Overview
ISO/TS 6336-20:2022 - "Calculation of load capacity of spur and helical gears - Part 20: Calculation of scuffing load capacity - Flash temperature method" is a Technical Specification from ISO that defines methods and formulae to evaluate the risk of scuffing in gear contacts using Blok’s contact (flash) temperature concept. It applies primarily to spur and helical gears and to other machine elements with moving contact zones where the Hertzian contact zone is band-shaped (or approximately so) and operating conditions have sufficiently high Péclet numbers.
This second edition updates and corrects earlier formulae and clarifies treatment of parameters such as thermal contact coefficients, the thermo-elastic factor and load-sharing factors.
Key topics
- Flash temperature concept (Blok): Separation of interfacial temperature into a slowly varying bulk temperature and a rapidly varying flash temperature, which together determine scuffing risk.
- Flash temperature formulae: Methods for computing local temperature rises in band-shaped Hertzian contacts, valid for high Péclet number regimes.
- Coefficient of friction: Procedures and approximations to estimate mean friction during incipient scuffing; multiple calculation methods are presented.
- Thermal and mechanical factors: Thermal contact coefficients, thermo-elastic factors, and reduced modulus considerations that influence heat generation and dissipation.
- Contact mechanics and geometry: Transverse unit load, parameter on the line of action, approach factor and load-sharing factor (X) including treatments for profile modification and buttressing.
- Scuffing criteria and safety: Definition of scuffing temperature, contact exposure time, structural factors and recommended safety ranges for gear testing.
- Annexes: Informative presentations of flash temperature formulae and guidance on optimal profile modification.
Applications and users
ISO/TS 6336-20:2022 is targeted at professionals who must assess or mitigate scuffing risk in gear systems:
- Gear designers and mechanical engineers calculating allowable loads and specifying geometry or profile modifications.
- Tribologists and lubrication engineers evaluating lubricant selection and friction behavior under transient high-temperature conditions.
- Test laboratories and OEMs using standardized methods to compare scuffing resistance and to define acceptance criteria (note: use of a TS as acceptance criteria should be agreed between purchaser and manufacturer).
- Maintenance and reliability teams assessing gear failure modes and root-cause scuffing investigations.
- Researchers developing advanced models of thermomechanical contact behavior.
Related standards
- ISO 6336 series (Parts 1–39) - gear load capacity and tribology methods
- ISO/TS 6336-21 - Integral temperature method for scuffing (complementary approach)
- ISO 6336-1 - Basic principles and general influence factors
- ISO 10825, ISO 1122-1 - related gear terminology and wear/damage guidance
Keywords: ISO/TS 6336-20:2022, scuffing load capacity, flash temperature, Blok, spur gears, helical gears, Hertzian contact, Péclet number, coefficient of friction, load-sharing factor.