Note: Descriptions are shown in the official language in which they were submitted.
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FEl~O-FLIJID ~EARI~G
B~Cl~GROUND OF THE I~r~TEN'rI0~
In recent years, bearing assemb:L:ies such as
those dlsclssed in United States I.etters Patent.s Nos.
3,726.574, 3,746,407, 3,8~1,2&2 and 3,91~,773 'nave
selr-contail-led fluid PO(J1S~ 'ihose l?atent:.s are ~s~i~ned
to the same assi~nee as the present invention. Such
fluidic, low frictlon sel,-contained bearlngs are made
~; possi~le by the develop,-nent of magnetically responsive
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mag-netizable fluid given the name ferrofluid by i-ts
d~veloper,-Dr. Ronald-E Rosens~eig. Ferrofluid is
~escribed in Rosensweig's "Progress in l~errohydrodyna.mics,"
industrial ~esealch, ~ctober, 1970, Vo3. 12, No. 1~,
36~40. Ferrofluid as defined therein is a dispersion of
colloi~al magnetic pa.rticles in a liquid carrier~ These
par~icles tend to align the.mselves with applied magnetic
fiel~s. ~-t should be noted from the descri.ption of ferro--
fluid that ferrofluid n~ed not necessarily contain iron
or ferrous-t~e meta.l.. It is onIy necessary, for a fluid
to be so-called, that the fluid be magneti~,able or capable
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Of being influenced by magnetic fields. The term
"magne-tic fluid" is used interchangeably herein with
the term "ferrofluid".
~ he bearings described in the above-iden-tified
letters patent each concentrate the magnetic field at
particular axial positions along the shaft to produce a
seal for the ferro~luid. Typically vanes, or the like,
are used to distribute ferrofluid on the bearing surface
to maintain a sufficient fluid thickness to support or
lubricate the bearing.
More recently the assignee has obtained United
States Patent Number 4,254,961 issued March 10, 1981 for
a "Seal for a Fluid Bearing". The bearing shown and des-
cribed in that patent also concentrates the magnetic
field at the seal points, but the structure may be modified
according to this invention.
BRIEF DESCRIPTION OF T~IE INVENTION
The ferrofluid bearing of this invention uses a
magnetic sleeve as a bearing for a shaft. The magnetic
sleeve is a permanent magnet which produces a magnetic
field, having both radial and axial components, between
the bearing and the shaft. The axial'components are
directed inwardly toward the center of the bearing, and
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the ferrofluid is held within the bearillg. I,'he op~os:ing
surfaces of the shaft ancl be~ring mdy he contoured or
smooth a-t the opt:ion of the desiyner.
To produce the desired magnet-ic Eield configura-
tion, the bear;llg sleeve is maynetized with the pole faceson the oute~ and inner surfaces of the sleeve instead of the
usual practice of placing the poles on the encls of the
cylinder. The internal magnetization of the slee~e is
-radially di^ected.
To produce d cylindrical sleeve having a high
intensity magnetic field in a small volume and having- the
pole fa~es on the outer-and inner su:faces, the sleeve may~
be made oE platinum cobalt alloy or rare earth cobalt a:Ll.o~s
such as samarium cobalt alloys. Other pe~lanent magnet
materials may be used, however, at considerably lower flu~
fields.
The sleeve is either fabricated in axial slices
or is cut into axial slices. The slices are each magnetized
by placing them into an eIectromagnetic field which is
poled-to induce permanent magnet pole positions on the
ou~er and inner surface of the slices. The slices are
t~len assembled or reassembled into a cylindrical sleeve.
The shaft mav be either ferLomagnetic or non-
~erromagnetic. In a typicaL embodiment the shaft may
2S ha~.Je a thin layer of ferromaynetic material on its outer
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surface. If t~e shaft has ferromagnet.ic materi.a.l., the
operation is enhanced by the incl-ease in magnetic field
intensity wi-th:in the r~gion between the shaft and be~ring
It is there-Eore an object of this inventi.~n to
teach a new ferrofluid bearillg.
It is another o~ject of this invention to teacll
a method for fabr:icating a hollow cylindrical magnet with
its pole faces on the inner and outer surfaces thereol.
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~RIEF DFSCRIPTION OF THE D~AWINGS
G-ther objects will become apparen-t fror,l the
follo~7in~ descrip-tion, taken in connec-ti.on with the
accompanying drawings, in which:
E`igure 1 is a profile view of a bearing and shaft
according -to this invention,
Figure 2 is an end view of the apparatus of Figure
1, .
Figure-3 is a sectional view taken at 3-3 in
Fig-ure 2 and diagramming the magnetic field of the ~ -
cylindrical magnet, and
: 20 Figure 4 is a profile view of a typical electro- :
magnet magnetizing an axial slice o-f a cylindrical sleeve
: to produce pole faces on the inner and outer surface of an
assem~led cylinder.
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DET~ILED ~ESCRIl'q'~:C)N 0~ THE` ~N~7ENTIOI~
The ferroEluid bearinc3 of this lnvention use~s a
permaneLIt magne~ bearing structure 10 which preferably
has a gerlerally circularly cylindrical shapeO The
apparatus is nGt limited, howe~er, to a circular shape.
The structure 10 i5 shown as a right circular
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c~ylincler having a coaxial rigl~t circular cylindrical bore
-therein fo-^ receiving a shaft 12 and a space containincJ
ferrofluid 14 therebetween. The ferrofluid 14 ser~es as
a lubricant between the shaft ]~ and the surace 18 o
tne bore 20.
r~he bearing 10 and shaft 12 may rotate relative
to each other, but it is not important which rotates.
Both may rotate if desired.
The bearing 10 is magnetized with a polarlty
configuration ~herein the pole faces are on the outer
surface 16 and the irmer surface 18 -thereof. Such
polarity configuration produces a magnetic field having
both radial and a~ial components within the ferrofluid 14,
and the a~ial components are directed toward the center
of the bearin~ bore 20. The magnetic field is indicated
at 24 in Figul^e 3. The magnetic field holds the ferro-
fluid 14 wit11in the bore 20.
Tl-le shaft 12 may be of ferromagnetic material
which erihances~t.he ma-~netic field intensity in the ferro-
fluid 1~. It need not, however, be of such ferromagnetic
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mater:ial. IJ-I one prefexred emboclirne7l-~, only the sur~ace
oL th~ sha-'t is cover~d with ferro,ma~ne-t:ic materi.al.
Mos-t of the bearing support occurs near the ends
of the bore 2C. To reduce power loss due to viscous
d~mping, -~hc cliamet~r oF the .slla:Et 12 optionally may be
reduced near the center of the bore 20 in the region 22.
To magnetize cylindrical member 10, the member
10 is axially sliced into slices lOa,lOb, lOc, lOd, lOe,
lOf, lOg, lOh, and disassembled ~or magnetizing.
Alternatively, the slices lOa, lOb, lOc, lOd, lOe, lOf,
10~, and lOh, may be fabricated into the shape shown in
E'igure 4.~ For ~xample, .he slices may be cast or forged,
or they may be made by powder metall~rgy tec~miques.
-. A~ter the slices lOa, lOb, lOc, lOd, lOe, lOfp lOg, lOht
have-been magnetized, they are assembled or reassembled
into the cylinder shown in Figures 1 and 2~
To magnetize the slices they are placed in the
field of an electromagnet whi.ch induces a permanent
ntagnetism into the slice lOa with the pole faces on the
inner and outer surfaces 28, 29. The electromagnet 30 is
shown with one coil turn, but obviously it may include :
many more turns to produce the requited field intensity.
The e.lectromagnet 30 is energized, for example, ~rom a
DC en`ergy source 32.
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The bearillg of this inventiorl, because of a
radially d;rected internal magnetiza-tion, is a simplified
bearing ~hich adeqllately confines the ferroEluid without
leakin~.
Althou~l a d~scrip~ion of a typical apparatu3
- and method of this invention is sho~ in the Fi~ures and
described above, it is not intended that the invention
shall be limited by that description alone, but only
together with the accompanying claims.
What is claimed is:
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