Micron Spherical Silica Gel Powder for Cosmetics Additive and Column Chromatography
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What is the target unit? How to convert meshes to micrometers?

Inner diameter of sieve( μ m) ≈ 14832.4/mesh size:


The particle size of the unit of measurement refers to the size of the raw material particles, which is generally expressed by the diameter and length of the particles. Mesh is the size of the mesh size of the standard sieve. In the Taylor standard sieve, the so-called mesh is the number of mesh in the 2.54 cm (1 inch) length, which is called mesh for short.


Taylor standard screening:


The graduation of Taylor sieve system is based on the size of 200 mesh sieve 0.074mm. Multiply or divide by the nth power of the square root of the main modulus (1.141) (n=1, 2, 3. It is similar to the magnification of metallographic structure.


A plus or minus sign before a mesh number indicates whether the mesh number of the mesh can be missed. A negative number indicates that the mesh size can be missed, that is, the particle size is smaller than the mesh size; A positive number indicates that the mesh size cannot be missed, that is, the particle size is larger than the mesh size. For example, the particle size is - 100 mesh -+200 mesh, which means that these particles can leak through the 100 mesh mesh but not through the 200 mesh mesh. When screening particles with this mesh size, the particles with large mesh size (200) should be placed under the screen with small mesh size (100), and the particles left in the screen with large mesh size (200) are - 100 - 200 mesh particles.


Mesh number is the number of holes, which is the number of holes per square inch. The larger the mesh, the smaller the aperture. Generally speaking, the mesh number × Aperture (microns)=15000. For example, the aperture of the 400 mesh screen is about 38 microns; The aperture of the 500 mesh screen is about 30 microns. Because of the problem of the open hole ratio, that is, because the thickness of the silk used in weaving is different, the standards in different regions are also different. At present, there are three kinds of standards: the American standard, the British standard and the Japanese standard. The British standard is similar to the American standard, while the Japanese standard is quite different. Our country uses the American standard, that is, the formula given above can be used for calculation. Comparison table of mesh size of American Taylor standard sieve. Details can be seen in the figure.



From this definition, it can be seen that the mesh size determines the size of the screen aperture. However, the size of the screen aperture determines the large particle Dmax of the sieved powder. Therefore, we can see that 400 mesh polishing powder may be very fine, for example, only 1-2 microns, or 10 microns or 20 microns. Because the aperture of the screen is about 38 microns. The D50 of 400 mesh polishing powder produced by us is 20 microns. The attached figure shows a picture of this polishing powder. Note that the scale is 50 microns.


Therefore, it is inappropriate to use the mesh number to measure the particle size of polishing powder. The correct way is to use the particle size (D10, median diameter D50, D90) to represent the particle size, and use the mesh number to convert the particle size. If you have seen the JIS standard on abrasives in Japan, you will find it very scientific. The requirements of D3, D50 and D97 are given for each of their abrasives, and the data are different when using particle size testers with different principles. The requirements are very strict. For example, D50 is a 2 micron powder, D3 is about 0.9 microns, and D97 is 4 microns. What do you mean? Among the so-called 2-micron powders, no more than 3% should be smaller than 0.9 microns, and no more than 3% should be larger than 4 microns. This is very strict. Most of the polishing powders (including those from abroad) seen in the market cannot meet this requirement, especially the fine powders exceed the standard seriously.


There is a reason to use mesh number to characterize the particle size of polishing powder. The old polishing powder factory adopts the process of dry ball milling and dry screening, so the D50 of 300 mesh powder is about 9 microns, and that of 500 mesh powder is about 2 microns. We have been using it in this way, and can basically guide production and use. However, with the emergence of new production processes and the demand for higher precision polishing, this method should also be improved.