DEVELOPMENT OF EMAT MONITORING SYSTEM OF FORMABILITY IN COLD-ROLLED SHEETS

Abstract A nondestructive Lankford value (r-value) evaluation system applicable to a production line was developed. The system measures ultrasonic velocity changes induced by texture with S0 Lamb wave Electromagnetic Acoustic Transducers (EMATs) The system is composed of EMATs, driving circuits, receiving circuits and the frame bridge. Three pairs of EMATs were placed at three different angles (0°, 45°, 90°) to the sheet rolling direction. The propagation time measured by the EMATs was analyzed and the averaged r-value was evaluated continuously Basic experiments with permanent-magnet and electromagnet type EMATs for S0 mode Lamb wave were made to investigate characteristics such as sensitivity, gap effect, magnetic effect, production line speed effect, etc. Finally, the electromagnet-type EMATs making use of the magnetostrictive effect were adopted, since they had a high sensitivity at 5mm air gap from a steel sheet in the production line. By using the system with this type of EMATs, we confirmed that the averaged r-value was estimated in the accuracy of σ = 0.07 in various kinds of low carbon steel sheets.