Journal of Loss Prevention in The Process Industries, Vol.17, No.1, 59-63, 2004
Effects of corona charging of coating polymer powders on their minimum ignition energies
In the electrostatic powder coating systems, coating powders are highly charged by corona discharge in a spray gun. The charge amount is affected by supply voltage to the spray gun and feeding rate of coating powders. On the other hand, the minimum ignition energy (MIE) of coating powder is used for the evaluation of ignition hazards due to static electricity in the powder coating systems. The MIEs of coating powders charged by corona discharge were investigated experimentally using an ultrasonic vibrating-mesh MIE testing apparatus with a corona discharge unit for dust clouds. Coating powders of polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and Nylon 11 (PA) were used. It was confirmed from the experiment that corona charging decreased the MIEs for all the coating powders used in this study. This result was attributed to both changes in dispersion of coating powders due to corona charging and in discharge characteristics due to free ions produced by corona discharge. Therefore, the effect of corona discharge must be considered both in the MIE measurements of coating powders and in the risk assessment of ignition hazards in electrostatic powder coating systems. (C) 2003 Elsevier Ltd. All rights reserved.