A new rail carriage door leaf has been developed by TRB Lightweight Structures Ltd with the help of biocomposite resin-based carbon fibre reinforced (CFRP) sandwich panel with a 100% recycled foam core. This new biocomposite door leaf is specifically designed and fire rated for both overground and underground rail use. The composite structural system is said to smoothly clear BS 6853 and BS 476, as well as being EN 45545 HL3 compliant. This has benefitted the rail industry to opt for a sustainable, ‘green’ composite material for producing carriage door leaves at a similar cost to aluminium bonded door leaves, along with a 35% reduction in weight. TRB has applied its expertise in composite materials technology in railway applications, which has expanded its product portfolio to its already established rail industry customer base in meeting the growing demand for greener and more energy efficient products.
TRB’s design and engineering team collaborated with a resin partner to develop a unique carbon fibre compatible bio prepreg resin. The priority for TRB was to make the new system highly sustainable and enable cost-effective manufacturing of lightweight composite parts that could easily resist the highest level of fire, smoke and toxic fumes (FST) specifications in subterranean rail applications. The new non-toxic ‘bio’ prepreg, does not contain volatile organic solvents and is purely based on a Polyfurfuryl alcohol (PFA) resin which is derived from renewable alcohol made from a completely natural bi-product waste of refined sugar.
As per the company, the new biocomposite prepreg system, which is first of its kind sustainable fire rated material has been exclusively developed to produce FST rail parts as well as carriage door leaves. It can also be useful for producing other rolling stock parts. The foam core used in the rail door leaf composite structure is manufactured from 100% recycled consumer plastic. TRB claims that the recycled foam core is highly sustainable and delivers the required performance of the sandwich panel construction when it's used in combination with the woven carbon fibre fabric on both sides and the bio-resin prepreg. Other matrix designs for applications using glass fibres, natural fibres, or aramid fibres can be custom produced by TRB on request. Depending on the requirements of rail customer, door leaves are offered with a gel coat, finish painted or primed ready to paint.
The biocomposite based system specified for rail carriage door leaves is said to deliver an outstanding performance against fire resistance. An independent data shows that the sandwich panel system easily achieved a Class 1 Category 1a rating when tested to BS 476 Part 7: 1977 for ‘Spread of Flame’, with a 30% less recorded flame spread of only 50mm in the 1.5 minute test time; the maximum allowable is 165mm for the Class 1a rating.
Lyndon Newman, Chief Engineer for TRB commented: “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. 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.”
Lyndon went on to say: “We initially developed this biocomposite product for rail door leaves, but it could be used for other mass transport interior applications. 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’ 40 kg aluminium door leaf excluding any fittings or door furniture to the same sized biocomposite CFRP prepreg sandwich panel system door, which weighs just 26kg.
The TRB biocomposite CFRP door leaf product is claimed to have a 40-year life cycle expectancy and is said to be more robust than its aluminium counterpart, delivering excellent fatigue resistance and low maintenance costs. Attributing to its significantly less weight, the composite door leaf needs a less heavy-duty door operating system and provides multiple cost-saving benefits to rail operators, such as saving energy consumed in every journey and minimised operational damage on tracks. On top of that, they allow for shorter dwell times at the station as the lighter door leaves open and close several seconds faster. Transport for London has adopted this as a way to develop its daily underground service when installed, by enabling an additional tube train to be run per day on a line which demands ease during peak time congestion.
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