Phosphating is a process in which a series of salts are applied to metal surfaces to improve their rust protection and painted surface adhesion. In order for phosphating to be effective, proper surface preparation must take place prior to its application. This includes ridding the metal surfaces of oils or other contaminants through degreasing and properly etching the metal surface to prepare it for phosphating.
Degreasing is the process of removing oils, lubricants, and other contaminants from metal surfaces. This is essential as these chemicals can act as a barrier and prevent the salts from properly reacting with the metal during phosphating. Common chemicals used in degreasing are cleaning solvents, fluosilicic acid, TSP, and alkaline solutions. Depending on the substrate, the appropriate degreaser should be used as to not cause any damage when cleaning the surface. After degreasing the surface, it must be thoroughly rinsed in order to avoid any residues that may remain on the surface and affect the quality of the phosphated surface.
Etching is the next step in the process. This involves the use of mild acids to help create a porous surface structure on the metal. This allows for the salts used in the phosphating process to be better able to penetrate the metal surface and result in a more uniform finish. These acids can be acidic solutions or a combination of electrolytes and acids. It is important to note that these etching chemicals are hazardous and must be handled with care.
Next, the chemical phosphating process is applied which involves the use of a solution containing zinc phosphate, iron phosphate, or manganese phosphate along with other acids and salts. The solution is applied with either a brush or spray and then left to react with the metal surface. The time and temperature of the reaction will affect the thickness of the phosphate layer and the denseness of its crystalline structure.
The final step in the process is to rinse the surface with water to remove any remaining salts and restore the neutral pH. This phosphated surface will now be much more rust-resistant and will have better adhesion with paint or other coatings.
To summarize, phosphating requires proper surface preparation in order to be effective. This includes degreasing the surface to remove oil and other contaminants as well as etching it to help improve the phosphating process. The phosphating process is then applied and followed by rinsing to remove any leftover salts. This will leave the surface with a rust-resistant phosphate layer that will be better suited to receive paint or other coatings.
