Why We Use…

Ceramic Hybrid Bearings

Even if wind-generated power isn’t the final answer for alternative energy sources, it has demonstrated its ability to substantially augment supplies of power presently in use. As of August 2003, U.S. wind turbines, from large commercial wind farms to smaller, localized services, were producing 4,719 MW, with California and Texas leading at greater than 1,000 MW each.

Jeff McLaughlin has had 10 years of experience assisting in the design of wind turbine systems, and is presently general manager of Machine Building Specialists, Manitowoc, WI. The company also provides engineering and manufacturing solutions to the power generation and the crane and construction equipment industries. McLaughlin points out that many wind towers stand 200 ft in height, such that, since they lack elevators, maintenance reduction becomes an important issue, particularly since installations are exposed to extremes of heat and cold, and the standard maintenance cycle is one visit every 6 months. Power generation revenues also demand that the generators run 24/7.

The blades of a wind turbine turn at speeds up to 30 rpm. A gearbox converts that speed to 1400-1600 rpm into the generator. “We first used hybrid ceramic bearings (which employ ceramic balls in steel races) earlier this year, first on machines with histories of bearing failure in the generators,” says McLaughlin. The failures were caused by a combination of high temperatures produced within the equipment, and the fact that the machinery was air-cooled, in environments that were often dirty. “There was, maybe, 12 months of bearing life in the generator, where the design called for 10 years, ” McLaughlin notes. A long life bearing is attractive because of the high cost of bearing replacement — bearing replacement can cost up to $10,000 because of the crews and cranes that must handle heavy equipment high above the ground.

Other changes and improvements were made at the time, but replacing the generator’s 8-in. diameter bearings with hybrid ceramic components helped put closure to the problems. According to McLaughlin, “the use of hybrid ceramic bearings has helped us achieve and surpass our goals of improved machine performance, reduced maintenance costs, and higher availability for our customers. The differential cost over standard bearings is easily justified in wind turbine generator applications, especially for high speed and generator shafting.” The hybrid bearings use the same lubrication on the standard bearings. The bearings are mounted within an endcap to block dust — tests indicate that bearings with dust seals prevent lubrication from reaching into bearing components. The hybrid bearings also eliminate electrical arcing.

As a result, no hybrid bearings have yet required replacement. The lower mass, thermal stability, reduced friction, and electrical isolation – when used as part of a comprehensive remediation plan – have resulted in ‘better than new’ OEM performance. Says McLaughlin, “Vibration levels are lower than they were when the machinery was new, while power output is 5-7% higher.”

McLaughlin says that his company is pursuing other applications for ceramic bearings. While he is not at liberty to say what they are, he says, “they are equally demanding in temperatures as wind generator, but with different loading.” In addition, he comments, “When one has to push equipment to the limit, it’s better to have a bearing that can take the stresses.”

The hybrid bearings that McLaughlin specified into the wind turbine application are manufactured by Koyo Corporation, with Cerbec ceramic balls made by Saint-Gobain Advanced Ceramics. Such bearings accommodate high operating speeds, have high resistance to corrosive applications, operate in high vacuum applications, and have high rigidity and non-magnetic properties.

Koyo Corp,
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Saint-Gobain Advanced Ceramics,
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