Fishplate Material Selection and Joint Maintenance Techniques
- Why do ordinary railways (120km/h) and heavy-haul railways (27t axle load) use different fishplate materials, and what are the core performance differences?
Ordinary railways use Q235 steel fishplates (tensile strength ≥375MPa, ~￥20/piece) for light loads; heavy-haul railways need Q460 steel (tensile strength ≥550MPa, yield strength 460MPa-50% higher than Q235) with ≥1.5 million cycle fatigue life. Core difference: Q460 has 1.26x better impact toughness (≥34J at -20℃ vs. ≥27J for Q235), resisting heavy-haul impacts. Service life: 15 years (Q460) vs. 10 years (Q235).
- Why must fishplate bolt hole tolerance be controlled at ±0.2mm, and what problems do excessive/insufficient tolerances cause?
±0.2mm tolerance ensures 0.5-1mm bolt-hole gap (for M24 bolts). Excessive tolerance (>+0.3mm) causes 0.15mm annual wear, leading to >1.5mm gap and loosening; insufficient tolerance (<-0.1mm) damages 10% of bolt threads, reducing preload to ≤250N·m (standard 300-350N·m). Drill with CNC machines, sample 20 holes/batch with internal micrometers to ensure tolerance compliance.
- How to test rail surface smoothness at fishplate joints, and what impacts does poor smoothness have on trains?
Use a 1m straightedge-gap ≤0.5mm (ordinary railways), ≤0.3mm (high-speed); check gauge deviation ≤±1mm. Poor smoothness (>0.8mm) increases wheel-rail impact, raising noise by 5-8dB and accelerating wear (1.5mm/year), shortening rail life from 20 to 15 years. Grind with an angle grinder (Ra ≤6.3μm) until smoothness meets standards.
- When do worn fishplate bolt holes require replacement, and how to repair minor wear?
Minor wear (≤1mm expansion, e.g., 25mm to 26mm): Install M25 bolts with 0.5mm gap, add 1mm metal washers; major wear (>1mm expansion, e.g., 25mm to 27mm): Replace immediately to avoid >2mm joint displacement. Retighten bolts with a torque wrench after repair/replacement.
- Why do fishplate maintenance cycles vary by line type, and what are the cycles and key items for ordinary, high-speed, and heavy-haul railways?
Cycles: 3 months (ordinary), 1 month (high-speed), 20 days (heavy-haul). Key items: ① Torque check (30% sampling for ordinary, 100% for high-speed); ② Magnetic particle testing for cracks (>3mm replacement for heavy-haul); ③ Grinding (every 2 months for high-speed); ④ Ballast tamping (every 6 months for ordinary). Targeted maintenance extends fishplate life.