Abstract:
A brush seal assembly and method for sealing a turbine machine rotary member relative to a stationary member circumscribing the rotary member. The seal assembly includes a first compliant seal component disposed at a radially inward region of the stationary member in rubbing contact with a surface of the rotary member. The seal assembly also includes at least one hard seal element formed integrally with a carrier of the first compliant seal component, located a specified axial distance from the first compliant seal component.

Description:
This invention is a continuation-in-part of application Ser. No. 11/282,703 filed Nov. 21, 2005, the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to dynamic seals of the type used in turbo machinery. 
     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. 
     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. 
     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. 
     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. 
     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. 
     BRIEF DESCRIPTION OF THE INVENTION 
     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. 
     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. 
     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 also 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. 
     Thus, the invention may be embodied in a brush seal carrier assembly comprising: a compliant brush seal component located between a backing plate and a forward plate, such that a radially inner portion of the compliant brush seal component projects radially beyond the backing plate; and at least one hard tooth seal element integrally formed with the forward plate so as to extend in generally parallel relation to the compliant brush seal component, wherein the hard tooth seal element extends radially beyond the backing plate but radially short of the compliant brush seal component; and wherein the at least one hard tooth seal element is axially spaced from the compliant brush seal element a distance at least three times a width dimension of the compliant brush seal component. 
     The invention may also be embodied in a seal assembly for a turbo machine having a rotor rotatable about an axis and a stationary nozzle assembly encircling the rotor, the rotor having a sealing surface and the stationary nozzle assembly having a radially facing portion opposed to the sealing surface, the seal assembly comprising: a seal carrier supported in the radially facing portion of the stationary nozzle assembly, the seal carrier comprising a backing plate, a hard tooth seal plate, and at a compliant seal component sandwiched between the backing plate and the hard tooth seal plate; the compliant seal component disposed in rubbing contact with the sealing surface; and at least one hard tooth seal element formed as one with said the hard tooth seal plate, the hard tooth seal element projecting radially toward but spaced from the sealing surface; wherein the hard tooth seal element is spaced axially from the compliant seal component by a distance equal to at least three times a width dimension of the compliant seal component. 
     The invention may further be embodied in a method of sealing a turbo machine rotary member relative to a stationary member encircling the rotary member, the rotary member having an outer circumferential sealing surface, the method comprising: (a) providing a first compliant seal component and a second hard seal element at a radially inward region of the stationary member, the first compliant seal component having a portion thereof in rubbing contact with the sealing surface of the rotary member, and the second hard seal element integrally formed in one piece with a carrier of the first compliant seal but radially spaced from sealing surface; and (b), locating the second hard seal element an axial distance upstream of the first compliant seal component of at least three times a width dimension of the first compliant seal component. 
     The 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 identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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; 
         FIG. 2  is a schematic representation of another sealing assembly of a related art; 
         FIG. 3  is a schematic representation of a sealing assembly according to an example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a diaphragm packing area of a steam turbine equipped with a sealing assembly in accordance with the &#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 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 in an axial direction, across the buckets  14  and nozzle partitions  20  as indicated by the flow arrow in  FIG. 1 . 
     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 . 
     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 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. 
     In another prior arrangement, as depicted in  FIG. 2 , a hard seal tooth  45  is machined to the nozzle structure  47  itself. However, if such a seal structure is worn through rubbing, the hard tooth seal structure cannot be replaced without also replacing the nozzle. 
       FIG. 3  represents a turbine similar to that illustrated in  FIG. 1  but wherein the seal assembly has been modified and relocated according to an example embodiment of the invention so as to reduce the footprint of the brush seal carrier or carrier assembly  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 carrier assembly  146  is comprised of compliant bristles  136  (also sometimes referred to herein as a compliant brush seal component or a “bristle pack”) extending radially towards the rotary number or turbine rotor  110  and providing a tight seal with the facing (or sealing) surface of the rotor. 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 , but it is to be understood that the disclosed exemplary embodiment enables certain related design changes. For example, the rotor in the example shown in  FIG. 3  includes an annular landing  142  adjacent the root portion of the bucket  143  that serves as the sealing surface for a reduced-footprint seal as described in further detail below. 
     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  formed directly in the diaphragm (or nozzle) inner ring or web  116  (and thus eliminating the need for carrier  28  shown in  FIG. 1 ), with a single hook  148  received in channel portion  152  of the groove  150 . In the illustrated example, moreover, the brush seal carrier  146  is a laminated structure comprised of the compliant bristles  136  sandwiched between the hard tooth seal  122  and a backing plate  156 . The hard tooth seal  122  is comprised of a forward, integrated hard tooth seal plate  154  formed with a spacer portion  158  to space the compliant bristles  136  from the balance of the hard tooth seal plate  154  to thereby allow forward axial flexing of the compliant bristles  136  in a conventional manner. The backing plate  156 , on the other hand, includes a projecting support  160  to limit aft axial flexing of the compliant bristles  136 . 
     In an example embodiment of the invention, at least one hard tooth seal element  162  is incorporated (e.g., machined) into the hard tooth seal plate  154 , at the radially inner end thereof, extending substantially parallel to the compliant bristles  136 . The hard tooth seal element  162  does not extend radially inwardly to the same extent as the compliant bristles  136  and thus serves as a backup seal to the bristles. 
     It has been discovered that the compliant bristles  136  and hard seal  122  are most effective when the following spatial relationships are observed. The radial clearance between the tip of the integrated hard tooth seal element  162  and the rotor land  142  should be at least 2W, where W is the width of the bristle pack  136 , as shown in  FIG. 3 ; the hard tooth element  162  must be located upstream (relative to the flow direction arrow F) of the bristle pack  136  by a distance equal to at least 3W; and in the event an aft hard tooth seal element is employed downstream of the bristle pack, then the hard tooth seal element must be located downstream of the bristle pack  136  by at least 2.5W. In a typical arrangement, the width of the bristle pack  136  may be in the range of from about 0.05 to 0.07 inch. This arrangement allows both the brush seal and hard tooth seal to act independently, without interference from the other, while at the same time, enabling an overall reduction in the footprint of the brush seal carrier  146 , as contrasted with the brush seal segment carrier  28  in  FIG. 1 . 
     In the example shown, the integrated hard tooth seal plate  154  is machined out of metal and includes at least one hard tooth seal element  162 . The brush seal bristle pack  136  is laminated with and welded between the integrated hard tooth seal plate  154  and the backing plate  156  to thus form the carrier assembly. As will be understood, hard tooth integration not only facilitates a reduction in the dimension of the seal carrier, but also facilitates replacement of the hard tooth if it is damaged as the result of rubbing against the rotor. 
     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  162 . 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 carrier  146  as compared to e.g. the seal carrier  28  depicted in  FIG. 1 . 
     It is to be understood that while the example carrier  146  includes the plates  154 ,  156  as described above, the carrier parts may have configurations and shape particulars that are different from the illustrated example. For example, although the backing plate  156  has been illustrated as including a hook  148  for engaging the channel  152  of the groove  150  in the nozzle web/diaphragm inner ring  116 , the integrated hard tooth seal plate  154  may also include such a hook instead of, or in addition to, the hook  148  for engaging a respective channel in the diaphragm inner ring/nozzle web structure. Furthermore, while a hard tooth  162  has been illustrated as integrated in the plate  154 , it is to be understood that in addition or in the alternative, either the plate  154  or the backing 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 hard 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. Similar seal arrangements may be provided at other locations as needed. 
     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.