Research On Two-Stage Classification Technology To Abtain Narrow Class Of Fine Powders By Turbo Air Classifier

The rapid progress of modern society and the development of science and technology urgently need narrow particle size distribution, or even a single particle size powders. However, currently, mechanically crushed powders generally have a wide size distribution and cannot meet a narrow class requirement. Thus, a new classification method must be developed. In the paper, the dispersion method of powders was firstly discussed. Secondly, the material distribution in turbo air classifier was studied. In the end, the narrow class classification process of ultrafine powders on two series turbo air classifier system was investigated with ultrafine aluminum oxide powders as raw material.The mechanical dispersion of raw materials was analyzed by the application of the dispersant. And the dispersion of the powder was characterized by the use of microscope observation, settling velocity and sediment volume methods. The results demonstrated that the application of the dispersant can improve the dispersion of talcum powder. The amount of the best insertion was 3%at from the conclusion of microscope observation, settling velocity and sediment volume. Material verification experiment also showed that the powder product yield was high after the use of the dispersant.The spreading plate experimental results showed that the speed increasing of the spreading plate can improve the dispersion of the large particle materials but the dispersion of the small particle materials; particle size distribution of the materials has a greater impact on the material dispersion, the wider range of particle size distribution, the poorer the dispersion. The results of grids number experiment demonstrated that the speed increasing of the spreading plate can improve the dispersion of the large particle materials but the dispersion of the small particle materials; because the materials could be divided into part A and B by two-layers spreading plate which would be scattered in two different positions of classifier, it could effectively improve the separation of powder dispersed in the circular dispersion region.Studies of two-stage classification technology demonstrated that:the highest classification accuracy was obtained with the higher speed difference between two sections of the rotor cage. A higher rotor cage speed and a lower feeding speed will increase the fine powder particles in the amount of-10μm. The "fish-hook" effect was demonstrated to increase with an increase in feeding speed, with more ultrafine particles getting mixed into the coarse product, leading to a decreased fine powder production rate. The best wind speed combination was "high front/low behind". With an increase in the second section of the wind speed, the "fish-hook" effect will be increased. The use of the scatter machine could obviously solute the dispersion of powder, meanwhile, the scatter machine also had a crush function, especially for the large particles.Two-stage series turbo air classifier could achieve ultra-fine powder of the narrow class of classification. By adjusting the parameters of two-stage series classification process, the product powder in -2μm size content was 87.71%,-3μm grain size powder content reached 89.08%,-5μm grain size powder content was 99.19%,10μm powder content in grain size to 100%.