Particle size - an important factor affecting mixing
Generally speaking, the particle size of powder is the average particle size of the powder, the size of the particle size and the difference of the particle size are all the important factors that influence the homogenization and mixing of the powder.
First, the particle size of the powder
       1, Particle size
Powder particle size represents the size of individual powder particles, expressed in powder diameter. General units with microns (μm); also commonly used to represent the number of heads. Most of the powder particle shape is irregular, for an irregular particle, the particle size of the determination of different methods, the physical significance of different measured values ​​are also different.
        2, The equivalent particle size
 Equivalent Particle Size Definition: When a certain physical behavior or physical parameter of an irregular body particle is the same or similar to a certain sphere of the same material, we call the diameter of the sphere as some equivalent particle of the irregular particle path. When the reference physical or physical parameters are different, measuring the same irregular body particle may yield multiple equivalent particle size values.
       3, Practical particle size
The actual application of the particle size is not very accurate description, because the actual situation of the powder is very complex (such as powder particle shape, powder surface shape, calculation methods, etc.), detection means difficult to achieve the precise purpose. Therefore, the practical application of the particle size used is only an approximation of the particle size.
        4, The average particle size and normal distribution of powder
The basic characteristics of the particle size is the normal distribution centering on the average particle size. Namely the largest number in the vicinity of the average particle size, as the particle size changes fewer and fewer as shown below.
Usually we use the particle size is the average particle size of the powder.
        5, particle size representation
           ① Particle size in microns (μm) as a unit of its size.
           ② Particle size with the mesh as a unit that size. Commonly used in the practical sieve to sort the powder, and sieve pore size is expressed in terms of mesh, so we also commonly used mesh that the size of the particle size.
           ③. Particle size of the two units: the conversion between micron and mesh
           50 mesh = 300 microns
          100 mesh = 150 microns
          500 mesh = 28 microns
         1000 mesh = 14 microns
         2000 mesh = 6.5 microns
         5000 mesh = 2.7 microns
        Other units can approximate the analogy.
Second, the measurement of particle size
        1, screening method: general powder materials, commonly used screening method. Sieve determination of powder, is the material through the mesh size of a different set of sub-sample size, determination of the percentage of various particle size. For example: need 200 mesh powder can choose 150 mesh sieve, 250 mesh sieve; need -200 mesh powder, select 200 mesh sieve directly.
     2, Electron microscopy: particle size smaller particles, ultra-fine powder, the general use of optical microscopy. Microscopy is the only way to observe the particle size of particles, but also to measure the particle size, scientists regarded as a more perfect way.
Third, the impact of particle size on the mixing
       The average size of the powder is also an important factor affecting the mixing:
       1, The powder particle size close to the powder mixture easy to achieve the purpose of mixing:
       This is because under the same conditions of other conditions, the same particle size of the powder during the movement is not likely to cause segregation segregation, so that the powder is uniformly mixed smoothly.
       2, Large differences in particle size powder difficult to achieve the purpose of mixing the powder:
        This is because the smaller the particle size of the powder, the finer the powder, the powder tends to float when mixed. Conversely, the larger the particle size of the powder, the more coarse the powder, the lower the tendency of the powder to mix when mixing. Resulting in segregation, mixing work to bring difficulties.
        3, Ultrafine powder (very small particle size powder) is not easy to mix the problem:
        When mixed powder has a particle size of less than 1000 mesh when we call the super-fine powder, the superfine powder because of its very floating ability, in the mixing device with a small kinetic energy can float to mix difficult.
       The cause of the problem and solutions:
        Ultrafine powder generally refers to the powder particle size less than 1000 mesh or 2000 mesh powder, for a single powder, when the average particle size is small to a certain extent, its physical characteristics will be a huge change, the original Will not float to become floating. After the particle is refined, the original gravitation to its inherent gravity is insignificant. Without the gravity, it can restrain its movement activity. The powder adsorbs each other, and the dough and the static electricity will be highlighted and the mixture will be difficult to carry out.
            ① Reduce the speed of the mixing equipment, increase the filling rate, packed into 85% of the mixing container, try to avoid the floating movement of ultra-fine powder, installed more in order to reduce the possibility of ultrafine powder floating to increase the pressure between the powder .
           ② Selection of dual-motion mixer, the use of its containers and leaf co-movement with the co-existence of the role of floating in the container above the ultra-fine powder pressed into the theme of the powder, so as to solve this problem.