Causes of high strength bolt looseness

When the high-strength bolt is loose, it will produce huge kinetic energy MV2. This huge kinetic energy directly acts on high-strength bolts and equipment, resulting in the damage of high-strength bolts. After the high strength bolt is damaged, the equipment can not work normally, which further leads to the equipment damage. The thread of the fastener subjected to axial force is damaged and the bolt is damaged. Under the action of radial force, the bolt is cut and the bolt hole is oval in the fastener. At present, the most advanced and effective anti loosing method is down's locking method for threaded fasteners. The down thread has the characteristics of left and right threads. It can be used with left and right threads. The connection uses nuts with two different directions of rotation. The nut on the working bearing surface is called the fastening nut, and the nut on the non bearing surface is called the lock nut. The fastening nut is pre tightened before the lock nut is pre tightened. In case of vibration and impact, the fastening nut will be loose. However, since the release direction of the fastening nut is the tightening direction of the fastening nut, tightening the lock nut can only prevent the fastening nut from loosening, thus leading to the failure of the fastening nut.

High strength bolt connection has the advantages of simple structure, good mechanical properties, detachable, strong resistance and not easy to loose under dynamic load. This is a good way to connect. High strength bolt is a special wrench for tightening nuts, which can produce huge and controllable pre tightening force. Through the nut and buffer plate, the same size of preload is produced on the connecting parts. Under the preloading, the contact surface of the joint will produce great friction. Obviously, as long as the axial force is less than its own friction force, the parts are not easy to loose and the connection can not be broken. This is the principle of high strength bolt connection. High strength bolted connections are based on friction between the contact surfaces of the connectors to prevent them from sliding. In order to make the contact surface have enough friction force, it is necessary to strengthen the clamping force of the component and the friction force of the contact surface. The clamping force between parts is achieved by pre tightening bolts, so the bolts must be made of high strength steel, which is also called high strength bolt connection. In the high strength bolt connection, the friction force has a great effect on its bearing capacity. The experimental results show that the friction coefficient is mainly affected by the contact surface shape and element material. In order to improve the friction coefficient of the contact surface, sandblasting and wire brush cleaning are usually used to deal with the contact surface of parts in the connection area.

There are actually two types of high strength bolts: friction type and compression type. The shear criterion of friction high strength bolt is that the shear force caused by design load does not exceed the friction force. The design criteria for compression high strength bolts are that the rods are not sheared or the plates are not crushed.