Q. We’re currently planning a layout for a powder coating line, and I have a question regarding the cure oven setup. I’m trying to evaluate the pros and cons for an elevated oven with a bottom entry and bottom exit when compared with a floor-mounted oven with a horizontal oven entrance and exit. We would use air-knives at the exit end to keep hot air in, but not at the entry because we know it will blow uncured powder off the parts.
What would be the total energy savings of an elevated oven per hour with bottom entry when compared to the floor-mounted oven? Any help would be appreciated. J.P.
A. A typical horizontal oven entry will lose around 50,000 Btu/hr/sq ft with no parts moving through the entry. When parts pass across the opening, the losses are double, worse than if there were no air curtain at all. If you decide to go with a floor-mounted oven, you should make the vestibule as long as possible, a minimum of eight feet at both ends.
Air knives are not too effective from a cost perspective, because they use a lot of electricity. It takes a lot of velocity to influence the migration of heat out of the oven and diminish the inflow of cooler air. The larger the opening (greater than 3” across) will be much less effective and require a lot more air. The net impact when compared with a longer vestibule is a more expensive operation with the air curtain than without.
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A bottom entry oven loses around 3,000 to 5,000 Btu/hr per square feet. Heated air expands in the oven and a small amount is pushed out of the bottom opening but not nearly as much as the horizontal opening. The entrance is usually larger to allow for the incline of parts. The losses are usually about 75% lower than a horizontal oven.