Fishplate Material Characteristics and Connection Functions
What is the core function of the fish plate, and why is it crucial to the safety of rail joints?
A1: Common materials for fish plates mainly include Q235 low-carbon steel, 45# medium-carbon steel and U71Mn high-strength steel. Q235 low-carbon steel has good plasticity, excellent welding performance and low cost, which is suitable for mining branches and special railways with small traffic volume and low speed; 45# medium-carbon steel, after quenching and tempering, has a tensile strength of more than 600MPa and stronger bearing capacity, which is widely used in ordinary railway trunks; U71Mn steel has high matching with rail material, whose hardness and strength are close to those of rails, which can effectively reduce stress mutation at joints and is mostly used in high-speed railways and heavy-haul railways to ensure the overall bearing performance of the joint area.
What are the mechanical property requirements for fish plates, and how do these requirements ensure the reliability of joint connections?
The core mechanical property requirements for fish plates include tensile strength, yield strength, elongation and impact toughness, with different standards for different application scenarios: the tensile strength of fish plates for ordinary railways is ≥400MPa, yield strength ≥235MPa; for high-speed railways, the tensile strength needs to be ≥880MPa, yield strength ≥785MPa, elongation not less than 12%, and impact toughness at -20℃ ≥27J. These requirements ensure that fish plates do not fracture or undergo plastic deformation when bearing train impact loads, and absorb vibration energy through good toughness to avoid track damage caused by rigid impact at joints.
What impact does the machining accuracy of bolt holes in fish plates have on the connection effect? What is the commonly used machining process?
The aperture deviation, hole spacing and perpendicularity of bolt holes directly affect the bolt installation accuracy. Excessively large aperture easily leads to bolt loosening, excessively small aperture makes bolt installation difficult and generates additional stress, and hole position deviation causes poor fit between fish plates and rails. The commonly used machining process is the combination of "drilling + reaming". First, rough drilling is carried out by a CNC drilling machine to control the aperture error within ±0.3mm, and then reaming process is used to improve the surface roughness to below Ra1.6μm, ensuring that the fit clearance between bolt and hole is controlled within a reasonable range of 0.1-0.2mm.
What are the main causes of cracks in fish plates during use, and how to prevent and handle them?
The main causes of cracks include excessive inclusions in the material, uneven hardness caused by improper heat treatment process, stress concentration caused by excessive bolt preload, and repeated action of wheel-rail impact loads at joints. Preventive measures should be taken from both production and use aspects: strictly control the quality of raw materials in production, and use flaw detection to eliminate internal defects; control the bolt preload according to specifications during use to avoid over-tightening. After cracks are found, if the crack length is less than 5mm, repair welding can be carried out; if it exceeds 5mm, it must be replaced immediately to prevent crack expansion from causing rail joint failure.
What special requirements does high-speed railway have for the connection accuracy of fish plates, and how to achieve these requirements?
High-speed railway fish plates need to meet the high-precision requirements of rail top height difference ≤0.3mm and side wear ≤0.2mm at joints to reduce wheel-rail impact. The realization methods include: adopting integral forging process instead of casting to improve the flatness of fish plates; ensuring the parallelism error of the fitting surfaces at both ends ≤0.1mm/m through CNC machining centers; using a torque wrench to accurately control the bolt preload at 300-350N·m during installation, and using a joint tamping machine to strengthen the ballast support to ensure the smooth and stable joint area.