Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 222 of 331

metal condition, allowing a significant loss of heat at the joint. This panel joint can be- come too hot. To solve this problem, the channel is slotted, greatly reducing the area avail- able for the migration of heat. This technique can reduce the joint temperature to less than 100°F in a 450°F oven, without losing the structural integrity of the channel. Personnel access must be provided into the enclosure. The door and hardware must seal the opening without the use of a positive latching device for safety rea- sons. (Any panic hardware with positive latching features must allow the door to be opened from the inside.) A good rule of thumb is to locate access doors so that when someone is working in an oven, once he reaches a wall, an exit is never more than 25 feet away. Windows in oven doors are a good way to make them easy to locate. A great source of oven problems are the enclosure openings. These are required for the product to enter and exit the enclosure. These holes are designed using a minimal clearance for the ware. Bottom entry/exit designs make use of the natural sealing features of hot air and present no real problems. Openings in the sides of ovens re- quire mechanical air seals to contain the environment. To seal an opening, it is best to draw hot air from the oven and force it back into the opening. For this to work, a significant velocity must be developed at the center of the opening. Additionally, the oven must be run on negative relative to the production en- vironment. These two requirements draw factory air into the oven. This pressuriza- tion must be relieved by exhausting the enclosure, a considerable source of heat loss. An alternative to traditional construction methods is the oven module, but it is rarely prac- tical due to its configuration. HEATER SYSTEM The second system at work in an oven is the heater unit, which generates the energy necessary for curing the coating and begins the distribution of the energy. The most significant components of the heater are the burner, the supply fan, and the filters. To properly size heater equipment, a detailed heat load must be carefully calculat- ed. Energy losses for the ware load, conveyor load, enclosure, and exhaust must be con- For over 50 years Steelman has been leading the way with our high-quality industrial curing and burn-off ovens! 221

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