DE1639547B1 - Process for the production of a magnetically anisotropic permanent magnet body - Google Patents

Description

The invention relates to a method for producing a magnetically anisotropic permanent magnet body, in which the particles with a magnetic Preferred direction directed in a magnetic field and combined into a compact structure will.

It is known to produce magnetically anisotropic permanent magnet bodies in that a permanent magnet Powder is compressed in a constant magnetic field, so that the magnetic anisotropic. Powder particles are directed parallel to the magnetic field, and the particles of the so obtained magnetic anisotropic conglomerate, e.g. B. by sintering to be combined into a compact structure. This The process does not present any particular difficulties when it comes to the permanent magnetic Particles by means of a linear magnetic field with their preferred magnetic directions parallel to each other to judge. The particles are generally compressed either in a direction parallel to that of the external magnetic field or in a direction perpendicular to this. The external magnetic field can be supplied by an electromagnet whose poles are sufficiently different can approach to in the cavity of the die in which the magnetically to be directed Particles are located to create a magnetic field that is strong enough to keep the particles in sufficient position Dimensions to be straightened magnetically.

For certain applications, especially for micror shaft equipment, there is a need for ring-shaped ones or toroidal permanent magnet bodies magnetized in such a way that the magnetic lines of force traverse the ring or toroid in a general direction parallel to its center line. To the To implement this magnetization process, it is desirable that the body to be magnetized are magnetically anisotropic in the sense that they have preferred magnetic lines that define the ring or also pass through the toroid in a general direction parallel to its center line. Under "Magnetic traction lines" are here to be understood as lines whose line of contact in any one Point coincides with the preferred magnetic direction of the body at this point. The concerned So preferred lines are lines along which the body can be easily magnetized. One can imagine that in a ring or a toroid with such preferred magnetic lines the permanent magnetic Particles, which can be regarded as micro-magnets, with their dissimilar., Magnetic poles coupled to one another, have formed chains along the straight lines.

If you want to produce a ring-shaped or toroidal body with the magnetic lines just mentioned, you have to let a magnetic directional field act on the magnetically anisotropic particles (which naturally must not be so tightly compressed that they can no longer move due to friction), whose lines of force run in the same sense as the preferred magnetic lines in the body to be produced. So is z. If, for example, the body to be produced is exactly ring-shaped, the lines of force of the magnetic field must be circles. This can be ensured if a current from / A is sent through an electrical conductor surrounded by the particles of the material, creating a magnetic field strength of H = ■ at a circumference with the center in the middle of the conductor and a radius of r cm - '"-

örsted is generated.

Magnetically anisotropic ceramic permanent magnets can, for. B. be prepared by placing a fine powder of crystals of materials with a chemical composition according to the formula MFe ₁₂ O ₁₉ (where M represents one or more of the metals Ba, Sr and Pb) in a magnetic field of about 2000 örsted simultaneous compression, the crystals and then the pressed product is sintered. In order to produce from this material a toroidal or ring-shaped body in which the crystal particles are directed in self-contained lines which traverse the ring or the toroid in a general direction parallel to its center line, the material would have to be placed in an annular die with a central shaft made of electrically conductive material through which a current of many thousands A would have to be sent. To z. B. to press toroids with an outer diameter of 0.7 cm and an inner diameter of 0.5 cm from this material, a direct current of 2500A would be required through the central shaft of the die, and for those with an outer diameter of 2.07 ^{cm unc} * an inner diameter of 1.44 cm would require currents of even 7000 to 8000A. This method requires an energy source that can deliver large currents, e.g. B. a large battery of capacitors charged to high voltage with an intricate switching system to discharge the capacitors through the conductor. This method is therefore cumbersome in practice.

The invention is aimed at eliminating the above-mentioned disadvantages, because it has surprisingly been found show that it is possible to magnetically anisotropic particles by means of a magnetic An alternating magnetic field that is sufficiently strong for this can be achieved in a simple manner are generated by alternating current.

Until now, nian believed that when using an alternating magnetic field for magnetic straightening a permanent magnetic powder, the particles move violently and so during the compression would result in a disorderly, undirected structure. However, it turned out contrary to the Expectation that magnetically uniaxial powder particles will also be satisfactory in an alternating current generated magnetic alternating field can be directed magnetically.

The invention is advantageously applicable in the manufacture of an annular or toroidal body of a uniaxial ferromagnetic material and with magnetic 'preferred lines in general Direction parallel to the center lines of the body at which. the powdery material in one with one electrically conductive central shaft and one or two movable punches provided die pressed together will. As already noted, this requires high currents. About the powder particles magnetically to a sufficient extent according to the preferred lines that form the ring or the toroid in a general direction parallel to its center line can now be used instead of a battery of capacitors and an intricate switching system, the required large amperage by connecting the

middle wave of the die can be achieved via a transformer to an AC power source.

To achieve the required high current intensity, a step-down transformer can be used, ie a transformer in which the voltage E ₁ in the primary winding is converted into a lower voltage E _s in the secondary winding according to the known ratio

where N ₁ , and JV _{S represent} the number of turns in the primary and secondary winding, respectively. At the same time, the current intensity / _s in the secondary winding is increased by the same ratio as compared to the current intensity I _p in the primary winding, since the energy consumed by the transformer is negligibly small. So z. B. with an alternating current of 60 periods a transformer with a secondary winding consisting of only one turn and with 328 turns in the primary winding a current intensity in the secondary winding with a peak value I _s of 1.4 * 328 l _p , where / _{p is} the square root of represents the mean value of the square of the current in the primary winding. This means that with an I _p of 15 to 16 A in the primary winding, an / _s of about 6500 A was achieved in the secondary winding; this amperage is large enough to magnetically straighten one of the toroids made of the above material in the desired manner.

According to the invention, a finely divided, uniaxial ferromagnetic material becomes a die introduced, and through a part of the die, which is electrically conductive, an alternating current is such Strength sent so that the material is magnetically judged, while at the same time the material is in the Die is compacted. Then, if desired, the material can be made into a coherent Body to be sintered.

The invention is particularly suitable for the production of bodies from materials with a chemical composition according to the formula MFe ₁₂ O ₁₉ , where M represents one or more of the metals Ba, Sr and Pb. These materials are obtained by mixing the oxides of one or more of the metals mentioned with iron oxide in a ratio of about 6 moles of iron oxide to 1 mole of the other metal oxide and then sintering the mixture. These materials are "magnetically uniaxial"; their single crystals in the order of 1 micron have a preferred direction of magnetization in the direction of the hexagonal crystallographic axis.

Another material with uniaxial magnetic crystal anisotropy, which is suitable for use in microwave equipment A material corresponding to the chemical formula is particularly suitable

According to the invention, this material was also used to produce ring-shaped and toroidal bodies with magnetic ones Preference lines are produced that run the body in a general direction parallel to its center line run through. Indeed, the invention is applicable to a wide variety of ferromagnetic materials with uniaxial magnetic Crystal anisotropy can be used, so z. B. also with manganese-bismuth alloys. Body too, which are made up of ferromagnetic materials in the form of small particles, which are magnetic Have shape anisotropy, such as elongated fine particles of iron and iron-cobalt alloys, can be produced according to the invention.

Although the application of the invention has its maximum usefulness in the manufacture of annular or toroidal permanent magnet bodies with magnetic lines running in a general direction run parallel to the center line of the body, the invention is also having good success in the Manufacture of bodies with a different shape and with a different type of magnetic anisotropy can be used.

It is noted that it was already known, fine particles of compounds with a chemical composition according to the formula MO · Fe ₂ O ₃ , where M represents one of the metals Ba, Sr and Pb and χ is between the values 3 and 8 * magnetic to be judged by means of a constant magnetic field on which an alternating magnetic field with a slightly smaller amplitude than that of the constant field is superimposed. The constant field here fulfills the function of a directional field, while the alternating field keeps the magnetic particles oscillating so that they can be more easily directed with their magnetic axes according to the lines of force of the magnetic constant field.

It should also be mentioned that in steel alloy magnets a magnetic field cooling in the magnetic Alternating field is known. However, no particles are aligned here. Rather, it is about an orientation of the atoms in the course of a diffusion process.

The invention is explained in more detail using a few examples.

Example II

F i g.l of the drawing shows a toroidal body with preferred magnetic lines that form the ring or traverse the toroid in a general direction parallel to its center line. The by dashed lines The indicated base planes of the crystals 2 extend in the radial direction, since the direction of magnetization is perpendicular to these base planes.

F i g. Figure 2 shows the hexagonal base planes of the crystals.

The in F i g. The toroidal body 1 shown in FIG. 1 was produced (see FIG. 3) by introducing a fine powder 4 of the material SrFe ₁₂ O ₁₉ into a die 3 made of a non-magnetic material. A central shaft 5, which consists of a copper rod with a diameter of 12.7 mm, which is connected to the secondary winding 7 of the transformer 8, the primary winding 9 of which was connected to an alternating current source, runs through the die cavity. The number of turns of the primary winding was 328 times as large as the number of turns of the secondary winding, so that with a current of 15 A in the primary winding, a current of about 650 A was achieved in the secondary winding. With an I _s of 650OA in the copper rod, a magnetic field strength of 1300 örsted was achieved on a circumference at a distance of 1 cm from the circumference of the copper rod, which is large enough to generate the

⁶ S SrFe ₁₂ O ₁₉ particles to be magnetically aligned. During the passage of current through the copper rod, the particles were pressed together in the die by means of a punch 6. The compressed material

was finally removed from the die and held for about 2 hours at a temperature of 1300 ° C sintered into a compact body.

The magnetic orientation of the crystal particles in the body thus obtained is shown in FIG. 4 and 5 shows in which the position of a (hexagonal) single crystal of the powder 4 in relation to the central shaft the die is shown. The base plane 2 of the crystal is directed radially with respect to the rod 5, and since the preferred magnetic direction of the crystal is perpendicular to the base plane, i.e. parallel to the Is the direction of the hexagonal axis, the direction of magnetization is according to a line of contact a circle concentric with the copper rod.

Example II

15th

In a die with a cavity 1.43 cm long and 1.43 cm wide, a powder with a chemical composition according to the formula SrFe ₁₂ O _{19 was} compressed to form a whole. At the same time, the particles of the powder were magnetically directed by an alternating magnetic field. The direction of this magnetic field was parallel to one of the edges of the cube and perpendicular to the direction of pressing. The number of cycles of the alternating current was 60 per second. The magnetically anisotropic conglomerate obtained was then removed from the die and sintered at about 1350 ° C. for about 2 hours. On completion of the sintering, the dimensions of the body in the preferred magnetic direction were reduced from 1.43 to 1.10 cm and in the direction perpendicular to this from 1.43 to 1.25 cm. Anisotropic shrinkage during sintering of magnetically anisotropic conglomerates of materials with the formula MFe ₁₂ O ₁₉ is a well-known phenomenon. The anisotropic shrinkage found here therefore indicates a pronounced magnetic anisotropy.

The high degree of magnetic anisotropy of the body obtained can also be seen from FIG. 6 and 7. In these figures, hysteresis loops of this body are shown, which are achieved by plotting the magnetic induction 4n7 over the associated magnetic field strength H. The in F i g. 6 is based on measurements that are carried out in a direction parallel to the preferred magnetic direction of the body. The hysteresis loop in question shows great agreement with that which is determined by measurements on a single crystal in the preferred magnetic direction of the same; namely, it shows a rapid increase in the magnetic induction with increasing magnetic field strength at low values of the latter, the saturation magnetization being reached already at relatively low values of the magnetic field strength. The hysteresis loop according to FIG. 7 is based on measurements in a direction perpendicular to the preferred magnetic direction of the body. This hysteresis loop is very similar to that of a uniaxial single crystal, which is determined by measurements in a direction perpendicular to the preferred magnetic direction; the magnetic induction increases here only slowly with increasing field strength, and the saturation magnetization is not yet reached even at a field strength of 10,000 örsted.

Claims (2)

Patent claims: 1. A method for producing a magnetically anisotropic permanent magnet body, in which the Particles of fine powder, which have a magnetic preferred direction, in a magnetic field pressed together and combined into a compact structure, characterized in that that the magnetic field is an alternating field. 2. The method according to claim 1 for producing a ring or toroid with magnetic Preferential lines which define the ring or toroid in a general direction parallel to its center line run through, characterized in that the alternating field by at least almost rectilinear electrical conductor is created which extends through the ring or toroid. 1 sheet of drawings BATH ORIGINAL