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Meaning of bolt classification and performance grade bolt: a kind of fastener composed of head and screw (cylinder with external thread), which needs to be matched with nut to fasten and connect two parts with through holes.
This type of connection is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a removable connection.
Bolt classification
1. According to the stress mode of the connection, there are ordinary and reamed holes. The bolts for reaming holes should match the size of the holes and be used in the case of transverse force. (the basic size of the unthreaded part of the reamed bolt is the same as that of the hole wall, which is a fit. This kind of bolt has the function of positioning in addition to the fastening function. However, the basic size of the unthreaded part of the ordinary bolt is different from that of the hole wall, which is not a fit. From the drawing, the reamed bolt and the hole wall are composed of one line, while the ordinary bolt and the hole wall are composed of two lines.)
2. According to the head shape, there are hexagonal head, round head, square head, countersunk head and so on. Generally, countersunk heads are used where the surface is required to be smooth without protrusions after connection, because countersunk heads can be screwed into parts. The round head can also be screwed into the part. The tightening force of the square head can be larger, but the size is large, and the hexagonal head is the most commonly used.
In addition, in order to meet the needs of locking after installation, there are holes in the head and holes in the rod, which can prevent the bolt from loosening when it is vibrated.
The smooth rod without thread of some bolts should be made thin, which is called thin waist bolt. This kind of bolt is conducive to the connection under variable force.
There are special high-strength bolts on the steel structure. The head will be larger. The size will also change.
In addition, there are special uses: T-shaped groove bolts, which are most used on machine tools and fixtures. The shape is special, and both sides of the head should be cut off. Anchor bolts, which are used to connect and fix the machine to the ground, have many shapes, such as U-shaped bolts, etc.
There are also special studs for welding, with threads at one end and no thread at the other, which can be welded on the parts, and the nuts can be screwed directly on the other side.
Meaning of bolt performance grade
The performance grades of bolts for steel structure connection are 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. The 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 referred to as high-strength bolts, and the rest are generally referred to as ordinary bolts. The bolt performance grade mark consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material. For example:
Performance grade 4.6 bolt means:
1. The nominal tensile strength of bolt material reaches 400MPa;
2. The yield ratio of bolt material is 0.6;
3. Nominal yield strength of bolt material reaches 400 × 0.6=240mpa grade
High strength bolts with performance grade of 10.9 can meet the following requirements after heat treatment:
1. The nominal tensile strength of bolt material reaches 1000MPa;
2. The yield ratio of bolt material is 0.9;
3. Nominal yield strength of bolt material up to 1000 × 0.9=900mpa grade
The meaning of bolt performance grade is an international general standard. The performance of bolts with the same performance grade is the same regardless of the difference in material and origin. Only performance grade can be selected in design. The strength grades of grade 8.8 and 10.9 refer to the shear stress grades of bolts of 8.8gpa and 10.9gpa, and s of 10.9s refers to steel structure.
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