Investigation of the atomization of waterborne automotive coatings
Coating of car bodies is usually performed via atomization using high-speed rotary bell atomizers. This application technique provides high transfer efficiency, uniform film thickness and high quality appearance at short process time. Since coating layer quality depends on atomization, it is essential to investigate this process. Our research work focuses on characterizing the disintegration of ligaments at the atomizer bell edge and pulsations occurring in this process. Therefore, atomization is recorded by a high-speed camera. Length and thickness of the ligaments are analyzed from the resulting images using a customized MATLAB-code. Droplet size is determined using Phase-Doppler Anemometry. Beyond, we investigate the influence of application parameters and coating composition (pigmentation, thickening concept) on shear and elongational flow behavior as well as characteristic features of atomization in a quantitative manner. A series of aqueous acrylate-type thickener solutions is used as model system. Additionally, commercial paint systems are investigated. The collected data will be used to develop a dimensional analysis based model allowing for prediction droplet size from rheological properties and application parameters. This project is carried out in collaboration with the group of Prof. Erhard, TU Dortmund and BASF Coatings GmbH.