The bolt connection pair was not tightened according to the specified torque; during the installation of the standard section, in order to complete the task quickly, the installer did not tighten the bolts according to the specified torque or the bolts were rusted and could not reach the tightening state at all. There is a gap between the two connecting parts of the standard section and the base, and there is a large matching gap between the bolt hole and the screw. During the operation of the tower crane, there will be shaking, and the gap between the two connecting parts will become larger and smaller, which will cause a strong The impact force causes the high-strength bolt rod to directly bear huge shear impact force and tensile impact force. Over time, the mechanical properties of the bolt will decrease, which may cause the screw rod to break or even collapse the tower, causing a major accident.
High-strength bolts are used and maintained improperly. The tower crane is in motion. During the working process, the bolts are constantly subjected to tension and shearing forces. As time goes by, the mechanical properties of the bolts will decrease. Therefore, for safety, high-strength bolts should be replaced regularly. According to national standards, Those that don't move should be replaced with new ones every 7 years; those that need to be disassembled and assembled will be scrapped after a maximum of 2 uses.
At present, during the installation process of tower cranes, as long as the bolts are not damaged, they will not be replaced no matter how many years they are used. This is an extremely dangerous practice. In fact, as long as one bolt is damaged, the rest of the bolts will be damaged to varying degrees, but it is just invisible to the naked eye. Therefore, high-strength bolts should be replaced regularly and from the same batch. After all, the cost and hidden dangers of buying bolts are incomparable.
Well-maintained bolts are easy to tighten in place when tightened.
Before installation, clean the dirt and rust on the washers, screws, nuts and threads, that is, the threads, and evenly apply a small amount of grease on the nuts and threads. High-strength bolt pairs that are not straight in the rod and have rust-damaged bolts, threads, nuts, and gaskets are not allowed to be used. Finally, during installation, do not force penetration, let alone knock penetration. After installation, the high-strength bolt connection pair must be provided with moisture-proof and waterproof measures to avoid corrosion.
