How to Control Orange Peel and Powder Thickness
Powder expert Rodger Talbert outlines three steps you can take to limit orange peel with powder coating.
Q. We converted from liquid high-solids paint to powder coating a few months ago, and we have seen a significant increase in the orange-peel look on our parts. Our target film build is 2.0 mils, and we often run as high as 4.0 mils. What causes the increase in orange peel, and how can we better control the film thickness?
A. Orange peel is a wavy appearance in the film that has the look of the peel of an orange. First, you must accept that the solids content of the powder is greater than your old liquid paint and will always show a little more orange peel.
There are several contributors to orange peel. Some powders are finer grinds or flow into more level films. Some are coarser or do not flow out as level as others. Test your powders to see how well they flow out at lesser film thicknesses.
Thicker film does contribute to orange peel simply because it is thicker. Electrostatic behavior is a key factor in the orange peel appearance. A higher number of free ions in the thicker film can cause some unwanted electrostatic movement within the film, and inhibit smooth flow of the powder during application and cure. Also, as the resistance grows on the part surface due to the insulating effect of the growing film, deposition is impacted. Smaller particles do not have enough cumulative charge to overcome the resistance, and the outer layer of film includes more and more larger particles that contribute to the orange -peel look.
There are three things you can do to limit orange peel: 1) Always maintain good ground to help keep electrons flowing away from the application area; 2) try to hold down the total level of current draw by using a current limiter, reducing voltage, keeping the gun farther from the target and using consistent stroke patterns; and 3) control the film thickness so you do not get to a heavier film.
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