Natural Rubber
Railway rubber pads are typically made of high-quality rubber that is capable of withstanding harsh weather conditions and heavy loads. The most commonly used rubber for railway pads is natural rubber, which is derived from the sap of rubber trees. Natural rubber provides excellent elasticity, high tensile strength and good resistance to abrasion and fatigue, making it suitable for standard rail fastening applications. It performs well under repeated compression and recovers its shape reliably, which maintains the pad stiffness and the rail support over a long service life.
Synthetic Rubbers: SBR and EPDM
Synthetic rubbers such as SBR, which stands for styrene butadiene rubber, and EPDM, which stands for ethylene propylene diene monomer, can also be used in the production of railway rubber pads. These synthetic rubbers provide enhanced resistance to oil, heat and weathering, making them an excellent choice for railway tracks in demanding environments. SBR offers good abrasion resistance and economy, while EPDM provides superior ozone and weather resistance, making it suitable for outdoor tracks exposed to sunlight and temperature extremes.
Other Pad Materials and Key Technical Parameters
Besides rubber, rail pads are also manufactured from HDPE, which is high-density polyethylene, EVA, which is ethylene-vinyl acetate, and polyurethane. These materials effectively meet the stiffness requirements for various application fields, from tram tracks to standard gauge railways and heavy-haul railways. HDPE pads offer high stiffness and low cost, EVA pads provide good elasticity and cushioning, and polyurethane pads deliver high durability and load capacity. The pad material is selected according to the rail section, the axle load and the fastening system design.
| Technical parameter | Unit | Value |
|---|---|---|
| Stiffness | kN | 90-130 |
| Hardness | Shore A | 72-80 |
| Electrical resistance | Ohm | ≥10^6 |
| Tensile strength before aging | MPa | ≥12.5 |
| Elongation before aging | % | ≥250 |
These parameters ensure stable support, sufficient elasticity, electrical insulation and resistance to aging. The electrical resistance of the pad is important for track circuit operation, because it prevents the rail from short-circuiting to the sleeper and the ground.
Functions of the Rail Pad in the Fastening System
The rail pad protects the sleeper top from wear and impact, distributes the wheel load over the sleeper bearing area, and provides the elasticity that keeps the rail in contact with the pad under dynamic loading. It also provides electrical insulation between the rail and the sleeper, which is essential for signaling circuits. In an elastic rail fastening system, the pad works together with the elastic clips, screw spikes, plastic dowels, guide plates and other components to provide a complete and reliable fastening.
How to Select the Right Rail Pad
Select the pad material and stiffness according to the rail section, the axle load, the fastening system type and the environmental conditions. For heavy-haul lines, use pads with higher stiffness and durability. For tram and light rail systems, use softer pads to reduce noise and vibration. For coastal and chemically aggressive environments, use EPDM pads for their superior weather and oil resistance. Verify the pad dimensions and the stiffness requirement with the fastening system supplier to ensure compatibility.
Inspection and Replacement
During track inspection, check the rail pads for wear, cracking, hardening and loss of thickness. A worn pad loses its elasticity and increases the impact on the sleeper, which can damage the track structure. Replace worn pads promptly and verify that the new pad matches the specified stiffness and dimensions. Keep spare pads for the most common fastening systems on the line.
Frequently Asked Questions
What is a railway rubber pad made of? It is typically made of natural rubber, or synthetic rubbers such as SBR and EPDM, with HDPE, EVA and polyurethane as alternatives.
Why is natural rubber commonly used? Natural rubber provides excellent elasticity, high tensile strength and good resistance to abrasion and fatigue at an economical cost.
What is the advantage of EPDM pads? EPDM provides superior resistance to ozone, weathering, oil and heat, making it suitable for demanding outdoor environments.
What are the typical parameters of a rubber pad? Typical stiffness is 90-130 kN, Shore A hardness 72-80, electrical resistance at least 10^6 ohm, and tensile strength at least 12.5 MPa.
Why must the pad provide electrical insulation? Electrical insulation is required for track circuit operation, preventing the rail from short-circuiting to the sleeper and the ground.
When should a rail pad be replaced? pad should be replaced when it shows wear, cracking, hardening or loss of thickness that reduces its elasticity and support.
