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Analysis Of Flange Bolt Anti-Loosening Measures (Up)

Feb. 05. 2020

1 Introduction:

Adhesive bolt supplier to share with you: Bolt connection is the most widely used node connection method in mechanical engineering, structural engineering and other fields. It is the most basic structural form in fastener connection. Mass production, simple structure, low cost, convenient installation, interchangeability and other advantages are widely used in modern structural engineering. The different types of bolts, the characteristics of the force, the environment of use, etc., the importance of the bolts is different, and the requirements for loosening are also different. In history, accidents of structural damage due to loose bolts are not uncommon. It can be seen that the importance of bolt anti-loosening to ensure the stress characteristics of bolts and the overall safety of the structure. Loose bolts have become a safety hazard for steel structure connections. The analysis shows that there are many reasons for bolt loosening, such as the initial deformation of the bolt connector, the effect of axial load, and the effect of lateral load. In engineering practice, many anti-loosening measures have also been proposed, such as accurately applying prestress, taking mechanical measures to prevent loosening, using punch points, glued bolts and nuts, and using self-locking anti-loosening nuts. Therefore, when anti-loosening measures are taken on bolts, all aspects of bolt performance must be fundamentally understood.

2Common bolt classification and current construction and anti-loose measures:

From the perspective of the stress mechanism of bolts, bolts can be divided into four types: ordinary bolts, high-strength ordinary bolts that bear vibration loads in high-rise structures, high-strength bolts, and high-strength bolts that undergo tensile and compression alternating loads. Ordinary bolts generally bear tensile or shear forces directly and are used in the connection of non-essential structural members. In the past, it was thought that only bolts were needed for bolt construction. However, at present, the construction quality acceptance regulations for power system and tower and mast steel structures have given relatively accurate torque value requirements for "tightening".

The second type of bolt is often used for tower flanges in high-rise structures, which can withstand tensile forces, and the structure can withstand certain vibrations.

The third type of high-strength bolt is subjected to a pre-tension force first, and then generates frictional resistance on the contact surface between the connected parts to bear the shear force or reduce its pre-pressure to receive the tensile force. Generally used in important industrial and civil buildings such as beam members, such bolts are generally constructed by the torque method, and bolts rely on friction generated by the compression between threads to prevent loosening. The bolt is a high-strength ordinary bolt. The bolt does not apply pretension, but it needs to be tightened, and a double nut is used to prevent loosening.

Expansion BoltAnalysis Of Flange Bolt Anti-Loosening Measures (Up)

Expansion Bolt

The fourth type of bolt is a bolt that undergoes alternating tension and compression. This bolt generally bears fatigue loads at the same time, requires pre-tensioning, and has high requirements for anti-loosening. It is common in the connection flange of wind turbine towers.

When the tightening torque of the first type of ordinary bolt reaches the value specified in the specification, the bolt will not loosen. expansion bolt with a certain vibration load in a high-rise structure has a good anti-loosening effect. For example, the 336-meter-high Heilongjiang TV Tower completed in 2000 did not find loose bolts. The anti-loosening effect of high-strength bolts in bridge structures is also very good. However, the fourth type of bolt has a significant deficiency in anti-loosening effect. In the field of wind power generation, using a torque wrench to check the bolt pre-tension during the operation of the wind turbine has become an important part of the regular maintenance of a wind farm, which consumes a lot of manpower and resources.