Dip coating and spray technology of Dacromet treatment

Dip coating and spin drying are suitable for standard parts and other small workpieces. Workpieces usually need to be immersed for 10 to 20 seconds to fully form a purification membrane between hexavalent chromium and steel substrate; The centrifugal dryer should rotate forward and reverse twice, 10 to 20 seconds each time. For special parts, the fixture should be used. For difficult parts, manual assistance should be used, such as stirring in the centrifugal basket with a rod, and the rotation speed should be fast. In short, it is necessary to ensure that there is no liquid accumulation, hanging liquid, bubbles, missing coating, etc. on the parts. The process parameters are determined according to the actual coating effect through multiple positive and negative liquid throwing and multiple adjustment of drying speed. 1.2. Spraying and brushing are generally used for large parts, which are difficult to dip and dry

The sprayed coating is uniform, thick, poor adhesion but good finish, strong corrosion resistance but low efficiency. Attention should be paid in the construction, and the viscosity of slurry should be properly reduced during spraying. Dacromet solution is divided into mother solution and base solution (some suppliers divide Dacromet solution into three kinds: main agent, bridging agent and tackifier, and three solvents are used together.) The base solution is composed of very fine flake aluminum powder and zinc powder, and the mother solution is composed of acid and chromium salts. When in use, the two are mixed to form tank liquid. The tank liquid must be continuously circulated or stirred to prevent the base material from settling. Because it is not easy to keep for a long time, it should be used now. When preparing, the bath temperature should not be too high (less than 20 ℃) to prevent the reaction of the solution itself. The thickness of the coating is determined by the process parameters such as immersion time, drying time and drying speed. It is usually dipped in Dacromet solution for 0.5-2.0 minutes. The rotation speed of different parts is different, generally 200-300 rpm. The times of immersion in Dacromet solution are determined according to the requirements of different parts. The Dacromet coating is thickened by three to four microns after immersion once, generally two to three times.