Fishplate and Bolt Connection Matching Technology
What are the bases for material selection of fish plates?
The material of fish plates must match the rail material. Q235 or 45# steel is commonly used in ordinary railways; these steels have good plasticity and machinability, and can adapt to the slight deformation of joints. High-speed and heavy-haul railways adopt alloy structural steels such as 40Cr, which have a tensile strength of over 800MPa and excellent wear resistance and fatigue resistance. Material selection also needs to consider environmental factors: stainless steel fish plates can be used in coastal areas to resist corrosion, and materials in cold regions must meet low-temperature toughness requirements.
How does the shape design of fish plates affect joint performance?
The cross-sectional shape of fish plates must fit the contour of the rail web to ensure uniform force transmission and reduce stress concentration. Their length is usually 600-800mm, and balanced fastening is achieved through the distribution of multiple sets of bolt holes to avoid excessive local stress. Some fish plates adopt a sloped end design, which can mitigate the impact during wheel-rail transition and reduce vibration noise at joints. The surface of fish plates for high-speed railways needs precision machining to ensure the fitting gap with rails is no more than 0.3mm.
Why do fish bolts often adopt oval neck or diamond neck structures?
The oval neck or diamond neck structure allows the bolt head to closely fit the bolt hole of the fish plate, preventing the bolt from rotating under train vibration and avoiding loosening. This structure can also position the bolt, ensuring alignment of the bolt axis with the hole axis during installation and reducing installation deviation. When the train generates lateral force during passage, the special neck structure can bear part of the shear force, share the bolt's load, improve the overall bearing capacity of the joint, and extend service life.
What are the different application scenarios of fish bolts with different strength grades?
Grade 4.8 fish bolts have a tensile strength ≥400MPa and yield strength ≥240MPa, suitable for low-load scenarios such as light rails or shunting lines. Grade 8.8 bolts have a tensile strength ≥800MPa and yield strength ≥640MPa, which are the mainstream choice for ordinary mainline railways. Grade 10.9 bolts have a tensile strength ≥1000MPa and yield strength ≥900MPa, mostly used in high-speed railways, heavy-haul railways and other lines with extremely high requirements for connection strength. On long steep slopes or curved sections, bolt grades usually need to be upgraded to enhance connection reliability.
What are the standards for pre-tightening force control of fish plate and bolt connections?
Pre-tightening force control must be determined based on the bolt grade: the pre-tightening force of M24 Grade 8.8 bolts is usually controlled at 250-300kN, while that of Grade 10.9 bolts needs to reach 400-450kN. The torque-angle dual-control method is mostly used in construction: first, a preset torque is used to eliminate gaps, then precise plastic deformation of the bolt is achieved through angle control to ensure the pre-tightening force error is less than 5%. Insufficient pre-tightening force will cause joint loosening, while excessive pre-tightening force may deform the bolt or fish plate, so a calibrated torque wrench must be used for operation.