Sealing Solutions for Industrial Bearings

Bearings must be shielded from lubricant loss and contaminants to operate reliably and last. Traditional contact oil seals often harm equipment. Non‑contact bearing isolators address this issue by safeguarding both bearings and the machinery.

Oil seals remain common, yet achieving the performance of one bearing isolator often requires two or three oil seals.

Early bearing isolators combined metal parts with simple sealing channels and O‑rings for static sealing. Modern units are precision‑engineered, featuring tight tolerances and intricate labyrinth pathways that bend sharply.

Bearing failures are often triggered by washdowns, poorly designed labyrinth excluder rings (LER), or chemical attack—issues that standard isolators effectively mitigate.

While size and temperature are key, the application itself, media, pressure, speed, and any special requirements must be known. Complete application data sheets and submit them to our engineers for review to ensure all relevant information is captured.

Bearing isolator construction

Industry standards narrow the field of suitable isolators. For instance, the American Petroleum Institute mandates non‑sparking materials for isolators used in petroleum, heavy‑chemical, and gas sectors.

This requirement has been embraced across sectors, making bronze the material of choice. Where metal construction is unnecessary, PTFE blends can produce chemical‑resistant isolators for pharmaceutical and other applications.

Standard isolators use O‑rings, which, if not properly selected, are the first point of failure under chemical attack or extreme temperatures. Depending on the application, PTFE‑encapsulated FKM, AFLAS, or silicone O‑rings may be specified instead of the default brown FKM.

Bearing isolators can outlast traditional oil seals by up to seven times, retaining lubricant while blocking contaminants. Modern designs also offer electrical sealing capabilities.

Electric induction motors driven by pulse‑width‑modulation (PWM) variable‑frequency drives (VFDs) can be operated at 40 % lower RPM, delivering significant power savings.

Uncontrolled induction motors run on a balanced three‑phase sine wave. VFDs supply power in controlled pulses—square‑wave or six‑step voltage—creating capacitive‑coupled common‑mode voltage (CMV) on the shaft.

The CMV follows the path of least resistance to ground, typically through the bearings. A thin oil film cannot insulate against this excess voltage, leading to arcing between the inner and outer races—effectively tack welding. The resulting electric‑discharge machining (EDM) pitting causes fluting damage and bearing failure, often audible as a high‑pitched noise.

Shaft grounding

To prevent this damage, conductive brushes have been incorporated into bearing isolators. They offer a lower‑resistance path than the bearings, shunting excess voltage safely to ground. This eliminates CMV and stops EDM.

Additional dynamic sealing can be applied to the motor’s non‑drive end by installing a traditional isolator. For large, high‑power motors, insulated bearings force stray voltage through the conductive brushes.

Bearings also require defense against external contamination. In mining, power generation, and primary metal production, bearing isolators can endure up to three years, compared to merely three to six months for a conventional contact lip seal.

Filters for external contamination

In extremely dirty environments—such as coal pulverizers and mine cars—air filters are now integrated into bearing isolators. Closed‑cell foam blocks contaminants from entering the seal pathways; the foam is mounted in a groove, directing debris to a drain port.

Split oil seals have long been favored to avoid equipment disassembly. Bearing isolators are also available in split designs, though restrictions apply: non‑metallic, flooded, and hybrid isolators cannot be split due to material or application constraints.

Flooded applications

When the lubricant level exceeds the drain port, traditional isolators are unsuitable, as lubricant will flow through labyrinth pathways and leak.

Similarly, unvented forced‑lubrication systems generate pressure differentials that cause lubricant to leak through the labyrinth, just as in flooded conditions. The pathways cannot retain positive or negative pressure.

The challenge has been addressed by hybrid seals, which combine the benefits of conventional isolators with flood‑tolerant performance. These seals can be fully submerged, retaining pressure comparable to general‑purpose oil seals.

Industrial sealing demands a tailored approach. Matching the right isolator to each application requires thorough data collection and analysis. Although time‑consuming, this diligence yields optimal solutions that protect bearings and extend equipment life.

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Patrick Rhodes is an applications engineer with Garlock Sealing Technologies, Palmyra, NY.