Anti-aging technology and adaptation schemes for different service environments of rail pads
What is the anti-aging technology of under-rail pads in high-temperature and strong ultraviolet radiation areas?
The core of anti-aging of under-rail pads in high-temperature and strong ultraviolet radiation areas is to improve the weather resistance and ultraviolet resistance of the material. Ethylene Propylene Diene Monomer (EPDM) is preferred, which has a stable molecular structure and excellent ultraviolet aging resistance. During production, 2%-3% ultraviolet absorber and 1%-2% antioxidant need to be added to the rubber formula. The ultraviolet absorber can absorb ultraviolet energy, and the antioxidant can inhibit the oxidative degradation of rubber. The surface of the pad should be treated with an anti-ultraviolet coating with a thickness of 5-8μm. The coating material is acrylate resin, which can effectively block the erosion of ultraviolet rays on the inside of the pad. At the same time, optimize the structural design of the pad, adopt a honeycomb internal structure to enhance the heat dissipation performance of the pad and reduce the thermal aging rate in high-temperature environments. In addition, it is necessary to control the compression set rate of the pad ≤20%. This index is the key to measuring anti-aging performance, and it is detected by dynamic compression test to ensure that the pad has no obvious aging after serving in high-temperature and strong ultraviolet environment for more than 5 years.
What is the anti-aging optimization scheme of under-rail pads in humid and corrosive areas?
The aging of under-rail pads in humid and corrosive areas is mainly caused by water immersion and chemical corrosion. The optimization scheme needs to start from both material selection and structural protection. Chloroprene Rubber (CR) is selected as the material, which has excellent water resistance and corrosion resistance, and its performance attenuation rate in acid-base environment is ≤10% per year. Structurally, a sealed edge design is adopted, and the edges of the pad are vulcanized and sealed to prevent moisture and corrosive media from penetrating into the pad and damaging the rubber molecular chain. At the same time, a polyethylene water barrier layer is added on the side of the pad in contact with the sleeper, with a thickness of 0.5-1mm, to further block moisture erosion. During production, it is necessary to strictly control the porosity of the pad ≤1%. Excessively high porosity will become a channel for moisture and corrosive media, accelerating pad aging. In addition, a layer of waterproof geotextile should be laid under the pad during laying, with a permeability coefficient ≤10⁻⁷cm/s, forming a double waterproof protection to extend the service life of the pad.
What are the anti-fatigue aging measures of under-rail pads for heavy-haul lines?
The under-rail pads for heavy-haul lines need to bear high-frequency cyclic loads. The core of anti-fatigue aging is to improve the compression fatigue resistance of the material. Polyurethane elastomer is preferred, which has better compression fatigue resistance than traditional rubber materials. During production, it is necessary to adjust the polyurethane formula, increase the hard segment content to 35%-40%, and improve the compressive strength and anti-fatigue performance of the material. At the same time, the compression molding vulcanization process is adopted to ensure that the internal structure of the pad is uniform, free of bubbles and impurities, and avoid internal defects becoming fatigue crack sources. The thickness of the pad should be adjusted according to the axle load. The thickness of the pad for 30t axle load lines should be 20mm, 5mm thicker than that for ordinary lines, to enhance the bearing capacity of the pad. In addition, the pad should be pre-compressed with a pre-compression amount of 5% to eliminate the initial deformation of the pad and improve the stability of long-term service. Through fatigue test, the stiffness attenuation rate of the pad under 10⁷ cyclic loads is ≤8%, which meets the anti-fatigue aging requirements of heavy-haul lines.
What are the detection indicators and test methods for the anti-aging performance of under-rail pads?
The detection indicators for the anti-aging performance of under-rail pads mainly include tensile strength retention rate, elongation at break retention rate, compression set rate and weather resistance. The test methods for tensile strength retention rate and elongation at break retention rate are: place the pad sample in an aging test chamber, simulate the temperature, humidity and ultraviolet irradiation conditions of the target environment, conduct tensile test after aging for 1000 hours, and a retention rate ≥70% is qualified. The compression set rate is tested by a compression set testing machine. Compress the pad to a deformation of 25%, keep it at 70℃ for 22 hours, measure the deformation after unloading, and a deformation rate ≤25% is qualified. The weather resistance test uses a xenon lamp aging test chamber to simulate the outdoor natural aging environment. After 500 hours of aging, observe whether the pad surface has cracks and chalking. No obvious aging is qualified. During detection, 10 samples should be taken from each batch, and the test results are averaged to ensure the accuracy of the detection data.
What is the anti-freeze-thaw aging technology of under-rail pads in alpine regions?
The aging of under-rail pads in alpine regions is mainly caused by freeze-thaw cycles. The core of anti-freeze-thaw aging is to improve the low-temperature toughness and frost heave resistance of the material. Butyl Rubber (IIR) is selected, which can still maintain good elasticity at -40℃, and its performance attenuation rate after freeze-thaw cycles is ≤8%. During production, 3%-4% plasticizer needs to be added to the rubber formula to improve the low-temperature flexibility of the material and avoid low-temperature brittle fracture. The inside of the pad should be added with an elastic fiber reinforcement layer, the fiber material is nylon, and the thickness of the reinforcement layer is 2-3mm, which can improve the frost heave resistance of the pad and prevent pad cracking caused by freeze-thaw cycles. At the same time, control the Shore hardness of the pad at 55-60HD. Excessively high hardness will reduce low-temperature toughness, and excessively low hardness will result in insufficient bearing capacity. In addition, the pad should be subjected to freeze-thaw cycle test. Freeze the pad at -40℃ for 12 hours, then thaw at 25℃ for 12 hours. After 50 cycles, test the performance. A tensile strength retention rate ≥80% is qualified to ensure the service stability of the pad in alpine regions.