Material Matching and Installation Tolerances for Rail Pads and Pressure Plates
- How to match the materials of under-rail pads and press plates?
Rubber pads with good elasticity should be matched with ductile iron press plates of moderate strength to avoid damage to the pads by too hard press plates; polyethylene pads with strong wear resistance can be matched with ordinary carbon steel press plates to reduce costs; polyurethane pads with high hardness need to use high-strength alloy steel plates to prevent press plate deformation; cold-resistant pads (such as styrene-butadiene rubber) should be matched with press plates with good low-temperature toughness (such as low-temperature tempered steel plates) to avoid brittle fracture of both at low temperatures.
- What are the requirements for the thickness tolerance of under-rail pads?
The thickness tolerance of pads for ordinary railways is ±0.5mm to ensure that the track height deviation is within the allowable range; the thickness tolerance of pads for high-speed railways must be controlled within ±0.2mm to ensure track smoothness and reduce train vibration; the thickness tolerance of pads in turnout areas can be relaxed to ±0.8mm due to the need for height adjustment, but the thickness difference of the same set of pads does not exceed 0.3mm to avoid uneven stress.
- What are the regulations on the installation position tolerance of press plates?
The lateral deviation between the center line of the press plate and the center line of the rail is ≤1mm to prevent the press plate from 偏压 the rail; the distance deviation between the press plate and the edge of the rail base is ±0.5mm to ensure uniform distribution of clamping force; the position deviation between the press plate bolt hole and the sleeper reserved hole is ≤2mm to avoid skew installation of bolts, affecting the tightening torque. Exceeding the tolerance range will cause abnormal stress on the press plate and shorten its service life.
- How does temperature change affect the cooperation between under-rail pads and press plates?
At high temperatures, the expansion of rubber pads may reduce the gap between the press plate and the rail, or even generate additional pressure, so a gap of 0.3-0.5mm should be reserved; at low temperatures, the contraction of the pad will increase the gap, which may cause the rail to loosen, so pad materials with small shrinkage should be selected; if the thermal expansion coefficient of the press plate and the pad differs too much, additional stress will be generated, so the materials of both should be selected with close thermal expansion coefficients.
- How to control the cooperation accuracy of under-rail pads and press plates through installation technology?
Before installation, check the pad thickness and press plate size with special measuring tools, and reject over-tolerance products; use positioning tools to fix the position of pads and press plates to ensure that the installation deviation is within the specified range; tighten bolts in symmetric order step by step, with each step torque increasing by 20%-30%, to avoid pad deformation or press plate offset due to uneven stress; after installation, check the gap with a feeler gauge, and re-adjust or replace parts for over-tolerance parts.