Calculation method and precautions for high-strength bolts

Calculation method and precautions for high-strength bolts

Bolts made of high-strength steel, which may require significant pre tightening force, can be referred to as Suzhou high-strength bolts. High strength bolts, including stainless steel bolts and other bolts, are commonly used for the connection of bridges, steel rails, high-pressure and ultra-high-pressure equipment. The cracking of this type of bolt is mostly brittle. High strength bolts applied to ultra-high pressure equipment require significant prestressing to ensure the sealing of the container.

The pre tension of high-strength bolts is completed by tightening the nut. The torque method, angle method, and torsion shear method are generally used.

(1) Torque method. Select a special wrench that can directly flash the torque, and apply the torque based on the connection between the pre measured torque and the bolt tension to reach the predetermined pre tension.

(2) Angle method. It is divided into two steps: initial tightening and final tightening. The initial tightening is to use a general wrench to tightly fit the connected components together. The final tightening is to start from the tightening direction of the initial tightening, and use a powerful wrench to rotate the nut according to the recognized final tightening viewpoint based on the bolt diameter and plate thickness. When the nut is tightened to the predetermined viewpoint value, the bolt tension reaches the required pre tension value.

(3) Torsional shear method. Twist off the plum blossom head at the end of the bolt. Firstly, tighten the bolts, and then use the two sockets of a special electric wrench to separate the nut and the end of the bolt's plum blossom head. During operation, the large socket is turned forward to apply tightening torque, while the small socket is tightened with counter torque. After the bolts are tightened, then unscrew the plum blossom head along the rear groove. Because the depth of the groove is recognized based on the connection between the final tightening torque and the pre tension force, the regular pre tension value is reached when the plum blossom head is unscrewed with the bolt.

Quality considerations

(1) The surface should be cleaned of floating rust, oil stains, burrs on the bolt hole wall, welding burrs, etc.

(2) After handling the collision surface, it is necessary to meet the anti scratch coefficient requirements of the rules. The high-strength bolts used should have matching nuts and washers, and should be used according to the matching requirements without communication.

(3) When handling the conflict surface equipment of components, it is not allowed to be contaminated with oil, dirt, and other debris.

(4) The conflicting surfaces of components during equipment operation should be monotonous and should not be operated in the rain.

(5) Thoroughly inspect and calibrate the deformation of the connected steel plates in front of the equipment.

(6) When using equipment, prevent hammering into bolts to avoid damage to bolt threads.

(7) Use an electric wrench with punctual detection to ensure torque accuracy and operate in the correct tightening sequence.

Primary safety technical measures

(1) The specification of the wrench should match the specification of the nut, and a small wrench should not be used with a sleeve. When working at heights, a dead wrench should be used. If a live wrench is used, a rope should be used to secure it, and people should fasten their safety belts.

(2) When assembling the connecting bolts of steel components, it is prohibited to insert the connecting surface or touch the screw holes with hands. When removing and placing the pad iron plate, fingers should be placed on both ends of the pad iron plate.