Abstract:
A brush seal, comprising: a bristle arrangement having a retention section; a pair of plates flanking the bristle arrangement and having a clamping section to frictionally engage the retention section. The clamping section allows movement of the retention section before the plates are secured together, to place the bristle arrangement at a desired position between the plates, and prevents movement of the retention section after the plates are secured together.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to pending U.S. patent application Ser. No. 10/074,191 (Attorney Docket Number EH-10536) filed on 12 Feb. 2002, herein incorporated by reference. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This invention relates to brush seals. Specifically, the present invention relates to brush seals with adjustable clearances. As used herein, the phrase brush seal clearance refers to the distance that the bristles extend past the plates.  
           [0003]    Proper operation of a turbine engine should occur when the myriad engine parts remain within acceptable limits of alignment with other engine parts. The performance of the engine tends to decline when the alignment exceeds these acceptable limits. This is particularly true when dealing with seals.  
           [0004]    Many factors influence whether parts maintain proper alignment. Assembly techniques and rotor balancing clearly affect part alignment Unexpected situations, like foreign object damage, can also create misalignments. Misalignment can even occur with normal operation of the engine. Typically, thermal conditions cause this type of misalignment. For example, steam turbine rotors can bow over time.  
           [0005]    Conventional methods exist to handle such misalignment. For example, the technician could re-machine certain features of the engine to return to proper alignment. Re-machining features on an installed turbine engine, however, can prove time consuming and costly.  
           [0006]    Another method is for the operator to maintain an inventory of spare engine hardware. This allows a technician to replace the misaligned parts rapidly. Likewise, this method can prove expensive in terms of inventory costs.  
         SUMMARY OF INVENTION  
         [0007]    It is an object of the present invention to provide a brush seal with an adjustable clearance.  
           [0008]    It is a further object of the present invention to provide a brush seal in which a technician can adjust the clearance in the field.  
           [0009]    It is a further object of the present invention to provide a brush seal that can adjust clearance without re-machining the brush seal.  
           [0010]    It is a further object of the present invention to provide a brush seal that allows replacement of specific components.  
           [0011]    It is a further object of the present invention to provide a brush seal with adjustable bristle stiffness.  
           [0012]    These and other objects of the present invention are achieved in one aspect by a brush seal, comprising: a bristle arrangement having a retention section; a pair of plates flanking the bristle arrangement and having a clamping section to frictionally engage the retention section. The clamping section allows movement of said retention section before the plates are secured together and prevents movement of the retention section after said plates are secured together.  
           [0013]    These and other objects of the present invention are achieved in another aspect by brush seal segment, comprising: a bristle arrangement having a retention section; a pair of plates flanking the bristle arrangement and having a clamping section to frictionally engage the retention section. The clamping section allows movement of the retention section before the plates are secured together and prevents movement of the retention section after the plates are secured together.  
           [0014]    These and other objects of the present invention are achieved in another aspect by a method of assembling a brush seal, comprising the steps of: providing a pair of plates and a bristle arrangement, the bristle arrangement locatable between the plates at a plurality of positions; selectively locating the bristle arrangement at a desired one of the positions; and securing the plates together to retain the bristle arrangement at the desired position. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    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:  
         [0016]    [0016]FIG. 1 is a cross-sectional view of a conventional brush seal;  
         [0017]    [0017]FIG. 2 is a perspective view of a brush seal of the present invention;  
         [0018]    [0018]FIG. 3 is a detailed view of the brush seal of FIG. 2; and  
         [0019]    [0019]FIGS. 4 a - d  are various views during the assembly of the brush seal of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    [0020]FIG. 1 displays a conventional annular brush seal  100 . Although shown as a single stage, the brush seal  100  could have multiple stages. The brush seal  100  includes several sub-assemblies, namely a back plate  101 , side plate  103  and a bristle pack  105 . The plates  101 ,  103  flank the bristle pack  105 .  
         [0021]    The bristle pack  105  comprises a plurality of densely arranged wire bristles. Each of the bristles has a first end  107  and an opposed second end  109 . While extending at an angle to a radial line, the first ends  107  of the bristles reside at the inner diameter of the brush seal  100 . The second ends  109  of the bristles reside at the outer diameter of the brush seal  100 .  
         [0022]    The plates  101 ,  103  and the bristle pack  105  are welded together to form the brush seal  100 . Specifically, the outer diameter of the plates  101 ,  103  and the bristle pack  105  are welded together to sandwich the bristles between the plates  101 ,  103 . Typically, the weld process occurs long before installation of the brush seal  100  in the engine. That means a clearance C between the bristle pack  105  and the back plate  101  is set long before installation. Accordingly, the brush seal  100  may not be able to accommodate, for example, any misalignment between the engine parts.  
         [0023]    In addition, welding the components  101 ,  103 ,  105  together requires the removal of the entire brush seal  100  despite instances where less than all of the components require replacement.  
         [0024]    [0024]FIGS. 2 and 3 display one embodiment of the present invention. The figures display the present invention in one possible embodiment—a packing ring segment  200 . Packing ring segments  200  includes both a labyrinth seal and a brush seal to prevent fluid from exiting through a gap between a stationary component (such as the engine case) and a rotating component (such as the rotor shaft). When fully arranged, the segments  200  form an annual packing ring (not shown) within the engine. The packing ring is typically spring loaded (not shown) to urge the ring against the rotor.  
         [0025]    Although the packing ring segment  200  has other features, only features relevant to the brush seal will be described. The segment  200  includes a first plate  201 , second plate  203  and a pre-assembled bristle arrangement  205 . The first plate  201 , located upstream, preferably acts like a side plate. The side plate could include a windage cover  207 . The second plate, located downstream, preferably acts like a back plate.  
         [0026]    The bristle arrangement  205  includes a plurality of bristles  211  secured together by a joint  213 . The bristles  211  could be made from any suitable material such as a cobalt alloy wire. FIGS. 2 and 3 show a radial brush seal arrangement with the bristles  211  extending radially. Alternatively, the brush seal could be an axial brush seal with the bristles  211  extending in the axial direction.  
         [0027]    The joint  213  secures one end of the bristles  211  together and obviates the need to weld the bristles  211  to the plates  201 ,  203 . Preferably, the joint  213  is a weld joint. U.S. patent application Ser. No. 10/074,191 describes in more detail the method of making the bristle arrangement  205 . The present invention could, however, use other methods to produce the joint  213 .  
         [0028]    Suitable fasteners  209 , such as machine screws, secure the plates  201 ,  203  together. When secured together, the plates  201 ,  203  sandwich the bristle arrangement  205  and prevent movement of the bristle arrangement  205  during operation of the turbine engine. In the radial arrangement shown in the figures, the plates  201 ,  203  prevent radial movement of the bristle arrangement  205 . The plates  201 ,  203  preferably restrain the bristle arrangement  205  without an interference fit. The present invention could have features (not shown) to prevent the fasteners  209  from backing out from engine vibration. Examples include a locking feature (not shown) or subjecting the segment  200  to chemical treatment (not shown) or staking of the surrounding packing body material (not shown).  
         [0029]    The present invention however, allows a technician to adjustably position the bristle arrangement  205  before the fasteners  209  secure the first and second plates  201 ,  203  together. In other words, the present invention allows the technician to adjust the bristle arrangement  205  radially to change the clearance of the brush seal. FIGS. 4 a - d  demonstrate this capability.  
         [0030]    [0030]FIG. 4 a  displays the second plate  203  before receiving the bristle arrangement  205 . The second plate  203  includes a clamping section to receive a retention section of the bristle arrangement  205 . Specifically, the second plate  203  includes a channel  215  in the surface of the second plate  203  that faces the first plate  201 . The joint  213  of the bristle arrangement  205  preferably acts as the retention section. At a minimum, the channel  215  receives the joint  213  of the bristle arrangement  205 . As seen in the figure, the channel  215  extends to a distal end  217  of the second plate  203  to receive the joint  213  and a length of the bristles  211  of the bristle arrangement  205 .  
         [0031]    Next, the technician places the bristle arrangement  205  in the channel  215  as seen in FIG. 4 b . At this point, the brush seal exhibits an initial clearance C′ between the bristle arrangement  205  and the second plate  203 .  
         [0032]    The technician can then adjust the bristle arrangement  205  in the channel  215  to achieve a desired clearance C as seen in FIG. 4 c . The desired clearance could be either larger or smaller than the initial clearance C′. Preferably, the present invention allows the technician to adjust the bristle arrangement  205  within a range of between approximately 25% below and above an average clearance.  
         [0033]    Although FIG. 4 c  shows just the second plate  203  and the bristle arrangement  205 , the technician could adjust the clearance C with the bristle arrangement  205  positioned between both plates  201 ,  203  (provided the technician has not yet tightened the fasteners  209 ).  
         [0034]    After selecting the proper clearance C, the technician secures the first plate  201  to the second plate  203  as discussed above. As seen in FIG. 4 d , the first plate  201  has a channel  219  corresponding to the channel  215  in the second plate  203 . Both channels  215 ,  219  define the clamping section of the brush seal.  
         [0035]    In an alternative arrangement, only one of the plates  201 ,  203  could contain such a channel. The other plate would have a planar surface. Regardless of whether one or both of the plates  201 ,  203  have such channels, the depth of the clamping section should correspond to the width of the joint  213  of the bristle arrangement  205 . Preferably, the plates  201 ,  203  frictionally retain the bristle arrangement  205  without an interference fit.  
         [0036]    Similarly, the clamping section of the plates  201 ,  203  should have a length greater than the retention section of the bristle arrangement  205 . This allows the technician to adjust the clearance C.  
         [0037]    Although described as useful during assembly of the brush seal, the present invention is also useful during maintenance, repair and/or overhaul of the engine. During a maintenance operation, the technician may remove the segment  200  using conventional techniques. Rather than scrapping the entire segment  200  due to worn or damaged bristles  211 , the present invention allows the technician to replace the used bristle arrangement  205  and to reuse the plates  201 ,  203 . Specifically, the technician removes the fasteners  209  to separate the plates  201 ,  203 . The technician then substitutes the used bristle arrangement  205  with a replacement bristle arrangement  205 . As described above, the technician adjusts the clearance C of the bristle arrangement  205  before securing the plates  201 ,  203  together with the fasteners. Using conventional techniques, the technician reinstalls the segment  200  in the engine.  
         [0038]    Another important aspect of the present invention is bristle stiffness. Conventionally, brush seals are designed to fit the needs of a specific location within an engine. A prime consideration during such design is the expected pressure drop at that engine location.  
         [0039]    The present invention, however, obviates the need to custom design seals for specific engine locations. In other words, the present invention allows the use of one seal design at different engine locations exhibiting different pressure drops. Varying the clearance C of the bristle arrangement  205  as described above also alters the stiffness of the bristles  211 . Similar to a cantilever beam, the free length of the bristles  211  determines stiffness. Free length is the distance from bristle pinch/clamping point (between side plate  201  and back plate  203 ) to the free end of the bristle  211 . As free length increases, stiffness decreases. This allows, for example, the technician to use a seal at an engine location having a smaller pressure drop by increasing clearance C. Conversely, the technician could use the same seal at an engine location having a larger pressure drop by decreasing clearance C.  
         [0040]    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.