1. What is CWR's "neutral temperature," and why is it important?
Neutral temperature is when CWR is stress-free-no tension (cold) or compression (heat). It's critical because CWR has no expansion joints: too low a temperature causes contraction/tension (cracks); too high causes expansion/compression (buckling). Neutral temperature is set by climate: 25–30°C (temperate), 30–35°C (hot), 15–20°C (cold). Crews use temperature sensors during installation to ensure correctness, preventing track failures.
2. What is rail wear, and which parts wear the most?
Rail wear is material loss from wheel contact/friction. The rail head wears most, as it's the primary wheel contact point. Key worn areas: 1. Running surface: Flattened by constant rolling (high-traffic lines). 2. Gauge corner: Worn by wheel flanges (curved tracks). 3. Field side: Worn on tight curves. Web/base wear is minimal (only from loose sleepers). When head wear exceeds 3–5mm (model-dependent), rails are replaced or ground.
3. What is rail corrugation, and how does it affect performance?
Corrugation is wave-like ridges (10–100mm wavelength) on the rail head, caused by wheel-rail resonance. It increases noise (up to 10dB), accelerates rail/wheel wear (2–3x faster), and damages track components (loose sleepers, cracked bolts). Common on curved/urban rails. Fixed via grinding machines to smooth the head; preventive grinding (6–12 months) reduces formation.
4. What is the difference between "new rails" and "relayed rails"?
New rails are factory-fresh (e.g., UIC 60) with no wear, used for new construction/mainline replacements. Relayed rails are used rails inspected, ground, and refurbished for reuse. Relayed rails serve low-traffic sections (branch lines, industrial sidings) where performance demands are low. They're 50–70% cheaper than new but have shorter lifespans-never used for high-speed/heavy-haul lines.
5. What is rail fatigue, and what causes it in UIC 60?
Rail fatigue is small cracks from repeated stress (even below tensile strength). In UIC 60, causes include: 1. Cyclic loading: Train passes weaken internal structures (especially at defects). 2. Thermal stress: CWR expansion/contraction adds stress. 3. Wear/corrugation: Reduced head thickness increases stress concentration. Cracks grow over time, risking rail breakage. Ultrasonic testing (3–6 months) detects cracks early.