Overview - ISO 6626-3:2019 (Piston rings, coil-spring-loaded oil control rings made of steel)
ISO 6626-3:2019 defines the essential dimensions and related specification elements for coil-spring-loaded oil control piston rings made of steel. The standard covers piston ring types SOR (R‑shaped groove) and SOV (V‑shaped groove) for reciprocating internal combustion engines and analogous compressors. It applies to steel oil control rings with nominal diameters from 60 mm up to and including 160 mm and is part of the ISO 6626 series addressing piston ring design and interchangeability.
Key technical topics and requirements
The standard concentrates on dimensional and functional parameters that ensure interchangeability, manufacturing consistency, and reliable oil control performance:
- Ring types and designation - formal naming and example designation strings (e.g., SOR-S - 100 × 3 × 0,20 – MC65/NT030 WF CSE PN1,5) to standardize identification.
- Essential dimensions - ring width (h), radial wall thickness (a), land width, land angles (α, β), land spacing (B), and groove depths.
- Slot sizes and arrangements - standard slot widths, lengths and position conventions for oil evacuation and performance.
- Coil springs - accepted coil-spring types (e.g., CSN, CSG, CSE), spring diameter, pitch variants, coil‑spring excursion and recommended gap/fixing positions.
- Surface treatments and coatings - nitrided case depth for peripheral surface and sideface, and PVD coating thickness classes.
- Contact pressure and tangential force - nominal contact pressure classes, actual tangential force Ft, normalized tangential force FN, and tolerances for Ft to govern sealing and friction behavior.
- Tables and dimensional data - comprehensive tables for recommended nominal tangential forces, dimensional tolerances and calculation criteria for both SOR and SOV ring families.
Practical applications and who uses this standard
ISO 6626-3:2019 is used wherever consistent, interchangeable steel oil control rings are required:
- Engine designers and powertrain engineers specifying piston ring geometry for internal combustion engines.
- Piston ring manufacturers and precision component suppliers implementing production tolerances, surface treatments, and spring assemblies.
- Automotive and industrial OEMs selecting standard ring types for engines and compressors.
- Quality, testing and procurement teams verifying compliance with dimensional tables, contact pressure classes and coating/nitriding requirements.
- Maintenance and aftermarket specialists seeking compatible replacement rings for engines within the 60–160 mm bore range.
Related standards
ISO 6626-3 is part of the broader ISO 6626 series and complements other piston ring standards (ISO 6621, ISO 6622, ISO 6623, ISO 6624, ISO 6625, ISO 6627) that cover materials, dimensions and performance of piston rings and rings for different applications.
Keywords: ISO 6626-3:2019, piston rings, coil-spring-loaded oil control rings, steel oil control ring, SOR, SOV, ring dimensions, tangential force, nitrided surface, PVD coating, reciprocating internal combustion engines.