Bolt hole position accuracy and connection strength of fishplate

Bolt hole position accuracy and connection strength of fishplate

• What are the precision requirements for fishplate bolt hole positions?​

The hole position spacing deviation must be ≤±0.5mm. For example, the bolt hole spacing of the fishplate matching 60kg/m rails is designed to be 140mm. If the actual measurement deviation exceeds this range, the bolt stress will be uneven. The deviation of the distance between the hole center and the edge of the fishplate must be ≤±0.3mm. Too small distance will weaken the strength of the fishplate, and too large distance will make it impossible to clamp the rail effectively. Ordinary railway fishplates must strictly control this parameter. The perpendicularity deviation of the bolt hole must be ≤1°. Excessive inclination will make the bolt bear additional bending moment and reduce the bearing capacity. High - speed railway fishplates have stricter requirements (≤0.5°). The hole diameter tolerance is + 0.2 - 0mm to ensure that the fitting gap with the bolt is ≤0.3mm. Too large gap will cause the bolt to shake and affect the connection stability.​

• What impact does insufficient hole position accuracy have on fishplate connection strength?​

Hole position deviation will make the bolt preload distribution uneven. The bolt preload deviation on the same fishplate may exceed 20%, leading to stress concentration at the rail joint. This problem in heavy - haul railways is easy to cause fishplate fracture. Hole position deflection will make the fishplate and rail fit poorly, reduce the contact area by 10% - 15%, reduce the bearing capacity at the joint by 20% - 25%, and aggravate vibration when the train passes. Excessive hole spacing deviation will cause steps at the rail joint, increase the impact force by 30% - 40% when the wheel passes, accelerate the wear of rails and fishplates, and shorten the service life. Insufficient distance from the hole edge will cause cracks in the fishplate under the action of bolt preload. This kind of disease may appear in ordinary railways after 1 - 2 years of use, and needs to be replaced in advance.​

• How to ensure the machining accuracy of fishplate bolt hole positions?​

CNC drilling machines are used for processing, with positioning accuracy up to ±0.1mm, ensuring that the hole position deviation is within the allowable range. After processing, a coordinate measuring machine must be used for 100% inspection, and unqualified products are prohibited from leaving the factory. Chamfering is carried out after drilling, with a hole edge chamfer of 0.5×45° to remove burrs and sharp corners, avoid stress concentration, and facilitate bolt installation, reducing wear on bolts. Secondary drilling is performed on heat - treated fishplates. Because heat treatment may cause deformation, secondary processing can correct the hole position deviation and ensure matching with rails. High - strength fishplates (such as 45# steel fishplates) must adopt this process. Trial installation tests are carried out before mass production. Connect the fishplate with standard rails and measure the bolt hole fitting. Mass production can be carried out only when the trial installation pass rate is ≥95%.​

• What are the differences in hole position accuracy among different types of fishplates?​

High - speed railway special fishplates have the highest hole position accuracy, with hole spacing deviation ≤±0.3mm and hole perpendicularity ≤0.5°, ensuring matching with high - precision bolts and meeting the stability requirements of high - speed trains. Heavy - haul railway fishplates focus on the accuracy of the distance from the hole edge (deviation ≤±0.2mm). Because they need to bear large axle load, to prevent the hole edge from tearing, 45# steel fishplates mostly adopt this standard. Ordinary railway fishplates have slightly lower hole position accuracy requirements (hole spacing deviation ≤±0.8mm), taking into account cost and performance, and Q235 steel fishplates can meet this requirement. Due to the brittleness of insulating fishplate materials (such as glass fiber reinforced materials), the hole position accuracy must be controlled within ±0.5mm to avoid cracking during installation and ensure insulation performance.​

• How to detect the accuracy of fishplate bolt hole positions?​

Use a coordinate measuring machine for comprehensive detection, measure the coordinate value of each bolt hole, calculate the deviation from the design value, and generate an accuracy report. 100% of high - speed railway fishplates must undergo this detection. Use special inspection tools for detection. Put the fishplate on the inspection tool with positioning pins. It is qualified if the pins can be smoothly inserted into all bolt holes without loosening. Ordinary railways can use this method for sampling inspection (5% per batch). Detect through assembly tests. Connect the fishplate with the rail and measure the tightening torque of the bolts. If the bolt torque deviation on the same fishplate exceeds 5%, it indicates insufficient hole position accuracy and needs rework. Check the quality of the hole edge. Observe whether there are cracks and burrs on the hole edge with a magnifying glass. Defective ones need to be polished and repaired, otherwise the service life of the bolt will be affected.