UIC Leaflet 520: Draw Gear and Screw Couplings for Rolling Stock

What is UIC Leaflet 520?

UIC Leaflet 520 is the fundamental technical standard titled “Wagons, coaches and vans – Draw gear – Standardisation.” It governs the mechanical assembly used to pull the train, known as the Draw Gear. This system must translate the massive tractive effort of a locomotive into the movement of a long consist of Freight Wagons or passenger coaches.

Because international rail traffic involves mixing vehicles from different owners, the coupling systems must be identical in geometry and strength. UIC 520 ensures this Interoperability by standardizing the Screw Couplers, draw hooks, and the elastic systems (springs) that absorb tension.

Components of the Draw Gear

The leaflet provides the Technical Delivery Conditions for several critical components that maintain the Structural Integrity of the train connection:

• The Draw Hook: The forged steel hook that protrudes from the headstock. It is designed to withstand standardized tensile loads (typically up to 1000 kN or 1500 kN depending on the version).
• Screw Coupler: The manual link consisting of a turnbuckle, links, and a shackle. It allows the shunter to tighten the connection until the Buffers are slightly compressed, creating a rigid consist.
• Draw Spring: A damping element (steel or elastomer) located behind the headstock that absorbs the “jerks” during acceleration to prevent the coupling from snapping.
• The Yoke: The internal frame that transfers the pulling force from the hook to the vehicle’s Underframe.

Safety and Strength Requirements

Safety is paramount in UIC 520, as a coupling failure can lead to a “train parting” incident. The standard dictates:

• Breaking Strength: The screw coupling must have a guaranteed breaking load significantly higher than the maximum tractive force to provide a safety margin (e.g., a 850 kN breaking load for a standard freight coupler).
• Dimensional Accuracy: Precise lengths for the links to ensure they can reach the hook of an adjacent wagon even in sharp curves or when vehicles have different buffer lengths.
• Material Quality: Mandatory use of high-strength forged steel with specific impact toughness to prevent brittle failure in cold climates.

Evolution and EN 15566

In modern European engineering, the technical specifications of UIC 520 have been largely adopted by the European Norm EN 15566 (Railway applications – Braking – Draw gear and screw coupling). While the EN standard is used for new vehicle certification, UIC 520 remains the global reference for the “UIC type” coupling system used across Europe, North Africa, and parts of Asia.

Comparison: Standard vs. Reinforced Draw Gear (UIC 520)