JPH0252413A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To efficiently manufacture a permanent magnet whose mechanical strength and magnetic characteristic are excellent by a method wherein a permanent-magnet metal powder is filled into a malleable metal container and is sealed hermetically, it is heated together with the container and it is compressed and sintered under a specific pressure. CONSTITUTION:During a heating process and a compression and sintering process to be executed after it, a powder at the inside is shut off from the outside by a container and is not oxidized. As a result, a non-oxidizing atmosphere is not required; accordingly, these processes can be executed by using facilities of a simple structure. When the container in which the powder has been enclosed is heated in advance by other means during the compression and sintering process, it is not required to heat a metal mold for pressurization use up to a treatment temperature; accordingly, it is possible to easily obtain a pressure of 2000kg/cm<2> or higher which is hard to realize in an industrial process. Thereby, it is possible to obtain a tough and high-density product where a void is hardly contained.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to a method for manufacturing permanent magnets by powder metallurgy, and in particular Nd-Fe-B, which is difficult to obtain excellent magnetic properties in a cast state. alloys and Sm-Co
This depends on the method of manufacturing permanent magnets such as alloys.

<Prior art> Rare earth magnets such as Nd-Fe-B alloys and Ss-Co alloys cannot have excellent magnetic properties in their cast state, so it is necessary to crush the cast product or to It is made by powder metallurgy using materials that have been pulverized by other suitable methods. Sintering methods for this purpose include cold press compression molding of the powder and then sintering in a vacuum or inert gas, or placing the powder in a mold and heating the mold together, then heating it to a high temperature with a ram. A hot press method of compression molding is known. A special method is to seal the powder in a metal container, etc., then confine the metal container, etc. with argon gas in a sealed chamber, and heat the entire body to increase the gas pressure, thereby compressing and molding the high-temperature powder. There is also an isostatic press method.

The raw material powder can be produced by a reduction method in which the metal powder obtained by reducing the oxide powder is heat-treated to produce the raw material powder, or by pulverizing an ingot made by melting and casting an alloy of the desired components. Melt method that heat-treats raw material powder,
A melt spinning method is practiced in which a quenched ribbon is obtained by thermally spraying an alloy of desired components onto a rotating cooling roller, and the quenched ribbon is pulverized to obtain a raw material powder.

For example, SmCo5 alloys are powdered by a reduction method or a melt method, 5112(:017 alloys are powdered by a melt method, and Nd-Fe-B alloys are powdered by a melt method or a melt-spinning method.

<Invention or problem to be solved> However, the manufacturing method involves sintering after cold-open forming.

This increases the number of man-hours and the time required, and the molded body may collapse during manufacturing or be significantly deformed during sintering. In addition, it is easily oxidized at high temperatures, which may cause it to fail to obtain desired magnetic properties, so the sintering atmosphere must be strictly controlled.

In addition, in the case of the hot press method, due to restrictions on the hot strength of the mold, industrially it is practical to operate at temperatures below 1000°C and 1000°C.
Kg/cs” or less, and due to friction between the powders and between the powder and the mold, fine pores remain in the product, making it difficult to obtain sufficient mechanical strength. , special consideration for oxidation prevention is required.

The hot isostatic pressing method can achieve higher temperatures and pressures than the hot pressing method, and does not cause oxidation because the powder is sealed in a metal container, but it takes a lot of time for one press.
This is extremely disadvantageous for industrial mass production.

This invention aims to efficiently produce a permanent magnet with excellent mechanical strength and magnetic properties through a simple process using powder metallurgy.

<Means for Solving the Problems> In the present invention, first, powder of the above-mentioned permanent magnet metal is filled into a container made of malleable carbon steel, stainless steel, high magnetic permeability steel, etc., and the container is sealed. do.

Next, the powder inside this container is heated. Finally, this heated container is placed in a pressurizing mold and heated to 2000K.
It is compressed and sintered at a pressure of more than g/c+++”.

Here, the powder filled in the container may be molded in advance by cold pressing into a shape that matches the internal dimensions of the container. It is desirable to evacuate the inside of the container to a vacuum, but since the amount of oxygen in the container is very small, strong oxidation and explosions will not occur even if deaeration is not performed. The container may be subjected to cold isostatic pressing prior to heating, and when this is done, the packing density of the powder increases and heating can be performed efficiently and quickly.

For pressure compression, it is advantageous to use a hot extruder and close the extrusion port.
By applying a pressure of about cm2, molding and sintering can be performed more quickly.

When pressurizing, it is preferable to raise the pressure from 0 to the target value within 10 seconds. Once the target pressure is reached, there is no need to maintain that pressure for a long time, and the pressurization should be immediately released and the container removed. Can be done.

After cooling, the removed container is sliced to a predetermined thickness, and if the metal layer transferred from the container is harmful, it is removed by grinding, and the product is polished.

<Function> In this invention, since the permanent magnet powder is housed in a container throughout the treatment period, handling is extremely easy. Then, in the heating and subsequent compression sintering process,
Since the powder inside is isolated from the outside world by the container and oxidation does not occur, a non-oxidizing atmosphere is not required, and therefore these steps can be carried out using equipment with a simple structure. In addition, in the compression sintering process, if the container containing the powder is heated beforehand, there is no need to heat the pressurizing mold to the processing temperature, so hot pressing is difficult to achieve industrially. It is possible to easily obtain a pressure of 2,000 Kg/am2 or more, which makes it possible to obtain a strong, high-density product with almost no pores.

Furthermore, while hot isostatic pressing has an extremely slow rate of pressure increase, in this invention the pressure rises almost instantaneously.
In order to reach the target value of 00Kg/cra2 or more, the powder particles undergo significant internal strain during this time.

The energy stored by this internal strain promotes diffusion between powder particles, and sintering progresses within an extremely short time.

Therefore, in the present invention, permanent magnets with high density and excellent mechanical strength can be efficiently produced using relatively simple equipment and relatively simple operations.

Ta.

Example: Nd, Fe, and B were adjusted to a ratio of 29.8: 691: 0.9% by weight, and after melting in vacuum, argon gas was introduced to bring the melting furnace atmosphere to normal pressure. I returned it. This molten alloy was then injected onto a rotating copper roll through which cooling water was passed to obtain a quenched ribbon. The obtained ribbon was broken into small pieces. This thin ribbon was pulverized in an inert atmosphere to obtain a quenched ribbon powder having an average diameter of 100 yen and an average wall thickness of 20 hi.

This powder has an outer diameter of 150cm, a length of 400cm, and a wall thickness of 25cm.
After vibration-filling into a pure iron capsule, the lid was sealed by electron beam welding while the inside of the capsule was degassed to produce a billet. This billet was heated to 700°C and loaded into a hot extruder having a cylinder with an inner diameter of 155 am, with the extrusion port closed, and the extrusion rate was 10.6 t/.
It was pressed with a pressure of cts2. The time from the start of pressing to reaching the maximum pressure is 2 seconds. After maintaining the maximum pressure for 10 seconds, the billet was taken out. Billet length is 365
The permanent magnet compressed to II11 obtained by the above manufacturing method is isotropic, and its properties are shown in the table below.

(Example 2) Mn: AIL: C=69.4: 30.2:
After adjusting the proportion to 0.4% by weight and melting in an argon atmosphere, the average particle size was reduced to 15% by argon gas atomization.
0, spherical powder was obtained. This powder has an outer diameter of 150+sm.
After vibrating and filling an SO3304 capsule with a length of 40,011 m and a wall pressure of 40 mm, the lid was sealed by electron beam welding while the inside of the capsule was degassed to produce a billet. This bereud was heated to 1150℃ and the inner diameter was 155cm.
The sample was loaded into a hot extruder having a cylinder with its extrusion port closed and pressed at a pressure of 10.6 t/cm''.

The time from the start of extrusion until the maximum pressure is reached is 2 seconds. After maintaining the maximum pressure for 10 seconds, the billet was removed. The length of the billet was compressed to 365cm.

The Mn-An-C alloy obtained by the above manufacturing method was
m, processed into a length of 80m+s and made into a billet for extrusion,
After heating to 680°C in a nitrogen gas atmosphere, extrusion was performed twice using a vertical extruder to produce a bar with a diameter of 10 mm. The Mn-Al-C magnet obtained by this method was anisotropic in the extrusion direction. The magnetic properties are shown in the table below.

<Effects of the Invention> As is clear from the above examples, according to the present invention, permanent magnets with almost no voids and excellent magnetic properties can be efficiently produced by a relatively simple process. Ta.

Claims (1)

[Claims] (1) Fill a malleable metal container with permanent magnet metal powder, seal it, and heat the container to 2000 kg/cm^
A permanent magnet manufacturing method characterized by compressing and sintering at two or more pressures.