Fishplate Function: Connection Strength and Installation Specifications
What principles should be followed in the material selection of fishplates?
The material of the fishplate must match the rail material; for example, U75V rails should be paired with corresponding low-alloy high-strength fishplates to ensure consistent mechanical properties. The material must have high tensile strength and toughness, with a tensile strength of not less than 880MPa and an elongation rate of ≥10% to avoid brittle fracture. It should have good welding performance; if on-site welding is required, the strength attenuation of the welded joint shall not exceed 10% to ensure connection reliability. Corrosion resistance cannot be ignored; fishplates used outdoors need to be treated with anti-rust coatings or made of weathering steel to extend service life. The hardness of the material should be close to that of the rail (260-300HB) to avoid contact stress concentration caused by excessive hardness difference and damage to the rail.
What are the requirements for the joint gap when installing fishplates?
The joint gap of fishplates on conventional lines is generally controlled at 2-3mm, reserving space for rail thermal expansion and contraction to avoid rail buckling or breaking due to temperature changes. High-speed railways have higher requirements for smoothness, so the joint gap needs to be reduced to 1-2mm to reduce jolting and impact when trains pass. In low-temperature winter environments, rails shrink significantly, and the joint gap can be appropriately increased to 3-4mm to prevent rails from breaking; in high-temperature summer, the gap can be maintained at 2mm. The contact surface between the fishplate and the rail must be flat; if the gap exceeds 0.5mm, a thin steel plate should be added for adjustment to ensure close fit. The joint gap must be uniform, with a deviation of no more than 0.5mm on the left and right sides to avoid uneven force leading to fishplate deformation.
What are the layout principles and tightening requirements of fishplate bolts?
Fishplate bolts are usually arranged symmetrically, with 4-6 bolts per fishplate to ensure uniform force on the rail joint. The bolt spacing must be uniform, generally 100-120mm, to avoid local stress concentration caused by excessive spacing and affect connection strength. During tightening, follow the diagonal symmetry principle and tighten evenly in stages: first pre-tighten to 30% of the torque, then gradually tighten to the standard value to avoid excessive force on one side. The torque of fishplate bolts for conventional railways is 80-120N·m, for high-speed railways 100-150N·m, and for heavy-haul lines it needs to be increased to 150-200N·m. After tightening, check the exposed thread length of the bolt, which is generally 2-3 threads to ensure reliable locking and facilitate subsequent disassembly.
What are the common damage forms and treatment methods of fishplates?
Common damage forms of fishplates include cracks, deformation, wear, and corrosion, among which cracks are the most dangerous and need immediate treatment. If a crack longer than 5mm is found, continued use is prohibited, and a new fishplate must be replaced; before replacement, the line must be cut off to ensure safety. When the deformation of the fishplate exceeds 2mm, it will affect the fit with the rail; correction treatment is required, and the flatness deviation after correction shall not exceed 0.3mm; if the deformation is too severe to be corrected, replace it directly. When the contact surface wear exceeds 1mm, grind it flat or add a pad for adjustment to ensure the contact area is not less than 80%; replace it when the wear is severe. When the corrosion area exceeds 50%, derust and apply anti-rust paint, or replace it directly to prevent accelerated corrosion leading to strength reduction.
What are the special design requirements for fishplates on heavy-haul lines?
The thickness of fishplates for heavy-haul lines is 2-3mm thicker than that for conventional lines, improving load-bearing capacity and anti-deformation performance to adapt to axle loads above 25t. The area around the bolt hole is thickened to increase local strength and prevent cracks in the bolt hole due to high-frequency impact. The material is high-strength alloy steel with added chromium and nickel elements, the tensile strength is increased to more than 1000MPa, and the fatigue resistance is better. The contact surface between the fishplate and the rail adopts a toothed design to increase friction, prevent relative sliding, and ensure connection stability. The surface is treated with thermal spray aluminum coating or dacromet coating with a thickness of ≥150μm to enhance corrosion resistance and adapt to the harsh working environment of heavy-haul lines.