Bearings enable inspection of hard drive disk coatings

The novel, custom-designed bearing units comprise a pair of angular contact, thin section, double-row bearings in a housed assembly, ready for fitting to the ellipsometer equipment. The bearing units are low torque, accurate running and incorporate stainless steel rings and balls. The bearings are oil lubricated, as the application is low speed and low torque. The bearings are manufactured to super precision standards (higher than ABEC 7). The angular contact, thin section double-row bearings have an outside diameter of 28.5mm with a width of just under 9mm and a bore of 19mm.

Barden custom engineered the bearings at its site in Plymouth. Barden took part of the ellipsometer housing and incorporated this into the first bearing's outer ring. The bearing units were supplied fully assembled with a flange to enable the customer to mount the units quickly and easily to the ellipsometer column.

Nick Dowding, Business Development Manager at Barden UK comments: "Hard drive disks are coated with a very thin magnetic film. The ellipsometer checks the integrity and consistency of this coating. The equipment uses a laser or polarised light source to scan the surface of the disk in order to ascertain its thickness, typically to nanometre accuracy. The ellipsometer checks are carried out immediately after the coating process, prior to assembly of the hard disk drives."

According to Dowding, the customer had been experiencing too many failures of the previous bearings on the ellipsometer turntable. These bearings were standard thin section pairs that were pre-loaded to ensure there was no internal play. However, the disadvantage of these bearings was the increased torque levels that were required.

Dowding adds: "A stationary light source inspects the disk surface which is periodically rotated to allow a new set of measurements to be made and so you need to ensure that the system is very stable and does not fluctuate. The customer approached us to see if we could supply a new design of bearing with lower torque but accurate running. We therefore looked at the existing configuration and recommended a new design approach that would incorporate part of the ellipsometer housing into the bearing unit. This would allow us to offer a solution that would be easier for the customer to fit to the ellipsometer column and that would help to locate the bearing unit accurately. This design would also be cleaner, would reduce manual handling and therefore reduce the risk of damage to the bearings."

Due to the low-speed low-torque application, the bearing units were fitted with special PTFE toroidal separators between the stainless steel balls. These encircle alternate balls.

For more information about super precision bearings from Barden, please visit the website at www.bardenbearings.co.uk.