Elastic Rail Clip Clamping Pressure and Rail Stability
Why does the standard range of rail clip clamping force vary by line type?
Conventional railways have low train speeds and small load fluctuations, so the rail clip clamping force standard is set at 10-12kN, balancing fixing effect and component life. High-speed railways have high train speeds and large wheel-rail impact forces, requiring greater clamping force (12-15kN) to prevent rail displacement and ensure operational smoothness. Due to the large axle load of heavy-haul lines, rail clips need to withstand long-term high pressure, and the clamping force is controlled at 15-18kN to avoid rail loosening. Urban rail transit has frequent starts and stops and concentrated impact loads, so the clamping force is set at 8-10kN to reduce damage to the track foundation. The operational characteristics of different lines determine the differentiated standards for rail clip clamping force, ensuring adaptability and safety.
What are the main reasons for the attenuation of rail clip clamping force?
Material fatigue is the core reason. Rail clips are subjected to periodic vibration for a long time, generating microcracks inside the metal, leading to decreased elasticity. Insufficient installation torque prevents the rail clip from achieving the designed deformation, resulting in rapid attenuation of clamping force after long-term use. Environmental corrosion has a significant impact. Rail clips in humid and saline-alkali areas corrode on the surface, weakening structural strength and elasticity. Rail displacement causes uneven stress on the rail clip, and local stress concentration accelerates the loss of clamping force. Unqualified rail clip materials, such as excessive carbon content or improper heat treatment process, will shorten fatigue life and exacerbate clamping force attenuation.
How to detect whether the rail clip clamping force meets the standard?
The torque wrench testing method is commonly used. The clamping force is inferred by measuring the bolt tightening torque, and the national standard requires the torque deviation to be ≤±5%. A dedicated clamping force tester can directly read the value by placing the sensor between the rail clip and the rail to display the clamping force in real time. Ultrasonic testing can evaluate the internal state of the rail clip and indirectly determine whether the clamping force has decreased due to fatigue. Regular dynamic monitoring with track inspection vehicles infers whether the rail clip clamping force is insufficient through changes in track geometric parameters. Sampling and disassembly testing is performed to conduct tensile tests on rail clips that have been in operation for a certain period to verify the degree of clamping force attenuation.
What are the characteristics of the clamping force design of FC-type foreign standard rail clips?
The FC-type foreign standard rail clip adopts a bolt-free structure, generating elastic deformation by inserting into the pre-embedded base, with a stable clamping force of 9-12kN. Its spring stroke reaches 12mm, which is larger than that of national standard rail clips, and can better adapt to the displacement caused by thermal expansion and contraction of the rail. Designed for high-speed lines, the clamping force fluctuation range is controlled within ±1kN to ensure the stability of track geometric parameters. Made of high-quality spring steel, after 3 million fatigue tests, the clamping force attenuation is ≤20%, with a longer service life. It is compatible with the 1435mm standard gauge and can be adjusted by replacing the insulated gauge block, and the clamping force remains stable without being affected by adjustment.
What chain problems can be caused by insufficient rail clip clamping force?
Insufficient clamping force first causes longitudinal movement of the rail, damaging track smoothness and increasing train jolting and wheel-rail wear. Rail displacement will cause excessive gauge deviation, affecting the passability of the train bogie and posing a derailment risk. Long-term movement will exacerbate the wear of fish plates and bolts, leading to overall failure of the fastening system. Unstable track geometric parameters will increase maintenance frequency and costs, reducing line operational efficiency. In severe cases, it can cause diseases at rail joints, such as depression and spalling, threatening train operation safety and causing operational interruption.