Galvanized coating is formed through a chemical reaction between steel and zinc. For this reason, the surfaces of products to be galvanized are subjected to a series of chemical cleaning processes to prepare them for coating. The cleaning process proceeds as follows: the materials are kept in a degreasing bath to remove oil and other contaminants from their surfaces. After the degreasing bath, they are kept in an acid bath to clean rust and other contaminants from the surface.
The surface must be completely free of oil, rust, and other contaminants. Otherwise, coating defects may appear in the uncleaned areas. Some materials, however, may have contaminants on their surfaces that leave uncoated areas and cause appearance defects after coating. These contaminants must be cleaned before the materials are taken into the galvanizing process.
Commonly Encountered Surface Contaminants
- Heavy oil, grease, tar, varnish, and anti-rust paints. These types of surface contaminants cannot be removed during the surface cleaning stage and create uncoated areas where they are located.
- They create extra labor and cost for rework, maintenance, and repair.
- Weld spatter and slag. Weld spatter and slag that form around the weld area after welding must be thoroughly cleaned once welding is finished. If weld spatter is not removed, it creates a rough, bumpy surface after coating, which galvanizers call a 'pimpled' structure.
- Weld continuity. Welds on materials to be galvanized must be smooth, pore-free, and continuous.
- Cutting burrs. Cutting burrs on materials to be galvanized must be removed, as they will show zinc build-up and similar appearance defects after coating.
- Marking. If materials are to be marked, the paint or marker used must be water-based.