Iron and steel are easy to oxidize in high temperature. Aluminizing diffusion is a reliable surface treatment process. Spraying aluminizing is one of them.It has the advantages of wide range of application, relatively simple process and good high temperature resistance.
The melting point of aluminum is 660 degree centigrade, and itself is not resistant to high temperature. However, aluminum has a characteristic that it has a strong tendency to combine with oxygen. After aluminizing the surface of steel or cast iron, the aluminizing layer is formed into aluminized ferroalloy. The higher of the surface, the higher of the aluminum content, in which aluminum reacts with oxygen at high temperature (4AL+3O2=2AL2O3) to form a dense protective film of alumina (AL2O3). This film is not only continuous, but also non-porous. With this layer of thin film, the general temperature resistant steel or cast iron into a good material heat and corrosion resistance.
Spraying aluminizing diffusion process procedure
1. Sand blasting on the surface of the workpiece, usually choose number 4 quartz sand. In addition, in order to ensure the quality of coating, before sandblasting must eliminate the workpiece surface edge, edge, burr. After sandblasting, the surface is grey metal, with a certain roughness, and the surface without oil.
2. Spray aluminum coating, using industrial pure aluminum (containing aluminum at least 99.7%), that is, ER1070 aluminum welding wire. The coating thickness of 0.25-0.50mm is the best.After diffusion, the surface should be livid.
3. Paint protection, paint with water glass.Water glass usable brush besmear method, want besmear 3, each layer appropriate is thin and even, wait for the first layer to be able to besmear since dry the 2nd and 3rd layer.After coating three self – drying process for the next step.
4. High-temperature diffusion treatment. The diffusion temperature is better than the working temperature of the workpiece. Practice shows that the use of 1100°C insulation for one hour is better, and the highest cost performance.The temperature of the furnace is 600-800°C, and the workpiece should be heated evenly. When the diffusion insulation time reaches 300-400°C, air cooling is taken out.That glassy shell starts to crack and fall off, which is normal.Do not fall off the shell, with a small hammer gently hit, make it fall off.The surface of the workpiece shall be livid.
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