ISO 6627:2022

Overview

ISO 6627:2022 - Internal combustion engines - Piston rings - Expander/rail oil-control rings specifies the essential dimensional features for expander/rail oil-control rings used in reciprocating internal combustion engines (road vehicles and other applications) and analogous compressors. It covers nominal assembly diameters from 40 mm to 140 mm and defines common geometries, surface treatments and designation conventions without prescribing every product detail (manufacturer–client interaction determines final designs). This is the third edition (2022), updating the 2011 edition with new rail types (barrel-faced), PVD rail specifications, revised figures/tables and expanded bore range.

Key topics and technical requirements

• Ring types and designations: Defines expander/rail types (ES1, ES2, ES3) and standardised naming examples to communicate diameter, axial width, material and surface treatments.
• Dimensional essentials: Specifies nominal assembly diameter (d), axial widths (h), gaps, tab angles and other essential features required for interchangeability and specification.
• Materials and surface finishes:
  • Chromium-plated rails with thickness codes (e.g., CR1 = min. 0.05 mm).
  • Nitrided rails with case-depth codes (NS010–NS050) specifying minimum depths for peripheral and inside surfaces.
  • Nitrided expanders with NX codes (e.g., NX003 = 0.003 mm, NX010 = 0.010 mm, up to NX025).
  • PVD-coated rails with coating thickness codes (PC001…PC010).
• Tab angle and assembly: Standard tab-angle codes (TT00…TT30) and assembly guidance (e.g., gap angle recommendations) to ensure proper sealing and fit in piston grooves.
• Performance parameters: Definitions and classes for tangential force (F) and nominal unit pressure (p) including pressure classes (PNL/PNM/PNH/PNR/PNV) that relate ring contact characteristics to engine requirements.
• Common features and tolerances: General design considerations (expander deflection, groove depth, pad sizing) and references to related ISO parts for vocabulary and material specs.

Practical applications and users

ISO 6627 is primarily for:

• Piston-ring manufacturers specifying expander/rail dimensions, coatings, nitriding depths and designation formats.
• Engine designers and OEMs selecting oil-control rings for passenger vehicles, commercial vehicles and other reciprocating engines.
• Compressor manufacturers using piston rings under analogous operating conditions.
• Quality and procurement teams drafting technical specifications, supplier requirements and inspection criteria.

Using ISO 6627 helps ensure compatibility, improve interchangeability, and reduce development friction between suppliers and customers when selecting oil-control ring assemblies.

Related standards

• ISO 6621-1 (Vocabulary)
• ISO 6621-3 (Material specifications)
• ISO 6621-2 and ISO 6621-4 (assembly and tolerances referenced in ISO 6627)
• Other piston-ring series: ISO 6622, ISO 6623, ISO 6624, ISO 6625, ISO 6626

Keywords: ISO 6627, expander/rail oil-control rings, piston rings, oil-control ring standards, chromium-plated rails, nitriding codes, PVD coating, tangential force, nominal unit pressure.