What are the characteristics of high-strength bolts?
High strength bolts are connection components made of high-quality carbon steel or low-alloy steel strengthened by heat treatment, with a performance level of 8.8 or above. With high pre tightening force and friction transmission mechanism, they have become the core connection components of heavy engineering such as steel structures. Its core features are as follows:
High strength grade, strong bearing capacity
The commonly used grades for high-strength bolts are 8.8 and 10.9, with some reaching 12.9. The tensile strength of grade 8.8 is ≥ 800MPa, and grade 10.9 is ≥ 1000MPa, far exceeding that of ordinary bolts of the same specification. It can withstand larger loads and is suitable for high load-bearing scenarios such as high-rise steel structures, bridges, and heavy-duty factories. Its material is mostly alloy steel such as 40Cr, 20MnTiB, etc. After quenching and tempering treatment, it has high hardness, good toughness, and strong deformation resistance.
High preload force, reliable friction transmission
This is its core characteristic. During installation, a torque wrench is used to apply 3-5 times the pre tightening force of ordinary bolts, creating a strong squeezing force on the contact surface of the connected parts. Shear force is transmitted through frictional force, rather than relying on screw compression and shear resistance. This friction type connection can effectively resist relative sliding of components, is not easy to loosen in vibration and dynamic load environments, has high connection stiffness and good stability.
Excellent anti fatigue and anti loosening performance
Ordinary bolts are prone to loosening and fatigue fracture due to vibration, while the pre tightening force of high-strength bolts makes the contact surface tightly fit, reducing stress concentration under alternating loads and significantly improving fatigue life. Twisted shear type high-strength bolts precisely control the pre tightening force by cutting off the tail plum blossom head. The large hexagonal head type is constructed using torque method, and the pre tightening force is controllable, further ensuring the anti loosening effect of long-term service.
Convenient construction, easy disassembly and maintenance
Construction is divided into initial and final tightening, using a dedicated electric wrench, which is easy to operate and highly efficient. Compared to rivet connections, it does not require on-site welding and has no risk of open flames, making it suitable for high-altitude and complex working conditions. And the bolts can be repeatedly disassembled and assembled, which facilitates component maintenance and replacement, reducing maintenance costs in the later stage.
High safety and wide applicability
There are obvious signs before the connection is broken, and it will not suddenly break, with a large safety reserve. At the same time, it can adapt to harsh environments and improve corrosion resistance and weather resistance through surface anti-corrosion treatment (such as galvanizing and weather resistant coatings). It is widely used in fields such as building steel structures, bridges, wind power, and offshore platforms.
