1. How are steel rails protected from corrosion in underground subway systems?
Underground subways face high humidity and potential water exposure, increasing corrosion risk. Rails here are often treated with anti-corrosive coatings, such as epoxy paints or zinc-rich primers, to seal the surface. Drainage systems in tunnels prevent water pooling around rails, while regular cleaning removes moisture and debris. Some subway networks use stainless steel cladding on rail heads for added protection, though this is less common due to cost. Additionally, the steel itself may include corrosion-resistant alloys like chromium to slow rust formation.
2. What is the impact of rail joint gaps on train ride quality?
Rail joint gaps, found in non-welded rails, cause a repetitive "clicking" noise and vibration as wheels pass over them. This impacts ride quality by creating jolts, especially at higher speeds, which can discomfort passengers and strain train components. Gaps also accelerate wear on both wheels and rails, as the impact force increases friction. For these reasons, modern railways increasingly use CWR to eliminate gaps, resulting in smoother, quieter rides and longer component lifespans.
3. How do steel rails support the weight of double-decker trains?
Double-decker trains, with heavier passenger loads, require rails designed to handle increased axle weights. These rails are typically 60 kg/m or heavier, made from high-strength alloy steel to resist deformation. The trackbed under such rails is reinforced with thicker concrete sleepers or slab tracks to distribute the weight evenly. Additionally, the rail fasteners are stronger to prevent shifting, and regular inspections check for signs of stress, such as cracks or uneven wear, to ensure the rails can sustain the higher loads.
4. What are the criteria for retiring steel rails from service?
Rails are retired when wear exceeds safe limits, typically when the rail head is worn down by 30% or more of its original thickness. Other criteria include severe cracks, corrosion that weakens the rail structure, or fatigue damage from repeated stress. For high-speed rails, even minor defects like uneven profiles can trigger retirement, as they risk vibration or derailment. Inspectors use ultrasonic tests and wear gauges to measure these factors, and rails failing the tests are removed, recycled, or repurposed for low-stress applications like industrial sidings.
5. How do steel rails in desert regions cope with extreme temperature fluctuations?
Deserts experience drastic day-night temperature swings, which cause rails to expand and contract significantly. To manage this, desert railways use rails with higher thermal tolerance, often made from low-carbon steel that is less prone to brittleness. Expansion joints are spaced more closely to accommodate length changes, and trackbeds use heat-resistant ballast (e.g., basalt) to reduce heat absorption. Some lines also install rail anchors to prevent buckling in daytime heat, while night-time contraction is managed by allowing controlled movement in joints.