Aerospace Manufacturer Turns to Self Locking Threaded Fasteners For Quick Production Changeover

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Innovative design offers thread locking nuts, taps, and wire inserts.

Once we’d proved the threadform’s reliability in testing, we changed our parts list to enable ordering the new nuts

Managers and engineers are understandably hesitant to change familiar production practices, but benefits to the bottom line through better joint integrity as well as streamlined assembly and maintenance are proving to be strong motivators in a range of industries, which are rapidly adopting a unique thread locking form with exceptional resistance to shock, load, and vibration. Production changeover to the self locking threaded fasteners, offered by Madison Heights, Mich.-based Spiralock Corp., is quick and seamless, usually requiring just an exchange of traditional lock nuts, taps, and wire inserts.

The thread locking form, which eliminates the sideways motion that causes vibrational loosening while distributing the threaded joint’s load throughout all engaged threads, not only helps manufacturers combat joint loosening and stripping, but also minimizes assembly, maintenance, and service costs and eliminates galling that occurs with traditional lock nuts.

With the Spiralock self locking threaded fasteners, however, standard external threads spin freely until clamped to a final torque-retaining position.

Always striving to improve the design and manufacture of its aerospace products, Hamilton Sundstrand had 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. When the prevailing torque nuts were applied correctly, they worked adequately in conjunction with redundant electric generating systems plus battery power. However, Hamilton Sundstrand wanted more than adequate performance, and took action to achieve this.

“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,” explains Darin Morman, Manager of Generator Engineering in Rockford, Ill. for Hamilton Sundstrand, a leading global aerospace supplier. .

To avoid any intermittent power disruption or maintenance under the severe shock, vibration, and thermal variation prevalent in aerospace, Hamilton Sundstrand tested and adopted the Spiralock self locking threaded fasteners. Hamilton Sundstrand’s field experience combined with their own tests indicated that “Spiralock self locking nuts not only met the required clamping force when exposed to 50 Gs of vibration and 200 Gs of shock load,” says Morman, “but also maintains this performance for thousands of hours of operational use and thousands of temperature cycles that can range from -65º F up to 500º F.”

In tests each lock nut was installed and removed up to 50 times retaining the initial clamping force, with virtually zero rundown torque. “This prevents galling and thread damage, thereby minimizing maintenance and part replacement over the life of each aircraft generator,” says Morman. The Spiralock self locking threaded fasteners are now used in virtually all Hamilton Sundstrand aircraft generator applications, and is our preferred choice for any new aircraft generator projects.”

“From an engineering standpoint, making the change from prevailing torque nuts to Spiralock self locking nuts was as easy as picking up the phone to place an order,” says “Once we’d proved the threadform’s reliability in testing, we changed our parts list to enable ordering the new nuts,” says Morman. “Implementation has been straightforward, transparent to our assemblers as well as our customers in the field.”

NASA was one of the first to appreciate the advantages of the new self locking threaded fasteners when designing the main engines of the Shuttle orbiter.

Spiralock Corporation

Phone: (248) 543-7800

Fax: (248) 543-1403

Kate Turowska

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