Abstract:
A brush seal, comprising: a side plate; a back plate; and a bristle arrangement between the side plate and back plate. At least a portion of the back plate is made from a material that tends not to burr when contacting a rotating component. The bristle arrangement could include a plurality of bristles secured together by a joint. The entire back plate could be made from the low coefficient of friction or low wear rate material. In addition, the side plate could also be made from the low coefficient of friction or low wear rate material. The material allows a reduced clearance between the brush seal and the component engaged by the brush seal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to a U.S. patent application Ser. No. (not yet assigned, but Attorney Docket Number EH-10586) filed on Feb. 12, 2002, herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to brush seals. Specifically, the invention relates to brush seals that have reduced clearances.  
           [0003]    A brush seal includes a side plate, a back plate and bristles between the plates. Gas turbine engines commonly use brush seals to prevent secondary flow from escaping through a gap between a stationary part (e.g. a diffuser case) and a rotating part (e.g. a turbine shaft). In this arrangement, the bristles of the brush seal impede the ability of the secondary flow to pass between the stationary and rotating parts. The bristles impede the secondary flow by extending from the stationary part, into the gap, and into contact with the rotating part.  
           [0004]    The back plate of the brush seal remains a distance away from the rotating part. The size of the clearance between the back plate and the rotating part directly affects the efficiency of the brush seal. A brush seal with a larger back plate clearance allows a greater amount of secondary flow to pass through the bristles. A brush seal with a smaller back plate clearance allows a lesser amount of secondary flow to pass through the bristles.  
           [0005]    Conventional brush seals tend to have larger clearances. While less efficient, these larger clearances help the brush seal to avoid contact between the back plate and the rotating component during operation of the engine. Contact between the metallic back plate of a conventional brush seal and the metallic rotating component can damage the brush seal. For example, such contact between the brush seal and the rotating component can wear away the back plate. Wearing away the back plate increases the clearance between the brush seal and the rotating component.  
           [0006]    Such contact between the metallic back plate and rotating component can also form burrs on the back plate. Any burrs present on the back plate could nick or cut the adjacently located bristles. Depending on the severity of damage to the bristles, the entire bristle pack could fail.  
           [0007]    One solution to this problem has been to allow the brush seal to float between the stationary component and the rotating component. The use of a floating brush seal, however, increases the complexity and part count of the brush seal assembly.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a new and improved brush seal.  
           [0009]    It is a further object of the present invention to provide a more efficient brush seal.  
           [0010]    It is a further object of the present invention to provide a brush seal that can be placed at a reduced clearance with the rotating component.  
           [0011]    It is a further object of the present invention to provide a brush seal that exhibits less wear after contact with the rotating component.  
           [0012]    It is a further object of the present invention to provide a brush seal that exhibits less damage after contact with the rotating component.  
           [0013]    It is a further object of the present invention to provide a brush seal that is not complex.  
           [0014]    It is a further object of the present invention to provide a brush seal that does not have a high part count.  
           [0015]    These and other objects of the present invention are achieved in one aspect by a brush seal, comprising: a side plate; a back plate; and a bristle arrangement between the side plate and back plate. At least a portion of the back plate is made from a material that tends not to burr when contacting a rotating component.  
           [0016]    These and other objects of the present invention are achieved in another aspect by a brush seal, comprising: a side plate; a back plate; and a bristle arrangement between the side plate and back plate. The bristle arrangement includes a plurality of bristles secured together by a joint. At least the back plate is made from a low coefficient of friction or low wear rate material.  
           [0017]    These and other objects of the present invention are achieved in another aspect by a brush seal, comprising: a side plate; a back plate; and a plurality of bristles between the plates. The bristles are metallic and at least one of the plates is plastic.  
           [0018]    These and other objects of the present invention are achieved in another aspect by a method of reducing a clearance between a brush seal and a component. The method comprises the steps of: providing a brush seal having a back plate and bristles; forming at least a portion of the back plate from a material that resists burring when contacting a rotating component; and spacing the portion from said component at a reduced distance. The reduced distance is less than a distance if the portion was not made from the low coefficient of friction or low wear rate material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which:  
         [0020]    [0020]FIG. 1 is a cross-sectional perspective view of a conventional brush seal engaging a rotor;  
         [0021]    [0021]FIG. 2 is a cross-sectional perspective view of a brush seal of the present invention;  
         [0022]    [0022]FIG. 3 a  is a detailed view of a section of the brush seal in FIG. 2;  
         [0023]    [0023]FIG. 3 b  is a detailed view of an alternative arrangement of the section in FIG. 3 a;    
         [0024]    [0024]FIG. 4 is a cross-sectional perspective view of another alternative embodiment of a brush seal of the present invention;  
         [0025]    [0025]FIG. 5 is a cross-sectional perspective view of another alternative embodiment of a brush seal of the present invention; and  
         [0026]    [0026]FIG. 6 is a side-by-side comparison of the conventional brush seal in FIG. 1 and the brush seal of the present invention in FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 displays a conventional brush seal arrangement  100 . The arrangement  100  includes a brush seal  101  rigidly secured to a first component  103  (typically a stationary component of the engine). The brush seal  101  extends from the first component  103  to engage a second component  105  (typically a rotating component of the engine).  
         [0028]    The brush seal  101  includes a side plate  107 , a back plate  109  and a bristle pack  111  between the plates  107 ,  109 . The plates  107 ,  109  are made from suitable alloys, such as Inconel® or 400-series stainless steel. The side plate  107  can include a windage cover  113 . Typically, the plates  107 ,  109  and the bristle pack  111  are welded together.  
         [0029]    As seen in FIG. 6, the back plate  109  of the brush seal  101  remains a distance d 1 , from the second component  105 . The distance d 1 , is sufficient to ensure that the metallic back plate  109  tends to avoid contact with the metallic second component  105 . As described above, avoiding contact between the back plate  109  and the second component  105  helps prevent damage to the brush seal  101 .  
         [0030]    [0030]FIG. 2 displays one embodiment of a brush seal arrangement  200  of the present invention. The arrangement likewise includes a brush seal  201  rigidly secured to a first component  203 . The brush seal  201  extends from the first component  203  to engage a second component  205 .  
         [0031]    Similar to the conventional brush seal  101 , the brush seal  201  includes a side plate  207 , a back plate  209  and a bristle pack  211  between the plates  207 ,  209 . The side plate  207  can include a windage cover  213 . The plates  107 ,  109  and the bristle pack  111  can be secured together using suitable techniques such as welding.  
         [0032]    [0032]FIG. 3 a  displays a detailed view of the distal end of the brush seal  201 . In the arrangement shown in the figures, the distal end of the brush seal  201  is the inner diameter of the annular brush seal  201 . The inner face of the back plate  209  has a coating  215  placed thereon using known techniques. Preferably, application of the coating  215  on the back plate occurs before assembly of the brush seal  201 .  
         [0033]    The coating  215  should be a material that tends not to produce burrs during contact with the rotating component. The coating  215  should also have capability to withstand the elevated temperatures encountered in the secondary flow of the engine. A suitable coating  215  could have a low coefficient of friction and/or a low wear rate. For example, the coating  215  could be a fluoropolymer such as PTFE. Alternatively, the coating  215  could be an abradable metal.  
         [0034]    [0034]FIG. 3 b  displays a detailed view of an alternate embodiment of the distal end of the brush seal  201 . Rather than the coating  215  of FIG. 3 a , the back plate  209  has an insert  217  secured thereto using known techniques. Depending upon the insert material, such techniques could include epoxy bonding or brazing. The back plate  209  could include a shoulder  219  to receive a correspondingly shaped extension  221  from the insert  217 . Preferably, bonding the insert  217  to the back plate occurs before assembly of the brush seal  201 .  
         [0035]    The insert  217  should likewise be a material that resists burrs during contact between the back plate  209  and the rotating component. The insert  217  should also have capability to withstand the elevated temperatures encountered in the secondary flow of the engine. As discussed above, a fluoropolymer like PTFE could be used. In addition, the insert  217  could also be made from carbon, graphite or sintered impregnated metal matrix materials.  
         [0036]    The alternative embodiments described above are preferably used with brush seals having the typical bristle arrangement shown in FIG. 2. The alternative embodiments described below are preferably used with brush seals having the bristle arrangement described in U.S. patent application Ser. No. (not yet assigned, but Attorney Docket Number EH-10586) filed on Feb. 12, 2002.  
         [0037]    [0037]FIG. 4 shows another alternative embodiment of a brush seal  301  of the present invention. The brush seal  301  rigidly secures to a first component (not shown) and engages a second component (not shown).  
         [0038]    The brush seal  301  includes a side plate  307 , a back plate  309  and a bristle pack  311  between the plates  307 ,  309 . The annular bristle pack  311  (also referred to as a bristle ring) includes a plurality of bristles  323  secured together by a joint  325 . The joint  325  forms while welding the alloy bristles  323  (such as cobalt) together during an earlier assembly step.  
         [0039]    The plates  307 ,  309  each include a groove  327 ,  329  to receive the joint  325 . The grooves  327 ,  329  preferably prevent radial movement of the bristle pack  311  during engine operation without creating an interference fit. Differently than the earlier embodiments, the back plate  309  is made entirely from the aforementioned materials. For example, the back plate  309  could be made entirely from a suitable low coefficient of friction or low wear rate material. The back plate  309  could be made from these materials using known techniques such as injection molding, machining or extruding.  
         [0040]    The plates  307 ,  309  secure together using suitable techniques such as epoxy or braze bonding or using rivets (not shown) or threaded fasteners (not shown). The metallic side plate  307  helps provide rigidity to the brush seal  301 . If rigidity is not a concern, then the side plate  307  could also be made from the aforementioned materials. For example, the side plate  307  could also be made from a low coefficient of friction or low wear rate material. Preferably, the side plate  307  would be made from the same material as the back plate  309 .  
         [0041]    [0041]FIG. 5 shows another alternative embodiment of a brush seal  401  of the present invention. The brush seal  401  has a one-piece body  431  rather than the discrete side plates and back plates of the earlier embodiments. The brush seal  401  also includes an annular bristle pack  411  with bristles  423  secured together by a joint  425 . The body  431  retains the joint  425  and a section of the bristles  423 .  
         [0042]    The body  431  is preferably made from the aforementioned materials. For example, the side plate  307  could be made from a low coefficient of friction or low wear rate material. Preferably, the body  431  is plastic and is overmolded about the bristle pack  411  using known techniques. Other methods of forming the brush seal  401  could be used.  
         [0043]    [0043]FIG. 6 displays the benefits of the present invention. Using suitable materials, the brush seal  201  of the present invention can position the back plate at a distance d 2  from the second component  105 . The distance d 2  of the present invention is less than the distance d 1 , of conventional brush seals with all-metallic back plates. The distance d 2  could be approximately 10-25% less than the distance d 1 , of conventional brush seals.  
         [0044]    The reduced clearance exhibited by the brush seal of the present invention helps increase efficiency. The efficiency of the brush seal increases as the gap between the brush seal and the rotating component decreases. A smaller gap impedes the ability of the secondary flow to pass between the stationary and rotating parts.  
         [0045]    The reduced clearance of the present invention also helps prevent bristle blowover. Blowover occurs when the secondary flow begins to urge the bristles in the flow direction. The bristles tend to wrap under the back plate. Such bending of the bristles introduces stresses to the bristles.  
         [0046]    Since the present invention has a reduced clearance, shorter lengths of the bristles extend in cantilever fashion from the back plate. In other words, the back plate of the present invention supports a greater length of the bristles. This support helps the bristles withstand the urging of the secondary flow. As a result, the bristles tend to exhibit less stress.  
         [0047]    Even with this reduced clearance, the present invention does not exhibit the damage encountered by conventional brush seals during contact with the rotating component. The aforementioned materials, such as a low coefficient of friction or low wear rate material, does not form burrs during such contact. Lacking burrs, the back plate does not nick or cut the bristles. With intact bristles, the efficiency of the brush seal tends not to degrade after contact between the back plate and the rotating component.  
         [0048]    The present invention has been described in connection with the preferred embodiments of the various figures. It is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.