JPS61276901A - Production of porous magnet - Google Patents

Abstract

PURPOSE:To produce a porous magnet undergoing no reduction in the magnetic flux density by mixing a magnetizable powdery substance with a substance volatilizable at a low temp., molding the mixture to a prescribed shape, baking the molded body to volatilize the volatilizable substance, and magnetizing the resulting porous body. CONSTITUTION:Powder of a magnetizable substance such as iron ferrite, rare earth elements or iron monoferrite having <=250 mesh particle size is mixed with crystalline cellulose volatilizable readily at >=100 deg.C and water. The mixture is molded to a desired shape, the molded body is baked at a high temp. in a kiln to volatilize the volatilizable substance, and the resulting porous body is magnetized to produce a porous magnet undergoing no reduction in the magnetic flux density.

Description

[Detailed Description of the Invention] Industrial Field of Application Conventional Technology Although it is not possible to find any particularly established technology as a method for manufacturing porous magnets, conventionally known powder metallurgy technology can be used to produce porous magnets. It is possible to apply this method to produce porous magnets. One example is JP-A-55-8166.
It can be found on page 5 of the specification of Publication No. 1.

Problems to be Solved by the Invention Conventionally known powder metallurgy techniques utilize the physical properties of powder, such as fluidity, divisibility, and mobility, to facilitate molding. However, there are many limitations to the extent that the strength or machinability can be brought close to that of generally known melt-formed metals. This is a drawback when producing porous magnets using powder metallurgy techniques. Although it depends on the amount of voids in the f11 porous magnet, it is necessary to limit the particle size used. (2) The particle shape must be circular or close to a circle. (3)
It has drawbacks such as difficulty in controlling the amount of voids. Regarding fl+, there is variation in particle size in the case of powder metallurgy. As a result, fine particles enter the voids formed by the relatively large particles and fill the voids. In (2), if the grain shape is polygonal, the corners will fill the voids, and if the grains have particularly acute corners,
When particles have a flat shape, it is very difficult to create voids. (3) When a certain particle size is selected and the particle size is made circular, the molding pressure must be a certain amount or more, and only in that case can a tangible metal with strength be obtained. However, reducing the molding pressure simply to increase the amount of voids will make the metal brittle and result in the production of a tangible metal that cannot withstand use.

Therefore, it would be too expensive to manufacture ideal porous magnets using conventional powder metallurgy techniques.

Means for Solving the Problems The present invention eliminates the drawbacks in the prior art and is not limited in any way to particle size and shape, but within a range (2% to 30%).
This is a porous magnet production method in which a magnet is obtained by magnetizing an object in which the amount of voids can be freely selected.More specifically, the magnetizable powder includes ferrite iron, monoferrite iron, or rare earth. The shape of these particles is not limited at all, and any shape can be used, and it is also possible to mix a plurality of shapes (for example, circular, polygonal, oblate, etc.). . On the other hand, the particle size is not particularly limited, or it is not preferable that it be smaller than the minimum size of the porous magnet to be molded, and it is desirable that the middle stage of the powder used be the maximum size of large particles. The most desirable result can be obtained if the size is less than /4 of the minimum dimension of the porous magnet. On the other hand, it is possible to use a vaporized substance that vaporizes at room temperature and normal pressure, since good results can be expected when it is used in a mixture, or preferably in a combination of a liquid and a solid or a colloid and a solid. However, components of the substance remain in the voids formed by vaporization, which may hinder secondary processing (drug impregnation, etc.). Therefore, it has to be removed in advance, which has the disadvantage of complicating the manufacturing process. Furthermore, when using a solid vaporized substance, it is desirable to make the particle size as small as possible, and it is desirable that the diameter of the largest particle is at least 8 times smaller than the minimum dimension of the porous magnet to be molded.

The materials (magnetizable powder and vaporized substance) having the above configuration are mixed in a ratio that matches the desired amount of voids, stirred so that the mixing ratio of each part is uniform, and the mixture is It is molded into the desired shape using a pressure molding machine.
At that time, there is no need to limit the shape to be molded or the molding pressure.In particular, unlike conventional powder metallurgy methods, there is no need to adjust the pressure at all, and molding at the maximum pressure of the molding machine is sufficient. It is sufficient. The molded product thus formed is placed in a firing furnace to vaporize the vaporized substance to obtain a porous metal, and the porous metal is magnetized to form a porous magnet.

Example 1: 80 parts of ferrite iron powder with a particle size of 250 mesh or less, 20 parts of crystalline cellulose (trade name Avicel, manufactured by Asahi Kasei Industries) with a particle size of 350 mesh or less, and 5 parts of water (all by volume) were uniformly mixed and stirred. Then, using a pressure molding machine, a diameter of 8
This was molded to a thickness of 3.5 mm and fired in a firing furnace at a temperature of about 1200°C to obtain a porous metal with a porosity of 16%.The porous metal was magnetized to have a magnetic flux density of 630G. We were able to obtain a porous magnet.

The second example was the same process as the first example except that 80 parts of rare earth powder with a particle size of 250 mesh or less was used, but the magnetic flux density was 9 in diameter.
We were able to obtain an 80G porous magnet.

3rd example, 80 parts of monoferrite iron powder of 300 mesh or less, 20 parts of polyethylene resin powder of 350 mesh,
7 parts (volume ratio) of denatured alcohol were mixed and stirred uniformly, and molded using a pressure molding machine to a diameter of 6cm and a thickness of 2.5m2.
After putting it into a drying oven and completely volatilizing the denatured alcohol in advance, it was fired in a baking oven at a temperature of about 600°C to obtain a porous metal with a porosity of 18%, which was then magnetized. As a result, a porous magnet with a magnetic flux density of 750G was obtained.

Effects of the Invention As described in detail in 2, unlike the conventional powder metallurgy method, there is no need to use a special binder, and there is no need to use a special binder, and there is no need to use molding pressure. It is possible to produce highly porous magnets without the need for additional adjustment, and the desired porosity can be easily obtained simply by changing the mixing ratio of magnetizable powder and vaporized substance. Done,
Further, when the magnetizable powders are of the same type and have the same porosity, it is possible to increase the magnetic flux density G by making the particles of the magnetizable powder smaller.

The present invention can be carried out as described below, does not require any advanced technology, and is therefore a useful invention that can produce excellent porous magnets at low cost.

Claims (4)

[Claims] (1) A porous object is formed by mixing magnetizable powder with a vaporized substance that vaporizes at a temperature of 100°C or higher, molding it into a certain shape, and firing it to vaporize the vaporized substance. A method for producing a porous magnet, which comprises obtaining a magnet by magnetizing the object. (2) A method for producing a porous magnet according to claim 1, in which ferrite iron is used as the magnetizable powder. (3) A method for producing a porous magnet according to claim 1, wherein a rare earth element is used as the magnetizable powder. (4) A method for producing a porous magnet according to claim 1, wherein monoferrite iron is used as the magnetizable powder.