JPH0798963B2 - Sintering furnace for rare earth magnet alloys - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sintering furnace for magnet alloys, especially rare earth magnet alloys.

(Prior Art) As shown in FIG. 2, a conventional sintering furnace for magnet alloys has a heating element 2 provided inside a heat insulating material 3 and a sintered body 1 placed between them. Heat reflection plates 4 are arranged above and below the sintered body. In this sintering furnace, the inside of the furnace is evacuated or filled with an inert gas during sintering. This is to prevent oxygen and other active gas components contained in the furnace atmosphere from being absorbed by the body to be sintered. Since the volume of the sintered body is usually much smaller than the internal volume of the furnace, gas components such as oxygen that may exist in the furnace have a large effect on the relatively small sintered body.

Here, for example, the amount of oxygen that can exist in the sintering furnace having the structure shown in FIG. 2 will be calculated based on the assumed numerical value.

First, the volume of the entire furnace is 5 cubic meters, and the weight of the sintered body is
If it is 50 kg, 1.25 × 10 ^-2 m ³ (ρ≈4.0 g / cm ³ ), the volume ratio with the furnace will be 400: 1. Next, the leak amount is set to 2 lusec and the sintering cycle is set to 6 hours.

Based on 10 ^-3 O ₂ amount when calculating the amount of O ₂ contained in the entire furnace 5 m ³ when the Torr assumptions above are 1.8 × 10 ^-2 (gr), the heated object of 50kg O ₂ amount of but the heated object if the trap all O ₂ becomes 0.36 ppm. However, for example, alloys containing active metals, such as Sm-Co based magnet alloys, usually contain about 3000 ppm of oxygen, and considering the amount of oxygen in the raw material of 300 to 400 ppm, the manufacturing process The amount of oxygen mixed in is extremely large.

This is mainly because the C-H-O compound adsorbed in the crushing and molding process is released from the molded body in the sintering temperature rising process and trapped in the low temperature part (furnace wall reflection plate, heat insulating material, etc.) in the furnace. This is because when the temperature is raised to the sintering temperature, it decomposes into C, H, O and is absorbed again by the object to be heated.

(Problems to be Solved by the Invention) In the conventional sintering furnace as described above, since the ratio of the internal volume of the sintering furnace to the volume (volume) of the sintered body is extremely large,
Gases such as oxygen released from the sintered body during sintering heating
(Not degassed) There is a problem that the characteristics of the sintered body are deteriorated by being trapped in the furnace wall, heat insulating material, etc., and then released from them again during the temperature rising process and absorbed by the sintered body. It was

Therefore, an object of the present invention is to minimize the amount of oxygen that is trapped in the sintering furnace constituents and is released again, even if the above-described inevitable release of gas such as oxygen from the body to be sintered. An object of the present invention is to provide a sintering furnace that can be made small and can prevent the deterioration of the characteristics of the material to be sintered.

(Means for Solving the Problems) In the sintering furnace according to the present invention, an airtight inner cylinder is provided in the furnace, and the body to be sintered is accommodated in the inner cylinder. Further, a getter made of a metal such as Ti or Al that reacts with an active gas such as oxygen or hydrogen is arranged near the vacuum exhaust port of the inner cylinder to capture the gas released from the sintered body.

(Operation) In the present invention, since the furnace has the airtight inner cylinder and the body to be sintered is housed therein, the volume around the body to be sintered is smaller than the conventional furnace volume. Become. The inside of this inner cylinder serves as a soaking zone for sintering. However, since the volume inside the airtight inner cylinder and the volume to be heated are close to each other during sintering, the amount of O ₂ mixed is small, During heating degassing, the inner cylinder is hotter than the object to be heated, so the released gas is less likely to adhere to the inner cylinder, and the getter provided at the vacuum exhaust port absorbs the emitted gas and returns O ₂ etc. from the exhaust system. By preventing this, the physical properties of the sintered body will not be deteriorated.

(Embodiment) FIG. 1 shows an embodiment of the present invention, 5 indicates an airtight inner cylinder arranged inside the heating element 2, and 6 indicates a getter. The sintering furnace according to the present invention includes a heating chamber 7, a sintering chamber 8 and a cooling chamber as shown in the figure.
9, and a vacuuming device 10 provided in each of them, and an elevator 11 provided in the cooling chamber, which works to carry in and carry out the body to be sintered and cool it. The heat insulating material 3 is arranged in the heating chamber 7. The heating element 2 is arranged inside the heat insulating material 3. The airtight inner cylinder 5 has its accommodation compartment narrowed to a position very close to the outer peripheral surface of the body to be sintered, so that the soaking zone for the body to be sintered is extremely narrowed. As a result, the retention space of active gas such as oxygen released when the sintered body is heated is reduced, and
Since the released gas does not come into contact with the heating element or the heat insulating material as in the conventional sintering furnace, the amount of trapping of the gas is reduced.

Here, based on the same assumptions as above, a trial calculation of the oxygen content in the structure shown in Fig. 1 shows that the inner cylinder volume is 0.2 m ² , the weight of the sintered body is 50 kg, and 1.25 × 10 ^-2. m ³ (ρ≈
If it is 4.0 g / cm ³ ), the volume ratio between the inner cylinder and the body to be sintered is about 16 to 1, which is extremely small. Further, when calculating the amount of O ₂ when the 10 ^-3 Torr Assuming no leakage vacuum, the amount of O ₂ contained in the confidentiality inner cylinder is 7.5 × 10 ^-5 (gr), the bake 50kg if sintered body was trapped all O _2, there is O ₂ amount of 1.5 × 10 ^-3 ppm. This amount is very small compared to the above-mentioned conventional example.

Next, the amount of O ₂ of the sintered body that has been heat-treated in the conventional sintering furnace and the sintering furnace having the airtight inner cylinder according to the present invention is shown below. From the above examples, it can be seen that the heat treatment in the present invention has an O ₂ amount of 1/3 or less than that in the conventional case. Therefore, it can be said that the structure of the furnace has an excellent getter effect, in which the gas released from the furnace wall, heating element, reflector, heat insulating material, etc. is suppressed as much as possible.

Further, the weight reduction rate of the sintered body due to the sintering of the Sm-Co magnet alloy is compared as follows.

Next, a method of sintering a rare earth magnet alloy according to the present invention will be described. First, the sintered body 1 is degassed in the cooling chamber 9 at room temperature, and the sintered body 1 is provided in the heating chamber 7 by the elevator 11. The gas is discharged from the body to be sintered by loading it into the airtight inner cylinder 5, operating the vacuuming device, heating the getter made of metal, and heating the body to be sintered by the heating element 2 by the gradually increasing method. The sintered body is removed, the sintering is advanced, and finally the body to be sintered, which has been sintered for a predetermined time, is lowered into the cooling chamber and rapidly cooled. In this case, a getter made of a plate-shaped metal made of Ti, Al, Ca, or the like, which is a material that reacts actively with a gas such as oxygen, hydrogen, or nitrogen, is used. In the sintering furnace having the airtight inner cylinder of the present invention, the getter provided at the vacuum exhaust port absorbs the released gas and prevents the return of O _{2 and the} like from the exhaust system, so that the O ₂ absorbed by the sintered body is absorbed. _There is no _{2 and} extremely clean sintering is possible.

Further, in the case of sintering an alloy containing an element having a high vapor pressure, such as an Sm-Co magnet alloy, the sintering furnace of the present invention has a small effective volume in the furnace. Even if Sm can be buried in the getter,
It has features such as being extremely advantageous.

Furthermore, if the sintering furnace according to the present invention is a rare earth alloy, Sm
It works effectively regardless of -Co system, Gd-Co system, and Tb-Co system.

(Effects) As described above, according to the sintering furnace of the present invention, when the rare earth magnet alloy is sintered, it does not absorb a gas such as oxygen that impairs the physical properties of the sintered body, and the physical properties are stable. The effect that a sintered body can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a side view of a sintering furnace according to the present invention, and FIG. 2 is a schematic view showing a side section of a conventional sintering furnace. In the figure 1 …… Sintered body, 2 …… Heating element, 3 …… Insulation material, 4 …… Reflector, 5 …… Inner cylinder, 6 …… Getter, 7 …… Heating chamber, 9 …… Cooling chamber , 10 ... vacuum evacuation device, 11 ... elevator.

Claims (1)

[Claims] 1. A heat insulating material disposed in a heating chamber, a heat generating element disposed inside the heat insulating material, and an inner cylinder having one end opening which is disposed inside the heat generating element and accommodates a body to be sintered. And a getter which is disposed near the opening of the inner cylinder and which reacts with an active gas such as oxygen and hydrogen, and a sintering furnace for rare earth magnet alloys.