INDUSTRIAL CASE STUDY:

THE CEMENT INDUSTRY

PREPARED BY

Condition Monitoring Cell

Shree Cement

Ras

S

HR

EE

CE

ME

NT

LT

D.

Plant : Shree Cement Limited

Location : Ras

Site : Unit – 5 Raw Mill

Equipment : Raw Mill Grinding Roller No. 1

Case : Analytical Ferrography diagnosed early warning of grinding roller bearing failure

Lubricant : BERU - 680

ABSTRACT

This paper elaborates how analytical ferrography helped us diagnose bearing failure in grinding roller. In Vertical Roller Mill, vibration analysis for grinding rollers is practically impossible. The only predictive maintenance procedure available is Oil Analysis. This case is related to one such case in Line - 5 Raw Mill Section. Abnormal size bearing wear particles were observed in roller since May 2016. Detailed analysis of wear debris was conducted through ferrography technique; concluding bearing wear profile was to be kept under monitoring. In July 2016, considering the ferrography report; it was suggested to inspect roller bearing. However very soon a time window for inspection was available, due to low dispatch and roller bearings were inspected. After observation it was concluded to replace the grinding roller considering the available time window. This case outlines how oil analysis technique can be useful in predicting equipment failure and also that regular monitoring of equipment can be a sign of good health for the machine and plant as well.

Plant Overview Shree Cement Ras Plant is located in the village Ras, Pali District, around 150 kms from Jodhpur. It has eight cement lines (Line 3 to Line 10) and three grinding units , two ball mills and one vertical roller mill: Line 3 to Line 8 are designed for annual production of 1 MT each and Line 9 & 10 both are designed to have an annual capacity of 2 MT. Two ball mills are designed with annual capacity of 4 MT each and vertical roller mill of 3 MT per year.

Case Analysis –

In May 2016, abnormal size bearing wear particles of size ranging up to 100 microns were observed in marginal quantities in grinding roller oil sample. But the ferrous concentration was 73 ppm. Based on the ferrography analysis, machine condition required close monitoring for wear particle generation. In June 2016, the size of bearing wear particle was within the same range. Although the size and texture of the wear particles suggested some abnormality in roller bearings.

Fig 1 – Bearing wear particle (100 micron) observed in ferrography analysis in May

Problem Diagnosis –

Since May 2016, grinding roller was kept under close surveillance. Scheduled oil samplings were done. However no abnormality was observed till July 2016. On 8th July 2016, in grinding roller oil sample ferrous concentration value hiked to 1233 ppm. Ferrography analysis showed large size abnormal bearing wear particles and copper alloy (bearing cage) wear particle. Particle size increased from 110

microns to 250 microns. Here forth the situation became alarming. However to ensure the results, oil was re-sampled. Next sample was received on 15th July 2016, ferrous concentration in the oil rose to 1425 ppm. Increasing trend of ferrous concentration was pointing towards some abnormal wear on the bearing surface. Ferrography of the sample showed large size bearing wear particles and large size copper alloy wear particle.

Fig 2 – Copper alloy wear particle (260 micron) observed in ferrography analysis on 15th July 2016

Considering the criticality of the case, management decided to inspect the bearing in the next available time frame. Meanwhile it was suggested to replace oil in the grinding roller so as to avoid secondary wear due to the presence of high ferrous concentration.

Bearing Inspection –

Soon there was a time window available due to excess clinker stock and the grinding roller bearing was inspected. On inspecting the grinding roller there was high concentration of metallic shining observed in roller.

Fig 3 – Metallic shining observed in grinding roller bearing Also minor pitting spots were felt in bearing rollers during inspection. Considering the observation, ferrography report and the available time frame it was decided to replace the grinding roller.

Bearing Observations–

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.

Fig 4 – Micro pitting spots on bearing rollers

Fig 5 – Pitting spots observed on bearing inner race

Both bearings of the roller along with both oil seals were replaced.

Conclusion–

This timely identification of bearing failure saved major breakdown at Line – 5 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.