Investigation of the Effect of Adhesive Coating on the Performance of Threaded Fasteners

This study investigates the effect of Teflon and adhesive coatings on the torque-tension relationship and the self-loosening performance of threaded fasteners. Two Teflon insulation coatings and one locking adhesive are considered. The torque-tension relationship is established for coated and uncoated fasteners for both tightening and loosening. Finally, the fasteners are tested to determine their self-loosening performance under cyclic transverse loads. A computer controlled fastener tightening system is used to establish the torque-tension relationship during tightening. The coefficients of thread and bearing friction, and the overall nut factor are measured. The breakaway loosening torque of tightened bolts, along with the coefficients of thread and underhead friction and nut factor are investigated. A modified Junker machine is used to evaluate the self-loosening performance of fasteners with various coatings.

Since the torque-tension relationship and the self-loosening performance of threaded fasteners are highly sensitive to the friction variables, the findings of this study would improve the reliability and safety of bolted assemblies, especially in critical applications.