Stiffness Grading Design of Rail Pads and Adaptation Schemes for Different Track Structures
What is the stiffness design standard of under-rail pads for high-speed ballastless tracks?
High-speed ballastless tracks have extremely high requirements for the stiffness of under-rail pads. The design standard must balance vibration reduction performance and track stability. First, the static stiffness of the pad should be controlled at 50-80kN/mm. This stiffness range can effectively buffer the wheel-rail impact load during the high-speed operation of high-speed trains, and at the same time avoid excessive track deformation affecting driving safety. The dynamic stiffness should be controlled at 1.2-1.5 times the static stiffness to ensure that the stiffness of the pad is stable under the dynamic load of the train without obvious stiffness attenuation. Ethylene Propylene Diene Monomer (EPDM) is selected as the material, which has stable elastic modulus and excellent anti-aging performance, and can adapt to the long-term high-frequency load of high-speed railway lines. The thickness of the pad is designed to be 12mm, including a 10mm elastic layer and 1mm wear-resistant layers on the upper and lower surfaces. The wear-resistant layers are made of polyurethane to improve the wear resistance of the pad. In addition, the Shore hardness of the pad should be controlled at 60-65HD. Too high hardness will reduce the vibration reduction effect, while too low hardness cannot support the stable stress of the rail.
What are the high-stiffness guarantee measures for under-rail pads in heavy-haul ballasted tracks?
Heavy-haul ballasted tracks bear large axle loads, and under-rail pads need to have high stiffness to resist track deformation. The first guarantee measure is to select high-stiffness material, using polyurethane elastomer, whose static stiffness can reach 120-150kN/mm, more than 2 times higher than that of ordinary rubber pads. Second, a glass fiber reinforcement layer with a thickness of 2mm is added inside the pad, arranged in a crisscross pattern, which can improve the compressive strength and anti-deformation ability of the pad and avoid permanent compression deformation of the pad under heavy-haul loads. The thickness of the pad is designed to be 15mm, including a 13mm elastic layer and a 2mm reinforcement layer, ensuring the balance between stiffness and elasticity. The production process adopts compression molding vulcanization to make the internal structure of the pad uniform without bubbles and impurities, further ensuring the stability of stiffness. In addition, the compression set rate of the pad should be controlled at ≤10%, detected by high-temperature compression test to ensure that it can still maintain stable stiffness performance after long-term service in heavy-haul lines.
What are the design points of low-stiffness vibration reduction for under-rail pads in urban rail transit?
Urban rail transit is close to residential areas, and the core of low-stiffness vibration reduction design of under-rail pads is to improve vibration and noise reduction effects. First, the static stiffness of the pad is controlled at 20-30kN/mm. This low-stiffness range can effectively absorb wheel-rail vibration energy and reduce the intensity of vibration transmitted to the track bed and surrounding buildings. Butyl rubber is selected as the material, which has excellent damping performance, and its vibration and noise reduction effect is more than 20% better than that of ordinary rubber pads. The pad adopts a double-layer composite structure: the upper layer is a low-stiffness butyl rubber layer with a thickness of 8mm, responsible for vibration reduction; the lower layer is a high-stiffness support layer with a thickness of 5mm, responsible for load bearing. The double-layer structure balances vibration reduction and load bearing requirements. In addition, the surface of the pad should be anti-slip treated with diamond-shaped anti-slip lines with a depth of 0.5mm, increasing the friction force between the pad and the sleeper and avoiding pad slippage during train operation. At the same time, the oil resistance of the pad must meet the standard, able to resist oil pollution that may exist in urban rail transit lines, ensuring service life.
What is the stiffness adaptation adjustment technology of under-rail pads in ordinary-speed ballasted tracks?
The traffic volume and axle load of ordinary-speed ballasted tracks fluctuate greatly, and the core of stiffness adaptation adjustment technology of under-rail pads is to adopt a design with replaceable stiffness modules. First, the pad is divided into a basic support layer and a replaceable elastic layer. The stiffness of the basic support layer is fixed at 50kN/mm, and the stiffness of the replaceable elastic layer is divided into three levels: 30kN/mm, 40kN/mm and 50kN/mm. According to the traffic volume changes of the line, elastic layers with different stiffness can be flexibly replaced. For example, a high-stiffness elastic layer is replaced when the traffic volume increases, and a low-stiffness elastic layer when the traffic volume decreases, without replacing the entire pad, reducing maintenance costs. The connection between the elastic layer and the basic support layer adopts a card slot structure, which is convenient for installation and disassembly, and can be replaced online. In addition, natural rubber is selected as the material of the elastic layer, which is low-cost and has stable elastic performance, suitable for the economic needs of ordinary-speed lines. At the same time, after adjusting the stiffness of the pad, track dynamic performance tests should be carried out to ensure that the wheel-rail impact coefficient is ≤0.3, meeting the operation requirements of ordinary-speed lines.
What are the detection methods and qualification standards for the stiffness of under-rail pads?
The stiffness of under-rail pads is mainly detected by static stiffness testing machines and dynamic stiffness testing machines. The steps of static stiffness detection are: place the pad between the upper and lower pressure plates of the testing machine, apply a pre-pressure of 1kN, then load to the rated load at a speed of 1mm/min, record the load-deformation curve, and calculate the static stiffness value (stiffness = load/deformation). Dynamic stiffness detection uses sinusoidal dynamic load with a frequency of 10Hz and a loading amplitude of 50% of the rated load, records the dynamic load-deformation curve, and calculates the dynamic stiffness value. The qualification standards are divided according to track structure types: the static stiffness of pads for high-speed ballastless tracks should be 50-80kN/mm, and dynamic stiffness 1.2-1.5 times the static stiffness; the static stiffness of pads for heavy-haul ballasted tracks should be 120-150kN/mm, with compression set rate ≤10%; the static stiffness of pads for urban rail transit should be 20-30kN/mm, with vibration and noise reduction ≥15dB; the static stiffness of pads for ordinary-speed ballasted tracks should be 30-50kN/mm, with stiffness deviation ≤±10%. 20 pads are sampled from each batch for testing, and the qualification rate must reach 100%. If unqualified products appear, the entire batch is re-inspected.