US3506023A - Apparatus for controlling the flow of particles of magnetic material through an orifice - Google Patents

Apparatus for controlling the flow of particles of magnetic material through an orifice Download PDF

Info

Publication number
US3506023A
US3506023A US3506023DA US3506023A US 3506023 A US3506023 A US 3506023A US 3506023D A US3506023D A US 3506023DA US 3506023 A US3506023 A US 3506023A
Authority
US
United States
Prior art keywords
flow
particles
apparatus
orifice
magnetic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
Inventor
Robert M Bogart
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
US Air Force
Original Assignee
US Air Force
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by US Air Force filed Critical US Air Force
Priority to US71933668A priority Critical
Application granted granted Critical
Publication of US3506023A publication Critical patent/US3506023A/en
Anticipated expiration legal-status Critical
Application status is Expired - Lifetime legal-status Critical

Links

Images

Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16KVALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
    • F16K31/00Actuating devices; Operating means; Releasing devices
    • F16K31/02Actuating devices; Operating means; Releasing devices electric; magnetic
    • F16K31/06Actuating devices; Operating means; Releasing devices electric; magnetic using a magnet, e.g. diaphragm valves, cutting off by means of a liquid
    • F16K31/08Actuating devices; Operating means; Releasing devices electric; magnetic using a magnet, e.g. diaphragm valves, cutting off by means of a liquid using a permanent magnet
    • F16K31/086Actuating devices; Operating means; Releasing devices electric; magnetic using a magnet, e.g. diaphragm valves, cutting off by means of a liquid using a permanent magnet the magnet being movable and actuating a second magnet connected to the closing element
    • F16K31/088Actuating devices; Operating means; Releasing devices electric; magnetic using a magnet, e.g. diaphragm valves, cutting off by means of a liquid using a permanent magnet the magnet being movable and actuating a second magnet connected to the closing element the movement of the first magnet being a rotating or pivoting movement
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/206Flow affected by fluid contact, energy field or coanda effect [e.g., pure fluid device or system]
    • Y10T137/2082Utilizing particular fluid
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/206Flow affected by fluid contact, energy field or coanda effect [e.g., pure fluid device or system]
    • Y10T137/218Means to regulate or vary operation of device
    • Y10T137/2191By non-fluid energy field affecting input [e.g., transducer]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/5109Convertible
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00Fluid handling
    • Y10T137/6851With casing, support, protector or static constructional installations

Description

3 1 2 m 0 e 6 0 a. 5% M 3 W e Eh TCS RI AF2 R. M. BOGART FOR CONTROLLING THE FLOW OF P GNETIC MATERIAL THROUGH AN ORI SA 0 H 8 P 6 T w w 8. u H A OW MW 1 l A F R mm m0 mm W a m xgigg M April 14, 1970 R. M. BOGART 3,506,023

APPARATUS FOR CONTROLLING THE FLOW OF PARTICLES OF MAGNETIC MATERIAL THROUGH AN ORIFICE Filed April 8, 1968 2 Sheets-Sheet 2 United States Patent 3,506,023 APPARATUS FOR CONTROLLING THE FLOW OF PARTICLES OF MAGNETIC MATERIAL THROUGH AN ORIFICE Robert M. Bogart, Arlington, Mass., assignor to the United States of America as represented by the Secretary of the Air Force Filed Apr. 8, 1968, Ser. No. 719,336 Int. Cl. F16c 1/04 US. Cl. 13781.5 11 'Claims ABSTRACT OF THE DISCLOSURE An apparatus for controlling the flow of particles of magnetic material through an orifice. The apparatus has, as principal components, a valve and a hollow conduit. The valve component includes a round horseshoe permanent magnet on a rotatable shaft, a rotary solenoid energized by a power source, linkage to rotate the magnet 90 when the solenoid is energized, and a suitably placed flat coiled spring to urge the counter-rotation, and the return to the original position, of the magnet when the solenoid is de-energized. The hollow conduit includes, as an integral unit, an upper and a lower portion of magnetic material, a spacer of non-magnetic material interposed therebetween, and an orifice at each end of the hollow conduit. The valve and the conduit are in close proximity to each other, with the long axis of the conduit in a vertical position and parallel to the pole face portions of the round horseshoe magnet. When particles of magnetic material are introduced into the hollow conduit through the upper orifice, the rotational position of the horseshoe magnet relative to the conduit allows or prevents, as desired, the flow of the particles through the lower orifice.

BACKGROUND OF THE INVENTION This invention relates to the art of valves and, more particularly, to an apparatus for controlling the flow of particles of magnetic material through an orifice.

The term magnetic material, as used herein, is intended to mean material or substance which can be magnetized, i.e., the material or substance is not non-magnetic. Such magnetic materials are intended to include those which are referred to as ferromagnetic, paramagnetic and diamagnetic, but are not intended to be synonymous with magnetized materials, i.e.. magnets. Similarly, the term magnetic particle is not intended to mean magnetized particle.

A specific application of this invention is as a valve for controlling the fiow of ballast, in magnetic particle form, used for changing the altitude of large high-altitude balloons, such as the type used in scientific research and in experiments.

With reference to such use for my invention, it is noted that the ballast container is tethered near the mouth, i.e., the appendix, of the balloon, that the ballast consists of particles of magnetic material, that such particles are in the order of from .0049 to .0394 inch in diameter, that such particles are referred to as dust or grit or clean shot, that the altitude of the balloon is controlled by release of quantities of the particletype ballast, and that the present state-of-the-art devices of this type permit the flow of only a maximum of seven pounds of the particles per minute, but do not prevent the clumping or bunching of the particles, withsresultant malfunction of the ballast flow device due to clogging of the output orifice, and, thereby, causes loss of control of the altitude of the balloon and, perhaps, loss of the balloon.

3,505,023 Patented Apr. 14, 1970 "ice My invention prevents clumping or bunching of the particles, permits uninterrupted, but controlled flow of them, and increases the flow of the particles to approximately fifty pounds per minute, if such rate .of flow is desired.

Therefore, my invention obviates current problems in balloon ballast magnetic particle control devices.

Although reference has been made to the use of my invention in balloon art, it is obvious, as noted above, that this is but one specific application of my invention. My invention may be used in any art where the control of flow of magnetic particles is desired.

SUMMARY OF THE INVENTION This invention provides for an apparatus which allows or prevents the flow of particles of magnetic material through an orifice.

Therefore, an object of this invention is to permit the uninterrupted, but controlled, flow of magnetic particles through an orifice.

Another object, obviously, is to prevent the flow of magnetic particles through an orifice.

A further object of my invention is to provide an apparatus which will permit a much higher rate of flow, than is obtainable by present state-of-the-art devices, of magnetic particles through an orifice.

A still further object of my invention is to provide a highly reliable, and yet economical, apparatus for controlling the fiow of magnetic particles through an orifice.

These, and still other, objects of my invention will become readily apparent after a consideration of the description of my invention and of the drawings.

DESCRIPTION OF THE DRAWINGS FIGURE 1 is a plan view, partially schematic and with a fragmented portion, of a preferred embodiment of my invention;

FIGURE 2 is a perspective view of the embodiment shown in FIGURE 1, with cover tilted back and fragmented in part;

FIGURE 3 is a side elevation view with some portions in vertical cross-section and some in fragmentary form, of a schematic representation of my invention in use as a balloon ballast magnetic particle flow control device;

FIGURE 4 is a side elevation view, partially in vertical cross-section and schematic in form, of the principal components of my invention, and how they interact as a result of the applicable magnetic phenomena, when in a no-flow, i.e., closed, mode; and

FIGURE 5 is an end elevation view, partially in vertical cross-section and schematic in form, of the principal components of my invention, and how they interact as a result of the applicable magnetic phenomena, when in a flow, i.e., open, mode.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference to FIGURES 1 and 2, wherein the same components are similarly numbered, a rotary solenoid 10, such as the commercially available Ledex No. 129737- 026, with drive gear 11, is mounted on plate 51 and retained by nut 12 on shaft 13. Interposed between rotary solenoid 10, and nut 12, is coiled fiat spring 14 which, at one of its ends, is affixed to shaft 13.

Leads 21 connect power source 20 to rotary solenoid 10'.

On shaft 33 are positioned, as shown, round horseshoe permanent magnet 30, such as General Electric No. 5U35B, driven gear 31, and set screw collar 32. Shaft 33 is mounted on, and through, plate 52 with bearing 53 and plate 51. Horseshoe magnet 30 is preferably of the Alnico type with a holding force of from 5 to 11 pounds and the face of magnet 30 is normal to the axis of shaft 33.

Hollow conduit assembly 40, i.e. orifice tube assembly, includes, as an integral unit, two conduit sections 4} and 42 of magnetic material, such as iron, with a spacer 43, preferably of brass, interposed between conduitsection 41 and 42 and silver soldered to them at their interfaces, thereby making the unit or assembly an integral one. The hollow portion 44 of conduit assembly 40 extends throughout the assembly, is cylindrical in shape, and has a diameter of approximately /4 inch. Conduit assembly 40 has an outlet or orifice portion 45 and 46 at each end. A push in type ping, such as 47 in FIGURE 1, may be used as an adapter to vary the diameter of either orifice 45 or 46.

All components of my invention are mounted on a base plate 50 and are covered with cover 54, except that base plate 50 has an opening to permit orifice 46 of conduit assembly 40 to protrude and, similarly, cover 54 has an opening to permit orifice 45 to protrude through. Cover 54 protects the components from the elements and prevents dust and the back iiow of magnetic particles 62 from interfering with the operation of the components.

It is to be noted that the pole face portions of magnet 30 are parallel to the long axis of conduit assembly 40 and approximately .032-.035 inch therefrom.

MODE OF OPERATION OF THE EMBODIMENT As has been previously stated, one specific application of .my invention is in the balloon art where my apparatus may be effectively used as a ballast flow control device. That utilization is pictorially represented in FIGURE 3.

With reference to FIGURE 3, my apparatus is connected, in an inverted position, to the opening 61 of ballast container, hopper or bin 60. With my apparatus in a flow mode, i.e., open position, as shown in FIGURE 3, ballast 62, which consists of magnetic particles, flows through ballast container opening 61, through input orifice 46 of hollow conduit assembly 40, through the hollow portion 44 of assembly 40., and is emitted through output orifice 45 of assembly 40.

A rotation of an integral odd multiple of 90 of magnet 30 will stop the flow.

A description of the flow and no flow action of my apparatus can best be explained by reference to FIG- URE 4 and FIGURE 5.

In FIGURE 4, the principal components of my invention are shown. These are hollow conduit assembiy 40 and round horseshoe permanent magnet 30. Their relative positioning, as shown in FIGURE 4, is a no flow mode, i.e., closed position.

The operation, and applicable theory, in the no fiow mode is as follows: Conduit sections 41 and 42 are in close proximity to magnet 30. Since conduit sections 41 and 42 are of magnetic material, they become magnetized. Further, since sections 41 and 42 are near each other and across the pole gap in magnet 30, the magnetic lines of rorce are directed and intensified across the gap be= tween sections 41 and 42. It is to be noted at this point that a brass spacer 43 is interposed between sections 41 and 42, that spacer 43 is non-magnetic, and that spacer 43 is located adjacent to the gap between the pole faces of magnet 30. Thereby, sections 41 and 42 become effectively extensions of magnet 30. If, now, magnetic particles 62 are introduced into hollow portion 44, each particle 62 will itself become a magnet, will be attracted to each other and to the walls of hollow portion 44, and will block hollow portion 44 at brass spacer 43. A no flow or closed position results.

The operation, and applicable theory, in the flow mode, i.e.,-open position, is shown in FIGURE and is as follows: If magnet 30 is rotated 90, or an integral odd multiple, the magnetic lines of force near and across spacer 43 are neutralized and particles 62 in that area are demagnetized. In addition, since each pole, i.e., N and S, of magnet 30 is attempting, at the same time, to magnetize the same conduit sections. 41 and 42, the lines of force are neutralized. As a result, conduit sections 41 and 42., and the remainder of particles 62, are demagnetized. Therefore, particles 62 flow freely from ballast bin 60, through conduit assembly 40, and from output orifice 45.

With regard to the mechanical, electromechanical, and magnetic actions involved in the actual utilization of my apparatus as a balloon ballast flow control device, it is best to return to FIGURES 1, 2 and 3, for a detailed description.

With reference to FIGURE 3, when my apparatus is connected, in an inverted position, to the ballast bin 60, it is in the no flow or closed position. After the balloon is released and is in flight, if it is desired to change the altitude of the balloon, the ballast particles 62 are released rom the ballast bin 60 and through my apparatus. This is done as follows; With reference to FIGURES 1 and 2, the power source 20 is turned on by suitable means, such as a command signal from a ground-based station. The power from power source 20 and through leads 31 energizes rotary solenoid 10 which turns drive gear 11. Driven gear 32 is thereby rotated, as are rotatable shaft 33 and magnet 30. However, since flat coiled spring 14 is constrained to permit the rotation of magnet 30 to integral odd multiples of when magnet 30 reaches that degree of rotation, it stops and remains in that position. That position, as hereinbefore described, is the flow or open position. Ballast particles 62 are thereby released and the altitude of the balloon is changed. To return my apparatus to the no flow or closed position, and thereby prevent the flow of ballast, the power source 20 is turned off. Coiled spring 14 which has been in an expanded state during the power on phase, recoils, causing the 90 rotation back of magnet 30, by causing the counter rotation of drive gear 11, driven gear 31, and shaft 33.

While there has been shown and described the fundamental features of my invention, as applied to a preferred embodiment, it is understood that various substitutions and omissions may be made by those skilled in the art without departing from the spirit of the invention. For example: (a) bar magnets or electromagnets may be substituted for the round horseshoe magnet; and (b) a motor, rather than a rotary solenoid, could be used.

I claim:

-1. An apparatus for controlling the flow of particles of magnetic material comprising:

(a) means for generating magnetic flux;

(b) means for orienting said means for generating magnetic flux, so that the direction of said magnetic flux may be changed to an integral odd multiple of 90;

(c) and a hollow conduit assembly comprising a pair of axially aligned sections, each insulated from the other, wherein each section is in close proximity to a pole of said means for generating a magnetic flux, with the passageway of each section orthogonal to the rines of magnetic flux.

2. An apparatus for controlling the flow of particles of magnetic material comprising:

(a) means for generating magnetic flux, connected to a rotatable shaft having thereon a gear to be driven;

(b) means for orienting said means for generating magnetic flux, so that the direction of said magnetic flux may be changed 90;

(c) a drive gear adjacent to and meshing with said gear to be driven, and connected to said means for orienting said means for generating magnetic flux;

(d) means for rotating said drive gear;

(e) a hollow conduit assembly, in close proximity to said means for generating magnetic flux, vertically disposed and parallel thereto, and including, as an integral unit, sections of magnetic material with a nonmagnetic spacer interposed therebetween, with said magnetic sections and spacer hav ng a continuous cylindrical hollow portion of constant diameter throughout, with said hollow portion having an orifice at each end;

(f) means for varying the diameter of the orifices of said hollow portion of said conduit assembly;

(g) and means for housing all components.

3. The apparatus, as described in claim 2, wherein said means for generating magnetic flux is a round horseshoe permanent magnet.

4. The apparatus, as described in claim 2, wherein said means for generating magnetic flux are bar magnets of the permanent type.

5. The apparatus, as described in claim 2, wherein said means for generating magnetic flux is a solenoid with a power source. I

6. The apparatus, as described in claim 2, wherein said means for orienting said means for generating magnetic flux is a rotary solenoid, with a power source, with the shaft of said rotary solenoid having a coiled flat spring restraining rotation of said shaft to allow the direction of said magnetic flux to be changed 90 only.

7. The apparatus, as described in claim 2, wherein said means for orienting said means of magnetic flux is a motor, with a power source, with the shaft of said motor having a coiled fiat spring restraining rotation of said shaft to allow the direction of said magnetic flux to be changed 90 only.

8. The apparatus, as described in claim 2, wherein said means for rotating said drive gear is a rotary solenoid with power source.

9. The apparatus, as described in claim 2, wherein said means for rotating said drive gear is a motor with power source.

10.;The apparatus, as described in claim 2, wherein said means for varying the diameter of the orifices of said hollow portion of said conduit assembly is a push in type plug of the desired diameter.

11, The apparatus, as described in claim 2, wherein said means for housing all components includes a base plate, to which are connected said components, having a suitably located opening to allow an orifice of said hollow conduit assembly to protrude, and a cover, fitting over said components and fitting onto said base plate, with said cover having a suitably located opening to allow the other orifice of said hollow conduit assembly to protrude.

References Cited UNITED STATES PATENTS 3,417,771 12/1968 Ernst 137-815 HAROLD w. WEAKLEY, Primary Examiner US. Cl. X.R.

US3506023D 1968-04-08 1968-04-08 Apparatus for controlling the flow of particles of magnetic material through an orifice Expired - Lifetime US3506023A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US71933668A true 1968-04-08 1968-04-08

Publications (1)

Publication Number Publication Date
US3506023A true US3506023A (en) 1970-04-14

Family

ID=24889672

Family Applications (1)

Application Number Title Priority Date Filing Date
US3506023D Expired - Lifetime US3506023A (en) 1968-04-08 1968-04-08 Apparatus for controlling the flow of particles of magnetic material through an orifice

Country Status (1)

Country Link
US (1) US3506023A (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3701357A (en) * 1968-09-30 1972-10-31 Asea Ab Electromagnetic valve means for tapping molten metal
US3995661A (en) * 1975-09-22 1976-12-07 Wheelabrator-Frye, Inc. Flow control valve for magnetic particulate
US5113890A (en) * 1989-11-14 1992-05-19 Hylsa S.A. De C.V. Method and apparatus for regulating the flow of particulate ferromagnetic solids
US6044858A (en) * 1997-02-11 2000-04-04 Concept Engineering Group, Inc. Electromagnetic flow control valve for a liquid metal
US6321766B1 (en) 1997-02-11 2001-11-27 Richard D. Nathenson Electromagnetic flow control valve for a liquid metal with built-in flow measurement
US7249604B1 (en) * 2002-05-10 2007-07-31 Vasmo, Inc. Medical devices for occlusion of blood flow
US20100243240A1 (en) * 2005-11-18 2010-09-30 Blange Jan-Jette Device and method for feeding particles into a stream

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3417771A (en) * 1965-09-24 1968-12-24 Ernst Hans Flow control apparatus for fluent magnetic materials

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3417771A (en) * 1965-09-24 1968-12-24 Ernst Hans Flow control apparatus for fluent magnetic materials

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3701357A (en) * 1968-09-30 1972-10-31 Asea Ab Electromagnetic valve means for tapping molten metal
US3995661A (en) * 1975-09-22 1976-12-07 Wheelabrator-Frye, Inc. Flow control valve for magnetic particulate
US5113890A (en) * 1989-11-14 1992-05-19 Hylsa S.A. De C.V. Method and apparatus for regulating the flow of particulate ferromagnetic solids
US6044858A (en) * 1997-02-11 2000-04-04 Concept Engineering Group, Inc. Electromagnetic flow control valve for a liquid metal
US6321766B1 (en) 1997-02-11 2001-11-27 Richard D. Nathenson Electromagnetic flow control valve for a liquid metal with built-in flow measurement
US7249604B1 (en) * 2002-05-10 2007-07-31 Vasmo, Inc. Medical devices for occlusion of blood flow
US20100243240A1 (en) * 2005-11-18 2010-09-30 Blange Jan-Jette Device and method for feeding particles into a stream
US8087480B2 (en) 2005-11-18 2012-01-03 Shell Oil Company Device and method for feeding particles into a stream

Similar Documents

Publication Publication Date Title
US3570807A (en) Electromechanical control valve
US3368788A (en) Magnetic latch valve
US3202886A (en) Bistable solenoid
US3604959A (en) Linear motion electromechanical device utilizing nonlinear elements
US4489863A (en) Precision fluid dispense valve
US3874407A (en) Pulse width modulation control for valves
US4574841A (en) Rocker lever solenoid valve
US3070730A (en) Three-position latching solenoid actuator
US3379214A (en) Permanent magnet valve assembly
US3469258A (en) Rotating magnetically actuated display or indicator
US4795929A (en) Rotary actuator
US5010911A (en) Electromagnetic valve operator
US3206160A (en) Electromagnetic flow control system
US3977436A (en) Bi-stable valve apparatus
US6098456A (en) Anti-fraud liquid meters having a drive and driven magnets with double polarity faces
HU0103522A2 (en) Valve and its application
US5185542A (en) Electromagnetic pulse operated bi-stable brake
JPS6138863A (en) Polishing apparatus
GB2079412A (en) Solenoid valve
GB747727A (en) Improvements in or relating to magnetic devices for converting rotary motion into reciprocating motion or conversely
US6040752A (en) Fail-safe actuator with two permanent magnets
US2603103A (en) Variable inertia device
HU181067B (en) Anisotropic permanent magnet and process for preparing such magnet
US3218523A (en) Electromagnetic device having a permanent magnet armature
GB1512315A (en) Switchable permanent magnetic holding devices