Ferrofluid seal for actuator bearing

Details Ferrofluid seal for actuator bearing Ferrofluid seal for actuator bearing

1998-11-13

2001-05-08

Nguyen, Hoa T. (Department: 2754)

Dynamic magnetic information storage or retrieval

Head mounting

For shifting head between tracks

C360S265600, C310S06700R

Reexamination Certificate

active

06229676

ABSTRACT:

TECHNICAL FIELD
This invention relates in general to hard disk drives and in particular to a seal for the actuator bearing of a hard disk drive.
BACKGROUND ART
Hard disk drives utilize a pivotable actuator with magnetic heads to read information from and to write information to magnetic disks. As shown in
FIG. 1
, the actuator
11
is typically mounted to a motor-driven pivot shaft
13
which rotates the heads on actuator
11
to precise locations on the disks (not shown). Shaft
13
is surrounded by a stationary housing
15
. At least one pivot bearing
17
is mounted between housing
15
and shaft
13
to enhance the stability of shaft
13
as it pivots actuator
11
. During operation, bearing
17
emits oil vapor and aerosol droplets of grease which are a potential source of contamination in the disk drive. Reducing this type of contamination is important to improve the reliability of disk drives.
Prior art disk drives have used several different types of seals to seal the actuator pivot bearings in disk drives. One type of bearing seal, known as a ferrofluid seal, is practically impermeable to emissions from bearings and is fairly well known in the art. Ferrofluids contain very small magnetic particles which are suspended in a carrier fluid. Ferrofluid seal
21
(
FIGS. 1 and 2
) utilizes shaft
13
which is formed from a magnetic material, such as
400
series martensitic stainless steel, and a magnet
23
mounted to housing
15
. Magnet
23
is spaced apart from shaft
13
by a very small gap
25
. Ferrofluid seal
21
functions by suspending a magnetically attracted fluid
27
in gap
25
between magnet
23
and shaft
13
to complete the magnetic circuit (see magnetic flux lines
29
in FIG.
2
). The suspended fluid
27
, which is essentially frictionless, forms an effective liquid seal between the pivoting shaft
13
and housing
15
.
Recently, non-magnetic materials for disk drives have become increasingly popular with disk drive designers for their ability to match the coefficient of thermal expansion of the actuator. Unfortunately, disk drives which utilize nonmagnetic actuator shafts are incompatible with conventional ferrofluid seals. A ferrofluid bearing seal for disk drives with nonmagnetic elements is needed.
DISCLOSURE OF THE INVENTION
A ferrofluid seal for a hard disk drive actuator bearing has two circular plates which are axially spaced apart about a nonmagnetic pivot shaft of the actuator. The plates are parallel and in close proximity to one another. The upper plate is made of magnetically-conductive steel and is mounted to a stationary sleeve which surrounds the shaft. The lower plate is mounted to the shaft and has an annular magnet with pole pieces on an upper surface. A magnetic ferrofluid is located between the magnet and the upper plate to complete the magnetic circuit and form a seal. The ferrofluid seal prevents bearing emissions such as grease oil vapor and aerosol droplets from contaminating the disk drive.


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Jul. 1983 IBM Internal Disclosure Bulletin (Seal To Isolate Actuator From Head/Disk Assembly).
Aug. 1983 IBM Internal Disclosure Bulletin (Enhanced Compact Magnetic Fluid Seal).

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