Fastenings
While the larger components like ballast, sleepers, and rails often steal the spotlight, fastenings play a crucial role in maintaining a properly functioning modern railway track system. In fact, when it comes to maintenance, issues with fastenings can be the root cause of track problems. Let's delve deeper into the world of railway fastenings and understand their significance.
The Importance of Fastenings
Fastenings are the connections that secure the rail to the baseplate or sleeper, providing essential support and stability to the track. They serve multiple functions, including:
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Connecting the rail to the baseplate/sleeper, ensuring a secure attachment.
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Providing vertical support during the load and unload cycle of passing trains.
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Offering lateral support to maintain proper gauge and resist horizontal forces from train movement or thermal effects.
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Resisting longitudinal movement caused by train braking/acceleration or temperature changes.
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Ensuring electrical insulation to avoid interference with track circuit signaling systems.
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Types of Fastening
Spike Type Fastenings: Spike type fastenings, including rail spikes, elasticated spikes, and Macbeth spikes, are driven directly into the sleepers next to the rail. While simple and cost-effective, these fastenings are prone to vibration and the non-uniform distribution of toe load on the rail foot. As a result, they are not suitable for use in stressed track conditions and can be prone to failure.
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Bolted or Threaded Fastenings: Bolted or threaded fastenings were introduced with the use of concrete sleepers. They involve a plate or fixing element that is bolted to a cast-in threaded bar with a nut and washer. By tightening the nut, a consistent toe load can be achieved, improving uniformity compared to spike type fastenings. However, these fastenings can be vulnerable to nut loosening over time, leading to a loss of toe load.
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Spring Type Fastenings: Spring type fastenings represent an evolution from bolted fastenings. These clips use holes or slots in the baseplate to restrain one end while the other end sits on the rail foot. When inserted with the rail in place, the clip exerts a designed level of force onto the rail, providing consistent toe load. This type of fastening is particularly well-suited for casting the housing directly into concrete sleepers, eliminating the need for additional holes and ensuring water-tightness. Spring fastenings are single-component designs, reducing cost and simplifying maintenance, and offering consistent performance, making them ideal for stressed track conditions.