Locking Strength Design of Pressure Plates and Rail Anti-Climbing and Anti-Slip Schemes
What are the core design indicators of the locking strength of pressure plates?
The core design indicators of the locking strength of pressure plates include longitudinal locking force, transverse clamping force and fatigue strength. The longitudinal locking force is a key indicator to resist the longitudinal creep of the rail. The longitudinal locking force of pressure plates for heavy-haul railways should be ≥80kN, and that for high-speed railways should be ≥60kN, ensuring that the rail will not produce longitudinal displacement under the action of train traction and braking force. The transverse clamping force is used to limit the transverse swing of the rail. The transverse clamping force of pressure plates for high-speed and heavy-haul railways should be ≥50kN, and that for ordinary-speed railways should be ≥30kN, preventing the rail from transverse deviation when the train passes through curves. Fatigue strength is an indicator to measure the long-term service performance of pressure plates. It is required that the pressure plate will not fracture under 1×10⁷ cycles of alternating load, and the fatigue strength should be ≥350MPa to meet the needs of long-term line operation. In addition, the locking deformation of the pressure plate is also an important indicator. Under the rated load, the deformation of the locking part should be ≤0.2mm to avoid locking failure caused by excessive deformation. These indicators should be comprehensively determined according to the axle load, traffic volume and operation speed of the line.
What are the high-strength material selection and heat treatment process of pressure plates for heavy-haul railways?
The high-strength material selection for pressure plates of heavy-haul railways prefers 42CrMo alloy structural steel. This material has a tensile strength ≥1080MPa, yield strength ≥930MPa, impact toughness ≥60J/cm², with excellent strength and toughness, and can withstand the huge load of heavy-haul trains. The heat treatment process adopts quenching and tempering treatment (quenching + high-temperature tempering). The quenching temperature is controlled at 850-870℃, and oil cooling is used to transform the internal structure of the steel into martensite, improving hardness and strength; the high-temperature tempering temperature is controlled at 550-580℃ for 2 hours, transforming martensite into tempered sorbite, reducing material brittleness and improving toughness. After tempering, surface induction quenching is carried out with a quenching depth controlled at 3-5mm, and the surface hardness reaches HRC50-55, enhancing the wear resistance and impact resistance of the locking part of the pressure plate, avoiding the decrease of locking force caused by wear of the locking part. In addition, stress relief annealing is carried out after heat treatment at a temperature of 300-350℃ for 1 hour to eliminate the internal stress generated during the heat treatment process and prevent the pressure plate from deformation and cracking.
What are the structural optimization design methods of pressure plates for high-speed railways for anti-creep and anti-slip?
The structural optimization design methods of pressure plates for high-speed railways for anti-creep and anti-slip are to enhance the contact friction between the pressure plate and the rail, sleeper and the locking stability. First, serrated locking teeth with a depth of 1.5mm and a tooth pitch of 3mm are set at the contact part between the pressure plate and the rail. The serrated locking teeth can be embedded into the anti-slip groove at the bottom of the rail, increasing the contact friction and improving the longitudinal locking force. Secondly, optimize the cross-sectional shape of the pressure plate, adopt an "L"-shaped thickened cross-section, and increase the cross-sectional thickness of the locking part from 12mm to 18mm, improving the bending stiffness of the pressure plate and reducing the deformation of the locking part. Anti-slip bosses with a height of 3mm and a spacing of 10mm are set at the contact part between the pressure plate and the sleeper. The anti-slip bosses can increase the contact area between the pressure plate and the sleeper and prevent the pressure plate from slipping itself. In addition, a double-bolt fastening structure is adopted, and the bolt spacing is increased from 80mm to 120mm. The double bolts can disperse the stress on the pressure plate, avoid stress concentration caused by single-bolt fastening, and improve the overall locking strength of the pressure plate. Through these structural optimizations, the longitudinal locking force of the pressure plate for high-speed railways can be increased by more than 20%, effectively preventing rail creep.
What are the transverse constraint strengthening measures of pressure plates for curve sections of urban rail transit?
The transverse constraint strengthening measures of pressure plates for curve sections of urban rail transit are to targetedly improve the transverse clamping force of the pressure plate to resist the transverse thrust of the rail. First, adopt a widened pressure plate design, increase the transverse width of the pressure plate from 60mm to 80mm, increase the contact width between the pressure plate and the rail, disperse the transverse load, and reduce local stress concentration. Limit stops are set on both transverse sides of the pressure plate, which are integrally formed with the pressure plate, with a stop height of 10mm, which can limit the transverse swing amplitude of the rail and control the transverse displacement of the rail within ±1mm. Secondly, select a high-elastic rubber buffer pad installed between the pressure plate and the rail, with a Shore hardness of 50-60 and an elastic modulus of 50-80MPa. The buffer pad can absorb the transverse impact force when the train passes through the curve and enhance the contact friction between the pressure plate and the rail. In addition, adopt a torque monitoring fastening process, control the bolt tightening torque at 250-300N·m with a torque deviation ≤±5N·m, ensure that the transverse clamping force of each pressure plate is uniform, and avoid the failure of some pressure plates caused by uneven torque. For small-radius curve sections (radius ≤300m), the installation spacing of pressure plates needs to be encrypted, shortened from 600mm to 400mm, to further strengthen the transverse constraint effect.
What are the detection methods and acceptance standards for the locking strength of pressure plates?
The detection methods for the locking strength of pressure plates mainly include longitudinal locking force test, transverse clamping force test and fatigue performance test. The longitudinal locking force test uses a tensile testing machine. After assembling the pressure plate and the rail sample, apply longitudinal tensile force, and record the maximum tensile force when the pressure plate fails, which is the longitudinal locking force. The transverse clamping force test uses a compression testing machine, apply transverse load, and record the maximum load when the pressure plate loses its clamping capacity, which is the transverse clamping force. The fatigue performance test uses a high-frequency fatigue testing machine, apply alternating load to the pressure plate (the maximum load is 80% of the rated locking force), cycle load 1×10⁷ times, and observe whether the pressure plate fractures or deforms. The acceptance standards are divided according to the line type. For heavy-haul railway pressure plates, the longitudinal locking force is ≥80kN, the transverse clamping force is ≥50kN, and there is no fracture or deformation after fatigue test; for high-speed railway pressure plates, the longitudinal locking force is ≥60kN, the transverse clamping force is ≥45kN, and the locking deformation is ≤0.2mm; for pressure plates in curve sections of urban rail transit, the transverse clamping force is ≥55kN, and the transverse displacement limit is ≤±1mm. The sampling ratio for inspection is 10 pressure plates per batch. If one is unqualified, double sampling shall be conducted. If the double sampling is still unqualified, the batch of pressure plates shall be judged as unqualified.