A second-generation transition beam has been designed and developed by Transnet Freight Rail (TFR) and INFRASET Railway Products. Transition beams smooth out the difference in resilience between normal ballast-mounted rail track and the concrete-mounted track found in tunnels.
The new beam represents a substantial advance over its first-generation counterpart, jointly developed by TRF and INFRASET for the Richards Bay coal line nine years ago, in that it is much easier to produce and simpler to install. Two beams (four in all) have been placed at each entrance to the only tunnel on the Saldanha / Sishen ore (Orex) line, the northern end being situated at Elands Bay on the West Cape coast.
Transition beams comprise individual sleepers which are post-tensioned to form a single ladder-shaped beam. Rails are secured to the beams with Pandrol fastenings. Because they rest on ballast, the beams provide intermediate resilience, approximately 50% less than normal ballast-mounted track and 50% greater than the concrete-mounted track found in tunnels.
Josia Meyer, senior engineer track technology at TFR, says the net effect of stepping resilience up or down – depending on the direction of the train – is that the frequency of maintenance required at tunnel entrances is reduced from three times to once annually. This in turn minimises line closures and improves overall productivity.
“Track assemblies at tunnel entrances, which are not protected by transition beams, are less able to withstand the additional vertical and horizontal forces generated by trains as they move from concrete-mounted to ballast-mounted track, and vice versa. These additional forces accelerate ballast deterioration by a factor of three – hence the higher maintenance requirement,” says Meyer.
Given that TFR intends increasing freight volumes on the line from the current 45 million tons to 60,000 million tons a year, any avoidance of line closures has a direct impact on tonnages hauled.
Attie Coetzee, civil maintenance manager on the Orex line, says that the line carries some of the longest production trains in the world.
“These stretch to over 10km and comprise up to 342 wagons and ten diesel locomotives each. The Orex line is undergoing continual improvements. For example, ten years ago its maximum carrying capacity was only 18 million tons,” said Coetzee.
Sizwe Mkhize, product manager of INFRASET Railway Products, says the joint development of a local transition beam first began in 1999 when Transnet decided to replace a Japanse beam, which precluded tamping of the ballast situated immediately beneath it.
“This first-generation replacement beam proved successful in reducing the amount of maintenance required on the coal line and the improvements now incorporated in the second- generation beam were installation and production driven,” concluded Mkhize.