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This paper gives insights on the failure analysis of the non-drive shaft of a conveyor in a coke plant of an integrated steel plant. The failure of the shaft was investigated in order to determine the root cause and contributing factors. Investigation methods included visual examination, optical and scanning electron microscope analyses, chemical analysis of the material, mechanical tests and life calculations based on design. The overall appearance of the fracture surface of the 45C8 grade shaft indicated rotating bending fatigue failure from a step location. Microstructural analysis revealed a crack from the sharp step and no metallurgical abnormalities. Apart from the metallurgical analysis, the design of shaft was also verified by calculating step profile, fillet radius and calculated stress in actual condition. It revealed that a shaft with a minimum diameter of 70 mm, made of 45C8 steel, can withstand the actual stress acting on it. In this design, the shaft diameter was found to be 65 mm which is insufficient to bear the actual stress. Shaft failures can be reduced by preventive mechanical maintenance and using safe design. To enhance the shaft life without an increase in shaft diameter, we recommend that the material be changed to 42CrMo4 grade steel, which, when appropriately heat treated, has higher stress limit, along with a modification in the step profile with a proper fillet radius.

Rolling bearings are machine elements found in a wide field of applications. They are reliable even under the toughest conditions. When bearings fail to meet their expected life, the consequences are increased down time, loss of revenue and missed delivery. Hence, it is important to know the bearing theoretical fatigue life. However, unfortunately, it sometimes happens that a bearing does not attain its calculated rating life. There may be many reasons for this—heavier loading than has been anticipated, inadequate or unsuitable lubrication, careless handling, ineffective sealing, improper mounting and improper clearance. This article describes the failure of a conveyor bearing in rolling contact fatigue. The investigation consists of visual observation, chemical analysis, characterization of microstructures using optical microscopes and hardness test. The study also calculates the bearing fatigue life (L10) under these operating conditions. Surface-initiated rolling contact fatigue, leading to spalling, is a life-limiting failure mode in bearings. Ferrography test, discussed in this paper, indicates fatigue spalling. Analysis suggested that the conveyor bearing failed near its calculated fatigue life and the failure occurred in rolling contact fatigue. Periodic schedule, after calculating L10 life, for changing the bearing and scheduled ferrography checks can eliminate this type of unplanned breakdown.

Disc springs of side arm changer of wagon tippler of an integrated steel plant were failing prematurely. Disc springs are used to absorb shock loads generated while coupling of wagons during the positioning of single/double wagons on tippler platform for unloading raw material. This paper describes techniques used to determine cause for premature failure of springs and relating them to mathematical calculation of expected fatigue life. These techniques include visual examination, fracture characteristics by scanning electron microscopy, metallographic observation, chemical analysis, mechanical testing and other techniques used for investigation. Suggestions given in paper were implemented resulting in an increase in spring life.

In the original version of the article, Prabhash Gokarn’s last name was misspelled. The original version of the article has been corrected.