Ball bearing oil/grease loss containment method

Details Ball bearing oil/grease loss containment method Ball bearing oil/grease loss containment method

1998-10-13

2001-01-30

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S480000, C384S484000, C277S562000, C277S925000

Reexamination Certificate

active

06179472

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to motors, and more particularly to methods for containing oil and/or grease loss in ball bearings of spindle motors.
2. Description of Related Art
Disk drives are computer mass storage devices from which data may be read and/or to which such data may be written. In general, they comprise one or more randomly accessible rotating storage media, or disks, on which data is encoded by various means. In magnetic disk drives, data is encoded as bits of information including magnetic field reversals grouped in tracks on the magnetically-hard surface of the rotating disks. The disks are stacked in a generally parallel and spaced-apart relationship and affixed at their inner diameter (“ID”) to a common hub which is rotationally coupled to a stationary spindle shaft by a pair of bearings, typically ball bearings.
Spindle motors for direct access storage devices (DASDs) currently utilize high quality ball bearings that are lubricated for life using a metered amount of grease. The ball bearings are generally fitted with non-contact rubber shields one on each side. The shields have a small radial gap (0.2 to 0.25 mm) at the ID side, which is principally determined by the manufacturing tolerances and are pressed lightly into the groove in the outer ring. The elastomer in the shield is compressed in the process to provide a sealing effect. In these shields, metal (steel) backing is bonded to the elastomer. The metal backing side faces the inside of the bearing the conventional approach used in most bearings today. The elastomer widely used in ball bearings today is Nitrile Butadiene Rubber (NBR).
Recent experiments and experiences have shown significant oil loss and grease loss for the above spindle motors when tested under accelerated conditions of temperature and speed. It appears that three of the significant sources of this loss are: (1) from the shield outer diameter (“OD”) contact area, (2) through the shield elastomeric material itself, and (3) from the shield ID gap.
The plausible mechanism of loss through shield/outer ring contact area is by creep or migration by virtue of insufficient scaling effect. The mechanism of oil loss through the shield is due to the permeation of oil molecules through the elastomer matrix. The plausible mechanisms are loss through aerosolization and loss via surface creep or migration and subsequent appearance of oil droplets on the outside surface of the shield. These droplets could then be either slung out due to centrifugal forces and/or evaporate. Loss through aerosolization increases greatly for increased rotational speeds and for higher temperatures because of reduced viscosity. Thus the ability to achieve higher than 10000 rpm for ball bearing based spindle motors depends on adequate containment of the grease and base oil within the bearings.
Previous designs in this area include various shield designs of the non-contacting type.
FIG. 1
shows the type of shield
100
currently used in most types of DASD spindle motors in use today.
FIG. 1
shows a cross sectional view of the shield
100
. The metal backing
100
is bonded to the elastomer shield
120
. The metal backing
110
faces the inside of the bearing in the conventional approach used in most bearings today. The elastomer
120
widely used in ball bearings today is Nitrile Butadiene Rubber (NBR). A first end
130
of the shield
100
contacts grooves at the outer race (not shown). A second end
140
forms a gap
142
at the inner race
144
.
Significant oil/grease loss can also occur at the shield ID gap in thc case of high speed (10000 rpm ) ball bearings especially at the upper end of the temperature specification (70 to 80 C). Prior shield designs of the non-contacting type however exhibit less than desirable oil/grease containment characteristics. For example,
FIGS. 2 and 3
show two types of shields
200
,
300
currently being used in two different types of spindle motors.
FIGS. 2 and 3
show a cross sectional view of the ball bearing, but because of symmetry only a portion of the view is shown.
In
FIG. 2
, a shield
210
faces the outer diameter
212
of the inner race
214
. Also shown is the cage
220
and the ball bearing
222
. In
FIG. 3
, the ID of the shield
310
faces a step
330
on the inner race
314
. The ID gap
318
offers some resistance to aerosol loss based on the gap
318
and the thickness of the shield
310
. The shield
310
in
FIG. 3
offers a slightly higher resistance to flow when compared to the shied
210
of
FIG. 2
by virtue of the small step
330
in the inner race
314
. Whether or not a step
314
is possible is determined by thickness of the inner race
314
.
Stainless steel shields are also used in ball bearings for spindle motors. Stainless steel shields offer some significant advantages over rubber shields: (1) Smaller gaps at the ID are possible with stainless steel shields because no molding process is involved. (2) Stainless steel shields can be much thinner than rubber shields (about one-half) because of higher strength, which would permit increased grease amounts to be charged into the bearings. In addition, stainless steel shields eliminate the mechanism of foil loss and of course a major source of outgassing (NBR) is eliminated with thc use of stainless steel shield.
FIG. 4
shows the front view of a commercially available stainless steel shield
400
for a 5×13 ball bearing, e.g. a stainless steel shield as manufactured by NSK Corporation, Japan. Eight equally spaced slits or slots
410
approximately 0.12 mm wide are made in the shield
400
for ease of insertion in the bearing outer ring groove. The stainless steel shields for a larger 6×15 bearing is of similar design also.
FIG. 5
shows the rear view
500
of the same shield. Protrusions
520
measuring approximately 0.08 mm are clearly visible at the positions corresponding to the slots
410
illustrated in FIG.
4
. Detailed and closer observations of these protrusions
520
reveal that the material
522
immediately next to them is not affected in terms of profile. Upon insertion of such a shield contact occurs at the protrusions
520
and far away from the protrusions. But, in the in-between areas
522
sufficient metal to metal contact is not likely to occur. This poses a major source of oil leakage path.
It can be seen that there is a need for improved shield designs for ball bearing based spindle motors that provide improved containment of grease and the base oil within the bearings at accelerated conditions of temperature and speed.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses improved shield designs for ball bearing based spindle motors that exhibit improved containment of grease and the base oil within the bearings at accelerated conditions of temperature and speed.
The present invention solves the above-described problems by providing improved shield designs at the shield OD contact area, the use of an impervious shield material, the use of barrier films, shield/bearing designs that use tortuous paths and labyrinth schemes for reducing the oil and grease loss from the shield ID gap of DASD spindle ball bearings, and improved stainless steel shield designs.
A system in accordance with the principles of the present invention includes at least one of an outer diameter shield improvements, an inner diameter shield improvements and an improved stainless steel shield design.
Other embodiments of a system in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that a ball bearing shield includes an elastomeric body having an outer diameter sealing structure at an outer contact area adjacent a race for providing a seal between the elastomeric body and the race.
Another aspect of the present inventi

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