The data shows that there are currently about 240 standards commonly used in automotive standard parts products, covering lumen sealing elements, pipe line connection fixing parts, washers, screws, nuts, bolts, etc., of which 115 standards are related to metal fasteners.
With the continuous development of the automobile industry, in order to curb the increase in production and management costs caused by the increasing number of automobile fasteners, automobile manufacturers have optimized the fasteners from the aspects of structural elements, materials, heat treatment and surface treatment.
The optimization of automotive fasteners is divided into: bolts, screws, nuts, threads, washers. Hexagon flange bolts are preferred. Hexagon head bolts, hexagon head bolts + spring washers, hexagon head bolts + spring washers + flat washers, hexagon head bolts + flat washers are restricted.
Since the requirements for assembly efficiency are also increasing, the hexagon socket screws are preferred, the standard structure is optimized, and the use of hexagon socket screws and cross recessed screws is gradually restricted. If the structure permits, hex flange nuts are preferred.
For parts with special anti-loosening requirements, consider using effective torque lock nuts, such as all-metal lock nuts and non-metal insert lock nuts.
Because the load-bearing capacity and anti-loosening ability of fine-threads are higher than those of coarse-threads, you should choose fine-threads as much as possible when selecting larger-scale threaded fasteners, and you can also reduce the variety of threaded fasteners.
In order to improve assembly efficiency and reduce the risk of missed assembly and errors, in principle, gasket products are not allowed to exist alone.
Automotive fasteners include bolts, nuts, washers, most of which must be surface-treated to protect them from corrosion, improve appearance, or achieve certain special functions.
With the gradual tightening of environmental protection, the use of trivalent chromium passivation and zinc-aluminum coatings for automotive fasteners is the future trend. The chromate passivation film is exposed to an environment of more than 70 ℃ for a long time, and the corrosion resistance Will be damaged, so for areas with high ambient temperature, galvanized passivation is used with caution.
The zinc-aluminum coating has no hydrogen embrittlement and meets environmental protection requirements. The color of the coating is black and gray. Bolts of grade 10.9 and above are preferred.
The adhesion strength of the zinc-aluminum coating to the substrate is not as good as galvanizing, and there is a phenomenon of powder falling during use, so it cannot be used inside the transmission parts, and it is not recommended for bolts that need to be repeatedly removed.
Compared with galvanizing, zinc-nickel alloy has greatly improved anti-corrosion ability. After passivation and sealing treatment, it also meets the requirements of high temperature resistance. The melting point of copper is around 1083 ℃. In high temperature environment, in order to avoid sintering of screw parts, copper plating is selected for surface treatment, especially automotive fasteners around the engine exhaust manifold.