AEGIS iPRO Rings Cut Bearing Failures, Boosting Uptime at Monarch Cement Plant

At Monarch Cement Company’s Humboldt, Kansas, a 5,000‑hp motor spins a ball mill that pulverizes 100 tons of clinker per hour. Yet the recurring squeal from its bearings was a warning that the motor’s life was slipping away.

Since the mill’s installation in 2001, its motor bearings have been replaced three times. Each replacement meant a 10‑day shutdown, costly downtime, and the logistics of hauling a 5,000‑hp motor off‑site for rebuild.

Electrical supervisor Randy Riebel knew the noise meant more than wear: stray shaft currents were eroding the bearings, creating fluting and eventually catastrophic failure. “We kept greasing them, but they kept on squealing,” Riebel recalls. “We had to act before the next replacement.”

Enter the AEGIS iPRO Bearing Protection Ring, a product of Maine‑based Electro Static Technology (EST). By channeling harmful electrical currents from the motor shaft to ground, the iPRO protects bearings in medium‑voltage motors and generators, extending their service life and reducing maintenance costs. Available in sizes for shafts up to 30 in., the iPRO is maintenance‑free and ideal for pumps, compressors, mixers, conveyors, and more.

Riebel partnered with Scott Wilkins, manager of motor shop operations at IEMCO, a local motor repair shop founded in 1906. IEMCO installed two iPRO split‑rings on the mill’s motor without decoupling the motor from the ball mill, thanks to the split‑ring design that allows field retrofits.

“IEMCO’s expertise in large motors made them the right choice,” Riebel says. “Scott’s hands‑on approach ensured the rings were installed correctly and efficiently.”

Mitigating Electrical Bearing Damage

Uncontrolled shaft voltages discharge through bearings, pitting balls and race walls. Over time, this creates fluting—washboard ridges that generate noise and vibration and eventually cause motor failure. Conventional solutions like spring‑loaded grounding brushes require maintenance, while insulation can shift the problem to other components.

The iPRO’s inner circumference is lined with conductive microfibers, locked in the patented AEGIS FiberLock channel. These microfibers create millions of discharge points, forming the path of least resistance that diverts currents away from the bearings to ground. The result is a sustainable technology that qualifies under the Federal Energy Management Program.

Impact Across the Plant

Monarch’s production chain is vast. From limestone crushed by 50‑ton dump trucks to the final cement shipped by truck and rail, every stage relies on electric motors. Variable frequency drives (VFDs) introduce high‑frequency currents that exacerbate bearing damage. After the successful installation on the ball mill motor, IEMCO installed iPRO rings on nine additional motors that had previously failed.

One notable case involved a 300‑hp cooler‑vent fan motor that required replacement every few months for eight years. “We used insulation on both bearings, but it only delayed the problem,” Riebel notes. “The iPRO gave the fan a fresh start and eliminated the squealing.”

Monarch has adopted a policy to fit iPRO rings on every VFD‑controlled fan motor during overhaul. Additional installations include a 2,250‑hp induced‑draft fan and several kiln and baghouse fan motors.

Recognizing the dusty, outdoor environment of cement plants, Monarch now specifies the AEGIS Severe‑Duty SGR Bearing Isolator Shaft Grounding Ring for new motors. This model adds an IP56 non‑contact isolation seal, protecting against dust, water, and contaminants.

Proven Results

Riebel now measures shaft voltages with a probe and oscilloscope. The readings are low, confirming the rings’ effectiveness in diverting shaft currents. “So far, so good,” he says. “The 5,000‑hp motor’s bearings have outlasted expectations—no squealing at all.”

“IEMCO’s service is top‑notch,” Riebel adds. “Scott’s dedication to getting it right the first time is unmatched.”

While the full cost savings are still being tallied, the iPRO’s proven ability to extend bearing life and reduce downtime is clear. For more information, contact John Shepherd, Midwest Regional Sales Manager at EST: (513) 417‑1161, jshepherd@est-aegis.com, or visit www.est-aegis.com.

Figure 1. Monarch Cement Company’s Plant in Humboldt, Kansas.

Figure 2. The ball mill where the first two grounding rings were installed. The bearings of the mill’s 5,000‑hp motor failed regularly until damaging voltages were diverted by an AEGIS iPRO Bearing Protection Ring (inset) at each end of the motor. These on‑site retrofits were accomplished without the need to decouple the motor from the mill, thanks to the split‑ring version of the iPRO.

Figure 3. An AEGIS iPRO Bearing Protection Ring installed in an internal bearing retainer at the IEMCO shop during a Monarch motor overhaul.

Figure 4. Following the success of the AEGIS iPRO Bearing Protection Ring on its ball mill, Monarch installed the ring on a baghouse fan motor (blue) that also required frequent bearing replacements.