Abstract: Pull rods made of alloy steel are used to exert grinding pressure on the rollers in the raw grinding mill. The grinding forces are transmitted vertically by three pull rods placed at 1200 apart directly into the hydraulic cylinder. This paper describes the metallurgical investigation that was carried on a failed pull rod to understand the cause of failure. The fracture surface of the failed pull rod with multiple ratchet marks indicated that the crack was initiated at multiple regions. Higher fatigue zone (55%) with low overload region (45%) indicated that the load was light, but there were high stress concentration zones on the pull rod. Macro-etch test and microstructure analysis indicated the presence of a non-homogeneous structure in the forged pull rod. The presence of unbroken dendrites, blowholes, and exogenous type inclusions was evident from the investigation. To confirm and identify the type of foreign particle, scanning electron microscope with energy dispersive X-ray (SEM-EDX) analysis was performed and concluded the presence of exogenous type of inclusions. The investigation clearly revealed that the crack was initiated due to the presence of non-homogeneous structure in the pull rod and propagated by fatigue mode.

Key words: Fatigue failure, fractography, exogenous inclusions, unbroken dendrites, raw grinding mill.

Cite: Biju Karakkunnummal, "A Case Study of a Pull Rod Failure in ATOX Raw Grinding Mill," International Journal of Materials Science and Engineering, Vol. 3, No. 2, pp. 90-103, June 2015. doi: 10.17706/ijmse.2015.3.2.90-103