Fishplate Connection Reliability and Maintenance
- How do the number and diameter of bolt holes in fishplates match rail specifications?
The number and diameter of bolt holes in fishplates must strictly match the rail type: fishplates for 43kg/m rails have 4 holes per end with a diameter of 24mm; fishplates for 50kg/m and 60kg/m rails have 4-6 holes per end with a diameter of 26mm; fishplates for 75kg/m heavy-haul rails have 6 holes per end with a diameter of 28mm. The hole spacing is designed to be uniform (e.g., 100mm for 60kg/m fishplates) to ensure balanced bolt stress and avoid local stress concentration. Excessively large hole diameter leads to excessive gap between bolt and hole, making the joint prone to loosening; excessively small hole diameter prevents installation, and forced installation damages the fishplate.
- What is the relationship between the tensile strength requirement of fishplate material and track load?
The tensile strength of fishplate material must match the track load: fishplates for ordinary railways use Q235 steel with tensile strength ≥375MPa, meeting the needs of mixed passenger and freight lines; fishplates for heavy-haul railways use Q345 steel with tensile strength ≥470MPa, coping with axle loads above 25t; fishplates for high-speed railways use Q355ND low-temperature toughness steel with tensile strength ≥510MPa, while ensuring impact energy ≥34J at -40℃. The larger the load, the higher the requirement for the tensile strength of the fishplate. If the material strength is insufficient, the joint is prone to plastic deformation when the train passes, leading to expanded rail gaps.
- What is the standard for reserved rail gaps when installing fishplates, and why is it important?
Reserved rail gaps are adjusted according to ambient temperature: for ordinary railways, the gap is ≥10mm in summer and ≤18mm in winter; for seamless track sections, the gap is ≤6mm; for alpine regions, the gap is ≤15mm in winter. Reserved gaps compensate for thermal expansion and contraction of rails: when the temperature rises, the rail expands, and the gap absorbs deformation to prevent track buckling; when the temperature drops, the rail contracts, and the gap prevents rail breakage. Excessively small gaps cause rails to be "locked" in high temperatures, leading to track arching; excessively large gaps intensify impact when the train passes, wearing the fishplate and bolts.
- What are the common damage forms of fishplates, and how to detect them through visual inspection?
Common damages include bolt hole cracks (extending from the hole edge to both ends), wear at the rail head contact part (thickness reduction ≥3mm), surface corrosion (area exceeding 20%), and overall deformation (flatness deviation ≥1mm/m). During visual inspection, first wipe the fishplate surface with a cotton cloth to check for cracks or rust; measure the thickness of the worn part with a vernier caliper; attach a straightedge to the fishplate surface and use a feeler gauge to detect flatness deviation. Damaged fishplates must be replaced in time to avoid expanded damage leading to joint failure.
- How to maintain the connection reliability of fishplates through torque retightening?
Fishplate bolts require regular retightening: once a quarter for ordinary railways, once a month for heavy-haul railways, and once every two months for high-speed railways. During retightening, use a calibrated torque wrench and operate in a diagonal order (first tighten holes 1 and 3, then holes 2 and 4), with the torque value meeting the standard (e.g., 300-350N·m for 60kg/m fishplate bolts). After retightening, check for bolt stripping or breakage. If the torque value decays repeatedly, check whether the fishplate bolt holes are worn or the bolts are fatigued, and replace the fishplate or bolts if necessary.