Failure Analysis of a Cylindrical Roller Bearing from a Rolling Mill
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CASE HISTORY—PEER-REVIEWED
Failure Analysis of a Cylindrical Roller Bearing from a Rolling Mill Goutam Mukhopadhyay • S. Bhattacharya
Submitted: 8 January 2011 / in revised form: 7 March 2011 / Published online: 23 March 2011 ASM International 2011
Abstract Premature failure of a cylindrical roller bearing of a gear box input shaft from a hot strip mill has been investigated. The pins of the cylindrical rollers of the bearing broke from the welded joints at their ends on the cage ring. Investigations were carried out on the failed roller pin and the welded joint. The investigation consists of visual observation, chemical analysis, characterization of macro- and microstructures, measurement of hardness profile, fractography, and energy dispersive spectroscopy (EDS). The fracture surface of the roller pins exhibits beach marks. Scanning electron microscopy (SEM) of the fracture surfaces reveals striations suggesting fatigue failure. The measured hardness profile along the welded joint shows very high hardness due to the presence of untempered martensite at the fusion boundary as revealed by the microstructural examination. Analyses of the results infer that the roller pins failed by the initiation of fatigue cracks from the welded joint because of the presence of untempered martensite originated due to improper welding process. Keywords Bearing Hot strip mill Weld joint Microstructure EDS
Introduction In this article, the results of the failure analysis of a cylindrical roller bearing from a hot strip mill have been presented. The hot strip mill produces strips of thickness in G. Mukhopadhyay (&) S. Bhattacharya Metallurgical Laboratories and QA Group, R&D and Scientific Services, Tata Steel Ltd., Jamshedpur 831001, India e-mail: [email protected]
the range of 1.6–12.5 mm. The annual production of the mill is approximately 3.7 million tons. The schematic layout of the process flow of the mill is shown in Fig. 1. There are six finishing stands out of which four stands (F1–F4) are gear box driven, while the other two (F5 and F6) are directly driven. The cylindrical roller bearing of the gear box input shaft at finishing stand F3 failed prematurely within 3 months of service. The gear box assembly and the location of the bearing in the assembly are shown in Fig. 2. The bearing has a maximum dynamic load carrying capacity of 3910 kN.
Investigation Methods and Results Visual Observation The general view of the various parts of the failed bearing is shown in Fig. 3. The outer race, inner race, and cylindrical rollers are shown in Fig. 3a, while the failed roller pins are shown in Fig. 3b. Failure has occurred from the pins at their both ends where they were welded with the circular cage rings. A broken and an unbroken roller–cage assembly are shown in Fig. 3c. The unbroken assembly shows the weld joints on the cage ring at the ends of the roller pins. Figure 3d shows the slots at the inner side of the cage ring of the failed bearing, where the pins were fitted and welded on the cage ring. In general, t
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