The requirements placed on flammable materials and components by the upcoming European standard on fire protection in rail vehicles are very strict for flame-retardant thermoplastics and virtually impossible to meet in some cases. Nonetheless, the polyamide 6 Durethan DP BM 65 X FM30 from LANXESS passes the tests for the upcoming standard with the best possible rating “Hazard Level 3” for specific applications. “This opens up numerous potential uses for our high-tech material in components employed in electrical equipment for rail vehicles at high risk of fire. These include chokes, voltage transformers, windings, contactors and switches,” said Alexander Radeck, an expert in flame-retardant thermoplastics in Applications Development in the Semi-Crystalline Products business unit. The relevant testing was carried out at the Fire Technology Department of Currenta GmbH & Co. OHG in Leverkusen, a test center accredited to DIN EN ISO/IEC 17025 and monitored and certified by the relevant German federal offices.
Classification in model and operating classes defines risk
The measures and requirements for the upcoming standard on fire protection in rail vehicles are currently still defined in the technical specification CEN/TS 45545. The conditions that components or materials need to fulfill in the tests laid down in this standard depend on the rail vehicle design and the type of rail transportation – referred to as the design and operation categories. This differentiation reflects how long passengers spend in the rail vehicle in the event of a fire and how much at risk they are as a result. A hazard level that classifies the potential risk is defined for each design category, depending on the operation category. Three hazard levels (HL 1-3) are defined in total, with HL 3 being the highest. The CEN/TS 45545 standard lists typical components and applications (“products”) in rail vehicles and assigns standardized fire protection test procedures for them. The relevant “product” must meet requirements of varying strictness in these tests, depending on the hazard level.
Low smoke gas density and toxicity, high oxygen index
Among other things, Currenta Fire Technology conducted tests on smoke gas toxicity (NF X 70-100-1) and density (EN ISO 5659-2) and the oxygen index (ISO 4589-2) for the polyamide 6 in accordance with the CEN/TS 45545 standard. The specific optical smoke gas density Ds(max) was found to be just 7 (total test duration 20 minutes). Hazard Level 3 is achieved for internal materials for Ds(max) values ≤ 150. A CIT (Conventional Index of Toxicity) value of 0.26 was determined for smoke gas toxicity. Hazard Level 3 classification is possible in this test for CIT values ≤ 0.75. At 52.6 percent, the oxygen index OI was much higher than the minimum requirement for Hazard Level 3 of 32 percent.
Halogen- and phosphorus-free flame retardance, high flowability
The excellent fire resistance of Durethan DP BM 65 X FM30 is based on a halogen-, phosphorus- and antimony-free flame retardance package. “The polyamide 6 has already proved a success in rail transportation and is used in the Channel Tunnel in holding elements for cable ducts, for example,” said Radeck. It is reinforced with 65 percent glass fibers/mineral by weight. Its melt is nevertheless easy flowing (EasyFlow technology), which means it can be used for even relatively thin wall thicknesses and intricate component geometries.
LANXESS (lanxess.com) is a leading specialty chemicals company with sales of EUR 7.1 billion in 2010 and currently around 15,500 employees in 30 countries. The company is at present represented at 46 production sites worldwide. The core business of LANXESS is the development, manufacturing and marketing of plastics, rubber, intermediates and specialty chemicals.