Electrical Supervisor Randy Riebel could not believe his ears. The huge ball mill at Monarch Cement Company’s Humboldt, Kansas, processing plant was making that sound again – the piercing squeal of fluted bearings. Riebel had replaced the bearings on the 5000 HP motor that drives the mill three times already! And he knew that the sound meant he would need to replace them again. What he didn’t know was how to prevent the damage from happening again in the future.

Cement Ball MillThe massive ball mill is capable of crushing 100 tons of clinker per hour. “We kept greasing those bearings, but they kept on squealing,” Riebel recalls. “We knew that if we waited too long, the bearing race walls would become fluted like they had in the past, and we weren’t looking forward to another replacement because of all the expense and downtime. It takes at least 10 days to pull that motor – it’s a major production. Sometimes we have to hire help, rent a hoist to put it on a truck, and take it away to be rebuilt.”

So this time Riebel decided to try something different. He had a local motor repair shop install an AEGIS® PRO Series ring on the mill’s motor. A larger version of the AEGIS® Shaft Grounding Ring, the PRO Ring is designed to protect the bearings of high-current and medium-voltage motors. With several rows of conductive microfibers that completely surround the motor shaft, it provides a path of least resistance for damaging shaft currents, channeling them safely to ground.

After the PRO was installed, Riebel took shaft voltage readings. They were very low, indicating that the ring has reduced damaging shaft voltages to negligible levels. Riebel noted, “The last set of bearings only lasted a year. But so far, we haven’t had any squealing.”

To read the full Monarch Cement case study, click here.

For more information on AEGIS® PRO Series Rings, click here.