Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2001

Transfer Efficiency of Various Spray Guns

Q. I realize that with all of the variables, nothing is etched in stone, but could you give a general idea of the difference in transfer efficiency between airless, air assist, and electrostatic process. This scenario would assume the same painter, the same product and the same target. Thanks for your help.

A. As you pointed out, there are lots of variables that determine transfer efficiency. One of the most important is the size and complexity of the object being coated. I mention this because each of the spray guns (compared with one another) mentioned in your question performs differently depending on the configuration of the object. For instance, airless spray guns are generally not suitable for applying coatings to small complex shapes. Electrostatic guns are generally not useful for painting objects that contain lots of crevices, tight angles and corners, etc. HVLP guns are not used on a beverage or food can coating production line because the high volume of air from the gun would blow the light weight cans off the conveyor line. Despite what I said above, specially designed airless guns are used to apply the internal epoxy coating into beverage cans, such as Coke, Pepsi, etc., with a transfer efficiency in excess of 90%!

This long preamble to my answer is given to illustrate that transfer efficiency for any spray gun is determined on a case-by-case basis.

To answer your question I will use only one scenario. If we were to apply a marginally conductive coating to a fairly large flat metal panel that is grounded, we could assume that the order of efficiency in descending order would be electrostatic, HVLP, air-assisted airless and finally airless.

All other parameters being equal, this relative order will change as the part configuration changes.