A leading company in the formulation, sale and application of protective and functional coatings for clear plastics and glass has added two electrically heated ovens from Heat-Pro by Lewco Inc., Sandusky, Ohio. Each of the Class A walk-in ovens will be used for curing parts coated with the company's coatings, a process that required a work space of 6' by 14' by 7' with an operating temperature of 500oF (260 oC).
Because the ovens are used to cure coatings containing solvents, an NFPA Class A oven design was required. As defined in NFPA Part 86, Section 18.104.22.168, a Class A oven has heat utilization equipment operating at approximately atmospheric pressure wherein there is a potential explosion or fire hazard that could be occasioned by the presence of flammable volatiles or combustible materials processed or heated in the oven. Such ovens are required to contain adequate safety ventilation to ensure the concentration of the volatile is well below the lower explosive limit. The amount of ventilation required is based upon the amount of solvent load per batch as well as the maximum operating temperature. Only the volatile content of the coating needs to be considered for this ventilation, not the non-volatile portion.
Heat-Pro by Lewco employed dual airflow (often called combination airflow), where the heated air is directed at the product both horizontally and vertically. Dual airflow typically is utilized to heat larger parts or products of irregular shape. The air enters the work space from both sides and returns to the heater box at the top.
The 180 kW required for the oven was wired into five standard 36 kW banks. The use of 36 kW banks allows 60 A wiring (with 480 V, three-phase power) to be used within the guidelines of the National Electric Code.
For ease of access, dual doors, both front and back, were requested by the customer with a top mounted heater box. The heater box was designed to be removable for shipping purposes with minimal time required in the field to reinstall.