Abstract
High-speed rotary bell atomization is the preeminent coating technique in the automotive industry. It is widely accepted that a narrow droplet size distribution and constant spray are necessary in order to guarantee uniform film thickness and high-quality appearance. This may be deteriorated by paint flow pulsations. So far, however, no studies exist regarding such fluctuations quantitatively for this type of atomizers. We fill this gap using image analysis of high-speed recordings close to the bell edge. We could show that the fundamental pulsation frequency increases linearly with rotational speed. A ratio of pulsation frequency and true rotational speed of about 3 was found, indicating that pulsations were initiated mainly by the three struts of the distributor disc. The coefficient of variation, i.e., the amplitude of fluctuation increased with decreasing liquid volume rate and rotational speed. Beyond that, we could show that the formation of droplets larger than 100 μm, which are assumed to cause paint defects, is promoted by the degree of fluctuation. These findings may stimulate development of bell cups showing less paint flow pulsations.
Highlights
Automotive coatings are usually applied via high-speed rotary bell atomization
6a shows the fundamental frequency from the fast Fourier transformation of paint flow pulsationsFigure as described for different flow rates and rotational speeds
The fraction of large droplets increases with decreasing nominal rotational speed since D10 but the whole droplet size distribution shifted to higher values
Summary
Automotive coatings are usually applied via high-speed rotary bell atomization. This coating technique provides the desired high-quality appearance and a high transfer efficiency at short process times. Soma et al 2015 [12] numerically studied the effect of pulsations originating from a gear pump on the flow pattern of a high-speed rotary bell atomizer. They could show that the frequency of flow rate pulsations in the liquid supply nozzle is the same as that of the fluctuations of film thickness at the bell edge. Salazar [13] investigated unsteady flow of paint on rotary bells cups using computational modeling He demonstrated that droplet formation is a pulsating-like phenomenon, since vortex waves are created on the bell surface. We correlate the degree of fluctuation with the occurrence of big droplets in the spray which are assumed to deteriorate the coating quality
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
