Fishplate Material and Connection Strength Control
- What are the differences in material properties and application scenarios between Q235 steel, Q345 steel, and stainless steel fishplates?
Q235 steel fishplates have a tensile strength ≥375MPa, yield strength ≥235MPa, good toughness (elongation ≥26%), and low cost. They are suitable for ordinary railways (speed ≤120km/h) and can withstand conventional train loads, but have poor corrosion resistance, requiring regular painting for rust prevention, with a service life of 8-10 years. Q345 steel fishplates have a tensile strength ≥470MPa, yield strength ≥345MPa, high strength, and excellent fatigue resistance (fatigue life ≥1 million cycles). They are suitable for heavy-haul railways (axle load ≥25t), can resist large load impacts, with a service life of 12-15 years, and cost 20% higher than Q235 steel. Stainless steel fishplates (304 material) have a tensile strength ≥515MPa, yield strength ≥205MPa, salt spray resistance, and moisture resistance. They are suitable for corrosive environments such as coastal areas and chemical industrial zones, requiring no rust prevention maintenance, with a service life of 15-20 years, but the cost is 4-5 times that of Q235 steel, only used in special environments.
- How to determine the number of bolt holes and hole diameter of fishplates according to rail specifications, and what are the impacts of insufficient holes or hole diameter deviation?
43kg/m rails are matched with 4-hole fishplates (hole diameter 24mm), 50-60kg/m rails with 6-hole fishplates (hole diameter 26mm), and 75kg/m heavy-haul rails with 8-hole fishplates (hole diameter 28mm). The number of holes is proportional to the rail weight, and more bolts can disperse the load and avoid stress concentration. Insufficient bolt holes (e.g., 4-hole fishplates for 60kg/m rails) will increase the force on each bolt (from 50kN to 75kN), exceeding the bolt bearing limit and easily causing bolt breakage; excessive hole diameter deviation (e.g., drilling a 26mm hole into 28mm) will increase the gap between the bolt and the hole (2mm), leading to fishplate displacement during train vibration, loose rail joints, and gauge deviation, affecting driving safety.
- How to detect the fit between fishplates and rails, what problems will poor fit cause, and how to adjust?
During detection, a feeler gauge is inserted into the contact surface between the fishplate and the rail to measure the maximum gap: the gap in straight sections ≤0.2mm, in curve sections ≤0.3mm, and the gap length ≤100mm. Poor fit will cause load concentration at the gap, accelerating local wear of the fishplate (wear depth >3mm/year), and increasing rail joint vibration, raising wheel-rail noise by 5-8 decibels. Adjustment methods: if poor fit is caused by fishplate deformation, replace with a new fishplate; if caused by uneven rail joints, grind the rail joints with an angle grinder (flatness ≤0.1mm/m after grinding); if caused by loose bolts, re-tighten the bolts according to standard torque (300-350N·m for M24 bolts), and re-detect the fit after re-tightening.
- When the bolt holes of fishplates are worn during use, to what extent do they need to be replaced, and how to repair slight wear?
After wear, if the hole diameter expands ≤1mm (e.g., a 26mm hole expands to 27mm), it is slight wear. Bolts with increased diameter (e.g., M25 bolts) can be installed, and metal gaskets (thickness 0.5mm) can be filled in the gap between the bolt and the hole to ensure tight fit; if the hole diameter expands >1mm (e.g., a 26mm hole expands to 28mm), the fishplate must be replaced, as excessive gaps will cause uneven force on the bolts, easily leading to shear fracture. Before replacement, record the fishplate model and rail specification to ensure the new fishplate is consistent with the original model. After installation, detect the bolt torque and fit, and put it into use only when meeting the requirements.
- What are the differences in the connection strength requirements of fishplates for different railway types (ordinary, high-speed, heavy-haul), and how to verify?
Ordinary railways require fishplate connection strength ≥600kN (tensile), high-speed railways ≥700kN, and heavy-haul railways ≥800kN. Verification method: conduct a tensile test in the laboratory, assemble the fishplate with the rail, apply axial tension, and record the tensile force at break. If the breaking force of ordinary railway fishplates is ≥600kN, high-speed ≥700kN, and heavy-haul ≥800kN, it is qualified. On-site verification can be done through train operation testing, monitoring the displacement of fishplate joints (ordinary railways ≤1mm, high-speed ≤0.5mm, heavy-haul ≤0.8mm). Excessive displacement indicates insufficient connection strength, requiring inspection of bolt torque or replacement of fishplates.