Case Study
Fault Diagnosis for GAP
Mill in Aluminium Industry
1. Abstract
Anode used in an aluminium smelter is made up of a precise combination of coke and coal tar. Coke should be of a specific size range to achieve the appropriate
strength in the anode. Ball Mill in a Green Anode Plant (GAP) grinds coke into small particles ranging from 0 to 0.08 mm. This study illustrates methods of identifying defects in gear drive of the ball mill which is single line critical with respect to
production.
2. Introduction
The Ball Mill schematic (Make: McNally Bharat, Model: 37TPH) is shown in Figure 1 installed at a GAP. Sensor nodes enabling fault diagnosis for this machine are
mounted at positions marked in red dots. These sensor nodes communicate to a cloud dashboard and provided comprehensive vibration signal analysis and fault diagnosis.
Figure 1: Ball Mill Construction & Sensor Positions
3. Background
3.1GAP Mill
Construction
The ball mill contains a hollow cylinder (filled with stainless steel or rubber balls) shell
that rotates about its axis for grinding the material to fine form. Ball Mill uses a motor and gearbox to reduce the speed and stable operation to have high reliability and high efficiency over a long period in harsh environments. The final torque from main
gearbox is transferred to a pinion and girth gear drive through a cardan shaft. Hence running this equipment under a fault condition is highly dangerous and could damage any drive component.
3.2Sequence of
Events
Figure 2 shows the sequence of events from fault diagnosis to corrective action.
4. Solution
The plots presented in this section validate the presence of the fault as predicted by the system.
- Figure 4 and Figure 5 show an increase in total acceleration & velocity trends.
- Figure 6 indicates the presence of Pinion/Girth gear defect frequencies & its harmonics predominating in the spectrum.
- Figure 7 shows an improvement in Total Acceleration after correction of root clearance of girth & pinion gear
Advanced Fault Diagnosis in IDAP Platform
A. Increase in total acceleration since 20 November 2021 in GB I/P DE Bearing
Figure 4: Increase in Total Acceleration
B. Pinion DE Bearing High-Velocity Values in all 3 directions from 05 February 2022 to 04 March 2022.
Figure 5: Increase in Velocity Values
C. Shockwave Spectrum – Outer Race defects observed in the spectrum.
Figure 6: Girth & Pinion Gear Mesh Frequencies
D. Decrease in Velocity values at Pinion DE bearing after root clearance adjustment
Figure 7: Trend reduction observed after maintenance
5. Site Inspection and Findings
Girth & pinion gear root clearance was adjusted from 3.8 to 5.5 mm on 04 March 2022 by the maintenance team. The inspection picture is shown in Figure 8
Figure 8: Girth & Pinion Gear
6. Conclusion
Shockwave and total acceleration are critical parameters which can be used to identify
defects between pinion and girth gears like misalignment, improper meshing and
bearing defects. Machine learning algorithms using these parameters were able to
accurately predict gear defects well in advance in the GAP ball mill avoiding an
estimated 48 hours of unplanned production downtime