8.8 grade 10.9 grade 12.9 grade bolts are made of high-strength steel, commonly used 45 steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA and so on.
From the strength level: high-strength bolts, the use of an increasingly wide range. Commonly used 8.8s and 10.9s two strength levels, of which 10.9 level is predominant. Ordinary bolt strength level to be low, generally 4.4, 4.8, 5.6 and 8.8.
Today's large aircraft, large power generation equipment, automobiles, high-speed trains, large ships, large-scale complete sets of equipment and other representatives of advanced manufacturing has been to enter an important direction of development. As a result, fasteners will enter an important stage of development. High-strength bolts are used for important mechanical connections, repeated disassembly or various types of installation torque method of high-strength bolts is extremely demanding.
Therefore, the surface condition and thread accuracy of the good and bad, will directly affect the service life of the host and safety. In order to improve the coefficient of friction, to avoid corrosion, bite or stuck in the process of use, the technical requirements of its surface should be nickel-phosphorus plating treatment. Plating thickness is guaranteed to be within the range of 0.02 ~ 0.03mm, the plating is uniform, dense, no pinholes, etc..
Bolt material: 18Cr2Ni4W, 25Cr2MoV steel; bolt specifications: M27 ~ M48.
Because of this type of steel is prone to the formation of a layer of passivation on the surface of the film, and this passivation film will make the bolts can not get good adhesion chemical nickel-phosphorus layer, so it must be a special pre-treatment measures will be the film removed first, and measures should be taken to prevent the generation of its again! Therefore, special pretreatment measures must be taken to remove the film first, and measures should be taken to prevent its re-generation, in order to ensure that the plated layer and the substrate after plating has a good bonding.
At the same time, because of the bolt geometry is large, all to the nickel-phosphorus plating treatment and process of quality inspection has increased the difficulty.
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