What is the specific process flow of Dacromet treatment technology?

The specific process flow of Dacromet coating technology is as follows:

Degreasing:

Workpieces with grease must be degreased to ensure coating adhesion and corrosion resistance. There are generally three degreasing methods: organic solvent degreasing, water-based degreasing agent degreasing, and high-temperature carbonization degreasing.

Rust and Deburring:

Workpieces with rust or burrs must undergo a rust and burr removal process. This process is best done mechanically to avoid acid pickling, which can cause hydrogen embrittlement and affect the corrosion resistance of the Dacromet coating.

Coating:

After degreasing and rust removal, the cleaned workpiece should be coated as soon as possible using dip coating, spraying, or brushing. During the coating process, the density, pH value, viscosity, Cr content, temperature, and flow conditions of the coating solution directly affect the coating effect and various properties of the coating. Therefore, it is essential to adjust the relationship between temperature, solution parameters, and centrifuge speed during dip coating.

Pre-baking:

The Dacromet wet film workpiece must be pre-baked at (120±20)℃ for 10-15 minutes as soon as possible to evaporate the moisture in the coating, allowing the coating to level and adhere to the workpiece surface.

Sintering:

The pre-baked workpiece must be sintered at a high temperature of approximately 300℃ for 20-40 minutes. The sintering time can be shortened by appropriately increasing the temperature. During this stage, some hexavalent chromium undergoes a redox reaction with ethylene glycol at high temperature to become trivalent chromium. This mixture adheres the flaky zinc and aluminum to the metal substrate surface, acting as a binder between the zinc and aluminum flakes, forming the final coating and improving its corrosion resistance and adhesion.

Cooling:

After sintering, the workpiece must be thoroughly cooled by a cooling system before subsequent processing or finished product inspection. Uneven cooling or excessively rapid cooling may lead to problems such as coating cracking or peeling.

For some workpieces with special requirements, secondary spraying and baking may be necessary to increase the coating thickness and further improve corrosion resistance.