JPS6070102A - Atmosphere sintering method - Google Patents

Abstract

PURPOSE:To sinter and produce a rare earth magnet having high quality with an inexpensive installation by replacing the inside of a furnace contg. a green compact of a rare earth cobalt alloy with an inert or reducing atmosphere, setting the pressure thereof higher than the atmospheric pressure and sintering the green compact while maintaining the furnace wall at a high temp. CONSTITUTION:A green compact of a rare earth cobalt alloy having high oxidation reactivity is housed into a vessel 33 provided with a cover 36 and the entire part of the vessel 33 is put into a furnace 32. The entire part of the wall of the vessel 33 is heated to the same temp. as the temp. of the green compact or above and at the same time the inside of the vessel 33 is replaced with an inert gas such as argon or a reducing gas such as gaseous hydrogen or a gaseous mixture composed thereof and is maintained under the pressure slightly higher by about 0.05-1.0 atm than the atmospheric pressure. The gas is released through a gas introducing pipe 34 and a lead-out pipe 35 and the abovementioned green compact is sintered. The decrease in the magnetic characteristic occuring in the reaction with the impurity gas that arises during sintering and particularly the variance thereof are thus prevented and the sintered magnet consisting of rare earth cobalt having excellent quality of the magnetic characteristic is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sintering and producing rare earth cobalt permanent magnets with high oxidation reactivity. The present invention relates to a sintering method that can significantly reduce variations in

Rare earth cobalt permanent magnets are made of a material whose component set is 1 to 4 to 1 to 5, and a 2-17 magnet made of a material whose component set is from 1 to 7 to 2 to 17. It is known that there is.

In terms of manufacturing methods, magnets are broadly classified into resin magnets and sintered magnets based on the method of solidifying the respective powders.

The present invention relates to sintered magnets, and is an invention that replaces or replaces both the 1-5 series and 2-17 series.

A conventional method for manufacturing a sintered rare earth magnet is as follows.

The rare earth cobalt alloy is ground into fine particles of 1 to ]0 μm, 4 to 15. 0.2 to 5 to in the magnetic field of koe
Compression molding is performed using a pressing force of n/cn12, and then the green compact is sintered. Before starting this sintering process, 10-"Hg Degassing treatment is performed at room temperature to 800°C in a vacuum of 10-6 mHg.After that,
It is sealed in an inert gas (mainly argon) or hydrogen gas and raised to the sintering temperature.

Meanwhile, no inert gas or hydrogen gas is used.

It is also a well-known technique to perform this in a vacuum.

As shown in Fig. 1, the furnace body structure for realizing these operations is an external heating type in which the workpiece 13 is placed in the center of a sealed steel pipe 11 and is heated from the outside of the steel pipe 11 by a heater 12. As shown in FIG. 2, an internal heating type furnace in which a heater 22 is constructed in a closed container 2 and a workpiece 23 is placed inside the heater 22 is known as a basic structure. However, these furnaces have common drawbacks in maintaining the quality of the processed materials inside. In other words, gas that is scattered in a vacuum at a temperature below the sintering temperature is adsorbed to a relatively low-temperature part of a sealed tube or container, and then as the temperature inside the furnace rises, impure adsorbed gas is scattered back into the furnace. The gas reacts with the highly reactive process material, causing quality deterioration.

In order to solve these drawbacks, the furnace chamber is divided and the furnace chambers are set up as the degassing process progresses from a relatively low temperature to a sequentially high temperature, so that the impurity gas generated at each temperature is exposed to the high temperature side. Measures are taken to prevent reaction with the processed material. However, when the furnace chambers are divided like this, each chamber has its own vacuum exhaust system and heater.

It is necessary to install a power source, etc., and to install dirt valves, etc. to separate each room, and the equipment cost is enormous.

Although it is possible to reduce the number of divided rooms in order to reduce equipment costs, in this case a decrease in quality is unavoidable. Therefore, to prevent these quality deteriorations.

Before the impure gas reacts with the object to be treated, the impure gas is reacted with another substance. Generally, a substance having a getter action is placed in the furnace to maintain the quality of the processed material.

In the case of rare earth cobalt magnets, there are many different materials used as getters, as long as they are more active than the rare earth elements and do not deteriorate the magnetic properties. especially,
Since the gas pressure of the rare earth metal vapor is high in the furnace, compounds or elements that disrupt the balance are not preferred. In this way, when a getter is used, even if the equipment cost is relatively low, it has the disadvantage that the cost of auxiliary materials for magnet sintering is enormous.

The present invention aims to provide a sintering method that can significantly reduce the cost of sintering equipment and auxiliary materials as described above, and dramatically improve the quality level of magnetic properties, which is the original objective. It is something.

The present invention involves placing a rare earth cobalt green compact in a heat-resistant airtight container, performing gas replacement without evacuating the inside of the container, filling the container with an inert gas such as argon gas, hydrogen, or a mixture thereof, and then replacing the gas with the gas. Start heating up the water without releasing water. The gas in this case.

A high purity gas is required, for example, an oxygen concentration of 1 ppm or less, preferably 0.5 ppm or less. Also, although airtight containers do not need to be completely airtight, it is important to note that the internal pressure of the container is
At temperatures above 00°C, it is necessary to keep the pressure higher than atmospheric pressure. ]The temperature limit is OO℃.

Generally, at higher temperatures, especially as the temperature increases (5), this is because the rare earth magnet powder comes into contact with oxygen and water molecules, and oxidation is rapidly promoted. As for the pressure, it must not be negative even if the external environment such as temperature changes.

As for the minimum pressure for that.

Preferably, the pressure is within a range where gas backflow does not occur, that is, atmospheric pressure plus 0.05 atmosphere or more. Also, if this gas pressure is increased,
Since it is necessary to increase the mechanical strength of the container, it is not preferable to set an excessive external pressure. Therefore, the optimum maximum pressure is about atmospheric pressure plus 1.0 atmosphere.

Incidentally, the gas discharge is basically neutralized during a series of heat treatment operations including sintering, but this discharge is especially essential between room temperature and 800°C. By this discharge, organic substances, moisture, oxygen, and ions generated from these adsorbed on the surface of the rare earth cobalt powder are released, and the magnetic properties of the rare earth cobalt magnet can obtain desired values. i.e. 1
The inventors of the present invention have discovered that these degassing actions, which were conventionally performed by vacuum evacuation, can also be performed in the discharged gas stream. In this case, if the discharge is stopped and the material is heated in a gas-tight atmosphere (6), the desired magnetic properties cannot be obtained, as a matter of course. It has also been found that even if the fluid is discharged, satisfactory magnetic properties cannot be obtained even when the pressure inside the container is between 0 and 0.05 atm. This is thought to be due to atmospheric back-diffusion into the container. 80
At a temperature of 0° C. or higher, the green compact gradually begins to undergo solid diffusion, resulting in so-called sintering, but from now on it is not always necessary to release the gas.

An important point of the present invention is that the effective inner wall portion of this sintered container must be at the same temperature as or higher than that of the rare earth cobalt compact. That is, the gas released from the rare earth cobalt powder surface at a relatively low temperature during the degassing process.

When you touch the inner wall of the furnace whose temperature is lower than that of the powder surface,
This is because there is a possibility that it will stick to the wall surface again. Therefore, the structure must be such that this adsorption does not occur on the inner surface of the container.

FIGS. 3 to 5 show the basic structure of a furnace body and a sintering container that satisfy these requirements.

Figure 3 shows a system in which the entire container 33 is kept within the uniform temperature range of the furnace 32, so that the effective inner wall of the container is uniformly at the same temperature as the powder compact or higher. , gas introduction pipe 34. Only the outlet pipe 35 communicates with the outside of the furnace. The positional relationship between the inlet pipe and the outlet pipe may be reversed. In this case, it is necessary to remove the lid 36 of the container 33 to take in and take out the green compact. In order to improve the degree of sealing of the lid 36, a metal gasket may be used.

All you have to do is increase the internal pressure of the container.

There is no need to use an expensive i4 fitting structure by increasing the fitting precision or using a screw mechanism.

This sealed part is the room temperature part, that is, outside the furnace.
3. That is, the outer container 43-] and the inner container 43-2 housed inside the outer container 43-2 form a storage space for the green compact to be sintered. In such an example, the gas introduction part 44 needs to be connected to a hot part of the container 43.

45 is a gas outlet.

According to such a table structure, impure gas generated as the temperature of the furnace increases is discharged to the outside of the furnace through the space between the outer container 43-1 and the inner container 43-2. However, there is a possibility that impure gas will be adsorbed to the inner wall of the furnace during the process.

Since the discharged gas stream always flows from the high-temperature area to the low-temperature area, there is no worry that impure gas will flow back into the furnace and stay there. Since the movement of the atmosphere inside the container is very complicated, in order to prevent impure gas from flowing back into the furnace, it is necessary to
The distance between the outer container 43-1 and the outer container 43-1 must be kept as small as possible.

The structure shown in FIG. 5 is sufficient as long as no backflow occurs within the container. That is, the container 53 is placed inside the furnace 52 so that its sealed portion is outside the furnace 52.

A gas inlet 54 is connected to the end of the container 53 inside the furnace, and a gas outlet 55 is connected to the container 53 outside the furnace. In such a structure, by ensuring that the discharge gas stream always flows from a hot section inside the furnace to a cold section outside the furnace, no accumulation of impure gases occurs.

(9) Explanation of the gas introduction, derivation system, and furnace control system will be omitted.

The present invention will be explained in detail below.

Example 1 An alloy with 35.8% Sm and residual co was ground to an average particle size of 2.5 microns and heated at 1 Ton/cf in a magnetic field of 7 koe.
Pressure molding of n2 was performed. The size of the press body is 18X7
It is X3 (honor). This press body] 90X75X4
5 (mm) case and stacked in 5 layers. The number of pressed bodies in the case is 500 in total: OXI OX5. The top of the press body was covered with a stainless steel plate that was two times smaller than the inside dimensions of the case.

Place this cased green compact into the furnace shown in Figure 1.

It was evacuated to 500°C using a rotary pump, a mechanical booster, and an X pump, and then filled with argon gas and sintered at a temperature of 1]00°C for 1 hour.

The temperature of the completed sintered body when it was taken out of the furnace was 40°C or lower. When the topmost stainless steel plate inside the case was removed, discoloration of the sintered body inside the case was observed along the outline of the stainless steel plate. Next, (10) the position of each magnet was clarified with respect to only the upper sintered body.'' At step 2, the magnets were polished to 2.3 degrees, and after cleaning, the position of each magnet was clarified.
It was magnetized in the magnetic field of an electromagnet e. The surface magnetic flux density of the magnet was measured using a glass meter.

The results for the first garment were obtained.

Margin below (11) Put a similar powder compact into the exact same case as above,
A plate was similarly covered and sintering was performed using the method shown in FIG. 80
Argon gas was flowed for 3117 minutes until the temperature reached 0°C, and then the argon flow was stopped and the internal pressure was set at 1.05 atm. The sintering temperature was kept at 00°C for a period of time. The gas pressure at this time was 1.8 atm (atmospheric pressure + 0.8 atm).

After the sintering was completed, the temperature of the sintered body was about 50° C. when it was exposed to the atmosphere. The sintered body inside the case had a very beautiful silver color. As in the previous test, the position of the magnet was clarified for only the uppermost sintered body, and the magnet was
After polishing to +mn and cleaning, it was magnetized to [8]<Oe.

The surface magnetic flux density of the magnet is shown in Table 2.

(12) In the case of the conventional method shown in Table 1, the magnets located on the outer periphery of the case have poor magnetic properties, whereas the results shown in Table 2 of the present invention have no drawbacks. I'm being watched.

Example 2 A green compact of the same material as in Example 2 was placed directly into a sintering container shown in FIG. The size of the container is the inner diameter]20. height 97
It is the throat. The green compacts were stacked in 12 stages of 62 pieces.
' The lid of this container was designed to be attached to the main body by cutting screws with a pitch of 2 mm. The temperature of the furnace was raised while flowing argon gas at a rate of about 11/min.

White smoke was observed coming out from the threaded portion in the range of 200°C to 400°C. The internal pressure of the container began to rise after 600°C, so the valve was opened and the internal pressure was reduced to 1.2 atm (normal pressure + 0
．． The atmospheric pressure was adjusted to 2 atm. After the sintering was completed, the temperature of the sintered body was about 80° C. when the argon gas was stopped.

The appearance of the sintered body was entirely silver except for the surface of one piece closest to the gas inlet which was partly gray. In addition, the magnetic properties were at the same level as Example 1, except for one gray one, which was slightly lower at 1790, and had a normal distribution.0 Example 3゜Sm 26%, Fe 20%, Cu 4.5%
, Zr 2.0%.

The remaining Co alloy was made into a green compact using the same pressing method with an average particle size of 3 μm. The sintering process was performed using the material shown in Figure 5 in a hydrogen stream. The sintering temperature was 1,190° C. for 2 hours, and then a solution treatment was performed at 1,160° C. for 2 hours, followed by a large amount of sintering from the furnace. All the sintered bodies were shining silver. After this sintered body was aged at 800° C. for 10 hours, the surface magnetic flux density was measured in the same manner as in the above example, and as a result, magnetic characteristic values with an ideal normal distribution were obtained.

The gas used in all of the experiments described above was directly piped from liquefied gas, and the oxygen concentration was less than O, ]ppm.

As mentioned above, since the sintering method according to the present invention does not require a high vacuum exhaust device, it is possible to significantly reduce equipment costs, and at the same time,
This has a dramatic effect on improving the quality of the magnetic properties of rare earth cobalt magnets. Of course, the present invention can be applied to the complete sintering of metal particles other than rare earth cobalt, and its industrial value is extremely large.

[Brief explanation of drawings]

Figures 1 and 2 each show a cross-sectional view of the schematic structure of a conventional sintering furnace, and Figures 3, 4, and 5 each show a schematic structure of a sintering furnace used in the present invention.゜Second. A schematic structure of a third example is shown in a cross-sectional view.

Claims (1)

[Claims] 1. In a furnace for sintering rare earth cobalt alloy compacts with high oxidation reactivity, the inside of the furnace is replaced with an inert or reducing atmosphere without creating a vacuum, and the effective furnace wall is kept at the same temperature as the material to be sintered. 1. A method for atmosphere sintering for a metal powder compact, characterized in that the atmosphere is maintained at a pressure slightly higher than atmospheric pressure.