High-tech wheel monitoring arrives in London: Metronet Rail is introducing a state-of-the-art system to monitor wear and detect faults on the wheels of trains operating on London Underground's sub-surface lines. The objective is to change from reactive to preventive maintenance

International Railway Journal, Oct, 2004 by David Briginshaw

METRONET Rail is responsible for maintaining and upgrading two-thirds of the London Underground (LUL) network under the public-private partnership (PPP) with LUL. Metronet is investing 15 million [pounds sterling] to improve the management of Fain wheels on its sub-surface fleet operating on the Metropolitan, Hammersmith & City, Circle, East London and District lines. The project is due to be completed in spring 2005.

There are two key elements to the programme: the installation of a new wheel monitoring and fault detection system by Talgo, Spain, and a new underfloor wheel lathe being supplied by Hegenscheidt MFD, Germany, to correct any defects and maintain profiles. The Talgo system is being installed at three depots: Neasden, Upminster, and Hammersmith to cover the three different fleets of trains operating on the subsurface lines. Upminster depot is being equipped with the new Hegenscheidt MFD tandem-head wheel lathe, while the existing single-head wheel lathe at Neasden depot is being upgraded.

"We are currently using a traditional system to repair wheels," Mr Michail Divaris, Metronet's project manager, explained to IRJ. "At present, we have to lift the train and remove the wheels to reprofile them. On the 44-year-old Metropolitan Line fleet, which is prone to autumn leaf-fall flats, we reprofile the wheels every two years compared with every four and a half years on average for the District Line fleet."

This is obviously very time-consuming and expensive, and it is reacting to problems, rather than trying to spot them before they become too serious. "We wanted to measure wheels at the tolerances we selected, and we wanted to identify defects up to a depth of 5mm," Divaris said. "Talgo was the only company that could guarantee the level of accuracy that we required."

Each set of Talgo equipment has to be housed in a pit in a position where as many trains as possible can pass over it. "Ideally, we would have liked to have put the equipment inside a depot building, but we chose the depot access tracks because we plan to redevelop the depots in the future," Divaris explained. "This meant that we had to cover over the area because the performance of the monitoring equipment could be affected by direct sunlight over the camera and laser lenses."

The wheel monitoring system operates automatically. Trains normally travel over the equipment at up to 8km/h, but monitoring will be aborted if the train is travelling too fast. The first module contains brushes to remove grease from the wheels to ensure accurate readings. The second module has two parts. The first conducts an ultrasonic scan of the wheels up to a depth of 5mm. The results are displayed on a screen. Surface defects and sub-surface cracks are identified. The second part contains lasers to illuminate the wheel profile, and cameras. Pictures of the actual wheel profile are then compared automatically with a standard wheel profile.

The equipment measures the following parameters: defects, flange height and thickness, cone angle, back flange wear, sharp flange, and the overall wheel profile. Information is stored in a database for future reference and to identify wear patterns.

A standard wheelset is lowered onto the track by crane every six months to recalibrate the equipment. All trains have been fitted with credit-card size electronic tags, one at each end, so that the system can identify each train.

The Talgo systems at Neasden and Hammersmith depots were completed in July and were due to become fully operational last month. The installation in Upminster depot is nearing completion and should be fully operational in November. The Talgo equipment cost about 1.5 million [pounds sterling]. Metronet is now negotiating a 10-year maintenance contract with Talgo.

A key issue to be decided was the time interval between monitoring, as Divaris explained. "Wheels do not wear that quickly, so there is no point in monitoring them too often, but if the intervals are too long then faults will not be detected. We will monitor wheels at three to six week intervals depending on the fleet, but we are still refining this."

Divaris is enthusiastic about the benefits of wheel monitoring. "The system will identify problems that need immediate attention, or that will require attention in the not too distant future. It will also identify if there is a problem on the track that is damaging wheels, for example if several trains start to exhibit the same faults or wear patterns. The key thing is to identify problems quickly to prevent further damage to either the wheels or the track.

"The results of our tests so far are very positive. We have achieved a 98% capture rate of wheels passing over the monitoring equipment, and measurement accuracy is very good."

Metronet recognises that it will have to do more work on the wheelsets initially to get them into good condition. This will then enable it to move from reactive to preventive maintenance.

The wheel lathes will be operated as part of a production line to minimise downtime. The objective is to treat half a train at once and to do as many activities as possible at the same time. This includes things such as adjusting ride height and the suspension, non-destructive testing of axles, and any light maintenance that is necessary This method of working was pioneered by Metronet and first used at Northumberland Park depot on the Victoria Line.