Century Cement found that the total life cycle of the original-equipment white-metal bearings on its raw-mill motor drives was becoming so poor, that it was willing to invest in completely new drive systems, if a lower maintenance, more cost-effective motor bearing solution could not be found.
Instead it found a long-life low maintenance SRB split-roller bearing solution.
Century Cement is part of the BK Birla Group of Companies, a leading Indian conglomerate. The plant is located in Baikunth, in the Indian district of Raipur, and is capable of producing 2.1 million tons of cement per annum.
"During routine review of the mill motor drives Century Cement engineers noted that the white metal bearings used on the induction motors required high levels of maintenance, including pumped oil recirculation lubrication systems, and often suffered from premature failure, says Adrian Menzies, Revolvo sales and marketing director. "The regular downtime and subsequent cost of these failures meant that either a suitable replacement bearing was required or the entire drive system would have to be replaced."
Revolvo is a manufacturer of specialist bearings, and designs and manufactures bespoke high performance bearings for demanding and safety critical applications, combining its expertise for both branded ball and roller bearings, and SRB split roller bearings. Its global headquarters is in Great Britain.
Finding the solution
Initially grease lubricated solid spherical roller bearings were considered; by using simple grease lubrication instead of oil recirculation systems, significant maintenance cost reductions can be realized. However Century Cement was concerned that in the event of a bearing failure the replacement cycle would still involve significant down time as the motor shaft would need to be decoupled from the raw mill transmission, and lifted to enable bearing replacement to take place.
Revolvo offer a long-term low-maintenance cost solution with their SRB split roller bearings, which offer the same grease lubricated benefits of solid-roller bearings but reduced bearing replacement times by 90%.
Unlike solid bearings, these roller bearings are totally split to the shaft; a design that both simplifies and expedites installation and significantly cuts downtime costs in comparison to replacing solid bearings of a similar size. SRB split bearings allow the shaft to be supported by the lower section of the bearing, whilst the upper section of the housing and bearing outer race can be removed, making bearing inspection fast and simple, without the need to disconnect drives or lift the shaft. This intrinsic feature is especially valuable regarding large rotating machines, where sheer weight and size can be a barrier to fast and effective servicing.
"We were able to show that not only would SRB split roller bearings last longer and require lower maintenance resources, bearing replacement would be far quicker compared to other solutions on the market when the time did come for bearings to be changed," Menzies adds.
Once the motor shafts were measured, it was found that where the OE white metal bearings had been in service for over 20 years, some shaft bearing journal wear had taken place. "This was probably exacerbated," Menzies says, "because of long-term lubrication oil contamination which can often be an issue in cement plants. This meant that their motor shafts were out of tolerance for using standard catalogue-sized bearings. Fortunately we are able to manufacture entirely bespoke bearings in-house on short lead times, meaning that the replacement project was completed on schedule."
The bearings have been so successful that Century Cement now specifies Revolvo’s SRB split bearings as their component of choice.
Speaking of the SRB bearings A. Patini, Executive President (Plant) of Century Cement, said: "Since the installation, we have been very satisfied with the performance of these units. Following the success of this project we will give consideration to the conversion of other applications within the plant as appropriate."