Failure Analysis and Repair of a Broken Extruder Shaft

Abstract

In this paper a failure analysis of a screw shaft used in a co-rotating intermeshing twin-screw extruder was carried out; furthermore a detailed description for the repair procedure of the fractured part was presented. By means of the preliminary analyses of the failed shaft which includes a visual examination, appearance of fracture face, and photographic documentation of the fractured surfaces, and by summarizing and analyzing all relevant data it was possible to determine that the combination of torsion and bending forces was the cause of the failure. The shaft fractured with evidences of fatigue failure. Repairing of the fractured shaft was mainly performed by welding technique followed by suitable heat treatments and appropriate inspection methods. After repair process is completed, the extruder was put back into service, the recorded data during the trial and regular operations were satisfactory and within the design limits. Finally, in order to avoid future accidents and to prevent such problems in similar equipment, precautionary measures and recommendations were proposed.