ISO 4263-4:2006

Overview

ISO 4263-4:2006 - "Petroleum and related products - Determination of the ageing behaviour of inhibited oils and fluids - TOST test - Part 4: Procedure for industrial gear oils" specifies a laboratory method to determine the accelerated ageing behaviour of industrial gear oils (categories CKC, CKD, CKS, CKT as defined in ISO 6743-6). The standard uses controlled exposure to air and elevated temperatures to evaluate oil degradation over a 312 h test period and reports changes in kinematic viscosity, insoluble content (precipitation number) and other indicators of oxidation and additive depletion.

Key topics and technical requirements

• Scope: Gear oils in categories CKC, CKD, CKS and CKT.
• Test principle: Oxidative ageing in glass oxidation cells under air flow and elevated temperature; end-point after 312 h ± 2 h.
• Temperature by oil type:
  • CKC: 95 °C
  • CKD: 121 °C
  • CKS / CKT: 150 °C
• Air flow: 10 L/h ± 0.5 L/h per cell (air dried and oil-free).
• Primary measurements:
  • Kinematic viscosity at 100 °C (ISO 3104) - report increase after ageing.
  • Insoluble content / precipitation number (Annex B) - quantify precipitate after solvent treatment and centrifugation.
  • Visual rating of deposits and adhesivity on the tube walls.
• Optional/augmenting analyses:
  • Acid number increase (ISO 6618 / ISO 6619).
  • Sediment content by filtration (Annex C).
  • Additives content variation (Annex D).
  • Infra‑red oxidation (IR spectrum, measure absorbance at 1 710 cm‑1; Annex E).
• Apparatus & preparation: Borosilicate oxidation cell (300 ml oil), thermostatted heating bath, flowmeters, air dryer, calibrated thermometers, and strict glassware cleaning procedures (warning on chromosulfuric acid disposal and safety).
• Reporting: Results expressed as viscosity increase, precipitation-number change, deposit severity/adhesivity and any additional test outcomes.

Applications and who uses it

• Lubricant manufacturers - R&D and formulation optimisation for oxidation resistance and additive performance.
• Quality control & certification labs - routine batch testing and conformity to purchasers’ specifications.
• OEMs and gear designers - verifying gear oil suitability and expected ageing behaviour for industrial gearboxes.
• Procurement and asset managers - specifying minimum ageing resistance and shelf-life criteria.
• Failure analysis teams - investigating oxidation-related lubricant degradation and deposits.

Keywords: ISO 4263-4:2006, TOST test, industrial gear oils, ageing behaviour, kinematic viscosity, precipitation number, oxidation cell, gear oil testing, accelerated ageing.

Related standards

• ISO 4263 Parts 1–3 (other fluid types)
• ISO 6743-6 (gear oil categories)
• ISO 3104 (kinematic viscosity)
• ISO 3170 (sampling)
• ISO 6618 / ISO 6619 (acid number)
• ISO 3696, ISO 12185 (supporting laboratory methods)

For laboratories and engineers specifying or testing gear oils, ISO 4263-4:2006 provides a reproducible TOST procedure to assess oxidative stability and practical ageing indicators used in product development, quality control and procurement.