How do you make a better bearing?

Sheila Kennedy says better materials, design, protective devices and lubricants mean better bearings.

By Sheila Kennedy, contributing editor

Bearings have existed since the invention of the wheel but they continue to evolve in response to present-day challenges. Innovations in bearing materials, design, protective devices, and lubricants are reducing risks caused by contamination, climatic conditions, electrical corrosion and destructive currents. And yet, one classic option still has its place in industry.

Environmental conditions

With an improved steel heat treatment process, SKF (www.skf.com) developed self-aligning roller bearings that exhibit a superior balance of hardness and toughness. Tests of SKF’s next-generation bearing steel versus the company’s original bearing steel found that the new bearings will provide almost twice the service life, under contaminated or poor lubrication conditions, and extend the time from initial spall to when the bearing becomes unserviceable.

"The enhanced robustness of the SKF next-generation bearing steel used on SKF self-aligning roller bearings provides significantly improved wear resistance,” says Sergio J. Notarmaso, applications engineer for SKF USA’s Off-Highway Team. “As a result, many applications may now benefit from increased performance in contaminated environments and therefore longer service life. This could allow for extended maintenance intervals, reduced maintenance costs, and less downtime.”

A multi-layered protection strategy is encouraged for metal mills, mining operations, and other processes prone to environmental conditions that put moving equipment and uptime at high risk. Dirt, dust, and other contaminants wreak havoc on bearings that lack adequate protection. Timken (www.timken.com) recommends rugged housings and tight seals to resist the sources of friction and damage that might otherwise shorten bearing life.

“Timken’s solid-block housed units help shield their spherical roller bearings (SRB) from particle contamination and moisture with a steel housing, plus optional seals and steel auxiliary covers,” says Cory Shaw, Timken’s business manager of SRB-housed units. The available steel covers have space for grease, and the seals can operate at high temperatures, resist damage from chemicals and abrasion, and help protect equipment running at high and low speeds.

Innovations in bearing materials, design, protective devices, and lubricants are reducing risks caused by contamination, climatic conditions, electrical corrosion and destructive currents.

For temperatures that exceed the operating limits of fluorine grease, an alternate lubricant is needed. NTN Bearing’s (www.ntnamerica.com) new Ultage deep groove ball bearings, designed with a special-composition solid lubricant, are suited to equipment used in ultra-high-temperature environments. A positioning ring between the shield and solid lubricant helps to feed lubricant in the direction of rotation for a smoother rotation. A metallic cover over the solid lubricant helps to keep the inner and outer rings from separating, even when the solid lubricant is heavily worn.

Electrical influences

A new material ceramic ball bearing was developed by NSK (www.nsk.com) to protect air conditioners, clean room equipment, and other devices with inverter-controlled fan motors from bearing damage caused by galvanic corrosion. Because the rolling element is ceramic, which is an insulator, it interrupts the current flowing inside the bearing to prevent damage from electrical corrosion.

When tested against conventional silicone nitride ceramic ball bearings, NSK’s oxide-based new material ceramic ball bearings exhibited the same anti-corrosion performance but with increased productivity and reliability. The new material ceramic balls were shown to reduce friction inside the bearing, prevent false brinelling damage, and ensure quiet operation by inhibiting increasing fan motor noise for a long time.

An upgraded current protection device from Inpro/Seal was designed to extend bearing life. Bearings for motors and coupled equipment can be damaged or destroyed when shaft currents produced by variable frequency drives (VFDs) are discharged through the bearings. Inpro/Seal’s (www.inpro-seal.com) second generation current diverter ring (CDR) has proprietary conductive filaments that protect bearings from stray shaft currents by providing a low impedance path to ground, thereby drawing the currents away from the bearings. It is more durable than the previous generation due to its new, single-piece design.

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"The Inpro/Seal CDR increases plant reliability by eliminating premature bearing failure caused by VFD-induced shaft currents,” says Dwight A. Vicars, CDR/MGS product manager for Inpro/Seal. “Custom engineered for optimal performance, the CDR can be shipped same day."

Timeless approach

While innovation makes news, some bearing choices are timeless. Wood was probably the first bearing material ever used, and it is still used in industry today. In certain hostile environments, rock maple’s properties allow it to perform efficiently while most metals and plastics would have a shorter service life, according to Woodex Bearing (www.woodex-meco.com), whose oil-impregnated rock maple bearings tolerate significantly higher shaft speeds and loads and have a coefficient of friction in the same range as synthetic materials.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at sheila@addcomm.com.

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