Root Cause Failure Analysis Report For BAll Mill Gear Box.

Major root causes of the problem

PROBLEM DESCRIPTION

Gearbox PC50-R11-V21-11,2-Z6 PIV installed at plant and in operation from July 2007 with working hours 35224

1.     In 2008 the backstop was broken and it was replaced with new backstop with our local team and assistance from Cemtec.

2.     In 2009 the backstop broke again and it was replaced with new backstop with our local team and assistance from Cemtec.

3.     On 11^th May 2011 the main motor of ball mill was overloaded because the backstop was blocked and broken the screw support of the auxiliary drive.

4.     In January 2015 the oil filter started to get clogged with small metal particles so we have to replace with new filters.

5.     During January 2015 to February 2016 we clean the filters and replace it monthly.

6.     On 17^th February 2016 first high temperature was noted for intermediate shaft (82 degree) and stopped the ball mill.

ROOT CAUSE SUMMARY:

1.     Mechanical blockage of the back stop happened 3 times which created shock on the teeth and it cracked.

2.     Because of the blockage the friction inside the clutch of backstop increases the temperature of the metallic plate and damage the plates. Due to this the metal particles from the plate enter the gear box through the bearing and circulate with the oil inside the gear box and damage the teeth.

3.     The broken teeth inside the bearing enters the gear and increase the distance of the shaft and damaged the bearing of the intermediate shaft.

4.     Due to this the temperature of the bearing increased more than the normal range.

Solutions chosen

1.     We replaced 4 No. of bearings for input and intermediate shaft and sealing of input shaft with assistance from Cemtec and SKF. 2.     Polished the broken teeth. 3.     Cleaning the interior of gear box. 4.     Change the oil. 5.     Alignment of gear box, motor and pinion shaft. 6.     Mounting the auxiliary drive without back stop.