In recent years, research and applications of powders have shown that only when the particle size distribution meets specific requirements can materials fully exhibit their optimal performance. Against this background, powder classification technology has emerged and gradually become the core of powder processing technology.
Specifically, powder classification refers to the process of separating particle groups into two or more size grades based on differences in settling velocity within the same medium. These differences arise from particle size, density, shape, or surface physicochemical properties. The key to powder classification technology lies in dispersion and separation:
- Dispersion means that the material entering the classifier should be as dispersed as possible, creating spatial distance between particles.
- Separation refers to completing the classification within a limited residence time under airflow, allowing particles of different sizes to exit from different outlets.
Fine Classification Types and Main Functions
Based on the classification medium, fine classifiers can be divided into two main categories:
- Dry classifiers using air as the medium – mainly rotor (turbine) air classifiers.
- Wet classifiers using water or oil as the medium – such as ultrafine hydrocyclones or horizontal spiral sedimentation centrifuges.
The main functions of fine classification are:
- Ensuring that the particle size distribution meets application requirements.
- Improving the efficiency of ultrafine grinding.
For example, many industries require not only specific mean or median particle sizes of non-metallic ultrafine powders but also strict particle size distributions. Grinding equipment such as ball mills, vibration mills, or dry stirred mills usually produce powders with broad distributions. Without classification, it is difficult to meet user demands.
In ultrafine grinding, prolonged grinding leads to both finer particles and increased agglomeration. At a certain point, particle size reduction balances with agglomeration – the so-called “grinding equilibrium.” Continuing grinding then fails to reduce particle size further, and may even increase it. To enhance efficiency, qualified fine powders must be separated promptly, preventing overgrinding and agglomeration. This explains why fine classification is essential in ultrafine grinding processes.
Performance Features
- Suitable for dry classification of micron-sized products, covering spherical, flaky, irregular, and even density-differentiated particles.
- Product fineness can reach D97 = 3–150 μm, continuously adjustable.
- Classification efficiency ranges from 60–90%, depending on powder properties and content of in-spec particles.
- High-speed classifier wheel ensures precise cut points.
- Multi-stage classifiers can be connected to produce multiple size ranges simultaneously.
- Can be integrated with grinding equipment such as ball mills, vibration mills, or Raymond mills for closed-loop circuits.
- Automated control with real-time status display; user-friendly operation.
- Negative-pressure operation with dust emissions below 40 mg/m³; noise ≤75 dB(A) with silencing measures.
Advantages of Air Classifiers
- Low energy consumption – up to 50% lower than other horizontal or vertical classifiers.
- High efficiency – classification efficiency up to 50% higher at the same throughput.
- High precision – eliminates oversized particles and residues.
- Low wheel speed – extends service life 5–8 times compared to traditional classifiers when processing hard powders.
- High output – large machines can reach 50 t/h.
- Flexible structure – customizable for specific applications.
- Compatibility – works with ball mills, Raymond mills, impact mills, and jet mills.
- Clean production – negative-pressure operation prevents dust pollution.
- High automation and stability – easy and reliable operation.
Application Fields
- Hard materials: SiC, alumina, boron carbide, zirconia, garnet, zircon sand, diamond.
- Non-metallic minerals: quartz, graphite, kaolin, calcium carbonate, mica, barite, mullite, wollastonite, talc, pyrophyllite.
- Chemicals: aluminum hydroxide, silica gel, dyes, epoxy resins, additives.
- Food & pharmaceuticals: pollen, hawthorn, pearl powder, Ganoderma, vegetable powders, herbal medicine, health products, cosmetics, antibiotics.
- Metal powders: aluminum, magnesium, zinc, tin, copper.
- Other materials: ceramics, refractories, electronic materials, magnetic materials, rare earths, phosphors, toner.
Conclusion
Powder classification technology is essential for modern materials processing, ensuring narrow particle size distributions and improving grinding efficiency. With advanced solutions such as air classifiers, industries can achieve high precision, high efficiency, and eco-friendly production. Epic Powder provides state-of-the-art classification equipment and customized solutions, helping customers optimize powder performance across energy, chemicals, minerals, and advanced materials industries.
