Fishplate Selection and Installation Technical Specifications
- The material selection of fishplates needs to match the rail material. What are the corresponding fishplate materials for different rail materials, and what is the matching principle?
Domestic standard U71Mn rails (ordinary railways) correspond to Q235 or Q345 steel fishplates. The tensile strength of Q235 steel fishplates is ≥375MPa, which is compatible with the strength of U71Mn rails and has low cost; U75V rails for heavy - haul railways need to be matched with Q460 steel fishplates. The tensile strength of Q460 steel is ≥550MPa, which can withstand the longitudinal tension and impact of heavy - haul trains. Foreign standard EN13674 rails (European high - speed rails) correspond to S355J2 steel fishplates. The chemical composition and mechanical properties of the two match, avoiding stress concentration at the joint due to material differences. The matching principle: The tensile strength of the fishplate is not less than 80% of that of the rail, and the yield strength is not less than 75% of that of the rail, ensuring that the fishplate and the rail deform synchronously when the joint is stressed, preventing local damage.
- How to determine the number of bolt holes and hole diameter of fishplates according to rail specifications, and what problems will unreasonable design lead to?
43kg/m rails (rail base width 114mm) are matched with fishplates with 4 bolt holes, and the hole diameter is 24mm (suitable for M22 bolts); 60kg/m rails (rail base width 150mm) are matched with fishplates with 6 bolt holes, and the hole diameter is 26mm (suitable for M24 bolts); 75kg/m heavy - haul rails are matched with fishplates with 8 bolt holes, and the hole diameter is 28mm (suitable for M27 bolts). The number of holes needs to meet the tensile requirements of the joint, and the hole spacing is uniform (the hole spacing of 60kg/m rail fishplates is 140mm) to ensure balanced stress. Problems caused by unreasonable design: Insufficient number of holes (such as using 4 - hole fishplates for 60kg/m rails) will cause the stress on a single bolt to exceed 30kN (standard ≤25kN), and the bolts are easy to break; too small hole diameter (such as M24 bolts with 25mm holes) is easy to damage the thread during installation; too large hole diameter (such as M24 bolts with 27mm holes) will cause the fishplate to shift during train vibration, and the joint gap increases (exceeding 2mm), causing wheel - rail impact noise.
- What are the requirements for the bolt tightening sequence and torque control when installing fishplates, and why must they be strictly followed?
The tightening sequence must follow the "diagonal cross" principle: 6 - hole fishplates are tightened in the order of "1 - 4 - 2 - 5 - 3 - 6", and 8 - hole fishplates are tightened in the order of "1 - 5 - 3 - 7 - 2 - 6 - 4 - 8" to avoid warping of the fishplate due to uneven stress. Torque control standards: The torque of M22 bolts (ordinary railways) is 180 - 220N·m, the torque of M24 bolts (main line railways) is 300 - 350N·m, and the torque of M27 bolts (heavy - haul railways) is 500 - 550N·m. The reasons for strict compliance: Wrong sequence will make the fitting gap between the fishplate and the rail exceed 0.3mm, resulting in local stress concentration when the train passes; insufficient torque (such as M24 bolt torque only 250N·m) will cause the bolt to loosen easily, and the joint displacement exceeds 1mm; excessive torque (such as M24 bolt torque exceeding 400N·m) will cause plastic deformation of the fishplate bolt hole, making it impossible to fasten normally later.
- What are the requirements for the fitting degree between the fishplate and the rail, how to detect the fitting degree, and what harms will poor fitting bring?
Fitting degree requirements: The contact area between the fishplate and the rail head, rail web, and rail base is ≥90%, and the local gap is ≤0.2mm (detected with a 0.2mm feeler gauge, the insertion depth ≤10mm). Detection method: Use a feeler gauge to measure point by point along the contact surface between the fishplate and the rail, measure 1 point every 100mm, and record the gap value; use a square to check the perpendicularity between the fishplate and the rail, with a deviation ≤0.5mm/m. Harms of poor fitting: When the gap exceeds 0.3mm, the train load will increase the local stress of the fishplate by 30%, and cracks are easy to occur; long - term poor fitting will accelerate the wear of the rail joint (annual wear amount exceeds 1.5mm), reducing the service life of the rail; at the same time, it will intensify train vibration, affect passenger comfort, and even cause joint diseases (such as depression and chipping).
- What are the differences in the service life requirements of fishplates for different line types (ordinary, high - speed, heavy - haul), and how to extend their service life?
The service life of fishplates for ordinary railways is required to be ≥8 years, for high - speed railways ≥12 years, and for heavy - haul railways ≥10 years (the service life is slightly lower than that of high - speed railways due to large heavy - haul impact). Measures to extend the service life: For ordinary railways, check the fishplate bolt torque regularly (every 6 months) and retighten in time; for high - speed railways, use stainless steel fishplates (304 material) or Dacromet - coated fishplates to improve corrosion resistance (salt spray resistance ≥500 hours); for heavy - haul railways, apply wear - resistant grease (such as lithium - based grease) on the contact surface between the fishplate and the rail to reduce friction and wear; for all lines, clean the debris on the surface of the fishplate every quarter to avoid the accumulation of corrosive media (such as deicing agents), and immediately replace the fishplate if cracks (length ≥3mm) are found.