Fishplate Joint Gap Control
- What is the allowable range for the longitudinal gap between fishplates and rails?
Longitudinal gap (along the rail length) must be ≤0.3mm, measured with a feeler gauge at both ends of the fishplate. Excessive gap (>0.5mm) causes impact loads when trains pass, doubling the loosening rate of fishplate bolts. Ensure close fit between rail ends and fishplates during installation; use 0.1-0.2mm thin steel sheets at rail ends if necessary. Longitudinal gaps in curves must be 0.1mm smaller than straight sections due to greater lateral forces.
- What are the requirements for the lateral gap between fishplates and rail heads?
Lateral gap (between rail head side and fishplate) should be ≤0.5mm, with uniform gap on each side, deviation ≤0.2mm. For excessive gaps, replace with appropriate thickness adjustment shims (0.3mm or 0.5mm); shims must be 65Mn steel, same strength as fishplates. Check with a 0.5mm feeler gauge after installation; insertion depth must not exceed 20mm, otherwise re-adjust.
- Do connection gaps differ for different types of fishplates?
Longitudinal gap for 60kg/m rail fishplates is stricter (≤0.2mm) due to higher load; 50kg/m rail fishplates can relax to ≤0.4mm. Insulated fishplates require additional gap control, with both longitudinal and lateral gaps ≤0.3mm to prevent insulation performance degradation (insulation resistance ≥10⁸Ω). Special turnout fishplates allow 0.1mm larger deviation due to complex structure but must ensure uniform force.
- How to measure fishplate connection gaps during installation?
Use a set of feeler gauges (0.02-1mm). For longitudinal gaps, take 3 measurements at both ends of the fishplate and record the maximum; for lateral gaps, take 2 measurements on each side of the rail head and average. Remove rust and impurities from contact surfaces before measurement to avoid reading errors. High-speed railways require digital gap gauges with 0.01mm accuracy, recording each gap value for archiving.
- What problems do fishplates with excessive gaps cause?
Excessive longitudinal gaps subject fishplates to alternating impact loads, shortening fatigue life by 30%-40% and easily causing cracks around bolt holes. Excessive lateral gaps increase rail lateral displacement, with gauge deviation exceeding ±1mm, affecting train guidance. Long-term excessive gaps also accelerate rail end wear, forming "saddle-shaped" wear; rails must be replaced when depth exceeds 2mm.