Multiple Heat Treating Batch Ovens For Precision Aging Of Aluminum Parts
Multiple Heat Treating Batch Ovens For Precision Aging Of Aluminum Parts
The Challenge
Epcon was approached to design and build multiple custom engineered Gas Fired Batch Type Aging Ovens with cooling capabilities for aging aluminum structural components for a Tier 1 Automotive supplier.
Several alloys are heat treated to increase the ease of forming or the strength of the finished product. Unlike steel or iron, aluminum requires rigid heat control to achieve optimal results, so specialized industrial ovens and equipment are required. With great attention to detail in the oven design, proper heat treating methods results in aluminum alloys that are easy to work during the forming process, then followed by a hardening process that will resist wear and corrosion, for a lasting aluminum product.
While some alloys can be processed at near ambient temperatures, the more specialized parts often use custom alloys which require a heat treating process called aging to fully precipitate out the dissolved elements and reach their maximum hardness. This process is also called precipitation hardening. While each alloy has an optimal aging temperature, in general, precipitation hardening happens between 240° F and 460° F.
The Solution
Theses ovens are used to control the heating and cooling of the aluminum products loaded into the batch chamber. Featuring a multiple tiered rack system that holds stackable wire heat treat bins, the unit has sufficient capability to handle multiple bins loading per batch. At maximum loading capacity, the ovens can heat 6500 lbs. of aluminum load from 70° F to 400° F in under two hours’ time period. In addition, the system was designed to meet stringent temperature uniformity requirements of +/5 °F (+/- 3°C) at setpoints of 320 °F (160 °C), 375 °F (190 °C) °F and 401 °F (205 °C) and a guarantee that the oven would meet all CQI -9 standards requirements.
The recirculation system utilizes combination airflow to maximize heating rates and temperature uniformity of the product. This is achieved by adding two (2) recirculation fans inside the oven, each at 10,000 CFM capacity, and equipped with VFD on each motor to regulate the air flow. The Oven chamber itself is constructed from 18 Gauge Aluminized steel interior and 18 Gauge Carbon Steel Exterior materials, with the Oven Wall Panel in a tongue & grove type assembly and insulated with 5” thick, mineral wool insulation. In addition, each oven has an exhaust/cooling blower with approximately 3,000 -CFM capacity and PLC controls. The blower can accept exhaust air up to 400°F. During the heat up and quench period, the exhaust fan operates at lower speeds and during cooling cycle speeds up to 100 % to remove heat from the parts.
The Oven burner has a specialized nozzle design that allows for the combustion air and fuel to be mixed directly inside the burner nozzle. These highly reliable burners, with a turndown ratio of 20:1, and are designed with link valves to control supply of combustion air as well as natural gas (fuel). The fuel flow is automatically adjusted allowing for the precise control of temperature, achieved by then modulating the fuel and combustion air supply. Continuous airflow is a also a key element, so the Oven design includes supply plenums installed on both sides of the work chamber and return plenum mounted on the ceiling of the work chamber. This allows the recirculation air to return through the ceiling mounted return plenum to back into Combustion/Recirculation chamber.
As this is a high velocity Oven with very high coefficient of heat transfer, creating uniform temperature throughout the Oven is a challenge. The Oven working or “Batch” chamber is also used as cooling zone. The cooling in the oven chamber shall be achieved using a modulating fresh air cooling damper and exhaust fan. After the heating soak cycle is complete, the burners shut off. At the same time, the fresh air cooling damper featuring a Variable Drive Frequency (VDF) control, regulates the exhaust fan speeds to the desired cool down tolerances, and fresh air is drawn back into the oven via the combustion chamber and supply plenum nozzles for effective cooling. The cooling fresh air pneumatic damper is installed on the oven combustion chamber and the cooling fan on top of the oven working chamber to ensure proper airflow.
The guillotine door system is an integral design element for these batch ovens. These heavy-duty guillotine door are equipped with pneumatic door latches on both ends of the door to prevent leakage and heat dissipation. To ensure operational ease the door latch mechanism is operated through touch screen button configured on HMI screen, with mechanical safety latch and a rod lock assembly to hold the door during upward position for personnel safety.
The Results
The batch ovens not only provided perfect heat treatment parameters for the aging of aluminum parts, but the guillotine door designs also allowed for ease of safe operations for the facility.
