POWDER COATING: CORONA CHARGE

Powder spraying

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, etc.) where a high potential gradient is created.

Coronas can be positive or negative which is 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.

CORONA AND FARADAY 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.

OVERCOATING POWDER

Powder can hardly be overcoated due to the high thickness and remaining charge.