An eddy-current-based sensor for preventing knots in metallic wire drawing processes

During metallic wire drawing processes, the presence of knots and the failure to detect them can lead to long production interruptions, significant economic losses and a lower quality of final product. Consequently, there is a pressing need to develop methods for real-time detection and prevention of this fault. In this paper a sensor to prevent the formation of knots during the metallic wire drawing process is presented and evaluated by means of experimental data. This fast, inexpensive, non-contact sensor is based on electromagnetic principles such as eddy current induction, magnetic reluctance variations and magnetic coupling. The proposed sensor can detect knots in a target metallic wire without direct contact by measuring the impedance variations of a calibrated sensing coil caused either by a knot or an unwound loop rising from a wire rod. The incorporation of this type of sensor into a wire drawing machine can avoid the tightening of the knot, thereby reducing downtime and increasing the security and reliability of the process. Experiments were conducted using a scale model of the above proposed system. This allowed to highlight the sensor’s potential by carrying out an automatic, real-time knot detection during steel wire drawing.