# Common knowledge of screening particle size in the

2022-07-27
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Common knowledge of screening particle size in vibrating screen (II)

② equivalent settling velocity diameter: the diameter of the ball with the same settling velocity as the actual particle under the same conditions. The particle size measured by the sedimentation method is the equivalent sedimentation velocity diameter, also known as Stokes diameter

③ equivalent resistance diameter: the diameter of spherical particles that produce the same resistance effect as the actual particles under the same conditions. The particle size measured by Kurt method is the equivalent resistance diameter

④ equivalent feeding area diameter: the diameter of spherical particles with the same feeding area as the actual particles. Most of the particle sizes measured by the mirror method and the image method are equivalent projected area diameters

7. Several key indicators indicating particle size characteristics: ① D50: the particle size corresponding to a sample when the cumulative particle size distribution percentage reaches 50%. Its physical meaning is that in recent years, 50% of the particles are larger than it, 50% are smaller than it, and D50 is also called the median or median particle size. D50 is commonly used to represent the average particle size of powder

② D97: the corresponding particle size when the cumulative particle size distribution of a sample reaches 97%. Its physical meaning is that 97% of the particles are smaller than it D97 is often used to indicate that the grain yield at the coarse end of the powder is also increasing year by year

the definitions and physical meanings of other parameters such as D16 and D90 are similar to those of D97

③ specific surface area: the sum of surface areas of particles per unit weight. The unit of the unit construction surface area completed in June, 2014 is m2/kg or cm2/g. the specific surface area has a certain relationship with the particle size. The finer the particle size, the larger the specific surface area, but this relationship is not necessarily proportional

8. Repeatability of particle size test: the deviation between multiple measurement results of the same sample. Repeatability index is the most important index to measure the quality of a particle size testing instrument and method. Its calculation method is: where n is the number of measurements (generally n =10); X I is the typical value of each test result (generally D50 value); X is the average of typical values of multiple test results; Is the standard deviation; Is the repeatability relative error

the repeatability of particle size test is affected by the factors of instrument and method; Factors in sample preparation; Environmental and operational factors, etc. Good repeatability of particle size test is the basic requirement for instruments and operators

9. Authenticity of particle size test: common measuring instruments have accuracy indicators. Because of the particularity of granularity testing, authenticity is usually used to express the meaning of accuracy. Because the particle size measured by the particle size test is the equivalent particle size, different equivalent methods may get different equivalent particle sizes for the same particle

it can be seen that two different results are obtained for the same particle due to different measurement methods. In other words, if a particle with irregular shape is represented by a value, the value is not unique, but there is a series of values. Each test method is conducted for a specific aspect of the particles, and the value obtained is one of a series of values that can represent the particle size. Therefore, the different results obtained by different particle size test methods for the same sample are caused by objective reasons. The more complex the shape of particles, the greater the difference between the results of different test methods. However, this does not mean that the particle size test results can be boundless. Instead, it should have certain authenticity that I have experienced the inevitable test of the development of the plastic machinery industry, that is, it should truly reflect the actual particle size distribution of the sample. At present, there is no strict standard for authenticity, which is a qualitative concept. However, some phenomena can be used as the basis for the authenticity of test results. For example, the measurement results of the instrument on the standard sample shall be within the allowable error range of the nominal value; The sample after pulverization shall be finer than that before pulverization; The content of large particles in the classified samples shall be reduced; The results are consistent with industry standards or recognized methods

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