The particle size of the powder material can be detected by various methods such as sieving method, sedimentation method, electric resistance method, laser method, and electron microscope method. Each method has its own characteristics, and the test results may also differ. For particles with finer particle size or smaller specific gravity, the detection results of the latter three methods are more reliable. For example, we usually process products with a maximum particle size of about 15~20μm. Although the measurement results of these instruments are different, the difference is not very large. If measured by the sedimentation method, a large measurement error may occur.
The particle population is usually composed of a large number of particles of different sizes. According to the particle size, it is divided into several series, indicating the relative content of each level of particles, called differential distribution; indicating the total content of particles smaller than a certain number, called the cumulative distribution.
The maximum particle size is the equivalent diameter of the largest particle in the particle size distribution curve. The average particle diameter is the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve is 50%. The D90 particle diameter, the D95 particle diameter, and the D98 particle diameter are the equivalent diameters of the largest particles when the cumulative distribution in the distribution curve is 90%, 95%, and 98%, respectively.
It can be seen from the analysis of the particle size distribution curve that if the grade of the powder is measured by the maximum particle size, it can be marked as 16 μm or 800 mesh. If expressed in terms of D90 particle size (or "90% pass particle size"), the grade of the powder can be increased to 6 μm or 2000 mesh. If expressed in terms of D50 particle size (or "average particle size", "median diameter"), the grade of the powder will jump to 2.8 μm or 4500 mesh. It can be seen that selecting different accumulated distribution data to represent the granularity index will result in different concepts with great differences.
Here is another example, there is a batch of ultra-fine powder detection data. According to the particle size distribution table, the maximum particle size is about 2.96μm (or 4000 mesh full pass). If you want to highlight the publicity effect, you can also change the D90 particle size to 1.54μm (or 8000 mesh) and the average particle size to 0.99μm. (or 12500 mesh) particle size indicator.
From this reasoning, if you want to know whether a certain ultra-fine powder reaches a few thousand or even a 10,000-mesh fineness, you must carefully understand what type of equipment is used for processing, whether it is a small sample test or a random sample for batch production. Method detection, it is necessary to understand at which level the accumulated particle size data obtained in order to understand the true quality indicators of this batch of powder materials.
Adding a plus or minus sign before the mesh number indicates whether the mesh of the mesh can be missed. A negative number indicates a mesh that can leak through the mesh, that is, the particle size is smaller than the mesh size; and a positive number indicates a mesh that cannot leak through the mesh, that is, the particle size is larger than the mesh size. For example, if the particles are -100 mesh to 200 mesh, it means that the particles can leak from the mesh of 100 mesh and cannot leak from the mesh of 200 mesh. When screening the particles of this mesh, the mesh should be large (200). Under the screen with a small mesh size (100), the particles of -100 to 200 mesh are left in the mesh with a large mesh size (200).
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