In modern wooden furniture factories, many carpentry work and planing are replaced by machines, but the grinding process is still done by hand. Different parts and processes require different grinding tools. sanded. Furniture manufacturers attach importance to the polishing of furniture before painting, and we can see its importance.
 
The aesthetics of the furniture surface depends to a large extent on the quality of the sanding. As we all know, for paint companies now, whether it is a solid wood company or a panel furniture company, the grinding workshop is the one with the most workload and the most number of people, and the grinding workshop is the one with the most problems. It is not an exaggeration to say that it is a sea of ​​​​tactics. Due to the particularity and difference of the material itself, as well as the large differences in the shape and shape of the processed parts, coupled with the limited processing functions and cost considerations of the sanding equipment, it has not completely replaced manual work. Sanding method.
 

Grinding directly affects the coating effect
1. Sand off the burrs, rust, oil, dust, etc. on the surface of the substrate;
2. Reduce the roughness of the painted surface of the workpiece. For example, after the surface of the putty is dried, the surface is generally rough and uneven, and it needs to be polished to obtain a smooth surface;
3. Enhance the adhesion of the coating. Coatings have poor adhesion on smooth surfaces, sanding enhances the mechanical adhesion of the coating. 
It can be seen that sanding is one of the important operations to improve the coating effect. During the whole process of painting the object, not only the white blank and the primer and putty need to be polished, but also after the primer and topcoat are applied. It is a key process and an important guarantee for whether the paint surface effect and strength are excellent.
 

grinding skills
1. Reasonable selection of sandpapers with different thicknesses: a. It should not be too thick, and one model should not be used too much; b. Sand should not be jumped (referring to the model of sandpaper), from 200# to 600# or 800#.
2. When grinding, sand along the wood grain, never vertically and horizontally, otherwise the wood grain will crack, and the painted furniture will leave permanent flaws. 
3. The corners and edges of the polished object should not be slumped, the action should be light, and the original round or square outline must be maintained. The decorative line must be kept straight and cannot be bent, broken or deformed.
4. When sanding, generally press with four fingers and palm, and hold the sandpaper with thumb. When sanding furniture with a large area, you can use a square wood strip to sand along the wood grain.
5. Brush while grinding. Since the sand of the sandpaper is easy to fall off, it is possible to grind off the wood grain after rubbing the surface of the object. In addition, the dust from grinding is easy to embed in the temples, therefore, the dust must be brushed off with a dry brush at any time during grinding, and the brush is brushed while grinding until the surface is smooth and smooth.
6. When the board is partially bumped and scratched, the iron should be heated with hot water first. After heating, try to restore the original plane before sanding. If you press the sandpaper with your thumb, index finger and middle thumb, it is only limited to the sand part and is not suitable for sanding workpieces with a large area, otherwise the overall flat sand will be uneven, and the concave phenomenon can be clearly seen after painting. .
7. When grinding the outer arc and inner bow plates, be sure to use a template (the template with the same shape as the plate, put the sandpaper on the template), such as using an electric or pneumatic small sanding machine, the machine falls The parts should be polished according to the shape of the plate to prevent the sand from becoming stepped.
The method of grinding
1. Dry grinding:
Sand with sandpaper. It is suitable for grinding 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:
Sand with water sandpaper dipped in water or soapy water. Water grinding can reduce wear marks, improve the smoothness of the coating, and save sandpaper and labor.
It should be noted that when spraying the lower layer after water grinding, the first is to wait until the water grinding layer is completely dry before applying the lower layer of paint, otherwise the paint layer will easily whiten. Another highly absorbent substrate should not be water milled.
3. Mechanical grinding:
During large-scale construction, in order to improve work efficiency, mechanical grinding methods, such as electric grinders (disc type, vibration type), can be used. 
4. Light grinding:
In addition to the above three common sanding methods, there is another kind of sanding, that is, coating requirements marked as "light sanding", such as recoating of sealer, old paint film, after local repair, etc. At this time, finer sandpaper should be used And the proficient to carry out, effectively "grind lightly". Otherwise, the opposite is true.
The importance of sandpaper in sanding
Choice of sandpaper
(1) Solid wood blank: use 180#-240# sandpaper for grinding
(2) Sanding of plywood or one layer: choose 220#-240# sandpaper
(3) Sanding of the leveling primer: choose 320# - 400# sandpaper
(4) The last primer or sanding: use 600#-800# sandpaper
(5) Polishing and polishing of topcoat: choose 1500#-2000# sandpaper
The use of sandpaper
When using sandpaper for manual sanding, generally cut the whole piece of sandpaper into four pieces. After folding each piece in half, use your thumb and little finger to clamp both ends. In addition, press the three fingers flat on the sandpaper, and sand the surface of the object back and forth.
According to the sanding object, it can be changed at any time, using the holes in the fingers and the expansion and contraction of the fingers, in the concave and convex areas and edges and corners, to flexibly sand.
When sanding a large area, it is necessary to master the principle of "highest priority". Use the palm of your hand to turn the sandpaper, or attach a slightly harder rubber such as sponge or cork block. Use your thumb and index finger to tightly pinch the left and right end surfaces, and level the sand. grind.
The length of the sander's nails should be moderate, and the fingers should be avoided during operation.
The generation of sand marks
 

Causes and Solutions
(1) Reason
Reverse wood grain sanding; sanding with too coarse sandpaper; sanding before the film is dry; using too slow drying solvent, so that the paint film cannot dry within a certain time; the upper paint film is too thin; When the sandpaper is used, due to the retention of paint powder on the surface, a certain part has no sanding function and will form moving traces.
(2) Solution
a. Choose the most suitable sandpaper. Generally, the sandpaper used for the first grinding is coarser, and the sandpaper used for the second grinding is finer, and the sand marks on the upper layer should be ground off;
b. When grinding, it should be ground in the direction of the wood grain;
c. It should be polished after the paint film is dry, and the dust paint powder should be removed;
d. After the sandpaper is used for a period of time, check whether the powder is retained and replace it;
e. Adjust the viscosity of the paint appropriately, and grasp the thickness of the paint film sprayed enough to cover the sand marks.