Selection of Standard Rail Length and Optimization of Track L
What are the differences in application scenarios between 25m standard length and 100m long length national standard rails?
The 25m standard length rail is the mainstream choice for ordinary-speed lines and yard lines. Due to its moderate length, it has low difficulty in transportation, loading, unloading and on-site laying, and is suitable for lines with many small and medium radius curves. The speed of trains on ordinary-speed lines is relatively low. Although the 25m standard length rail has many joints, it can meet the operation requirements through standardized installation of fish plates. The 100m long length rail is mainly used for the main lines of high-speed railways and heavy-haul railways, which have extremely high requirements for smoothness. The long length can greatly reduce the number of welded joints. Yard lines are not suitable for 100m long length rails due to dense turnouts and limited laying space, which cannot carry out long-distance welding. In addition, the 100m long length rail has higher requirements for transportation vehicles and laying equipment, and needs to be equipped with special rail transport vehicles and track laying machines.
Why can long length national standard rails effectively reduce track joint diseases?
Track joints are weak links in the track structure. When trains pass, impact vibration will occur, and joint settlement, fish plate wear and other diseases are prone to occur under long-term action. The length of the long length national standard rail is 4 times that of the 25m standard length. Under the same line length, the number of joints can be reduced by 75%, which greatly reduces the frequency of impact vibration. After the number of joints is reduced, the continuity of the track is better, the wheel-rail contact stress distribution is more uniform, and the stress concentration at the joints is avoided. At the same time, the long length rail forms a seamless line through on-site welding. The strength and integrity of the weld are better than ordinary bolted joints, and it can resist greater longitudinal force. Therefore, the use of long length rails can significantly extend the service life of track components and reduce the later maintenance workload.
What transportation and loading/unloading factors should be considered when selecting the fixed length of national standard rails?
The primary transportation factor for selecting the fixed length of national standard rails is the carrying length of railway freight cars. The 25m fixed length can be adapted to ordinary open cars, while the 100m long fixed length must use special long rail transport vehicles. In terms of loading and unloading, the 25m fixed length rail can be completed by ordinary cranes and rail clamps, with simple operation and low cost. Due to the excessive length of the 100m long fixed length rail, two cranes are required for synchronous operation during loading and unloading to avoid bending deformation of the rail due to its own weight. In addition, during transportation, special supporting sleepers should be set for the long fixed length rail, with the spacing controlled at 5-6m to prevent distortion during transportation. For lines in mountainous areas or with inconvenient transportation, the transportation difficulty and cost of long fixed length rails will increase significantly, so it is more suitable to choose 25m fixed length rails.
When laying national standard rails, how to optimize the joint position according to the fixed length?
Before laying national standard rails, it is necessary to draw a joint layout according to the line design drawings and the fixed length of the rails. The core principle is to avoid joints appearing at key positions such as the frog center of turnouts and the sudden change of sleeper spacing. For 25m fixed length rails, the joints should be aligned with the center line of the sleepers, and a suspended joint design should be adopted, so that both ends of the rail at the joint are supported by two sleepers each. The welded joints of long fixed length rails should be avoided more than 3m from the start and end of the curve to prevent the lateral force of the curve section from aggravating weld damage. At the same time, the joints of adjacent rails should be staggered, with the staggering distance not less than 3m, to avoid the formation of continuous joints leading to sudden changes in track stiffness. After laying, it is necessary to check the gauge and level deviation at the joints to ensure they meet the specification requirements.
In seamless lines, what impact does the welding joint quality of long length national standard rails have on line performance?
The weld quality of seamless lines formed by welding long length national standard rails directly determines the overall smoothness and safety of the line. If the weld has defects such as slag inclusion and porosity, the weld strength will be insufficient, and cracks are prone to occur when the train passes, which may even cause rail fracture in severe cases. The smoothness of the weld is also crucial. If the rail head at the weld is uneven, it will increase wheel-rail impact, leading to train jolting and affecting riding comfort. High-quality welds should be equal in strength to the rail base metal, and the surface should be smooth without obvious steps. Therefore, the welding of long fixed length rails must adopt the rail flash welding process, and strict ultrasonic flaw detection must be carried out to ensure the weld quality meets the standard.