The railway runs on sleepers – literally. Apart from a few miles of track which has a fully-concrete base (slab track), usually in tunnels with tight clearances, Network Rail’s 20,000 miles of railway track are mounted on sleepers.
Let’s consider the maths. 20,000 miles of track with a sleeper every 650mm (sorry about the mixed units) – that’s around 49 million sleepers in total. Now some routes have wooden sleepers, and some medium-speed lines have steel ones. But the bulk of the main line railway uses concrete.
On average, a railway has to be replaced after 40 years. So it’s a simple calculation to come up with the fact that Network Rail needs one million sleepers a year just to keep up with its replacement programme.
A reliable supply of volume sleepers is therefore essential to Network Rail’s business. However, it had only two main suppliers, Cemex in Washwood Heath, Birmingham, and Tarmac’s Tallington factory in Lincolnshire which was scheduled to close. Although some were also being sourced from Turkington Precast in Portadown, Northern Ireland, something needed to be done.
One of the largest manufacturers of concrete sleepers on the continent is Leonhard Moll. With factories in Hanover and Laußig near Leipzig, as well as foreign subsidiaries in Poland and Croatia, it is a major player.
Britain’s Trackwork, based at Kirk Sandall near Doncaster, is a major supplier of wooden sleepers as well as complete track items such as switches and crossings. So the two companies got together to look at setting up a new sleeper factory in the UK in a former Pilkington Glass building that adjoined the Trackwork site. However, the logistics were difficult and initial costings didn’t show the savings that Network Rail needed.
So, instead, a tri-partite arrangement was made. Network Rail would build a brand-new factory on the Woodyard site on Ten Pound Walk in Doncaster. This would have a mainline connection, making the logistics much more acceptable, and there would be space for a stockyard and distribution hub as well as a factory. Trackwork Moll would supply the machinery inside the factory and the technology to actually make the sleepers by a highly automated process which would reduce costs as well.
Trackwork Moll has a ten year contract to supply up to 400,000 sleepers a year – which was a good justification for the whole project.
The site was cleared, with a few unused buildings being demolished and some disused sidings lifted, so that work could start at the beginning of October 2012. Trackwork Moll contracted Sheffield-based contractor JF Finnegan to carry out the work as part of a policy to involve local companies in non- railway work wherever possible.
One early constraint was the problem of rainwater run-off. The local drains would not cope if the large, 200 metre long factory was subjected to a major downpour – they could only take a maximum of five litres a second from the whole site. Therefore, principal consultant Hannah Reed developed a SUDS (sustainable urban drainage system) solution which created a water reservoir under the external hard-standing of the factory. This would be filled by the run-off from heavy rain, and then released to the local sewers in a controlled manner. EPG (Environmental Protection Group) carried out the design which was installed by specialist contractor SEL Environmental Ltd.
The building itself is a conventional steel- framed structure finished in a gun-metal grey cladding. It has a 22 metre high ‘tower’ at one end that contains the silos for the concrete batching plant and allows the attached Network Rail logos to be seen from some distance away. In fact, the silos were installed first and the factory then built around them.
To one side of the new building are the main stockyard and railway sidings. A large gantry crane spans the stockyard and will be used to both move finished sleepers into place and to load and unload supply trains (recycled sleepers from the high-output track replacement trains will come in here as their wagons are reloaded).
On the other side, there is a storage area for all the Pandrol clips and cast-in shoulders that will be installed in the sleepers themselves.
Construction took almost exactly a year – 11 months plus one month of snagging. Peter Heubeck was very pleased with the way everything had gone.
Inside, all the kit is now in place. When The Rail Engineer first visited at the end of October, some equipment commissioning was still going on, but trial production runs started in December.
The production process is interesting in itself. Although Leonhard Moll has a wealth of experience in making concrete sleepers, it tends to do this using a carousel process with moulds mounted on rotating beds. This was to be the first factory to use a long-line method.
Peter Heubeck, general manager of Trackwork Moll, explained why: “The carousel method is not as efficient for Network Rail’s design of sleepers. The G44 is a big, heavy sleeper, designed for 30 tonne axle loads and 140mph running. If the carousel manufacturing process was used, it would require quite chunky steel end anchors at both ends of each sleeper for the tensioning strand which would significantly increase the cost.”
So production manager Ralph Kortmann had to come up with an automated long line process. Long line methods are not new, they have traditionally been used in the British market, but not on this scale.
Looking at the factory, it is easy to see how the process works. There are four production lines, running side-by-side up the length of the building. Each line has a row of moulds, one sleeper long by eight sleepers wide, and there are 44 rows of them arranged end-to-end. The moulds are designed so that sleepers are cast upside down, with all the markings machined into the mould and the flat bottom of the sleeper ending up on top. The shoulders for Pandrol rail clips are also placed in the bottom of each mould, ready to be cast in.
Once a complete line of moulds is in place, the reinforcement strands can be positioned. Reels of spirally-wound reinforcement strand are positioned at one end of the line, and the individual wires picked up by a moving carrier. That then proceeds down the line, pulling the strands behind it, until it reaches the far end. There it is locked into a 900-tonne concrete block, as are the wires at the reel end, and a 7.5 tonne tension applied. This not only gives the required pre-tensioning, but the arrangement of the wires in the carriers gives the correct strand pattern as well.
Now it is time for the concrete to be applied. This is mixed in the batching plant up in the tower and transported down the line in a skip suspended from the overhead crane. A precise amount is released into each mould, which is then vibrated to make the concrete settle around the reinforcement wires and to fill the mould without airholes or voids. Once the complete line is full, it is left to cure.
Three of the four lines are identical, and will make only G44 sleepers. The fourth line can be changed over from G44 to the lighter EG47 type. This, being shallower, needs a slightly different wire arrangement than the regular G44 but Ralph Kortmann was able to come up with an arrangement that suits both the EG47 and the G44. For the moment, these are the only sleeper designs that the new factory will make.
By the end of a shift, all four lines of moulds will be full and curing- a process which largely happens overnight. The next morning, work starts on stripping sleepers out of the first line of mould that was filled the previous day. Tension is released on the cables and each set of sleepers cut free. These are then turned the right way up, Pandrol Fastclips are attached, and piles of sleepers moved to an interim stock line outside. They will be released into the main stockyard later. Meantime, the individual moulds are cleaned, sprayed with an oily release agent and fitted with cast-in shoulders – ready for the whole process to start again.
Samples of sleepers, and of each batch of concrete, are tested in the in-house laboratory so that quality can be assured.
So that’s the process, which itself imposed limitations on the construction of the factory. The ground in the old Woodyard site was not the best – soft material over sandstone that was eight metres down and a very high water table. This necessitated 1500 piles to support the equipment – particularly the heavy concrete tension blocks which themselves reach down 3.5 metres into the ground.
Once approval testing has been completed on all three styles of finished sleepers (G44, EG47 and G44 with an EG47 wire pattern), the factory will be in full production in January. It has already had its official opening – Secretary of State Patrick McLoughlin did that in mid- December. The first task will be to build up some stock, the stockyard can hold around 90,000 sleepers or three months’ production, and then sleepers will start appearing on the Network with TWM-D (Trackwork Moll Doncaster) written on them.
Which will allow Network Rail’s procurement team to relax a little, knowing it has now secured a strategic supply of concrete sleepers for the next ten years.