DuPont interlayers for lightweight and secure train carriage balustrades

Balustrades made from Siglaplus laminated safety glass from Flachglas Wernberg prevent, says the German company, passengers from falling from the upper floor of the newly-developed double-decker train…

Balustrades made from Siglaplus laminated safety glass from Flachglas Wernberg prevent, says the German company, passengers from falling from the upper floor of the newly-developed double-decker train carriages from the Swiss company Stadler Rail AG. Thanks to the use of strong and stiff DuPont SentryGlas interlayers, the glazing – which reaches up to the carriage“s ceiling – can be produced at a very low thickness yet provides high levels of safety. Accordingly, the curved panels also fulfil a principal requirement that applies to all forms of transport – the reduction of weight wherever possible. The Swiss Federal Railways (Schweizerischen Bundesbahnen or SBB) will start to operate the new RABe 511 trains during 2011. Laminated safety glass with SentryGlas interlayers combines a multitude of benefits when compared to standard alternatives. For example, a similarly lightweight toughened safety glass would require the use of an additional guardrail because it will break into a thousand pieces when overloaded – for instance if struck by heavy, sharp-edged luggage during an emergency stop. Even the use of an externally-applied shatter protective film provides only a slight improvement. On top of this, there is always the risk of a spontaneous breakage caused by a nickel sulphide inclusion. Martin Rdel, sales manager for transport at Flachglas Wernberg adds: Stadler Rail sought a safe solution for every eventuality, which would neither require a guardrail, nor would it be heavier than toughened safety glass. By using Siglaplus with SentryGlas interlayers, we have been able to provide them with a solution. In general, a principal benefit of laminated safety glass is that the glass fragments remain stuck to the interlayer, significantly reducing the risk to passengers. Moreover, the glass panel remains intact overall, and is still capable of withstanding relatively high loads, explains Ingo Stelzer, design specialist at DuPont Glas Laminating Solutions. By using high stiffness SentryGlas interlayers instead of standard PVB (polyvinyl butyral), the glass laminate is able to withstand greater loads and can therefore be produced at a comparably lower thickness. Moreover, should the glass break, the DuPont interlayer ensures a considerably higher post breakage strength than PVB. Accordingly, and despite the use of point fixings in the new trains, it is able to provide sufficient resistance to prevent passengers and luggage from falling to the lower floor of the carriage. In order to emphasise these benefits, DuPont carried out finite element calculations to understand the behaviour of different glass structures when subjected to a centralised load of 5 kN (500kg). They show that laminated safety glass with a PVB interlayer needs to be produced at a thickness of 17.52mm (8mm glass/1.52mm PVB/8mm glass) in order to obtain the same level of resistance to deformation as a 10mm thick panel of toughened safety glass. Stelzer continues: When using a SentryGlas interlayer, which is also 1.52mm thick, then two glass panels each with a thickness of just 5 mm are sufficient to replicate the performance of toughened safety glass. Accordingly, the weight saving in comparison to standard laminated safety glass with PVB is close to 40%. The difference in weight to toughened safety glass is purely down to the low additional weight of the interlayer. Further calculations revealed that a laminate construction consisting of just two 4 mm-thick panes of heat-strengthened glass and a 0.9mm thick SentryGlas interlayer would suffice to meet current regulations such as UIC 566 Loadings of coach bodies and their components. Comprehensive laboratory testing conducted by Flachglas Wernberg, which included pendulum impact tests from a great height, confirmed DuPont“s calculations. The glass panels supplied to Stadler Rail, each 800mm wide and 1,370mm high, are indeed neither thicker nor heavier than their toughened safety glass counterparts, confirms Martin Rdel. Nevertheless, they meet the very high safety requirements demanded of them for the application, and without increasing energy use of the train itself. Using the screen printing process, Flachglas Wernberg applies two different finishes to the balustrade panels with SentryGlas interlayers. In its opaque form, the balustrade acts as a so-called privacy wall for passengers in the first class carriages, performing a visually separative function. In the second class carriages, the panels are mostly produced with a high degree of clarity, providing an impression of openness and space. The SBB will use our new trains on the Zurich district line, and the demands placed on the glass panels will be correspondingly high, explains Andreas Lunardon, who, as interior engineering manager at Stadler Rail, was very much involved in the specification of the glass. The manufacturer designed the Siglaplus laminated safety glass panels in such a way that they remain durably attractive in the long-term, even despite such tough conditions. The surface, including the printed sections, is extremely scratch resistant. The very high edge stability of laminates made with SentryGlas interlayers means that the panels will retain their crystal-clear transparency even at the edges – and this for the full duration of their expected lifetime of close to 40 years and despite intensive cleaning with highly-effective aggressive agents. Stadler Rail will supply a total of 50 double-decker trains to the SBB as from 2011. Divided into six sections, the 150 metre long trains weigh 296 tons and achieve a top speed of 160 km/h (100 mph). They each have space for 1,694 passengers, 535 of whom can be seated. A later order has been placed for a further 24 trains, in this case divided into four sections, to be used on the SBBs regional express lines. Our positive experience with this lightweight form of laminated safety glass has led to its planned use by Stadler Rail in future double-decker projects currently under development.