Factors Affecting the Maximum Tightening Torque of Lock Nut

The maximum tightening torque of the lock nut is affected by many factors. For the research on the low cycle fatigue performance of Steel Lock Nuts, the pitch diameter of the thread, spiral rise angle, and tooth profile inclination angle remain unchanged, and only the maximum elastic restoring force and equivalent friction angle of the threaded piece will change to a certain extent after repeated use. Therefore, it is only necessary to analyze the variation law of the maximum screw torque of the Steel Lock Nuts under cyclic load from these two aspects.

Material strain hardening

During cyclic loading, the material will appear the phenomenon of "cyclic strain hardening" or "cyclic strain-softening", that is, under the condition of constant amplitude cyclic strain, the stress amplitude will increase or decrease with the increase of the number of cycles. After several cycles, the stress amplitude enters the cyclic stable state. The low cycle fatigue of the Steel Lock Nut is carried out when the strain is constant. The strain hardening or softening of the threaded piece will affect the maximum tightening torque. The alloy steel used to manufacture the lock nut belongs to the cyclic strain hardening material. The hardening of the material will increase the elastic restoring force FN of the threaded piece and the tightening torque.

Low cycle fatigue

Low cycle fatigue means that the fatigue stress is close to or exceeds the yield limit of the material. The material has a certain amount of plastic deformation in each strain cycle. Life is generally in the range of 102 to several times 104. The fatigue curve is generally used in curve representation. The finite element calculation results show that after the bolt is screwed into the Steel Lock Nut, the stress at the root of the threaded piece is large, and some areas of the surface layer are in the yield state, while the strain in the central area of the root of the threaded piece is very small, and the strain situation is more complex. The area with high strain at the root of the threaded piece experiences reciprocating loading, which is prone to low cycle fatigue, which reduces the pressure of the threaded piece and the screw-out torque.

Friction coefficient

The friction angle is an important factor affecting the screw-out torque, and the existence of friction is the basis of the normal operation of the Steel Lock Nut. When the lock nut works, there is pressure and friction on the contact surface under the elastic restoring force of the threaded piece. In the process of repeated use, the rough position and edges and corners of the contact surface are smoothed and the friction coefficient becomes smaller under the cyclic friction, to reduce the maximum tightening torque of the nut.

Manufacturing and assembly

Due to the limitation of manufacturing technology and accuracy, there are sharp corners at the edge of the thread or the dimensional coordination between parts is inconsistent. During the initial assembly, the screw in and screw out torque may fluctuate or fluctuate. It needs a certain number of running in to get a more accurate reuse characteristic of the Steel Lock Nut.

Closing value

After the material and geometric parameters of the nut are determined, the change of the closing value has an important impact on the reuse characteristics of the Steel Lock Nut. When the closing value increases, the deformation of the threaded piece increases when it is opened, the strain of the thread piece increases, the strain cyclic hardening phenomenon intensifies, and the pressure FN of the thread piece increases, which has the trend of increasing the screw out torque; On the other hand, the width of the threaded piece decreases, the total area of the threaded piece decreases, the friction with the bolt decreases, the strain of the thread piece increases, and the low cycle fatigue performance decreases, which has the trend of reducing the maximum screwout torque. Under the joint action of many factors, the change of the maximum screwout torque with the number of reuse is difficult to predict, so it can only be observed through experiments.

Make a purchase of Nylon Anchor Nut, Steel Wing Nuts from China, you can get them at a good price if you have a large quantity. We hope to be your long-term partner.