What is the purpose of UIC Leaflet 800-51 Chapter 8?

Chapter 8 defines the permissible dimensional variations (general tolerances) for welded structures when the technical drawing does not specify a specific tolerance. It ensures a baseline quality standard for railway manufacturing.

Why are tolerances necessary for welded structures?

Welding involves high heat which causes metal to expand and shrink (distortion). Tolerances are necessary to define how much deviation from the perfect design is acceptable without compromising the safety or function of the railway vehicle.

The Default Rule: Permissible Variations in UIC 800-51 Welded Structures

When drawings lack specific limits, UIC Leaflet 800-51 Chapter 8 sets the standard. Learn the permissible geometric variations for welded railway structures.

September 24, 2023 9:58 am

What is UIC Leaflet 800-51?

UIC Leaflet 800-51 serves as a guideline for the specific tolerances required in the construction of welded railway vehicles and components. Welding is a process that naturally introduces heat and distortion into metal. Therefore, achieving “exact” dimensions is physically impossible. Chapter 8 specifically addresses “Permissible variations on dimensions when no tolerances are given.” It acts as the safety net for manufacturing, defining the default acceptable error margins when a technical drawing does not explicitly state a tolerance (e.g., ±1mm).

Understanding Chapter 8: General Tolerances

In railway manufacturing, not every single dimension on a blueprint is assigned a specific tolerance. Chapter 8 provides a standardized table of General Tolerances based on the size of the dimension. This ensures that a 10-meter long wagon body and a 10-centimeter bracket are judged by appropriate standards. It generally aligns with international standards like ISO 13920.

Key Areas Covered

Linear Dimensions: Length, width, and height measurements. The allowable deviation increases as the dimension gets longer.
Angular Dimensions: The permissible deviation in degrees for angles (e.g., weld preparations or frame corners).
Shape and Position: Tolerances for straightness, flatness, and parallelism, which are critical for the stability of rolling stock.

Tolerance Classes: How Precision is Categorized

Chapter 8 typically categorizes tolerances into classes (often A, B, C, or D), ranging from precision engineering to coarse structural work. The longer the nominal dimension, the larger the permissible variation.

Nominal Length Range (mm)	Permissible Variation (Precision Class)	Permissible Variation (Coarse Class)	Impact on Assembly
2 to 30 mm	± 1 mm	± 2 mm	Critical for small fittings and brackets.
120 to 400 mm	± 1 mm	± 3 mm	Affects sub-assemblies and mounts.
1000 to 2000 mm	± 2 mm	± 6 mm	Critical for bogie frames and door openings.
Above 4000 mm	± 4 mm	± 10 mm	Used for main car body structures (shell).

*Note: Values are illustrative of general tolerance principles found in welded structure standards like ISO 13920/UIC 800-51.

Why This Chapter Matters for Safety

If a bogie frame is welded with excessive distortion, it can lead to poor wheel-rail contact or derailment risks. Chapter 8 ensures that even “non-critical” dimensions stay within a controlled range, preventing cumulative errors that could make final assembly impossible or unsafe.

TAGS: ISO 13920, UIC 800, UIC 800-51

COMMENTS

[ Cancel replying ]

This site uses Akismet to reduce spam. Learn how your comment data is processed.

No comments yet, be the first filling the form below.