Application of boxer charger for charging polymer powder without free ion current

The Boxer Charger developed by S. Masuda is a potential option for electrostatic powder coating applications that require charging polymer powder without generating the free ions that can cause destructive back corona effects. In a boxer charger, powder particles moving through the charging zone are bombarded alternately from two sides by ions of the same polarity, resulting in unipolar charging without free ion current. The boxer charger is a versatile charging device with high-performance charging efficiency up to 53% of the Pauthenier limit. Industrial epoxy powder was charged to an average charge-to-mass (Q/M) of +0.50 /spl mu/C/g when charging positively and -0.61 /spl mu/C/g when charging negatively, in good agreement with the calculated 53% Pauthenier limit based on the particle size distribution. Powder deposition on the walls of the charging unit was minimized by using high flow rate sheath air at the powder inlet and ozone generated by the charging unit was suppressed to below the OSHA maximum permissible exposure level by implementing an ozone trap of activated charcoal at the powder outlet.