Wear tooth load

Machine Design

Gear Drive

Wear tooth load

Introduction:

The maximum load that gear teeth can carry, without premature wear, depends upon the radii of curvature of the tooth profiles and on the elasticity and surface fatigue limits of the materials.

Calculations:

The maximum or the limiting load for satisfactory wear of gear teeth, is obtained by using the following Buckingham equation, i.e

W_w = D_P.b.Q.K

where

W_w = Maximum or limiting load for wear in newtons,
D_P = Pitch circle diameter of the pinion in mm,
b = Face width of the pinion in mm,
Q = Ratio factor

V.R. = Velocity ratio = TG / TP,
K = Load-stress factor (also known as material combination factor) in N/mm².

The load stress factor depends upon the maximum fatigue limit of compressive stress, the pressure angle and the modulus of elasticity of the materials of the gears. According to Buckingham, the load stress factor is given by the following relation :

where σ_es = Surface endurance limit in MPa or N/mm²,
φ = Pressure angle,
E_P = Young's modulus for the material of the pinion in N/mm², and
E_G = Young's modulus for the material of the gear in N/mm².

Notes :

1. The surface endurance limit for steel may be obtained from the following equation : σ_es = (2.8 × B.H.N. – 70) N/mm²
2. The maximum limiting wear load (W_w) must be greater than the dynamic load (W_D).