1. What is the difference between "standard gauge" and "narrow-gauge" rails, and what models are used?
Standard gauge (1435mm) rails are wider, handling heavier trains (e.g., UIC 60, AREMA 115RE). Narrow-gauge (≤1067mm) rails are lighter, for small trains (e.g., UIC 33, 33kg/m, used in mountain railways; Indian 52kg/m for 1000mm gauge). Standard gauge rails have thicker heads/webs for heavy loads; narrow-gauge rails are more compact. Standard gauge dominates mainlines; narrow-gauge serves rural/industrial routes.
2. What is rail plastic deformation, and which rails are most prone to it?
Plastic deformation is permanent rail head dents from wheel impacts (e.g., hard braking, heavy axles). Rails with softer heads (e.g., non-heat-treated UIC 54) are prone to it, as their heads can't resist indentation. Heat-treated rails (AREMA 132RE, CRTS 300N) with hardened layers (340–400HB) resist deformation. Deformation ruins the rail profile, increasing vibration-affected rails are ground or replaced.
3. What is the service life of a UIC 60 rail, and what affects it?
UIC 60 has a 15–25 year service life, depending on traffic: 1. Traffic density: High-speed lines (100+ trains/day) last 15–20 years; rural lines 20–25 years. 2. Axle load: 25t axles shorten life to 15 years; 20t axles extend to 25 years. 3. Maintenance: Regular grinding/inspections add 5–10 years. Poor maintenance (ignoring cracks/wear) reduces life to 10 years.
4. What is rail ultrasonic testing, and why is it critical for heavy-haul rails?
Ultrasonic testing uses sound waves to detect internal rail defects (fatigue cracks, inclusions) invisible to the naked eye. For heavy-haul rails (AREMA 132RE, GB 75kg/m), it's critical because heavy axles accelerate crack growth-undetected cracks cause rail breakage/derailment. Testing is done every 3–6 months; advanced systems can scan rails at 40km/h, ensuring fast, thorough inspections.
5. What is the difference between "quenched and tempered" and "as-rolled" rails?
Quenched and tempered (Q&T) rails undergo heat treatment (heat → quench → temper) to harden the head (300–400HB) and keep the core tough. Used for high-speed/heavy-haul (CRTS 300N, AREMA 132RE). As-rolled rails are cooled naturally after rolling, with softer heads (260–280HB) for low-speed lines (e.g., branch line UIC 54). Q&T rails resist wear/fatigue better; as-rolled rails are cheaper but less durable.