New Bolt Tightening Method with High Accuracy Utilizing Real-time Measurement of Nut Factor

Abstract

Torque control method is widely used when tightening bolt-nut connections owing to its easy operation. However, it usually involves a fair amount of scatter in bolt preloads. In contrast, elastic angle control method can provide bolt preloads with higher accuracy, though its tightening operation requires longer working hours and higher costs. In this study, a new tightening principle is proposed by combining the two methods, which achieves greater accuracy and ease of operation simultaneously. The proposed method can precisely estimate the critical value of “nut factor” in the course of tightening operations, thereby modifying the objective torque into the proper one enabling the attainment of the target bolt preload. Tightening equipment, which was manufactured for trial based on the proposed principle, successfully tightened the target bolts with scatter staying within 5% of the objective bolt preload.