Evaluation of a Failed Extrusion Auger Shaft That Fractured in Two Locations

A large, horizontal extrusion auger, used to convey, heat and extrude ingredients to make a type of synthetic polymer, failed in service. The shaft was in operation for approximately 18 years prior to failure. The end-user was interested in extending the life of the auger shaft as much as possible, due to its expense and the lead times involved in its manufacture. Failure of this auger shaft was unique in that it included two fracture locations, both associated with the helical flights. In addition, multiple partial cracks were observed in other specific locations along the shaft. Non-destructive, metallurgical, chemical, and mechanical evaluations were performed to isolate the modes of failure at each fracture site. Beam bending stress calculations were performed to estimate the amount of deflection required to produce the resultant stresses necessary for shaft failure. Scenarios under which this auger failure occurred and opportunities for future design improvements to increase the operating life span are presented.

Keywords: failure analysis, shaft, non-destructive, metallurgical, mechanical, fatigue, testing