This paper presents the results of a systematic investigation undertaken t6 determine the cause of premature failure of a prototype ferritic - pearlitic nodular cast iron wheel of an adaptable motorized worm gear box. The nodular cast iron,conforming to IS grade SG 500/7, had been chosen as a substitute for centrifugally cast phosphor bronze on the basis of its superior mechanical and tribological properties. Based on a comprehensive theoretical and experimental analysis, the root cause ofthe failure was identified to be the absence of stable thick film EHD lubrication in the contact zone. Further, using fault tree analysis, this failure mode was correlated with the more fundamental material and system related conditions.
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