Recent advances in computer disk drive technology are likely to completely eliminate the use of ball bearings from disk motor and spindle mechanisms.

In 2000, over 188 million computer disk drives were manufactured using ball bearings in their spindle drive motors.

Over the next few years, however, it is likely that ball bearings will no longer be used as drive manufacturers move to “fluid bearings” or “liquid bearings” in the spindle motors. “If you think of this as a Lazy Susan, what we are doing is replacing the Lazy Susan with liquid,” said IBM’s David Uriu.

Currently, almost every disk drive uses a motor which also serves as the center spindle supporting the disk drive platters. Tiny ball bearings support the spindle motor and locate the bearing platters. By locating the motor in the middle of the spinning platters, drives have been made smaller and are able to spin faster. The faster the drive can spin, the faster the data is transferred to and from the drive. IBM’s new Travelstar (which uses fluid bearings) spins at 5,400 RPM, up from 4,200 RPM in previous models.

The other driving issue in disk drive technology is storage density. Today’s disk drives can store magnitudes more information than drives made only a few years ago. Higher density magnetic media, advancements in location technology, more precise control of the read/write head location and other factors have greatly improved storage density capabilities. The Travelstar 2.5″ disk drive has a capacity of 48 gigabytes (the current industry capacity leader is another IBM drive with 32 gigabytes). Only months ago, 10 gigabytes was considered large, and 2 gigabytes was standard as recently as 2-3 years ago. A recent IBM white paper (see link below) predicts storage density will continue to increase 60% to 100% per year.

Lately, a third issue has begun to arise as computers become fixtures everywhere in the home and workplace: noise. Disk drive noise levels are especially important with laptop computers where there is no noisy fan to mask the sound of the disk drive. The Travelstar, for example, makes less noise during constant operation than the previous generation drives made at rest.

Disk drive manufacturers are now finding that the physics of ball bearings in the drive motors have become the limiting factor in advancing disk drive technologies. Ball bearings now hinder all three design criteria: rotational speed, storage capacity and noise issues.

Rotational speed: Ball bearings can only turn so fast before they begin to have heat issues, lifespan issues, and lubricant problems such as outgassing.

Storage capacity: Ball bearings are not perfect. The measurement of how much they wobble is called runout. Current disk drive bearing technology offers runout in the range of 0.1 microinch. That amount of wobble is now the limiting factor on how tightly information can be packed together on a disk drive - data cannot be packed more tightly than 0.1 microinch or the inherent bearing wobble causes mis-registration.

Among the leading vendors for drive motor ball bearings are Timken Aerospace & Super Precision and NSK Corporation.

Fluid bearings or liquid bearings are beginning to replace ball bearings in the newest disk drives, a trend which is predicted to eventually spread to every disk drive. A fluid bearing is essentially a small quantity of lubricant trapped in a carefully machined housing. Fluid bearings answer the multiple issues of speed, density and noise, while at the same time offering the side benefit of better shock resistance than ball bearings.

Fluid bearings are able to support higher speeds because there are no interactions between balls and races and no mechanical nodal vibration. Some heat buildup from lubricant shear is the only concern with fluid bearings, but engineers believe that can be addressed.

Higher recording densities are possible with fluid bearings because the runout of a fluid bearing is currently only 10% the runout of the best ball bearing…fluid bearings are achieving runouts in the area of .01 microinch.

Dramatically reduced noise levels are an important benefit of fluid bearings. Because there is no longer a mechanical connection between the housing and the turning part of the motor, vibrations and noises are not transmitted between the two. The fluid also acts as a damping agent, further limiting noise levels.

In the disk drive industry today, we are seeing the beginnings of the movement away from ball bearing spindle motors. According to this IBM white paper, there is no longer a future for ball bearings to be used in disk drives.