JPH0645167A - Manufacture of isotropic bond magnet - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing an isotropic bond magnet of rare earth metal, iron, cobalt, and boron high in strength and excellent in magnetic properties. CONSTITUTION:Resin binder is added to magnetic powder composed of rare earth metal, iron, cobalt, and boron and formed through a quench solidifying method, resin binder-loaded magnetic powder is compression-molded by a pressure of over 120kgf/mm<2>, a molding die is released from a clamping force once and clamped again by a clamping pressure over a molding pressure, a molded magnet is released from the molding die and heated to harden resin. At this point, 1 to 3% by weight of resin binder is added to magnetic powder 30 to 155mum in average grain diameter.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has a composition of rare earth metal / iron /
The present invention relates to a method for producing an isotropic bonded magnet in which RTB magnetic powder made of cobalt / boron is bonded with a resin, and can be used for a stator or a rotor of a motor.

[0002]

2. Description of the Related Art RTB-based isotropic bonded magnets have superior magnetic properties to conventional hard ferrite and alnico magnets, and are more magnetic than anisotropic Sm-Co based bonded magnets. Although slightly inferior in characteristics, expensive Sm
Since it is not used and no magnetic anisotropy is given, the manufacturing process is simplified and it is advantageous in terms of cost. It is used as a stator for motors such as electric tools and hard disks.

A method for producing an isotropic bonded magnet is, for example, as follows.
As disclosed in Japanese Patent Laid-Open No. 59-2111549, RTB-based magnetic powder is manufactured by a rapid solidification method and a crushing method, and an organic material, an inorganic material, which is a binder, is added to the magnetic powder.
Alternatively, a low melting point metal such as solder is mixed, and this mixed powder is compression-molded at a pressure of about 110 kgf / mm ² . The obtained density is about 6.0 g / cm ³ (density ratio 8
0%).

Further, as described in JP-A-1-281707, a magnetic powder surface is coated with a certain resin, and during molding, the powder particles are made slippery and have good flowability to form a molded article. There is a proposal to increase the density and improve the magnetic characteristics. By the way, although the magnetic characteristics of the isotropic bonded magnet can be used in the current quality, further improvement of the characteristics is desired in order to improve the output of the motor and reduce the power consumption. For that purpose, since the magnetic properties depend on the density of the compact, it is necessary to increase the space factor of the magnetic powder in the compact.

On the other hand, higher mechanical strength is required in applications of moving members such as motor rotors. However, the RTB-based magnetic powder is obtained by crushing a ribbon-shaped material produced by using a rapid solidification apparatus with a stamp mill or the like, and the powder has a flat shape and a hardness of HV7.
HV1 of powder for ordinary powder metallurgy
Very hard compared to 00-250. Further, since this magnetic powder contains active Nd, a powder having a small particle size is likely to cause an oxidation reaction in the atmosphere, which not only causes deterioration of the powder but also may cause ignition. Average particle size is 1
It is as rough as about 55 μm. Therefore, the powder has remarkably poor moldability, which makes it difficult to increase the density and improve the strength.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing an isotropic bonded magnet having excellent mechanical properties and magnetic properties, and particularly a molding method capable of improving mechanical strength even with the same product density. It is what

[0007]

In order to solve the above-mentioned problems, the present invention has a composition prepared by a rapid solidification method containing rare earth metal
In a method of compression-molding magnetic powder of iron / cobalt / boron based using a resin binder, the powder in which the resin binder is attached to the magnetic powder is filled in a die and the pressure is 120 kgf.
/ Mm ² or more, compression-molding is performed to release the pressure once, and then the mold is compressed again at a pressure equal to or higher than the molding pressure and released.
The present invention provides a method for producing an isotropic bonded magnet, which is characterized by heating and curing a resin.

In the above manufacturing method, a magnetic powder having an average particle diameter of 30 to 155 μm coated with 1 to 3% by weight of a resin binder is used. Epoxy resin is suitable as the binder resin. The resin is kneaded with a magnetic powder together with a solvent and then dried to form a cake, which is crushed to prepare a powder for molding.

In order to reduce the average particle size of the magnetic powder, commercially available magnetic powder, a predetermined amount of resin binder and solvent are put into a vessel of a vibration mill together with grinding media, and the vessel is replaced with an inert gas atmosphere. After crushing the magnetic powder by vibrating for a predetermined time in a state of, the solvent contained in the suspension of the obtained magnetic powder is volatilized and removed in an inert gas atmosphere to form a cake consisting of the magnetic powder and the resin. The cake is crushed in an inert gas atmosphere to obtain a resin-coated magnetic powder.

As a molding method, a normal molding apparatus using a die and a punch is used to perform the first molding and the second molding at a predetermined pressure, and a mold made of an elastic material such as rubber. Powder is filled in, the first stage is shaped by CIP to remove the pressure, and then the second stage is pressed to release the mold, or
After filling powder in a die with a tapered inner hole and compressing with a punch, after moving this preform to the side with a larger inner hole size of the die with a punch to release the pressure applied to the first stage formed body, There is a method of releasing the die from the side having a larger inner hole size by applying the second pressure.

In the resin hardening treatment of the molded body, the temperature is about 160.
It is carried out at a temperature of up to 180 ° C. for a period of time during which the resin is cured. The powder adjustment, compression molding, and heat treatment are preferably performed in an inert gas atmosphere such as argon gas in order to prevent the magnetic powder from being oxidized as much as possible.

[0012]

First, the resin as the binder affects the strength of the product depending on the adhesion method and the adhesion amount. Examples of the adhesion method include a powder mixing method and a coating method by kneading. The coating method is superior because it has higher strength and covers the surface of the magnetic powder to prevent oxidation.

The amount of resin adhered affects the molding density and the strength of the molded body. The strength of the molded product rises almost in proportion to the adhesion amount up to 2.0% by weight of the resin.
It does not rise even if it adheres in excess of weight%. On the other hand, if the amount of resin is less than 1%, the molded product will crack. Further, the molding density shows the maximum value when the amount of resin is 1.5 to 2% by weight, and it is 2% by weight.
If it exceeds 3% by weight, it tends to decrease, and if it exceeds 3% by weight, it decreases sharply. Therefore, the amount of resin is 1 to 3% by weight, preferably 1.5 to 2.5% by weight.

Secondly, the particle size of the magnetic powder affects the strength and magnetic properties of the product. The strength of the product gradually increases as it becomes finer than the average particle size of 155 μm on the market, and reaches the maximum at 40 μm.
The strength at μm shows almost the same value, and if it is smaller than 30 μm, the strength sharply decreases. The magnetic properties are equivalent when the average particle size is 155 to 40 μm, and deteriorates when the average particle size is less than 30 μm. Therefore, the particle size of the magnetic powder is 30 to 155 μ.
m, preferably 40 to 100 μm.

Next, regarding the molding method, in the case of ordinary one-time molding, the density of the product increases with the increase of the molding pressure,
Along with that, strength and magnetic properties are improved. However, even if the molding pressure is 250 kgf / mm ² or more, the density does not increase. On the other hand, although it is a two-step molding method, the density is increased by the increase of the pressing force, and the strength and the magnetic characteristics are improved accordingly, as in the former case. However, the strength of the product has high characteristics that cannot be obtained by ordinary single molding. What is important here is that the molding pressure must be above a certain pressure
The effect of step forming is not recognized at all. That is, when the molding pressure in the first stage is 110 kgf / mm ² or less, 1
There is no difference from the case of single molding. First stage molding pressure 120
At kgf / mm ² or higher, the molding pressure in the second step becomes equal to or higher than that in the first step, and the effect of improving strength appears.
For example, a density of 6.35 g / cm ³ and a strength of 1830 k obtained at a pressure of 250 kgf / mm ² in a usual single molding.
Compared with gf / cm ² , when the first stage and the second stage were each molded at 200 kgf / mm ² , the density was 6.35 g /
The strength is 2130 kgf / cm ² at cm ³ , and 6.40 g when the first stage and the second stage are respectively molded at 250 kg / mm ^2.
/ Mm ³ gives a strength of 3000 kgf / cm ² .

Considering this from the process of pressure-molding the flat magnetic powder coated with resin, the space between the powders gradually decreases and the density increases as the pressing force increases. When the pressure is further increased, the density is further increased while some particles are crushed, but the particles are in a bridge state in which the flat particles are randomly arranged, and even if the pressure is increased, the density is further increased. Disappear. Then, when the pressure is released, the molded body springs back to form a slight gap between the particles. It is speculated that when the second step of pressing is performed, most of the flat particles are arranged in a direction perpendicular to the pressing direction, the density increases, and the contact area between particles increases, resulting in higher strength. To be done.

[0017]

[Example 1] The magnetic powder used was iron 67.
0 wt%, Cobalt 5.2 wt%, Neodymium 2
It was produced by a rapid solidification method containing 4.6% by weight and 1.7% by weight of boron, and has an average particle diameter of 155 μm.

For resin coating, an epoxy resin was dissolved in a solvent, and this solution and magnetic powder were kneaded with a kneader.
Then, the solvent was dried using a thermostatic bath replaced with argon gas, and the magnetic powder surface was coated with an epoxy resin. The amount of resin is 2.0% by weight. With this powder,
A sample molded at a first stage pressure of 100 to 300 kgf / mm ² was prepared.

Next, a mold having a slightly larger inner hole than the mold used in the first stage is used, and the pressure in the first stage is 100 to 250 kgf.
/ Mm ² pressure molded test piece 100~250kgf
The second stage molding was performed at / mm ² . After that, each of the sample molded once (comparative example) and the sample molded in two stages was heated at a temperature of 160 ° C. for 1 hour and further at a temperature of 180 ° C. for 1 hour in a thermostatic chamber in which argon gas was replaced to cure the resin. . The sample size is 11.3 mm in diameter and 10 mm in height.

Next, the density, the residual magnetic flux density and the maximum energy product as the magnetic characteristics, and the compressive strength in the axial direction of the sample were measured for each sample. Compressive strength, using a compression tester,
It is the maximum value in the stress-strain curve diagram when the test piece is compressed at a compression rate of 0.5 mm / min. First, comparative example 1
Regarding the characteristics of the sample of the re-molding, FIG. 4 shows the relationship between molding pressure and density, FIG. 5 shows the relationship between density and compressive strength, FIG. 6 shows the relationship between density and maximum energy product, and FIG. 7 shows the relationship between density and residual magnetic flux density. Show.

From FIG. 4, a molding pressure of 250 kgf / mm ²
The maximum value was 6.35 g / cm ³ , and it was found that the density did not increase even if pressure was applied further. From FIG.
There is a correlation between the density and the compressive strength, and the maximum value of the compressive strength is 1830 kgf / cm ² . It can be seen from FIGS. 6 and 7 that the higher the density, the better the magnetic properties.

Next, FIG. 1 shows the effect of the present invention on the strength of a test piece manufactured by the two-step molding method. For comparison, the results of the normal single molding shown in FIG. 5 are also shown. White circles show the values obtained by normal single molding,
Black circles are values for the two-step molding method. Regarding the molding pressure of the two-stage molding method, the pressure of the first stage is shown on the left side of the arrow, and the pressure of the second stage is shown on the right side of the arrow.

The test piece having a pressure of 100 kgf / mm ^{2 in} the first stage has strength that can be achieved by a normal molding method even when the pressure of the second stage is 150 kgf / mm ² , and the effect of the present invention is not obtained. However, when the pressure in the first stage is 120 kgf / mm ² or more, the strength is dramatically improved. What should be noted here is
Molding pressure of the first stage 150kgf / mm ² , pressure of the second stage 1
50 kgf / mm ² of the specimen, the test piece and the density despite the intensity is the same prepared in a pressure 200 kgf / mm ² in the usual molding method is a high value, further, the conventional molding method It is a value higher than 250 kgf / mm ² .

Further, both the first stage and the second stage are 250 kgf /
The molded product having a size of mm ² can obtain 3000 kgf / cm ^2, which is 1.6 times the maximum value of the compressive strength obtained by the conventional method. Example 2 The magnetic powder used in Example 1 having an average particle diameter of 155 μm, the epoxy resin dissolved in a solvent and the balls for grinding were put in a planetary ball mill, and the inside of the mill was replaced with argon gas and sealed. After operating for a predetermined time, it was taken out in a thermostatic chamber replaced with argon gas, the solvent was dried, and the cake-like powder was crushed in argon gas to prepare magnetic powders having different average particle diameters coated with epoxy resin. . The amount of resin is 2.0% by weight.

Next, using a variable atmosphere molding press, the mold was placed in an argon gas atmosphere, each powder was compression-molded by a two-stage molding method, and then a resin hardening treatment was carried out in the same manner as in Example 1. The molding pressure is 250 kgf / mm ^{2 for} both the first and second stages.
Is. The compressive strength, residual magnetic flux density and maximum energy product of the obtained sample were measured.

FIG. 2 shows the relationship between the average particle size and each measurement result. The compressive strength gradually increases as the particle size decreases, and shows the maximum value when the average particle size is 40 μm. 40
When the particle size is smaller than μm, the strength is decreased and the average particle sizes of 30 μm and 155 μm show almost the same value. The magnetic properties show equivalent values when the average particle size is 155 to 40 μm, and tend to deteriorate when the average particle size is smaller than 40 μm.

From this fact, the average particle diameter of the magnetic powder is
Good characteristics can be obtained even at 155 μm as it is on the market,
It can be seen that an average particle size of about 50 μm is preferable for obtaining higher strength. Example 3 Using magnetic powder having an average particle size of 155 μm,
Example 1 powders having different coating amounts of epoxy resin
It was manufactured by the same method as.

Next, each powder having a different resin amount was added to the first stage and 2
After molding both stages at a pressure of 150 kgf / mm ² , the resin was cured in the same manner as in Example 1 to obtain a sample, and the density and compressive strength were measured. FIG. 3 shows the relationship between the resin amount and the density and compressive strength. If the amount of resin is less than 1% by weight, the molded product will crack.

The density shows a maximum value when the amount of resin is between 1.5 and 2% by weight, and when it exceeds 3% by weight, the decrease is remarkable.
The compressive strength increases with increasing amount of resin, 2.5% by weight
Shows the maximum value, and no effect is obtained if more is added. From this, the amount of resin is required to be 1% by weight or more so that cracking does not occur, and up to 3% by weight which does not significantly lower the density. It can be seen that it is preferably around 2% by weight.

[0030]

According to the manufacturing method of the present invention, it is possible to manufacture a bonded magnet having magnetic characteristics and high strength, which cannot be achieved by a usual molding method. Currently, it can be applied to OA equipment, which is becoming smaller and lighter, or to electric tool motors that require high torque characteristics, at low cost. In addition, the magnetic properties of the isotropic bonded magnet manufactured by the present invention are comparable to those of a general-purpose anisotropic Sm-Co bonded magnet, and since Sm is not required, the industrial value is great.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between density and compressive strength in the present invention.

FIG. 2 is a graph showing the relationship between the average particle size of magnetic powder, the compressive strength, the residual magnetic flux density, and the maximum energy product in the present invention.

FIG. 3 is a graph showing the relationship between the amount of resin and the density and compressive strength in the present invention.

FIG. 4 is a graph showing a relationship between a molding pressure amount and a density in conventional single molding.

FIG. 5 is a graph showing the density and the compressive strength in the conventional one-time molding.

FIG. 6 is a graph showing the relationship between the density and the maximum energy product in conventional single molding.

FIG. 7 is a graph showing the relationship between the density and the residual magnetic flux density in the conventional one-time molding.

Claims (2)

[Claims] 1. A method of compression-molding a magnetic powder having a composition of rare earth metal / iron / cobalt / boron, which is produced by a rapid solidification method, using a resin binder, and powder obtained by attaching a resin binder to the magnetic powder. With a pressure of 120 kg
An isotropic bond characterized by compression-molding at f / mm ² or higher, releasing the pressure once, then compressing again at a pressure equal to or higher than the molding pressure to release the mold, and then heating to cure the resin. Magnet manufacturing method. 2. The method for producing an isotropic bonded magnet according to claim 1, wherein a magnetic powder having an average particle diameter of 30 to 155 μm coated with 1 to 3% by weight of a resin binder is used.