The use and requirements of high-strength bolts

The use and requirements of high-strength bolts

According to the performance grade of high-strength bolts, they are divided into grade 8.8 and grade 10.9, of which the torsional shear type is only used in grade 10.9. In the marking method, the number before the Decimal separator represents the tensile strength after heat treatment, and the number after the Decimal separator represents the yield ratio, that is, the ratio of the measured value of yield strength to the measured value of ultimate tensile strength. Grade 8.8 indicates that the tensile strength of the bolt rod is not less than 800MPa, and the yield strength ratio is 0.8; Grade 10.9 indicates that the tensile strength of the bolt rod is not less than 1000MPa, and the yield strength ratio is 0.9. In structural design, the diameter of high-strength bolts is generally M16/M20/M22/M24/M27/M30, but M22/M27 is the second choice series. Normally, M16/M20/M24/M30 is the main choice.

When assembling high-strength bolt connections, the side of the nut with a circular countertop should face the chamfered side of the washer. For the assembly of high-strength bolts with large hexagonal heads, the chamfered side of the washer under the bolt head should face the bolt head. The large hexagonal high-strength bolt is a pressure bearing type.

Grade strength

The performance Elo rating system of bolts for steel structure connection can be divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9. Among them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and heat treated (quenched and tempered), which are generally called high-strength bolts, and the rest are generally called ordinary bolts. The bolt performance grade label consists of two parts of numbers, representing the nominal tensile strength value and yield strength ratio of the bolt material. For example, bolts with a performance level of 4.6 mean:

1. The nominal tensile strength of bolt material reaches 400MPa level;

2. The yield strength ratio of bolt material is 0.6; The nominal yield strength of bolt material reaches 400 × 0.6=240MPa level.

Performance grade 10.9 high-strength bolts, after heat treatment, can achieve:

1. The nominal tensile strength of bolt material reaches 1000MPa level;

2. The yield strength ratio of bolt material is 0.9; The nominal yield strength of bolt material reaches 1000 × 0.9=900MPa level.

The meaning of bolt performance grade is an internationally recognized standard. Bolts with the same performance grade, regardless of their material and origin, have the same performance, and only the performance grade can be selected for design.

The company's main products include high-strength bolts, high-strength nuts, steel structural bolts, steel structural nuts, grid sealing plates, grid bolts, etc.