ISO 6336-2:2019

Overview

ISO 6336-2:2019 - "Calculation of load capacity of spur and helical gears - Part 2: Calculation of surface durability (pitting)" defines the established method for assessing surface load capacity (surface durability / permissible contact stress) of cylindrical gears with involute external or internal teeth. The standard provides the fundamental formulae and derating factors needed to evaluate pitting risk for oil‑lubricated transmissions and for slow‑running grease‑lubricated applications when adequate lubricant is present. Calculations are based on Hertzian contact theory and are applicable to tooth profiles conforming to the basic rack in ISO 53 and to conjugate profiles where the transverse contact ratio εαn < 2.5.

Key topics

• Basis and scope: Use of Hertzian pressure as the working hypothesis for contact stress and pitting assessment. Limits on applicability (lubrication, tooth profile, contact ratio).
• Safety and damage: Definitions of pitting damage and safety factor S for surface durability; note that other surface failures (plastic yielding, scratching, scuffing) are not covered except where referenced.
• Fundamental formulae: Calculation of contact stress and permissible contact stress (σHP), including Method B options and life‑dependent values.
• Influence factors and correction terms:
  • Zone factor (ZH) and contact factors (ZB, ZD)
  • Elasticity factor (ZE) and contact ratio factor (Zε)
  • Helix angle factor (Zβ), life factor (ZNT), size factor (ZX)
  • Lubricant film influence (ZL, ZV, ZR), work hardening factor (ZW)
• Allowable stress numbers and life factor methods (A/B) for different design scenarios.
• Scope constraints and assumptions: Recommendations and cautions for large helix angles and pressure angles; reference to experimental validation and agreement with other methods.

Applications

• Gear designers and mechanical engineers performing gear rating and pitting risk analysis for spur and helical gears.
• Transmission system design (industrial gearboxes, wind turbines, automotive drivetrains) where oil lubrication is used.
• Standards-based validation in procurement, acceptance testing, and reliability evaluation of gear sets.
• Inputs for CAE tools and fatigue life estimation, and for specifying material, surface treatment, and lubrication regimes.

Who should use it

• Gear design engineers, reliability engineers, tribologists, and standards compliance teams.
• Manufacturers specifying gear geometry, material hardness and lubrication requirements.
• Consultants performing fatigue and life assessments or creating calculation software aligned with ISO 6336.

Related standards

• ISO 6336-1:2019 - Basic principles and general influence factors
• ISO 6336-3: Calculation of tooth bending strength
• ISO 6336-20 / -21: Scuffing load capacity methods
• ISO 6336-22: Micropitting load capacity
• ISO 6336-30: Calculation examples

Using ISO 6336-2:2019 helps ensure consistent, validated assessment of gear surface durability (pitting) and supports robust, standards‑based gear design and specification.