Temperature deformation characteristics of pressure plate and track adaptability
- What are the forms of temperature deformation of pressing plates?
Thermal expansion and contraction are the main forms. Steel pressing plates can have a length change of 0.5 - 1.0mm/m in the temperature range of - 30 - 50℃. They may elongate and squeeze the pressing plates in high temperature in summer, and may produce gaps due to contraction in winter. Bending deformation caused by temperature stress: after both ends of the pressing plate are fixed, temperature changes will cause bending in the middle. The radius of curvature decreases with the increase of temperature difference. The bending amount of 6m long pressing plates can reach 1 - 2mm under 50℃ temperature difference, affecting the fit with the rail. Differences in thermal expansion coefficients of different materials: the thermal expansion coefficient of composite pressing plates (such as glass fiber) (2×10⁻⁶/℃) is much smaller than that of steel (12×10⁻⁶/℃). Under the same temperature difference, the deformation is only 1/6 of that of steel pressing plates, suitable for areas with large temperature fluctuations. Temperature changes will also change the hardness of the pressing plate. The hardness of steel pressing plates increases slightly (1 - 2HRC) at low temperatures and decreases slightly at high temperatures, affecting the stability of clamping force.
- What impact does temperature deformation have on the fit between the pressing plate and the rail?
In summer high temperature, the elongation of the pressing plate may increase the clamping force by 5% - 10%, exceeding the bearing range of the rail, leading to plastic deformation of the rail bottom and dents. It is necessary to control the expansion of the pressing plate ≤0.5mm/m. Winter low - temperature contraction will cause a gap (0.1 - 0.3mm) between the pressing plate and the rail, the clamping force will decrease by 10% - 15%, and the rail is easy to loosen. This problem is more obvious in cold areas in the north, and winter inspection must be strengthened. Uneven temperature deformation will cause the pressing plate to tilt, reduce the contact area with the rail by 10% - 15%, concentrate pressure locally, and accelerate rail wear. Due to large temperature gradient, uneven deformation is more common in curve sections. Long - term temperature cycles will cause fatigue deformation of the pressing plate. Repeated expansion and contraction will increase the clamping force attenuation rate by 20% - 30% and shorten the service life. The service life of pressing plates in temperate regions is 5% - 10% shorter than that in tropical regions.
- How to reduce the adverse effects of temperature deformation of pressing plates?
Select materials with low expansion coefficient, such as composite pressing plates with carbon fiber, with a thermal expansion coefficient ≤5×10⁻⁶/℃, reducing deformation by more than 50% compared with steel, suitable for areas with large temperature differences (such as the north). Reserve expansion joints (0.5 - 1mm) between the pressing plate and the sleeper to allow free expansion and contraction of the pressing plate, avoid excessive temperature stress. The expansion joints must be filled with elastic materials (such as silica gel) to prevent debris from entering. Adopt sliding pressing plate design, which can slide ±1mm along the sleeper to adapt to temperature deformation, while maintaining stable clamping force. High - speed railways and passenger dedicated lines often use this structure, and the sliding surface must be lubricated regularly. For long rail sections, reasonably set expansion joints, one every 500m, to allow the overall expansion and contraction of the pressing plate, reduce the accumulation of local deformation. Heavy - haul railways must strengthen the fastening at joints.
- What are the differences in temperature deformation characteristics among pressing plates of different materials?
Steel pressing plates (Q235) have a large thermal expansion coefficient (12×10⁻⁶/℃) and obvious temperature deformation. The length changes 0.96mm/m under ±40℃ temperature difference, requiring more compensation measures, but with high strength, suitable for heavy - haul railways. Cast iron pressing plates have a thermal expansion coefficient close to that of steel (11×10⁻⁶/℃), but are brittle. Temperature deformation is easy to cause cracking. The temperature difference change rate must be controlled ≤5℃/h to avoid rapid cooling and heating, suitable for ordinary railways. Aluminum alloy pressing plates have a high thermal expansion coefficient (23×10⁻⁶/℃), with deformation twice that of steel, only suitable for areas with small temperature fluctuations, and need to increase thickness (30% thicker than steel) to resist deformation. The lightweight advantage is suitable for subways. Composite pressing plates (glass fiber + resin) have the lowest thermal expansion coefficient (2 - 4×10⁻⁶/℃) and small deformation, without complex compensation measures, but with low bearing capacity, suitable for light - load lines and plateau areas with large temperature differences.
- What are the special requirements for pressing plate selection in different climate zones?
In cold temperate zones (- 30 - 20℃), materials with low expansion coefficient must be selected, such as composite pressing plates or treated steel pressing plates (adding nickel), with a thermal expansion coefficient ≤8×10⁻⁶/℃, to reduce gaps caused by winter contraction, and the clamping force retention rate must be ≥85%. In subtropical zones (0 - 40℃) with moderate temperature difference, ordinary steel pressing plates can be used, but expansion joints must be reserved. The clamping force increase in summer high temperature must not exceed 10% to avoid rail damage. In plateau areas (diurnal temperature difference ≥20℃), composite pressing plates must be selected. Their low expansion characteristics can reduce diurnal deformation differences, control clamping force fluctuation within ±5%, and need UV aging resistance, with service life ≥8 years. In tropical zones (20 - 50℃) with long - term high temperature, heat - resistant steel pressing plates (adding chromium) must be selected. The hardness decrease at 50℃ must not exceed 2HRC, and the clamping force attenuation ≤5%/year to ensure long - term stability.