Stress analysis of low speed sugar mill gearing

A Common cause of concern in low speed, sugar mill gearing is the development of cracks in the root region of the gear teeth. Fracture analysis teChniques can provide an estimate of crack growth rates and thus the remaining life of the gear in some cases. However, low speed mill drive gearing often develops root cracks on the 'compressive' side of the gear teeth. Fracture analysis techniques are not suited to the analysis of such cracks since the theory does not allow for crack propagation under the nominally compressive stress state which exists in the region of the crack. Residual stresses from manufacture have sometimes been put forward as a possible cause of root cracking on the 'compression' side of gear teeth. This explanation does not seem entirely satisfactory. One would generally expect the superposition of a tensile operating stress on the tensile residual stress to be the more damaging combination. This paper presents the results of a finite element stress analysis of a cracked, low speed mill drive gear at Millaquin Mill. The two-dimensional stress analysis is simplistic in that no attempt is made to model the presence of cracks in the material. However, the results suggest that, for certain gear rim geometries, crack initiation and growth are possible in the apparently compressive stress region at the root of gear teeth.