The strength grade of bolts is an important index to evaluate the mechanical properties of bolts, which is directly related to the bearing capacity and safety of bolts during use. The following is a detailed explanation of the bolt strength rating, including its meaning, application scenarios, and impact on bolt performance.
First, the meaning of bolt strength grade
The strength rating of the bolt is usually composed of two parts, such as “4.8”, “8.8”, “10.9” and so on. These two figures represent the nominal tensile strength value and the flexure ratio of the bolt material respectively. For example, the “8.8” class bolt indicates that its nominal tensile strength is 800MPa(8×100MPa) and the bending strength ratio is 0.8, that is, its yield strength is 80% of the tensile strength, that is, 640MPa(800MPa×0.8).
According to the international standard, the same performance grade of bolts, regardless of the difference in material and origin, its performance is the same. Therefore, only the performance level can be selected in the design.
Second, application scenarios
Bolts of different strength grades are suitable for different application scenarios. The following are some common bolt strength levels and their application scenarios:
4.8 bolt: It is an ordinary bolt, and its material is mostly low carbon steel. Due to the low strength grade, it is mainly used for some light mechanical structure connections and some fasteners that do not need to bear too much load. For example, everyday household appliances such as locks, furniture, bicycles, etc.
Class 8.8 bolt: made of medium carbon steel, it has high strength and toughness after heat treatment. Suitable for bearing a certain load, such as large machinery and equipment, steel structure, large vehicles, construction machinery, ships and other relatively durable machines.
10.9 bolts: belong to high strength bolts, and their materials are mostly alloy steel. Because of its very strong carrying capacity, it is suitable for mechanical structures with large loads or requiring extremely high strength, such as high-speed railways, Bridges, power generation equipment and large engineering buildings.
Class 12.9 bolt: Also high strength bolt, its material is also alloy steel. Because the strength level is very high, it is suitable for applications that need to withstand very large loads, such as heavy machinery, structures under extreme conditions, and defense fields.
Third, the influence of different strength grades on bolt performance
Bolts of different strength grades have differences in performance, mainly reflected in the following aspects:
Bearing capacity: The higher the strength level of the bolt, the stronger its bearing capacity, can withstand greater loads.
Safety: High-strength bolts are less likely to break and other failures in use, thus improving the safety of the structure.
Fastening effect: Bolts of higher strength grade can provide better fastening effect and reduce loosening after fastening.
Fourth, summary
The strength grade of bolts is an important index to evaluate the mechanical properties of bolts, which is directly related to the bearing capacity and safety of bolts during use. Different strength levels of bolts are suitable for different application scenarios, engineers in the design and selection of bolts, should be based on the specific working conditions and requirements to choose the appropriate strength level. This ensures the reliability and safety of the bolted connection while improving the overall performance of the mechanical structure.
