The Unshakeable Connection: UIC 802-24 Sealing Ring Bolts

Definition and Scope

UIC Leaflet 802-24 titled “Selective List of Sealing Ring Bolts,” defines the technical and dimensional specifications for a specific class of permanent fasteners often referred to in the industry as Lockbolts or Huckbolts. Unlike traditional threaded fasteners that rely on torque and friction to hold a nut in place, these components use a swaged collar to create a permanent, vibration-proof bond.

This standard is crucial for the assembly of rolling stock components that endure constant dynamic loads, such as bogie frames, underframe equipment, and wagon bodies. The primary goal of UIC 802-24 is to standardize these components to ensure interchangeability and consistent mechanical performance across international fleets.

Technical Mechanism: How It Works

The fastening system described in UIC 802-24 operates on a different principle than standard bolts. The installation process involves a hydraulic tool that performs a direct tensioning and swaging operation:

• Pin Placement: The pin (bolt) is inserted into the hole, and a collar is placed over the pintail.
• Tensioning: The tool pulls the pintail, closing the gap between materials and generating a high, pre-determined clamp load.
• Swaging: The tool’s anvil pushes the collar into the locking grooves of the pin, permanently deforming the metal (cold forming) to lock it in place.
• Pintail Break: The excess pintail snaps off at a designed breakneck groove, leaving a clean, flush installation.

Key Advantages in Rail Applications

UIC 802-24 compliant fasteners are preferred over traditional DIN/ISO bolts in critical areas due to specific mechanical properties:

• Vibration Proof: Since there are no threads to “unscrew,” the connection cannot loosen under the intense vibrations of wheel-rail interaction.
• Consistent Clamp Load: The tension is determined by the tool and the design of the breakneck groove, eliminating torque scatter caused by friction variations (oily vs. dry threads).
• Visual Inspection: A quick visual check confirms if the collar is swaged, removing the need for torque wrenches during maintenance inspections.

Comparison: Standard Bolt vs. UIC 802-24 Lockbolt

Understanding when to use a sealing ring bolt versus a standard threaded bolt is vital for structural engineers.

Maintenance and Removal

While UIC 802-24 fasteners are “maintenance-free” in terms of retightening, they pose a challenge during heavy maintenance (overhaul). Removal requires cutting the collar with a specialized cutter or grinding it off. Therefore, they are typically specified for structural components that do not require frequent disassembly.