Study on the fastening property of precision locknut under simulated dynamic impact loading with consideration of interference factors

Abstract

Screw thread fastening system is the category of mechanical connection utilizing both wedge and friction actions to transfer clamping force and torque. This fastening system shows the advantages of simple in structure and ease in application. However, its shortcomings include the performance limitation by dimension and precision, stress concentration induced by the notch geometry, loosening in dynamical service, susceptible to atmospheric condition, etc. Therefore, the possible interference on the anti-loosening property of the locknut by noise factors of the ambient temperature, operator characteristics, and type of torque wrench used was investigated using Taguchi method in this study beside the main control factors of type of locknut, fit clearance, and type of lubrication grease. The goal was to evaluate the anti-loosening property of the locknut, i.e. the anti-loosening ratio and axial force ratio, in a more realistic manner. The connection joint of the locknut was subjected to cyclic transverse impact and the anti-loosening property was measured after a specified number of cycles. The loading effect on the surface roughness of thread surface was examined and discussed after the test. It was found that the factor of locknut type dominated the influence over the lubrication grease and fit clearance factors. Through the analysis, the design with optimal combination of the control factors improved the axial force ratio and anti-loosening ratio by 7.8% and 47.9%, respectively.