INDUSTRIAL CASE STUDY:

THE CEMENT INDUSTRY

PREPARED BY

MAUSAM SHARMA

with assistance from

RAHUL MUNDRA

S

HR

EE

CE

ME

NT

LT

D.

Plant : Shree Cement Limited

Location : Ras

Site : Cement Mill - IV

Equipment : Cement Mill Roller Press Bearing Fix Side (Non Drive Side) Make – KHD

Case : Warning of Roller press bearing failure

ABSTRACT

This paper contains case study of bearing damage at Cement Mill – IV in Shree Cement Ltd., Ras. In a large scale industry oriented, to minimize downtime and improve production; machine downtime have to be reduced. 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 as the problem was identified and the corrective actions were taken within time. In slow rpm drives like roller press, spectrum analysis is practically impossible. In these types of drives ferrography technique can be used to predict machine wear condition. Also the study focuses on how ferrography has been useful to reduce the downtime, running cost and improve plant efficiency. For slow rpm drive, equipment temperature also plays an important tool for fault identification. 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, due to slow rpm of roller press no significant change was observed in bearing spectrum. Equipment was kept under micro level monitoring since past few months. Finally criticality of fault was identified within time and proper actions were taken to save the equipment from other damage.

Case Analysis –

In August 2015, in regular sampling of Roller press fix side non drive end bearing grease; ferrous concentration went high but the wear particle size was not significant. Considering the criticality of the equipment, bearing was kept under close monitoring. Further in Jan 2016, ferrous concentration hiked to 8660 ppm from 2084 ppm in August 2015. Also bearing wear particle size increased to 250 microns in January 2016. Based on the sample report of January 2016, equipment was kept in close surveillance.

In May 2016, ferrous concentration in grease was 8750 ppm and bearing particle size observed was up to 200 microns. As per ferrography the condition of the bearing was more or less similar to as it was in January. There was no major development in bearing since then. However in June 2016, bearing wear particles indicating towards pitting on bearing internals were observed. Also there were several stoppages in roller press due to abnormality in temperature.

Problem Diagnosis –

Ferrography helps us to observe & trend generation of wear particles. Ferrography plays an important predictive maintenance tool in drives where vibration analysis is practically impossible. In this case abnormal size bearing wear particles were observed on ferrogram since January 2016. However no major development was seen in the bearing wear pattern in ferrography till May 2016. In June 2016 bearing wear particles indicating towards pitting were observed on ferrogram.

Ferrography helps us identify wear particle depending on the shape, size, colour and surface texture. Considering this case, surface texture of bearing wear particles observed in May 2016 was finished whereas in June 2016 particles with pits and unfinished surface were observed under microscope. Images below are of bearing wear particle observed in June 2016.When we compare these two images we see the difference in texture. Surface texture of wear particles indicated development of pitting.

Ferrous concentration monitoring in equipment is also an important tool for identification of abnormality. Ferrous concentration in this bearing was in higher range since January 2016. This rise in ferrous ppm pointed towards certain abnormality which required immediate attention. Since then the equipment was kept under regular monitoring.

Aug-2015 Jan-2016 Mar-2016 May-2016 Jun-2016

2084 8660 8681 8750 8776

Table 1 – Table showing ferrous concentration trend

Bearing Inspection –

Considering the criticality as per ferrography report and higher temperature trend in roller bearing, it was decided to inspect roller bearing on immediate basis. Pitting was observed in bearing inner race. Also bearing inner race was found cracked. Images below show the condition of the bearing inner race in the roller.

Benefits –

The oil analysis technique has helped us to detect this failure and hence avoid a major breakdown at the most critical drive in Cement Mill Section. Secondary damage due to this could be observed on all other connected drives. Hence timely monitoring and physical inspection along with pro-active maintenance practices has helped us to avoid a possible major breakdown, adding to plant productivity and increasing MTBF.

Conclusion –

This timely identification of failure prevented the breakdown at Cement Mill Unit which saved production loss and additional damage. This is all possible due to efforts and support added by our management to promote oil analysis technique in our plant and make us equipped with the latest technologies of oil analysis in-house.

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