In sanding, the surface of the coated object or coating film is rubbed with a friction medium such as sandpaper, pumice stone, fine stone powder, etc., which is called grinding. It is an important step in the painting process. Generally, it is a manual operation, and it can also be performed by air or electric equipment. Sanding is used throughout the coating process. Not only the white blank, the primer or the putty need to be sanded, but also after the topcoat. Its function is to remove burrs, rust, oil, and dust on the surface of the substrate; remove coarse particles and impurities on the surface of the coating to obtain a flat surface; smooth the coating surface to a certain roughness to enhance the coating's adhesion. Focus. Divided into dry sanding and wet sanding, the latter is lubricated with water or other wetting agents to obtain a smoother surface and wash away the grinding powder.