Magnetic materials

A basic characteristic of the magnetic material

1. The magnetic magnetization curve

Magnetic material is composed of a ferromagnetic material or ferrimagnetic material composition, in the role of an external magnetic field H, there must be a corresponding magnetization M or the magnetic induction B, which changes with the magnetic field strength H curve is called the magnetization curve (M ~ H or B ~ H curve). Magnetization curve is generally non-linear, has two characteristics: magnetic saturation and hysteresis. That is, when the magnetic field strength H is large enough, the magnetization M reaches a certain saturation value Ms, continues to increase H, Ms unchanged; and when M reaches the saturation value of the material, when the external magnetic field H is reduced to zero, M and not restored to zero, but along MsMr curve. Working state of the material corresponds to a certain point, this point is often referred to as the operating point M ~ H curve or B ~ H curve.

2. The soft magnetic material commonly used in the magnetic energy parameters

Saturation magnetic flux density Bs: its size depends on the composition of the material, it corresponds to the physical state of the material inside the magnetization vector aligned.

Residual magnetic flux density Br: is the characteristic parameter hysteresis loop line, H B value back to 0:00.

Squareness ratio: Br / Bs

Coercive force Hc: represents the amount of material is magnetized degree of difficulty, depending on the material composition and defects (impurities, stress, etc.).

Permeability μ: is the ratio of the hysteresis loop at any point in the corresponding B and H, and closely related to the device operation status.

The initial permeability μi, maximum permeability μm, differential permeability μd, amplitude permeability μa, effective permeability μe, pulse permeability μp.

Curie temperature Tc: magnetization of the ferromagnetic material decreases with increasing temperature, reaches a certain temperature, the spontaneous magnetization disappears into a paramagnetic, the critical temperature of the Curie temperature. It identifies the upper limit temperature magnetic devices work.

Loss P: Ph hysteresis loss and eddy current loss Pe P = Ph + Pe = af + bf2 + c Pe α f2 t2 /, ρ decreases,

Hysteresis loss Ph approach is to reduce the coercive force Hc; reduce eddy current loss Pe method is thinning and increase thickness t magnetic resistivity of the material ρ. In the still air temperature relationship between freedom core loss and core are:

Total Power Dissipation (mW) / surface area (cm2)

3. Conversion of electrical parameters of soft magnetic materials and magnetic parameters between devices

In the design of the soft magnetic devices, the first to determine the voltage - current characteristics of the device in accordance with the requirements of the circuit. Voltage - current characteristic of the device is closely related to the geometry and the magnetization state of the magnetic core. The designer must be familiar with the magnetization process materials and take relationship between magnetic parameters and the device converts the electrical parameters of the grip material. Design soft devices typically involves three steps: correct selection of magnetic materials; reasonably determine the geometry and dimensions of core; The magnetic parameters required to simulate the core of the work of the state to give the corresponding electrical parameters.

Second, the development of soft magnetic materials and types

1. Development of soft magnetic materials

Soft magnetic materials in the industry began in the late 19th century. With the rise of electric power engineering and telecommunications technology, began using low carbon steel motors and transformers, telephone lines core inductor is used in tiny iron, iron oxide, and other fine wire. By the early 20th century, it developed the silicon instead of the low-carbon steel, to improve the efficiency of the transformer, reducing the losses. Until now in power industry ranking the first silicon soft magnetic material. To the 1920s, the rise of radio technology, promoting the development of highly permeable material, there has been permalloy and permalloy powder cores. From the 1940s to the 1960s, was a period of rapid development of science and technology, radar, television broadcasting, the invention of the integrated circuit, etc., for soft magnetic materials have higher demands to produce a soft magnetic alloy strip and ferrite materials . In the 1970s, with the development of telecommunications, automatic control, computer and other industries, developed a magnetic head with a soft magnetic alloy, in addition to the traditional crystalline soft magnetic alloy, and the rise of another class of materials - amorphous soft magnetic alloy .

2. Common types of soft core

Iron, cobalt, nickel three kinds of ferromagnetic elements constitute the basic component of the magnetic material.

Press (the main component of the magnetic characteristics, structural features) products morphological classification:

(1) powder core categories: magnetic core, comprising: iron core, sendust powder core, high magnetic flux cored (High Flux), permalloy powder core (MPP), the ferrite core

Silicon steel, permalloy, amorphous and nanocrystalline alloys: (2) tape wound core

Features and application of three common soft core

(A) Cored class

1. The magnetic core

Magnetic core is made of a soft magnetic material to suppress mixture of ferromagnetic particles and insulating medium. Since small ferromagnetic particles (at high frequency used is 0.5 to 5 microns), and was separated by a nonmagnetic electrically insulating film material, and therefore, can be isolated from the vortex on the one hand, the material is suitable for higher frequencies; the other hand, since the particles the gap between effects, resulting in a material having a low permeability and permeability characteristics of constant; but due to the small particle size, substantially no skin occurs, change the permeability versus frequency also more stable. Mainly used for high-frequency inductors. Magnetic properties of magnetic core particles depends primarily on the material permeability, the size and shape of particles, their fill factor, the content of the insulating medium, forming pressure and heat treatment processes.

Commonly used iron powder cores have core, permalloy and sendust powder core cored three.

The formula effective permeability of the core of μe and the inductor is: μe = DL / 4N2S × 109

Where: D is the average diameter of the core (cm), L is the inductance (shared), N of winding turns, S is the core effective cross-sectional area (cm2).

(1) iron core

Common iron core is made of carbon-based iron powder and resin carbon-based iron powder composition. In cored lowest price. Saturation magnetization value of about 1.4T; permeability ranging from 22 to 100; initial permeability μi with the change of frequency stability; Good DC current superimposed performance; but at the loss of high-frequency high.

Iron core initial permeability changes with the dc magnetic field strength

Iron core initial permeability with frequency variation

(2) alloy powder core permalloy

Permalloy powder core mainly Molypermalloy powder core (MPP) and high flux cored (High Flux).

MPP is 81% Ni, 2% Mo and Fe powder composition. The main features are: saturation magnetization value of about 7500Gs; large magnetic permeability ranging from 14 to 550; has the lowest loss in the powder magnetic core; excellent temperature stability, widely used in space equipment, outdoor equipment; magnetic electrostrictive coefficient close to zero, no noise at work at different frequencies. Mainly used 300kHz below the high quality factor Q filters, inductive load coil, the resonant circuit, commonly used, the output inductor, power factor compensation circuit, commonly used in high temperature stability requirements of the LC circuit in AC circuits, cored the most expensive.

High Flux cored HF by 50% Ni, 50% Fe powder composition. The main features are: saturation magnetization value of about 15000Gs; permeability ranging from 14 to 160; the highest magnetic flux density, the highest DC bias capability in the powder magnetic core; the core is small. Mainly used in line filters, AC inductance, output inductor, power factor correction circuits, etc., used in the DC circuit, high DC bias voltage, much lower with the high DC and AC. Prices are lower than MPP.

(3) Alumina powder iron core (Kool Mμ Cores)

Kool cored by a 9% Al, 5% Si, 85% Fe powder composition. Mainly replace iron core, low loss ratio of 80 percent iron core, can be used at frequencies above 8kHz; saturation magnetic induction at 1.05T; permeability from 26 to 125; magnetostriction coefficient close to 0, at different frequencies When working without noise; higher than the MPP DC bias capability; with the best cost performance. Mainly used in AC inductors, output inductors, line filters, power factor correction circuit. Sometimes alternative gapped ferrite transformer cores for use.

2. Ferrite (Ferrites)

Ferrite is mainly composed of Fe2O3 magnetic ferrous oxide, produced by powder metallurgy. There Mn-Zn, Cu-Zn, Ni-Zn several categories, including production and consumption biggest Mn-Zn ferrite, Mn-Zn ferrite low resistivity of 1 to 10 ohm - meters, usually in 100kHZ following the use of frequencies. Cu-Zn, Ni-Zn ferrite resistivity of 102 to 104 ohm - meters, a small loss in 100kHz ~ 10 MHz of radio frequency bands, the use of the radio antenna coil, radio intermediate frequency transformer. Core shape variety, there are E, I, U, EC, ETD, square (RM, EP, PQ), pot (PC, RS, DS) and round like. On the application is very convenient. Since the ferrite does not use scarce materials such as nickel can give a high magnetic permeability, powder metallurgy method and is suitable for mass production, and therefore lower costs, but also because it is a large sintered material hardness, not sensitive to stress, in the application of very Convenience. And permeability changes with frequency characteristic stable, 150kHz or less remained unchanged. With the emergence of soft ferrite, magnetic core production greatly reduced, many of the original places are using a magnetic ferrite core instead.

Many domestic and foreign manufacturers of ferrite, in which only American Magnetics produced by Mn-Zn ferrite example to explain the application status. Divided into three basic materials: Telecom with basic materials, broadband and EMI materials, power-type material.

Telecom magnetic permeability ferrite from 750 to 2300, with low loss factor, high quality factor Q, stable magnetic conductivity with temperature / time relationship is the permeability of the slowest decline in work, about a decline of 3% to 4% every 10 years. Widely used in high-Q filters, tunable filters, load coils, impedance matching transformers, proximity sensor. Broadband ferrite is often said that the high permeability ferrite, respectively 5000,10000,15000 permeability. Having the characteristics of low loss factor, high permeability, high impedance / frequency characteristics. Widely used in common mode filter, saturation inductors, current transformers, leakage protection, insulation transformer, signal and pulse transformers, broadband transformers and EMI in multi-purpose. Power ferrite with high saturation flux density for 4000 ~ 5000Gs. Also with low loss / frequency relationships and low loss / temperature relationship. That is, with increasing frequency, the loss is not increased; increase with temperature, loss changed little. Widely used in power chokes, parallel filters, switching power transformers, switch power inductors, power factor correction circuit.

(B) the band around the core

1. The silicon steel core

Silicon steel is an alloy, a small amount of silicon in iron in iron-silicon alloys (typically 4.5% or less) formed called silicon steel. This class has the highest core saturation magnetic flux density is 20000Gs; because they have good magnetic properties, but also easy to mass production, cheap, mechanical stress etc, and get a very wide range of applications in power electronics industry, such as power transformers, distribution transformers, current transformers and other core. Soft magnetic materials is the largest production and use of materials. Power transformer also the largest amount of material with magnetic material. Especially in the most suitable low frequency, high power. Commonly used cold rolled silicon steel sheet DG3, cold rolled non-oriented electrical steel DW, cold rolled grain-oriented electrical steel DQ, applicable to all types of electronic systems, household appliances in the medium and small power low-frequency transformers and chokes, reactors inductor core, good toughness, these alloys may punching, cutting and other processing, there are laminated core and winding type. But high frequency loss increased dramatically, the general use of the frequency does not exceed 400Hz. From the application point of view, the choice of silicon to consider two factors: magnetic and costs. For small motors, reactors and relays, an optional low iron or steel sheet; for large motors, optional high silicon hot-rolled steel sheet, cold-rolled grain-oriented or non-oriented silicon steel sheet; transformers are often used for grain-oriented silicon steel cold rolling sheet. When used in power frequency, commonly strip thickness of 0.2 to 0.35 mm; when used at 400Hz, often choose 0.1 mm thickness is appropriate. The thinner the thickness, the higher the price.

2. permalloy

Permalloy often refers to iron-nickel-based alloys, nickel content is within the range of 30 to 90%. It is widely used in soft magnetic alloys. Through appropriate technology, can effectively control the magnetic properties, such as initial permeability than 105, more than 106 of the maximum permeability, low to 2 ‰ Oe coercivity, rectangular coefficient close to 1 or close to zero, Poe has a face-centered cubic crystal structure of Mo alloy has good plasticity, can be processed into thin belt 1μm and various use forms. Commonly used alloys 1J50,1J79,1J85 like. 1J50 saturation magnetization lower than silicon, but the permeability several times higher than silicon steel, iron loss of 2 to 3 times lower than silicon. Make high frequency (400 ~ 8000Hz) of the transformer, no-load current is small, suitable for the production of small high frequency transformer 100W or less. 1J79 has a good overall performance, suitable for high frequency low voltage transformers, leakage protection switch core, a common mode inductor core and current transformer core. 1J85 initial permeability up to 105 million or more, suitable for the low-frequency or high frequency weak signal input and output transformers, common mode inductance and high-precision current transformers.

3. amorphous and nanocrystalline soft magnetic alloy (Amorphous and Nanocrystalline alloys)

Silicon steel and permalloy soft magnetic materials are crystalline materials, atoms are arranged in three-dimensional space to make the rules, a periodic lattice structure, there is a grain, grain boundaries, dislocations, interstitial atoms, the magnetic anisotropy, etc. defects detrimental to the soft magnetic properties. From the magnetic physics, the atomic irregular arrangement, there is no periodic amorphous structure and crystal grain boundaries in obtaining excellent soft magnetic properties are ideal. Amorphous metals and alloys is a new field of materials 70s came. It's completely different from the traditional preparation technology methods, instead of using a cooling rate of about one million degrees per second, ultra rapid solidification technique, a thin strip from liquid steel to the finished molding, than ordinary cold-rolled metal strip manufacturing process reducing the number of intermediate steps, this new technology is known as a revolution to the traditional metallurgical processes. Since the ultra-rapid solidification, when atoms ordered alloy solidification late crystallized solid alloy obtained long-range disordered structure is not crystalline alloy grains, grain boundaries, called amorphous alloy, known as metallurgical material A revolution in science. This amorphous alloy has many unique properties such as excellent magnetic properties, corrosion resistance, abrasion resistance, high strength, hardness and toughness, high resistivity and electromechanical coupling properties. Because of its excellent performance, simple process, from the 1980s to become the domestic and foreign materials science research and development focus. Currently the United States, Japan, Germany, already has a sound production scale, and a lot of amorphous alloy products gradually replace silicon steel and permalloy and ferrite flood the market.

Since the 1970s, the country began to research and development of amorphous alloys, through the "Plan", "Plan", the completion of major scientific and technological project "85" period, a total of 134 achievements in scientific research, the National Invention Award 2, patented 16, has nearly a hundred varieties of alloys. Steel Research Institute now has four production line of amorphous alloy strip, an amorphous alloy core components production line. Production of various stereotypes of iron, iron-nickel based, cobalt-based and nanocrystalline strip and core for power inverters, switching power supply, power transformers, leakage protection, inductor core members, the annual production value of nearly 2000 million. "Nine Five" is being established kiloton iron-based amorphous production line, into the ranks of the advanced international level.

Currently, the best individual performance levels achieved amorphous soft magnetic alloy is as follows:

Initial permeability μo = 14 × 104

Co-based amorphous maximum permeability μm = 220 × 104

Co-based amorphous coercive force Hc = 0.001 Oe

Co-based amorphous squareness Br / Bs = 0.995

Co-based amorphous saturation magnetization 4πMs = 18300Gs

Fe-based amorphous resistivity ρ = 270μΩ / cm

Common types of amorphous alloys are: iron, iron-nickel-based and cobalt-based amorphous alloys and nanocrystalline alloys. Its national grades and performance characteristics are shown in Table and Figure, for ease of comparison, the corresponding properties are listed in the crystalline silicon alloy, permalloy 1J79 and ferrites. These types of materials have different characteristics, be applied in different ways.

Grades basic components and features:

1K101 Fe-Si-B-based soft magnetic iron-based alloy quenched

1K102 Fe-Si-B-C-based soft magnetic iron-based alloy quenched

1K103 Fe-Si-B-Ni-based soft magnetic iron-based alloy quenched

1K104 Fe-Si-B-Ni Mo-based soft magnetic iron-based alloy quenched

1K105 Fe-Si-B-Cr (and other elements) line of rapid quenching soft magnetic iron-based alloy

1K106 high-frequency low-loss Fe-Si-B-based soft magnetic iron-based alloy quenched

1K107 high-frequency low-loss Fe-Nb-Cu-Si-B system quenched nanocrystalline soft magnetic alloy

1K201 high pulse permeability rapid quenching soft magnetic cobalt-based alloys

1K202 high remanence faster than the quenching soft magnetic cobalt-based alloys

1K203 high magnetic induction low loss rapid quenching soft magnetic cobalt-based alloys

1K204 high-frequency low-loss rapid quenching soft magnetic cobalt-based alloys

1K205 high initial permeability rapid quenching soft magnetic cobalt-based alloys

1K206 quenched high permeability soft magnetic cobalt-based alloys

1K501 Fe-Ni-P-B-based rapid quenching soft magnetic nickel-based alloys

1K502 Fe-Ni-V-Si-B-based rapid quenching soft magnetic nickel-based alloys

400Hz: Amorphous silicon steel core core

Power (W) 45 45

Core loss (W) 2.4 1.3

Excitation power (VA) 6.1 1.3

Total weight (g) 295 276

(1) iron-based amorphous alloy (Fe-based amorphous alloys)

Fe-based amorphous alloy is composed of 80% Fe and 20% Si, Class B metal elements of the composition, it has a high saturation magnetic flux density (1.54T), iron-based amorphous alloy and silicon loss comparison

All aspects of permeability, excitation current and iron loss characteristics are superior to silicon, particularly low iron loss (oriented silicon steel sheet of 1 / 3-1 / 5), instead of the silicon make energy savings of 60- Distribution Transformer 70%. Strip thickness of iron-based amorphous alloy is about 0.03mm, widely used in distribution transformers, high-power switching power supply, pulse transformers, magnetic amplifiers, intermediate frequency transformer and the inverter core is suitable for use at frequencies below 10kHz