Background

The Australian Rail Track Corporation (ARTC) in Australia runs a section of track that winds it’s way 50 kilometres through the Adelaide Hills in South Australia, negotiating many tight curves and steep grades through densely populated suburban locations. Trains travelling on this track can produce extremely loud wheel squeal and flanging noise. Not only does this upset the residents, but also these friction-induced noises are indicative of increased and irregular wear on both the wheels and the track itself. A large percentage of rolling stock with this problem have been found to have an irregular angle of attack or inter-axle misalignment (referred to as "bad actors"). ARTC needed to measure these noise events, but was there a way to collect acoustic data that was sensitive enough to detect and isolate the bad actors, as well as uncover the underlying relationships to help develop new and informed maintenance and management regimes?

An advanced acoustic array system, RailSQAD® - Railway Squeal Acoustic Detection System, developed by Vipac Engineers and Scientists Ltd., provided the solution. This sensitive measurement instrumentation system has been successfully installed at Heathfield in the Adelaide Hills to detect, follow, record and trend a range of train and wheel/rail noise sources. The system allows managers to distinguish between freight and passenger trains, and it reports exceedances, and other valuable information to the various stakeholders.

A RailSQAD® trackside installation consists of a cabinet housing a microphone array and trackside sensors, to measure wheel speed and direction. Rail cars are tagged with wagon identification AEI tags enabling the system to analyse and trend individual wheelsets. All data streams are connected to a PC-based data acquisition system that applies advanced signal processing techniques that record and analyse the noise emitted by wheel/rail interaction.
Wheelset noise emissions are first classified as Squealing or Flanging, and then ranked according to noise level, against user agreed criteria. This processed data is imported into the RailSQAD® Trending Acoustic Database. The database then produces statistical information for analysis against varying train operating parameters, rollingstock condition and environmental conditions. Stakeholders simply access the database via an ARTC portal.
Using this system, a problematic wheelset can be individually identified, which enables the operator to implement efficient, precisely targeted maintenance regimes, which are more cost effective and prevent disruption to service.

Overall Results

RailSQAD® data collected at the Heathfield Site provides information about the number, loudness and relative occurrences of squealing and flanging events, as well as revealing significant environmental variables affecting wheel noise. The RailSQAD® database also enables the rail operators to identify those freight cars that produce the highest wheel/rail noise emissions: "repeat offenders" are identified and efficient maintenance regimes implemented. Several causal relationships have also been successfully identified and tested, which will assist ARTC in the future management of all their lines.

Future Application

The RailSQAD® system can also be used over a test track to investigate the effectiveness of lubrication and friction modifiers available in the market and to determine if the application of such products at the test site will have a statistically significant effect on the severity and frequency of the noise emissions.
The potential benefits of such monitoring programs are many. Firstly, noise control methods can be targeted, and their effectiveness analysed with reliable statistics. Noise control products can also be tested, and accurately compared against each other. Managers can take a pro-active approach instead of waiting for alarm bells to ring, and RailSQAD® gives the rolling stock and rail asset managers the ability to extract the maximum noise control benefit through improved wheel/rail interfacing which will improve rollingstock and track component life.
VIPAC Engineers and Scientists have agents located worldwide to service the acoustic monitoring needs of the rail industry.