Anti-aging Modification Technology and Enhanced High-Temperature Durability of Track Pads
What are the core formula optimization measures for anti-aging modification of under-rail pads?
The core formula optimization for anti-aging modification of under-rail pads is to add three types of functional additives to the styrene-butadiene rubber matrix to synergistically improve high-temperature resistance and anti-aging performance. First, antioxidant 1010 is added with an amount of 0.5%-1.0% of the rubber mass. This antioxidant can capture free radicals, inhibit the oxidative degradation of rubber, and significantly slow down the thermo-oxidative aging rate. Second, heat-resistant agent carbon black N330 is added with an amount of 30%-40% of the rubber mass. Carbon black can not only improve the strength and wear resistance of the pad but also reflect ultraviolet rays and heat, reducing the damage of high temperature to rubber. Finally, reinforcing agent silica is added with an amount of 10%-15% of the rubber mass. Silica forms a stable network structure with rubber molecular chains, enhancing the anti-deformation ability of rubber and preventing permanent deformation of the pad at high temperatures. The aging rate of the modified rubber material at 100℃ is only 1/3 of that of traditional materials, and the heat-resistant life is increased to more than 15 years. In addition, the addition amount of paraffin oil in the formula should be controlled ≤5% to avoid surface stickiness of the pad caused by paraffin oil migration.
What are the high-temperature performance differences between modified under-rail pads and ordinary pads?
The high-temperature performance differences between modified under-rail pads and ordinary pads are mainly reflected in three aspects: elasticity retention rate, anti-aging life and dimensional stability. At a high temperature of 80℃, after 5000 hours of aging, the elastic modulus retention rate of modified pads is ≥85%, while that of ordinary pads is only about 50%, with severe elastic attenuation. In terms of anti-aging life, the service life of modified pads in high-temperature ballast bed environment can reach 15 years, which is more than twice that of ordinary pads, greatly reducing replacement costs. In terms of dimensional stability, the thermal shrinkage rate of modified pads at 100℃ is ≤2%, while that of ordinary pads is ≥8%, which is easy to cause poor fit between the pad and the sleeper. In addition, the modified pads have better weather resistance, and the aging rate under ultraviolet radiation is only 1/4 of that of ordinary pads, suitable for open-air lines exposed to high-temperature sunlight. The compression set rate of modified pads is ≤15%, while that of ordinary pads is ≥30%, which is easy to lose elasticity under long-term load.
What are the adaptation requirements of modified under-rail pads for different high-temperature environments?
The adaptation requirements of modified under-rail pads for different high-temperature environments are core to adjusting the additive ratio and rubber matrix type. The temperature in desert high-temperature exposure environment can reach 70-80℃, and the ultraviolet radiation is strong. It is required to increase the antioxidant addition amount to 1.0%, the carbon black N330 addition amount to 40%, and add 2% ultraviolet absorber. The rubber matrix adopts nitrile rubber to improve weather resistance and heat resistance. The tropical humid high-temperature environment is characterized by high temperature and high humidity. It is required to add 1.5% fungicide, 0.8% antioxidant, 35% carbon black. The rubber matrix adopts neoprene to balance heat resistance and water resistance. The industrial plant high-temperature environment has acid-base corrosion. It is required to add 5% anti-corrosion agent, 0.7% antioxidant, 30% carbon black. The rubber matrix adopts EPDM rubber to improve chemical corrosion resistance. The plateau high-temperature low-oxygen environment has low oxygen content, and the oxidative aging rate is relatively slow. The antioxidant addition amount is 0.5%, the carbon black addition amount is 30%, and the rubber matrix adopts styrene-butadiene rubber to balance performance and economy.
What are the key vulcanization molding process points of modified under-rail pads?
The key vulcanization molding process points of modified under-rail pads are concentrated in temperature control and pressure adjustment to ensure the crosslinking density and performance stability of rubber. In the mixing stage, rubber and additives must be mixed in an internal mixer, the mixing temperature is controlled at 80-90℃, and the mixing time is 10-15 minutes to avoid decomposition of additives due to high temperature. In the vulcanization stage, a flat vulcanizing machine is used, the vulcanization temperature is 150-160℃, the vulcanization pressure is 15-18MPa, and the vulcanization time is 20-25 minutes. Excessively high vulcanization temperature will cause rubber scorching, and excessively low temperature will result in incomplete vulcanization. Segmented temperature control should be adopted during vulcanization, the heating rate is 5℃/min, the temperature is kept constant in the heat preservation stage, and the cooling rate is 3℃/min in the cooling stage to avoid internal stress of the pad caused by excessive temperature difference. After vulcanization, secondary vulcanization is carried out at 100℃ for 2 hours to further improve the anti-aging performance of the pad. After forming, hardness testing should be carried out, the Shore hardness of the pad is controlled at 55-60HA, with a deviation ≤±2HA to ensure that the elastic performance meets the design requirements.
What are the on-site laying and maintenance points of modified under-rail pads?
The on-site laying and maintenance of modified under-rail pads need to focus on laying environment and aging detection. Laying should be carried out when the temperature is below 35℃ to avoid pad deformation due to high-temperature laying. Before laying, debris and oil stains on the top surface of the sleeper should be cleaned to ensure that the pad is fully attached to the sleeper, with a contact area ≥95%. The laying direction of the pad must be strictly implemented according to the mark, the wear-resistant surface faces up to contact the rail, and the anti-slip surface faces down to contact the sleeper; reversed laying is strictly prohibited. After laying, the elasticity of the pad should be tested with a static compression testing machine, and the rebound rate when the compression amount is 10% is ≥90%. During maintenance, the aging degree of the pad should be tested regularly with an inspection cycle of 1 year. The testing indicators include hardness change rate and elastic modulus retention rate. If the hardness change rate exceeds 10% or the elastic modulus retention rate is lower than 80%, the pad should be replaced in time. In addition, avoid contact between the pad and organic solvents such as engine oil and diesel oil to prevent rubber swelling and aging.