1. What is rail "thermal expansion," and how do jointed rails handle it?
Rail thermal expansion is the increase in rail length when heated (≈1mm per meter for every 10°C temperature rise). Jointed rails handle it by including small gaps (10–15mm) between rail sections-these gaps let the rail expand in hot weather without buckling. When temperatures drop, the rail contracts, and the gaps widen slightly. Fishplates and bolts hold the rail sections together, ensuring the gaps don't affect train movement. However, jointed rails have more vibration and wear than CWR, so they're only used for low-speed lines (≤100km/h) where CWR's neutral temperature management is impractical.
2. What is the American AREMA 115RE rail's head profile, and why is it optimized for mixed traffic?
AREMA 115RE has a "symmetrical" head profile with a 73mm width and 31mm height, optimized for mixed passenger-freight traffic. The profile has a rounded running surface that matches both passenger train wheels (smaller contact patch for speed) and freight train wheels (larger contact patch for heavy loads). It also has a reinforced gauge corner (thicker than UIC 54) to resist wear from freight wheel flanges. The symmetrical design ensures even wear when traffic shifts between passenger (day) and freight (night), reducing the need for frequent grinding. This balance makes AREMA 115RE ideal for North American mainlines that carry both Amtrak passenger trains and Union Pacific freight trains.
3. What is rail "recycling," and how are old rails (e.g., UIC 60) recycled?
Rail recycling is the process of repurposing old or damaged rails into new steel products, reducing waste. For old UIC 60 rails: 1. Collection: Rails are removed from tracks, inspected, and sorted (wear vs. cracked). 2. Preparation: Removed from sleepers, cleaned of ballast/rust, and cut into 1–2m lengths. 3. Melting: Loaded into electric arc furnaces (1600°C) to melt into molten steel, with impurities removed via slag. 4. Reforming: Molten steel is cast into new rail blooms, rolled into new rails (e.g., UIC 54) or other steel products (construction beams). Recycling old UIC 60 rails saves 70% of the energy needed to make new rails from iron ore, making it an eco-friendly practice for railways worldwide.
4. What is the Chinese CRTS 300N rail's neutral temperature range, and how is it adjusted for different climates?
CRTS 300N's neutral temperature range is 25–35°C, adjusted based on the climate of the installation region: 1. Temperate regions (e.g., East China): Laid at 28–30°C, balancing summer heat (≤38°C) and winter cold (≥-5°C) to avoid excessive stress. 2. Hot regions (e.g., South China): Laid at 32–35°C, as summer temperatures often exceed 40°C-higher neutral temp reduces compression. 3. Cold regions (e.g., Northeast China): Laid at 25–28°C, as winter temperatures drop to -20°C-lower neutral temp reduces tension from contraction. Crews use portable temperature sensors to confirm rail temperature during installation, ensuring it matches the regional neutral temp to prevent buckling or cracking.
5. What is the difference between "heavy-haul rail" and "high-speed rail" in terms of material purity?
Heavy-haul rails (e.g., AREMA 132RE, GB 75kg/m) require high material purity (sulfur ≤0.025%, phosphorus ≤0.03%) to resist fatigue from heavy axles, but allow small inclusions (≤50μm) as long as they don't affect strength. High-speed rails (CRTS 300N, UIC 60 for 350km/h) have stricter purity standards (sulfur ≤0.015%, phosphorus ≤0.025%) and almost no inclusions (≤20μm). This is because high-speed rails experience frequent, high-frequency vibrations (300+km/h) that can turn small inclusions into fatigue cracks. High-speed rails also use more advanced steelmaking processes (e.g., vacuum degassing) to remove impurities, while heavy-haul rails prioritize strength over ultra-low inclusions.