ISO/AWI 6336-21

Calculation of load capacity of spur and helical gears — Part 21: Calculation of scuffing load capacity — Integral temperature method

Scope

This document specifies the integral temperature method for calculating the scuffing load capacity (hot scuffing) of oil-lubricated cylindrical spur, helical and double helical gears with involute external or internal teeth. It includes formulae for a quantitative assessment of factors influencing the scuffing load capacity.
The given formulae in this document are valid for cylindrical gears with tooth profiles in accordance with the basic rack standardized in ISO 53. They can also be used for teeth conjugate to other basic racks where the virtual contact ratio of the virtual spur gear is less than εαn = 2,5. For double helical gears it is assumed that the circumferential load is equally distributed on both helices. Else, e.g. for presence of external axial forces, this must be considered in the calculation by treating the two gearings of a double helical gear as two adjacent helical gears.
The methods are validated for:
— normal working pressure angle from 15° to 25°;
— reference helix angle from -30° up to 30°;
— virtual contact ratio of the virtual spur gear from 1,0 to 2,5.
If this scope is exceeded, the calculated results will need to be confirmed by experience.
The formulae are not applicable when any of the following conditions exist:
— gears with transverse contact ratios less than 1,0;
— interference between tooth tips and root fillets;
— teeth are pointed;
— backlash is zero.
The calculation methods are based on results from gear running tests with circumferential velocities of the working pitch circles vw < 80 m/s. If the formulae are applied to higher speed ranges, increasing uncertainty needs to be considered. This uncertainty results from the calculation of the mass temperature which is not uniform across the tooth width, but showing a complex distribution. The experience of gear manufacturers must be taken into account here.
The given formulae are not directly applicable for the assessment of types of gear tooth surface damage such as cold scuffing, plastic deformation, abrasive wear and so on other than that described in Clause 4.
If this scope does not apply, refer to ISO 6336-1:2019, Clause 4.