At approximately 0840 hours on Thursday, 1 August 2013, it was reported that hoist crane No ‘2’ had fallen after hoisting a set of screws. Further inspection conducted on the hoist crane revealed that one of the planetary wheel gears inside the gearbox had fractured. No casualty was reported at that time as the mill was not in production.
The fractured planetary wheel gears were delivered to Approved Forensics Sdn Bhd (AFSB), named afterwards as Sample ‘A’ and ‘B’.
Further metallurgical examination of the samples indicated that the crack had initiated near the circumference of the fracture surface, at the change cross section between Samples ‘A’ and ‘B’. The crack then propagated towards the centre of the samples and finally the samples failed through ductile fracture.
Multiple ratchet marks indicating multiple crack initiation sites were observed on the circumferences of the fracture surface.
Macro examination of Sample ‘B’ under x 10 magnification at the 3 o’clock position showed several crack initiation sites on the circumferences of the fracture surface. Further magnification of x 15 revealed the beach marks near to the crack initiation site.
Based examination of the fractured surface of the planetary gears and the available evidence, the gears fractured due to fatigue failure.
