Static structures (e.g. – buildings) – Composite prefabricated panel including adjunctive means – Sandwich or hollow with sheet-like facing members
Reexamination Certificate
1999-02-03
2001-10-09
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Composite prefabricated panel including adjunctive means
Sandwich or hollow with sheet-like facing members
C052S749100, C052S787110, C052S787120
Reexamination Certificate
active
06298633
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to spacers for mounting fasteners in sandwich panels, a method of installing the spacers so that the spacers are flush with an upper surface of the panels and can provide a liquid tight seal and a resultant improved panel assembly, such as a floor of an aircraft.
2. Description of Related Art
In the aerospace field a premium is placed upon light-weight but strong structural components. For example, a floor of an aircraft must be lightweight and strong and also must accommodate the stresses imposed upon the bulkhead by the flexing of the wings during flight. The aircraft industry uses composite or sandwich panels that are fastened to spars and bulkheads by a large number of fasteners that are secured to the panels by extending through corresponding spacers mounted in the panels. Frequently, the sandwich panels are formed of thin aluminum face plates with expandable aluminum foil strips to form a core or laminated plastic resin upper and lower surface face sheets that sandwich a honeycomb interior structure of resin and paper. Both configurations provide excellent strength to weight or stiffness to weight relationships in comparison to solid metallic panels. Alternative face sheets or skins for sandwich panels can include steel, titanium, magnesium, aluminum alloys, and alloy steels, while cores can also be formed of plastic foam, balsa wood, high temperature alloys, plastic syntactic and steel foil. Generally, the core is honeycomb and has hexagonal cells with walls perpendicular to the face sheets.
Composite panels are frequently used in aircraft with high-strength, high-modulus, fiber-reinforced, thermostat or thermoplastic resins. However, such fiber-reinforced composite panels do not necessarily respond well to localized concentrated loading forces. As can be appreciated, when a composite structure is used as a floor panel or wall panel in an aircraft, it is frequently necessary to fasten objects to the panels. Thus, a number of different fasteners and spacers have been developed to accommodate resin sandwich panels and to prevent a localized concentration of loading.
Some of the problems that have been recognized in the installation of a spacer are the necessary chemical compatibility of any fastener or spacer used in sandwich panels so that there is not any galvanic corrosion. This issue frequently arises when the sandwich panels contain carbon fiber, and if the fibers come in contact with a less noble metallic fastener, there can be corrosion, thus, magnesium, aluminum, aluminum alloys, and alloy steels are frequently not compatible with a graphite based structure.
Another problem that has occurred with mounting fasteners and spacers in a sandwich panel is that the panel does not have a significant transverse reinforcement. Thus, when a hole is drilled for mounting a spacer, the edge of the hole can be crushed, since there is relatively little resistance to a crushing force.
As can be appreciated, the application of a fastener or spacer to a sandwich panel can damage the panel in drilling holes in the panels in that surface ply splintering, surface ply delaminating, heat damage, and irregularities inside the hole can occur.
When composite panels are drilled or machined, the natural sealing process of lamination is disrupted. In areas where the fibers become exposed, an action can take place in which water, fuel, spilt liquids, etc. can be slowly absorbed through the fiber matrix interface into the structure, additionally, the liquid can leak into the interior core of the panel. These leakage problems can result in weight gain, laminate degradation, destruction of the core, and even unpleasant odors.
It is highly desirable that at most only a minimum portion of a fastener or spacer extend above the upper surface of a sandwich panel. One of the approaches in the prior art to address this issue has been to provide a rim in a spacer member that is mechanically locked by flaring the rim over the edge of the hole. Some installation of spacers in an aircraft floor sandwich panel have intentionally dimpled a metallic face skin where each spacer is to be inserted in order to insure a flush mounting. Another approach has been to provide a sleeve and plug composite spacer with a pair of flanges that overlap both sides of the hole. Any protrusions above the upper surface can be abraded and can further cause carpet wear. Adhesives can be applied to flanges to directly adhere a spacer member to the surface of a sandwich panel. In an attempt to seal an aperture in the spacer, ring seals washers have sometimes been used on fasteners in an attempt to sealingly compress them in the aperture. Additionally, a potting material of an appropriate epoxy can be used for further securing these types of spacers and fasteners.
The aerospace industry generally desires to automate the installation of spacers and fasteners to eliminate the high labor cost, wherever possible, particularly when hundreds and thousands of fasteners and spacers can be used in an aircraft.
Thus, the prior art is still attempting to optimize the design of spacers and fasteners used in sandwich panels in aircraft and the problems of sealing with a flush installation of spacers with a surface of a panel has yet to be optimized.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention provides an improved spacer and/or fastener that can be mounted within a panel, such as a composite or sandwich structure panel of a predetermined thickness with a drilled hole to provide a flush mounting of an upper edge of an upper rim member of the spacer with an upper face surface of the panel. A spacer can include a body member having a central aperture with a larger lower flange member that extends radially outward from the body member. The flange member will bear against the lower face surface of the sandwich structure panel. An adhesive can be applied between the lower flange member and the lower face surface of the panel to assist in securing the spacer to the panel. The upper rim member extends upward from the body member and is concentric with the central aperture. The rim member has a larger inner diameter, than the diameter of the central aperture, with an inner flange extending from the rim member to the central aperture. The spacer will be sized for a particular panel thickness, such that the upper edge of the upper rim member will initially be extended above the upper panel surface when the lower flange member is in contact with the lower panel surface by a predetermined distance.
A sealing compound or sealant, such as, but not limited to, a thermoplastic resin or a silicon resin, can be positioned annularly over the inner flange so that any fastener mounted within the central aperture can contact and deform the sealing compound to encourage a seal between the spacer and the fastener. Another outer ring or coating of sealing compound can be positioned around the outer surface of the rim member to facilitate the sealing with the edge of the hole in the sandwich structure panel.
The resultant combination of the spacer sealed with the panel provides an improved panel assembly of particular advantage in wet area applications, such as a floor panel in a galley of an aircraft.
An alternative embodiment of the spacer can provide an upper rim member with an indented or annular recess relative to the outer diameter of the body member. A ledge or undercut is provided below a coating of sealant to thereby facilitate the carrying of the sealant through the sandwich structure panel so that it is positioned adjacent the upper edge of the hole or bore in the sandwich panel. Thus, when the rim member is contacted by a setting tool designed to provide a specific application of force for seating within and flush to the upper surface of the panel, the sealing compound will be distributed at the interface between the panel edge and the rim member to automatically effectuate a seal. Such a seal can not only render the joint liquid tight but can also address the g
McCorkle Daniel J.
Riveron, Jr. Faustino
Secrets Paul M.
Waits Robert L.
Friedman Carl D.
Nguyen Chi
Price and Gess
Shur-Lok Corporation
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