JPH0742484B2 - Method for forming anisotropic magnetic powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic magnetic powder having a high performance, that is, a method for forming an anisotropic magnetic powder for producing a high performance permanent magnet having a metallic function by using an orientation magnetic powder. It is a thing.

[0002]

2. Description of the Related Art Generally, a magnetic material having a coercive force of about 100 Oe or more is called a hard magnetic material, and a magnetic material having a coercive force of less than that is called a soft magnetic material. In recent years, the demand for high-performance magnetic materials has increased more and more with the advancement of various industries, and this is the same also in the case of hard magnetic permanent magnets.

Hard magnetic powder used for permanent magnets is classified into isotropic magnetic powder used for non-orientation during molding and anisotropic magnetic powder used for orientation, that is, mechanical orientation or magnetic field orientation. The magnetic properties differ depending on the orientation. For example, as a magnetic characteristic of strontium ferrite-based material and barium ferrite-based material, the theoretical value of their residual magnetic flux density Br is true density 5.11 G / cm ³
It is said to be 4650 gauss. On the other hand, in the case of the isotropic magnetic powder used in the non-oriented state, the magnetic powder particles are orientated at random, which is about half the theoretical value.

Further, when the molded body of the isotropic magnetic powder is not densified, or when the plastic or rubber for the binder is used, the magnetic characteristics are "weight of magnetic powder per unit volume of magnetic body". (g / cm ³ ) ”can be used to control the rate. On the other hand, the magnetic properties of anisotropic magnetic powder used for mechanical orientation are as follows: "weight of magnetic powder per unit volume of magnetic material"
(g / cm ³ ), it is not possible to control the rate, and even if the magnetic powder weight per unit volume is the same, the magnetic properties differ depending on the orientation ratio of the magnetic powder, and the orientation is 100%. The above theoretical value of 46
You will get 50 Gauss. Therefore, in the case of anisotropic magnetic powder, orientation and densification of particles are important for improving magnetic properties.

As a method of orienting particles in the anisotropic magnetic powder, there is a method of magnetic field orientation. In this case,
For example, as disclosed in Japanese Patent Publication No. 60-37603, a thermoplastic polyamide as a binder and a stearic acid metal salt (calcium stearate, magnesium stearate, aluminum stearate, etc.) as a kneading aid are generally used. Because it is mixed,
Despite the complicated method of magnetic field orientation, the magnetic properties are considerably inferior to the theoretical values. This is because the use of thermoplastics or kneading aids as the binder reduces the amount of magnetic powder by the proportion of these compounds and reduces the "weight of magnetic powder per unit volume of magnetic material". Is. Therefore, there is a demand for a simple molding method for sufficiently exhibiting the properties of the anisotropic powder.

On the other hand, a molded product of 100% by weight of magnetic material has excellent magnetic properties, but has poor metallic properties such as conductivity and reworkability. There is a demand for a technique for easily obtaining a magnetic substance having a function.

[0007]

In order to improve these drawbacks, the inventors of the present invention have conducted extensive studies, and as a result, it has been sufficient to add superplastic metal powder and a thermally decomposable binder to anisotropic magnetic powder. Is mixed and kneaded, and the magnetic powder is mechanically or magnetically oriented to give orientation, and then the binder is thermally decomposed to disappear, and further, main firing, hot press molding, and HIP molding are performed to obtain a fired body. It was confirmed that the high-performance permanent magnet having a metallic function can be manufactured by densifying the.

The present invention is based on such findings, and therefore, its technical problem is to fully exhibit the magnetic characteristics of anisotropic magnetic powders, that is, oriented magnetic powders, and further to improve the conductivity and reworkability. An object of the present invention is to provide a simple molding method for obtaining a molded product excellent in metallic function such as.

[0009]

Means and Actions for Solving the Problems A first molding method of the present invention for solving the above problems is an anisotropic magnetic powder,
Sufficiently mix superplastic metal powder and pyrolytic binder
By kneading and hot rolling or hot extruding this, the magnetic powder is mechanically oriented to give orientation, and then the binder is thermally decomposed to disappear, and then main firing is performed, and then metal It is characterized by producing a high-performance permanent magnet having a sexual function. In this method, the fired body that has been subjected to the main firing can be further subjected to hot press molding or HIP molding to further densify the fired body.

In the second method of the present invention, anisotropic magnetic powder, superplastic metal powder, and thermally decomposable binder are sufficiently mixed and kneaded, and hot rolling or hot extrusion is carried out. In order to produce a high-performance permanent magnet having a metallic function by mechanically orienting the magnetic powder to impart orientation, and then thermally decomposing and eliminating the binder, followed by hot press molding or HIP molding. It is a feature.

Further, in the third method of the present invention, anisotropic magnetic powder, superplastic metal powder, and thermally decomposable binder are sufficiently mixed and kneaded, and this is extruded using a fine die. Thereby, the magnetic powder is mechanically oriented to provide orientation, and then the binder is thermally decomposed to be eliminated and then sintered to give a high-performance thin hard magnetic molded body having a metallic function. It is characterized by being manufactured.

Further, in the fourth method of the present invention, anisotropic magnetic powder, superplastic metal powder, and thermally decomposable binder are sufficiently mixed and kneaded, and this is put in a mold and placed in a magnetic field. Place, press-mold under a state of magnetic field orientation, and then pyrolyze the binder to disappear and then perform main firing,
It is characterized by producing a high-performance permanent magnet having a metallic function.

More specifically, as the anisotropic magnetic powder used in the molding method of the present invention, strontium ferrite-based or barium ferrite-based anisotropic magnetic powder is generally used. Alternatively, rare earth-based anisotropic magnetic powder such as neodymium-based or samarium-based can be used.

As the superplastic metal powder, Zn-22Al superplastic alloy powder is preferably used, but it is not limited thereto, and zinc-based aluminum-based, copper-based, iron-based, titanium-based, nickel-based, etc. Can also be used. Even if such a superplastic alloy powder such as Zn-22Al is mixed, the orientation of the magnetic powder does not deteriorate, but rather it is possible to give the composite magnetic body a metallic function. In addition, it is possible to reduce the spring back of the molded body after rolling and to ensure the dimensional accuracy of the molded body, which is advantageous. This has the effect of preventing the particles of the magnetic powder, which have been bent at an angle, from rotating due to the spring back after the molding, and preventing the magnetic characteristics from deteriorating.

In addition, addition of metal powders such as super-composition metal powders prevents sticking (welding) of the kneaded material to rolls during hot rolling, and prevention of burrs during hot extrusion and hot closed mold forming. Is also effective in terms of. This, in turn, makes it possible to improve the molding temperature and also serves as a basis for promoting the orientation of the magnetic powder.

The conditions required for the thermally decomposable binder are that the magnetic powder has excellent kneading properties, and that it emits harmful substances that impair the properties of the magnetic powder during thermal decomposition and substances that reduce the life of the heat treatment furnace. There is a possibility that the shape and dimensional accuracy of the molded body are not lowered as much as possible, and the material is selected in consideration of these conditions. Specifically, in addition to the binder containing ethylene vinyl acetate + acrylic polymer as a main component, which will be described later, and the like, various materials that meet the above conditions can be used.

As a mixing ratio of the thermally decomposable binder and the anisotropic magnetic powder and the superplastic alloy powder, a binder amount capable of sufficiently kneading the magnetic powder and the superplastic alloy powder is required. Generally, 5 to 40 wt% of binder can be used with respect to magnetic powder and superplastic alloy powder, but since the binder is decomposed and disappears after molding, it should be mixed and molded in a sufficient range. It is desirable that the amount is the minimum necessary. The mixing ratio of the superplastic alloy powder to the magnetic powder varies depending on the degree of metal function to be imparted, reworkability, etc., but is preferably 2 to 50 wt%.

On the other hand, for mechanical orientation by a plastic working method, hot rolling or hot extrusion is performed, or extrusion processing is performed using a thin die. In this case, kneading is first performed in order to perform sufficient orientation. It is important to perform the molding after carefully performing the rolling and the extrusion ratio, etc. as much as possible. However, if the mechanical orientation reaches a substantially steady state, the number of steps only increases even if a reduction ratio or an extrusion ratio higher than that is applied. Therefore, the minimum necessary processing rate is sufficient. The minimum required processing rate is
The rolling reduction is about 60%. The rolling reduction is a quantity that represents the workability of rolling, and the material thickness before and after rolling is h ₁
And h ₂ , the rolling reduction is [(h ₁ −h ₂ ) / h ₁ ] × 1
Expressed as 00%.

The thermal decomposition of the thermally decomposable binder can be carried out by heating it at 100 to 600 ° C. for several hours to several tens of hours, although it depends on the kind of the binder to be used. Can be eliminated by thermal decomposition. In this case, distortion and deformation of the molded body can be prevented by gradually performing it over a long period of time.

Further, in the magnetic field molding, an anisotropic magnetic powder, a superplastic metal powder, and a thermally decomposable binder are sufficiently mixed and kneaded into a metal mold for magnetic field press molding.
It is important to heat the kneaded material so that it has fluidity so that the magnetic powder is easily oriented. Then, it is important to apply pressure with a press after the orientation.

The firing for promoting the densification is sufficient in the air atmosphere or the nitrogen atmosphere. In the case of strontium-based and barium-based ferrite powder, it is preferable that the firing is usually performed at a temperature of 1000 to 1300 ° C. If the temperature is lower than this temperature, the densification of the fired body does not proceed, so that the magnetic properties are deteriorated. On the other hand, when the temperature is higher than the above temperature, although it is densified, the crystal grains are coarsened and the magnetic properties are deteriorated. The optimum temperature is 1150 ℃ -1200 ℃. In order to further promote densification, hot press or HI after main firing.
It is more effective to perform the P treatment or perform hot pressing or HIP molding instead of firing.

Next, for example, in the case of roll forming, the sintered body that has been subjected to the above-mentioned firing is magnetized in the height direction, that is, in the rolling thickness direction (direction perpendicular to the rolling axis). Use a permanent magnet. As a result, it is possible to easily obtain a molded body that fully exhibits the magnetic characteristics of anisotropic magnetic powder, that is, oriented magnetic powder, and that has excellent metallic functions such as conductivity and reworkability. Become.

[0023]

【Example】

Example 1 Anisotropic strontium-based ferrite having an average particle diameter of 1.5 μm (FH-801 manufactured by Toda Kogyo Co., Ltd.), Zn-22Al superplastic alloy powder of 44 μm or less manufactured by an air injection method, ethylene vinyl acetate, acrylic polymer , And a thermally decomposable binder consisting of paraffin wax, etc. in a weight ratio of 63.
6%: 27.3%: 9.1% were mixed and kneaded, and this was subjected to magnetic field molding. In that case, 50 × 50 × 50 made of non-magnetic steel
The kneaded material was put into a cubic mold of mm, and the mold was heated with a heater to 135 ° C. Then, after applying a magnetic field, 50 ° C from the parallel direction of the magnetic field with the temperature lowered to 70 ° C.
Pressing was performed by applying a pressure of MPa. At that time, the magnitude of the applied magnetic field was changed and the influence on the magnetic properties of the molded body was investigated. The results are shown in Table 1. Here, the magnetic properties were measured in the state before debinding, and the measurement direction was measured in the direction in which the magnetic properties were maximized, that is, from the magnetic field direction.

[0024]

As a result, it was found that the magnetic characteristics were almost constant when the magnitude of the magnetic field was 20 A or more. Therefore, it was confirmed that the molding method of this example is a simple method that does not require a strong magnetic field. Further, Br / 4πIs, which is a measure of the orientation, is 0.87 or more, which indicates that the orientation is remarkably promoted by the use of the pyrolytic binder.

Example 2 Using the same kneaded material as used in Example 1, magnetic field molding was carried out to examine the influence of the molding temperature on the magnetic properties. In that case, the magnetic field interval is 50 mm, the magnetic field magnitude is 60 A, and the pressure of the press does not act at the molding temperature.
It was performed from the same direction as the magnetic field direction (parallel direction) in the state where The magnetic property was measured before the binder was removed, and the magnetic property was measured from the direction in which the magnetic property was maximized, that is, from the magnetic field acting direction. The measurement results are shown in Table 2.

[0027]

As a result, when the molding temperature is 100 ° C.,
The magnetic properties were slightly inferior because the effect of the thermally decomposable binder was not sufficiently exerted, but almost constant magnetic properties were obtained at 120 ° C or higher.

[0029]

As described above, according to the molding method of the present invention, anisotropic magnetic powder is oriented and molded by a relatively simple method, and thereby the magnetic characteristics of the anisotropic magnetic powder are improved. It is possible to manufacture a high-performance permanent magnet that is sufficiently exerted and has excellent metallic functions such as conductivity and reworkability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Yamaguchi 428 Furukawa, Aji-in, Usa-gun, Oita Prefecture (72) Hiroshi Mizue 3239-4 Chidori, Oita-shi, Oita Pref. Examiner Mari Okada

Claims (5)

[Claims] 1. An anisotropic magnetic powder, a superplastic metal powder, and a thermally decomposable binder are sufficiently mixed and kneaded, and this is hot-rolled or hot-extruded to mechanically orient the magnetic powder. Forming an anisotropic magnetic powder characterized by producing a high-performance permanent magnet having a metallic function by subjecting the binder to thermal orientation to cause the binder to undergo thermal decomposition and disappearing, and then performing main firing. Method. 2. The method according to claim 1, wherein the fired body subjected to the main firing is further subjected to hot press molding or HIP molding to further densify the fired body, thereby forming an anisotropic magnetic powder. Method. 3. Anisotropic magnetic powder, superplastic metal powder, and thermally decomposable binder are sufficiently mixed and kneaded, and this is hot-rolled or hot-extruded to mechanically orient the magnetic powder. To give orientation, and then the binder is pyrolyzed to disappear and then hot press molding or HI
A method for molding anisotropic magnetic powder, which comprises P-molding to produce a high-performance permanent magnet having a metallic function. 4. An anisotropic magnetic powder, a superplastic metal powder, and a thermally decomposable binder are sufficiently mixed and kneaded, and this is extruded with a fine die to mechanically orient the magnetic powder. To give orientation, and then thermally decompose the binder to eliminate it, and then perform sintering to produce a high-performance thin-line hard magnetic compact having a metallic function. Method for forming magnetic powder. 5. An anisotropic magnetic powder, a superplastic metal powder, and a thermally decomposable binder are sufficiently mixed and kneaded, and the magnetic powder is magnetically sealed by hot-sealing in a magnetic field. An anisotropic magnetic powder characterized by producing a high-performance permanent magnet having a metallic function by orienting and imparting orientation, and then thermally decomposing and eliminating the binder to perform main firing. Molding method.