Surface preparation includes:
Cleaning – mechanical or chemical
Mechanical cleaning includes methods like scratch brushing and sand blasting. This by abrasive action not only removes the surface impurities but also eliminate scratches and surface irregularities. Cleaning is very good, however, coating must be done immediately because the cleaned surface is in a highly reactive state and corrosion occurs very soon.
Chemical cleaning includes removal of dirt, oil and grease, and the oxidation products present on the surface by means of chemicals. The chemicals may be applied by wiping, spraying or dipping. The nature of chemicals used depends upon the base metal.
Conversion coating. – These are applied for three purposes:
1) provide temporary in process corrosion protection before application of powder coating.
2) promote good adhesion of powder coating to the substrate.
3) impart under paint corrosion & thereby improve the life of the powder coating. The type of the conversion coating used also depends upon the base metal.