Are the shapes of high-strength bolts and nuts the same as ordinary bolts?
The shape and connection structure of high-strength bolts and nuts are basically the same as ordinary bolts. The main difference between the two is that the ordinary bolt connection relies on the shaft pressure and shear to transmit the shear force. When the nut is tightened, the pre-tension produced by the bolt is very small, and its impact is not considered; the work of the high-strength bolt and nut connection The principle is to intentionally apply a large pre-tension to the bolts, so that there is a squeezing force between the contact surfaces of the connected parts, so there is a large friction force perpendicular to the direction of the screw, relying on this friction force to transfer the connection shear force. The pre-tension of high-strength bolts and nuts is achieved by tightening the nuts. Common high-strength nuts generally use the torque method and the corner method. Torsional shear type high-strength nuts use twisted bolt tails to control pretension.
High-strength bolt-nut connection bolts are made of 10.9S grade or 8.8S grade high-quality alloy structural steel and processed by heat treatment. High-strength bolt holes should be drilled. The hole diameter of the high-strength bolt of the friction connection is 1.5 ~ 2.0mm larger than the nominal diameter d of the bolt; the hole diameter of the high-strength bolt of the pressure connection is 1.0 ~ 1.5mm larger than the nominal diameter d of the bolt.
Analysis of three different materials for high-strength hexagon bolts
Currently, high-strength hexagon bolts on the market mainly include carbon steel, stainless steel and copper.
(1) Carbon steel.
We distinguish low carbon steel, medium carbon steel and high carbon steel and alloy steel by the carbon content in carbon steel.
- Low carbon steel C% ≤ 0.25% is usually called A3 steel in China. It is basically called 1008, 1015, 1018, 1022, etc. abroad. It is mainly used for products with no hardness requirements such as grade 4.8 bolts, grade 4 nuts and small screws.
- Medium carbon steel 0.25% 0.45%. Currently not used in the market
- Alloy steel: Add alloy elements to ordinary carbon steel to increase some special properties of steel: such as 35, 40 chromium molybdenum, SCM435, 10B38. Fangsheng screws mainly use SCM435 chromium molybdenum alloy steel, the main components are C, Si, Mn, P, S, Cr, Mo.
(2) Stainless steel.
Performance level: 45, 50, 60, 70, 80 mainly sub-austenite (18% Cr, 8% Ni) good heat resistance, good corrosion resistance and good weldability A1, A2, A4 martensite, 13% Cr has poor corrosion resistance, high strength and good wear resistance. C1, C2, C4 ferritic stainless steel. 18% Cr has good upsetting properties and stronger corrosion resistance than martensite. Mainly divided into SUS302, SUS304, SUS316 by level.
The commonly used material is brass … zinc-copper alloy. H62, H65 and H68 copper are mainly used as standard parts in the market.
Classification of high-strength bolts
Friction type high-strength bolts: suitable for steel frame structure beam and column connection, solid web beam connection, heavy crane beam connection of industrial plant, brake system and connection of important structures under dynamic load.
Pressure-bearing high-strength bolts: Can be used for shear connections in static load structures that allow a small amount of slippage or indirectly subjected to dynamic loads.
Tensile high-strength bolts: When the bolt is tensioned, the fatigue strength is low, and under dynamic load, its load-carrying capacity is not easy to exceed 0.6P (P is the allowable axial force of the bolt), so it is only suitable for use under static load For example, the French-blue butt joint and T-joint of the pressure bar
Our company has various specifications, (standard and non-standard) materials (copper, carbon steel, etc.) bolt nut washer gasket
Ordinary external hex-widely used, characterized by a relatively large tightening force, the disadvantage is that there is sufficient operating space during installation, you can use a spanner or open-end wrench, or a wrench above the eyeglass wrench needs a large Operating space.
Hexagonal head with cylindrical head-widely used in all screws, because of its relatively high tightening force, it can be operated using an hexagonal wrench. It is very convenient to install. It is almost used in various structures and has a beautiful and neat appearance. The fixed force tip is lower than the outer hexagon. In addition, the repeated use can easily damage the inner hexagon and make it impossible to disassemble.
Pan head hexagon-rarely used mechanically, mechanical performance is the same as above, used in special environments and conditions.
Hexagon headless head-must be used on certain structures, such as the top wire structure that requires a lot of top tension, or where the cylindrical head needs to be hidden.
According to the different shapes and uses of bolt heads, they are divided into hexagon head bolts, square head bolts, semi-circular head bolts, countersunk head bolts, bolts with holes, T-head bolts, hook head (foot) bolts, etc.
High-strength bolts, high-precision bolts and anti-loosening bolts can be derived according to the materials used in production and manufacturing precision.
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