Calibration of a turbo air classifier is the systematic process to match operating parameters with target PSD, so that kaolin finished powder maintains stable D50, D97 and narrow span during continuous production. Proper calibration eliminates drift caused by powder buildup, rotor wear, airflow fluctuation or raw material variation. Calibration follows a stepwise workflow: pre-calibration inspection, baseline test, parameter tuning, verification, and formal locking of operating setpoints.
1. Pre-calibration inspection and preparation
Before parameter calibration, inspect mechanical and system conditions to avoid false calibration results.
- Check the classifier rotor: inspect blade wear, powder caking and dynamic balance. Worn or fouled rotor blades distort the internal flow field and make calibration invalid. Clean powder deposits on rotor, chamber wall and secondary air channels.
- Verify all air ducts, seals and soft connections. Air leakage changes actual airflow and negative pressure, leading to unstable cut size. Repair air leaks before calibration.
- Confirm fan, damper and pressure transmitters work normally. Calibrate pressure gauges and flow sensors.
- Stabilize raw kaolin feed: fix ore source, moisture and pre-treatment process. Material property changes will interfere with PSD test results.
- Prepare particle size test equipment (laser particle size analyzer) and sampling ports at finished product and return coarse material outlets.
2. Establish baseline operating conditions
Run the closed-loop grinding system under steady state before sampling.
- Set a fixed feeding rate and let the whole line run for sufficient time to reach thermal and mass balance. Avoid sampling during startup or load fluctuation.
- Record baseline parameters: rotor speed, main fan frequency, secondary air damper opening, system negative pressure, solid-gas ratio, circulating load.
- Take paired samples: finished kaolin powder and coarse return material. Test PSD, record D50, D97 and span. This dataset becomes the baseline reference.
3. Iterative parameter tuning for target cut size
Tune rotor speed and airflow step by step, one variable at a time, to avoid confusing effects.
- Rotor speed adjustment: Rotor speed is the primary cut-size knob. If finished powder is too coarse (high D97), increase rotor speed moderately. If product is too fine with low throughput and high circulating load, reduce rotor speed. Make small incremental changes instead of large jumps.
- Secondary air fine-tuning: Adjust secondary air to deagglomerate kaolin clusters. Insufficient secondary air leaves fine particles attached to coarse fractions, causing misclassification. Too much secondary air disturbs the classification flow field.
- Main fan airflow matching: After changing rotor speed, adjust induced draft fan frequency to maintain target solid-gas ratio. Higher rotor speed usually needs higher airflow to carry fine kaolin out.
- Re-stabilize the system after each adjustment, wait for 10–20 minutes, then sample and test PSD again. Repeat until PSD meets specification.
4. Verify classification sharpness and circulating load
Qualified calibration is not only about finished product PSD; return material quality must also be checked.
- Check return material PSD. If return material still contains large amounts of fine kaolin, the classifier is losing fine particles, which causes over-grinding and high energy consumption. Increase secondary air or slightly adjust rotor speed.
- Confirm circulating load stays within the design window. Abnormally high circulating load indicates over-separation.
- Run continuous stability test for several hours. If PSD remains consistent during the test, the calibration is successful.
5. Lock operating setpoints and build a parameter recipe library
Once target PSD is achieved:
- Record the full recipe: raw ore type, feed rate, rotor speed, fan frequency, secondary air opening, negative pressure and temperature. Save this recipe for this specific kaolin grade.
- Mark alarm thresholds for drifting parameters: rotor vibration, pressure deviation, feed fluctuation.
- Create a regular re-calibration schedule. Recalibrate after rotor overhaul, blade replacement, major cleaning, raw ore switching or when PSD trend drifts.
6. Routine post-calibration monitoring
- Take periodic offline PSD samples. Install online particle size monitoring for real-time trend tracking in high-end production lines.
- Track signs of drift: gradual rise of D97, wider PSD span or fluctuating product gloss/viscosity. These signal rotor fouling, blade wear or air leakage requiring re-calibration.
Classifier calibration for stable kaolin particle size starts with mechanical cleaning and leak inspection, followed by steady-state baseline sampling, iterative fine adjustment of rotor speed, secondary air and fan airflow. Each parameter change requires stabilization and PSD verification. After meeting target PSD, lock the complete parameter recipe and schedule periodic re-calibration. This procedure minimizes PSD fluctuation and keeps consistent kaolin quality for paper coating, plastic filler and ceramic applications.
