Q. We currently are using spray guns where we can only control the KV and not the micro amps and are having a problem with the film thickness of a particular polyolefin powder. The data sheet says we need to set spraying at 5-15 micro amps and the voltage at 100 kV or, on our type of gun, 30-50 kV. Before I invest in a new spray gun, I would like to read your comments. We are trying to achieve a film thickness of ±250 microns, and the only way we are able get there is to hot-flock spray the parts, which adds cost. L.N.
A. It is hard to achieve that much film build with a thermoplastic coating and negative charge without heating the part. Thermoplastic powder can be hard to apply with a negative charge because it does not take on electrons very well. I am surprised that you cannot adjust the amps to help overcome the charging characteristics of the powder. You should speak with your gun supplier about your options for adjustment or other guns with the needed flexibility. Another gun may be the answer, but you should try before you buy. It may still be hard to get the film you need without preheating the part. Double coating is the only other option I can think of that may help get that film build.