Cleaning quality level
a. Most thorough cleaning level (Sa3)
The cleaned steel surface is completely consistent in silver gray, with a certain surface roughness to improve the adhesion ability of the coating;
b. Very thorough cleaning level (Sa2.5)
The cleaned steel surface is free of grease, dirt, scale, rust, corrosion products, oxides, and other impurities. Shadows and color differences caused by incomplete cleaning are allowed, but at least 95% of the surface per square inch must reach the level of the most thorough cleaning, and the remaining parts only show mild shadows and color differences;
c. Thorough cleaning level
The cleaned steel surface is free of grease, dirt, rust, and other impurities, and the oxide skin, rust, and old paint are removed. Mild shadows and color differences caused by incomplete removal of rust and oxide skin are allowed, with an area not exceeding 33% per square inch; If pitting has already occurred on the surface of the steel, a small amount of rust and old paint is allowed to exist at the depth of the pitting;
d. Non thorough cleaning level
After comprehensive cleaning of the surface, grease, dirt, loose oxide skin, and loose paint skin are removed. The oxide skin, rust, paint, and coating that are firmly bonded to the substrate and cannot be removed with a very sharp shovel are allowed to remain on the surface after cleaning. A large number of evenly distributed metal spots appear on the surface. [3]
Surface roughness
Surface roughness and surface cleanliness are generated simultaneously, and determining the appropriate surface roughness is equally important as determining the correct cleanliness requirements.
The Role of Surface Roughness
1) Increasing the actual bonding area between the coating and the surface of the workpiece is beneficial for improving the coating adhesion;
2) During the curing process of the coating, significant internal stress is generated, and the presence of roughness can effectively eliminate stress concentration in the coating and prevent cracking;
3) The presence of surface roughness can support a portion of the quality of the coating, which is beneficial for eliminating sagging, especially for vertically coated surfaces.
