i need advice on transfer of atomized charged paint to ground....?

Question

when you transfer charged particles (in this case atomized paint) to a grounded surface, would you want the ground to have the least resistivity possible? i would imagine that you would want the least amount possible to transfer paint. we spray from 30-70 kv's at a distance of 1" for every 10 kv's. so if the resistivity is as low as possible, what could be the low points? the positive is better transfer of paint. i am new to electricity properties, so i would think as long as the resistivity is low on the ground part, then charged paint would be optimal process. i would like to know if i am wrong, or if there needs to be some resistance of the grounded part. BTW - the grounded part i refer to is plastic, and we create a bridge between the plastic and a metal rack with conductive primer. so the primer is really what i would need to know resistivity for. i need charged paint to go to the part and i think less resistivity would allow that if current could fully go to the ground.

Answer 1

If you have a stream of charged particles flowing onto the surface, that constitutes an electrical current I. You'll need to measure I. Basically what you want to know is whether or not the surface is conductive enough to keep the whole object well grounded during spray operation. Normally this isn't a problem with metals, but your coating isn't that conductive. This is an application of Ampere's law V=I*R. The characteristic (rough magnitude of) voltage V on the surface is the paint current I times the characteristic R where R=r*L/(W*d). L is the approximate length of the part, W is it's width, d is the depth of paint, and r is the intrinsic resistivity of the cured paint. You want to make sure V is much less than 30-70kV for it to be considered grounded.

Meanwhile, one finds r experimentally by solving the above equation for it and measuring the resistance with an Ohm meter across two metal bars of length W separated by distance L and glued by the paint to a flat test surface.