Monitoring wheel defects on a metro line: System description, analysis and results

This paper presents a system developed to monitor wheel defects on metro vehicles in order to reduce annoyance and infrastructural damage due to noise and vibrations. Information about the wheel state and its evolution can be added to the mere mileage to improve the efficiency of the reprofiling decisions. In addition, sudden defects, that could potentially be severe, are detected and an alarm is raised to take the necessary actions. Some other systems have been developed to monitor wheel state by means of measuring the vibrations or noises generated by vehicles; however, the case of a metro is somewhat distinct. Wheel thread defects on a metro vehicle are not necessarily related to overloads or rolling contact fatigue. Damage to infrastructure and noise emission generated by small defects are particularly important due to the high frequency of the service and the proximity of the track to residential buildings, especially in the case of an open-air section that runs though a neighbourhood as some sections of the Metrobilbao. The system measures vibrations at a specific location on the rail as the vehicle passes over it, then analyzes these signals and stores the information in a specific database that can be easily queried from any computer on the intranet. The system has been installed on the Metrobilbao line and tested for three years. During this period, more than 8500 trains, or 272000 wheels, have passed over the accelerometers and corresponding data was stored in a database. 448 wheels threads were physically measured in order to check the accuracy of the system. This data has been used to fit the statistics for new or newly machined wheels and estimate the alarm threshold, and finally tuned in agreement with the maintenance workshop.