Due to the different bolt structures and construction methods, Heavy Hex Bolt can be divided into two types: large hexagon head high-strength bolts and torsional shear-type high-strength bolts. The large hexagonal head type is the same as the ordinary hexagonal head rough bolt, and the torsional shear type bolt head is similar to the rivet head, but the threaded end of the torsional shear type is provided with a plum blossom chuck and an annular groove that can control the tightening torque. This difference needs attention.
A bolt connection pair includes three parts: bolt, nut, and washer. The construction and arrangement requirements of high-strength bolts are the same as those of ordinary bolts. Then it must be used in accordance with the specifications. Only grade 8.8 high-strength bolts can be used for large hexagonal heads, and only grade 10.9 high-strength bolts can be used for torsional shear-type high-strength bolts.
The pre-tension of high-strength bolts in steel structures is realized by tightening nuts. Usually, the torque method, the angle method, or the method of twisting off the bolt tail Torx chuck is used to control the pretension.
At present, there is a special wrench that displays the torque. Through the relationship between the measured torque and the bolt tension, the torque is applied to achieve the necessary overextension value.
Corner method The corner method is divided into two steps, one is the initial screwing, and the other is the final screwing. To put it simply, the initial tightening is usually the worker uses a common wrench to make the connected components fit closely to each other, while the final tightening is the final tightening angle determined according to the diameter of the bolt and the thickness of the plate stack, starting from the tight position of the initial tightening. Rotate the nut with a strong wrench, and when it is screwed to a predetermined angle value, the tension of the bolt can reach the required pre-tension value. In order to prevent the torque coefficient of high-strength bolts from being affected by the external environment, the initial tightening and final tightening should generally be completed on the same day.
The stress characteristics of torsional shear high-strength bolts are the same as those of ordinary high-strength bolts, except that the method of applying pre-tension is to control the value of pre-tension by twisting off the cross-section at the notch of the Torx head of the bolt.
Friction-type high-strength bolt connections rely entirely on the frictional resistance between the connected components, and the size of the frictional resistance is not only the pre-tension of the bolts but also the anti-slip of the friction surface determined by the material of the connected components and the surface treatment of the contact surface. coefficient.