Synergistic Effect of Rail Pads and Clamping Plates and System Stiffness Matching Technology
Why is the compression set index of under-rail pads a key factor affecting the cooperative work with pressure plates?
The compression set of under-rail pads refers to the permanent deformation that cannot be recovered under long-term load, which directly determines the elevation stability of the rail. If the permanent deformation of the pad is excessive, the rail will sink gradually, causing the contact position between the pressure plate and the rail to shift, and the originally designed clamping force direction will form an angle. This angle will reduce the effective clamping force of the pressure plate, making it unable to fully lock the rail, thereby causing lateral displacement of the rail. At the same time, after the pad sinks, the pre-tightening force of the fastening system will be redistributed, and some bolts may loosen due to overload. Therefore, controlling the compression set of the pad within 3% ensures that the pressure plate is always in the optimal stress position, achieving long-term synergy between the two.
How does the "three-point contact" design of the pressure plate ensure force coordination with the under-rail pad?
The "three-point contact" design of the pressure plate means that the plate stably contacts the sleeper support surface, the rail jaw, and the anti-lift limit point. This design can transmit the clamping force exerted by the pressure plate to the underlying under-rail pad evenly through the rail, avoiding excessive local stress on the pad. Under the action of train lateral force, the three-point contact forms a stable force triangle, limiting the overturning of the rail and thus protecting the pad from shear failure. If the pressure plate is in surface contact or the contact points are unstable, slight oscillation of the rail will cause stress concentration at the pad edges, accelerating pad damage. A pressure plate with three-point contact design ensures more uniform compressive deformation of the pad, giving full play to the elastic buffering effect of the pad and extending the service life of both.
Which material pressure plates are suitable for different types of under-rail pads (rubber, polyurethane, composite)?
Rubber pads have good elasticity and low cost but low hardness, and are usually matched with forged steel pressure plates. Forged steel plates have high strength and rigidity, providing stable clamping force to prevent excessive compression of rubber pads. Polyurethane pads have high hardness and wear resistance, suitable for matching with cast steel pressure plates. Cast steel plates have more complex shapes and can be designed with limit structures matching polyurethane pads, making them suitable for the harsh requirements of high-speed lines. Composite pads (e.g., rubber + nylon interlayer) combine elasticity and rigidity, and are generally matched with light alloy steel pressure plates. These plates are lightweight with moderate clamping force, avoiding damage to the interlayer structure of composite pads due to excessive rigidity. In special areas such as turnouts, high-strength rubber pads are often used with adjustable pressure plates to cope with complex stress conditions. The selection must ensure that the hardness of the pressure plate is higher than that of the pad, forming a "rigid-flexible combination" matching relationship.
How does the thickness selection of under-rail pads affect the overall stiffness matching of the fastening system?
The thickness of under-rail pads is the most direct means to adjust the vertical stiffness of the track. Thickness is inversely proportional to stiffness-thicker pads result in lower vertical stiffness and better elasticity. In ordinary-speed lines, pads with a thickness of 10-12mm are usually selected to obtain greater elasticity, matching the clamping force of ordinary pressure plates. In high-speed railways, to ensure high track smoothness, higher vertical stiffness is required. Therefore, the pad thickness is usually controlled at 6-8mm, combined with high-rigidity special pressure plates. If the pad thickness is too large, even if the clamping force of the pressure plate is sufficient, the overall track stiffness will be insufficient. Large rail sinkage when trains pass will cause fatigue cracking of the pressure plate. Conversely, excessively thin pads will lead to excessive stiffness, increasing wheel-rail impact and accelerating the aging of under-rail pads. Therefore, the pad thickness must be accurately calculated and matched with the stiffness of the pressure plate according to the line design stiffness value.
What different damages will excessive or insufficient pre-tightening force of the pressure plate cause to the under-rail pad?
Excessive pre-tightening force of the pressure plate will put the under-rail pad in an over-compressed state. The rubber molecules or polyurethane material inside the pad will experience severe stress relaxation, causing the pad to lose elasticity in a short time and become a "rigid block". In this case, the pad cannot absorb vibration, and wheel-rail impact force will directly act on the pressure plate and bolts, causing chain damage. Insufficient pre-tightening force means the pressure plate cannot effectively lock the rail, and the rail will slide back and forth on the pad surface when the train is running. This sliding will cause severe wear and scratches on the pad surface, and even lead to curling and falling off of the pad edges. In addition, insufficient pre-tightening force will cause the pad to undergo extrusion deformation under lateral force, damaging the geometric dimensions of the track. Therefore, a torque wrench must be used during construction to control the pre-tightening force within the design range to protect the under-rail pad.