Plastics on track for success on railway

Rail vehicles, ranging from trams to high speed trains, are making use of more and more plastics as substitutes for traditional materials. However, this displacement process is not limited to the vehicles themselves, as rail networks are undergoing a similar, if somewhat slower, transformation.

Wood or concrete has been the conventional choice for rail track sleepers for decades, but these materials could soon be replaced by polyurethane. The process has been underway in Japan for some 25 years, with Sekisui Chemical supplying its Eslon Neo Lumber FFU (Fibre reinforced Foamed Urethane) product that was laid under the track for the Shinkansen high speed train, for example.

More than 90,000 FFU sleepers are being laid every year in Japan and more than 1.3m units are estimated to be in service today.

Now the FFU sleepers have been premiered in Germany, in the Leverkusen Chempark, where a 74m stretch of track has been installed to improve the link between the site and the German Railways network.

The installation used 136 sleepers produced by Sekisui from a long fibre integral skin PU foam, Baydur 60, supplied by Sumika Bayer Urethane, the Japanese PU systems house in the Bayer MaterialScience (BMS) global BaySystems network.

Frequent temperature changes, UV radiation and permanent atmospheric moisture can begin to negatively affect wooden sleepers in a very short time, says Sekisui, which produces its FFU sleepers using pultrusion technology and claims a 50 year service life.

The pultrusion technology also allows it to produce sleepers of any length – a unique advantage over concrete sleepers. This feature proved particularly useful at the Leverkusen installation, where the specific nature of the track led to the use of sleeper lengths of between 2.2m and 4.5m.

The closed cell structure of the FFU sleepers also means they absorb little water, so that their electrical properties are not affected, and the material is naturally resistant to hydrolysis, greases, oils and de-icing salt.

Polyurethane is also finding applications between the sleepers. German rail engineering company Frenzel-Bau has teamed up with BMS to develop Durflex, a new railway track ballast solution using Bayflex flexible PU foam to infill the cavities between the ballast stones.

The Durflex system prevents movement and compression of the ballast as the train passes, increasing the durability of the installation and absorbing structure-generated noise where it is created.

During the summer of 2007, a 300m pilot section of track was laid with the Durflex system at Uelzen on the Hamburg to Hanover high speed rail link. The system has been shown to reduce vibration of the track system and structure-generated noise by 40%. This translates into a 1.5 to 3db reduction in air-borne noise emissions, depending on the type of train travelling over it.

Since then, the system has been applied during renovation of a test track at the main workshop of BVG, the Berlin public transportation company that operates a 350km network in the city. BVG is evaluating the impact on maintenance and noise levels.

Meanwhile, safety requirements are the absolute priority for materials used inside rail cars and two new grades of BMS’s Bayblend PC/ABS sheet meet these demanding criteria.

Both of the new grades, Bayblend FR 3030 and Bayblend MTR, fulfil the full flammability requirements of UL 94 and meet the strict French rail standards. The MTR grade also meets US standards for train applications (Docket 90 A/ASTM E162 and E662).