Investigation of the Shaft Failure Connected to Extruder
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CASE HISTORY—PEER-REVIEWED
Investigation of the Shaft Failure Connected to Extruder S. S. Pelaseyed . F. Mashayekhi . A. Movahedi-Rad
Submitted: 19 July 2015 / in revised form: 27 September 2015 ASM International 2015
Abstract In this study, the failure analysis of a shaft of a unit, which had been failed during the service, was studied. This shaft was welded to the blades, and their chemical compositions were determined by spectroscopy method. In order to determine the root cause of failure and contribution factors, different investigation methods including visual examination, optical microscopy and scanning electron microscope analysis, and hardness test were carried out. It was concluded that the shaft was failed due to fatigue. The failure was caused by improper welding of blades to the shaft. At the end, in order to prevent or decelerate such failure, some recommended remedies were suggested. Keywords Failure analysis Fatigue Fracture surface Ratchet mark Weld metal HAZ Steel
Introduction Shafts are one of the most important components in power transmission system in different industries. The most common cause of failure of shafts is fatigue. Fatigue is progressive and localized damage of a material, which is subjected to the cyclic loading patterns. In general, the shafts in power plant systems run with a steady torsion combined with cyclic bending stress due to the self-weight S. S. Pelaseyed Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran F. Mashayekhi A. Movahedi-Rad (&) School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran e-mail: [email protected]
bending during rotation or possible misalignment between journal bearings [1]. There are several investigations in the literature, which have reported the failure of shafts in different industries. Pavan et al. [2] studied the root cause analysis of bowl-mill pinion shaft failures. They reported that the shaft had failed due to low stress, high stress concentration torsional fatigue, although fatigue marks were not observed as the fractured surfaces rubbed against each other after failure, and as a result, crack had initiated from the keyway corner. In another work, the failure of the gear shaft connected to extruder was investigated [3]. They deduced that while the extruder was running, the fatigue failure occurred due to the high mean stress. Also, they observed material strength degradation, which could have made the shaft fatigue life shorter. Similarly, Go¨ksenli and Eryu¨rek [5] studied the failure analysis of an elevator drive shaft, which had failed at the keyway of the shaft. Zangeneh et al. [4] also reported the failure of AISI 304L stainless steel shaft. There are some reports in the literature, which have also identified the failure of shafts by performing finite element (FEM) method [5–7]. Researchers also have considered the failure analysis of shafts in vehicles. Farrahi et al. [8] investigated the failure analysis of a c
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