Abstract:
A ceramic finger seal for use between a housing and a combustor liner to inhibit air passage therebetween and for use in fluid sealing between a rotating shaft and a housing circumscribing the rotating shaft. The ceramic finger seal has at least two annular diaphragm members constructed of two or more diaphragm segments bonded end to end by ceramic cement or other high temperature joining compounds. The diaphragm members may be partitioned into a generally continuous inner diameter portion and a segmented outer diameter portion or the reverse thereof. The segmented portion includes finger elements spaced uniformly apart forming gaps therebetween and extend radially outward or inward terminating in a foot portion. The rolled edge on the finger is formed by laser cutting to prevent gouging of the combustor liner surface.

Description:
GOVERNMENT RIGHTS 
     This invention was made with Government support under Contract No. N00421-97-C-1049 awarded by the U.S. Navy, BAA High Temperature Rise Combustor Program. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to sealing devices disposed relative to two generally stationary structures of approximately cylindrical shape as well as to other objects such as two relatively rotating members requiring a fluid seal therebetween. The present invention may provide for air sealing of ceramic combustor liners that typically have large temperature excursions as well as excessive surface temperature that may exceed the temperature capability of metallic sealing devices and that may experience deflection relative to the adjacent structure. The device also may be used to provide fluid sealing between a rotating shaft and a housing circumscribing the rotating shaft. 
     The present art uses a series of interlocking ceramic segments disposed around a combustor liner for sealing. The ceramic segments may be biased against the combustor by metallic springs or fingers. This seal structure provides air-to-air sealing between the two elements while allowing axial and radial relative motions between the bodies. Seals that use a spring loading feature in other sealing applications may be as disclosed in U.S. Pat. No. 4,415,317; however, they are expensive to manufacture, subject to premature failure of individual spring elements and are complex to install in the application. 
     Use of ceramic materials for seals has been hypothesized for brush type seals in U.S. Pat. No. 4,600,202. This patent discloses a brush type seal between machine components in relative motion, of which at least one member rotates, in which strands or bristles consist of composite fibers designed for good thermal conductivity in at least portions of their surface and at least a portion has flexible, elastic properties. The disclosure indicates the bristles can be made from various types of glass, glass-metals, glass-ceramics, or a combination thereof. However, this proposed type of bristle seal with ceramic content flexible enough to perform as a seal and not fracture in use has been found to be difficult to manufacture and to have low reliability in application. 
     Laminated finger seals are known in the art as exemplified by U.S. Pat. No. 5,108,116. These seals are designed for fluid sealing between relatively rotating elements as for example a shaft and a housing. As a result of this application, the fingers, which may have a foot element, are designed to slide on the shaft element when rotating. The finger portion provides pressure through the foot portion to maintain contact with the rotating shaft. A balance must be maintained to avoid excessive wear of the foot portion and the rotating shaft. There exist various improvements in designs for the foot portion, as for example to give it aerodynamic properties to glide over the surface of the shaft. In such an application a considerable amount of pressure can be exerted by the finger elements to maintain a tight seal interface and aerodynamic or sliding motion at low friction levels is not required. However, the use of a ceramic composition as in the instant invention includes a ceramic finger seal that can withstand the excessive heat generation caused by the friction between the seal and the rotating shaft. 
     For the combustion liner type interface sealing application, the combustor liner in operation may be at an elevated temperature relative to the surrounding structure. A finger seal inserted therebetween may have the finger elements extended radial outward for engagement with the combustor liner. The inner circumference of the seal may then be attached to the housing. Use of ceramic composition finger seals allows application of such combustion liner seals to be used in very high temperature environment. For combustion liner applications the ceramic composition finger seals may be fabricated with the finger elements oriented radial inward for sealing the outer most portion of the combustor. 
     As can be seen, there is a need for a generally circular sealing device for air and fluid sealing between two bodies experiencing relative radial or axial motion and elevated temperatures. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a set of laminated ceramic finger seal may be inserted between two generally stationary structures to inhibit airflow therebetween. The seal may have multiple diaphragm segments and diaphragm members laminated together and fixed in a holding device. The diaphragm members may be circumferential bands having a generally continuous inside diameter portion and a segmented outside diameter portion or a reverse orientation thereof and may be designated as inside diameter and outside diameter seals. 
     The segmented portion defines a circumferentially uniform array of finger elements spaced apart to define a plurality of uniform gaps. When the seal is clamped in the holding device attached to the housing and assembled into the combustor the finger elements are deflected toward the inner circumference of the ceramic finger seal thereby applying pressure against the combustor liner wall to affect the sealing between the structures. For use in sealing the outermost portion of the combustor the finger elements are deflected toward the outer circumference of the ceramic finger seal. 
     With relative rotating elements the circumferential bands may have a general continuous outside diameter portion and a segmented inside diameter portion. The finger elements with a foot portion contact the rotatable shaft to apply pressure to effect the sealing between the structures. 
     In another aspect of the present invention, the uniform gaps of the diaphragm members may have a stress reducing keyhole formed at the terminal end thereof. The diaphragm members may be laminated together with a high temperature joining compound and disposed between a pair of spacers with the combination clamped between a pair of endplates. 
     In a further aspect of the present invention, the finger elements have a foot portion at an outermost end for sealing engagement with a combustor liner or a rotating shaft. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a partial perspective view of an inside diameter liner with inside diameter ceramic finger seal installed according to the present invention; 
     FIG. 1 a  illustrates a partial perspective view of an outside diameter liner with outside diameter ceramic finger seal installed according to the present invention; 
     FIG. 2 illustrates a view of a diaphragm segment of the present invention; 
     FIG. 3 illustrates a perspective view of a plurality of diaphragm segments with adjacent segments offset for assembly according to the present invention; 
     FIG. 3 a  illustrates a cross-sectional view of a finger seal taken along line  3 — 3  of FIG. 3; 
     FIG. 3 b  illustrates a close-up view of a finger element of a finger seal taken at circle B of FIG. 3; 
     FIG. 4 illustrates a cross-sectional view of an assembled finger seal of the present invention; 
     FIG. 5 illustrates a partial view of a housing and inside diameter combustor liner with inside diameter finger seal contained therebetween according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Referring to FIG. 1, use of an inside diameter ceramic seal  20  for sealing against an inside diameter combustor liner  14  adjacent to a turbine nozzle (not shown) discloses an embodiment of the invention. The ceramic finger seal  20  may be disposed circumferentially about and attached to a housing  10 . The outer circumference  22  of the seal  20  may then engage the wall of combustor liner  14 . The seal  20  serves to inhibit leakage of air into the turbine nozzle, downstream of the combustor liners. While an embodiment for use in sealing a combustor is presented, the use of a ceramic finger seal in a structure such as disclosed in U.S. Pat. No. 5,108,116, hereby incorporated by reference, for relative rotating bodies may also be used. In such case, the ceramic finger seal would also have a foot portion and a keyhole as disclosed herein for fluid sealing performance and stress reduction. 
     Referring to FIGS. 1 through 5, the ceramic seal  20  may be comprised of a plurality of diaphragm members  30  or thin annular ceramic bands laminated together and retained between spacers  50 . The diaphragm members  30  have a generally continuous inner diameter portion  32  and a segmented outer diameter portion  34  having relatively flexible finger elements  36  extending radially outward from an inner relatively rigid portion. The spacers  50 , resembling washers, when clamped with the diaphragm members  30  between endplates  60  prevent the segmented outer diameter portion  34  from being axially pinched by directing the clamping load through the radially inner diameter portion  32 . End plates  60  provide structure for engagement with a holding device such as a clamp mechanism  64  shown in FIG.  5 . Depending on the particular application the end plates  60  may not be necessary. The use of the ceramic finger seal type configuration in a non-rotational sealing application allows for a tight air seal with flexibility for radial motion of a housing and combustor liner as compared to prior art use of blades or wire sealing methods. In a rotational application the ceramic finger elements  36  and foot portions  38  thereof allow for use in high temperature environments such as approximately 2200 degrees F. which may be caused by rotational friction forces as well as other factors. In addition, the stress relief keyhole  44  located at the terminal end of the gaps  42  formed between the flexible finger elements  36 , as illustrated in FIGS. 2 and 3, increases the useful life of the ceramic seal  20 . 
     Referring to FIGS. 1 through 3 b , the ceramic finger seal  20  may be comprised of a plurality of diaphragm segments  28 . The diaphragm member  30  may be segmented to increase the yield in manufacturing when using ceramic materials and to minimize handling and shipping damages. Increase yield in manufacturing is a result of using low cost process such as high shear roll compaction. As illustrated, the diaphragm segments  28  represent one quarter of the circumference of a diaphragm member  30  to complete a circular seal element. While quarter section elements are illustrated other segment proportioning may be used. The diaphragm segments  28  may be bonded end to end with a first end  50  mating to a second end  52  and attached by ceramic cement or other high temperature joining compounds wherein four diaphragm segments  28  form a diaphragm member  30 . Use of ceramic cement or other high temperature joining compounds in a bonding process is known in the ceramic manufacture art. Examples of ceramic materials suitable for ceramic seals  20  include but are not limit to silicon nitride, silicon carbine, aluminum oxide and zirconia. Such materials have a temperature capability of up to and exceeding 2200° F. A commercial example of a silicon nitride is “Honeywell AS 800” ceramic. These example ceramic materials have a low fracture toughness relative to metal and therefore use of the bonding process without riveting enables the ceramic finger seal to be used in this environment. 
     One example of a manufacturing technique may be to form the diaphragm segment  28  using thin sheets, between 0.020 inches and 0.040 inches thick, of “Honeywell AS 800” silicon nitride formed from a high shear roll compaction process. The sheets may be thermally processed through binder burnout and sintering. The dense sheets may then be surface ground to the desired thickness that may be 0.020 inch to 0.040 inch. The ceramic seal  20  finger and hole patterns as described herein may then be laser cut from the thin sheet material. The use of laser cutting may cause a rounding  70  of edges  39  on the finger elements or foot portion  38  that may reduce gouging or scaring of a sealing surface. 
     In structure, the outer diameter portion  34  may be comprised of finger elements  36  extending radially outward from the inner diameter portion  32  and having a foot portion  38  at their radially outermost end  40  cooperatively defining an outer diameter. The form of the finger elements is generally a comb-like structure as with other finger seal devices known to those skilled in the art. The finger elements  36  may be spaced apart by gaps  42  in a uniform manner with the finger elements  36  and inner diameter portion having about the same thickness. The finger elements  36  extend radially outward and the foot portion  38  outer circumferential  22  surface (base portion of foot portion  38 ) requires no provision for contact with a rotating surface. Rounding  70  may be formed where side portions  58  meet outer circumferential  22  surface. 
     In addition the diaphragm segment  28  and thereby the assembled diaphragm member  30  has a keyhole  44  formed at the terminus end  46  of gaps  42  for stress relief of the finger elements  36  by increasing the relative small diameter terminal end of gaps  42  allowing additional dispersion of stress force to the inner diameter portion  32  and to minimize crack initiation. 
     The finger and gap structure of the seal  20  facilitate sealing contact with a surface such as that of inside diameter combustor liner  14 . When inserting the housing  10  and attached inside diameter ceramic seal  20 , a slight rotation of the seal in a counter clockwise direction as viewed in FIG. 1 allows firm seating of the outer circumference foot portion  38 . The foot portion  38  outer face is pressed against the inside diameter combustor liner  14  inner wall as the finger elements  36  are deflected radially inward. The rotation of the ceramic seal  20  in a counter clockwise direction utilizes the generally clockwise orientation of the finger elements  36 , as best viewed in FIG. 1, to facilitate deflection and seating of the finger elements  36 . 
     In use, there generally is no relative motion between the housing  10  and liner  14  in a rotational direction, the ceramic seal  20  may be seated such that the finger elements  36  engage the liner  14  using the desired pressure or force to achieve the required air-to-air sealing between structures. Therefore, within the deflection stress limits of the ceramic material structure of the finger elements  36  and the desired relative deflection extremes between the housing  10  and combustor liner  14 , the ceramic seal  20  may be seated between the bodies to minimize air leakage. 
     There normally may be relative radial and axial motion between the housing  10  and liner  14  due to temperature differential caused expansion and contraction as well as structure vibration motion. Such movement may be accommodated by the finger elements  36  of the ceramic seal  20 . A diaphragm member  30  constructed of ceramic material as discussed above provides suitable air flow sealing in this application. As can be appreciated, the flexibility of the finger elements  36  allows deflection between the structures by compression and extension of finger elements in the direction of an applied force such as a vibration. 
     Referring to FIGS. 4 and 5 the ceramic seal may be an assembly of a plurality of diaphragm members  30 , spacers  58  and endplates  60 . The diaphragm members  30  may be laminated together in quantities of 2 or more depending on the sealing requirements. The laminates may be bonded along the inner diameter portion  32  of the diaphragm members  30  thereby allowing freedom of motion of the finger elements  36 . This bonding may be by use of ceramic cement or other high temperature joining compounds to form a stack of diaphragm members  30 . The diaphragm members  30  are assembled side by side with adjacent laminates offset or positioned such that the fingers of one block the gaps of the other. The diaphragm members  30  may have pairs of apertures  48 , as illustrated in FIG. 3, to allow offset of adjacent members. 
     The laminated diaphragm members  30  may be disposed between spacers  50  and a pair of endplates  60  for attachment to the housing  10 . The ceramic seal  20  may then be attached circumferentially around the housing  10  with a clamping mechanism  64 , as illustrated in FIG.  5 . Thus the inner diameter portion  32  of each diaphragm member  30  may be fixedly restrained and the outer diameter portion  34  rests in flexible contact with the liner  14 . The use of the ceramic seal  20  in such static applications may allow for low stress levels because of the low deflection due to a similar coefficient of thermal expansion between a ceramic combustor and the ceramic seal  20 . 
     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.