JPS6349883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sintered magnetic core material having excellent magnetic flux density and coercive force.

The material of the sintered magnetic core used as the yoke of a permanent magnet is usually pure iron, and its characteristics are magnetic flux density B25
is around 11-15KG, and the coercive force Hc is around 0.6-2.5Oe.

However, some permanent magnet yokes have applications that require the above-mentioned level of magnetic flux density and larger coercive force, and it has been desired to improve the material.

In order to increase the coercive force of pure iron sintered material, it is effective to add carbon or copper to it. but,
Since the magnetic flux density of Fe-C based materials is lower than that of pure iron, they are not suitable for the intended purpose. Further, when a typical iron-copper-based sintered alloy is sintered, a "copper expansion" phenomenon occurs, resulting in a decrease in sintered density and a corresponding decrease in magnetic flux density.

Previously, the applicant found that copper expansion during sintering in iron-copper sintered alloys was suppressed by the presence of boron of 0.03% or more by weight, and this was found to be suppressed in iron-copper-based high-density sintered alloys. It was applied to the production of gold and the production of composite sintered machine parts by joining green compacts. The content of the earlier invention (Japanese Patent Application No. 54-96389) has been published as Japanese Patent Application Laid-open No. 56-20142.

This invention is based on the idea of improving magnetic flux density by suppressing density reduction, and applies the above-mentioned previous invention to a sintered magnetic core.

That is, this invention provides a method for obtaining a magnetic core by sintering an iron-copper compact containing 0.5% to 15% copper.
The gist of this method is to add 0.03 to 0.3% of boron to the powder compact in advance.

The present invention will be described in detail below based on experimental results including examples thereof.

In Figure 1, the horizontal axis shows the copper content in the iron-copper sintered material.
The vertical axis represents sintering density, coercive force, and magnetic flux density.
It is a graph showing how the presence or absence of boron influences the dimensional change that occurs when a green compact of a mixed powder of iron powder and copper powder is sintered. Sample preparation is based on particle size
Atomized iron powder with a particle size of 100 mesh or less and a purity of 99% or more, a specified amount of electrolytic copper powder with a particle size of 200 mesh or less and a purity of 99.6% or more, and zinc stearate as a lubricant.
0.5%, and only for samples containing boron, the particle size is less than 250 mesh and the boron content is 20%.
% of ferroboron powder was thoroughly mixed, molded into a specified test piece at a molding pressure of 5t/ ^cm2 , and heated at a temperature of 1150℃ in a sintering furnace in an ammonia decomposition gas atmosphere.
Sintered for 40 minutes.

As shown in Figure 1, the coercive force of the iron-copper sintered material (dotted line) increases as the copper content increases;
On the other hand, as the sintered density decreases due to the effect of expansion during sintering, the magnetic flux density decreases. However, when 0.2% boron is added (solid line), although the rate of increase in coercive force is somewhat smaller, "copper expansion" is suppressed and the sintered density does not decrease, so the magnetic flux density remains at the level of pure iron. ing.

In other words, this result shows that, according to the present invention, a sintered magnetic core with magnetic flux density equivalent to that of conventional material (pure iron) and superior coercive force can be obtained. Expressed in another way, this means that a magnetic material with greater magnetic energy (product of magnetic flux density and coercive force) can be obtained. The preferred content of copper varies depending on whether the use of the magnetic core emphasizes more on magnetic flux density or coercive force, but is often 8 to 12%, with a center of 10%. However, if it exceeds 15%, the magnetic flux density will deteriorate to below the level of pure iron, so it should be kept at 15%. On the other hand, if it is less than 0.5%, no significant difference from that of pure iron is observed, so 0.5% is set as the lower limit. Of course, this value is extremely small considering the range of normal use.
It has only marginal significance.

Next, Figure 2 shows that the copper content is 10% (solid line) and 4%.
% (dotted line), it shows the relationship between the amount of boron added and various properties of the sintered material. Overall, the coercive force is higher when the copper content is higher, and the magnetic flux density is higher when the copper content is lower. shows a tendency to be superior.

The sintered density increases with the addition of boron and forms a peak at an addition amount of 0.1 to 0.2%.After that, the graph shows the optimal result at 0.2%, but there is almost no change up to 0.3%, and after that it gradually decreases. .

The magnetic flux density increases rapidly with the addition of boron, forming a peak at an addition amount of 0.05 to 0.1%, and after that it increases to 0.3%.
% remains at almost the same level.

Coercive force also increases with the addition of boron, but its peak differs depending on the copper content. After the peak, it gradually decreases to 4.6 at 0.2% boron.
5.6, but at 0.3% it drops by about 10% to 4.0-5.0.

Overall, from the above results, the lower limit for the amount of boron added should be 0.03%, which is the critical value that produces the effect of suppressing copper expansion, and the range of 0.1 to 0.2%, where the sintered density, coercive force, and magnetic flux density are in harmony, is the best. preferable.

Regarding the upper limit, unlike the lower limit, no clear critical phenomenon is observed. However, it is clear that excessive addition tends to lower the coercive force, and since the sintered density also gradually decreases, it should be kept at 0.3% or less.

As detailed above, according to the method of the present invention, a considerable amount of copper can be contained without causing copper expansion, which was a drawback of iron-copper sintered alloys, and as a result, magnetic flux density and coercive force can be improved. In both cases, we were able to provide excellent sintered magnetic core materials.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effects of copper content and the presence or absence of boron on the density and magnetic properties of iron-copper sintered materials, and FIG. 2 is a graph showing the effects of the amount of boron added.

Claims (1)

[Claims] 1 Iron-copper based sintered alloy with boron content in weight ratio
A sintered magnetic core with high magnetic flux density and coercive force, characterized by comprising 0.03% to 0.3% copper, 0.5% to 15% copper, and the balance iron.