JPH0436563B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for producing an R ₂ Co ₁₇ -based intermetallic compound consisting of a rare earth metal R and Co, typified by a Sm ₂ Co ₁₇ -based permanent magnet. In particular, the present invention relates to improvements in the method of manufacturing magnets by powder metallurgy.

Methods for manufacturing R ₂ Co ₁₇ magnets can be roughly divided into two methods. One is the liquid quenching method, which uses a thin ribbon of super-quenched molten alloy. The other type is a sintered magnet, which is manufactured by pulverizing a melted magnetic alloy ingot, molding the resulting powder in a magnetic field, and then sintering it.
The present invention relates to sintered magnets.

[Prior art]

Generally, the manufacturing process of this type of magnet using the powder metallurgy method includes melting, crushing, orientation in a magnetic field, compression molding, sintering,
They proceed in the order of the statute of limitations. Melting is usually carried out in a vacuum or inert atmosphere, such as by arc, radio frequency, etc. Grinding is divided into coarse grinding and fine grinding, and coarse grinding is carried out using a geocrusher, a sharp mortar, a disc mill, a roll mill, or the like. Fine pulverization is performed using a ball mill, vibration mill, jet mill, or the like. Magnetic field orientation and compression molding are usually performed simultaneously in a magnetic field using a mold. Sintering is performed in a vacuum or inert atmosphere at around 1200°C. Aging is performed at a temperature around 800°C.

[Problems with conventional technology]

The sintered rare earth magnet manufactured by the method described above does not suffer from the occurrence of cracks etc. during molding and sintering.
It has the drawbacks of poor yield due to shrinkage during sintering and difficulty in processing.

Fine alloy powder is usually compression molded using just the powder, and the strength and density of the compact are proportional to the molding pressure. However, as the molding pressure increases, the rate at which cracks occur in the molded product increases, and the life of the mold used for molding also shortens. Therefore, attempts have been made to coat fine alloy powder with various additives in order to increase the strength and density of compacts even at low pressures. However, many of the additives deteriorate the magnetic properties when mixed into the fine alloy powder in an amount sufficient to obtain the desired strength and density of the compact.

Therefore, an object of the present invention is to provide a manufacturing method that can increase the strength and density of a compact at low pressure without affecting the magnetic properties.

Another object of the present invention is to produce a sintered magnet with less cracking during molding and sintering, less shrinkage during sintering, and therefore less machining and a high yield. The purpose is to provide a method.

[Means for solving problems]

In order to achieve the above object, the present inventors conducted various experiments and found that by mixing and coating an alloy powder mainly composed of R ₂ Co ₁₇ with an appropriate amount of polyisobutylene, and then molding it in a magnetic field. It was discovered that the strength and density of the compact can be increased without affecting the magnetic properties.

The present invention is based on such a discovery.

That is, the present invention provides R ₂ Co ₁₇ alloy powder,
This is a method for producing an R ₂ Co ₁₇ permanent magnet, in which 1 to 3 wt% of polyisobutylene is mixed and coated on the surfaces of alloy particles, which is then pressure-molded and sintered.

Note that it is preferable to use polyisobutylene having a viscosity of 50 to 10,000.

Here, set the viscosity of polyisobutylene to 50~
The reason why we chose 10,000 cp is that if it is less than 50 cp, the strength of the pressed body will decrease. If it exceeds 10,000 cp, when mixed and coated with magnet powder, the bond between the magnet powders will become too strong, causing problems during molding. This is because magnetic field orientation becomes difficult.

The reason why the mixing amount is 1 to 3 wt% is that if it is less than 1%, the strength of the press body will not be sufficient, and the reason why the mixing amount is 3 wt% or less is because if it exceeds this, it will affect the magnetic properties.

Examples of the present invention will be described below.

Example 1 Sm is 26.0wt%, Fe is 14.8wt%, Cu is 4.8wt%,
An ingot was produced by high-frequency heating in an argon atmosphere so that Zr was 2.3 wt%, Ti was 0.2 wt%, and the balance was Co.

Next, this alloy was coarsely ground, and then finely ground to an average particle size of about 3.6 μm using a ball mill. Add 1 to 5 wt% of polyisobutylene with a viscosity of 100 cp to this powder.
A toluene solution was mixed and coated to give the following properties, and then dried.

This molding powder was pressed at 1 TON/cm ² in a magnetic field of 20 KOe perpendicular to the applied magnetic field. This molded body was heated at a rate of 300°C/hour, held at 1210°C in vacuum for 2 hours, further held in Ar for 3 hours, and then rapidly cooled to room temperature.

Next, after holding this sintered body at 800℃ for 8 hours,
It was rapidly cooled and its magnetic properties were measured. As a comparative example, paraffin wax (melting point 68°C to 70°C), which is an additive widely used to improve the properties of alloy powders, etc.
The same treatment as above was performed using polyisobutylene.

The results are shown in FIG. As the amount of additives mixed increases, when paraffin wax is used as the additive, the magnetic properties deteriorate significantly. In comparison, when polyisobutylene is used as an additive, there is almost no deterioration in magnetic properties within the range of 1 to 3 wt%.

Example 2 The magnet powder mixed and coated with additives in Example 1 was
Using a 30 x 40 x t (mm) mold without a magnetic field,
The test pieces were pressure-molded so that their weight remained constant (height: 7 mm to 10 mm). Next, a shear pressure strength test was conducted using this test piece. The test method is two-point support center loading.

The test results are shown in Figure 2. Compared to the case where paraffin wax was added as an additive, higher green compact strength was obtained even with the same amount of polyisobutylene added.

〔Effect of the invention〕

Although the present invention has been explained in detail above, Sm ₂
In a method for producing Co _17- based magnetic alloy by powder metallurgy, one portion of polyisobutylene is added to fine alloy powder.
The compact coated with ~3% mixture and compression molded has sufficient strength to prevent slips, cracks, and chips, and has a high green density, so the shrinkage rate during sintering is low. Since deformation is reduced and a molded body closer to the product shape can be obtained during compression molding, processing can be reduced and yields can be significantly improved. Moreover, the mixing amount within this range does not affect the magnetic properties in any way, so it is very useful industrially.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the amount of polyisobutylene and paraffin wax mixed with the Sm ₂ Co ₁₇ alloy powder and the magnetic properties in Example 1. FIG. 2 shows the relationship between the amount of polyisobutylene and paraffin wax mixed with the Sm ₂ Co ₁₇ alloy powder and the shear pressure in Example 2.

[Claims]

1 Fe ₂ O ₃ 50 mol% to 70 mol, MnO 10 mol% to 40 mol%, ZnO 5 mol% to 30 mol%, CaO 0.01 wt% to 0.2 wt%, Ca, Mg, A Mn-Zn ferrite is produced by adding 0.005wt% to 0.2wt% of a type of silicate of Zr and Al to the calcining raw material having the above basic composition, pulverizing it, then molding and sintering it. Production method.