Annealing Control Systems
for Rolling Mills
Ultrasound signals reflected by metallic material. Under a certain angle a maximum signal is detected (about 31° for stainless steel). The received signal includes information on the grain size which can be compared with a calibration curve. Thus the values of the grain size can be calculated. In case of the used ultrasound frequency of 25 MHz the measuring range is about 8 to 40 mm. Typical accuracy is +/- 2 mm.
After being cold-rolled, steel strip is annealed to achieve recrystallization. In case of ferritic stainless steel there is a clear correlation between grain structure, mechanical properties and magnetic behavior. During the annealing process the values of the apparent remanence drop significantly, reaching a minimum value in case of full recrystallization. Overannealing can be observed by increasing values because of the formation of Martensite. The measuring system consists of a magnetizing roller and a field detecting roller which are mounted over strip guiding roll.