Silicon carbide powder is a kind of superhard material, which is widely used as an abrasive tool, resin polishing grinding wheel and diamond polishing grinding wheel, etc. Silicon carbide itself has high hardness, to make its particle size distribution reach the limited range, it is very difficult for the grinding and grading of silicon carbide powder, and with the development of industrial production, scientific and technological progress and the increasing market demand, Higher requirements are put forward for the production of SIC powder, including high productivity, low energy consumption, narrow particle size distribution and low pollution. The jet mill is suitable for ultrafine grinding of superhard materials such as silicon carbide, diamond and cubic boron nitride.
The principle of the air mill is that under the action of high-speed air flow, the particles are crushed through the impact collision, friction and shear between the particles or the particles and the target. Air flow grinding has the following characteristics:
(1) The high-speed air flow will produce a high speed on the particles, the impact strength of the particles is large, and the ultrafine powder of micron or even sub-micron level can be obtained;
② The particle product has high purity and small pollution;
③ The obtained product has narrow particle size distribution, smooth particle morphology and good particle dispersion;
④ The temperature of the air flow from the nozzle will be reduced because of the throttling effect, which can be used to crush heat-sensitive materials.
At present, the air crushing and grading equipment is an irreplaceable ultra-fine processing equipment in the silicon carbide powder industry, taking the air crushing and grading system as an example, the air crushing and grading process is as follows:
(1) The effect of grading wheel and system air volume on silicon carbide powder products
According to the principle of classification, the classification of silicon carbide powder obviously needs to improve the speed of the grading wheel, the level of the grading wheel speed determines the size of the centrifugal force field, and the size of the system air volume affects the size of the resistance of the particles, in principle, to make the particles obtain as much centrifugal force as possible and the least resistance.
In order to obtain the precise classification of SIC powder, it is not economical to simply increase the classification wheel speed, and it is necessary to reasonably control the proportion of auxiliary air and main air volume. When the system is running with relatively small air volume, adjusting the classification wheel speed is more sensitive to the change of particle size. However, the reduction of the total air volume will lead to a reduction in the processing capacity, which is obviously uneconomical, so the system should weigh the advantages and disadvantages and choose the best operating parameters.
(2) The impact of the feeding method and dispersion of raw materials on product performance
The commonly used vibration feeders and spiral feeders not only have poor uniformity and serious wear, but also agglomerate and caking directly affect the classification effect. In the production, the method of vibration feeder + shut-off fan + long tube gas conveying can be used to ensure that the powder entering the classification chamber is uniform and quantitative feeding. The introduction of three air by the grading outdoor jacket further assists in the dispersion of fine powder, which makes the production run stable and easy for workers to operate, while also ensuring the quality of the product. At the same time, ensuring the proper gas-solid concentration and good dispersion of raw materials is the key to improve the classification efficiency.
(3) Product performance
The silicon carbide powder products produced by the air mill and grading system can fully meet the particle size distribution requirements of W14, W10, W7, WS and other fine powder products in the GB/T 2477-83 standard used in China's abrasive industry. Moreover, it meets the particle size distribution requirements of F1000, F1200, F2000 and other products in JIS 86001-1987 industrial standard for the abrasive powder used for consolidation abrasives, and the fine powder yield reaches 85%.
For the ultrafine grinding of silicon carbide, the air mill has the advantages of high precision, no wear, high yield and so on, and has been widely used in many superhard material manufacturers at home and abroad.
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