Bolts made of high-strength steel, or bolts that require a large preload force, can be called high-strength bolts. High strength bolts are widely used for the connection of Bridges, rails, high pressure and ultra-high pressure equipment. The fracture of such bolts is mostly brittle fracture. For high-strength bolts used in ultrahigh pressure equipment, in order to ensure the sealing of the container, a large prestress is required.
The difference between high-strength bolts and ordinary bolts:
The material of ordinary bolts is made of Q235(i.e. A3).
The material of high-strength bolts is 35# steel or other high-quality materials, which are heat treated after being made to improve the strength.
The difference between the two is the strength of the material.
From the raw materials:
High strength bolts are made of high strength materials. The screw, nut and washer of the high-strength bolt are made of high-strength steel, commonly used 45 steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA and so on. Ordinary bolts are commonly made of Q235(A3) steel.
From the strength level:
High-strength bolts are commonly used in two strength grades of 8.8s and 10.9s, of which 10.9 is the majority. Ordinary bolt strength grade is low, generally 4.8, 5.6.
From the point of view of force characteristics: high-strength bolts exert pre-tension and transfer external force by friction. Ordinary bolt connection relies on bolt shear resistance and hole wall pressure to transfer shear force, and the pretension generated when tightening the nut is small, its influence can be ignored, and the high-strength bolt in addition to its high material strength, also exerts a large pretension on the bolt, so that the extrusion pressure between the connecting members, so that there is a lot of friction perpendicular to the direction of the screw. In addition, the pretension, anti-slip coefficient and the type of steel directly affect the bearing capacity of high-strength bolts.
According to the force characteristics, it can be divided into pressure type and friction type. The two methods of calculation are different. The minimum specification of high-strength bolts is M12, commonly used M16~M30, the performance of oversized bolts is unstable, and should be used carefully in the design.
From the point of use:
The bolt connection of the main components of the building structure is generally connected by high-strength bolts. Common bolts can be reused, high-strength bolts cannot be reused. High strength bolts are generally used for permanent connections.
Post time: Oct-25-2024
