Flaw Detection of Railroad Wheel Tread Using EMAT

Abstract

Since railroad wheels undergo high stresses due to dynamic or static loads continuously, flaws may be produced on the tread surfaces and they can lead to catastrophic failures of the wheels. In this study an EMAT system for inspecting every wheel of a train in a roll-by mode will be introduced. Two EMATs were installed in two shielding boxes separately for generating and receiving surface wave respectively. The boxes were designed for the EMAT to keep up the lift-off of 0.2 mm over the entire surface. The system was able to observe at least 10 round-trips with the EMAT on an unflawed railroad wheel. Four flaws were made on a wheel surface to evaluate the flaw detectability of the system and the signal from the 3 mm deep notch showed good signal to noise ratio. Since the variations in the lift-off due to some factors such as dirt can be caused in rail yard usages, flaw signals were divided by the round-trip signal for the normalization. And a new algorithm to distinguish the flaw signal from abrupt noise was suggested. EMAT & System ConstructionWave Generation. EMAT consists of a coil and a magnet array as shown in Fig. 1 [3][4]. When the alternating current flows in the coil above the surface of electrically conductive materials, eddy