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Magnetic-fluid technology brings compact, low-friction, self-contained bearings capable of speeds to 30,000 rpm.
Bearings in precision equipment such as computer disk-drive spindles, laser scanners/printers, and gyroscopes, need excellent stiffness and damping qualities to run true at high speeds. Until recently, designers of these applications relied on hydrodynamic oil and gas bearings, or ball bearings.
But sliding bearings that employ magnetic fluid (ferrofluid) for both lubrication and sealing have several advantages over conventional designs. For example, miniature ball bearings run at high rotational speeds tend to vibrate and make noise because of the motion of the balls. High rotational speeds can also change properties of lubricating greases that, in turn, trigger large and rapid torque fluctuations. These fluctuations make it difficult to control the speed of the bearing unit. Operation at elevated temperatures can as well alter lubricating-grease properties and shorten bearing life.
In contrast, ferrofluid bearings that carry loads on a film of oil don't suffer friction fluctuation and are more controllable. Ferrofluid bearings also have extremely low nonrepetitive runout and maintain high rotational accuracy at high speeds. They run quietly and need no mechanical seals as do conventional designs, so they last a long time and without periodic maintenance.
Air bearings as well have negligible nonrepetitive runout. And they operate with low friction. But the low viscosity of air necessitates bearing clearances on the order of a few microns and large bearing diameters. In addition, bearing surfaces must contain highly precise, shallow herringbone grooves to generate sufficient aerodynamic pressure and boost bearing stiffness. These features require a special, high-tolerance manufacturing process that adds costs and is difficult to maintain for mass production. Another concern: The small clearances make the bearings susceptible to...