Conveyor Oven Utilizes Threading Device for Drying Impregnated Fibers

The Engineers at LEWCO, Inc. were recently challenged to design and develop a custom oven for a leading global materials company. The result was a 650°F. electric conveyor oven with a custom threading device that will be used to dry a special type of impregnated fibers. The threading device was included to pull the fibers through the oven prior to being heated. The device can thread up to 200 fibers at once and it pulls them through the oven with a powered dual chain strand conveyor.

The oven was designed with two heating zones, each with independent temperature control and four process monitoring thermocouples. Overall, the combined heating zones measures 39 ft. long by 10 ft. wide. An exhaust fan with balancing dampers was employed to control the exhaust rate of each zone. The oven is NFPA 86, Class A design due to flammable violates present in the workspace.

Due to the criticalness of this process, the customer required a temperature uniformity of +/-10°F. throughout the entire oven. To retain heat and help improve temperature uniformity, pneumatic bottom-up doors were installed at each end of the oven. The unload end of the oven features a 6 ft. long cooling zone with two fans, one to feed ambient air and the other to exhaust the hot air. This was required to cool the fibers prior to moving onto the next step in production.

The oven is controlled by a Eurotherm Nanodac temperature controller with a redundant high-limit controller. A stack-light was included to notify operators when the oven has reached temperature set-point. The circulating fans are controlled by variable speed drives which allow operators to adjust the air speed within each oven zone. Each end of the oven is equipped with push button stations to control the movement of the threading device. All controls are tied into an Allen Bradley PLC with a touch screen operator interface terminal. The PLC communicates with the system’s supervisory PLC to provide status feedback of the oven for process control and data logging.