Plastic Plating-Application and Development of Electroplating in the Automotive Industry
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Piston, piston ring, connecting rod
Piston, piston rings, and connecting rods are three-person moving parts of automobile engines, and their friction losses account for about 40-50% of the total engine losses. Reducing the weight of pistons, piston rings, and connecting rods and improving their friction environment are of great significance to reducing engine vibration, noise plates, and reducing fuel consumption. In the past, pistons were not subjected to any surface treatment or were just chemically tinned (forming an initial running-in layer): the piston rings were plated and phosphorized; only one screw connected to the connecting rod was oxidized; the bearing pads on the connecting rod were made of electroplated Pb-Sn binary alloy and electroplated Sn treatment. These electroplated layers can no longer meet the needs of modern engines for high speed, high power, compactness and the development of ECR technology.
bearing bush
In order to prevent Sn in the coating from thermally diffusing into the slave body to form a brittle phase, on the bearing bush of high-power engines, it is necessary to coat a layer of nickel grid on the slave body, and use electroplated Pb-Sn-Cu primary alloy instead of Pb-Sn binary alloy coating.
Inlet and exhaust valves
The friction loss of inlet and exhaust valves is about 2% of the engine energy loss. Measures to reduce losses: Reduce the structural size of inlet and exhaust valves, and use lightweight materials such as titanium alloy Depu heat resistant steel. Working at a high temperature of 750 ° C, and due to the friction of scales in the engine exhaust gas, the titanium exhaust valve will undergo intense oxidation, and potassium must be carried out on the surface, which is usually treated by molybdenum spraying and salt bath furnace nitriding. Recently, the treatment method that has attracted people's attention is plasma carburizing treatment. This process has little impact on the environment. The TiC hardened layer formed on the surface is 50μm deeper than the carburizing layer treated in a heat-resistant steel salt bath furnace, and its hardness reaches HV700. Oxidation resistance and wear resistance are the same as the heat-resistant steel air valve, and the treatment cost is more expensive than that of a salt bath furnace treatment
Exhaust cylinder, muffler
The exhaust system installed on the chassis of the automobile is not only subject to environmental corrosion such as the impact of road mud and sand, but also withstands the erosion and oxidation corrosion of high-temperature exhaust gas above 400 ° C. The working environment is very harsh. Most materials for the exhaust system are stainless steel and hot-dip aluminized plate. During work and use, aluminum-plated plates often suffer from blackening and corrosion. In the 40 cycles of the vehicle corrosion resistance test, level 5 corrosion occurred, and the corrosion resistance was not as good as that of stainless steel. Adding silicon elements to hot-dip aluminum plating can inhibit the growth of iron-aluminum alloy layers and improve processing properties. The service life of hot-dip aluminized sheet is related to the thickness of the coating, forming process, and working temperature.
shock absorber link
In the past, the shock absorber connecting rods were electroplated with hard chromium, but the corrosion resistance could not meet the requirements. Recently, the HEEF25 micro-crack chromium plating process has been used all over the world, with a coating thickness of 20±5μ. Compared with the 10l ±3μ specification, the number of cracks is generally required to be 400 - 600 per cm, which is to ensure the corrosion resistance and lubrication of the shock absorber connecting rod. Have a positive effect. In this process, the current density has an obvious relationship with the number of microcracks, crack shape and air penetration amount in the chromium plating layer. Generally controlled at 58A/dm2. The design of the cylindrical anode and the polishing after plating have an impact on the quality.
decorative parts
Most of the decorative parts of modern cars use plastic parts. High-end automotive plastic decorative plated parts require extremely high corrosion resistance, thermal shock resistance and decorative properties.
