Abstract:
A brush seal for sealing gaps, such as those found in gas turbine engines, includes a plurality of metallic bristles mechanically captured by a support member. The support member includes at least one flexible plate extending at least substantially along the bristle length of the plurality of bristles. The support member is constructed and arranged to support the plurality of metallic bristles during operation.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of U.S. Utility application Ser. No. 11/121,872, filed May 4, 2005, entitled “Non-metallic Brush Seals,” which claims the benefit of U.S. Provisional Application No. 60/567,905 filed May 4, 2004. The entire content of the above applications is incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the invention relate to brush seals for sealing a gap between a high pressure and a low pressure area. 
       BACKGROUND 
       [0003]    The use of brush seals for sealing gaps, such as those found in gas turbine engines, is known in the art. For example, in gas turbine engines brush seals are often utilized to minimize leakage of fluids at circumferential gaps, such as between a machine housing and a rotor, around a rotary shaft of the engine, and between two spaces having different fluid pressure within the engine. The fluid pressure within the system, which may be either liquid or gas, is greater than the discharge pressure (the pressure outside the area of the engine housing, toward which the fluid will tend to leak), thus creating a pressure differential in the system. As used herein, the system pressure side of the brush seal is referred to as the high pressure side, while the discharge pressure side of the brush seal is referred to as the low pressure side. 
         [0004]    Conventional brush seals include a bristle pack which is traditionally flexible and includes a plurality of bristles for sealing the gap, the bristles having a free end for contacting one component, such as the rotor. Circular brush seals have been utilized in gas turbine engine applications to minimize leakage and increase engine fuel efficiency. Conventional brush seals are made from metallic fibers, which are typically cobalt or nickel-base high temperature superalloy wire products suitable for elevated temperature operation. 
         [0005]    Because brush seals are contacting seals where bristle tips establish sealing contacts against the rotor surface, their applications are generally limited to surface speeds of less than about 1200 ft/sec and temperatures below about 1500° F. and usually below about 1200-1300° F. At extremely high surface speeds and temperatures, metallic brush seals have been found to suffer from excessive wear resulting from bristle tip melting. There are many areas in existing gas turbine engines, such as balance piston and other secondary flow areas near the gas path where surface speed and temperature conditions are typically beyond the capabilities of conventional metallic brush seals. As such, these locations are generally sealed by large-gap labyrinth seals which have been found to have high levels of leakage during use as compared to contacting seals such as carbon seals and metallic brush seals. Rotating intershaft seals, for both co-rotating and counter-rotating shafts, for example in advanced military aircraft engines, are also generally labyrinth type seals. 
         [0006]    Metallic brush seals are also traditionally not used for sealing buffer air near the bearing cavity. Buffer air is used to seal the bearing lubricant by pressurizing the buffer air higher than that of bearing lubricating oil pressure. Metallic brush seals are not used because of metallic debris could reach the interface between the bearing elements (e.g., balls, pins, etc.) and races causing bearing and rotor damage and possibly failure. Again, current seals used at these locations are generally high-leakage labyrinth seals. Higher leakage for bearing oil seals is not desirable because of contamination of downstream components and cabin air that can be introduced through the leak path. Appropriate carbon seals have not yet been developed for such applications because of their fragile characteristics and low damage tolerance. 
         [0007]    Large diameter main shaft bearing oil seals for large aircraft engines or land based turbo machinery are also typically labyrinth seals with large clearances that lead to oil contamination. In these applications large diameter carbon seals are expensive and metallic brush seals are not suitable. 
         [0008]    Although there have been developments in creating non-metallic brush seals, the use of polymeric or ceramic material to replace the metallic bristles has met with many design challenges due, in part, to the difficulty in handling and fabricating brush seals from such material. Typically ceramic or polymeric fibers are very thin, averaging in the range of about 2-3 μm in diameter. Fibers that are this thin have not traditionally been considered suitable for fabricating bristle strips. For example, the flexibility of the fibers can make it difficult to machine the inner diameter (ID) of the brush seal to the required tolerances. 
         [0009]    Therefore, there exists a need for a contacting seal that minimizes leakage as compared to traditional labyrinth type seals and which can operate under higher temperatures and/or higher speeds than existing metallic brush seals and which can be readily fabricated. 
       SUMMARY 
       [0010]    In accordance with one embodiment of the present invention, there is provided a contacting brush seal including a plurality of fibers fabricated from non-metallic materials, the fibers being twisted or braided together substantially along their length (L). The fibers may be particularly made from ceramic or polymeric materials, and in one embodiment are more particularly fabricated from NOMEX®, a synthetic aromatic polyamide polymer, manufactured by DuPont for high temperature applications. The non-metallic ceramic brush seals disclosed herein have melting points much higher than those of nickel and cobalt base superalloys and, therefore, should prevent the tips from melting under most conditions. In addition, brush seals made from softer high strength polymeric fibers with moderate (about 500-700° F.) temperature capability, may also be used for high performance bearings such as counter-rotating bearing cavities of advanced gas turbine engines. 
         [0011]    In accordance with one embodiment, a brush seal includes a plurality of metallic bristles and a support member that mechanically captures the plurality of metallic bristles. In one arrangement, the support member includes a pair of relatively rigid front and back plates and a pair of relatively flexible front and back plates, the plurality of metallic bristles, such as formed as a flexible bristle pack, being disposed between the front and back plates. The support member provides a level of rigidity to the flexible fiber pack. In one arrangement, the support member is configured to hold the flexible fiber pack in an axially inclined position such that the flexible fiber pack is coned either toward a low pressure area or a high pressure area in a brush seal system. 
         [0012]    In one arrangement, a brush seal includes a plurality of metallic bristles having a bristle length and a support member constructed and arranged to support the plurality of metallic bristles. The support member includes at least one flexible plate extending at least substantially along the bristle length of the plurality of bristles. 
         [0013]    In one arrangement, a brush seal system includes a contact rotor and a rotatable shaft, the contact rotor and the rotatable shaft defining a space therebetween. The brush seal system also includes a brush seal disposed between the contact rotor and the rotatable shaft to divide the pathway into a high pressure side and a low pressure side. The brush seal includes a plurality of metallic bristles having a bristle length and a support member constructed and arranged to support the plurality of metallic bristles. The support member has at least one flexible plate extending at least substantially along the bristle length of the plurality of bristles. 
         [0014]    In one arrangement, a brush seal includes a plurality of brush seal members having a brush seal member length and a support member constructed and arranged to support the plurality of brush seal members. The support member includes at least one flexible plate extending at least substantially along the brush seal member length of the plurality of brush seal members. The plurality of brush seal members is configured as a brush seal pack. The support member is constructed and arranged to mount to a base and to orient the brush seal pack in an axially inclined position relative to the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    It should be understood that the drawings are provided for the purpose of illustration only and are not intended to define the limits of the invention. The present invention is not limited to the precise arrangements and instrumentalities shown in the drawings and the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles disclosed herein. 
           [0016]      FIG. 1  is a perspective view of a mechanically captured brush seal. 
           [0017]      FIG. 2  is schematic illustration of a brush seal design including a flexible front and back plate. 
           [0018]      FIG. 3  is a schematic illustration of the flexible front and back plates of  FIG. 2  including radial slots. 
           [0019]      FIG. 4  is a photograph of twisted NOMEX® brand fibers such as used for the brush seal of  FIG. 2 . 
           [0020]      FIG. 5  illustrates a configuration of a support member of  FIG. 2  having a single flexible plate. 
           [0021]      FIG. 6  illustrates a configuration of a support member of  FIG. 2  positioning a fiber pack toward a high pressure area. 
           [0022]      FIG. 7  illustrates a configuration of a support member of  FIG. 6  having a single flexible plate. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring initially to  FIG. 2 , there is illustrated a brush seal  10  including a brush strip or pack  17  having a plurality of brush seal members  12  supported around a rod or core  14 . The plurality of brush seal members  12  can be formed of a ceramic or polymeric material (e.g., non-metallic fibers) to form a fiber pack. The plurality of brush seal members  12  can also be formed of a metallic material (e.g., metallic bristles) to form a bristle pack. In one arrangement, the brush seal members  12  are mechanically captured and secured as part of the brush strip  17 . The brush seal members  12  may be folded or wound about the core  14  as shown schematically in  FIG. 1 . In the present embodiment, a clamping channel  13 , such as the conventional channel or U-ring, may be utilized to further secure the brush seal members  12  to the core wire  14  by crimping the channel  13  over the wound brush seal members  12 . For added security, the brush seal members  12  may be glued or cemented to the rod  14  in the mechanically captured condition, as desired. Additionally, in the case where the brush seal members  12  are formed as metallic bristles, the metallic bristles can be welded to the core  14  to form the brush seal. 
         [0024]    In the case where the brush seal members  12  are formed as ceramic or polymeric fibers, the ceramic or polymeric fibers are preferably twisted or braided, as illustrated in  FIG. 4 , into thicker diameter filaments about 0.02″-0.05″ in diameter. Brush seals  10  can be fabricated from these braided filaments as described below. Ceramic fibers may be made from suitable high temperature ceramic filaments, including, but not limited to: Aluminum Oxide/Silicon Oxide/Boron Oxide or Nextel™ fiber (3M, St. Paul, Minn.); Silicon carbide fiber; other ceramic fibers generally made for ceramic/metal or ceramic/ceramic composites. Polymeric fibers may be made from suitable high temperature polymeric materials, including, but not limited to: KEVLAR® brand filaments for extremely high strength; and NOMEX® filaments for high strength and moderate temperature (˜300° C.) applications. Both KEVLAR® and NOMEX® are synthetic aromatic polyamide polymer manufactured by DuPont. Other suitable polymeric materials may be utilized for the twisted or braided filaments for brush seals  10 , as would be known to those of skill in the art. 
         [0025]    In one embodiment, NOMEX®, can be selected for brush seal fabrication because the NOMEX® fibers are generally made into strong fabrics for applications where thermal and flame resistant properties are essential. NOMEX® is the high temperature version of KEVLAR® which is as strong as or stronger than high strength steel. Other general properties of NOMEX® include: 1.) usable in wide range of temperatures from −196° C. to over 300° C.; 2.) broad compatibility with industrially used oils, resins, adhesives and refrigerants; 3.) chemical resistance to acids, alkalis and solvents; 4.) non-toxic; 5.) self-extinguishing; 6.) does not support combustion; and 7.) does not drip or melt when heated or burned. 
         [0026]    In one embodiment, Nextel™ can be selected for brush seal fabrication. Nextel™ fibers are very thin, in the range of about 25 μm to 0.001″ in diameter, and have a low modulus of elasticity. In this embodiment, the fibers are twisted as shown in  FIG. 4  to fabricate the brush strips. The twisted Nextel™ fibers are much thicker than the individual fibers, the twisted fibers having a thickness in the range of about 900 μm to 0.036″ in diameter and they are rigid enough to make brush strips using the conventional automatic brush strip manufacturing process. This helps to reduce the fabrication cost of Nextel™ brush strips which will be formed or rolled into brush seal inserts as explained below. Current automated mechanically captured brush strip manufacturing processes are suitable for producing brush strips where brush seal members  12  are inclined at about 90° to the strip axis  15  and are disposed normal to a rotor surface as indicated in  FIG. 1 . Typically, for metallic brush seals, bristles are inclined at about 0° to 45° to the strip length in the direction of rotation to provide flexibility and aid in bristle bending during rotor excursion. When bristles are normal to the strip length or to a rotor surface, they tend to buckle rather than bend, thereby increasing the mechanical contact pressure (P mc ) at bristle tips. Increased P mc  accelerates bristle wear and shortens the seal life. In one embodiment, as shown in  FIG. 2 , in order to facilitate bending of the brush seal members  12  during rotor excursions, the brush member pack  17  is inclined axially, such as in the direction of the fluid flow (e.g., toward a low pressure (L P ) side within an engine). For example, the brush seal  10  can be attached to a stator housing or to a rotating shaft  24  at a first end and can contact a rotor  26  at a second to form an intershaft seal configuration. The flexible brush member pack  17  is held in an axially inclined position by a support member  19  having a pair of thinner front and back plates  30 ,  32  which are attached to more rigid front and back plates  34 ,  36  as shown in  FIG. 2 . The support member  19  is configured to provide some rigidity to the brush seal members  12  of the brush member pack  17 . 
         [0027]    The thinner and more flexible front and back plates,  30 ,  32  located near an inner diameter (ID) of the brush seal  10 , protect the brush seal members  12  from damage during installation, aid in holding the brush member pack  17  together, and minimize its flaring. The flexible plates  30 ,  32  help to control axial and radial displacements of the brush seal members  12  by supporting the brush member pack  17  against pressure and centrifugal forces within a brush seal system (e.g., engine). The front plate  30  may be fabricated from a thin metallic strip which is configured to contact the brush member pack  17  when the brush seal system builds up pressure. Thus, the front plate  30  acts as a flow deflector minimizing brush seal members blow-down on a rotating surface, such as the rotor  26 , causing excessive brush member wear. The flexible back plate  32  may also be made from a metallic sheet stock. However, the thickness of the flexible back plate  32  may be greater than the front plate thickness  30 . The relatively thicker back plate  32  is designed to support the brush member pack  17  under pressure. 
         [0028]    The flexible front and back plates  30 ,  32  may also be divided into segments  21  by radial slots  20  as shown in  FIG. 3 , thereby allowing the segments  21  to bend. By optimizing the design of the radial segments  21  of the flexible front and back plates  30 ,  32 , the displacement of the brush member pack  17  caused by differential pressure and centrifugal forces at various operating conditions in a brush seal system can be controlled. For example, the brush member pack  17  is allowed to bend axially as the differential pressure and centrifugal force within the brush seal system increase with the rotor speed. By controlling axial bending of the brush member pack  17 , the radial clearance between the ID of the brush seal  10  and an outer diameter (OD) of the rotor  26  or its interference can be maintained relatively constant throughout the engine operating cycle (e.g., after engine excursion). 
         [0029]    The flexible plates  30 ,  32  can extend a predetermined length  38  of the brush seal members  12  so as to expose only a brush seal members tip area  22 , and protect the brush seal members  12  from being damaged during installation and/or mishandling. The brush seal  10  may be attached to the rotating shaft  24  at a first end can contact the rotor  26  at a second end with the rotating shaft  24  and the rotor  26  configured to rotate in relatively opposing directions. For a rotating seal, the stresses in the brush seal members  12  resulting from the centrifugal force are minimized as the brush member pack  17  is supported by flexible metallic back plate segment  21 . The metallic segments  21  are designed to withstand the maximum bending stress due to centrifugal force. By securing the brush member pack  17  between axially inclined (e.g., coned) front and back plates  30 ,  32  in the direction of the fluid flow, the front plate  30  can control brush memberpack  17  displacement and can minimize stresses in the brush member pack  17 . 
         [0030]    An order of magnitude value of the maximum bending stress induced in a rotating flexible metallic segment is estimated in the following example. The following example is provided for purposes of illustration only and is not intended to limit the scope of the present invention. 
         [0031]    Assuming that the flexible back plate  32  is made from age hardened Inco 718 (density=0.295 lbm/(in) 3  and Y.S=130,000 psi); the size of each finger segment  21  is: 
         [0032]    width=1.0″, length=0.25″ and thickness=0.05″, 
         [0033]    mass of each finger=1.0×0.25×0.05×0.295 lbm=0.0037 lbm 
         [0000]    and at the center of mass of each finger segment  21 , 
         [0034]    surface speed=500 ft/sec 
         [0035]    radius=0.5 ft; 
         [0000]    centrifugal force (F cf ) acting radially outward on each finger segment  21  is given by: 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     0.0037 
                     ) 
                   
                   × 
                   
                     
                       ( 
                       500 
                       ) 
                     
                     2 
                   
                 
                 .5 
               
                
               lbf 
                
               
                   
               
                
               or 
                
               
                 
                     
                 
                  
                 
                     
                 
               
                
               
                 F 
                 cf 
               
             
             = 
             
               1850 
                
               
                   
               
                
               
                 lbf 
                 . 
               
             
           
         
       
     
         [0036]    If the cant angle of the finger segments  21  with respect to a vertical plane=10°, the bending force (F n ) acting normally through the center of mass of each finger  21  is: 
         [0000]        F   n   =F   cf  Sin 10°=1850×0.174=322 lbs. 
         [0000]    [Note: The F cf  will vary along the length of the finger segment  21  and it needs to be integrated for a more accurate estimate] 
         [0037]    Therefore, the maximum bending stress (σ max ) generated at the surface of each finger segment  21  is: 
         [0000]    
       
         
           
             
               σ 
               max 
             
             = 
             
               
                 3 
                 · 
                 
                   F 
                   n 
                 
                 · 
                 L 
               
               
                 w 
                 · 
                 
                   t 
                   2 
                 
               
             
           
         
       
     
         [0038]    where,
       F n =normal force acting through the center of mass=322 lbf   L=length of finger=0.25″   w=width of fingers=1″   t=thickness of finger=0.05″       
 
         [0000]    
       
         
           
             
               σ 
               max 
             
             = 
             
               
                 
                   3 
                   × 
                   322 
                   × 
                   .25 
                 
                 
                   1 
                   × 
                   
                     
                       ( 
                       .05 
                       ) 
                     
                     2 
                   
                 
               
               = 
               
                 
                   96,000 
                 
                  
                 
                     
                 
                  
                 psi 
               
             
           
         
       
     
         [0043]    This stress is well below the yield stress of Inco 718. The rest of the rigid structure of the rotating seal can easily be optimized to maintain stresses below the yield stress. For design optimization, detailed Finite Element Analysis (FEA) of the entire structure may be performed. 
         [0044]    It will be appreciated that the braided ceramic brush seals, as disclosed herein, can operate effectively at relatively high temperatures (above about 1500° F.) and at high surface speeds (exceeding about 1000 ft/sec) while being capable of being manufactured using standard automatic and low-cost brush strip manufacturing process. Controlled bending of the flexible plates  30 ,  32  and the brush member pack  17  also aid in controlling seal radial clearance or interference throughout the operating cycle of the bush seal system. 
         [0045]    It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope, spirit and intent of the invention. 
         [0046]    For example, although the fibers are illustrated as twisted in  FIG. 4 , the term “twisted” as used herein is intended to include braided configurations, or any configuration where the fibers intentionally overlap or are wound about at least a portion of the length of the fibers. Likewise, non-metallic materials other than those described herein may be utilized for the twisted fibers. 
         [0047]    As indicated above with respect to  FIG. 2 , the brush seal  10  can be attached to a rotating shaft  24  (e.g., base) at a first end for an intershaft seal configuration and can contact a rotor  26  at a second end. Such description is by way of example only. In one arrangement, the brush seal  10  is attached to a stationary housing and contacts a rotor operable to rotate about an axis of rotation. 
         [0048]    As indicated above with respect to  FIG. 2 , the brush member pack  17  is held in an axially inclined position toward the low pressure side by a support member  19  having a pair of thinner front and back plates  30 ,  32  and a pair of more rigid front and back plates  34 ,  36 . Such description and illustration is by way of example only. In one embodiment, the support member  19  includes a single flexible plate attached thereto. For example, as shown in  FIG. 5 , brush member pack  17  is held in an axially inclined position toward the low pressure side by a support member  19  having rigid front and back plates  34 ,  36  and a single flexible back plate  32 , such as formed from a metallic sheet stock, disposed in proximity to the low pressure side. The back plate  32  is designed to protect the brush seal members  12  from damage during installation and support the brush member pack  17  while under pressure, for example. Additionally, in one embodiment, the brush member pack  17  can be held in an axially inclined position toward the low pressure side by a support member  19  having rigid front and back plates  34 ,  36  and a single flexible front plate  30 , such as formed from a metallic sheet stock, disposed in proximity to the high pressure side. In one arrangement, the flexible front plate  30  provides a restoring force to the brush seal members  12  to return the brush seal members  12  to a given position after a deformation of the brush seal members  12 . 
         [0049]    As indicated above with respect to  FIG. 2 , the brush seal pack  17  can be attached to a rotating shaft  24  (e.g., base) at a first end for an intershaft seal configuration and contact a rotor  26  at a second end. In order to facilitate bending of the brush seal members  12  during rotor excursions, the brush seal pack  17  is inclined axially (i.e., coned) in the direction of the fluid flow, i.e., toward the low pressure (L P ) side. In such an arrangement, the net radial deflection of the flexible plates  30 ,  32  resulting from centrifugal force and pressure, causes the brush seal  10  to act as a controlled gap seal for relatively high surface speeds. In another embodiment, as shown in  FIG. 6 , the support member  19  (i.e., the rigid front and back plates  34 ,  36  and the flexible front and back plates  30 ,  32 ) inclines (i.e., cones) the brush seal pack  17  axially toward a high pressure (H p ) side. In such an arrangement, as the brush seal system is pressurized, the flexible front and back plates  30 ,  32  bend to close a sealing gap or increase a seal contact pressure with the rotor  26  to reduce leakage. In such an arrangement, the brush seal  10  can act as a contacting seal for low leakage at relatively lower surface speeds. 
         [0050]      FIG. 6  illustrates the brush seal pack  17  as being inclined axially (i.e., coned) by the rigid front and back plates  34 ,  36  and by the flexible front and back plates  30 ,  32 , toward a high pressure (H p ) side. Such an illustration is by way of example only. In one arrangement, the support member  19  includes rigid front and back plates  34 ,  36  and a single flexible plate attached thereto. For example, as shown in  FIG. 7 , the brush seal pack  17  is held in an axially inclined position by rigid front and back plates  34 ,  36  as well as by a flexible front plate  30 , such as formed from a metallic sheet stock. The front plate  30  is designed to contact the brush seal pack  17  when the system builds up pressure. In such an arrangement, the front plate  16   a  can act as a flow deflector minimizing brush seal member blow-down on the rotating surface causing excessive brush seal member wear. Additionally, the front plate  30  can provide a restoring force to return the brush seal pack  17  into a sealing configuration after rotor excursion. Also, in one embodiment, the brush member pack  17  can be held in an axially inclined position toward the high pressure side by a support member  19  having rigid front and back plates  34 ,  36  and a single flexible back plate  32 , such as formed from a metallic sheet stock, disposed in proximity to the low pressure side. As indicated above, the brush seal members  12  can be formed from a metallic material which are mechanically captured by the support member  19  and supported during use. Such mechanical capturing of the metallic brush seal minimizes or can eliminate the need to weld metallic bristles to fabricate brush seals. While a variety of metallic materials can be used to form the bristles, in one example, the bristles can be formed from a nickel and cobalt based superalloy. In such an arrangement, the metallic bristles can be used in applications requiring surface speeds of less than about 1200 ft/sec and temperatures below about 1500° F. and usually below about 1200-1300° F.