Track Pad Elastic Modulus Grading Technology and Adaptation Schemes for Different Track Vibration Reduction Requirements
What are the core basis and grading interval division of the elastic modulus grading of under-rail pads?
The core basis for the elastic modulus grading of under-rail pads is two dimensions: vibration reduction demand and load level of the line. The two need to be coordinated to ensure line stability and vibration reduction effect. The vibration reduction demand is determined by the train operating speed. The higher the speed, the higher the wheel-rail vibration frequency, and the more low-elastic modulus pads are needed to buffer vibration. The load level is determined by the train axle load. The larger the axle load, the greater the pressure on the pad, and the more high-elastic modulus pads are needed to resist plastic deformation. Based on these two criteria, the elastic modulus is divided into three core intervals: the low elastic modulus grade is 200-300MPa, suitable for high-speed railway lines with a speed of 250-350km/h; the medium elastic modulus grade is 400-600MPa, suitable for ordinary-speed railways and urban express rails with a speed of 120-200km/h; the high elastic modulus grade is 700-1000MPa, suitable for heavy-haul railways with an axle load of more than 30t. The division of grading intervals is not fixed. It also needs to be adjusted according to the geological conditions of the line. For example, soft soil subgrade lines can choose a lower limit of elastic modulus within the corresponding grade to improve vibration reduction and buffering capacity. This grading method not only meets the differentiated needs of different lines, but also provides a basis for the standardized production of pads.
What are the material formula optimization points of low elastic modulus high-speed railway pads?
The material of low elastic modulus high-speed railway pads is based on polyurethane elastomer (PU). The core of formula optimization is to balance vibration reduction performance and compression set performance. First, it is necessary to adjust the ratio of hard segments to soft segments of polyurethane. The soft segment content is increased to 65%-70%. The soft segments are composed of polyether polyol, which can increase the elasticity and flexibility of the pad and reduce the elastic modulus. The hard segment content is controlled at 30%-35%. The hard segments are composed of isocyanate to ensure the tensile strength and tear resistance of the pad. Second, nano-calcium carbonate reinforcing agent is added with a dosage of 5%-8% of the matrix material. Nano-calcium carbonate can be uniformly dispersed in the polyurethane matrix to improve the compressive performance of the pad and avoid excessive deformation under long-term load. At the same time, anti-aging agent and anti-hydrolysis agent are added, each with a dosage of 1%-2%. The service environment of high-speed railway lines is complex. The anti-aging agent can improve the UV resistance of the pad, and the anti-hydrolysis agent can prevent the pad from hydrolytic aging in humid environments. Finally, a dynamic vulcanization process is adopted to make the material form an interpenetrating network structure. The elastic modulus of the optimized pad is stably maintained at about 250MPa, and the compression set rate is ≤5%, which fully meets the vibration reduction requirements of high-speed railway lines.
What are the structural design points of high elastic modulus heavy-haul pads?
The structural design of high elastic modulus heavy-haul pads should focus on three goals: enhancing load-bearing capacity, dispersing stress, and improving wear resistance. First, an embedded steel skeleton structure is adopted. A stainless steel skeleton with a thickness of 2mm is embedded in the middle of the pad. The shape of the steel skeleton is consistent with the pad, and the edges are chamfered to avoid stress concentration. The steel skeleton can evenly distribute the load to the entire pad, improve the anti-deformation ability, and enable the pad to withstand repeated impacts of axle loads above 30t. Second, diamond-shaped anti-slip lines are designed on the upper and lower surfaces of the pad. The depth of the lines is 1.5mm and the width is 3mm. The anti-slip lines can increase the friction between the pad and the rail, sleeper, prevent the pad from slipping during train operation, and the lines can store a small amount of lubricating oil to reduce friction and wear between the pad and the rail. Finally, the edge of the pad is designed as an arc transition structure with a transition radius of 10mm. In heavy-haul lines, the edge of the pad is prone to cracking due to stress concentration. The arc transition can reduce the edge stress concentration factor and improve the fatigue resistance of the pad. After the structural design is completed, finite element simulation analysis is required to simulate the load conditions of heavy-haul trains, ensuring that the maximum stress of the pad ≤ the allowable stress of the material and the deformation ≤ 0.5mm.
What are the testing methods and precision control points of the elastic modulus of under-rail pads?
The testing of the elastic modulus of under-rail pads is carried out in accordance with Rubber, vulcanized or thermoplastic - Determination of compression stress-strain properties (GB/T 7757). The core testing steps are divided into three links: sample preparation, compression test, and data calculation. For sample preparation, samples should be taken from different parts of the pad, 5 samples per batch. The sample size is a cylinder with a diameter of 29mm and a height of 12mm. When sampling, reinforced structures such as steel skeletons should be avoided to ensure sample uniformity. The compression test uses an electronic universal testing machine. The sample is placed between the upper and lower pressure plates of the testing machine, and a compression load is applied at a speed of 5mm/min. The stress value when the compression amount is 10% is recorded. The elastic modulus is calculated by the formula E=εσ, where σ is the compressive stress and ε is the compressive strain. There are three main precision control points: first, the test environment temperature should be controlled at 23±2℃. Excessively high or low temperature will affect the elastic properties of the material and lead to deviations in test results; second, the parallelism deviation of the sample ≤ 0.05mm. Failure to meet the parallelism requirements will cause uneven stress on the sample and affect the accuracy of the stress value; third, the standard deviation of the test results of 5 samples per batch ≤ 10MPa. If the standard deviation is too large, re-sampling and testing are required to ensure the reliability of the test results.
What are the elastic modulus adaptation and adjustment schemes of under-rail pads in different climatic environments?
The elastic modulus adaptation and adjustment of under-rail pads in different climatic environments should be combined with the influence laws of temperature and humidity, and the material formula and structure should be optimized in a targeted manner. In alpine regions (annual average temperature ≤ -10℃), the elastic modulus of the material will increase with the decrease of temperature. Therefore, the lower limit of the elastic modulus interval of the corresponding line grade should be selected. For example, the elastic modulus of high-speed railway pads is adjusted to 200-220MPa. At the same time, cold-resistant plasticizers are added to the material with a dosage of 3%-5% to improve the low-temperature toughness of the pad and prevent low-temperature brittle fracture. In high-temperature and high-humidity regions (annual average temperature ≥ 25℃, relative humidity ≥ 80%), the material is prone to softening and hydrolysis. It is necessary to select the upper limit of the elastic modulus. For example, the elastic modulus of ordinary-speed railway pads is adjusted to 550-600MPa. At the same time, heat-resistant stabilizers and anti-hydrolysis agents are added to improve the high-temperature resistance and hydrolysis resistance of the pad and avoid rapid attenuation of the elastic modulus. In saline-alkali regions, saline-alkali ions in the soil are prone to corrode the pad. A fluorocarbon coating with a thickness of 0.5mm should be sprayed on the surface of the pad. The coating can isolate the erosion of saline-alkali ions, and the coating has high hardness, which can improve the wear resistance of the pad. The elastic modulus does not need to be adjusted significantly, and the standard value of the corresponding line can be maintained. The adjusted pad needs to undergo an environmental simulation test. After aging for 1000 hours in the corresponding climatic environment, the elastic modulus change rate ≤ 8% before it can be put into use.