Fishplate Connection Characteristics and Maintenance
- What are the differences in material and structure between ordinary fishplates and insulated fishplates, and what are their application scenarios?
Ordinary fishplates are mostly made of Q235 and Q345 steel, with an all-metal structure and no insulating layer, suitable for non-electrified railways or sections without track circuits, such as ordinary freight branch lines, with low cost and easy installation. Insulated fishplates add insulating materials (such as fiberglass boards) between the metal bodies. In addition to the metal base material, the material also needs to select insulating materials that are high-temperature resistant and aging resistant. They are suitable for track circuit sections of electrified railways to prevent current leakage from interfering with the signal system and ensure normal train operation control.
- How to determine the number and specification of bolts for fishplates according to the rail model, and what is the basis?
The fishplate matching 43kg/m rail is equipped with 4 bolts per end, and the bolt specification is mostly M22. Because this type of rail is light in weight and has a small load, 4 bolts can meet the load transmission demand; the fishplate for 50kg/m and 60kg/m rails is equipped with 6 bolts per end, and the bolt specification is M24. As the rail weight increases and the load increases, increasing the number and specification of bolts can disperse stress and avoid stress concentration at the joint; the fishplate for 75kg/m heavy-haul rail is equipped with 8 bolts per end, and the bolt specification is M27. The basis is that the heavy-haul rail needs to bear an ultra-large axle load (≥30t), and more and larger-sized bolts can improve the connection strength and prevent bolt breakage or deformation.
- What problems will be caused by excessive or insufficient reserved rail gaps when installing fishplates, and how to determine a reasonable rail gap?
Excessive rail gaps will generate strong impact noise when the train passes, accelerate the wear of fishplates and bolts, and at the same time increase the vibration at the rail joint, leading to premature damage to sleepers and ballast; insufficient rail gaps will prevent the rail from expanding freely when heated in high-temperature seasons, easily generating huge longitudinal stress, which may cause the rail to arch (rail buckling), seriously threatening driving safety. The reasonable rail gap needs to be calculated according to the local maximum and minimum temperatures. The formula is: reserved rail gap = 0.0118×(local maximum temperature - installation temperature)×rail length + structural rail gap (generally 2mm), ensuring that the rail can expand and contract freely when the temperature changes.
- What are the common damage forms of fishplates during use, and how to find these damages through appearance and testing?
Common damages include surface wear, bolt hole deformation, and cracks. Surface wear can be observed visually. If the working surface of the fishplate in contact with the rail has obvious depressions or wear marks, and the wear depth exceeds 3mm, it needs attention; bolt hole deformation can be measured by a caliper. If the hole diameter is more than 1mm larger than the standard value, it is determined to be deformed; cracks can be checked visually. If obvious surface cracks (length >5mm) are found, further testing is required, or a magnetic particle flaw detector can be used to detect internal micro-cracks (≥0.2mm) that are difficult to see with the naked eye.
- How to replace fishplates when they are severely worn or cracked, and what precautions are there during the replacement process?
Before replacement, the same type of fishplate and bolts should be prepared in advance, loosen the bolts of the old fishplate, remove the old fishplate, and clean the debris and rust at the rail joint; install the new fishplate, ensure that the fishplate is closely attached to the rail, adjust the rail gap to a reasonable value, tighten the bolts in a diagonal order, and the torque must meet the standard (such as 300-350N·m for M24 bolts). Precautions: the line must be blocked during replacement to avoid train passage; the bolt tightening order must be correct to prevent uneven stress on the fishplate; after replacement, the rail gap and bolt torque must be tested to ensure compliance with requirements, and at the same time, observe the joint state when the train passes to confirm no abnormalities.