US3341940A - Method of making a permanent magnet - Google Patents

Method of making a permanent magnet Download PDF

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US3341940A
US3341940A US268782A US26878263A US3341940A US 3341940 A US3341940 A US 3341940A US 268782 A US268782 A US 268782A US 26878263 A US26878263 A US 26878263A US 3341940 A US3341940 A US 3341940A
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conglomerates
magnetically anisotropic
particles
receptacle
magnetic field
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US268782A
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Tomholt Frits
Witteveen Willem Eise
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0273—Imparting anisotropy
    • Y—GENERAL 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
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/4902—Electromagnet, transformer or inductor
    • Y10T29/49075—Electromagnet, transformer or inductor including permanent magnet or core
    • Y10T29/49076—From comminuted material

Definitions

  • ABSTRACT DISCLOSURE Our invention relates to a method of manufacturing a magnetically anisotropic body and to a magnetically anisotropic body manufactured by this method.
  • Magnetically anisotropic magnets have been made by compressing a finely divided permanent magnetic material .in a magnetic field which orients the magnetic material, after which the compressed oriented material is sintered into a highly coherent body. Naturally, it is desirable in this case that the magnetic orientation produces a maximum effect, so that the compressed mass is indeed strongly magnetically anisotropic.
  • the particles which should be oriented mutually in parallel with their easy direction of magnetization show a tendency to conglomerate because they attract each other magnetically while forming magnetically isotropic conglomerates, as a result of which the effect of the magnetic orientation is decreased.
  • a further object of our invention is to provide a meth- 0d of manufacturing anisotropically permanent magnets having improved anisotropic properties.
  • the invention is of particular importance for the manufacture of ceramic anisotropic magnets having as the constituent essential for the permanent magnetic properties at least one material, in the form of hexagonal crystals, with a chemical composition according to the formula M0.6Fe- O where M is at least one of the metals Ba (barium), Sr (strontium) and Pb (lead).
  • M is at least one of the metals Ba (barium), Sr (strontium) and Pb (lead).
  • the proportions of the Weiss domains of the said crystals generally lie within the range of approximately 1 to 3 microns, so that for an average particle size under 1 micron, for example approximately 0.3 micron, by far most of the particles each are single Weiss domains.
  • these particles are micro-magnets magnetized spontaneously and up to the saturation, which have a strong tendency to conglomerate while forming the above-mentioned magnetically isotropic conglomerates.
  • the present invention offers a means which is excellently suited to this purpose.
  • the permanent magnetic material from which the magnet body to be manufactured is constituted, is disintegrated and whirled to form a cloud of dust in a container which is closed with a cover on the inside of which the above-mentioned magnetically anisotropic conglomerates, i.e. threads, chains or skeins deposit.
  • the magnetic field under the influence of which the magnetically anisotropic threads, chains or skeins are formed, is usually produced by an electromagnet which is rendered operative after at least a part of the permanent magnetic material is disintegrated to an average particle size under 1 micron and is whirled to form a cloud of dust.
  • the electromagnet is provided in the cover of the container.
  • Finely-divided permanent magnet material 8 e.g. barium hexaferrite, BaO.6Fe O initially ground in a ball mill, is placed in a metal container 1 provided with a metal cover 4 which hermetically seals the container.
  • Cover 4 is provided with a neck 5 in which a soft iron magnet core 6 is provided which is wound with wire turns 7, the core and the wire turns together forming an electromagnet.
  • Extending through the bottom of the container is a shaft 2 which supports a set of blades 3 for rotation.
  • the permanent magnetic powder is disintegrated by the metal bands. rotating at high speed, to an average particle size of approximately 0.5 micron, and whirled to form a cloud of dust.
  • the electromagnet is switched on.
  • the cover is removed from the container, its lower side placed over a filling funnel, and the electromagnet switched off.
  • the magnetically anisotropic chains are no longer attracted by the cover and fall into the filling funnel. From there the mass is transferred to a die, in which by means of an electromagnet a substantially homogeneous magnetic field is produced.
  • the mass is then compressed in the magnetic field under a pressure of 0.5 ton/cmfi.
  • the compressed body is removed from the die and sintered by heating it for 24 hours at a maximum temperature of 1290 C.
  • the resulting magnet body at room temperature has a (BH) of 3.8 l0 gauss oersted and a magnetic anisotropy, expressed in the value of the quotient B ll/B l, of 4.0 (where 13,11 is the maximum remanence measured in a direction parallel to the principal direction of magnetization and B l the remanence measured in the direction at right angles to the di- J; rection in which the maximum remanence B ll is measured).
  • a method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles in the presence of a magnetic field into a body, and sintering said body to form the same into a highly coherent body.
  • a method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material having a composition consisting of MO-6Fe O where M is a metal selected from the group consisting of Ba, Sr and Pb in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles in the presence of a magnetic field into a body, and sintering said body to form the same into a highly coherent body.
  • a method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material consisting essentially of BaO-6Fe O in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles into a body in the presence of a magnetic field to form a magnetically anisotropic body, and sintering said body to form the same into a highly coherent body.
  • a method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material consisting essentially of BaO-6Fe O in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles into a body in the presence of a magnetic field to form a magnetically anisotropic body, and sintering said body at a temperature of about 1290 C. for twenty-four hours to form the same into a highly coherent body.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Hard Magnetic Materials (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)

Description

Sept 1967 F. TOMHOLT ETAL v METHOD OF MAKING A PERMANENT MAGNET Filed March 28, 1963 INVENTOR FRITS TOMHOLT BY WILLEM EISE WITTEVEEN W AGENT United States Patent 3,341,940 METHOD OF MAKING A PERMANENT MAGNET Frits Tomholt and Willem Eise Witteveen, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 28, 1963, Ser. No. 268,782 Claims priority, applicatizo7rzNgtherlands, Mar. 29, 1962,
4 Claims. (51. 29-608) ABSTRACT DISCLOSURE Our invention relates to a method of manufacturing a magnetically anisotropic body and to a magnetically anisotropic body manufactured by this method.
Magnetically anisotropic magnets have been made by compressing a finely divided permanent magnetic material .in a magnetic field which orients the magnetic material, after which the compressed oriented material is sintered into a highly coherent body. Naturally, it is desirable in this case that the magnetic orientation produces a maximum effect, so that the compressed mass is indeed strongly magnetically anisotropic. However, it has been found that the particles which should be oriented mutually in parallel with their easy direction of magnetization show a tendency to conglomerate because they attract each other magnetically while forming magnetically isotropic conglomerates, as a result of which the effect of the magnetic orientation is decreased.
It is a principal object of our invention to minimize the tendency of the particles to form isotropic conglomerates during orientation.
A further object of our invention is to provide a meth- 0d of manufacturing anisotropically permanent magnets having improved anisotropic properties. These and further objects of the invention will appear as the specification progresses.
According to the invention, We completely disintegrate the material from which a permanent magnet is to be made, in a closed receptacle, to a powder having an average particle size under 1 micron. This powder is then whirled or centrifuged to form a cloud of dust from which the powder particles are separated under the influence of a magnetic field produced within the closed receptacle and united to form magnetically anisotropic threads, chains or skeins hereinafter referred to as magnetically anisotropic conglomerates. The latter, after removal from the closed receptacle, are compressed into a body which then is sintered to form a highly-coherent body.
These magnetically anisotropic threads, chains or skeins are unexpectedly quite resistant to the disorienting influence of external mechanical forces which are exerted on them when they are transferred to a die; in fact, formation of magnetically isotropic conglomerates virtually does not take place.
The invention is of particular importance for the manufacture of ceramic anisotropic magnets having as the constituent essential for the permanent magnetic properties at least one material, in the form of hexagonal crystals, with a chemical composition according to the formula M0.6Fe- O where M is at least one of the metals Ba (barium), Sr (strontium) and Pb (lead). The proportions of the Weiss domains of the said crystals generally lie within the range of approximately 1 to 3 microns, so that for an average particle size under 1 micron, for example approximately 0.3 micron, by far most of the particles each are single Weiss domains. That is to say, these particles are micro-magnets magnetized spontaneously and up to the saturation, which have a strong tendency to conglomerate while forming the above-mentioned magnetically isotropic conglomerates. However, if it is possible to substantially prevent this conglomeration, a maximum magnetic orientation effect can actually be obtained just in this case. The present invention offers a means which is excellently suited to this purpose.
According to a particular embodiment of the invention, the permanent magnetic material from which the magnet body to be manufactured is constituted, is disintegrated and whirled to form a cloud of dust in a container which is closed with a cover on the inside of which the above-mentioned magnetically anisotropic conglomerates, i.e. threads, chains or skeins deposit.
The magnetic field, under the influence of which the magnetically anisotropic threads, chains or skeins are formed, is usually produced by an electromagnet which is rendered operative after at least a part of the permanent magnetic material is disintegrated to an average particle size under 1 micron and is whirled to form a cloud of dust. Preferably, the electromagnet is provided in the cover of the container.
The invention will now be described with reference to a particular example which is illustrated only, and the accompanying drawing the sole figure of which shows an apparatus for carrying out the invention.
Finely-divided permanent magnet material 8, e.g. barium hexaferrite, BaO.6Fe O initially ground in a ball mill, is placed in a metal container 1 provided with a metal cover 4 which hermetically seals the container. Cover 4 is provided with a neck 5 in which a soft iron magnet core 6 is provided Which is wound with wire turns 7, the core and the wire turns together forming an electromagnet. Extending through the bottom of the container is a shaft 2 which supports a set of blades 3 for rotation.
After the apparatus has been switched on, the permanent magnetic powder is disintegrated by the metal bands. rotating at high speed, to an average particle size of approximately 0.5 micron, and whirled to form a cloud of dust. Two minutes later the electromagnet is switched on. In the neck of the cover the magnetically anisotropic threads, chains or skeins 9 of powder particles soon deposit in large numbers. After another two minutes grinding is discontinued, the cover is removed from the container, its lower side placed over a filling funnel, and the electromagnet switched off. The magnetically anisotropic chains are no longer attracted by the cover and fall into the filling funnel. From there the mass is transferred to a die, in which by means of an electromagnet a substantially homogeneous magnetic field is produced. The mass is then compressed in the magnetic field under a pressure of 0.5 ton/cmfi. The compressed body is removed from the die and sintered by heating it for 24 hours at a maximum temperature of 1290 C. The resulting magnet body at room temperature has a (BH) of 3.8 l0 gauss oersted and a magnetic anisotropy, expressed in the value of the quotient B ll/B l, of 4.0 (where 13,11 is the maximum remanence measured in a direction parallel to the principal direction of magnetization and B l the remanence measured in the direction at right angles to the di- J; rection in which the maximum remanence B ll is measured).
While we have described the invention with reference to a particular apparatus and a particular material, it will be obvious to those skilled in the art that other forms of apparatus and other materials could be used equally well. For instance, instead of barium hexaferrite, other wellknown magnetic materials such as magnetic alloys which can be formed into sintered bodies may be subjected to a similar treatment. Likewise, the material could be ground initially to the required fine state of subdivision and centrifuged by a conventional centrifuge, the magnetic field being applied from an external source.
Therefore, we wish it to be clearly understood that the foregoing example is illustrative only, the invention itself being limited only and defined by the appended claims.
We claim:
1. A method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles in the presence of a magnetic field into a body, and sintering said body to form the same into a highly coherent body.
2. A method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material having a composition consisting of MO-6Fe O where M is a metal selected from the group consisting of Ba, Sr and Pb in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles in the presence of a magnetic field into a body, and sintering said body to form the same into a highly coherent body.
3. A method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material consisting essentially of BaO-6Fe O in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles into a body in the presence of a magnetic field to form a magnetically anisotropic body, and sintering said body to form the same into a highly coherent body.
4. A method of manufacturing a magnetically anisotropic body comprising the steps, disintegrating a finelydivided magnetic material consisting essentially of BaO-6Fe O in a closed receptacle, whirling said material in said receptacle to form a dust cloud of said material, separating particles of said material in said dust cloud with a magnetic field which forms magnetically anisotropic conglomerates of said particles, removing said conglomerates from said receptacle, compressing the magnetically anisotropic conglomerates of said particles into a body in the presence of a magnetic field to form a magnetically anisotropic body, and sintering said body at a temperature of about 1290 C. for twenty-four hours to form the same into a highly coherent body.
References Cited UNITED STATES PATENTS 2,186,659 1/1940 Vogt 29-155.6 2,384,215 9/ 1945 Toulmin et al 29-420 2,856,273 10/1958 Beeber et al 23--288.3 2,974,887 3/1961 Grandinetti 241-101 3,033,474 5/1962 OToole 241l01 3,090,107 5/1963 Minden et a1 29-155.6 3,189,667 6/1965 Buttner et al. 29155.6
CHARLIE T. MOON, Primary Examiner.
C. E. HALL, I. W. BOCK, Assistant Examiners.

Claims (1)

1. A METHOD OF MANUFACTURING A MAGNETICALLY ANISOTROPIC BODY COMPRISING THE STEPS, DISINTEGRATING A FINELYDIVIDED MAGNETIC MATERIAL IN A CLOSED RECEPTACLE, WHIRLING SAID MATERIAL IN SAID RECEPTACLE TO FORM A DUST CLOUD OF SAID MATERIAL, SEPARATING PARTICLES OF SAID MATERIAL IN SAID DUST CLOUD WITH A MAGNETIC FIELD WHICH FORMS MAGNETICALLY ANISOTROPIC CONGLOMERATES OF SAID PARTICLES, REMOVING SAID CONGLOMERATES FROM SAID RECEPTACLE, COMPRESSING THE MAGNETICALLY ANISOTROPIC CONGLOMERATES OF SAID PARTICLES IN THE PRESENCE OF A MAGNETIC FIELD INT A BODY, AND SINTERING SAID BODY TO FORM THE SAME INTO A HIGHLY COHERENT BODY.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3766642A (en) * 1971-09-27 1973-10-23 Shell Oil Co Process for preparing a ductile metal ferrite

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2186659A (en) * 1936-07-17 1940-01-09 Micro Products Corp Magnetic powder for iron dust cores
US2384215A (en) * 1944-07-03 1945-09-04 Hpm Dev Corp Powder metallurgy
US2856273A (en) * 1953-12-28 1958-10-14 Pure Oil Co Apparatus for low velocity fluidization
US2974887A (en) * 1960-01-25 1961-03-14 Edward M Grandinetti Salt shaker and pepper mill
US3033474A (en) * 1960-05-27 1962-05-08 Murray J O'toole Power take off for disposal unit
US3090107A (en) * 1958-07-24 1963-05-21 Sylvania Electric Prod Method of making a permanent magnet
US3189667A (en) * 1960-11-23 1965-06-15 Deutsche Edelstahlwerke Ag Method of producing pressings to form permanent magnets

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2186659A (en) * 1936-07-17 1940-01-09 Micro Products Corp Magnetic powder for iron dust cores
US2384215A (en) * 1944-07-03 1945-09-04 Hpm Dev Corp Powder metallurgy
US2856273A (en) * 1953-12-28 1958-10-14 Pure Oil Co Apparatus for low velocity fluidization
US3090107A (en) * 1958-07-24 1963-05-21 Sylvania Electric Prod Method of making a permanent magnet
US2974887A (en) * 1960-01-25 1961-03-14 Edward M Grandinetti Salt shaker and pepper mill
US3033474A (en) * 1960-05-27 1962-05-08 Murray J O'toole Power take off for disposal unit
US3189667A (en) * 1960-11-23 1965-06-15 Deutsche Edelstahlwerke Ag Method of producing pressings to form permanent magnets

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3766642A (en) * 1971-09-27 1973-10-23 Shell Oil Co Process for preparing a ductile metal ferrite

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