Abstract:
A seal has a first endplate and has a second endplate. A first bellow spring spans first lateral portions of the first and second endplates. A second bellow spring spans second lateral portions of the first and second endplates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of Ser. No. 11/339,914, filed Jan. 25, 2006, and entitled “Seal”, which claims the benefit of U.S. Patent Application Ser. No. 60/648,017, filed Jan. 27, 2005, and entitled “Seal”, the disclosures of which are incorporated by reference herein in their entirety as if set forth at length. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to seals. More particularly, the invention relates to metallic seals for high temperature applications. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention involves a seal having a first endplate and having a second endplate. A first bellows spring (i.e., a spring element having a bellows like cross-section transverse to a longitudinal direction) spans first lateral portions of the first and second endplates. A second bellows spring spans second lateral portions of the first and second endplates (e.g., laterally opposite the respective first portions of the first and second endplates). The springs may be welded to the first and second endplates, the first and second bellows like spring elements biasing the first and second endplates apart when the seal is placed under compression. One or both of the endplates may be longitudinally segmented. One or both of the springs may be longitudinally segmented and may have apertures reducing an effective spring constant. The seal may consist essentially of the first and second endplates and the first and second spring elements. In cross-section, the first and second endplates may consist essentially of single pieces (thus accounting for the possible segmenting). 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of the exemplary embodiment of the seal. 
         FIG. 2  is a sectional view of the seal of  FIG. 1  mounted in a first environment. 
         FIG. 3  is a sectional view of the seal of  FIG. 1  mounted in a second environment. 
         FIG. 4  is an isometric view of an alternate embodiment of the seal, with apertures provided in the endplates to provide cooling to the seal interior. 
         FIG. 5  is an isometric view of an alternate embodiment of the seal, with apertures provided in the spring elements to reduce the bias load of the seal. 
         FIG. 6  is an isometric view of an alternate embodiment of the seal, with the upper endplate divided into three sections in order to allow locally increased compression of the seal. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a seal  20  extending from a first end  22  to a second end  24 . The seal comprises a pair of connector bands or endplates  30  and  32 , and a pair of bellows-like spring elements  34  and  36 , for biasing the endplates apart when the seal is placed under compression. In the exemplary embodiment, the bands and the springs are longitudinally coextensive (e.g., extending between parallel planes at the first and second ends  22  and  24 ). In the exemplary embodiment, both the first and second endplates  30  and  32  are continuous along the full length of the seal  20 . 
     In the exemplary embodiment, the springs  34  and  36  are mirror images of each other across a longitudinal medial plane. Each of the springs is characterized by a bellows-like transverse cross section having one or more convolutions. The embodiment of  FIG. 1  has a minimum extent of an outwardly-open C. An additional convolution would form an outwardly open E, etc. Each spring has a first, generally interior, surface  60  and a second, generally exterior, surface  62  both extending between first and second edges  64 A;  64 B and  66 A;  66 B. The endplates each have an interior surface  70  and an exterior surface  72 . The first band  30  has edges approximately aligned with the first edges  64 A;  64 B of the respective springs and the second band  32  has edges respectively aligned with the second edges  66 A;  66 B of the springs. The bands and springs are welded to each other adjacent to such edges. Each endplate has a pair of sealing regions (surface portions)  74 A;  74 B and  84 A;  84 B aside a central recess  76  and  86 . 
     In the exemplary embodiment, surfaces  74 A;  74 B and  84 A;  84 B contact and seal with surfaces of one or more environmental elements. For example, sealing surfaces  74 A and  74 B may seal with the same environmental element or two different environmental elements (e.g., surfaces  400 A and  400 B of elements  402 A and  402 B) of  FIG. 2 . Similarly, surfaces  84 A and  84 B may seal with surfaces  404 A and  404 B of one or more environmental elements  406 A and  406 B. 
     Alternatively, the seal may be positioned to seal between two environmental elements  100 A and  100 B ( FIG. 3 ), with opposing slots  114 A and  114 B. In the exemplary embodiment, the first slot  114 A of one element is aligned with and facing the second slot  114 B of the next, approximately symmetric across the seal longitudinal medial plane  500 . 
     The endplates  30  and  32  and/or the springs  34  and  36  may each be provided with vent apertures to provide a desired degree of venting and to keep the seal interior cool (especially in whichever endplate is oriented/positioned facing toward the cool side/zone).  FIGS. 4 and 6  show exemplary apertures  150  in the relatively thin endplate  30 . The endplate  32  is relatively thicker to withstand exposure to the hot side/zone. 
     Additionally, apertures may be provided in the springs to reduce the spring constant (and thus the bias force) of the seal, as shown in  FIG. 5 . In this embodiment, the apertures  160  are formed as rectangular slots having ends close to the spring edges. Thus they reduce the spring rate by essentially their fraction of the spring longitudinal span (e.g., an exemplary 30 to 70%). These apertures may extend the full length of the seal, or may be localized to one or more areas in order to optimize the performance of the seal for various environmental conditions. 
     The endplates and  30  and  32  may be longitudinally coextensive with one another and with the springs  34  and  36 . Alternatively, one or both of the endplates may be segmented into two or more sections in order to allow locally increased compression of the seal. In  FIG. 6 , the endplate  30  is shown divided into three distinct sections L 1 , L 2  and L 3 . These sections may be of equal or unequal length. Sections L 1  and L 2  are shown compressed to a greater extent than section L 2 . This may accommodate additional elements such as retention clips holding the elements being sealed or other elements. 
     Exemplary materials for the springs and endplates are one or more nickel-based or cobalt-based superalloys. The springs and endplates may be made of the same or different materials and different material thickness in order to optimize their performance for various environmental conditions. For example, one of the endplates exposed to a hotter or chemically more reactive environment may be of a more oxidation-resistant material and/or a material having greater high temperature strength (and/or may also be thicker). Similarly one of the endplates may be exposed to greater frictional and/or vibratory loads and may be of a stronger material (and/or may also be thicker). Cost may also suggest use of a less expensive material for the endplate subject to less heat, wear, etc. When of different thicknesses, exemplary characteristic thicknesses of the thicker endplate are 1.1-3.0 times that of the thinner. In an exemplary application for the seal, one endplate may be exposed to high-temperature combustion gases, while the other endplate is exposed to a cooling medium. In this application, the material type and thickness of the first endplate may be optimized to provide maximum resistance to oxidation, while the material type and thickness of the second endplate may be optimized for maximum wear resistance. 
     In an exemplary process for manufacture, the springs and endplates are blanked and roll-formed from sheet stock. The apertures  150  and  160  may be cut either before or after the roll forming. The first and second springs are then welded to the first and second endplates. 
     One or more of the embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.