The rapid development of China's machinery industry has put forward higher and higher requirements for the quality of vehicle products. Therefore, the surface protection technology of fasteners has a significant manifestation in the high safety, high environmental protection and diversified personality of vehicles.
Fastener surface treatment process
There are many kinds of fastener surface treatment processes:
1. Plating surface treatment
The parts to be plated are immersed in an aqueous solution containing the deposited metal compound, and the electroplating metal is precipitated and deposited on the parts by passing the current through the plating solution. Generally, electroplating includes zinc plating, copper, nickel, chromium, copper nickel alloy, etc., and sometimes includes blackening (bluing), phosphating, etc.
2. Mechanical plating surface treatment
Impact the product surface through the particles of coated metal, and cold weld the coating onto the product surface. Generally, the screws are mostly electroplated, but the hexagonal wood screws used outdoors in electric power, highways, etc. are hot-dip galvanized; The cost of electroplating is generally 0.6-0.8 yuan per kilogram, and that of hot-dip galvanizing is 1.5-2 yuan per kilogram, which is relatively high.
3. Hot dip galvanized surface treatment
This is accomplished by immersing carbon steel parts in a bath of molten zinc with a temperature of about 510 ℃. The result is that the iron zinc alloy on the surface of the steel part gradually becomes the passive zinc on the external surface of the product.
At present, the surface treatment technology of automobile fasteners mainly includes oxidation (blackening), phosphating, electroplating (zinc, zinc nickel alloy, decorative chromium), Dacromet coating, etc. It is well known that oxidation treatment has many defects, such as high energy consumption, unstable process and unstable film; The corrosion resistance of phosphating film is poor; The passivation treatment solution for electroplating and Dacromet coating contain Cr6+, which is not environmentally friendly. The corrosion resistance of ordinary electroplating coating can reach 500-1000h. However, the cost is high, the film has poor moisture resistance (120h moisture heat resistance), and is not wear-resistant.
Cathodic electrophoretic coating process
In order to improve the surface treatment quality of fasteners and meet the requirements of environmental protection laws and regulations, in addition to the above surface treatment processes, foreign companies such as General Motors and Ford Motor Company in the United States apply cathodic electrophoretic coating process to surface treatment of bolts. According to different quality requirements of fasteners and different process schemes, the salt spray resistance test can reach more than 240-1000h, and the friction coefficient of the paint film is appropriate, which does not affect product assembly, can replace the passivation process of electroplating, and is conducive to environmental protection.
Cathodic electrophoretic coating is highly mechanized, environmentally friendly, and the paint film has excellent corrosion resistance. It has been used in vehicle coating for many years. According to the types and performance requirements of automotive fasteners, the high-strength 8.8 and 10.9 bolts for automotive chassis, engine and transmission are tested. The scheme is as follows:
① Black cathodic electrophoretic coating, electrophoretic coating for fastener coating;
② Black cathodic electrophoretic coating with adjusted formula, suitable for fastener coating;
③ Black cathodic electrophoretic coating, electrophoretic coating for common parts.
Focus on testing several main properties of fastener coating (plating).
a. Corrosion resistance (salt spray test) performance.
b. Damp heat resistance.
c. Assembly performance.
At present, domestic high-strength fasteners for automobiles basically rely on imports, and an important bottleneck in the localization of fasteners is the control of friction coefficient. Under the condition of ensuring the assembly performance, the longer the time of salt spray resistance test and damp heat resistance, the better. In addition, the paint film will not fall off when the pneumatic wrench is used for assembly, which are the key technologies for fasteners to adopt the electrophoresis coating process.
With three schemes of electrophoretic coating ①, ② and ③, there is no change on the surface of the paint film after 500h, and the total friction coefficient and dispersion (uniformity) of the friction coefficient are better than those of galvanized parts. The electrophoretic coating ① scheme is the best, the coating thickness is 15-18 μ m, the salt spray resistance test is 240-1000h, and the comprehensive cost is low, 15-20 yuan/mm2.
Therefore, the following conclusions are drawn from the application test of electrophoretic coating on automobile fasteners.
1. The process scheme of surface treatment of fasteners with electrophoretic coating is feasible;
2. The special electrophoretic coating for fasteners must be used to meet the quality requirements of fastener surface treatment;
3. Compared with the electrogalvanizing process, the electrophoretic coating process has made progress in various indicators and costs less.
Summary
In fact, cathodic electrophoretic coating process is also one of the surface treatment processes. The surface treatment process is the process of forming a coating on the surface of the workpiece through a certain method. Its purpose is to give the product a beautiful surface and anti-corrosion effect. It can be seen that the surface treatment process is indispensable in the automobile manufacturing industry. It not only plays a role in beautifying the decoration, It can also reduce the corrosion degree of the metal surface of the car, increase the wear resistance of the car surface, play a protective role, and have a longer service life.
Guangzhou Tuoshen Surface Treatment Co., Ltd., the spraying manufacturer, is preferred for purchasing spraying, Spray processing Factory, trustworthy
