INTRO: Richard Hope reports on a cheap and simple development
AN ECONOMICAL way of mechanising the renewal of track by lifting sections up to 270m long straight out of the ballast has been devised by Jarvis, which currently owns and operates around 55% of all on-track plant in the UK.
Jarvis commissioned in 2000 a fully automated Track Renewal Train acquired from Harsco Track Technologies in the USA. Like similar machines widely used in continental Europe, the Harsco TRT replaces rails and sleepers in the track on which it is running. However, it is heavily engaged on the West Coast main line upgrade.
Jarvis has now deployed the much simpler and cheaper Slinger TRT. Like the twin-jib relaying machines introduced by British Rail in the 1960s to lift out or place an 18·3m standard track panel, Slinger works off the adjacent track. Whereas this would normally be used to pass traffic in both directions on railways elsewhere, British tracks are so close together that a double-track line is normally closed whenever relaying takes place.
The first version, Slinger 1, was introduced in July 2002 primarily to avoid manual handling of steel sleepers, which are now used by Network Rail in large numbers on secondary routes. The bodies of surplus curtain-sided vans were replaced by a pair of swivelling post and cantilever-beam hoists mounted on one side of the wagon. Each Slinger 1 hoist can lift 3·5 tonnes, and a rake of wagons is marshalled with a generator van at one end.
Instead of dropping bundles of steel sleepers by the lineside during an earlier possession and then placing them in position manually on the scarified ballast bed, the sleepers are now pre-loaded in pallets on the Slinger wagons. They are then hooked individually to a spreader beam and placed accurately in their final position.
The third version, Slinger 3, is the track renewal train. Its efficiency was demonstrated at Formby during a four-day blockade in February where it was used to replace 6·9track-km on the Merseyrail route to Southport electrified at 750V DC third rail.
Slinger 3 consists of 12 wagons plus a generator at each end. With 24 synchronised hoists, 270m of old track including rails and sleepers - provided their fastenings hold - can be picked up in a single lift. The old track is placed on the wagon decks, and the process is repeated until up to 1080m is stacked four-high. Slinger 3 unloads the old track on to an adjacent stretch of the same line for cropping into shorter lengths and subsequent removal on conventional wagons.
Trackbed preparation is carried out by another Jarvis innovation. Mole can excavate up to 1000 tonne/h of fouled ballast and dump it via conveyors into wagons standing on the adjacent track. The machine then prepares a bed for the new sleepers using laser-levelling techniques.
Meanwhile, Slinger 3 returns to the other end of the site to pick up from loaded wagons sufficient concrete sleepers for 270m of new track. It then places them on the prepared trackbed at the correct line and spacing, as described for steel sleepers. Finally, Slinger collects the new rails and places them on the sleepers ready for welding. All lifts and drops are carried out by one operator using radio control of all the hoists.
However, an 18·3m track panel with concrete sleepers weighs 11 tonnes - too much in terms of the overturning moment on the wagons. The innovation that made Slinger 3 possible was a retractable leg on the outer end of each beam, which is lowered on to the ballast on the far side of the track being lifted. Slinger 3 is fitted with 6 tonne hoists, and with props in place a pair of hoists can safely lift 12 tonnes.
When Slinger is working on canted track, it is necessary to ensure that the beams on which the hoists run are level. This is achieved by jacking up the structure carrying the post and beam, which is hinged to the wagon. The outer props have a ball-jointed elephant’s foot that is lowered manually to make contact with the ground before a track panel is lifted.
Slinger and Mole cost substantially less than the high-output Track Renewal Train. Being much simpler to build and operate, Jarvis hopes that they will also prove to be more reliable. A 15-wagon version able to lift 320m of track is planned.
CAPTION: The 24 synchronised 6 tonne hoists on Slinger 3 can remove 270m of old track - including rails and sleepers - in a single lift
CAPTION: To ensure that the hoists run level, the beams are hinged to the wagon and the support posts are carried on ball-jointed feet