Q. We have installed a powder coating system in our factory, and the problem we encountered is that we do not have an air barrier for the openings of the curing oven. We would like to have one for the system, so please give us some advice on what kind of fan and what kind of nozzle we should use. L.D.
A. This is a difficult question. First of all, an air barrier on a powder cure oven entrance is not a good idea. It can blow powder off of the parts before they enter the oven. A heat relief hood or an extended vestibule or a combination of the two is a better solution for heat control at the oven entrance. A heat relief hood is a canopy over the oven entrance with a stack up through the roof to create a natural warm-air updraft. It does not save energy, but it does get the heat out of the building. It does not induce any additional energy losses. Keep in mind that an air curtain uses a fairly large motor that does cost money to operate, so the cost issue is not much different.
You can use an air barrier at the exit end. The fan type and size depends a lot on the opening size, width and height. It also depends on whether you will blow air from the top or the sides. An SWSI (Single-Width-Single-Inlet) plug fan is typical for an air curtain with a motor size based on the opening size.
Another factor to keep in mind is the width of the opening. Air discharged from a duct to create an air barrier has to be moving at several thousand feet per minute to work correctly but it loses speed very quickly over distance. If the opening is more than around 3–6 feet, the air curtain will have very modest impact on heat loss and it will need a big motor to power that kind of air speed. An extended vestibule is always the best way to keep heat in the oven but it takes space.