Standard Dimensions And Influencing Factors Of Lock Nuts

Lock nuts are commonly used fasteners, with detailed specifications stipulated in national standards. The main factors affecting the performance of lock nuts include material strain hardening, low-cycle fatigue, friction coefficient, manufacturing and assembly precision, and crimp allowance.

Lock nuts are generally made of alloy steel, which is a material subject to cyclic strain hardening. Under cyclic loading, strain hardening of the thread locking segments increases their elastic restoring force, thereby raising the unscrewing torque.

During service, lock nuts are subjected to alternating cyclic loads. Such loads tend to induce low-cycle fatigue of the thread locking segments, reducing the clamping force of the locking segments and lowering the unscrewing torque.

The friction coefficient is one of the key factors governing the maximum unscrewing torque of lock nuts. After repeated friction, surface asperities and sharp edges on the thread locking segments are worn smooth, the friction coefficient decreases, and consequently the maximum unscrewing torque of the nut drops.

Manufacturing processes and assembly precision also affect the critical performance of lock nuts. If burrs or sharp edges exist on the thread crests, or the dimensional fit between mating components is poor, the tightening and loosening torque will fluctuate. A certain number of running-in cycles are required to obtain stable reusability of the lock nut.

Crimp allowance refers to the opening deformation of the thread locking segments of a lock nut. Variations in crimp allowance directly affect the reusability of the lock nut. When the crimp allowance increases, the opening deformation of the thread locking segments rises, the cyclic strain hardening effect intensifies, and the clamping force of the locking segments grows, which tends to increase the unscrewing torque. On the other hand, a larger crimp allowance reduces the effective contact area of the thread locking segments, lowers the friction against the bolt thread, increases strain on the locking segments, degrades low-cycle fatigue performance, and tends to reduce the maximum unscrewing torque.

In summary, under the combined effect of multiple factors, the variation of the maximum unscrewing torque of lock nuts with repeated usage cycles is difficult to predict and can only be observed and verified through tests. In practical applications, suitable lock nuts shall be selected according to specific working conditions, and regular inspection and replacement shall be carried out to ensure stable locking performance and meet operational requirements.