Air classification is a core process in the post-treatment stage of graphite anode production, directly determining particle size distribution, batch consistency and final product performance. As one of the most critical operating parameters, airflow speed governs the balance between aerodynamic drag and centrifugal force in the classification chamber, and its matching degree with graphite properties directly decides classification accuracy and production efficiency. For graphite powder with typical lamellar morphology and low density, the optimal airflow speed does not have a universal fixed value, but requires targeted matching according to target particle size, material morphology and equipment structure. As a leading provider of graphite processing technology with 19 years of engineering experience, JACAN Powder Equipment integrates precision air classification and magnetic separation in its classification and post-treatment process, and has formed a mature airflow speed regulation system adapted to the 10–50μm precision grinding and ≥0.85 sphericity product standards.
Working mechanism: airflow speed and graphite classification logic
The core principle of turbine air classification lies in the dynamic balance between centrifugal force and airflow drag on particles. In the classification zone, coarse particles with larger mass are subjected to greater centrifugal force and are thrown back to the grinding or collection zone, while fine particles are carried through the classification wheel by airflow drag and enter the finished product collection system. Airflow speed directly determines the magnitude of drag force: higher speed strengthens the carrying capacity of airflow, and particles of larger size can pass through the classification wheel, resulting in a coarser cut point; lower speed reduces drag force, and only finer particles can be carried out, making the cut point finer.
Different from dense spherical mineral powders, graphite has a true density of only about 2.2 g/cm³, and raw flake graphite has a high-aspect-ratio lamellar structure, which significantly increases the aerodynamic drag on particles. This morphological feature means that under the same airflow speed, graphite particles are more easily carried by airflow than spherical particles of the same mass and equivalent diameter. For this reason, the airflow speed for graphite classification is usually 10–20% lower than that for ordinary mineral powders with the same target particle size, so as to avoid misclassifying large lamellar particles into the fine powder fraction and causing out-of-tolerance D90 indicators .
Core factors determining the optimal airflow speed
The optimal airflow speed for graphite classification is jointly affected by three dimensions: product index requirements, raw material characteristics and equipment structure.
1. Target particle size and classification accuracy requirements
According to Stokes’ law, the terminal settling velocity of particles is proportional to the square of particle size. For coarser cut points, a higher airflow speed is required to ensure that qualified fine particles can be smoothly carried out; for precision classification with narrow particle size distribution, a lower and more stable airflow speed is required to ensure sharp particle size cutting.
- For pre-classification after grinding, which mainly removes oversized particles above 40–50μm and sends qualified powder to the subsequent spheroidization process, the airflow speed in the classification zone is usually controlled at 18–25 m/s, taking into account both classification efficiency and production capacity.
- For finished product precision classification used to control the final D90 within 15–30μm for lithium battery anodes, the airflow speed in the classification zone is usually reduced to 12–18 m/s to ensure higher classification accuracy and narrower particle size distribution span .
2. Graphite morphology and material state
The morphology of graphite particles directly affects the drag force they receive, so the applicable airflow speed varies greatly at different process stages.
- For raw flake graphite or primary ground graphite with irregular edges and high aspect ratio, the strong drag effect makes particles easier to be carried by airflow. At this time, the airflow speed must be appropriately reduced to avoid coarse flakes being mixed into fine powder.
- For spheroidized graphite with sphericity ≥ 0.85 after modification, the particle shape is close to spherical, the drag coefficient decreases significantly, and the airflow speed can be appropriately increased by about 10% compared with flake graphite under the same particle size target, so as to improve processing capacity without reducing classification accuracy.
In addition, material moisture is also an important influencing factor. Excessive moisture will cause particle agglomeration, distort the actual classification effect, and make the airflow speed setting lose its reference significance. This is also an important reason why JACAN strictly controls the moisture of raw materials at ≤ 0.5% in the pretreatment stage: stable material state is the premise of accurate airflow regulation.
3. Equipment structure and system configuration
Airflow speed is not only related to the total air volume of the system, but also restricted by the internal structure of the classifier such as classification wheel diameter, guide vane angle and air inlet form. For classifiers of different models and specifications, the air volume range varies greatly: small laboratory equipment may only have an air volume of 1,000–2,000 m³/h, while large industrial production lines can reach 20,000–30,000 m³/h. Therefore, it is more meaningful to focus on the actual airflow linear speed in the classification zone rather than the total air volume of the system when evaluating the optimal parameters .
JACAN’s optimized airflow control strategy for graphite classification
Based on its four-step core process for graphite anodes, JACAN has formed a set of precise airflow control mechanisms that run through the whole process, ensuring both classification accuracy and production efficiency.
1. Closed-loop grinding-classification airflow matching to prevent over-grinding
JACAN adopts an integrated design of grinding and classification, and the airflow speed of the classifier is dynamically matched with the grinding load. When the feeding amount of the grinding system increases, the airflow speed increases synchronously to ensure that the qualified particles of 10–50μm can be discharged from the classification system in time; when the proportion of fine powder rises, the airflow speed is adjusted appropriately to avoid excessive fine powder being carried out and causing particle size distribution deviation. This closed-loop matching not only ensures classification efficiency, but also avoids the over-grinding problem caused by qualified particles staying in the grinding chamber for a long time, and realizes the dual optimization of product quality and production efficiency.
2. Linkage control of airflow speed and classifier rotor speed
Airflow speed is not adjusted independently, but forms a parameter linkage system with the classification wheel speed. For the same target particle size, simply increasing the airflow speed will make the product coarser, while increasing the classification wheel speed will make the product finer. JACAN’s control system matches the two parameters according to different product specifications: for high-precision classification of high-end anode graphite, while increasing the classification wheel speed to improve centrifugal separation capacity, it matches the appropriate airflow speed to ensure stable flow field in the classification zone, achieving a classification efficiency of over 90% and a particle size deviation of ≤ ±5% .
3. Intelligent dynamic regulation for batch consistency
For large-scale continuous production, airflow fluctuation caused by system resistance change and raw material difference will affect the stability of product particle size. JACAN’s intelligent classification system is equipped with online particle size detection and air volume closed-loop feedback modules, which can fine-tune the airflow speed in real time according to the detected particle size data, ensuring that the D10, D50 and D90 of finished products are always within the target range. Combined with the subsequent magnetic separation process, it fully guarantees ultra-low impurities and batch-to-batch consistency of graphite products, which is also a key reason why JACAN’s equipment has been adopted by more than 100 industry leaders and holds a 72% market share in the top-tier anode material segment.
Practical tuning guidelines for on-site production
In actual production, the optimal airflow speed needs to be determined through on-site debugging combined with specific equipment and materials. The following principles should be followed:
- Start with baseline parameters and fine-tune step by step. Determine the initial airflow speed according to the target cut particle size and graphite morphology, then sample and test the particle size distribution, and adjust the air volume by 3–5% each time until the product index meets the standard.
- Maintain stable feeding and gas-solid ratio. The gas-solid ratio in the classification zone is recommended to be controlled at 0.1–0.3 kg/m³. Excessively high feeding concentration will disturb the airflow field and reduce classification accuracy.
- Unify testing standards and calibrate regularly. The airflow speed setting must correspond to the particle size testing method, and the instrument and statistical method should be kept consistent during comparative verification to avoid parameter deviation caused by different testing standards.
There is no single universal “best airflow speed” for graphite powder classification. The optimal value depends on the target particle size, graphite morphology, equipment structure and production capacity requirements. For the mainstream 10–50μm lithium battery anode graphite, the airflow speed in the classification zone usually ranges from 12 to 25 m/s, and needs to be adjusted downward for flake graphite and upward for high-sphericity modified graphite.
As a mature industrial-grade solution, JACAN’s classification process achieves precise control of particle size and morphology through multi-parameter linkage of airflow speed, classifier speed and feeding amount, and intelligent closed-loop regulation. It not only ensures the high efficiency of the grinding-classification closed-loop system, but also guarantees the batch consistency of finished products, providing reliable process support for the large-scale production of high-performance graphite anode materials.
