ISO 12925-3:2021

Overview

ISO 12925-3:2021 specifies classification and minimum requirements for greases used in enclosed and open gear systems. It covers mineral- and synthetic-base greases assigned to categories CKG (enclosed gear systems) and CKL (open/semi-enclosed gear systems) per ISO 6743-6. The standard defines grease consistencies, typical compositions, environmental options, sampling and the suite of referenced test methods used to verify product characteristics. It does not cover extreme temperature or extreme-load cases - for those, suppliers and purchasers should agree on additional tests and acceptance criteria.

Key topics and technical requirements

• Scope and classification
  • Greases for gears are NLGI-consistency greases typically in the 000 to 1 range overall; CKL greases are often NLGI 0–1 (occasionally 2).
  • ISO-L symbols are completed by NLGI grade and by subcodes for composition/functional properties (examples: CKGB, CKGD, CKGPG, CKGPR; environmentally acceptable: CGTG, CGES).
• Typical base oils and thickeners
  • Base stocks: mineral oils and synthetic oils (poly-α-olefins, poly-glycols, esters, triglyceride derivatives mentioned).
  • Thickeners: commonly lithium or lithium/calcium soaps.
  • Additives: antioxidants, corrosion inhibitors, friction modifiers, extreme-pressure agents; CKL greases may include solid lubricants (e.g., graphite, MoS2).
• Viscosity guidance
  • Enclosed gear greases often use base oils in roughly ISO VG 150–460; open gear greases commonly use ISO VG 680–3200 (ranges cited as typical).
• Environmental and ecotoxicity aspects
  • Includes provisions for biodegradable / low-eco-toxicity greases and references biodegradability and aquatic-toxicity tests.
• Sampling and test methods
  • Sampling per ISO 23572. Normative test methods referenced include cone penetration (ISO 2137), dropping point (ISO 2176), kinematic viscosity (ISO 3104), copper strip corrosion (ISO 2160), water content (ISO 3733), FZG scuffing (ISO 14635-3), biodegradability (ISO 9439/14593) and aquatic toxicity tests (ISO 6341, ISO 14669).

Practical applications and users

• Intended for:
  • Lubricant manufacturers formulating gear greases
  • OEMs and gearbox designers specifying lubrication requirements
  • Maintenance and reliability engineers selecting greases for enclosed splash-lubricated gears or exposed open-gears
  • Procurement and QA specialists verifying supplier conformity
  • Environmental compliance teams evaluating biodegradable or low-toxicity options
• Typical applications: industrial gearboxes in mining, steel, cement, machine tools, conveyors and other heavy rotating equipment where splash or tooth-surface greasing is used.

Related standards

• ISO 6743-6 (gear lubricant classification), ISO 6743-99 (NLGI consistency), ISO 23572 (sampling) and the many test method standards referenced in ISO 12925-3:2021 are essential cross-references. For exceptional service conditions consult suppliers and agree on additional testing beyond this standard.

For specification limits, acceptance criteria and full test details, consult the full ISO 12925-3:2021 document.