Method for manufacturing Fe-based amorphous metal powder and method for manufacturing amorphous soft magnetic cores using same

Abstract

A manufacturing method of an amorphous soft magnetic core using a Fe-based amorphous metallic powder includes size-sorting an amorphous metallic powder obtained by pulverizing an amorphous ribbon prepared by a rapid solidification process (RSP) and then using the amorphous metallic powder having a particle size distribution so as to comprise 10 to 85 wt. % of powder having a particle size of 75 to 100 m, 10 to 70 wt. % of powder having a particle size of 50 to 75 m, and 5 to 20 wt. % of powder having a particle size of 5 to 50 m to manufacture an amorphous soft magnetic core with excellent high-current DC bias characteristic and good core loss characteristic.

Claims

1. A method for manufacturing an amorphous soft magnetic core, comprising: preparing a composite powder; adding a binder to the composite powder and molding the composite powder and the binder to obtain a molded core material; and annealing the molded core material, wherein the preparing consists of: preparing a Fe-based amorphous metallic ribbon; pulverizing the amorphous metallic ribbon to obtain an amorphous metallic powder; size-sorting the amorphous metallic powder to obtain size-sorted amorphous metallic powders; and mixing, among the size-sorted amorphous metallic powders, a size-sorted amorphous metallic powder having a particle size of 5 to 100 m to obtain the composite powder, wherein the composite powder consists of: 40 to 85 wt. % of powder having a particle size of 75 to 100 m, 10 to 50 wt. % of powder having a particle size of 50 to 75 m, and 5 to 20 wt. % of powder having a particle size of 5 to 50 m.

2. The method as claimed in claim 1, wherein the binder comprises 0.5 to 3 wt. % of any one selected from the group consisting of phenol, polyimide, and epoxy.

3. The method as claimed in claim 1, wherein the annealing is performed at a temperature of 300 to 500 C. under an atmospheric condition for 0.3 to 4.3 hours.

4. A method for manufacturing an amorphous metallic powder for an amorphous soft magnetic core, consisting of: preliminarily heat-treating a Fe-based amorphous metallic ribbon prepared by a rapid solidification process (RSP); pulverizing the amorphous metallic ribbon to obtain an amorphous metallic powder; and size-sorting the amorphous metallic powder to obtain size-sorted amorphous metallic powders; and mixing, among the size-sorted amorphous metallic powders, a size-sorted amorphous metallic powder having a particle size of 5 to 100 m to obtain a composite powder, wherein the composite powder consists of: 40 to 85 wt. % of powder having a particle size of 75 to 100 m, 10 to 50 wt. % of powder having a particle size of 50 to 75 m, and 5 to 20 wt. % of powder having a particle size of 5 to 50 m.

5. The method as claimed in claim 4, wherein the amorphous metallic powder is used for a soft magnetic core having an improved DC bias characteristic.

6. The method as claimed in claim 1, after the annealing, further comprising: coating the molded core material with an insulating resin.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram showing the manufacturing process from the manufacture of an amorphous metallic powder according to the present invention to the molding of an inductor.

(2) FIG. 2 is a graph showing a comparison of the change in DC bias characteristic between the soft magnetic core prepared according the present invention and the prior art material.

(3) FIG. 3 is a graph showing a comparison of the core loss at 100 kHz between the soft magnetic core prepared according to the present invention and the prior art material.

BEST MODES FOR CARRYING OUT THE INVENTION

(4) Hereinafter, a detailed description will be given as to a manufacturing method of a Fe-based amorphous metallic powder and an amorphous soft magnetic core using the Fe-based amorphous metallic powder according to the present invention.

(5) FIG. 1 is a schematic diagram showing the manufacturing process from the manufacture of an amorphous metallic powder according to the present invention to the molding of an inductor. Referring to FIG. 1, in order to obtain a Fe-based amorphous metallic powder, an amorphous metallic ribbon with a desired composition as prepared by a rapid solidification process (RSP) is preliminarily heat-treated at 100 to 400 C. under the atmospheric condition for about one hour and then subjected to a pulverization step.

(6) After the preliminary heat treatment, the amorphous metallic ribbon is pulverized with a milling machine to obtain an amorphous metallic powder. During the pulverization step, the pulverizing speed and the pulverizing time are appropriately controlled to manufacture a powder that comes in different shapes and particle size distributions. Subsequently, the pulverized amorphous metallic powder is size-sorted into powders having a particle size of 75 to 100 m, 50 to 75 m, or 5 to 50 m.

(7) The desirable particle size distribution of the amorphous metallic powder used in the present invention is given such that the amorphous metallic powder comprises 10 to 85 wt. % of powder having a particle size of 75 to 100 m, 10 to 70 wt. % of powder having a particle size of 50 to 75 m, and 5 to 20 wt. % of powder having a particle size of 5 to 50 m. This is a particle size composition for acquiring optimum physical characteristics and magnetic characteristics. With such a particle size composition, it is possible to obtain a molded core material having a good molding density of about 83 to 84 during the molding step.

(8) The reason of determining such a particle size distribution in the present invention can be described in detail as follows.

(9) Firstly, when the powder having a particle size of 75 to 100 m is greater than 85%, the eddy current loss increases to deteriorate the core loss characteristic and lower the eddy current loss, but part of the powder may be crystallized during the step of pulverizing the ribbon to increase the hysteresis loss and deteriorate the core loss characteristic. When the powder having a particle size of 75 to 100 m is less than 10%, the molding density is reduced to make an insignificant effect of improving the DC bias characteristic. When the powder having a particle size of 5 to 50 m is greater than 20%, the hysteresis loss increases to remarkably deteriorate the core loss characteristic, making it impossible to acquire a desired magnetic permeability. When the powder having a particle size of 5 to 50 m is less than 5%, fine cracks appear on the surface of the core after the molding step to lower the molding density, which makes it difficult to improve the DC bias characteristic.

(10) In order to manufacture a soft magnetic core from the amorphous metallic powder prepared as described above, a binder, such as phenol, polyimide, epoxy, or water glass, is added in an amount of 0.5 to 3 wt. % with respect to the total weight of the amorphous metallic powder, and the mixture is then subjected to a drying step. The drying step is to eliminate the solvent used in mixing the amorphous metallic powder with phenol, polyimide, epoxy, water, or water glass.

(11) Subsequent to the drying step, the powder is pulverized with a milling machine. After the milling, any one lubricant selected from Zn, ZnS, and stearate is added to the pulverized powder and the mixture is molded with a press under a molding pressure of about 20 to 26 ton/cm.sup.2 to form a toroidal core. The lubricant is used to reduce the friction between the powers or between the molded material and the mold. Preferably, Zn-stearate generally used as a lubricant is added in an amount of less than 2 wt. % with respect to the total weight of the pulverized powder.

(12) Subsequently, the toroidal core is subjected to a heat treatment (annealing) under the atmospheric condition at 300 to 500 C. for 0.3 to 4.3 hours to eliminate the residual stress and deformation and then coated with a polyester or epoxy resin in order to protect the core characteristics against moisture or air, thereby completing a soft magnetic core. In this regard, the thickness of the epoxy resin coating is preferably about 50 to 200 m.

EXAMPLES

(13) Hereinafter, the present invention will be described in further detail with reference to Examples.

Examples 1 to 4

(14) A Fe78-Si13-B9 amorphous metallic ribbon prepared by a rapid solidification process (RSP) is subjected to a one-hour preliminary heat treatment at 300 C. under the atmospheric condition. The amorphous metallic ribbon thus obtained is pulverized with a milling machine to obtain an amorphous metallic powder. The amorphous metallic powder is size-sorted and mixed so as to have a particle size distribution as presented in Table 1 according to the present invention, thereby preparing a composite powder of amorphous metals. In this regard, the unit % means wt. %.

(15) The composite powder thus obtained is mixed with 2.0 wt. % of water glass and then dried out. After the drying step, the lump of powder is pulverized again with a ball mill and then mixed with 0.5 wt. % of Zn-stearate. The mixture is molded under the molding pressure of 22 ton/cm.sup.2 with a core mold to complete a toroidal core as a molded material.

(16) Subsequently, the molded core material is annealed at 450 C. for 30 minutes and then coated with an epoxy resin in thickness of 100 m to manufacture a soft magnetic core. The soft magnetic core thus obtained is measured in regards to magnetic permeability, DC bias characteristic, and core loss characteristic. The measurement results are presented in Table 1.

(17) TABLE-US-00001 TABLE 1 Magnetic characteristics of soft magnetic core according to the present invention. Div. Example 1 Example 2 Example 3 Example 4 75~100 m(wt. %) 70 85 40 60 50~75 m(wt. %) 20 10 50 20 5~50 m(wt. %) 10 5 10 20 Permeability () 60 60 60 60 Molding density (%) 84 83 83 83 DC bias 74 73 73 73 characteristic (% ) Core loss (mW/cm.sup.3) 700 750 800 750 Surface cracks x x x x

(18) As for the permeability () in Table 1, an enameled copper wire is wound around the soft magnetic core 30 times, and the inductance L (H) is measured with a precise LCR meter. The inductance L is applied to the relational expression of the toroidal core as given by (0.4N.sup.2 A10.sup.2)/l (where N is the number of winding frequencies; A is a cross-sectional area of the core; and l is the average length of the magnetic path) to determine the magnetic permeability (). The measurement is carried out under the conditions including frequency of 100 kHz and AC voltage of 1V, without DC bias (I.sub.DC=0 A). Further, the change of permeability is measured while varying the DC current to evaluate the DC bias characteristic. The measurement conditions are the frequency of 100 kHz, AC voltage of 1V, and the intensity of magnetization (100 Oe) given by H.sub.DC=0.4NI/l, where I is the peak magnetization current. The core loss is measured with a B-H analyzer, while the numbers of the primary and secondary windings are 30 times and 5 times, respectively.

(19) It can be seen from the measurement results for the Examples 1 to 4 of the present invention in Table 1 that the soft magnetic core manufactured by controlling the particle size distribution of the amorphous powder within a defined range according the present invention can acquire effects of improving the surface conditions of the core, enhancing the DC bias characteristic and reducing the core loss.

(20) For a comparison with the present invention, there is used a prior art material (Korean Patent No. 10-0545849), which is an amorphous soft magnetic core manufactured by using an amorphous powder of the same constituent components of the Examples at a mixing ratio so as to comprise 40% of powder having a particle size of 100 to 150 m and 60% of powder having a particle size of 75 to 100 m. The prior art material is measured in regards to the magnetic characteristics under the same measurement conditions of the Examples of the present invention. The measurement results are presented in Table 2.

(21) TABLE-US-00002 TABLE 2 Comparison of characteristics between the present invention and the prior art material. DC bias Permeability () characteristic Core loss (mW/cm.sup.3) (100 KHz, 1 V) (% ) (100 Oe) (100 KHz, 0.1 T) Prior art 60 65 1000 Example 1 60 74 700 Example 2 60 73 750 Example 3 60 73 800 Example 4 60 73 750

(22) As can be seen from Table 2, relative to the prior art material, the soft magnetic core of the present invention is improved in the DC bias characteristic and the core loss. In other words, the present invention controls the particle size distribution of the amorphous metallic powder to increase the content of the powder having a relatively small particle size and then enhance the insulating effect caused by the binder on the surface of the powder, thereby reducing the magnetic flux leakage (MFL), fills the large pores between the powders with fine powder to eliminate the large pores in the molded material, and has the micro pores uniformly distributed to improve the DC bias characteristic and reduce the eddy current loss, which leads to the enhanced core loss.

(23) FIG. 2 is a graph showing the change of permeability with DC bias at 100 kHz and 1 V for the Example 1 (novel material) of the present invention and the prior art material as presented in Table 2. As can be seen from FIG. 2, the novel material (.square-solid.) that is the soft magnetic core manufactured according to the present invention is superior in the DC bias characteristic to the prior art material (.circle-solid.). In other words, the change in the particle size distribution of the amorphous powder according to the present invention makes an effect to improve the DC bias characteristic by about 8 to 10% (based on 100 Oe) in relation to the prior art material. Besides, the graph of FIG. 3 that represents the core loss at 100 kHz for the soft magnetic core of the present invention and the prior art material shows that the novel material of the present invention (dotted line) is considerably improved in the core loss characteristic relative to the prior art material (solid line).

(24) In order to evaluate the change in the characteristics as a function of the change in the particle size distribution, the composite amorphous powder is composed so as to have the particle size distribution out of the defined range of the present invention in the test for characteristics.

Comparative Example 1

(25) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 90% of powder having a particle size of 75 to 100 m, 5% of powder having a particle size of 50 to 75 m, and 5% of powder having a particle size of 5 to 50 m.

Comparative Example 2

(26) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 5% of powder having a particle size of 75 to 100 m, 75% of powder having a particle size of 50 to 75 m, and 20% of powder having a particle size of 5 to 50 m.

Comparative Example 3

(27) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 20% of powder having a particle size of 75 to 100 m, 75% of powder having a particle size of 50 to 75 m, and 5% of powder having a particle size of 5 to 50 m.

Comparative Example 4

(28) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 80% of powder having a particle size of 75 to 100 m, 5% of powder having a particle size of 50 to 75 m, and 15% of powder having a particle size of 5 to 50 m.

Comparative Example 5

(29) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 60% of powder having a particle size of 75 to 100 m, 15% of powder having a particle size of 50 to 75 m, and 25% of powder having a particle size of 5 to 50 m.

Comparative Example 6

(30) The procedures are performed in the same manner as described in Example 1 to manufacture a soft magnetic core, excepting that the amorphous powder has a particle size distribution so as to comprise 60% of powder having a particle size of 75 to 100 m, 38% of powder having a particle size of 50 to 75 m, and 2% of powder having a particle size of 5 to 50 m.

(31) The individual soft magnetic cores obtained in the Comparative Examples are measured in regards to the core permeability, DC bias characteristic, core loss, and the existence of surface cracks. The measurement results are presented in Table 3 together with the results of Example 1.

(32) TABLE-US-00003 TABLE 3 Comparative Example Div. 1 2 3 4 5 6 7 75~100 m (%) 90 5 20 80 60 60 70 50~75 m (%) 5 75 75 5 15 38 20 5~50 m (%) 5 20 5 15 25 2 10 Permeability () 60 51 60 60 49 60 60 Molding density 81 82 82 80 82 81 84 (%) DC bias 66 68 70 65 68 66 70 characteristic (%) Core loss 1,000 800 950 800 1,050 700 700 (mW/cm.sup.3) Surface cracks X X X X

(33) Referring to Table 3, when the powder having a particle size of 75 to 100 m is less than 10% or greater than 85%, fine cracks appear on the surface of the molded core material, or there is no effect to improve the magnetic characteristics, causing deterioration in the magnetic permeability and core loss characteristic. Further, when the powder having a particle size of 50 to 75 m is less than 10% or greater than 70%, fine cracks appear on the surface of the molded core material, or there is only a little effect to improve the DC bias characteristic or the core loss characteristic. In addition, when the powder having a particle size of 5 to 50 m is less than 5% or greater than 20%, a desired magnetic permeability cannot be acquired, and only a slight effect is made to improve the DC bias characteristic appears insignificantly.

(34) More specifically, the Comparative Example 1 has fine cracks on the surface of the core, has no improvement in the core loss characteristic and displays no improvement in the DC bias characteristic due to the low molding density.

(35) As for the Comparative Example 2, the magnetic permeability is about 51, which is lower than the magnetic permeability of the core according to the Example 1 of the present invention by about 15%. It is therefore considered that a desired magnetic permeability cannot be acquired with such a particle size distribution of the metallic powder.

(36) As for the Comparative Example 3, the magnetic permeability and the DC bias characteristic may be good to some degree, but the stress caused during the step of pulverizing the ribbon into powder increases the hysteresis loss, which means that it is substantially difficult to improve the core loss characteristic. The Comparative Example 4 creates fine cracks on the surface of the core and acquires a molding density of 80%, which also means that the DC bias characteristic is substantially difficult to improve.

(37) As for the Comparative Example 5, the magnetic permeability is about 49, which is lower than the magnetic permeability of the core according to the Example 1 of the present invention by about 19%. Also, the core loss characteristic is deteriorated to 1,050 mW/cm.sup.3 in relation to the prior art conditions because of the increased content of the amorphous powder already under crystallization. It is therefore considered that such a particle size distribution of the metallic powder can result in neither a desired level of magnetic permeability nor a desired magnetic characteristic. As for the Comparative Example 6, fine cracks appear on the surface of the core, and the molding density is reduced to 81%, which means that it is impossible to make an effect of improving the DC bias characteristic.

(38) Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.

INDUSTRIAL APPLICABILITY

(39) The present invention relates to a manufacture of an amorphous soft magnetic core using a Fe-based amorphous metallic powder, to acquire an excellent high-current DC bias characteristic and a good core loss characteristic, and this invention will be used for an amorphous soft magnetic core.