Spiralock Fasteners Make Descent to Saturns Largest Moon

Alternative industrial fastener design lends fail-safe fastening performance to the Huygens probe in its descent to the surface of Titan, Saturns largest moon

January 25, 2005 -- After a seven-year, two billion mile journey strapped to the side of the Cassini orbiter, the Huygens probe decelerated 12,000 mph in less than two minutes, before parachuting to the frozen surface of Titan, Saturns largest moon, on Jan. 14th this year where it was to measure wind, pressure, temperature, and electromagnetic fields as well as take photos of the surface.

For fail-safe atmospheric measurement of both Saturn from the Cassini orbiter and of Titan from the Huygens probe, several hundred bolt fasteners have had to keep vacuum-tight sealed cavities with no thread loosening or stripping, despite shock, vibration, and temperature extremes including rocket launch, atmospheric re-entry, and the sub-zero chill of space.

Although your product may not travel the same distance as the Cassini-Huygens spacecraft in its exploration of Saturn and its moons, it must function in your marketplace with minimal failure, since your brands reputation and future sales depend on its reliability. Yet your products underlying reliability depends on how well it is physically held together by fasteners such as nuts and bolts - which may loosen or fail under shock, vibration, or extreme temperature even if its not hurtling through space.

Though some earthbound manufacturers resort to adhesives, deformed threads, nylon rings, prevailing torque nuts, and other traditional means of preventing joint loosening, these methods simply dont measure up in high load, shock, and vibration environments experienced by an industrial fastener, particularly when resistance to thermal expansion and contraction is also necessary.

To survive the vibration and high temperatures of launch, we required the most reliable locking engagement thread, said Dan Harpold, a NASA scientist who worked on the project. Screws had to remain tight without opportunity for re-tightening. With conventional threading, however, screws loosened up and backed out under testing.

In an effort to satisfy NASAs stringent reliability requirements on the Cassini orbiter and the European Space Agencys on the Huygens probe, an alternative thread form designed to address the problems associated with traditional fasteners was used.

With no ability to tighten or replace loose or stripped fasteners after launch, the chosen thread form, by Madison Heights, Mich.-based Spiralock Corp., would have to hold until mission completion. What makes the Spiralock thread form unique is a 30 wedge ramp cut at the root of the female thread. Under clamp load, the crests of the threads on any standard male bolt are drawn tightly against the wedge ramp. This not only eliminates sideways motion that causes vibrational loosening but also distributes the threaded joints load throughout all engaged threads, a claim supported by a research study conducted by the MIT.

In other studies, the Spiralock thread forms load percentage on the first engaged thread was significantly lower than standard thread forms, which further reduces possible bolt failure. The thread form also allows for thermal expansion and contraction without slippage.

NASA conducted a number of tests including a series of about twelve high-temperature bake outs, where screws and their matching internal thread forms were heated from room temperature to 300 C to simulate temperature-induced thread loosening. According to Harpold, the fasteners held up.

The Spiralock thread form retained a tight seal at 300 C, says Harpold. Once torqued down properly, the screws stayed put in the threads, which helped us meet our flight schedule. To date, not one has come loose that Im aware of.

Visit www.spiralock.com for more information.

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