1.What is the purpose and process of air knife zinc layer control?
Purpose: Adjusts the zinc coating thickness and ensures uniform distribution.
Process: When a steel plate is removed from the zinc bath, excess zinc accumulates on its surface. Air knives (high-pressure air nozzles) mounted on the upper and lower sides of the plate spray compressed air onto the surface, removing the excess zinc and smoothing the zinc coating. By adjusting the pressure, distance, and angle of the air knives, the zinc coating thickness can be precisely controlled (e.g., common values such as 80g/m² and 120g/m²).
2.What is the purpose and process of alloying treatment?
Purpose: Converts a pure zinc layer into a zinc-iron alloy layer, improving its hardness, wear resistance, and adhesion. This method is suitable for applications requiring high surface properties (such as automotive exterior panels).
Process: The galvanized steel sheet is placed in an alloying furnace and heated to approximately 500°C. This allows the zinc layer to further react with the iron in the steel substrate, forming a uniform alloy layer. The layer is then cooled.
3.How does cooling work?
The temperature of the galvanized (or alloyed) steel sheet is lowered to room temperature by spraying water or cooling with air to prevent the zinc layer from oxidizing or deforming at high temperatures.
4.What are the steps for leveling and straightening?
Leveling: A leveling mill gently rolls the steel plate to improve its surface finish, eliminate minor wavy deformation, and adjust its mechanical properties (such as yield strength).
Stretching and straightening: A leveling mill stretches and straightens the steel plate to eliminate warping, camber, and other shape defects, ensuring its flatness.
5.What are the post-processing steps?
Passivation: A passivating agent (such as chromate or a chromium-free passivating agent) is applied to the steel surface to form a protective film, further improving the corrosion resistance of the zinc layer and preventing the formation of white rust (a corrosion product of the zinc layer).
Oil application: A small amount of rust-inhibiting oil is applied to the surface as needed for rust protection during short-term storage or transportation (this can be removed by washing before subsequent use).