Fishplate Material Selection and Compatibility Technology for Different Rail Joints
What are the material selection points of fish plates for ordinary joints of national standard 60kg/m rails?
Fish plates for ordinary joints of national standard 60kg/m rails should preferably use Q345B low-alloy high-strength steel, which has a tensile strength ≥510MPa and a yield strength ≥345MPa, meeting the load requirements of ordinary lines. When selecting materials, it is necessary to focus on checking the elongation index of the material. An elongation ≥21% can ensure that the fish plate is not prone to brittle fracture when subjected to train impact loads. At the same time, attention should be paid to the cold bending performance of the material. A 180° cold bending test without cracks is a necessary condition to avoid brittle fracture of the fish plate in low-temperature environments. It is also necessary to check the sulfur and phosphorus content of the material. A sulfur content ≤0.040% and a phosphorus content ≤0.040% can reduce the risk of temper brittleness of the material. Finally, it is necessary to match the heat treatment process of the fish plate. The fish plate after normalizing treatment has uniform hardness, and the HB value is controlled between 180-220, which can better bear force together with the rail joint.
What are the special material requirements of fish plates for insulated joints of foreign standard rails?
The core requirement of fish plates for insulated joints of foreign standard rails is to have both high strength and insulation performance. The material should be glass fiber reinforced epoxy resin composite material, whose volume resistivity ≥10¹²Ω·cm can effectively block current conduction. The tensile strength of the material should be ≥450MPa to meet the stress requirements of heavy-haul foreign standard lines (such as AREMA standard lines). At the same time, the aging resistance of the material should be guaranteed. Under the action of ultraviolet radiation and temperature-humidity cycles, the insulation performance attenuation rate is ≤5% per year. Attention should also be paid to the corrosion resistance of the material. After being immersed in a salt spray environment for 1000 hours, there are no obvious corrosion spots on the surface to ensure the use safety of coastal lines. In addition, the thermal expansion coefficient of the material should be close to that of the rail to avoid the increase of joint gaps caused by temperature changes and affect line smoothness.
What are the material modification measures of fish plates for rail expansion joints in alpine regions?
Fish plates for rail expansion joints in alpine regions should use Q345D steel and undergo low-temperature toughness modification treatment. The core of modification is to reduce the brittle transition temperature of the material so that it can still maintain good toughness at -40℃. The first modification measure is to add nickel element during smelting, and the nickel content is controlled at 1.0%-1.5%, which can significantly improve the low-temperature impact toughness of the steel. Second, the quenching and tempering heat treatment process is adopted, with a quenching temperature of 880℃ and a tempering temperature of 600℃, so that the low-temperature impact energy of the material is ≥34J. At the same time, the surface of the fish plate should be zinc-sprayed, and the zinc layer thickness is ≥80μm to prevent corrosion by ice, snow and deicing agents in alpine regions. In addition, it is necessary to optimize the cross-sectional transition arc of the fish plate, increasing the transition radius from 5mm to 8mm, reducing the stress concentration factor, and avoiding cracking caused by stress concentration at low temperatures.
What is the influence of fish plate machining accuracy on rail joint smoothness?
The machining accuracy of the fish plate directly determines the rail surface smoothness of the rail joint, and its key dimension deviation must be strictly controlled within ±0.2mm. If the flatness deviation of the rail surface contact part exceeds 0.3mm, obvious wheel-rail impact will occur when the train passes, aggravating wheel-rail wear and line vibration. If the position deviation of the bolt hole exceeds 0.5mm, the fish plate will not fit closely with the rail, and gaps will appear at the joint, which will lead to uneven settlement of the rail joint. Excessive thickness deviation of the fish plate will cause high and low staggered teeth of the rail at the joint, affecting the smooth operation of the train. In addition, the surface roughness Ra of the fish plate should be ≤3.2μm. Excessively high roughness will increase the frictional resistance with the rail, leading to uneven stress distribution at the joint and reducing the fatigue life of the joint.
What are the cooperative stress matching principles between fish plates and bolts?
The core of cooperative stress matching between fish plates and bolts is strength matching and stiffness matching. The tensile strength of the two should be at the same level to avoid the situation of "strong parts damaging weak parts". The tensile strength of the bolt should be slightly higher than that of the fish plate, with a difference of 50-100MPa, so that the bolt will undergo plastic deformation first when overloaded, playing the role of overload protection. In terms of stiffness matching, the elastic modulus of the fish plate should be close to that of the bolt to ensure that the deformation of the two is coordinated under load, avoiding stress concentration on a certain component. At the same time, it is necessary to control the preload of the bolt. Insufficient preload will cause the fish plate to not fit tightly with the rail, while excessive preload will cause plastic deformation of the fish plate. Usually, the preload is controlled at 60%-70% of the bolt yield strength. In addition, the number and arrangement spacing of bolts should be adapted to the length of the fish plate. The 6 bolts supporting the 60kg/m rail fish plate should be evenly distributed with a spacing deviation ≤2mm to ensure uniform force bearing.