Introduction to high-strength bolt connection

High-strength bolts can be divided into two types: friction type connection and pressure type connection according to their stress state.

How to make friction between the plates of the friction type high-strength bolt connecting members, generally adopting the torque method in the construction is to tighten the nuts to achieve the specified pre-tensioning force. In order to ensure that the specified pre-tension is achieved in the bolts, the wrenches used are required to be calibrated and inspected before and after the construction. In the process of screwing, it should be carried out in two stages of initial screwing and final screwing.

The initial tightening torque must not be less than 30% of the final tightening torque. The final tightening torque must be determined by calculation according to the specifications. When applying the screw, only the torque should be applied to the nut. When the initial screwing and final screwing are performed, the screwing is performed one by one from the center outward in strict accordance with the tightening sequence. After the initial screwing is completed, the final tightening is performed according to the torque method. The screw-in vortex flowmeter must be completed in one working day.

At present, high-strength bolts are divided into torsion-cut high-strength bolts and high-strength hex bolts For the torsion-cut type high-strength bolt final screwing quality, the tail plum blossom chuck is screwed off as the control means, and the final acceptance and evaluation are easy to control. However, for the final screwing quality of high-strength hex bolts, construction and supervision personnel are difficult to control, resulting in some steel structure high-strength bolt connection projects in the uncontrolled state of quality inspection.

For example, a high-strength bolt connection of a steel structure has been completed, and the construction and supervision personnel have not checked the quality of the high-strength hex bolt final screwing of the torque method. Some inspectors use a torque wrench directly on the bolt after the final screwing. Check, so it is easy to over-tighten the bolts.

The torque value used by other inspectors is the torque value at the end of construction, not the check torque value calculated according to the specifications. The extra tightening hazard will change the physical properties of the high-strength bolts and even break the screw. During the construction of the steel structure, a qualified torque wrench is sealed. The wrench is used to check the torque wrench of the high-strength bolts before and after each shift. The wrenches that exceed the data are sent to the professional inspection department for calibration and repair. After passing the test, it is used for construction.

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