ISO 14635-2:2023

Overview

ISO 14635-2:2023 defines the FZG step load test A10/16, 6R/120 for evaluating the relative scuffing load‑carrying capacity of high EP oils. The method uses an FZG four‑square (recirculating power loop) test machine and quantifies lubricant performance by measuring gear surface damage (scuffing) under controlled step loads, speeds and temperatures. This part of the ISO 14635 series is technically equivalent to CEC L‑84‑02 and is aimed at oils used with highly stressed cylindrical gearing (not hypoid bevel gears).

Key topics and technical requirements

• Test condition: A10/16,6R/120 - A10 gear geometry; 16 m/s pitch‑line circumferential velocity; reverse rotation (wheel drives pinion); initial oil temperature ~120 °C (117–123 °C from load stage 4 onward).
• Apparatus: FZG four‑square test rig with a fixed torque loading arm, torsional shafts and dip lubrication mode.
• Load regime: Step load sequence defined in the standard; test proceeds through load stages until failure or completion up to stage 10.
• Failure criteria:
  • Pinion scuffing: failure when the summed scuffed area on the 16 pinion teeth exceeds 100 mm² (an exclusion zone of the top 1 mm of pinion tip is omitted until damage extends below that level).
  • Wheel wear: if wheel mass loss (dedendum) exceeds 20 mg, the test is invalidated.
• Precision: repeatability r = 1 load stage; reproducibility R = 2 load stages (per ISO 5725‑2 evaluation).
• Test materials & preparation: A10 test gears (each pair may be used twice); cleaning fluid per ASTM D235 (petroleum spirit).
• Documentation and support: Annexes provide visual examples of flank damage, a typical test report sheet and a maintenance checklist for the rig.

Applications and users

• Who uses it: lubricant formulators, additive suppliers, automotive drivetrain engineers, gearbox OEMs, independent test laboratories and tribology researchers.
• Practical uses:
  • Rank and compare high EP gear oils for scuffing resistance under conditions representative of automotive driveline and other highly stressed cylindrical gearing.
  • Provide lubricant characteristic values for gear design and load‑carrying capacity calculations.
  • Support product development, quality control and supplier qualification of extreme‑pressure gear lubricants.

Related standards

• ISO 14635‑1 (FZG A/8,3/90 for general scuffing testing)
• Other parts of the ISO 14635 series (gear lubricant test methods)
• ISO 1328‑1, ISO 21920‑2, ISO 18265 (referenced measurement and gear geometry standards)
• CEC L‑84‑02 (technical equivalence)

Keywords: ISO 14635-2, FZG test, step load test A10/16 6R/120, scuffing, high EP oils, gear test, four‑square test machine, scuffing load‑carrying capacity.