Seeking advice on particle size control in air jet milling
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This post was last edited by Mo You on 2024-5-8 at 16:48. Hello, experts. I have been working with air jet milling for some time now, and I have encountered a problem in my current workplace that I would like to discuss with you: For graphite products, when using an air jet mill, increasing the inlet pressure results in an increase in the D50 particle size, while decreasing the inlet pressure leads to a decrease in the D50 particle size. I seek your advice!
During air jet milling, the adjustment of the inlet pressure affects the particle size distribution. As pressure increases, the greater force usually leads to more intense particle collisions, resulting in a decrease in particle size ； However, if the pressure is too high, it may lead to a decrease in equipment efficiency, or the particles may be discharged without being fully crushed due to inertia, thereby increasing the D50 particle size. When the intake pressure is reduced, collisions between particles decrease, but it may be more conducive to the thorough crushing of the particles. It is recommended to adjust the pressure gradually and carry out optimized control in combination with other parameters (such as feed rate, temperature, etc.). .
The pressure adjustment is not significant; the pressure after adjustment is only around 6 kilograms. Generally, this pressure is considered low for air jet milling
At lower inlet pressures (around 6 kilograms), if the D50 particle size decreases, it may be because this pressure is more suitable for using the equipment to grind graphite to the desired particle size. Too low a pressure may not be sufficient to break the particles, while an appropriate pressure can enable the particles to be crushed more effectively during collisions. It is recommended to continue fine-tuning the pressure, while also monitoring other operating conditions and the supply status of graphite, in order to achieve the best gas-flow crushing effect. .
Hello, the owner. My current company specializes in airflow equipment. There are many factors that affect the particle size produced by air jet mills; if the pressure of the air supply used by the equipment is too high, it may carry some of the material along with it. Generally, we set the pressure for testing at 0.7 Mpa and then adjust other relevant parameters. For example, uneven feeding and the particle size of the feed can have an impact. Factors such as the frequency of the classification wheel, the frequency of the fan at the rear end, and whether there are multiple grading units (such as cyclones) also play a role. The height-to-diameter ratio of the classification wheel as well as the number of teeth on it can all affect the air pressure required; it’s not necessarily the case that higher air pressure always leads to better results. You can try various optimal parameters depending on your equipment, or you can contact the manufacturer of your equipment for on-site assistance. In one recent project I was involved in regarding the crushing of expanded graphite, the requirement was to achieve D50=10μm and D90<30μm. By comparing the production rates under different air pressure levels, it was found that the production rate was twice as high at 0.7 MPa compared to 0.4 MPa. At 0.7 MPa, the fan operated at 28 Hz while the classification wheel operated at 40 Hz; at 0.4 MPa, the fan still operated at 28 Hz but the classification wheel operated at 43 Hz
High inlet pressure means larger particle sizes; only a longer residence time can result in smaller particle sizes
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I agree with the last point regarding residence time, but for the inlet pressure mentioned earlier, the particle size is definitely larger – no, there are many factors that influence this