Q/M distribution in pulsed corona powder coating spray cone

The advantages of using a high voltage pulsed corona superimposed on a lower voltage DC bias electrostatic field have been well-documented for the case of electrostatic precipitation of high resistivity dusts. The high voltage, short pulses achieve adequate charge-to-mass ratios, while reducing the total ionic current landing on the dust layer and thus minimizing the deleterious back corona effects. To throw further light on this corona charging process, which up to the present has not been put to wide use by the electrostatic painting industry, the authors present a preliminary experimental study applied to powder coating. Measurements are presented for the Q/M ratios of the charged powder fractions collected in an ensemble of 5 double Faraday pails mounted in a cross behind the target plane. The results indicate, on average, a substantial increase in the charge-to-mass ratio of powder, combined with a reduction of the total ionic current which bombards the painting target.