Regarding the particle size and roughness of sandpaper, the Media Department of Grinding Library Network will introduce it to you

The woodworking and metal industries cannot do without the assistance of sandpaper and sanding cloth. How to use sandpaper in a targeted manner? How to choose the correct type and particle size of sandpaper? Today, I will introduce to you the grain size and roughness of sandpaper. 

1. Sandpaper particle size 

Due to the different objects being polished, there are particle size requirements for sandpaper. The particle size unit of sandpaper is represented by "mesh". So we can see that the back of the sandpaper will be labeled with numbers such as 60 mesh, 100 mesh, 200 mesh, etc. 

The definition of "purpose" is determined based on the grading scale established by the Coating Abrasive Manufacturers Association (CAMI) in the United States. 

The larger the value, the higher the number of abrasive particles per unit area, which also means that the abrasive particles are smaller, so the sandpaper particle size is finer. On the contrary, the smaller the number, the larger the abrasive particles, and the rougher they are. A 100 grit sandpaper. The small particle size on sandpaper is about 141 microns, which is very small. 

In addition to the CAMI standard, sandpaper also has a standard from the European Federation of Abrasive Producers (FEPA). The particle number is represented by the first letter 'P'. 

There are slight differences between FEPA standards and CAMI standards. Taking the following image as an example: 

2. Choose the correct thickness 

In addition to detailed particle size labeling, manufacturers will also label the packaging with "roughness grade", which means a range of particle sizes, making it easier for people to make appropriate choices based on polishing work.
 
Many times, when choosing sandpaper, a certain roughness level is chosen instead of selecting a specific sandpaper grain size with precision. To choose the right sandpaper, it is important to know which items are suitable for each grade. 

Between 24-36 mesh, it refers to the particle size range of ultra coarse sandpaper, which is used to remove difficult to peel off paint and varnish. 

The particle size range of 40-50 refers to coarse sandpaper, which is used for rough processing of wood and removal of light colored polyurethane coatings and other finishes. 

60-100 grit refers to medium sandpaper, used for the final polishing before painting. Medium grit sandpaper can also be used for preliminary polishing of rough wood, removing planning marks on the wood. 

120-220 mesh refers to fine sandpaper. Used for the final polishing of woodworking. 

240 mesh, 320 mesh, and 400 mesh belong to ultrafine sandpaper, which is used between paints or varnishes. Special grade or ultrafine abrasives with particle sizes up to 600 mesh are most suitable for polishing operations. 

During the polishing process, it is necessary to start with a rough grit of sandpaper and then switch to a finer grit in order to achieve a smooth surface effect.