BS ISO 6336-3:2019

What is ISO 6336-3 - Calculation of tooth bending strength of spur and helical gears about?    

The formulae in the ISO 6336 series are intended to establish a uniformly acceptable method for calculating the load capacity of cylindrical gears with straight or helical involute teeth.  

ISO 6336-3 is the third part of the multi-series that is applicable to the calculation of load capacity of spur and helical gears. It details best practices to minimize fatigue failure and prolong service-life of spur and helical gears. 

ISO 6336-3 specifies the fundamental formulae for use in tooth bending stress calculations for involute external or internal spur and helical gears with a rim thickness sR > 0,5 ht for external gears and sR > 1,75 mn for internal gears. In service, internal gears can experience failure modes other than tooth bending fatigue, i.e. fractures starting at the root diameter and progressing radially outward. 

Note: ISO 6336-3 does not provide adequate safety against failure modes other than tooth bending fatigue.  

Who is ISO 6336-3 - Calculation of tooth bending strength of spur and helical gears for?   

 ISO 6336-3 on the calculation of load capacity of spur and helical gears are useful for:   

• Manufacturers and suppliers of spur and helical gears  
• Product design engineers  
• Mechanical engineers  
• Industries/applications such as automotive, marine, railway, steel, and power plants  

Why should you use ISO 6336-3 - Calculation of tooth bending strength of spur and helical gears?    

Helical gears are becoming more popular as power transmission gears, not only because they can bear bigger loads due to their reduced dynamic load, but also because their noise and vibration levels are lower in operation than spur gears. The calculation methods provided in ISO 6336-3 constitute empirical means for comparing stresses in gears of different dimensions with experimental results. 

ISO 6336-3 provides the tooth breakage and safety concerns that often bring a transmission's service life to an end. The destruction of all gears in a gearbox can sometimes be caused by the breakage of a single tooth. The transmission path between the input and output shafts can be broken in various cases. As a consequence, according to ISO 6336-3, the safety factor (SF) against tooth breakage should be greater than the safety factor against pitting. 

As a result, ISO 6336-3 aids in the accurate and precise calculations of tooth bending strength that can help you manufacture spur and helical gears as per the need of the end-application to meet its load bearing capacity requirements, for optimal operational efficiency. Enhanced service-life of gears can ultimately help avoid fatigue failure and disruptions to the overall system. 

What’s changed since the last update?   

BS ISO 6336-3:2019 supersedes BS ISO 6336-3:2006, which is withdrawn. BS ISO 6336-3:2019 includes some technical changes with respect to BS ISO 6336-3:2006. These include:   

• Modification of the Yβ factor in Clause 8 "Helix angle factor, Yβ" 
• Modification of the YF factor in 6.2 “Calculation of the form factor, YF: Method B” 
• Integration of 6.2.4 "Tooth root normal chord, sFn, the radius of root fillet, ρF, bending moment arm, hFe, for external gears generated with a shaper cutter" 
• Integration of 6.2.5 "Tooth root normal chord, sFn, the radius of root fillet, ρF, bending moment arm, hFe, for internal gears generated with a shaper cutter" 
• Integration of a new Annex C