Aerospace Industry Turns to Innovative Fastener Thread to Keep the Mission from Falling Apart

         Extreme shock, G-force, vibration, and temperature cycles assault every jet, rocket and spacecraft repeatedly during thousands of hours of operational use. True mission success depends on how reliably these aerospace vehicles operate for the long haul. Whether the challenge is mounting critical aircraft avionics, clamping onboard generator cables for continuous power, or securing interplanetary satellite instrumentation, inadequate performance from conventional fasteners can diminish or even prevent mission success.
         Striving to improve the design and manufacture of its aerospace products, Hamilton Sundstrand, a leading global aerospace supplier, examined the effectiveness of conventional prevailing torque nuts used to clamp electrical cables to the generator's terminal block in a wide range of aircraft from commercial to military. "The issue was that prevailing torque nuts can gall or freeze on threaded bolts during installation, leading to intermittent power availability if the nuts' rundown torque exceeded the final torque limit before clamping," said Darin Morman, Hamilton Sundstrand's Manager of Generator Engineering in Rockford, Ilinois.
         In an effort to avoid any intermittent power disruption or maintenance under severe shock, vibration and thermal variation prevalent in aerospace, Hamilton Sundstrand tested and adopted Spiralock thread form, designed to address not only fastener loosening and stripping under high load and vibration, but also galling as well as slippage due to thermal expansion and contraction. The company's field experience combined with their own tests indicated that "each Spiralock nut not only met the required clamping force when exposed to 50 Gs of vibration and 200 Gs of shock load," says Darin Morman, Hamilton Sundstrand's Manager of Generator Engineering in Rockford, IL, "but also maintains this performance for thousands of hours of operational use and thousands of temperature cycles that can range from -65° F to 500° F."
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