Understanding 'Mesh': Converting to Microns Easily

Explanation 1

Screen diameter (μm) ≈ 14832.4 / Mesh number

The unit of measurement, mesh granularity, refers to the particle size of the raw material, typically represented by the maximum particle length. The mesh represents the size of the openings of a standard sieve. In the Tyler standard sieve system, mesh refers to the number of openings per inch (2.54 cm), simply known as mesh.

Tyler standard sieving: Tyler sieving system gradation is based on 200 mesh opening size, 0.074 mm, multiplied or divided by the nth power of the root of the main module (1.141) (where n = 1, 2, 3…), to obtain sieve sizes finer or coarser than 200 mesh. If the fourth root of 2 (1.1892) raised to the nth power is multiplied or divided by 0.074 mm, a series of sieve sizes with finer gradations can be obtained.

The higher the mesh number, the finer the particles. This is similar to the enlargement of metallographic structures.

A plus or minus sign before the mesh number indicates whether particles can pass through the mesh of that size. A negative number means that particles can pass through, indicating that their size is smaller than the mesh size; a positive number means they cannot pass through, indicating that their size is larger than the mesh size.

For example, particles with mesh size -100 to +200 can pass through a 100 mesh sieve, but not a 200 mesh sieve. When sieving such particles, the sieve with the highest mesh number (200) should be placed below the one with the lowest mesh number (100), and the particles retained on the sieve with the largest mesh (200) will be those between -100 and + 200 mesh.

The mesh number equals the number of holes per square inch. The higher the mesh number, the smaller the opening.

Generally, mesh number × opening size (in micrometers) = 15,000. For example, a 400 mesh sieve has an opening size of about 38 micrometers; a 500 mesh sieve is about 30 micrometers.

Due to the variable proportion of open area, which is affected by the thickness of the yarn used in weaving the mesh, different countries have different standards: American, British and Japanese, with British and American standards being similar and Japanese standards differing significantly.

China uses the American standard, which can be calculated using the formula given above. American Tyler standard sieve mesh size comparison chart can be viewed on the page below.

From this definition, we see that the mesh number determines the size of the sieve opening, which in turn determines the maximum particle size (Dmax) of the sieved powder.

Thus, it is possible for the 400 mesh polishing powder to be very fine, such as just 1-2 micrometers, or as large as 10 or 20 micrometers, because the sieve opening is about 38 micrometers. The D50 of the polishing powder we produce in 400 mesh is 20 micrometers.

Therefore, using mesh number to quantify polishing powder particle size is inappropriate. The correct approach is to represent particle size using grain size (D10, average diameter D50, D90), converting to maximum grain size using mesh number. The Japanese standards for abrasives (JIS standards) are very scientific in this regard.

Each grade of abrasive specifies requirements for D3, D50, D97, and the data differs when using different principles of particle size measuring instruments. The standards are very strict. For example, for powder with D50 of 2 micrometers, D3 is approximately 0.9 micrometers and D97 is 4 micrometers.

This means that in powder declared to be 2 micrometers, less than 0.9 micrometers cannot exceed 3% and more than 4 micrometers cannot exceed 3%. This is a strict requirement that most polishing powders on the market, including those from abroad, cannot meet, especially with severe excess fine powder.

The use of mesh numbers to characterize the granularity of polishing powder has its reasons. Older polishing powder factories used dry grinding and dry sieving processes, resulting in powders with a D50 of about 9 micrometers for 300 mesh and about 2 micrometers for 500 mesh.

This method generally guided production and use. However, with the emergence of new production processes and higher precision polishing requirements, this method also needs to be advanced.

Explanation 2

Mesh refers to the number of openings per square inch in a screen, with 50 mesh indicating 50 openings per square inch and 500 mesh indicating 500 openings.

The higher the mesh number, the more openings there are. In addition to denoting the number of openings in a screen, the mesh also represents the particle size that can pass through the screen – the higher the mesh number, the smaller the particle size.

The size of the powder particles is known as particle granularity. Due to the complex shapes of particles, there are several methods to represent their size, including screening granularity, sedimentation granularity, equivalent volume granularity, and equivalent surface area granularity.

Sieve granularity refers to the size of particles that can pass through the screen openings, represented by the number of openings in a 1 inch (25.4 mm) wide screen, therefore called “mesh”.

Currently, there is no internationally unified standard for powder granularity, and each company has its own definitions and representation methods for particle size. Screen specifications and the meaning of “mesh” vary between different countries and industries, making standardization difficult.

Internationally, the equivalent volume particle calculation diameter is commonly used to represent particle size, expressed in μm or mm.

China typically uses a comparison chart between mesh number and particle size (μm).