Types and Applications of National Standard Rails
- What are the common types of domestic standard rails, and how do their weight specifications correspond to different lines?
Common types of domestic standard rails include 43kg/m, 50kg/m, 60kg/m, 75kg/m, etc. 43kg/m rails are mostly used in branch railways, factory and mine special lines, and other lines with small traffic volume, meeting the operation requirements of trains with low axle loads; 50kg/m rails are suitable for ordinary main lines, undertaking mixed passenger and freight transportation tasks, and can withstand certain axle loads and traffic volumes; 60kg/m rails are widely used in high-speed railways and busy main lines, with high strength and stability to cope with high-speed and high-volume transportation; 75kg/m rails are mainly used in heavy-haul railways, capable of withstanding heavy-haul trains with axle loads exceeding 25t to ensure the safety of the track structure.
- What are the material grades of domestic standard rails, and how do chemical compositions affect their performance?
Common material grades include U71Mn, U75V, etc. U71Mn contains 0.65 - 0.76% carbon, 0.70 - 1.20% manganese, etc., with good comprehensive performance, moderate strength and good toughness, suitable for various lines; U75V adds 0.04 - 0.12% vanadium on the basis of U71Mn, refining the grains and improving strength and wear resistance, often used in lines with high wear resistance requirements for rails. The carbon content affects strength and hardness. An increase in carbon content raises strength and hardness but reduces toughness; manganese enhances strength and hardenability; vanadium can refine grains and improve strength, toughness, and wear resistance.
- What are the length standards of rails, and what precautions should be taken when laying rails of different lengths?
The standard lengths of 43kg/m rails are 12.5m or 25m; for rails of 50kg/m and above, there are three lengths: 25m, 50m, and 100m. When laying short rails of 12.5m or 25m, reasonable rail gaps need to be reserved, considering the influence of temperature changes on rail expansion and contraction to prevent excessive or too small rail gaps from affecting driving smoothness and the track structure; when laying long rails of 50m and 100m, especially the 100m fixed-length rails for seamless tracks, high requirements are placed on the welding process. The welding quality must be strictly controlled to ensure joint strength and smoothness and reduce the impact when the train passes.
- How to select appropriate domestic standard rails according to the curve radius of the railway?
When the curve radius is small, the rail is under complex stress, and a rail with high strength and good wear resistance should be selected. For curves with a radius less than 800m, rails of 60kg/m and above are preferred; for curves with a radius between 800 - 1200m, 50kg/m or 60kg/m rails can be selected according to the traffic volume; for curves with a radius greater than 1200m, the special requirements for the rail are reduced, and it can be selected according to the general main line standard. At the same time, the outer rail in the curve section wears quickly. If necessary, wear-resistant alloy rails can be used or the rail can be specially heat-treated to improve its service life.
- What are the appearance quality standards of domestic standard rails, and how to detect them?
The appearance quality requires the rail surface to be smooth, free of cracks, folds, scabs, and other defects; the transitions between the rail head, rail waist, and rail bottom are smooth, without obvious edges and corners; the rail end cut is flat, and the verticality deviation meets the standard. During detection, visual inspection is carried out, using a strong flashlight to check the rail surface meter by meter; a straightedge is used to measure the verticality of the rail end; ultrasonic flaw detectors, magnetic particle flaw detectors, and other equipment are used to conduct flaw detection on the inside and surface of the rail to ensure that there are no internal defects affecting the performance and safety of the rail.