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来源:https://www.xjnwz.com 日期:2021-09-08 发布人:admin


1、 Bolt overview
Bolts, mechanical parts, cylindrical threaded fasteners with nuts. 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 belongs to removable connection.
According to the stress mode of connection, it is divided into ordinary and reamed holes. According to the head shape: T-shaped, hexagonal, round, square, countersunk, etc. Hexagon head is commonly used. Generally, countersunk head is used where connection is required. It is widely used.
There are many names for bolts, and everyone may have different names. Some are called screws, some are called bolt nails, some are called standard parts, and some are called fasteners. Although there are so many names, they all mean the same. They are all bolts. Bolt is a common term for fasteners. The principle of bolt is a tool for fastening utensils and mechanical parts step by step by using the physical and mathematical principles of inclined circular rotation and friction of objects.
Bolts are indispensable in daily life and industrial production and manufacturing. Bolts are also known as the rice of industry. It can be seen that bolts are widely used. The application scope of bolts includes: electronic products, mechanical products, digital products, power equipment, electromechanical mechanical products. Bolts are also used in ships, vehicles, hydraulic engineering, and even chemical experiments. Anyway, bolts are used in many places. Such as precision bolts used in digital products. Micro bolts for DVD, camera, glasses, clocks, electronics, etc; General bolts for TV, electrical products, musical instruments, furniture, etc; As for engineering, construction and bridges, large bolts and nuts are used; Transportation equipment, aircraft, trams, automobiles, etc. are both large and small bolts. Bolts have important tasks in industry. As long as there is industry on the earth, the function of bolts will always be important.
2、 Bolt mark and performance grade
(1) . signs. Hexagon head bolts and screws (thread diameter ≥ 5mm). It is necessary to mark the head with convex or concave characters on the top surface or concave characters on the side of the head. Including performance grade and factory standard. Carbon steel: the strength grade marking code consists of two parts separated by "·". The meaning of the number before "·" in the marking code indicates the nominal tensile strength. For example, "4" in grade 4.8 indicates 1 / 100 of the nominal tensile strength of 400N / mm2. The meaning of "·" and the number after the point in the marking code indicates the yield ratio, that is, the nominal yield point or the ratio of nominal yield strength to nominal tensile strength. For example, the yield point of grade 4.8 products is 320n / mm2. The strength grade mark of stainless steel products consists of two parts separated by "-". The symbol before "-" in the sign code indicates the material. For example, A2, A4 and other signs indicate strength after "-", such as A2-70
(2) , grade. Carbon steel: the mechanical property grade of metric bolt can be divided into 10 performance grades: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9. Stainless steel is divided into 60, 70 and 80 (austenite); 50,70,80110 (martensite); 45,60 (ferrite) three types.
3、 At present, the bolt standard parts in the market mainly include carbon steel, stainless steel and copper.
(1) Carbon steel. We distinguish low carbon steel, medium carbon steel, high carbon steel and alloy steel by the content of carbon in carbon steel.
1. Low carbon steel C% ≤ 0.25% is commonly referred to as A3 steel in China. It is basically called 1008101510181022 abroad. It is mainly used for grade 4.8 bolts, grade 4 nuts, small bolts and other products without hardness requirements( Note: the drill tail nail is mainly made of 1022 material.)
2. Medium carbon steel 0.25% < C% ≤ 0.45%   It is generally called No. 35 and No. 45 steel in China and 1035, ch38f, 1039, 40ACr, etc. in foreign countries. It is mainly used for Grade 8 nuts, grade 8.8 bolts and grade 8.8 hexagon socket products.
3. High carbon steel C% > 0.45%. It is basically not used in the market at present
4. Alloy steel: alloy elements are added to ordinary carbon steel to increase some special properties of steel, such as 35, 40 chromium molybdenum, SCM435, 10b38. The aromatic screw mainly uses SCM435 chromium molybdenum alloy steel, and the main components are C, Si, Mn, P, s, Cr and mo.
(2) Stainless steel.
It is mainly divided into austenite (18% Cr, 8% Ni) with good heat resistance, corrosion resistance and weldability. A1,A2,A4
Martensite and 13% Cr have poor corrosion resistance, high strength and good wear resistance. C1, C2, C4 ferritic stainless steel. 18% Cr has better upsetting property and stronger corrosion resistance than martensite. At present, the imported materials on the market are mainly Japanese products. It is mainly divided into SUS302, SUS304 and SUS316 by level.
(3) Copper. Common materials are brass... Zinc copper alloy. H62, H65 and H68 copper are mainly used as standard parts in the market.
Bolts are divided according to material: the grade of carbon steel is different from that of stainless steel.
Commonly used carbon steels are: grade 3.6, grade 4.6, grade 4.8, grade 5.6, grade 5.8, grade 6.8, grade 8.8, grade 9.8, grade 10.9 and grade 12.9. You can refer to GB / t3098.1-2000.
Each grade has its own regulations, including material grade, product hardness, tensile strength, yield strength, failure torque, etc.
For example, take grade 9.8 bolt as an example: 9 refers to the nominal tensile strength of the material is 900N / mm2, and 8 refers to the ratio of yield strength to tensile strength of 0.8 (take the eighth place after the decimal point). The addition of a point between these two numbers means 9.8. Its hardness is hv290-360
4、 Technical parameters of various bolts
According to relevant standards, the performance grades of bolts are divided into more than 10 grades, such as 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 are generally called high-strength bolts after heat treatment (quenching and tempering), and the rest are generally called ordinary bolts. The bolt performance grade is composed of two numbers, which respectively represent the nominal tensile strength value and