Visualization and Measurement of Automotive Electrostatic Rotary-Bell Paint Spray Transfer Processes

In order to improve the transfer efficiency and finish quality in automotive spray painting, a better understanding of the paint spray structure and transfer processes of the electrostatic rotary bell applicators is needed. This paper briefly reviews the current technological challenges and research issues, and then describes the spray atomization, visualization, droplet size, and velocity measurement results of a water-borne paint spray system under various operating parameters. The optical techniques used are copper vapor laser light sheet visualizations and the phase Doppler particle analyzer. Four main operating parameters are varied in this study: liquid flow rate (100 ml/min to 250 ml/min), shaping airflow rate (120 l/min to 180 l/min), bell rotational speed (20,000 rpm to 50,000 rpm), and high voltage setting (60 kV to 90 kV, and 0 V for comparison). For simplicity, water is used as the paint surrogate, and a flat metallic panel is used as the target surface. The results show that bell speed dominates the atomization, but high voltage and flow rate settings significantly modify the spray transport. The results of this study also provide detailed information on the paint spray structure and transfer processes, which can be used on model development and validation in future. Also, the microscopic visualization images provide qualitative information on the atomization mechanism.