High-strength bolts are distinguished from ordinary bolts.

Update time:06 Sep 2019
abstract:

High-strength bolts differ from ordinary bolts: High-st […]

High-strength bolts differ from ordinary bolts:
High-strength bolts are more affordable than ordinary bolts of the same specification.
The material of the ordinary bolt is made of Q235 (ie A3).
The high-strength bolt material 35# steel or other high-quality materials are heat-treated to improve the strength.
The difference between the two is the difference in material strength.
From the raw materials:
High-strength bolts are made of high-strength materials. The screws, nuts and washers of high-strength bolts are made of high-strength steel, usually 45 steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA, etc. Ordinary bolts are commonly made of Q235 (equivalent to the past A3) steel.
From the perspective of strength grade: high-strength bolts are increasingly used. Commonly used 8.8s and 10.9s two intensity levels, of which 10.9 level is mostly. Ordinary bolt strength grades are low, generally 4.4, 4.8, 5.6 and 8.8.
From the point of view of the force characteristics: the high-strength bolt exerts a pre-tension and transmits the external force by friction. Ordinary bolt connection relies on the shearing of the bolt and the pressure of the hole wall to transmit the shear force. When the nut is tightened, the pre-tension is small, and the influence is negligible. However, the high-strength bolt not only has a high material strength, but also exerts a large bolt. The pre-tensioning force causes a pressing force between the connecting members, so that a large frictional force is perpendicular to the screw direction, and the pre-tensioning force, the anti-slip coefficient and the type of the steel directly affect the bearing capacity of the high-strength bolt.
According to the characteristics of the force, it is divided into bearing type and friction type. The calculation methods are different. High-strength bolts have a minimum specification of M12, and M16~M30 are commonly used. The performance of bolts with large specifications is unstable, and should be used with caution in the design.

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