JPH0410602A - Isotropic permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a magnet having a relative density of 70% or more and make it possible to miniaturize electrical appliances by hot pressing powder in the shape of a thin piece without using a special biding agent. CONSTITUTION:An alloy composed of 13 atomic % Nd and/or Pr, 15 atomic % Co, 6 atomic % B, the balance being Fe, is rapidly cooled and solidified by a meltspining method and formed into powder in the shape of a thin piece having a thickness of 20 to 30 microns. This powder is housed in a space 3 formed of a non-conductive ceramics cavity 1 and a pair of conductive ceramic electrode punches 2. A pressure is applied to the pair of electrode punches, and further the space is made to a vacuum atmosphere of 10 to 10Torr. A DC voltage of 20V is applied for 60sec in a pulse width of 40msec. Thereafter, a DC current of 1.5kA is directly made to flow between the pair of electrodes for 40 to 60sec. Finally, the temperature of the powder inside the cavity reaches 700 deg.C to 750 deg.C. By cooling this powder, various magnets having different relative densities are obtained by a permeance 1 having an outer diameter of 20mm.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to rare earth iron permanent magnets used in motors. More specifically, a thermally stable and magnetically isotropic permanent magnet made from rare earth iron flakes or powder obtained by a liquid quenching method as a starting material and aggregated without using a binder, and its production. It is about the method.

Conventional motor magnets vary depending on the motor used, with some requiring high magnetic properties per unit volume, and others with low properties being more appropriate.

Since this magnetic property can be regarded as the amount of magnetic powder packed per volume, that is, the relative density of the magnet, it is desired to develop magnets with a wide range of relative densities using the same magnetic powder.

As one of the raw materials for conventional rare earth iron permanent magnets,
No. 9-64739 discloses an isotropic magnetic powder produced by a liquid quenching method, which has been widely used as a resin magnet.

This magnetic powder is blended with a resin as a binder and then molded into a specific shape as an aggregate by injection molding or compression molding. These resin magnets have a limit in the blending ratio of magnetic powder and resin depending on the respective molding method, so there is also a limit in their relative density; for example, in the compression molding method, it was about 82%.

Furthermore, since the alloy composition of this magnet is Fe-based, which is less susceptible to oxidation, it rusts more easily than S m -Co magnets (for this reason, its surface is subjected to various anti-corrosion treatments). These anti-corrosion methods can be roughly divided into methods of coating with a thin metal film and methods of coating with an organic or non-metallic inorganic material. However, it has not been put to practical use in general, and currently the main method used is to coat it with an organic substance, specifically, anti-corrosion treatment using epoxy resin spray coating or electrodeposition coating.

On the other hand, JP-A-60-100402 discloses a full-density isotropic magnet that is hot compression molded using the same magnetic powder as the above-mentioned magnetic powder without using a binder. This magnet has a relative density of over 95%, and has a higher performance than the resin magnet described above. Since this isotropic full density magnet does not use a binder, there is no limit to the operating temperature due to the heat resistance of the binder, and the operating temperature is limited only by the thermal demagnetization characteristics of the magnet itself. Also, unlike resin magnets, the entire aggregate of this magnet is magnetic powder, and unlike resin magnets, the surface of the magnet is not a mixture of resin and magnetic powder, that is, metal and resin. Inorganic anti-rust treatments that cannot be used with magnets, such as water glass, have been adopted as anti-rust treatments.

Problems to be Solved by the Invention The resin magnet obtained by the above conventional manufacturing method has a relative density of 82% or less, and isotropic full-density magnets cannot produce a measuring stick with a relative density of 95% or more, so magnets are used. It has been impossible to obtain a magnet with a relative density of more than 82% and less than 95%, which matches the characteristics of the motor to be used.

Furthermore, in the case of resin magnets, the temperature at which they can be used is limited by the heat resistance of the resin used as a binder, so there are cases where resin magnets cannot be used.

Furthermore, spray painting with epoxy resin is low cost, but in order to ensure the reliability of the paint film, a film thickness of 25 microns or more is required, and for cylindrical magnets, the inner diameter side It is difficult to guarantee the reliability of the coating.

On the other hand, electrodeposition coating can guarantee the reliability of the coating film at a thickness of 10 microns and has a degree of freedom in shape, but has the drawback of high processing costs.

In view of the above-mentioned problems, the present invention aims to select a magnet having magnetic properties suitable for the motor to be used. It can be used without being affected by the heat resistance of the agent.
A further object of the present invention is to provide an isotropic permanent magnet that can be subjected to low-cost water glass rust prevention treatment and a method for manufacturing the same.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the present invention provides a method of hot compression molding magnetic powder obtained by a liquid quenching method.
The present invention provides magnets with arbitrary density of 0% or more.

More specifically, the basic composition is R-Fe-Co-B.

A magnetically isotropic flaky powder having a microcrystalline structure is obtained by melt spinning the alloy, and this powder is placed in a molding cavity to cause an electric discharge in a vacuum of 10-1)-1 or more. This method compresses the material to a predetermined size at the same time by applying a direct current to the material.

EffectThe flaky powder is caused by plasma generated by electric discharge.
Oxides and gases adhering to the surface are removed and activated. Furthermore, by direct energization, Joule heat is generated, the temperature rises to a predetermined temperature, and at the same time, the powder is softened and compressed to a predetermined size by the applied uniaxial pressure, causing diffusion of atoms between the powders. are formed into an atomic bond. This results in a magnetically isotropic aggregate of a predetermined shape.

In the magnet of the present invention, the powder is activated by plasma before hot compaction, so the powder can be reduced by 95%, which was previously impossible.
Even at low densities below, atomic diffusion occurs between powders and sufficient bonding strength is developed, so special bonding means such as adhesives are not required. However, if the relative density of the magnet is less than 70%, the bonding strength is insufficient and the magnet may be damaged by the act of magnetization, so that it cannot be used as a practical magnet. In addition, the basic composition determines the magnetic properties of the magnet, and at the same time
In particular, Co increases the Curie temperature of the alloy and improves the temperature characteristics of residual magnetic flux density, and is an important element for achieving the object of the present invention, which is to provide a magnet with good thermal stability. Furthermore, in the magnet of the present invention, since the direct energization method is used as the heating means in the process of agglomerating and solidifying the powder, the process can be completed in a short time, and coarsening of the fine crystal grains of the magnetic powder can be prevented. No reduction in temperature characteristics of coercive force occurs.

Example The details of the present invention will be explained below based on one embodiment.

FIG. 1 is a diagram showing the structure of a cavity and an electrode punch related to the manufacturing method of the present invention. Nd or/and Pr
is 13 at%, CO is 15 at%, B is 6 at%, F
The alloy consisting of the remainder e was rapidly solidified by melt spinning to form flaky powder with a thickness of 20 to 30 microns. This powder was placed in a space 3 consisting of a non-conductive ceramic cavity 1 with an inner diameter of 20 mm and a pair of conductive ceramic electrode punches 2 shown in Fig. 1, and 250 kg f/cn? , a vacuum atmosphere of 10-1 to 10' Torr was applied, and a DC voltage of 20 V was applied for 60 sec with a pulse width of 40 m5 ec.
Then, a direct current of 1.5 kA was applied directly between the pair of electrodes for 40 to 60 seconds, and the pair of electrode punches were moved under pressure to a predetermined position. Finally, what is the temperature of the powder inside the cavity? , O
The temperature reached 0-750°C. After cooling this, the outer diameter was 20 m.
Various magnets with different relative densities were obtained with m permeance of 1. FIG. 2 shows the magnetic properties of a magnet with a relative density of 85% at room temperature. Curve 10 is the compression direction of the magnet of the example of the present invention, curve 12 is the estimated value in the direction perpendicular to the compression direction, and curve 14 is the characteristic of the magnetic powder used. curve 10
The residual magnetic flux density J of curve 14 is the relative density of J (85%
). Also, there is a slight difference between curves 10 and 12, which indicates that the magnet is slightly anisotropic, but with such a difference, the magnet should essentially be isotropic. be. On the other hand, in terms of magnetic exploration force, the magnet of the present invention has a higher magnetic force of about 2 k Oe than the raw material powder.
expensive. This is a feature of the magnet of the present invention, and the coercive force Hcj increases because the powder is cleaned by activation by plasma. Figure 3 shows the magnetic properties of magnets with different relative densities. Each magnet has a residual magnetic flux density that is proportional to its relative density, while the retrieval force is approximately constant.

The above-mentioned magnet of the present invention and a resin magnet manufactured by compression molding using the same magnetic powder were each subjected to electrodeposition coating and coating with water glass, and were heated to 600C, 90RH.
The rust prevention ability was evaluated in an environment of The result is the first
Shown in the table.

In the case of electrodeposition coating on the first surface of the margin below, any magnet will exhibit sufficient rust prevention power, but for water glass, which is low cost, resin magnets
Although the film will peel off within 0.00 hours, the magnet of the present invention has good adhesion (sufficient rust prevention) because its surface is entirely metal.

The coating thickness of water glass is 2 to 3 microns, which is less than 1/2 the thickness of electrodeposition coating and exhibits the same anti-corrosion ability.

Effects of the Invention As mentioned above, the magnet of the present invention is practical due to only atomic bonding achieved by hot compression molding without using any special binder, and has a relative density of 70%.
Magnets of any density above can be provided. This eliminates the use temperature limitations due to the heat resistance of the binder. Furthermore, since the magnet of the present invention does not use a binder such as a resin, it is possible to use a water glass-based rust prevention treatment, which is impractical due to poor adhesion with resin magnets. Since the coating thickness is 2 to 3 microns, which is less than half of that of organic coatings, it exhibits sufficient performance, so when magnets are incorporated into electrical equipment,
This reduces the generation of magnetic spaces in the magnetic circuit, making it possible to increase the permeance of the magnet, which is effective in downsizing electrical equipment. Furthermore, since this anti-corrosion treatment is inorganic, it has a sufficiently high operating temperature limit and does not limit the usable range of the magnet, which is a very expensive treatment.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the structure of a cavity and an electrode punch in an embodiment of the manufacturing method of the present invention, and Fig. 2 is an embodiment of the magnet of the present invention, showing the magnetic properties of a magnet with a relative density of 85%. The graph in FIG. 3 is a diagram showing the magnetic properties of magnets of the present invention having different relative densities. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 2 Figure 1 Hc/koe

Claims (2)

[Claims] (1) Alloy whose basic component is R-Fe-Co-B (R:
An isotropic permanent magnet that uses flakes or powder as a starting material obtained by rapidly cooling and solidifying one or more rare earths (including Nd), in which the flakes or powders are atomically bonded, and An isotropic permanent magnet characterized by a relative density of 70% or more. (2) Putting the raw material according to claim 1 into a molding cavity,
A method for producing an isotropic permanent magnet, in which a discharge is caused in a vacuum of 10^-^1 Torr or more, a direct current is applied, heating is performed, and compression molding is performed at the same time.