ISO 6743-6:2018

Overview

ISO 6743-6:2018 is an international ISO standard that defines the detailed classification of fluids in Family C (gear systems) within Class L (lubricants, industrial oils and related products). It covers classification codes, typical compositions (mineral, semi‑synthetic, synthetic, biodegradable), and notation conventions (e.g., ISO‑L‑CKD 220). The standard applies to industrial gear oils and gear lubricants (enclosed, open, splash or splash/ circulation, and grease applications) and explicitly excludes automotive gear lubricants. It is intended to be read in conjunction with ISO 6743‑99.

Key topics and technical requirements

• Classification system and symbols: Products are grouped using a code beginning with “C” (e.g., CKB, CKD, CKSMP) that identifies application, properties and composition. Viscosity grades can be appended per ISO 3448.
• Composition categories: Distinguishes mineral, semi‑synthetic, synthetic (esters, poly‑glycols, poly α‑olefins), environmentally acceptable fluids and special categories for micro‑pitting protection.
• Performance attributes: Classification addresses requirements such as oxidation stability, corrosion protection (for ferrous and non‑ferrous metals), extreme‑pressure (EP) and anti‑wear properties, anti‑foaming and low‑friction formulations for worm gears.
• Operating conditions and selection parameters: Annex A lists key parameters for lubricant selection:
  • Stabilized oil / ambient temperature bands (e.g., Very low < −34 °C; Normal −16 °C to +70 °C; Very high > +120 °C).
  • Tooth loading definitions (Moderate vs. High load) including a Hertz pressure reference of 500 MPa and sliding velocity criteria (high load may exceed one third of pitch line velocity).
• Compatibility notes: The standard flags miscibility and compatibility issues (e.g., poly‑glycol based oils vs. hydrocarbon oils) and advises consideration of equipment designed for specific oil types.

Practical applications

• Specifying and labeling industrial gear oils for enclosed gearboxes, planetary gears, worm gears, open/hand‑lubricated gears and gear greases.
• Guiding lubricant selection based on temperature, load, speed and environmental requirements (biodegradability, eco‑toxicity).
• Supporting procurement specifications, OEM recommendations, maintenance procedures and lubricant product data sheets.

Who uses this standard

• Lubricant manufacturers and formulators
• Gearbox/OEM designers and engineers
• Maintenance, reliability and lubrication engineers
• Specification writers, purchasers and testing laboratories

Related standards

• ISO 3448 (viscosity classification)
• ISO 6743‑1, ISO 6743‑9, ISO 6743‑99 (other parts of the Class L classification series)

Keywords: ISO 6743-6, gear lubricants classification, industrial gear oils, lubricant classification, gear systems, ISO standard.