JPH07240330A - Manufacture of rare-earth intermetallic compound magnet - Google Patents

Abstract

PURPOSE:To provide a means which can continuously mold powder for rare- earth intermetallic compound magnet without lowering the strength of molded bodies by dissolving such a problem that a metallic mold is damaged power adhering to the metallic mold at the time of molding. CONSTITUTION:A rare-earth intermetallic compound magnet manufacturing method comprises the step of pulverizing coarse particles of an Nd-Fe-B rare- earth intermetallic compound permanent magnetic alloy after adding and mixing a hydrocarbon-based lubricant and binder to and with the coarse particles and molding and sintering the pulverized fine particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth intermetallic compound magnet.

[0002]

2. Description of the Related Art In recent years, along with the market trend of miniaturization and weight reduction of electronic devices and precision machines, rare earth magnets have been used in many fields in permanent magnets instead of conventional alnico and ferrite magnets. It was Rare earth magnets are manufactured using powder metallurgy except for some applications. Among rare earth magnets, the demand for Nd-Fe-B based rare earth intermetallic compound permanent magnets is increasing. A method of manufacturing an Nd-Fe-B system rare earth intermetallic compound magnet by powder metallurgy is to melt an alloy into a desired composition to obtain an ingot, which is roughly crushed to an average particle size of about 20 to 500 μm, 1 more
After finely pulverizing to a powder of about 20 μm, molding, sintering,
A method that goes through a heat treatment step is generally used. In this process, in order to obtain a molded body from the melt-casting ingot, 1 or less of coarse powder mechanically or chemically preliminarily made to 20 to 500 μm
The powder finely pulverized to ˜20 μm is filled in a mold and then pressed at 0.5 to 5 ton / cm ² to obtain a molded body. Generally, in order to obtain high magnetic properties, a magnetic field is applied during molding to impart anisotropy to the molded body.

However, in molding rare earth intermetallic compound permanent magnet powder, the raw material powder adheres to the inner wall of the mold due to friction between the inner wall of the mold and the raw material powder or the molded body during molding, and scratches occur on the inner wall of the mold. Damage the mold. In order to avoid this, the die dies must be exchanged vigorously, resulting in a decrease in molding work efficiency and an increase in die retirement costs. In order to avoid this, a method of applying a powdery or liquid lubricant to the inner wall of the mold is generally used, but this method does not have a permanent lubricating effect, so the lubricant must be applied vigorously. However, it has a drawback that the molding efficiency is lowered.

As an alternative to the method of lubricating the inner wall of the mold, it has been proposed to add a lubricant for improving the moldability to the raw material powder. For example, Japanese Patent Publication No. 5-61340 proposes to add at least one kind of stearic acid, zinc stearate and bisamide, and JP-A No. 5-214406 proposes to add at least one kind of solid paraffin and camphor. However, these proposals have the following problems because the lubricant is added and mixed by a mechanical mixer. That is, it is difficult to uniformly disperse a lubricant having a high cohesive property with a mechanical mixer, and therefore, a lubricant aggregate exists in the mixture. In addition, since the true specific gravities of the rare earth intermetallic compound fine powder and the lubricant are significantly different, it is difficult to uniformly disperse the lubricant in mechanical mixing. Therefore, the lubrication method proposed above has an insufficient lubrication effect, and continuous molding is impossible. Further, if the agglomerated lubricant is present in the molded body, it has a drawback that the magnetic properties are deteriorated and the quality is deteriorated.

[0005]

As means for solving the above-mentioned problems, Japanese Patent Laid-Open No. 4-191302 and Japanese Patent Laid-Open No. 5-191302 are available.
Japanese Patent No. 94922 proposes a production method in which a mixture containing the above lubricant is finely pulverized by an air flow type pulverizer, and then molded and sintered. According to this coarse powder lubrication (hereinafter referred to as coarse powder lubrication), the lubricant is extremely uniformly dispersed by air flow type grinding. Therefore, it is possible to prevent the agglomeration of the lubricant by adding a relatively small amount of the lubricant.

Although coarse powder lubrication is an extremely effective technique as described above, it has the following problems. That is, as a result of the uniform dispersion of the lubricant, the strength of the molded body is lowered, and peeling or cracking occurs in the molded body, making it extremely difficult to obtain a sintered body with desired dimensional accuracy. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to efficiently perform continuous molding of rare earth intermetallic compound permanent magnet powder.
The present invention provides a means for continuously molding a rare earth intermetallic compound magnet without eliminating damage to the mold due to adhesion of powder to the mold during molding and without lowering the strength of the molded body.

[0007]

According to the present invention, a rare earth intermetallic compound permanent magnet alloy coarse powder is mixed with a hydrocarbon lubricant and a binder, and then finely pulverized by air flow pulverization, followed by molding and sintering. The above-mentioned problems of the prior art have been solved.

The present invention will be described in detail below. In the present invention, first, a hydrocarbon-based lubricant and a binder are added to and mixed with the rare earth intermetallic compound permanent magnet alloy coarse powder. Mixing is performed by a dry method using a V-type mixer, a Henschel mixer, a ball mill or the like. Here, as the hydrocarbon-based lubricant, liquid paraffin, natural paraffin, microcrystalline wax, polyethylene wax, synthetic paraffin, chlorinated naphthalene, etc. are effective. As the anti-caking agent, one kind or two or more kinds of polyvalent alcohol and its derivatives are effective. These added mixtures are then finely pulverized to 1 to 20 μm by an air flow pulverization method such as a jet mill. In the pulverizing step, the hydrocarbon lubricant is melted and fixed on the surface of the powder and uniformly applied on the surface of the fine powder. The melt-coated lubricant reduces friction between fine powder particles and between the particles and the inner wall of the mold.

The form of the lubricant to be added is not particularly limited, but a powdery lubricant is preferable for efficient and uniform dispersion. Addition amount of hydrocarbon lubricant is 0.05w
If it is less than t%, a sufficient lubricating effect cannot be obtained. Further, if the addition amount exceeds 5.0 wt%, C exceeding the allowable range in the sintered body is obtained.
Remain and deteriorate magnetic properties remarkably. Further, if the addition amount is 0.5 to 2.0 wt%, high strength of the molded body can be obtained. Therefore, the addition amount of the hydrocarbon lubricant is 0.05 to 5.0 wt%, more preferably 0.5 to 2.0.
wt%. The boiling point or decomposition temperature of the polyvalent alcohol or its derivative used as the binder is preferably 300 ° C or lower. Particularly by mixing ethylene glycol, diethylene glycol, polyethylene glycol and the like, the strength of the molded body is improved and the depressurizing pressure at the time of releasing the molded body is reduced. The presence of the polyvalent alcohol or its derivative in the compact strengthening agent, when present between the fine powder particles coated with the lubricant or between the compact and the inner wall of the mold, reinforces the compact and lowers the drawing pressure. The addition amount of these is 0.01 to 2 wt%, more preferably 0.0.
It is good to set it to 1 to 0.2%. Since these reinforcing agents generally have an extremely small amount of dissolution in an organic solvent, addition of 2 wt% or more makes degreasing of a molded body difficult and causes deterioration of magnetic properties.

The molding is performed without a magnetic field or in a magnetic field.
The obtained molded body is degreased by being immersed in an organic solvent for a predetermined time. As the organic solvent, toluene, cyclohexane, normal hexane, kerosene, xylene, mineral tape, etc. are preferable. By immersing the molded body in these organic solvents for a predetermined time, the added amount of about 9
0% of lubricant is removed. In order to accelerate the degreasing speed of the lubricant, it is effective to heat, stir and apply ultrasonic vibration to the organic solvent.

The molded body previously immersed in the organic solvent is sintered in vacuum or in an inert atmosphere such as argon. In the case of sintering a molded body that is not pretreated with an organic solvent, a degreasing step is required in the sintering step. Ie 100
After the molded body is heated and held at ˜500 ° C. to remove the lubricant and the binder from the molded body, it is necessary to perform the main sintering at 1000 to 1200 ° C. Therefore, 16 to
It takes 24 hours, and the production efficiency is extremely poor in industry. According to the present invention, the green body pretreated with an organic solvent does not need a degreasing step during the sintering step, and it is possible to perform the sintering by holding the green body for a certain time at the sintering temperature, Further, since the sintering furnace does not require a special device such as a wax trap or a degreasing chamber, the facility cost of the sintering furnace is remarkably reduced, which is extremely advantageous in industry.

Further, the binder according to the present invention forms a uniform protective film on the surface of the fine powder and is effective in preventing the fine powder from being oxidized.
The oxygen content of the sintered body after degreasing and cleaning is suppressed to 0.6 wt% or less. Carbon content of sintered body after degreasing is 0.15wt%
If it exceeds, the magnetic properties will be significantly deteriorated. Although there is no restriction on the lower limit of the amount of C in terms of magnetic properties, since the main element of the lubricant and the binder is carbon, it is substantially 0.03 to 0.10 wt% even after sufficient degreasing and cleaning. It is inevitable that% of carbon remains in the sintered body. The amount of carbon remaining in the sintered body depends on the amount and combination of the lubricant and the binder. Since the binder according to the present invention has an extremely small amount of dissolution in an organic solvent, most of it decomposes and scatters in the sintering process. Therefore, using a binder having a decomposition temperature or a boiling point of 300 ° C. or higher is magnetic. Not preferable.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples. The present invention is not limited to the following examples.

(Example 1) Nd-F having an average particle size of 40 μm
e-B permanent magnet alloy coarse powder with 2% by weight of microcrystalline wax and 100% molecular weight polyethylene glycol
Of 0.5 wt% was added and mixed in a V-type mixer for 10 minutes. After mixing, the coarse powder was pulverized by a jet mill to obtain fine powder having an average particle size of 3.5 μm. Table 1 shows the results of comparison of the lubricating effect and the strength of the molded body when the obtained fine powder was molded in a magnetic field, compared with the fine powder to which no lubricant or binder was added. The fine powder according to the present invention was continuously molded 10,000 times or more, and no damage was found on the molded body and the mold. On the other hand, the additive-free fine powder was continuously molded 20 times. Molding could not be continued. Also, it can be seen that the strength of the molded body is increased by about 2 times according to the fine powder of the present invention.

[0015]

[Table 1]

(Example 2) Paraffin wax (1 wt%) and diethylene glycol (2 wt%) were added to Nd-Fe-B system permanent magnet alloy coarse powder, and fine powder having an average particle size of 4.2 µm was obtained by pulverizing with a jet mill. . Table 2 shows the results of a comparative study of the lubricity and compact strength of the fine powder according to the present invention with the non-added powder and the wax-added powder. For paraffin wax and diethylene glycol-free powder, 2
While the molded body was scratched at the time of molding 0 times, the fine powder to which the paraffin wax and diethylene glycol were added together did not show any scratches on the molded body even after continuous molding at 10,000 times. Further, with fine powder containing only paraffin wax, continuous molding was possible up to 2000 times, but the mold release resistance gradually increased, and mold release became impossible after 2000 times.

[0017]

[Table 2]

(Example 3) Nd-F having an average particle size of 40 μm
Natural wax 1 wt% and molecular weight 20 on e-B coarse powder
0.2 wt% of polyethylene glycol of 0 was added and mixed, and the mixture was pulverized by a jet mill to obtain fine powder having an average particle diameter of 3.8 μm. After molding this fine powder in a magnetic field, the molded body was immersed in toluene for 2 hours, molded at 1000 ° C. for 2 hours, and then rapidly cooled to room temperature. Magnetic Properties of Sintered Body and Remaining C Content and O
The amount is shown in comparison with the sintered body which was not subjected to the immersion treatment.

[0019]

[Table 3]

(Example 4) Nd-F having an average particle size of 30 μm
Micro wax to e-B system permanent magnet coarse powder 0.01 to 6
wt% and 0.2 wt% of ethylene glycol were added and mixed, and finely obtained by jet mill grinding and molding in a magnetic field. Then, the compact was immersed in cyclohexane for 3 hours, and
Vacuum sintering was performed at 0 ° C. for 2 hours. Table 4 shows the relationship among the amount added, the continuous formability, the coercive force of the sintered body, and the amount of C.

[0021]

[Table 4]

(Example 5) Nd-F having an average particle size of 30 μm
1 wt% of liquid paraffin was added to e-B type permanent magnet coarse powder and mixed and jet milled to obtain fine powder, and 0.005 to 0.3 wt% of calcium stearate was additionally mixed. The molded body was immersed in kerosene for 3 hours and vacuum-sintered at 1100 ° C. for 2 hours. Table 5 shows the relationship among the amount of calcium stearate added, continuous formability, compact strength, sintered body coercive force, and C content.

[Table 5]

[0023]

According to the present invention, damage to a mold and peeling and cracking of a molded body at the time of molding can be eliminated, and molding of rare earth permanent magnet alloy powder can be carried out semipermanently and continuously. It is possible to obtain a permanent magnet without deterioration of magnetic properties without using an exclusive sintering furnace having an expensive dewaxing mechanism.

Claims (9)

[Claims] 1. A Nd-Fe-B-based rare earth intermetallic compound permanent magnet alloy coarse powder is mixed with a hydrocarbon-based lubricant and a binder, and then finely pulverized by an air flow pulverization method, followed by molding and sintering. A method of manufacturing a rare earth intermetallic compound magnet. 2. A Nd-Fe-B-based rare earth intermetallic compound permanent magnet alloy coarse powder is mixed with a hydrocarbon-based lubricant and a binder, then finely pulverized by an air flow pulverization method, and then molded, and lubricated from this molded body. A method for producing a rare earth intermetallic compound permanent magnet, which comprises performing a pretreatment for removing an agent and then sintering. 3. The addition amount of the hydrocarbon lubricant is 0.05 to 5.
It is 5.0 wt%, The manufacturing method of the rare earth intermetallic compound permanent magnet of Claim 1 or Claim 2. 4. The addition amount of the hydrocarbon lubricant is 0.5 to 2.
It is 0 wt%, The manufacturing method of the rare earth intermetallic compound magnet of Claim 1 or 2. 5. The method for producing a rare earth intermetallic compound magnet according to claim 1, wherein the amount of the binder added is 0.01 to 2 wt%. 6. The amount of the binder added is 0.02 to 0.1 wt%.
The method for producing a rare earth intermetallic compound permanent magnet according to any one of claims 1 to 4. 7. The production of a rare earth intermetallic compound permanent magnet according to claim 1, wherein the binder is one kind or two or more kinds of polyvalent alcohol or its derivative. Method. 8. The rare earth metal-intermetallic compound according to claim 1, wherein the binder is one kind or two or more kinds of ethylene glycol, diethylene glycol and polyethylene glycol. Compound permanent magnet. 9. The pretreatment for removing the lubricant from the molded body,
9. The method for producing a rare earth intermetallic compound permanent magnet according to claim 2, wherein the molded body is dipped in an organic solvent for a predetermined time.