The heart of the process is the annealing and cooling technology. At speeds of about 100 meters per minute, the strip is guided, without contact, through the over 100-meter-long floatation furnace in a sinusoidal wave. Here, the material is initially heated to a defined temperature and then held there for a material-dependent minimum of time, with temperature accuracy being of great importance for achieving the desired material property. To have the furnace certified by the NADCAP (National Aerospace and Defense Contractors Accreditation Program) for the production of aerospace grades, it is indispensable to provide evidence that, among others, air temperature accuracy is within +/- three kelvins over the entire width and length of the furnace. Complying with these conditions, the furnaces made by SMS group can be certified for the important supply industries.
SMS group developed a special water cooling system to achieve high cooling rates. The 2xxx and 7xxx series aerospace-licensed alloys, in particular, require high cooling rates of more than 400 kelvins per second. For the 6xxx series automotive alloys moderate but flexible cooling rates between 25 and 200 kelvins per second will do. In addition to achieving the needed cooling rate, extremely uniform cooling over strip length and width is crucial to largely prevent material distortion. A special feature in this connection is the predefined strip crossbow that has two major functions. On the one hand, the water may run off the strip in a controlled manner due to this curvature, and on the other, the stable strip shape ensures the required consistent cooling effect through a special spray bar system and the centered strip guidance.
Another highlight of the furnace is a mathematical model calculating the settings for the annealing and cooling processes with regard to the mechanical properties.