Air deflector-augmented cyclone design for superior powder coating particle-size distribution and performance

Particle-size distribution (PSD) is a crucial parameter in the powder industry. Powder coating, a prime example of the powder industry, has been commonly used in many fields due to its zero volatile organic compounds emissions. However, current powder coatings face challenges in achieving the same level of thinness and smoothness as liquid-borne paints. A wide PSD negatively influences powder and film performance in flowability, sieving, spraying, and coating uniformity. Powder coating typically exhibits a wide PSD, characterized by a span between 1.6 and 2.0. To improve the performance of powders and films, this study proposed and investigated a method to narrow the PSD of powder coating fabricated by an air classifying mill. This method employed air deflectors (AD) at the bottom of the cyclone to introduce a stream of spinning secondary air, which removes the ultrafine fraction of the powder. Various geometrical configurations of the AD, including shape and thickness, were experimentally tested. It was found that the span of the polyester powder coating was reduced from 1.62 to 1.42 for linear AD and from 1.62 to 1.35 for convex AD. Furthermore, the powder flowability, film smoothness, and gloss were enhanced after narrowing the PSD. The AD design effectively heightened the cyclone classification capability, eventuating superior powder flowability and film performance.