Aluminum Coil Annealing Furnace using High Convection Vortex® Jet Airflow
SECO/WARWICK provides custom engineered aluminum annealing furnaces for coil and foil with capacities ranging from single coil furnaces to multi-zone furnaces with tight zone control. These units are used by aluminum manufacturers from around the world, i.e. in North & South America, Europe or Asia.
Using patented Vortex jet airflow technology, SECO/WARWICK’s Vortex® aluminum coils annealing system, combined with optional Bypass Cooler and SeCoil® control and simulation software, provides coils producers the ability to significantly reduce the overall cycle time of their furnaces, resulting in energy savings, increased productivity, and improved surface quality. The key to the system is an increased heat transfer coefficient achieved by high-speed air impinging on both sides of the coil. The idea is to transfer heat through the coil’s edges as opposed to only through the outside layer of the coil.
The challenge in aluminum coil annealing furnace is to optimize the process by shortening the cycle time to the greatest extent possible, while maintaining the desired metallurgical properties over the entire load. The components used in SECO/WARWICK’s aluminum coil annealing furnace succeed in providing both greater efficiency and better quality
Vortex® Jet Heating System
The effective thermal conductivity in a strip coil is much lower in the radial direction than in the axial direction, therefore, the most effective way of heating the coil is through the edges of the coil layers. The difference between the thermal conductivity for the two directions is caused by the heat-insulating effect of the gas between the coil layers. Also, winding force of the coil plays crucial role in the process. The Vortex Jet Airflow Heating System incorporates arrays of round-nozzle jets, pointing at multiple angles, which generate a spiral vortex motion of the air or the protective Nitrogen atmosphere, that results in high heat transfer without generating hot spots in the coil. The high-volume flow of this nozzle system in conjunction with a unique air or atmosphere distribution, system and centrifugal fan design allows the coil to be heated more uniformly by a high speed atmosphere.
Analysis of infrared pictures shows, that a more uniform surface temperature can be achieved by using the Vortex Jet Airflow Heating System. The coil surface temperature uniformity profiles present an overview of temperature uniformity for the entire heat up cycle. These profiles demonstrate that a better surface uniformity is achieved using the vortex nozzle system thanks to this, the load surface is “washed” by the atmosphere and not locally over heated. Vortex system allows for faster load heating thanks to better heat transfer coefficient up to 150 W/m2K in relation to approx. 110 W/m2K for the standard straight nozzle system.
SECO/WARWICK proprietary bypass cooler design for annealing furnaces provides cooling under a protective atmosphere. Cooling is very important in this application for both metallurgical and handling considerations. The coolers use an internal bypass arrangement which limits the temperature of the atmosphere going through the heat exchangers below 175°C. This prevents baking of the volatized rolling oil on the fins of the heat exchanger. The coolers are designed to provide in-depth, programmed, or auxiliary cooling and are available in standard or custom sizes. The coolers can be rear or side mounted according to space availability. Additionally, users can also add a Bypass Cooler to an existing bypass cooler ready annealing furnace. SECO/WARWICK has large numbers of these coolers in operation in coil and foil annealing applications. Newest bypass cooler design elimintates the need of any foundation pit.
SeCoil® process control and simulation software
SeCoil® is a software wchich includes Simulator and Controller app. Simulation option, as described below is developed to predict heating processes, and Controller is developed to control entire process basing on furnace sensors.
SeCoil® is a simulator for heating a coil in a Vortex® furnace, based on a mathematical model that has been derived from well-known laws of physics using well-known mathematical principles (in brief: phenomenological modeling). The SeCoil® simulator can be supplemented by a meta-model that uses artificial intelligence methods (behavioral modeling). The advantage of the phenomenological model is its great universality, since it is based on the known laws of physics. The developed mathematical model takes into account the variability of numerous parameters, such as temperature and outlet velocity of the heating medium, type of alloy, sheet thickness, and roll dimensions. The use of modern numerical calculation techniques allows for the current identification of the temperature field in the cross-section of the heated coil. With the SeCoil® simulator you can simulate the heating curve of any point located in the longitudinal section of the coil (virtual thermocouple). The SeCoil® simulator provides us with knowledge about the thermal state of the coil at any time during the process. It may, therefore, be used in many ways, including for forecasting heating curves for different types of coil and process conditions (furnace temperature, mixer efficiency) and for continuous control of the annealing process without the need to use batch thermocouples (controller). The meta-model was created using artificial intelligence methods (behavioral modeling), and can be an alternative or a supplement to a simulator based on phenomenological modeling. In contrast to the phenomenological model, the behavioral model applies only to the tested system and within the assumed limits of operating conditions. However, its accuracy for the analyzed range of data may be greater than in the case of the phenomenological model.
From a metallurgical point of view, the important process parameters are the final batch processing temperature and the soaking time which define the process of recrystallization annealing and must be met precisely. As such, the SeCoil® automatic regulation and control system has two main tasks: to maintain, for the longest time possible, an adequate air-to-work (head) temperature to minimize heating time and after reaching the load temperature setpoint, to reduce the head temperature to avoid any overshot of the load setpoint.
From an economic point of view, the most important parameter is the total process time, which directly affects the energy consumption. Due to SECO/WARWICK’s unique system, shorter process time can be achieved without the risk of overheating the load. After the operator enters process and coil parameters the system can then simulate the process and he collected data can ultimately be used to fine-tune the recipe and optimize the process time before processing begins.
/ High-Efficiency Process
Process efficiency can be significantly improved comparing to traditional annealing systems – without local overheating.
/ High Quality Process
Improves aluminum properties especially at edges and minimizes cracking or staining of milling oil.
/ Lower Cost Operation
Uses less electricity for gas circulation.
/ Flexible System Design
Various coils diameters, widths, sheet thicknesses.
/ High Heating Head
Possibility to use heating head even up to 150°C.
/ Coil and Foil Application
Aluminum foil from 120mic and thicker can be processed