In powder production—especially in the preparation of ultrafine powders—overgrinding and agglomeration are two common challenges. Overgrinding refers to a situation in which qualified fine particles continue to be ground. This leads to energy waste, a broader Partikelgröße distribution, and, in some cases, degraded product performance. Agglomeration occurs when ultrafine particles attract each other through van der Waals forces, electrostatic forces, or liquid bridge forces. As a result, secondary particles are formed, which negatively affect powder dispersion, flowability, and end-use performance. These issues not only reduce production efficiency but also increase energy consumption and operating costs. As a highly efficient dry classification device, the air classifier can effectively address these problems by precisely separating particles.
Causes of “Overgrinding” and “Agglomeration” in Powder Production
During mechanical grinding processes (such as ball milling or Strahlmahlen), particles become progressively finer as grinding time increases. However, once a certain fineness is reached, a grinding equilibrium phenomenon appears: while fine particles increase, ultrafine particles begin to agglomerate. The rate of particle size reduction gradually balances with the rate of agglomeration. If grinding continues beyond this point, particle size may no longer decrease and may even increase due to agglomeration.
Meanwhile, if qualified fine powder is not separated in time, it repeatedly re-enters the grinding zone, leading to overgrinding.
These phenomena are particularly prominent in the production of ultrafine powders such as Kalziumkarbonat, quartz, and silicon carbide, significantly affecting product quality and throughput.
Working Principle of an Air Classifier
Ein Windsichter separates particles based on the combined effects of airflow and centrifugal force. Common types include turbo (dynamic) air classifiers and cyclone-based systems. A typical turbo air classifier consists of a feed dispersing plate, a classification wheel (rotor cage), guide vanes, and a secondary air inlet.
Operating principle:
Material enters the classification zone with the airflow. Under the action of centrifugal force generated by the high-speed rotating classification wheel and the drag force of the airflow, fine particles pass through the gaps of the classification wheel and are collected, while coarse particles are thrown toward the housing wall and fall back to the grinding zone. The secondary airflow further washes the coarse fraction, dispersing entrained fines and reducing carryover.
By adjusting parameters such as rotor speed and airflow rate, the cut size can be precisely controlled (typically D97 ≈ 3–150 μm), achieving a narrow particle size distribution.
Wie Luftklassierer Solve “Overgrinding” and “Agglomeration”
Preventing Overgrinding
- An air classifier is connected in series with grinding equipment (e.g., ball mills or jet mills) to form a closed-circuit system. After grinding, material enters the classifier; qualified fine powder is immediately separated and collected, while coarse particles return to the grinding zone for further size reduction. This prevents fine particles from being repeatedly ground, avoids overgrinding, improves grinding efficiency, and reduces energy consumption.
- Compared with open-circuit systems, closed-circuit systems significantly reduce excessive grinding and produce a narrower particle size distribution.
Mitigating Agglomeration
- Airflow dispersion and secondary air washing during classification help break up weak agglomerates and improve powder dispersion.
- Timely separation of fine particles prevents prolonged residence in the grinding zone, reducing the likelihood of agglomeration.
- Modern air classifiers feature optimized designs (such as improved feed dispersers and turbulence cones) to further enhance dispersion and reduce the “fish-hook effect” (misclassification of fine particles as coarse).
In addition, negative-pressure operation and dust-free system design ensure clean and environmentally friendly production.
Application Advantages and Key Considerations
Air classifiers are widely used in nichtmetallische Mineralien, chemicals, pharmaceuticals, and battery materials. Their main advantages include:
- High classification accuracy with efficiencies of 60%–90%
- Capability for multi-stage classification to produce multiple particle size fractions
- Energy-saving, low-noise operation, and easy control
In practice, operating parameters (such as rotor speed and airflow) should be optimized according to material properties (e.g., moisture content and flowability). If necessary, additives can be used to further prevent agglomeration.
Building a closed-circuit grinding system with an air classifier is one of the most effective ways to solve overgrinding and agglomeration problems in powder production. It improves product quality and yield while enabling green and efficient manufacturing, driving the powder industry toward higher precision and refinement.
Abschluss
In the field of powder processing, Qingdao Epic Powder Machinery (EPIC Powder) is a professional supplier of ultrafine powder processing equipment. Its advanced air classifiers include the HTS series turbo classifiers , the ITC series vertical classifiers and CTC series air classifiers. These systems are renowned for high classification accuracy, narrow particle size distribution, and excellent dispersion performance.
By integrating air classifiers into closed-circuit grinding processes, EPIC Powder effectively eliminates overgrinding and agglomeration. At the same time, the system achieves lower energy consumption, improved product quality, and environmentally friendly production.
Choosing EPIC Powder’s classification equipment helps manufacturers move toward a more efficient and refined era of powder processing.
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— Gepostet von Emily Chen