Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2003

Measuring Transfer Efficiency

Q. I'm tryng to calculate the transfer efficiency rate of the automatic parts of a primer process which uses electrostatic guns. I'm calculating this by measuring the net thickness betwen e-coat and primer application with an special program on a vertical plane pannel. The robot makes 5 passes until it is all painted. The distance betwen the robot passes is half of the spectrum which is a consequence of the combination of the fan and atomized pressures ( and of course the Q of paint in m3/min). The question is: Am I doing it correctly?

A. There are two basic methods for measuring Transfer Efficiency The first is to accurately weigh the panels before you start painting.

1. Weight the paint before you start painting.
2. Apply the coating to the panels
3. Bake the coating at your normal baking temperature, OR if you don't normal cure the coating at high temperature, then in this particular case, dry (bake) the coating in an oven at 230F (110C) for one hours.
4. Take a sample of the coating exactly as you apply it. In other words, take a sample of the coating at the point of application.
5. Deterrmine the percentage weight solids of the coating by following ASTM D3359, and make sure that you follow exactly the same curing time and temperature as you do for the panels. If you cure the panels at 230F (110C), then determine the solids content of the coating under exactly the same conditions. If you bake the coating at a higher temperature, then do the same for the sample coating.
6. Measure by weight the amount of coating that was applied to the panels. You can do this by weighing the paint reservoir before and after the painting application
7. Weigh the coated panels after the coating has cured.

   Calculate TE by the following equation:

   TE = Wt of coating deposited on the panels / Weight of SOLID coating used

   Where "Weight of SOLID coating used" = Weight of wet coating used * percentage volume solids of coating.

1. Weigh the panels before and after painting the same way you do so in Method #1.
2. Determine the percentage volume solids of the coating as in Method #1.

   To determine the volume of solid coating applied to the panels by measuring the surface area of the panels and the film thickness of the coating.

   TE = Volume of coating deposited on the panels / Volume of SOLID coating used

   Where "Volume of SOLID coating used" = Volume of wet coating used * percentage volume solids of coating.