What Is A Railroad Frog?

railroad frog

A railroad frog is a device that helps the wheels rolling from one track to another. It is also called the “common crossing”. As a part of the railroad switch, it takes the area where two rails cross. Crossing nose and wing rails are main parts of the frog. 

To understand how the railroad frog work, we need to get a whole picture of the railroad switch first. A railroad switch is a collective of devices working together enabling wheels running from one railroad track to another. The working group mainly includes stock rails, switch points, closure rails, frogs, guard rails and other connecting parts. The switch points are the section of the switch that moves. The closure rails connect the switch points to the frog. The guard rails are opposite the frog up next to the stock rails which lead the wheels to run down the right flangeway and avoid train derail.

how railroad frog works

The wheels roll along onto the wing rail and it rides along the wing rail until it catches the point of the Frog. At no point is the wheel support of able to drop into the flangeway into the gap between the two rails, because it is firmly supported on those two rails, so it just rolls along the wing catches on to the Frog point as it is handed off onto the Frog rail and it rolls through. Because of this geometry, it will ensure that the equipment will roll through the frog without any bumping or dropping into the flangeway in the Frog. It’s key that the flangeway is as narrow as possible and the tread of the wheel is as wide as possible to allow that to happen. It allows the wheel to roll down the wing rail span across onto the frog point and then roll on to the frog.  

Types of railroad track frogs

According to the plane form, there are straight-line railroad frog and curved railroad frog. Another way of classification is according to the structure type. Railroad track frog can be either fabricated, made up of two machined rails joined together, or they can be cast as a single unit.

Fixed Frog

  • Combined frog

The combined frog is made of steel rails and other parts which are cut and assembled. It is composed of the crossing nose, wing rail, a spacer iron, a frog pad and other parts. The manufacturing process is simple since there are no special process requirements. However, it has been rarely used because of the heavy maintenance workload.

Combined frog
  • One-piece cast frog

Modern railroad frog is cast from manganese steel which is an advanced alloy that gets harder with use. This is an important property, as the nose of crossing can take high impact loads as train wheels pass through.

One-piece cast frog

Movable point frog (swingnose crossing)

Unlike the fixed railroad frogs, movable point frogs have special movable components such as movable wing rails or movable crossing nose. By changing the position of the movable part in the frog, the working side of the wing rail or the crossing nose can be overlapped to provide a continuous trajectory for the passing train. This can eliminate the gap at the crossing point, which provides the possibility to greatly increase the speed of the trains passing through switches.

Movable point frogs extend the service life of the frog. Long-term operating practices have shown that the service life of the movable point frog is 6-9 times that of the same model of high manganese steel cast frog. What’s more, the maintenance and repair work is reduced by 40%, which greatly reduces the impact of rolling stock when passing through.

Movable point frog

Railroad frog welding

High-manganese steel frogs and high-carbon steel rails are of different welding process requirements. The differences make them difficult to be welded together. Direct welding will have crack defects. The current advanced technology is to choose a material with good welding performance as an intermediate medium to achieve the welding connection.

High-manganese steel is a single-phase austenitic steel. This structure has a high sensitivity to hot cracks and easily induces liquefaction cracks in the heat-affected zone. Therefore, the degree of heating and heating time should be reduced during welding. The steel rail has a high carbon content. To prevent welding cracks during welding, it is necessary to preheat before welding and cool after welding. If weld high manganese steel frogs and high carbon steel rails directly, both the welding process and the selection of welding materials are more difficult. Therefore, the most advanced technology in the world is to choose a material with good welding performance as the intermediate medium to realize the welding connection of the two materials. In the past, only a few countries such as Austria and France mastered this welding technology. Later, scientific researchers from all over the world, including China, after unremitting efforts, used flash butt welding to successfully combine high manganese steel frogs and high carbon steels welded together.

AGICO provides railroad frogs and other track material. Feel free to contact us for more information.

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