Abstract:
A variable pressure washer has two interlocking channel rings separated by a channel and retained by a captive set of fasteners. Within the channel between the rings are multiple rows of springs having at least two different spring moduli. The washer is particularly suited for use with a polar boss assembly secured to a bulkhead of a pressure vessel such as of propellent tank dome structure where the washer allows for the substantially uniform deflection of multiple O-rings as affected by the curved structure.

Description:
ORIGIN OF THE INVENTION  
       [0001] This invention was made by an employee of the United States Government together with government support under contract awarded by the National Aeronautics and Space Administration and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or thereof. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a washer apparatus designed to apply a specified varying load along different radians of a washer for a given deflection, and more specifically to a washer adapted to seal with a non-parallel surface.  
           [0004]    2. Prior Art  
           [0005]    Although a plurality of seals and washers are known in the art which are adapted to seal planar, parallel members, there is not known to be any effort made to seal a curved member to a planar member. Specifically, when a curved surface such as a dome is equipped with a polar boss, or a seal along an opening of the curved surface, additional force is necessary on an outer portion of the seal than on the inner portion of the seal to achieve equal O-ring compression. A need exists to provide a washer or seal design that can provide relatively equal force along a curved surface.  
         SUMMARY OF THE INVENTION  
         [0006]    Consequently, it is a primary object of the present invention to apply a specified varying load along a radian for each cross section of a circumference of a washer.  
           [0007]    It is a further object of the present invention to provide a washer to deploy a seal wherein the seal transfers a uniform load from one surface to a linearly varying load on another surface.  
           [0008]    Another object of the present invention is to provide a washer adapted to provide relatively constant force along an external surface when one surface of the washer contacts a curved surface.  
           [0009]    Accordingly, the present invention provides a variable pressure washer having two interlocking rings, preferable channel rings defining a channel there between. A captive set of fasteners may be utilized to prevent the channel rings from coming apart. In the preferred embodiment, a plunger moving within a plunger housing acts as the captive fastener set and determines the range of movement of the channel rings relative to one another. Within the channel between the rings are at least two compressible springs which exhibit different characteristics, specifically, differing stiffness or spring modulus values. The springs are preferably devices such as metallic springs, thermoplastic rings, etc. . . . Retaining members, such as cups, may be utilized to locate the springs in a desired position within the rings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 is a top perspective view of a polar boss assembly mounted to a bulkhead;  
         [0012]    [0012]FIG. 2 is a cross sectional view of the polar boss assembly of FIG. 1; and  
         [0013]    [0013]FIG. 3 is a cross sectional view of an alternative embodiment of the polar boss assembly of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring to the FIG. 1, a polar boss assembly  10  is illustrated in FIG. 1 connected to a bulkhead illustrated as dome  12 . In the preferred embodiment, the assembly  10  is a polar boss joint assembly sealed to a composite dome. However, various other applications are believed to exist.  
         [0015]    The assembly  10  may be utilized to provide a low leakage seal to allow for the passage of material into domes  12 , such as fiber reinforced plastic composite domes. The polar boss assembly  10  comprises a first clamping surface  14  which is obscured from view in FIG. 1, but visible in the cross sectional view of FIG. 2. The first clamping surface  14  is located on stationary arm  16  which connects to assembly shaft  18 . The shaft  18  connects to the arm  16  and cooperates with the moving arm  20  to clamp the dome  12  between the moving arm  20  and the stationary arm  16 .  
         [0016]    In the preferred embodiment of FIGS. 1 and 2, the moving arm  20  has threads  22  which cooperate with threads  24  on the shaft  18  whereby rotation of the moving arm  20  relative to the shaft  18  displaces the moving arm  20  towards and away from the stationary arm  16 . A second clamping surface  26  contacts the top of the dome  12  when the dome is secured to the boss assembly  10 . The first clamping surface  14  contacts the bottom of the dome  12  when the boss assembly  10  is secured to the dome  12 .  
         [0017]    The second clamping surface  26  is located on a bottom portion of a ring  28 , preferably a ring  28  with a lip  34  as illustrated in FIG. 2. The ring  28  is illustrated having an inner edge  30  which would define an inner radius about a center of the ring  28 , and an outer edge  32  which would define an outer radius about a center of the ring  28 . Lip  34  of the ring  28  assists in defining a channel  36  between the first ring  28  and second ring  38  which, in this embodiment, is a portion of the moveable arm  20 . In the alternatively preferred embodiment, washer  82 , illustrated in FIG. 3, the second ring  40  is separate from the moveable arm  42 .  
         [0018]    Referring back to FIG. 2, two variable stiffness, deformable members described as first and second springs  44 ,  46  are illustrated as a part of washer  80 . Of course, more springs  44 , 46  could be utilized if so desired. The first spring  44  has a first spring modulus, while the second spring  46  has a second spring modulus. The second spring modulus is greater than the first spring modulus. Using a simple mechanics formula, Force=Kx where x is the spring deflection and K is the spring modulus, one can quickly see that if the force is maintained constant, then for two different springs  44 ,  46  having two different spring moduli, the deflection of the springs will be different. Accordingly, if the spring modulus is greater for the second spring  46  than for the first spring  44 , the deflection will not be as great for the same force transmitted across both springs. This is the physics behind the washer  80  of FIG. 2 and the washer  82  of FIG. 3. Of course, more springs  44 , 46  could be utilized with other spring moduli depending on the expected positions of the springs in a deflected position to accommodate a nonparallel surface to at least one of the gripping surfaces  26 , 14  so that a uniform load could be placed on the non-parallel surface. In another embodiment, the first ring  28  of the washer  80  is not a continuous circular member. This embodiment provides for an arc-length split in ring  28  or for a section of ring  28  to overlap. This discontinuity feature would allow the outer edge  32  of ring  28  to move in a direction perpendicular to the face of the dome  12  while the inner edge  30  remained stationary. This would cause the flat washer-like geometry of ring  28  to deform into the shape of a truncated cone in order to match the geometry of the dome  12  and maintain pressure along the dome surface.  
         [0019]    In order to retain the first ring  28  relative to the second ring  38 , a captive fastener device  48  is utilized. The captive fastener device  48  of the preferred embodiment includes a plunger  50  and a plunger housing  52 . The plunger housing  52  allows the plunger  50  to move until the first ring  28  is a maximum distance from the first ring  38  and then prevents the first ring  28  from moving any farther away from the second ring  38 . The plunger  50  is connected to the first ring  28  and has a plunger head  54  which contacts a shelf  56  to prevent further outward travel of the first ring  28  relative to the second ring  38 .  
         [0020]    First and second retaining members  58 ,  60  are preferably utilized to locate, or retain, the first and second springs  44 , 46  relative to the first ring  28 . Third and fourth retaining members  62 , 64  retain the first and second springs  44 , 46  relative to the second ring  38 . The retaining members  58 , 60 , 62 , 64  are preferably cup shaped and extend about a radian of the ring to which they are connected.  
         [0021]    Referring to FIG. 3, the alternatively preferred embodiment has a washer  82  separate from the moveable arm  42 . A first ring  66  is a channel ring as is the second ring  40 . The second ring  40  is illustrated nesting within the first ring  66  to form the channel  68 . Both the first and the second ring  66 , 40  have lips  70 , 72 , 74 , 76  which assist in defining the channel  68  in this embodiment.  
         [0022]    Referring back to FIG. 2, when the boss assembly  10  is applied to the dome  12 , the moveable arm  20  is screwed about the shaft  18  to seal the dome between the gripping surfaces  14 ,  26  until the desired compression is applied to the springs  44 , 46 . It is expected that the deflection of the springs  44 , 46  and/or the forces experienced by the springs  44 , 46  will differ. In the preferred embodiment, the expected deflection and the spring moduli are selected so that the O-rings  78 , 80  will be substantially equally compressed to form a substantially low leakage seal.  
         [0023]    The rings  28 , 38 , 66 , 40  may be made of a metal, thermoplastic or other appropriate material. Additionally, the springs  44 , 46  may be made of an appropriate spring material including metal, polymer or other appropriate material.  
         [0024]    The rings  28 , 38 , 66 , 40  are preferably substantially circular and the springs  44 , 46  are located along the radius portions of the rings  28 , 38 , 66 , 40  in order to apply a specific load at a specific radian relative to the respective ring  28 , 38 , 66 , 40 . The springs  44 , 46  are also preferably substantially circular.  
         [0025]    Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.