Q: What is the most reliable way to measure transfer efficiency of a powder coating? To spray some known amount powder to the plate is one way, but it’s not reliable due to variables such as distance, voltage, etc. What is your suggestion?
A: There are a few techniques to measure transfer efficiency. The simplest is to set up a fixed gun in your laboratory spray booth and evenly feed powder to the gun. Secure a test panel at a fixed distance from the gun and apply the powder under constant conditions.
Specifically:
1. Clamp your spray gun with a ring stand. Set it up inside the spray booth.
2. Tape the trigger to the “on” position. Do this with the gun control turned off.
3. Hang a test panel 20 cm from the discharge of the gun. A 150 x 300 mm test panel is a good size.
4. Set your air velocity and voltage/current. Use standard conditions.
5. Set up a consistent powder feed. This can be with a fluidized hopper or a vibratory feeder. We use a vibratory feeder for best precision.
6. Weigh the test panel to 0.1 grams precision.
7. Load the feed system (hopper or vibratory feeder) with a prescribed amount of powder.
8. Turn on the feed.
9. Turn on the spray gun at the control unit.
10. Feed powder for 5 seconds.
11. Weigh the test panel.
12. Bake the test panel and measure film thickness.
The weight of the powder is the most important value to record, but the film thickness offers corroborative data.