Reducing comminution over-grinding of powder coatings with modified grinding pins in an air classifier mill

Air classifier mill (ACM) is widely used in powder coating and mineral comminution process. One of the problems typically presenting in ACM is over-grinding, which leads to high energy consumption and broad particle size distribution (PSD). To decrease the excessive amount of fine particles in the products, 6 configurations of grinding pins with ditches in the impact surface were used in the experiments. The width and depth of ditches varied from 1.35 mm and 1 mm to 4.75 mm and 3 mm, respectively, while the interior angles in the ditches are the same. The particle size and PSD show that the ditches on the grinding pins have significant effect on the D₁₀ values and the particle size span. The deepest and widest ditches (P4) result in largest D₁₀ and smallest span in this study. The D₁₀s of products ground by P4 increase by 24.1% for fine powder (D₅₀ = 25 μm) and 16.0% for coarse powder (D₅₀ = 33 μm), while the span decreases by 6.9% (D₅₀ = 25 μm) and 6.4% (D₅₀ = 33 μm) compared to regular cylindrical pins (PC), respectively. Meanwhile, it is found that the P4 configuration improves the energy utilization efficiency by 7.6% (D₅₀ = 25 μm) and 3.4% (D₅₀ = 33 μm), compared to that of the original PC pins.