In the production of iron powder-based soft magnetic materials, there are two commonly used to reduce eddy current loss method.
(1) One is to use alloy additives to increase material resistivity and reduce Eddy current loss, such as iron-silicon alloy (usually containing 3% Si) iron-phosphorus alloy (Generally P 0.45%~0.75%), iron-nickel alloy (50% iron, nickel 50%) etc. But this reduces the saturation magnetic induction, and the alloy content. There are certain limits in commercial use. This method is suitable for DC or Lower frequency AC device.
(2) Another method is to conduct insulation coating treatment on magnetic particles. It is the Soft Magnetic Composite (SMC), its structure as shown in Figure SMC material, sometimes called "insulating coated iron powder", is a new type of iron-based powder soft magnetic material that has gradually developed in recent years. It usually chooses the base material of high-purity iron powder is treated by insulating and coating of organic and inorganic materials, use powder metallurgy technology to make mixed powders into isotropic materials.
According to different insulation coating materials, SMC materials can be roughly divided into the following categories:
In the 1990s, it was thought that ferromagnetic powder coated with organic resin could be used as a raw material for iron cores in electromagnetic conversion devices from medium to high frequencies. This type of material is composed of iron powder and resin, and sometimes a small amount of lubricant is added; in the pressing-heat treatment process, the insulation of iron powder is realized.
At the end of the 20th century, Japan had used epoxy resin and phenolic resin as binders to directly produce powder magnetic cores.
Quebec of Canada pointed out in 2000 that this type of iron-resin SMC material can also be used in lower frequency applications as long as it uses high-compressibility and high-purity water atomized iron powder. In 2005, Japan's JFE company has developed and put into production the iron-resin hybrid powder. This SMC material is based on pure iron-type reduced iron powder with a particle size of about 100μm.
The technology has been successfully developed to directly coat the insulating film on the surface of the magnetic powder. The double-layer coating method of iron powder particles is to first coat the surface of the iron powder with a 10~100nm thick ultra-thin phosphate film, and then just add the pole A small amount of resin can realize the insulation coating of the resin during the pressing and heat treatment process, and finally obtain a soft magnetic material with high magnetic properties and high insulation. This technology not only increases the density of the green compact, but also enhances the thermal stability of the insulating coating; and experiments have shown that the phosphate coating can also inhibit the surface oxidation of iron powder.
At present, the SMC material invented by Höganäs AB and its commercialized phosphate insulation coating technology represents the international advanced level. This type of material not only effectively reduces eddy current loss, but also has better magnetic and mechanical properties. Many recent studies have used SomaloyTM series SMC powder as raw materials to study the effects of different preparation processes on various properties of SMC cores.
This type of SMC core has high mechanical strength, high magnetic flux density, low-medium and low-frequency iron loss performance; but when the frequency is 1KHz, its iron loss is 2-3 of the traditional laminated silicon steel sheet (sheet thickness 0.35 mm) Times. For high-frequency applications, T. MAEDA and others have tried to improve the mixing method of inorganic insulating coated iron powder and resin. Before pressing, they wet-coated the resin on the iron powder with an inorganic insulating layer. This improvement increases the heat treatment temperature by nearly 150°C, when used above 300Hz, the iron loss is also low.
