DE1571622A1 - Method of manufacturing magnets - Google Patents

Description

The invention relates to a method of manufacture of high-energy permanent magnets, in particular permanent magnets made from very small particles are composed of ferritic material. The particle size preferably corresponds to the size of individual magnetic ones Unit cells.

Numerous types of permanent magnets are already known, the Maine discrete particles of barium ferrite, strontdum ferrite and / or contain lead ferrite »In these magnets, the magnetic particles are bound by a non-magnetic binder connected with each other. The binding agent provides a 'uniform self-supporting body, which by common processing techniques such as turning, drilling, sawing, milling or the like can be processed. The maximum energy product of these magnets depends on the manufacturing process used

009382/1698

- 2 ORIGINAL BATHROOMS *

Hannoverii340O · Commenbank Honnevtr 3/1073 * 8 · t) ri »dn« r Banfc Kcsiincvsr 44181 · Β · υί «Λ» lank Hannovtr 1/38405

1571822

procedure and depending on some other factors generally on the order of 0.4 to 1.1 or 1.2x10 Gauss-Oersted.

They are also made of fine magnetic particles Compound magnets have been proposed in which the maximum energy product is in the much higher range of about 1.3-3 »5 x 10 Gauss-Oersted. These highly energetic However, magnets have heretofore been subjected to sintering during manufacture in order to improve magnetic quality to create. But ferrites are very naturally very strong hard ceramic-like or refractory materials, so that when the ferrites are sintered they become harder, more brittle and more coherent Body arises. As an unavoidable result of sintering, this body cannot be processed in the usual way, but can at most be brought into an exact shape by grinding. In addition, sintered magnets can withstand rough handling break or shatter very easily. Thus, the practical usability of the previous high-energy sintered Magnets quite limited.

For the purposes of the following description, the term "sintering" should be understood to mean that a powdery or earth-like substance without complete melting of the individual particles into a coherent solid mass is baked together. When sintering very small particles such as ferrites, the individual particles weld together in

009882/1688 " ³ "

their Eontaktsonen to each other, whereby the size of the contact zones •• tv.-at: growing. In the course of this sintering process, the resulting Magnetic alignment somewhat larger, namely open-1 ar by absorption of unoriented particles by larger, aligned particles. As a result of the enlargement of the contact zone Between the particles there continues to be a shrinkage of the mass, which is paralleled by an increase in density. The increase the density can be on the order of about 75 - 100.5 of the original Density lie.

The sintering conditions for a given material ■ depend on the particle size, the packing density, the presence of small amounts of impurities and other factors. For example, substances such as lead monoxide, lead monosilicate and calcium oxide are used with barium ferrite BaPe ₁ 9 ⁰ Iq in order to modify the sintering conditions, in particular to lower the sintering temperature.

The sintering time and the sintering temperature of a certain ase are related to one another in such a way that the required sintering time increases sharply with decreasing sintering temperature. For example, a given l'aterial which requires a sintering time of 8 h at about 790 ° C, at 1150 ⁰ C in the time even be sintered liin of about 10 degrees. The minimum sintering time that is necessary for a given temperature can be varied by examining the cohesion of the heated cash register

009882/1698 sad oriG'NAL

"Determine the heating times. As soon as the particles are sintered are, namely the mechanical strength of the mass increases very sharply. Likewise, the density also increases by about $ 75-100 or more.

In contrast, a heated but not yet sintered hate is crumbly and fragile. It can be cut and is often easy to chop by hand. Their density is consistently no more than 20 ^ 'higher than the density of the unheated material. If such a mass is impregnated with a binder to increase its mechanical strength, it can be machined, for example. A sintered ferritic body has a much lower porosity than an unsintered heated material, so that ereelbet after impregnation with a binding agent is still too hard for any kind of processing (with the exception of the sole) and bursts in the event of sudden vibrations.

In our own older German patent application L 32 950 YIb / 80b, a method for manufacturing is workable Permanent magnets described in which - according to a

Execution example - ferriferous particles the average size of about a unit cell are suspended in water or acetone whereupon the suspension is used to align the magnetic particles. exposed to a magnetic field. The field rotates the anisitropic particles in the low-viscosity dispersion medium in such a way that the preferred magnetic axes of the individual particles are set parallel to one another. According to the alignment of each

009882/1898 _fiAn

^ß AD OR / Gi _NAL - 5 -

Particles is drawn off the dispersion medium when the magnetic field is maintained, for example by pressing out by means of a Stamp that engages with slight play in a form containing the suspension. The particles will eventually be in theirs aligned state solidified by a binder, which is introduced in liquid form into the spaces between the individual particles and then made to solidify. To this This results in a durable self-supporting body.

The magnets produced in the manner described above are machinable because the particles are not sintered together, but are only held together by the binder which has solidified after alignment around the particles and which in turn is machinable. A typical ferritic magnet produced in this way can have an energy product of about 1.2 × 10 Gauss-Oersted.

While such an energy product is quite excellent for machinable magnets, it is quite desirable to be machinable Making magnets with an even higher energy product. -

This is possible with the present invention. In the present invention, an unsintered one is anisotropic and a material composed of fine particles, for example that according to the said earlier application produced material. After the magnetic alignment of the TpIl-

009882/1698 ~ * "

SäD ORiQlNAt

A sequence of further work steps is applied to this material. The first of these working steps consists in gradually burning out any binder or lubricant that may be present correspond to them, but come close to them, and the conditions of which are chosen so that the density of the mass does not increase by more than about 15 - 20? which still allows manual crumbling of the mass and is not too strong with regard to machineile processing. The heating stage is followed by a third step in which the mass is impregnated with a binding agent and thereby solidified into a workable body.

Through the additional steps described above during the manufacture of the magnet, the magnetic properties of the material in a surprising way; improved to such an extent that it is very near dtn properties come from sintered magnets or these in;

\ individual cases can even be fully achieved. On the other

Page does not turn the crowd into an unworkable, hard and

- 7 -009882/169 «bad _{Ofi / G} , _NÄL

fragile product transformed. It is therefore by no means necessary to subject an agneten composed of fine ferritic particles to a sintering process to a considerable extent To achieve an increase in the magnetic quality of the product. Rather, the invention leads to the knowledge that already one Heating the product under conditions that are not necessary. Sintering conditions, a considerable and practical the result is an optimal increase in the energy product, and that any further heating at most leads to a deterioration of the mechanical properties of the first magnet, but not to a further increase in the magnetic quality, and therefore in favor of a more effective method of mechanical strengthening of the "eilchen can be passed over.

Preferably, but not necessarily necessarily, the magnetically aligned cash register in one of the initially mentioned own earlier patent application L 32 950 described .'is generated. The procedure dealt with there has namely opposite the known method of aligning the magnetic particles directly in a liquefied binder, the advantage that the magnetic Alignment of the particles is much more effective because of the low viscosity of the dispersion medium. In addition, I knew It is also possible with this method to adjust the binder phase in the intermediate product formed after the alignment to the extent to limit that for sufficient adherence of the particles while handling the body before the heating process *

009882/1698

BAD ORIGWAL

is just necessary. This eliminates the need to burn out excessively large amounts of binder before the actual Heating level. This is because the binder evaporates during of burning out and thereby causes the risk of cracking or bursting of the mass, so that the use of superfluous ^ sigem binders should be avoided whenever possible.

In the process described in our own earlier application, the amount of binder can very easily be reduced to just that limit necessary amount, since the binding agent in precisely meterable ^ tight only after the alignment of the particles is made to solidify. Good results can be achieved if the ferritic body contains about $ 0.25 - $ 1 stearic acid is admitted. The stearic acid acts both as a light binder and as a lubricant that prevents the mass from sticking on the connections of the Porm used during manufacture. Although this binder is to some extent soluble in acetone, it does not make the viscosity of the acetone unacceptable increased if the agent is used in low concentrations.

Further details and advantages of the invention will be given explained in more detail below in exemplary embodiments.

example 1

Z. Zt. Is used as a magnetic component for the invention manufactured magnets preferably lead ferrite)

008882/1698 «ο p _fl | _G%

used because this material has very good magnetic properties and is also easily accessible. In addition, owns Lead ferrite has the advantage that it

the

temperature responds as, for example, barium ferrite, so that / by the invention Treatment achievable improvement of the magnetic quality of the magnets earlier (based on the sintering point) occurs. The fact that the improvements in magnetic quality are produced well before the occurrence of sintering means that the point at which the heating must necessarily be stopped in order to prevent the formation of a hard coherent sintered Avoiding the body is less critical than with barium ferrite. Lead ferrite is poisonous and also at higher levels Temperatures volatile, but according to the present invention it can still be treated at temperatures at which the Volatility of the material is not an overly serious problem.

Suitable lead ferrite powder that is used in the inventive Methods that can be used are commercially available. With lead ferrite, barium ferrite and strontium ferrite the size of the unit cell is in the range of fO.5 - 1 / u .. This range is optimally suited for the purposes of the invention. However, particle sizes are also in the range of about 0.3 10 yU Durohaus usable in practice without a serious loss of quality.

For the production of the permanent magnets according to the invention a suspension of lead ferrite in acetone is assumed,

- 10 * -

00808271698

^ SAD ORIGINAL

- ίο -

• χ

about 1 cnr acetone / g perite is used. The dispersed Powder is added to stearic acid in an amount of about 0.1-1.0.6, based on the weight of the ferrites. • The stearic acid acts as a lubricant during the alignment process and at the same time creates the necessary cohesion within the mass formed from the oriented and compressed particles. This means that this mass can be used before heating reduced risk of crumbling. However, it is advised that the use of stearic acid or another binder in this first stage of the process is by no means necessary. Rather, it is also possible to dispense with any binding agent at this point, or an equivalent one can be used Substance can be used which will burn out during subsequent heating.

The suspension is placed in the cavity of my mold, which is equipped with movable punches. These stamps serve as follower pieces for an electromagnet and are slightly smaller than the cavity. With a total diameter of 1.25 cm, the play can be approximately 0.001-0.0025 cm. A magnetic field is generated between the stamps, which aligns the suspended, anisotropic particles in such a way that their preferred magnetic axes are parallel. If the magnetic field _{i is maintained} , the punches are moved against one another, the dispersion medium because of the play mentioned laterally next to the punches

I - 11 -

001112 / ftl8

emerges from the mold. With an original field strength of around 2300 Oersted and a compression ratio of 6: 1, it increases the field strength to a maximum of about 14000 Oersted. A field strength of at least about 10,000 - 12,000 Oersteds are required. During compression The stamp does not lose the magnetic alignment of the "particles. The particles are not in the process either but remain essentially within the cavity between the two Stamp. The last compression pressure applied can be on the order of about 3400 kg / cm. This print is in Not very critical with regard to the mechanical properties of the magnet body, but the resulting increase in density is of great advantage. Generally, the compression pressure can be in the range from about 420-5000 kg / cm. At high pressures stratification occurs within the agnet body. These However, stratification does not interfere, since the binder, which is added to the magnet body after the heating, has such layers connects sufficiently firmly together.

The binder consisting of stearic acid or the like gives the aligned and compressed particles a strength, which is just sufficient to ensure safe handling of the magnetic body before heating. Although it can always use a larger amount of binding agent,

- 12 -

009882/1698.

BATH ORIGINAL

which leads to a somewhat increased strength of the magnetic body. V. 'As mentioned above, difficulties then arise when the binder burns out.

The compressed and aligned magnetic body is carefully removed from the mold and placed in an oven to burn out the binder and then heat it. The body is heated in an air atmosphere with gradually increasing temperature. The ^fi 'omperatur is thereby increased purpose moderately from room temperature auegehend within about 4 hours to about 75O ⁰ C (1382 ⁰ F). The heated I: af; se is then cooled down as quickly as possible, but without subjecting the mass to a thermal shock, which could possibly cause a breakage the binder burns out.

The heating conditions mentioned above are far below the sintering conditions for the material used. Tas heating the mass under the chosen, preceding explained conditions leads to the state of so-called "green firmness", in which the Yanse already under a slight "jerk or Crumbles if handled normally, but not too carefully, but not closed after impregnation with binding agent hard for machining. A hard, highly coherent sintered body is therefore not formed, of course the crumbly mass produced after heating cannot yet be used as such because of its low mechanical strength.

009882/1698

BAD OR / Gi _NAL

However, compared to the unheated mass, it has considerably improved magnetic properties. The necessary mechanical properties of the mass, however, are determined by the following Bringing in a binder caused. During the heating process, the mass shrinks only very slightly, and that in general to an extent that is hardly sufficient for the subsequent reintroduction of the mass into the mold. The shrinkage lies in the A few thousandths of a cm / cm in length. In contrast, the production of a hard, dense, highly coherent result sintered body has a much greater shrinkage, the typical value (measured linearly) of which is about 20: ί.

The product heated in the manner described above but not yet sintered is highly porous compared to a sintered product. It is impregnated with a binding agent that gives the product the desired final mechanical strength. A low-viscosity plastic (epoxy resin, phenolic resin, acrylic resin or the like) can be used, for example, as the binding agent. The magnetic body is then preferably returned to its original shape in order to emboss and harden the resin. In this case, depending on the type of binder, a temperature of about 200 - applied 26O ⁰ C and a pressure of about 350 kg / cm. A sintered ferritic product cannot be embossed without breaking, while the product produced according to the invention "flows" somewhat under the embossing pressure and thus adapts precisely to the shape.

-H-

009882/1698

BATH ORIGINAL

The one produced in the above-described V. r.Tagnetkörper is easy to work with, even with a In addition, it has a much higher energy product than a body that has not been heated. As already mentioned, the energy product of the unheated body is etv / a 1.2 χ 10 Gauss-Oersted, while the energy product in the case of the magnet produced according to the invention, etv / a is 1.5 × 10 Gauss-Oersted and is thus about 25 $ higher lies.

Since in the treatment described above, the heating of the magnetically aligned body under ^ eit-, Temperature conditions were carried out, which are far below the sintering conditions, has consequently by the Heating does not result in any appreciable cohesion of the individual magnetic particles. This is the main reason that the impregnated end product can be easily processed.

Example 2

A lead ferrite powder with a particle size approximately the size of a unit cell is suspended in acetone, again using about 1 cm acetone / g ferrite. The suspension is introduced into the cavity of a mold which has the design already described in Example 1. Within the mold, the particles are aligned by a magnetic field, the initial strength of which is about 2300 Oersted, and then compressed, the final pressure being in the range of about 5500 kg / cm . ■

009882/1698

ORiGiNAt

The aligned and compressed ^r agnetkörper is then with a: a chlorinated naphthalene, for example that commercially available under the name "Halowax 101.1"
Product, impregnated. The impregnation is carried out at a temperature ■ above the melting point of the binder.
^T ). The agent is then hardened.

In the subsequent heating stage, the magnet ifirper, starting from zero temperature, within a period from about 4 h gradually to a mixed temperature of about 750 ° C heated.

After heating, the body is then coated with a binding agent impregnated, provides the necessary final mechanical strength generated. The impregnation is carried out by minder.iGiin Immersing the body in a low viscosity epoxy resin for six hours. The body is then returned to its original shape used and under moderated ".'ärraesufuhr and Druckai-wer.dun-." embossed and hardened.

The magnetic body produced in accordance with the present example is easy to process and has an 'eetinduktion} ^; , of 2480 Gauss, a coercive force H of 2160 Oersted and a maximum energy product of 1.5 χ 10 Gauss-Oersted.
The apparent density of the body is 4.14 g / cm.

Example 3

Lead ferrite about the size of a unit cell corresponding particle size is in a low viscosity

- 16 009882/1698

BAD OFHGWA !.

sen liquid suspended and aligned in a magnetic field, the initial strength of which is about 2300 Oersted. After the dispersant has been squeezed out, the powder is compressed under a pressure of about 2500 kg / cm. The body is then impregnated with chlorinated naphthalene, this impregnation being expediently carried out within the mold so as not to destroy the shape produced by the compression. After the impregnation is complete, the magnet body is removed from the mold and, starting from room temperature, gradually ^{heated to 800 °} C. (1472 ^° F.) over a period of 4 hours. During this heating *? the binder burns out and the body gets into the state of "green firmness". After cooling slowly, the body is immersed in a low-viscosity epoxy resin for about 6 hours for impregnation. The impregnated body is then returned to the original mold, where it is embossed and cured under moderate pressure and temperature conditions.

The magnetic body produced according to the present example has a residual induction B of 2300 Gauss, a coercive force H of 2000 Oersted and a maximum energy product of 1.2 χ 10 Gauss-Oersted. It can be assumed that the compared to the magnet according to example 2 lower energy product based on the lower density of the body, which in turn again goes back to the lower compression pressure. It's in

- 17 009882/1698

In this context it is pointed out at this point that the maximum energy product in the final finished magnet is present, also with the type of ferrites, the type of their production and also the type of binder and the introduction of the binder changes.

Example 4

Lead ferrite powder is described in Example 2 Way aligned in a low viscosity liquid »ITafter removing the dispersant, the powder is under

ο
a pressure of about 3500 kg / cm * ", then impregnated with a binder and then gradually heated up to about 85O ⁰ G (1562 ⁰ F) over a period of about 3 years. After heating, the body becomes with a low viscosity Epoxy resin impregnated and finally embossed and cured.

The magnetic body produced according to the present example has a residual induction B of 2480 Gauss, a coercive force H _n of 2140 Oersteds and a maximum energy product of 1.44 × 10 Gauss-Oersteds. The apparent density of the body is 4 »14 g / cm and the body is easily machinable.

Example 5

An aligned magnetic body produced according to example 2 is over a period of 3 ·? heated at a temperature gradually increasing up to about 880 ⁰ G (1607 ° F). After the impregnation, embossing and curing of the body carried out according to the preceding examples, a

- 18th

009882/1698

PAD ORIGINAL

Ke3tinduction B of 2640 Gauss, a coercive force H of 2200 Oersted and a maximum energy product of 1.7 x 10 Gauns-Oersted. The apparent density of the body is 4.26 g / cm. The body is easy to work with and its dimensions correspond exactly the dimensions of the mold in which the embossing was carried out.

Example 6

An aligned lead ferrite powder is used in a

Pressure of about 5000 kg / cm compressed and then impregnated with chlorinated naphthalene in the Ί / iron described in lie Example 2. A residual induction B_ of 2400 Gauss, a coercive force H of 1270 Oersted and * a maximum energy product of 1.33 x 10 Gauss-uersted are established for the magnet body. The body v / ill then, starting from room temperature, for about 4 hours heated, up to a gradually increasing to about 80O ⁰ G temperature. After cooling, the body is impregnated with a low-viscosity epoxy resin. This results in a residual induction B of 2680 Gauss, a coercive force of 1570 Oersted and a maximum energy product of 1.68 χ 10 Gauss-Oersted for the magnet body. The apparent density of the material

amounts to 4 »34 g / cm. The considerable improvement in the energy product, which are achieved by the heating interrupted before reaching the sintering conditions result from the foregoing Numbers very obvious.

- 19 009882/1698

Example 7

Bariümferrit is an e! .. ^f a is the size of a particle size corresponding EIernentarzelle ground and suspended in acetone, conveniently a ratio of about 1 cm acetone / g ferrite is used again. The suspension is placed in a non-magnetic form. The ferrite is mixed in a proportion of about ₁ V 5 weight percent stearic acid. After the stamps have been placed in the mold, an alignment field with an initial value of 2300 Oersted is created. The acetone is then pressed out without destroying the magnetic alignment, and the ferritic particles are then subjected to a final pressure

2
compressed by 35CG kg / cm. Thereafter, the body is heated gradually from room temperature to about 1065 ° C (1 "'. O ⁰ F) increasing temperature for about 6 hours, maintaining the peak temperature for about 10-15 minutes, during which time the binder burns After the heated body has slowly cooled down, which is expediently carried out inside the oven, the body is impregnated and finally embossed and cured under moderate temperature and pressure conditions Magnetic body produced on this Yfeise has a maximum energy product of 1.8 χ 10 Gauss-Oersted and is easy to process

Example 8

Strontium ferrite is ground to a particle size roughly the size of a 10-unit cell and placed in acetone

- 20 -009882/1698

1571822

suspended, again a ratio of about 1 cm acetone / g ferrite is expedient. The suspension is placed in a non-magnetic porin and, after the punches have been inserted, exposed to an orientation field with an initial strength of about 2300 oersted. After the acetone has been squeezed out, which is carried out without destroying the alignment, the ram pressure for compressing the quay is increased up to about 3250 kg / cm. The body is then impregnated within the mold with chlorinated naphthalene, taken out from the mold and with a ovens, starting from room temperature, gradually increasing heated up to about 850 C (1562 F ⁰⁾ 'emperature. During this heating process, the binder burns out and the body reaches the state of "green strength", which ensures that it can later be processed. After slow cooling down inside the oven, the body is impregnated and finally embossed and hardened under moderate temperature and pressure changes. The body produced on this Veiee has a hectinduction B of 2200 Gauss, a coercive force of 1700 Oersted and a maximum energy product of 1.12 10 Gauss-Oersted. The apparent density of the body is 3.23 g / cm ⁵ .

In some of the examples explained above, eats as a binder for attaching a not yet heated Body "tearic acid has been used, while other examples

009882/1698

len chlorinated naphthalene was used. An epoxy resin is preferred as the final binder in all palls. However, the invention is in no way restricted to the use of these substances; rather, numerous suitable substances are available for the impregnations that are pressurized in the process according to the invention. The nature of the final binding agent is by no means critical, because it must only be ensured that the binding agent can be introduced into the porous magnetic body without adverse chemical effects or an adverse influence on the magnetic alignment occurring. For example, plastics, axis and also low-melting metal alloys can be used. If a binder is used to solidify the magnet body before the heating stage, this should preferably be volatile in the Y arm, ie it should be used for heating As already mentioned, it is also easily possible to get by with the compressed but not yet heated magnetic body without a binding agent, if the body is handled with appropriate care.

The main advantage of the method according to the invention it can be seen that magnets can be produced with significantly increased energy products other than the detrimental mechanical properties of the sintered magnets, but

- 22 -

009882/1698

BATH ORIGINAL

whose mechanical properties change the mechanical properties the previous unsintered and a lower energy product exhibiting! agnete equal.

The invention was explained above using the example of the production of magnetic bodies from ferritic violets. In addition, the invention can also be applied equally well to all magnets which are composed of small magnetic particles. In particular, the invention is also advantageous in so £. Alnico: laterialien that also are so hard usually, dai: it _# only ground but not machined to v / ground. · ■ ·

KRE / Ki - claims -

009882/1698 ⁰ ^ D ofu _q , nal

Claims (8)

Dt. Expll571i22 claims: 1. Process for the production of machinable permanent magnets ,, where small particles (preferably of the order of a magnetic unit cell) made of magnetically anisotropic material magnetically aligned and then into a compact ;.! agnetkörper are connected, characterized in that the compact magnetic body under "et. and 'J Temperaturbedingungen, which come close to the conditions for sintering, but do not yet achieve them, is heated, whereby a crumbly, relatively porous body whose density is the same as before the "Jrhitson uu does not exceed 15-20 'and that the heated .Body then cooled and without destroying the niagnetiechen Alignment of the particles is impregnated with a workable binder. 2. The method according to claim 1, characterized in that the Magnetic particles are suspended in a liquid medium such as water or acetone that aligns the suspension the particles is exposed to this magnetic field, and that the bispersion medium is then squeezed out. 3. The method according to claim 1 or 2, characterized in that the magnetic particles ferritic particles of the lead ferrite type, Are barium ferrite or strontium ferrite. . 009882/1698 " ^A2 " BATH ORIGINAL A * 4. The method according to any one of the preceding claims, characterized in that a small ^ narrow one volatilizable by Yfärme Binder for solidification in the composed of aligned and compressed magnetic particles, but not yet heated body is inserted, which this body is sufficient for handling during further processing Gives firmness and that during the subsequent heating gradually burns out as the heating temperature rises. 5. The method according to claim 4, characterized in that the intermediate binding agent (aB stearic acid) is used in an amount of about C, 1-1 ″, based on the weight of the magnetic particles in the compressed body. 6. The method according to any one of the preceding claims, characterized in, that the body after heating under moderate temperature and vacuum conditions (for example about 20 ° 0 and 35 kg / cm * ") is embossed and hardened. 7. The method according to any one of the preceding claims, characterized in, that the heating temperature over a period of time gradually increased from about 4 hours to a maximum temperature will. 8. The method according to claim 7, characterized in that the maximum heating temperature is in the range of about 730 to 900 ⁰ C when using lead ferrite. 009882/1698 ORIGINAL BATHROOM