ISO 14635-3:2023

Overview

ISO 14635-3:2023 specifies the FZG test method A/2,8/50 for evaluating the relative scuffing load-carrying capacity and wear characteristics of semi‑fluid (NLGI 0 to 000) gear greases. Based on an FZG four‑square test machine, the method defines a stepped load procedure, inspection criteria for scuffing damage, weight‑loss measurement and temperature control to provide comparative performance data for greases used in highly stressed, enclosed gear drives. The method is technically equivalent to DIN Fachbericht 74.

Keywords: ISO 14635-3, FZG test method, scuffing load-carrying capacity, semifluid gear greases, NLGI 0, gear lubricant testing.

Key topics and requirements

• Test rig and gear set: Uses an FZG four‑square machine with Type A test gears (module 4.5 mm, 16‑tooth pinion; circumferential pitch‑line velocity 2.8 m/s).
• Lubricant class: Intended for semi‑fluid greases that provide sufficient flow in the FZG test gearbox (typically NLGI 0–000).
• Test conditions: Condition A/2,8/50 - A = gear tooth form, 2.8 m/s pitch‑line speed, 50 °C initial lubricant temperature (from load stage 4 onward, controlled at 50 ± 3 °C).
• Procedure: Dip lubrication, stepped loading (load stages as defined in the standard), fixed number of revolutions per stage, inspection of pinion tooth flanks after each stage.
• Failure criterion: Scuffing failure is reached when total scuff width on active pinion flanks exceeds one gear tooth width (20 mm). Continuous wear alone is not a failure criterion.
• Measurements and reportables: Pre‑ and post‑test gear weights to 0.001 g, photographic/visual inspection of damage, reporting of failure load stage and specific weight loss. Cleaning fluid conforming to ASTM D235 is specified.
• Precision guidance: While r/R for this specific method are not established, ISO 14635‑1 experience suggests repeatability r ≈ 1 load stage and reproducibility R ≈ 2 load stages for comparable tests.

Practical applications

• Comparative screening of semi‑fluid gear grease formulations for scuffing resistance and wear performance.
• Specifying or validating lubricants for enclosed industrial and heavy‑duty gear drives where semi‑fluid greases are used.
• Quality control and batch acceptance testing in lubricant manufacturing.
• Design input for gear engineers and OEMs to include lubricant characteristic values in gear load‑carrying capacity calculations.
• Tribology labs and third‑party test houses performing standardized gear lubricant evaluations.

Who should use this standard

• Lubricant formulators and R&D teams
• Gear and transmission designers (OEMs)
• Independent test laboratories and certification bodies
• Maintenance and reliability engineers specifying gear greases for enclosed drives
• Tribologists and materials test specialists

Related standards

• ISO 14635‑1 (FZG test method A/8,3/90 for oils)
• ISO 14635‑2 (FZG step load test for high‑EP oils)
• ISO 1328‑1, ISO 21920‑2, ISO 12925‑1, ISO 6743‑6, ISO 18265

Use ISO 14635-3 when you need reproducible, comparative data on the scuffing resistance of semifluid gear greases under defined FZG conditions to support lubricant selection, specification and gear design decisions.