Rail Clip Clamping Pressure Attenuation Law and Routine Maintenance and Calibration Methods
What are the main causes of the attenuation of elastic strip buckling pressure?
The primary cause of the attenuation of elastic strip buckling pressure is material fatigue. The elastic strip is in a state of repeated elastic deformation for a long time, and the internal microstructure will change, leading to a decrease in elasticity and a subsequent reduction in buckling pressure. Temperature change is also an important factor. At high temperatures, the elastic strip will expand when heated, the deformation will increase, and the buckling pressure will decrease; at low temperatures, internal stress will be generated due to contraction, and long-term repeated temperature cycles will accelerate fatigue. The continuous vibration generated by train operation will cause slight slip between the elastic strip and the rail and pad, leading to the deviation of the installation position of the elastic strip, thereby causing the attenuation of buckling pressure. In addition, the corrosion on the surface of the elastic strip will weaken its cross-sectional size, reduce the structural strength, and also lead to the decrease of buckling pressure. Insufficient pre-tightening force during installation or improper selection of elastic strip models will also aggravate the later attenuation of buckling pressure.
To what extent does the attenuation of elastic strip buckling pressure require replacement?
The replacement standard of elastic strip buckling pressure should be determined according to the line type. High-speed railways have stricter requirements. When the buckling pressure attenuates to 80% of the design value, it must be replaced. When the buckling pressure of elastic strips on ordinary-speed railways attenuates to below 70% of the design value, it should be replaced in a timely manner. If it continues to be used, the longitudinal displacement of the rail will increase, affecting track stability. To judge whether the buckling pressure meets the standard, it is necessary to conduct on-site testing with a special elastic strip buckling pressure tester, not just by visual inspection. For elastic strips with obvious deformation, cracks or corrosion perforation, they should be replaced immediately regardless of whether the buckling pressure meets the standard. In addition, at the same joint, if one elastic strip needs to be replaced, the adjacent elastic strips should be replaced together to ensure uniform buckling pressure at the joint.
How to timely detect the problem of elastic strip buckling pressure attenuation through daily inspection?
During daily inspection, inspectors can timely detect the problem of elastic strip buckling pressure attenuation through three methods: "observing, tapping and testing". "Observing" is to observe the appearance of the elastic strip. If the elastic strip has obvious enlarged opening, deformation or poor contact with the rail, it indicates that the buckling pressure may have attenuated. "Tapping" is to flick the elastic strip with an inspection hammer. If the sound is dull, it indicates that the elasticity of the elastic strip has decreased and the buckling pressure is insufficient; if the sound is crisp, it means the elastic strip is in good condition. "Testing" is to regularly conduct sampling tests on elastic strips with a buckling pressure tester. The sampling ratio for high-speed railways is not less than 5%, and for ordinary-speed railways not less than 3%. For disease-prone areas such as curve sections and turnout areas, the testing frequency should be increased. During the inspection, if problems such as elastic strip slip and pad damage are found, the possibility of buckling pressure attenuation should also be vigilant.
What are the on-site calibration methods for elastic strip buckling pressure, and what are their respective application scenarios?
There are two main on-site calibration methods for elastic strip buckling pressure: one is to adjust the bolt pre-tightening force. Tighten the fastening bolts corresponding to the elastic strip with a torque wrench to increase the pre-tightening force, thereby restoring the buckling pressure of the elastic strip. This method is applicable to the case of slight attenuation of buckling pressure and no deformation of the elastic strip. The second is to replace the elastic strip gasket. Adjust the installation height of the elastic strip by increasing or decreasing the thickness of the gasket, so that the elastic strip returns to the designed deformation, thereby restoring the buckling pressure. This method is applicable to the case where the elastic strip has slight deformation and cannot be solved by adjusting the bolt. For the case of severe attenuation of buckling pressure or damage to the elastic strip, calibration is not possible, and only new elastic strips can be replaced. The method of adjusting bolt pre-tightening force is simple to operate and low in cost, and is the first choice for daily maintenance; the method of replacing gaskets requires disassembling the elastic strip, with relatively large workload, and is applicable to targeted repair.
Why is the attenuation speed of elastic strip buckling pressure in turnout areas faster than that in ordinary lines?
The attenuation speed of elastic strip buckling pressure in turnout areas is faster, mainly because the track structure in turnout areas is complex, and the load borne by elastic strips is more special. There are a large number of rail splicing and turning parts in turnout areas. When trains pass, the lateral and longitudinal forces between the wheel and rail are much greater than those in ordinary lines, and the elastic strips need to bear greater reaction forces. Secondly, the vibration frequency in turnout areas is higher. When train wheels pass through the turnout frog and point rail, severe impact vibration will be generated, accelerating the material fatigue of the elastic strip. In addition, there are various types of under-rail pads in turnout areas, and the contact state between the elastic strip and the pad is complex, which is prone to stress concentration, leading to increased local wear of the elastic strip. Maintenance operations in turnout areas are frequent, and repeated disassembly and installation of elastic strips will also damage their elasticity, further accelerating the attenuation of buckling pressure.