Replacement bearing proves effective

8th November 2013 By: Jonathan Rodin

Since Bearings supplier OE Bearings, an agent for Revolvo split roller bearings (SRBs), installed new bearings for Century Cement, the applications have run with far greater operational efficiency and economy.

The original bearings have been so success-ful that Century Cement, a division of textile, cement and paper manufacturer Century Textiles & Industries, now specifies Revolvo’s SRBs as its component of choice.

Century Cement is part of the BK Birla group of companies. The plant is located in Baikunth, in Raipur, India, and is able to produce 2.1-million tons of cement yearly. The company places a strong focus on plant efficiency, so when it was discovered that OE white metal bearings on a 2 000 kW induction motor were regularly failing, the company decided to look for an alternative solution.

The first mill motor drive conversion was made in 2008, and now has a record of six years operational reliability. With the success of the initial conversion, further mill motors have been converted, and other applications, such as bucket elevator conversions, have also been undertaken.

The cost savings to Century have been sub- stantial, amounting to in excess of R600-million.

OE Bearings managing director Warwick Steinhobel explains that abrasive dust, which is ever present in cement production plants, results in a dramatically reduced bearing life owing to particle ingress causing lubricant contamination and wear damage.

He highlights that, during a 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 and used pumped oil recirculation lubrication systems. “The bear-ings, therefore, often suffered from premature failure. 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,” he explains.

Initially, grease-lubricated solid spherical roller bearings were considered, as using simple grease lubrication instead of oil recirculation systems significantly reduces maintenance costs. However, Century Cement was concerned that, in the event of a bearing failure, the replacement cycle would still involve significant downtime as the motor shaft would need to be decoupled from the cement mill transmission and lifted in order to replace the bearing.

Fortunately, Revolvo SRB was able to offer a long-term low-maintenance cost solution. Its SRBs, which offer the same grease-lubricated bearings benefits as solid roller bearings, reduce bearing replacement times by up to 90%.

Unlike solid bearings, Revolvo’s SRBs are split to be fitted around the shaft, a design that both simplifies and expedites installation and significantly cuts downtime cost, compared with replacing solid bearings of a similar size. Revolvo SRBs enable the shaft to be supported by the lower section of the bearing, while 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 when dealing with large rotating machines where sheer weight and size can limit fast and effective servicing.

Steinhobel adds that OE Bear- ings was approached by engi-neering company M/S Bhavesh Engineering to propose an alter- native solution to Century Cement for the replacement of the OE white metal bearings. The com- pany was able to show that the SRBs would last longer and require lower maintenance resources.

“Bearing replacement would also be far quicker, compared with other solutions on the market when the time did come for bear-ings to be changed,” he noted.

Steinhobel highlights that, once the motor shafts were measured, it was found that where the original-equipment white metal bearings had been in service for over 20 years, some shaft bearing journal wear had taken place. He says that this was probably exacerbated because of long-term lubrication oil contamination, which can often be an issue in cement plants. This meant that Century Cement’s motor shafts were out of tolerance with standard catalogue-sized bearings.

“Fortunately, we are able to manufacture entirely bespoke bearings in-house on short lead times, meaning that the replace-ment project was completed on schedule,” Steinhobel adds.