What Is a Rail Clip?
A rail clip, also called an elastic rail clip, is used to fasten the rail tracks together with the railroad spike, rail pad, track bolt and rail joint bar. It is also usually used as a part of the rail fastening system. There is huge demand for rail clips on the railway line, about 7000 pieces per kilometre, which is directly related to rail safety. Each clip must work correctly because a failed clip can lead to gauge widening, rail creep and eventually a derailment risk.
The rail track supports the vehicle and is fixed to the railway sleeper by the rail fastening system. As the core part of the fastening system, the bending and distortion of the rail clip produces a crimping force on the rail track, which ensures a reliable connection between the rail and the sleeper and keeps the integrity of the rail track. Besides, the rigid contact of the vehicle and the rail track causes vibration; the elastic structure of the rail clip can absorb the impact energy during train operation and reduce the shocking. The elastic rail clip works under repeated alternating stress. It bears various effects such as bending, torsion, fatigue and corrosion. When the vehicle passes, it also bears extremely high instantaneous impact load.
Clip Types Around the World
According to the specific situation and habit of each country, different standards of rail clips have been developed for railway construction. In North America and parts of Asia, the elastic clip with a simple omega or E shape is widely spread to the railway networks. In central Europe, the tension clamp type fastening system is very popular, and based on its good performance it has been applied in many countries and regions. In other European networks, clip type fastening systems with threaded inserts or clamped spring elements are adopted, and omega-shaped spring clip fastening systems are popular in several Asian markets. The common point of all these designs is that they apply a defined elastic clamping force to the rail foot, and the differences are mainly in the clip geometry, the base plate design and the installation method.
Spring Blade Clips and Design Lessons
For the spring blade type clip, it is relatively easy to make use of the bending deformability of the material, and the cost is often relatively low. However, due to the openings for the rail bolt, stress concentration is easy to occur in this part, and the maximum bending moment of the surface is exactly the weakest area. The arch elastic clip fastening developed in the early stage of the Chinese railway was found to be easily broken when bolts were tightened, and the vibration generated during train passage made the elastic pieces loose, and even some nuts withdrew from the bolts. Another gauge baffle under vibration was easy to climb to the bottom of the rail, contributing to a widening rail gauge. These historical problems show why modern clip designs avoid sharp stress concentration points and why the fastening set must be maintained as a whole.
How Clips Adapt to Different Track Conditions
With the increase of the axle load of railway vehicles and the improvement of train running speed, as well as the development of urban rail transit and subway, the rail clip, as a key link of the track structure, is constantly developing, and its importance has attracted more and more attention from various countries. Different track conditions need clips with different performance. For example, on the conventional line, the elastic rail clip must meet the needs of heavy load and high-speed lines. However, on the seamless track of a viaduct, in order to reduce the interaction between the rail and the bridge, the fastener resistance is required to be small, and the elastic rail clip is guaranteed to have a low degree of stiffness, so that the fastening does not loosen when the rail foot compresses the underlayer during train passage.
Quality Control, Selection and Maintenance of Rail Clips
Quality control starts with the raw material. For the inspection and testing of raw materials, the supplier is required to provide the production batch number, chemical composition, mechanical performance and other test indicators. Quality control inspectors take the means of sample sampling and batch testing and provide a raw material certificate for control during the testing process. Corresponding physical and chemical tests are made according to the different requirements of the products; if the result does not meet the requirements, the material is refused, and only materials that meet the standards are received. For semi-finished products and their external suppliers, quality control coordination meetings are organized regularly, and technical support and guidance are provided to ensure that qualified products are delivered before shipment.
Select the clip type according to the fastening system, the rail section and the track conditions, and verify the toe load and fatigue life against the traffic on the line. During installation, check that the clip is seated evenly and that the toe load is within the specified range. During maintenance, inspect the clips for cracks, permanent deformation and corrosion, and retighten or replace any clip that has lost its clamping force.
A common misconception is that a rail clip only holds the rail down. In fact it also absorbs impact energy and controls the longitudinal resistance of the fastening, which affects rail creep and bridge-track interaction. Another misconception is that stiffer clips are always better; on viaducts a low resistance fastening is needed to reduce the interaction between the rail and the bridge. It is also wrongly assumed that a broken clip can be ignored until the next maintenance cycle; because each kilometre of track uses about 7000 clips, the failure of a few clips can quickly affect the safety of the whole section.
Frequently Asked Questions
What does a rail clip do? It clamps the rail to the sleeper, holds the gauge, prevents rail creep and absorbs impact energy during train operation.
How many rail clips are used per kilometre? about 7000 pieces per kilometre are required for a typical railway line.
What forces does a rail clip bear? It works under repeated alternating stress including bending, torsion, fatigue and corrosion, plus high instantaneous impact loads.
Why did early spring blade clips fail? Stress concentration at the bolt openings and vibration loosening caused fractures and gauge widening in early designs.
What clip is used on viaduct seamless track? clip with low longitudinal resistance is used to reduce the interaction between the rail and the bridge.
How is clip quality controlled? Raw materials are verified by batch number, chemical composition and mechanical tests, and batch testing is applied during production.
