The corona effect is a physical process by which a current flows from a high potential electrode into air and ionizing it. The cloud of ions generated can transfer electrical charges to nearby lower potential surfaces.
Corona effect usually forms at sharp boundaries or edges of surfaces (corners, projecting points, small diameter wires, ...) where a high potential gradient is created.
Coronas can positive or negative, determined by the polarity of the voltage applied to the electrode.The difference between positive and negative effect is noticeably different, resulting in the difference in mass between electrons and positive charge ions.
Charging by CORONA effect
Ions collision to the powder particle creates the charge around it. Other ions are then attracted and increase the total charge of the particle.
Bell CORONA charge
Bell cup edge is a wide electrod increasing the field intensity and generating powerfull charging effect.
The shape of the targeted part to coat will influence the spray. In cavities electrostatic field is nil, therefore few powder will be attracted when sharp edges will maximize the field and generate additional thickness locally.
Powder can hardly be overcoated due to the high thickness and remaining charge.
Thanks to the long experience of SAMES KREMLIN in powder coating, the High voltage management allows to reduce the impact of faraday effect and also the overcoating problems.
With the right parameters (I, V) the spray can effectively coat the part in the most difficult conditions.