Powder Coating Q&A: Airflow in a Powder Booth
One of the potential suppliers has offered a booth with a cartridge collector on one side only and the other supplier recommends we have a collector on both sides of the booth.
Q. We are going to purchase a new powder booth for our facility. It will be a batch operation, but we plan to use a hand-push trolley rail to reduce handling and make it easier to move the parts around. A load of parts will be pulled into the booth and then coated in a stationary position. After coating, the load will be pulled to the oven and cured. The booth will be around 10 ft. wide × 20 ft. long and 10 ft. high. One of the potential suppliers has offered a booth with a cartridge collector on one side only and the other supplier recommends we have a collector on both sides of the booth, asserting that the two collectors will improve the airflow inside the booth. Can you comment on this and help us understand why one might be better than the other?
A. In any spray booth it is desirable to have air flowing away from the operator holding the spray gun. In an inline powder with a motorized conveyor, the booth is usually narrow enough for the hand sprayer to stand outside the booth and work through a window. These booths often have just one collector on one side, even though there are two sprayers—one on each side of the booth. It is an optimum way to move the air, and there are several practical reasons for doing it. The air is pulled across the booth for the one operator and to the side away from the other, so the operator is never standing with his back facing the collector while he sprays. The capture efficiency of the collector in this arrangement is good and the impact on transfer efficiency is modest.
In a batch system where the operator is standing inside the booth, you can get away with a collector on one side only, but it is much better to use a collector on both sides. With one collector, the operator will have no choice but to stand inside the booth with his back facing the collector while spraying. The powder that is pulled by the collector will flow back over the operator and the powder that is over-sprayed away from the operator will wind up on the floor on the quiet side of the booth that has very low airflow. The side opposite the collector is low in airflow because the air being drawn to the collector is coming from inlets that are usually in the ends of the booth.
By contrast, with a collector on both sides, the airflow is more uniform and less aggressive near the collector. The total cubic feet per minute is evenly divided between the two inlet locations and the operator always has air draw away from their face. The powder is contained better and there is less dust in the air. So, either design can work for your operation, but if it was my decision, I would go for the two collectors. Not everyone will suggest it because it costs a little more, but it will be a better atmosphere inside the booth.
Originally published in the September 2015 issue.
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