Zmart is a representative organization of Kistler Remscheid (formerly Schatz) in Germany and AFS Advanced Connection Technology Research Institute in China. It was funded by Zwick China and has a German enterprise background. Its headquarters are located in Shanghai, and it has a joint laboratory for fastening connection technology with Huace Testing in Shanghai.
Technical Focus: Analysis of the Truth about the Friction Coefficient of Locking Nuts
Classification： Course Introduction
Release time：2020-07-09 13:53
The thread friction coefficient angle and total friction coefficient angle curves of the locking nut are shown in Figure 6. From the thread friction coefficient curve, it can be seen that the friction coefficient changes with the tightening angle. After the nut fully fits the connected part, the thread friction coefficient and total friction coefficient decrease with the increase of axial force (or rotation angle), which indicates that if the tightening torque of the locking nut is relatively low, The setting or calculation of tightening torque cannot be based on the normal torque axis force, and needs to be calculated based on the actual friction coefficient, or a certain amount of screwing in torque needs to be considered in order to be more in line with the actual situation.
The friction coefficient of the support surface of the locking nut has relatively little change. After the nut fits the connected part, the friction coefficient of the support surface of the nut is basically consistent with the friction coefficient curve of the normal non locking nut. With the increase of the pre tightening force (bolt axial force), the friction coefficient of the support surface will not have a significant change. As shown in Figure 7.
For example, when installing nuts between the shock absorber piston rod and the mount, as shown in Figure 8, due to factors such as weight reduction, the outer diameter of the piston rod is not designed to be very large, and the effective contact surface is often only about 3mm, or even smaller in some designs. Therefore, on the premise of meeting the requirements, the tightening torque of the installation nut cannot be set too high, otherwise it may easily cause the mount to collapse or permanent plastic deformation, resulting in the attenuation of the tightening torque.
If the lock nut is tightened normally, and the lock nut is developed according to the required friction coefficient, it can be tightened according to the normal tightening torque without considering the issue of screwing in torque. Therefore, during the development of lock nuts, the friction coefficient test is also carried out at a guaranteed load of 75%, which means that the friction coefficient meets the required friction coefficient during normal tightening torque.