Powder Coating Q&A: What is Causing White Specks in the Black Powder?
Q. We are experiencing an issue with our blue and black powder paint. There are white specks all over the parts. What could be causing this issue?
A. It is difficult to be certain of the cause, but the most likely suspect is cross-contamination of white powder in your black film. Do you spray a white or light colored powder? If so, consider all the opportunities for the white to get into the delivery system.
The starting point is the gun, hose, hopper (if you use a feed hopper) or pump. If the gun has been completely cleaned and you are sure it is not in the delivery system, the next thing to look at is the collector. If you reclaim powder you may have some white in your recovery system that is getting into the darker powder. If you use a cyclone, you may have powder inside the duct or cyclone that is causing the problem.
I worked in a facility a year ago where we found white powder inside the collector along seams and in the transfer pumps that had completely contaminated the black powder in the collector. The black powder had white specks on it. We had to replace all the membranes, gaskets, pump inserts and cartridges to get rid of it.
The booth is also a potential source. Are you getting the walls clean enough? The area surrounding the powder booth should also be kept clean so that you do not track powder into the booth. If you are doing any air blow off, floor sweeping or other activities in the room and you have white powder on the floor or surrounding area, you will have white specks in your black powder.
If you check every piece of equipment and cannot find any trace of lighter powder anywhere or you do not spray a light powder, then the issue may be with the powder material. It may have traces of a white powder that came in the box. This is rare, but possible.
Originally published in the February 2016 issue.
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