High-strength bolts are high-strength bolts and are a standard part. In general, high-strength bolts can withstand loads larger than normal bolts of the same specification.
The shape and connection structure of the high-strength bolt are basically the same as those of the ordinary bolt. The main difference between the two is that the ordinary bolt connection relies on the pressure and shear of the shaft to transmit the shear force, and the pre-tension of the bolt is small when the nut is tightened. The effect of the high-strength bolt connection is to intentionally apply a large pre-tension to the bolt, so that a pressing force is generated between the contact surfaces of the connected parts, so that there is a large friction force perpendicular to the screw direction, relying on this Friction to transmit the connection shear. The pre-tension of the high-strength bolt is realized by tightening the nut. The ordinary high-strength bolt generally adopts the torque method and the corner method. Twist-cut high-strength bolts use a twisted bolt tail to control the pre-tension.
High-strength bolt-connected bolts are made of high-quality alloy structural steel of 10.9S or 8.8S and heat-treated. High-strength bolt holes should be drilled into holes. The diameter of the friction-type high-strength bolt is 1.5 to 2.0 mm larger than the nominal diameter d of the bolt; the diameter of the high-strength bolt connected by the pressure type is 1.0 to 1.5 mm larger than the nominal diameter d of the bolt.
Advanced manufacturing represented by large aircraft, large-scale power generation equipment, automobiles, high-speed trains, large ships, and large-scale complete sets of equipment has entered an important development direction. As a result, the fasteners will enter an important stage of development. High-strength bolts are used for important mechanical connections, and repeated disassembly and assembly or various mounting torque methods are extremely demanding for high-strength bolts. Therefore, its surface condition and thread accuracy will directly affect the service life and safety of the mainframe. In order to improve the friction coefficient and avoid rust, seizure or seizure during use, the technical requirements stipulate that the surface should be nickel-phosphorus plated. The thickness of the coating is guaranteed to be in the range of 0.02 to 0.03 mm, and the plating layer is uniform, dense, and free of pinholes.
4.Typical grades of high-strength bolts are: 45 steel, Q235
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