Evolution of Rail
Originally rails were only available in lengths of about 5 m. Over the years rail lengths have increased dramatically and are now available in sections well in excess of 100 m. The reason for the significant increase in rail length is the drive to minimise the number of joints or welds in the track to improve reliability, (as joints/welds have a much higher failure rate). Traditionally with short rails, gaps are left at the rail ends to allow for thermal expansion in hot weather but they also result in a less smooth ride. Modern long-rail practice is to use continuous welded rail where adjacent sections of rail are flash butt welded (or aluminothermic welded) which allows much smoother rides which is especially important for high speed trains. Buckling, due to the lack of expansion gaps at rail ends is prevented in hot weather by stretching the rail in situ to limit the thermal expansion forces generated. In the UK below 27 oC the rail is in tension and above this in compression.
For these very long lengths the only practical means of transporting the rails is by using the existing rail network!
120m rails being shipped from UK to Germany
Despite the long history new rail products continue to be developed to cope with the increased demands on the railway. One such new product from British Steel is Zinoco – a corrosion protected rail for use in aggressive areas such as level crossings and wet tunnels. Traditionally rails corrode very slowly with some 50 year old rails still being fit for service. However in some particularly aggressive areas corrosion lifespan can be measured in months rather than years. To extend rail life to an acceptable level, a Zinc rich alloy is thermally sprayed on to the rail to deliver both barrier and cathodic protection. This protection greatly enhances the corrosion life, meaning rails are safer for longer and ready for the ever increasing demands we put on our railways.
108m long Zinoco rails awaiting installation into a UK tunnel