Patent Application
20090145524
The present invention relates to a magnetic core using an Fe-based amorphous alloy ribbon mainly for the purpose of reducing noise, and can be used for an applied product such as a motor, a transformer, a choke coil, a generator or a sensor.
An Fe-based amorphous alloy ribbon receives attention as a magnetic core material of a transformer, a motor, a choke coil, a sensor and the like, because of excellent soft magnetic properties, particularly a low core loss among them. It has been practically used for various magnetic cores, parts and apparatuses. Among the Fe-based amorphous alloy ribbons, an FeSiB-based amorphous alloy ribbon has been widely used in particular, because it shows comparatively a high saturated magnetic flux density Bs and superior thermal stability. However, the FeSiB-based amorphous alloy ribbon has problems that the magnetic core becomes large because the FeSiB-based amorphous alloy ribbon has lower Bs than a silicon steel sheet, and that the magnetic core generates a high level of noise. As a method for increasing Bs in the Fe-based amorphous alloy ribbon, there have been practically carried out methods of: increasing an amount of Fe which bears magnetism; inhibiting thermal stability from deteriorating due to increased amount of Fe by adding Sn, S or the like; adding C; or adding C and P. JP-A-05-140703 discloses a method of increasing Bs by employing a composition of FeSiBCSn, enhancing the formability of amorphous in an Fe-rich area by adding Sn. On the other hand, JP-A-2002-285304 discloses a method of increasing Bs by employing a composition of FeSiBCP, greatly increasing the Fe content specifically by adding P into a limited composition range of Fe, Si, B and C. Regarding reducing magnetostriction, which is necessary for reducing a noise level, the saturation magnetostriction of the Fe-based amorphous alloy ribbon is approximately proportional to the square of Bs. Accordingly, the Fe-based amorphous alloy ribbon having high Bs and low magnetostriction has not been realized yet. For this reason, an amorphous or a nano-crystalline alloy ribbon with low Bs and low magnetostriction has been used for the magnetic core and an applied product with the use of the magnetic core, which is required not to cause a problem of noise.
[Patent Document 1]
JP-A-05-140703 ((0008) to (0010), and FIG. 1)
[Patent Document 2]
JP-A-2002-285304 ((0010) to (0016), and Table 1)
As described above, a magnetic core made from a conventional Fe-based amorphous alloy ribbon with high Bs has high saturation magnetostriction and causes a high level of noise. In other words, there has not been such a magnetic core as to concurrently satisfy high Bs and a low level of noise. For this reason, an object of the invention is to provide a magnetic core making use of an Fe-based amorphous alloy ribbon that simultaneously attains miniaturization and noise reduction through realization of high Bs, and an applied product making use of the same.
In order to realize miniaturization through the realization of high Bs and noise reduction, the causes of noise have been studied, and it is found that the squareness of an Fe-based amorphous alloy ribbon has a close relationship with the noise generated from a magnetic core made from the Fe-based amorphous alloy ribbon, and that the squareness is further improved by optimizing a composition of the alloy, a composition in the vicinity of the surface, and a segregation in the alloy, and by improving the surface condition. As a result, it is found that the magnetic core which generates an unprecedentedly low level of noise can be made from an Fe-based amorphous alloy ribbon, and the invention is accomplished.
A magnetic core according to the invention employs an Fe-based amorphous alloy ribbon characterized in that the ribbon has a saturated magnetic flux density Bs of not lower than 1.60 T, and a ratio B80/Bs of not less than 0.90, which is the ratio of a magnetic flux density B80 generated in an external magnetic field of 80 A/m applied to the magnetic core in relation to Bs.
The magnetic core made by using the Fe-based amorphous alloy ribbon having the adequate squareness shows the magnetic flux density of 1.4 T and a core loss W14/50, at a frequency of 50 Hz, being not higher than 0.28 W/kg. Furthermore it can provide a product which generates such an unprecedentedly low level of noise as 20×log [(L2×10−9+2×10−5)/(2×10−6)] dB or less when a magnetic flux density is 1.4 T, a frequency is 50 Hz and an average magnetic path length is L mm. The average magnetic path length “L” mm means a circumferential length at the middle of the thickness of the magnetic core. For instance, when the magnetic core has a perfectly circular shape and an average diameter ((outside diameter+inside diameter)/2) being R, the length L becomes πR (L=πR). The above expression on the noise level shows a boundary in the form of an approximate expression, between the invention and comparative example, when a relationship between the average magnetic path length and the noise level of the invention and comparative example are measured.
The Fe-based amorphous alloy ribbon used in the magnetic core preferably employs such a material with high Bs as to have a composition that is expressed by a formula TaSibBcCd (wherein T represents Fe, or Fe and at least one element of Co and Ni in an amount of not more than 10% with respect to Fe), in which the suffixes satisfy the expressions of, by atom %, 76≦a<84%, 0<b≦12%, 8≦c≦18%, and 0.01≦d≦3%, and that includes unavoidable impurities. The ribbon to be used has a thickness of 5 μm to 100 μm. When it has a thickness of not more than 5 μm, the Fe-based amorphous alloy ribbon is difficult to be manufactured, and cannot obtain uniform properties because the surface condition affects the properties much. When it has a thickness exceeding 100 μm, it tends to suffer from surface crystallization and deterioration of the properties.
The Fe-based amorphous alloy ribbon used in the magnetic core showing higher Bs and high squareness preferably has a composition, in which, by atom %, an amount of Fe is 81≦a≦83; an amount of Si is 0<b≦5; an amount of B is 10≦c≦18; and an amount of C is 0.2≦d≦3. The alloy having this composition shows particularly high squareness in the previously described composition range. The ribbon having the above composition shows a ratio B80/Bs of not lower than 0.93, which is the ratio of a magnetic flux density B80 generated in an external magnetic field of 80 A/m applied to the magnetic core in relation to Bs.
The reason for the above limitation to the composition will be described below. Hereinafter, the unit merely described as “%” represents atomic percent.
When an Fe content “a” is less than 76%, the amorphous alloy ribbon does not obtain sufficient Bs for a core material and thus the size of a magnetic core is increased, which is unpreferable. When the Fe content “a” is not less than 84%, on the other hand, the amorphous alloy ribbon shows low thermal stability and cannot be stably manufactured. In order to obtain high Bs, the value “a” is preferably not less than 81% but not more than 83%. Not more than 10% of the Fe content can be replaced by at least one element of Co and Ni depending on required magnetic properties.
An element Si contributes to the capability of forming an alloy into amorphous. An Si content “b” is not more than 12% in order to increase Bs. It is preferably not more than 5% in order to obtain high Bs.
An B (boron) content “c” contributes most significantly to the capability of forming an alloy into amorphous. When the boron content “c” is less than 8%, the thermal stability of the amorphous alloy decreases, but even though the boron content “c” is more than 18%, the capability of forming amorphous is not improved any more. The boron content “c” is preferably not less than 10% in order to keep the thermal stability of the amorphous material having high Bs.
An element C (carbon) has an effect of improving squareness and Bs of the material as to miniaturize a magnetic core and reduce noise. When a carbon content “d” is less than 0.01%, the effect is not shown. When it is more than 3%, the amorphous alloy becomes brittle and thermal stability is decreased so that it becomes difficult to be manufactured into a magnetic core, which is undesirable. In order to impart high Bs and high squareness to the amorphous alloy, the carbon content “d” is preferably not less than 0.2%, and is further preferably not less than 0.5%.
When not more than 10% of an Fe content is replaced by one or two elements of Ni and Co, Bs increases, which contributes to the miniaturization of a magnetic core. However, it is not practical for the amorphous alloy to contain more than 10% of the elements, because the raw materials of the elements are expensive. An element Mn shows an effect of increasing Bs even when a slight amount is added. When not less than 0.50 at % of Mn is added, Bs is decreased. Accordingly, an amount of Mn is preferably not less than 0.1% but not more than 0.3%.
In addition, the amorphous alloy may include one or more elements of Cr, Mo, Zr, Hf and Nb in an amount of 0.01 to 5%, and may include at least one element of S, P, Sn, Cu, Al and Ti in an amount of not more than 0.50% as an unavoidable impurity.
Means for improving squareness will be specifically described.
In order to further improve squareness, it is preferable to employ an Fe-based amorphous alloy ribbon having a carbon segregation layer which shows a peak value in a 2 to 20 nm deep region from a free surface and/or a rolled surface. A magnetic core using the Fe-based amorphous alloy ribbon shows a ratio B80/Bs of not lower than 0.95, which is the ratio of a magnetic flux density B80 in an external magnetic field of 80 A/m applied to the magnetic core in relation to a saturated magnetic flux density Bs of the Fe-based amorphous alloy ribbon.
In general, carbon is not positively added, because the addition of carbon produces a carbon segregation layer on the surface of a ribbon, which causes an embrittlement and thermal instability of the ribbon, and increases a core loss at a high magnetic flux density. An influence of an added carbon and the behavior of carbon distribution on the surface have been examined, and it has found that an amorphous alloy can be obtained having high squareness, low brittleness and high thermal stability, by controlling a ratio of a carbon content to a Si content and a surface state as to control a position of the carbon segregation layer and a peak position of the segregation layer into a predetermined range. The formed carbon segregation layer causes structural relaxation in the vicinity of the surface at a low temperature, which has a great effect on stress relaxation. When a stress relaxation is high, high squareness is obtained and a noise level and a core loss in a high magnetic flux density region are reduced. It is important to position the carbon segregation layer at a predetermined portion and a peak value in a predetermined range in order to make the carbon segregation layer show the effect. When the surface of the amorphous alloy ribbon has a large roughness due to an air pocket or the like, the thickness of an oxide layer becomes non-uniform, and thereby the position and thickness in a depth direction of the carbon segregation layer become non-uniform. Thereby, the structural relaxation becomes non-uniform, and a partially brittle part is produced. In addition, since the unevenness of the surface decreases cooling rate thereof, a surface of the carbon segregation layer in the vicinity is promoted to crystallization and thus the squareness is decreased. Accordingly, it is important to control the surface roughness and form the peak position of the carbon segregation layer in a 2 to 20 nm uniformly deep region from the surface. As a method thereof, it is effective to blow a CO2, He or Ar gas onto a roll during casting the alloy, or to blow CO gas to burn it for reducing. It was found that the surface roughness is greatly improved and the peak position of the carbon segregation layer can be controlled into the 2 to 20 nm deep position, by controlling oxygen concentration in the vicinity of an outlet of a nozzle tip into not more than about 10%. In order to control the oxygen concentration in atmospheric air to not more than about 10% at the outlet of the nozzle tip, it is effective to blow the gas onto a roll portion in the rear side of the outlet as shown in
The effect can be further enhanced by controlling the surface state and besides controlling an Si content to a certain level or lower with respect to a carbon content. Although depending on the carbon content, the effect can be enhanced by decreasing a value of b/d with respect to a fixed carbon content.
An Fe-based amorphous alloy ribbon can be impregnated or coated as needed. It can be used as a wound and cut core or a multilayered core by impregnated in a resin, such as an epoxy resin, an acryl resin or a polyimide resin, or bonded to an alloy. The magnetic core is generally used after having been accommodated in a resin case or having been coated.
As described above, such a magnetic core can be obtained as to generate little noise, cause a low core loss, suppress embrittlement, and the degradation of thermal stability, by employing a material with high Bs and increasing B80/Bs. Furthermore, an alloy composition capable of effectively increasing B80/Bs are found, so that such a magnetic core can be provided as to have a value B80/Bs of not less than 0.93 and be further preferable for reducing noise. In addition, the magnetic core can be provided which has a value B80/Bs of not less than 0.95 and be further preferable for reducing noise, by using an amorphous alloy ribbon which has a controlled composition and surface state and a controlled position and peak value of a carbon segregation layer in a fixed range. By using such magnetic cores, an applied product can be provided which can generate little noise, cause a low core loss, suppress embrittlement, and the degradation of thermal stability.
Next, the present invention will be specifically described with reference to examples, but the invention is not limited to the examples.
An amorphous alloy ribbon having a thickness of 23 to 25 μm and a width of 5 mm was produced by the steps of: preparing 200 g of a mother alloy having a composition of Fe82Si2B13.9C2Mn0.1; heating the mother alloy to 1300° C. with a high-frequency power to melt it and preparing the molten metal; and spouting the molten metal onto a Cu—Be alloy roll which is rotating at 25 to 30 m/s. A port for blowing CO2 gas was installed at a position of 10 cm apart from an exhaust nozzle of a Cu roll in a rear direction so that the port for blowing CO2 gas forms an angle of 45 degrees with respect to the roll surface. The amorphous alloy was cast while adjusting the blowing pressure of CO2 gas and controlling the gas pressure in the vicinity of the roll at the exhaust nozzle to 0 (no gas blown), 0.1 and 0.3 MPa. Then, it was found that oxygen concentrations in the vicinity of the exhaust nozzle (within 3 cm apart from the place at which the molten metal contacts with the roll) were 20.5, 8.5 and 7.5% respectively. It was confirmed from a measurement result that the amorphous alloy ribbon manufactured with the gas pressure controlled to 0.1 MPa in the vicinity of the roll at the exhaust nozzle (8.5% oxygen in the vicinity of the exhaust nozzle) has a peak of a carbon segregation layer in a position of 2 to 20 nm deep from the surface. The amorphous alloy ribbon was slit into the width of 5 mm, and three toroidal magnetic cores were produced having inner diameter/outer diameter of, respectively, 20/25, 25/35 and 70/75 mm. Then, the properties were measured. The amorphous alloy ribbon had a width of 5 mm and a thickness of 23 to 25 μm. The magnetic cores were annealed. Specifically, they were heated to 300 to 370° C. at the heating rate of 5° C./min, held at the temperature for one hour, and then cooled in a furnace, while a magnetic field of 1500 A/m was applied to the magnetic core in a circumferential direction of the magnetic core in argon atmosphere. The properties were compared at the annealed temperature at which a core loss is least. The properties are shown in Table 1. Bs was measured by using a vibrating sample magnetometer (VSM) in which a magnetic field of 5 kOe was applied to a single sheet sample. B80, a core loss W13/50 at 1.3 T by the frequency of 50 Hz, and a core loss W14/50 at the magnetic flux density of 1.4 T by the frequency of 50 Hz were measured on the toroidal magnetic cores. A noise level was measured in an anechoic room at a background noise level of 12 to 14 dB under conditions of the magnetic flux density of 1.4 T by the frequency of 50 Hz. In the room, a microphone was set at a position of 10 cm apart from the toroidal magnetic core. A stress relaxation degree was determined by the steps of: winding the single sheet sample around a quartz ring; measuring the diameter in the initial stage (that is, the diameter of the sample when being wound around the quartz ring), defining the value as R0; annealing the single sheet sample wound around the quartz ring; measuring the diameter of the sample after having been removed from the quartz ring, defining the value as R; and calculating the value of R0/R×100 from the measured values. The surface roughness of the rolled surface was 0.30 to 0.50 μm. All samples showed B80/Bs of not less than 0.95, which means squareness. The result showed that the higher was the value of the squareness, the lower was the value of the noise level.
Samples were produced so that each sample can acquire different B80/Bs in a range of less than 0.90 by annealing magnetic cores in a non magnetic field at 320° C., in a non magnetic field at 250° C., and in a magnetic field applied in a direction perpendicular to a circumferential direction (axial direction of magnetic core) at 320° C., on conditions similar to the case of Example 1. The properties are shown in Table 2. A noise level increased from a low magnetic flux density region, and increased to 24 dB, 28 dB and 35 dB along with the decrease of B80/Bs, at 1.4 T. All samples showed that B80/Bs, which means squareness, was less than 0.90. It was confirmed that the magnetic cores showed higher values of the noise level than 20×log [(L2×10−9+2×10−5)/(2×10−6)] dB which is specified in the invention.
Amorphous alloy ribbons having a width of 5 mm was produced by preparing 200 g of a mother alloy having compositions shown in Table 3, and then by similar steps to the case of Example 1, and the properties were measured on a toroidal magnetic core with an inner diameter/outer diameter of 25/35 mm. The properties are shown in Table 3. A position of a carbon segregation layer was measured by quantitatively analyzing elements from the rolled surface in a depth direction by using GD-OES (glow discharge optical emission spectrometer) made by Horiba, Ltd. In the result, a portion having a higher carbon concentration than the uniform concentration in the inner part was regarded as the carbon segregation layer, and the position at which the concentration is highest and the concentration value were read out as the position of the carbon segregation layer and the value of the carbon peak. It is understood that a noise level has highly relevant to B80, that noise can be reduced by enhancing Bs and a squareness ratio, and further that a carbon addition is effective in enhancing the squareness and reducing noise.
Amorphous alloy ribbons having compositions shown in Table 4 was produced in a similar way to the case of Example 1, and the properties were measured on a toroidal magnetic core with an inner diameter/outer diameter of 25/35 mm. The properties are shown in Table 4. The addition of 4% of carbon increases a core loss of the amorphous alloy ribbon due to the increase of coercive force, and may cause a problem in a step of manufacturing the magnetic core because the amorphous alloy ribbon becomes brittle. The addition of 0.7 at % Mn decreases Bs, lowers squareness, increases the coercive force and increases the core loss. The addition of a large amount of both carbon and Mn increases a noise level as well.
A toroidal magnetic core with an inner diameter/outer diameter of 25/35 mm was produced by using samples which were cast at gas pressures of 0 and 0.30 MPa in the vicinity of the roll surface at the exhaust nozzle, among amorphous alloy ribbons prepared in Example 1, and the properties were measured. The result is shown in Table 5. Sample No. 33 was a sample produced at a gas pressure of 0 MPa (20.5% oxygen by concentration), and sample No. 34 was a sample produced at a gas pressure of 0.3 MPa. Both samples had surface roughness on the rolled surface of 0.64 to 0.70 and 0.63 to 0.82 μm respectively. The samples had a peak position of a carbon segregation layer in the outside of the range, and showed all deteriorated values of squareness, a core loss and a noise level.
The above described toroidal magnetic core of Sample 2 and a magnetic core having an inner diameter/outer diameter of 90/120 mm were primarily and secondarily wound with a wire, and properties were measured. As a result, both samples showed that B80/Bs is improved by 3%, and a noise level is lowered by 3 to 5 dB. Thus, the magnetic cores were confirmed to be hopeful as magnetic cores of a transformer, a motor and an electric reactor.
The invention provides a magnetic core which has high squareness, a high magnetic flux density, a low noise level and a low core loss, by controlling heat treatment, surface roughness, an amount of carbon to be added and a ratio of a Si content to a carbon content. An applied product using the same is also provided. The magnetic core can be used as magnetic cores for a transformer, a motor and a choke coil.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-094877 | Mar 2005 | JP | national |
| 2006-063540 | Mar 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/306304 | 3/28/2006 | WO | 00 | 11/6/2007 |
