NO119261B - - Google Patents

Description

Method for producing a permanent magnetic body.

Permanent magnetics are known

bodies which essentially consist of single crystals or mixed crystals which

has a composition corresponding to the formula

MxCa(1 _x)0. 6 Fe203,

where M means one or more of the metals Ba,

Sr or Pb and where 0.6<:x<; 1 (see e.g.

French Patent No. 1,048:792 and Philips Technical Review, Volume 13, No. 7, January 1952,

pages 194—208). It is also known to produce (see French patent no. 1,080,514)

crystal oriented or anisotropic permanent magnetic bodies consisting of such

materials. You mainly walk below that

forward in the following way: A powder of one

or several of the crystal species described above are suspended in an indifferent liquid

(usually water) and the obtained suspension is placed between the poles of a magnetic net, while the liquid is squeezed out (in the following

referred to as the "wet press method"). As

as a result, the particles of the powder are exposed

for a saving effect while at the same time

are pressed together. The manufactured press body is then sintered at a temperature

between 1100 and 1450°C. This method has already led to the production of

permanent magnetic bodies with a

(BH)max value of over 2 x 106 gauss-ørsted. Also the mechanical properties of

bodies produced in this way are usually very satisfactory.

The relevant method is, however, less satisfactory when it

concerns the production of bodies which

have more or less complicated forms.

It must be remembered that they press matrices

which is used for carrying out the method in question in these cases must of course also have a complicated structure and at the same time be completely waterproof and strong in mechanical terms, which properties are usually difficult to achieve at the same time. In practice, it also turned out that such press matrices were often damaged due to wear and tear when relatively large amounts of water had to be removed.

These difficulties can of course be avoided by making permanent magnetic bodies of a simpler shape and then afterwards, by mechanical processing, giving the bodies the desired, more complicated shape, but even this method is not entirely satisfactory as the bodies in question are not well suited to mechanical processing, as they are too hard.

In the above-mentioned French patent no. 1,080,514, the possibility of pressing the crystal powder together in a magnetic field into a permanent magnet as such is also mentioned, i.e. without the introduction of any liquid, while the particles of the powder still have a certain freedom of movement just above each other (hereafter called "dry pressing method"), and then sinter the resulting pressed body so that a permanent magnetic body is obtained. However, the mechanical properties and density of the permanent magnetic bodies produced by this method to date were not satisfactory.

The invention solves the problem of producing anisotropic permanent magnetic bodies of the aforementioned kind and

which has a more or less complicated form,

using a method that includes characteristic features from both the "wet" and the "dry" pressing method. According to the invention, one proceeds in the following way: as with the "wet" pressing method, the permanent magnetic powder is suspended in an indifferent liquid, for example water, and while the suspension is placed between the poles of a magnet, the liquid is removed from the suspension, f e.g. by filtering. In this way, you get a conglomerate that has a directive effect, i.e. it is magnetically anisotropic. This conglomerate is now granulated, e.g. by means of a sieve, through which the solid substance is pressed. The granulate thus obtained is then placed in a press matrix in which it is pressed together while it is between the poles of a magnet. The obtained pressed body whose (magnetically anisotropic) grain is relatively well parallel

slightly oriented as a result of the last-mentioned processing, is finally sintered into the finally desired permanent magnetic body. In this way, it is possible to produce permanent magnetic bodies with a (BH)max value of over approx. 1.5 x 10'1 gauss ørsted. Granules are preferably added

tet, before it is processed into a press body in the manner described above, a substance which gives the press body a good connection and yet does not increase the friction between the grains during the pressing operation. For this, solid organic substances which turn into liquid form under low pressure (of less than 500 kg/cm?) are particularly suitable. Particularly suitable are e.g. camphor or substances chemically related to camphor. Camphor turns into liquid form at a pressure of 75-100 kg/cm?. The best approach is to add camphor or a similar substance in the form of an alcohol solution, for example

show a solution containing 2% by weight of the substance, and that this solution is sprayed over the granules to be pressed.

Instead of camphor or something similar

dense material can, e.g. kerosene is also well used.

In the following, the invention is explained in more detail in connection with two design examples.

Example 1:

Barium carbonate, BaCO3, and iron (III) oxide, Fe2O3, are thoroughly mixed in a finely divided state in a molecular ratio of 1.1:6. The mixture is pressed into blocks and these blocks are heated for approx. 15 minutes at 1280° C. After cooling, the blocks are pulverized,

and after adding a small amount of water and 1% by weight calcium carbonate, calculate

net in relation to the amount of carbonate added, a suspension is obtained. This suspension is affected in a magnetic field and

net is removed by filtration, after which the resulting filter cake is dried in the air. The air-dried fabric is then pressed through a sieve with meshes of approximately 2 X 2 mm. The bodies thus obtained are then pressed together in a magnetic field and finally heated for approx. 5 minutes at approximately 1250°C.

The properties of a permanent magnet produced in this way are the following:

Br = 3050 gauss

BHc = 1450 ørsted

IHc = 1600 ørsted

(BH)mic.. = 1.8 x 106 gauss.ørsted

(at H = 1000 ørsted).

Example 2:

Barium carbonate, BaCO3, and iron (III) oxide Fe203, in a finely divided state, are thoroughly mixed in a molecular ratio of 1.1:6, and then heated approx. 15 minutes at 1280°C. After adding a small amount of water and 1% by weight calcium carbonate CaC03,

calculated in relation to the amount of carbonate added, it becomes a permanent magnet

isic reaction product processed into a suspension. The water is removed from this suspension by filtration in a magnetic field, after which the resulting filter cake is dried in the air.

The air-dried fabric is then pressed through a sieve with meshes of approx. 1 XI mm. An alcoholic solution with 2% by weight of camphor, calculated in proportion, is sprinkled over the grains thus obtained

to the weight of the grains. The alcohol is evaporated by allowing the granules to stand in the air for some time.

The grains mixed with camphor are then pressed together in a magnetic field and the thus obtained pressing body is finally heated approx. 5 minutes at approximately 1240°C. The properties of a permanent magnet produced in this way were as follows:

Br = 3340 gauss

BHc= 1240 ørsted

I"c = 1280 ørsted

(BH)m.lks <=> 2.8 x 106 gauss.ørsted

(at H = 1100 ørsted).

Claims (5)

1. Method for producing an anisotropic permanent magnetic body with a (BH)m:lks value of over approx. 1.5 X 10<0> gauss. ørsted, which essentially consists of single crystals or mixed crystals that have a composition corresponding to the formula MvCan_x)0. O. 6Fe20K in which M denotes one or more of the metals Ba, Sr or Pb and where 0.6 <; X <:{ 1, in which method a powder of one or more of the above-mentioned crystal types is suspended in an indifferent liquid, and the liquid is removed from the suspension — for example by filtration — under the simultaneous action of an external magnetic field, whereby a magnetic anisotropic conglomerate, characterized in that this conglomerate is granulated by being pressed through a sieve and that the granulate, possibly with the addition of a lubricant, is pressed in a magnetic field to the shape the desired permanent magnetic body should have, after which the body is finally pressed on in and of itself known method is sintered at a temperature between 1100° and 1450°C. 2. Method according to claim 1, characterized in that, before the granulate is processed into a compact, an available organic substance is added which turns into liquid form under a low pressure (below 500 kg/cm2). 3. Method according to claim 2, characterized in that camphor or a chemically related substance is added to the granulate before it is processed into a compact. 4. Method according to claim 3, characterized in that camphor or the similar substance is added in the form of an alcoholic solution. 5. Method according to claim 4, characterized in that an alcoholic solution of camphor or a similar substance is sprayed over the grains.