Condition monitoring system keeps check on railway axle vibration and temperature to prevent failures in use.
Railway operators across the world are faced with a constant challenge of ensuring that wheelsets on rolling stock are monitored, maintained and are always in a safe condition for use.
The wheelsets are made up of a number of critical components, all of which need to be checked and maintained, including axle boxes and bearings, suspension elements and joints and the wheels themselves, which can suffer from damage, wear and flat spots that reduce performance and affect the ability to use the wheels safely. However, it is the axle box and bearings that are the most likely components to fail and the least easy to detect defects in with a purely visual inspection.
As rotating mechanical assemblies, bearings will always emit a certain level of vibration and noise during normal operation in good, lubricated condition. As the bearings wear and when they exhibit defects, the signature of the vibration and the acoustic emissions changes and so monitoring these parameters will provide engineers with some idea of the level of wear, the probability of impending failure and the need for lubrication, repair or maintenance.
Maintenance and monitoring strategies
Lubrication problems such as contamination, incorrect or insufficient lubrication and duration between maintenance events, are the most common causes of bearing failure and a planned or scheduled maintenance schedule is critical to achieving reliable performance over the expected life of the bearing.
Bearing condition through loading and monitoring can be performed during maintenance intervals to determine whether the bearing needs replacing or not and to gauge the remaining expected life. In some critical applications, bearings are replaced at set intervals regardless of condition.
Monitoring during maintenance is one option for assessing axle bearing condition, an approach favoured by many operators. The other option is to constantly monitor the bearing during operation on the train. Whilst this technique has its advantages in terms of coverage, it requires sensors that can cope with the harsh environment of constant in-service use as well as complex data acquisition and analysis for large numbers of components.
Condition Monitoring Test Rig
Faced with the need to ensure the safety of its operations in Asia, one railway company is using a condition monitoring test rig from bearing and Noise, Vibration & Harshness (NVH) specialist, Schaeffler. The rig is being used by the operator to inspect train wheelsets and gearboxes to eliminate unplanned train downtimes and minimise maintenance costs.
Local public transport with regional rail vehicles is part of the operator’s core business and so low maintenance costs and high train availability are crucial factors for the company. Any downtime or delays can mean considerable costs and financial penalties.
In order to ensure the best possible availability, the gearboxes and wheels of all the wheelsets of the company’s trains, including their axle and gearbox bearings, are regularly inspected, overhauled or replaced. The operator was therefore looking for a system that would ensure the reliability and accuracy of checks, while also minimising the downtimes of the trains.
With its special condition monitoring test rig for railway gearboxes and axlebox bearings, Schaeffler implemented a cost effective method optimised for the customer’s specific application.
The system uses Schaeffler SmartCheck sensors, which are simply attached to the components to be monitored using magnets and undertake precise measurements of vibration and temperature without a requirement for further installation outlay. Components monitored include gears in gearboxes, gearbox bearings, wheel axles and axlebox bearings.
For data acquisition and analysis, the sensors are directly connected via a Schaeffler SmartController to the input and output terminals of an acquisition system such as an HMI touchscreen control panel, an external monitor and alarm and data processing systems.
The axles are driven by means of an integrated electric motor for the test runs and, in addition, the system can reliably check whether the bearings were correctly mounted, for example, after bearing replacement. Parameters monitored include vibration, temperature, speed and bearing end position.
For the Asian rail operator, the integrated system for the inspection of gearboxes and wheelsets is an important tool in eliminating unplanned downtimes and malfunctions in rail applications. The investment in the test rig is also significantly lower compared to the cost of complex onboard monitoring systems, which are often used in long distance trains. By adequately planning maintenance intervals during which the monitoring takes place, there is no need for the complexities of constant onboard monitoring.
In addition, the rail operator gains benefits through reliable and very precise monitoring, simple and full integration with the operator’s own systems and infrastructure and a user friendly method of performing the monitoring.
The gearboxes can be inspected without dismantling them or changing the oil and the bearings can be similarly inspected without removing them or having to replace any seals. Once the monitoring is completed, if any bearings are replaced, they can be checked again for correct mounting using the same equipment.
Unplanned downtime of trains can always result in direct and indirect costs for rail operators. The reputation of the operator can also be damaged, particularly in public transport applications. In this particular case, there is an additional significant risk because any downtime or delays in rail traffic is penalised in the form of severe financial penalties stipulated by national regulations. Following the positive experience with Schaeffler’s test rig, the customer is now planning to use the system at other locations.
The compact and modular SmartCheck sensor from Schaeffler provides the capability to perform online measurements for the decentralised and continuous monitoring of machinery and process parameters.
It is particularly suitable for the early detection of roller bearing damage as well as imbalances and misalignments on motors, vacuum and fluid pumps, ventilators and fans and gearboxes and compressors as well as spindles and machine tools.
The sensor is equipped with predefined parameter presets for monitoring and has an integrated bearing database, which can be accessed when using the parameter presets. The presets can be easily adapted to specific monitoring tasks with the aid of assistants.
SmartCheck is Power-over-Ethernet (PoE) enabled so doesn’t need separate power cabling and can use both Fieldbus and Ethernet TCP/IP protocols. With service and maintenance functions rapidly being incorporated into digital Industry 4.0 enterprises, the SmartCheck sensor is compatible with such environments.