Anti-loosening design technology for elastic clips and adaptation solutions for different service environments
What are the key points of anti-loosening design for elastic strips in sandy and windy areas?
The core of anti-loosening design for elastic strips in sandy and windy areas is to prevent sand and dust from invading the contact gap between the elastic strip, rail and sleeper, and avoid sand accumulation leading to deformation and failure of the elastic strip. First, an annular dust-proof groove with a width of 3mm and a depth of 2mm is added inside the hoop of the elastic strip, which can trap intruded sand and dust and prevent them from entering the stress surface of the elastic strip and affecting the preload. Second, a closed elastic strip structure is adopted instead of the traditional open structure, which reduces the channel for sand and dust to enter from the opening. At the same time, the closed structure can improve the anti-deformation ability of the elastic strip and prevent it from opening due to wind and sand impact. The surface of the elastic strip shall be sprayed with plastic, with a plastic layer thickness ≥80μm. Epoxy resin powder resistant to wind and sand wear is selected to enhance the wear resistance of the elastic strip surface and prevent corrosion caused by wind and sand erosion. In addition, a nylon dust-proof gasket with a thickness of 2mm shall be installed on the contact surface between the elastic strip and the under-rail pad, which can not only buffer the vibration of the elastic strip but also block sand and dust from entering the contact gap. During installation, the initial preload of the elastic strip shall be controlled at 22-25kN, and the preload attenuation shall be sampled regularly to ensure that the preload attenuation rate is ≤8% after 1 year of service.
What is the integrated anti-loosening and anti-corrosion design scheme for elastic strips in humid coastal areas?
The anti-loosening design of elastic strips in humid coastal areas should be combined with anti-corrosion requirements to avoid corrosion failure of elastic strips in high salt spray environment. First, the elastic strip is made of weather-resistant spring steel (model 09CuPCrNi-A), which contains corrosion-resistant elements such as copper and chromium. A dense passivation film can be formed on the surface in salt spray environment, and its corrosion resistance is more than 3 times that of ordinary spring steel. In terms of anti-loosening structure, serrated anti-loosening teeth with a height of 1.5mm and a pitch of 2mm are arranged at the end of the elastic strip, which mesh with the anti-slip lines on the rail base to increase contact friction and prevent the elastic strip from slipping under vibration load. The anti-corrosion treatment adopts hot-dip galvanizing + sealant double protection, with a zinc layer thickness ≥120μm and a sealant thickness ≥20μm. The sealant can fill the pores of the zinc layer and prevent salt spray from corroding the base metal of the elastic strip through the zinc layer. In addition, the installation torque of the elastic strip shall be controlled at 160-180N·m to ensure that the elastic strip is closely attached to the rail and reduce the occurrence of crevice corrosion. Anti-corrosion inspection of elastic strips shall be carried out every six months. If the zinc layer is damaged, anti-corrosion paint shall be touched up in time to ensure the anti-loosening and anti-corrosion effect.
What are the low-temperature anti-loosening design measures for elastic strips in alpine permafrost areas?
The anti-loosening design of elastic strips in alpine permafrost areas needs to solve the problems of low-temperature brittle fracture and preload fluctuation caused by permafrost heave. First, the elastic strip is made of low-temperature spring steel (model 60Si2MnDR), whose impact energy at -40℃ low temperature is ≥34J, avoiding brittle fracture of the elastic strip in low-temperature environment. At the same time, the change rate of its elastic modulus at low temperature is ≤5%, ensuring stable preload. The anti-loosening structure adopts double-limb anti-loosening elastic strips. The double-limb structure can disperse stress concentration at low temperature. When one limb fails, the other limb can still maintain the fastening force, improving system redundancy. The threaded connection part of the elastic strip shall be coated with low-temperature anti-loosening grease with a freezing point ≤-55℃, which does not solidify or fail at low temperature and can effectively prevent thread loosening. In addition, to solve the problem of sleeper displacement caused by permafrost heave, the elastic strip shall be used with adjustable gauge blocks with an adjustment range of ±3mm, which can compensate for the gauge change caused by permafrost heave and avoid the elastic strip being pulled and cracked due to gauge deviation. After installation, low-temperature freeze-thaw cycle test shall be carried out. After 50 freeze-thaw cycles from -40℃ to 20℃, the preload attenuation rate of the elastic strip shall be ≤10%.
What is the anti-loosening strengthening technology for elastic strips in heavy-haul lines with large axle loads?
The anti-loosening design of elastic strips in heavy-haul lines with large axle loads needs to cope with high-frequency impact loads of axle loads above 30t, and the core is to improve the fatigue resistance and anti-slip ability of elastic strips. First, a variable-section elastic strip structure is adopted. The diameter of the root section of the elastic strip is increased to 18mm, 2mm more than that of ordinary elastic strips, improving the fatigue resistance of the root and avoiding root fracture under heavy-haul loads. In terms of anti-loosening structure, an annular anti-loosening flange with a height of 3mm is arranged in the middle of the elastic strip, which cooperates with the limit groove on the sleeper to limit the lateral displacement of the elastic strip, and the anti-slip coefficient is ≥0.45. The elastic strip is made of high-strength spring steel (model 55SiCrA), whose hardness reaches HRC48-52 after quenching and tempering, tensile strength ≥1900MPa, yield strength ≥1700MPa, meeting the stress requirements of heavy-haul lines. In addition, a torque multiplier is used for the installation of elastic strips to ensure that the preload reaches 35-40kN, 50% higher than that of elastic strips in ordinary lines. High preload can effectively resist the impact vibration of heavy-haul trains. During service, ultrasonic flaw detection shall be used to detect fatigue cracks of elastic strips to ensure that no cracks occur after 2×10⁶ fatigue cycles.
What are the detection indicators and acceptance standards for the anti-loosening performance of elastic strips?
The detection indicators for the anti-loosening performance of elastic strips mainly include five aspects: preload attenuation rate, anti-slip coefficient, low-temperature impact energy, fatigue life and anti-corrosion performance. The preload attenuation rate is regularly detected by a torque wrench: the attenuation rate of elastic strips in sandy and windy areas is ≤8% after 1 year of service, ≤10% in humid areas, and ≤12% in alpine areas; the anti-slip coefficient is detected by a shear testing machine: ≥0.45 for elastic strips in heavy-haul lines and ≥0.4 for ordinary lines; the low-temperature impact energy is detected by an impact testing machine: ≥34J for elastic strips in alpine areas at -40℃; the fatigue life is detected by a pulsating fatigue testing machine: ≥2×10⁶ cycles without cracks for elastic strips in heavy-haul lines; the anti-corrosion performance is detected by a salt spray test: the corrosion resistance time of elastic strips in humid coastal areas is ≥1500 hours. The acceptance standard is: 30 elastic strips are sampled from each batch for testing, and the qualification rate of each indicator shall reach 100%. If 1 elastic strip is unqualified, double sampling shall be carried out; if there are still unqualified products in double sampling, the batch shall be judged unqualified. After passing the acceptance, the applicable environment type and test batch shall be marked on the surface of the elastic strip to facilitate accurate selection during on-site installation. At the same time, a test file shall be established to record the service environment and test data of the elastic strip, providing a basis for subsequent maintenance.