The grinding process has three main functions:
1 in the substrate is to remove burrs on the surface of the substrate, oil dust, etc.;
2 For the scratched surface, the surface is generally rough and needs to obtain a flat surface, so the grinding can reduce the roughness of the surface of the workpiece;
3 enhance the adhesion of the coating. Before spraying a new paint film, it is generally necessary to polish the old paint film layer after drying, because the adhesion on the excessively smooth surface is poor, and the mechanical adhesion of the coating can be enhanced after grinding.
There are three methods of grinding, dry grinding, wet grinding and mechanical grinding.
1 dry grinding: sanding with sandpaper. It is suitable for the grinding of hard and brittle paints. The disadvantage is that a lot of dust will be generated during the operation, which will affect the environmental sanitation.
2 Wet sanding: sanding with water sandpaper or soapy water. Water mill can reduce wear marks, improve the smoothness of the coating, and save sandpaper and labor. However, after water grinding, it should be noted that when spraying the lower layer, one must wait until the water-grinding layer is completely dry before applying the layer of paint, otherwise the paint layer is easy to whiten. Another substrate with a strong water absorption is not suitable for water milling.
3 Mechanical grinding: In order to improve work efficiency during large-area construction, mechanical grinding methods such as electric grinding machine (disc type, vibrating type) can be used.
There is also a kind of grinding: the painting requirements are marked as “light grinding”, for example, after sealing paint, old paint film recoating, partial repair, etc., at this time, fine sandpaper and hands should be used for “light grinding”. Otherwise, it is counterproductive.
When grinding, the grinding material should be selected strictly according to the process requirements. Generally, the sandpaper can be selected according to the following rules:
Solid wood white blank grinding selection 180#——240# sandpaper
Splint or a grinding of 220#-240# sandpaper
Polishing of the primer is 320#——400# sandpaper
The last primer or sanding is selected from 600#——800# sandpaper
Topcoat polishing and grinding use 1500#——2000# sandpaper
When sanding paper is used by hand, the whole piece of sandpaper is generally cut into four pieces. After each piece is folded, the two ends are clamped with the thumb and the little finger. In addition, the three fingers are flattened on the sandpaper and sanded on the surface of the object.
According to the sanding object, it can be changed at any time, and the holes in the fingers and the expansion and contraction of the fingers are used, and the concave and convex areas and the corners are mechanically polished.
When grinding a large area, it is necessary to master the principle of “being high”. Use the palm to rotate the sandpaper, or attach a slightly hard rubber such as sponge or cork block. Hold the left and right end faces tightly with your thumb and forefinger. mill.
The length of the sander must be moderate and avoid hurting the fingers during operation