Fishplate and Bolt Installation and Matching Knowledge
What are the requirements for grade matching between fishplates and bolts?
60kg/m rails need to be matched with 10.9-grade high-strength joint bolts and 10-grade nuts, while 50kg/m rails adopt 8.8-grade or higher bolts and 10-grade nuts, which is clearly specified in TB/T 2347 standard. The bolt grade must correspond to the material strength of the fishplate; Q345 steel fishplates need to be equipped with high-strength bolts to achieve the best connection effect. Spring washers must comply with TB/T 2348 standard, forming a complete anti-loosening system with bolts and nuts. In insulated joint scenarios, insulated sleeves and insulated fishplates are also required to ensure electrical isolation performance. Mismatched grades will lead to uneven force distribution, which may reduce connection strength at best or cause bolt fracture or fishplate deformation at worst.
What are the specifications for the tightening torque of fishplate bolts?
Different rail types and bolt grades correspond to different torque standards. The torque of 10.9-grade bolts in P60 seamless line buffer zones is not less than 900N・m, and not less than 700N・m in ordinary lines. The torque of 10.9-grade bolts for P50 lines must be above 700N・m, and that for 8.8-grade bolts is not less than 600N・m, with deviations controlled within ±5%. The torque of special fishplate bolts for contact rails is usually 70±5N・m; excessive torque is prone to thread slipping, and insufficient torque will cause loosening. Tightening must adopt a diagonal alternating or inside-out order to avoid uneven force on the fishplate. Torque must be measured with a calibrated torque wrench, and manual tightening based on experience is prohibited.
What are the key steps for contact surface treatment before fishplate installation?
It is necessary to thoroughly remove dust, rust and oil stains from the contact surface between the rail and fishplate with a steel wire brush and abrasive cloth, especially impurities around the bolt holes. In insulated joint scenarios, the rail bonding surface must also be ground and derusted to ensure a flat surface without burrs. Power compound grease or long-acting grease should be evenly applied to the contact surface, with a thickness of 0.5~1mm, fully covering the butt joint surface. Installation should be carried out promptly after application to avoid dust adhesion affecting contact effect and electrical conductivity (for conductive joints). The treated contact surface must be free of scratches and deformations; otherwise, the effective contact area will be reduced and the connection strength will be lowered.
What are the accuracy requirements for fishplate installation?
The gap between the fishplate and the rail contact surface shall not exceed 0.1mm, and the insertion depth of a 0.05mm feeler gauge shall not exceed 5mm. The alignment deviation of bolt holes shall be ≤1mm to ensure smooth bolt penetration and uniform force bearing. After installation, the rail surface misalignment shall not exceed 2mm, and the height difference between the top of the fishplate and the top of the rail shall be ≤0.3mm. The gauge deviation at the line joint shall be within ±1mm, and the lateral flatness deviation shall not exceed 0.5mm. The bolt retightening sequence is different for curved lines and straight lines, and the corresponding specifications must be followed to ensure balanced overall force.
How to avoid bolt loosening after fishplate installation?
In addition to tightening according to the standard torque, it is necessary to install compliant spring washers with the notches facing downward. Lock nuts or thread-locking adhesive can be used to enhance tightening stability in vibrating environments. Regularly retighten and inspect bolts, especially in sections with high-frequency train passage, and shorten the inspection cycle. Ensure consistent bolt penetration direction during installation, and no skew after nut tightening to avoid local stress concentration. Avoid installation when the rail is unlocked or under stress to prevent abnormal bolt force caused by temperature changes or line deformation.