Elastic Modulus Matching Technology for Rail Pads and Track Vibration and Noise Reduction Solutions
What are the core influencing factors of the elastic modulus of under-rail pads?
The core influencing factors of the elastic modulus of under-rail pads include material formula, vulcanization process and structural design. The material formula is the basis for determining the elastic modulus. For pads based on ethylene propylene diene monomer (EPDM), the elastic modulus can be changed by adjusting the carbon black filling amount. When the carbon black filling amount is increased from 30 parts to 60 parts, the elastic modulus can be increased by more than 50%. The vulcanization temperature and time in the vulcanization process also affect the elastic modulus. When the vulcanization temperature is controlled at 150-160℃ and the vulcanization time is 15-20 minutes, the crosslinking density of the pad is moderate and the elastic modulus is stable; excessive temperature or too long time will lead to excessive crosslinking, making the pad hard and brittle with a high elastic modulus. In terms of structural design, hollow pads with grooves or round holes have an elastic modulus 10%-20% lower than that of solid pads, because the hollow structure can increase the deformation of the pad and reduce the overall stiffness. In addition, the ambient temperature will also affect the elastic modulus. The pad material will shrink and harden in low temperature environment, increasing the elastic modulus; the material will soften in high temperature environment, decreasing the elastic modulus. Therefore, the formula should be adjusted according to the climatic conditions of the area where the line is located.
What are the elastic modulus matching requirements for under-rail pads in high-speed railways?
The elastic modulus matching requirements for under-rail pads in high-speed railways are to balance high elasticity and high stability. The elastic modulus should be controlled at 80-120MPa. This range can not only ensure that the pad has sufficient elasticity to absorb the vibration energy generated by high-speed train operation and reduce wheel-rail contact noise, but also avoid excessive deformation of the pad and ensure the stable geometric position of the rail. High-speed railways have higher requirements for the dynamic elastic modulus of the pad. The ratio of dynamic elastic modulus to static elastic modulus should be controlled between 1.2 and 1.5, ensuring that the elastic performance of the pad will not be significantly attenuated under high-frequency vibration load. At the same time, the elastic modulus of the pad should have good aging resistance. Under the action of natural environments such as ultraviolet rays and rainwater, the change rate of elastic modulus within 5 years should be ≤10% to ensure the long-term stable vibration reduction effect of the line. In addition, the under-rail pad for high-speed railways should adopt a layered structure design. The upper layer is a low elastic modulus layer (80-90MPa), which is in direct contact with the rail and plays a major vibration reduction role; the lower layer is a high elastic modulus layer (100-120MPa), which is in contact with the sleeper to improve the bearing capacity. The precise matching of elastic modulus is realized through layered design.
What are the technical points of anti-compression set technology for under-rail pads in heavy-haul railways?
The technical points of anti-compression set technology for under-rail pads in heavy-haul railways are to improve the fatigue resistance and creep resistance of the material. First, select high-wear-resistant and high-elastic styrene-butadiene rubber (SBR) and natural rubber (NR) blended material with a blending ratio of 7:3. This combination can balance the elasticity and anti-compression deformation ability of the material. Add anti-aging agent and reinforcing agent to the material formula. Select 4010NA as the anti-aging agent with an addition amount of 2 parts to delay material aging; select silica as the reinforcing agent with an addition amount of 40 parts to enhance the crosslinking strength of rubber molecular chains and improve the anti-compression deformation ability. The vulcanization process adopts a two-stage vulcanization process. The first-stage vulcanization temperature is 145℃ for 12 minutes, and the second-stage vulcanization temperature is 100℃ for 4 hours. The crosslinking density of the material is further improved through two-stage vulcanization, and the compression set rate is reduced, which is required to be ≤25% (70℃×22h×25% compression rate). In addition, the structural design of the pad adopts an arc structure with thick middle and thin edges, with a middle thickness of 20mm and an edge thickness of 15mm. The arc structure can disperse the concentrated load of heavy-haul trains and reduce the local compression deformation of the pad. At the same time, anti-slip convex lines with a height of 2mm are set at the bottom of the pad to enhance the friction between the pad and the sleeper and prevent the pad from slipping.
What are the noise reduction optimization design methods for under-rail pads in urban rail transit?
The noise reduction optimization design methods for under-rail pads in urban rail transit are to reduce wheel-rail contact noise from both material and structure aspects. In terms of material, damping rubber material with a damping factor ≥0.3 is selected. Damping rubber can convert vibration energy into heat energy and dissipate it, and its noise reduction effect is 15%-20% higher than that of ordinary rubber. Add sound insulation filler such as vermiculite powder with an addition amount of 15 parts to the material. The layered structure of vermiculite powder can hinder sound wave propagation and further enhance the noise reduction effect. In terms of structure, a porous honeycomb structure is adopted with a honeycomb aperture of 5mm and a hole spacing of 8mm. The honeycomb structure can increase the number of reflections of sound waves inside the pad, consume sound wave energy and reduce noise propagation. At the same time, arc grooves with a depth of 3mm and a width of 10mm are set on the pad surface. The arc grooves can change the propagation direction of wheel-rail vibration and reduce the transmission of vibration to the sleeper. In addition, a sound insulation buffer layer made of polyurethane foam with a thickness of 5mm should be installed between the under-rail pad and the rail for urban rail transit. The sound insulation buffer layer can absorb the vibration noise at the bottom of the rail to achieve double noise reduction, reducing the train operation noise by 8-10dB and meeting the noise emission standards of the urban environment.
What are the detection methods and judgment standards for the elastic modulus of under-rail pads?
The detection method for the elastic modulus of under-rail pads mainly adopts the compression test method in accordance with the national standard GB/T 531.1-2008. An electronic universal testing machine is used to make the pad sample into a standard test piece with a diameter of 29mm and a thickness of 12mm. Under the room temperature (23±2℃) condition, load is applied at a compression speed of 5mm/min, the load-deformation curve is recorded, and the elastic modulus is calculated by the formula (elastic modulus = stress/strain). During detection, 3 test pieces of the same batch of pads should be sampled for testing, and the average value is taken as the elastic modulus value of the batch of pads. The judgment standards are divided according to the line type. The elastic modulus of under-rail pads for high-speed railways should be in the range of 80-120MPa with a deviation ≤±10MPa; the elastic modulus of under-rail pads for heavy-haul railways should be in the range of 150-200MPa with a compression set rate ≤25%; the elastic modulus of under-rail pads for urban rail transit should be in the range of 60-90MPa with a damping factor ≥0.3. If the test result is out of the standard range, the batch of pads is judged as unqualified and shall not be put into use. In addition, high and low temperature elastic modulus tests should be carried out to test the elastic modulus at -40℃ and 60℃ respectively, requiring the elastic modulus change rate ≤20% to ensure the performance stability of the pad under extreme temperatures.