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TRB Lightweight Structures has developed a carbon fibre reinforced plastic (CFRP) sandwich panel door leaf using a bio-based resin and a 100% recycled foam core.
The new biocomposite door leaf product has been designed and fire-rated for both overground and underground rail use. The composite system passes BS 6853 and BS 476 and is EN 45545 HL3 compliant.
TRB says it can now offer the rail industry a sustainable composites option for carriage door leaves at a comparable cost to aluminium bonded door leaves, with a 35% weight saving. This product broadens its offering to rail industry customers to meet a growing global market need for more energy efficient products.
The design and engineering team at TRB worked closely with a resin partner to develop a new, proprietary carbon fibre compatible prepreg resin. The new system had to be highly sustainable and enable TRB to cost effectively manufacture lighter weight composite parts that would meet even the most demanding fire, smoke and toxic fumes (FST) specifications in subterranean rail applications. The new ‘bio-prepreg,’ which is non-toxic and does not use volatile organic solvents, is based on a polyfurfuryl alcohol (PFA) resin derived from a renewable alcohol produced from a natural waste bi-product from refined sugar production.
The new prepreg, which TRB states is the first sustainable fire-rated material of its type on the market, has been developed exclusively for TRB to manufacture components for FST rail applications. As well as carriage door leaves, the prepreg can be used for other rolling stock parts. The foam core used in the rail door leaf composite structure is produced from 100% recycled consumer plastic. The recycled foam core meets TRB’s ‘high sustainability’ specification objective and delivers the desired overall material properties performance of the sandwich panel construction when used in combination with the woven carbon fibre fabric on both sides and the bio-resin prepreg. Matrix design options for other applications using glass fibres, natural fibres or aramid fibres can be custom made by TRB on request. Depending on rail customer needs, door leaves are supplied with a gelcoat, finish painted or primed ready to paint.
According to independent data, the sandwich panel system when tested to BS 476 Part 7: 1977 for ‘Spread of Flame’ achieved a Class 1 Category 1a rating, with a 30% less recorded flame spread of only 50 mm in the 1.5 minute test time. The maximum allowable is 165 mm for the Class 1a rating.
“We are extremely pleased with the overall performance data for the new biocomposite carbon fibre prepreg sandwich panel system, in particular the FST specifications achieved,” states Lyndon Newman, Chief Engineer for TRB. “In the 30 years I have been in the industry I have never seen such impressive fire performance test results for a non-phenolic based thermoset system, achieving the BS standard so comfortably. Our PFA bio-resin prepreg has fire retardant properties greater than phenolics, plus excellent temperature and chemical resistance.”
“We initially developed this biocomposite product for rail door leaves, but it could be used for other mass transport interior applications,” he adds. “We have brought aerospace prepreg technology to our rail customers and can now offer them a truly ‘green’ material design option that is 35% lighter than a bonded aluminium door at a comparable cost.”
The data provided by TRB compares a ‘like for like’ door leaf in aluminium which weighed 40 kg excluding any fittings or door furniture, to the same sized door produced by TRB in its new biocomposite CFRP prepreg sandwich panel system, which weighs just 26 kg.
The TRB biocomposite CFRP door leaf product, which has a 40 year life cycle expectancy, is reported to be more robust than its aluminium equivalent, has superior fatigue resistance and low maintenance costs. Due to the significant weight reduction, the composite door leaf requires a less heavy duty door operating system and provides a number of cost saving benefits to rail operators, such as reduced energy consumption per journey and less track wear and tear. Additionally, they provide the opportunity for shorter station dwell times as the lighter door leaves open and close several seconds faster. For Transport for London, this has been calculated as a way to improve its daily underground service when installed, by enabling an additional tube train to be run per day on a line where needed to ease peak time congestion.
Image provided by TRB
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