Authors: Oswald, Walter
Lauk, Jan
Gödeke, Lutz
Erhard, Peter
Willenbacher, Norbert
Title: Analysis of paint flow pulsations during high-speed rotary bell atomization
Language (ISO): en
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.
Subject Headings: Pulsation
High-speed rotary bell atomization
Automotive coatings
Image analysis
Fourier transformation
Issue Date: 2019-10-17
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Appears in Collections:Arbeitsgruppe Strömungsmechanik

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