Control point in the powder coating process
The first control point is pretreatment during the cleaning process, which involves a six-stage parts washer. The washer must be controlled within the parameters specified by the chemical supplier to ensure adhesion of powder to metal, so the machine is monitored every two to three hours.
Four of the six stages incorporate V-jet nozzles to help maximize the directional pressure of the spray patterns. The third stage, phosphatizing, contains hollow cone nozzles for a flooding action that promotes high-phosphate powder coating weights. Phosphate acts like a primer—it adheres powder coat paint to metal. The sixth stage incorporates misting nozzles for the light rinsing.
Deionized water mist is used for a final rinse in the sixth stage. By removing the particulates of hard water, this rinse reduces the dissolved solids remaining on the parts before they are dried. A dissolved-solids meter helps keep solids levels at less than 10 parts per million. The drain water is relatively pure and is recycled back to stage two, another rinse stage.
A second control point in the powder coating process is the paint booth itself, where painters apply the powder manually. Control at this stage is difficult because of the possibility of human error.
Theories abound for controlling quality in a manual paint booth, but painter training seems to be the key. Application equipment continues to advance, and operators must be familiar with the principles of electrostatic attraction. When changing colors, they must know what is needed to eliminate even the slightest potential for contamination.
Methods for eliminating contamination include cleaning all gun parts with compressed air, vacuuming all powder from the walls and floor, and keeping the outside area of the booth clean at all times. A lead painter, one who has been coating parts for at least one year, trains new painters to clean with utmost quality and efficiency.
