A magnetic track brake (Mg brake) is a brake for rail vehicles. It consists of brake magnets, pole shoes, a suspension, a power transmission and, in the case of mainline railroads, a track rod. When current flows through the magnet coil, the magnet is attracted to the rail, which presses the pole shoes against the rail, thereby decelerating the vehicle.
While brakes such as disc brakes or shoe brakes depend on the frictional connection between wheel and rail, the magnetic track brake acts directly on the rail. Therefore, its brake effect is not limited by wheel-rail contact. Thus, environmental factors such as wetness or contamination of the rail have less influence on the brake force.
Usage
Magnetic track brakes are used on rail vehicles in addition to the primary, wheel-effective brake systems. As an additional brake system, they help to ensure that the prescribed brake distances of rail vehicles can be complied with.
Since magnetic track brakes always act unregulated and at their maximum brake force, they are only used as safety and emergency brakes. They can be used at speeds of up to 280 km/h. With the usage of special friction materials they can be used up to speeds of 350 km/h.
Due to their track cleaning effect, magnetic track brakes increase the coefficient of adhesion between the following wheels and the rail during the brake process. This additionally leads to an improvement of the wheel-effective brake systems.
Basically, magnetic track brakes are distincted between rigid and articulated magnets.
History
On April 5, 1900, the patent (AT11554) for the first electromagnetic brake for rail vehicles was registered by the Westinghouse Air Brake Company London. Three years later, the electromagnetic track brake was introduced in Germany by the Westinghouse Company.
The Mg brake was characterized by the fact that the electromagnets were magnetized to different degrees by the exciter coils, which made the brake force dependent on the strength of the brake current. Even the winding numbers of the exciter coils were different in order to be able to regulate the brake force. Thus, the track brake was also equipped with several shoes in order to be able to adapt to possible unevenness of the rails.
In 1905, the first tests were carried out by the Rhine Railway Company. These were track magnets with an attractive force of around 4 kN, which lowered automatically onto the rails when the current was switched on, pressing onto the brake shoes and on the wheels of the cars via a lever rigging. At that time, it had not yet been recognized that track brakes should work independently of the friction between the rail and the wheel.
In 1908, Mr. Jores took over the Westinghouse representation for track brakes in Germany and played a major role in their continuation. After World War I, Jores led the production of his own track brakes after the patent rights had expired. The track brakes were based on drawings taken from Westinghouse. They were manufactured until 1929 without any major changes. The main feature of the track brake at that time were the rail shoes, which were made of a special rolled section.
In 1920, the Magnetic Brake Company, headed by Mr. M. Müller, entered the market with track brakes. Müller attempted to improve the track brake with new designs. For example, he replaced the profiled shoe with a pole shoe made of commercially available flat iron. Until then, track brakes had only been used for streetcars and thus for speeds of up to 40 km/h.
At the beginning of 1930, the German Imperial Railways initiated a high-speed rail project that envisaged speeds of up to 160 km/h and was to be of great significance for the track brake.
In 1931, Jores´ company was bought by Knorr-Bremse AG and the technical director Müller from the Magnetic Brake Company was convinced to join the company. Now, for the first time, the track brake for fast-moving vehicles was developed within the Knorr-Bremse company. In cooperation with the German Imperial Railways, the first tests were carried out with the "Flying Hamburgian". For braking, special brake pads with linings made of synthetic friction materials were used, which acted on brake drums and were attached to the wheel spiders. There was also an electromagnetic track brake available, which however was only to be used as an additional emergency brake.