CASE HISTORY—PEER-REVIEWED Failure Analysis of Fan Motor Shafts of a Tunnel Dryer David A. Serje . Enrique E. Niebles . Sheila K. Lascano Submitted: 11 July 2018 / Published online: 1 August 2018 Ó ASM International 2018 Abstract This article details the analysis of two con- ducting shafts operating on blowers of a tunnel dryer. A deductive analysis was applied looking toward a successful recognition of root cause(s), where based on knowledge of background, and failure characteristics, multiple hypothesis are exposed that are further confirmed or rejected accord- ing to different tests, material analysis or maintenance history. In both shafts, failure arises from inadequate repairing. In order to confirm this, the failure analysis methodology included the following steps: technical review, visual inspection, fractography, penetrating inks, metallography, optic microscopy and stress analysis. Evi- dence obtained through these techniques indicates a fatigue failure induced by inadequate repairing procedures; there- fore, main recommendation is to take the necessary precautions in order to guarantee minimal alterations on shaft geometry or material microstructure. Keywords Shaft fatigue Á Fracture Á Stress concentrators Á Weld Á Inclusions Introduction Tunnel dryers are a direct continuous type of dryers used in several process lines as in pharmaceutical, food, chemical industry, etc. Materials to be dried like wet solids, granules or powder are sent to the air-heated tunnel for drying purpose, entering at one end, so the dried material is col- lected at the other end of the tunnel. Fans are used to circulate the air and allow a proper drying curve of working material [1]. In a gelatin-processing plant located in Barranquilla, Colombia (South America), wet gelatin is dried in a tunnel dryer with six zones fed with low humidity and high quality filtered air through fans located in each zone. Each fan shaft is powered through a belt reduction drive from a driving motor with a continuous output of 40 HP at 1750 RPM (Fig. 1). Motors are operating 24 h/day con- tinuously in a room with 35 °C and RH [ 70%. Two motor shafts failed. Three months before failure, shaft #1 had been repaired/reconditioned through circular patch welding with SMAW technique [2] (Fig. 2) followed by machining to achieve required tolerances for proper fitting with ball bearings (Fig. 3). Shaft #2, installed on another motor, was repaired 2 months before failure with the same procedure and for the same issue (lost fit tolerance). Figure 3 gives schematic details of the fractures location and shaft dimensions. Most shafts are subjected to fluctuating bending and torsion stresses with a common failure mechanism asso- ciated with material fatigue [3–5]. Fatigue failures begin at critical points where metallurgical, structural defects, machining marks and/or stress concentrators are present. Shoulders, grooves, holes, keyways, threads and other features result in a modification of the simple stress D. A. Serje (&) Deparment of Mechanical Engineering, Universidad del Norte, Barranquilla, Colombia e-mail: serjed@uninorte.edu.co; dserje@ingenieros.com E. E. Niebles Industrial Engineering Program, Universidad Auto ´noma del Caribe, Barranquilla, Colombia S. K. Lascano Deparment of Mechanical Engineering, Universidad Te ´cnica Federico Santa Marı ´a, Valparaiso, Chile 123 J Fail. Anal. and Preven. (2018) 18:1053–1061 https://doi.org/10.1007/s11668-018-0523-4