Abstract
A rotating spray paint atomizer consists of a spinning cup from which paint droplets are ejected. Around the periphery of this disk, an axial air flow blows these liquid particles, which are projected against the surface to be painted. Under some particular circumstances which occur in industry, this axial air flow may be stopped and, owing to the Coanda effect, the radial flow of paint may be attracted backwards in the direction of the atomizer itself. This flow is detrimental to industrial performance, and it is the purpose of this work to consider the possibility of predicting and even preventing this phenomenon. Using computational software, a simplified model of an atomizer is first considered and the illustration of the reverse flow effect is shown. In the second part, a full numerical modeling of a real geometry is treated and a solution is suggested to improve the performances of this type of equipment. Recommendations are given for an optimal design which prevents the reverse flow effect in a rotating atomizer. For a given air flow rate, it is shown that the highest output momentum of the jet flow should be obtained.
Highlights
Electrostatic spray technique is the most common method available for applying liquid paints to metal products such as automotive components
Atomized paint droplets are charged at the tip of a spray gun by a charged electrode
The part to be painted, which is attached to a grounded conveyor, is electrically neutral, and the charged paint droplets are attracted toward that part
Summary
Electrostatic spray technique is the most common method available for applying liquid paints to metal products such as automotive components. Rotary atomization is a variation of electrostatic spraying that uses centrifugal force generated by a rotating disk with various profiles to atomize the paint which is driven away from the nozzle. NOMENCLATURE h p Po Qshaft,sk.irt r, 8, z R R e0 v p n diameter of the skirt flow injection port (m) radial shift between skirt port diameter and rotating disk diameter (= d/2 - R) (see Fig. 12), m air-gap thickness of the shaft flow, m distance parameter in the simplified geometry (m) fluid pressure, Pa atmospheric pressure, Pa volumetric flow rate ofthe shaft, skirt flow (liters/min) radial, azimuthal and axial coordinates, m rotating disk radius, m. --i:t""-ilro:: Fig. 1 Rotary paint atomizer: the liquid paint is injected at the center of a rotating disk, which drives it at its rim, where two different air flows assist its atomization into fine droplets
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