Improvements to torque versus tension relationship considering nut dilation effects

Abstract

Torque as a tightening method is a simple technique that can be used to tighten a bolt to a given pre-load. Therefore, it is important to theoretically derive an accurate torque vs tension relationship for threaded fasteners as this would enable the industry to achieve a reliable pre-load. Various attempts were made to develop a complete theoretical relationship between torque and tension. Due to the thread angle there exists a nut dilation force causing the nut to expand radially out wards. This effect is more prominent in nuts with smaller height (Style 0 hex nut, refer ISO 4035 1 ). This nut dilation force creates a combined frictional effect with the drive torque thus affecting the torque tension relationship. This paper proposes a novel 3D formulation for torque tension relationship taking into consideration the nut dilation effect. This paper further develops new formulae for tightening and loosening torque, retaining torque, tension vs nut rotational angle relationship as well as formula for nut dilation force for both tightening and loosening.

Assembly method for two symmetrical bolt-bearing joints based on the tightening model and angle-eccentricity relationship

“…Where, d 2 is the pitch diameter of the bolt. K is the new torque coefficient of single bolt-bearing joint, and it can be calculated by equation (14). From equation ( 14), the parameter K cannot be seen as a constant value, due to parameter b and θ are changing during the tightening process.…”

“…Then the torque-time control method was proposed based on the relationship in the elastic stage between the applied torque and the rotation angle, and the linear relationship between applied torque and time under constant speed. Saman 14 took the nut dilation effect into consideration and proposed a novel 3D formulation for torque preload relationship for improving the tightening quality. What’s more, the neural networks, 15 fuzzy logical control, 16 and adaptive sliding control 17 are also used to improve the single bolt tightening quality.…”