Grinding out a result

Recent developments in wheel lathe technology mean mobile lathes can now be a viable alternative to fixed installations. Andrew Roden talks to London Underground PPP contractor Tube Lines about its experiences.

GRINDING wheels on London Underground’s Jubilee Line fleet at Stratford depot, East London, has long been a challenge. The conventional solution of an underfloor wheel lathe has never been an option because of significant archaeological remains on the depot site, meaning that trains had to be taken out of service at weekends and taken to another depot off-site for wheel reprofiling. It was expensive, time-consuming, and engineers have long sought a better way of reprofiling wheels, preferably at the depot.

The contract engineer for Tube Lines, the company responsible for maintaining the Jubilee Line, is Mr Nick Clyne, and he is candid about the limitations of this policy: “Because of the equipment mounted on the trains, you can’t simply take the wheels off and send them for reprofiling, and we had to do without two trains for a whole week, putting the fleet under pressure at peak times. “I was really stumped about finding a solution until I discovered the idea of using a mobile wheel lathe. You jack the train up, and the wheel lathe drives underneath the vehicles and reprofiles the wheels.”

After investigation, Clyne believed a mobile wheel lathe would allow two trains - one three-car and one four-car set usually coupled together - to be reprofiled at a weekend, and still be available for traffic at busy times from Mondays to Fridays. “It gave us an extra two trains a week, compared with the previous method,” confirms Clyne.

Clyne was quickly in touch with German manufacturer Hegenscheidt, which makes the Mobiturn range of wheel lathes. These are mounted above ground, and are particularly suitable where space for a conventional underfloor lathe is limited, such as Stratford. A few are already in use in Europe, mostly on light rail systems, but Clyne and Tube Lines recognised that the technique was ideal for the heavy metro operation of the Jubilee Line.

	The Mobiturn wheel lathe travels along the length of the train and grinds each axle in-situ.

The machine was delivered in 2007, just three months after being ordered as it had already been built by Hegenscheidt. It made its first cuts in August that year, and quickly dispelled the speculation of some more traditional engineers used to fixed underfloor lathes that it wasn’t up to the job. Since then, under a service agreement with Hegenscheidt, it has been in use 24-hours a day at weekends. Some have questioned the performance of mobile lathes compared with fixed installations. Clyne says that while it is slower at reprofiling wheels, the fact that arc shields designed to limit the effects of arcing from the conductor rails do not have to be removed because of the Mobiturn’s close clamping arrangement means that overall there is little in it: a four-car train, with 16 axles, can be reprofiled in 12 to 16 hours.

And Clyne pays tribute to its reliability too: “When the machine arrived, we plugged it in, and it worked - to use a cliché - straight out of the box: its reliability has been exceptional and I’ve been very impressed.” The success has been noted by the British main line track authority, Network Rail, which has ordered a pair of mobile wheel lathes though it is yet, IRJ understands, to commission them fully into service.

Of course, given enough space, then an underfloor wheel lathe will usually be preferable, but the success of Mobiturn means that it is becoming increasingly possible for even small depots to have their own wheel reprofiling facility - something Hegenscheidt is no doubt keen to encourage. This mobile lathe is having a profound impact on the Jubilee Line fleet already, with intervals between reprofiling now standing at 63 weeks, compared with three years on other London Underground lines. This should mean that track quality is maintained for longer (replacing track on underground metros can be and often is a lengthy and difficult process) while passengers get a smoother ride, and trains suffer fewer potentially damaging vibrations.

On the face of it, a single wheel lathe might seem unlikely to transform service reliability for passengers, but Tube Lines’ Mobiturn at Stratford is doing just that, quietly, unassumingly, but assuredly.