GB2233828A

GB2233828A - Improving magnetic properties of ferromagnetic material

Info

Publication number: GB2233828A
Application number: GB9013653A
Authority: GB
Inventors: James Chen Min Li; Der-Ray Huang
Original assignee: China Steel Corp
Current assignee: China Steel Corp
Priority date: 1989-07-01
Filing date: 1990-06-19
Publication date: 1991-01-16
Anticipated expiration: 2010-06-19
Also published as: GB2233828B; JPH0346205A; DE4019636A1; GB9013653D0; DE4019636C2

Abstract

A method of improving the magnetic properties of a ferromagnetic material comprises locating a specimen of ferromagnetic material in a magnetizing/demagnetizing field and applying an alternating or pulsed current through the specimen to improve its soft magnetic properties. The applied AC can have a frequency of 50 to 50K Hz, a sine, triangular or square wave form, and a current density of 10 to 500 A/cm<2>. The magnetic properties of the ferromagnetic materials are improved by achieving a coercivity ratio less than 0.5, a magnetic induction ratio greater than 1 and a core loss ratio less than 0.3. Arrangements for measuring the hysteresis is loop of flat and toroidal ribbons are described.

Description

1 MMOD OF IMPROVING MAGNETIC PROPERTIES The present invention relates to a

method for improving the magnetic properties of a magnetic material, especially ferromagnetic amorphous alloys. Such alloys have been widely used in many magnetic application such as distribution transformers, DC power supplies, motors, current amplifiers and magnetic shielding. Iron-based amorphous alloys will produce an annealing embrittlement after the conventional furnace annealing. This is a serious problem in certain applications.

In the past, efforts have been made to find new magnetic materials suitable for many applications with better magnetic properties such as higher magnetic induction (Bm), lower coercivity (He), and therefore low core loss when the transformer core is made of such materials. For ferromagnetic materials used in the past for the manufacture of transformer cores, it is very difficult to change their magnetic properties in operation.

The present invention provides a method of improving the magnetic properties of ferromagnetic materials comprising the steps of locating a specimen of ferromagnetic material in a magnetizing/demagnetizing field; and applying an alternating or pulsed current to pass through the said specimen.

An important feature of the present invention is the step of applying an alternating or pulsed current to the ferromagnetic amorphous alloy during the magnetization of the alloys to increase the maximum value of the magnetic induction (Bm) and decrease the minimum value of the coercivity (He).

The alternating current originates from an AC power supply and is fed into the specimen of the ferromagnetic materials by directly connecting the specimen to a pair of electrodes. It is believed that the current passing the ferromagnetic material causes the domain wall in the material to shift in response to the current density and frequency. Therefore, the soft magnetic properties of the ferromagnetic materials are improved. The method of the present invention further comprises a step of applying an alternating or pulsed current to a specimen of alloy that has been treated by AC Joule beating or pulsed high current heating process. This amorphous alloy 2 will not have annealing embrittlement during annealing process. The AC Joule heating or pulsed high current processes for improving the magnetic properties and annealing embrittlement of the alloy are set out in pending US Patent Application No. 338,895, filed on 14 April 1989.

The applied alternating or pulsed-current has a frequency ranging from 50 to 50K Hz, a current density of 10 to 500 A,,cm2 and a wave form of sine wave, triangular wave or square wave.

The method of the present invention may include a further step of detecting and recording the magnetic induction and coercivity of the specimen during magnetization and demagnetization.

Preferred embodiments of the invention are described in detail with reference to the accompanying drawings, in which:- Figure 1 is a schematic diagram of a system for measuring B-H loop of a straight specimen according to the method of the present invention; Figure 2 is a schematic diagram of a system for measuring B-H loop of a toroidal specimen according to the method of the present invention; Figure 3 is a perspective view of a ferromagnetic amorphous alloy ribbon showing its magnetic domain structure; Figure 4 is a graph showing variation off magnetic induction and coercivity of a Fe78B 13% straight specimen with a 60 Hz sine wave current passing through it; Figure 5 is a graph showing variation of magnetic induction and coercivity of a Fe78B 13% straight specimen carrying AC with differing frequencies; and Figure 6 is a graph for the B-H loop of a Fe 78B 13% straight specimen as-east after AC Joule heating and by passing AC through it.

Specimens Ferromagnetic amorphous ribbons with different compositions, especially for Fe and Ni base amorphous ribbons, were used.

Crystalline material is also suitable.

The shapes were (a) straight long ribbon, (b) toroid core wound by a long ribbon, (c) C-type, E-type or rectangular core.

3 Specimens of compositions Fe78B13S'9 were made into straight and toroidal shapes.

2. Measuring the magnetic properties with AC or pulsed current 5 passing through the specimen.

A. Straight specimen A straight amorphous ribbon was put in the centre of a uniform magnetic field (H) produced by a long solenoid which was connected to the DC bipolar power supply of a function generator. Both ends of the straight amorphous ribbon were clamped by two square copper plates which were connected to the output terminals of an AC supply. A search coil (S) combined with a compensating coil (C) was connected to a fluxmeter (or integrator) to measure the magnetic flux density (B) of the specimen. By connecting the terminals of the applied magnetic field (H) and magnetic flux density (B) to an X-Y recorder, the B-H hysteresis loop was obtained.

B. Toroidal specimen A toroidal specimen was made by winding a long amorphous ribbon coated with insulation materials. The two ends of the long ribbon were connected to the output terminals of the AC supply. The toroidal core was wound by two coils, the primary coil (Ni) was connected to a DC bipolar supply or a function generator to produce the applied magnetic field (H), and the second coil (N2) was connected to a fluxmeter (or integrator) to measure the magnetic flux density (B). Then, by connecting the terminals of H and B to a X-Y recorder, the B-H hysteresis loop was obtained. (Figure 2) 3.

Conditions of the applied AC current through the specimen frequency range: 50 Hz to 50 KHz wave form: sine wave, triangular wave and square wave current density: J = 10 A/cm2 to 500 A-icm2 Transverse field is induced by AC or pulsed current. Except in the vicinity of the ribbon edges, the magnetic field produced by applying a current 1 through a rectangular specimen is essentially transverse and varies linearly with the distance from the midplane of the ribbon. Figure 3 shows the cross-section of the amorphous ribbon and its possible magnetic domain structure.

4 4. The following Examples show improvements in the various kinds of ferromagnetic amorphous alloys resulting from the method of the invention by applying AC passing through a specimen made of ferromagnetic materials.

Example 1

Specimen: straight shape (15.24 em x.05 mm x 25 m) Composition: Fe 78B 135'9 Reference magnetic properties of as-ease specimen: When applied magnetic field: Hm = + 0.296 Oe a. magnetic induction: Bmo = 0.074 Oe b. coercive force: Heo = 0.074 Oe Effects of magnetic properties under AC passing through the specimen: A. Dependence of AC density When a 60 Hz sine wave current passing through the specimen with different current density J = 0" 334 A/cm2 (1 = 0- 250 mA), the variations of the magnetic induction and coercivity of the specimen are shown in Figure 4. The magnetic inductions under different current densities are almost the same, i.e. a little higher than the value of the as-ease specimen. However, the coercivity of the specimen decreases significantly as the current density increases. The decrease 2 is slower after the current density is higher than 150 A/cm. When the 2 current density is 334 A/em ' the coercivity will be lower than half that of the as-east specimen.

B. Frequency dependence When the specimen was carrying the same alternating current (current density J = 160 A/cm2) with a different frequency (50 Hz-20 KHz), the variations of magnetic induction and coercivity of the specimen are shown in the Figure 5. Also, the magnetic inductions are almost the same and a little higher than the value for the as-east specimen. The values of the coereivity ratio are around 0.5 and the minimum values of coercivity are between the frequency range 100 Hz1 KHz. C. Wave form dependence The wave form used in the AC passing through the specimen may be sine wave, triangular wave or square wave. Under the same peak current, the effect of improving the magnetic properties by a square wave is the best, and the effect of a sine wave and a triangular wave are almost the same. For 300 Hz current passing through the specimen, the variations of magnetic induction and coereivity when applied magnetic field is Hm = +0.296 Oe are listed as follows:

wave form current (M) Bm (Kg) He (0e) 0 7.16 0.074 sine 200 7.72 0.044 triangle 200 7.72 0.044 square 200 7.72 0.035 sine 250 7.86 0.029 triangle 250 7.86 0.029 square 250 7.86 0.026 Example 2

Specimen: toroidal specimen Composition: Fe78B135'9 A five-layer amorphous core with diameter 3.8 em was wound by a em-long ribbon (width 7.5 em, thickness 25 ym, and weight 6.623 g) Reference magnetic properties of as-ease specimen:

When applied magnetic field in measuring B-H loop is

Hm = +0.15 Oe a. magnetic induction Bm. = 6.71 Kg b. coercivity Heo = 0.073 Oe Applying 60 Hz sine wave through the core, the improved magnetic induction and coereivity of the specimen are as follows:

Current density M/cm2) Bm Rg) He (0e) 0 6.71 0.073 6.80 0.039 500 6.88 0.030 Example 3

Specimen: straight shape (15 em x 3.05 mm x 25xm) Composition: Fe 78B 13% A. As-ease specimen When applied magnetic field in measuring B-H loop is Hm = +0.292 Oe, magnetic induction Bm 40 He = 0. 075 Oe.

= 7.07 Kg and coercive force 6 Hm = C.

B. After AC Joule heating Conditions of AC Joule heating: frequency f = 60 Hz current density J = 3000 A/CM2 heating time th 50 see applied field Hp 100 Oe When applied magnetic field in measuring B-H loop is +0.292 Oe magnetic induction Bm = 9.70 Kg and coereivity He = 0.04 Oe And, fracture strain 1 (ductility) Passing AC current through the specimen after AC Joule heating Conditions of AC frequency: f = 300 Hz wave form: square current density: 160 A/cm2 When applied magnetic field in measuring B-H loop is

Hm +0.292 Oe magnetic induction Bm = 9.89 Kg coercivity He = 0.017 Oe The DC B-H loops of the specimen as-east, after AC Joule heating and AC current passing through the specimen, are shown in Figure 6.

7

Claims

1. A method of improving the magnetic properties of ferromagnetic materials comprising the steps of locating a specimen of ferromagnetic material in a magnetizing/demagnetizing field and applying an alternating or pulsed current to pass through the said specimen.

2. A method as claimed in Claim 1 including the further step of recording the improved magnetic properties of said specimen.

3. A method as claimed in Claim 2 in which the recording step detects and records the magnetic induction and coercivity of the specimen.

4. A method as claimed in any preceding claim in which the specimen is made of a ferromagnetic amorphous alloy.

5. A method as claimed in Claim 4 in which the specimen is made of an Febase amorphous alloy, an Ni-base amorphous alloy or a Co-base 20 amorphous alloy.

6. A method as claimed in any preceding claim in which the current applied is AC with a frequency in the range from 50 to 5OK Hz.

7. A method as claimed in any preceding claim in which the current applied is AC with a sine, triangular or square wave form.

8. A method as claimed in any preceding claim in which the current 2 applied is AC with a current density of 10 to 500 A/em

9. A method as claimed in Claim 1 in which the specimen is straight, toroidal shape or any transformer-core shape.

10. A method as claimed in Claim 1 substantially as hereinbefore 35 described with reference to the accompanying drawings.

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