U.S. patent number 3,848,363 [Application Number 05/334,000] was granted by the patent office on 1974-11-19 for apparatus for treating objects with particles moved by magnetic force.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to James F. Feldhaus, William R. Lovness.
United States Patent |
3,848,363 |
Lovness , et al. |
November 19, 1974 |
APPARATUS FOR TREATING OBJECTS WITH PARTICLES MOVED BY MAGNETIC
FORCE
Abstract
The apparatus comprises a device for generating a rotating
magnetic field, small magnetic particles capable of being moved by
the rotating magnetic field, and a surface or container to confine
the moving particles to a predetermined area.
Inventors: |
Lovness; William R. (West Saint
Paul, MN), Feldhaus; James F. (Oak Park Heights, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
23305120 |
Appl.
No.: |
05/334,000 |
Filed: |
February 20, 1973 |
Current U.S.
Class: |
451/36; 451/113;
241/1; 366/273; 241/170 |
Current CPC
Class: |
B24B
31/102 (20130101) |
Current International
Class: |
B24B
31/00 (20060101); B24B 31/10 (20060101); B24b
031/00 (); B24b 001/00 () |
Field of
Search: |
;51/7,17,26,163,313-318
;259/1,DIG.46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kelly; Donald G.
Attorney, Agent or Firm: Alexander, Sell, Steldt and
Delahunt
Claims
What is claimed is:
1. An apparatus for treating objects with particles moved by
magnetic force comprising in combination:
a. means for generating a rotating magnetic field,
b. magnetic particles which are capable of being rotated by the
magnetic field, and
c. means confining the rotating magnetic particles to a
predetermined area within the effective influence of said magnetic
field, wherein said means for generating a rotating magnetic field
comprises at least four overlapping coils that are arranged in a
generally circular pattern of opposed pairs and that are energized
with two or more out of phase sources of alternating current so
that opposed coils are of opposite magnetic polarity and of the
same phase, and generation of said rotating magnetic field causes
rotation of the magnetic particles on their axes and also causes
their rotation in an orbital path about the axis of rotation of the
rotating field and objects placed in their path are subjected to
aggressive surface treatment.
2. The apparatus of claim 1 wherein the magnetic particles have a
magnetization of about 50 gauss/gm. and a magnetic coercivity of at
least 100 oersteds.
3. Method for treating objects with particles moved by magnetic
force comprising:
confining magnetic particles to a predetermined area,
generating a rotating magnetic field with a single axis of rotation
within said predetermined area, said magnetic field comprising at
least four overlapping coils that are arranged in a generally
circular pattern of opposed pairs that are energized with two or
more out of phase sources of alternating current so that opposed
coils are of opposite magnetic polarity and of the same phase, said
magnetic field being of sufficient intensity to cause rotation of
the magnetic particles on their axes and also to cause their
rotation in an orbital path about the axis of rotation of the
rotating field, and
placing the object to be treated within the path of said rotating
magnetic particles for a period of time sufficient to cause surface
treatment thereof.
4. An apparatus for treating objects with particles moved by
magnetic force comprising in combination:
a. means for generating a rotating magnetic field,
b. magnetic particles which are capable of being rotated by the
magnetic field, and
c. means confining the rotating magnetic particles to a
predetermined area within the effective influence of said magnetic
field, wherein said means for generating a rotating magnetic field
comprises overlapping coils that are arranged about said
predetermined area and that are energized with two or more out of
phase sources of alternating current which will produce a rotating
magnetic field having a single axis of rotation within said
predetermined area, and generation of a rotating magnetic field
causes rotation of the magnetic particles on their axes and also
causes their rotation in an orbital path about the axis of rotation
of the rotating field and objects placed in their path are
subjected to aggressive surface treatment.
5. Method for treating objects with particles moved by magnetic
force comprising:
confining magnetic particles to a predetermined area,
generating a rotating magnetic field with a single axis of rotation
within said predetermined area by use of a generating device
therefor comprising overlapping coils that are arranged about said
predetermined area and that are energized with two or more out of
phase sources of alternating current, said magnetic field being of
sufficient intensity to cause rotation of the magnetic particles on
their axes and also to cause their rotation in an orbital path
about the axis of rotation of the rotating field, and
placing the object to be treated within the path of said rotating
magnetic particles for a period of time sufficient to cause surface
treatment thereof.
Description
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for treating objects with
particles moved by magnetic force.
For a long time there has been a need for an apparatus which could
be used to surface treat, e.g., finish or clean, irregular-surfaced
solid articles. Heretofore surface finishing, e.g., polishing,
descaling, deburring, and the like, has been achieved by tumbling,
sandblasting, mechanical or hand buffing, or by other means which
are not entirely satisfactory for various reasons. Tumbling and
sandblasting are difficult to control. Sandblasting also presents a
health hazard due to the considerable air-borne particulate matter
produced by such an operation. Machine and hand buffing are both
difficult and extremely expensive.
Prior to our invention, cleaning methods utilized cleaning baths
agitated by mechanical or ultrasonic stirring devices, soaking in
chemical solutions, vapor degreasing, and other less efficient or
more hazardous methods. While all of these methods have some merit,
each has one or more drawbacks. Solutions containing cleaning
compositions are generally corrosive. Solvents used in vapor
degreasing produce toxic vapors. Mechanical and ultrasonic
agitation of cleaning solutions fail to provide the cleanliness
required by some specifications.
Surface treating apparatus may be seen in Simjian U.S. Pat. No.
2,735,232, wherein an alternating magnetic field is applied to
magnetizable particles to magnetize them and cause them to move in
small circular or spiral paths to polish objects placed in their
such paths. And, although Simjian alleges he utilizes a rotating
magnetic field, his disclosure fails to teach the use of his
device, as will hereinafter be shown. Rather, Simjian's device
generates a magnetic field which sets up a complex magnetic flux
pattern causing the magnetizable particles to move as described
above. See also Hershler, U.S. Pat. No. 3,219,318, wherein motion
is imparted to permanent magnets by a magnetic field which varies
in direction with time, causing the magnets to move in a complex
pattern for a similar purpose. Although Hershler suggests that the
magnetic field may be provided by a number of ways, he does not
mention the use of a rotating magnetic field among them. These
prior art devices do not utilize a rotating magnetic field and
hence are far less efficient than the apparatus of the present
invention.
SUMMARY OF THE PRESENT INVENTION
The present invention provides an apparatus which is capable of
efficiently cleaning and finishing regular or irregular shaped
solid articles of metal, plastics, wood, ceramic, glass and other
materials. The apparatus is far more economical to operate than the
surface treating devices mentioned above. The apparatus of the
invention cleans articles much more rapidly than the prior art
devices described above. Typically, the apparatus of the invention
cleans (to the same degree of cleanliness) in half the time
required for such prior art devices, as will be shown, providing a
considerable savings in time and expense. Additionally, the
apparatus of the invention can clean to a degree of cleanliness
heretofore unattainable by use of prior art devices and clean a
number of articles in a single cleaning operation with an unusually
high degree of cleaning uniformity from article to article.
The apparatus comprises a means for generating a rotating magnetic
field, magnetic particles which are capable of being rotated by the
magnetic field and a surface or container for confining the
magnetic particles to a predetermined area or volume. It has been
discovered that magnetic particles acted upon by a rotating
magnetic field will rotate on their axes and the rotating particles
will revolve in an orbital path about an axis established by the
center of rotation of the rotating magnetic field. Such rotation
and revolution produces aggressive movement of the particles,
providing unexpectedly superior surface treatment of objects placed
in their path.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of one embodiment of an apparatus according
to the invention, with some parts being shown in section to
facilitate understanding.
FIG. 2 is a vertical section view, taken at line 2--2 of the
apparatus shown in FIG. 1, but reduced in scale.
FIG. 3 is a graphic illustration depicting two-phase alternating
current.
FIG. 4 is a plan view of a slotted annulus which may provide one
component for the apparatus of the invention.
FIGS. 5 and 6 show a preferred wiring arrangement for the device
depicted in FIG. 1 and its relationship to the annulus shown in
FIG. 4, the annulus being shown in an expanded view revealing its
entire inner edge.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred device for generating a rotating magnetic field is
characterized by having at least four overlapping coils or windings
of insulated wire that are arranged in a generally circular pattern
of opposed pairs and that are energized with two or more
out-of-phase sources of alternating current, so that opposed coils
are in phase but of opposite magnetic polarity.
Such a device is illustrated in FIGS. 1 and 2 wherein opposed coil
pair 30a and 30b is arranged about a cylindrical container 32 and
encircled by opposed coil pair 31a and 31b such that the abutting
ends of the outermost coil pair 31a and 31b lie intermediate the
ends of the inner coil pair 30a and 30b, producing an overlapping
arrangement. Coils 30a and 30b are energized from the same
alternating current supply in such a way as to provide opposite
magnetic polarity in each. Similarly, coil pair 31a and 31b are
operated from the same alternating current supply so that they,
too, are of opposite polarity.
The alternating currents energizing each coil pair must have a
phase relationship which is not the same. FIG. 3 illustrates two
alternating currents I.sub.x and I.sub.y, whose amplitudes are the
same but whose phase relationship is 90.degree.. If current I.sub.x
were used to energize coil pair 30a, and 30b, e.g., and current
I.sub.y used to energize coil pair 31a and 31b, a north and south
pole would be produced opposite one another in the annulus defined
by the coils, which poles would rotate as the current alternates.
Hence a rotating magnetic field is produced.
The speed at which the magnetic field rotates depends upon the
frequency of alternating current. For a typical 60 Hz power supply,
60 revolutions will be made in 1 second, or 3,600 revolutions in 1
minute.
The presently most preferred rotating field generating device has
four or more coils, which may be wound on a slotted annulus 26 such
as that shown in FIG. 4. The wires forming each coil pass through
slots 1-24 of annulus 26 and form overlapping coil groups A, B, C
and D, as shown in FIGS. 5 and 6.
The annulus upon which the wires are wound may be formed of laminae
of high permeability steel containing from 0.25 percent to about
3.50 percent silicon, individual laminae being generally from 0.005
to 0.100 inch thick. The laminae may be coated with an insulating
varnish to reduce eddy-current losses.
A simple embodiment of the rotating field generating device
described above may be provided by the stator of a conventional AC
electric motor, with some modification thereof. Alternatively, the
rotating field generating device can be disposed within a
cylindrical container and used to rotate magnetic particles about
its exterior surface. Such a generating device would resemble the
rotating part of two pole wound rotor-type electric motor.
Additionally, a rotating field generating device for moving the
magnetic particles on a flat surface may be prepared by forming
coil slots circumferentially about one end of a suitable cylinder,
inserting the coils and energizing the coils, thus producing a
rotating field adjacent the end. Magnetic particles on a flat or
otherwise shaped surface adjacent the end will be revolved about
the axis of rotation of such a device. It is also possible to
generate a rotating magnetic field by mechanically revolving
permanent magnets either around or within the container.
As previously mentioned, the apparatus utilizes magnetic particles,
each of which is an individual permanent magnet and hence
susceptible to the influence of an electro-magnetic field. Such
particles include gamma iron oxide (Fe.sub.2 O.sub.3), hard barium
ferrite, (BaO .sup.. 6Fe.sub.2 O.sub.3), particulate
aluminum-nickel-cobalt alloys, or mixtures thereof. Suitable
magnetic particles have been found to have a magnetization (M) in
excess of 10 gauss per gram, magnetization being a measure of the
magnetic field intensity of the material from which the particles
are prepared. Hard BaO .sup.. 6Fe.sub.2 O.sub.3 has a magnetization
of about 70 gauss/gm. and gamma Fe.sub.2 O.sub.3 has a
magnetization of about 50 gauss/gm. Also, it has been found that
suitable magnetic particles should have a magnetic coercivity
(defined as the opposite sign field necessary to reduce the
magnetization to zero) greater than the electro-magnetic field (H)
applied to cause physical movement of the particle.
Electro-magnetic fields of about 100 to about 1000 oersteds and
higher have been used to move the particles. Hard BaO .sup..
6Fe.sub. 2 O.sub.3 has a magnetic coercivity of about 3000 oersteds
and gamma Fe.sub.2 O.sub.3 has a magnetic coercivity of about 300
oersteds. Magnetic particles having a magnetic coercivity less than
about 100 oersteds have been found not to be particularly suited
for use in the invention because application of external
electro-magnetic fields sufficiently strong to move the particles
causes demagnetization. Application of an electro-magnetic field to
the permanently magnetic particles causes them to experience a
torque tending to rotate them to an alignment parallel to the
field. Rotation of the magnetic field causes the particles to
rotate on their axes and to revolve in an orbital path about the
axis defined by the rotating field.
The size of the magnetic particles will vary over a considerable
range depending upon the particular use. For cleaning, the
particles may be between 0.01 - 20 microns in diameter, or larger.
Other applications, e.g., grinding, polishing, burnishing,
ball-milling, etc., may utilize particles from 0.1 micron to 2
inches in diameter, or larger.
For some applications it may be advantageous to provide the
magnetic particles with an inert coating to protect them from
chemical attack by the media in which they are used. For other
applications it may be advantageous to provide the magnetic
particles with an abrasive coating to increase their
abrasiveness.
The magnetic particles may be used in a gaseous atmosphere such as
air or in a carrier liquid such as water, kerosene, carbon
tetrachloride, acetone, benzene, toluene, perchloroethylene, etc.
The carrier liquid should be chosen so that it will not react with
the magnetic particles or the articles being cleaned or polished.
The carrier liquid may contain additional components such as
abrasive particles, bactericides, pH regulators, alkaline builders,
buffing agents, softeners, surfactants, etc.
For cleaning operations, the incorporation of a cleaner in the
carrier liquid is required. The specific cleaner composition
preferably utilized is one which would normally be used to clean
the articles and which is compatible with the carrier liquid.
Oil-based cleaners are generally used with organic solvent carrier
liquids, and surfactants are generally used with aqueous carrier
liquids. The pH of the carrier solution should not be excessively
high or low because strongly acidic or strongly alkaline solutions
may attack the particles or the articles being cleaned.
If desired, non-magnetic particles such as abrasive particles or
particles which may be non-abrasive or weakly abrasive (e.g., small
glass spheres) may be incorporated into the liquid cleaner to
obtain enhanced cleaning. Additionally, surfactant may be coated on
the magnetic particles to provide enchanced cleaning; surfactant
coated magnetic particles are disclosed in Feldhaus U.S. Pat. No.
3,695,934. For effective cleaning, the volume ratio of particulate
(whether magnetic particles or abrasive particles) to liquid is in
the range of about 1:100 to 30:100, preferably about 15:100 to
25:100.
Cleaning or polishing of objects is preferably achieved by placing
the object to be cleaned, magnetic particles, carrier liquid (if
used), abrasive particles (if used), and cleaner (if used) in a
non-magnetic container within the rotating field generating device.
The rotating field is generated by energizing the previously
described coil arrangement with alternating current.
In accordance with the invention, apparatus comprised of a rotating
field generating device, container, and magnetic particles was used
to clean synthetically soiled test tags to determine cleaning
efficacy. Additionally, prior art devices according to
aforementioned U.S. Pat. Nos. 2,735,232 and 3,219,318 were prepared
and also evaluated for cleaning efficacy for purposes of
comparison. When the evaluations were made, care was taken to
operate each device in a particular test situation at the same
energy level per unit volume of magnetic particles.
The magnetic particles used in the evaluations described below
consisted of surfactant-coated barium ferrite particles prepared by
mixing 2000 parts distilled water, 400 parts of an aqueous solution
of 30 parts polyethylene glycol ether surfactant ("Tergitol
15-S-12"), 15 parts polyethylene glycol ether surfactant ("Tergitol
15-S-5"), 5 parts triethanol amine and 50 parts water, 800 parts
one-micron unmagnetized barium ferrite, and 800 parts 500-mesh
silicone carbide abrasive powder, then ballmilling the mixture for
16 hours, and finally magnetizing the mixture by briefly exposing
400 gram portions thereof to a 6000-10000 gauss magnetic field. (In
the mixture described above, and in the description which follows
all "parts" are by weight unless otherwise specified.)
The effectiveness of cleaning utilizing both the apparatus of the
invention and the prior art devices was determined by first soiling
round aluminum tags with a predetermined amount of synthetic soil,
cleaning the articles, and determining the amount of residual soil.
The aluminum tags, 24 gauge and 13/8 inch diameter, were first
polished to a surface roughness of RMS-12 micro inches, thoroughly
cleaned, and then synthetic soil applied.
The synthetic soil was comprised of 1.2 parts by weight anhydrous
lanolin, 0.0485 part C.sup.14 tagged 1-micron carbon black, 29.3
parts untagged carbon black, 23.4 parts magnesium silicate, 117
parts kerosene, and 29.3 parts lubricating oil. This mixture was
first ball milled 1 hour, then painted in the center of one surface
of the tag as a three-fourths inch diameter dot and dried thereon
at 65.degree.C. for 1 hour.
The initial concentration of radioactivity is determined with a gas
Geiger counter and the tags are then subjected to various surface
treatment procedures as hereinafter described, the radioactivity
again determined. The amount of residual radioactivity was
subtracted from the initial concentration, the difference divided
by the initial radioactivity and the product multiplied by 100, the
result being expressed as "percent soil remaining" in tabular form
below.
EVALUATION NO. 1
The apparatus according to the invention included a rotating
magnetic field generating device which was originally a one-half
horsepower electric motor stator comprised of a ring-like
lamination (formed of 53 0.029-inch thick high permeability steel
annuli) having a 5.5-inch outer diameter, a 2.8-inch inner diameter
and having 24 slots uniformly about its inner circumference, with
windings formed of insulated copper wire of the size designated
below, forming a two pole single phase arrangement. The lamination
is shown in FIG. 4 by reference numeral 26 with the slots being
numbered from 1 to 24. FIG. 5 shows the placement of the starting
windings with respect to the slots of the laminations, the windings
forming coil groups A and B, and FIG. 6 shows the placement of the
running windings which form coil groups C and D. The A coil group
was wound with the same number of turns as the B coil group, and
the C coil group with the same number of turns as the D coil group
in the following manner:
Starting Winding (21 AWG copper) Slots Group A Group B Turns
______________________________________ 1 and 12 13 and 24 40 2 and
11 14 and 23 32 3 and 10 15 and 22 30 4 and 9 16 and 21 23 5 and 8
17 and 20 14 Running Winding (19 AWG copper) Slots Group A Group B
Turns ______________________________________ 7 and 18 6 and 19 56 8
and 17 5 and 20 52 9 and 16 4 and 19 46 10 and 15 3 and 18 37 11
and 14 2 and 17 18 ______________________________________
The stator was modified to provide a phase difference as close to
90.degree. as possible by adding a 215-259 microfarad capacitor in
parallel with its existing 324-389 microfarad starting capacitor
and energized with 24 to 36 volts at 60 Hz, producing an energy
input of 8.8 watts per cubic inch.
A 400 ml "Pyrex" glass breaker was situated within the opening of
the device described above to contain magnetic particles and five
of the test tags were held on a rack within the beaker.
The prior art device, made according to FIG. 1 of U.S. Pat. No.
3,423,880, consisted of a 3-inch diameter, 4-inch long cylindrical
tank having a solenoid formed of 400 turns of 18 AWG insulated
copper wire on a steel laminate adjacent one side of its
cylindrical wall. Five of the previously described soiled test tags
were attached on a rack within the tank. The tank then was filled
with the previously described magnetic particles and the apparatus
was operated with 60 Hz current at a voltage sufficient to provide
8.8 watts per cubic inch.
After cleaning for 30 seconds each device was shut off and the tags
removed, rinsed with deionized water, dried and checked for
radioactivity. Thereafter the same tags were returned to their
respective devices for additional 30 second periods, and cleaned
therein until the tags were substantially clean, i.e., until only
about 5-6 percent of the soil remained, with results as
follows:
Table 1 ______________________________________ % Soil Remaining Run
Time U.S. Pat. No. Present (sec.) 3,423,880 S.D..sup.1 Invention
S.D..sup.1 ______________________________________ 30 65 18 43 7 60
43 7 19 5 90 21 6 6 3 120 16 7 2 1 150 6 5 -- --
______________________________________ .sup.1 Standard
deviation
The prior art device moved the magnetic particles in a linear path
away from the surface adjacent the solenoid, producing a stream
which separated at the opposite surface and attempted to converge
again at its source, the gross effect being movement of the
particles in small circular paths. The apparatus of the invention,
on the other hand, moved the particles in a circular path about a
single axis defined by the axis of the rotating field generating
device.
As is apparent, the apparatus of the present invention cleaned the
test tags much faster than did the prior art device. For an
equivalent run time, i.e., 120 seconds, the apparatus of the
invention had cleaned 800 percent better than the prior art
device.
EVALUATION NO. 2
The apparatus according to the invention was the same as that
described in Evaluation No. 1 above except the operating power was
increased to 17.6 watts per cubic inch.
The prior art device was also that of U.S. Pat. No. 3,423,880
(described above) except that it was operated with the cleaning
tank only half full, as recommended therein, thereby increasing the
operating power to 17.6 watts per cubic inch. The test results were
as follows:
Table 2 ______________________________________ % Soil Remaining Run
Time U.S. Pat. No. Present (sec.) 3,423,880 S.D..sup.1 Invention
S.D..sup.1 ______________________________________ 30 65 -- 37 -- 60
26 -- 6 -- 90 3 -- -- -- ______________________________________
.sup.1 Standard deviation cl EVALUATION 3
The apparatus according to the invention included a rotating
magnetic field generating device comprised of a 33/4 -inch high,
10-1/2 -inch outer diameter, 6-3/8 -inch inner diameter annulus
having 27 slots equally spaced about its inner wall, the device
being wired in a 3 phase arrangement with 136 turns of number 20
insulated copper wire per coil. The magnetic particle container,
5-inches in diameter and 31/4 -inches long, was fitted within the
central opening of the annulus. Test tags were held in the
container on a rack therefor, and the container was filled with
magnetic particles.
The prior art device was a 3 pole annular arrangement prepared
according to FIG. 3 of U.S. Pat. No. 2,735,232 approximately the
same size as the apparatus described in the previous paragraph,
including the same size particle container. Each of the poles was
wound with 200 turns of 18 AWG insulated copper wire.
Test tags were attached to racks in the containers of each device
and their containers filled with the magnetic particles described
above. Both devices were energized at 6.3 watts per cubic inch for
30 second time periods as described above with results as
follows:
Table 3 ______________________________________ % Soil Remaining
FIG. 3 Run Time U.S. Pat. No. Present (sec.) 2,735,232 S.D..sup.1
Invention S.D..sup.1 ______________________________________ 30 62
13 27 12 60 32 15 19 12 90 22 17 2 2
______________________________________ .sup.1 Standard
deviation
EVALUATION NO. 4
The apparatus according to the invention included a rotating
magnetic field generating device comprised of a two pole, three
phase alternator stator having 35 turns per coil of 17 AWG
insulated copper wire. The stator was 3-3/4 -inches high, had an
outer diameter of 10-1/2 -inches and an inner diameter of 6-3/8
inches. A 6-3/8 inch diameter 3-3/4 -inch high container was
inserted into the bore of the stator to contain the magnetic
particles and test tags.
The prior art device was a 4 pole annular arrangement prepared
according to FIG. 4 of U.S. Pat. No. 2,735,232 approximately the
same size as the apparatus described in the previous paragraph.
Each pole was wound with 180 turns of 15 AWG insulated copper wire
and connected as shown in the aforementioned patent drawing.
Utilizing equivalent amounts of magnetic particles and test tags,
the devices were operated at 6.3 watts per cubic inch for 30 second
periods with results as follows:
Table 4 ______________________________________ % Soil Remaining
FIG. 4 Run Time U.S. Pat. No. Present (sec.) 2,787,854 S.D..sup.1
Invention S.D..sup.1 ______________________________________ 30 50
17 10 8 60 23 11 2 3 90 7 5 -- --
______________________________________ .sup.1 Standard
deviation
* * * * *