Electronic Thesis and Dissertation Repository


Master of Engineering Science


Chemical and Biochemical Engineering


Jingxu Zhu


Powder coating is a dry coating technology, which has several advantages over conventional liquid coatings. However, wider applications were limited by its inferior surface finish and increased film thickness. Making powder finer (fine powder technology) can provide much better surface appearance and smaller film thickness comparable to liquid coating, but it’s much more difficult to produce fine powder products with narrow particle size distributions than coarse powder. Another issue that restricts the applications is its electrostatic spraying method, which limits the applications mainly to be with conductive substrates, like metals.

In this study, to ensure a narrow particle size distribution of fine powder products, nine kinds of modification were conducted with the classifier of widely-used air classifying mill (ACM) by changing the air flow through it. For each kind of modification, the experiments were conducted under five operating conditions and were repeated for three times. According to the results of 150 samples, the particle sizes and particle size distributions of products were greatly affected by the classifier configuration. All nine kinds of modification showed better performance than the original classifier on narrowing particle size distributions, without compromising any collection efficiency.

In addition, non-conductive plastics were employed as substrates in fine powder experiments, using two popular commercial coating powders. Results showed that lowering the particle sizes and narrowing particle size distributions of coating powders contributed to better surface finishes on the workpieces. Besides, due to the poor flowability of fine powder, different amounts of flow additives were used with fine coating powders, and the optimum amount of additives was selected considering the effects on both flowability and surface quality. Furthermore, utilizing voltage was proven to be an effective method assisting pre-heating to increase transfer efficiency.