The following five processes are commonly used for color-coated sheets

March 10, 2024
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(1) Phosphating process for steel, zinc layer and aluminum;

(2) Complex oxidation process for zinc layer;

(3) Chromating process for aluminum and aluminum-zinc alloy layer;

(4) Chromic acid phosphating process for aluminum;

(5) Chromic acid-free process for aluminum.

After the conversion films are generated, they must be rinsed with water and post-treated to remove surface residues. Most of the post-treatments of the conversion film processes are based on chromic acid. The post-treatment of the chromic acid-free process requires an organic substance.

On a continuous unit, cold-rolled strip steel and galvanized strip steel (electrogalvanized and hot-dip galvanized) are used as substrates. After surface pretreatment (degreasing and chemical treatment), one or more layers of liquid coating are applied by roller coating. The resulting sheet after baking and cooling is the coated steel sheet.

In general, the chemicals used for degreasing of coil color-coated sheets in various processes are basically universal, but the chemicals used for subsequent conversion film treatment are different. The pretreatment process is generally distinguished by it.