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Electrostatic powder coating of insulating surfaces using an alternating polarity internal corona gun

Electrostatic powder coating has been widely utilized in metal finishing industries for items such as appliances and consumer products. Recently, powder coating has been making inroads in the automotive industry. Here, he authors describe how an internal corona (IC) gun operated at 1 Hz alternating polarity (AP) was used in an attempt to powder coat insulating plastic plates without using conductive primers, metal backings, or ion "backings". The IC gun was effective in charging the powder particles and emitted very few free ions, but it required frequent cleaning. The Q/M ratios obtained using DC voltage were very good, with negative polarity better than positive. The use of charge separation electrodes verified that the 1 Hz AP gun emitted "waves" of oppositely charged particles. The charged powder average velocity between the gun and the target (3.8 m/s) was calculated from the measured transit time (0.13 s), and was dominated by the airflow.