Bolt clamping force versus torque relation (F-T relation) during tightening and untightening the nut having slight pitch difference

Abstract

In this study, tightening and untightening experiments were conducted for pitch difference nuts toward realizing good anti-loosening performance. By applying the three-dimensional FEM, the relationship between the tightening force F and the tightening torque T was clarified by varying the pitch difference α during the whole nut tightening/untightening process. The well-known F-T formula available for tightening the normal nut (α = 0) agrees with the FEM results and the F-T formula for untightening the normal nut (α = 0) was newly proposed. Then, the loosening resistance ability of the pitch difference nut was clarified focusing on the untightening in comparison with the normal nut.

Keywords:

• Bolt-Nut connection
• pitch difference
• anti-loosening
• screwing
• tightening
• untightening
• unscrewing