The rotor speed of a turbo air classifier is the primary adjustable parameter that defines the cut particle size for kaolin powder. It directly governs centrifugal force on particles, determines classification sharpness, and strongly influences classification efficiency and final PSD of kaolin products. In kaolin ultrafine closed-loop grinding lines, rotor speed is the core tuning knob for switching between different product grades.
1. Determine the cut point (D97 / D50)
The classifier rotor spins and generates centrifugal force outward, while the circulating airflow creates drag force toward the center.
- Higher rotor speed: Greater centrifugal force. Only very fine kaolin particles have enough air drag to pass through the turbine blades into the finished product. This results in a finer cut size, smaller D50 and D97.
- Lower rotor speed: Weaker centrifugal force. Larger particles can follow airflow through the rotor, so the cut point becomes coarser, producing bigger particle size kaolin powder.
For kaolin processing, small adjustments in rotor speed can shift the cut size significantly, especially for ultrafine grades such as D97=5–10 μm used in paper coating.
2. Control classification sharpness and PSD width
Rotor speed affects how cleanly coarse and fine fractions are separated, which decides whether you get a narrow PSD kaolin.
- When speed is properly matched with airflow: The separation boundary is sharp. Few oversized particles leak into finished powder, and fewer fine particles are trapped with coarse return material.
- If speed is too high with unchanged airflow: Over-separation occurs. Many qualified fine kaolin particles are thrown back to the mill as coarse material, reducing yield and increasing circulation load and energy consumption.
- If speed is too low: Coarse kaolin particles can penetrate the rotor, leading to high oversized residues and broad PSD in final products.
3. Impact classification efficiency and system throughput
Rotor speed changes the solid-gas balance inside the classification chamber.
- Excessively high rotor speed increases particle collision inside the turbine area. Kaolin, which easily forms soft agglomerates, may re-agglomerate, lowering fine particle recovery and classification efficiency.
- Too low rotor speed may raise throughput at the cost of product quality, since coarse contaminants escape into finished powder.
- For each target kaolin grade, there is an optimal rotor speed window to balance classification efficiency, production capacity and PSD quality.
4. Match with secondary air and fan airflow
Rotor speed cannot be adjusted independently. It must coordinate with main fan airflow and secondary air washing:
- After raising rotor speed for finer kaolin, airflow usually needs to be increased to maintain stable solid-gas ratio.
- Secondary air helps break kaolin agglomerates; it removes fine powder stuck on coarse particles so rotor separation works correctly. Without proper secondary air, changing rotor speed alone will not achieve expected PSD.
5. Equipment operation limits
Rotor speed has mechanical boundaries. Maximum speed is restricted by rotor material, dynamic balance and safety limits. Operating beyond rated speed risks vibration, blade wear and powder buildup, which will destabilize long-term kaolin production.
Rotor speed is the main parameter to set cut size for kaolin in turbo air classifiers. Higher speed gives finer kaolin products; lower speed produces coarser powder. It also controls classification sharpness, PSD span, classification efficiency and system circulation load. Operators must tune rotor speed together with fan airflow and secondary air volume, rather than adjusting it alone, to get stable, narrow PSD kaolin powder with acceptable energy consumption and yield.
