For a cargo door application on a major manufacturer’s new generation of commercial aircraft, fastener supplier Click Bond Inc. (Carson City, Nev.) is providing composite bonded nut plate stand-off fasteners, consisting of a nut plate attached to a stand-off bracket, as attachment points for the cargo door’s liner. The nut plate is adhesively bonded to an aircraft structure, eliminating the need for drilled holes and rivets. It is “self-fixturing,” that is, when the fastener site is determined, structural adhesive is applied to the fastener base or nut plate, and its clear plastic fixture (at right in photo) is pushed against the adherend surface, activating a pressure-sensitive adhesive on the fixture’s
“feet.” Manual pressure “clicks” the fixture downward by activating a series of plastic hinges. This applies pressure to the nutplate bondline, removing trapped air. The fixture also maintains accurate placement of the nut plate while the adhesive cures. After cure, the fixture is pulled off and discarded or recycled.
Says Mark Egeberg, Click Bond Pacific region manager, “The self-fixturing parts eliminate the need for special tools, clamps and drills, thus speeding up the process of installing attachment bracket hardware. Our ‘fixture-in-place’ process allows the adhesive to cure with constant pressure and consistent bondline thickness.” Adhesive bonding saves significant time and money, he adds, should an misaligned nut plate require relocation, because no holes are drilled. Eliminating rivet holes reduces the potential for fatigue and corrosion. Self-fixturing nut plates also facilitate fastening where drilling can’t be done due to poor access.
According to Egeberg, trademarked VICTREX PEEK, a glass fiber-reinforced polyetheretherketone (PEEK) thermoplastic polymer from VICTREX (W. Conshohocken, Pa. and Cleveleys, Lancashire, U.K.), was selected for the fastener because it could be injection molded to form the nut plate’s thin walls at a high glass loading of 60 percent with thorough fiber wetout and thus provide the high strength and stiffness necessary to meet the fastener’s performance requirements. Reportedly, the material also provides good bond strength, high resistance to flame and hydraulic fluid and good service temperature performance.