Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
1999-04-23
2001-01-30
Evans, Jefferson (Department: 2754)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C360S099080, C360S264100
Reexamination Certificate
active
06181509
ABSTRACT:
FIELD OF THE INVENTION
Embodiments of the present invention relate generally to disk drive systems and to components within the disk drive systems.
DESCRIPTION OF RELATED ART
Magnetic storage systems are information storage devices which utilize at least one rotatable magnetic disk having concentric data tracks defined for storing data, and a magnetic recording head or transducer for reading data from and writing data to the various data tracks. In typical disk drive systems, a stack of one or more magnetic disks is mounted over a spindle on a drive motor. The disks are separated by spacers. The system also includes a head actuator for moving the magnetic recording head relative to the disk surfaces, and a printed circuit board (PCB) with electronic circuitry for processing signals to implement various functions of the disk drive.
One failure mechanism for disk drive systems relates to failure of the magnetic disks. In order to achieve a large recording density, magnetic disks are typically made from non metallic substrate materials such as glass and ceramic. However, glass and ceramic disks are brittle and can easily break when subjected to stress. As a result, it is conventional in the art to choose the components in the disk drive system to minimize stresses caused by thermal expansion mismatch between adjoining components. This has been accomplished by fabricating the parts such as the hub and spacers from materials having similar coefficients of thermal expansion to the materials the disks are fabricated from.
In addition to failure of the disks, matching the coefficients of thermal expansion is important to minimize the occurrence of thermal track shift. Thermal track shift is caused by thermal expansion mismatch between the disks and parts in contact with the disks, which causes the disks to shift radially. The radial shift leads to eccentric data tracks, which are more difficult for the actuator to accurately follow. In addition, different disks in the disk stack may have different levels of thermal track shift. These problems are minimized by using materials having similar coefficients of thermal expansion.
Metals such as conventional steels have been used for structural components in the disk drive. Stainless steels offer the additional benefit of better corrosion resistance. However, conventional stainless steels are difficult to machine to the fine tolerances necessary for disk drive components and are therefore expensive. Certain types of stainless steels are known as free machining stainless steels. Free machining stainless steels have similar properties to regular stainless steels, but are easier to machine due to their microstructure. In particular, free machining stainless steels include additional elements including sulfur, which is beneficial to machining. The sulfur forms sulfur-rich inclusions, such as manganese sulfide, which benefit machinability by lowering the shear strength of the metal chips formed during machining, which increases the machining efficiency. A free machining stainless steel which has been used for disk drive components is known under the AISI designation 430F, and includes approximately three tenths of one percent sulfur.
It has been observed, however, that when using free machining stainless steel for disk drive components, a certain amount of disk drive failures still occur. It would be desirable to reduce the number of such failures.
SUMMARY
It is an object of certain embodiments of the present invention to inhibit corrosion of disk drive wiring lines when utilizing free machining stainless steels for certain components in the drive assembly.
These and other objectives may be carried out in one embodiment by providing a disk drive including a drive motor assembly including at least one component selected from the group consisting of a rotatable hub, disk spacer, disk clamp, lower bearing bushing, and lower mounting flange. At least one of the components comprises a low sulfur outgassing free machining stainless steel material.
The low sulfur outgassing free machining stainless steel material may be a free machining stainless steel that outgases sulfur at a rate insufficient to cause visually observable (without magnification) sulfide corrosion when tested by placing a copper strip into contact with the free machining stainless steel in an environment having a temperature of 50° C. and 90% relative humidity for a 7 day test period and then observing the copper strip.
Embodiments may also include a head arm assembly including thin film heads for accessing data tracks on a disk. The head arm assembly includes wiring lines for transmitting electrical signals. A voice coil motor assembly may also be included to control the head arm assembly. The voice coil motor assembly preferably includes at least one spacer post comprising the low sulfur outgassing free machining stainless steel material.
Other embodiments relates to a disk drive including a drive motor assembly including at least one component selected from the group consisting of a rotatable hub, disk spacer, disk clamp, backiron, lower bearing bushing, and lower mounting flange. At least one of the components comprises a free machining stainless steel including manganese and sulfur in a ratio of no greater than 2 to 1.
Other embodiments relate to a disk drive including a drive motor assembly including at least one component selected from the group consisting of a rotatable hub, disk spacer, disk clamp, backiron lower bearing bushing, and lower mounting flange. At least one of the components comprises a free machining stainless steel including chromium and manganese, wherein the chromium to manganese ratio is at least 30 to 1.
Yet other embodiments relate to a spindle motor assembly for use in a magnetic recording device. The spindle motor assembly includes a shaft and a spindle hub. The spindle hub comprises a free machining stainless steel including manganese and sulfur in a ratio of no greater than 2 to 1.
Still other embodiments relate to a magnetic disk drive for reading and writing magnetically, including a plurality of magnetic disks and a plurality of magnetic read/write heads, each head being associated with the surface of a disk. The disk drive also includes an actuator for supporting the heads and moving the heads across the disks. A drive motor including a rotatable hub for mounting the disks, a disk spacer separating the disks, a disk clamp disposed above the disks and a lower bearing bushing below the disks is also included. At least one of the hub, disk spacer, disk clamp or lower bearing bushing comprises a low sulfur outgassing free machining stainless steel.
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Aerospace Structural Metals Handbook, 1997 Ed., code 1401, pp. 1-4.
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Slater Steels Corp., Stainless Type 430F information pages, 1998.
Canlas Eduardo Gatmaitan
Hanlon Andrew Keith
Johnson Brad Vaughn
Wood Keith Freeman
Yaney Deborah L.
Evans Jefferson
International Business Machines - Corporation
Konrad Raynes & Victor
Raynes Alan S.
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