Paint transfer in electrostatic air sprays

James Edward McCarthy, Purdue University

Abstract

Electrostatic air spray guns are widely used to apply paints. In spite of their common use, the basic process by which a bulk volume of paint is transported to the workpiece is poorly understood. The goal of this research is to develop an improved understanding of paint transfer in electrostatic air-spray processes for which there is considerable margin to improve appearance and reduce both paint usage and solvent emissions. A paint transport simulation that accounts for the paint momentum, aerodynamic drag, gravitational forces and electrostatic attraction is developed and used to provide insight into the electrostatic augmentation of paint transfer efficiency. The paint transfer simulation uses a Lagrangian particle tracking, an Eulerian air flow and an Eulerian electrostatic field solution. The unsteady aerodynamic drag on the paint is incorporated using a stochastic separated flow approach. Measurements of paint transfer characteristics are used as input and boundary conditions to the simulation as well as to verify the simulation. Paint transfer efficiency measurements are used to identify a set of operational conditions that have a significant electrostatic augmentation. The atomization characteristics are accounted for through measured boundary conditions of paint drop size, drop velocity and volume flux. Paint charge-to-mass ratio measurements are used as input conditions to the electrostatic field solution. The simulation results are verified using measurements of paint transfer efficiency and drop transfer efficiency. The simulation results and measurements reveal that the amount of charge on the paint directly alters the paint flow structure, deposition characteristics and paint transfer efficiency.

Degree

Ph.D.

Advisors

Senser, Purdue University.

Subject Area

Mechanical engineering

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