Rail Fastenings, Baseplates and Pads
Early railways adopted various forms of cast iron chair which were fixed to the sleepers and in which rails sat, being held in position by hardwood wedges or ?keys'. All railways which used bu which were basically of this type. With the introduction of flat bottomed railstarting in the late 1940's, a new form
The need was to design a resilient connection between rail and sleeper capable of resisting all forces induced by the passage of trains and by temperature and weather variations over a long period of time.
It was soon found that too rigid fixings became loose under vibration and that some degree of elasticity was necessary to resist both creep and buckling. Maintenance of the clip clamping force on the ra load' was soon realised as being of crucial Since the 1940's many FB rail resilient fast manufactured and used throughout the world, with varying degrees of success.
These fastenings can be grouped into three distinctive types as shown below:
•An elastic rail spike. This is driven into pre-drilled holes in sleepers and can be used with or without a steel or cast iron base plate.
•A spring clip bearing on the foot of the rail held down by a nut and bolt element tightened to a predetermined torque. This type of fastening is still used widely in France and Germany.
•A spring clip driven into a hole or slot in
the sleeper or part of a base plate. The act of driving in the clip either twists or bends the clip thus creating a toe load on the rail.
In the UK in recent years most railways, both main line and Metro, as well as some light railways, have adopted the last type when using FB rail. The standard fastening used by British Rail on all new FB track in recent years has been the ?Pandrol' clip. Th section spring steel bar by a process which involves heating the bar, hot pressing into shape and then quenching and annealing. The majority of plain line track on BR is laid on concrete sleepers without baseplates and in this case the anchorage shoulder is cast into the sleeper during manufacture. Where Pandrol rail clips are used in conjunction with base plates the latter are secured to the timber or sleeper by chair screws.
Where DC electrified railways have conductor rails running close to running rails, it is necessary to ensure that rail clips can be placed and maintained without potential damage or dislocation of the conductor rails and insulators. With the Pandrol clip this condition is satisfied as the clip is introduced into the shoulder and driven in a direction parallel to the running rail. Some earlier spring clips were driven at right angles to the rail which certainly would not be possible close to conductor rails.
Fastenings require insulation both from electrical current and from vibration/noise. This is achieved by the introduction of resilient insulating pads at points of contact.