Ignitability of aluminous coating powders due to electrostatic spark

Electrostatic Powder coating which is a surface finishing technique has widely been used in paint industry since its invention in the 1960s. However, so far, insufficient attention has been paid to the powder fires and/or explosion hazards caused by electrostatic spark during coating process. This paper is a report of the electrostatic spark ignitability of aluminous coating powders (dry blend-type) used in practical electrostatic powder coating. The Hartman vertical-tube apparatus was used for the minimum ignition energy (MIE) test. Various aluminous coating powders, different with respect to the amount of aluminum pigment, were used in this study. Experimental results obtained in this study are as follows: (1) The aluminous coating powder was so sensitive that even an electrostatic spark with an energy as low as 10 mJ could ignite it. (2) The particle size of aluminous coating powder has a considerable effect on the ignitability when the aluminum pigment concentration is within 6 wt% of the practical coating powder manufacturing standards. Thus, the conventional expression for estimating the MIE can be useful when assessing the electrostatic hazards associated with aluminum coating powders.