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To protect public safety, fire risk is carefully considered by European train manufacturers and their suppliers. “Different requirements apply for railway vehicles than for buildings,” explains Thomas Lorenz, managing director of the Lorenz Kunststofftechnik GmbH (Wallenhorst, Germany). “They require the use of different plastics, and pose difficulties for manufacturers of material and components.” A new fire protection standard for German rail transport, DIN EN 45545-2, put forth by DIN (Berlin, Germany) now will regulate and standardize the fire protection requirements on a European level so that interoperability in the trans-European high-speed traffic as well as the safety of rail passengers will be guaranteed. The fire protection standards for railway vehicles have been tightened, compared to the previous regulations.

To meet the new requirement, Lorenz Kunststofftechnik developed two new thermoset molding compounds, BMC 0204 and SMC 0208. They have been designed to address the broad range of new requirements in rail vehicle construction with regard to their mechanical properties and flame retardant behavior, and are among the first to pass the fire protection test in conformity with the new standard.

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The new material test procedures focused on flammability, flame dispersion, and in particular, the development of smoke gas and its density and toxicity. Thermoplastics, the most commonly used material in rail vehicle construction, will not fulfill the new standards in all of these areas, says Lorenz Kunststofftechnik. The company says thermoplastics show extensive smoke development and due to their low softening point, melt too quickly. Especially with critical parts, such properties may become a risk for passengers. Therefore, the new standards consider flammability and flame dispersion (ISO 5668-2), the thermal release rate (ISO 5660-1) and smoke gas density as well as the toxicity of the smoke gas (ISO 5659-2) for the classification of the fire behavior and fire side effects.

To calculate the Hazard Level (HL), on which the requirements of the classification system are based, the operating and construction categories of DIN EN 45545-2 were used, with various fire protection tests required. For example, the material is differentiated into “generally accessible” and “not accessible” areas, based on general range of application inside or outside the train and specific usage, such as furniture or mechanical facilities. Surfaces made of SMC, for example, have been approved for the highest HL tier (HL3).

SMC, available as semi-finished product in rolls, is used where high mechanical strength and stiffness is required. In the rail sector SMC is commonly used for the exterior and interior cladding, window frames, seats and hubcaps. BMC is especially suitable for the production of small parts, for example, light switches or electrical plug connections, as it can be manufactured by compression molding, injection molding, transfer molding and injection-compression molding. Due to its comparative tracking index (CTI) values of 600 volts and a thermal conductivity of 1,35 W/mK, BMC is an excellent insulator for electronic components.

The various fields of application of BMC and SMC at all risk levels help reduce the amount of material used in the rail vehicle construction, due to lighter weight, and thus reduce production and warehousing expense. With regard to the trend to employ more composite components for weight, design and comfort reasons, these new thermosets provide options for many applications thanks to their advantageous fire behavior.