## Electrostatic Induction and Spray Painting

Hi,

What is the charge on a droplet of paint?

Im trying to understand what's going on in electrostatic spray painting - specifically at the spray nozzle (this could also be crop spraying too)

My understanding so far is that a paint supply is fed into a grounded nozzle. An electrode (le'ts say it's ring shaped) sits around the nozzle. The electrode is insulated from the paint so that no current can flow between the two.

The electrostaic field impinges on the paint. In the paint like charges are repelled and unlike charges attract towards the electrode. The paint in the end of the nozzle is charged.

When droplets of paint are formed in spray they are also charged. I want to develop and expression for the charge on the droplet of paint.

I imagine I'm going to break the problem down as follows:

1. the electrostatic field strength in the paint is a function of the electrode voltage, distance, and a property of the air seperating the two.

2. the density of the charge induced in the paint is a function of the electrostatic field strength, and a property of the paint to do with the mobility of electrons in the paint.

3. the charge on a droplet will depend on its volume, and the charge density of the paint it came from.

Does this seem about right or have I made some dumb mistakes in this?
I have read some info on Coulombs law, but I dont seem to be able to relate it here.....I think that's the burden of my lumbering brain though.

Any pointers to equations / laws for 1,2, & 3 above would be very helpful - I can then try to get my head around it - I'm just finding it difficult to get started.

Thanks very much for any help with this, I'm really stuck.