Metal Finishing Guide Book


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tions, indirect heating equipment can require a third more energy. As the heater unit discharges the supply air, it is directed into the oven supply system. The purpose of the supply system is to deliver and distribute the energy developed in the heater unit. The supply duct is constructed of aluminized metal and is rectangular in shape. For proper operation, velocities in the duct should not exceed 2, 500 fpm. This assures good laminar flow in the duct and good temperature control. AIR SUPPLY SYSTEM The actual delivery of the supply air into the oven is achieved through some type of discharge device. The simplest of these is a hole in the side or top of the duct; however, this provides no control over the air. A better design is to provide a control device or slide damper over the opening. The slide allows the size of the opening to be adjusted to change the amount of air leaving the supply duct at a particular opening. The total area of these openings should approximate the cross-sectional area of the ductwork. Because of the poor control available with these devices, more discharge area is not better as the air will leave the duct at the point of the highest pressure differential. Too many openings will allow a large volume of air to escape the duct near the heater, leaving very little air to do the work in remote locations. Simple openings in the duct have a second problem. Simply allowing it to escape the duct does not assure that it will change directions, mix with the oven environment, and find its way back to the recirculation system. One effective tool to correct or change the direction of discharged air is a discharge nozzle. These devices are inserted over the discharge openings and give the air a new direction, away from problem areas. RECIRCULATION SYSTEM The purpose of the recirculating system is to return the oven air to the heater unit so the process of adding energy to the oven can continue. This is accomplished by using the duct with the supply fan to create a negative pressure condition within the enclosure. The oven air will naturally migrate to the areas of low pressure, be captured For over 50 years Steelman has been leading the way with our high-quality industrial curing and burn-off ovens! 791

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