Electric Class A Truck Oven for Drying Magnesium Oxide in Tubular Resistive Heating Elements

The project required a repeatable truck-loaded batch oven for drying magnesium oxide within tubular resistive heating elements inside the customer electric-heater manufacturing environment. The customer needed a production-ready oven platform sized for batches of tubular elements that had to move through a controlled convection-drying cycle with consistent temperature performance and reliable exhaust and purge protection.

APPLICATION REQUIREMENT

• The project supported a manufacturing environment producing electric heaters, electric heating systems, and tubular resistive heating elements.
• The oven had to support batch drying of magnesium oxide packed within tubular resistive heating elements.
• The process required a machine platform appropriate for daily production use with repeatable drying performance from batch to batch.

WORK CHAMBER / LOADING REQUIREMENT

• Required internal work chamber: 36 in W x 36 in D x 60 in H.
• The oven had to support truck-guided loading for organized batch handling.
• The machine required front loading and unloading through two swing doors.
• The loading arrangement had to accommodate batches of tubular elements while maintaining airflow through the chamber.

QUALITY REQUIREMENT

• The process required controlled elevated-temperature drying with +/-10°F work-area uniformity.
• The system needed dependable control of temperature, airflow, exhaust, and safety interlocks so moisture could be removed consistently from batch to batch.
• The oven had to provide a stable production environment for repeatable high-temperature drying cycles.

SAFETY / ENVIRONMENTAL REQUIREMENT

• The project required an NFPA 86 Class A oven architecture.
• The drying cycle required powered exhaust, airflow verification, and purge sequencing to manage chamber ventilation safely as moisture was driven from the magnesium oxide fill.
• The final design basis included a documented Class A exhaust basis of 0.29 gal/batch on an o-xylene calculation basis.

SITE / UTILITY REQUIREMENT

• Required electrical service: 460V / 3PH / 60Hz.
• Design elevation basis: 4,300 ft.
• The customer also required the oven to use a the customer-branded control package aligned with the application.

The project required a high-temperature forced-convection drying process that could drive moisture from magnesium oxide packed within tubular resistive heating elements while maintaining even heat exposure across truck-loaded batches.

TEMPERATURE REQUIREMENT

• Operating temperature basis: 700°F.
• Maximum temperature capability: 800°F.
• Required work-area uniformity: +/-10°F.

AIRFLOW / HEAT-TRANSFER REQUIREMENT

• Required airflow pattern: full horizontal airflow.
• The process required forced convection across the full chamber width to move heated air through and around the loaded element batches and support moisture removal.
• Using the final recirculation airflow and chamber cross-sectional area in the airflow direction, the first-pass average chamber air velocity is approximately 124 FPM.

HEAT-INPUT REQUIREMENT

• Heat source: electric resistance heat.
• Installed heat basis: 54 kW total.
• Heating arrangement basis: two 27 kW heater banks.
• The oven required staged electric heat delivery with controlled temperature response at elevated operating temperatures.

VENTILATION REQUIREMENT

• The process required exhaust and purge sequencing to remove moisture-laden air generated during drying.
• Powered exhaust basis: 550 CFM.
• The documented Class A exhaust design basis was 0.29 gal/batch on an o-xylene calculation basis.
• The exhaust and safety basis had to remain valid at 4,300 ft design elevation.

CONTROL / SEQUENCING REQUIREMENT

• The process required verified safe-start sequencing before heat could be energized.
• Exhaust airflow and recirculation airflow had to be proven before the oven could complete purge and enable the heater banks.
• The thermal cycle required dedicated temperature control and separate excess-temperature protection.

COOLDOWN REQUIREMENT

• The process required continued fan operation during cooldown.
• The final control sequence states that the fans are not to be shut down while oven temperature is above 250°F.

To satisfy those requirements, Precision Quincy configured the project as a 73-800 electric Class A truck oven dedicated to drying magnesium oxide in tubular resistive heating elements, using horizontal airflow, dual-bank electric heat, powered exhaust, and interlocked controls.

OVERALL CONCEPT

• One electric Class A truck oven platform for truck-loaded batches of tubular resistive heating elements.
• Front-loading batch configuration for organized product handling.
• Compact insulated oven body with integrated recirculation, exhaust, and controls.

HEATING ARCHITECTURE

• Heat source: electric resistance heat.
• Total installed heat: 54 kW.
• Heating split into two 27 kW heater banks.
• Final wiring basis shows 18 total heating elements at 3000 W each, arranged as 9 elements per bank.
• Heater power is controlled through solid-state relays with backup contactors.

AIRFLOW ARCHITECTURE

• Airflow pattern: full horizontal airflow.
• Recirculation system based on a 13.5 in x 5 in forward-curved fan wheel delivering 1,856 CFM at 2 in. W.c.
• Recirculation fan motor: 1.5 HP.
• The chamber arrangement supports horizontal air movement across truck-loaded product to provide repeatable convective drying.

EXHAUST / VENTILATION ARCHITECTURE

• Class A exhaust based on a PQ1 exhauster delivering 550 CFM at 1 in. W.c.
• Exhaust fan motor: 0.75 HP.
• The oven includes a fresh-air inlet / damper arrangement integrated into the body.
• Purge timing and airflow-switch logic are interlocked with the heat system to support safe chamber ventilation and moisture removal during drying.

CHAMBER / SHELL ARCHITECTURE

• Internal work chamber: 36 in W x 36 in D x 60 in H.
• Wall construction: 6 in insulated oven walls.
• Standard wall insulation: 5 in of 6 lb mineral wool.
• Heat-chamber wall insulation: 1 in of 8 lb Super Wool plus 5 in of 6 lb mineral wool.
• Interior material: unpainted aluminized steel.
• Exterior finish: PQ Blue.
• The floor includes integrated truck guide tracks for repeatable loading alignment.

DOOR / LOADING ARCHITECTURE

• Two swing doors.
• Truck-guided loading through the front of the chamber.
• The chamber and door arrangement support organized loading of tubular element batches with repeatable placement inside the work area.

CONTROLS ARCHITECTURE

• Customer-specific the customer temperature controller.
• Customer-specific the customer high-limit controller.
• NEMA 1 control enclosure built as a UL508A open industrial control panel.
• Separate operator controls for exhaust fan, recirculation fan, and each heater bank.
• Panel arrangement includes purge complete, fan on, and heater bank on indication.

SAFETY ARCHITECTURE

• Applicable standards basis: NFPA 79, NFPA 86, UL508A.
• Safety logic includes:
• Exhaust airflow proving
• Recirculation airflow proving
• Timed purge before heat enable
• Excess-temperature shutdown
• Automatic heat shutdown if safe operating conditions are not met