Sources of Surface Contamination and Their Effects
dirt type | source of pollution | Effect on Coating | Clearing method |
Oxide | Hot working (forging, hot rolling, etc.) and heat treatment | The scale peels off together with the paint film. Combining firm and uniform oxide skin, it has no obvious effect on the coating under normal conditions, but when used in high humidity conditions and in corrosive media, the oxide scale must be removed when the coated object is painted | mechanical or acid corrosion |
yellow rust | Use and storage in unprotected conditions | It can promote the re-extension of corrosion products under the coating, so that the coating loses its shielding and moisture impermeability. Can cause early damage to coatings and metals under high humidity conditions, loose yellow rust has poor adhesion, and can fall off with the paint layer | mechanical or acid corrosion |
Mineral oil, grease, animal and vegetable oils | Acts as a metal against rust during storage and transportation. Also used in machining | 1. The adhesion of most paints is severely reduced, and their drying is affected, and the hardness and gloss of the paint film are also reduced | Degreasing (cleaning with lye or organic solvent) |
Alkalis and Alkaline Salts | Used during heat treatment and machining | Make the coating easy to foam and damage the interface between the primer and the metal. Adhesion is severely deteriorated, especially in high humidity conditions | Cleans with water and proprietary components |
neutral salt | used in heat treatment. Rinse with hard water with high salt content; after treatment with special solution | The coating is prone to blistering under high humidity conditions, especially in the case of phosphating film | Rinse with special solution, deionized water or distilled water |
Acids (other than phosphoric acid) and acid salts | Poor cleaning after pickling, using acidic flux when soldering and tinning | Make the coating easy to foam and accelerate the corrosion of metal under the coating | Cleans with water and proprietary components |
Mechanical dirt (sand, soil, square dust, etc.) | During production, storage and transportation (casting sand, grinding ash, etc.) | Deteriorating the appearance of the coating, peeling off the dirt, destroying the coating, and making it easy for moisture to penetrate under the paint film | Clean with solution and water, blow out with compressed air or wipe with special components |
Mechanical dirt (sand, soil, square dust, etc.) | During production, storage and transportation (casting sand, grinding ash, etc.) | The appearance of the coating will be deteriorated, the dirt will peel off, the coating will be damaged, and the moisture will easily penetrate under the paint film. | Clean with solution and water, blow out with compressed air or wipe with special components |
Steel, tin, lead, and other metals with a higher potential than iron | Plated by copper mold rolling, field, solder and other | Under high humidity conditions, it can promote the corrosion of the base metal under the paint film, and in many cases, make the adhesion of the coating worse
| corroded or polished away |
Old paint and hard organic coatings (plastics) | Temporary anti-rust coatings and repair parts used in long-term storage | Deteriorates the adhesion and appearance of the coating | Cleaning with organic solvents, concentrated lye, grinding in individual cases |
