Q&A's on Electrostatic Transfer Efficiency: Problems and Solutions

A. You have likely heard of the great gains in deposition efficiency available through electrostatic application. If you have no direct contact in this area, your coating supplier should be able to provide some guidance. When a coating is sprayed with electrostatic equipment there is a charge applied to the paint particle or droplet. The charged paint is then drawn to the grounded substrate at a rate much higher than if it were not charged, resulting in more paint on the part and less over-spray.

A. Hi, Hank. Jeff may be correct that you are thinking of electrostatic spraying... but it also sounds like you might be thinking of Electropainting (all called electrocoating, e-coating, or CED coating). In this process the parts are immersed in a bath which relies on electricity to convert ions in the bath to paint on the part. It's very similar to electroplating, but involves the deposition of paints rather than metal. This is the priming process you see on all automobile bodies. Good luck.

Regards,

A. The paint resistivity is not a main factor in efficiency. But rather the charge to mass that you achieve on the droplets after or during atomization. If you use a water soluble coating and isolate so that the extreme conductivity does not cause high current flow to ground, you can achieve high efficiency. More important is how you handle the following.
1. Current to ground.
a. The current reduces the voltage, which lowers the charge to mass ratio achievable.
2. The conductive charge, or contact with the charged tool.
3. The ion field, generated off the edge of the tool, sharper is better for ion field.
4. The droplet distribution, the largest most uniform droplets which provide the desired film formation will achieve the best charge to mass and have the best attraction to the field.
5. The field generated to the workpiece, proper distance, etc.
6. The lowest droplet velocity which achieves the desired film formation.
Also critical are the conditions of the booth air flow.

A. The resistivity recommended by the finishing tool is not the gating factor for efficiency. Generally it will be set so that the equipment is in a good range for current draw and will have a low limit which keeps it in the safety range of what ever rating it has. The metal in the fluid stream as well as the material before ground must be considered in the calculation for capacitance and power.
The resistivity to use is the material manufacturers, this may need to tested for given many materials are made and tested for appearance and durability with conventional airspray. Another consideration is the type of meter you use, there are three measurements I am aware of in use. There are conversions to move from one to the other.
1. Kilohm per centimeter
2. Megohm per square centimeter
3. Megohm per cubic centimeter
The main issue with changing the solvent diluent or other additives is that this may well affect the final appearance or desired characteristics of the material; it is best to do this with the material suppliers support.

Hi Andy. More words please ... I don't know if you are looking for an instructional book or a base coat. Thanks.

Regards,

A. I would ask the gun supplier if you can borrow a demo gun of each one you wish to evaluate for a few days... then after using each one on your plant YOU will be the one who knows which gun is suitable.

Ajay,
If "Electrostatic paint" means what I assume it means, I think you've just answered your own question.

Q. The Paint is coming back towards the operator while spraying with electrostatic spray guns.