Enhancing powder coating classification accuracy via mesh-modified classifier design and operational parameter optimization

Abstract

The regulation of particle size distribution (PSD) plays a critical role in determining the performance of powder coatings. Given the limitations of current grinding and classification technologies in meeting industrial requirements, a method has been developed for narrowing PSD through modifying the classifier impeller of an air classifier mill (ACM) by installing a wire mesh. It is found that when the particle size is adjusted by individually varying the three operating parameters, the installation of wire mesh on the classifier impeller effectively reduces the particle size span and thus enhances classification accuracy in the ACM. This improvement is attributed to the mesh's increasing resistance to airflow and suppressing macro-scale vortices, generating micro-scale vortices that induce particle rotation which leads to more hydrodynamic-spherical particle characteristics, and further enhancing classification through the mesh's quasi-sieving function. Changes in mesh pore size exert the strongest influence on classification performance when particle size is controlled via impeller frequency adjustment. After mesh installation, the improvement in classification performance is more pronounced for products with larger particle sizes. By quantitatively evaluating the effects of operating parameters and mesh pore size on PSD, it is demonstrated that adjusting classifier impeller and fan frequencies is a more effective strategy for producing powders with a narrow PSD. Through investigation of the combined effects of classifier impeller and fan frequencies, an optimal operating range is identified that minimizes span for a given particle size and delineates the corresponding operating conditions. Finally, the results demonstrate that powders produced with a mesh-affixed impeller exhibit significantly enhanced flowability and improved coating-film appearance compared to powders produced with the original impeller.