Detection of sub-surface defects: Mechatronic innovation at voestalpine Stahl GmbH

Focus on quality control in the steel industry in recent years has shifted to inline non-destructive testing (NDT) in order to detect defects at the earliest possible stage in the production process. Using highly sensitive sensors based on the giant magneto resistive effect (GMR), it is possible to detect the magnetic flux leakage caused by a defect near the surface of a steel strip. The detection and elimination of such defects is vital to sustaining product quality and reducing costs. The R&D activities dedicated to the innovative process model currently being developed by voestalpine Stahl GmbH have been divided into three phases. Phase 1 (basic research mechatronics) was spent investigating a variety of defect detection methods and subsequently discussing and evaluating the sensitivity and speed required for inline inspection. Phase 2 (applied mechatronics) included the construction of a prototype and test measurements that produced the promising results presented in this paper. Based on the results of the preliminary tests and simulations of the magnetic field, a second prototype is now being built for offline measurement and further development of the sensor design. In the event that this second prototype is successful, an inline configuration will be implemented in Phase 3 (integrated mechatronics).