The influences of corrosion on the tightening and anti-loosening properties of a flank-locking precision locknut

Abstract

ABSTRACT Locknut is a critical component used in the precision machinery and its stable service performance over a long period of time in a variety of different environments presents a crucial challenge. In this study, a flank-locking precision locknut was pretreated in an immersion corrosion of 5 wt% NaCl solution to simulate the possible corrosion effects. The tightening and loosening of the locknut after 0-, 1-, 2- and 4-h corrosion treatments, respectively, was tested according to the ISO 2320 Standard. An in-house test setup with horizontal configuration was employed in measuring the torque–axial force characteristics under loading–unloading cycles. It was found that the corrosion of the locknut accelerated after 1-h immersion. The corroded specimens after 2- and 4-h treatment demonstrated more variance in measured tightening and loosening torques than their less corroded counterparts. However, after five loading–unloading cycles, the variance in measured torque decreased and the associated torque constants became more stable. Moreover, the torque constants were ∼10% higher for the 2- and 4-h corrosion-treated locknuts than their pristine counterpart. The surface morphology after corrosion and friction wear was closely related to the measured testing results.