Types of污物 on metal surfaces primarily include: oxide scale, yellow rust, mineral oil, lubricants, animal and vegetable fats, alkalis and alkaline salts, neutral salts, acids (excluding phosphoric acid) and acidic salts, mechanical contaminants (sand, mud, dust), copper, tin, lead, and other metals with higher electrochemical potentials, old paint, and hard organic coatings.
Metal surface treatment methods vary for different types of dirt:
Oxide Scale
Heat treatment processes such as hot forging and hot rolling, along with oxidation scales, peel off simultaneously. The combined, even oxidation scale has minimal impact on the coating under normal conditions. However, in high humidity environments or when exposed to corrosive media, the coated material must have the oxidation scale thoroughly removed before painting.
Treatment Methods: Mechanical processing or acid etching.
2. Yellow Rust
Under unprotected conditions, usage and storage can promote the spread of corrosion products under the coating, rendering it ineffective in shielding and impermeable to moisture. In high humidity conditions, it can lead to early deterioration of the coating and metal, with loose yellow rust having poor adhesion, which can detach along with the paint film.
Treatment Methods: Mechanical processing or acid etching.
Acids (excluding phosphoric acid) and acidic salts
Poor cleaning after pickling, the use of acidic soldering flux during soldering causes the coating to easily bubble, accelerating the corrosion of metal beneath the coating.
Method: Clean with water and a specialized cleaning agent.
4. Mechanical Debris (Sand, Mud, Dust)
During the production, storage, and transportation processes (such as molding sand, grinding sludge, etc.), the coating's appearance is compromised, with dirt falling off and damaging the coating, making it more susceptible to moisture penetration beneath the paint film.
