Standard Corona Characteristics:

EXPLANATION:

When standard corona is used to charge powder, the electrode emits a constant flow of ions in an electrostatic field.  After a short period of time, the ions begin to build up on the tip of the electrode. Once too many ions gather on the electrode, the excess ions start to separate and travel with the powder cloud.

With standard corona charging, the powder cloud is pulled towards the closest ground by the electrostatic field.  As a result, the electrostatic field prevents the penetration of Faraday cage areas. The normal way to overcome this problem is to reduce the voltage to the gun.  As the voltage drops, so does the electrostatic field intensity. This allows the powder to move with the air flow and penetrate the recessed areas.

Obtaining a uniform paint film thickness on parts with deep configurations presents a similar problem for corona charging. The electrostatic field and powder cloud are drawn to the part in the area closest to the gun.  Only after that area becomes covered, does the powder migrate into the deeper areas.

Back ionization is from the excess ions trying to find a ground through the thicker paint. These ions have a higher charge, because they are not bound to the paint particles. If they cannot become attached to the powder particles before reaching the part, the charge is high enough to burn through the thickness of the powder on the surface. This burning or arcing to reach the part is called back ionization.

The problem with back ionization on recoats is also from the excess ions trying to reach ground through the paint.  Because the part already has a cured coat of paint, the charge burns through the thickness of powder and cured paint at the weakest or thinnest point on the parts surface.

Pulse Charging Characteristics:

EXPLANATION:

When the pulse technology is used, there are two levels of output for both kV and UA. The diagram shows A and B as the two different levels in a single cycle.  Level A is the higher of the two outputs with a maximum of 100 kV.  Level B is the lower of the two levels with a minimum of 0 kV. The pulse charge technology produces a large number of pulse cycles per minute to provide the best possible penetration and transfer efficiency.

When the first charge (A) is activated, the ions build up on the electrode and the electrostatic field is generated. This is typical of the standard corona charge. When the second charge (B) is activated, the reduction in charge prevents the accumulation of ions on the electrode, and also the development of free ions. This occurs because the excess ions are released from the electrode and then absorbed by the powder particles before they reach the part.

Faraday cage areas are easier to penetrate with the pulse technology. When the second charge (B) is activated, the overall charge reduces and  the electrostatic field, loosing its attraction for the powder, allows the powder to freely flow into the Faraday cage areas of the parts.

Back Ionization is greatly reduced with the pulse technology. Since the electrode maintains a lower number of excess ions, less are released into the powder cloud. As the number of excess ions decreases, so does the occurrence of back ionization.