Failure analysis of the high-speed shaft of a winch speed reducer
A catastrophic failure was presented in the power transmission system of a skip during the mineral extraction operation in a subterranean mine. In the inspection of the equipment it was found that the high-speed shaft of the winch speed reducer had been the cause of the failure. This problem generated a stop in the production system during several hours.
The analysis of the failure surface showed beach marks with convergence to the internal corner of the keyway, which are high stress concentration zones due to the low fillet radius. The small final region of fracture indicated that the shaft was submitted to low nominal stresses before the failure.
The stress state of the component was determined as well as the static and fatigue safety factors using ANSYS® software. The results showed high stress concentration in the keyway and in one of the changes of diameter; the magnitude of these stress levels did not allow to withstand the fatigue conditions in the shaft neither “infinite life”.
The results allow to conclude that the shaft failed due to the high stress concentration in the internal corner of the keyway, where the failure started, due to its low radius and the inadequate shape of the keyway.
It is recommended to increase the fillet radius of the keyway in this sort of applications, as well as change the geometry of the key for round shape in its ends, therefore this component will not try to indent the shaft and it will be prevented the notch generation in this zones.
Similarly, it is recommended to carry out a performance analysis with simulation tools like ANSYS®, during the purchase or design process, in order to make changes in the component shape without invest in the manufacturing of prototypes. In this way it will avoid loss of money in purchasing of spare parts and loss of profit due to non-scheduled stops.