The Pivot Point: UIC 802-32 Pins Without Heads

Definition and Scope

UIC Leaflet 802-32 titled “Selective list of pins without heads,” defines the dimensional and material standards for simple cylindrical pins used as pivot points in railway vehicle linkages. Unlike bolts or headed pins (UIC 802-31), these components are purely cylindrical shafts, designed to be secured at both ends using washers and split pins (cotter pins) or retaining rings (circlips).

These pins are ubiquitous in the underframe of rolling stock, particularly within brake rigging (the mechanical linkage that transfers force from the brake cylinder to the brake block) and suspension dampers. The standard ensures that these consumable wear parts are interchangeable across international borders, simplifying maintenance and overhaul operations.

Technical Specifications

UIC 802-32 focuses on ensuring the pin can withstand high shear loads while resisting wear caused by constant rotation and vibration.

1. Dimensional Tolerances

Since these pins often fit into hardened steel bushes (defined in UIC 802-33), the diameter tolerance is critical.

• Fit Class: The pins are typically manufactured to an h11 or h12 ISO tolerance class. This provides a “clearance fit,” allowing the pin to rotate freely without excessive play that could lead to rattling or impact damage.
• Chamfered Ends: The standard mandates chamfered (beveled) ends to facilitate easy insertion into the assembly during maintenance.

2. Material and Hardening

The steel grade is selected to balance toughness (to prevent snapping under shock loads) and surface hardness (to resist abrasion). Common materials include C45 or similar carbon steels, often surface-hardened (induction hardened) to prolong service life in abrasive, dirty track environments.

Comparison: Headed vs. Headless Pins

In railway mechanical design, the choice between a pin with a head (UIC 802-31) and a pin without a head (UIC 802-32) is driven by assembly constraints.

Installation and Safety

The safety of a pin-joint relies entirely on the locking mechanism. UIC 802-32 pins usually feature drilled holes at both ends. During installation, it is mandatory to use new split pins (UIC 802-40) every time. Reusing old split pins can lead to fatigue failure, causing the main pin to vibrate out of the joint—a catastrophic failure mode for brake systems.