Application Verification of Fire Retardant Coatings for Aluminum Alloy Carbody Underframes in Urban Rail Transit Vehicles

ObjectiveHigh-power electrical equipment is often arranged centrally beneath the underframe of urban rail transit vehicles. Due to the operational characteristics of the equipment, this area is usually regarded as a potential fire source. Therefore, it is necessary to conduct systematic research on the fire performance of the vehicle floor structure. MethodA fire resistance test is conducted on a vehicle body sample from a Beijing metro line. Its structural integrity and thermal insulation performance are systematically evaluated to verify whether the fire resistance duration meets customer requirements. The vehicle body and interior structure design, as well as the composition characteristics of the fire-retardant coating, are analyzed in depth. Result & Conclusion When the test duration is 5 min, the specimen exhibits slight inward concave deformation. After 12 min testing, the maximum inward concave deformation at the exact center of the carbody floor reaches 3.4 mm. At 25 min, smoke begins to escape and at 28 min, the smoke volume increases significantly. The test is terminated at 31 min, with no structural damage or thermal insulation failure observed in the specimen. The fire-retardant coating on the fire-exposed surface of the specimen undergoes carbonization and expansion, forming a stable isolation layer that can effectively protect the aluminum alloy carbody and interior materials from high-temperature damage. The fire resistance performance of the specimen fully meets the fire duration requirements specified in the standard EN 45545-3：2013 Railway applications—Fire protection on railway vehicles—Part 3：Fire resistance requirements for fire barriers, therefore suitable for the vehicle body fire protection design of the designated line.