Fishplate Structure and Connection Reliability
- How does the structural design of fishplates match the rail specifications?
The length and width of fishplates need to match the dimensions of the rail head and rail bottom. For example, a fishplate matching a 60kg/m rail has a length of approximately 500mm, and its width must cover both sides of the rail head to ensure tight fitting. The number of bolt holes and their diameter are determined by the rail weight: a fishplate for a 43kg/m rail has 4 bolt holes per end with a diameter of 24mm; a fishplate for a 60kg/m rail has 6 bolt holes per end with a diameter of 26mm. More bolts can disperse the load and avoid stress concentration at the joint. The thickness of the fishplate must match the rail strength; fishplates for heavy-haul railways are 2-3mm thicker than those for ordinary railways to enhance load-bearing capacity.
- What are the differences in application scenarios of different types of fishplates?
Ordinary fishplates have a symmetrical structure and are suitable for rail connections in straight sections, such as the straight parts of ordinary railway main lines and branch lines. They are easy to install and can meet the needs of conventional load transmission. Special-shaped fishplates have an asymmetrical structure, with one side adapting to standard rails and the other to switch points. They are suitable for turnout areas, enabling smooth transition between standard rails and switch points and avoiding impact when trains pass through turnouts. Insulated fishplates contain an internal insulating layer and are suitable for track circuit sections of electrified railways. They prevent current leakage through the fishplate, ensuring the normal operation of the signal system and avoiding interference with train operation control.
- What are the requirements for the bolt tightening sequence and torque when installing fishplates?
During installation, the "diagonal symmetrical tightening" principle must be followed. For a 4-hole fishplate, first tighten the diagonal bolts 1 and 3, then bolts 2 and 4; for a 6-hole fishplate, tighten in the order of 1-4, 2-5, 3-6. This ensures that the fishplate fits evenly with the rail and avoids local stress concentration. The bolt tightening torque is determined by the fishplate material and rail specification: for ordinary carbon steel fishplates (Q235 material) with M24 bolts, the torque is controlled at 300-350N·m; for high-strength fishplates (Q345 material) with M26 bolts, the torque must be increased to 400-450N·m to prevent joint displacement due to bolt loosening.
- What are the standards for reserved rail gaps at fishplate joints?
In straight sections of ordinary railways, the rail gap is reserved at 8-10mm in summer and 12-15mm in winter to adapt to thermal expansion and contraction of the rail, preventing the rail from being "locked" at high temperatures or excessive gaps at low temperatures. The rail gap in curve sections must be 2-3mm smaller than that in straight sections. Due to the complex stress on rails in curve sections, smaller gaps can reduce joint impact when trains pass. The rail gap at fishplate joints in seamless track sections must be ≤6mm, which cooperates with the locking device of the seamless track to reduce the impact of rail expansion and contraction on the fishplate and improve track smoothness.
- What are the common damage forms of fishplates and their repair methods?
Common damages include bolt hole wear (hole diameter expanded by more than 1mm), surface cracks (length ≤5mm), and edge deformation (warpage exceeding 2mm). For slight bolt hole wear, reaming can be used followed by replacing with larger-diameter bolts (e.g., expanding a 24mm hole to 26mm and using M26 bolts); if wear is severe (hole diameter expanded by more than 2mm), the fishplate must be replaced. Small surface cracks can be repaired by arc welding; after welding, the surface must be ground flat and flaw detection must be performed. Cracks longer than 5mm or deeper than 3mm cannot be repaired and require direct replacement. Edge deformation can be flattened using a dedicated correction tool; if obvious warpage remains after correction, a new fishplate must be replaced.