Sekisui Chemical Co., Ltd. (SEKISUI) has refined its Fiber reinforced Foamed Urethane synthetic railway sleeper, designed to provide the best qualities of wood and high performing synthetic technology in a single product.
As freight, heavy haul and passenger rail networks have grown in Australia and New Zealand, the sector has become more focused on not only the capital cost, but also the ongoing cost of maintaining its fixed assets.
Track owners take upfront and ongoing costs, along with a range of other factors, into account when choosing railway sleepers. While the choice has primarily been between wooden and concrete sleepers, a growing market for alternative materials has emerged over time.
One manufacturer operating in this space is Sekisui. Sekisui uses Fiber reinforced Foamed Urethane (FFU) to manufacture a synthetic railway sleeper, designed to be light and workable like a wooden sleeper, but consistent and durable, making it far more resistant to wear and tear and environmental factors over the long term. The core design feature of an FFU sleeper is its collection of continuous glass fibres which run from one end to another. These fibres reinforce the thermosetting resin foam comprised of rigid urethane resin, which is poured over the glass fibres and then sets during the manufacturing process.
The aim of using FFU is to combine the best features of a wooden sleeper with those of a high performing synthetic sleeper. The FFU synthetic sleepers are a similar weight to natural lumber.
Bending strength is stronger than natural lumber, and maintains this strength for a long period, and the FFU manufacturing process means sleepers can be fabricated to a specific height, width, and length.
“The light weight makes it easy to work on site,” Sekisui’s Yuri Otsuka tells Rail Express. “Like a wooden sleeper, we can also do pre-drilling of holes or grooves for cable protection, for example, and we can paint it a specific colour as well.”
Meanwhile, the glass fibre used gives the FFU sleepers high durability. Sekisui says the anti-corrosive material that constitutes the sleepers is extremely resistant to acids, alkalis, chlorine and sea water. Also like composites, the FFU sleepers are uniform in their quality, and the continuous pultrusion method used makes it possible to manufacture FFU sleepers up to 10 metres long, providing an ideal and reliable solution for transoms and other large and complex pieces of rail infrastructure.
Ongoing cost savings
The overall benefit, Sekisui Marketing Manager for Asia Pacific and the Americas Masaki Hayashi says, is in ongoing costs for the operator.
“The difference between timber and FFU is that FFU has longevity,” Hayashi says. “FFU doesn’t rot like timber, and it comes with uniform quality. When you work with timber it’s very difficult to obtain uniform quality over a large batch.”
According to the test report ‘Follow-up Survey on FFU Synthetic Sleepers after 30 Years in Service’ in 2011 by Railway Technical Research Institute (Japan), the expected life of an FFU sleeper is around 50 years.
“While timber might last that long under specific circumstances. A natural unprotected timber sleeper in some environments may have to be replaced up to seven times during the lifetime of an FFU sleeper,” Hayashi says. “Installation costs including labour, track equipment and safety measures are generally higher than material costs, so with 50 years without replacement, FFU works out much better than natural timber in many applications. FFU also allows for very precise sleeper dimensions compared to wood, making the sleepers even easier to install exactly.”
Proven life cycle
FFU was originally developed in 1974; the railway sleeper application was not developed until 1980. Since then, FFU synthetic sleepers have been used in more than 1,500 kilometres of track. All are still in service after 39 years. Since 1988, they have been used on Japan’s high speed lines, a.k.a. Shinkansen, with service speeds increasing year by year, and currently around 300km/h on FFU sleepers.
“The sleeper has been installed in both passenger and freight applications,” Otsuka says. Australian operators using the FFU sleepers include Queensland Rail, Sydney Trains, CRN John Holland, WA’s PTA and TasRail. It is approved by Queensland Rail and Transport for NSW, and has provisional type approval from CRN John Holland. “It has been specified in transom design by Transport for NSW since December 2018, meaning during sleeper replacement on bridges, operators can use FFU sleepers,” Otsuka adds.
The FFU sleeper has been approved by many other railways, including EBA and Deutsche Bahn in Germany, Network Rail in the UK, and more. Surveys of the FFU sleeper in the field show the same density (0.74g per cubic centimetre) when the product is manufactured, and after 10 years, 15 years and 30 years of use. The follow-up testing also showed FFU sleepers were much above Japanese Industrial Standard levels for a range of strength and flexibility measurements, even after 30 years.
Another technical element Hayashi says separates the FFU sleeper from alternative options is its low thermal expansion coefficient.
“There are different composite sleepers in the world,” Hayashi says. “One greatly unique advantage of FFU is very low thermal expansion due to the continuous long glass fibre pultrusion technology. Many composite sleepers have much larger thermal expansions – so they will change length/gauge as the temperature gets much higher or lower. This makes it difficult to keep the correct gauge – a very important aspect. An FFU sleeper is very reliable for maintaining gauge width.”
Find Sekisui at AusRAIL PLUS at Stand 190.
Contact: sekisui-rail.com