Last week marked a proud moment for Trelleborg when our fire retardant protective coating, DragonCoat, was shortlisted for two coveted UK Rail Industry Awards.
DragonCoat, which began development back in 2006, is designed to address fire safety issues across all industries working with rubber components, namely anti-vibration and suspension mounts. Here we take a look at steps we at Trelleborg went through in order to develop this innovative product.
The idea for DragonCoat came about after an internal safety review of rubber suspension components on mass transit vehicles. These components are typically made from natural rubber, which whilst it provides unparalleled performance, comes with a fire risk. When exposed directly to a high heat source the rubber can burn, thus providing additional fuel in the event of a fire and also additional smoke emissions.
Although Trelleborg had been engineering railway suspension solutions for over 50 years, we had little information relating to the burning behaviour of suspension products. Partnering with the University of Bolton, we set out to develop a fundamental understanding of the effects of fire on rubber and establish the best remedy. Six months of research found that by changing the composition of the rubber compound to include fire retardant materials was not a viable route, as it was impossible to retain the precise performance characteristics our customers rely on.
After considering various options it was decided to concentrate on the development of a coating. The main challenges here were threefold:
- To get the required fire retardant performance from a relatively thin layer which would no impact the performance of the product.
- To impart sufficient flexibility to remain effective through the working life of the product
- For the coating to permanently adhere to the rubber parent body
This was a balancing act as the elastomers that give the required operational material characteristics tend to be flammable, and fire retardant materials tend to impede flexibility, especially when included in the proportions required to form a physically substantial barrier. Thereby jeopardising the suspension performance the product was designed for.
The problem was solved by incorporating a chemical intumescence making the coating expand when heated to give the required heat and fire resistance without adversely affecting flexibility or adherence. The development was meticulous and very time consuming, with detailed testing on these specific characteristics along with simple burning tests conducted in-house. Validation on burning behaviour was carried through our University partners, and finally Exova, an accredited independent testing house.
Our internal product tests included a large DragonCoat covered bearer spring, with an otherwise identical non-coated product, containing 10 litres of natural rubber. Both were exposed to a gas flame for two minutes. The non-coated product showed characteristics of standard natural rubber, igniting easily and yielding heat, dripping molten rubber, and emitting and heavy smoke. The treated product allowed initial localized ignition but released minimal heat and smoke, and self-extinguished at 12 minutes.
In the context of a fire occurring on a train, these factors reduce the risk of passenger exposure, increasing evacuation time by up to 3 minutes, as demonstrated by these individual results:
- Heat Release (MAHRE) 180 seconds gained (complies to EN ISO 45545 category HL2)
- Smoke Toxicity 180 seconds gained (complies to EN ISO 45545 category HL2)
- Carbon Monoxide 180 seconds gained
- Carbon Dioxide 195 seconds gained
The coated part was also shown to:
- Maintain consistent suspension and suspension performance
- Retain full cohesion between the coating and the rubber section of the spring
- Survive extreme load and displacement test conditions
Tests to the new EN 45545 standards have shown broad compliance to HL2 standards without any effects on the spring performance. The coating also remained adhered to the product during durability trials equivalent to the service life of the springs.
DragonCoat has been nominated in both the Product Innovation and Design Innovation categories at the URKIA. The awards, which recognizes and honours significant contributions to the growth and development of the rail industry, will take place in London on the 11th February 2016. We look forward to hearing the final result!