as a result of nonuniform thermal expansion about the rotor circumference, thereby exacerbating vibration and rotor dynamics concerns.  
         [0005]     In commonly assigned U.S. Pat. No. 6,821,086, the disclosure of which is incorporated herein by this reference, a seal assembly and method therefor are disclosed that are capable of significantly reducing vibration and rotor dynamics concerns that arise in turbo machinery, such as steam turbines, as a result of localized heating caused by seals in rubbing contact with a rotary member of the turbo machine.  
         [0006]     The configuration of the &#39;086 patent is acceptable when multiple hard teeth are needed and when there is sufficient room for a large dovetail hard tooth carrier. For cases where fewer hard teeth are needed and there is little room, however, the large hard tooth carrier and brush seal carrier configuration of the &#39;086 patent may not work. A smaller design would therefore be desirable. As depicted in  FIG. 2  some hard teeth are actually machined to the nozzle structure. However, if such a seal structure is worn through rubbing, the hard tooth seal structure cannot be replaced.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     As noted above, current brush seal carriers take up significant room, driving up the amount of material needed to hold the carriers in place and restricting where the seals can be installed. As also noted above, some hard teeth are actually machined to the nozzle assembly so if the seal is worn, it cannot be replaced.  
         [0008]     The invention proposes to reduce the amount of material necessary for forming a seal assembly while allowing all sealing devices to be replaced if necessary without any manufacturing or modification to the nozzle.  
         [0009]     In an example embodiment of the invention, a brush seal carrier is provided that reduces the footprint of the brush seal assembly and its carrier while also integrating a hard tooth seal as a secondary/redundant/backup seal into the carrier. Integrating the hard tooth seal into the carrier provides for ease of replacement while the small footprint allows the brush seal to be installed in smaller areas. Integrating the hard tooth structure allows the hard tooth to be provided with minimal support structure and yet allows the hard tooth to be replaced in the event it becomes worn.  
         [0010]     Thus, the invention may be embodied in a seal member for a turbo machine comprising: a brush seal carrier; a brush seal component mounted to said brush seal carrier so that a portion of said brush component projects from said brush seal carrier, and at least one hard tooth seal element integrally formed with said brush seal carrier so as to extend in generally parallel relation to at least a part of said portion of said brush component that projects from said brush seal carrier.  
         [0011]     The invention may also be embodied in a seal assembly for a turbo machine having a rotary assembly rotatable about an axis and a stationary assembly encircling the rotary assembly, the rotary assembly defining outer peripheral surfaces and the stationary assembly having a portion radially facing the rotary assembly so as to be in opposed facing relation to an outer peripheral surface thereof, the seal assembly comprising at least a portion of said outer peripheral surface of the rotary assembly and a plurality of seal elements provided on a seal carrier on said radially facing portion of the stationary assembly, said plurality of sealing elements including at least one seal element mounted to said seal carrier and disposed in rubbing contact with said outer peripheral surface and at least one hard tooth seal element that is spaced from said outer peripheral surface, and wherein said hard tooth seal element is defined integrally in one piece with said seal carrier.  
         [0012]     The invention may further be embodied in a method of providing a seal in a turbo machine, between a rotary member rotatable about an axis and a stationary member encircling the rotary member, the rotary member having an outer circumferential surface; comprising: providing a seal assembly including first and second seal components at a radially inward region of the stationary member, the first seal component having a portion thereof in rubbing contact with the outer circumferential surface of the rotor and the second seal component being integrally formed in one piece with a carrier of said first seal component and extending in generally parallel relation to the first seal component but spaced from said outer circumferential surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     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:  
         [0014]      FIG. 1  represents a fragmentary longitudinal cross-sectional view of a diaphragm packing area of a steam turbine equipped with a sealing assembly of a related art;  
         [0015]      FIG. 2  is a schematic representation of another sealing assembly of a related art;  
         [0016]      FIG. 3  is a schematic representation of a sealing assembly according to an example embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring to  FIG. 1 , a diaphragm packing area of a steam turbine equipped with a sealing assembly in accordance with &#39;086 patent is illustrated. The steam turbine has a rotor  10  on which axially spaced wheels  12  are formed or mounted and to which buckets  14  are attached. The rotor  10 , wheels  12 , and buckets  14  rotate about the rotor axis and, therefore form part of a rotary portion of the turbine. A diaphragm (nozzle) inner ring (web)  16  extends radially inwardly between wheels  12 , defining separate stages of the turbine. A casing  18  surrounds rotor  10  and with nozzle inner ring  16  supports a nozzle partition  20 . The ring  16 , partition  20  and casing  18  together form part of a stationary portion of the turbine, disposed in a plane normal to the rotor axis and surrounding an outer circumferential region of the rotor  10 . Steam flows through the bucket  14  and nozzle partition  20 .  
         [0018]     The turbine depicted in  FIG. 1  is equipped with Labyrinth packings  22 ,  24  and  26 . Labyrinth packings  22  and  24  are mounted to a packing ring segment or a hard tooth carrier  28  and Labyrinth packing  26  is mounted to a packing ring segment  30 . As is conventional, each packing ring segment  28 ,  30  is one of multiple arcuate segments that are assembled circumferentially to the nozzle inner ring  16  or casing  18 , respectively. The Labyrinth packings  22 ,  24  and  26  reduce secondary flow losses between the rotary and stationary components, more particularly, between the rotor  10  and nozzle inner ring  16  and between the buckets  14  and casing  18 . While effective, it is understood that the Labyrinth packings  22 ,  24  and  26  cannot reduce secondary flow losses to the extent possible with brush seals because of the gap between the hard teeth  32 ,  33  of the respective Labyrinth packings and the opposing surfaces with which they seal. Thus, in accordance with the &#39;086 patent, the packing ring segment or hard tooth carrier  28  mounted to the nozzle inner ring  16  further includes a brush seal  34  situated axially between the sets of Labyrinth packings  22  and  24 . The Labyrinth packings  22  and  24  thus serve as a backup seals to the brush seal  34 . In contrast to packings  22  and  24 , brush seal  34  is adapted to continuously contact the surface with which it is intended to seal, thereby effecting a better seal than possible with the Labyrinth packings  22  and  24 . As is conventional, brush seal  34  is equipped with bristles  36  and, as mentioned above, Labyrinth packings  22  and  24  are equipped with hard teeth  32  that project radially towards rotor  10 .  
         [0019]     As understood, the rubbing contact that occurs between brush seal  34  and rotor  10  inherently causes frictional heating. In the &#39;086 patent, better distribution and dissipation of the heat are achieved by including a raised section  38  on the rotor which projects radially outward beyond axially adjacent surface regions  40  to define a platform  42 . The raised section  38  defines a cavity  44  that is completely enclosed so that it contains, e.g., only air that was trapped during formation thereof.  
         [0020]      FIG. 3  represents the same turbine illustrated in  FIG. 1  but wherein the seal assembly has been modified according to an example embodiment of the invention so as to reduce the footprint of the brush seal carrier  146  while also integrating a hard tooth seal  122  to serve as a backup seal to the brush seal. Referring more specifically to the example embodiment of the invention schematically depicted in  FIG. 3 , the brush seal assembly  146  is comprised of a compliant bristle  136  extending radially towards the rotor and providing a tight seal with the facing surface of the rotating shaft (not shown). Although not illustrated in detail in  FIG. 3 , in an example embodiment, the rotor structure in opposed relation to the brush seal may include a platform structure  42  of the type depicted in  FIG. 1  and disclosed with reference thereto, to effectively distribute and dissipate heat generated by the rubbing contact of the brush seal and the rotary member as it rotates about its axis.  
         [0021]     In the illustrated embodiment, rather than providing a dovetail for receipt in a dovetail groove, the carrier  146  has a single engaging hook or flange  148 . The carrier  146  is illustrated as received in a shaped groove  150  in the diaphragm inner ring (nozzle web)  116  so that the hook  148  is received in channel  152 . In the illustrated example, moreover, the brush seal carrier  146  is a laminated structure comprised of the compliant bristle  136  sandwiched between front and back plates or carrier parts  154 ,  156 . The front carrier part  154  includes a spacer portion  158  to space the compliant bristle  136  from the balance of the front plate, to allow forward axial flexing in a conventional manner. The back plate  156 , on the other hand, includes a projecting support  160  to limit aft flexing of the compliant bristle  136 .  
         [0022]     In an example embodiment of the invention, at least one hard tooth seal element  131  is incorporated in the brush seal carrier  146  to extend radially in parallel to, but to a lesser extent than the bristles  136  to thus provide a backup seal to the bristles  136 . To reduce the footprint of the brush seal carrier  146 , rather than providing a separate hard tooth element  32  as in the  FIG. 1  structure, an integrated hard tooth  131  is provided. Thus, the carrier part ( 154  in the illustrated embodiment) is machined out of metal and includes a hard tooth  131  integrally machined into it. The brush structure  136  is laminated with and welded into the carriers  154 ,  156  to provide the rotary part of the seal assembly  146 . The remaining parts of the turbine structure generally correspond to those as depicted by way of example in  FIG. 1  and therefore are not illustrated again in  FIG. 3 , even through it is to be understood that those corresponding parts are advantageously provided in this example embodiment.  
         [0023]     As will be understood, hard tooth integration facilitates a reduction in the dimension of the seal carrier while allowing the hard tooth to be replaced if it is rubbed out. This also allows for a reduction in the amount of parts required for assembly. As described above, the  FIG. 1  configuration included a large brush seal carrier  34  that is installed into a hard tooth carrier  28  for multiple hard teeth. This adds to the material and space requirements for the assembly. It also dictates using more hard teeth  32  than may be necessary because of the sealing efficacy of the brush seal. The integrated configuration proposed hereinabove and schematically depicted in  FIG. 3  allows the carrier  146  to be designed to have as few as one hard tooth  131 . Furthermore, as will be appreciated, configuring the brush seal carrier  146  as a laminated assembly of plates and bristles that is mounted directly to, e.g., the nozzle web  116  further substantially reduces the axial dimension of the seal assembly  146  as compared to e.g. the seal carrier  28  depicted in  FIG. 1 .  
         [0024]     It is to be understood that while example carrier part  154 ,  156  configurations have been illustrated and described, the carrier parts may have configurations and shape particulars that are different from the illustrated example. For example, although the back plate has been illustrated as including a hook for engaging the channel  152  of the groove  150  in the nozzle web/diaphragm inner ring  116 , the front plate may include such a hook instead or in addition for engaging a respective channel in the diaphragm inner ring/nozzle web structure. Furthermore, while a hard tooth  131  has been illustrated as integrated in the front plate  154 , it is to be understood that in addition or in the alternative either the front plate  154  or the back plate  156 , or both, could have a hard tooth integrated therewith. Additionally, while only a single hard tooth has been illustrated, it is to be understood that the axial thickness of the respective plate could be adjusted to accommodate a varying number of teeth. Even further, while an example embodiment of the seal has been illustrated and described as going directly into the diaphragm (nozzle) inner ring (web), additionally, the new seal assembly could go directly into a groove in the stator above the bucket tip and create a seal there. This could be part of the casing or part of the diaphragm outer ring.  
         [0025]     Thus, 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.