Reasons for loosening of high-strength bolts

Reasons for loosening of high-strength bolts

When high-strength bolts become loose, they generate enormous kinetic energy mv2. This huge kinetic energy directly acts on high-strength bolts and equipment, causing damage to high-strength bolts. After the high-strength bolts are damaged, the equipment cannot function properly, further leading to equipment damage. The threads of fasteners subjected to axial force are damaged and the bolts are damaged. Under the action of radial force, the bolt is cut and the bolt hole is elliptical in the fastener. At present, the most advanced and effective locking method is Down's Threaded fastener locking method. Down's threads have the characteristics of left and right threads. It can be used in conjunction with left and right threads. Connect using nuts with two different directions of rotation. Nuts on the working support surface are called fastening nuts, while nuts on non supporting surfaces are called locking nuts. Before pre tightening the locking nut, the fastening nut is pre tightened. Under vibration and impact, the fastening nut will loosen. However, since the release direction of the fastening nut is the tightening direction of the fastening nut, tightening the locking nut can only prevent the fastening nut from loosening, leading to the failure of the fastening nut.

High strength bolt connection has the advantages of simple structure, mechanical performance bar, detachable, strong resistance, and dynamic load is not easy to loosen. This is a great connection method. High strength bolts are a special wrench used to tighten nuts, which can generate a huge and controllable pre tightening force. By using nuts and buffer plates, a pre pressure of the same size is generated on the connecting components. Under the pre pressure, the contact surface of the joint will generate significant friction. Obviously, as long as the axial force is less than the frictional force itself, the parts are not easy to loosen, and the connection cannot be damaged. This is the principle of high-strength bolt connection. High strength bolt connections are based on friction between the contact surfaces of the connectors to prevent them from sliding. In order to provide sufficient frictional force on the contact surface, it is necessary to strengthen the clamping force of the components and the frictional force on the contact surface. The clamping force between components is achieved by pre tightening the bolts, so the bolts must be made of high-strength steel, which is also known as high-strength bolt connection. In high-strength bolt connections, the magnitude of friction has a significant impact on their bearing capacity. The experimental results indicate that the friction coefficient is mainly influenced by the shape of the contact surface and the element material. In order to improve the friction coefficient of the contact surface, sandblasting and wire brushing cleaning methods are usually used to treat the contact surface of the connecting area parts.

There are actually two types of high-strength bolts: friction type and compression type. The bearing shear criterion for frictional high-strength bolts is that the shear force caused by the design load does not exceed the frictional force. The design standard for compression high-strength bolts is that the rod body does not shear or the plate is not crushed.