Device of dilation (railway)

It exsite, on a Railway, particular cases requiring free a Dilation Rails higher than that permitted by the current joints.

the crossing of expansion joints suitable for a Work of art, Bridge or Viaduct, whose permissiveness (free plan left with dilation) is too important.
extremity of a Long rail welded (LRS).

In these cases, one calls upon devices of dilations punctually authorizing a free movement of the sufficient rail without to induce too important cut in the continuity of the rail with respect to the bearing.

Types of devices of dilation

The device with JGP

One calls JGP (Joined to Large Permissive) a joint between two rails allowing a free dilation higher than that of the ordinary joints while preserving a gap (hiatus between the rails) compatible with the circulation of the trains. Only one JGP not being sufficient to absorb the totality of awaited dilation, one distributes the play necessary on a succession of JGP separated by rails moderate length.

In France, the two principal devices with JGP used are the 3x18m and the 2x9m . They consist one of three successive rails of 18m length, the other in two successive rails of 9m length, these rails being connected between them and to the rails framing them by JGP. The least number of joints on the 2x9m is compensated by the least length of dilating rail.

The device of dilation to JGP with the advantage of being easy to implement, not to require of particular material and to be simple to maintain.

It on the other hand presents the disadvantage of being rather long, but especially to introduce in way of the gaps which, if they remain compatible in full safety with a circulation, are sources of shocks important to the passage of the wheels. More than one problem of comfort of the passengers, these shocks generate a wear premature of the various components of the way, rails, fish-plates, cross-pieces and ballast, which thus requires one maintains more frequent.

For these reasons, one holds this device with the free dilation of the LRS is:

with the lines with weak or moderate traffic of which authorized maximum speed is not by very high.
on any way in LRS at the time of operation requiring the cut of the rails for the duration of the work. The zone concerned with work will then be cut up in order to insert joints there transforming it into zone of " bars normales" and framed devices of dilation to JGP.

The apparatus of dilation

In the cases or one cannot use device with JGP, case of a line with strong traffic and/or raised speed, but also crossing of expansion joints of works of art, one will use a apparatus of dilation (AD).

It is about a Trackside equipment made up of two rails (needles) cut in bevel coming to plate itself against two other machined rails (stock-rails) so that there is no discontinuity in the riding surface. The couple switches/stock-rail is maintained in contact by bearings prohibiting any side displacement to them while authorizing a free longitudinal displacement. The cross-pieces on which put back this device are connected between them by metal parts (inter-ties) attaching their displacement.

It exsite a whole range of AD according to the type of the rail of the way and the object of its installation: extremity of LRS or Joint of work.

See too

Railway | Rail | Long rail welded

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