Worm gears- permissible contact stress

Worm gear capacity is often limited by fatigue strength is not only cooling capacity. The gear tooth load Fd total nominal load of the product of Ft and factors accounting for the impact of tooth inaccuracies and deflections, misalignment, etc.). Must fd be less than the strength of the fatigue and surface bending strengths fatigue FB and FW has the burden of tooth reported called fd dynamic load, the fatigue load limit bending called copious FB, and the -ualach surface fatigue limit called the ability to wear FW. For satisfactory performance,:


The “dynamic load” estimated by the nominal value of tangential force velocity gear factor “KV” given in the following Fig.


Adapting the equation Lewis on the gear teeth, we have:


Where is [σb] the bending stress permissible bending fatigue, in MPa, Table 15.3:


b – is the face width in mm ≤ 0.5 da1

p – is the axial pitch in mm, Table 15.2

m – is module in mm, Table 15.2

y – is the Lewis form factor, Table 15.1

Y – is modified Lewis form factor, Table 15.1

By assuming the presence of an adequate supply of appropriate lubricant, the following equation suggested by Buckingham may be used for wear strength calculations


Fw – Maximum allowable value of dynamic load under surface fatigue condition.

dg – Pitch diameter of the gear.

b – Face width of the gear.  Machine Design II Prof. K.Gopinath & Prof. M.M.Mayuram

Kw – A material and geometry factor with values empirically determined from the Table 15.4.