Track brake

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Magnetic track brakes (Mg brakes) are a braking system for rail vehicles that act directly on the rail. They consist of brake magnets with pole shoes, a suspension, a brake frame, track rods on mainlines, and an air-powered actuator. When current flows in the magnet coil, the magnet is pulled to the rail and presses the pole shoes against it. The friction between the shoes and the rail slows the train. Because they press on the rail instead of relying on wheel-rail contact, their braking force is less affected by wet or dirty rails.

They are used in addition to the vehicle’s main wheel brakes and serve as safety or emergency brakes. They work at full strength when activated and are designed to be independent of wheel-rail friction. They can operate at speeds up to 280 km/h (170 mph). With special friction materials, they can reach up to 350 km/h (220 mph). They can also improve the adhesion of the following wheels during braking, helping the wheel brakes work better.

There are two main magnet designs: rigid magnets (a single steel core) and articulated magnets (split cores that can move to follow rail unevenness). Track rods keep the magnets aligned and the brake frame parallel to the rail.

Key parts include the brake magnets, pole shoes, suspension, and the actuating cylinders that lower and raise the brake frame. The brake frame is lowered by compressed air when braking and lifted by springs when released. The system stays ready even if the main brake pipe fails because of an independent power supply from the vehicle’s batteries.

Pole shoes can be steel, sintered, or cast iron, with different braking performance and wear. Steel is common; sintered offers higher braking but wears faster; cast iron is used in some mainlines.

Magnetic track brakes are common on many rail vehicles. High-speed trains usually use eddy current brakes instead. In some networks, magnetic track brakes are limited due to signaling concerns. Streetcars often use rigid magnets; mainlines use articulated magnets.