Improving Bolt Tightening Accuracy in Torque Control Method

Abstract

Torque control method is widely used when tightening bolt-nut connections due to its easy operations. However, it inevitably involves the essential problem of generating a fair amount of bolt preload scatter, even when applying the same amount of torque. The primary reason for this is the scatter of friction coefficients of thread and nut loaded surfaces. By using tightening equipment which can accurately evaluate the scatter of friction coefficients, this study has shown that the use of plain washer is effective to lower the scatter of friction coefficient of the nut loaded surface, thus lowering the bolt preload scatter as much as 10% of the target value.