The document describes how ferrography analysis of oil samples from a raw mill grinding roller at a cement plant detected early signs of bearing failure. Particle size and ferrous content in the oil samples increased over several months, indicating abnormal wear developing in the roller bearing. By closely monitoring the trends in ferrography results, the plant was able to schedule maintenance before a breakdown occurred, avoiding production losses and further equipment damage.

1. CASE STUDY
Analytical Ferrography Diagnosed Early Warning of Raw Mill
Grinding Roller Bearing Failure at Ras Plant
Ferrography helps to examine wear rate of the system internals irrespective of
wear particle size along with material composition effectively and provides early
warning of machine failures.
UNIT – III RAW MILL GRINDING ROLLER
Plant : Shree Cement Limited
Location : Ras
Lubricant : BERU - 680
Equipment : RAW MILL GRINDING ROLLER
Roller Installation : June 2015
Running Hours : 7000 hours (approx.)

2. ABSTRACT
This paper contains case study of bearing damage in Raw Mill Grinding Roller at Shree
Cement Ltd., Ras. In a large scale industry oriented, to minimize downtime and improve
production; machine downtime have to be reduce. This case study focuses on one such case,
where the machine failure was identified at an early stage and corresponding measures were
taken to avoid machine failure. The case highlights the symptoms shown when the problem
was identified and the corrective actions taken within time. Also the study focuses on how oil
analysis practice has been useful to reduce the downtime, running cost and improve plant
efficiency. Specifically in the case of grinding rollers in VRM’s, vibration analysis is
practically impossible. Here the only pro-active maintenance that can be carried out is oil
analysis. This case specifies that constant monitoring of equipment as soon as a basic
indication is obtained can be beneficial for plant life. Particularly in this case symptoms were
generated months back and since then changes in the equipment were noticed till the situation
got alarming. Equipment was kept under micro level monitoring since past six months. Finally
criticality of fault was identified within time and proper actions were taken to save the
equipment from other damage.
Case Analysis –
From October 2015, grinding roller rating was marginal due to presence of bearing wear particles.
However the ferrous ppm in oil was within range. This was an indication of abnormal wear
development in roller bearing. Further in January 2016, bearing wear particle size went to 200
micron from 60 microns in Oct. 2015. But the ferrous ppm in oil was in the same range. Due to
increase in wear particle size and wear rate, oil change was recommended.
In February 2016, bearing wear particle of size 300 microns were observed in grinding roller oil
sample. This was an alarming stage and machine condition was declared critical here forth. From
Feb. 2016 onwards, machine was kept under regular monitoring.

3. Problem Diagnosis –
Ferrography helps us to observe & trend generation of wear particles in machines. Specifically for
this case, ferrography did showed increasing trend of bearing wear particles. Figure below shows
the overall trend of severity as observed in ferrography which is seen out to be positive slope
curve.
Fig 1 – Ferrography trend pattern
Bearing wear particle size trend also proved to be a major tool for confirmation of bearing
damage in the grinding roller. In December 2015 bearing wear particle of size up to 60 microns
were observed on ferrogram which gradually kept growing and in April 2016 it went up to 400
micron. Table below shows wear particle size trending for past six months.
Bearing Wear Particle Size
Dec-15 Jan-16 Feb-16 Mar-16 Apr-16 May-16
60 200 300 150 400 400
Table 1 – Bearing particle size trend

4. Bearing wear particle were observed from October 2015 on regular basis. There was a noticeable
rise in the wear particle size in grinding roller oil. Initially starting from 60 microns in December
2015, it gradually kept growing and went up to 400 microns in May 2016. This was a critical
situation and immediate inspection of grinding roller bearing was suggested. Figure below shows
increasing trend of bearing wear particle observed on ferrogram.
Fig 2 – Particle size trending
Also the ferrous ppm trend in the case was an important indication for failure analysis. Ferrous
ppm trend can help us predict pre-mature failure and abnormal wear in equipment. Ferrous ppm
trend of the grinding roller kept on rising with running hours. In March 2016, it went on an
alarming situation. At this stage oil change was suggested to avoid secondary wear due to
presence of excessive wear particles in oil. However in May 2016 along with increase in particle
size, ferrous ppm also went to 2176. At this stage management decided to change the grinding
roller and accordingly a shutdown was planned.
Ferrous PPM Trend
Dec-15 Jan-16 Feb-16 Mar-16 Apr-16 May-16
85 100 134 337 438 2176
Table 2 – Ferrous ppm trend

5. Actions Taken –
Based on criticality of machine as per ferrography and oil analysis report by Condition
Monitoring Cell, it was decided to inspect roller bearings on priority basis. Hence a shutdown was
planned considering the severity of the case and the grinding roller was replaced to avoid
production loss and other damages.
Inspection –
After replacement of the grinding roller, old roller was sent to mechanical workshop for
overhauling. Bearing inspection was carried out. Pitting was observed on bearing inner race and
bearing roller. Bearings were replaced and the entire grinding roller was reassembled. Images
below show bearing inner race and bearing roller condition in grinding roller.
Benefits –
This timely identification of failure prevented the breakdown at Line – 3 Raw Mill which saved
production loss and additional damage. This was all possible due to efforts and support added by
our management to promote oil analysis practices in our plant and make us equipped with the
latest technologies for oil analysis in-house.
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