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Publication numberUS3694115 A
Publication typeGrant
Publication dateSep 26, 1972
Filing dateMar 30, 1970
Priority dateNov 9, 1967
Publication numberUS 3694115 A, US 3694115A, US-A-3694115, US3694115 A, US3694115A
InventorsSteingroever Eric
Original AssigneeMagnetfab Bonn Gmbh
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Molding apparatus for making anisotropic ring-shaped magnets with zones having a preferred radial direction
US 3694115 A
Apparatus for the production of ring-shaped permanent magnets having radial lines of force from permanent magnet powder and a binder comprises a die holder provided with a liner of hard having high mechanical strength and/or abrasion resistance magnetic material for cooperation with a center ram and opposed end wall rams.
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Description  (OCR text may contain errors)

United States Patent Steingroever [451 Sept. 26, 1972 [54] 1 MOLDING APPARATUS FOR MAKING ANISOTROPIC RING-SHAPED MAGNETS WITH ZONES HAVING A PREFERRED RADIAL DIRECTION [72] V Inventor: Eric Steingroever, Bonn, Germany [73] Assignee: Magnetfabrik Bonn Gmbl-I. vorm. Gewerkschaft, Windhorst, Postfach, Germany [22] Filed: March 30, 1970 [2-1] Appl. No.: 29,311

Related US. Application Data [62] Division of Ser. No. 759,393, Sept. 12, 1968,


[30] Foreign Application Priority Data Nov. 9, 1967 Germany ..P 16 13 319.0

[52] US. Cl ..425/3 [51] Int. Cl. .1330!) 11/04 [58] Field of Search..18/5 H, 16 R, 16.5, 17 R, 17 H, 18/34 R, DIG. 33

[56] References Cited UNITED STATES PATENTS 3,250,831 5/1966 Hooper ..18/D1G. 33 3,555,621 1/1971 l-lara ..18/5 H X 3,452,121 6/1969 Cochardt et a1. ..18/l6.5 X 3,274,303 9/1966 Muller ..18/16.5 X 2,384,215 9/1945 Toulmin ..18/D1G. 33 2,999,271 9/1961 Falk et a1. ..18/16.5 X 3,416,191 12/1968 Richter et a1. ..18/16.5

Primary Examiner--J. Howard Flint, Jr. Atlorney-Christen & Sabol [5 7 ABSTRACT Apparatus for the production of ring-shaped permanent magnets having radial lines of force from permanent magnet powder and a binder comprises a die holder provided with a linerof hard having high mechanical strength and/or abrasion resistance mag netic material for cooperation with a center ram and opposed end wall rams.

5 Claims, 4 Drawing Figures INVENTOR ERICH STEINGROEVER PATENTEDsP2s I972 SHEET 2 OF 2 F I G 3 INVENTOR ERICH STEINGROEVER ATTORNEYS MOLDING APPARATUS FOR MAKING. ANISOTROPIC RING-SHAPED MAGNETS WITH ZONES HAVING A PREFERRED RADIAL DIRECTION This application is a division of my copending application Ser. No. 759,393, filed Sept. 12, 1968, for Anisotropic Ring-Shaped Magnets With Zones Having A Preferred Radial Direction" and now abandoned.

The invention is concerned with apparatus for the production of ring-shaped permanent magnets having circumferentially disposed poles for electric machines, generators, amplitude drives, speedometers, etc., which are made from a permanent magnetic powder and a non-magnetic binder.

It has been known to produce such annular magnets from an isotropic raw material, e.g., barium ferrite, and to magnetize them, in such a manner that one or several pairs of poles are located on the side wall; because of the low remanence of these raw materials (Br 2,0002,300 Gausses), those machines equipped with such magnets have only low values of torque and of the degree of effectiveness.

For that reason, often ring magnets are used which can be produced with a preferred radial direction of the magnetic values, and one arranges these segments on the inside wall of a return ring made of iron; barium ferrite is pertinent for this purpose as a raw material, if need be with additions of strontium of lead, with a remanence of 3,500--4,200 Gausses; however, itis expensive to produce and to assemble these anisotropic segments.

Furthermore, ring-shaped barium-strontium-ferrite magnets with a preferred radial direction have been known which are made by compression process from a permanent magnet powder and a by the binder, whereby, during the compression, a radial magnetic field is applied between the center ram and the wall of the mold; in the case of these magnets, the alignment of the particles of powder in a radial direction is only imperfect, because the magnetic flux must be fed to the hollow space of the mold via the center ram and it is limited through the cross section of said ram. In the case of a saturation induction of the raw material from which the center ram of the mold has been made, of approximately 18,000 Gausses, and in the case of the customary dimension of the magnet rings for small type motors, e.g., 30 (b X 23 4: X 20 mm, an induction ofonly (18,000 X 2.3 X 1r/4) (2.65 X 11 X 4) 2,200 Gausses, will be achieved in the compression hole, whenever the bulk density of the magnet powder amounts to 2 g/cc and the density of the compressed magnet 4 g/cc. This induction is not enough to align the powder particularly sufficiently.

The invention avoids these disadvantages by providing apparatus capable of producing a ring-shaped magnet for electric machines from a permanent magnetic powder and a non-magnetic binder by way of the compression process, whereby during the compression, a dual or multi-pole magnetic field is applied from the outside perpendicularly in relation to the wall of the ring, so that the powder particles with their magnetic preferred direction are aligned in the one or several desired directions. The ring produced in this manner is characterized in that it has one or several pairs of zones with a radial or approximately radial preferred direction of magnetization. In the neutral zones between the poles, the preferred direction is not radial but perhaps in connecting lines going from pole to pole.

A ring magnet 1 produced by the apparatus according to the invention is shown in FIG. 1 in top view and in FIG. 2 in section with the magnetic preferred ring magnet direction shown by the poles N and S in broken lines. Within the area of the poles N and S, the preferred directions run radially, at their edge approximately radially. Between the poles lie the zones 2, in which the preferred directions lie approximately tangentially. In the case of alignment of the magnet powder through the magnetic directional field, the powder particles are drawn out of the zones 2 to the poles N and S, so that at 2 a lesser density of the raw material will result after compressing. In order to avoid this, according to the invention, grooves are provided at 2, so that at these places too the correct densification of the raw material will be achieved through the shape of the rams corresponding to the grooves; at the same time these grooves serve for the characterization of the perpendicular line on the magnetic preferred direction, whose position at the time of insertion of the magnet into the electric machine must be taken into consideration.

A pressing tool for anisotropic ring magnets according to the invention is presented in FIG. 3 in top view in FIG. 4 in section. In FIG. 3, the reference numbers signify:

3 a thin-walled extruding die,

4 a holding element into which the extruding die is pressed or shrunk in,

5 the center ram made of ferromagnetic raw material, e. g., hard steel or hard metal,

6 the iron poles N and S of a magnetic circle 7 the frame made of iron in which the poles 6 are attached,

8 is the course, drawn in broken lines, of the magnetic flux which is energized by the coils 9 and which penetrates the press hole 10; further lines of force are drawn in broken lines in the press hole 10, whose course is not shown in the magnetic circle.

FIG. 4 shows the pressure tool in section. The parts enumerated in FIG. 3 have been designated with the same reference numbers; furthermore 11 is a non-magnetic base plate on which the matrix is attached with its holders as well as the magnetic circle with its coils, 12 is the lower ram, 13 is the upper ram, 14 is a cover plate which covers up the pressure tool upwardly. The movements of the ram in relation to the matrix take place in a known manner in the sequence of the letters a to d, shown at the pertinent arrows.

In order to achieve a radial course of the magnetic field within the area of the zones of the poles in the press hole, it is necessary that the center ram 12 consist of ferromagnetic raw material. The remaining parts of the mold (die liner 3, holding part 4, lower ram 12 and upper 13) should, according to the present status of the prior art, consist of a non-magnetic raw material, so that the directional field develops radially. Simultaneously, however, these parts (outside part 4) must have great magnetic strength and resistance to wear in order to be able to resist the high compression strength and the friction of the hard powder particles. According to another realization of the inventor, the die liner 3, the lower ram 12, and the upper ram 13 can, against expectations, also consist of hardened steel or of a magnetic hard metal, without essentially disburbing the radial course of the field in the press hole. This is to be traced back to the fact that in the case of the high magnetic inductions, with which we are dealing here, they will be sufficient to achieve the magnetic saturation of these parts, so that a screening or a change in the course of the magnetic lines of force in the press hole occurs only to a small degree.

inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for the production of ring-shaped magnets having radially oriented lines of force defining a plurality of circumferentially disposed magnetic poles from permanent magnet powder and non-magnetic binder, comprising a ring-shaped die liner of magnetic material having high mechanical strength and/or resistance to wear defining the outer wall of the magnets to be produced, a die holder surrounding said die liner,

means to produce a multi-pole magnetic field to magnetically saturate the die liner and having the lines of force disposed in planes perpendicular to the axis of said ring-shaped die liner, a center ram defining the inner wall of a ring-shaped magnet to be produced, and a pair of annular opposed movable ram elements to define the opposite end walls of a ring-shaped magnet to be produced.

2. The invention as claimed in claim 1 wherein said center ram is made of ferromagnetic material.

3. The invention as claimed in claim 1 wherein said ram elements are made of ferromagnetic material.

4. The invention as claimed in claim 1, wherein at least one of said annular rams includes an axial projection to form an indentation in a portion of an end wall of a magnet to be produced.

5. The invention as claimed in claim 1, wherein said multi-pole magnetic field is arranged to produce a pair of poles disposed diametrically on opposite sides of the axis of the ring-shaped magnet to be produced, and at least one of said annular rams includes a pair of circumferentially spaced projections to form indentations in portions of an-end wall of a magnet to be produced, said projections being generally located between said pair of magnetic poles of said magnet.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2384215 *Jul 3, 1944Sep 4, 1945Hpm Dev CorpPowder metallurgy
US2999271 *Aug 30, 1960Sep 12, 1961Gen ElectricMagnetic material
US3250831 *Dec 20, 1962May 10, 1966Gen ElectricMagnetic material
US3274303 *Dec 18, 1962Sep 20, 1966Magnetfabrik Bonn GewerkschaftMethod and apparatus for making magnetically anisotropic permanent magnets
US3416191 *Mar 14, 1966Dec 17, 1968Deutsche Edelstahlwerke AgApparatus for compacting permanent magnet powders into pressings
US3452121 *Mar 11, 1968Jun 24, 1969Westinghouse Electric CorpApparatus and process for forming or molding magnetic substances
US3555621 *Apr 15, 1968Jan 19, 1971Tamagawa Kikai Kinzoku KkCompacting apparatus for magnetic powders
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4250128 *Aug 16, 1976Feb 10, 1981Magna Motors CorporationProcesses and apparatuses for preparing permanent magnet stators
US4911627 *Jan 26, 1989Mar 27, 1990The United States Of America As Represented By The Secretary Of The ArmyApparatus for fabrication of permanent magnet toroidal rings
US4948999 *Mar 2, 1989Aug 14, 1990U.S. Philips CorporationSelf-starting two-pole single-phase synchronous motor
US5049053 *Aug 16, 1989Sep 17, 1991Hitachi Metals, Ltd.Metal mold for molding anisotropic permanent magnets
US6080352 *Mar 31, 1997Jun 27, 2000Seagate Technologies, Inc.Method of magnetizing a ring-shaped magnet
US6855917 *Dec 6, 2001Feb 15, 2005The Boeing CompanyInduction processable ceramic die with durable die liner
US7560841Jul 22, 2004Jul 14, 2009Aichi Steel Corporation, Ltd.Thin hybrid magnetization type ring magnet, yoke-equipped thin hybrid magnetization type ring magnet, and brush-less motor
US7750776Feb 2, 2009Jul 6, 2010Aichi Steel CorporationAnisotropic bonded magnet for use in a 4-pole motor, a motor employing that magnet, and an alignment process apparatus for the anisotropic bonded magnet for use in a 4-pole motor
US8039998 *Dec 19, 2005Oct 18, 2011Hitachi Metals, Ltd.Rotor for motor and method for producing the same
EP0272243A2 *Dec 4, 1987Jun 22, 1988ELIN-UNION Aktiengesellschaft für elektrische IndustrieApparatus for making pressed objects
EP1548761A1 *Aug 27, 2003Jun 29, 2005Shin-Etsu Chemical Co., Ltd.Radial anisotropic ring magnet and method of manufacturing the ring magnet
EP1648073A1 *Jul 22, 2004Apr 19, 2006Aichi Steel CorporationThin hybrid magnetization type ring magnet, yoke-equipped thin hybrid magnetization type ring magnet, and brush-less motor
U.S. Classification425/78
International ClassificationB30B11/00, H01F41/02
Cooperative ClassificationB30B11/008, H01F41/028
European ClassificationB30B11/00M, H01F41/02B6B