Konversiopäällysteiden

Konversiopäällysteiden, also known as conversion coatings, are a type of surface treatment applied to metals to improve their corrosion resistance and prepare them for subsequent painting or powder coating. These coatings are formed through a chemical reaction between the metal surface and the coating solution, creating a thin, insoluble layer of metal oxides, hydroxides, or phosphates.

The primary function of conversion coatings is to create a passive layer on the metal surface that inhibits the electrochemical processes responsible for corrosion. This layer acts as a barrier, preventing the direct contact of the metal with corrosive agents like moisture and oxygen. Additionally, the micro-roughness of the conversion coating enhances the adhesion of subsequent organic coatings, such as paint or powder coating, by providing a better mechanical key.

Common types of conversion coatings include phosphating (iron phosphating, zinc phosphating, manganese phosphating) and chromating. Phosphating involves immersing the metal in a phosphoric acid solution, which reacts with the metal to form a crystalline phosphate layer. Chromating, traditionally used on aluminum and galvanized steel, involves a solution containing hexavalent or trivalent chromium compounds, which form a protective chromate film. Newer, environmentally friendly alternatives like zirconium-based and titanate-based coatings are also gaining popularity.

The application process typically involves cleaning the metal surface to remove grease and dirt, followed by the immersion or spray application of the conversion coating solution. After rinsing and drying, the metal is ready for further finishing. Conversion coatings are widely used in industries such as automotive, appliance manufacturing, and construction for protecting and preparing metal components.