Abstract:
An insulated, sealed cap overlies and protects a fastener component or the like on a substrate in association with a substrate opening. The sealed cap includes an outer cap component filled partially with a selected sealant material and assembled with an inner collet sized and shaped to fit with a slip fit about the fastener component such as a nut or the like at one side of a selected substrate, such as the skin of an aircraft. An inboard edge of the inner collet seats on and substantially seals with the substrate. The outer cap component is then displaced toward the substrate to extrude the sealant material into a thin and substantially uniform layer joined with an extruded outer bead on the substrate, and then permitted to cure. Tapered ribs on the inner collet effectively lock with the outer cap component during sealant material curing and subsequently.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to an insulated and sealed cap for use with a fastener component or the like passed through an opening formed in a selected substrate, to seal and protect the fastener component and/or the substrate opening against contact with and/or leakage of fluids contained within the substrate, or to safeguard system components and/or fluids contained within the substrate against damage attributable to electrical discharges and the like associated with the fastener component. More particularly, this invention relates to an improved insulated and sealed cap and related method of use wherein a relatively rigid or sturdy yet lightweight sealed cap is mounted onto the substrate in a position over a fastener component and related substrate opening. 
     Fastener components such as nuts and bolts are commonly mounted onto a substrate such as the skin of an aircraft or the like in association with a substrate opening. In this regard, such fastener components typically comprise a nut or nutplate at one side of a substrate opening adapted to receive a threaded bolt or the like therethrough for anchored engagement with the nut or nutplate. In modern aircraft, system components such as electronic devices are often disposed on one side of the substrate, such as internal system components mounted within an aircraft fuselage. Alternatively, the substrate commonly comprises a wing structure or the like defining one wall of an aircraft fuel tank containing corrosive and volatile aircraft fuel and perhaps some water. 
     In either case, it is highly desirable to seal the substrate and related substrate opening as well as the fastener component from contact or communication in either direction with the system components and/or fluids such as fuel. That is, it is desirable to prevent fluid leakage from the fuel tank into potentially corrosive contact with the fastener component and/or leakage through the substrate opening. Similarly, it is desirable to prevent damage to the system components and/or to the aircraft fuel supply attributable to electrical discharges associated with the fastener component. Moreover, it is desirable to prevent such damage by providing a sealed and insulated cap which is relatively study in design to withstand normal maintenance procedures without damage to the sealed cap. In an aircraft environment, in order to maximize overall fuel efficiency, it is desirable to provide these important sealing and insulating functions with minimal overall weight addition. 
     There exists, therefore, a need for an improved insulated and sealed protective cap for use on an aircraft substrate and the like. The present invention fulfills these needs and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an insulated, sealed cap is provided for overlying and protecting a fastener component or the like on a selected substrate in association with a substrate opening. The sealed cap includes an outer cap component filled partially with a selected sealant material and assembled with an inner collet sized and shaped to fit relatively loosely but nonrotationally about the fastener component such as a nut or the like at one side of the selected substrate, such as the skin of an aircraft. An inboard edge of the inner collet seats on and substantially seals with the substrate. The outer cap component is then displaced toward the substrate to extrude the sealant material into a thin and substantially uniform insulation layer joined with an extruded outer bead on the substrate, and then permitted to cure. Tapered ribs on the inner collet effectively lock with the outer cap component during sealant material curing and subsequently. 
     In one preferred form, the outer cap component is partially filled with a metered quantity of the selected sealant material, followed by nested assembly of the inner collet into the outer cap component. In this configuration, the assembled insulated cap can be installed immediately in insulative and protective relation covering the fastener component at one side, such as the blind side, of the substrate. Alternately, the assembled insulated cap can be chilled and preferably frozen to prevent immediate curing of the sealant material until time for use. In the latter case, the frozen insulated cap with the sealant material therein is thawed and preferably heated slightly before use. 
     The assembled insulated cap is fitted over the fastener component such as a nut or a nutplate adapted to receive a threaded bolt or the like passed through the substrate opening, with an inboard edge of an inner collet side wall landing in seated and substantially sealed relation onto the substrate in a position circumscribing the fastener component and associated substrate opening. The fit between the inner collet of the assembled cap and the fastener component is preferably a slip fit. In this initial configuration, the sealant material remains primarily within a space between closed end walls of the outer cap component and the inner collet. 
     The outer cap component is then pressed downwardly, or in a direction toward the substrate, to extrude the sealant material between the outer cap component and the inner collet in a direction toward the substrate. In this regard, the outer cap component and the inner collet are preferably formed from a relatively rigid or sturdy, and preferably nonmetallic material such as a selected and relatively lightweight molded plastic or fiber composite or the like. These interfitting structures each define a substantially closed end wall joined with a side wall such as a generally cylindrical side wall having a selected and preferably matching taper. Tapered lock ribs are formed between these two interfitted components, such as external ribs formed on the inner collet to extend from the inner collet inboard edge over about ½ of the side wall height, for effectively locking the interfitted components together while maintaining a desired yet relatively thin or uniform spacing between the component side walls. 
     The metered quantity of sealant material is selected so that as an inboard edge of the outer cap component lands on the substrate, said inboard edge of the outer cap component contact and seals with a bead of the extruded sealant material. Importantly, following a suitable cure time, this extruded bead provides an effective seal between the outer cap component and the substrate, regardless of the specific substrate geometry. That is, the substrate geometry may require this extruded bead to be thicker in some areas than in others. 
     The resultant insulated cap assembly installed onto the substrate in surrounding relation with the fastener component thus provides a substantially effective yet relatively thin and lightweight insulative seal to overlie and protect the fastener component and associated substrate opening. That is, the sealed cap presents a relatively sturdy cap construction constructed from a lightweight molded plastic or the like having sufficient structural rigidity to withstand typical maintenance procedures without puncture and/or damage which might otherwise undesirably interfere with the desirable insulative and sealed functions. Similarly, the sealed cap insulates the system components and/or fluids on the opposite side of the sealed cap against potential damage to attributable to electrical discharges and the like at the fastener component and/or through the substrate opening. If desired, one of the outer cap component and the inner collet, such as the inner collet, can be constructed from an at least partially electrically conductive material to define a Faraday shield separating the fastener component from internal aircraft components and/or the aircraft fuel supply. 
     Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  is an exploded perspective view depicting an outer cap component and an inner collet of an insulated and sealed cap for mounting onto a selected substrate to overlie and protect a fastener component or the like; 
         FIG. 2  is an inverted and fragmented perspective view showing partial filling of the outer cap component thereof with a metered quantity of a curable sealant material; 
         FIG. 3  is an inverted perspective view showing the outer cap component in assembled relation with the inner collet; 
         FIG. 4  is a perspective view depicting placement of the insulated and sealed cap of  FIGS. 1 and 3  over a fastener component previously installed onto the substrate; 
         FIG. 5  is an enlarged vertical sectional view showing initial placement of the insulated and sealed cap onto a substrate, with the inner collet positioned over a nut or other fastener component; 
         FIG. 6  is an enlarged vertical sectional view similar to  FIG. 5 , and illustrating advancement of the outer cap component in a downward direction toward the substrate relative to the inner collet to extrude the sealant material therebetween; 
         FIG. 7  is an enlarged vertical sectional view similar to  FIGS. 5 and 6 , but depicting final extruded displacement of the sealant material for protectively overlying and sealing the nut or other fastener component on the substrate; and 
         FIG. 8  is a perspective view similar to  FIG. 4 , but showing the insulated and protective cap installed onto the substrate in protective relation over the nut or other fastener component. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the exemplary drawings, an insulated and sealed cap referred to generally in FIGS.  1  and  3 - 8  by the reference numeral  10  is provided for insulating and sealing a fastener component  12  such as the illustrative nut shown in FIGS.  1  and  4 - 7  mounted at one side of a selected substrate  14 . This fastener component  12  is commonly associated with an opening or passage  16  (FIGS.  1  and  5 - 7 ) formed in the substrate  14  through which a threaded bolt  18  or the like is commonly fitted for threaded assembly with the nut  12 . The insulated and sealed cap  10  of the present invention overlies and protects the fastener component  12  and the substrate opening  16  against undesirable damage to the fastener component  12  attributable to contact with system components (not shown) and/or with fluids (also not shown) on the fastener component side of the substrate  14 . In addition, the insulated and sealed cap  10  of the present invention beneficially protects the system components and/or fluids against damage attributable to the presence of the typically metallic fastener component  12 , such as electrical discharges and the like. These bidirectional insulating and sealing functions are advantageously provided by the cap  10  in a lightweight but sturdy cap construction that is conducive to quick and easy mounting onto the substrate  14 . 
     As shown in  FIGS. 1 and 3 , the insulated and sealed cap  10  of the present invention comprises an outer cap component  20  having a preferred, generally hat-shaped configuration to include a substantially closed top end wall  22  joined to a depending side wall  24  which in turn has a generally open lower edge  26  defined by an outwardly radiating lower flange  28 . This outer cap component  20  is initially and partially filled with a metered quantity of a selected and uncured but curable sealant or adhesive material  30  by means of a suitable dispenser  32  ( FIG. 2 ). While a manual dispenser  32  is shown in  FIG. 2 , persons skilled in the art will understand that a succession of the outer cap components  20  may be partially filled with the desired metered quantity of the selected sealant material by means of an automated dispenser, if desired. 
     One preferred sealant material comprises a polysulfide sealant. An exemplary sealant material is available from PPG Aerospace, division of PPG Industries, Pittsburgh, Pa., under product designation PR 1440. An alternative exemplary sealant material is available from the same company under product designation PR 1422. 
     With the metered quantity of the selected sealant material contained within the inverted outer cap component  20 , an inner collet  34  is partially assembled within the outer cap component  20 , as viewed best in  FIG. 3 . As shown, this inner collet  34  also defines a substantially closed end wall  36  joined to a side wall  38  defining a lower or free edge  40  at the axial end thereof opposite the end wall  36 . In addition,  FIGS. 1 and 3  show the collet  34  to include a plurality of typically at least three equiangularly spaced internal or inwardly radiating ribs  42 , and a plurality of external lock ribs  44  projecting radially outwardly therefrom over at least about the lower ½ of the height of the associated side wall  38  from the lower free edge  40 . In a preferred form, these lock ribs  44  have a downwardly (toward the lower free edge  40 ) expanding taper on the order of about 1-3 degrees. 
     The inner collet  34  has a slightly tapered side wall shape for substantially nested but relatively close slide-fit reception into a matingly tapered side wall  24  of the outer cap component  20 , with the respective end walls  22 ,  36  in adjacent albeit spaced relation (shown best in  FIG. 5 ). The outer lock ribs  44  of the inner collet  34  are engaged but not locked with the outer cap component  20 . In addition, as shown in  FIG. 5 , the lower or free edge  40  of the inner collet  34  is axially spaced below the lower edge  26  and flange  28  of the outer cap component  20 . In this position, the metered quantity of sealant material  30  fills the space between the end walls  22 ,  36  of the outer cap component  20  and the inner collet  34 , and partially fills the narrow radial space between the respective side walls  24 ,  38  ( FIG. 5 ). Importantly, a leading annular edge  46  of the sealant material  30 , in this position, is retracted as viewed in  FIG. 5  from the lower edge  26  and related flange  28  of the outer cap component  20 , so that physical contact with the uncured sealant material  30  is not possible. 
     In this configuration, with the insulated and sealed cap  10  containing the uncured sealant material  30 , the cap  10  can be employed immediately (as will be described herein), or alternately the cap  10  with the uncured sealant material  30  can be chilled and preferably frozen to prevent curing of the sealant material  30  until the cap  10  is ready for installation. In this regard, the cap  10  is preferably frozen for shipment and/or storage preparatory to use. Just before cap usage is desired, the frozen cap  10  with frozen sealant material  30  therein is thawed preferably by short heating in a microwave oven or the like to melt the sealant material  30  and permit curing thereof. 
     In use, the assembled insulated and sealed cap  10  is placed onto the fastener component  12 , such as the illustrative nut, with the lower free edge  40  of the inner collet  34  substantially seated and substantially sealed upon the substrate  14  in circumscribing relation but with a slip fit relative to the fastener component  12 . FIGS.  1  and  4 - 5  show this fastener component  12  in the form of a nut having a generally circular base segment  48  for suitable engagement with the internal collet ribs  42  to prevent easy rotation of the cap  10  relative to the fastener component  12 . Persons skilled in the art will recognize and appreciate that the fastener component  12  may take other known forms, such as a standard nut lacking the cylindrical base  48 , a nutplate mounted onto the substrate  14 , etc. 
     After initial seating of the lower or free edge  40  of the inner collet  34  onto the substrate  14 , as viewed in  FIG. 5 , the outer cap component  20  is displaced relative to the inner collet  34  in a downward direction (as viewed in  FIGS. 6-7 ) toward the substrate  14 . Such outer cap displacement in the direction of arrow  50  in  FIGS. 6-7  effectively extrudes the sealant material  30  downwardly from between the end caps  22 ,  36  and through a narrow annular space between the side walls  24 ,  38 , between the lock ribs  44 , to extrude outwardly at the bottom of the outer cap component  20  to form an annular bead  52 . As the outer cap component  20  is displaced further in the direction of arrow  50  ( FIG. 7 ), the lower edge  26  thereof at the underside of the flange  28  lands in this sealant material bead  52  for secure and sealed attachment to the substrate  14 . As shown in  FIG. 7 , this bead  52  can be of a varying geometric shape to accommodate fillets and the like formed in a substrate  14  of complex geometry. That is, the specific size and/or height of this bead  52  can be larger on one side of the fastener component  12  than on the other or opposite side. 
     Full displacement of the outer cap component  20  until the lower edge  26  thereof is fully landed within the bead  52  of sealant material  30  is accompanied by effective locking of the outer cap component  20  onto the inner collet  34  by means of the lock ribs  44 . That is, as the outer cap component  20  is displaced toward the substrate  14 , the magnitude of engagement between the outer cap component  20  and the inner collet  34  is effectively increased and rigidified by the lock ribs  44 . In the fully landed position of the outer cap component  20 , the sealant material  30 ,  52  is allowed to cure typically for a few hours. 
       FIG. 8  shows the protective cap  10  of the present invention in insulated and sealed mounting relation onto the substrate  14 , in a position covering the underlying fastener component (not shown in  FIG. 8 ) and related access opening (also not shown in  FIG. 8 ) formed in the substrate  14 . In this position, the cap  10  functions to effectively insulate and seal the fastener component or components  12  from potential damage due to system components (not shown) or fluids (also not shown) on the cap side of the substrate  14 . Similarly, the cap  10  functions to effectively insulate and seal any system components and/or fluids at the illustrated cap side of the substrate  14  from potential damage attributable to events and/or structures (not shown) located at the opposite side of the substrate  14  and/or the fastener component or components  12  associated with the substrate access opening  16 . 
     The insulated and sealed cap  10  provides a substantially effective yet relatively thin and lightweight insulative seal to overlie and protect the fastener component or components and associated substrate opening. That is, the sealed cap presents a relatively sturdy cap construction constructed from a lightweight molded plastic or the like having sufficient structural rigidity to withstand typical maintenance procedures without puncture and/or damage which might otherwise undesirably interfere with the desirable insulative and sealed functions. If desired, one of the outer cap component  20  and the inner collet  34 , such as the inner collet  34 , can be constructed from an at least partially electrically conductive material, such as an at least partially metallic material, to define a Faraday shield separating the fastener component from internal aircraft components and/or the aircraft fuel supply. 
     A variety of further modifications and improvements in and to the improved insulated and sealed cap of the present invention, and its related method of use, will be apparent to those persons skilled in the art. As one example, although the illustrative drawings shown interfitting side walls  24 ,  36  of the outer cap component  20  and the inner collet  34  to be of generally cylindrical shape, persons skilled in the art will understand and appreciate that the interfitting side walls  24 ,  36  may be of any selected shape, including but not limited to a noncircular shape suitable to fit nonrotationally over a fastener component  12 , and/or an elongated shape such as an oval suitable to fit over multiple closely spaced fastener components. Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except at set forth in the appended claims.