SOFT MAGNETIC CORE AND MANUFACTURING METHOD OF THE SAME

There is provided a soft magnetic core, including: a soft magnetic metal powder; a ferriferous oxide (Fe3O4) layer formed on a surface of the soft magnetic metal powder; and an insulating layer formed on the ferriferous oxide (Fe3O4) layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a perspective view of a soft magnetic core according to an embodiment of the present invention.

FIG. 3is a flow chart illustrating a manufacturing method of a soft magnetic core according to an embodiment of the present invention.

FIG. 4is a view sequentially showing processes of manufacturing a soft magnetic core according to an embodiment of the present invention.

Soft Magnetic Core200

A soft magnetic core200according to an embodiment of the present invention will be described with reference toFIGS. 1 and 2.

The soft magnetic core200according to the embodiment of the present invention may include a soft magnetic metal powder particle1, a ferriferous oxide (Fe3O4) layer2, and an insulating layer3.

That is, the soft magnetic core may include a plurality of soft magnetic complex powder particles10having the ferriferous oxide (Fe3O4) layer2and insulating layer3formed on surfaces thereof.

Although the soft magnetic metal powder particle1is depicted as having a spherical shape in the drawings for the sake of convenience, the shape thereof is not limited thereto but may have a typical powder particle shape such as an ovoid or polygonal shape.

(a) Soft Magnetic Metal Powder Particle1

The soft magnetic metal powder particle1included in the soft magnetic core200according to the embodiment of the present invention is not specifically limited as long as it has soft magnetic properties.

The average grain size of the soft magnetic metal powder particle1may be between 50 μm and 200 μm. If the average grain size of the soft magnetic metal powder particle1is below 50 μm, the magnetic flux density of the soft magnetic core may be reduced. If the average grain size of the soft magnetic metal powder particle1is above 200 μM, although the magnetic flux density is increased, core loss increases, and in particular, eddy current loss drastically increases, which causes a problem at high frequency. Accordingly, it is desired that the soft magnetic metal powder particle1has the average grain size between 50 μm and 200 μm.

The soft magnetic metal powder particle1may be formed of pure iron or an iron (Fe)-based alloy.

Technically, pure iron refers to iron having a purity of 100% with no impurities contained therein. However, since it is difficult to completely remove impurities such as carbon, nitrogen, silicon, phosphorus, and sulfur from pig iron, pure iron commonly refers to iron having a higher purity than other iron, and the term is used in the same sense herein.

The iron (Fe)-based alloy is made of iron (Fe) and at least one other alloy element, and has the properties of metal. The alloy element is not specifically limited, as long as it increases electric resistance, and may include at least one of silicon (Si), aluminum (Al), chrome (Cr), molybdenum (Mo), and boron (B).

Among others, silicon (Si), aluminum (Al), chrome (Cr), molybdenum (Mo), and boron (B) have excellent effects in increasing resistance.

On the surface of the soft magnetic metal powder particle1, a ferriferous oxide (Fe3O4) layer2may be formed. By virtue of the ferriferous oxide (Fe3O4) layer2, the bonding force between the insulating layer3and the soft magnetic metal powder particle1may be enhanced, and corrosion resistance, abrasion resistance and yield stress may be increased.

Unlike Fe2O3, Fe3O4has Fe2+and Fe3+in a 1:1 ratio so that it has improved magnetic properties, as compared to α-Fe2O3which has Fe3+ only. Accordingly, employing Fe3O4in molding the core is advantageous in terms of permeability, compared to employing conventional Fe2O3.

The thickness of the ferriferous oxide (Fe3O4) layer2may be between 50 nm and 700 nm. If the thickness of the ferriferous oxide (Fe3O4) layer2is below 50 nm, an enhancement of bonding force between the insulating layer and the powder is not sufficiently obtained, and cracks may be generated in the ferriferous oxide (Fe3O4) layer2so that tunneling may occur.

If the thickness of the ferriferous oxide (Fe3O4) layer2is above 700 nm, the overall magnetic flux density of the core is decreased because the portion of the ferriferous oxide (Fe3O4) layer2relative to the soft magnetic metal powder may become too large, whereas the effect of enhancement in yield stress of the soft magnetic core is saturated and thus no further increased.

On the ferriferous oxide (Fe3O4) layer2formed on the surface of the soft magnetic metal powder particle1, the insulating layer3may be formed.

The insulating layer3serves to electrically insulate the magnetic metal powder particles1so as to reduce eddy current loss, and may include, but are not limited to, a phosphate compound, an epoxy resin, and a ceramic.

Moreover, the insulating layer3may have a thickness between 30 nm and 300 nm. If the thickness of the insulating layer is above 300 nm, the magnetic flux density of the core may be decreased. If the thickness of the insulating layer is below 30 nm, insulation may be insufficient, so that core loss is increased. Moreover, cracks may occur during a compression molding process, such that tunneling may be generated, thereby further deteriorating insulation properties.

Manufacturing Method of Soft Magnetic Core200

In the following, a manufacturing method of a soft magnetic core200according to an embodiment of the present invention will be described with reference toFIGS. 3 and 4.

In describing a manufacturing method of the soft magnetic core, redundant descriptions with respect to the above-described soft magnetic core200will be omitted.

The manufacturing method of a soft magnetic core according to an embodiment of the present invention includes: preparing a soft magnetic metal powder particle1; forming an insulating layer3; preparing a slurry20; manufacturing a molded core100; and forming a ferriferous oxide (Fe3O4) layer2.

Further, the method may further include forming a lubricating wax coating layer (not shown) on the insulating layer3, after the forming of the insulating layer3and before preparing the slurry20.

Initially, a soft magnetic metal powder particle1is prepared, and then an insulating layer3is formed on the soft magnetic metal powder. As described above, the insulating layer may include, but is not limited to, a phosphate compound, an epoxy resin, and a ceramic.

Subsequently, the slurry20including the soft magnetic metal powder particle1having the insulating layer3thereon is produced. The slurry may include the soft magnetic metal powder particle1having the insulating layer3formed thereon and an additive11. The additive may include, but is not limited to, a binder, a solvent or the like.

The binder may be, but is not limited to, at least one selected from a group consisting of water glass, a polyimide, a polyamide, silicon, a phenol resin, and acryl.

In addition, a volatile solvent may be added in order to adjust viscosity of the slurry20. The volatile solvent may include, but is not limited to, at least one of toluene, alcohol, and methyl ethyl ketone (MEK).

A soft magnetic core mold100having a desired core shape is produced using the slurry20. This may include, but is not limited to, injecting the slurry20into a molding21having a core shape and then compression molding it using a presser22.

(4) Heat Treatment

Subsequently, the soft magnetic molded core100is subjected to heat treatment, such that a ferriferous oxide (Fe3O4) layer2is formed between the soft magnetic metal powder particle1and the insulating layer3. Further, a ferriferous oxide (Fe3O4) layer2may be formed on the surface of the soft magnetic molded core produced through the heat treatment.

The ferriferous oxide (Fe3O4) layer2formed on the surface of the soft magnetic metal powder may enhance the bonding force between the soft magnetic metal powder and the insulating layer, and the ferriferous oxide (Fe3O4) layer2formed on the surface of the soft magnetic core molded article may increase corrosion resistance, abrasion resistance and yield stress of the soft magnetic core itself.

After the forming of the insulating layer and before the preparing of the slurry, the method may further include forming a lubricating wax coating layer (not shown) on the insulating layer3. By forming the lubricating wax coating layer on the powder, the frictional force between the soft magnetic complex powder particles or between the soft magnetic complex powder and the mold wall may be minimized. That is, in molding a core with the soft magnetic metal powder having the wax coating layer formed on the insulating layer3, during a warm pressing in which powder particles are in contact with one another and crushed by external pressure, the lubricating wax changes from a solid state to a liquid state, thereby reducing frictional force, such that residual stress generated due to the compression molding is reduced and hysteresis loss is reduced. Ultimately, a core having lower core loss may be obtained.

Conventionally, molding has been performed by mixing lubrication powder particles on the scale of several μm with soft magnetic metal powder particles. However, in the case that the lubrication powder particles are not uniformly mixed, hysteresis loss is increased in the area in which the lubrication powder particles are not present in high amounts so that frictional force is greater, whereas magnetic properties are deteriorated in areas in which too many lubrication powder particles are present, so that actual carbon increases. Accordingly, as taught by the present invention, the above shortcoming may be overcome by coating lubricating wax on the insulating layer3of the soft magnetic metal powder particle1.

The forming of the lubricating wax coating layer may include, but is not limited to, melting the wax for lubrication into a liquid state and then dipping the soft magnetic metal powder particle1having the insulating layer3thereon into the wax for lubrication, or spraying lubricating wax in a liquid state on the insulating layer3formed on the surface of the soft magnetic metal powder particle1and then drying the wax thereon.

The lubricating wax for the lubricating wax coating layer has a melting point between 100° C. and 150° C. This is because the molding temperature is often above 80° C. in molding a core using the soft magnetic metal powder. Further, if the melting point of the lubricating wax exceeds 150° C., the lubricating wax does not change into a liquid state at a molding temperature so that the effect of reducing the frictional force between the powder particles or between the powder and the molding is significantly reduced.

The lubricating wax may include at least one of ethylene bis (stearamide) (EBS), Zn-stearate and polyethylene.

The melting point of the ethylene bis (stearamide) (EBS) is between about 141° C. and 146° C., the melting point of Zn-stearate is between about 121° C. and 124° C., and the melting point of polyethylene is between about 100° C. and 110° C.

The lubricating wax coating layer may have a thickness of between 300 nm and 700 nm. If the thickness of the lubricating wax coating layer is below 300 nm, during a compression molding process, the melted lubricating wax may fail to sufficiently cover the powder particles to reduce friction between powder particles or between the powder and the molding, such that an insulating film may be damaged and core loss thus increased. Further, if the thickness of the lubricating wax is above 700 nm, the portion of the magnetic material in a core is reduced and thus molding density and flux density are reduced, such that core loss is increased again. Therefore, it is desired that the lubricating wax coating layer may have a thickness between 300 nm and 700 nm.

Example

Table 1 below represents physical properties according to thicknesses of the ferriferous oxide (Fe3O4) layer of the soft magnetic complex powder in the soft magnetic core.

The soft magnetic complex metal powder used in manufacturing the soft magnetic core of the example includes an iron-based power having D50=170 μm, an insulating layer including a phosphate compound and having a thickness of 150 nm, and a lubricating wax coating layer having a thickness of 400 nm.

As can be seen from the example, as the thickness of the ferriferous oxide layer increases, the permeability, the magnetic flux density, and the yield stress tended to be increased. It is considered that this results from the fact that the ferriferous oxide layer is formed between the iron-based powder and the insulating layer after heat treatment, such that the bonding strength therebetween is increased and ultimately the yield stress of the core is enhanced. It can also be seen, however, that once the thickness of the ferriferous oxide layer reaches 700 nm, i.e., the threshold, the yield strength as well as the permeability and the magnetic flux density are not increased but saturated, and thereafter it have negative effects.

Further, although not provided as experimental data, when the thickness of the ferriferous oxide layer is below 50 nm, tunneling occurs, as described above.

Therefore, it is desirable that the thickness of the ferriferous oxide layer be between 50 nm and 700 nm.

According to the embodiment of the present invention, by forming the ferriferous oxide (Fe3O4) layer on the surface of the soft magnetic metal powder and the surface of the soft magnetic core, the soft magnetic core having excellent bonding force between the soft magnetic metal powder and the insulating layer and having enhanced corrosion resistance, abrasion resistance and yield stress, and a manufacturing method thereof can be provided.

As set forth above, according to the embodiments of the present invention, a high-efficiency, high-strength soft magnetic core having low eddy current loss and enhanced mechanical strength and a manufacturing method of the same are provided.