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Getting Reliability Right with Self Locking Threaded Fasteners
Date: 05/31/2007
Now that manufacturers' products have advanced to the point where most consumers and contractors can no longer repair and maintain their own products due to sealed components and electronic complexity, reliability must be incorporated into the design. Toward this back to nuts and bolts effort, innovative self locking threaded fasteners such as Spiralock®, the first re-engineered thread form since WWII can help engineers limit warranty claims and potential liability while boosting profitability and customer satisfaction.
Much of this reliability challenge stems from screw thread design, which was standardized during WWII to promote compatibility and has remained virtually unchanged since then. Under ideal conditions, standard male and female threads would fit together perfectly. In the real world, however, under the constraints of mass production and JIT delivery, this seldom happens.
While secondary locking devices attempt to address this shortfall, at best they simply prevent the threads from catastrophically coming apart. Because none holds the clamp load in the joint, they're susceptible to vibrational loosening, fatigue, or temperature-related joint failure.
At the heart of the matter is a design problem with the standard 60-degree thread form: the gap between the crest of the male and female threads can lead to vibration-induced thread loosening. Stress concentration and fatigue at the first few engaged threads is also a problem, along with an increased probability of shear, especially in soft metals, due to its tendency toward axial loading. Temperature extremes can also expand or contract surfaces and materials, potentially compromising joint integrity.
To address these reliability concerns while reducing component weight and enabling re-usability, engineers have turned to the first thread innovation since WWII, Spiralock self locking threaded fasteners. This re-engineered thread locking form of the self locking fasteners adds a unique 30-degree wedge ramp at the root of the thread which mates with standard 60-degree male thread fasteners.
The wedge ramp of Spiralock self locking threaded fasteners allows the bolt to spin freely relative to female threads until clamp load is applied. The crests of the standard male thread form are then drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line contact along the entire length of the thread engagement. This continuous line contact spreads the clamp force more evenly over all engaged threads, improving resistance to vibrational loosening, axial-torsional loading, joint fatigue, and temperature extremes.
The innovative self locking threaded fasteners compensate for variations in manufacturing tolerance and process due to mass production with its locking thread inside the joint. This eliminates the need for secondary thread locking devices or procedures, and can significantly reduce costly warranty claims and potential liability.
Though the company is celebrating its 80th anniversary, it's still innovating self locking threaded fasteners with manufacturers in mind. For engineers seeking the added strength and reduced weight of softer metals like magnesium or aluminum is a new type of wire thread insert the company is developing. Besides providing greater component reliability in high vibration, RPM, and temperature environments, the wire thread insert which has no tang yet supplies thread locking in the joint itself, will offer threaded joints additional strength, secure locking, and multiple reusability.
For detailed test data, including comparative graphic loading characteristics or photoelastic analysis/load vector comparison animation, contact:
Spiralock
Kate Turowska
KTurowska@spiralock.com
Madison Tech Center
www.spiralock.com
Phone (800) 521-2688
Technorati Tags: self locking threaded fasteners, thread locking, self locking fasteners, spiralock
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