A railway elastic clip is a spring steel fastener used to secure railway rails to the underlying sleeper. Clips of this type are used in fastening systems that require minimal maintenance and are known for their strong toe load, which prevents relative movement between the rail and the sleeper. They are commonly used with concrete sleepers and can be fixed with ancillary fittings and a base plate. This article focuses on clips manufactured from 38Si7 spring steel.
Material Properties of 38Si7 Spring Steel
38Si7 is a silicon alloy spring steel with a carbon content of 0.35 to 0.42 percent, silicon of 1.50 to 1.80 percent and manganese of 0.50 to 0.80 percent, with phosphorus and sulfur limited to 0.03 percent. The high silicon content provides a high elastic limit and good fatigue resistance, while the moderate carbon content gives good formability and heat treatment response. After hardening and tempering, 38Si7 steel achieves the hardness and toughness required for rail clips working under alternating repeated stress. The steel grade follows reference standards such as DIN 17221, BS 970 and GB/T 1222.
Hardness and Fatigue Performance
38Si7 railway elastic clips are heat treated to a hardness of 44 to 48 HRC. At this hardness, the clip provides the required clamping force while retaining sufficient toughness to resist impact and avoid brittle fracture. Under fatigue testing, clips with a diameter below 20 mm withstand 3 million cycles without breaking, and clips of 20 mm diameter withstand 5 million cycles without breaking. The combination of hardness, surface quality and correct installation is essential to achieve the designed fatigue life.
Common Clip Sizes
| Clip class | Wire diameter | Hardness |
|---|---|---|
| Light clip | 13 mm | 44-48 HRC |
| Medium clip | 19 mm | 44-48 HRC |
| Heavy clip | 20 mm | 44-48 HRC |
| Heavy clip | 20 mm | 44-48 HRC |
| Extra heavy clip | 22 mm | 44-48 HRC |
Other elastic clips can be manufactured according to customer drawings, with the same material and hardness range.
How the Clip Works in the Fastening System
The clip is installed on a base plate or shoulder embedded in the concrete sleeper, and its bent toe presses down on the rail foot. The elastic deformation of the clip generates the toe load that holds the rail firmly, while the flexibility of the clip absorbs vertical and lateral forces from passing trains. The fastening system also includes a tie plate, rail insulator, screw spikes or dog spikes, and a rail pad. The tie plate is typically made of Q235 steel or ductile iron, the insulator of PA66 reinforced with glass fiber, and the rail pad of rubber, EVA or other elastic material.
Surface Treatment and Common Misconceptions
Surface treatments include plain oiled finish, oxide black and color painting, according to customer requirements. The plain oiled and oxide black finishes are economical for dry climates, while painting provides additional corrosion protection. For humid and coastal environments, hot-dip galvanizing can be considered, although the process must be controlled to preserve the fatigue performance of the spring steel.
Installation and Maintenance
Install the clip with the correct tool so that the toe presses the rail foot at the designed position, and verify that the insulator and pad are correctly seated. Apply the specified installation force and avoid impact loading. During inspection, check the clips for cracks, rust, loss of toe load and displacement, and replace damaged clips promptly. Check the torque of the screw spikes and replace worn insulators and pads as required.
A common misconception is that a harder clip always performs better. Hardness above the specified range increases the risk of brittle fracture, while hardness below the range reduces the clamping force. Another misconception is that the clip alone provides the full fastening; in fact, the base plate, insulator, pad and spikes all contribute to the system performance. Some also believe that clips never need maintenance; in reality, they work under repeated stress and must be inspected regularly.
Frequently Asked Questions
What is 38Si7 steel? It is a silicon alloy spring steel with 0.35-0.42 percent carbon and 1.50-1.80 percent silicon, providing high elastic limit and fatigue resistance.
What hardness do these clips have? The clips are heat treated to 44-48 HRC.
What is the fatigue life of the clips? Clips below 20 mm diameter withstand 3 million cycles, and 20 mm clips withstand 5 million cycles without breaking.
What are the common clip diameters? Common diameters are 13 mm, 19 mm, 20 mm and 22 mm, with different models for each size.
What components are used with the clip? tie plate, rail insulator, screw spikes or dog spikes, and a rail pad form the complete fastening set.
What standards are referenced for the material? DIN 17221, BS 970 and GB/T 1222 are the reference standards for the spring steel.
