Sliding chair plate
On slide chair are switching devices in railway points transversely mounted . In one end position, the tongues are close to an outer rail (stock rail) and the tip of the tongue is in contact with it without any gaps. The outer foot of the tongue is more (at the tip) or less narrowed (asymmetrical tongue profile). In the other end position there is enough space between the outer rail and the tongue for the wheels to pass through.
The second function of this plate, which is collectively referred to as the sliding chair plate, is the joint fastening of the bearing point (the actual sliding chair) and the nearby outer rail on the sleeper. It also solves the problem that there is no or too little space between the outer rail and tongue for the inner attachment of the outer rail on the threshold. The base of the sliding chair plate extends outwards under the outer rail. The inner foot of the outer rail is attached to it, and the unit consisting of the sliding chair and the outer rail is fastened on the outside and inside on the threshold with the means used for fixed rails.
In contrast to the sliding chair plates, the earlier rail chairs were fasteners for rails that were simply fixed to the sleepers.
Inner fastening of the outer rail
Positive fastening
The inner part of the rail foot engages in a horizontal groove made under the inner end of the sliding surface of the sliding chair (vertical form fit). In this position, the outer rail is prevented from slipping out from the outside (horizontal form fit).
First a so-called stock rail support ( Stü 7 ) was used, which is supported horizontally on the base plate via a thin wedge-shaped clamping plate with which the base plate is attached to the outside of the sleeper.
In 1958, the wedge-tensioned rail support ( type M ) was introduced. The horizontal form fit of the outer rail in the slide chair groove is supported by pressing. A solidly designed bracing element engages between the head and foot of the rail and is secured against longitudinal displacement by means of a grooved pin. It is pressed against the stock rail by a separate wedge clamping plate with its own wedge counter surface attached to the base plate.
Non-positive (springy) fastening
The main disadvantage of form-fitting connections are deformations that occur when there is excessive or alternating stress (vibrations). The consequences are often only loosening, which can be eliminated by retightening the screws involved until the next time. Such designed turnouts are particularly affected because of the increased transverse loads in them. From the 1970s onwards, an elastically yielding (resilient) fastening of the stock rail was used. This type of fastening is called IBAV (Inner Jaw Bracing) and has now become standard. Schwihag AG was the pioneer.
Instead of trying to keep the stock rail from tilting by pressing its foot into the slide chair groove, the groove was abandoned and the inside of the foot is pressed onto the rail via the base plate with an elastically yielding (springy) element (clamping bracket SSB ). This means that the rail can tilt slightly in the event of vibrations caused by the train journey, so that there is no loosening of components or wear on components. Since then, the stock rails have of course also been attached elastically and flexibly on the outside.
The Schwihag Gleistuhlplatte is hollow under the sliding surface to accommodate the clamping bracket and its support points. At Deutsche Bahn AG, the sliding chair plates were further developed, with the tensioning brackets becoming more accessible from the outside.