clips
A diferencia de las sujeciones rígidas, las sujeciones elásticas que utilizan clips continúan manteniendo la posición del carril, aunque ceden momentáneamente bajo el efecto de las cargas del tráfico. Por lo tanto, se oponen al deslizamiento longitudinal instantáneo, y son adecuadas para la instalación de carriles en forma de barras largas soldadas").
Los diferentes tipos de sujeciones elásticas se basan en el uso de una pieza metálica elástica (clip) fijada a la traviesa, que presiona la base del carril contra una almohadilla elastomérica. Durante el paso de la circulación, el resorte acompaña el movimiento del carril, mientras asegura constantemente su acción de retención.
Se instalan con suelas elastoméricas, que se colocan entre la parte superior de la traviesa y la cara inferior del carril. Estas suelas tienen la función de amortiguar parte de las vibraciones y de permitir desplazamientos longitudinales lentos del carril sin dañar las traviesas.
A menudo también se montan cuñas de plástico de alta resistencia, que se utilizan para proporcionar soporte lateral al carril.
Las diferencias entre los distintos cierres elásticos disponibles se relacionan esencialmente con el tipo de resorte utilizado, así como con su método de fijación a las traviesas.
Existe una gran variedad de diferentes tipos comerciales de clips de alta resistencia, utilizados para sujetar los carriles a la placa de asiento subyacente. Entre los más comunes figuran la sujeción Pandrol"), con una particular forma retorcida similar a una letra "e",[39] y la abrazadera Vossloh,[40] con una configuración que recuerda a una letra "M" con los vértices redondeados (ambos dispositivos llevan el nombre de sus empresas fabricantes).
Elastic fasteners fixed with screws or lag bolts
The fasteners are fixed to the sleepers using lag screws, tightened using motorized torque wrenches:.
Indirect installation consists of using an intermediate metal plate, which is fixed to the sleeper using traction screws. The advantage of this method is that it does not wear out the sleeper during disassembly and assembly of the fastening during rail maintenance work.
Precise tightening must be scrupulously observed, adjusting the torque applied when fixing the lag bolts to ensure optimal rail maintenance. To do this, torque wrenches must be used, capable of adjusting the tightening torque. As fasteners tend to loosen gradually due to vibrations caused by rolling stock, it is necessary to check at regular intervals that the fastening pressure is sufficient, and increase it if necessary.
In wooden sleepers, it is always an indirect fixation. The metal part that presses on the rail shoe is held under pressure by a screwed helical spring.
This type of fastening is very widespread.
The function of the spring is ensured by the use of a more or less flat piece of metal fixed to the crossbar, which presses the rail shoe. In this family of fastenings we can mention the "RN" and "Nabla" types, of French design. They have been installed on numerous roads in France, as well as in other countries to which this technology has been exported.
As in the case of tongue clips, a metal piece is used that tightens the rail skate, but in this case it is a spring made with a steel bar with a circular section folded in the shape of an "M", which is fixed to the sleeper by means of a system of lag bolts.
This type of fastening was developed by the Vossloh company, and tends to replace spring fastenings with indirect fixation during track renovations.
Elastic snap fasteners
It is a fastening whose spring, of the same type as that of the "M" fastening, is not fixed by screwing it, but by forcing it to pass through a ring fixed to the crossbar. The elastic deformation to which the spring is subjected ensures both its retention in its installation location and the elastic fixation of the rail (the device for installing the clips weighs 143 kg).
The absence of screws eliminates "de facto" the risk of unscrewing. Therefore, it is no longer necessary to periodically check the pressure of the clips, and therefore it is possible to "set them and [forget them]". (Set and forget, manufacturer's motto). This is a point of view or a sales argument, because this type of binding tends over time to come off your chair, which is as problematic as loosening it. Furthermore, during interventions that require the removal of the clips, their replacement requires that the sleeper be at the same level as the rail flange, which in the case of tracks in poor condition is not always easy, and may require additional operations to be carried out. Unlike a more traditional fastening with traction lag screws (Nabla or others), in which simply tightening the traction screw allows the sleeper to be raised.
This type of fastening was developed by the British manufacturer Pandrol. It is very widespread in the United Kingdom, but also, due to its great ease of use and lack of maintenance (questionable point of view), in a large number of networks that do not have reasons of a protectionist nature to favor other types of fastenings. In France, Fastclip fastenings are used on new tracks (mainly high speed), as well as during certain track and ballast renewal operations of a certain length. The Pandrol quick clip mounts at right angles to the rail. Due to its captive configuration, it must be installed at the time of manufacturing the concrete sleeper, to be later adjusted to the rail flange on site.