Rack and pinion turnouts

With normal points, in most cases only the two point blades need to be moved. The larger the deflection radii, the more switch motors are required. Only with special high-speed turnouts is the movable frog added to reduce wear on the frog.

Rack and pinion turnouts, on the other hand, are much more complex in their design than normal turnouts. As the top edge of the rack is above the top edge of the rail, the rail and rack must be moved in the centre section so that the wheel can pass.

This requires a second point motor. Due to the heavy weight of the centre section, high actuating forces are necessary, so it is not advisable to operate rack and pinion points using a linkage and only one motor. The sliding plates must be lubricated once a week and the individual elements must be carefully cleared of snow and ice, especially in winter.

Due to the maximum speed in rack and pinion operation of 35 - 40 km/h, rack and pinion turnouts do not require large branching radii. The largest turnout radii have a radius of 250 m, but the radii are usually much smaller: 100, 80 or even just 60 m. Nevertheless, most rack and pinion turnouts are unique, because together with the track gauge, the rack system, the rack height and the branching angle, this results in a huge range of different models. For this reason, rack and pinion turnouts are never kept in stock and are only made to order.

In contrast to normal turnouts with only slight gradients, the so-called helical twist must be taken into account for gearwheel turnouts. As the turnout itself must not be curved, the inclination of the turnout results in a superelevation in the deflection. This does not yet represent a twisting of the track, as the turnout is level from the start of the turnout to the last continuous sleeper. Only then can the track be twisted, whereby care must be taken to ensure that the maximum permissible twist is not exceeded.

Roll profiles are used within a rack switch and connected to Riggenbach or Strub profiles at the end as appropriate. The Abt system is different: Due to the offset toothed discs, an additional moving element is required to guide the cogwheel onto the correct double disc.

Just like the rails, the rack is subjected to high forces under thermal load. Due to the interruption of the rack in the points, it must be ensured that the rack does not move longitudinally in the points, as this would lead to the tooth pitch no longer being correct on the one hand and the moving elements being blocked on the other. For this reason, the racks must be anchored in the ground at the start of the points and at both ends of the points so that the longitudinal forces can be dissipated.