Gearbox Failure Analysis
Keywords:
Department of Mechanical Engineering, University of Port Harcourt, NigeriaAbstract
An analysis of the failures of gearbox units after about 10,000 service hours
when the design service life of 45,000 hours was expected was performed to establish the
cause of failure. The gear tooth characteristics, namely, beam strength, maximum allowable
dynamic load, allowable static load and limiting tooth wear load were analysed for ability
to cope with the duty load. The failed gear components were examined visually and
metallurgically. Lubrication oil used in the gearboxes was examined for consistency with
manufacturer’s standards. The observed failures were due to design and manufacturing
errors: for instance, the duty load on the gear teeth exceeded the maximum tooth beam
strength, allowable dynamic load and limiting wear load. The out-of-tolerance surface
finish also contributed as it resulted in the misalignment of pinions and gears. To prevent
these failures required adequate sizing of the gear teeth and face width as well as better
choice of materials with higher allowable static stresses to bear the loads imposed. The
surface roughness should be within tolerance.
