Molding Apparatus For Making Anisotropic Ring-shaped Magnets With Zones Having A Preferred Radial Direction

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 liner of hard having high mechanical strength and/or abrasion resistance magnetic material for cooperation with a center ram and opposed end wall rams.

Parent Case Text

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.

Description

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 2,000--2,300 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, it is 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 .phi. .times. 23 .phi. .times. 20 mm, an induction of only (18,000 .times. 2.3.sup.2 .times. .pi./4) .div. (2.65 .times. .pi. .times. 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.

Claims

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.